Seasonal variation of the auroral E-region neutral wind for different solar activities

Seasonal variations in the auroral E-region neutral wind for different sola r activity periods are studied. This work is based on neutral wind data obt ained over 56 days between 95-119 km altitude under geomagnetic quiet condi tions (A(p) < 16) during one solar cycle by the European Incoherent Scatter radar located in northern Scandinavia. In general, the meridional mean win d shifts northward, and the zonal mean wind increases in eastward amplitude from winter to summer. The zonal mean wind blows eastward in the middle an d lower E-repion for each season and for each solar condition except for th e equinox, where the zonal mean wind blows westward at and below 104 km. So lar activity dependence of the mean wind exists during the winter and equin ox seasons, while in summer it is less prominent. Under high solar activity conditions, the altitude profiles of the horizontal mean winds in winter a nd the equinoxes tend to resemble those in summer. The horizontal diurnal t ide is less sensitive to solar activity except during summer when the merid ional amplitude increases by similar to 10 m s(-1) and the corresponding ph ase shifts to a later time period (1-2 h) during high solar activity. Seaso nal dependence of the semidiurnal tide is complex, but is found to vary wit h solar activity. Under low solar activity conditions the horizontal semidi urnal amplitude shows seasonal dependence except at upper E-region heights, while under high solar activity conditions it becomes less sensitive to se asonal effects (except for the meridional component above 107 km). Comparis ons of mean winds with LF and UARS observations are made, and the driving f orces for the horizontal mean winds are discussed for various conditions. ( C) 1999 Elsevier Science Ltd. All rights reserved.