Showing papers on "Convective available potential energy published in 1980"

Broken Cumulus Bases and Modeling

Abstract: Convective cumuliform clouds are sustained by thermal upcurrents produced by solar heating of the ground. Under these conditions, the slice of atmosphere between the ground and the cumulus base is thoroughly mixed by the thermals, so that the water vapor content is the same at all levels in this slice, and the temperature lapse rate is constant, being almost the same as the dry adiabatic value. Thus, the level where condensation begins (i.e. the base of the cumulus cloud) can be predicted fairly accurately from ground-level measurements of air temperature and humidity, provided that the convective updraughts are strong and sustained. If this is so, then the cumulus base will be flat and at least as wide as the main body of the cloud. Special thermodynamic diagrams (tephigrams and others) can be used to estimate this cloud-base level by means of a quick and simple construction.

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 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 described using total time derivatives of pressure or net vertical displacement, potential temperature, and vector wind calculated by following air parcels.