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Some Documented Solar Influences on Weather

By Joe D'Aleo
Monday, July 13, 2009

In a
number of posts this last year, we have addressed the unusually long and quiet solar cycles. A few weeks back, we noted the sunspot minimum seemed at hand as the month of June started with a series of cycle 24 sunspots and it appeared we would exceed the monthly sunspot number of 3.3 necessary to make the sunspot minimum (the lowest value in 13 month average) November 2008.

Well June despite numerous other small microdots characteristic of this cycle ended up with a monthly average of 2.6 which allowed December to drop from the 1.8 to 1.7 making December the earliest candidate for solar minimum.  July would have to average below 3.5 in order for the minimum to move to January. It is unlikely to move to February as the month August would have to average below 0.5, the number in the month it will replace.   


December had a 13 month average sunspot number of 1.7. Only three minima since 1750 had official minima below 1.7 (1913 1.5, 1810 0, 1823 0.1). Of course modern measurement technologies are better than older technologies so there is some uncertainty as to whether microdots back then would have been seen.


In a post Mt, Redoubt, a Quiet Sun and Your Morning Coffee, we showed how the solar cycle seems to have an influence on world production and spot market prices of coffee likely by influencing weather in the tropical growing areas.




Lower solar activity has a significant correlation with drought in Argentina. The last two years have seen a devastating drought in that country with major impact on winter wheat, corn and beans.  This year’s drought is expected to produce lowest winter wheat yields in two decades.


You can see the drought reflected in the satellite derived vegetation index (NDVI) (Source USDA Spot NDVI) which is a measure of the health of vegetation. The recent NDVI for South America is shown below. Note how the drought has extended into southern Brazil at times (Rio Grande do Sul) although recent rains have helped recharge soil moisture there. You can compare the NDVI with the correlation of precipitation rate with solar flux (Source NOAA CDC).



In that recent story, mentioned above, we showed how high latitude volcanoes, El Ninos and low solar activity can negatively impact tropical monsoon in places like India

R. S. Reddy, V. R. Neralla and W. L. Godson did a  study is to examine critically the relationship between solar cycles and Indian monsoon rainfall, for the period 1871–1984, and to search for significant periodicities, by utilizing the maximum entropy spectral technique (MEST). The results of this study using MEST showed clearly a significant 11-year cycle in solar activity and rainfall.

Last year an erratic monsoon affected coffee and other crops in India, this year as of the end of June, India had had just 54% of its normal rainfall. Though showers were moving north, they were producing less rain than in a good year. You can see the current NDVI relative to the 5 year average.

Compare that to the CDC anomaly of annual rainfall correlation to solar flux. Yellow and orange areas have a tendency to be below normal in low solar years. These are not strong correlations because the solar factor sometimes runs counter to other factors like ENSO.



Hydrologist Dr. Will Alexander found in a multi-author study in the Journal of the South African Institution of Civil Engineering, a strong correlation of rainfall and river flow in the Vaal River. He showed a deficit in the three years leading up the minimum and heavy rainfall in the three years following.

In all but one sequence (Vaal River 1965/66, data not available), the three-year totals after the minima of both river flow and sunspot numbers, are substantially greater than the three-year totals before the minima. This information demonstrates the close association between major variations in river flow and corresponding variations in sunspot activity, with a high degree of confidence.


There are several interesting features in this table. There is an almost three-fold, sudden increase in the annual flows in the Vaal River from the three previous years to the three subsequent years. This is directly associated with a six-fold increase in sunspot numbers. The second important point is the consistency in the range of sunspot numbers before and after the reversal. The totals for the three prior years varied between 25 and 60, and the totals of the three immediately subsequent years varied between 250 and 400. It is very clear that these are systematic changes associated with the sunspot minima, and are not random events. (Journal of the South African Institution of Civil Engineering • Volume 49 Number 2 June 2007)


Given this study, one should expect the upcoming three years to be wet as we come off the protracted minimum.




Karin Labitzke of the University of Berlin has done a lot of wok showing major differences in low and mid latitudes of temperatures and pressure/heights from the stratosphere down to the middle troposphere. This chart below from one of her studies shows the differences of the annual means.


It shows higher temperatures and heights during solar maximum years versus solar minimum. She used solar flux which relates to ultraviolet radiation which increases 6 to 8% over the 11 year cycle compared to 0.1 in the visible part of the spectrum.



This was clearly seen in the winter of 2001/02, when a strong second solar maximum caused significant low and middle latitude warming and a shrinking of the polar vortex.




Shindell et al NASS GISS (1999) showed results from a global climate model including ozone and UV found UV induced stratospheric ozone changes and generated heat that penetrates into the troposphere, in effect confirming Labitzke’s findings. He used it to show the likely pattern during the little ice age.