Thursday, 31 August 2023
Boundary Waters (Hyatt Regency Minneapolis)
During NASA’s IMPACTS (The Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms) field campaign, for one month each during the winters of 2022 and 2023, a group from OU (University of Oklahoma) collected datasets using the RaXPol (Rapid-scan, X-band, polarimetric) mobile Doppler radar. RaXPol has been used since 2011, mainly for probing severe convective storms and tornadoes in the Southern Plains; this was its first dedicated use for probing mesoscale structures such as snow bands in winter storms during a large field experiment.
This presentation will detail a representative sample of significant observations from three field operation periods: (1) from a blizzard associated with a rapidly-deepening midlatitude cyclone in Plymouth, MA on 29 Jan. 2022; (2) a warm-advection snowstorm in Albany, NY on 25 Feb. 2022; and (3) a warm-advection, mixed-precipitation, winter storm in Albany, NY on 25 Jan. 2023.
During the first event, periods of translating snow bands, both translating and propagating snow bands, and a stationary snow band, were documented. Approximately 24 inches of snow and wind gusts to 70 mph and greater were measured near the radar.
During the second event, RHIs were collected while the NASA ER-2 aircraft, equipped with several nadir-pointing radar systems, flew by overhead at ~ 20 km AGL during ten passes. The fine-scale structure of the Doppler wind, reflectivity, and polarimetric fields will be described. The most notable features were a low-level south-southeasterly low-level jet at ~ 2 km ARL and a two-layer reflectivity structure. As this snowstorm, which produced ~ 7 – 8 inches of snow at the radar, evolved, heavy snow turned into large snowflake conglomerates, then mixed with ice pellets, and then back to light snow. Coordinated space/time matched polarimetric radar observations have been compared to simultaneous observations by the ER-2 radars (Dunnavan et al. 2023. in review, Geophy. Res. Letters).
During the 25 Jan. 2023 winter storm, co-located MRR observations and ER-2 nadir-pointing radar data were collected in two mesoscale snow bands (only during the first of five ER-2 overpasses happened during the end of the second snow band) and in convective cells late in the deployment period. Snow, snow mixed with ice pellets, light freezing drizzle, a mixture of light freezing drizzle and ice pellets, and light rain were observed along with the transition periods.
Another significant aspect of these datasets was the collection of raw, I/Q data, which allowed for the computation of polarimetric Doppler spectra. These spectra depict polarimetric measurements as a function of Doppler velocity and can be used to link dynamics and microphysics of storms. Examples and interpretations of a few of these spectra will be discussed, with an explanation of how the spectra can increase our understanding of microphysical process that occurred in the storms.
This presentation will detail a representative sample of significant observations from three field operation periods: (1) from a blizzard associated with a rapidly-deepening midlatitude cyclone in Plymouth, MA on 29 Jan. 2022; (2) a warm-advection snowstorm in Albany, NY on 25 Feb. 2022; and (3) a warm-advection, mixed-precipitation, winter storm in Albany, NY on 25 Jan. 2023.
During the first event, periods of translating snow bands, both translating and propagating snow bands, and a stationary snow band, were documented. Approximately 24 inches of snow and wind gusts to 70 mph and greater were measured near the radar.
During the second event, RHIs were collected while the NASA ER-2 aircraft, equipped with several nadir-pointing radar systems, flew by overhead at ~ 20 km AGL during ten passes. The fine-scale structure of the Doppler wind, reflectivity, and polarimetric fields will be described. The most notable features were a low-level south-southeasterly low-level jet at ~ 2 km ARL and a two-layer reflectivity structure. As this snowstorm, which produced ~ 7 – 8 inches of snow at the radar, evolved, heavy snow turned into large snowflake conglomerates, then mixed with ice pellets, and then back to light snow. Coordinated space/time matched polarimetric radar observations have been compared to simultaneous observations by the ER-2 radars (Dunnavan et al. 2023. in review, Geophy. Res. Letters).
During the 25 Jan. 2023 winter storm, co-located MRR observations and ER-2 nadir-pointing radar data were collected in two mesoscale snow bands (only during the first of five ER-2 overpasses happened during the end of the second snow band) and in convective cells late in the deployment period. Snow, snow mixed with ice pellets, light freezing drizzle, a mixture of light freezing drizzle and ice pellets, and light rain were observed along with the transition periods.
Another significant aspect of these datasets was the collection of raw, I/Q data, which allowed for the computation of polarimetric Doppler spectra. These spectra depict polarimetric measurements as a function of Doppler velocity and can be used to link dynamics and microphysics of storms. Examples and interpretations of a few of these spectra will be discussed, with an explanation of how the spectra can increase our understanding of microphysical process that occurred in the storms.
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