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2. Significance Statements Communicate Our Science More Widely.
- Author
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Smith, Anne K.
- Subjects
ATMOSPHERIC sciences ,EMAIL ,WEBSITES - Abstract
The editor and peer reviewers who evaluate the paper will also review the significance statement. EDITORIALS SignificanceStatementsCommunicateOurScienceMoreWidely KEYWORD: Editorial The American Meteorological Society (AMS) mission statement specifically calls for advancing "the atmospheric and related sciences ... for the benefit of society.". [Extracted from the article]
- Published
- 2020
- Full Text
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3. Biogeochemical Coupling between Ocean and Atmosphere--A Tribute to the Lifetime Contribution of Robert A. Duce.
- Author
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BROOKS, SARAH D., JICKELLS, TIM D., LISS, PETER S., THORNTON, DANIEL C. O., and RENYI ZHANG
- Subjects
ATMOSPHERIC sciences ,OCEAN ,BIOLOGICAL interfaces ,ATMOSPHERE ,AEROSOLS - Abstract
To mark the publication of the special collection in honor of Robert (Bob) A. Duce in the Journal of the Atmospheric Sciences, we have summarized his most important contributions to the subject of biogeochemical coupling between the atmosphere and ocean. Here we have divided these contributions into four themes--deposition from the atmosphere and its effects on the oceans, volatile elements emitted from the oceans, sea surface biology and aerosol formation, and marine aerosols and clouds. It is our intent that this summary along with the papers in this special collection provide an overview of the enormous contributions that Bob Duce has made to the subject during his distinguished scientific career. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
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4. A Unified Formulation of Radiative Transfer in Plane-Parallel Atmospheres Based on General Decomposition of Radiance. Part II: An Exemplifying Application to the Hemispherical Harmonics Method with Four Components.
- Author
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Wang, Biao
- Subjects
RADIATIVE transfer ,HEMISPHERICAL scale ,ATMOSPHERIC sciences ,OPTICAL depth (Astrophysics) ,GAUSSIAN quadrature formulas - Abstract
Based on the unified formulation, the so-called hemispherical harmonics method with four components (HSHM4) is derived following the general procedure described in the first paper of this series. The numerical results of this method, including the flux reflections, transmissions, and absorptions for different optical depths, incident beam angles, and single-scattering albedos and the emissions for different optical depths and single-scattering albedos, are reported, in comparison with the results of DISORT with 128 streams as a benchmark. The application of the method to the radiation scheme for climate models is illustrated with the numerical results, including the heating-rate profiles for the shortwave and longwave radiation, radiative fluxes at the top and the bottom boundaries of the atmosphere, and the actinic flux profiles, for typical model atmospheres of Earth and different clear or cloudy conditions. The comparison of results with those of the discrete ordinate methods (DOMs) and the spherical harmonic method (SHM) with four components shows that the HSHM4 has comparable accuracy with the four-stream DOM with double-Gaussian quadrature and is more accurate than the four-stream SHM and the four-stream DOM with full-range Gaussian quadrature in general, especially in the cases of longwave radiation when the multiple-scattering effect should be accounted for. The HSHM4 can be deployed consistently to all of the bands without artificial division between the longwave and shortwave. The development and validation of the HSHM4 exhibit the usefulness of the unified formulation in the study of atmospheric radiative transfer. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
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5. The Vorticity Budgets of North Atlantic Winter Extratropical Cyclone Life Cycles in MERRA Reanalysis. Part I: Development Phase*.
- Author
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Azad, Roohollah and Sorteberg, Asgeir
- Subjects
CYCLONES ,VORTEX motion ,ATMOSPHERIC thermodynamics ,EQUATIONS ,ATMOSPHERIC sciences - Abstract
This series of papers (parts I and II) examines the vorticity budgets of winter North Atlantic extratropical cyclones during the period 1979-2009 using the Modern-Era Retrospective Analysis for Research and Application (MERRA). The authors use a new partitioning technique to combine the Zwack-Okossi (Z-O) equation with the omega equation. The combination provides a possibility to partition the adiabatic term in the Z-O equation into its different forcing mechanisms. Thus, both the direct effect of the dynamic and thermodynamic forcings and their indirect effect on the adiabatic term can be calculated to provide the total effect (direct plus indirect) on the 950-hPa geostrophic vorticity tendency. It is demonstrated that the total-effect diagnostic is a suitable tool to identify the dynamically consistent characteristics of cyclone development in midlatitudes because it possesses less case-to-case variability. The authors found that the vorticity advection is the major forcing process, the tendencies attributed to the ageostrophic vorticity tendency term are considerable, and the opposing effect of the friction term in moderating the deepening is significant. In general, the upper-level dynamics drive the deepening of the cyclones, except at the end of development, where a combination of midlevel latent heating, positive ageostrophic vorticity tendency, and positive indirect effect of vorticity advection contribute to the development. Additionally, the total effects of temperature advection and latent heating on the intensification of cyclones are reduced because of the inclusion of counteractive indirect effects, as are their variabilities within the cyclone composite. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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6. Gravity Wave-Fine Structure Interactions. Part II: Energy Dissipation Evolutions, Statistics, and Implications.
- Author
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Fritts, David C. and Wang, Ling
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GRAVITY waves ,ATMOSPHERIC sciences ,WAVE mechanics ,ATMOSPHERIC turbulence ,ENERGY dissipation - Abstract
Part I of this paper employs four direct numerical simulations (DNSs) to examine the dynamics and energetics of idealized gravity wave-fine structure (GW-FS) interactions. That study and this companion paper were motivated by the ubiquity of multiscale GW-FS superpositions throughout the atmosphere. These DNSs exhibit combinations of wave-wave interactions and local instabilities that depart significantly from those accompanying idealized GWs or mean flows alone, surprising dependence of the flow evolution on the details of the FS, and an interesting additional pathway to instability and turbulence due to GW-FS superpositions. This paper examines the mechanical and thermal energy dissipation rates occurring in two of these DNSs. Findings include 1) dissipation that tends to be much more localized and variable than that due to GW instability in the absence of FS, 2) dissipation statistics indicative of multiple turbulence sources, 3) strong influences of FS shears on instability occurrence and turbulence intensities and statistics, and 4) significant differences between mechanical and thermal dissipation rate fields having potentially important implications for measurements of these flows. [ABSTRACT FROM AUTHOR]
- Published
- 2013
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7. Toward Multiscale Simulation of Moist Flows with Soundproof Equations.
- Author
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Kurowski, Marcin J., Grabowski, Wojciech W., and Smolarkiewicz, Piotr K.
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ATMOSPHERIC ozone ,ATMOSPHERIC sciences ,ATMOSPHERIC circulation ,THERMODYNAMICS ,CONDENSATION (Meteorology) - Abstract
This paper discusses the incorporation of phase changes of the water substance that accompany moist atmospheric flows into the all-scale atmospheric model based on soundproof equations. A specific issue involves developing a theoretical basis and practical implementation to include pressure perturbations associated with atmospheric circulations, from small scale to global, into representations of moist thermodynamics. In small-scale modeling using soundproof equations, pressure perturbations are obtained from the elliptic pressure solver and are typically excluded from the moist thermodynamics. This paper argues that in larger-scale flows, at least the hydrostatic component of the pressure perturbation needs to be included because pressure variation in synoptic weather systems may affect moist thermodynamics in a way comparable to the temperature variations. As an illustration, two idealized test problems are considered: the small-scale moist thermal rising in a stratified environment and the moist mesoscale flow over idealized topography. The paper compares numerical solutions obtained with a fully compressible acoustic mode-resolving model and with two versions of the anelastic model, either including or excluding anelastic pressure perturbations in moist thermodynamics. The two versions of the anelastic model are referred to as the generalized and standard anelastic. In agreement with the scaling arguments, only negligible differences between anelastic and compressible solutions are simulated. Incorporation of the anelastic pressure perturbations into moist thermodynamics paves the way for future studies where larger-scale moist dynamics will be considered. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
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8. Hurricane Kinetic Energy Spectra from In Situ Aircraft Observations.
- Author
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VONICH, P. TRENT and HAKIM, GREGORY J.
- Subjects
HURRICANES ,CYCLONES ,NATURAL disasters ,ATMOSPHERIC sciences ,KINETIC energy ,RELATIVISTIC energy ,ATMOSPHERE - Abstract
Since the pioneering paper by Nastrom and Gage on aircraft-derived power spectra, significant progress has been made in understanding the wavenumber distribution of energy in Earth's atmosphere and its implications for the intrinsic limits of weather forecasting. Improvements in tropical cyclone intensity predictions have lagged those of global weather forecasting, and limited intrinsic predictability may be partially responsible. In this study, we construct power spectra from aircraft data of over 1200 missions carried out by the National Oceanic and Atmospheric Administration (NOAA) and Air Force Reserve Command (AFRC) Hurricane Hunters. Each mission is parsed into distinct flight legs, and legs meeting a specified set of criteria are used for spectral analysis. Here, we produce power spectra composites for each category of the Saffir-Simpson scale, revealing a systematic relationship between spectral slope and storm intensity. Specifically, as storm intensity increases, we find that 1) spectral slope becomes steeper across scales from 10 to 160 km and 2) the transition zone where spectral slope begins to steepen shifts downscale. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
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9. Barotropic and Baroclinic Eddy Feedbacks in the Midlatitude Jet Variability and Responses to Climate Change-Like Thermal Forcings.
