Nighttime thermospheric winds over Sondre Stromfjord, Greenland

Observations of nighttime thermospheric neutral winds made at Sondre Stromfjord, Greenland, with optical and radar instrumentation, showed an occasional abatement in the equatorward meridional wind at a magnetic local time corresponding to the nighttime division between the evening and morning convection cells. This abatement appeared primarily in the poleward observations. In contrast, however, the characteristic midnight “surge” was usually seen in the equatorward set of observations. The apparent acceleration of about 250 m/s or greater within 4.6° latitude we attribute, in part, to a merging of neutral jet streams generated by polar cap ion drag adjacent to the auroral zone boundary, and, in part, to the higher electron densities and plasma convection speeds adjacent to the auroral zone. Comparison of these results with those from NCAR/TGCM computations that assumed an analytical plasma convection model showed reasonable agreement, except for the abatement feature.