Winter snowstorms can frequently case major disruption to transportation, commerce and public safety especially in densely populated areas like the northeastern US. The forecast of the timing and duration of winter have greatly improved over the last 30 years. However, the complexity of cold microphysical processes results in a large natural variability of ice/snow hydrometeor sizes, habits, densities, orientations, and particle size distributions and this makes the quantitative forecast of snowfall and snow accumulation far more challenging. Today, the remote sensing capabilities have advanced significantly making now an ideal time to study the microphysics and dynamics of winter storms and understand what factors control the growth of ice particles. In this study, the research team used state-of-the-art remote sensing capabilities to study winter storms, assess the quality of current snowfall amount estimates, and investigate the relative strength of different microphysical processes in determining surface snow accumulation.

One of the first outcomes of our studies was to illustrate the capabilities of dual-wavelength ratio (DWR) measurements coupled with Doppler velocity measurements from profiling radar and polarimetric measurements from scanning radars to discern riming and aggregation processes. Our research highlighted that dual-frequency measurements coupled with Doppler velocity measurements – typically available from all cloud radar systems – not only are more practical than the triple-frequency measurements (since they only involve two radars) but are more effective in separating the two processes as well. Such remote sensing capabilities can reveal complex microphysics and therefore improve quantitative estimations of snow amount (i.e., IWC, snow rate) and microphysical quantities such as rime mass fraction.

The analysis of observations collected in Long Island, NY documented the turbulent nature of winter storms and the presence of updrafts throughout the depth of winter storms (Fig. 1). Statistics on their frequency of occurrence, duration, magnitude and vertical extend were provided. These updrafts are responsible for upward mass flux and then contribute to the precipitation mass growth. Our study was one of the first to highlight the frequently occurrence of updrafts and turbulence zones in winter storms. The relative role of the frequently observed microscale updrafts and turbulent zones that are not represented in forecast models compared to mesoscale and synoptic scale updrafts (that are resolved by forecast models) is now an area of active research.

Another research focus area was the evaluation of ice water content (IWC, amount if ice mass per unit of volume) estimates from polarimetric radars.  IWC estimation using millimeter-wavelength radar measurements has been challenging for decades, because of complexities of snow particle properties and size, which can cause complex scattering at the shorter radar wavelengths. The suggested polarimetric techniques overcome this difficulty via utilizing specific differential phase K_DP which is higher at millimeter wavelengths than centimeter wavelengths. Our research proposes new IWC relationships for Ka-band polarimetric radar measurements and evaluates them using a Ka-band Scanning Polarimetric Radar (KASPR) and a nearby NEXRAD (S-band) polarimetric radar for the U.S northeast coast winter storms. The proposed techniques can be applied to other mm-wavelength radars and shed light on the millimeter-wavelength polarimetric radar IWC estimation.

The project provided the opportunity to train undergraduate and graduate students in field experimental setup and operations and to obtain expertise in the analysis of sounding measurements, millimeter-wavelength radar analysis, and ground-based in-situ data analysis for snow. This professional opportunity has provided skills and understanding of meteorological measurements, including measurement uncertainties and how to calibrate the observation data.

Last Modified: 06/07/2024
Modified by: Pavlos Kollias