Samsonov, A;
Bogdanova, Y;
Branduardi Raymont, G;
Safrankova, J;
Nemecek, Z;
Park, J-S;
(2019)
Long-term variations in solar wind parameters, magnetopause location, and geomagnetic activity over the last five solar cycles.
Journal of Geophysical Research: Space Physics
, 124
(6)
pp. 4049-4063.
10.1029/2018JA026355.
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Abstract
We use both solar wind observations and empirical magnetopause models to reconstruct time series of the magnetopause standoff distance for nearly five solar cycles. Since the average annual interplanetary magnetic field (IMF) Bz is about zero, and the annual IMF cone angle varies between 54.0° and 61.2°, the magnetopause standoff distance on this time scale depends mostly on the solar wind dynamic pressure. The annual IMF magnitude well correlates with the sunspot number (SSN) with a zero time lag, while the annual solar wind dynamic pressure (Pdyn) correlates reasonably well with the SSN but with 3 years time lag. At the same time, we find an anticorrelation between Pdyn and SSN in cycles 20–21 and a correlation in cycles 22–24 with 2 years time lag. Both the annual solar wind density and velocity well correlate with the dynamic pressure, but the correlation coefficient is higher for density than for velocity. The 11‐year solar cycles in the dynamic pressure variations are superimposed by an increasing trend before 1991 and a decreasing trend between 1991 and 2009. The average annual solar wind dynamic pressure decreases by a factor of three from 1991 to 2009. Correspondingly, the predicted standoff distance in Lin et al.’s (2010) magnetopause model increases from 9.7 RE in 1991 to 11.6 RE in 2009. The annual SSN, IMF magnitude and magnetospheric geomagnetic activity indices display the same trends as the dynamic pressure. We calculate extreme solar wind parameters and magnetopause standoff distance in each year using daily values and find that both extremely small and large standoff distances during a solar cycle preferably occur at solar maximum r0061ther than at solar minimum.
| Type: | Article |
|---|---|
| Title: | Long-term variations in solar wind parameters, magnetopause location, and geomagnetic activity over the last five solar cycles |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1029/2018JA026355 |
| Publisher version: | https://doi.org/10.1029/2018JA026355 |
| Language: | English |
| Additional information: | This is the published version of record. For information on re-use, please refer to the publisher’s terms and conditions. |
| Keywords: | Magnetopause model, Solar cycle, Solar wind dynamic pressure |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10073175 |
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