A Method for Retrieving Vertical Air Velocities in Convective Clouds over the Tibetan Plateau from TIPEX-III Cloud Radar Doppler Spectra

Abstract

Abstract:In the summertime, convective cells occur frequently over the Tibetan Plateau (TP) because of the large dynamic and thermal effects of the landmass. Measurements of vertical air velocity in convective cloud are useful for advancing our understanding of the dynamic and microphysical mechanisms of clouds and can be used to improve the parameterization of current numerical models. This paper presents a technique for retrieving high-resolution vertical air velocities in convective clouds over the TP through the use of Doppler spectra from vertically pointing Ka-band cloud radar. The method was based on the development of a "small-particle-traced" idea and its associated data processing, and it used three modes of radar. Spectral broadening corrections, uncertainty estimations, and results merging were used to ensure accurate results. Qualitative analysis of two typical convective cases showed that the retrievals were reliable and agreed with the expected results inferred from other radar measurements. A quantitative retrieval of vertical air motion from a ground-based optical disdrometer was used to compare with the radar-derived result. This comparison illustrated that, while the data trends from the two methods of retrieval were in agreement while identifying the updrafts and downdrafts, the cloud radar had a much higher resolution and was able to reveal the small-scale variations in vertical air motion.

Characteristics of Warm Clouds and Precipitation in South China during the Pre-Flood Season Using Datasets from a Cloud Radar, a Ceilometer, and a Disdrometer

“…First, a technology called "small-particle-trace" was applied to estimate the V A from Doppler spectra. This approach has been applied and verified by Gossard, Kollias, Shupe, Zheng, and Sokol in different cloud and precipitation type studies [39,50,[56][57][58]. The V T was then obtained by subtracting V A from V M .…”

Applications of QC and Merged Doppler Spectral Density Data from Ka-Band Cloud Radar to Microphysics Retrieval and Comparison with Airplane in Situ Observation

“…K Z = 0.00087Z 0.93 (7) where K Z is the attenuation coefficient (dB km −1 ) and Z is reflectivity (mm 6 m −3 ). The attenuation coefficients from retrieved DSD is calculated by using Equation (1).…”

“…In Kollias' work, precipitation attenuation was not corrected and coherent integration effects on Doppler spectral data were not discussed.Before the recording of Doppler spectral density data, vertical air motion has often been retrieved on the basis of a fixed empirical relationship between radar reflectivity and hydrometeor terminal velocity [5,6]. However, establishing a straightforward relationship among these variables has been difficult and thus is not known in the case of thunderclouds [7].Lhermitte first proposed a methodology for retrieving vertical air motion from Doppler spectral density data that Kollias verified and applied to the study of strong convective precipitation [8,9]. Vertical air velocity can be directly estimated using the velocity bin of small particles such as liquid droplets and small ice crystals; therefore, these particles can be considered tracers of clear-air motion in the measured spectra [10][11][12][13].…”

“…The consistency of radar reflectivity, velocity, and Doppler spectral density measured in the different modes was analyzed, and an algorithm integrating reflectivity, velocity, and spectral width from various operational modes was proposed [20,21]. Doppler spectra obtained from single-mode operation were used to retrieve high-resolution vertical air velocities in convective clouds over the Tibetan Plateau based on the "small-particle-traced" idea [7]. However, there were large reflectivity sensibility gaps of 20.8 dB between the precipitation mode and cirrus mode, which limit cloud observations below 2 km height.…”

“…Before the recording of Doppler spectral density data, vertical air motion has often been retrieved on the basis of a fixed empirical relationship between radar reflectivity and hydrometeor terminal velocity [5,6]. However, establishing a straightforward relationship among these variables has been difficult and thus is not known in the case of thunderclouds [7].…”