Tr. Parish et Dh. Bromwich, ON THE FORCING OF SEASONAL-CHANGES IN SURFACE PRESSURE OVER ANTARCTICA, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 102(D12), 1997, pp. 13785-13792
A 10-year record (1985-1994) of output statistics from the European Ce
ntre for Medium-Range Weather Forecasts (ECMWF) model shows that profo
und seasonal changes in surface pressure take place over the Antarctic
continent. The most pronounced changes occur during the periods strad
dling the brief Antarctic summer, fr-om September to December and agai
n from January to April. Surface pressures atop the high Antarctic pla
teau often display changes in excess of 20 hPa during these periods. T
emperatures in the lower troposphere also exhibit marked changes durin
g these transitional periods; surface temperature changes during these
3-month periods reach a maximum near 40 K over the high interior of A
ntarctica. Hydrostatic considerations suggest that the thermal adjustm
ent in the lowest levels of the atmosphere alters the vertical distrib
ution of pressure with height and hence is consistent with the dramati
c seasonal surface pressure changes over the elevated Antarctic ice sh
eets. A strong interplay exists between the thermal forcing and the ka
tabatic wind circulation over the continent. The large seasonal change
s in solar insolation reaching the Antarctic ice surface modulate the
intensity of the katabatic wind regime and thus the resulting mean mer
idional circulation between the continent and the subpolar latitudes.
It is proposed that the diabatic adjustment in the lower levels of the
atmosphere over Antarctica disrupts the mean meridional circulation c
reating a seasonal mass imbalance and hence surface pressure changes.
It is through the meridional transports that the mass and wind fields
reach a quasi-equilibrium adjusted state. The seasonal mass movement o
ver Antarctica requires large-scale mass compensation over much of the
southern hemisphere and shows that the diabatic influences at the Ant
arctic surface have far-field impacts.