Climatological lower tropospheric frontogenesis in the midlatitudes due to horizontal deformation and divergence

The frontogenetic function given by Petterssen is calculated for Jan., April, July, and Oct. and the year as a whole by using the climatological wind and temperature data for 85- and 70-kPa levels over the global band between similar to 45 degrees N and similar to 45 degrees S. The well-known frontogenetic regions of the Northern Hemisphere (NH) off the Rockies and the Japan Sea are reproduced satisfactorily. Four NW-SE-inclined bands of frontogenesis are observed in the Southern Hemisphere (SH). The middle 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 long-wave radiation (OLR) charts. The other two are located in the western Indian Ocean and western Australia. The frontogenetic function in the SACZ region is strongest in southern summer in contrast to the NH case, which is dominant in winter.