Keeping with the pattern of the past few days, thunderstorms and occasional severe weather are occurring across the Tennessee Valley, generated along and in the vicinity of a stubborn stationary front that has wavered back and forth across the area. Severe thunderstorm and tornado watch boxes were issued across Arkansas, Mississippi and Alabama through the early morning hours and are likely to continue. This area of active weather was sampled by CloudSat, the first orbiting94 GHz Cloud Profiling Radar, and member of the NASA “Afternoon Train” or “A-Train” of polar-orbiting, Earth observing satellites. Several SPoRT products are developed from MODIS and AIRS data made available by the Aqua satellite, which flies in line with CloudSat, CALIPSO and other instruments, providing a broader view of cloud characteristics versus traditional two dimensional cloud mapping.
The image below is provided by the Naval Research Laboratory, showing the CloudSat orbit track (red) during a descending pass around 08 UTC. Although the two image segments break up the block of profiles, CloudSat basically sampled both the trailing stratiform and convective line associated with the morning MCS across eastern Arkansas and western Mississippi. Since CloudSat samples vertical profiles and has a greater sensitivity to small cloud ice and water droplets, it provides a better estimate of cloud top versus traditional ground based radars. However, CloudSat attenuates significantly in regions of light to moderate liquid precipitation. Therefore, in many cases the radar reflectivity decreases at low altitude — although precipitation was widespread at the surface. The freezing level is estimated by model forecasts (overlaid contours), and reflectivity decreases, then increases again in the vicinity of this layer, which has been cited by researchers as a “dim band” that occurs with this type of radar. Meanwhile, since the bulk of the attenuation is caused by precipitation, methods are being developed to exploit the 94 GHz attenuation to estimate precipitation for global cloud systems, which will broaden our knowledge of global climate and weather processes. Attenuation is particularly strong at about 33-34 degrees latitude, where strong echos are detected aloft. This is likely the “overshooting top” or vigorous updrafts of the convective line, coincident with the highest altitude cloud tops at 15km (~50kft). Large hydrometeors (supercooled rain, hail, graupel) extinguish much of the signal below 5 km AGL.
Although CloudSat attenuates significantly in liquid precipitation, it is ideal for studying snow processes, including those that contribute to the widespread stratiform precipitation that occurs with mesoscale convective systems. Within SPoRT, CloudSat is being used to investigate forecast model parameterizations used in forecasts for winter storms, using the CloudSat radar to check that simulated cloud reflectivity reasonably approximates that observed from space. These parameterization improvements may in turn benefit a variety of forecast precipitation processes.