On the forcing of seasonal changes in surface pressure over Antarctica
Abstract. A 10-year record (1985-1994) of output statistics from the European Centre for Medium-Range Weather Forecasts (ECMWF) model shows that profound seasonal changes in surface pressure take place over the Antarctic continent. The most pronounced changes occur during the periods straddling the...
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| Format: | Text |
| Language: | English |
| Published: |
1997
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.670.3319 http://polarmet.osu.edu/PMG_publications/parish_bromwich_jgr_1997.pdf |
| Summary: | Abstract. A 10-year record (1985-1994) of output statistics from the European Centre for Medium-Range Weather Forecasts (ECMWF) model shows that profound seasonal changes in surface pressure take place over the Antarctic continent. The most pronounced changes occur during the periods straddling the brief Antarctic summer, from September to December and again from January to April. Surface pressures atop the high Antarctic plateau often display changes in excess of 20 hPa during these periods. Temperatures in the lower troposphere also exhibit marked changes during these transitional periods; surface temperature changes during these 3-month periods reach a maximum near 40 K over the high interior of Antarctica. Hydrostatic considerations uggest hat the thermal adjustment in the lowest levels of the atmosphere alters the vertical distribution of pressure with height and hence is consistent with the dramatic seasonal surface pressure changes over the elevated Antarctic ice sheets. A strong interplay exists between the thermal forcing and the katabatic wind circulation over the continent. The large seasonal changes in solar insolation reaching the Antarctic ice surface modulate the intensity of the katabatic wind regime and thus the resulting mean meridional 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 creating 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 over Antarctica requires large-scale mass compensation over much of the southern hemisphere and shows that the diabatic influences at the Antarctic surface have far-field impacts. 1. |
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