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Abstract We extend the locking technique to separate the poleward shift of the atmospheric circulation in response to quadrupled CO2into contributions from (1) CO2increase, (2) cloud radiative effects, and (3) wind and surface humidity‐induced surface heat exchange. In aquaplanet simulations, wind and surface humidity‐induced surface heat exchange accounts for 30–60% of the Hadley cell edge and midlatitude eddy‐driven jet shift. The increase of surface specific humidity dominates and mostly follows global mean warming. Consistent with previous work the remaining shift is attributed to cloud radiative effects. Across CMIP5 models the intermodel variance in the austral winter circulation shift in response to quadrupled CO2is significantly correlated with the response of the subtropical‐subpolar difference of surface heat exchange. The results highlight the dominant role of surface heat exchange for future circulation changes.
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Quantifying Key Mechanisms That Contribute to the Deviation of the Tropical Warming Profile From a Moist Adiabat
Abstract Climate models project tropical warming is amplified aloft relative to the surface in response to increased CO2. Here we show moist adiabatic adjustment overpredicts the multimodel mean 300 hPa temperature response by 16.6–25.3% across the CMIP5 model hierarchy. We show three mechanisms influence overprediction: climatological large‐scale circulation, direct effect of increased CO2, and convective entrainment. Accounting for the presence of a climatological large‐scale circulation and the direct effect of CO2reduces the CMIP5 multimodel mean overprediction by 0.7–7.2% and 2.8–3.9%, respectively, but does not eliminate it. To quantify the influence of entrainment, we vary the Tokioka parameter in aquaplanet simulations. When entrainment is decreased by decreasing the Tokioka parameter from 0.1 to 0, overprediction decreases by 9.6% and 10.4% with and without a large‐scale circulation, respectively. The sensitivity of overprediction to climatological entrainment rate in the aquaplanet mostly follows the predictions of zero‐buoyancy bulk‐plume and spectral‐plume models.
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- Award ID(s):
- 1742944
- PAR ID:
- 10455581
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 47
- Issue:
- 20
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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