- Author
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ALEX BURROWS, D., GANG CHEN, and LANTAO SUN
- Subjects
CLIMATOLOGY ,BAROTROPIC equation ,CLIMATE change ,WEATHER ,ATMOSPHERIC sciences - Abstract
Studies have suggested that the persistence in the meridional vacillation of the midlatitude jet (i.e., annular mode time scale) in comprehensive climate models is related to the model biases in climatological jet latitude, with important implications for projections of future climates and midlatitude weather events. Through the use of the recently developed finite-amplitude wave activity formalism and feedback quantifying techniques, this paper has quantified the role of barotropic and baroclinic eddy feedbacks in annular mode time scales using an idealized dry atmospheric model. The eddy-mean flow interaction that characterizes the persistent anomalous state of the midlatitude jet depends on processes associated with the lower-tropospheric source of vertically propagating Rossby waves, baroclinic mechanisms, and processes associated with upper-tropospheric wave propagation and breaking, barotropic mechanisms. A variety of climate change-like thermal forcings are used to generate a range of meridional shifts in the midlatitude eddy-driven jet. The idealized model shows a reduction in annular mode time scale associated with an increase in jet latitude, similar to comprehensive climate models. This decrease in time scale can be attributed to a similar decrease in the strength of the barotropic eddy feedback, which, in the positive phase of the annular mode, is characterized by anomalous potential vorticity (PV) mixing on the equatorward flank of the climatological jet. The decrease in subtropical PV mixing is, in turn, associated with a stronger subtropical jet as the eddy-driven jet is more distant from the subtropics. These results highlight the importance of subtropical eddy-mean flow interactions for the persistence of an eddy-driven jet. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
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10. Satellite Observations of an Unusual Cloud Formation near the Tropopause.
- Author
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Ferlay, Nicolas, Garrett, Timothy J., and Minvielle, Fanny
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CLOUDS ,TROPOPAUSE ,MIDDLE atmosphere ,ARTIFICIAL satellites ,METEOROLOGY ,ATMOSPHERIC sciences ,ATMOSPHERIC physics - Abstract
This paper describes observations of a field of deep and regular cloud formations that spans several hundreds of kilometers at the top of a midlatitude frontal system in the North Pacific storm track. Space-based imagery of the event from active and passive measurements reveals smooth, clearly defined cloud lobes approximately 10 km across and 2-4 km deep that resemble upside-down mammatus. These observations, together with theoretical arguments and prior modeling work, suggest that the lobes were part of a deepening turbulent mixed layer that formed as a consequence of strong cloud-top radiative cooling. Over the course of a day, the cloud-top formation evolved to leave behind a sheet of cumuliform cirrus that stretched hundreds of kilometers across. The potential is for such clouds to facilitate mixing across the tropopause, much as cloud-top cooling drives the entrainment of free-tropospheric air into stratocumulus-topped boundary layers. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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11. Data Archiving and Citation within AMS Journals.
- Author
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Mayernik, Matthew S., Ramamurthy, Mohan K., and Rauber, Robert M.
- Subjects
DOCUMENTATION ,METEOROLOGY ,ATMOSPHERIC sciences ,EARTH sciences - Abstract
The author presents information on a new set of recommendations for AMS journals titled, "Data Archiving and Citation," which was posted in the American Meteorological Society (AMS) author guidelines by AMS on 25 February 2015. These recommendations support the documentation of data linked to papers published in AMS journals.
- Published
- 2015
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12. Factor Effects in Numerical Simulations.
- Author
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CLEVELAND, JUDAH L., SMITH, JEFFREY A., and COLLINS, JAMES P.
- Subjects
COMPUTER simulation ,EXPERIMENTAL design ,ATMOSPHERIC sciences - Abstract
Numerical simulations allow users to adjust factor settings in experimental runs to understand how changes in those factors affect the output. However, it is not straightforward to analyze these outputs when multiple input factors are changed, especially simultaneously. For the atmospheric sciences, Stein and Alpert introduced a method they termed "factor separation" in order to separate the "pure contribution" of a factor from "pure interactions" of combinations of factors. Although factor separation appears to be used exclusively within the atmospheric sciences, other communities achieve a similar result by computing "main effects" via design of experiments methods. While both methods yield different estimates for the factor effects or contributions, we show that factor separation effects are identical to "simple effects" in the design of experiments literature. We demonstrate how both factor separation effects and design of experiments main effects correspond to multiple linear regression coefficients with different coding methods; thus, effect estimates produced by each method are equivalent through a variable transformation. We illustrate the application of both methods using a shallow-water simulation. This connection between factor separation and the design of experiments discipline extends factor separation to more applications by making available design of experiments methods for decreasing the computational cost and calculating effects for factors with more than two settings, both of which are limitations of factor separation. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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13. The Application of Nonlinear Local Lyapunov Vectors to Ensemble Predictions in Lorenz Systems.
- Author
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Feng, Jie, Ding, Ruiqiang, Liu, Deqiang, and Li, Jianping
- Subjects
ATMOSPHERIC sciences ,VECTOR analysis ,PERTURBATION theory ,NONLINEAR statistical models ,MONTE Carlo method - Abstract
Nonlinear local Lyapunov vectors (NLLVs) are developed to indicate orthogonal directions in phase space with different perturbation growth rates. In particular, the first few NLLVs are considered to be an appropriate orthogonal basis for the fast-growing subspace. In this paper, the NLLV method is used to generate initial perturbations and implement ensemble forecasts in simple nonlinear models (the Lorenz63 and Lorenz96 models) to explore the validity of the NLLV method. The performance of the NLLV method is compared comprehensively and systematically with other methods such as the bred vector (BV) and the random perturbation (Monte Carlo) methods. In experiments using the Lorenz63 model, the leading NLLV (LNLLV) captured a more precise direction, and with a faster growth rate, than any individual bred vector. It may be the larger projection on fastest-growing analysis errors that causes the improved performance of the new method. Regarding the Lorenz96 model, two practical measures-namely the spread-skill relationship and the Brier score-were used to assess the reliability and resolution of these ensemble schemes. Overall, the ensemble spread of NLLVs is more consistent with the errors of the ensemble mean, which indicates the better performance of NLLVs in simulating the evolution of analysis errors. In addition, the NLLVs perform significantly better than the BVs in terms of reliability and the random perturbations in resolution. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
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14. Stability and Charging Characteristics of the Comma Head Region of Continental Winter Cyclones.
- Author
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Rauber, Robert M., Wegman, Joseph, Plummer, David M., Rosenow, Andrew A., Peterson, Melissa, McFarquhar, Greg M., Jewett, Brian F., Leon, David, Market, Patrick S., Knupp, Kevin R., Keeler, Jason M., and Battaglia, Steven M.
- Subjects
CYCLONES ,CONVECTION (Meteorology) ,WINTER ,LIGHTNING research ,ATMOSPHERIC sciences - Abstract
This paper presents analyses of the finescale structure of convection in the comma head of two continental winter cyclones and a 16-storm climatology analyzing the distribution of lightning within the comma head. A case study of a deep cyclone is presented illustrating how upper-tropospheric dry air associated with the dry slot can intrude over moist Gulf air, creating two zones of precipitation within the comma head: a northern zone characterized by deep stratiform clouds topped by generating cells and a southern zone marked by elevated convection. Lightning, when it occurred, originated from the elevated convection. A second case study of a cutoff low is presented to examine the relationship between lightning flashes and wintertime convection. Updrafts within convective cells in both storms approached 6-8 m s
−1 , and convective available potential energy in the cell environment reached approximately 50-250 J kg−1 . Radar measurements obtained in convective updraft regions showed enhanced spectral width within the temperature range from −10° to −20°C, while microphysical measurements showed the simultaneous presence of graupel, ice particles, and supercooled water at the same temperatures, together supporting noninductive charging as an important charging mechanism in these storms. A climatology of lightning flashes across the comma head of 16 winter cyclones shows that lightning flashes commonly occur on the southern side of the comma head where dry-slot air is more likely to overrun lower-level moist air. Over 90% of the cloud-to-ground flashes had negative polarity, suggesting the cells were not strongly sheared aloft. About 55% of the flashes were associated with cloud-to-ground flashes while 45% were in-cloud flashes. [ABSTRACT FROM AUTHOR]- Published
- 2014
- Full Text
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15. Diurnal Spatial Variability of Great Plains Summer Precipitation Related to the Dynamics of the Low-Level Jet.
- Author
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Pu, Bing and Dickinson, Robert E.
