MMM SEMINAR NCAR
A
Case Study of Squall Line Based on the PWV Data from the
Ground-Based
GPS Network in the Yangtze River Delta Area
Shanghai Meteorological Bureau
Shanghai, China
A squall Line swept eastward across the Yangtze River Delta area and produced gusty winds and heavy rain from the afternoon to the evening hours on August 24, 2002. This presentation focuses on the analysis of the temporal and spatial variations of moisture during the genesis and development of the squall line, based on the precipitable water vapor (PWV) data from the ground-based GPS network in the Yangtze River Delta in China and the forecasts of the MM5 model. During the 12 h period prior to the arrival of the squall line, the PWV at a ground-based GPS station increases continuously in two different stages, and provide ample moisture to support the squall line development. In the first stage the moisture increases mainly in the middle levels due to the unstable stratification with moist air in low levels and dry air in middle levels. In the second stage the moisture increases substantially, because the low level moist layer expands upwards. We find that the temporal variation of PWV at a GPS station is a better indicator for the development and movement of the squall line than other surface meteorological elements such as temperature and humidity. The squall line always forms and moves in the area with high PWV. But the dry trough in the PWV distribution sometimes indicates the unstable stratification there and it can play an important role in the development of the squall line. The isoline of 2 mm of PWV positive variation in 3 hours provides a good indication of the location of the squall line approximately 2 hours later.
Key words: Squall
line, GPS, Precipitable water vapor (PWV).
Tuesday, 1 February 2005,
10:30 AM
Refreshments 10:15 PM
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