Wind Profiler Observations of Vertical Motion and Precipitation Microphysics of a Tropical Squall Line

Abstract

Data from a wind profiler located at Darwin, Australia, have been used to examine the vertical motions and precipitation microphysics in a well-developed squall line. Both a mature and developing convective cell are well sampled. The vertical motions within the mature cell are dominated by the effect of glaciation and a convective downdraft feeding a cold pool. The strong updrafts are accompanied by supercooled water as much as 2 km above the freezing level. The two cells are separated by a narrow region of deep descent. The developing cell has a low-level maximum in upward motion coinciding with high radar reflectivity below 3 km, suggesting warm rain processes. There is a large transition region with deep descent and a stratiform region with a classic up- and downdraft circulation. The precipitation characteristics show the aggregation of ice particles as they descend in the stratiform region. Over half of the rain is seen to evaporate between 4 and 2 km. The cooling implied by this and the heating by the growth of ice particulates above the melting level balance the mesoscale circulation in the stratiform region. The Q1, heating profile is consistent with previous studies above 4 km but shows a net cooling below this. This may in part be due to the storm being sampled when the system was mature with extensive convective downdrafts.