Comprehensive climate models exhibit a large spread in the magnitude of projected poleward eddy‐driven jet shift in response to warming. The spread has been connected to the radiative response to warming. To understand how different radiative assumptions alone affect the jet shift in response to warming, we introduce a new clear‐sky longwave radiation hierarchy that spans idealized (gray versus four bands; without or with interactive water vapor) through comprehensive (correlated‐k) radiation in the same general circulation model. The new hierarchy is used in an aquaplanet configuration to explore the impact of radiation on the jet stream response to warming, independent of mean surface temperature and meridional surface temperature gradient responses. The gray radiation scheme produces a split jet and its eddy‐driven jet shifts equatorward as climate warms, whereas the storm track shifts equatorward then poleward. Including four longwave bands leads to a merged jet that shifts slightly poleward with warming, and the storm track shifts monotonically poleward. Including interactive water vapor makes the poleward jet shift comparable to the jet shift with comprehensive radiation and interactive water vapor. These jet and storm track differences are linked to the radiation response of the stratospheric temperature, the tropopause height, and the meridional gradient of the radiative forcing to warming. Dynamically, the equatorward jet shift with the gray scheme is consistent with reduced wave reflection on the poleward flank of the jet, whereas the poleward jet shift with the other schemes is consistent with increased eddy length scale that favors equatorward wave propagation.
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Stratospheric ozone, and its response to anthropogenic forcings, provides an important pathway for the coupling between atmospheric composition and climate. In addition to stratospheric ozone’s radiative impacts, recent studies have shown that changes in the ozone layer due to 4xCO2have a considerable impact on the Northern Hemisphere (NH) tropospheric circulation, inducing an equatorward shift of the North Atlantic jet during boreal winter. Using simulations produced with the NASA Goddard Institute for Space Studies (GISS) high-top climate model (E2.2), we show that this equatorward shift of the Atlantic jet can induce a more rapid weakening of the Atlantic meridional overturning circulation (AMOC). The weaker AMOC, in turn, results in an eastward acceleration and poleward shift of the Atlantic and Pacific jets, respectively, on longer time scales. As such, coupled feedbacks from both stratospheric ozone and the AMOC result in a two-time-scale response of the NH midlatitude jet to abrupt 4xCO2forcing: a “fast” response (5–20 years) during which it shifts equatorward and a “total” response (∼100–150 years) during which the jet accelerates and shifts poleward. The latter is driven by a weakening of the AMOC that develops in response to weaker surface zonal winds that result in reduced heat fluxes out of the subpolar gyre and reduced North Atlantic Deep Water formation. Our results suggest that stratospheric ozone changes in the lower stratosphere can have a surprisingly powerful effect on the AMOC, independent of other aspects of climate change.
more » « less- Award ID(s):
- 1902409
- NSF-PAR ID:
- 10521248
- Publisher / Repository:
- AMS
- Date Published:
- Journal Name:
- Journal of Climate
- Volume:
- 37
- Issue:
- 10
- ISSN:
- 0894-8755
- Page Range / eLocation ID:
- 2897 to 2917
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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