ИСТИНА

Long-period pulsations in the nominal Pc5-6 band (periods about 3-20 min) have been known to be a persistent feature in the ULF activity at dayside high latitudes. 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 Pc5-6 pulsations. 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 ULF pulsations recorded by magnetometers covering near-cusp latitudes. This structure has been compared with the instant location of the equatorward boundary of the cusp aurora, assumed to be a proxy of the OCB. OCB was identified by an automatic algorithm, using data from the meridian scanning photometers at Longyearbyen. The latitudinal maximum of the broadband Pc5-6 pulsations lies in a close vicinity of the OCB proxy, but equatorward from it. These pulsations hardly could be the ground image of the magnetopause surface modes, though essentially non-dipole geometry of field lines and high variability of this region may suppress the excitation efficiency. However, in some events, besides those features, additional peak of green 557.7 nm emission can be seen in latitudinal profile of auroral intensity, poleward from the OCB. This peak is accompanied by the occurrence of specific Pc5 pulsations with f~5 mHz. These "green emission associated" Pc5 pulsations are relatively weak, but discernible. A localized green emission poleward of OCB could be a result of electron precipitation. This localized green emission/precipitation is a signature of dynamic phenomena in the cusp/mantle. This work was partially supported by the grant of Russian Foundation for Basic Research № 15-05-01814 and PolarProg research program under the Researh Council of Norway (Project № 246725).