On the annual and semi‐annual cycles of precipitation across Antarctica

Abstract

AbstractIn this study, we examine the importance of the annual and semi‐annual cycles of precipitation (H1(P) and H2(P), respectively) across Antarctica utilizing the ERA‐40 re‐analysis from 1980 to 2001. A qualitative comparison between monthly precipitation from ERA‐40 and precipitation reports from Antarctic bases reveals that the re‐analysis successfully captures the seasonal cycle of precipitation at coastal sites. However, likely excessive summer precipitation on the high Antarctic Plateau in ERA‐40 means the re‐analysis is uncertain in the continental interior.The spatial variability in the amplitude of both H1(P) and H2(P) reveals coastal maxima with a clear wavenumber 3 pattern: unsurprisingly, maximum values are located east of climatological low‐pressure centres, where moisture advection into the continent is greatest. This pattern is particularly pronounced for H1(P), for which the amplitude exceeds 25 mm water equivalent (WE) in coastal west Antarctica. In the Antarctic coastal region H1(P) often explains greater than 50%—and sometimes more than 80%—of the total variance of the seasonal precipitation cycle. In contrast, the northwest Antarctic Peninsula has a higher amplitude in H2(P) that is linked to its location within the circumpolar trough (CPT).A marked change in the magnitude of H1(P) between the 1980s and 1990s in parts of coastal west Antarctica and the west coast of the Antarctic Peninsula was observed in the ERA‐40 data and confirmed by similar changes in the seasonal cycle of precipitation reports. The principal modification to H1(P) results from a decrease in winter precipitation that can be linked to a weaker and smaller winter Amundsen Sea Low, which in turn is known to be influenced by El Niño‐Southern Oscillation (ENSO). A simple estimate indicates that the observed change in the seasonal cycle of precipitation would lead to an apparent warming of ∼0.6 °C in a proxy of mean annual temperature derived from oxygen isotope measurements. Copyright © 2009 Royal Meteorological Society