Identification of snowfall microphysical processes from Eulerian vertical gradients of polarimetric radar variables

International audiencePolarimetric radar systems are commonly used to study the microphysics of precipitation. While they offer continuous measurements with a large spatial coverage, retrieving information about the microphysical processes that govern the evolution of snowfall from the polarimetric signal is challenging. The present study develops a new method, called process identification based on vertical gradient signs (PIVSs), to spatially identify the occurrence of the main microphysical processes (aggregation and riming, crystal growth by vapor deposition and sublimation) in snowfall from dual-polarization Doppler radar scans. We first derive an analytical framework to assess in which meteorological conditions the local vertical gradients of radar variables reliably inform about microphysical processes. In such conditions, we then identify regions dominated by (i) vapor deposition, (ii) aggregation and riming and (iii) snowflake sublimation and possibly snowflake breakup, based on the sign of the local vertical gradients of the reflectivity ZH and the differential reflectivity ZDR. The method is then applied to data from two frontal snowfall events, namely one in coastal Adélie Land, Antarctica, and one in the Taebaek Mountains in South Korea. The validity of the method is assessed by comparing its outcome with snowflake observations, using a multi-angle snowflake camera, and with the output of a hydrometeor classification, based on polarimetric radar signal. The application of the method further makes it possible to better characterize and understand how snowfall forms, grows and decays in two different geographical and meteorological contexts. In particular, we are able to automatically derive and discuss the altitude and thickness of the layers where each process prevails for both case studies. We infer some microphysical characteristics in terms of radar variables from statistical analysis of the method output (e.g., ZH and ZDR distribution for each process). We, finally, highlight the potential for extensive application to cold precipitation events in different meteorological contexts

Radar and ground-level measurements of precipitation during the ICE-POP 2018 campaign in South-Korea

This dataset contains radar measurements, as well as ground-based observations of hydrometeors collected in the Gangwon-do province in South-Korea. It includes observations from an X-band dual-polarisation Doppler radar, a W-band Doppler cloud profiler, a multi-angle snowflake camera and a two-dimensional video disdrometer. Classifications of hydrometeor types based on dual-polarisation measurements and snowflake photographs are also available. The dataset covers the period from 15 November 2017 to 18 March 2018 and features nine precipitations events with a total accumulation of 195 mm of equivalent liquid precipitation

Meteorological observations from automatic weather station located at Davis, Antarctica (2019-01-01 - 2019-01-31)

This dataset contains the data from an automatic weather station located at Davis, Antarctica in January 2019

Radiosonde measurements from Davis Station (2019-01)

This dataset contains the radiosoundings at 00:00 or 12:00 at Davis Station in January 2019

Microphysics and dynamics of snowfall associated with a warm conveyor belt over Korea

On 28 February 2018, 57 mm of precipitation associated with a warm conveyor belt (WCB) fell within 21 h over South Korea. To investigate how the large-scale circulation influenced the microphysics of this intense precipitation event, we used radar measurements, snowflake photographs and radiosounding data from the International Collaborative Experiments for Pyeongchang 2018 Olympic and Paralympic Winter Games (ICE-POP 2018). The WCB was identified with trajectories computed with analysis wind fields from the Integrated Forecast System global atmospheric model. The WCB was collocated with a zone of enhanced wind speed of up to 45 m s−1 at 6500 m a.s.l., as measured by a radiosonde and a Doppler radar. Supercooled liquid water (SLW) with concentrations exceeding 0.2 g kg−1 was produced during the rapid ascent within the WCB. During the most intense precipitation period, vertical profiles of polarimetric radar variables show a peak and subsequent decrease in differential reflectivity as aggregation starts. Below the peak in differential reflectivity, the specific differential phase shift continues to increase, indicating early riming of oblate crystals and secondary ice generation. We hypothesise that the SLW produced in the WCB led to intense riming. Moreover, embedded updraughts in the WCB and turbulence at its lower boundary enhanced aggregation by increasing the probability of collisions between particles. This suggests that both aggregation and riming occurred prominently in this WCB. This case study shows how the large-scale atmospheric flow of a WCB provides ideal conditions for rapid precipitation growth involving SLW production, riming and aggregation. Future microphysical studies should also investigate the synoptic conditions to understand how observed processes in clouds are related to large-scale circulation

Radar, meteorological measurements, and WRF simulations from 08 to 10 January 2019 at Davis station, Antarctica

This dataset contains radar and ground-based measurements of precipitation collected from 08 to 10 January 2019 at Davis station, Antarctica. It includes observations from an X-band dual-polarisation Doppler radar, a W-band Doppler cloud profiler, a VHF wind profiler, and a Raman Lidar. A classification of hydrometeor types based on dual-polarisation measurements is also available. The dual-frequency ratio based on the X-band and W-band reflectivity measurements is made available on a common grid. WRF simulations at 27, 9, 3, and 1 km resolution centred around Davis are provided. Finally, automatic weather station and radiosounding measurements are also included

Orographic Flow Influence on Precipitation During an Atmospheric River Event at Davis, Antarctica

International audienceIntense snowfall sublimation was observed during a precipitation event over Davis in the Vestfold Hills, East Antarctica, from 08 to 10 January 2019. Radar observations and simulations from the Weather Research and Forecasting model revealed that orographic gravity waves (OGWs), generated by a north-easterly flow impinging on the ice ridge upstream of Davis, were responsible for snowfall sublimation through a foehn effect. Despite the strong meridional moisture advection associated with an atmospheric river (AR) during this event, almost no precipitation reached the ground at Davis. We found that the direction of the synoptic flow with respect to the orography determined the intensity of OGWs over Davis, which in turn directly influenced the snowfall microphysics. We hypothesize that turbulence induced by the OGWs likely enhanced the aggregation process, as identified thanks to dual-polarization and dual-frequency radar observations. This study suggests that despite the intense AR, the precipitation distribution was determined by local processes tied to the orography. The mechanisms found in this case study could contribute to the extremely dry climate of the Vestfold Hills, one of the main Antarctic oases

Precipitation over the Southern Ocean: comparison of several ship-based measurement techniques during the Antarctic Circumnavigation Expedition

Published in: Geophysical Research Abstracts. Vol. 21, EGU2019-15209, 2019 - EGU General Assembly 2019. © Author(s) 2019. CC Attribution 4.0 license