ON THE RELATIONSHIP BETWEEN SOLAR WIND CHARACTERISTICS AND GEOMAGNETIC ACTIVITY

1. Workshop & Plasma Physics School, Sozopol, 31 Aug. - 7 Sep. 2008 ON THE RELATIONSHIP BETWEEN SOLAR WIND CHARACTERISTICS AND GEOMAGNETIC ACTIVITY Cristina Pirvutoiu Dan Nicolae Vladoiu

2. Workshop & Plasma Physics School, Sozopol, 31 Aug. - 7 Sep. 2008 OUTLINE • Solar Activity • Solar Cycles (by sunspot relative numbers); • High Speed Streams in the Solar Wind • Geomagnetic Activity • Aa and Ap indices • Solar and Geomagnetic Variability • Correlation coefficients; • Spectral Analysis • Conclusions

3. Workshop & Plasma Physics School, Sozopol, 31 Aug. - 7 Sep. 2008 Sunspots The 11 years cycle: • Characteristics: minimum, ascendent, maximum, descendent • The switch of the magnetic field in the maximum phase  inverse dipole in the new cycle W=k(10g+s)‏ The 11-years cycle (Schwabe) ‏ The 22 years cycle (Magnetic Cycle or Hale Cycle) : a pair of 11-years cycles “even+odd’’ in which the first one has a smaller intensity The pair ’’22+23’’ is an exception !

4. HSSs Sources and Parameters • SOLAR SOURCES OF THE HSSs: • Coronal holes: CH_HSSs • Solar flares (and/or other eruptive solar events): FG_HSSs • HSS PARAMETERS: • HSS duration–d (days); • HSS maximum velocity–Vmax (km/sec); • HSS velocity gradient–Vmax= Vmax- Vo; • HSS importance (intensity)–I = Vmax× d The I parameter used in this paper: the monthly values, I , of all HSSs, FG_HHSs, CH_HSSs that were registered during a month. The average monthly values : I=I / no. of event. The same average monthly values were calculated for the other parameters.

5. Workshop & Plasma Physics School, Sozopol, 31 Aug. - 7 Sep. 2008 The HSS intensity during the SC 20-23 interval • In the first 63 months of SC 23 a high number of CHs (494) was reported in comparison with only 274 for SC 22 and ~192 CHs in CS 21  an excess of HSSs and large values for their intensity (down, left panel) in SC 23; • There were reported strong flares in SC 23 (2000 – 2001) and also during the descendant phase (2003 – 2005) which determined high values of the intensity for FG_HSSs (upper, right panel)

6. Workshop & Plasma Physics School, Sozopol, 31 Aug. - 7 Sep. 2008 The solar and geomagnetic activity

7. Workshop & Plasma Physics School, Sozopol, 31 Aug. - 7 Sep. 2008 The connection between Aa and I_HSS during SCs 20-23 (monthly values) ‏ The correlation coefficient between Aa and I_HSS (1964-2007, SC 20 – 23): r = 0,31

8. Workshop & Plasma Physics School, Sozopol, 31 Aug. - 7 Sep. 2008 The connection between Aa and I_HSS during SCs 20-23 (2) SC 23, r = SC 23, r = 0.47 SC 20, r = 0,53 The correlation coefficient between Aa si I_HSS SC 21, 1976 – 1986: r = 0,42 SC 22, 1986 – 1996: r = 0,17 SC 23, 1996 – 2007 (?): r = 0,46

9. Workshop & Plasma Physics School, Sozopol, 31 Aug. - 7 Sep. 2008 The connection between Aa and solar wind velocity during SCs 20-23 (3-hour values) • A more detailed study: the 3-hour values of the Aa index and solar wind speed were used for a correlation analysis during SC 23 (for this interval there are the best registrations of the solar wind outside of the terrestrial magnetosphere – SOHO and ACE missions, orbiting around the Lagrangean point L1 at ~ 1,500,000 km from the Earth to the Sun): r0 = 0.47; r1= 0.42; r2 = 0.36 • This means that 3 hours are enough time for the solar wind plasma to induce some disturbances into geomagnetic field. The correlation coefficient is practically equal to that between the monthly values of the Aa and I_HSS during SC 23 that proves once more the geoeffectivity of the high energy (high speed) solar wind.

10. Workshop & Plasma Physics School, Sozopol, 31 Aug. - 7 Sep. 2008 Spectral Analysis of the Aa index and I_HSS • We have represented the Fourier Spectra of the Aa and I_HSS (all HSSs) monthly value series for 1964 - 2007 period (SCs 20-23); • Although the series are relatively short, we could notify some common periodicities, namely: • ~6 months and 8 months (under one year ); • ~ 12 months  one year; • 20.1 months  it is near quasi-biannual periodicity found in many solar and terrestrial variability; • 47.6 months for I_HSS and 43.6 & 52.4 for Aa  near four years.

11. Workshop & Plasma Physics School, Sozopol, 31 Aug. - 7 Sep. 2008 CONCLUSIONS • The higher value of the intensity of HSSs in the 23rd cycle compared with the precedent cycles does not revel a better correlation with the geomagnetic index Aa ; • The pair of SCs 22+23, does not respect the general rule of magnetic cycles: the intensity of the even cycle is grater then the odd one. The atypical behaviour may reside in the low geoefectivity of solar streams for the 22 cycle. It is worth to notify that during SC 22 there are a lot of gaps in the solar wind velocity registration that made often impossible to determine HSSs; • The correlation analysis on the monthly values of Aa and I-HSS shows relative small correlation coefficients we did not take into consideration the magnetic field polarity of the wind plasma (the polarity of the interplanetary magnetic sector); • The correlation between Aa and solar wind velocity (3-hours values) shows the same degree of dependence between solar wind plasma and geomagnetic variability; • The spectral analysis of the Aa index and I_HSS put in evidence some common periods of variability: about one half of year, one year, quasi-biannual period and, about four years.

12. Workshop & Plasma Physics School, Sozopol, 31 Aug. - 7 Sep. 2008 THANK YOU FOR YOUR ATTENTION!