Post by missouriboy on Apr 26, 2021 17:06:17 GMT
We are starting to discuss North American drought and the on-going La Nina ENSO event. I gathered the US Palmer Drought Index data set by month and year since 1895, and plotted these against solar cycles and ENSO indexes. The two charts below show Spring (March-June) aggregated values classified as Very Dry and Very Wet in percentage of U.S. area.
Two general observations are apparent. First, major Spring drought years appear to be related to the onset on new solar cycles and La Nina events. There is one exception to this observation: the drought of 1910-11, which follows solar cycle 14. No obvious current explanation for this. Also, major spring droughts are sometimes 22 years apart (Hale Cycles), and sometimes 11 years apart (Schwabe Cycles). The later seems to occur in the transistion from weaker cycles to stronger cycles (SC16-SC17) and stronger cycles to weaker cycles (SC19-SC20). Another 11 year separation appears to be developing between SC24 and SC25. We will see how this shapes up. Note that the 2021 spring value is only based on March and partial April values. In most cases, major spring droughts seem to be associated with the onset of major La Nina events. Since Nina's of various strength seem to occur at the begining of every solar cycle, this relationship may be something of a chicken-egg situation.
Major Spring droughts have also affected different areas of the U.S. centering on the upper-central-west-midwest (1988), the Mid-west central and plains area (1934-37, 1956, 2012), and the SW US (developing 2021). This is not meant to be a comprehensive geographic analysis. That can follow.
Another observation that may provoke comments is that there seems to be an increase in "very wet" spring events covering larger areas of the US in recent decades.
Two general observations are apparent. First, major Spring drought years appear to be related to the onset on new solar cycles and La Nina events. There is one exception to this observation: the drought of 1910-11, which follows solar cycle 14. No obvious current explanation for this. Also, major spring droughts are sometimes 22 years apart (Hale Cycles), and sometimes 11 years apart (Schwabe Cycles). The later seems to occur in the transistion from weaker cycles to stronger cycles (SC16-SC17) and stronger cycles to weaker cycles (SC19-SC20). Another 11 year separation appears to be developing between SC24 and SC25. We will see how this shapes up. Note that the 2021 spring value is only based on March and partial April values. In most cases, major spring droughts seem to be associated with the onset of major La Nina events. Since Nina's of various strength seem to occur at the begining of every solar cycle, this relationship may be something of a chicken-egg situation.
Major Spring droughts have also affected different areas of the U.S. centering on the upper-central-west-midwest (1988), the Mid-west central and plains area (1934-37, 1956, 2012), and the SW US (developing 2021). This is not meant to be a comprehensive geographic analysis. That can follow.
Another observation that may provoke comments is that there seems to be an increase in "very wet" spring events covering larger areas of the US in recent decades.
