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Atmospheric Energy Transport Over North America For Three Winter Months

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  • 1 Department of Meteorology, Florida State University, Tallahassee, Fla.
  • | 2 Department of Meteorology, University of Wisconsin, Madison, Wis.
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Abstract

The excellent North American radiosonde network is used to calculate the poleward energy transport for the continental area during the period January–March 1966. The transport of sensible and latent heat and geopotential and kinetic energy is partitioned according to four circulation modes—mean and transient meridional circulations and stationary and transient eddy circulations. In addition, the roles of various synoptic features in the transient eddy flux are examined.

The mean meridional transport was computed in two ways. One involved a calculation of the contribution of the North American sector to the hemispheric mean meridional transport. Because of strong meridional flow at high levels and a lack of compensating flow at low levels, very large transports were obtained. The transports were much greater than the average for the entire hemisphere and point up the helical structure of the meridional cells. To obtain comparisons with other modes of transport, we made another calculation of the mean meridional transport by subtracting the vertical mean component from the longitudinal average. The results show that the energy transports were large and positive in subtropical latitudes and were zero or small and negative in middle latitudes.

Of the remaining modes, the transient eddy mode was the most effective in transporting energy poleward. The maximum transport occurred at 40°N for both the hemisphere and for North America; however, the value for North America was about 50 percent larger and the latitudinal variation was considerably greater than for the hemisphere. Sensible heat transport was largest, with the maximum latent transport amounting to one-half the sensible heat. Energy fluxes by the standing eddy and transient meridional modes were relatively small.

A brief study of the importance of various large-scale synoptic features in transporting energy indicated that large-amplitude troughs with closed 500-mb Lows are most effective in the transient eddy transport. Indications exist that the largest poleward energy transport is accomplished during the intensifying stage of baroclinic disturbances associated with the 500-mb Lows.

Abstract

The excellent North American radiosonde network is used to calculate the poleward energy transport for the continental area during the period January–March 1966. The transport of sensible and latent heat and geopotential and kinetic energy is partitioned according to four circulation modes—mean and transient meridional circulations and stationary and transient eddy circulations. In addition, the roles of various synoptic features in the transient eddy flux are examined.

The mean meridional transport was computed in two ways. One involved a calculation of the contribution of the North American sector to the hemispheric mean meridional transport. Because of strong meridional flow at high levels and a lack of compensating flow at low levels, very large transports were obtained. The transports were much greater than the average for the entire hemisphere and point up the helical structure of the meridional cells. To obtain comparisons with other modes of transport, we made another calculation of the mean meridional transport by subtracting the vertical mean component from the longitudinal average. The results show that the energy transports were large and positive in subtropical latitudes and were zero or small and negative in middle latitudes.

Of the remaining modes, the transient eddy mode was the most effective in transporting energy poleward. The maximum transport occurred at 40°N for both the hemisphere and for North America; however, the value for North America was about 50 percent larger and the latitudinal variation was considerably greater than for the hemisphere. Sensible heat transport was largest, with the maximum latent transport amounting to one-half the sensible heat. Energy fluxes by the standing eddy and transient meridional modes were relatively small.

A brief study of the importance of various large-scale synoptic features in transporting energy indicated that large-amplitude troughs with closed 500-mb Lows are most effective in the transient eddy transport. Indications exist that the largest poleward energy transport is accomplished during the intensifying stage of baroclinic disturbances associated with the 500-mb Lows.

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