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In this study, we utilize a novel approach to solve the Ekman equations for eddy-viscosity profiles in the stable boundary-layer. By doing so, a well-known expression for the stable boundary-layer height by Zilitinkevich (Boundary-Layer Meteorology, 1972, Vol. 3, 141–145) is rediscovered.

In this study, we utilize a novel approach to solve the Ekman equations for eddy-viscosity profiles in the stable boundary-layer. By doing so, a well-known expression for the stable boundary-layer height by Zilitinkevich (Boundary-Layer Meteorology, 1972, Vol. 3, 141–145) is rediscovered., Atmospheric Remote Sensing

Through comparing the mean wind profiles observed overland during the passages of four typhoons, and the gradient wind speeds calculated based on the sea level pressure data provided by a numerical model, the present paper discusses, (a) whether the gradient balance is a valid assumption to estimate the wind speed in the height range of 1250 m ∼1750 m, which is defined as the upper-level mean wind speed, in a tropical cyclone over land, and (b) if the super-gradient feature is systematically observed below the height of 1500 m in the tropical cyclone wind field over land. It has been found that, (i) the gradient balance is a valid assumption to estimate the mean upper-level wind speed in tropical cyclones in the radial range from the radius to the maximum wind (RMW) to three times the RMW, (ii) the super-gradient flow dominates the wind field in the tropical cyclone boundary layer inside the RMW and is frequently observed in the radial range from the RMW to twice the RMW, (iii) the gradient wind speed calculated based on the post-landfall sea level pressure data underestimates the overall wind strength at an island site inside the RMW, and (iv) the unsynchronized decay of the pressure and wind fields in the tropical cyclone might be the reason for the underestimation.

Through comparing the mean wind profiles observed overland during the passages of four typhoons, and the gradient wind speeds calculated based on the sea level pressure data provided by a numerical model, the present paper discusses, (a) whether the gradient balance is a valid assumption to estimate the wind speed in the height range of 1250 m ∼1750 m, which is defined as the upper-level mean wind speed, in a tropical cyclone over land, and (b) if the super-gradient feature is systematically observed below the height of 1500 m in the tropical cyclone wind field over land. It has been found that, (i) the gradient balance is a valid assumption to estimate the mean upper-level wind speed in tropical cyclones in the radial range from the radius to the maximum wind (RMW) to three times the RMW, (ii) the super-gradient flow dominates the wind field in the tropical cyclone boundary layer inside the RMW and is frequently observed in the radial range from the RMW to twice the RMW, (iii) the gradient wind speed calculated based on the post-landfall sea level pressure data underestimates the overall wind strength at an island site inside the RMW, and (iv) the unsynchronized decay of the pressure and wind fields in the tropical cyclone might be the reason for the underestimation.

Through comparing the mean wind profiles observed overland during the passages of four typhoons, and the gradient wind speeds calculated based on the sea level pressure data provided by a numerical model, the present paper discusses, (a) whether the gradient balance is a valid assumption to estimate the wind speed in the height range of 1250 m ∼1750 m, which is defined as the upper-level mean wind speed, in a tropical cyclone over land, and (b) if the super-gradient feature is systematically observed below the height of 1500 m in the tropical cyclone wind field over land. It has been found that, (i) the gradient balance is a valid assumption to estimate the mean upper-level wind speed in tropical cyclones in the radial range from the radius to the maximum wind (RMW) to three times the RMW, (ii) the super-gradient flow dominates the wind field in the tropical cyclone boundary layer inside the RMW and is frequently observed in the radial range from the RMW to twice the RMW, (iii) the gradient wind speed calculated based on the post-landfall sea level pressure data underestimates the overall wind strength at an island site inside the RMW, and (iv) the unsynchronized decay of the pressure and wind fields in the tropical cyclone might be the reason for the underestimation.

The marine atmospheric boundary layer is strongly influenced by the moving surface in the presence of surface waves; the impact depends on the wave conditions and the interaction with the atmosphere. Previous studies using measurements as well as numerical simulations with large-eddy simulations have shown that surface waves propagating faster than the wind (swell) alter the surface exchange as well as turbulence properties in the atmosphere. This impact is here introduced in a coupled wave-atmosphere regional climate model with a so-called E − l turbulence scheme (where E is the turbulent kinetic energy and l is a mixing length). A wave age dependent coefficient (here called Wmix) is added to the mixing length in the turbulence parameterization. This acts similarly to inducing additional convection, with larger mixing length and increased eddy diffusivity, when we have near neutral stratification and strong swell. For shallow boundary layers the regional coupled climate model shows a larger response to the introduced wave coupling with increased near surface wind speed and smaller wind gradient between the surface and middle part of the boundary layer. The impact for the studied areas is relatively minor for parameters averaged over 1 year, but for limited periods and specific situations the impact is larger. One could expect a larger impact in areas with stronger swell dominance. We thus conclude that the impact of swell waves on the mixing in the boundary layer is not insignificant and should be taken into account when developing wave-atmosphere coupled regional climate models or global climate models.