- Subjects
METEOROLOGICAL precipitation ,CONVECTION (Meteorology) ,DIURNAL variations in meteorology ,JETS (Fluid dynamics) ,ATMOSPHERIC sciences - Abstract
Diurnal variations of the Great Plains low-level jet (GPLLJ) and vertical motions have been related to the development of summer precipitation individually, but their underlying connection and consequences for the nocturnal and afternoon precipitation peaks are less discussed. This paper examines how together they help explain the spatial pattern of the frequency of summer convective precipitation over the Great Plains. A one-layer linearized boundary layer model is used to reproduce the diurnal cycle of the GPLLJ. Its periodic rising and sinking motions compare favorably with those of the North American Regional Reanalysis (NARR) climatology. Its development of rising motion is also consistent with the enhanced occurrence of nocturnal convective precipitation over the central and eastern Great Plains (90°-100°W) and afternoon maximum over the western Great Plains (100°-105°W). The diurnal phasing of the vertical motions can be captured by the model only if the diurnal oscillation of the jet is forced by both near surface geopotential gradients and friction with observed diurnal variability. The diurnal variation of the vertical velocity (or boundary layer convergence and divergence) is explained by local vorticity balance; that is, following the diurnal oscillation of the jet, the zonal gradient of the meridional wind oscillates and, thus, relative vorticity and its tendency. The slowing down of the jet after midnight decreases the anticyclonic (cyclonic) vorticity and consequently gives a positive (negative) vorticity tendency to the east (west) of the jet core; anomalous rising (sinking) motions occur to balance these positive (negative) vorticity tendencies. The pattern reverses when the jet is relatively weak. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
16. Numerical Simulations of Sheared Conditionally Unstable Flows over a Mountain Ridge.
- Author
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Miglietta, Mario Marcello and Rotunno, Richard
- Subjects
WINDS ,CLOUDS ,MOUNTAINS ,COMPUTER simulation ,ATMOSPHERIC sciences - Abstract
In two recent papers, the authors performed numerical simulations with a three-dimensional, explicitly cloud-resolving model for a uniform wind flowing past a bell-shaped ridge and using an idealized unstable (Weisman-Klemp) sounding with prescribed values of the relevant parameters. More recently, some observed cases of orographically forced wind profiles were analyzed, showing that, in order to reproduce larger rainfall rates, it was necessary to initialize the sounding with low-level flow toward the mountain with weak flow aloft (as observed). Additional experiments using the Weisman-Klemp sounding, but with nonuniform wind profiles, are performed here to identify the conditions in which the presence of a low-level cross-mountain flow together with calm flow aloft may increase the rain rates in conditionally unstable flows over the orography. The sensitivity of the solutions to the wind speed at the bottom and the top of a shear layer and the effect of different mountain widths and heights are systematically analyzed herein. Large rainfall rates are obtained when the cold pool, caused by the evaporative cooling of rain from precipitating convective clouds, remains quasi stationary upstream of the mountain peak. This condition occurs when the cold-pool propagation is approximately countered by the environmental wind. The large precipitation amounts can be attributed to weak upper-level flow, which favors stronger updrafts and upright convective cells, and to the ground-relative stationarity of the cells. This solution feature is produced with ambient wind shear within a narrow region of the parameter space explored here and does not occur in the numerical solutions obtained in the authors' previous studies with uniform wind profiles. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
17. A Shallow-Water Model for Convective Self-Aggregation
- Author
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Yang, Da
- Subjects
Gravity waves ,Radiative-convective equilibrium ,Atmospheric Sciences ,Meteorology & Atmospheric Sciences - Abstract
Randomly distributed convective storms can self-aggregate in the absence of large-scale forcings. Here we present a 1D shallow-water model to study the convective self-aggregation. This model simulates the dynamics of the planetary boundary layer and represents convection as a triggered process. Once triggered, convection lasts for finite time and occupies finite length. We show that the model can successfully simulate self-aggregation, and that the results are robust to a wide range of parameter values. In the simulations, convection excites gravity waves. The gravity waves then form a standing wave pattern, separating the domain into convectively active and inactive regions. We analyze the available potential energy (APE) budget and show that convection generates APE, providing energy for self-aggregation. By performing dimensional analysis, we develop a scaling theory for the size of convective aggregation, which is set by the gravity wave speed, damping time scale, and number density of convective storms. This paper provides a simple modeling framework to further study convective self-aggregation.
- Published
- 2021
18. The Implications of an Idealized Large-Scale Circulation for Mechanical Work Done by Tropical Convection.
- Author
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KAMIENIECKI, JAN A., AMBAUM, MAARTEN H. P., PLANT, ROBERT S., and WOOLNOUGH, STEVEN J.
- Subjects
THERMODYNAMICS ,CLIMATOLOGY ,ATMOSPHERIC sciences ,METEOROLOGY ,CLIMATE change - Abstract
A thermodynamic analysis is presented of an overturning circulation simulated by two cloud-resolving models, coupled by a weak temperature gradient parameterization. Taken together, they represent two separated regions over different sea surface temperatures, and the coupling represents an idealized large-scale circulation such as the Walker circulation. It is demonstrated that a thermodynamic budget linking net heat input to the generation of mechanical energy can be partitioned into contributions from the large-scale interaction between the two regions, as represented by the weak temperature gradient approximation, and from convective motions in the active warm region and the suppressed cool region. Model results imply that such thermodynamic diagnostics for the aggregate system are barely affected by the strength of the coupling, even its introduction, or by the SST contrast between the regions. This indicates that the weak temperature gradient parameterization does not introduce anomalous thermodynamic behavior. We find that the vertical kinetic energy associated with the large-scale circulation is more than three orders of magnitude smaller than the typical vertical kinetic energy in each region. However, even with very weak coupling circulations, the contrast between the thermodynamic budget terms for the suppressed and active regions is strong and is relatively insensitive to the degree of the coupling. Additionally, scaling arguments are developed for the relative values of the terms in the mechanical energy budget. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
19. Corrigendum.
- Author
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Adames, Ángel F. and Kim, Daehyun
- Subjects
HUMIDITY ,ATMOSPHERIC sciences - Abstract
A correction is presented to the article "The MJO as a dispersive, convectively coupled moisture wave: Theory and observations" that appeared in a 2016 issue.
- Published
- 2017
- Full Text
- View/download PDF
20. Symmetric Instability in the Outflow Layer of a Major Hurricane.
- Author
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Molinari, John and Vollaro, David
- Subjects
HURRICANES ,HURRICANE Ivan, 2004 ,CYCLONES ,TEMPERATURE ,ATMOSPHERIC sciences ,METEOROLOGY - Abstract
A set of 327 dropsondes from the NOAA G-IV aircraft was used to create a composite analysis of the azimuthally averaged absolute angular momentum in the outflow layer of major Hurricane Ivan (2004). Inertial instability existed over a narrow layer in the upper troposphere between the 350- and 450-km radii. Isolines of potential and equivalent potential temperature showed that the conditions for both dry and moist symmetric instability were satisfied in the same region, but over a deeper layer from 9 to 12 km. The radial flow maximized at the outer edge of the unstable region. The symmetrically unstable state existed above a region of outward decrease of temperature between the cirrus overcast of the storm and clear air outside. It is hypothesized that the temperature gradient was created as a result of longwave heating within the cirrus overcast and longwave cooling outside the cloudy region. This produced isentropes that sloped upward with radius in the same region that absolute momentum surfaces were flat or sloping downward, thus creating symmetric instability. Although this instability typically follows rather than precedes intensification, limited numerical evidence suggests that the reestablishment of a symmetrically neutral state might influence the length of the intensification period. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
21. The physics of orographic elevated heating in radiative-convective equilibrium
- Author
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Hu, S and Boos, WR
- Subjects
Meteorology & Atmospheric Sciences ,Atmospheric Sciences - Abstract
Elevated heating of the atmosphere by large plateaus has been argued to influence regional climate in Asia and other regions, but the mechanisms that cause the troposphere to equilibrate at warmer temperatures over elevated terrain are not well understood. This paper quantitatively describes the physics that controls temperatures over elevated terrain in radiative-convective equilibrium (RCE). First, a cloud-system-resolving model (CSRM) is used to simulate RCE states over surfaces with various elevations. Then, a theory for the influence of surface elevation on temperatures in RCE is presented. Together with offline radiative transfer calculations, this theory is used to quantitatively attribute the magnitude of the elevated heating effect to topof- atmosphere radiative flux changes caused by decreases in longwave absorption, shortwave scattering, and the moist lapse rate that occur as surface pressure drops. Sensitivity functions obtained through these offline calculations suggest that elevated heating is weaker in warmer climates, and additional CSRM simulations support this hypothesis. Under certain circumstances, even the sign of the elevated heating effect can change to produce cooler temperatures at a given pressure level as the surface is lifted in RCE.
- Published
- 2017
22. Data Availability Principles and Practice.
- Author
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Smith, Anne K., Barth, Mary, Boos, William R., Bou-Zeid, Elie, Kawatani, Yoshio, Lee, Sukyoung, Mechem, David, Remer, Lorraine, Rozoff, Christopher, van den Heeve, Susan, Wang, Zhuo, Wicker, Louis, and Yang, Ping
- Subjects
WORD frequency ,INFORMATION sharing ,ATMOSPHERIC sciences ,EMAIL - Abstract
The American Meteorological Society (AMS) recently updated its data policy guidelines (https://www.ametsoc.org/ index.cfm/ams/publications/ethical-guidelines-and-ams-policies/data-policy-and-guidelines/) to require, amongotherthings,thatpapersinitsjournalsincludeaDataAvailabilityStatement. AnneK.Smith Chief Editor,JAS MaryBarth Editor,JAS WilliamR.Boos Editor,JAS ElieBou-Zeid Editor,JAS YoshioKawatani Editor,JAS SukyoungLee Editor,JAS Denotescontent that is immediately availableupon publicationas openaccess. For information regarding reuse ofthis content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses). [Extracted from the article]
