Indian Monsoon Rainfall Shows Short Solar Cycles?

The Indian rainfall is largely governed by the Monsoon season when it rains heavily for 4 months each year. The following graph shows the very strong seasonal cycle:

To see other than seasonal fluctuations and cycles it is necessary to remove the seasonal components. It was found that the variations during the wet and dry seasons have different proportionalities. To make these extremely different seasons have similar amounts of variations it was found that using the square root of monthly rainfall was a good measure. So the following graph shows (monthly rainfall)^0.5 after removing the seasonal cycle.

When the spectrum of rainfall is determined, the seasonal cycles dominate, with 1 year, 1/2 year, 1/3 year cycles being very strong and 1/4 and 1/5 also showing. Other cycles are present, but these are more easily studied after removing the strong seasonal cycles.

The following graph therefore shows the spectrum of (Indian monthly rainfall)^0.5 with seasonal variations removed:

There are some long cycles present, namely 19 years, 10 years, 7.0 years, and 3.86 years. Of these we might suspect that the 19 year cycle is related to any of several lunar cycles that affects ocean and atmospheric tides.

Of seven strong shorter cycles, four have been marked with green triangles at the exact locations of harmonics in repeated 2:1 ratios. The periods found were 627, 303.5, 153.0 and 75.75 days. Each is rather close to half of the previous one. Not only that, but these cycles have very similar periods to a series of cycles found in solar activity and reported extensively in peer reviewed journals. The most commonly reported one of these cycles is generally called the 154 day cycle (or sometimes from 150 to 160 days) and it is noted that the relationship of 308 – 154 – 77 days and 103 – 52 – 26 days are all present in a variety of solar phenomena. Indeed, the 26 day period is the solar siderial rotation period which we see as 28 days because the earth is moving around the Sun a little each solar rotation.

For more about these solar cycles please see:


About Ray Tomes

Ray's career was in computer software development including system software design, economic modeling, investments. He spent 15 years full time on cycles research and has spoken on cycles and related topics at conferences and seminars around the world. He retired at age 42 to study cycles full time and work out “The Formula for the Universe” and as a result developed the Harmonics Theory as an explanation for observed patterns of cycles and structure of the Universe. His current project is the development of CATS (Cycles Analysis & Time Series) software, and collecting and organizing large quantities of time series data and analyzing this data to test and confirm Dewey's findings in an organized way. Interested in all aspects of cycles especially climate change and causes.
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One Response to Indian Monsoon Rainfall Shows Short Solar Cycles?

  1. shyam says:

    Sir, Cycles @ ~ 19, 10, 7 and 3 year in IInd fig in indian monsoon data shown by you concur well the sunspot’s MTM harmonic stpectral analysis as shown in Gupta (2010, cf. fig.6 G,J,K). I feel that monsoon rains are somehow relate to sunspot phenomenon on sub-decadel, decadal to cenetinial scale. shyam gupta

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