Climatological Lower Tropospheric Frontogenesis in the Midlatitudes Due to Horizontal Deformation and Divergence

Abstract

The frontogenetic function given by Petterssen is calculated for the four months, January, April, July and October and the year as a whole using the climatological wind and temperature data for 85 and 70 kPa levels over the global band between ?45°N and ?45°S. The well?known frontogenetic regions of the Northern Hemisphere (NH) off the Rockies and Japan Sea are reproduced satisfactorily. Four NW-SE inclined bands of frontogenesis are observed in the Southern Hemisphere (SH). The mid-South Pacific and the western South Atlantic bands correspond, respectively, to the South Pacific convergence zone (SPCZ) and the South Atlantic convergence zone (SACZ) which are observed in the outgoing longwave radiation (OLR) charts. The other two are located in the western Indian Ocean and west Australia. The frontogenetic function in the SACZ region is strongest in southern summer in contrast to the NH case, which is dominant in winter.