- Published
- 2020
- Full Text
- View/download PDF
23. A Unified Representation of Deep Moist Convection in Numerical Modeling of the Atmosphere. Part I.
- Author
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AKIO ARAKAWA and CHIEN-MING WU
- Subjects
CONVECTION (Meteorology) ,ATMOSPHERIC circulation ,ATMOSPHERE ,ATMOSPHERIC sciences ,CUMULUS clouds - Abstract
A generalized framework for cumulus parameterization applicable to any horizontal resolution between those typically used in general circulation and cloud-resolving models is presented. It is pointed out that the key parameter in the generalization is σ, which is the fractional area covered by convective updrafts in the grid cell. Practically all conventional cumulus parameterizations assume σ << 1, at least implicitly, using the gridpoint values of the thermodynamic variables to define the thermal structure of the cloud environment. The proposed framework, called "unified parameterization," eliminates this assumption from the beginning, allowing a smooth transition to an explicit simulation of cloud-scale processes as the resolution increases. If clouds and the environment are horizontally homogeneous with a top-hat profile, as is widely assumed in the conventional parameterizations, it is shown that the σ dependence of the eddy transport is through a simple quadratic function. Together with a properly chosen closure, the unified parameterization determines σ for each realization of grid-scale processes. The parameterization can also provide a framework for including stochastic parameterization. The remaining issues include parameterization of the in-cloud eddy transport because of the inhomogeneous structure of clouds. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
24. Interannual variability in North Atlantic weather: Data analysis and a quasi-geostrophic model
- Author
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Feliks, Yizhak, Robertson, Andrew W, and Ghil, Michael
- Subjects
Atmospheric Sciences ,Meteorology & Atmospheric Sciences - Abstract
This paper addresses the effect of interannual variability in jet stream orientation on weather systems over the North Atlantic basin (NAB). The observational analysis relies on 65 yr of NCEP-NCAR reanalysis (1948-2012). The total daily kinetic energy of the geostrophic wind (GTKE) is taken as a measure of storm activity over the North Atlantic. The NAB is partitioned into four rectangular regions, and the winter average of GTKE is calculated for each quadrant. The spatial GTKE average over all four quadrants shows striking year-to-year variability and is strongly correlated with the North Atlantic Oscillation (NAO). The GTKE strength in the northeast quadrant is closely related to the diffluence angle of the jet stream in the northwest quadrant. To gain insight into the relationship between the diffluence angle and its downstream impact, a quasigeostrophic baroclinic model is used. The results show that an initially zonal jet persists at its initial latitude over 30 days or longer, while a tilted jet propagates meridionally according to the Rossby wave group velocity, unless kept stationary by external forcing. A Gulf Stream-like narrow sea surface temperature (SST) front provides the requisite forcing for an analytical steady-state solution to this problem. This SST front influences the atmospheric jet in the northwest quadrant: It both strengthens the jet and tilts it northward at higher levels, while its effect is opposite at lower levels. Reanalysis data confirm these effects, which are consistent with thermal wind balance. The results suggest that the interannual variability found in the GTKE may be caused by intrinsic variability of the thermal Gulf Stream front.
- Published
- 2016
25. Interannual variability in north Atlantic weather: Data analysis and a quasigeostrophic model
- Author
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Feliks, Y, Robertson, AW, and Ghil, M
- Subjects
Meteorology & Atmospheric Sciences ,Atmospheric Sciences - Abstract
This paper addresses the effect of interannual variability in jet stream orientation on weather systems over the North Atlantic basin (NAB). The observational analysis relies on 65 yr of NCEP-NCAR reanalysis (1948-2012). The total daily kinetic energy of the geostrophic wind (GTKE) is taken as a measure of storm activity over the North Atlantic. The NAB is partitioned into four rectangular regions, and the winter average of GTKE is calculated for each quadrant. The spatial GTKE average over all four quadrants shows striking year-to-year variability and is strongly correlated with the North Atlantic Oscillation (NAO). The GTKE strength in the northeast quadrant is closely related to the diffluence angle of the jet stream in the northwest quadrant. To gain insight into the relationship between the diffluence angle and its downstream impact, a quasigeostrophic baroclinic model is used. The results show that an initially zonal jet persists at its initial latitude over 30 days or longer, while a tilted jet propagates meridionally according to the Rossby wave group velocity, unless kept stationary by external forcing. A Gulf Stream-like narrow sea surface temperature (SST) front provides the requisite forcing for an analytical steady-state solution to this problem. This SST front influences the atmospheric jet in the northwest quadrant: It both strengthens the jet and tilts it northward at higher levels, while its effect is opposite at lower levels. Reanalysis data confirm these effects, which are consistent with thermal wind balance. The results suggest that the interannual variability found in the GTKE may be caused by intrinsic variability of the thermal Gulf Stream front.
- Published
- 2016
26. Realization of Self-Preserving Size Distribution Theory for the Evolution of Tropospheric Atmospheric Aerosols through an Inverse Gaussian Distribution.
- Author
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Shen, J., Yu, M., Koivisto, A. J., Jiang, H., Liu, Y., Wang, L., and Hussein, T.
- Subjects
ATMOSPHERIC aerosols ,TROPOSPHERIC aerosols ,INVERSE Gaussian distribution ,EVOLUTIONARY theories ,ATMOSPHERIC sciences ,LOGNORMAL distribution - Abstract
The inverse Gaussian distributed method of moments (IGDMOM) was developed to analytically solve the kinetic collection equation (KCE) for the first time. Using the IGDMOM, we obtained both new analytical and asymptotic solutions to the KCE. This is shown for both the free-molecular and continuum regime collision frequency functions. The new analytical solutions are highly suitable for demonstrating the self-preserving size distribution (SPSD) theory. The SPSD theory is considered one of the most elegant research works in atmospheric science for aerosols or small cloud droplets. It was initially discovered by Friedlander and then developed by Lee with an assumption of the time-dependent lognormal size distribution function. In this study, we demonstrate that the SPSD theory of coagulating atmospheric aerosols can be presented in a simpler and more rigorous theoretical way, which is realized through the introduction of the IGDMOM for describing aerosol size distributions. Using the IGDMOM, the new formulas for the SPSD, as well as the time required for aerosols to reach the SPSD, are analytically provided and verified. Furthermore, we discover that the SPSD of atmospheric aerosols undergoing coagulation is only determined using a shape factor variable Ω, which is composed of the first three moments at an initial stage. This study has critical implications for developing tropospheric atmospheric aerosol or small cloud droplet dynamics models and further verifies the SPSD theory from the viewpoint of theoretical analysis. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
27. Dynamics of Cloud-Top Generating Cells in Winter Cyclones. Part II: Radiative and Instability Forcing
- Author
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Brian F. Jewett, Lulin Xue, Greg M. McFarquhar, Gregory Thompson, Roy Rasmussen, Changhai Liu, Jason M. Keeler, and Robert M. Rauber
- Subjects
Atmospheric Science ,010504 meteorology & atmospheric sciences ,Cloud top ,0208 environmental biotechnology ,02 engineering and technology ,Forcing (mathematics) ,Radiative forcing ,Atmospheric sciences ,01 natural sciences ,Instability ,020801 environmental engineering ,Weather Research and Forecasting Model ,Climatology ,Middle latitudes ,Radiative transfer ,Environmental science ,Precipitation ,0105 earth and related environmental sciences - Abstract
Recent field observations suggest that cloud-top precipitation generating cells (GCs) are ubiquitous in the warm-frontal and comma-head regions of midlatitude winter cyclones. The presence of fallstreaks emanating from the GCs and their persistence either to the surface or until merging into precipitation bands suggests that GCs are a critical component of the precipitation process in these cyclones. This paper is the second part of a three-part series that investigates the dynamics of GCs through very-high-resolution idealized Weather Research and Forecasting (WRF) Model simulations. This paper assesses the role of cloud-top instability paired with nighttime, daytime, or no radiative forcing on the development and maintenance (or lack) of GCs. Under initially unstable conditions at cloud top, GCs develop regardless of radiative forcing but only persist clearly with radiative forcing. Cloud-top destabilization due to longwave cooling leads to development of GCs even under initially neutral and stable conditions, providing a physical explanation for the observed ubiquity of GCs atop winter cyclones. GCs do not develop in initially stable simulations with no radiation. Decreased range in vertical velocity spectra under daytime radiative forcing is consistent with offset of the destabilizing influence of longwave cooling by shortwave heating.
- Published
- 2016
28. A PDF-Based Formulation of Microphysical Variability in Cumulus Congestus Clouds*
- Author
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Yefim L. Kogan and David B. Mechem
- Subjects
Atmospheric Science ,Cloud microphysics ,010504 meteorology & atmospheric sciences ,Meteorology ,Accretion (meteorology) ,Mesoscale meteorology ,Cloud water ,010502 geochemistry & geophysics ,Atmospheric sciences ,01 natural sciences ,Environmental science ,Probability distribution ,Simulation based ,Field campaign ,0105 earth and related environmental sciences - Abstract
Calculating unbiased microphysical process rates over mesoscale model grid volumes necessitates knowledge of the subgrid-scale (SGS) distribution of variables, typically represented as probability distribution functions (PDFs) of the prognostic variables. In the 2014 Journal of the Atmospheric Sciences paper by Kogan and Mechem, they employed large-eddy simulation of Rain in Cumulus over the Ocean (RICO) trade cumulus to develop PDFs and joint PDFs of cloud water, rainwater, and droplet concentration. In this paper, the approach of Kogan and Mechem is extended to deeper, precipitating cumulus congestus clouds as represented by a simulation based on conditions from the TOGA COARE field campaign. The fidelity of various PDF approximations was assessed by evaluating errors in estimating autoconversion and accretion rates. The dependence of the PDF shape on grid-mean variables is much stronger in congestus clouds than in shallow cumulus. The PDFs obtained from the TOGA COARE simulations for the calculation of accretion rates may be applied to both shallow and congestus cumulus clouds. However, applying the TOGA COARE PDFs to calculate autoconversion rates introduces unacceptably large errors in shallow cumulus clouds, thus precluding the use of a “universal” PDF formulation for both cloud types.
