Statistical analysis of long-duration low-density solar wind events
Low solar wind density with long duration was measured by in situ observation between 11 and 12 May 1999. As a result of this low-density solar wind condition, the magnetosphere of the Earth expanded considerably. We used a database of one-hour-averaged solar wind (1963–1999) near 1 AU to determ...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2001-01-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/19/17/2001/angeo-19-17-2001.pdf |
| Summary: | Low solar wind density
with long duration was measured by in situ observation between 11 and 12 May
1999. As a result of this low-density solar wind condition, the magnetosphere of
the Earth expanded considerably. We used a database of one-hour-averaged solar
wind (1963–1999) near 1 AU to determine whether or not the observed
low-density event was extremely abnormal. As a result it was found that this
event has the longest duration in approximately 36 years of solar wind
observations. There are three events with density 0.5 cm<sup>-3</sup> or less and
duration ten hours or longer. They were observed on 4 and 31 July 1979, and 11–12
May 1999. The 4 July 1979 event recurred on 31 July 1979. The events were
characterized by low-beta, low Alfven Mach number (<i>M<sub>A</sub></i><sub> </sub> ), and low dynamic
pressure. The occurrence rate of low-density solar wind with density 0.5 cm<sup>-3
</sup>
or less shows several peaks near solar maxima. However, it is difficult to find
a clear relationship between the sunspot number and the occurrence rate.<br><br><b>Key words. </b>Interplanetary physics (flare and stream
dynamics; solar wind plasma; sources of the solar wind) |
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| ISSN: | 0992-7689 1432-0576 |