Winter temperature tides from 30 to 110 km at McMurdo (77.8°S, 166.7°E), Antarctica: Lidar observations and comparisons with WAM

Abstract

We provide the first characterization of diurnal and semidiurnal thermal tides in temperature from 30 to 110 km in the winter season (May through August) at McMurdo (77.8°S, 166.7°E), Antarctica. The observations were made with an Fe Boltzmann temperature lidar in 2011 and 2012. Over 330 h of winter data are compiled into a composite day of temperature perturbations that significantly reduce the incoherent wave effects while preserving the coherent tidal signatures. Both diurnal and semidiurnal tides have small amplitudes (less than 3 K) below 100 km with vertical wavelengths of ~29 and ~23 km, respectively. A new finding of this study is the fast growth of diurnal and semidiurnal tidal amplitudes above 100 km to at least 15 K near 110 km, exceeding that of the freely propagating tides originating from the lower atmosphere. Such fast growth exists for all Kp index cases and diurnal amplitude increases to 15–30 K at 110 km with larger Kp indices corresponding to larger tidal amplitudes and faster growth rates. The slopes of diurnal tidal phases become steeper above 100 km, and the tidal phases barely change with altitude from 100 to 106 km. The tidal growth behavior is reproduced in the Whole Atmosphere Model (WAM) with phases comparable to the observations but magnitudes significantly underestimated. WAM compares reasonably well with the observations below 100 km. The observed significant amplitude increases and phase structure changes suggest additional tidal sources near or above 100 km, which deserve future investigation.