Airborne studies of cloud structures over the Arctic Ocean and comparisons with retrievals from ship-based remote sensing measurements

Information on the heights and microphysical structures of two cloud systems derived from a 35 GHz radar, microwave and infrared radiometers, and a lidar aboard a ship in the Arctic Ocean are compared with simultaneous airborne in situ measurements. The cloud systems considered are a single layer of thin altocumulus with virga (June 3, 1998), and a more complex cloud system consisting of several altocumulus-altostratus layers that precipitated into a boundary layer, stratus-stratocumulus system (May 29, 1998). For the first cloud system the cloud top deduced from the 35 GHz radar was close to that measured from the aircraft. The radar detected virga below cloud base even when the virga was composed of very low concentrations of ice crystals; this prevented measurement of the cloud base height with the radar. Because of the sensitivity of the 35 GHz radar to ice crystals, cloud liquid water contents derived from it are confounded by just a few ice crystals. In the case of the second more complex cloud system, embedded cloud liquid water layers into which ice particles fell were not resolved by the radar. Consequently, although five altocumulus layers were intercepted by the aircraft, the radar display depicts a single deep precipitating system. These cases illustrate that liquid water content in mixed-phase clouds cannot be retrieved reliably using the radar-microwave radiometer technique.