During southward the interplanetary magnetic field(IMF) period, the magnetic reconnection can take place. It often happens when the solar activity is high, particularly after a solar flare or CME happens. Through the magnetic reconnection, the solar wind and the Earth's magnetosphere interact. As a ...
During southward the interplanetary magnetic field(IMF) period, the magnetic reconnection can take place. It often happens when the solar activity is high, particularly after a solar flare or CME happens. Through the magnetic reconnection, the solar wind and the Earth's magnetosphere interact. As a result, the magnetic storm and the substorm frequently occur. In addition to energy input from the Earth's magnetosphere during the magnetic storm, the ionospheric electric density and the composition and circulation of the thermosphere change. In this paper, we investigate the response of the Earth's magnetosphere and ionosphere to solar activity. In Chapter Ⅱ, attempts to show how the geomagnetic indices, AU, AL and Dst, respond to the interplanetary parameters, more specifically, the solar wind electric field VBz during southward IMF period. The AU index does not seem to respond linearly to the variation of southward IMF. Only a noticeable correlation between the AU and VBz is shown during summer, when the ionospheric conductivity associated with the solar EUV radiation is high. Thus, one should be very cautious in employing the AU as a convection index during other seasons. The AL index shows a significantly high correlation with VBz regardless of season. Considering that the auroral electrojet is the combined result of electric field and ionospheric conductivity, this suggests that the AL index behaves more like a convection index rather than a substorm index as far as hourly mean AL index is concerned. As expected, the Dst index tends to become more negative as VBz gets intensified. However, the Dst index (nT) is less than or equal to 15VBz (mV/m) + 50(Bz 0.5 mV/m and Q (nT/h) = 0 for VBs ≤ 0.5 mV/m. The (hour) is estimated as 0.060Dst* + 16.65 for Dst* > -175 nT and 6.15 hours for Dst* ≤ -175 nT. Based on these empirical relationships, we predict the 60 magnetic storms and find that the correlation coefficient between the observed and predicted Dst* is 0.88. Our model is slightly improved over the other two models(Burton et al. (1975) and O'Brein & McPherron (2000a)) as far as the correlation coefficients is concerned. Particularly our model does a better job than the other two models in predicting intense magnetic storms(Dst* ≤ -200 nT). In Chapter Ⅳ, we examine the ionospheric F2-layer electron density variation by solar activity in middle latitude by using foF2 observed at the Kokubunji ionosonde station in Japan for the period from 1997 to 2008. The semi-annual variation of foF2 shows obviously in high solar activity(2000-2002) than low solar activity(2006-2008). It seems that variation of geomagnetic activity by solar activity influences on the semi-annual variation of the ionospheric F2-layer electron density. According to the Lomb-Scargle periodogram analysis of foF2 and Ap index, IMF Bs, solar wind speed, solar wind number density and flow pressure which influence the geomagnetic activity, we find that the semi-annual variation of daily foF2, Ap index and IMF Bs appear clearly during the high solar activity. It suggests that the semi-annual variation of geomagnetic activity, caused by Russell-McPherron effect, contributes greatly to the ionospheric F2-layer semi-annual electron density variation, except dynamical effects in the thermosphere. In Chapter Ⅴ, we investigate how the change of geomagnetic activity by season and latitude affects the ionospheric F2-layer electron density. First af all, two magnetic storms occurred in equinox(31 March 2001) and solstice(20 November 2003) are selected. Then we investigate foF2, which are observed at Kokubunji, Townsville, Brisbane, Canberra and Hobart, Dst index, Ap index, and AE index. Then, we investigate the relation between the foF2 by latitude and the [O]/[N2] ratio, which is observed TIMED/GUVI satellite, especially, during 19-22 November 2003. In addition, we consider TEC variations during the same period. As a result, the variation of [O]/[N2] ratio by latitude is closely related with the variation of foF2. This corresponds with the variation of TEC during same period. We find that the foF2 changes differently by latitude because of the variation of mean meridional circulation of the thermosphere, particularly upwelling and downwelling of neutral atmosphere.
