Abstract:
There is strong statistical evidence that solar activity influences the Indian
summer monsoon rainfall. To search for a physical link between the two, we
consider the coupled cloud hydrodynamic equations, and derive an equation
for the rate of precipitation that is similar to the equation of a forced harmonic oscillator, with cloud and rain water mixing ratios as forcing variables.
Those internal forcing variables are parameterized in terms of the
combined effect of external forcing as measured by sunspot and coronal hole activities
with several well known solar periods (9, 13 and 27 days; 1.3, 5, 11 and 22
years). The equation is then numerically solved and the results show that the variability of the simulated rate of precipitation captures very well the actual variability of the Indian monsoon rainfall, yielding vital clues for a
physical understanding that has so far eluded analyses based on statistical
correlations alone. We also solved the precipitation equation by allowing for
the effects of long-term variation of aerosols. We tentatively conclude that
the net effects of aerosols variation are small, when compared to the solar
factors, in terms of explaining the observed rainfall variability covering the
full Indian monsoonal geographical domains.