- Published
- 2015
29. Idealized Quasi-Biennial Oscillations in an Ensemble of Dry GCM Dynamical Cores
- Author
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Weiye Yao and Christiane Jablonowski
- Subjects
Physics ,Atmospheric Science ,Momentum (technical analysis) ,Oscillation ,Atmospheric circulation ,Atmospheric model ,Dissipation ,Atmospheric sciences ,Computational physics ,symbols.namesake ,symbols ,Relaxation (physics) ,Rayleigh scattering ,Stratosphere ,Physics::Atmospheric and Oceanic Physics - Abstract
The paper demonstrates that quasi-biennial oscillation (QBO)-like oscillations can be simulated in an ensemble of dry GCM dynamical cores that are driven by a simple Held–Suarez temperature relaxation and low-level Rayleigh friction. The tropical stratospheric circulations of four dynamical cores, which are options in NCAR’s Community Atmosphere Model, version 5 (CAM5), are intercompared. These are the semi-Lagrangian (SLD) and Eulerian (EUL) spectral transform, finite-volume (FV), and spectral element (SE) dynamical cores. The paper investigates how the model design choices impact the wave generation, propagation, and dissipation mechanisms in the equatorial region. SLD, EUL, and SE develop spontaneous QBO-like oscillations in the upper equatorial stratosphere, whereas FV does not sustain the oscillation. Transformed Eulerian-mean (TEM) analyses reveal that resolved waves are the dominant drivers of the QBOs. However, the Eliassen–Palm flux divergence is strongly counteracted by the TEM momentum budget residual, which represents the forcing by diffusion and thermal damping. Interestingly, a reversed Brewer–Dobson circulation accelerates the downward propagation of the SLD’s QBO, whereas the EUL’s and SE’s QBOs are slowed by a mean ascent. Waves are abundant in the SLD’s, EUL’s, and SE’s tropical atmosphere despite the absence of moist convection as a typical wave trigger. Dynamic instabilities are suggested as a wave-triggering mechanism in the troposphere and wave-dissipation process in the stratosphere. In particular, there are indications that the increased occurrences of strongly negative instability indicators in SLD, EUL, and SE are related to more vigorous wave activities and higher magnitudes of the resolved wave forcing in comparison to FV.
- Published
- 2015
30. Theory of Time-Dependent Freezing. Part I: Description of Scheme for Wet Growth of Hail
- Author
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Eyal Ilotoviz, Nir Benmoshe, Alexander Khain, and Vaughan T. J. Phillips
- Subjects
Atmospheric Science ,Cloud microphysics ,Materials science ,Accretion (meteorology) ,Liquid water ,Particle ,Precipitation ,Supercooling ,Atmospheric sciences ,Graupel - Abstract
At subzero temperatures, cloud particles can contain both ice and liquid water fractions. Wet growth of precipitation particles occurs when supercooled cloud liquid is accreted faster than it can freeze on impact. With a flexible framework, the theory of wet growth of hail is extended to the case of the inhomogeneities of surface temperature and of liquid coverage over the surface of the particle. The theory treats the heat fluxes between its wet and dry parts and radial heat fluxes from the sponge layer through the liquid skin to the air. The theory parameterizes effects of nonsphericity of hail particles on their growth by accretion. Gradual internal freezing of any liquid soaking the hail or graupel particle’s interior during dry growth (“riming”) is treated as well. In this way, the microphysical recycling envisaged by Pflaum in a paper in 1980 is treated, with alternating episodes of wet and dry growth. The present paper, the first of a two-part paper, describes the scheme to treat wet growth, accounting for dependencies on condensate content, temperature, and particle size. Comparison with the laboratory experiments is presented.
- Published
- 2014
31. Reply to ‘‘Comments on ‘How Much Does the Upward Advection of the Supergradient Component of Boundary Layer Wind Contribute to Tropical Cyclone Intensification and Maximum Intensity?’’’.
- Author
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LI, YUANLONG, WANG, YUQING, and LIN, YANLUAN
- Subjects
BOUNDARY layer (Aerodynamics) ,TROPICAL cyclones ,ADVECTION ,ATMOSPHERIC sciences ,PERIODICAL publishing - Abstract
This is a reply to the comments by , hereafter ) on the work of , hereafter ) recently published in the Journal of the Atmospheric Sciences. All the comments and concerns by have been well addressed or clarified. We think that most of the comments by are not in line with the intention of and provide one-sided and thus little scientifically meaningful arguments. Regarding the comment on the adequacy of the methodology adopted in , we believe that the design of the thought (sensitivity) experiment is adequate to address the scientific issue under debate and helps quantify the contribution by the upward advection of the supergradient component of boundary layer wind to tropical cyclone intensification, which is shown to be very marginal. Note that we are open to accept any alternative, better methods to be used to further address this scientific issue. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
32. The Mystery of Ice Crystal Multiplication in a Laboratory Experiment
- Author
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Gianni Santachiara, Franco Belosi, and Franco Prodi
- Subjects
Atmospheric Science ,Materials science ,Atmospheric pressure ,Ice crystals ,Atmospheric sciences ,Molecular physics ,Physics::Geophysics ,Sea ice growth processes ,Pancake ice ,Amorphous ice ,Ice nucleus ,Astrophysics::Earth and Planetary Astrophysics ,Clear ice ,Physics::Atmospheric and Oceanic Physics ,Frazil ice - Abstract
This paper addresses the problem of the large discrepancies between ice crystal concentrations in clouds and the number of ice nuclei in nearby clear air reported in published papers. Such discrepancies cannot always be explained, even by taking into account both primary and secondary ice formation processes. A laboratory experiment was performed in a cylindrical column placed in a cold room at atmospheric pressure and temperature in the −12° to −14°C range. Supercooled droplets were nucleated in the column, in the absence of aerosol ice nuclei, by injecting ice crystals generated outside in a small syringe. A rapid increase in the ice crystal concentration was observed in the absence of any known ice multiplication. The ratio between the mean number of ice crystals in the column, after complete droplet vaporization, and the number of ice crystals introduced in the column was about 10:1. The presence of small ice crystals (introduced at the top of the column) in the unstable system (supercooled droplets) appears to trigger the transformation in the whole supercooled liquid cloud. A possible explanation could be that the rapidly evaporating droplets cool sufficiently to determine a homogeneous nucleation.
- Published
- 2013
33. A Revised Conceptual Model of the Tropical Marine Boundary Layer. Part III: Bragg Scattering Layer Statistical Properties
- Author
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Robert M. Rauber, Margaret A. LeMone, Jennifer L. Davison, and Larry Di Girolamo
- Subjects
Atmospheric Science ,Boundary layer ,Mixed layer ,Diurnal cycle ,law ,Bragg's law ,Humidity ,Relative humidity ,Radar ,Layering ,Atmospheric sciences ,Geology ,law.invention - Abstract
This paper examines the structure and variability of the moisture field in the tropical marine boundary layer (TMBL) as defined by Bragg scattering layers (BSLs) observed with S-band radar. Typically, four to five BSLs were present in the TMBL, including the transition layer at the top of the surface-based mixed layer. The transition-layer depth (~350 m) exhibited a weak diurnal cycle because of changes in the mixed-layer depth. BSLs and the “clear” layers between them each had a median thickness of about 350 m and a lifetime over the radar of 8.4 h, with about 25% having lifetimes longer than 20 h. More (fewer) BSLs were present when surface winds had a more southerly (northerly) component. Both BSLs and clear layers increased in depth with increasing rain rates, with the rainiest days producing layers that were about 100 m thicker than those on the driest days. The analyses imply that the relative humidity (RH) field in the TMBL exhibits layering on scales observable by radar. Satellite and wind profiler measurements show that the layered RH structure is related, at least in part, to detraining cloudy air. Based on analyses in this series of papers, a revised conceptual model of the TMBL is presented that emphasizes moisture variability and incorporates multiple moist and dry layers and a higher TMBL top. The model is supported by comparing BSL tops with satellite-derived cloud tops. This comparison suggests that the layered RH structure is related, in part, to cloud detrainment at preferred altitudes within the TMBL. The potential ramifications of this change in TMBL conceptualization on modeling of the TMBL are discussed.
- Published
- 2013
34. Improvements to an Empirical Parameterization of Heterogeneous Ice Nucleation and Its Comparison with Observations
- Author
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Kerri A. Pratt, R. Subramanian, Vaughan T. J. Phillips, Cynthia H. Twohy, Constantin Andronache, Kimberly A. Prather, and Paul J. DeMott
- Subjects
Atmospheric Science ,Sea ice growth processes ,Ice crystals ,Ice nucleus ,Nucleation ,Environmental science ,Carbon black ,Atmospheric sciences ,Multiple species ,Aerosol - Abstract
A framework for an empirical parameterization (EP) of heterogeneous nucleation of ice crystals by multiple species of aerosol material in clouds was proposed in a 2008 paper by the authors. The present paper reports improvements to specification of a few of its empirical parameters. These include temperatures for onset of freezing, baseline surface areas of aerosol observed in field campaigns over Colorado, and new parameters for properties of black carbon, such as surface hydrophilicity and organic coatings. The EP’s third group of ice nucleus (IN) aerosols is redefined as that of primary biological aerosol particles (PBAPs), replacing insoluble organic aerosols. A fourth group of IN is introduced—namely, soluble organic aerosols.The new EP predicts IN concentrations that agree well with aircraft data from selected traverses of shallow wave clouds observed in five flights (1, 3, 4, 6, and 12) of the 2007 Ice in Clouds Experiment–Layer Clouds (ICE-L). Selected traverses were confined to temperatures between about −25° and −29°C in layer cloud without homogeneously nucleated ice from aloft. Some of the wave clouds were affected by carbonaceous aerosols from biomass burning and by dust from dry lakebeds and elsewhere. The EP predicts a trend between number concentrations of heterogeneously nucleated ice crystals and apparent black carbon among the five wave clouds, observed by aircraft in ICE-L. It is predicted in terms of IN activity of black carbon.The EP’s predictions are consistent with laboratory and field observations not used in its construction, for black carbon, dust, primary biological aerosols, and soluble organics. The EP’s prediction of biological ice nucleation is validated using coincident field observations of PBAP IN and PBAPs in Colorado.
