Hydrometeor Distribution and Linear Depolarization Ratio in Thunderstorms

Abstract

<jats:p>The distribution of hydrometeors in thunderstorms is still under investigation as well as the process of electrification in thunderclouds leading to lightning discharges. One indicator of cloud electrification might be high values of the Linear Depolarization Ratio (LDR) at higher vertical levels. This study focuses on LDR values derived from vertically pointing cloud radars and the distribution of five hydrometeor species during 38 days with thunderstorms which occurred in 2018 and 2019 in Central Europe, close to our radar site. The study shows improved algorithms for de-aliasing, the derivation of vertical air velocity and the classification of hydrometeors in clouds using radar data. The comparison of vertical profiles with observed lightning discharges in the vicinity of the radar site (≤1 km) suggested that cloud radar data can indirectly identify “lightning” areas by high LDR values observed at higher gates due to the alignment of ice crystals, likely because of an intensified electric field in thunderclouds. Simultaneously, the results indicated that at higher gates, there is a mixture of several hydrometeor species, which suggests a well-known electrification process by collisions of hydrometeors.</jats:p>

Using Factor Separation to Elucidate the Respective Contributions of Desert Dust and Urban Pollution to the 4 January 2020 Tel Aviv Lightning and Flash Flood Disaster

“…The LDR is the difference of the horizontal plane reflectivity to the reflectivity in the vertical plane when the radar beam is polarized vertically. As noted in Hubbert et al (2018) and Sokol et al (2020), the LDR of large oblong raindrops, irregular, aggregated snowflakes, and vertically oriented wet graupel/hail or large oblate hail can vary between −20 and −25 dB, while the LDR of symmetric liquid and ice particles is closer to −30 dB (or even lower for completely symmetric ice particles).…”

“…This implies that the simulations with continental aerosols produced more asymmetric hydrometeors than simulations with either maritime or dust combined with urban aerosols. As noted by Sokol et al (2020), smaller negative values indicate a distribution of mixed particles conducive to the production of lightning. This can be seen in the simulations by comparing the simulated LPI in Figures 16c and 16e to Figures 16b and 16d.…”

Differences in Cloud Radar Phase and Power in Co- and Cross-Channel—Indicator of Lightning

“…The cloud radar MIRA 35c processes obtained Doppler spectra using an IDL software, which enables also a first visualization of the data (http://metek.de/product/mira-35c/). In this paper, we do not provide the reader with the detailed description of the process of basic Doppler spectra processing, instead we refer the reader to our previous works by Sokol et al [23,26]. However, what is important to mention is that (i) the cloud radar provides measurements with a time step of 2 s (i.e., the obtained data have high temporal resolution); (ii) the gate size (i.e., vertical resolution) is approximately 28.8 m and (iii) the data are measured from 4th up to maximum 512th gate (i.e., up to a height of 14 km above the radar approximately).…”

“…These were mainly focused on the alignment of cloud particles in intensified electrostatic field [14][15][16][17][18][19][20][21][22]. This paper builds on our previous work [23], where we dealt with the differences in selected quantities derived from the data of a cloud profiler (Ka-band), which has been installed at the top of the Milešovka mountain (Czech Republic, Central Europe). In the mentioned work, we used almost exclusively data from the co-channel; only the variable called Linear Depolarization Ratio (LDR) used information from both the co-and the cross-channel.…”

“…Based on analysis of 38 days with thunderstorms, which occurred in 2018 and 2019 in Central Europe, Sokol et al [23] concluded that the cloud radar data can identify "lightning" areas indirectly -by higher values of LDR measured at higher gates. The higher values of LDR were associated with the alignment of ice crystals, likely caused by strong electric field in the thundercloud.…”