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Abstract Synoptic eddies embedded in a westerly flow undergo downstream developments due to their dispersive nature. This paper examines the finite-amplitude aspects of downstream development with the budget of local wave activity (LWA), including explicit contributions from diabatic heating. LWA captures well individual troughs/ridges and the wave packet, and its column budget affords simplified interpretations. In the LWA framework, (linear) downstream development demonstrated in previous analyses is represented by the LWA advection by the zonal reference flow plus LWA flux induced by the radiation of Rossby waves. In addition, convergence of nonlinear advective LWA flux, baroclinic sources at the lower boundary, meridional redistribution by eddy momentum flux, and diabatic sources and sinks complete the column budget of LWA. When applied to the life cycles of troughs within coherent wave packets in the Southern Hemisphere, the LWA budget reveals that individual troughs grow mainly through downstream development, convergence of nonlinear advective flux by eddies, and diabatic heating. Downstream development and divergence of nonlinear flux also dominate trough decay. Contributions from nonlinear advective eddy flux are large in the presence of a strong ridge either immediately upstream or downstream of the trough. Furthermore, anticyclonic components of advective LWA fluxes associated with the upstream or downstream ridge transfer LWA into or out of the trough. Diabatic contributions are significant when the heating exhibits a tilted vertical structure that gives rise to enhanced vertical gradient in heating.
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Imprint of Diabatic Processes in the Waviness of the Jet Stream: An Analysis of Local Wave Activity Budget
Abstract Given the widespread presence of clouds in the midlatitudes, one expects significant effects of condensational and radiative processes on the large-scale circulation of the atmosphere, but these diabatic effects are hard to constrain from observation. The authors propose a simple method to estimate the diabatic effects on the waviness of the jet stream based on the observed column-mean budget of Rossby wave activity. Wave activity in the midlatitudes is maintained by injection due to surface baroclinicity and/or diabatic sources, downstream transport due to advection and wave radiation, and eventual dissipation through mixing and thermal damping. Once the diabatic sources of wave activity are identified from the residual of the budget, one can suppress them and recompute the budget assuming that the transport velocity and damping rate do not change and thereby assess the impact of the diabatic sources. For the Northern Hemisphere, we found significant positive values of the residual in regions coincident with high column cloud water, suggesting that there are diabatic sources of wave activity associated with clouds. In winter, maritime diabatic sources contribute to wave activity over the Atlantic and the Pacific by about 33% and 30%, respectively, while in summer, the numbers are lower. The estimates are based on the assumptions that the perturbed wave sources do not alter the flow and that sources and sinks are geographically separated. For the Southern Hemisphere, this last assumption is questionable, and therefore, the confidence level of the estimates is low.
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- Award ID(s):
- 2154523
- PAR ID:
- 10550146
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of Climate
- Volume:
- 37
- Issue:
- 22
- ISSN:
- 0894-8755
- Format(s):
- Medium: X Size: p. 5703-5719
- Size(s):
- p. 5703-5719
- Sponsoring Org:
- National Science Foundation
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