Stratospheric and Tropospheric contributions to the Poleward Energy Flux across 70ºN
Abstract
Poleward atmospheric energy transport plays a key role in the Arctic climate, supplying nearly 100 W/m2 heating to the polar cap. This flux is usually studied from a vertically integrated perspective (Fwall). Here we examine the detailed vertical and temporal structure of Fwall, using the NASA MERRA-2 reanalysis to compute three-hourly fluxes of sensible, latent and potential energy across 70ºN for the period 1980-2016. The flux is bimodal, with peaks in the lower troposphere and in the middle stratosphere, and is near zero at the tropopause. In the lower troposphere, there is a downward progression of the MSE flux maximum from around 850 hPa in the winter to near the surface in the spring. The fraction of Fwall occurring in the stratosphere is 20% during winter and only 7% during summer. Variability of the stratospheric flux is intimately connected to sudden stratospheric warming (SSW) events. Composite analysis shows that SSW events are associated first with a dramatic increase in the stratospheric fraction of Fwall, followed by an increase in the polar-cap averaged outgoing long-wave radiation (OLR), with relatively little influence on Arctic surface temperatures. On the other hand, surface warming tendencies are much more strongly correlated with the tropospheric fraction of Fwall. Our analysis suggests that the effects of heat transport on Arctic climate would be best studied by filtering out the stratospheric contributions to Fwall.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A53K3031C
- Keywords:
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- 3310 Clouds and cloud feedbacks;
- ATMOSPHERIC PROCESSES;
- 3359 Radiative processes;
- ATMOSPHERIC PROCESSES;
- 0764 Energy balance;
- CRYOSPHERE;
- 1621 Cryospheric change;
- GLOBAL CHANGE