DP2 TYPE ELECTRIC FIELD FLUCTUATIONS OBSERVED BY FM-CW HF RADAR NETWORK

Shinohara M.1, Ikeda A.2, Nozaki K.3, Yoshikawa A.2, Vasily V. Bychkov4, Boris M. Shevtsov4, Yumoto K.5, 6, and MAGDAS/CPMN Group
  1. Kagoshima National College of Technology, Kirishima, Kagoshima, 899-5193, Japan, shino@kagoshima- ct.ac.jp
  2. Department of Earth and Planetary Sciences., Kyushu University, Japan
  3. National Institute of Information and Communication Technology, Japan
  4. Institute of Cosmophysical Research and Radiowaves Propagation of the Far Eastern Branch of Russian Academy of Sciences
  5. Department of Earth and Planetary Sciences., Kyushu University, japan
  6. Space Environment Research Center, Kyushu University, Japan

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. By using new MNL radar data, similar comparison will be extended to the equatorial
region.