Impacts of the seesaw mode between the Indian and East Asian summer monsoons on interannual variations in surface solar radiation across the low-latitude highlands of China

The relationship between the seesaw mode that connects the Indian summer monsoon (ISM) and East Asian summer monsoon (EASM), and variations in summer surface solar radiation (SSR) across the low-latitude highlands of China (CLLH), was investigated using atmospheric reanalysis and NOAA global gridded precipitation and outgoing longwave radiation datasets. Singular value decomposition, correlation analysis, and composite analysis were employed. The results indicate that the interannual variations in summer SSR in the CLLH are significantly modulated by the seesaw mode that connects the ISM with the EASM. During the boreal summer, the CLLH SSR variability is positively correlated with ISM intensity, but negatively correlated with EASM intensity. When a strong ISM and a weak EASM occur together, significant anomalous northeasterly winds appear over the CLLH, which reduces the moisture supply to the region from the Bay of Bengal. In addition, significant anomalous descending motion dominates the CLLH, leading to significant negative relative humidity anomalies over the CLLH. Consequently, water vapour, total liquid water form column clouds and high cloud cover decreased significantly over the CLLH, resulting in a higher CLLH SSR than average. Conversely, a lower-than-normal CLLH SSR seems to result from the approximately opposite physical process during the years where the ISM is weak and EASM is strong over the CLLH. Given the fact that the correlation between the aerosol optical depth (AOD) and the CLLH SSR is relatively weak, the AOD variability may not be the main control on interannual variations of summer CLLH SSR.