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

Information on the heights and microphysical structures of two cloud system s derived from a 35 GHz radar, microwave and infrared radiometers, and a li dar aboard a ship in the Arctic Ocean are compared with simultaneous airbor ne in situ measurements. The cloud systems considered are a single layer of thin altocumulus with virga (June 3, 1998), and a more complex cloud syste m consisting of several altocumulus -altostratus layers that precipitated i nto 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 crystal s; this prevented measurement of the cloud base height with the radar. Beca use of the sensitivity of the 35 GHz radar to ice crystals, cloud liquid wa ter 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 wat er layers into which ice particles fell were not resolved by the radar. Con sequently, although five altocumulus layers were intercepted by the aircraf t, the radar display depicts a single deep precipitating system. These case s illustrate that liquid water content in mixed-phase clouds cannot be retr ieved reliably using the radar-microwave radiometer technique.