Proceedings with Extended Abstracts (single PDF file) - Radio ...

ROCKET OBSERVATION OF ELECTRIC FIELDCONDUCTED IN THE SEEK-2T. Yokoyama 1 , M. Yamamoto 1 , S. Fukao 1 , R. F. Pfaff 21Radio Science Center for Space and AtmosphereKyoto University, Uji, Kyoto, Japan2NASA/Goddard Space Flight Center, Greenbelt, MD, USA1. INTRODUCTIONQuasi-periodic (QP) echoes associated with a sporadic-E (Es) layer in the midlatitudeE-region have been intensively studied since the first discovery with the MU radar [Yamamotoet al., 1991]. In order to investigate the mechanism for the generation of QP echoes, the SEEK(Sporadic-E Experiment over Kyushu) campaign was conducted in 1996 [e.g., Fukao et al.,1998] in which two sounding rockets were launched from Kagoshima Space Center (KSC) inUchinoura, Japan. A double-probe electric field sensor was loaded on the S-310-25 rocketwhich was launched at 23:00 LT on August 26, 1996. The detected electric field revealedcomplex electrodynamics that intense DC electric fields of 20 mV/m associated with narrowplasma density depletions, and a sinusoidal variation of ±3 mV/m between 130-170 km [Pfaffet al., 1998]. The mechanism to generate such a large polarization electric field has been oneof the important subjects associated with the QP echoes since the SEEK campaign.In 2002, the SEEK--2 campaign was conducted as a succeeding project of the SEEKcampaign. An electric field detector (EFD) was boarded on the S-310-31 rocket that deploysorthogonal double probes of 4.0 m tip-to-tip length from a rocket body. Four spherical sensorsof 44.5 mm in diameter are attached on the tip of each probe to measure potentials with highimpedance (>10 12 Ω) pre-amplifiers. The potential differences along the main diagonal axeswere obtained in 1600 Hz sampling with 16-bit onboard A/D converters. The S-310-31 rocketwas launched at 23:24 LT on August 3, 2002 from KSC and reached an apogee of 152 km at194 s after liftoff. All instruments boarded on the rocket worked successfully.2. OBSERVATIONAL RESULTSFigure 1 shows the derived electric field during the upleg; the zonal component is shown inpanel (a), the meridional component in (b), the magnitude in (c), and the direction of vectorsin (d). Below 108 km, electric fields fluctuate strongly with an amplitude of less than 10mV/m in each component which should be associated with Es layers and plasma irregularities.The fluctuation of electric fields is strongest from 95 to 102 km in which the direction isgenerally northwestward. The amplitude is relatively small from 102 to 106 km, and theintense peaks appear around 107 km. Above 108 km, on the other hand, such strongfluctuations disappear and 10 km-scale wavelike vertical structure remains up to the apogeewith an amplitude of less than 5 mV/m. The direction of electric fields is mainly southward orsouthwestward but suddenly change to northeastward at 115, 128, and 139 km. They rotateclockwise with altitude from northeast to southwest and change to northeast again. Comparedwith the electric field measured in SEEK campaign, the major characteristics of strongfluctuations in lower altitudes and large scale structures in higher altitudes are quite similar.However, the magnitude of electric field in SEEK is nearly twice as SEEK-2 and strongfluctuations appeared up to 130 km. One possibility of this difference is solar activity (low in126