- Published
- 2013
35. Effects of Three-Dimensional Photon Transport on the Radiative Forcing of Realistic Contrails
- Author
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Linda Forster, Simon Unterstrasser, Bernhard Mayer, and Claudia Emde
- Subjects
Atmospheric Science ,radiative forcing ,Photon ,Microphysics ,Scale (ratio) ,Meteorology ,contrail-cirrus ,Longwave ,contrail cluster ,contrail ,Radiative forcing ,Atmospheric sciences ,3d effects ,Radiative transfer ,Environmental science ,Dynamik der Atmosphäre ,MYSTIC ,Climate model ,Monte Carlo ,Shortwave - Abstract
Estimates of the global radiative forcing (RF) of line-shaped contrails and contrail cirrus exhibit a high level of uncertainty. In most cases, 1D radiative models have been used to determine the RF on a global scale. In this paper the effect of neglecting the 3D radiative effects of realistic contrails is quantified. Calculating the 3D effects of an idealized elliptical contrail as in the work of Gounou and Hogan with the 3D radiative transfer model MYSTIC (for “Monte Carlo code for the physically correct tracing of photons in cloudy atmospheres”) produced comparable results: as in Gounou and Hogan’s work the 3D effect (i.e., the difference in RF between a 3D calculation and a 1D approximation) on contrail RF was on the order of 10% in the longwave and shortwave. The net 3D effect, however, can be much larger, since the shortwave and longwave RF largely cancel during the day. For the investigation of the 3D effects of more realistic contrails, the microphysical input was provided by simulations of a 2D contrail-to-cirrus large-eddy simulation (LES) model. To capture some of the real variability in contrail properties, this paper examines two contrail evolutions from 20 min up to 6 h in an environment with either high or no vertical wind shear. This study reveals that the 3D effects show a high variability under realistic conditions since they depend strongly on the optical properties and the evolutionary state of the contrails. The differences are especially large for low elevations of the sun and contrails spreading in a sheared environment. Thus, a parameterization of the 3D effects in climate models would need to consider both geometry and microphysics of the contrail.
- Published
- 2012
36. Overlap of Solar and Infrared Spectra and the Shortwave Radiative Effect of Methane
- Author
-
Z. Sun, Jiangnan Li, F. Zhang, and Charles L. Curry
- Subjects
Earth's energy budget ,Atmospheric Science ,Meteorology ,business.industry ,Radiative forcing ,Atmospheric sciences ,Solar irradiance ,Solar energy ,Atmospheric radiative transfer codes ,Radiative transfer ,Environmental science ,Shortwave radiation ,business ,Shortwave - Abstract
This paper focuses on two shortcomings of radiative transfer codes commonly used in climate models. The first aspect concerns the partitioning of solar versus infrared spectral energy. In most climate models, the solar spectrum comprises wavelengths less than 4 μm with all incoming solar energy deposited in that range. In reality, however, the solar spectrum extends into the infrared, with about 12 W m−2 in the 4–1000-μm range. In this paper a simple method is proposed wherein the longwave radiative transfer equation with solar energy input is solved. In comparison with the traditional method, the new solution results in more solar energy absorbed in the atmosphere and less at the surface.As mentioned in a recent intercomparison of the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) and line-by-line (LBL) radiation models, most climate model radiation schemes neglect shortwave absorption by methane. However, the shortwave radiative forcing at the surface due to CH4 since the preindustrial period is estimated to exceed that due to CO2. The authors show that the CH4 shortwave effect can be included in a correlated k-distribution model, with the additional flux being accurately simulated in comparison with LBL models.Ten-year GCM simulations are presented, showing the detailed climatic effect of these changes in radiation treatment. It is demonstrated that the inclusion of solar flux in the infrared range produces a significant amount of extra warming in the atmosphere, specifically (i) in the tropical stratosphere where the warming can exceed 1 K day−1, and (ii) near the tropical tropopause layer. Additional GCM simulations show that inclusion of CH4 in the shortwave calculations also produces a warming of the atmosphere and a consequent reduction of the upward flux at the top of the atmosphere.
- Published
- 2010
37. Modeling Mesoscale Cellular Structures and Drizzle in Marine Stratocumulus. Part II: The Microphysics and Dynamics of the Boundary Region between Open and Closed Cells
- Author
-
Hailong Wang and Graham Feingold
- Subjects
Atmospheric Science ,Circulation (fluid dynamics) ,Microphysics ,Mesoscale meteorology ,Environmental science ,Liquid water path ,Precipitation ,Drizzle ,Atmospheric sciences ,Marine stratocumulus ,Aerosol - Abstract
This is the second of two companion papers on modeling of mesoscale cellular structures and drizzle in marine stratocumulus. In the first, aerosol–cloud–precipitation interactions and dynamical feedbacks were investigated to study the formation and evolution of open and closed cellular structures separately. In this paper, coexisting open and closed cells and how they influence one another are examined in a model domain of 180 × 60 × 1.5 km3. Simulations show that gradients in aerosol at the open–closed-cell boundary cause gradients in precipitation that generate a mesoscale circulation. The circulation promotes precipitation in the polluted closed cells but suppresses it in open cells by transporting water vapor to the closed-cell regime and carrying drier air and aerosol back to the open cells. The strength of this circulation depends on the contrast in precipitation under clean and polluted conditions at the boundary. Ship plumes emitted into clean, precipitating regions, simulated as a special case of a clean–polluted boundary, develop a similar circulation. Drizzle in the ship track is first suppressed by the increase in aerosol particles but later recovers and becomes even stronger because the local circulation enhances liquid water path owing to the convergence of water vapor from the region adjacent to the track. This circulation modifies the transport and mixing of ship plumes and enhances their dispersal. Finally, results show that whereas ship emissions do increase cloud albedo in regions of open cells, even the addition of very large aerosol concentrations cannot transform an open cellular structure to a closed one, for the case considered.
- Published
- 2009
38. Empirical Master Equations. Part II: Application to Stratospheric QBO, Solar Cycle, and Northern Annular Mode
- Author
-
Mauro Dall’Amico and Joseph Egger
- Subjects
Atmospheric Science ,Series (mathematics) ,Arctic oscillation ,Phase space ,Climatology ,Master equation ,Flux ,Probability density function ,Atmospheric sciences ,Stratosphere ,Geology ,Solar cycle - Abstract
Time series of stratospheric climate variables are used to derive master equations in the discretized phase space spanned by three variables. The empirical master equation (EME) predicts the probability density function (PDF) in this phase space. The numerical properties of EMEs have been investigated in the first part of this paper using synthetic time series. In this part of the paper, the time series consist of normalized and deseasonalized daily and zonally averaged meteorologically relevant quantities obtained from the 40-yr ECMWF Re-Analysis (ERA-40) and observations. One EME reproduces the climatological features of the quasi-biennial oscillation (QBO) of stratospheric equatorial zonal wind including the probabilistic character of transitions between phases. Also, the Arctic stratosphere at 10 hPa is about 2 K warmer during the easterly phase of the QBO than during the westerly phase. Another EME including a time series of the solar radio flux at 10.7 cm hints that the relationship between the QBO and the temperature in the Arctic stratosphere is shifted toward warmer (colder) states by about 1 K during periods of high (low) solar activity. Finally, an EME is derived from time series of variables highly correlated with the northern annular mode (NAM). The EME shows that NAM anomalies in the middle stratosphere propagate into the lower stratosphere and then into the lower troposphere with a time scale of about two and four weeks, respectively. The influence of strong tropospheric NAM anomalies is confined to the lower stratosphere.
- Published
- 2007
39. A Gray-Radiation Aquaplanet Moist GCM. Part I: Static Stability and Eddy Scale
- Author
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Isaac M. Held, Pablo Zurita-Gotor, and Dargan M. W. Frierson
- Subjects
Troposphere ,Convection ,Atmospheric Science ,Boundary layer ,Mixed layer ,Latent heat ,Baroclinity ,Radiative transfer ,Atmospheric sciences ,Physics::Atmospheric and Oceanic Physics ,Water vapor - Abstract
In this paper, a simplified moist general circulation model is developed and used to study changes in the atmospheric general circulation as the water vapor content of the atmosphere is altered. The key elements of the model physics are gray radiative transfer, in which water vapor and other constituents have no effect on radiative fluxes, a simple diffusive boundary layer with prognostic depth, and a mixed layer aquaplanet surface boundary condition. This GCM can be integrated stably without a convection parameterization, with large-scale condensation only, and this study focuses on this simplest version of the model. These simplifications provide a useful framework in which to focus on the interplay between latent heat release and large-scale dynamics. In this paper, the authors study the role of moisture in determining the tropospheric static stability and midlatitude eddy scale. In a companion paper, the effects of moisture on energy transports by baroclinic eddies are discussed. The authors vary a parameter in the Clausius–Clapeyron relation to control the amount of water in the atmosphere, and consider circulations ranging from the dry limit to 10 times a control value. The typical length scale of midlatitude eddies is found to be remarkably insensitive to the amount of moisture in the atmosphere in this model. The Rhines scale evaluated at the latitude of the maximum eddy kinetic energy fits the model results for the eddy scale well. Moist convection is important in determining the extratropical lapse rate, and the dry stability is significantly increased with increased moisture content.
