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There are differences between existing models of solar EUV with λ < 1050 Å and between laboratory measurements of the O+ + N2 – reaction rate coefficient, both parameters being crucial for the F2-region modeling. Therefore, indirect aeronomic estimates of these parameters may be useful for qualifying the existing EUV models and the laboratory measured O+ + N2 – rate coefficient. A modified self-consistent method for daytime F2-region modeling developed by Mikhailov and Schlegel was applied to EISCAT observations (32 quiet summer and equinoctial days) to estimate the set of main aeronomic parameters. Three laboratory measured temperature dependencies for the O+ + N2 – rate coefficient were used in our calculations to find self-consistent factors both for this rate coefficient and for the solar EUV flux model from Nusinov. Independent of the rate coefficient used, the calculated values group around the temperature dependence recently measured by Hierl et al. in the 850–1400 K temperature range. Therefore, this rate coefficient may be considered as the most preferable and is recommended for aeronomic calculations. The calculated EUV flux shows a somewhat steeper dependence on solar activity than both, the Nusinov and the EUVAC models predict. In practice both EUV models may be recommended for the F2-region electron density calculations with the total EUV flux shifted by ±25% for the EUVAC and Nusinov models, correspondingly.Key words: Ionosphere (ion chemistry and composition; ionosphere atmosphere interactions; modeling and forecasting)

Bursts of very intense kilometre-scale field-aligned currents (KSFACs) are observed quite frequently by the CHAMP satellite when passing through the auroral region. Typical scale sizes of these KSFACs are 1km. In extreme cases estimated current densities exceed 3mA/m2. The low-Earth, polar orbiting satellite CHAMP allows assessing KSFACs down to scales of a couple of 100m based on its high-precision magnetic field vector data sampled at 50 Hz. Using data from 5 years (2001 - 2005) the details of these currents have be investigated. Our statistical study reveals that most of the KSFAC bursts and the strongest events are encountered in the cusp/cleft region. Significantly fewer events are found on the night side. There seems to be no dependence of the peak current intensity on the level of magnetic activity, Kp, sunspot number, solar flux level, F10.7 or solar zenith angle. On the other hand, the occurrence frequency is strongly dependent on all these indices. The KSFACs are generally part of strong large-scale FAC sheets, and they are predominantly associated with Region 1 currents. We propose an explanation of the KSFACs in terms of Alfvén waves trapped in a recently proposed resonator, which is initiated when a topside reflector is set up. Many properties of such a resonator are in agreement with our ’KSFAC’ results, as for example the switch on/off behaviour, the association to strong large-scale FACs and the current density peak at the critical scale size.

According to current understanding Sudden Commencements (SC) in magnetometer records are caused by a sudden compression of the magnetosphere by shocks (dynamic pressure steps) in the solar wind. So far SCs have mainly be studied with the help of magnetometer arrays, only very few systematic studies with satellite borne magnetometers have been published. We present a systematic study of 30 SCs observed by CHAMP on the night side (between 18 and 06 MLT) at low mid- latitudes (between -45° and +45° MLat) between July 2000 and December 2006. CHAMP is a polar orbiting satellite (87.25° inclin.) cruising at altitudes between 360 and 430 km. The SCs are recorded with the onboard fluxgate magnetometer and identified after subtracting the main magnetic field. For comparison, ground-based magnetometer records with 1-s time resolution from stations close to the satellite track have been used. During night-time, effects of ionospheric currents on the magnetic field are believed to be negligible, thus the SC magnetic signature represents only the effect of magnetospheric compression. The shape of the magnetic field step should therefore look very similar at satellite altitudes and on the ground. We demonstrate this with three (out of our 30 analysed) events observed at different geographical locations. Moreover, the magnitude of the magnetic field step is clearly related to the step size in the solar wind dynamic pressure.

「あけぼの」に搭載された熱的電子エネルギー分布測定器及び電子密度, 電子温度測定器を概説しプロトノスフェア及び沿磁力線電流領域に関して初期に得られたデータを紹介する。, Thermal electrons in the upper ionosphere are being studied by means of the scientific satellite "AKEBONO". The measurements are electron temperature, electron density and the distribution of electrons in the energy range of 0&acd;5eV. An overview of the experiment is given and preliminary results on the protonosphere and field aligned current region are presented., 資料番号: SA0166934000