MMM SEMINAR NCAR
The
Effects of Trends and Variability in the Antarctic Circulation on the
Atmospheric Boundary Layer over the South Pole
W.D. Neff
NOAA/ETL
The Antarctic has recently received attention because of apparent regional enhancements of what may be a global warming signal along the Antarctic Peninsula (in contrast to cooling of the surface over the interior of the continent) and because of model predictions of an intensifying polar vortex in response to global warming combined with springtime ozone depletion. In addition, recent results from a series of atmospheric chemistry experiments at the South Pole revealed high surface concentrations of NO in December (Davis et al, Atmos. Env. Submitted) that appear to be modulated by the state of the Antarctic Oscillation (AAO; also know as the Southern Annular Mode, SAM) which provides a measure of the strength of the circumpolar vortex. Confounding the interpretation of these changes has been the paucity of observations in the Southern Hemisphere and known biases in the NCEP-NCAR Reanalysis (NNR) surface pressures and geopotential heights in the pre-satellite era, particularly south of 60oS. In this talk I will briefly review results from Neff (J. Geophys. Res., 1999) that revealed the strong control of the boundary layer properties at the South Pole by large scale dynamics and identified responses in tropospheric dynamics to spring time ozone depletion. I then describe a procedure to “correct” the Antarctic Oscillation Index derived from the first EOF of 700-hPa heights in the NNR using the difference between NNR heights and observations. This is then followed by an analysis of trends in the circulation from 1957 to the present and a comparison with other results in the literature, including 1) those of Thompson and Solomon (Science, 2002) who examined the period from 1969 to 1998 using sounding data obtained primarily along the coast of East Antarctica that faces the Indian Ocean, and 2) of Jones and Widmann (J. Clim, 2003) who used station analyses and paleoclimate proxies from mid-latitudes to extend the AAO index to pre-instrumental eras. I will then close with a description of ongoing collaborative efforts associated with the Antarctic Tropospheric Chemistry Investigation (ANTCI: http://acd.ucar.edu/~mauldin/ANTCI_Web/ANTCI_Home.htm) that will examine synoptic to mesoscale influences on the mixing layer at the South Pole in the context of trends and variability in the Antarctic circulation.
Tuesday, June 1 at 9:00 a.m.
Refreshments 8:45 PM
3450 Mitchell
Lane, Bldg 2 (Rm 1022)