- Published
- 2006
40. On the Forcing of the Summertime Great Plains Low-Level Jet.
- Author
-
Parish, Thomas R.
- Subjects
SUMMER ,ATMOSPHERE ,TOPOGRAPHY ,ATMOSPHERIC sciences ,WEATHER forecasting - Abstract
The low-level jet (LLJ) is a ubiquitous feature of the lower atmosphere over the Great Plains during summer. The LLJ is a nocturnal phenomenon, developing during the 6–9-h period after sunset. Forcing of the LLJ has been debated for over 60 years, the focus being on two processes: decoupling of the residual layer from the surface owing to nighttime cooling and diurnal heating and cooling of the sloping Great Plains topography. To examine characteristics and forcing mechanisms for the LLJ, composite grids were compiled from the North American Mesoscale Forecast System for the summertime months of June and July over a 5-yr period (2008–12). One composite set was assembled from well-developed LLJ episodes during which the maximum nocturnal jet magnitude at 0900 UTC over northwestern Oklahoma exceeded 20 m s−1. A second set consists of nonjet conditions for which the maximum nighttime wind magnitude in the lowest 3 km did not exceed 10 m s−1. The intensity of the horizontal pressure gradient and hence background geostrophic flow at jet level was the dominant difference between composite cases. The horizontal pressure gradient forms in response to the thermal wind above jet level that results primarily from seasonal heating of the sloping Great Plains. Thermal wind forcing is thus the key link between the Great Plains and the high frequency of LLJ occurrence. The nocturnal wind maximum develops primarily because of the inertial oscillation of the ageostrophic wind occurring after decoupling of the lower atmosphere from the surface owing to radiational cooling in the early evening. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
41. Drizzle in Stratiform Boundary Layer Clouds. Part II: Microphysical Aspects
- Author
-
Robert Wood
- Subjects
Coalescence (physics) ,Atmospheric Science ,Boundary layer ,Exponential distribution ,Meteorology ,Log-normal distribution ,Extrapolation ,Drizzle ,Atmospheric sciences ,Geology ,Aerosol ,Exponential function - Abstract
This is the second of two observational papers examining drizzle in stratiform boundary layer clouds. Part I details the vertical and horizontal structure of cloud and drizzle parameters, including some bulk microphysical variables. In this paper, the focus is on the in situ size-resolved microphysical measurements, particularly of drizzle drops (r > 20 μm). Layer-averaged size distributions of drizzle drops within cloud are shown to be well represented using either a truncated exponential or a truncated lognormal size distribution. The size-resolved microphysical measurements are used to estimate autoconversion and accretion rates by integration of the stochastic collection equation (SCE). These rates are compared with a number of commonly used bulk parameterizations of warm rain formation. While parameterized accretion rates agree well with those derived from the SCE initialized with observed spectra, the autoconversion rates seriously disagree in some cases. These disagreements need to be addressed in order to bolster confidence in large-scale numerical model predictions of the aerosol second indirect effect. Cloud droplet coalescence removal rates and mass and number fall rate relationships used in the bulk microphysical schemes are also compared, revealing some potentially important discrepancies. The relative roles of autoconversion and accretion are estimated by examination of composite profiles from the 12 flights. Autoconversion, although necessary for the production of drizzle drops, is much less important than accretion throughout the lower 80% of the cloud layer in terms of the production of drizzle liquid water. The SCE calculations indicate that the autoconversion rate depends strongly upon the cloud droplet concentration Nd such that a doubling of Nd would lead to a reduction in autoconversion rate of between 2 and 4. Radar reflectivity–precipitation rate (Z–R) relationships suitable for radar use are derived and are shown to be significantly biased in some cases by the undersampling of large (r > 200 μm) drops with the 2D-C probe. A correction based upon the extrapolation to larger sizes using the exponential size distribution changes the Z–R relationship, leading to the conclusion that consideration should be given to sampling issues when examining higher moments of the drop size distribution in drizzling stratiform boundary layer clouds.
- Published
- 2005
42. A Multiple Mass Flux Parameterization for the Surface-Generated Convection. Part II: Cloudy Cores
- Author
-
Sylvain Cheinet
- Subjects
Physics::Fluid Dynamics ,Mass flux ,Surface (mathematics) ,Convection ,Atmospheric Science ,Atmospheric convection ,Cloud cover ,Surface layer ,Atmospheric sciences ,Physics::Atmospheric and Oceanic Physics ,Free convective layer ,Geology ,Mixing (physics) - Abstract
The multiple mass-flux approach introduced in a companion paper aims at parameterizing the surface-generated convection in the atmosphere. The original aspects of this model are as follows. A number of convective updrafts are released in the surface layer. They initially have distinct fractional area and thermodynamic properties, determined through surface layer similarity; that is, by assuming that the thermodynamic fluxes are constant throughout the surface layer. Each updraft ascent is diagnosed using an entraining plume model. In the case of cumulus convection, this comprehensive formulation provides consistent representations of the subcloud mixing, the cloud mixing, and the associated cloudiness. In the present paper, this model is evaluated in two shallow moist convection cases, using the one-dimensional modeling framework. In the continental convection case, the diurnal cloud growth and the related subcloud layer ventilation agree with large eddy simulations. In the oceanic convection cas...
- Published
- 2004
43. Toward Multiscale Simulation of Moist Flows with Soundproof Equations
- Author
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Wojciech W. Grabowski, Piotr K. Smolarkiewicz, and Marcin J. Kurowski
- Subjects
Atmospheric Science ,010504 meteorology & atmospheric sciences ,Perturbation (astronomy) ,Atmospheric model ,Solver ,Atmospheric sciences ,01 natural sciences ,010305 fluids & plasmas ,law.invention ,Soundproofing ,13. Climate action ,law ,0103 physical sciences ,Thermal ,Environmental science ,Hydrostatic equilibrium ,Physics::Atmospheric and Oceanic Physics ,0105 earth and related environmental sciences - Abstract
This paper discusses the incorporation of phase changes of the water substance that accompany moist atmospheric flows into the all-scale atmospheric model based on soundproof equations. A specific issue involves developing a theoretical basis and practical implementation to include pressure perturbations associated with atmospheric circulations, from small scale to global, into representations of moist thermodynamics. In small-scale modeling using soundproof equations, pressure perturbations are obtained from the elliptic pressure solver and are typically excluded from the moist thermodynamics. This paper argues that in larger-scale flows, at least the hydrostatic component of the pressure perturbation needs to be included because pressure variation in synoptic weather systems may affect moist thermodynamics in a way comparable to the temperature variations. As an illustration, two idealized test problems are considered: the small-scale moist thermal rising in a stratified environment and the moist mesoscale flow over idealized topography. The paper compares numerical solutions obtained with a fully compressible acoustic mode–resolving model and with two versions of the anelastic model, either including or excluding anelastic pressure perturbations in moist thermodynamics. The two versions of the anelastic model are referred to as the generalized and standard anelastic. In agreement with the scaling arguments, only negligible differences between anelastic and compressible solutions are simulated. Incorporation of the anelastic pressure perturbations into moist thermodynamics paves the way for future studies where larger-scale moist dynamics will be considered.
- Published
- 2013
- Full Text
- View/download PDF
44. A Very High Resolution General Circulation Model Simulation of the Global Circulation in Austral Winter
- Author
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Philip W. Jones, Kevin Hamilton, and R. John Wilson
- Subjects
Atmospheric Science ,Atmospheric circulation ,Polar vortex ,Climatology ,Extratropical cyclone ,Westerlies ,Gravity wave ,Atmospheric sciences ,Surface pressure ,Stratosphere ,Physics::Atmospheric and Oceanic Physics ,Geology ,Vortex - Abstract
This paper discusses a simulation obtained with the Geophysical Fluid Dynamics Laboratory ‘‘SKYHI’’ troposphere‐stratosphere‐mesosphere general circulation model run at very high horizontal resolution (;60-km grid spacing) and without any parameterization of subgrid-scale gravity wave drag. The results are for a period around the austral winter solstice, and the emphasis is on the simulated Southern Hemisphere (SH) winter circulation. Comparisons are made with results obtained from lower horizontal resolution versions of the same model. The focus in this paper is on two particularly striking features of the high-resolution simulation: the extratropical surface winds and the winter polar middle atmospheric vortex. In the extratropical SH, the simulated surface westerlies and meridional surface pressure gradients in the high-resolution model are considerably stronger than observed and are stronger than those simulated at lower horizontal resolution. In the middle atmosphere, the high-resolution model produces a simulation of the zonal mean winter polar vortex that is considerably improved over that found with lower resolution models (although it is still significantly affected by the usual cold pole bias). Neither the improvement of the middle atmospheric polar vortex simulation nor the deterioration of the simulation of surface winds with increased model resolution shows a clear convergence, even at the ;60-km grid spacing employed here.
- Published
- 1997
45. A Gravity Wave Drag Matrix for Complex Terrain.
- Author
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SMITH, RONALD B. and KRUSE, CHRISTOPHER G.
