The results showed peak of irregularity activities around June solstice, which again confirmed the breakthrough findings by satellites as one typical characteristics of ionospheric structures during low solar activity. We also found that we cannot use typical types of SF for equatorial stations as the ones observed at non-equatorial stations. | Vietnam Journal of Earth Sciences 37 (2015) 307-317 Vietnam Academy of Science and Technology Vietnam Journal of Earth Sciences (VAST) Website: On new detailed ionogram signatures of Equatorial Plasma Bubbles from non-equatorial station during low solar activity Nguyen Thu Trang*1, Roland T. Tsunoda2, Le Huy Minh3 1 Ho Chi Minh City Institute of Physics, Vietnam Academy of Science and Technology 2 Center for Geospace Studies, SRI International 3 Institute of Geophysics, Vietnam Academy of Science and Technology Accepted 20 December 2015 ABSTRACT A first - time direct comparison between climatology of spread F (SF) observed at Phu Thuy and DMSP, C/NOFS satellite measurements during years of low solar activity conditions 2007 - 2010, together with ionosonde observations under the same solar conditions 1953 - 1955 in Baguio, is made to show good relationship of SF at off-equator and equatorial plasma bubbles (EPB) over the dip equator. The results showed peak of irregularity activities around June solstice, which again confirmed the breakthrough findings by satellites as one typical characteristics of ionospheric structures during low solar activity. We also found that we cannot use typical types of SF for equatorial stations as the ones observed at non-equatorial stations. Instead, we suggested a new method to classify SF types in the relation to ionospheric structures at the off-equator stations of interests. Consequently, we can explain, in the simplest cases, for the first time, complex range type SF observed at off-equatorial stations and name a new type as indicator of EPB occurrence. Keywords: Spread F, equatorial plasma bubble, ionogram signature. ©2015 Vietnam Academy of Science and Technology 1. Introduction Equatorial plasma bubbles (EPBs) are referred to as locally depleted irregularity region which their densities are less than those of ambient. The newest working hypothesis, which is most capable for high .
