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Aerosols affect Earth's climate both directly and indirectly, which is the largest uncertainty in the assessment of radiative forcings affecting anthropogenic climate change. The standard Aerosol Robotic Network (AERONET) aerosol products have been widely used for more than 30 years. Currently, there is strong community interest in the possibility of determining aerosol composition directly from remote sensing observations. This work presents the results of applying such a recently developed approach by Li et al. to extended datasets of the directional sky radiances and spectral aerosol optical depth (AOD) measured by AERONET for the retrievals of aerosol components. First, the validation of aerosol optical properties retrieved by this component approach with AERONET standard products shows good agreement. Then, spatiotemporal variations of the obtained aerosol component concentration are characterized globally, especially the absorbing aerosol species (black carbon, brown carbon, and iron oxides) and scattering aerosol species (organic carbon, quartz, and inorganic salts). Finally, we compared the black carbon (BC) and dust column concentration retrievals to the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), products in several regions of interest (Amazon zone, Indo-China Peninsula, North India, southern Africa, sub-Sahel, Gobi Desert, Middle East, Sahara Desert, and Taklamakan Desert) for new insights on the quantitative assessment of MERRA-2 aerosol composition products (R = 0.60-0.85 for BC; R = 0.75-0.90 for dust). The new value-added and long-term aerosol composition product globally is available online (https://doi.org/10.6084/ m9.figshare.25415239.v1), which provides important measurements for the improvement and optimization of aerosol modeling to enhance estimation of the aerosol radiative forcing. SIGNIFICANCE STATEMENT: In the assessment of climate change, the uncertainty associated with aerosol radiative forcing is the largest one. The purpose of this study is to provide a new value-added and long-term aerosol composition (including absorbing and scattering aerosol species) inversion dataset derived from Aerosol Robotic Network (AERONET) measurements for characterizing their spatiotemporal variations at global scale. We find some new insights on the quantitative assessment of black carbon and dust column concentration products in the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2). Our results and aerosol composition inversion dataset will provide robust support for the overall improvement and optimization of aerosol modeling to better understand the aerosol radiative forcing. KEYWORDS: Algorithms; Remote sensing; Aerosol optical properties; Air pollution; Atmospheric composition, 1. Introduction Atmospheric aerosols are considered to be an important climate forcing factor that plays a key role in the global climate system (Charlson et al. 1992; IPCC 2021). For [...]

The Deep Propagating Gravity Wave Experiment (DEEPWAVE) was designed to quantify gravity wave (GW) dynamics and effects from orographic and other sources to regions of dissipation at high altitudes. The [...]

Author(s): Michaela I. Hegglin (corresponding author) [1] The atmosphere has a self-cleansing ability [1] that stops certain air pollutants and greenhouse gases from accumulating, thereby preventing catastrophic consequences for air [...]

Author(s): Kevin Zahnle (corresponding author) [1]; Roger Buick (corresponding author) [2] It is a truth almost [1] universally acknowledged that Earth's atmosphere before about 2.5 billion years ago had little [...]

INTRODUCTION MAKING ATMOSPHERIC MEASUREMENTS in the High Arctic is challenging because of the remoteness of the area, the difficult transportation, the inconsistent communications, and the extreme environmental conditions. In 2003, [...]

Byline: Jenet Austin (1), Lu Zhang (1), Roger N. Jones (2), Paul Durack (3), Warrick Dawes (1), Peter Hairsine (1) Abstract: Climate change has potentially significant implications for hydrology and the quantity and quality of water resources. This study investigated the impacts of climate change and revegetation on water and salt balance, and stream salt concentration for catchments within the Murray-Darling Basin, Australia. The Biophysical Capacity to Change model was used with climate change scenarios obtained using the CSIRO DARLAM 125 (125 km resolution) and Cubic Conformal (50 km resolution) regional climate models. These models predicted up to 25% reduction in mean annual rainfall and a similar magnitude of increase in potential evapotranspiration by 2070. Relatively modest changes in rainfall and temperature can lead to significant reductions in mean annual runoff and salt yield and increases in stream salt concentrations within the Basin. The modelled reductions in mean annual runoff were up to 45% in the wetter/cooler southern catchments and up to 64% in the drier/hotter western and northern catchments. The maximum reductions in salt yield were estimated to be up to 34% in the southern catchments and up to 49% in the northern and western catchments. These changes are associated with average catchment rainfall decreases of 13 to 21%. The results suggest that percentage changes in rainfall will be amplified in runoff. This study demonstrates that climate change poses significant challenges to natural resource management in Australia. Author Affiliation: (1) CSIRO Land and Water, Private Bag 5, Wembley, WA 6913, Australia (2) Centre for Strategic Economic Studies, Victoria University, Melbourne, Australia (3) CSIRO Marine and Atmospheric Research, Hobart, Tasmania Article History: Registration Date: 07/09/2009 Received Date: 09/01/2008 Accepted Date: 28/07/2009 Online Date: 07/11/2009

Byline: Barrie Pittock (1) Abstract: Climate change is now a hot political topic that blurs the boundary between policy relevant and policy prescriptive (as contained for example in the avowed stance of the Intergovernmental Panel on Climate Change). The growing political relevance of climate change science necessarily places a premium on timely advice and on risk assessment and management. What is the role of climate scientists in that new situation? Author Affiliation: (1) CSIRO, Marine & Atmospheric Research, Private Bag 1, Aspendale, VIC, 3195, Australia Article History: Registration Date: 17/02/2010 Received Date: 11/02/2010 Accepted Date: 11/02/2010 Online Date: 20/05/2010 Article note: This essay is in part drawn from the author's book 'Climate Change: The Science, Impacts and Solutions' (CSIRO Publishing and Earthscan, 2009).

