Variational Analysis of Temperature and Moisture Advection in a Severe Storm Environment

[摘要] Horizontal wind components, potential temperature, and mixing ratio fields associatedwith a severe storm environment in the south central U.S, were objectively analyzed from synoptic upper air observations with a non-homogeneous, anisotropic weighting function. The grid dimensions of the area of study were near 125 kilometers horizontally and 50 millibars vertically at 18 pressure levels. Each data field was filtered and the vertical motion field was then analyzed using variational methods to insure that the three-component wind field satisfied mass continuity. The local time change of potential temperature and mixing ratio was determined in order to correlate the temperature and moisture advection patterns with severe storm development. A three-dimensional advection equation was used to produce advective forecasts of the potential temperature and mixing ratio fields. The case study discussed in this article is 26 May 1973, when a tornado producing squall line moved through eastern Oklahoma. The synoptic situation which preceded squall line development was cyclogenesis and frontogenesis in the lee-of-the-mountain trough, which produced a well-defined surface dry line (or dew point front) and a pronounced mid-level dry air intrusion.Results indicated that the mid-level dry air intrusion was also characterized by warm air, with a lapse rate approaching the dry adiabatic. The advection of this warm air produced a well-defined upward motion pattern. A corresponding downward motion pattern apparently comprising a deep vertical circulation in the warm air sector of the low pressure system was detected. The squall line that subsequently developed was aligned closely with the axes of the maximum dry and warm advection above the 850mb surface. Below the 850mb surface, the squall line coincided with the axis of maximum moisture advection.

[学科分类] 大气科学