In search of a ground image of the surface oscillations at the magnetopauseстатья

Дата последнего поиска статьи во внешних источниках: 4 сентября 2019 г.

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[1] In search of a ground image of the surface oscillations at the magnetopause / V. Pilipenko, D. Lorentsen, V. Belakhovsky, O. Kozyreva // Physics of Auroral Phenomena. — 2017. — P. 54–57. Magnetopause surface eigenmodes were suggested as a potential source of dayside high-latitude broadband pulsations in the Pc5-6 band (∼1-2 mHz) and as a mechanism of the magic frequency occurrence. However, the search for a ground signature of these modes has not provided encouraging results. The comparison of Svalbard SuperDARN radar data with the latitudinal structure of Pc5-6 pulsations recorded by magnetometers covering near-cusp latitudes showed that often the latitudinal maximum of the pulsation power maximizes ∼2o-3o deeper in the magnetosphere than the dayside open-closed field line boundary (OCB). Here the OCB-ULF correspondence is further examined by comparison of the latitudinal profile of the near-noon pulsation power with the equatorward edge of the auroral red emission from the scanning photometer data. In most analyzed events the epicenter of the Pc5-6 power is at ∼2o lower latitude than the optical OCB proxy. Therefore, the dayside Pc5-6 pulsations cannot be associated with the ground image of the magnetopause surface modes or last field line oscillations. A lack of ground response to these modes beneath the ionospheric projection of the OCB is puzzling. As a possible explanation, we suggest that a high variability of the outer magnetosphere near the magnetopause region may suppress the wave excitation efficiency. This additional mechanism of damping of field line oscillations is caused by stochastic fluctuations of the magnetospheric plasma and background magnetic field. To quantify this hypothesis, we consider a driven field line resonator terminated by conjugate ionospheres with stochastic fluctuations of the eigenfrequency. The solution of this problem predicts a substantial deterioration of resonant properties of the MHD resonator even under a relatively low level of background fluctuations. This effect may explain why a ground response to magnetopause surface modes or last field line oscillations is lacking at the OCB latitude, but can be seen at somewhat lower latitudes with more regular and stable magnetic and plasma structure. With an account of ∼2o offset, the maximum of Pc5-6 power can be used as a simple indicator of the dayside OCB latitude.

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