Mesosphere and Lower Thermosphere Dynamics Studies Employing the Southern Argentina Agile MEteor Radar (SAAMER), Correlative Measurements, and Modeling

点击翻译按钮获取中文摘要

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). This award supports the continued operations of a suite of instruments including the SAAMER meteor radar at the southern tip of South America known as Terra del Fuego. The award will support the continued study of large- and small-scale dynamics that play many roles in the mesosphere and lower thermosphere (MLT). Tides and planetary waves (PWs) account for the major variability on larger horizontal and vertical scales because they propagate largely without strong attenuation from sources in the troposphere and stratosphere into the MLT and above. These have been studied using MLT radar, lidar, and satellite measurements for many years, and they account for the major large-scale variability of the MLT. Smaller-scale gravity waves (GWs) arise from multiple sources modulated by tropospheric weather, especially mountain waves (MWs), convective GWs, inertia-GWs, and secondary GW (SGW) generation where GWs from other sources attain large amplitudes. Most of these dynamics have been studied extensively, both observationally and via modeling, but the smaller scales, and their large range of dynamics, interactions, and instabilities have prevented a quantitative understanding of their dynamics and influences to date. The importance of these large- and small-scale dynamics derives from their major influences in the MLT and extending to lower and higher altitudes. Observations and analyses of large- and small-scale dynamics play central roles in identifying and understanding the diverse processes that determine the structure and variability of the atmosphere. Such efforts are especially needed in the MLT, where the dynamics are driven by energy and momentum fluxes due to GW propagation from sources at lower altitudes that vary strongly with tropospheric weather. MLT responses are often strongly nonlinear due to large GW amplitude increases leading to instabilities, turbulence, and forcing of mean and large-scale wave motions that are poorly understood at present. Analyses of observations by Aura MLS and MLT radars will quantify key PW and tidal dynamics. Observational guidance of GW responses at TdF and NAVGEM re-analyses would aid the detailed modeling addressing MW and more general GW dynamics, instabilities, forcing, and responses in the MLT. A Univ. of Colorado (CU) graduate student would receive training in state-of-the-art GW, KHI, and geophysical turbulence modeling and supercomputing. The collection, formatting, and provision of global MLT radar data for NAVGEM data assimilation would also be a significant benefit for the CEDAR community. The major larger-scale forcing and smaller-scale forcing and variability of the MLT is driven by GWs that account for the major vertical fluxes of horizontal momentum driving MLT dynamics where GW breaking and dissipation cause energy and momentum deposition. These lead to local flow accelerations, mixing, feedbacks on the larger-scale dynamics contributing to GW breaking, and induced residual circulations having impacts at lower altitudes. All these dynamics have been assessed to varying degrees in previous observational and/or modeling studies. The new award would study different processes that include the following: 1)effects of GW/tidal interactions on tidal amplitudes & phases and GWs at higher altitudes, 2) influences of intermittency in GW breaking, energy & momentum deposition, and mixing, 3) influences of large-scale Kelvin-Helmholtz instabilities (KHI) in GW & tidal shears, 4) sources and effects of GW “self-acceleration” dynamics, for which there is significant modeling & observational support, but the implications of which are largely unknown, and 5) influences on MLT structure and variability by transient PWs arising at lower altitudes. Initial conditions for these models would be provided by NAVGEM re-analyses extending to 140 km based on global MLT radar winds supporting the NAVGEM data assimilation efforts coordinated by GATS personnel.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.