Yue Wang1,2,* , Xingxing Wang1 , Shuai Zhang3 , Guo Chen2 , Daoyu Wu4 , Hang Deng2 , Minsha Tang2 , Haowen Dang1 and Zhimin Jian1
1 State Key Laboratory of Marine Geology, Tongji University, Shanghai, China
2 School of Ocean and Earth Science, Tongji University, Shanghai, China
3 College of Oceanography, Hohai University, Nanjing, China
4 Department of Atmospheric and Oceanic Sciences, Fudan University, Shanghai, China
*Corresponding author.
Email address: 163wangyue@tongji.edu.cn(Y. Wang)
Abstract
Modern studies suggest that the upper ocean heat content (OHC) in the tropical Indian Ocean (TIO) is a better qualitative predictor of the Indian summer monsoon rainfall (ISMR). But it is still unknown how the OHC is mechanically linked to ISMR and whether it can be applied to long-term climate changes. By analyzing reanalysis datasets across the 20th century, we illustrate that in contrast to those anomalies associated with stronger ISM westerlies, higher ISMR is accompanied with summer surface high pressure and east wind anomalies from the South China Sea to the Bay of Bengal (BOB), and is loosely related to increased western TIO OHC during decayed phases of positive Indian Ocean dipole (IOD) and of El Nino. Except for ˜ 1944–1968 AD, this interannually lagged ISMR response to winter OHC is insignificant, probably suppressed by those simultaneous effects of positive IOD and El Nino on ISMR. In our ˜ paleoclimatic simulations, this modern observed lagged response is interrupted by seasonally reversed insolation anomalies at the 23,000-year precessional band. Our sensitivity experiments further prove that, the ISMR can be simultaneously reduced by positive IOD-like summer OHC anomalies both for modern and precessional situations. This damping effect is mainly contributed by the warmer western TIO that triggers anomalous surface high pressure, easterly winds, and drastically reduced rainfall from BOB to Arabian Peninsula, but with slightly increased rainfall in the northern ISM region. And the cooler southeastern TIO will only moderately increase rainfall in the southern ISM region.
Full article: https://doi.org/10.1017/S0016756824000189.
Fig. (a) Modern observed time series of ISM rainfall index (ISMR, green line) and ISM wind index (DNS, with linear trend removed, no units) from the year 1871 to 2010 AD. (b) Time series of SOI indexes during DJF and JJA (gray line for SOIDJF and orange line for SOIJJA, no units). (c) ASO DMI index (brown line, units: K) is compared with the OHC26_WIO time series (cyan line). (d) 20-year moving correlations for ISMR in Yr 1 with three indexes: DMI(-) in Yr 1 (multiplied by -1, brown line), SOIJJA(+) in Yr 1 (orange line), SOIJJA(-) in Yr 0 (gray line). (e) Moving correlations for OHC26_WIO in Yr 1 with three indexes: ISMR(+) in Yr 1 (cyan line), DMI(+) in Yr 0 (black line), SOIDJF(-) in Yr 1 (gray line), and for DMI (+) in Yr 0 with two indexes: ISMR(+) in Yr 1 (brown line), SOIJJA(-) in Yr 0 (red line). (f) Lead-lag correlations (R) between different time series. In (d), (e), and (f), those positive or negative signs in parentheses show the anomalous status of SOI, DMI, OHC26, and ISMR in the corresponding year.