Abstract
Abstract. The response of atmospheric energy transport during Northern Hemisphere cooling and warming from present day (PD) and Last Glacial Maximum (LGM) conditions is investigated using sea surface temperature anomalies derived from a freshwater hosing experiment. The present day climate shows enhanced sensitivity of the atmospheric mid-latitude energy transport compared to that of the LGM, suggesting its ability to reorganize more easily and thereby dampen high latitude temperature anomalies that may arise from changes in the oceanic transport. This effect is found to be a result of both the atmospheric and surface flux response. The increased PD transport sensitivity relative to that of the LGM is linked to a stronger dry static energy transport response which, in turn, is mainly driven by larger changes in the transient eddy heat flux. In comparison, changes in mid-latitude latent heat transport play a minor role in the overall transport sensitivity.
Highlights
Proxy climate data from around the world show enhanced variability, such as the presence of Dansgaard-Oeschger events, during glacial periods compared to the interglacials (Greenland ice cores, NGRIP Members, 2004; Antarctic ice cores, EPICA Members, 2006; Cariaco Basin sediment cores, Peterson et al, 2000; Asian cave stalagmites, Wang et al, 2001; and Arabian Sea sediment cores, Banakar et al, 2010)
Such analysis shows that the drier low-level Last Glacial Maximum (LGM) atmosphere increases the total gross moist static stability (2.6 × 104 J kg−1 compared to 2.0 × 104 J kg−1 in PD), weakens the canceling effect that the latent heat transport has on the dry static energy transport (DSE) transport and yields a larger LGM total northward transport in the low latitudes compared to the present day
Our study demonstrates enhanced mid-latitude atmospheric heat transport sensitivity to the imposed high latitude surface temperature perturbations under warm compared to cold conditions
Summary
Numerous modeling studies have addressed communication between high and low latitudes, showing that changes in ice cover, the Atlantic Meridional Overturning Circulation (AMOC) or generally antisymmetric interhemispheric heating in the high latitudes can induce a displacement of the Intertropical Convergence Zone (ITCZ) (Zhang and Delworth, 2005; Chiang and Bitz, 2005; Broccoli et al, 2006; Chiang et al, 2008). Trenberth and Caron (2001) and Wunsch (2005) have demonstrated a dominance of atmospheric over oceanic transport in the extratropics. The sensitivity of the atmospheric energy transport to global mean temperature and meridional temperature gradients was previously studied by Caballero and Langen (2005) in a series of aquaplanet simulations They found atmospheric heat transport independent of global mean temperature in cases when the global mean temperature was high and meridional temperature gradient low. A weakened atmospheric transport sensitivity, i.e. a less negative atmospheric feedback, would imply a climate state with the atmosphere less capable of damping high latitude temperature anomalies arising from changes in the oceanic transport. In this case, the climate is likely to be influenced more strongly by excursions in the oceanic circulation. The sensitivity of the atmospheric response to different sea ice extents and SSTs is tested with the anomalies applied in two background climates, PD and LGM
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