| As important parts of Asian Summer monsoon, the South China Sea Summer monsoon(SCSSM) and the South Asian Summer monsoon(SASM) have a significant impact on the local people the South Asian Summer The relationship between the upper ocean heat content(HC) in the tropical Indo-Pacific Ocean and the intensity/onset of SCSSM and SASM are investigated using the ocean-atmosphere reanalysis data, CMIP5 output, Fgoals_s2 coupled model, etc. According to previous studies, the SASM is divided into the Southwest Asian Summer Monsoon(SWASM)(2.5°N-20°N, 35°E-70°E) and the Southeast Asian Summer Monsoon(SEASM)(2.5°N-20°N, 70°E-110°E) in this paper. The different influences of the Indo-Pacific Ocean heat content on the intensity of SWASM/SEASM before and after 1976/1977 is compared; the skills of the CMIP5 coupled climate models in simulating the relation between the heat content and the intensity of SCSSM-ASSM are assessed; the performance of FGOALS-s2 in simulating the relation between the heat content in the tropical Western Pacific Warm Pool(WPWP) and the SCSSM onset is also evaluated. The main results are as follows.(1)Comparing with WPWP SST, the WPWP upper ocean HC is a more effective predictor of the SCSSM intensity. The SCSSM intensity is positively and negatively correlated with the WPWP upper ocean HC and the western tropical Indian Ocean HC during the preceding winter–spring, respectively. The tropical Pacific impacts the SCSSM by means of affecting the Walker circulation, the Western Pacific subtropical high and the South China Sea cross equatorial flow; while the tropical Western Indian Ocean affects the SCSSM through influencing the pressure gradient and the anti-cyclone over the Indian Ocean.(2)Before the 1976/77 climate shift, SWASM is highly related to the HC in the Southern Indian Ocean and the tropical Pacific Ocean, SEASM is poorly related to the HC in the tropical Indo-Pacific Ocean. However, there is no significant correlation between the SWASM and HC in the tropical Indo-Pacific Ocean and a good correlation between the SEASM and the central tropical Pacific HC after the 1976/77 climate shift. The Southern Indian Ocean can influence the pressure gradient between Southern Africa and the Northern Indian Ocean, which leading to the variation of the Somali cross equatorial flow and hence the SWASM; while the tropical Pacific impacts the SWASM and SEASM through the remote forcing of ENSO.(3)Through assessing the skills of the CMIP5 coupled climate models in simulating the relation between the HC and the intensity of summer monsoon, we find that few models can simulate the spatial distribution of the correlation coefficient between the SCSSM intensity and the HC; few models can simulate the change of the SWASM’s intensity before and after the 1976/77 climate shift, most models can simulate the change of the SEASM’s intensity before and after the 1976/77 climate shift; most models can simulate the spatial distribution of the correlation coefficient between the intensity of SWASM(SEASM) and HC; all the models do not reproduce the different relationship of the Indo-Pacific Ocean HC and the SWASM/SEASM before and after 1976/1977. Though some models can simulate the spatial distribution of the correlation between the intensity of summer monsoon and the HC, the simulated correlations are generally weaker than that from the reanalysis data.(4)The negative correlation between the WPWP HC and the SCSSM onset is reproduced by Fgoals-s2. In the reanalysis data, the onset time of SCSSM has a peak correlation of-0.67 with the April WPWP heat content above 100 m; while from the Fgoals-s2 output, we find that the SCSSM onset shows the significant correlation(-0.47) with the February WPWP heat content above 65 m. |
