SOUTHTRAC-GW: An Airborne Field Campaign to Explore Gravity Wave Dynamics at the World’s Strongest Hotspot

Markus Rapp,Stefanie Knobloch,Felix Friedl-Vallon,Natalie Kaifler,Peter Preusse,Andreas Dörnbrack,Wolfgang Woiwode,Diego Janches,Ramona Eckert,Peter Hoor,Björn-Martin Sinnhuber,Andreas Giez,Jorge L Chau,Markus Garhammer,Robert Reichert,Markus Geldenhuys,Norman Wildmann,Andreas Engel,Sonja Gisinger,Lukas Krasauskas,J Federico Conte,Martin Riese,Bernd Kaifler,Tyler Mixa,A De La Torre ,José Luis Hormaechea ,P Alexander

doi:10.1175/bams-d-20-0034.1

Abstract

AbstractThe southern part of South America and the Antarctic peninsula are known as the world’s strongest hotspot region of stratospheric gravity wave (GW) activity. Large tropospheric winds are deflected by the Andes and the Antarctic Peninsula and excite GWs that might propagate into the upper mesosphere. Satellite observations show large stratospheric GW activity above the mountains, the Drake Passage, and in a belt centered along 60°S. This scientifically highly interesting region for studying GW dynamics was the focus of the Southern Hemisphere Transport, Dynamics, and Chemistry–Gravity Waves (SOUTHTRAC-GW) mission. The German High Altitude and Long Range Research Aircraft (HALO) was deployed to Rio Grande at the southern tip of Argentina in September 2019. Seven dedicated research flights with a typical length of 7,000 km were conducted to collect GW observations with the novel Airborne Lidar for Middle Atmosphere research (ALIMA) instrument and the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) limb sounder. While ALIMA measures temperatures in the altitude range from 20 to 90 km, GLORIA observations allow characterization of temperatures and trace gas mixing ratios from 5 to 15 km. Wave perturbations are derived by subtracting suitable mean profiles. This paper summarizes the motivations and objectives of the SOUTHTRAC-GW mission. The evolution of the atmospheric conditions is documented including the effect of the extraordinary Southern Hemisphere sudden stratospheric warming (SSW) that occurred in early September 2019. Moreover, outstanding initial results of the GW observation and plans for future work are presented.

Highlights

The southern part of South America and the Antarctic peninsula are known as the world’s strongest hotspot region of stratospheric gravity wave (GW) activity
mountain waves (MWs) propagation from 40°S to jet exit region at 60°S; polar night jet (PNJ) edge disturbed by GWs
At approximately 65 km, the Airborne Lidar for Middle Atmosphere research (ALIMA) measurements suggest unstable breakdown of the GW and secondary wave generation: i.e., wave amplitudes of the primary GW decrease strongly above this altitude while simultaneously occurring oppositely aligned smaller-scale phase fronts could be interpreted as features of secondary waves as discussed in N

Summary

Introduction

The southern part of South America and the Antarctic peninsula are known as the world’s strongest hotspot region of stratospheric gravity wave (GW) activity. While GLORIA and ALIMA enable characterization of the atmosphere below and above the aircraft, respectively, the BAHAMAS system consists of a nose tip probe with a 5-hole wind sensor and yields in situ measurements of horizontal and vertical winds along with temperatures and pressures at flight level at high temporal resolution, i.e., of up to 100 Hz (Giez et al 2017, 2019).

Results

Conclusion