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- Author or Editor: Thomas J. Greenwald x
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Abstract
In this study, the ability of different combinations of bulk cloud microphysics and planetary boundary layer (PBL) parameterization schemes implemented in the Weather Research and Forecasting Model to realistically simulate the wide variety of cloud types associated with an extratropical cyclone is examined. An ensemble of high-resolution model simulations was constructed for this case using four microphysics and two PBL schemes characterized by different levels of complexity. Simulated cloud properties, including cloud optical thickness, cloud water path, cloud-top pressure, and radiative cloud phase, were subsequently compared to cloud data from three Moderate Resolution Imaging Spectroradiometer (MODIS) overpasses across different portions of the domain. A detailed comparison of the simulated datasets revealed that the PBL and cloud microphysics schemes both exerted a strong influence on the spatial distribution and physical properties of the simulated cloud fields. In particular, the low-level cloud properties were found to be very sensitive to the PBL scheme while the upper-level clouds were sensitive to both the microphysics and PBL schemes. Overall, the simulated cloud properties were broadly similar to the MODIS observations, with the most realistic cloud fields produced by the more sophisticated parameterization schemes.
Abstract
In this study, the ability of different combinations of bulk cloud microphysics and planetary boundary layer (PBL) parameterization schemes implemented in the Weather Research and Forecasting Model to realistically simulate the wide variety of cloud types associated with an extratropical cyclone is examined. An ensemble of high-resolution model simulations was constructed for this case using four microphysics and two PBL schemes characterized by different levels of complexity. Simulated cloud properties, including cloud optical thickness, cloud water path, cloud-top pressure, and radiative cloud phase, were subsequently compared to cloud data from three Moderate Resolution Imaging Spectroradiometer (MODIS) overpasses across different portions of the domain. A detailed comparison of the simulated datasets revealed that the PBL and cloud microphysics schemes both exerted a strong influence on the spatial distribution and physical properties of the simulated cloud fields. In particular, the low-level cloud properties were found to be very sensitive to the PBL scheme while the upper-level clouds were sensitive to both the microphysics and PBL schemes. Overall, the simulated cloud properties were broadly similar to the MODIS observations, with the most realistic cloud fields produced by the more sophisticated parameterization schemes.
Abstract
A cloud-resolving model was used in conjunction with a radiative transfer (RT) modeling system to study 10.7-μm brightness temperatures computed for a simulated thunderstorm. A two-moment microphysical scheme was used that included seven hydrometeor types: pristine ice, snow, aggregates, graupel, hail, rain, and cloud water. Also, five different habits were modeled for pristine ice and snow. Hydrometeor optical properties were determined from an extended anomalous diffraction theory approach. Brightness temperatures were computed using a delta-Eddington two-stream model.
Results indicate that the enhanced “V,” a feature sometimes seen in satellite infrared observations, may be formed through an interaction between the overshooting dome and the upstream flanking region of high pressure. This idea is contrary to one in which the overshooting dome is viewed as an obstacle to the environmental flow. As expected, the radiative effects of pristine ice particles within the anvil largely determined the brightness temperature field. Although brightness temperatures were found to be insensitive to microphysical characteristics of moderate to thick portions of the anvil, a strong relationship did exist with column-integrated pristine ice mass for cloud optical depths below about 5. Precipitation-sized hydrometeors and surface precipitation rate, on the other hand, failed to exhibit any meaningful relationship with the cloud-top brightness temperature. The combined mesoscale model and RT modeling system used in this study may also have utility in satellite product development prior to launch of a satellite and in satellite data assimilation.
Abstract
A cloud-resolving model was used in conjunction with a radiative transfer (RT) modeling system to study 10.7-μm brightness temperatures computed for a simulated thunderstorm. A two-moment microphysical scheme was used that included seven hydrometeor types: pristine ice, snow, aggregates, graupel, hail, rain, and cloud water. Also, five different habits were modeled for pristine ice and snow. Hydrometeor optical properties were determined from an extended anomalous diffraction theory approach. Brightness temperatures were computed using a delta-Eddington two-stream model.
Results indicate that the enhanced “V,” a feature sometimes seen in satellite infrared observations, may be formed through an interaction between the overshooting dome and the upstream flanking region of high pressure. This idea is contrary to one in which the overshooting dome is viewed as an obstacle to the environmental flow. As expected, the radiative effects of pristine ice particles within the anvil largely determined the brightness temperature field. Although brightness temperatures were found to be insensitive to microphysical characteristics of moderate to thick portions of the anvil, a strong relationship did exist with column-integrated pristine ice mass for cloud optical depths below about 5. Precipitation-sized hydrometeors and surface precipitation rate, on the other hand, failed to exhibit any meaningful relationship with the cloud-top brightness temperature. The combined mesoscale model and RT modeling system used in this study may also have utility in satellite product development prior to launch of a satellite and in satellite data assimilation.
Abstract
Assimilating satellite radiance data under all weather conditions remains an outstanding problem in numerical weather prediction. This study develops an observational operator for use in radiance assimilation under both clear and cloudy conditions specifically for mesoscale models containing explicit microphysics. It is part of a larger research effort to build a 4D variational radiance assimilation system for optimal use of satellite data. The operator is suitable for radiance calculations at visible/infrared wavelengths and is adaptable to the different spectral characteristics of many types of narrowband satellite sensors. The new operator makes use of a gas extinction model and fast, multiple-scattering radiative transfer models, and relies on physical approximations for deriving cloud optical properties. One property, the asymmetry factor, is estimated through a new application of anomalous diffraction theory.
A test of the observational operator's ability to estimate cloudy radiances was performed by forecasting a continental stratus system using the Regional Atmospheric Modeling System and computing radiances at all channels of the Geostationary Operational Environmental Satellite-9 imager. The forecasted radiances were found to reproduce very well the frequency distributions of observed cloudy radiances, particularly, the subtle temporal changes in the distributions that occurred between the early and late stages of development of the cloud system. These results are very encouraging and hold promise for future application of this observational operator in a full radiance assimilation system for satellite data across a wide range of wavelengths.
Abstract
Assimilating satellite radiance data under all weather conditions remains an outstanding problem in numerical weather prediction. This study develops an observational operator for use in radiance assimilation under both clear and cloudy conditions specifically for mesoscale models containing explicit microphysics. It is part of a larger research effort to build a 4D variational radiance assimilation system for optimal use of satellite data. The operator is suitable for radiance calculations at visible/infrared wavelengths and is adaptable to the different spectral characteristics of many types of narrowband satellite sensors. The new operator makes use of a gas extinction model and fast, multiple-scattering radiative transfer models, and relies on physical approximations for deriving cloud optical properties. One property, the asymmetry factor, is estimated through a new application of anomalous diffraction theory.
A test of the observational operator's ability to estimate cloudy radiances was performed by forecasting a continental stratus system using the Regional Atmospheric Modeling System and computing radiances at all channels of the Geostationary Operational Environmental Satellite-9 imager. The forecasted radiances were found to reproduce very well the frequency distributions of observed cloudy radiances, particularly, the subtle temporal changes in the distributions that occurred between the early and late stages of development of the cloud system. These results are very encouraging and hold promise for future application of this observational operator in a full radiance assimilation system for satellite data across a wide range of wavelengths.
