Evidence of deep convection as a source of synoptic-scale kinetic energy

In a previous paper, Kornegay and Vincent (1976) calculated the kinetic energy budget during 12 hours in the life of a tropical depression over the United States. The dissipation term, calculated as a residual in the kinetic energy budget equation, was positive in areas of convective precipitation, prompting the authors to speculate that a subgrid-scale process, namely, deep cumulus convection, could supply kinetic energy to the synoptic-scale flow. That possibility is further examined here. The earlier case study is extended from 12 to 36 hours and additional evidence is presented, including a comparison with some theoretical results.

The case study involved a tropical depression, the remains of tropical storm Candy, and its interaction with a developing extratropical cyclone between 1200 GMT, June 24 and 0000 GMT, June 26, 1968. The kinetic energy budget is based upon multivariate statistical analyses of radiosonde observations. Areas of kinetic energy increase and positive dissipation (dissipation acting as an energy source) are roughly the same; they are marked by deep convection as evidenced by radar reports and precipitation amounts. The kinetic energy increase and positive dissipation are initially greatest in the 700–500 mb layer as the tropical depression and mid-latitude cyclone begin to interact. Twelve hours later, however, the largest increase in kinetic energy and greatest positive dissipation occur higher in the troposphere, from 500 to 300 mb.