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Wang D.,Chinese Academy of Meteorological Sciences | Wang D.,Science System and Applications Inc. | Li X.,The Center for Satellite Applications and Research | Tao W.-K.,NASA
Meteorology and Atmospheric Physics

Ice clouds are an important component in precipitation systems. The radiative processes of ice clouds directly impact radiation in heat budget and the microphysical processes of ice clouds directly affect latent heat and net condensation through deposition processes, which may eventually change surface rainfall. Thus, torrential rainfall responses to radiative and microphysical processes of ice clouds during a landfall of severe tropical storm Bilis (2006) are investigated with the analysis of sensitivity experiments. The two-dimensional cloud-resolving model is integrated for 3 days with imposed zonally uniform vertical velocity, zonal wind, horizontal temperature and vapor advection from NCEP/GDAS data. One sensitivity experiment excludes the radiative effects of ice clouds and the other sensitivity experiment excludes ice microphysics and associated radiative and microphysical processes. Model domain mean surface rain rate is barely changed by the exclusion of radiative effects of ice clouds due to the small decrease in net condensation associated with the small reduction in latent heat as a result of the offset between the increase in radiative cooling and the decrease in heat divergence. The exclusion of microphysical effects of ice clouds decreases the mean rain rate simply through the suppression of latent heat as a result of the removal of deposition processes. The total exclusion of ice microphysics decreases the mean rain rate mainly through the exclusion of microphysical effects of ice clouds. © 2010 Springer-Verlag. Source

Wang D.,Chinese Academy of Meteorological Sciences | Wang D.,Science System and Applications Inc. | Li X.,The Center for Satellite Applications and Research | Tao W.-K.,NASA
Atmospheric Research

The cloud radiative effects on responses of rainfall to the large-scale forcing during a landfall of severe tropical storm Bilis (2006) are investigated by analyzing sensitivity experiments imposed by large-scale forcing from NCEP/GDAS data in a two-dimensional cloud-resolving model. The daily average analysis is conducted on 15 and 16 July 2009, respectively, due to dominant stratiform and convective rainfall associated with different large-scale forcing. When cloud radiative effects are excluded, the increased mean rainfall is associated with the increased mean radiative cooling through the enhanced mean latent heat on 15 July. The reduction in mean rain rate is related to the slowdown in the mean net condensation while the enhanced mean radiative cooling from the removal of cloud radiative effects is balanced by the suppressed heat divergence on 16 July. The increased mean rainfall on 15 July and decreased mean rainfall on 16 July are mainly from raining stratiform regions. The enhanced stratiform rainfall is associated with the weakened local atmospheric moistening and strengthened local hydrometeor loss on 15 July, whereas the reduced stratiform rainfall is related to the weakened water vapor convergence on 16 July.When cloud-radiation interaction is excluded, the decreases in the mean rain rate are associated with the slowdown in the mean hydrometeor loss on 15 July and the suppression in the net condensation on 16 July. The decreased mean rainfall is mainly from convective regions on 15 July and raining stratiform regions on 16 July. The reduced convective rainfall is associated with strengthened transport of hydrometeor concentration from convective regions to raining stratiform regions on 15 July, whereas the decreased stratiform rainfall is related to the weakened water vapor convergence on 16 July. © 2010 Elsevier B.V. Source

Jackson T.J.,U.S. Department of Agriculture | Cosh M.H.,U.S. Department of Agriculture | Bindlish R.,Science System and Applications Inc. | Starks P.J.,U.S. Department of Agriculture | And 5 more authors.
IEEE Transactions on Geoscience and Remote Sensing

