Dr. Tamao’s contribution to studies of geomagnetic sudden commencement T. Araki [Tamao Workshop, Fukuoka, ]

SC : June 24, 1885 [Adams, 1892] Brown : Europe Green : Asia- Oceania Blue : America SC simultaneous occurrence of SC : long lasting problem EM wave : not well recognized ( : Marconi experiments)

Four wave forms of SC [around 1950]

Equivalent current system for PI （ Prelminary Impulse) of SC [Nagata & Abe, 1955] PRI PPI No equatorial stations. No concept of FAC/magnetosphere at that time. 1st pulse : 2nd pulse:

[Obayashi & Jacobs, 1957] Mathematical decomposition but suggests essential features of SC

Relationship between equatorial & high latitude PRI : not known

Wilson, C.R., and M. Sugiura ; Hydromagnetic interpretation of sudden commencements of magnetic storms. Nishida, A. ; Ionospheric screening effect and storm sudden commencements. Tamao, T. ; 1964 Hydromagnetic interpretation of geomagnetic ssc*. (based on 3D structure of HM waves) Papers on physics of SC : 1960’s

Model of high latitude PI (Preliminary Impulse) of SC [Tamao, 1964]

Mechanism of equatorial PRIs of SC [Tamao, 1964] When the westward electric field of CT-mode penetrates to the ionosphere near the magnetic equator, the westward electrojet current will flow within the narrow belt around the equator in the day time. Therefore, variations of the horizontal intensity of the geomagnetic field near the equator will be a sum of increase associated with the isotropic mode and decrease due to this westward electrojet. If the latter contribution predominates, PRI will be also observed near the dip equator.

PRIs are detected in afternoon high latitudes and the dayside equator but disappear in low latitudes (10-20 deg ．）. Should we consider different mechanisms for each of high latitude and equatorial PRIs? It was important to check the relationship between the high latitude and equatorial PRI. Problems to be answered

Equivalent current system for PI one-to-one correspondence of equatorial and high lat. PRI

Equivalent current system for PI (= PRI+PPI) Equatorial PRI  extension of afternoon current vortex

[Han et al.,2007] PI MI Detection of ionospheric currents for PI and MI near the dip equator PI MI

Essentially important points in consideration of SC 1. Wide source area, 2. Long wave length, 3. Super position of sub-fields.

１． The source of SC distributes on a wide geo-effective area of the magnetopause （ It is not a point source ）. The IP shock/discon. sweeps this geo-effective length, L, emitting disturbances of SC. The rise time, ΔT, of SC is determined mainly by sweeping time of shocks over the geo-effective length. ΔT ≈ L/V shock L ≈ 30 Re

２ ． SC has a large wave length (λ) If we take, ΔT (rise time of SC) ~ 200 sec, V (magnetospheric wave vel.) ~ 600 km/s, then λ ~ 4*V*ΔT ~ 1.2*10**5 ~ 72Re >> size of the dayside magnetosphere, size of the source region. That is, we observe SCs in a distance less than one wave length from the source. It means “near field dominates over the wave field” Static calculations work effectively.

3. It is essential to decompose the SC-field into DL- and DP-subfield. D sc = DL (stepwise increase ) + DP (t wo pulse structure ) = DL + DP pi ( 1 st pulse )+ DP mi(2 nd pulse ) pi : preliminary impulse mi : main impulse Characteristics of SC (onset time, rise time, amplitude, ---) can not be interpreted without this superposition.

Aurora and ionospheric convection during SC [Liu et al., 2010] PI MI

Contribution of Aikitu Tanakadate ( ） 1892 – Initiated : Geomagnetic observations in Japan by Mascart self-recording magnetometers (France) Joined in “International simultaneous special observation of Earth’s magnetism” 1903 International Association of Geodesy (IAG  IUGG) General Assembly (Copenhagen): Proposed : Observations of geomag. rapid variations 1919 International Geodetic and Geophysical Union (IGGU) Chairman : Section of Terr. Mag. and Electricity (STME  IAGA ） 1924 STME Meetig (Madrid) Chairman : Special Committee for SC ．

Aikitu Tanakadate ( ）