Can volcanic eruptions enhance the monsoon precipitation?
Can Volcanic Eruptions Enhance the Monsoon Precipitation?
Volcanic eruptions are known to slow down the water cycle by reducing the net surface shortwave radiation. The explosive volcanos erupted at the Southern Hemisphere can enhance the Northern Hemispheric monsoon precipitation in a few years after the eruption. This is the finding of our study in the Scientific Reports. The intensification of monsoon precipitation has been observed in the long-term reconstructions and 1500-Year CESM simulation. The formed aerosols in the stratosphere of these Southern Hemispheric volcanos are confined in the Southern Hemisphere, resulting in strong surface cooling in the Southern Hemisphere, while the Northern Hemisphere is less affected. The enhanced hemispheric thermal contrast drives low-level cross-equatorial flows from the Southern Hemisphere, which converges into the monsoon trough regions and enhance the monsoon precipitation in the Northern Hemisphere. The volcano-induced monsoon intensification is caused by the enhanced circulation. This is different from the monsoon intensification induced by anthropogenic greenhouse gases. Under the global warming induced by strong greenhouse-gas concentration, the GM precipitation is enhanced by the moistened atmosphere, while the circulation is weakened.
Liu F., J. Chai, B. Wang, J. Liu, X. Zhang, and Z. Wang, 2016:Global monsoon precipitation responses to large volcanic eruptions. Sci.Rep. 6, 24331; doi: 10.1038/srep24331.
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Figure 1. GM precipitation domain and annual reversal of precipitation. Shading shows the climatological mean MJJAS-minus-NDJFM precipitation using the GPCP data. The observed GM precipitation domains and the counterparts simulated in the 1500-year run are denoted by thick black and green lines, respectively. The GM precipitation domains outlined by the thick lines are defined by local summer-minus-winter precipitation rate exceeding 2.0 mm/d and the local summer precipitation exceeding 55% of the annual total.
Figure 2. Simulated superposed epoch analysis of normalized monsoon responses to different large volcanic eruptions. The GM precipitation intensity in responses to (a) NH, (b) SH, (c) equatorial, and (d) total volcanic eruptions. The responses of NH monsoon and SH monsoon precipitation are shown in the middle (e-h) and bottom (i-l) panels. Confidence limits (90%, 95%, 99%) are marked by horizontal lines. Blue and red colors mark the pre- and post-eruption composites, respectively. “-1st” and “1st” in the x-axis denote the first year before and after the eruptions, respectively.