Abstract
A simple automated objective analysis scheme is developed to analyze upper air sounding data from the National Severe Storm Laboratory mesonetwork. This scheme uses a combination of Cressman' successive correction technique and cubic spline curve fitting.
This scheme is applied to a squall line case that occurred on 8 June 1966 along the confluent line where and air from the desert southwest was brought into juxtaposition with moist air from the Gulf of Mexico. The first radar echoes were detected at about 1600 CST and a nearly continuous band was formed by 1830. At 2000 the intense squall line became disorganized and it dissipated by 2300. Serial sounding were started at 1400 and continued until 2300.
The analysis results indicate that a well–defined narrow band of convergence (and consequently upward motion) with a width of about 100 km was present at low levels prior to the appearance of first radar echoes. The location and orientation of the line of maximum upward motion and of the subsequent squall line formation agree well. This low–level upward motion continued to increase in intensity until 1830 with its peak value at 800 mb. A well–defined mixed layer also developed in low levels because of the strong solar heating at the earth's surface. The height of the mixed layer increased and became very close to the lifting condensation level of near–surface air by early afternoon. The low–level convergence then provided the final push needed to release the potential instability.
Shortly after 1700, the development of a second maximum in the vertical velocity was observed in the 450–400 mb layers. This second maximum reached its peak value of about 1.7 m s−7 at 2000 and apparently was a manifestation of the development of deep penetrative Invective clouds. The mesoscale heat and moisture budgets are also investigated by calculating the apparent beat source and moisture sink for the mature stage of the squall line. The horizontal distribution of accumulated rainfall estimated from the apparent moisture sink agrees fairly well with that observed. The decay of the squall line occurred when the low–level horizontal moisture convergence became disorganized.
