Reconciling cloud and drizzle liquid water path information from active and passive sensors: A case study

 

Authors

Maria Paola Cadeddu — Argonne National Laboratory
Virendra Prakash Ghate — Argonne National Laboratory

Category

General topics – Clouds

Description

The partition of cloud and drizzle liquid water in precipitating clouds has important repercussion on the studies of the cloud life cycle and onset of precipitation. Liquid water path (LWP) retrievals in drizzling clouds from microwave radiometers that use frequencies at 90 GHz have sensitivity to scattering by drizzle drops larger than 100 microns. Recent theoretical studies have shown that this sensitivity allows in principle to separate cloud and drizzle LWP above and below the cloud base. This is possible by including the drizzle microphysical properties derived from active sensors in an optimal estimation microwave retrieval model. It remains to be determined, however, to what extent the microwave retrievals are able to separate cloud and drizzle LWP in real case scenarios where a priori assumptions and environmental factors may affect the effectiveness of the retrievals. To this end, Doppler spectra from the cloud radar provide valuable independent information on the coexistence of cloud and drizzle drops in the cloud that can be used to better understand the passive remote sensing retrievals. In this work, the temporal evolution of cloud and drizzle LWP retrieved in and below the cloud from microwave radiometer, cloud radar and ceilometer is examined in conjunction with the Doppler spectra from a cloud radar. Data are collected during a precipitation event at the ARM Program ENA site. Because the below-cloud microwave retrievals are well constrained by the radar-ceilometer data, the Doppler spectra analysis will help to understand how much information the microwave retrievals can provide on the partitioning between cloud and drizzle LWP above the cloud base. We will assess whether the retrievals of cloud and drizzle LWP from the passive sensors are broadly consistent with the partition between drizzle and cloud droplets in the cloud gathered from the radar Doppler spectra. This can potentially open the possibility of including the information provided by radar Doppler spectra in the passive microwave retrieval algorithm for improved quantification of in-cloud drizzle and cloud liquid water path.