A Life History of an Intense Mesoscale Convective Storm in Oklahoma

• Published in: Journal of the atmospheric sciences 1977-09, Vol.34 (9), p.1458-1476
• Main Authors: Ogura, Yoshmitsu, Chen, Yi-Leng
• Format: Article
• Language: English
• ISSN: 0022-4928; 1520-0469
• DOI: 10.1175/1520-0469(1977)034<1458:ALHOAI>2.0.CO;2

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's successive correction technique and cubic spline curve fitting. The scheme is applied to a squall line case that occurred on June 8, 1966, along the confluent line on which arid air from the desert southwest was brought into juxtaposition with moist air from the Gulf of Mexico. The first radar echoes were detected at 1600 hr CST, and a nearly continuous band was formed by 1830 hr. At 2000 hr, the intense squall line became disorganized; it dissipated by 2300 hr. Serial soundings began at 1400 hr and continued until 2300 hr. The analysis results indicate that a well defined, narrow band of convergence (and, consequently, upward motion) with a width of 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 hr, with its peak value at 800 mb. A well-defined mixed layer developed in low levels because of the strong solar heating at the Earth's surface. The height of the mixed layer increased and became close to the lifting condensation level of near-surface air by early afternoon. The low-level convergence provided the final push needed to release the potential instability. Shortly after 1700 hr, the development of a second maximum in the vertical velocity was observed in the 450-400-mb layer. This second maximum reached its peak value of approximately 1.7 m sec super(-) super(1) at 2000 hr, and was a manifestation of the development of deep penetrative convective clouds. The mesoscale heat and moisture budgets are investigated by calculating the apparent heat 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.