An Assessment of CloudSat Southern Ocean Precipitation Retrievals Using Ground-based Instruments at Macquarie Island

Abstract:

CloudSat W-band spaceborne radar retrievals of precipitation characteristics are widely used, particularly for their sensitivity to light precipitation. These data are especially important over remote regions such as the Southern Ocean (SO) where there are few other measurements. In this presentation, the seasonal and synoptic variability of SO precipitation are studied by blending Parsivel disdrometer and W-band radar measurements collected at Macquarie Island during the Macquarie Island Cloud and Radiation Experiment. Our retrievals include precipitation thermodynamic phase, hydrometeor size distributions and rain rates, enabling a more detailed examination of SO precipitation characteristics than has been previously possible. In particular, we find that small-particle (drizzle) precipitation occurs 30 to 50% of the time at Macquarie Island, depending on the season. Glaciated precipitation is observed most often during fall and winter, and to the southeast of SO cyclonic systems. Comparisons of the Macquarie Island observations to precipitation estimates from the CloudSat Cloud Profiling Radar show good agreement in the distribution of rain rates for rates >0.5 mm/hour, which comprise the bulk of the total accumulated precipitation. However, even CloudSat misses much of the light precipitation, comprised of small particles (<0.5 mm). Light precipitation includes essentially all precipitation events with rain rates <0.1 mm/hr, and about half of events with rain rates between 0.1 and 0.5 mm/hr. There is a small but noteworthy diurnal cycle of precipitation at Macquarie Island. CloudSat overpasses of Macquarie Island occur at about 1:30 AM and 2:20 AM, and the analysis includes an examination of diurnal variations.