The South Asian high (SAH) is a huge anticyclone in the upper troposphere and lower stratosphere. It is the background flow of some key teleconnections which affect the summer climate of China. Understanding the modulation of the SAH under the scenario in which the concentration of greenhouse gases (GHGs) is higher favors the future projection of the climate change of China. 

Using the output of the coupled general circulation model in the Coupled Model Intercomparison Project Phase 5 (CMIP5), Dr. QU Xia and Prof. HUANG Gang in Institute of Atmospheric Physics, Chinese Academy of Sciences investigated the responses of the SAH to the GHGs. It is found that the coupled models all project equatorwards shift of the SAH under a higher GHGs-emission scenario. Some factors lead to two responses. First, modulation of latent heating. Under such scenario, the precipitation over the Bay of Bengal and the equatorial west Pacific changes due to the weakening of Walker circulation, “wet-get-wetter” and “warmer-get-wetter” mechanism. The associated latent heating change leads to the equatorwards shift of the SAH.  

Figure 1 The CMIP5 MME time serials of SAH ridge latitude (red) and center latitude (blue) from 1975 to 2100. 1976-2005 (2006-2099) is the results of the historical (RCP4.5) simulation.(Figure plotted by IAP)

Figure 2 The spatial correlation coefficients between the Linear Baroclinic Model (LBM) results and CMIP5 MME results. a is the results of 100 hPa geopotential height, b is the results of 100 hPa zonal wind. LH^*, MASC and RE^* respectively mean the response results of the LBM to latent heating change, mean advection of stratification change and residual terms. (Figure plotted by IAP)  

Second, The interaction between global mean stratification change and mean vertical motion. Under the scenario, the global mean atmospheric warming peaks at 300 hPa. The associated stratification change is transported by mean vertical motion and forms unique heating structure over the Tibetan Plateau and its south: heat sink (source) is found below 300 hPa (above 250 hPa). The heating excites anomalous cyclone over the climatological position and favors the southwards movement of the SAH.  

Further investigation reveals that the above factors are also responsible for the different amplification of the equatorwards movement projected by the coupled models. 

The above results are published on Journal of Climate and Theoretical and Applied Climatology. 

References： 

Qu, X., and G. Huang, 2016: The Global Warming–Induced South Asian High Change and Its Uncertainty. J. Climate, 29, 2259-2273, doi:10.1175/JCLI-D-15-0638.1. (URL: http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0638.1 ) 

Qu, X., G. Huang, K. Hu, S.-P. Xie, Y. Du, X.-T. Zheng and L. Liu, 2015：Equatorward shift of the South Asian high in response to anthropogenic forcing. Theor. Appl. Climatol., 119, 113-122, doi:10.1007/s00704-014-1095-1. (URL: http://link.springer.com/article/10.1007%2Fs00704-014-1095-1) 

Contact: Dr. QU Xia, quxia@mail.iap.ac.cn