Byline: Jean-Philippe Boulanger (1), G. Brasseur (2), Andrea Fabiana Carril (3), Manuel de Castro (4), Nicolas Degallier (1), Carlos Ereno (5), H. Le Treut (6), Jose Antonio Marengo (7), Claudio Guillermo Menendez (3), Mario Nestor Nunez (3), Olga C. Penalba (5), Alfredo Luis Rolla (3), Matilde Rusticucci (5), Rafael Terra (8) Abstract: The goal of the CLARIS project was to build an integrated European--South American network dedicated to promote common research strategies to observe and predict climate changes and their consequent socio-economic impacts taking into account the climate and societal peculiarities of South America. Reaching that goal placed the present network as a privileged advisor to contribute to the design of adaptation strategies in a region strongly affected by and dependent on climate variability (e.g. agriculture, health, hydro-electricity). Building the CLARIS network required fulfilling the following three objectives: (1) The first objective of CLARIS was to set up and favour the technical transfer and expertise in earth system and regional climate modelling between Europe and South America together with the providing of a list of climate data (observed and simulated) required for model validations (2) The second objective of CLARIS was to facilitate the exchange of observed and simulated climate data between the climate research groups and to create a South American high-quality climate database for studies in extreme events and long-term climate trends (3) Finally, the third objective of CLARIS was to strengthen the communication between climate researchers and stakeholders, and to demonstrate the feasibility of using climate information in the decision-making process. Author Affiliation: (1) LOCEAN, UMR CNRS/IRD/UPMC, Tour 45-55/Etage 4/Case 100, UPMC, 4 Place Jussieu, Paris Cedex 05, 75252, France (2) National Center for Atmospheric Research (NCAR), Earth and Sun Systems Laboratory (ESSL), P.O. Box 3000, Boulder, CO, 80307, USA (3) CONICET, CIMA.Pabellon 2, Piso 2, Ciudad Universitaria, (1428), Buenos Aires, Argentina (4) Universidad de Castilla-La Mancha, Avda. Carlos III, 21., 45071, Toledo, Spain (5) Depto Ciencias de la Atmosfera y los Oceanos-UBA, Intendente Guiraldes 2160, Pab II, Ciudad Universitaria, C1428EGA, Buenos Aires, Argentina (6) Laboratoire de Meteorologie Dynamique, Institut-Pierre-Simon-Laplace et Ecole Doctorale 'Sciences de l'Environnement en Ile de France', Paris, France (7) Instituto Nacional de Pesquisas Espaciais INPE, Rodovia Dutra Km 40, 12630 000, Cachoeira Paulista, Sao Paulo, Brasil (8) IMFIA, Facultad de Ingenieria, Universidad de la Republica, Julio Herrera y Reissig 565, Montevideo, Uruguay Article History: Registration Date: 17/09/2009 Received Date: 23/06/2008 Accepted Date: 03/08/2009 Online Date: 14/11/2009

Stable carbon ([delta][sup.13]C) and oxygen ([delta][sup.18]O) in the otolith cores of Atlantic bluefin tuna (Thunnus thynnus) vary temporally, with changes that quantitatively follow interdecadal variation in atmospheric and oceanic reservoirs. Both carbon and oxygen isotopic signatures vary significantly by year of birth over the range investigated (1947-2006), with [delta][sup.13]C decreasing and [delta][sup.18]O increasing (-2.56 x [10.sup.-2][per thousand] and 4.3 x [10.sup.-3][per thousand] [yr.sup.-1], respectively). The rate of change in otolith [delta][sup.13]C was similar to reported rates of atmospheric [delta][sup.13]C depletion, attributed to deforestation and the burning of fossil fuels (referred to as the Suess effect), suggesting a close link between atmospheric and oceanic carbon pools. Increases in otolith [delta][sup.18]O were evident but less pronounced, with observed variation possibly attributable to changing salinity in the Atlantic Ocean. Otolith cores of bluefin tuna effectively track interdecadal trends and record past seawater [delta][sup.13]C and [delta][sup.18]O.

Retrievals of atmospheric carbon dioxide (C[O.sub.2]) from space-borne measurements of backscattered near-infrared sunlight are hampered by aerosol and cirrus cloud scattering effects. We propose a retrieval approach that allows for the retrieval of a few effective aerosol parameters simultaneously with the C[O.sub.2] total column by parameterizing particle amount, height distribution, and microphysical properties. Two implementations of the proposed method covering different spectral bands are tested for an ensemble of simulated nadir observations for aerosol (and cirrus) loaded scenes over low- and mid-latitudinal land surfaces. The residual aerosol-induced C[O.sub.2] errors are mostly below 1% up to aerosol optical thickness 0.5. The proposed methods also perform convincing for scenes where cirrus clouds of optical thickness 0.1 overlay the aerosol. OCIS codes: 010.0280, 010.1280, 010.1310, 120.6200, 290.1090.

The quasigeostrophic equations consist of the advection of linearized potential vorticity coupled with advection of temperature at the bounding upper and lower surfaces. Numerical models of quasigeostrophic flow often employ greater (scaled) resolution in the horizontal than in the vertical (the two-layer model is an extreme example). In the interior, this has the effect of suppressing interactions between layers at horizontal scales that are small compared to N[delta]z/f (where [delta]z is the vertical resolution, N the buoyancy frequency, and f the Coriolis parameter). The nature of the turbulent cascade in the interior is, however, not fundamentally altered because the downscale cascade of potential enstrophy in quasigeostrophic turbulence and the downscale cascade of enstrophy in two-dimensional turbulence (occurring layerwise) both yield energy spectra with slopes of -3. It is shown here that a similar restriction on the vertical resolution applies to the representation of horizontal motions at the surfaces, but the penalty for under-resolving in the vertical is complete suppression of the surface temperature cascade at small scales and a corresponding artificial steepening of the surface energy spectrum. This effect is demonstrated in the nonlinear Eady model, using a finite-difference representation in comparison with a model that explicitly advects temperature at the upper and lower surfaces. Theoretical predictions for the spectrum of turbulence in the nonlinear Eady model are reviewed and compared to the simulated flows, showing that the latter model yields an accurate representation of the cascade dynamics. To accurately represent dynamics at horizontal wavenumber K in the vertically finite-differenced model, it is found that the vertical grid spacing must satisfy [[delta].sub.z] [??] 0.3f/(NK); at wavenumbers K > 0.3f/(N[delta]z), the spectrum of temperature variance rolls off rapidly.

