Low-latitude thermal semidiurnal tide: Longitudinal and seasonal variations based on ground-based measurements from Arecibo and Maui, space-based measurements by SABER, and modeling with GSWM-02

摘要

We have combined ground-based and space-based measurements and modeling of the mesosphere-lower thermosphere to study the zonal and seasonal variability of the semidiurnal thermal tide. This study uses resonance lidar soundings of temperatures from 80-100 km at Arecibo, PR (18°N, 67°W) and Maui, HI (20°N, 156°W) and observations from the SABER instrument aboard TIMED. Findings include general dominance of migrating tides through most of the year, excepting January, when the lidar-measured Maui phase front is much shallower than that observed by SABER or Arecibo lidar. At both sites the GSWM-02-predicted phase is later at lower altitudes than observations. GSWM-02 has difficulty reproducing the observed phase structure for July and August as well, months when observed phases are in fairly good agreement. Observations also show that the semidiurnal thermal tide phase has a 6-h (or 180-degree) shift between winter and the other seasons. The winter phase structure appears to set up in late November for Arecibo, and the structure returns to the non-winter phase between late February and early March. SABER observations show that the longitudinal phase variation is large in January and small for other seasons. A modal decomposition shows that the (2, 3) Hough mode is large most of the year but small in January, setting up an asymmetric tidal structure in the solstice periods. Solstice ground-observed amplitudes are large, while from space the winter amplitudes are small, indicating the importance of local effects.