A Comparison of Observed and Simulated Precipitation Objects During the IMPACTS Campaign

The Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) is a field campaign operated by NASA from 2020-2023 to investigate the structure of mesoscale snowbands through the use of both airborne and ground-based instrumentation. While a climatology and conceptual model of banded events in the Northeast U.S. has been developed by Ganetis et al. (2018), the broader spectrum of precipitation structures do not all fit the rigid categories of primary or multibands, as defined in previous literature. Some multibands last several hours as discrete, convective-like features, while others may be transient, weaker-reflectivity structures that rapidly grow and dissipate, or merge with and split from each other.

This talk will address the differences between three IMPACTS cyclones, featuring long structures along a cold frontal boundary on 4 February 2022, small transient structures in the comma head of a developing cyclone on 17 February 2022, and medium-sized structures on the backside of a departing mature cyclone on 23 January 2023. The high-altitude ER-2 and the in-situ P-3 aircraft flew coordinated legs for each case. To provide environmental context, WRF version 4.4 was configured and run for the duration of each event. The WRF, rawinsondes, and reanalysis are used to investigate the role of shear, frontogenetical lift, and instability in generating and maintaining these precipitation features. MRMS reflectivity, the ER-2 downward pointing radars, and the P-3 cloud probes will be used to understand the microphysical structure.

Preliminary results show that WRF lacks mid-sized precipitation features, and they are more amorphous than their MRMS counterparts. Conditional and potential instability is typically found near cloud top, above the layer of sloping frontogenesis, in the vicinity of these features. Slantwise instability near cloud top is found to be ubiquitous in all three cases and is likely not a sufficient cause for band formation. An analysis of dual frequency ratio and particle size distributions suggests that particles grow through aggregation as they fall out from generating cells near cloud top, and are organized into band-like structures at the surface. Sensitivity tests show that increasing horizontal or vertical resolution both improve the structure of these objects in WRF for the 17 February 2022 case. It is hypothesized that the higher horizontal and vertical resolution improves the depiction of cloud-top generating cells, which are necessary for the formation of bands.