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Abstract Future projections of the poleward eddy heat flux by the atmosphere are often regarded as being uncertain because of the competing effect between surface and upper-tropospheric meridional temperature gradients. Previous idealized modeling studies showed that eddy heat flux response is more sensitive to the variability of lower-tropospheric temperature gradient. However, observational evidence is lacking. In this study, observational data analyses are performed to examine the relationships between eddy heat fluxes and temperature gradients during boreal winter by constructing daily indices. On the intraseasonal time scale, the surface temperature gradient is found to be more effective at regulating the synoptic-scale eddy heat flux (SF) than is the upper-tropospheric temperature gradient. Enhancements in surface temperature gradient, however, are subject to an inactive planetary-scale eddy heat flux (PF). The PF in turn is dependent on the zonal gradient in tropical convective heating. Consistent with these interactions, over the past 40 winters, the zonal gradient in tropical heating and PF have been trending upward, while the surface temperature gradient and SF have been trending downward. These results indicate that for a better understanding of eddy heat fluxes, attention should be given to zonal convective heating gradients in the tropics as much as to meridional temperature gradients.
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On the Causes of Synoptic‐Scale Eddy Heat Flux Decline
Abstract The poleward heat flux by atmospheric waves plays a pivotal role in maintaining the meridional temperature gradient. A recent study found that in the Northern Hemisphere the heat flux by transient eddies has been weakening, and the study attributed this weakening to the smaller equator‐to‐pole temperature gradient caused by Arctic warming. During the period of 1979–2019 examined here, for the annual mean, both the synoptic‐scale eddy heat flux and the temperature gradient had indeed declined. However, from October to April, the synoptic‐scale eddy flux trend is more closely tied to the planetary‐scale eddy heat flux trend, than to the temperature gradient trend. From June to August, the synoptic‐scale eddy flux decline can be attributed to a warming of the high‐latitude land areas. Therefore, a more comprehensive interpretation of the synoptic‐scale eddy heat flux trend needs to include the dynamics of the planetary‐scale waves and summer land warming.
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- Award ID(s):
- 1948667
- PAR ID:
- 10393775
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 49
- Issue:
- 24
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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