Study of generating mechanism of ionospheric E-region irregularities with rocket/radar simultaneous observations

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Ionospheric irregularities in the mid-latitude E-region has been a study topics for more than ten years. The epoch was the discovery of the quasi-periodic (QP) structure in the E-region FAI (Field-Aligned Irregularity) echoes observed with the MU radar in Japan. The QP structures appear in the E-region FAI as a reflection of modulation pattern in the Sporadic-E (Es) layers. The structures are associated with polarization electric field, which suggests strong coupling process between the ionized and neutral atmosphere. In August 2002, we conducted SEEK-2 (Sporadic-E Experiment over Kyushu 2) campaign in Japan under collaboration with scientists from Japan, USA and Taiwan. The SEEK-2 consists of two sounding rockets of Institute of Space and Aeronautical Sciences that include in-situ experiment of electron density, electron temperature, electric field, plasma fluctuation and waves, and geomagnetic field as before. This research program is mainly dedicated to conduct the SEEK-2 ground-based observations. We operated two radars of 24.5 MHz and 31.6 MHz, ionosonde network of Japan, an MF radar, several airglow imagers, and a GPS scintillation-receiver system. We observed intense QP echoes with radars after 23 LT (= UT + 9 hours) on August 3, 2002, and launched rockets into the E-region at 2324 LT and 2339 LT. The operation of the SEEK-2 was very successful as we could, select a good event for the launches. All instruments on the rockets worked fine. We have found that the rockets detected multi-layered Es-layers at 103, 105 and 129 km altitudes, and intense electric fields that approach +-10 mV/m. In March 2003, we hosted the SEEK-2 workshop for data comparison and analysis. From this observation program we published more than 30 papers in the international journals. Numbers of oral presentations from the SEEK-2 results were 21 in international conferences, and 54 in domestic meetings.