The statistics of atmospheric stability and non-dimensional wind profiles are studied using the standard surface-layer theory at Egmond aan Zee in the North Sea. Measurements at 21, 70 and 116 m are used to validate the theoretical profiles. Charnock’s relation is used to estimate the sea surface roughness. Bulk Richardson number is used to estimate the Obukhov length. The measured sea water temperature has a positive bias of 0.82?C resulting in the dominance of unstable conditions and a poor agreement of the theoretical wind profiles with the measurements. The conditions at Egmond aan Zee are dominated by unstable and neutral stabilities. The theoretical wind profiles agree very well with the measurements in the unstable and neutral conditions. In stable conditions, the wind profiles are over-predicted significantly as the height increases. The scaling of the wind profile with respect to the boundary layer height is necessary under stable conditions and the addition of another length scale parameter is preferred., Aerodynamics, Wind Energy & Propulsion, Aerospace Engineering

The statistics of atmospheric stability and non-dimensional wind profiles are studied using the standard surface-layer theory at Egmond aan Zee in the North Sea. Measurements at 21, 70 and 116 m are used to validate the theoretical profiles. Charnock’s relation is used to estimate the sea surface roughness. Bulk Richardson number is used to estimate the Obukhov length. The measured sea water temperature has a positive bias of 0.82?C resulting in the dominance of unstable conditions and a poor agreement of the theoretical wind profiles with the measurements. The conditions at Egmond aan Zee are dominated by unstable and neutral stabilities. The theoretical wind profiles agree very well with the measurements in the unstable and neutral conditions. In stable conditions, the wind profiles are over-predicted significantly as the height increases. The scaling of the wind profile with respect to the boundary layer height is necessary under stable conditions and the addition of another length scale parameter is preferred., Aerodynamics, Wind Energy & Propulsion, Aerospace Engineering

Results from large-eddy simulations and field measurements have previously shown that the velocity field is influenced by the boundary layer height, z (i) , during close to neutral, slightly unstable, atmospheric stratification. During such conditions the non-dimensional wind profile, phi (m) , has been found to be a function of both z/L and z (i) /L. At constant z/L, phi (m) decreases with decreasing boundary layer height. Since phi (m) is directly related to the parameterizations of the air-sea surface fluxes, these results will have an influence when calculating the surface fluxes in weather and climate models. The global impact of this was estimated using re-analysis data from 1979 to 2001 and bulk parameterizations. The results show that the sum of the global latent and sensible mean heat fluxes increase by 0.77 W m(-2) or about 1% and the mean surface stress increase by 1.4 mN m(-2) or 1.8% when including the effects of the boundary layer height in the parameterizations. However, some regions show a larger response. The greatest impact is found over the tropical oceans between 30A degrees S and 30A degrees N. In this region the boundary layer height influences the non-dimensional wind profile during extended periods of time. In the mid Indian Ocean this results in an increase of the mean annual heat fluxes by 2.0 W m(-2) and an increase of the mean annual surface stress by 2.6 mN m(-2).

The ability of the U.S. Navy's Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS) (Trademark) to accurately forecast the height and structure of the Marine Boundary Layer (MBL) in the coastal zone is analyzed and compared to surface and aircraft observations from the Dynamics and Evolution of Coastal Stratus (DECS) field study conducted along the central coast of California from June 16 to July 22, 1999. The stratus field was found to have significant mesoscale variability within 100 km of the coast due to interaction between the mean flow and the coastal terrain. This structure is consistent with general hydraulic flow theory and the development of a low-level coastal jet. However, the specific characteristics on any given day were very sensitive to flow direction, inversion height, and synoptic conditions. With some modifications, the model predicted the general evolution of these events with qualitative fidelity, but was slow to dissipate the cloud and frequently produced surface fog versus stratus. A consistent tendency was found in the model's predictions of inversion heights 200-300 meters too low, weak inversion strengths, high integrated liquid water content, and weak buoyancy flux near the cloud top. These observed biases are consistent with underestimating the cloud top entrainment velocity and entrainment fluxes in the modeled boundary layer. An explicit entrainment parameterization was developed to better represent the sub-grid scale processes at cloud top and was tested in the single column and 3D versions of COAMPS. The entrainment parameterization was found to improve the boundary layer height and cloud liquid water content as compared to field observations, but the modeled boundary layer still exhibited a low bias, and the entrainment velocity was higher than is generally expected from field studies for this regime. (2 tables, 53 figures. 80 refs.), The original document contains color images.

