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Abstract A global climate model is run in radiative‐convective equilibrium including a slab ocean with a specified ocean heat transport analogous to what is seen in the tropical Pacific. The insolation is varied to create a range of global mean equilibrium temperatures. These results are compared with experiments that do not include a specified ocean heat transport. The ocean heat transport cools the coldest Sea Surface Temperatures (SSTs) and increases the SST contrast. The warmest SSTs change much less with the addition of ocean heat transport because increased atmospheric transport moves energy away from the warm region. The ocean heat transport also increases the efficiency of cooling by outgoing longwave radiation in the subsiding region, allowing for a cooler global mean SST. At colder global mean temperatures ocean heat transport creates a high‐contrast state in which abundant low clouds play a strong role in maintaining the SST contrast. This high‐contrast state abruptly transitions to a warmer, low‐SST‐contrast state as the climate is warmed by increasing insolation. At warmer temperatures comparable to the current tropics, the low cloud response is less important than longwave emission in maintaining the SST contrast. Although ocean heat transport cools the climate, it does not much affect the sensitivity of the model climate to increasing insolation. Comparison of the model results to ERA5 reanalysis data shows that mechanisms responsible for the SST distribution and energy budget changes in this idealized model are analogous to variability that occurs over the tropical Pacific Ocean.
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Global Radiative Convective Equilibrium With a Slab Ocean: SST Contrast, Sensitivity and Circulation
Abstract Warming experiments with a uniformly insolated, non‐rotating climate model with a slab ocean are conducted by increasing the solar irradiance. As the global mean surface temperature is varied across the range from 289 to 319K, the sea surface temperature (SST) contrast at first declines, then increases then declines again. Increasing SST contrast with global warming is associated with reduced climate sensitivity, while decreasing SST contrast is associated with enhanced climate sensitivity. The changing SST contrast and climate sensitivity are both related fundamentally to the effect of water vapor on clear‐sky radiative cooling. The clouds in the convective region are always more reflective than those in the subsiding region and so always act to reduce the SST contrast. At lower temperatures between 289 and 297 K the shortwave suppression of SST contrast increases faster than the longwave enhancement of SST contrast. At warmer temperatures between 297 and 309 K the longwave enhancement of SST contrast with warming is stronger than the shortwave suppression of SST contrast, so that the SST contrast increases. Above 309 K the greenhouse effect in the subsiding region begins to grow, the SST contrast declines and the climate sensitivity increases. The transitions at 297 and 309 K can be related to the increasing vapor pressure path with warming. The mass circulation rate between warm and cool regions consists of shallow and deep cells. Both cells increase in strength with SST contrast. The lower cell remains connected to the surface, while the upper cell rises to maintain a roughly constant temperature.
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- Award ID(s):
- 2124496
- PAR ID:
- 10446013
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 127
- Issue:
- 12
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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