| The Amundsen Sea Low (ASL) is a climatological low pressure system located between
170-300 ∘ E and 60-75∘S and is a key component of the non-zonal climatological circulation
at high southern latitudes. With reanalysis output identifying that climatologically the low in
the Amundsen Sea is the deepest of three mean sea level pressure (MSLP) centres
observed around Antarctica. The ASL strongly modulates West Antarctic climate
with impacts on sea ice extent, temperature and precipitation, via its controlling
influence on the variability of the meridional wind field. It has also been shown to
have a significant influence on the atmospheric circulation in the Ross Sea region
and to strongly modulate temperature and moisture advection over the Antarctic
Peninsula.
Previous work has demonstrated strong relationships between the depth of the
ASL and cyclone densities in the region. However, interestingly a recent review
identified that it is not easy to relate the storm density and depths of the cyclones to the
climatological ASL, since the climatological location of the ASL does not occur at a clear
maximum of storm activity. This study examines output from the ERA-interim
reanalyses around Antarctica to further understand the contributors to the climatological
pattern, partially in an effort to identify whether a more physically meaningful ASL
depth index (normally simply defined as the monthly minimum MSLP) can be
created. In this effort, storm track data derived from the ERA-Interim reanalysis
and mean sea level pressure data bandpass filtered to accentuate synoptic scale
variability are first examined. The contribution of persistent positive anomalies in the
mean sea level pressure (defined as 8hPa positive anomalies from the climatological
mean for a period of 5 days) in the region surrounding the Amundsen sea is also
examined to identify whether blocking plays a role. Finally, the frequency of persistent
negative anomalies (defined as a negative 8hPa occurring for 5 days or longer) is also
examined around Antarctica and in the vicinity of the Amundsen Sea. We show
that these persistent positive and negative anomalies likely contribute to the ASL
depth. |