Investigating Small-Scale Dynamical Features in the Mesopause Region

• Main Author: Simkhada, Deepak B.
• Format: Others
• Published: DigitalCommons@USU 2010
• Subjects: Space and Atmospheric Physics; Atmospheric Sciences; Physics
• Online Access: https://digitalcommons.usu.edu/etd/731; https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1727&context=etd

Utilizing analyses of observational data, we performed a detailed study to investigate short-period atmospheric gravity waves and ripples, and instabilities in the mesopause region. Recent coordinated measurements from Haleakala Observatory, Maui, HI via airglow wave imaging, meteor wind radar, and Na wind temperature lidar have provided a unique dataset for this study. Gravity waves generated in the lower atmosphere propagate energy upwards into the mesosphere and lower thermosphere region where they modulate the airglow emissions, and later break and deposit their momentum, causing significant perturbations in winds and temperatures. Ripples, on the other hand, are likely generated by localized shear instabilities in the background wind eld, and are also observed frequently in airglow images. First, we investigated the frequency of occurrence and climatology of ripples and their seasonal variation in propagation directions of motion. These novel results were then used to characterize the nature of the observed ripples and to identify individual Kelvin Helmholtz instability events as their sources, which were consistent with theoretical computations. The results provided insight to better quantify seasonal wave anisotropy and instability dynamics in the mesopause. Second, we investigated ground-relative and intrinsic properties of gravity waves that were Doppler-ducted or evanescent. The results were then compared with an analytical model and numerical model simulations for the Doppler-ducted and evanescent waves, demonstrating signicant dierences in wave structures for apparently similar wave events. Results reinforced the need to better understand the dynamics of wave ducting and their importance for momentum and energy transports at upper mesosphere and lower thermosphere heights. Third, we investigated the frequency of occurrence of frontal disturbances and the appearance of complementary intensities in OH and O2 airglow emissions. We have analyzed ducting conditions of mesospheric bores. One bore event was trapped in a stable Doppler duct arising from wind structure, and other bore events were trapped within thermal inversion layers. Analysis confirmed that the measured ducted bore events were separately consistent with theoretical Doppler-ducted and thermal-ducted wave characteristics. These studies provide an extensive dataset for detailing the morphology and dynamics of mesospheric frontal events.