Showing papers by "David C. Fritts published in 2021"

Mesospheric Mountain Wave Activity in the Lee of the Southern Andes

Abstract: Gravity waves (GWs) generated by orographic forcing, also known as mountain waves (MWs) have been studied for decades First measured in the troposphere, then in the stratosphere, they were only imaged at mesospheric altitude in 2008 Their characteristics have been investigated during several recent observation campaigns, but many questions remain concerning their impacts on the upper atmosphere, and the effects of the background environment on their deep propagation An Advanced Mesospheric Temperature Mapper (AMTM) and the Southern Argentina Agile MEteor Radar (SAAMER) have been operated simultaneously during the Austral winter 2018 from Rio Grande, Argentina (538°S) This site is located near the tip of South America, in the lee of the Andes Mountains, a region considered the largest MW hotspot on Earth (eg, Eckermann & Preusse, 1999; Hendricks et al, 2014; Jiang et al, 2003, 2005, 2002; Wright et al, 2016) New AMTM image data obtained during a 6-month period show almost 100 occurrences of MW signatures penetrating into the upper mesosphere They are visible ∼30% of time during the period corresponding to the middle of the winter season (mid-May to mid-July) Their intermittency is highly correlated with the zonal wind controlled by the semi-diurnal tide, revealing the direct effect of the atmospheric background on MW penetration into the mesosphere lower thermosphere (MLT, altitude 80–100 km) Measurements of their momentum fluxes (MFs) were determined to reach very large values (average for 36 events ∼250 m2/s2), providing strong evidence of the importance and impacts of small-scale gravity waves at mesospheric altitudes

Instabilities, Dynamics, and Energetics accompanying Atmospheric Layering (IDEAL) Campaign: High-Resolution in situ Observations above the Nocturnal Boundary Layer

Abstract: . The Instabilities, Dynamics, and Energetics accompanying Atmospheric Layering (IDEAL) project was conceived to improve our understanding of the dynamics of sheet and layer (S&L) structures in the lower troposphere under strongly stable conditions. The approach employed a synergistic combination of targeted multi-point observations using small unmanned aircraft systems (sUAS) guiding direct numerical simulation (DNS) modeling to characterize the dynamics driving the S&L structures and associated flow features. The IDEAL research program consisted of two phases. The first was an observational field campaign to systematically probe stable lower atmosphere conditions using multiple DataHawk-2 (DH2) sUAS. Coordinated, simultaneous multi-DH2 flights were guided by concurrent Integrated Sounding System (ISS) wind profiler radar and radiosonde soundings performed by NCAR Earth Observing Laboratory (EOL) participants. Additional sUAS flight guidance was obtained from real-time sUAS measurements. Following the field campaign, the second phase focused on high-resolution DNS modeling efforts guided by in-situ observations made during the first phase. This overview focuses on the details of the observational phase that took place from 24 October to 15 November 2017 at Dugway Proving Ground (DPG), Utah. A total of 72 DH2 flights coordinated with 93 balloon-borne radiosondes were deployed in support of the IDEAL field campaign. Our discussion addresses the average atmospheric conditions, the observation strategy, and the objectives of the field campaign. Also presented are representative flight sorties and sUAS environmental and turbulence measurements.