Study of the tidal variations in mesospheric temperature at low and mid latitudes from WINDII and potassium lidar observations

M Shepherd,C Fricke-Begemann

doi:10.5194/angeo-22-1513-2004

Abstract

Abstract. Zonal mean daytime temperatures from the Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS) and nightly temperatures from a potassium (K) lidar are employed in the study of the tidal variations in mesospheric temperature at low and mid latitudes in the Northern Hemisphere. The analysis is applied to observations at 89km height for winter solstice, December to February (DJF), at 55° N, and for May and November at 28° N. The WINDII results are based on observations from 1991 to 1997. The K-lidar observations for DJF at Kühlungsborn (54° N) were from 1996–1999, while those for May and November at Tenerife 28° N were from 1999. To avoid possible effects from year-to-year variability in the temperatures observed, as well as differences due to instrument calibration and observation periods, the mean temperature field is removed from the respective data sets, assuming that only tidal and planetary scale perturbations remain in the temperature residuals. The latter are then binned in 0.5h periods and the individual data sets are fitted in a least-mean square sense to 12-h and 8-h harmonics, to infer semidiurnal and terdiurnal tidal parameters. Both the K-lidar and WINDII independently observed a strong semidiurnal tide in November, with amplitudes of 13K and 7.4K, respectively. Good agreement was also found in the tidal parameters derived from the two data sets for DJF and May. It was recognized that insufficient local time coverage of the two separate data sets could lead to an overestimation of the semidiurnal tidal amplitude. A combined ground-based/satellite data set with full diurnal local time coverage was created which was fitted to 24h+12h+8h harmonics and a novel method applied to account for possible differences between the daytime and nighttime means. The results still yielded a strong semidiurnal tide in November at 28° N with an amplitude of 8.8K which is twice the SD amplitude in May and DJF. The diurnal tidal parameters were practically the same at 28° N and 55° N, in November and DJF, respectively, with an amplitude of 6.5K and peaking at ~9h. The diurnal and semidiurnal amplitudes in May were about the same, 4K, and 4.6K, while the terdiurnal tide had the same amplitudes and phases in May and November at 28° N. Good agreement is found with other experimental data while models tend to underestimate the amplitudes. Key words. Atmospheric composition and structure (pressure, density and temperature) – Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)

Highlights

Solar driven migrating thermal tidal perturbations are one of the strongest perturbations affecting the dynamics of the mesosphere and the lower thermosphere (MLT) region
As each of these data sets is limited by the local time coverage of the diurnal cycle we examine the semidiurnal and terdiurnal tidal signatures at 28◦ N and 55◦ N latitude detected by both techniques, where weak diurnal tidal activity has been observed (Manson et al, 1989a, b; Fesen et al, 1991; Forbes et al, 1994) and modeled (Forbes and Vial, 1989; Hagan, 1996; Hagan et al, 1999; Yudin et al, 1997; Khattatov et al, 1997; McLandress, 1997)
The annual march of Wind Imaging Interferometer (WINDII) temperature observations (Shepherd et al, 2003) have shown that in winter there is a large day-to-day temperature variability associated with effects of stratospheric warmings and planetary waves, which can be seen in the zonal daytime means and affects the quality of the fit to these data sets

Summary

Introduction

Solar driven migrating thermal tidal perturbations are one of the strongest perturbations affecting the dynamics of the mesosphere and the lower thermosphere (MLT) region. Tidal theory and mechanistic models have predicted the dominance of the 24-h (diurnal-D) and 12-h (semidiurnal-SD) westward migrating modes, following the apparent motion of the Sun. The first ground-based lidar studies of diurnal and semidiurnal tides in the MLT region were conducted by Clemesha et al (1982), who derived tidal information from the variations in atmospheric sodium density. Ground-based lidars usually provided high vertical and temporal resolution but only nighttime observations, which limited the ability to investigate the characteristics of the main tidal modes – the 24-h and 12-h oscillations. To resolve this problem atomic resonance lidars

Results

Discussion

Conclusion