  We present two examples from the cusp ionosphere over Svalbard,where poleward
moving auroral forms (PMAFs) are causing significant phase scintillation in
signals from navigation satellites. The data were obtained using a combination
of ground-based optical instruments and a newly installed multiconstellation
navigation signal receiver at Longyearbyen. Both events affected signals from
GPS and Global Navigation Satellite System (GLONASS). When one intense PMAF
appeared, the signal from one GPS spacecraft also experienced a temporary loss
of signal lock. Although several polar cap patches were also observed in the
area as enhancements in total electron content, the most severe scintillation
and loss of signal lock appear to be attributed to very intense PMAF activity.
This shows that PMAFs are locations of strong ionospheric irregularities, which
at times may cause more severe disturbances in the cusp ionosphere for
navigation signals than polar cap patches.
