Abstract
Large-amplitude internal gravity waves were observed using Rayleigh lidar temperature soundings above Rio Grande, Argentina (54^circ ; hbox {S}, 68^circ ; hbox {W}), in the period 16–23 June 2018. Temperature perturbations in the upper stratosphere amounted to 80 K peak-to-peak and potential energy densities exceeded 400 J/kg. The measured amplitudes and phase alignments agree well with operational analyses and short-term forecasts of the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF), implying that these quasi-steady gravity waves resulted from the airflow across the Andes. We estimate gravity wave momentum fluxes larger than 100 mPa applying independent methods to both lidar data and IFS model data. These mountain waves deposited momentum at the inner edge of the polar night jet and led to a long-lasting deceleration of the stratospheric flow. The accumulated mountain wave drag affected the stratospheric circulation several thousand kilometers downstream. In the 2018 austral winter, mountain wave events of this magnitude contributed more than 30% of the total potential energy density, signifying their importance by perturbing the stratospheric polar vortex.
Highlights
The Tierra del Fuego archipelago at the southern tip of South America is known as the world’s gravity wave hot spot[1]
Increased momentum fluxes leeward of the Andes have been correlated with rare, large-amplitude orographic waves based on satellite data as well as model s imulations[13,33]
Our measurements of mountain wave-induced temperature perturbations of 80 K are a factor of two or more larger than the strongest events observed by satellite instruments with amplitudes in the range [10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30] K1,14,15,29,30,32
Summary
The Tierra del Fuego archipelago at the southern tip of South America is known as the world’s gravity wave hot spot[1]. Our lead question is: can local, continuous and high-temporal- and high-vertical-resolution observations of gravity waves in the lee of the Andes enhance our knowledge about the magnitude of the momentum that is deposited in the stratosphere? To target the worlds’s largest gravity waves, we installed the Compact Autonomous Rayleigh lidar (CORAL) at Rio Grande, Tierra del Fuego, Argentina, for night-time measurements of atmospheric temperature. We will present a case study of an exceptionally strong mountain wave event with peak-to-peak temperature amplitudes up to 80 K and a long duration of eight days during austral winter 2018. The observations of temperature perturbations, momentum flux and gravity wave drag will be complemented with and compared to data from an operational numerical weather prediction (NWP) model. The seasonal evolution of the stratospheric gravity wave activity above Rio Grande will be documented based on observations and NWP data. The CORAL lidar’s long-term dataset with dense temporal coverage will be exploited to assess the contributions of mountain wave events with similar magnitude to the total gravity wave activity during austral winter 2018
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