Validation is an important and particularly challenging task for remote sensing of soil moisture. A key issue in the validation of soil moisture products is the disparity in spatial scales between satellite and in situ observations. Conventional measurements of soil moisture are made at a point, whereas satellite sensors provide an integrated area/volume value for a much larger spatial extent. In this paper, four soil moisture networks were developed and used as part of the Advanced Microwave Scanning RadiometerEarth Observing System (AMSR-E) validation program. Each network is located in a different climatic region of the U.S., and provides estimates of the average soil moisture over highly instrumented experimental watersheds and surrounding areas that approximate the size of the AMSR-E footprint. Soil moisture measurements have been made at these validation sites on a continuous basis since 2002, which provided a seven-year period of record for this analysis. The National Aeronautics and Space Administration (NASA) and Japan Aerospace Exploration Agency (JAXA) standard soil moisture products were compared to the network observations, along with two alternative soil moisture products developed using the single-channel algorithm (SCA) and the land parameter retrieval model (LPRM). The metric used for validation is the root-mean-square error (rmse) of the soil moisture estimate as compared to the in situ data. The mission requirement for accuracy defined by the space agencies is 0.06 m 3/m3. The statistical results indicate that each algorithm performs differently at each site. Neither the NASA nor the JAXA standard products provide reliable estimates for all the conditions represented by the four watershed sites. The JAXA algorithm performs better than the NASA algorithm under light-vegetation conditions, but the NASA algorithm is more reliable for moderate vegetation. However, both algorithms have a moderate to large bias in all cases. The SCA had the lowest overall rmse with a small bias. The LPRM had a very large overestimation bias and retrieval errors. When site-specific corrections were applied, all algorithms had approximately the same error level and correlation. These results clearly show that there is much room for improvement in the algorithms currently in use by JAXA and NASA. They also illustrate the potential pitfalls in using the products without a careful evaluation. © 2010 IEEE. Source

Wang D.,Chinese Academy of Meteorological Sciences | Wang D.,Science System and Applications Inc. | Li X.,The Center for Satellite Applications and Research | Tao W.-K.,NASA
Advances in Atmospheric Sciences

The responses of vertical structures, in convective and stratiform regions, to the large-scale forcing during the landfall of tropical storm Bilis (2006) are investigated using the data from a two-dimensional cloud-resolving model simulation. An imposed large-scale forcing with upward motion in the mid and upper troposphere and downward motion in the lower troposphere on 15 July suppresses convective clouds, which leads to ~100% coverage of raining stratiform clouds over the entire model domain. The imposed forcing extends upward motion to the lower troposphere during 16-17 July, which leads to an enhancement of convective clouds and suppression of raining stratiform clouds. The switch of large-scale lower-tropospheric vertical velocity from weak downward motion on 15 July to moderate upward motion during 16-17 July produces a much broader distribution of the vertical velocity, water vapor and hydrometeor fluxes, perturbation specific humidity, and total hydrometeor mixing ratio during 16-17 July than those on 15 July in the analysis of contoured frequency-altitude diagrams. Further analysis of the water vapor budget reveals that local atmospheric moistening is mainly caused by the enhancement of evaporation of rain associated with downward motion on 15 July, whereas local atmospheric drying is mainly determined by the advective drying associated with downward motion over raining stratiform regions and by the net condensation associated with upward motion over convective regions during 16-17 July. © Chinese National Committee for International Association of Meteorology and Atmospheric Sciences, Institute of Atmospheric Physics, Science Press and Springer Berlin Heidelberg 2010. Source

Kato S.,NASA | Rose F.G.,Science System and Applications Inc. | Liu X.,NASA | Wielicki B.A.,NASA | Mlynczak M.G.,NASA
Journal of Climate

A surface, atmospheric, and cloud (fraction, height, optical thickness, and particle size) property anomaly retrieval from highly averaged longwave spectral radiances is simulated using 28 years of reanalysis. Instantaneous nadir-view spectral radiances observed from an instrument on a 908 inclination polar orbit are computed. Spectral radiance changes caused by surface, atmospheric, and cloud property perturbations are also computed and used for the retrieval. This study's objectives are 1) to investigate whether or not separating clear sky from cloudy sky reduces the retrieval error and 2) to estimate the error in a trend of retrieved properties. This simulation differs from earlier studies in that annual 108 latitude zonal cloud and atmospheric property anomalies defined as the deviation from 28-yr climatological means are retrieved instead of the difference of these properties from two time periods. The root-mean-square (RMS) difference of temperature and humidity anomalies retrieved from all-sky radiance anomalies is similar to the RMS difference derived from clear-sky radiance anomalies computed by removing clouds. This indicates that the cloud property anomaly retrieval error does not affect the retrieved temperature and humidity anomalies. When retrieval errors are nearly random, the error in the trend of retrieved properties is small. Approximately 30% of 108 latitude zones meet conditions that the true temperature and water vapor amount trends are within a 95% confidence interval of retrieved trends, and that the standard deviation of retrieved anomalies sret is within 20% of the standard deviation of true anomalies σn. If σret/σn - 1 is within ± 0.2, 91% of the true trends fall within the 95% confidence interval of the corresponding retrieved trend. © 2014 American Meteorological Society. Source

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