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Energy Transformations in the East Asia-West Pacific Jet Stream

George P. CressmanNational Meteorological Center, National Weather Service, NOAA, Washington, DC 20233

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Abstract

Kinetic energy budgets were prepared for the East Asia-West Pacific region to obtain a quantitative description of the sources and sinks of kinetic energy for the jet stream of that region. Budgets were prepared for locations of jet stream acceleration and deceleration for the period 12–16 January 1979, during the Global Weather Experiment. The region of generation of kinetic energy in East Asia was characterized by a large-scale direct solenoidal circulation, with a five-day average generation rate of 95 × 1010 kW or 34 W m−2. Orographic forcing over the east edge of the Himalayan plateau is suggested as a process partly responsible for the geographic reliability of the generation region over China. In the west Pacific region kinetic energy was destroyed by pressure forces at a rate of 61 × 1010 kW or 57 W m−2. This region was characterized by a vigorous indirect solenoidal circulation. The kinetic energy generation and destruction took place mainly at jet stream levels and are seen as successive phases of a modified inertial oscillation of the jet. Kinetic energy conversion at these rates greatly exceeds that in a typical vigorous extratropical cyclone, which could be in the range of 10–20 × 1010 kW.

The subgrid-scale motions were a sink of kinetic energy during jet stream acceleration and a source during jet stream deceleration. This observation is confirmed on a more general basis by a literature review demonsrating a fundamental consistency among the many studies of the energeties of large-scale systems. The kinetic energy changes of the small (subgrid) scale flow paralleled those of the large-scale flow and were about 11 W m−2. The magnitude of consistent subgrid- to grid-wale energy transfer over the Pacific (and elsewhere) indicates a need for considering the apparent phenomenon of negative viscosity in numerical atmospheric modeling.

Abstract

Kinetic energy budgets were prepared for the East Asia-West Pacific region to obtain a quantitative description of the sources and sinks of kinetic energy for the jet stream of that region. Budgets were prepared for locations of jet stream acceleration and deceleration for the period 12–16 January 1979, during the Global Weather Experiment. The region of generation of kinetic energy in East Asia was characterized by a large-scale direct solenoidal circulation, with a five-day average generation rate of 95 × 1010 kW or 34 W m−2. Orographic forcing over the east edge of the Himalayan plateau is suggested as a process partly responsible for the geographic reliability of the generation region over China. In the west Pacific region kinetic energy was destroyed by pressure forces at a rate of 61 × 1010 kW or 57 W m−2. This region was characterized by a vigorous indirect solenoidal circulation. The kinetic energy generation and destruction took place mainly at jet stream levels and are seen as successive phases of a modified inertial oscillation of the jet. Kinetic energy conversion at these rates greatly exceeds that in a typical vigorous extratropical cyclone, which could be in the range of 10–20 × 1010 kW.

The subgrid-scale motions were a sink of kinetic energy during jet stream acceleration and a source during jet stream deceleration. This observation is confirmed on a more general basis by a literature review demonsrating a fundamental consistency among the many studies of the energeties of large-scale systems. The kinetic energy changes of the small (subgrid) scale flow paralleled those of the large-scale flow and were about 11 W m−2. The magnitude of consistent subgrid- to grid-wale energy transfer over the Pacific (and elsewhere) indicates a need for considering the apparent phenomenon of negative viscosity in numerical atmospheric modeling.

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