Radar based remote sensing of cloud liquid water – application of various techniques – a case study

Abstract

During the BALTEX BRIDGE Campaign (BBC) of CLIWA-NET, conducted at Cabauw, The Netherlands, from 1 August through 31 September 2001, cloud radar parameters like reflectivity, linear depolarization ratio and Doppler velocities have been observed using a 95 GHz cloud radar. These observations along with other remotely sensed parameters from the ground, have been used to derive the liquid water content of clouds which is one of the most important parameters to be known when the radiative transfer of clouds needs to be calculated. Simultaneously a multi-channel passive microwave radiometer and a lidar ceilometer have been operated close to the radar. While drizzle could be ruled out to have a significant impact on the return signal, corrections due to atmospheric absorption (gaseous) and attenuation due to clouds (mainly loss of signal due to absorption) had to be applied to the radar data. The corrections will be discussed in detail and have been applied to the radar reflectivity profiles before estimating cloud liquid water profiles. After the liquid water content profile has been calculated (for a fixed integrated liquid water path) the maximum in liquid water content of the cloud increased by about 14% and shifted upward within the cloud. The applied corrections bring the liquid water profile closer to adiabatic in the middle and upper part of the cloud. Examples of time series of corrected vertical profiles and average profiles are shown and are discussed. The ground based remotely sensed liquid water profiles show, on average, excellent agreement with simultaneously in situ measured liquid water content from aircraft measurements.