A simple and inexpensive fully automated all-sky imaging system based on a commercial digital camera with a fish-eye lens and a rotating polarizer is presented. The system is characterized and two examples of applications in atmospheric physics are given: polarization maps and cloud detection. All-sky polarization maps are obtained by acquiring images at different polarizer angles and computing Stokes vectors. The polarization in the principal plane, a vertical cut through the sky containing the Sun, is compared to measurements of a well-characterized spectroradiometer with polarized radiance optics to validate the method. The images are further used for automated cloud detection using a simple color-ratio algorithm. The resulting cloud cover is validated against synoptic cloud observations. A Sun coverage parameter is introduced that shows, in combination with the total cloud cover, useful correlation with UV irradiance. OCIS codes: 010.1615, 100.2960, 110.5405, 120.5410.

ABSTRACT The National Ambient Air Quality Standard (NAAQS) for ground-level ozone, previously set as an 8-hr average of 0.08 parts per million (ppm), has been revised by the U.S. Environmental [...]

An airborne microwave temperature profiler (MTP) was deployed during the Texas 2000 Air Quality Study (TexAQS-2000) to make measurements of boundary layer thermal structure. An objective technique was developed and tested for estimating the mixed layer (ML) height from the MTP vertical temperature profiles. The technique identifies the ML height as a threshold increase of potential temperature from its minimum value within the boundary layer. To calibrate the technique and evaluate the usefulness of this approach, coincident estimates from radiosondes, radar wind profilers, an aerosol backscatter lidar, and in situ aircraft measurements were compared with each other and with the MTP. Relative biases among all instruments were generally less than 50 m, and the agreement between MTP ML height estimates and other estimates was at least as good as the agreement among the other estimates. The ML height estimates from the MTP and other instruments are utilized to determine the spatial and temporal evolution of ML height in the Houston, Texas, area on 1 September 2000. An elevated temperature inversion was present, so ML growth was inhibited until early afternoon. In the afternoon, large spatial variations in ML height developed across the Houston area. The highest ML heights, well over 2 kin, were observed to the north of Houston, while downwind of Galveston Bay and within the late afternoon sea breeze ML heights were much lower. The spatial variations that were found away from the immediate influence of coastal circulations were unexpected, and multiple independent ML height estimates were essential for documenting this feature.

The limited atmospheric predictability has been addressed by the development of ensemble prediction systems (EPS) that are now routinely applied for mediumrange synoptic-scale numerical weather prediction (NWP). With the increase of computational power, interest is growing in the design of high-resolution (cloud resolving) NWP models and their associated short-range EPS. This development raises a series of fundamental questions, espe cially concerning the type of error growth and the validity of the tangent-linear approximation. To address these issues, a comparison between perturbed medium-range (10 day) synoptic-scale integrations (taken from the operational ECMWF EPS with a horizontal resolution of about 80 km) and short-range (1 day) high-resolution simulations (based on the Lokal Modell of the Consortium for Small-Scale Modeling with a grid spacing of 2.2 km) is conducted. The differences between the two systems are interpreted in a nondimensional sense and illustrated with the help of the Lorenz attractor. Typical asymptotic perturbation-doubling times of cloud-resolving and synoptic-scale simulations amount to about 4 and 40 h, respectively, and are primarily related to convective and baro clinic instability. Thus, in terms of growth rates, integrating a 1-day cloud-resolving forecast may be seen as equivalent to performing a 10-day synoptic-scale simulation. However, analysis of the prevailing linearity reveals that the two systems are fundamentally different in the following sense: the tangentlinear approximation breaks down at 1.5 h for cloud resolving against 54 h for synoptic-scale forecasts. In terms of nonlinearity, a 10-day synoptic-scale integration thus corresponds to a very short cloudresolving simulation of merely about 7 h. The higher degree of nonlinearity raises questions concerning the direct application of standard synoptic-scale forecasting methodologies (e.g., optimal perturbations, 4D variational data assimilation, or targeted observations) to 1-day cloud-resolving forecasting.

Observations of supercooled drizzle aloft within two storms impacting the Oregon Cascades during the second Improvement of Microphysical Parameterization through Observational Verification Experiment (IMPROVE-2) field project are presented. The storms were characterized by a structure and evolution similar to the split-front model of synoptic storms. Both storms were also characterized by strong cross-barrier flow. An analysis of aircraft and radar data indicated the presence of supercooled drizzle during two distinct storm periods: 1) the intrafrontal period immediately following the passage of an upper cold front and 2) the postfrontal period. The conditions associated with these regions of supercooled drizzle included 1) temperatures between -3[degrees] and -19[degrees]C, 2) ice crystal concentrations between 1 and 2 [L.sup.-1], and 3) bimodal cloud droplet distributions of low concentration [cloud condensation nuclei (CCN) concentration between 20 and 30 [cm.sup.-3] and cloud drop concentration Unique to this study was the relatively cold cloud top ( One of the key observations in the current storms was the persistence of drizzle drops in the presence of significant amounts of ice crystals over the steepest portion of the mountain crest. Despite the high radar reflectivity produced by the ice crystals (>15 dBZ) in this region, the relatively high condensate supply rate led to hazardous icing conditions. The current study reveals that vertical motions generated by local topographic features are critical in precipitation processes such as drizzle formation and thus it is essential that microphysical models predict these motions.

In this paper, the degree of scatter in flux-gradient relationships for stably stratified conditions is analyzed. It is generally found that scatter in the dimensionless lapse rate [[phi].sub.h] is larger than in the dimensionless shear [[phi].sub.m] when plotted versus the stability parameter z/A (where A is the local Obukhov length). Here, this phenomenon is explained to be a result of self-correlation due to the occurrence of the momentum and the heat flux on both axes, measurement uncertainties, and other possibly relevant physical processes left aside. It is shown that the ratio between relative errors in the turbulent fluxes influences the orientation of self-correlation in the flux-gradient relationships. In stable conditions, the scatter in [[phi].sub.m] is largely suppressed by self-correlation while for [[phi].sub.h] this is not the case (vice versa for unstable stratification). An alternative way of plotting is discussed for determining the slope of the linear [[phi].sub.m] function.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2005.02.010 Byline: A. Lester (a), D.R. Myers (b) Keywords: Pyranometer; Responsivity; Calibration; Uncertainty Abstract: Accurate global solar radiation measurements are crucial to climate change research and the development of solar energy technologies. Pyranometers produce an electrical signal proportional to global irradiance. The signal-to-irradiance ratio is the responsivity (RS) of the instrument (RS=signal/irradiance=microvolts/(W/m.sup.2)). Most engineering measurements are made using a constant RS. It is known that RS varies with day of year, zenith angle, and net infrared radiation. This study proposes a method to find an RS function to model a pyranometer's changing RS. Using a reference irradiance calculated from direct and diffuse instruments, we found instantaneous RS for two global pyranometers over 31 sunny days in a two-year period. We performed successive independent regressions of the error between the constant and instantaneous RS with respect to zenith angle, day of year, and net infrared to obtain an RS function. An alternative method replaced the infrared regression with an independently developed technique to account for thermal offset. Results show improved uncertainties with the function method than with the single-calibration value. Lower uncertainties also occur using a black-and-white (8-48), rather than all-black (PSP), shaded pyranometer as the diffuse reference instrument. We conclude that the function method is extremely effective in reducing uncertainty in the irradiance measurements for global PSP pyranometers if they are calibrated at the deployment site. Furthermore, it was found that the function method accounts for the pyranometer's thermal offset, rendering further corrections unnecessary. The improvements in irradiance data achieved in this study will serve to increase the accuracy of solar energy assessments and atmospheric research. Author Affiliation: (a) Smith College, Northampton, MA 01063, USA (b) National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401, USA Article History: Received 22 September 2004; Revised 27 January 2005; Accepted 2 February 2005 Article Note: (miscellaneous) Communicated by: Associate Editor Pierre Ineichen

