Decadal coupling between storm tracks and sea surface temperature in the Southern Hemisphere midlatitudes
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Decadal coupling between storm tracks and sea surface temperature in the Southern Hemisphere midlatitudes Li Zhang1 · Bolan Gan1 · Chuan‑Yang Wang1 · Lixin Wu1 · Wenju Cai1,2 Received: 28 June 2020 / Accepted: 9 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The relationships between the seasonal mean storm-track anomalies and sea surface temperature anomalies (SSTAs) in the midlatitude Southern Hemisphere (SH) on the decadal time scale are investigated using the lagged maximum covariance analysis (MCA). It shows that the coupling between storm-track anomalies and SSTAs is most prominent in austral summer (January–March, JFM). Firstly, large cold SSTAs in the western South Indian Ocean (SIO), corresponding to the strengthened SST front on the equator side, substantially intensify the storm-track activity manifested by the increased low-level poleward transient eddy heat flux over the entire SH. The coherent intensification of the atmospheric baroclinicity and the subtropical jet associated with such strengthened SST front provides baroclinic energy for the growth of synoptic eddies. Further, the intensified storm-track activity induces large cold SSTAs in the South Atlantic (SA), the SIO and the subtropical South Pacific (SP), primarily via anomalous net surface heat fluxes. The mean SST advection by the anomalous Ekman current also contributes to the cold SSTAs in the SA, which is related to the anomalous westerlies induced by the anomalous storm-track activity.
1 Introduction Storm tracks, identified as regions where synoptic storms are most prevalent in the midlatitudes (Blackmon et al. 1977), are a pivotal component in extratropical weather and climate systems. They shape local weather extremes and interfere with extratropical climate by poleward transporting heat, moisture and momentum (Chang et al. 2002), and by interacting with the low-frequency mean flows (Kug et al. 2010). Hence, the extratropical weather and climate are profoundly altered by any significant changes in storm tracks. Understanding the decadal climate variability is one of the greatest challenges to the climate research community. The influence of ocean on the atmosphere, especially the response of the large-scale atmospheric circulation to the midlatitude sea surface temperature anomalies (SSTAs) * Li Zhang [email protected] 1
Physical Oceanography Laboratory/CIMST, Ocean University of China and Qingdao National Laboratory for Marine Science and Technology, 238 Songling Road, Qingdao 266100, People’s Republic of China
CSIRO Oceans and Atmosphere Flagship, Aspendale, VIC 3195, Australia
2
at the frontal-to-basin scale, is the key to understand the extratropical climate variabilities on seasonal to decadal time scales. With focus on the Northern Hemisphere (NH), many efforts have been made on this topic (e.g., Sen Gupta and England 2007; Kwon et al. 2010), but there are still great discrepancies among observational and modelling analyses in terms of the spatial vertical structure of atmospher
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