DP2 type electric field fluctuations observed by FM-CW HF radar network

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   DP2 type geomagnetic fluctuations are associated with field aligned
   currents between the magnetosphere and the polar ionosphere. Field aligned
   currents impose a dawn-to-dusk and/or a dusk-to-dawn electric fields on
   the polar ionosphere. These electric fields penetrate instantaneously to
   the middle, low, and equatorial ionosphere and cause east-west electric
   field fluctuations in both the dayside and the nightside ionosphere. It
   shows an energy transfer process from the magnetosphere to the
   low-latitude ionosphere through the polar region. In order to observe the
   penetration of electric field fluctuations in the ionosphere, a chain of
   the FM-CW (Frequency Modulated Continuous Wave) HF radar has been
   developed along the 210 magnetic meridian. Our first radar was installed
   at Sasaguri (Geomagnetic Latitude = 26), Japan in 2002. The second radar
   was installed at Paratunka (Geomagnetic Latitude = 46), Kamchatka, Russia
   in 2006. And the third radar was installed at Manila (Geomagnetic Latitude
   = 6), Philippine in 2009. The MAGDAS FM-CW radar network covered widely
   from 6 to 46 degrees geomagnetic latitudes. The FM-CW HF radar is a kind
   of the ionosonde. The radar transmits high frequency wave to the
   ionosphere and observes the Doppler shift of the received wave frequency
   which is reflected by the F region ionosphere. The magnitude of the
   Doppler shift of the received wave frequency corresponds to the vertical
   drift velocity of the reflecting layer in the ionosphere. The ionospheric
   plasma is moving by the E x B drift, where B is the local ambient magnetic
   field. The east-west electric field becomes a possible source of the
   vertical drift of the ionospheric plasma in the low latitude ionosphere.
   According to this feature of the low latitude ionosphere, the FM-CW HF
   radar can observe east-west electric field fluctuations. DP2 fluctuations
   were observed and were statistically analyzed by using the radar data at
   PTK and SAS stations and the magnetic data observed by the MAGDAS/CPMN
   network. The amplitude ratio of DP2 type electric field fluctuations in
   the nightside observed by the radar at PTK and SAS to magnetic field
   fluctuations observed at the dayside equator are 0.107 mV/m/nT and 0.030
   mV/m/nT, respectively. The amplitude of DP 2 electric field fluctuations
   decreased with decreasing latitude in the nightside ionosphere. In the
   observed events, amplitude ratio of electric field fluctuations at 26
   degrees geomagnetic latitude to those at 46 degrees was about 1/4.