During southward the interplanetary magnetic field(IMF) period, the magnetic reconnection can take place. It often happens when the solar activity is high, particularly after a solar flare or CME happens. Through the magnetic reconnection, the solar wind and the Earth's magnetosphere interact. As a result, the magnetic storm and the substorm frequently occur. In addition to energy input from the Earth's magnetosphere during the magnetic storm, the ionospheric electric density and the composition and circulation of the thermosphere change. In this paper, we investigate the response of the Earth's magnetosphere and ionosphere to solar activity. In Chapter Ⅱ, attempts to show how the geomagnetic indices, AU, AL and Dst, respond to the interplanetary parameters, more specifically, the solar wind electric field VBz during southward IMF period. The AU index does not seem to respond linearly to the variation of southward IMF. Only a noticeable correlation between the AU and VBz is shown during summer, when the ionospheric conductivity associated with the solar EUV radiation is high. Thus, one should be very cautious in employing the AU as a convection index during other seasons. The AL index shows a significantly high correlation with VBz regardless of season. Considering that the auroral electrojet is the combined result of electric field and ionospheric conductivity, this suggests that the AL index behaves more like a convection index rather than a substorm index as far as hourly mean AL index is concerned. As expected, the Dst index tends to become more negative as VBz gets intensified. However, the Dst index (nT) is less than or equal to 15VBz (mV/m) + 50(Bz 0.5 mV/m and Q (nT/h) = 0 for VBs ≤ 0.5 mV/m. The (hour) is estimated as 0.060Dst* + 16.65 for Dst* > -175 nT and 6.15 hours for Dst* ≤ -175 nT. Based on these empirical relationships, we predict the 60 magnetic storms and find that the correlation coefficient between the observed and predicted Dst* is 0.88. Our model is slightly improved over the other two models(Burton et al. (1975) and O'Brein & McPherron (2000a)) as far as the correlation coefficients is concerned. Particularly our model does a better job than the other two models in predicting intense magnetic storms(Dst* ≤ -200 nT). In Chapter Ⅳ, we examine the ionospheric F2-layer electron density variation by solar activity in middle latitude by using foF2 observed at the Kokubunji ionosonde station in Japan for the period from 1997 to 2008. The semi-annual variation of foF2 shows obviously in high solar activity(2000-2002) than low solar activity(2006-2008). It seems that variation of geomagnetic activity by solar activity influences on the semi-annual variation of the ionospheric F2-layer electron density. According to the Lomb-Scargle periodogram analysis of foF2 and Ap index, IMF Bs, solar wind speed, solar wind number density and flow pressure which influence the geomagnetic activity, we find that the semi-annual variation of daily foF2, Ap index and IMF Bs appear clearly during the high solar activity. It suggests that the semi-annual variation of geomagnetic activity, caused by Russell-McPherron effect, contributes greatly to the ionospheric F2-layer semi-annual electron density variation, except dynamical effects in the thermosphere. In Chapter Ⅴ, we investigate how the change of geomagnetic activity by season and latitude affects the ionospheric F2-layer electron density. First af all, two magnetic storms occurred in equinox(31 March 2001) and solstice(20 November 2003) are selected. Then we investigate foF2, which are observed at Kokubunji, Townsville, Brisbane, Canberra and Hobart, Dst index, Ap index, and AE index. Then, we investigate the relation between the foF2 by latitude and the [O]/[N2] ratio, which is observed TIMED/GUVI satellite, especially, during 19-22 November 2003. In addition, we consider TEC variations during the same period. As a result, the variation of [O]/[N2] ratio by latitude is closely related with the variation of foF2. This corresponds with the variation of TEC during same period. We find that the foF2 changes differently by latitude because of the variation of mean meridional circulation of the thermosphere, particularly upwelling and downwelling of neutral atmosphere.
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#태양풍 지자기 활동 지수 F2층 전자밀도
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