Optical and radar wind comparisons in the mesosphere and lower thermosphere
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This project involved the comparison of horizontal winds in the upper mesosphere at 80-105 km which were obtained by two different ground-based techniques located in Canterbury. Optical Doppler winds were derived from night time observations of the mesospheric 557.7 nm airglow emission near 95 km (FWHM intensity ∼10-12 km) using a Fabry-Perot Spectrometer (FPS) during the period February 1991 to July 1994. These were compared to simultaneous radar winds obtained using a partial-reflection MF (2.4 MHz) wind-profiling radar. The comparisons were made on 103 nights considered suitable by exhibiting no cloud and low magnetic activity (low Kp) in order to eliminate the possibility of auroral contamination in the FPS measurements. The results of the FPS/radar wind comparisons were of limited success due to the significant effect of RF noise associated with the radar wind measurements. The meridional optical/radar wind comparisons produced more consistent results than the zonal wind comparisons. The distribution of daily mean radar wind vectors for all 103 days was aligned perpendicular to the direction of the magnetic meridian. This indicates that the radar winds at 85-105 km are possibly under partial geomagnetic control. The mean height of best agreement from the cross-correlations between the night time FPS and radar hourly mean winds was 95.8 km with a standard deviation of 6.4 km. This height is agrees closely with the average height of 95.2 km obtained from studies of (satellite) WINDII 557.7 nm emission data. In a second comparison of simultaneous hourly FPS and radar winds, observations averaged over several nights during March/ April 1993 were compared with a mean 557.7 nm emission height profile at 44°S from WINDII data for March/ April. There was good agreement between the FPS and radar hourly winds height in the 88-96 km height region, with best agreement at 92 km. In an alternative, best agreement between the comparison of phase of the semidiurnal tide fitted to the optical and radar winds was found to occur in the 100-105 km height region. The amplitudes of the semi-diurnal tide as exhibited in the optical and radar wind fields were investigated and the optical tidal amplitudes were generally larger than the corresponding radar amplitudes. The median optical/radar semi-diurnal amplitude at a height of 95 km was 1.4 with a lower and upper quartile values of 1.0 and 2.5, respectively. The amplitude discrepancy was largest near 95 km.