Dynamics matter: The partitioning of poleward energy transport and its changes from the Last Glacial Maximum to CO2 quadrupling in coupled global climate models
Abstract
We partition the poleward energy transport (PET) in an ensemble of coupled climate model simulations of climate states ranging from the Last Glacial Maximum (LGM) to a world with quadrupled CO2. PET is partitioned into oceanic and atmospheric contributions which are subdivided into overturning circulations, transient eddies (TE) and stationary eddies (SE). We also consider the moist and dry energy flux partitioning. We show that PET is nearly invariant to climate state, except for a modest (4%, 0.3PW) enhancement of PET in the Northern Hemisphere during the LGM. However, the partitioning of PET changes dramatically between climate state and differs drastically between different ensemble members.
In response to CO2 quadrupling, the poleward ocean heat transport decreases while the poleward atmospheric energy transport increases by a nearly compensating amount. The increase in annual mean atmospheric energy transport is a smooth function in latitude but encompasses a complicated superposition of processes acting in different regions and seasons: 1) increased stationary eddy moisture fluxes in the subtropics during the summer, 2) mid-latitude TE moisture flux increases during the winter exceeding decreases in the TE dry energy flux and, 3) increased winter SE dry energy flux into the high latitudes. During the LGM, the increase in wintertime SE dry energy flux in the Northern Hemisphere mid-latitudes exceeds the decrease in TE moist and dry energy flux resulting in enhanced total PET. In the Southern Hemisphere, the changes in both SE and TE fluxes are negligible with the latter resulting from near compensation of moist and dry components. These results suggest that the net top of atmosphere radiative constraints on total PET are relatively inflexible to climate forcing due to near compensation of changes in absorbed solar radiation and outgoing longwave radiation. However, the partitioning of PET depends on detailed regional and seasonal factors. It is unclear how local dynamics adjust to satisfy large-scale radiative constraints of near invariance and latitudinal smoothness of PET. We speculate that TE fluxes adjust to the residual net diabatic heating from changes in radiation and SE flux divergence to efficiently smooth the resultant temperature and radiative gradients.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.A53N2715D
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSESDE: 3319 General circulation;
- ATMOSPHERIC PROCESSESDE: 1620 Climate dynamics;
- GLOBAL CHANGEDE: 1630 Impacts of global change;
- GLOBAL CHANGE