First-principles atmospheric compensation of Earth-viewing spectral imagery requires atmospheric property information derived from the image itself or measured independently. A field experiment was conducted in May, 2003 at Davis, CA to investigate the consistency of atmospheric properties and surface reflectances derived from simultaneous ground-, aircraft- and satellite-based spectral measurements. The experiment involved the simultaneous collection of HyMap hyperspectral and Landsat-7 multispectral imagery, in situ reflectance spectra of calibration surfaces, and sun and sky radiances from ultraviolet and visible multifilter rotating shadowband radiometers (MFRSRs). The data were analyzed using several different radiation transport and atmospheric compensation algorithms. Reasonable self-consistency was found between aerosol property retrievals from the radiometers and from dark pixels of the imagery, and, when using the most accurate algorithm, there was excellent agreement between the retrieved surface spectra and the ground truth measurements. Index Terms--Atmospheric, compensation, correction, HyMap, hyperspectral, radiometer, shadowband.

The likely existence of bodies orbiting the Sun with aphelia Q < 0.983 AU has been suggested by numerical simulations of the dynamical evolution of the near-Earth objects (NEOs) population. For obvious reasons, these hypothetical minor bodies are called inner-Earth objects (IEOs). While much progresses has been made in learning more about the Amor, Apollo, and Aten population from surveys optimized for their discovery, no large, systematic, and similar observation projects devoted to the search of IEOs have been started. For their own orbital nature, IEOs can be observed only at small solar elongations ( Keywords: Asteroids; Experimental techniques

Information about the vertical microphysical cloud structure is useful in many modeling and predictive practices. Radiometers and radars are used to observe hydrometeor properties. This paper describes an iterative retrieval algorithm that combines the use of airborne active and wideband (10-340 GHz) passive observations to estimate the vertical content and particle size distributions of liquid and frozen hydrometeors. Airborne radar and radiometer observations from the third Convection and Moisture Experiment (CAMEX-3) were used in the retrieval algorithm as constraints. Nadir profiles were estimated for 1 min each of flight time (approximately 12.5 km along track) for anvil, convective, and quasi-stratiform clouds associated with Hurricane Bonnie (August 1998). The physically based retrieval algorithm relies on high frequencies ([greater than or equal to] 150 GHz) to provide details on the frozen hydrometeors. Neglecting the high frequencies yielded acceptable estimates of the liquid profiles, but the ice profiles were poorly retrieved. The wideband observations were found to more than double the estimated frozen hydrometeor content as compared with retrievals using only 90 GHz and below. The convective and quasi-stratiform iterative retrievals quickly reached convergence. The complex structure of the frozen hydrometeors required the most iterations for convergence for the anvil cloud type. Nonunique profiles, within physical and theoretical bounds, were retrieved for thin anvil ice clouds. A qualitative validation using coincident in situ CAMEX-3 observations shows that the retrieved particle size distributions are well corroborated with independent measurements.

Six different convective-stratiform separation techniques are compared and evaluated using 2D numerical simulations of a tropical and a midlatitude continental squall line. The techniques used include a texture algorithm applied to surface rainfall, a similar algorithm but with additional criteria applied to vertical velocity and cloud, a texture algorithm applied to vertical velocities below the melting layer, a simple approach that assumes a constant characteristic width for the convective region, a more sophisticated texture algorithm applied to radar reflectivities below the melting layer, and a new technique based on the premise that the fall speed of precipitation particles is large relative to air velocity in regions of stratiform precipitation. Comparisons are made in terms of rainfall, mass fluxes, apparent heating and moistening, hydrometeor contents, reflectivity and vertical-velocity contoured-frequency-with-altitude diagrams (CFAD), microphysics, and latent heating retrieval. Overall, it was found that the different separation techniques produced results that qualitatively agreed. However, the quantitative differences were significant. The texture algorithm applied to surface rain consistently produced the most stratiform rain while the texture algorithm applied to radar reflectivities below the melting layer and the new method comparing air velocities to terminal velocities consistently produced the most convective rain. The simple constant-area method performed comparably to the others in this squall line setting. Observational comparisons within the context of the model were unable to identify a superior technique. However, all of the methods were able to generate CFADs that were consistent with observations. Latent heating retrieval was shown to be sensitive to the use of separation technique mainly as a result of differences in the stratiform region. Methods that found very little stratiform rain resulted in exaggerated rain-normalized stratiform heating profiles.

