1. Monday Seminar Talk (short) 17 November, 2003 Taro Morimoto

2. Abstract The solar polarity reversal The cessation of high latitude CMEs Close Relationship - based on the observations for cycles 21 & 23. The polar crown filaments need to be removed before the poles could acquire open field structure of the opposite polarity. Because :

3. Introduction Disappearance and reformation of polar coronal holes. (Webb, Davis & McIntosh 1984; Bilenko 2002; Harvey & Recely 2002) Disappearance of polar crown filaments (PCF). (Waldmeier 1960; Makarov, Tlatov & Sivaraman 2001) Goplaswamy et al.(2003) Prominence eruptions at high latitudes subsided around the time of the polarity reversals. (From SOHO/LASCO & NoRH observations)

4. Introduction Using CME data of cycles 21 & 23, they tested how CMEs are intimately connected to the mechanism of polarity reversal. Data 21 CME Solwind 23SOHO/LASCO Prominence Eruption (PE) Nobeyama radio heliograph Kitt Peak magnetograph measurements for polar region magnetic field strength

5. PE and CMEs epochs of cessation of HL activity (north; : south) HCS Max. excursions of heliospheric current sheet. (from Wilcox Obs.) North-south asymmetry in the high latitude (HL) activities.

6. CME occurence rate HL : High Latitude ( ≧ 60°) [PCF-related = 1159 CMEs] LL : Low Latitude ( ≦ 40°) [AR-related = 4607 CMEs] SSN: daily Sun Spot Number CME peak SSN peak

7. Cycle 23 01 33 33 05 10 0310 month: North South Northern HL(NHL) HL CME peak mid/99 A rapid increase 03/00 – 09/00 A broad maximum Polar field reversal: 10/00 from data 02/01 (Bilenko 2002) 05/01 (Durrant & Wilson 2003) PCF disappearance 10/00 (Harvey & Recely 2002; Lorenc, Pasorek & Rybansky 2003; Gopalswamy et al. 2003) Disappearance of PCF

8. Cycle 23 01 33 33 05 10 0310 month: North South Southern HL(SHL) HL CME peak mid/99 – 03/02 Polar field reversal: 05/01 from data 09/01 (Durrant & Wilson 2003) 01/02 (Bilenko 2002) PCL disappearance 02/02 (Lorenc et al. 2003) 04/02 (Harvey & Recely 2002) Disappearance of PCF

9. Cycle 21 33 33 North South Northern HL(NHL) Disappearance of PCF Polar field reversal: 02/82- 03/82 (Webb et al.1984) 09/80 & 07/82 from data. PCL disappearance ① Webb et al. 1984 ② Lorenc et al. 2003 ① ② HL CME peak light blue shadow region

10. Cycle 21 33 33 North South Southern HL(SHL) Disappearance of PCF Polar field reversal: 09/80 (Webb et al. 1984) 02/83 from data. PCL disappearance ① Webb et al. 1984 ② Lorenc et al. 2003 ① ② HL CME peak (pink shadow region)

11. Summary The epochs of solar polar reversal are closely related to the cessation of HL CME activities. Before the completion of the reversal, several temporary reversals take place with corresponding spikes in the HL CME rates. The North-South asymmetry of the polarity reversal time and HL activity is of high importance. The CME process helps the closed field lines overlying PCFs become open to complete the polarity reversal. (c.f.: Low (1997))