Gravity Wave and Turbulence Transport in the Mesopause Region

Vertical transport due to dissipating gravity waves and turbulence in the mesopause region (85-100 km) are analyzed with observational data obtained from a narrow-band sodium wind/temperature lidar located at Andes Lidar Observatory (ALO), Cerro Pach´on (30.25 S, 70.73 W), Chile. The Na lidar at ALO has been in regular operation since 2010. The upgrade of the lidar system in May 2014 resulted in great improvements of the signal levels, which enabled data acquisition of high temporal and vertical resolutions reaching 6 s and 25 m. Traditional data processing utilizes signals at lower resolutions, typically at 60 s and 500 m, to reduce the measurement errors caused by photon noise. By using the high quality signals at much higher resolutions, the lidar is capable determined. of resolving smallest scale gravity waves and even turbulence. This dissertation focuses on characterizing the vertical heat flux induced by both dissipating gravity waves and turbulence with observations after the upgrade. The vertical heat flux is defined as the covariance between vertical wind and temperature perturbations (also called sensible heat flux or enthalpy flux if it is potential temperature). The associated cooling and heating effects on the atmosphere due to this heat transport are also determined. Starting from the observational data, the increased signal of ALO Na lidar significantly reduces the photon noise error but leads to challenges with photomultiplier tube (PMT) saturation at the same time. Corrections to this effect can be measured in a laboratory setting but may have large uncertainties at high photon count rates. Results show that this laboratory-correction can induce large errors for temperature, wind, and Na density measurements, which generates significant bias in the heat flux calculation due to the inherent correlation between vertical wind and temperature errors. A calibration procedure is developed to remove such PMT correction errors from laboratory measurements; then, the revised PMT correction curves are applied to reprocess the data. The corresponding heat flux bias is also calculated with numerical simulations and observations, and both conclude that it is necessary to eliminate this bias from heat flux calculations. Next, the seasonal variation of gravity wave vertical fluxes is calculated from over 400 hours of observations. The flux of potential temperature (enthalpy flux) and sensible heat are related through energy flux. The energy flux is estimated from vertical wavenumber (m) and frequency (w) spectra of temperature perturbations. Flux of potential temperature exhibits a strong semi-annual variation with maximum downward transport appears at 95 km in Jan and 88 km in Aug. Energy flux decreases exponentially with altitude from 10 2 to 10 4 Wm 2 and is larger during southern hemisphere winter. In order to investigate the dissipation of different scale gravity waves and their contributions to the vertical transports, perturbations are separated into three scale ranges. Results show that shorter period gravity waves tend to dissipate at higher altitudes and generate more heat transports. Wave vertical group velocity is estimated from energy flux and total wave energy. The averaged vertical group velocities for high, medium, and low frequency waves are 3.9ms 1, 0.9ms 1, and 0.3ms 1, respectively. In the end, with the high resolution raw data, a new method is developed to derive the turbulence by relating the turbulent perturbations to the photon count fluctuations. Using 150h of lidar observations kH is directly derived for the first time from eddy heat transport. Other key parameters such as the energy dissipation rate and the associated heating rate are also derived from the measurements without resorting to complex turbulence theory. Turbulence w and m spectra are calculated, which follow the power law with slopes consistent with theoretical models. The eddy heat flux generally decreases with altitude from about 0:5Kms 1 at 85km to 0:1Kms 1 at 100km, with a local maximum of 0:6Kms 1 at 93km. The derived mean turbulence thermal diffusivity and energy dissipation rate are 43m2s 1 and 37mWkg 1, respectively. The mean net cooling resulted from the heat transport and energy dissipation is 4:9 1:5Kd 1, comparable to that due to gravity wave transport at 7:9 1:9Kd 1. Turbulence key parameters show consistency with turbulence theories. The results presented in this dissertation can contribute to a more comprehensive parameterization scheme in terms of the thermal structure and wave dissipation for the general circulation models (GCMs). The derived turbulence parameters and cooling/heating rates can provide significant references for parameterizing the wave-driven residual circulation by generating more realistic global thermal structures