Interaction between equatorially trapped disturbances and tropical convection is investigated using a non-hydrostatic global model that applies the cloud-resolving convection parameterization (CRCP). The CRCP represents subgrid scales of the global model by embedding a 2D cloud-resolving model in each column of the global model. The modeling setup is a constant-SST aquaplanet, with the size and rotation of earth, in radiative-convective quasi equilibrium. The global atmosphere is assumed to be initially at rest. No large-scale organization of convection is present outside the equatorial waveguide. Inside the waveguide, on the other hand, the model simulates spontaneous formation of coherent structures with deep convection on the leading edge and strong surface westerly winds to the west, the westerly wind bursts. These coherent structures resemble the Madden-Julian oscillation (MJO) observed in the terrestrial Tropics and are present in simulations applying prescribed and interactive radiation, and increased horizontal resolution of the global model. The MJO-like structures are essential for the development of the mean westerly flow, the superrotation, within the equatorial waveguide. Sensitivity simulations suggest that the coupling among deep convection, free-tropospheric moisture, and the large-scale flow is essential for coherence of the MJO-like structures. When large-scale fluctuations of convectively generated free-tropospheric moisture are removed on a timescale of a few hours, the coherent structures do not develop and, if already present, these structures disintegrate rapidly. It follows that the moisture-convection feedback, postulated previously to explain the large-scale organization of tropical convection and its coupling with SST fluctuations, operates very efficiently in the CRCP global model. It is also argued that the feedback plays a role in sensitivity simulations with horizontally uniform surface fluxes, where horizontal variability of the fluxes is required for the development, but not the maintenance, of MJO-like coherent structures. These results are discussed in the context of existing theories and modeling studies, which aim to explain the coupling between convection and the large-scale dynamics in the Tropics on intraseasonal timescales.

A procedure for identifying the resolved scales in nested limited-area models (LAMs) and for computing the nonlinear interactions between these scales is sketched in this paper. The spectral perspective is adopted and implemented semiempirically by analogy with global and r-periodic sectorial models. The analysis indicates that resolved scales are limited in LAMs and sectorial models compared to global models of similar resolution, and that nonlinear interactions may be treated less accurately in LAMs than in global models. A further result of the analysis is the evidence of the paramount importance of nesting, which acts as a type of closure scheme required by LAMs due to their limited computational domain. The assignment of lateral boundary values (LBVs) is responsible for making LAMs nonperiodic; these LBVs include scales exceeding the size of the LAM's domain and several other shorter scales that are nonperiodic on the limited computational domain.

Hourly UV index values at 45 sites in Canada were estimated using a statistical relationship between UV irradiance and global solar radiation, total ozone, and dewpoint temperature. The estimation method also takes into account the enhancement of UV irradiance by snow using an empirical correction derived from Brewer UV measurements. Different characteristics of UV index distribution over Canada were estimated from the derived UV irradiance for the period 1979-87 and then presented in the form of monthly maps. Direct comparisons of Brewer measurements at seven Canadian sites with derived UV irradiance show agreement within 2%-3% except for periods of melting snow when variations in snow albedo yield higher errors in the derived UV irradiance.

A new and flexible ray-tracing procedure for calculating astronomical refraction is outlined and applied to the US1976 standard atmosphere. This atmosphere is generalized to allow for a free choice of the temperature and pressure at sea level, and in this form it has been named the modified US1976 (MUSA76) atmosphere. Analytical expressions and numerical procedures are presented for calculating dry-air refractions and for the water-vapor correction. Results for all apparent altitudes are presented and compared with The Star Almanac for Land Surveyors (1951), The Nautical Almanac (1958), and the Pulkovo tables (Refraction Tables of the Pulkovo Observatory, 1985). Dependences on sea-level pressure, temperature, and temperature gradient and on humidity are discussed. OCIS codes: 010.1290, 010.4030, 010.7030.

The spatiotemporal distribution of observations plays an essential role in the data assimilation process. An adjoint sensitivity method is applied to the problem of adaptive location of the observational system for a nonlinear transport-chemistry model in the context of 4D variational data assimilation. The method is presented in a general framework and it is shown that in addition to the initial state of the model, sensitivity with respect to emission and deposition rates and certain types of boundary values may be obtained at a minimal additional cost. The adjoint modeling is used to evaluate the influence function and to identify the domain of influence associated with the observations. These essential tools are further used to develop a novel algorithm for targeting observations that takes into account the interaction among observations at different instants in time and spatial locations. Issues related to the case of multiple observations are addressed and it is shown that by using the adjoint modeling an efficient implementation may be achieved. Computational and practical aspects are discussed and this analysis indicates that it is feasible to implement the proposed method for comprehensive air quality models. Numerical experiments performed with a two-dimensional test model show promising results.

The purpose of this paper is to clarify the relation between canonical correlation analysis, autoregressive models (also called linear inverse models), and a relatively new statistical technique known as predictable component analysis. Predictable component analysis is a procedure for decomposing forecast error into a complete set of uncorrelated patterns that optimize the normalized error variance. As such, the procedure determines the components of a forecast, out of all possible components, that are predicted the best and worst on average, in a normalized error variance sense. This procedure has been suggested previously in the context of information theory and of maximizing the variance of prewhitened forecast errors. It is shown that the most predictable components of a linear, first-order, autoregressive model are identical to the canonical patterns that optimize the temporal correlation between the original and time-lagged time series. Also, canonical patterns define a transformation that diagonalizes the propagator of the autoregressive model. Finally, the singular vectors of an autoregressive propagator have a one-to-one correspondence to the canonical patterns, provided that the singular vectors are computed with respect to a norm related to a prewhitening transformation. Forecasts based on canonical correlation analysis are shown to be identical to forecasts based on autoregressive models when all canonical patterns are superposed. The advantage of canonical correlation analysis is that it allows one to filter out the 'unpredictable components' of autoregressive models, defined as components in the forecast with skill below some statistical threshold of significance. Predictable component analysis allows a generalization of this filtering procedure to any forecast model.

Area equivalent latitude based on potential vorticity (PV) is a widely used diagnostic for isentropic transport in the stratosphere and upper troposphere. Here, an alternate method for calculating equivalent latitude is explored, namely, a numerical synthesis of a PV-like tracer from a long-term integration of the advection-diffusion equation on isentropic surfaces. It is found that the tracer equivalent latitude (TrEL) behaves much like the traditional PV equivalent latitude (PVEL) despite the simplified governing physics; this is evidenced by examining the kinematics of the Arctic lower stratospheric vortex. Yet in some cases TrEL performs markedly better as a coordinate for long-lived trace species such as ozone. These instances include analysis of lower tratospheric ozone during the Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment (SOLVE) campaign and three-dimensional reconstruction of total column ozone during November-December 1999 from fitted ozone-equivalent latitude relationship. It is argued that the improvement is due to the tracer being free from the diagnostic errors and certain diabatic processes that affect PV. The sensitivity of TrEL to spatial and temporal resolution, advection scheme, and driving winds is also examined.

