A multi-frequency spaceborne radar perspective of deep convection

TL;DR

This paper compares deep convection observations across Ku-, Ka-, and W-band spaceborne radars, showing that Ka-band can effectively substitute Ku-band for characterizing convection, especially when Ku-band data is unavailable.

Contribution

It provides a comprehensive analysis of multi-frequency radar data, demonstrating the potential of Ka-band to replace Ku-band in future convection monitoring missions.

Findings

W-band reflectivity peaks near Ku-band echo-top.

Ka-band echo-tops are often 4-5 km below Ku-band.

Ka-band echo-tops correlate with Ku-band with R^2 of 0.62.

Abstract

Global numerical weather models are starting to resolve atmospheric moist convection which comes with a critical need for observational constraints. One avenue for such constraints is spaceborne radar which tend to operate at three wavelengths, Ku-, Ka- and W-band. Many studies of deep convection in the past have primarily leveraged Ku-band because it is less affected by attenuation and multiple scattering. However, future spaceborne radar missions might not contain a Ku-band radar and thus considering the view of convection from Ka-band or W-band compared to the Ku-band would be useful. This study examines a coincident dataset between the Global Precipitation Measurement (GPM) Mission and CloudSat as well as the entire GPM record to compare convective characteristics across various wavelengths within deep convection. We find that W-band reflectivity (Z) tends to maximize near the Ku-band defined echo-top while Ka-band often maximizes 4-5 km below. The height of the maximum Z above the melting level for W-band does not linearly relate to the Ku-band maximum. However, using the full GPM record the Ka-band 30 dBZ echo-tops can be linearly related to the Ku-band 40 dBZ echo-top with an $R^2$ of 0.62 and a root mean squared error of about 1 km. The spatial distribution of echo-tops from Ka-band corresponds well to the Ku-band echo-tops, highlighting regions of relatively large ice water path. This paper suggests that Ka-band only missions, like NASA's Investigation for Convective Updrafts, should be able to characterize global convection in a similar manner to a Ku-band system.