A Statistical Characterization of the Phase Shift between Vertical Wind and Temperature Perturbations Induced by Gravity Waves in the MLT above McMurdo, Antarctica.

Since 2018, the CU McMurdo Lidar Campaign has provided high-resolution observations with the STAR Lidar system that have revealed complex and variable GW activity in the mesosphere and lower thermosphere (MLT). Despite extensive studies on the middle atmosphere at McMurdo—an area with strong GW activity due to Trans-Antarctic Mountains, Mount Erebus, the polar vortex and geomagnetic storms—the phase shift between temperature and vertical wind perturbations caused by these waves remains underexplored in this remote region. This phase shift relation is important because of the surprising discoveries from lidar observations at McMurdo, which show upward (positive) sensible heat fluxes from 97 to 106 km (Chu et al. 2022). This observation counters the prior popular understanding of GW and rectifies this misunderstanding in correcting that the phase shift between T’ and w’ can be less than 90 degrees for non-dissipative and weakly dissipated gravity waves, leading to the positive sensible heat flux observed. However, the actual phase shift has not been verified and characterized with real observational data at McMurdo. One of the few studies which characterized such phase difference used Na Doppler lidar data (Lu et al. 2017) collected over Boulder, CO and developed a methodology to classify and characterize mesoscale GW (including the extraction of the phase difference).
This project aims to analyze the phase difference of these temperature and wind waves using high-resolution data from the STAR Na-Doppler lidar system at McMurdo. Building methods developed for similar studies in Boulder (Lu et al. 2017), the study will identify and develop a methodology for the identification of dominant GW frequencies and derive phase differences, offering new insights into polar MLT dynamics and extending the applicability of lidar-based GW analysis to Antarctic conditions. This endeavor seeks to follow the methods of the 2017 project structurally, but to adjust for the different conditions and GW present in the modern McMurdo data collection in the efforts to expand the applicability of the Table Mountain group to the polar MLT region. The ultimate objective of this work is to extract the phase differences observed in the most common and prominent wave frequencies in the MLT captured by the Antarctic Na Doppler lidar system at the laboratory of Dr. Xinzhao Chu and further utilize those phase differences to verify the fully compressible (non-Boussinesq) polarization equations, have challenged the conventional understanding of the nature of sensible heat flux in the MLT (Chu et al. 2022). The extended observational period enabled by STAR's continuous operation will allow for an assessment of interannual variability, further refining our understanding of GW behavior in the polar middle atmosphere. Furthermore, this work will contribute to improving parameterizations of GW effects in polar climate models, addressing the gaps in current numerical simulations of Antarctic MLT dynamics.