A new mechanism is proposed that explains two key features of the observed El Nino-Southern Oscillation (ENSO) phenomenon--its irregularity and decadal amplitude changes. Using a low-order ENSO model, the authors show that the nonlinearities in the tropical heat budget can lead to bursting behavior characterized by decadal occurrences of strong El Nino events. La Nina events are not affected, a feature that is also seen in ENSO observations. One key result of this analysis is that decadal variability in the Tropics can be generated without invoking extratropical processes or stochastic forcing. The El Nino bursting behavior simulated by the low-order ENSO model can be understood in terms of the concept of homoclinic and heteroclinic connections. It is shown that this new model for ENSO amplitude modulations and irregularity, although difficult to prove, might explain some features of ENSO dynamics seen in more complex climate models and the observations.

Spectroscopic images of atmospheric chemiluminescent airglow contain fundamental diagnostic information about the structure and dynamics of the upper atmosphere. However, west-ward movement of stars causes nonnegligible contamination in the two-dimensional horizontal wavenumber spectra extracted from all-sky airglow images. The conventional star-removing scheme is not effective in attenuating the star artifacts in the spectra of emission intensities of gravity wave perturbation, hindering the subsequent calculation of the angular spectra and the momentum fluxes of the profiles. To address this problem, a gradient-based edge detection algorithm for locating and attenuating the undesired star signal is developed. Comparatively, this algorithm is more effective than the conventional star-removing methods. The algorithm is validated in the context of experimentally obtained spectra. Index Terms--Atmospheric measurements, feature extraction, point-source attenuation, spectroscopic imaging.

The objective of this study is to examine the effectiveness of the variational objective analysis (VOA) for producing realistic diagnoses of atmospheric field program data. Simulations from the Naval Research Laboratory's Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) were sampled in a manner consistent with a typical field program using idealized sounding arrays and, surface and top of the atmosphere flux information. These data were then subject to a conventional form of analysis in which only a mass constraint was applied, hereafter referred to as the reference analysis, as well as to the complete VOA procedure. The diagnosed results from both analyses were then compared to time- and domain-averaged quantities from the model. The results showed that for diagnosed vertical velocity and vertical advective tendencies, the VOA values typically exhibited considerably smaller errors compared to the values from the reference analyses, with the level of improvement and overall accuracy being dependent on synoptic and sampling conditions. The improvements tend to be greatest during disturbed conditions, with the errors typically being smaller and comparable between the two analyses during undisturbed conditions. The errors for both analyses increase as the spatial domain decreases and for the most part decrease with more frequent temporal sampling. However, the improvement achieved by having more frequent sampling is rather modest for the VOA since it already incorporates time-mean surface and TOA fluxes as constraints and thus indirectly incorporates some aspects of the variability between soundings. Highly relevant is the finding that overall the errors in vertical velocity and vertical advective tendencies from the reference analyses have a magnitude similar to, or greater than, the variability of the field being diagnosed, whereas the errors in these quantities from the VOA are typically less than the variability of the field. The analysis also showed no obvious systematic level-by-level improvement gained by the VOA analysis over the reference analysis in diagnosing the horizontal moisture flux convergence, mass divergence, or horizontal advective tendencies, notwithstanding the VOA's application of column-integrated constraints of mass, moisture, heat, and momentum conservation. Additional soundings were found to be more beneficial to the reference analyses than the VOA analyses and in some cases allowed the error characteristics of the reference analysis to become similar to those of the VOA analysis. Noteworthy is the finding that the results from the VOA analyses using five soundings were often as good or better than the results from the reference analyses using nine soundings. The impact that hydrometeor measurements would have in providing additional constraints on the VOA was also investigated. The impact was found to be mostly negligible when averaging over relatively large space scales or timescales. On the other hand, for frequent sampling (e.g., 1-3 h) and small spatial scales (i.e.,

An updated NCEP-NCAR reanalysis, covering 1979-present, features newer physics and observed soil moisture forcing and also eliminates several previous errors

A diagnostic algorithm, based on the empirical normal mode decomposition technique, is proposed as a diagnostic tool in studies of the atmospheric variability. It begins by analyzing the transient eddies in terms of empirical modes that are orthogonal with respect to wave activities. Time-dependent amplitudes together with wave activity spectra are used to classify the modes and compute their propagation properties. The algorithm is applied to a sequence of four Northern Hemisphere winters taken from the National Centers for Environmental Prediction reanalyses, with a focus on the upper troposphere and lower stratosphere, giving a set of empirical modes of wind, pressure, specific volume, and potential vorticity. Results indicate that most of the wave activity is carried by large-scale, eastward-propagating modes centered at middle and high latitudes. Some properties of the leading modes, such as their average phase speeds, are in good agreement with the predictions of linear dynamics. Characteristics of the leading wavenumber-5 mode, such as its dipolar pressure pattern near the summer hemisphere tropopause, its propagation speed of 12 m [s.sup.-1] and decay rate of 3 days, can be explained by the theory of quasi modes, defined as superpositions of singular modes sharply peaked in the phase speed domain. Other large-scale, midlatitude modes also show properties compatible with the quasi-modal description, suggesting that quasi modes play an important role in the upper-troposphere dynamics.

Perturbation growth in uncertain systems is examined and related to previous work in which linear stability concepts were generalized from a perspective based on the nonnormality of the underlying linear operator. In this previous work the linear operator, subject to an initial perturbation or a stochastic forcing distributed in time, was either fixed or time varying, but in either case the operator was certain. However, in forecast and climate studies, complete knowledge of the dynamical system being perturbed is generally lacking; nevertheless, it is often the case that statistical properties characterizing the variability of the dynamical system are known. In the present work generalized stability theory is extended to such uncertain systems. The limits in which fluctuations about the mean of the operator are correlated over time intervals, short and long, compared to the timescale of the mean operator are examined and compared with the physically important transitional case of operator fluctuation on timescales comparable to the timescales of the mean operator. Exact and asymptotically valid equations for transient ensemble mean and moment growth in uncertain systems are derived and solved. In addition, exact and asymptotically valid equations for the ensemble mean response of a stable uncertain system to deterministic forcing are derived and solved. The ensemble mean response of the forced stable uncertain system obtained from this analysis is interpreted under the ergodic assumption as equal to the time mean of the state of the uncertain system as recorded by an averaging instrument. Optimal perturbations are obtained for the ensemble mean of an uncertain system in the case of harmonic forcing. Finally, it is shown that the remarkable systematic increase in asymptotic growth rate with moment in uncertain systems occurs only in the context of the ensemble.

