Precipitation profiling from vertically-looking ground-based radar profilers operating at frequencies of 915- and 2835-MHz have been demonstrated to be useful tools in several field campaigns during the past decade. When combined with a surface disdrometer and a nearby scanning radar, the calibrated profiling radar provides high resolution details of the precipitation vertical structure while the scanning radar provides the horizontal context of the precipitation relative to the profiler site. Profiling radars provide detailed information of reflectivities and drop-size distributions that are essential for quantitative precipitation estimation (QPE). One role that profiling radars have in QPE is monitoring the calibration of the scanning radar reflectivity used to map the precipitation over a large area. The concept of up-scaling uses a surface disdrometer to calibrate the profiling radar which is then used to calibrate the scanning radar. This method of up-scaling the reflectivities observed by the surface disdrometer to the scanning radar reflectivities eliminates some of the uncertainties of Z-R relationships inherent in surface rain gauge to scanning radar calibrating and monitoring techniques.
During the past decade Doppler radar profilers that operate near 1 GHz and 3 GHz have been developed at the NOAA Aeronomy Laboratory for use in dynamics and precipitation research. The profilers have been used extensively in numerous field campaigns during the past decade. In the presence of precipitating clouds, backscattering from hydrometeors is dominant and the Doppler velocity provides a measure of the fall velocity of hydrometeors. Profiler observations yield time height cross-sections of equivalent reflectivity, Doppler velocity and spectral width that illustrate the evolution of precipitating clouds systems. The vertical structure of these parameters has been used to classify the precipitating cloud systems into several different categories. These observations document the prevalence of deep anvil cloud systems over the Pacific warm pool region. They also show the relative abundance of rainfall from stratiform and convective components of precipitating cloud systems and the continuous observations reveal the diurnal evolution of the precipitating clouds over the profiler. The profiler observations provide important information for the calibration and validation of precipitation measurements by other instruments and platforms. For example, direct comparisons of profiler reflectivities with scanning radar reflectivities provide a direct means for calibration of scanning radars. The profilers are calibrated with a collocated disdrometer. An important objective of the profiler observations is to retrieve drop-size distributions and to determine the variability of the drop-size distributions in diverse precipitating cloud systems. Recent developments provide optimism that drop-size distribution retrievals can be made by profilers operating at 1 GHz or 3 GHz without complementary measurement of vertical air motions.
The use of meteorological radar reflectivity Z to estimate rainfall rate R is approached using a different perspective from the classical Z-R relation. Simultaneous rain measurements from different sensors are combined to construct a model that estimates the vertical air velocity by minimizing the error in reflectivity between the different sensors. This model is based on the fact that rain rate and reflectivity are both dependent on the integrals of rain drop size distribution (DSD) but only R depends on vertical air velocity. This study attempts to validate the vertical air velocity estimates and quantify their affects on the rainfall rate estimation. Disdrometer Flux Conservation Model (DFC) uses measurements from disdrometers and other sensors such as vertically pointing radar profilers and scanning radars. Disdrometers measure a drop size flux (Phi) (D), defined as the number of drops passing a horizontal surface per unit time, per unit area, per drop size. The flux is equal to the product of the drop size distribution near the ground NG(D) and drop velocity near the ground vG(D). The drop velocity is the difference between the droplet terminal velocity and the vertical component of the wind velocity, which varies with altitude. The estimates derived from the DFC model using two pair wise selected sensors are used to study the change of reflectivity and vertical air velocity with altitude. Sensitivity tests for the DFC model are also discussed and these outcomes are validated by comparison with independent profiler vertical velocity observations.
With their high vertical and temporal resolution, vertically-pointing profilers offer valuable information about the vertical structure of precipitating cloud systems. The observed vertical structure of the precipitating cloud is related to the latent heating profile in the cloud system. The different precipitation regimes (e.g., convective, stratiform, and transitional precipitation) can be identified by diagnosing the profiler resolved vertical structure of reflectivity, mean Doppler velocity, and turbulence. The classifications based on these vertical profiles are important for estimating the frequency and percent occurrence of the precipitation regimes.
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