Derived Observations From Frequently Sampled Microwave Measurements of Precipitation-Part I: Relations to Atmospheric Thermodynamics

This is the first of two papers that quantify the high added value of frequent 3-D radar observations of the atmosphere to capture the dynamics of weather systems. Recent advances in small-satellite and radar technologies, such as the "Radar in Cubesat" developed at the Jet Propulsion Laboratory, are paving the way for the design of convoys of spaceborne radars that can directly observe the evolution of severe weather at very fine temporal scales. The analyses presented here are to establish the relation between such observations to the underlying cloud variables and processes, and to quantify the sensitivity to the different physical and instrument parameters. In this first part, a robust algorithm is proposed to estimate the horizontal advection from successive radar reflectivity measurements, and use it to compute total time derivatives d_{t} Z of the observed radar reflectivity factors Z . As illustrated using Next-Generation Radar measurements in a blizzard coupled with an atmospheric river in California, the maps of d_{t} Z reveal features about locations of sources and sinks of condensed water, which are, otherwise, not visible in the maps of Z alone. Using numerical simulations of the blizzard and a radiative-transfer model to forward calculate the corresponding reflectivity factors Z in the S-band, we show the robust correlation between d_{t} Z and the moistening of the troposphere.