Spaceborne lidar observations have a great potential to improve our knowledge of the atmosphere. However, contrary to ground-based or airborne lidar measurements in observations from space multiple scattering (MS) has to be accounted for under all atmospheric conditions. A simple way to achieve this is to introduce the approximative MS factor F in the single scattering lidar equation. We determined F for measurements of aerosols, ice and water clouds as they were planned with the Japanese space lidar ELISE. We found that F is almost constant in cirrus clouds and in water clouds which are penetrable by lidar. In aerosol layers F depends on penetration depth, extinction coefficient and aerosol type. In comparison to LITE the MS factor is smaller (for aerosols and water clouds) or almost equal (cirrus). Index Terms--Multiple scattering, space lidar.

The sensitivity of radar backscatter to the amount of intercepted rain in temperate deciduous forests is analyzed to determine the feasibility of retrieval of this parameter from satellite radar data. A backscatter model is validated with X-band radar measurements of a single tree exposed to rain. A good agreement between simulation and measurements is observed and this demonstrates the ability of radar to measure the amount of intercepted rain. The backscatter model is next applied to simulate different satellite radar configurations. To account for forest variability, the backscatter difference between a wet and dry forest canopy is calculated for four deciduous tree species, above a wet and a dry soil. On average, the simulated backscatter of a wet forest canopy is 1 dB higher than the backscatter of a dry forest canopy at co-polarized L-band and 2 dB at co-polarized C and X-band. The simulated sensitivity is in agreement with observations. It is argued that current satellites can retrieve the amount of intercepted rain at best with a reliability of 50%, due to the variability in soil moisture, species composition and system noise. We expect that the reliability will improve with the launch of the next generation radar satellites. The results of this analysis may also be used to assess the influence of rain, fog or dew upon other radar applications for temperate deciduous forests. Index Terms--Dew, fog, forest, interception, radar, rain.

This paper introduces a new ground clutter suppression technique which preserves weather echoes. This clutter suppression method uses both statistical and polarimetric properties of the target and clutter. This technique is intended for use in atmospheric studies for weather echoes the spectral properties of which do not differ much from those of ground clutter. This technique can be applied both to the total signal or to its separate Doppler frequency components. Index Terms--Atmospheric radars, ground clutter suppression, polarimetry.

Interpolation of digital elevation models becomes necessary in many situations, for instance, when constructing them from contour lines (available e.g., from nondigital cartography), or from disparity maps based on pairs of stereoscopic views, which often leaves large areas where point correspondences cannot be found reliably. The absolutely minimizing Lipschitz extension (AMLE) model is singled out as the simplest interpolation method satisfying a set of natural requirements. In particular, a maximum principle is proven, which guarantees not to introduce unnatural oscillations which is a major problem with many classical methods. We then discuss the links between the AMLE and other existing methods. In particular, we show its relation with geodesic distance transformation. We also relate the AMLE to the thin-plate method, that can be obtained by a prolongation of the axiomatic arguments leading to the AMLE, and addresses the major disadvantage of the AMLE model, namely its inability to interpolate slopes as it does for values. Nevertheless, in order to interpolate slopes, we have to give up the maximum principle and authorize the appearance of oscillations. We also discuss the possible link between the AMLE and Kriging methods that are the most widely used in the geoscience literature. We end by numerical comparison between the different methods. Index Terms--Digital elevation models, image interpolation, partial differential equations.

The presence of trees in a given scene can hamper detection of nearby targets by millimeter-wave (MMW) radars especially at near grazing incidence. Proper characterization of scattering and attenuation in tree canopies is important for optimal detection algorithms. In this paper, a new technique for determining the extinction and volume backscattering coefficients in tree canopies using the measured radar backscatter response is proposed and verified experimentally. The technique, which can be applied to already available wideband radar backscatter data, is used to compute the extinction and volume backscattering coefficients of different tree canopies under various physical conditions. The dynamic range of these coefficients are presented and results at 35 GHz are compared with results at 95 GHz. Index Terms--Attenuation measurements, clutter, millimeter wave propagation, radar.

Characteristic polarization state theory is restudied for the symmetric coherent Sinclair scattering matrix case. First, the geometric relations of the characteristic polarization states on the Poincare sphere are derived. Based on these relations, simple formulas are given for all of the characteristic polarization states of this Sinclair matrix in Stokes vector form. From the formulation, it is clear that the CO-POL Nulls are fundamental characteristic polarization states for the symmetric coherent Sinclair scattering matrix case, in that the others can straightforwardly be obtained from the Stokes vectors of the CO-POL Nulls. For further study of the characteristic polarization state and the distribution of the received powers on the Poincare sphere, we introduce the concept of the equi-power curve. It is defined as the curve on the Poincare sphere on which the received powers in some defined channel have the same value. We deal with the characteristics of the equi-power curves for various special cases. In addition, we show how the characteristic polarization states are generated by the equi-power curves. It is demonstrated that the characteristic polarization states can usually be regarded as the points of contact of the Poincare sphere and a conicoid representing a power-related quadratic form. This leads to a new method to introduce the characteristic polarization states. The new method provides a geometric interpretation for visualization of changes in polarized states on the Poincare sphere. Index Terms--Polarization, radar polarimetry, scattering matrix.

