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Н. В. Ягова 1 , Е. Н. Федоров 1 , Б. Хэйлиг 2 1 ИФЗ РАН

Геомагнитные пульсации диапазона Pc 2-3 по результатам измерений в магнитосфере, F -слое ионосферы и на поверхности Земли на спутниках THEMIS , CHAMP и наземной сети магнитометров MM 100. Н. В. Ягова 1 , Е. Н. Федоров 1 , Б. Хэйлиг 2 1 ИФЗ РАН

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Н. В. Ягова 1 , Е. Н. Федоров 1 , Б. Хэйлиг 2 1 ИФЗ РАН

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  1. Геомагнитные пульсации диапазона Pc2-3 по результатам измерений в магнитосфере, F-слое ионосферы и на поверхности Земли на спутниках THEMIS, CHAMP и наземной сети магнитометров MM100. Н. В. Ягова1, Е. Н. Федоров1, Б. Хэйлиг2 1 ИФЗ РАН 2Tihany Geophysical Observatory MFGI, Tihany, Hungary

  2. Abstract • We analyze Pc2-3 pulsations recorded at quiet geomagnetic conditions in the F-layer of the Earth's ionosphere, on the ground and in the magnetosphere. Ionospheric pulsations are characterized by high in comparison with ground measurements, contribution of high frequencies f>50 mHz, i.e.above the fundamendal Alfven frequency. High quality signals with dominating frequencies 70-150 mHz is a regular phenomenon in the F-layer and in the magnetosphere. The mean maximum of the latitude distribution of Pc2-3 occurrence rate in the F-layer lies at latitudes 55<F<60o CGM, under the average plasmapause position. Day-to-day variations of L value of CHAMP Pc2-3occurremce rate maximum follow the plasmapause day-to-day variations.

  3. Introduction • Pc3 and Pc1 are typical at middle latitudes. Pc2 and Pc3 above the first Alfvenic frequency are not often observed on the ground. • This frequency range corresponds to higher harmonics of magnetospheric Alfven resonator and to ion-cyclotron resonance on heavy ions in the outer magnetosphere. • The other possible reason for excitation of pulsations with in this frequency range is the formation of sub-resonators or waveguides inside the magnetosphere. The latter can appear because of steep gradients of Alfven velocity. The most essential gradient is related with plasmapause Also density irregularities can occur inside the plasmasphere at different stages of plasmaspheric depleting and refilling

  4. Introduction. Pc2-3 observations • Pc2 are typical on the ground surface at high geomagnetic latitudes and are attributed to cusp (Bering,1998) and auroral regions. • In our early report (Yagova, 2009) we have found that the Pc3spectra in the F-layer is enriched with high frequencies in comparison with ground observations. However, it was impossible to discriminate spatial from temporal variation on the basis of only CHAMP measurements. Moreover, spatial structures do exist in the ionospheric F-layer and contribute to the ULF spectrum of magnetic field oscillations recorded by CHAMP. A detailed analysis of spatial structures near the plasmapause has been done by (Heilig,2013). • The first publication occurred in • Le, G., P. J. Chi, R. J. Strangeway, and J. A. Slavin (2011), Observations of a unique type of ULF wave by low-altitude Space Technology 5 satellites, J. Geophys. Res., 116, A08203, doi:10.1029/2011JA016574.

  5. Experimental data. CHAMP. • We use for the analysis data of several months of observations in2007 for which high resolution data from CHAMP and THEMIS satellites and MM100 magnetometer network are available. The geomagnetic conditions during the observation period are very quiet.

  6. THEMIS • THEMIS magnetic measurements with 0.25 s resolution are available from February of 2007. THEMIS orbits pass through the magnetosphere during ~12 hours and through the plasmasphere during ~2 hours at each orbit and the velocity of its ionospheric projection at middle latitudes is about 200 m/s i.e. it is low in comparison with CHAMP velocity and THEMIS data also can be used to discriminate temporal and spatial structures.

  7. MM100

  8. Difference in Pc2-3 spectra in the F-layer and on the ground • Higher amplitudes at CHAMP at f>50 mHz. • Maximum amplitude at CHAMP is recorded in azimuthal component and in the frequency band 40-150 mHz it exceeds PSD of both horizontal components on the ground. Amplitudes of vertical component in the F-layer is low. • PSD spectra averaged over 6 days of observations in September 2007 (DOY 253-258) at CHAMP and NUR (L=3.7). 12-16 MLT sector, at night-time the picture is qualitatively similar.

  9. Example. Daytime. CHAMP. • CHAMP passes along MM11 in afternoonsector (MLT=14). Peak-to-peak amplitude reaches 1nT. Df=120o.

  10. Example. Coherent night-time pulsations • Both CHAMP and NUR are in post-midnight sector, MLT=3. Peak-to-peak amplitude at CHAMP reaches 0.4 nT, and at NUR it is about 5 times lower.

  11. PSD spectra, coherence and phase diffference

  12. Example. CHAMP-THEMIS • During the interval THEMIS was near the plasmapause position (L=4.3) andCHAMP was passing alongMM230. Both satellites are in near-noon sector (MLT=12 forCHAMP and 10 for THEMIS). Pulsations with centralfrequency f=90 mHz with peak-to-peak amplitude 0.3-0.5 nT are seen on the background of Pc4 pulsations with f=25 mHz. Pc4 are in phase at both satellites and for Pc2-3 DF=220o at the central frequency.

  13. CHAMP. Spatial distribution

  14. Spatial distribution. Ground surface

  15. Spatial distribution. THEMIS

  16. Pc2-3 and plasmapause • Day-to-day variations of the L-value of Pc2-3 occurrence rate maximum (LPc23) with plasmapause position determined from Carpenter formula Lpp=5.7-0.47Kp. Two-day mean values LPc23 from CHAMP measurements in 0-6 MLT sector in the Southern hemisphere

  17. Colnclusion • Pc2-3 are a common phenomena in the F-layer. Average amplitudes and occurrence rates in the F-layer are 4-5 times higher than on the ground and 2-3 times higher than near the equatorial plane of the magnetosphere. The occurrence rate for CHAMP Pc2-3 has a maximum at 2.5<LPc2-3<4 i.e. inside the plasmasphere and its day-to-day variation repeats the plasmapause motion. LPc2-3 position in the magnetosphere is shifted to higher L-values. • The frequency range studied (70-150 mHz) lies above the fundamental FLR harmonic. It coincides with the oxygen cyclotron frequency in the outer magnetosphere. However, O+ ions are recorded in the outer magnetosphere during magnetic storms and we have studied an absolutely quiet interval. • The other possibility can be related with minimum of the Alfven velocity under the plasmapause forming the waveguide for FMS waves. The existence of the second low-latitude maximum in the F-layer can be the indirect argument in favor of this hypothesis. • The difference in the wave polarization exists between waves inside and outside the plasmasphere. The amplitudes for transversal and field-aligned components in the outer magnetosphere are comparable. At lower L the wave polarization is typical for the ALfven waves. The azimuthal component dominates also in the F-layer. So Pc2-3 may be generated in the outer plasmasphere as FMS waves and then transformed into the Alfven waves at the plasmapause. • Two maxima in F-layer occurrence rate and PSD may correspond to two zones of minimal Alfven velocity: the first one repeats L-shell and the second lies near the equatorial plane. The growth of amplitude in the ionosphere is the result of geometrical factor and minimum of the Alfven velocity in the F-layer.

  18. СПАСИБО ЗА ВНИМАНИЕ!

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