A case study of the auroral E region neutral wind on a quiet summer day: Comparison of the European Incoherent Scatter UHF radar for deriving the E region wind

Comparison study of three methods of the European Incoherent Scatter (EISCA T) radar for furnishing E region neutral wind data is performed on the basi s of observational data. A Special Program by using the EISCAT UHF radar lo cated in northern Scandinavia was conducted for 24 hours starting at 1000 U T on July 14, 1997. Two modes of EISCAT Common Program 1 and 2 are combined in this Special Program, so that the capability of the tristatic method an d monostatic (or beamswinging) methods are compared on the basis of observa tions at four heights between 99 and 108 km under geomagnetic quiet conditi ons. The meridional neutral wind is derived by the field-aligned method as well. Derived wind Velocities by the three methods are compared, and fairly good agreement is found in terms of a relatively longer temporal variation (similar to 2-3 hours). The comparison of the derived velocities shows tha t the tristatic method (i.e., Common Program I) is superior to the monostat ic method (i.e., Common Program 2) in terms of an instantaneous measurement , while the monostatic method has an advantage on a tidal study. Regarding the meridional wind component, the filed-aligned method has significant adv antages compared to the other methods concerning temporal data coverage, er ror, and height coverage. The derived neutral wind in this Special Program is compared with that from a statistical study by Nozawa and Brekke [1999a] . Generally good agreement for mean and semidiurnal winds is found with the statistical result, but relatively strong amplitude (similar to 35 m s(-1) ) of 8-hour meridional component is found in this case study. Comparison of the zonal mean wind and mean temperature is made with the CIRA (1986) mode l as well. Good agreement is obtained for the temperature, while poor agree ment is found for the zonal mean wind.