A Kinetic Energy Budget over North America During a Period of Short Synoptic wave Development

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  • 1 Department of Geosciences, Purdue University, West Lafayette, Ind. 47907
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Abstract

A kinetic energy budget over North America is computed using standard rawinsonde data during 11–24 April 1970, a period of repeated short synoptic wave development. A comparative analysis with energy transformation documented for periods of intermediate synoptic wave influence is presented. In both the abort and intermediate wave periods, horizontal flux convergence is an important energy source. However, the two periods differ in both their kinetic energy generation and dissipation. In contrast to the intermediate wave case, the short wave period is dominated by negative generation of kinetic energy. In addition, the vertically-integrated dissipation, determined as the residual term in the kinetic energy budget, is substantially smaller for the short wave case. This latter result, which occurs primarily because the residual quantity is positive in the upper troposphere, is hypothesized to be associated with subgrid-to-grid-scale kinetic energy exchange.

Of particular interest is a secondary wave which developed on a preexisting wave system on 16 April. The subgrid-scale source of kinetic energy was important in the maintenance of this secondary wave. A substantial amount of subgrid-to-grid-scale energy exchange occurred west of the secondary wave and was transported into the wave system by horizontal flux convergence of kinetic energy. This pattern persisted as this secondary wave propagated across the United States.

Abstract

A kinetic energy budget over North America is computed using standard rawinsonde data during 11–24 April 1970, a period of repeated short synoptic wave development. A comparative analysis with energy transformation documented for periods of intermediate synoptic wave influence is presented. In both the abort and intermediate wave periods, horizontal flux convergence is an important energy source. However, the two periods differ in both their kinetic energy generation and dissipation. In contrast to the intermediate wave case, the short wave period is dominated by negative generation of kinetic energy. In addition, the vertically-integrated dissipation, determined as the residual term in the kinetic energy budget, is substantially smaller for the short wave case. This latter result, which occurs primarily because the residual quantity is positive in the upper troposphere, is hypothesized to be associated with subgrid-to-grid-scale kinetic energy exchange.

Of particular interest is a secondary wave which developed on a preexisting wave system on 16 April. The subgrid-scale source of kinetic energy was important in the maintenance of this secondary wave. A substantial amount of subgrid-to-grid-scale energy exchange occurred west of the secondary wave and was transported into the wave system by horizontal flux convergence of kinetic energy. This pattern persisted as this secondary wave propagated across the United States.

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