Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsm22b..04h&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SM22B-04
Physics
1555 Time Variations: Diurnal To Secular, 2778 Ring Current, 2784 Solar Wind/Magnetosphere Interactions, 2788 Storms And Substorms
Scientific paper
In this presentation we examine systematic diurnal and seasonal variation of the Dst index. A part of this variation arises from geometrical differences in the Earth's and its magnetosphere's position in the heliosphere. Three such effects have been identified: the heliographic latitude of the Earth, the equinoctial effect and the Russell-McPherron effect. Besides these three external drivers a part of the observed variability arises from factors that are not directly related to magnetospheric activity. The locations of the Dst stations are one such factor. Differences in individual station properties, such as local ground conductivity structures resulting in differences in induction contributions, may lead to apparent diurnal variations in the Dst index. The asymmetric north-south distribution of the stations affects the seasonal variation pattern of the Dst index. To remove the internal effects and to estimate the relative importance of the three external drivers we have studied data from many magnetic observatories (including those used to compute the Dst index) over several solar cycles. From the Dst data for 1957-1999 we have identified more than 2000 magnetic storms and divided our data set into storm main phases, recovery phases and non-storm periods and examined the diurnal and seasonal variability of each of these data sets separately. The results indicate that the three external effects account for only about 50% of all daily and seasonal variation of the Dst index with Russell-McPherron effect as the leading external driver. For storm periods the Russell-McPherron effect is again the dominant effect while for non-storm periods all three effects are equally significant.
Häkkinen L. V.
Nevanlinna Heikki
Pirjola Risto J.
Pulkkinen Tuija I.
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