Heading into Solar Minimum what can we expect?
Evidence of a 22-year Rhythm of Drought in the Western United States Related to the Hale Solar Cycle since the 17th Century
Abstract
Families of Drought Area Indices (DAI) have been derived from tree-ring data for the entire U.S. west of the Mississippi River, for each year back to either 1700 or 1600 A.D., depending on the data base used. Each DAI is expressed in terms of the relative area in which the Palmer Drought Severity Index (PDSI) lies below a specified threshold value between −1 (mild drought) and −4 (extreme drought). Three families of DAI are considered in the analysis reported in this paper. Each DAI family is based on reconstructions from a selection of between 40 and 65 tree-ring sites ranging from Canada to Mexico and from the west coast to the Plains states. Variance spectrum analysis of the DAI series shows a concentration of variance at periods near 22 yr, at significance levels ranging from 5 to 0.1% (relative to a pink noise continuum). Band-pass filters tuned to periods near 22 yr are used in a form of harmonic dial analysis proposed by G. W. Brier to verify the extent of phase locking between the drought area variations and the Hale sunspot cycle since 1700 A.D. Phase locking is confirmed at significance levels of order 1 to 0.1% for all DAI families and all drought severity limits except extreme drought (PDSI < −4). A tendency is found for the amplitude of the 22 yr drought rhythm to vary systematically in parallel with the amplitude (envelope) of the Hale sunspot cycle, on the Gleissberg time scale of about 90 yr. This relationship is statistically significant between the 5 and 1% levels, and is independent of the phase locking found within the Hale cycle. The DAI series that extend back to 1600 A.D. reflect a well-defined 22 yr drought rhythm during the early stages of the Maunder Minimum of solar activity, but a very weak rhythm near the end of the Maunder Minimum. The average areal extent of drought was relatively low, and remained low for a prolonged period, during the Maunder Minimum. This analysis strongly supports earlier evidence of a 22 yr drought rhythm, or “cycle,” in the U.S. and suggests that the drought rhythm is in some manner controlled by long-term solar variability directly or indirectly related to solar magnetic effects. The solar control is best described as a modulation of terrestrial drought-inducing mechanisms, such that it alternately encourages and discourages the development of major continental droughts which are set up by evolutionary climatic processes unrelated to solar activity.
https://pageone.springer.com/pdf/preview/10.1007/978-94-009-9428-7_13
Evidence of a 22-year Rhythm of Drought in the Western United States Related to the Hale Solar Cycle since the 17th Century
Abstract
Families of Drought Area Indices (DAI) have been derived from tree-ring data for the entire U.S. west of the Mississippi River, for each year back to either 1700 or 1600 A.D., depending on the data base used. Each DAI is expressed in terms of the relative area in which the Palmer Drought Severity Index (PDSI) lies below a specified threshold value between −1 (mild drought) and −4 (extreme drought). Three families of DAI are considered in the analysis reported in this paper. Each DAI family is based on reconstructions from a selection of between 40 and 65 tree-ring sites ranging from Canada to Mexico and from the west coast to the Plains states. Variance spectrum analysis of the DAI series shows a concentration of variance at periods near 22 yr, at significance levels ranging from 5 to 0.1% (relative to a pink noise continuum). Band-pass filters tuned to periods near 22 yr are used in a form of harmonic dial analysis proposed by G. W. Brier to verify the extent of phase locking between the drought area variations and the Hale sunspot cycle since 1700 A.D. Phase locking is confirmed at significance levels of order 1 to 0.1% for all DAI families and all drought severity limits except extreme drought (PDSI < −4). A tendency is found for the amplitude of the 22 yr drought rhythm to vary systematically in parallel with the amplitude (envelope) of the Hale sunspot cycle, on the Gleissberg time scale of about 90 yr. This relationship is statistically significant between the 5 and 1% levels, and is independent of the phase locking found within the Hale cycle. The DAI series that extend back to 1600 A.D. reflect a well-defined 22 yr drought rhythm during the early stages of the Maunder Minimum of solar activity, but a very weak rhythm near the end of the Maunder Minimum. The average areal extent of drought was relatively low, and remained low for a prolonged period, during the Maunder Minimum. This analysis strongly supports earlier evidence of a 22 yr drought rhythm, or “cycle,” in the U.S. and suggests that the drought rhythm is in some manner controlled by long-term solar variability directly or indirectly related to solar magnetic effects. The solar control is best described as a modulation of terrestrial drought-inducing mechanisms, such that it alternately encourages and discourages the development of major continental droughts which are set up by evolutionary climatic processes unrelated to solar activity.
https://pageone.springer.com/pdf/preview/10.1007/978-94-009-9428-7_13