Mind-the-gap part I: Accurately locating warm marine boundary layer clouds and precipitation using spaceborne radars

Abstract. Ground-based radar observations show that, in the eastern north Atlantic, 50 % of warm marine boundary layer (WMBL) hydrometeors occur below 1.2 km and have reflectivities Surface clutter limits the CloudSat-Cloud Precipitation Radar (CPR)’s ability to observe true cloud base in ~ 52 % of the cloudy columns it detects and true virga base in ~ 80 %, meaning the CloudSat-CPR often provides an incomplete view of even the clouds it does detect. Using forward-simulations, we determine that a 250-m resolution radar would most accurately capture the boundaries of WMBL clouds and precipitation; That being said, because of sensitivity limitations, such a radar would suffer from cloud cover biases similar to those of the CloudSat-CPR. Overpass observations and forward-simulations indicate that the CloudSat-CPR fails to detect 29–41 % of the cloudy columns detected by the ground-based sensors. Out of all configurations tested, the 7 dB more sensitive EarthCARE-CPR performs best (only missing 9.0 % of cloudy columns) indicating that improving radar sensitivity is more important than shortening surface clutter for observing cloud cover. However, because 50 % of WMBL systems are thinner than 400 m, they tend to be artificially stretched by long sensitive radar pulses; hence the EarthCARE-CPR overestimation of cloud top height and hydrometeor fraction. Thus, it is recommended that the next generation of space-borne radars targeting WMBL science shall operate interlaced pulse modes including both a highly sensitive long-pulse and a less sensitive but clutter limiting short-pulse mode.