[1] An empirical model of the quiet daily geomagnetic field variation has been constructed based on geomagnetic data obtained from 21 stations along the 210 Magnetic Meridian of the Circum-pan Pacific Magnetometer Network (CPMN) from 1996 to 2007. Using the least squares fitting method for geomagnetically quiet days (Kp ≤ 2+), the quiet daily geomagnetic field variation at each station was described as a function of solar activity SA, day of year DOY, lunar age LA, and local time LT. After interpolation in latitude, the model can describe solar-activity dependence and seasonal dependence of solar quiet daily variations (S) and lunar quiet daily variations (L). We performed a spherical harmonic analysis (SHA) on these S and L variations to examine average characteristics of the equivalent external current systems. We found three particularly noteworthy results. First, the total current intensity of the S current system is largely controlled by solar activity while its focus position is not significantly affected by solar activity. Second, we found that seasonal variations of the S current intensity exhibit northsouth asymmetry; the current intensity of the northern vortex shows a prominent annual variation while the southern vortex shows a clear semi-annual variation as well as annual variation. Thirdly, we found that the total intensity of the L current system changes depending on solar activity and season; seasonal variations of the L current intensity show an enhancement during the December solstice, independent of the level of solar activity.

[1] The objective of this study is to understand better the propagation of Pi 2 waves in the nighttime region. We examined Pi 2 oscillations that showed high correlation between high-and low-latitude Magnetic Data Acquisition System/Circum Pan-Pacific Magnetometer Network stations (correlation coefficient: jgj ! 0.75). For each horizontal component (H and D) we examined the magnetic local time (MLT) dependence of the delay time of high-latitude Pi 2 oscillations that corresponds to the highest correlation with the low-latitude Pi 2 oscillation. We found the delay time of the high-latitude H showed remarkable MLT dependence, especially in the premidnight sector: we found that in the premidnight sector the high-latitude H oscillation tends to delay from the low-latitude oscillation (<100 s). On the other hand, the delay time of the high-latitude D oscillation was not significant ($±10 s) in the entire nighttime sector. We propose a Pi 2 propagation model to explain the observed delay time of high-correlation highlatitude H. The model quantitatively explains the trend of the event distribution. We also examined the spatial distribution of high-correlation Pi 2 events relative to the center of auroral breakups. It was found that the high-correlation Pi 2 events tend to occur away from the center of auroral breakups by more than 1.5 MLT. The present result suggests that the high-correlation H component Pi 2 oscillations at high latitude are a manifestation of forced Alfvén waves excited by fast magnetosonic waves.

[1] This paper describes ionospheric current systems associated with the counter-electrojet during sudden stratospheric warming (SSW) events in the northern winter months of 2001-2002 and 2002-2003. Magnetic data from 20 stations in the East Asian region, covering both the Northern Hemisphere and the Southern Hemisphere, are analyzed. Additional current systems that are superposed on the normal S q current system and related to the counter-electrojet during the SSW events show a global semidiurnal current pattern, which shifts to later local times approximately by 0.8 hour/day. The results indicate that abnormally large lunar tidal winds played a main role to produce the additional current system and counter-electrojet during the SSW events.

Abstract. To investigate the generation and propagation mechanisms of Pi 2 magnetic pulsations, we have analyzed magnetic field data t?om the 210 ø magnetic meridian (MM) stations. We used 50 Pi 2 events that were simultaneously observed at seven stations along the 210 ø MM during January 1995, and tbcused our analysis on associated magnetic energy, ((/X/--D2+(AD)2)/kt 0. The times when the amplitude of the magnetic energy attained the maximum (T,,,,x) were compared among these stations. We tbund that T,,,,,. has a latitudinal dependence. especially at highel' latitudes. which has not been previously reported. At Kotel'nyy (L=8.50) on the poleward side of the auroral region. T,,,,.,. occurred an average of 21 seconds earlier than T,,,,,. at Guam (L=I.01). and often as much as one minute earlier. The existence of latitudinal variation has implications tbr interpretation of issues related to timing of substorm onset; it is necessaD to consider the global t•atures of Pi 2 events in the study of auroral and magnetospheric substorms. We present ncx• 11ndings on the latitudinal dependence o1' Pi 2 energy translbr. especially at highel' latitudes and near the plasmapause. These findings can affect the interpretation of some results concerning substorm onset-timing issues. Statistical AnalysisThe magnetic pressure, or magnetic energy density, is defined as B-/2t, to. The magnetic energy carned by MHD waves is expressed by ((A/Dr+ (AD)2+ (ALD2)//a0 . That is, the variation of the magnetic energy is proportional to the squared amplitude of magnetic field variation. For Pi 2 events used in this paper, the contribution to the magnetic energy fi'om the Z component is small and negligible, and when the Z component has constant and significant contribution to the magnetic energy, the induction effect caused by ground conditions is considered. rather than the external source. Thus.•xe use ((_XH) 2 + (,_XD)2)//a0 as the estimate of variation in We note that the ZYK data had a timing error during Jan. -Mar. 1995. According to Kikuchi and Araki [1979]. the variation in the electric field accompanying a DP-2-type sudden commencement (sc) is transmitted instantaneously fi'om high latitude to the equator by Earth-ionosphere waveguide mode. Thus. by using three sc events that occurred in the interval, we have adjusted the timing of the ZYK data 1619

We analyzed ground magnetometer data for the 10 International Quiet Days during 1996–2007. The data were obtained from 19 stations along 210°magnetic meridian (MM) of the Circum‐pan Pacific Magnetometer Network (CPMN) covering both the Northern Hemisphere and Southern Hemisphere. From the daily variations of the geomagnetic field, we deduced the latitude‐local time (LAT‐LT) diagram of the equivalent Sq current system, which can be regarded as the superposition of the following three current systems: Sq0, Sq1, and Sq2. The Sq0, Sq1, and Sq2 current systems are equivalent current systems for the yearly average, annual variation, and semiannual variation of the Sq field, respectively. We have examined temporal and spatial features of these current systems. The principal features are as follows: (1) The total current intensities of the Sq1 and Sq2 current systems are about 35% and 15% of that of the Sq0 current system, respectively. (2) The Sq0 and Sq2 current systems have a dayside vortex in each hemisphere, while the Sq1 current system has a single vortex centered at the equatorial region in the morning sector (∼1000 LT).