Solar Wind Interaction and Orthogonal Magnetospheric Indices
Abstract
Multivariate methods can help to untangle connections between indices of magnetospheric activity and solar wind (SW) parameters. The data are 3-hour resolution time series spanning the period 1996 JAN 25 to 2004 SEP 17. The time series include Kp, the Dst and PC (polar cap) indices and an auroral POES index derived from NOAA satellite observations, plus OMNI SW data. The Kp index correlates with many other indices of magnetospheric activity due to its association with the convection electric field (see the survey in Thomsen 2004). We find correlation coefficients C(Kp,PC)=0.57, C(Dst,Kp)=-0.44 and C(Dst,PC)=-0.37. POES correlations are small. We replace PC with a variable PC/Kp containing that part of PC orthogonal to Kp. Likewise we replace Dst with Dst/KpPC, orthogonal to both Kp and to PC/Kp. The independent indices behave very differently from the original ones. Factor analysis gives five latent factor modes relating the terrestrial and SW sets. (1) The only factor containing the solar cycle connects sunspot number fluctuations to POES and PC/Kp only. This is the only factor containing POES or PC/Kp, so these vary mainly together. (2) Only one factor contains the south IMF, and this connects its fluctuations to Kp only. (3) A third factor relates strong responses in Dst/KpPC to increases in SW ram pressure, temperature and to alpha/proton ratio, an indicator of solar ejecta in the SW. (4) A fourth factor relates strong responses in Dst/KpPC to increases in excess SW coolness, another indicator of solar ejecta, along with drops in mean IMF, SW ram pressure and plasma beta. (5) The fifth factor relates increases in Kp to increased mean IMF, SW speed, coolness and plasma beta. We present a path analysis calculation quantifying the web of causal relations between the SW and the independent terrestrial indices via the intermediate latent factors. Thomsen, M.F. 2004, Space Weather, 2, S11004, doi:10.1029/2004SW000089
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFMSM43A1214L
- Keywords:
-
- 2784 Solar wind/magnetosphere interactions;
- 2788 Magnetic storms and substorms (7954);
- 3235 Persistence;
- memory;
- correlations;
- clustering (3265;
- 7857);
- 3270 Time series analysis (1872;
- 4277;
- 4475);
- 7974 Solar effects