Thunderstorm Influence on Boundary Layer Winds.
Abstract
The objective of this thesis was to develop a conceptual model of selected pre-storm ambient conditions as a function of the strength of a thunderstorm's outflow. The time of maximum rainfall in relation to the time of maximum outflow was a thunderstorm characteristic which helped explain the downdraft mechanism and was included in the model. The results indicated that two conceptual models were necessary to describe the pre-storm ambient conditions that led to thunderstorm development and outflow. One model contained the weaker outflows and the other described the stronger outflows. Six significant ambient conditions contributed to the thunderstorm building process, i.e., 1) horizontal moisture convergence below cloud base, 2) vertical flux divergence of latent heat energy below could base, 3) vertical wind shear in the 850 mb to 300 mb layer, 4) an environmental lapse rate approaching dry adiabatic at least in the lower subcloud layer, 5) potential instability below cloud base and, 6) potential evaporative cooling below cloud base. The model for the weaker outflows had relatively small magnitudes of ambient conditions, while the model for the stronger outflows had relatively large magnitudes of ambient conditions. The weaker outflows were associated with maximum rainfall that occurred 1 h after maximum outflow. Frictional drag of the falling raindrops was the dominant mechanism over evaporative cooling in maintaining the downdraft. The stronger outflows were associated with maximum rainfall that occurred 1 h prior to or during maximum outflow. Evaporative cooling was the dominant mechanism over frictional drag in maintaining the downdraft.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1986
- Accession Number
- ADA176543
Entities
People
- Jill M. Schmidt
Organizations
- Air Force Institute of Technology