For millions of people, the intensity of East Asian summer monsoon indicates the wet or dry conditions there. Plenty of previous studies have proved that the first leading mode of the interannual variability of the Indian Ocean sea surface temperature, also called the Indian Ocean Basin Mode (IOBM), features a basin-wide warming or cooling and that it exerts great influences on the East Asian climate. When the Indian Ocean is warmer than normal, warm tropospheric Kelvin wave is triggered, contributes to the development of an anomalous anticyclone over the Northwestern Pacific via the “capacitor effect” and affect the East Asian summer monsoon. Two recent studies based on CMIP5 revealed the change of the IOBM and its capacitor effect under global warming.

"Our work suggests that the IOBM is slightly intensified, but more obvious enhancement in its ‘capacitor effect’, causing the strengthened anomalous Northwest Pacific anticyclone," said HUANG Gang, a scientist of Institute of Atmospheric Physics (IAP). His team recently published two papers about this finding. One is about the future adjustment of “capacitor effect”, released in Journal of Climate and written by HU Kaiming; the other is about the IOBM, released in International Journal of Climatology and written by TAO Weichen.

HUANG Gang’ team examined the depth of climatological thermocline in the southwestern tropical Indian Ocean and ENSO activity, which are considered to favor the change of the IOBM in observation, and found the two factors cannot explain the strengthened sea surface temperature anomalies under global warming scenarios. Then, what causes the strengthened IOBM and “capacitor effect”?

Finally, they found that the increased saturated specific humidity plays an important role. Increased saturation specific humidity makes significant contribution to the enhanced tropospheric temperature response (Fig 1), causing the strengthened “capacitor effect”. Moreover, the enhanced tropospheric temperature provides the positive feedback to the IOBM. The detailed mechanism diagram is shown in Fig 2.

References

Hu, K., G. Huang*, X. Zheng, S.-P. Xie, X. Qu, Y. Du and L. Liu,2014: Interdecadal variations in ENSO's influences on the Northwest Pacific and East Asia summertime climate simulated in the CMIP5 models, Journal of Climate, 27, 5982–5998. DOI: 10.1175/JCLI-D-13-00268.1

Tao, W., G. Huang*, K. Hu, X. Qu, G. Wen and H. Gong, 2014: Interdecadal modulation of ENSO teleconnections to the Indian Ocean Basin Mode and their relationship under global warming in CMIP5 models, International Journal of Climatology, in press. DOI: 10.1002/joc.3987

Funded by:

National Basic Research Program of China

National Natural Science Foundation of China

Strategic Priority Research Program of the Chinese Academy of Sciences

Fig 1. The response of tropospheric temperature to the anomalies of sea surface temperature and saturated specific humidity.

Fig 2. The diagram about the strengthened IOBM and its capacitor effect under global warming.