CEDAR: Quantifying Mesospheric Gravity Waves and Associated Temperature Variability Over the Andes

Utah State University, Logan UT

Investigators

Abstract

This project is a novel experimental investigation to quantify the role of gravity waves on the dynamics, momentum transport, deposition and subsequent forcing of the Mesosphere and Lower Thermosphere (MLT) region (~80-100 km) over South America, and specifically near the Andes Mountains. The Andes region is an excellent natural laboratory for investigating gravity wave influences on the MLT dynamics. During the summer months the dominant gravity wave forcing results from deep convection arising from severe thunderstorms over the continent to the east. During the winter, strong orographic forcing dominates, due to intense prevailing zonal winds blowing eastward from the Pacific Ocean which suddenly encounter the towering Andes mountain range. This creates large amplitude waves that have been measured well into the stratosphere but have yet to be unambiguously measured at MLT heights. There are strong theoretical reasons to expect them to penetrate well into the mesosphere, especially during the winter months. Building on extensive experience gained as part of the highly successful Maui-MALT program (2002-2006), this project will deploy and remotely operate the Utah State University CEDAR Mesospheric Temperature Mapper (MTM) at Cerro Tololo, Chile (30.1 S, 70.8 W). The MTM is a robust, high-performance CCD imaging system designed to provide key temperature and intensity measurements on gravity waves using precise observations of two prominent airglow emissions, the NIR OH(6,2) centered near 87 km, and the O2(0,1)Atmospheric band, near 94 km. These data afford a unique capability to quantify wave propagation, growth, and dissipation at MLT heights. It is planned to perform these new measurements in coordination with Na wind-temperature lidar, meteor radar, all-sky imager and other optical instruments as part of a well proven instrument cluster, as employed successfully during the Maui-MALT program. The primary goals are: 1) To quantify the impact and seasonal variability of a broad spectrum of waves (including gravity waves, tides and planetary waves) over the Andes using coordinated wave, wind, and temperature measurements; 2) To perform a unique investigation of mountain waves present at MLT heights during winter months, quantifying their characteristics and associated momentum fluxes, and comparing with similar measurements during the summertime due to convective forcing. The broader impact of the project includes strong student involvement, which will contribute to training the next generation of researchers in novel optical measurements and image processing techniques. In addition, the recognized role of gravity waves in driving the mean and variable structure of the MLT makes an understanding of their various contributions a high priority for the aeronomy community. In particular, the need to be able to accurately describe these effects in state-of-the-art models has broad implications for predicting their regional, seasonal and global influences under variable solar forcing and climate change conditions.