Microphysical Properties and Radar Polarimetric Features within a Warm Front

Keppas, Stavros; Crosier, Jonathan; Bower, Keith

doi:10.1175/mwr-d-18-0056.1

Cited by 9 publications

(18 citation statements)

References 98 publications

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“…5c), and explains why the altitude of aggregation enhancement by turbulence decreases with time. This was also observed by Keppas et al (2018), who attributed this altitude decrease of the maximum of wind speed to the passage of the warm front. On the other hand, the altitude of the onset of aggregation could increase with time as the warm front passes, because the altitude of the -15 • C isotherm [relative maximum of aggregation in Hobbs et al, 1974] is higher at 09:00 UTC than at 06:00 UTC.…”

Section: 1supporting

confidence: 76%

“…A region of enhanced positive Doppler velocity can be observed from 07:30 to 08:00 UTC between 4000 and 6000 m where the mean Doppler velocity amounts to approximately 2 m s −1 , indicating the presence of embedded convection in the WCB. Recently, case studies by Keppas et al (2018); Oertel et al (2019a) and Oertel et al (2019b) also identified embedded convection within the large-scale WCB. Oertel et al (2019a, b) showed that embedded convection leads to a local increase in precipitation intensity, while Oertel et al (2019b) found that it also promotes the formation of graupel particles in the model simulations.…”

Section: The Evolution Of Clouds and Precipitation Over Pyeongchangmentioning

confidence: 99%

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

Gehring¹,

Oertel²,

Vignon³

et al. 2020

Preprint

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Abstract. On 28 February 2018, 57 mm of precipitation associated to 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. 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. Vertical profiles of polarimetric radar variables show during the most intense precipitation period 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 convection 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 the large-scale circulation.

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Section: 1supporting

confidence: 76%

Section: The Evolution Of Clouds and Precipitation Over Pyeongchangmentioning

confidence: 99%

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

Gehring¹,

Oertel²,

Vignon³

et al. 2020

Preprint

View full text Add to dashboard Cite

show abstract

“…The vertical wind shear reaches values of 15 m s −1 km −1 in speed and 0.27 • m −1 in direction. Keppas et al (2018) identified similar values of vertical wind shear, which triggered Kelvin-Helmholtz instabilities. In Sect.…”

Section: The Evolution Of Clouds and Precipitation Over Pyeongchangmentioning

confidence: 78%

“…However, they did not consider the interactions between large-scale flow and microphysics. Keppas et al (2018) studied the microphysical properties of a warm front with radar and in situ measurements in clouds. They found that a WCB formed a widespread mixed-phase cloud by producing a significant amount of liquid water, which favoured riming and secondary ice generation.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2020

View full text Add to dashboard Cite

Abstract. 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.

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“…Pfitzenmaier et al (2017) presented a new algorithm to retrieve FSs within a radar time-height plot based on genuine high-resolution wind information obtained with the Transportable Atmospheric Radar (TARA). Keppas et al (2018) used the data obtained from dual-polarization radars to provide analyses of the structure, the origin, and the effects of the FSs associated with warm fronts. However, the research on the vertical structure and dynamical characteristics of the entire stratiform region is less than that on GC regions.…”

Section: Introductionmentioning

confidence: 99%

Vertical Structure and Dynamical Properties during Snow Events in Middle Latitudes of China from Observations by the C-band Vertically Pointing Radar

Cui

Ruan

Wei

et al. 2020

Journal of the Meteorological Society of Japan

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Data from the continuous observations of 4 shallow snow events (echo top <8 km) and 2 deep events (>10 km) were obtained by the C-band vertically pointing radar with frequency modulation continuous wave technology (VPR-CFMCW) with extremely high resolution during the winter of 2015-2016 in middle latitudes of China. Generating cells (GCs) were found near the cloud top in each event. Reflectivity (Z), radial velocity (V r), the vertical gradient of Z (dZ/dh, h is the vertical distance) and V r (dV r /dh) showed different vertical distribution characteristics between the upper GC and lower stratiform (St) regions. The fall streaks (FSs) associated with GCs were embedded in the St regions. In the deep events, the proportions of GC regions were slightly larger, but the average contributions to the growth of Z (33%) were lower than those in the shallow events (42%). The average dZ/dh were usually 2-3 times larger inside GCs and FSs compared to outside. Bimodal Doppler spectra were used to establish the relationships between the Z and the reflectivity-weighted particle fall speed (V z) for the 2 regions. The vertical air velocity (W a) and V z were then retrieved. The results show that both updraft and downdraft were alternately observed in GC regions. GC locations usually accompanied strong upward air motions, with average speeds mostly distributed around 1.2 m s −1 , while downward air motions often appeared between GCs. In the St regions, the speeds of W a were mainly within 0.5 m s −1. The upper areas of the St regions consisted primarily of weak upward motions, while weak downward motions dominated the lower areas. There was no apparent difference in W a inside and outside Radar system Frequency Center frequency MHz Beam width ≤2.6° Band width 6 MHz±3 MHz/±3.5 MHz isolation between antennas 90 dB Transmit power ≥150 W Antenna gain ≥35 dB Antenna types Bistatic and parabolic antenna Antenna diameter 1.6 m

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Microphysical Properties and Radar Polarimetric Features within a Warm Front

Cited by 9 publications

References 98 publications

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

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

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

Vertical Structure and Dynamical Properties during Snow Events in Middle Latitudes of China from Observations by the C-band Vertically Pointing Radar

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