The influence of the interplanetary magnetic field Y component on ion and neutral motions in the polar thermosphere

Neutral thermospheric winds and ion‐drifts at F region heights, observed at Longyearbyen, Spitsbergen (78.2°N, 15.6°E, 75°Λ) show a definite dependence on the sign of the interplanetary magnetic field Y component (IMF By). The neutral and ion measurements were made near winter solstice in the period 1979 to 1983 and were derived from optical interferometric observations of the Doppler shift of the oxygen emissions, OI 630 nm and OII 732 nm respectively, which occur in the aurora and airglow. The hourly averaged components of the wind and ion drift in the magnetic zonal direction were found for the 4 hour period spanning magnetic local noon. These zonal components were both westward when IMF By was positive, the neutrals reaching half the zonal speed of the ions. When IMF By was negative, the average zonal ion drift was eastwards but the neutral wind had a less symmetrical response, reaching only one sixth of the averaged ion zonal speed. These observations demonstrate that in general the ion convection is well coupled to the neutral thermosphere on the dayside at high latitudes but that clockwise vorticity is more readily generated in the northern hemisphere than anticlockwise vorticity.