Analytical solutions of a set of equations that couples the Ekman and the Prandtl boundary layer (BL) equations were obtained; closure on the subgrid scale was via the eddy exchange (K) approach, where K was made to depend on both the internal stability (μ) and height raised to an arbitrary power. The boundary layer height (h) wis also made to depend on μs. As byproducts of these solutions, generalized expressions for the universal functions of μ, A, B and C and for the resistance and heat-transfer laws (i. e. a, u*/G ind T*/0, respectively) for a given set of external parameters (X, Ro and S) for the general case of the slope angle 0~~~10 rad were presented. From this, an interesting and novel result is the finding that there are three different regimes of solutions depending on whether S (or ~) is less than, equal to or greater than certain critical value S (or ~ ). The solutions for all three regimes were presented in graphical form, from which the appreciable influence of terrain slope on the cross-isobaric inflow angle, the momentum- and heat-transfer is clearly discernible. Also in a preliminary test of the results of this investigation with observations, it is found that the theoretical values of the cross-isobaric angle are in good agreement with the observed values in Antarctica and therefore encouraging for further research.

The objective of this thesis is to investigate the vertical structure of the atmosphere and to assess the performance of several radiosonde- and lidar-based methods to detect the boundary layer height within the Inn Valley. All of these methods are developed for horizontally homogeneous and flat terrain. Radiosonde methods include different versions of the parcel and Richardson number methods and are, therefore, based on vertical profiles of virtual potential temperature, potential temperature, and horizontal wind speed, while lidar methods are based on vertical profiles of velocity variance, dissipation rate of turbulent kinetic energy, and backscatter intensities. The investigation of the performance of these methods as well as the vertical structure is based on data collected during the CROSSINN field campaign in summer 2019 in the lower Inn Valley near Kolsass and mainly focuses on two case studies. Potential temperature profiles measured by radiosondes during daytime confirm previous studies with regard to the existence of two nearly neutral layers, separated by a region of enhanced stability. The case studies illustrate that the depth of the upper layer is larger than the depth of the lower layer. In both case studies, the elevated near-neutral layer extended above mean crest height. The case studies also indicate that the radiosonde methods and the lidar methods based on turbulence determine mixing heights that can be related to the top of the lower well-mixed layer during convective conditions, while mixing heights derived from backscatter profiles are not determined by unique but rather case-dependent processes. From the radiosondes, it is found that the surface connected mixed layer only extends up to around 300 to 500~m~above ground level on average. Nevertheless, warming occurred above this mixed layer, which is too strong to be explained by large-scale advection alone. This result demonstrates the importance of additional transport and mixing processes, by Paul Josef Ladstätter, Masterarbeit University of Innsbruck 2020

The statistical properties of five boundary layer height definitions were examined in 6,593 NCAR GPS dropsonde observations of the hurricane environment. Based on similar composite analysis studies, these boundary layer height estimates were divided into two categories based on their analytical characteristics. Three dynamical methods of estimating the boundary layer height were combined with two thermodynamical methods of estimating the mixed layer depth to numerically interrogate the physical properties of hurricanes within two primary modes of variability: azimuthal and geographic region. The results confirmed the vertical bifurcation of dynamical and thermodynamical height estimates and indicated a consistent distinction in the radial variability of each class. Moreover, the tangential wind field was well-described by the modified Rankine vortex. A characteristic decrease in boundary layer height with decreasing radius to the storm center was expressed in four of the five definitions. The non-uniform azimuthal distribution of relative radial winds and ill-behaved inflow layer depths precluded meaningful comparisons of boundary layer height in the rear storm-relative semicircle. While boundary layer height estimates failed to exhibit any significant regional variability, the right-front storm-relative quadrant appeared to exhibit non-trivial increases in mean boundary layer height., http://archive.org/details/variabilityinhur1094542751, Lieutenant, United States Navy, Approved for public release; distribution is unlimited.

The objective of this thesis is to investigate the vertical structure of the atmosphere and to assess the performance of several radiosonde- and lidar-based methods to detect the boundary layer height within the Inn Valley. All of these methods are developed for horizontally homogeneous and flat terrain. Radiosonde methods include different versions of the parcel and Richardson number methods and are, therefore, based on vertical profiles of virtual potential temperature, potential temperature, and horizontal wind speed, while lidar methods are based on vertical profiles of velocity variance, dissipation rate of turbulent kinetic energy, and backscatter intensities. The investigation of the performance of these methods as well as the vertical structure is based on data collected during the CROSSINN field campaign in summer 2019 in the lower Inn Valley near Kolsass and mainly focuses on two case studies. Potential temperature profiles measured by radiosondes during daytime confirm previous studies with regard to the existence of two nearly neutral layers, separated by a region of enhanced stability. The case studies illustrate that the depth of the upper layer is larger than the depth of the lower layer. In both case studies, the elevated near-neutral layer extended above mean crest height. The case studies also indicate that the radiosonde methods and the lidar methods based on turbulence determine mixing heights that can be related to the top of the lower well-mixed layer during convective conditions, while mixing heights derived from backscatter profiles are not determined by unique but rather case-dependent processes. From the radiosondes, it is found that the surface connected mixed layer only extends up to around 300 to 500~m~above ground level on average. Nevertheless, warming occurred above this mixed layer, which is too strong to be explained by large-scale advection alone. This result demonstrates the importance of additional transport and mixing processes, by Paul Josef Ladstätter, Masterarbeit University of Innsbruck 2020