A Climatology of the Precipitation over the Southern Ocean based on the Surface and Satellite Observations

Macquarie Island (MAC) (54.50 °S, 158.94 °E) is an isolated island with modest orography in the midst of the Southern Ocean with precipitation records dating back to 1948. These records are of particular interest due to the relatively large biases in the energy and water budgets commonly found in climate simulations and reanalysis products over the region. A basic climatology of the surface precipitation is presented and compared against the ERA-Interim (ERA-I) reanalysis. The annual ERA-I precipitation (953 mm) is found to underestimate the annual MAC precipitation (1023 mm) by 6.8 % from 1979 to 2011. The frequency of the 3-h surface precipitation (MAC) is 36.4 % from 2003 to 2011. Light precipitation (0.066 ≤ P < 0.5 mm hr-1) dominates this precipitation (29.7 %), while the heavy precipitation (P ≥ 1.5 mm hr-1) is rare (1.1 %). Drizzle (0 < P < 0.066 mm hr-1) is commonly produced by ERA-I (43.9 %), but is weaker than the detectable threshold of MAC. Warm rain intensity and frequency from CloudSat products were compared with those from MAC. These CloudSat products also recorded considerable drizzle (16-30 %), but were not significantly different than MAC when P ≥ 0.5 mm hr-1. Heavy precipitation events were, in general, more commonly associated with fronts and cyclonic lows. Some heavy precipitation events were found to arise from weaker fronts and lows that were not adequately represented in the reanalysis products. Yet other heavy precipitation events were observed at points/times not associated with either fronts or cyclonic lows. Two case studies are employed to further examine this.