Abstract
The 28 June 1974 squall line over the ship army of the Global Atmospheric Research Programme's Atlantic Tropical Experiment (GATE) has been examined. Aircraft, radar, satellite, sounding and surface data have been employed in the analysis. This squall line is the third GATE oceanic squall line to have been subjected to intensive case study analysis. The vertical air motions and the relative amounts of convective and stratiform rain in this case were similar to those of the other two lines. However, this squall line moved more slowly, without discrete jumps, and the horizontal airflow relative to the system was quite different from that associated with the other two lines. Except at the surface, the strong front-to-rear relative flow normal to the line observed at most levels in the other cases was absent, with the relative flow tending instead to be parallel to the line. In the low to middle troposphere, relative flow parallel to the line from the north fed a post-squall mesoscale downdraft. In the middle to upper troposphere, relative flow parallel to the line from the south fed a post-squall mesoscale updraft. This upper-tropospheric relative flow from the south turned northwestward across the squall line and apparently advected enough condensate forward to produce a radar echo overhang and stratiform rain area ahead of the squall line.
