Swedish Institute of Space Physics, Kiruna (M.Yamauchi@irf.se) Singular years of high geomagnetic responses to the same solar wind input M. Yamauchi, B. Olsthoorn, G. Nicolaou Swedish Institute of Space Physics, Kiruna (M.Yamauchi@irf.se) Acknowledgement: Dst, Kp, AL, SYM/ASY, PC and sunspot numbers (RI) are are provided by World Data Center for Geomagnetism, Kyoto University, Japan, GFZ, Adolf-Schmidt-Observatory Niemegk, Germany, and the Royal Observatory of Belgium, Brussels. Including these indices, all data in hourly values are obtained from NASA-GSFC/SPDF through OMNIWeb (http://omniweb.gsfc.nasa.gov/ow.html). poster X4.95@ST4.1 (EGU2016-3482), Friday (2016-4-22) 1

Last year’s summary (hourly value) 1: Yamauchi (2015): doi:10.1186/s40623-015-0211-5 (open access) Geomagnetic activity for the same Akasofu ’ =VBtan2sin4(C/2) is not constant, i.e., smaller during 2005-2014 (x ~ cycle #24) than before (lines & o). The result the same if we use NP, PSW, EY=-VBZ, and d/dt = (V2Btansin4(C/2))2/3. 2

Last year’s summary (hourly value) 2: Spike years during declining phase (1974, 1983, 1994, 2003)  We need to examine with high-resolution data. Change from 2006 is more outstanding at equatorial stations (Dst) than auroral zone (AE)  M-I coupling auroral current system IS NOT the major cause. 3

Purpose and Method To examine the spiky variation in the Sun-Earth coupling efficiency, we obtain higher time resolution than 1 year. 3-months resolution (defined around equinox and solstice). ⇒ Can remove the effect of seasonal variation Use 5-min resolution data instead 1-hour resolution data, i.e., first calculate 5-min Akasofu ' (= VBtan2sin4(C/2)), and then take average to estimate “integrated input” for 60 min before (we also examined 40 min and instantaneous 5 min average, but the correlation is best for 60 min average) Examine AU, AL, SYM-H, and ASY-H (instead of Dst and Kp). Travel time from the spacecraft to the Earth is introduced (not in the last year’s work). 4

5

(since AU is mainly dayside event, Summer-Winter difference is strong 6

At mid-low latitude, the singular year effect diminished. The trend is also different from AL/AU. 7

Summary (1) AL and AU response to the same (and moderate) solar wind energy input occasionally increased beyond the seasonal variation for about half a year during the declining phase of solar cycles at 1994, 2003, and 2015 (Confirm 1-hour resolution result). (2) Excluding these singular years and seasonal variation, AL and AU response to the same (and moderate) solar wind energy input continuously decreased over the past three decades. (3) The singular year is not as clear for SYM-H/ASY-D as AL/AU (4) The 2009 dip (seen in AL/AU) is visible for SYM-H but not in ASY-D. ⇓ 8