Improving Vertical Velocity Estimation Using Nadir-pointing Airborne Measurements

Vertical air velocity, w, in convective storms is of intense interest for understanding storm dynamics and microphysics. Various radar-based approaches have been used to estimate vertical air motions using ground and airborne radars. We focus here on estimating w from nadir-pointing airborne Doppler radars, where Doppler velocities are a measure of the reflectivity-weighted hydrometeor vertical motions. These Doppler velocities are typically corrected with an estimate of hydrometeor fallspeed to produce an estimate of w. The NASA ER-2 instrumented with nadir-pointing radars, has been used for a number of years for examining vertical motions in various weather phenomena (e.g., Heymsfield et al. 2010). These airborne measurements introduce additional uncertainties when compared to ground-based scanning and zenith pointing radars that arise from corrections for aircraft motions. Both for airborne and ground-based radars, the fallspeeds can be challenging particularly in convective storms which may have large ice hydrometeors.

Measurements for this study are from convection during the 2020 Investigation of Microphysics and Precipitation for Atlantic-Coast Threatening Snowstorms (IMPACTS) field campaign. Multifrequency radar measurements were collected from the NASA ER-2 that was coordinated with the in-situ NASA P-3 aircraft. One of these cases (25 January 2020) provides an excellent opportunity to evaluate w in convection over the ocean. The approach here is to use a variational adjustment to improve w estimates that is based on work by Matejka and Bartels (1998) and others. This variational adjustment uses an estimate of divergence in each profile as well a fixed w=0 at the top and surface boundaries. The approach appears to improve the vertical velocity estimates and it is more physically consistent. The variationally adjusted w estimates will be discussed and compared with the in-situ measured vertical motions.