ИСТИНА

Long-period pulsations in the nominal Pc5-6 band (periods about 3-20 min) have been known to be a persistent feature of the ULF activity at dayside high-latitudes. A mixture of broadband Irregular Pulsations at Cusp Latitudes (IPCL) and narrowband Pс5 waves is observed often, though there is no well-established criterion to separate these phenomena. The mechanism and origin of these pulsations have not been firmly established yet. Magnetopause surface eigenmodes were suggested as a potential source of high-latitude ULF waves with frequencies less than 2 mHz. A ground response to these modes is expected to be beneath the ionospheric projection of the open-closed field line boundary (OCB). To unambiguously resolve the uncertainties regarding the mechanism of the dayside high-latitude ULF activity, a multi-instrument study using data from Svalbard has been undertaken. We examine the local latitudinal structure of high-latitude Pc5-6 pulsations recorded by magnetometers covering near-cusp latitudes. This structure was compared with the instant location of the equatorward boundary of the cusp aurora, assumed to be a proxy of the OCB. The OCB latitude has been identified by an automatic algorithm, using data from the meridian scanning photometer at Longyearbyen. The comparison has shown that a latitudinal maximum of the broadband pulsations maximizes very close to the instant OCB proxy. However, in some events the local latitudinal distribution of band-integrated ULF power is shifted ~1-2o southward from the equatorward cusp boundary. Therefore, it still has to be comprehended why the ULF response to the solar wind driving may be displaced from the magnetosheath/magnetosphere interface. Therefore, the association of dayside broadband (IPCL) pulsations with ground image of the magnetopause surface modes is still an open question.