Decadal coupling between storm tracks and sea surface temperature in the Southern Hemisphere midlatitudes

2020 ◽  
Author(s):  
Li Zhang ◽  
Bolan Gan ◽  
Chuan-Yang Wang ◽  
Lixin Wu ◽  
Wenju Cai
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Southern Hemisphere ◽  
Sea Surface ◽  
Storm Tracks

scholarly journals Seasonal Dependence of Coupling between Storm Tracks and Sea Surface Temperature in the Southern Hemisphere Midlatitudes: A Statistical Assessment

2018 ◽  
Vol 31 (10) ◽  
pp. 4055-4074 ◽  
Author(s):  
Li Zhang ◽  
Bolan Gan ◽  
Lixin Wu ◽  
Wenju Cai ◽  
Hao Ma
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Southern Hemisphere ◽  
Storm Track ◽  
South Atlantic ◽  
Sea Surface ◽  
Storm Tracks ◽  
Seasonal Dependence ◽  
Sst Anomalies ◽  
Southern Oceans

Two-way coupling between sea surface temperature (SST) variations in the midlatitude southern oceans and changes of synoptic-scale (2–8 day) eddy activities in the lower and upper troposphere throughout the year is investigated based on lagged maximum covariance analysis using reanalysis datasets from 1951 to 2000. Results show a strong seasonal dependence of the coupling, as characterized by the most prominent one in austral midsummer (January). On one hand, SST variations in austral late spring (primarily October) are likely to influence storm tracks in the following January. That is, significant warm SST anomalies in the western midlatitude areas of South Atlantic and south Indian Ocean could result in the systematic strengthening of the low-level and upper-level eddy activities, which is presumably attributed to the coherent intensification of the SST front and the lower-tropospheric baroclinicity. Particularly, interannual variability (a spectral peak at 4 yr) of SST in the western midlatitude South Atlantic in October could play a predominant role in driving the corresponding variability of the Southern Hemisphere storm tracks three months later. The timing of the discernible response of storm tracks is also discussed based on the preliminary results of sensitivity experiments. On the other hand, the strengthened eddy activities in January continue to induce the dipolelike patterns of SST anomalies in the midlatitude southern oceans. Those SST response patterns are, to the first order, determined by changes of the net surface heat flux. The anomalous Ekman advections in part driven by the storm-track changes also contribute to SST anomalies in the southern subtropical South Atlantic and the western midlatitude South Pacific.

scholarly journals The influence of direct radiative forcing versus indirect sea surface temperature warming on southern hemisphere subtropical anticyclones under global warming

2021 ◽  
Author(s):  
Abdullah A. Fahad ◽  
Natalie J. Burls
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Southern Hemisphere ◽  
Radiative Forcing ◽  
Diabatic Heating ◽  
Sea Surface ◽  
Atmospheric Response ◽  
Austral Winter ◽  
Subtropical Anticyclone ◽  
Surface Temperature Warming

AbstractSouthern hemisphere subtropical anticyclones are projected to change in a warmer climate during both austral summer and winter. A recent study of CMIP 5 & 6 projections found a combination of local diabatic heating changes and static-stability-induced changes in baroclinic eddy growth as the dominant drivers. Yet the underlying mechanisms forcing these changes still remain uninvestigated. This study aims to enhance our mechanistic understanding of what drives these Southern Hemisphere anticyclones changes during both seasons. Using an AGCM, we decompose the response to CO2-induced warming into two components: (1) the fast atmospheric response to direct CO2 radiative forcing, and (2) the slow atmospheric response due to indirect sea surface temperature warming. Additionally, we isolate the influence of tropical diabatic heating with AGCM added heating experiments. As a complement to our numerical AGCM experiments, we analyze the Atmospheric and Cloud Feedback Model Intercomparison Project experiments. Results from sensitivity experiments show that slow subtropical sea surface temperature warming primarily forces the projected changes in subtropical anticyclones through baroclinicity change. Fast CO2 atmospheric radiative forcing on the other hand plays a secondary role, with the most notable exception being the South Atlantic subtropical anticyclone in austral winter, where it opposes the forcing by sea surface temperature changes resulting in a muted net response. Lastly, we find that tropical diabatic heating changes only significantly influence Southern Hemisphere subtropical anticyclone changes through tropospheric wind shear changes during austral winter.

scholarly journals Using data assimilation to investigate the causes of Southern Hemisphere high latitude cooling from 10 to 8 ka BP

2013 ◽  
Vol 9 (2) ◽  
pp. 887-901 ◽  
Author(s):  
P. Mathiot ◽  
H. Goosse ◽  
X. Crosta ◽  
B. Stenni ◽  
M. Braida ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Southern Ocean ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Atmospheric Circulation ◽  
Southern Hemisphere ◽  
Sea Surface ◽  
Freshwater Flux ◽  
West Antarctic ◽  
The Impact

Abstract. From 10 to 8 ka BP (thousand years before present), paleoclimate records show an atmospheric and oceanic cooling in the high latitudes of the Southern Hemisphere. During this interval, temperatures estimated from proxy data decrease by 0.8 °C over Antarctica and 1.2 °C over the Southern Ocean. In order to study the causes of this cooling, simulations covering the early Holocene have been performed with the climate model of intermediate complexity LOVECLIM constrained to follow the signal recorded in climate proxies using a data assimilation method based on a particle filtering approach. The selected proxies represent oceanic and atmospheric surface temperature in the Southern Hemisphere derived from terrestrial, marine and glaciological records. Two mechanisms previously suggested to explain the 10–8 ka BP cooling pattern are investigated using the data assimilation approach in our model. The first hypothesis is a change in atmospheric circulation, and the second one is a cooling of the sea surface temperature in the Southern Ocean, driven in our experimental setup by the impact of an increased West Antarctic melting rate on ocean circulation. For the atmosphere hypothesis, the climate state obtained by data assimilation produces a modification of the meridional atmospheric circulation leading to a 0.5 °C Antarctic cooling from 10 to 8 ka BP compared to the simulation without data assimilation, without congruent cooling of the atmospheric and sea surface temperature in the Southern Ocean. For the ocean hypothesis, the increased West Antarctic freshwater flux constrainted by data assimilation (+100 mSv from 10 to 8 ka BP) leads to an oceanic cooling of 0.7 °C and a strengthening of Southern Hemisphere westerlies (+6%). Thus, according to our experiments, the observed cooling in Antarctic and the Southern Ocean proxy records can only be reconciled with the reconstructions by the combination of a modified atmospheric circulation and an enhanced freshwater flux.

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