posted on 2020-06-05, 09:39authored byKatia Lamer, Pavlos Kollias, Alessandro Battaglia, Simon Preval
Ground-based radar observations show that, over the eastern North Atlantic,
50 % of warm marine boundary layer (WMBL) hydrometeors occur below 1.2 km
and have reflectivities of < −17 dBZ, thus making their detection from
space susceptible to the extent of surface clutter and radar sensitivity. Surface clutter limits the ability of the CloudSat cloud profiling radar (CPR) to
observe the 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. Observations and forward simulations indicate that the CloudSat CPR
fails to detect 29 %–43 % of the cloudy columns detected by 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
decreasing the vertical extent of surface clutter for measuring 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 should operate interlaced pulse modes including both a
highly sensitive long-pulse mode and a less sensitive but clutter-limiting
short-pulse mode.
Funding
This research has been supported by the U.S.Department of Energy Biological and Environmental Research pro-gram (grant nos. DE-SC0016344 and DE-SC0017967)
All CloudSat CPR observations were obtained from the CloudSat data processing center (http://www.cloudsat.cira.colostate.edu/, last access: 12 June 2019, CloudSat, 2019). All ARM observations were obtained from the ARM archive (https://www.archive.arm.gov/discovery/, last access: 12 June 2019, ARM Data Discovery, 2019). Output of all forward simulations is fully reproducible from the information given.