Abstract
Updated analyses of in situ microphysical properties of three Arctic cloud systems sampled by aircraft in July 1998 during the Surface Heat Budget of the Arctic Ocean (SHEBA)/First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment–Arctic Clouds Experiment (FIRE–ACE) are examined in detail and compared with surface-based millimeter Doppler radar. A fourth case is given a cursory examination. The clouds were at 78°N over a melting ice surface, in distinctly different yet typical synoptic conditions. The cases comprise a midlevel all-ice cloud on 8 July; a deep, weakly forced, layered, mixed-phase stratus cloud system with pockets of drizzle, large dendrites, rimed ice and aggregates on 18 July; and a deep, mixed-phase cloud system with embedded convection on 28 July followed by an all-water boundary layer cloud on 29 July. The new observations include measured ice water content exceeding 2 g m−3 on 18 and 28 July and 3-cm snowflakes and 5-mm graupel particles on 28 July, unexpected in clouds close to the North Pole. Radar–aircraft agreement in reflectivity and derived microphysical parameters was reasonably good for the all-water and all-ice cases. In contrast, agreement in radar–aircraft reflectivity and derived parameters was generally inconsistent and sometimes poor for the two mixed-phase cases. The inconsistent agreement in radar–aircraft retrievals may be a result of large uncertainties in both instrument platforms and the algorithms used to retrieve derived parameters. The data also suggest that (single-wavelength) radar alone may not be capable of accurately retrieving the microphysical effects of cloud drops and drizzle in mixed-phase clouds, especially radiative properties such as extinction, albedo, and optical depth. However, more research is required before this generalization can be considered conclusive.
Corresponding author address: R. Paul Lawson, 3022 Sterling Circle, Suite 200, Boulder, CO 80301. Email: plawson@specinc.com
