Thunderstorm-environment interactions determined with three-dimensional trajectories

Abstract

Diagnostically determined three-dimensional trajectories were used to reveal some of the scale interaction processes that occur between convective storms and their environment. Data from NASA's fourth Atmospheric Variability Experiment (AVE IV), conducted on 24-25 April 1975, are analyzed. Two intense squall lines and numerous reports of severe weather occurred during the period. Convective storm systems with good temporal and spatial continuity are shown to be related to the development and movement of short-wave circulation systems aloft that propagate eastward within a zonal mid-tropospheric wind pattern. These short-wave systems are found to produce the potential instability and dynamic triggering needed for thunderstorm formation. The environmental flow patterns, relative to convective storm systems, are shown to produce large upward air parcel movements in excess of 50 mb/3h in the immediate vicinity of the storms. The air undergoing strong lifting originates as potentially unstable low-level air traveling into the storm environment from southern and southwestern directions. The thermo- and hydrodynamical processes that lead to changes in atmospheric structure before, during, and after convective storm formation are successfully described using total time derivatives of pressure (dp/dt) or net vertical displacement (NVD), potential temperature (0), and vector wind -> (dV/dt) calculated by following air parcels. The high degree of scale interaction between synoptic- and convective-scale systems is demonstrated statistically, using multiple linear regression, by combining NVD's and static stability measurements to successfully locate convective activity of various intensities over the AVE IV network. After storm formation, interactions between severe convective systems and the environment alter the synoptic-scale flow field in the mid-troposphere in such a manner that the storm "selfpropagates" itself by increasing the large-scale vertical motion field...