Publisher： John Wiley & Sons Inc
E-ISSN： 2169-9402|120|4|2662-2674
ISSN： 2169-9380
Source： JOURNAL OF GEOPHYSICAL RESEARCH: SPACE PHYSICS, Vol.120, Iss.4, 2015-04, pp. : 2662-2674
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Abstract
AbstractWe investigate geomagnetic activity at two high‐latitude, two midlatitude, and two low‐latitude stations of the northern hemisphere and find that the increasing trend of geomagnetic activity in 1914–2000 is considerably lower at the two midlatitude stations (Niemegk and Fredericksburg) than at low‐ or high‐latitude stations. As Niemegk occupies a specific position among geomagnetic stations, serving as the standard station for the K/Ak index derivation, it is crucial to understand the origin and long‐term characteristics of this difference. We show here that geomagnetic activity at the studied midlatitude stations is relatively stronger in the declining phases of the 1 and 2 first solar cycles (15 and 16) than elsewhere, leading to the smaller long‐term trend. We also find that the latitudinal differences in the trends are strongly dependent on local time, being considerably larger in the dawn sector. These differences can be explained by the relatively stronger contribution of high‐speed streams to geomagnetic activity at the particular range of midlatitudes, compared to the stations at lower and higher latitudes.
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JOURNAL OF GEOPHYSICAL RESEARCH: SPACE PHYSICS, Vol. 120, Iss. 4, 2015-04 ,pp. :
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