Abstract
Abstract. Multi-Doppler-radar network observations have been used in different configurations over the last several decades to conduct three-dimensional wind retrievals in mesoscale convective systems. Here, the impacts of the selected radar volume coverage pattern (VCP), the sampling time for the VCP, the number of radars used, and the added value of advection correction on the retrieval of the vertical air motion in the upper part of convective clouds are examined using the Weather Research and Forecasting (WRF) model simulation, the Cloud Resolving Model Radar SIMulator (CR-SIM), and a three-dimensional variational multi-Doppler-radar retrieval technique. Comparisons between the model truth (i.e., WRF kinematic fields) and updraft properties (updraft fraction, updraft magnitude, and mass flux) retrieved from the CR-SIM-generated multi-Doppler-radar field are used to investigate these impacts. The findings are that (1) the VCP elevation strategy and sampling time have a significant effect on the retrieved updraft properties above 6 km in altitude; (2) 2 min or shorter VCPs have small impacts on the retrievals, and the errors are comparable to retrievals using a snapshot cloud field; (3) increasing the density of elevation angles in the VCP appears to be more effective to reduce the uncertainty than an addition of data from one more radar, if the VCP is performed in 2 min; and (4) the use of dense elevation angles combined with an advection correction applied to the 2 min VCPs can effectively improve the updraft retrievals, but for longer VCP sampling periods (5 min) the value of advection correction is challenging. This study highlights several limiting factors in the retrieval of upper-level vertical velocity from multi-Doppler-radar networks and suggests that the use of rapid-scan radars can substantially improve the quality of wind retrievals if conducted in a limited spatial domain.
Highlights
Measurements of vertical air motion in deep convective clouds are critical for our understanding of the dynamics and microphysics of convective clouds (e.g., Jorgensen and LeMone, 1989)
Three time periods are considered here for the completion of the radar network volume coverage pattern (VCP): (i) snapshot, where it is effectively assumed that the first Weather Research and Forecasting (WRF) model output is frozen in time and the radars instantaneously collect data according to their VCP without any cloud evolution; (ii) a 2 min radar network VCP to emulate the performance of rapid scanning radar networks; and (iii) a 5 min radar network VCP to emulate the performance of the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) network during MC3E and the performance of other mechanically scanning radar networks
While there is a plethora of studies illustrating the ability of multi-Doppler-radar observations to capture the low-level wind divergence and circulation, there is little to show regarding the capability of this observing system to capture the upper-level convective dynamics
Summary
Measurements of vertical air motion in deep convective clouds are critical for our understanding of the dynamics and microphysics of convective clouds (e.g., Jorgensen and LeMone, 1989). The interpolation and smoothing techniques used (Cressman, 1959; Barnes, 1964; Given and Ray, 1994; Miller and Fredrick, 1998) can have an impact on the quality of Doppler radar wind retrieval (e.g., Collis et al, 2010) Another source of uncertainties is related to the hydrometeor fall speed estimates (e.g., Steiner, 1991; Caya, 2001), especially at shorter wavelengths (e.g., X and C bands) where the signal attenuation can bias the estimates. They pointed out that missing low-level measurements and poor vertical sampling could produce significant uncertainties in retrieval of lowlevel wind fields These investigations have been conducted by formulating suitable Observing System Simulation Experiments (OSSEs). We investigate the impacts of the selected radar volume coverage pattern (VCP), the sampling time for the VCP, the number of radars used, and the added value of advection correction upon the uncertainties of multi-Doppler-radar wind retrieval
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