A procedure for inverting the nonlinear relationship between the waveheight spectrum and the SAR image spectrum is presented, and this procedure is evaluated using simulated data as well as actual ERS SAR data collected near Duck, NC. Results of this nonlinear inversion are compared with those obtained from a quasi-linear estimation procedure using simulated data, in order to illustrate the effects of nonlinearities in the imaging process. These effects include the well-known azimuth falloff effect as well as the generation of harmonics which appear in the background region of the spectrum. The nonlinear inversion technique is able to reproduce the input image spectrum to high accuracy, although the wave spectrum obtained by this procedure is not necessarily the same as the input wave spectrum. In general, the estimated wave spectrum is quite similar to the portion of the input wave spectrum within the SAR passband region, but none of the energy outside the passband is recovered. The background signals due to nonlinear effects can cause large errors in the quasi-linear estimation procedure because these signals appear in regions of the spectrum where the SAR modulation transfer function (mtf) is small. Results using actual SAR data also indicate that energy within the passband is recovered fairly accurately, although energy outside the passband is clearly lost. Estimates of the mean wavelength and direction for the in-band components become more accurate as the signal level increases, indicating that the errors are predominantly due to speckle noise rather than nonlinear imaging effects. Estimates of the significant waveheight are less influenced by speckle noise, and are accurate to within 0.14 m for this data set, if wind wave spectral peaks that are clearly outside the SAR passband are neglected. Index Terms--Inverse methods, ocean wave spectra, synthetic aperture radar.

RADARSAT synthetic aperture radar (SAR) data acquired at C Band, HH polarization, and for the 20 [degrees]-27 [degrees] and 45 [degrees]-49 [degrees] incidence angle ranges were available over northern Quebec, Canada, (54 [degrees] N, 72 [degrees] 12'W), in the fall of 1996, the winter of 1997, and the spring of 1997. The main land occupation of this area is sparse black spruce (Picea mariana) forests. Vegetation characteristics are jointly used with snow and soil observations coinciding with the satellite overpasses to simulate the seasonal changes in the backscattering coefficient of the subarctic forest. The aim of this study is twofold. First to evaluate the effects of the seasonal changes in vegetation on the RADARSAT SAR data, and second to use backscattering models as a tool for a better interpretation and understanding of the RADARSAT SAR data over snow-covered forested areas. Simulations show the importance of the surface-vegetation interaction term and the wet snow surface roughness on the discrimination between open forest and denser forest, and on the contrast between wet snow and dry snow covers. When comparing the simulations to the RADARSAT SAR data, the poorest results are obtained in the spring for a rough wet snow. It is shown that they are mainly due to a crude evaluation of the vegetation dielectric constant rather than to uncertainties introduced by the spatial variability in the wet snow surface roughness. Index Terms--Dry snow, RADARSAT (synthetic aperture radar (SAR) data, seasonal changes, subarctic forest, surface-vegetation interaction term, wet snow, wet snow surface roughness.

The development and validation of altimeter wind speed algorithms is investigated following the collation of the largest dataset to-date of coincident altimeter/buoy open ocean measurements. Nonlinear relationships between buoy wind and Topex backscatter are fitted to the 4500 points dataset using least-squares (LSQ). The addition of altimeter significant wave height (SWH) information causes a small but significant reduction of about 10% in root-mean-square (rms) error. The new LSQ algorithms yield significant improvement of the global wind speed bias and rms error compared to earlier models, but describe the wind to backscatter relationship poorly at extreme wind speeds. Best results are obtained with the Gourrion et al. (2000) model, improving on the Witter and Chelton (WC91) (1991) model used operationally. A residual dependence on sea state persists in all wind algorithms, which underestimate winds in young sea conditions on average by 1-1.5 m/s. A case study confirms that ordinary LSQ attribute excessive weight to the peak of the wind speed histogram and yield algorithms with poor performance at extreme winds. Measurement errors are shown to greatly influence the fitted models performance, as accounting for normally distributed errors in both altimeter and buoy measurements with orthogonal distance regressions (ODRs) yields significant improvements. Hence, algorithms developed from relatively small collocated datasets (few thousand points) may perform as well as models developed from much larger datasets (tens of thousands of points) given adequate treatment of errors. However, it is anticipated that the ultimate accuracy of wind speed algorithms is still dependent on the quality of the fitted datasets. Index Terms--Algorithm development, altimeter wind speed, collocated dataset, wave age.

The Independent Component Analysis (ICA) is a recently developed technique for component extraction. This new method requires the statistical independence of the extracted components--a stronger constraint that uses higher-order statistics--instead of the classical decorrelation (in the sense of 'no correlation'), which is a weaker constraint that uses only second-order statistics. This technique has been used recently for the analysis of geophysical time series with the goal of investigating the causes of variability in observed data (i.e., exploratory approach). The authors demonstrate with a data simulation experiment that, if initialized with a Principal Component Analysis (PCA), the ICA performs a rotation of the classical PCA (or EOF) solution. This experiment is conducted using a synthetic dataset, where the correct answer is known, to more clearly illustrate and understand the behavior of the more familiar PCA and less familiar ICA. This rotation uses no localization criterion like other rotation techniques; only the generalization of decorrelation into full statistical independence is used. This rotation of the PCA solution seems to be able to avoid the tendency of PCA to mix several components, even when the signal is just their linear sum.

The concepts of multiplicative stochastic perturbations and noise-induced transitions are applied to a quasi-geostrophic [beta]-plane model of barotropic flow over topography. The spectral three-component low-order representation of this configuration yields the Charney-DeVore (CDV) model. The externally prescribed damping of the system is allowed to scatter around a mean value. The stochastic representation of the damping term leads to a multiplicative stochastic forcing. The Fokker-Planck equation and the stochastic differential equation of the low-order CDV model are solved numerically. It is found that the qualitative behavior of the system is a function of the multiplicative noise level. In particular, the effect of multiplicative noise is not simply a smoothing of the probability density function, as it would be for pure additive noise. Rather, multiplicative noise leads to the high-index state being favored over the low-index state. The concept of noise-induced transitions explains this behavior. The noise-induced transition of the stochastic low-order model is confirmed by numerical integrations of a corresponding gridpoint model with many more degrees of freedom than the spectral model. It is suggested that the statistics of the unresolved physical processes could be an important factor in understanding the behavior of midlatitude large-scale atmospheric dynamics.

Fourier Transform infrared (FT-IR) spectra of nitrogen dioxide, hydrogen chloride and sulfur dioxide have been recorded in the spectral region 400-4000 cm(super -1) with 1-4 cm(super -1) resolution under quasi-static and flow-through conditions through tubings of aluminum, copper, stainless-steel and Teflon. Qualitative and quantitative spectral changes in the FT-IR data are discussed in the context of atmospheric phenomena. Keywords: FT-IR; Atmospheric; Spectroscopy; Infrared radiation