- Subjects
GRAVITY waves ,HYDRODYNAMICS ,WAVES (Physics) ,COMPUTER simulation ,ATMOSPHERIC waves ,CLIMATOLOGY ,ATMOSPHERIC sciences - Abstract
We propose a simplified scheme to predict mountain wave drag over complex terrain using only the regional-average low-level wind components U and V. The scheme is tuned and tested on data from the South Island of New Zealand, a rough and highly anisotropic terrain. The effect of terrain anisotropy is captured with a hydrostatically computed, 2 3 2 positive-definite wave drag matrix. The wave drag vector is the product of the wind vector and the drag matrix. The nonlinearity in wave generation is captured using a Gaussian terrain smoothing inversely proportional to wind speed. Wind speeds of |U| 5 10, 20, and 30 m s
1 give smoothing scales of L 5 54, 27, and 18 km, respectively. This smoothing treatment of nonlinearity is consistent with recent aircraft data and high-resolution numerical modeling of waves over New Zealand, indicating that the momentum flux spectra shift to shorter waves during high-drag conditions. The drag matrix model is tested against a 3-month time series of realistic full-physics wave-resolving flow calculations. Correlation coefficients approach 0.9 for both zonal and meridional drag components. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
46. Simulated Kelvin-Helmholtz Waves over Terrain and Their Microphysical Implications.
- Author
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CONRICK, ROBERT, MASS, CLIFFORD F., and QI ZHONG
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METEOROLOGICAL precipitation ,ATMOSPHERIC physics ,CLIMATOLOGY ,ATMOSPHERIC circulation ,ATMOSPHERIC sciences - Abstract
Two Kelvin-Helmholtz (KH) wave events over western Washington State were simulated and evaluated using observations from the Olympic Mountains Experiment (OLYMPEX) field campaign. The events, 12 and 17 December 2015, were simulated realistically by the WRF-ARW Model, duplicating the mesoscale environment, location, and structure of embedded KH waves, which had observed wavelengths of approximately 5 km. In simulations of both cases, waves developed from instability within an intense shear layer, caused by low-level easterly flow surmounted by westerly winds aloft. The low-level easterlies resulted from blocking by the Olympic Mountains in the 12 December case, while in the 17 December event, the easterly flow was produced by the synoptic environment. Simulated microphysics were evaluated for both cases using OLYMPEX observations. When the KH waves were within the melting level, simulated microphysical fields, such as hydrometeor mixing ratios, evinced considerable oscillatory behavior. In contrast, when waves were located below the melting level, the microphysical response was attenuated. Turning off the model's microphysics scheme and latent heating resulted in weakened KH wave activity, while removing the Olympic Mountains eliminated KH waves in the 12 December event but not the 17 December case. Finally, the impact of several microphysics parameterizations on KH activity was evaluated for both events. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
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47. Kelvin-Helmholtz Waves in Precipitating Midlatitude Cyclones.
- Author
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BARNES, HANNAH C., ZAGRODNIK, JOSEPH P., MCMURDIE, LYNN A., ROWE, ANGELA K., and HOUZE JR., ROBERT A.
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CLIMATOLOGY ,METEOROLOGY ,METEOROLOGICAL precipitation ,THEORY of wave motion ,ELECTROMAGNETIC waves ,CYCLONES ,ATMOSPHERIC sciences - Abstract
This study examines Kelvin-Helmholtz (KH) waves observed by dual-polarization radar in several precipitating midlatitude cyclones during the Olympic Mountains Experiment (OLYMPEX) field campaign along the windward side of the Olympic Mountains in Washington State and in a strong stationary frontal zone in Iowa during the Iowa Flood Studies (IFloodS) field campaign. While KH waves develop regardless of the presence or absence of mountainous terrain, this study indicates that the large-scale flow can be modified when encountering a mountain range in such a way as to promote development of KH waves on the windward side and to alter their physical structure (i.e., orientation and amplitude). OLYMPEX sampled numerous instances of KH waves in precipitating clouds, and this study examines their effects on micro-physical processes above, near, and below the melting layer. The dual-polarization radar data indicate that KH waves above the melting layer promote aggregation. KH waves centered in the melting layer produce the most notable signatures in dual-polarization variables, with the patterns suggesting that the KH waves promote both riming and aggregation. Both above and near the melting layer ice particles show no preferred orientation likely because of tumbling in turbulent air motions. KH waves below the melting layer facilitate the generation of large drops via coalescence and/or vapor deposition, increasing mean drop size and rain rate by only slight amounts in the OLYMPEX storms. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
48. The Role of Cold Pools in Tropical Oceanic Convective Systems.
- Author
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GRANT, LEAH D., LANE, TODD P., and VAN DEN HEEVER, SUSAN C.
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CLIMATOLOGY ,ATMOSPHERIC sciences ,METEOROLOGY ,CONVECTION (Meteorology) ,ATMOSPHERIC circulation - Abstract
The processes governing organized tropical convective systems are not completely understood despite their important influences on the tropical atmosphere and global circulation. In particular, cold pools are known to influence the structure and maintenance of midlatitude systems via Rotunno-Klemp-Weisman (RKW) theory, but cold pools may interact differently with tropical convection because of differences in cold pool strength and environmental shear. In this study, the role of cold pools in organized oceanic tropical convective systems is investigated, including their influence on system intensity, mesoscale structure, and propagation. To accomplish this goal, high-resolution idealized simulations are performed for two different systems that are embedded within a weakly sheared cloud population approaching radiative-convective equilibrium. The cold pools are altered by changing evaporation rates below cloud base in a series of sensitivity tests. The simulations demonstrate surprising findings: when cold pools are weakened, the convective systems become more intense. However, their propagation speeds and mesoscale structure are largely unaffected by the cold pool changes. Passive tracers introduced into the cold pools indicate that the convection intensifies when cold pools are weakened because cold pool air is entrained into updrafts, thereby reducing updraft intensity via the cold pools' initial negative buoyancy. Gravity waves, rather than cold pools, appear to be the important modulators of system propagation and mesoscale structure. These results reconfirm that RKW theory does not fully explain the behavior of tropical oceanic convective systems, even those that otherwise appear consistent with RKW thinking. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
49. Nondissipative and Dissipative Momentum Deposition by Mountain Wave Events in Sheared Environments.
- Author
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KRUSE, CHRISTOPHER G. and SMITH, RONALD B.
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CLIMATOLOGY ,METEOROLOGY ,NUMERICAL analysis ,ATMOSPHERIC models ,GRAVITY waves ,ATMOSPHERIC sciences - Abstract
Mountain waves (MWs) are generated during episodic cross-barrier flow over broad-spectrum terrain. However, most MW drag parameterizations neglect transient, broad-spectrum dynamics. Here, the influences of these dynamics on both nondissipative and dissipative momentum deposition by MW events are quantified in a 2D, horizontally periodic idealized framework. The influences of the MW spectrum, vertical wind shear, and forcing duration are investigated. MW events are studied using three numerical models--the nonlinear, transient WRF Model; a linear, quasi-transient Fourier-ray model; and an optimally tuned Lindzen-type saturation parameterization--allowing quantification of total, nondissipative, and dissipative MW-induced decelerations, respectively. Additionally, a pseudomomentum diagnostic is used to estimate nondissipative decelerations within the WRF solutions. For broad-spectrum MWs, vertical dispersion controls spectrum evolution aloft. Short MWs propagate upward quickly and break first at the highest altitudes. Subsequently, the arrival of additional longer MWs allows breaking at lower altitudes because of their greater contribution to u variance. As a result, minimum breaking levels descend with time and event duration. In zero-and positive-shear environments, this descent is not smooth but proceeds downward in steps as a result of vertically recurring steepening levels. Nondissipative decelerations are nonnegligible and influence an MW's approach to breaking, but breaking and dissipative decelerations quickly develop and dominate the subsequent evolution. Comparison of the three model solutions suggests that the conventional instant propagation and monochromatic parameterization assumptions lead to too much MW drag at too low an altitude. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
50. The Transition from Downward to Upward Air-Sea Momentum Flux in Swell-Dominated Light Wind Conditions.
- Author
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HÖGSTRÖM, ULF, SAHLÉE, ERIK, SMEDMAN, ANN-SOFI, RUTGERSSON, ANNA, NILSSON, ERIK, KAHMA, KIMMO K., and DRENNAN, WILLIAM M.
- Subjects
CLIMATOLOGY ,ATMOSPHERIC sciences ,METEOROLOGY ,NUMERICAL analysis ,COMPUTER simulation - Abstract
Fifteen hours of consecutive swell data from the experiment Flux, État de la Mer, et Télédétection en Condition de Fetch Variable (FETCH) in the Mediterranean show a distinct upward momentum flux. The characteristics are shown to vary systematically with wind speed. A hysteresis effect is found for wave energy of the wind-sea waves when represented as a function of wind speed, displaying higher energy during decaying winds compared to increasing winds. For the FETCH measurements, the upward momentum transfer regime is found to begin for wind speeds lower than about U 5 4m s
1 . For the lowest observed wind speeds U , 2.4 m s1 , the water surface appears to be close to dynamically smooth. In this range almost all the upward momentum flux is accomplished by the peak in the cospectrum between the vertical and horizontal components of the wind velocity. It is demonstrated that this contribution in turn is linearly related to the swell significant wave height Hsd in the range 0.6 , Hsd , 1.4 m. For Hsd , 0.6 m, the contribution is zero in the present dataset but may depend on the swell magnitude in other situations. It is speculated that the observed upward momentum flux in the smooth regime, which is so strongly related to the cospectral peak at the dominant swell frequency, might be caused by the recirculation mechanism found by Wen and Mobbs in their numerical simulation of laminar flow of a nonlinear progressive wave at low wind speed. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
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