On the decadal to multi-decadal evolution and correlations of geomagnetic indices in relation to variations in solar activity

Details On the decadal to multi-decadal evolution and correlations of geomagnetic indices in relation to variations in solar activity On the decadal to multi-decadal evolution and correlations of geomagnetic indices in relation to variations in solar activity

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm51c2105l&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SM51C-2105

Astronomy and Astrophysics

Astrophysics

[1530] Geomagnetism And Paleomagnetism / Rapid Time Variations, [7524] Solar Physics, Astrophysics, And Astronomy / Magnetic Fields, [7536] Solar Physics, Astrophysics, And Astronomy / Solar Activity Cycle, [7537] Solar Physics, Astrophysics, And Astronomy / Solar And Stellar Variability

Scientific paper

Magnetic indices measure magnetic activity occurring over periods of time from minutes to hours, as recorded at geomagnetic observatories. They address in principle specific features of geomagnetic activity, with an origin in Earth's ionosphere or magnetosphere. In the present study, we use daily indices, which can be arranged in two classes: roughly speaking, some reflect properties of magnetic field disturbances integrated over one day (1st family or A-type), whereas others reflect the maximal values of these disturbances (ranges) for that day (2nd family or B type). We analyze correlations between the evolutions of classical (daily) indices aa, Ap (B-type) and Dst and recently introduced absolute 3-day slopes ζ (A-type) at decadal time scales. Pairs of indices (aa and Ap on one hand, Dst and ζ on the other hand) display decade-long periods of high correlation interrupted by shorter periods of reduced correlation and even anti-correlation. Decadal variations of mutual correlation between A and B-type indices are governed by solar cycle evolution. Loss of correlation between geomagnetic indices coincides with loss of correlation between geomagnetic indices and solar activity. In the past half-century, such sharp losses have occurred in the declining phases and minima of solar cycles 20 and 23. Differences between these two solar cycles in terms of correlation properties of geomagnetic indices will be briefly discussed.

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