Physics of auroral phenomena : proceedings of the 37th Annual seminar, Apatity, 25 - 28 February, 2014 / [ed. board: A. G. Yahnin, N. V. Semenova]. - Апатиты : Изд-во Кольского научного центра РАН, 2014. - 125 с. : ил., табл.

A.G. Yahnin et al. 2. Data The data base used in this study consists of observations of four NOAA satellites ( NOAA-15, -16, -17, and -18) frying at altitude -800 km during the interval from 25 July to 31 August 2005, which is characterized by the variable geomagnetic activity. To measure charged particles with energy E>30 keV, NOAA POES are equipped with the Medium Energy Proton and Electron Detector (MEPED) instrument ( Evans and Greer, 2004). This instrument consists, particularly, of two pairs of directional telescopes. The directional telescopes are oriented such that they sample from the local vertical (zenith) and horizontal (“backwards” along the direction of travel) fields of view (0-degree and 90-degree telescopes, respectively). At sufficiently high latitudes 0-degree telescopes measure precipitating (within the loss cone) particles, while 90-degree telescopes measure particles, which are just outside the loss cone at the equatorial plane (e.g. Rodger et al., 2010). Electron telescopes have three nominal energy channels: E l (>30 keV), E2 (>100 keV), and E3 (>300 keV). Proton directional telescopes are designed to measure ions in six channels: PI (30-80 keV), P2 (80-250 keV), P3 (250-800 keV), P4 (800-2500 keV), P5 (2500-6900 keV), and P6 (>6.9 MeV). Measurements of protons in the channel P6 are rare, but it is contaminated with relativistic (>700 keV) electrons (e.g., Yando et al., 2011). Situation with the relativistic electron contamination can be easily distinguished from the proton event by comparison with counts in the channel P5, which is not contaminated by electrons. If there are no particles detected in P5, the particles observed in P6 are relativistic electrons. This criterion (the lack of response in P5 during a detectable signal in the 0-degree telescope of the channel P6) was used to select REP events. Following to Carson et al. (2012), we excluded from the consideration those NOAA POES passes, which were in the vicinity of SAMA. The sampling rate of the 0- and 90 degree detectors of the MEPED instrument is 2 s (each detector alternately accumulates the signal during one second). Thus, it is clear that NOAA POES are not appropriate for investigation of microbursts. We considered an enhancement of the relativistic electron precipitating flux as the event if its duration was at least 4 seconds (two samples). In all, 209 REP events were selected during the interval under study having the duration from 4 to 32 seconds. Fig. 1 presents some examples of the 0- and 90-degree fluxes of particles registered in some channels of the MEPED instrument. The upper panel shows the data from channel PI (Ep=30-80 keV), second and third panels show the fluxes of electrons in channels El (Ee>30 keV) and E3 (Ee>300 keV), respectively. The data from channel P6 (Ee>700 keV) are shown at the bottom. 60 65 65 70 60 65 Corrected Geomagnetic Latitude, deg Corrected Geomagnetic Latitude, deg Corrected Geomagnetic Latitude, deg a b c Figure 1 6 August 2005 NOAA-17 04:45 UT 28 July 2005 NOAA-15 01:47 UT 3. Results Careful inspection of selected REP events enables us to divide them into three groups. The first group is represented by events of isotropization of fluxes (that is, equality of the precipitating and 90-degree flux) in the channel P6, which occurs right at the poleward (outer) boundary of the 90-degree flux, and which do not coincide with any enhancement of the 0-degree flux in any other electron channel. An example of the REP event belonged to this group is shown in Fig. la. In such cases the fluxes of >30 and >300 keV electrons also demonstrate the isotropization at the trapped boundary, but the latitude of the isotropy boundary (that is, boundary between isotropic and anisotropic fluxes) of electrons measured in channels E1-E3 and P6 exhibits clear energy dispersion. The higher the energy of electrons, the lower the latitude of the isotropy boundary. This suggests that the electron isotropization and precipitation is related to violation of the adiabatic movement, which occurs when the Larmor radius of the particle is comparable with the curvature radius of the magnetic field line in the vicinity of the equatorial plane of the magnetosphere (e.g., Sergeev and Tsyganenko, 1982). Note, that the isotropy boundary for 30-80 keV protons is 47