Polarimetric Observations and Simulations of Sublimating Snow: Implications for Nowcasting

Abstract

Snow sublimating in dry air is a forecasting challenge and can delay the onset of surface snowfall and affect storm-total accumulations. Despite this, it remains comparatively less studied than other microphysical processes. Herein, the characteristics of sublimating snow and the potential for nowcasting snowfall reaching the surface are explored through the use of dual-polarization radar. Twelve cases featuring prolific sublimation were analyzed using range-defined quasi-vertical profiles (RDQVPs) and compared with environmental model analyses. Overall, reflectivity Z significantly decreases, differential reflectivity ZDR slightly decreases, and copolar-correlation coefficient ρhv remains nearly constant through the sublimation layer. Regions of enhanced specific differential phase Kdp were frequently observed in the sublimation layer and are believed to be polarimetric evidence of secondary ice production via sublimation. A 1D bin model was initialized using particle size distributions retrieved from the RDQVPs using numerous novel polarimetric snowretrieval relations for a wide range of forecast lead times, with the model environment evolving in response to sublimation. It was found that the model was largely able to predict the snowfall start time up to six hours in advance, with a 6-h median bias of just -18.5 minutes. A more detailed case study of the 08 December 2013 snowstorm in the Philadelphia region was also performed, demonstrating good correspondence with observations and examples of model fields (e.g., cooling rate) hypothetically available from such a tool. The proof-of-concept results herein demonstrate the potential benefits of incorporating spatially averaged radar data in conjunction with simple 1D models into the nowcasting process.

Evaluation of polarimetric ice microphysical retrievals with OLYMPEX campaign data

“…( 15) in regions where Z DR >0.4 dB and Eq. ( 17) elsewhere, as suggested by Carlin et al (2021), leverages the strengths of both formulas and denoted as IWC Carlin estimator in the following.…”

“…Another set of polarimetric relations to quantify snow properties was derived by Bukovčić et al (2018) exploiting Z H and K DP . More recently, Carlin et al (2021) suggested a hybrid application for estimating IWC by combining the complementary strengths and optimal ranges of the IWC retrievals following Bukovčić et al (2018) and Ryzhkov and Zrnić (2019). Apart from IWC retrievals, polarimetric retrieval relations have been suggested for D m and total number concentration of ice particles per unit volume N t based on approaches utilizing combinations of three or two polarimetric variables, always including K DP (Ryzhkov et al, 2018;Bukovčić et al, 2020).…”

The influence of multiple groups of biological ice nucleating particles on microphysical properties of mixed-phase clouds observed during MC3E

“…Moisseev et al (2015), for example, noted an increase in observed K DP because of aggregation. In addition, a few studies have hypothesized evidence of SIP via K DP (e.g., Sinclair et al, 2016;Kumjian and Lombardo, 2017;Carlin et al, 2021). In this study, we attempted to detect secondary ice formation signatures by implementing K DP estimations into AC.…”

Climatology of the Vertical Profiles of Polarimetric Radar Variables and Retrieved Microphysical Parameters in Continental/Tropical MCSs and Landfalling Hurricanes

“…The radar retrieval equations for computing microphysical variables in rain and ice which we utilize in our study can be found in Ryzhkov and Zrnic (2019, Chapter 11), Ryzhkov et al (2020), Bukovcic et al (2018), and Carlin et al (2021. These equations are listed herein.…”

“…However, they are very sensitive to possible errors in the Z dr measurements, particularly at lower values of Z DR . For this reason, Equations 5 and 6 are utilized if Z DR > 0.4 dB (Carlin et al, 2021). Otherwise, IWC and D m are estimated from Equations 7 and 8 that do not contain differential reflectivity.…”