Rayleigh Lidar Observations of Gravity Wave Activity above the Southern Tip of South America

DE LA TORRE, A.; LLAMEDO, P.; SALVADOR, J.; ALEXANDER, P.; SCHMIDT, T.; HIERRO, R.

Potsdam

Workshop; IAGA/ICMA/SCOSTEP Workshop on Vertical Coupling in the Atmosphere-Ionosphere System; 2018

Gravity wave (GW) activity is analyzed using temperature (T) data retrieved from a Rayleigh lidarat Río Gallegos, Argentina (51.6º S, 69.3º W). GW characteristics are derivedfrom 302 profiles providing more than 1018 h of high-resolution lidar databetween 20 km and 56 km height from August 2005 to December 2015. T measurements are carried out byoff-wavelength at 355 nm of a Differential Absorption Lidar (DIAL) instrument. Thislidar was the southernmost outside Antarctica until the end of 2017. RíoGallegos is an exceptional place to observe large amplitude GW. Every lidarmeasurement is classified according to its relative position to the polarvortex. In general the median of the mass specific GW potential energy (PE) is larger during winter and springthan during summer and autumn. The largest median of PE is found inside the vortex and decreases at its edge, inside itand when there is no vortex. Outside the vortex, the lowest PE is found during summer and thelargest during autumn. The lidar measurements are compared with collocatedSABER (Soundingof the Atmosphere using Broadband Emission Radiometry) and GPS-RO (Global PositioningSystem-Radio Occultation) data. The different instruments show differentspectral windows of the GW spectrum, providing complementary observations. Onaverage, it can be seen that lidar observations provide larger PE values than limb soundingmeasurements. From a Morlet continuous wavelet transform analysis, 3 distinct timemodes are captured from SABER and GPS RO data at the upper and lowerstratosphere, respectively. In particular, a systematic 3.5-4 years oscillationwith minimum / maximum wave activity amplitude in September from GPS RO / SABERdata are observed. Starting in the southern winter of 2018, T measurements of GW parameters during intenseobservational periods in the polar vortex evolution, simultaneously observed atRio Gallegos and Río Grande, Argentina (53.7°S, 67.7°W) will be available. The instruments at disposal deployedat Río Gallegos include an airglow imager. At Rio Grande, a second Rayleighlidar, a second airglow imager, an advanced mapper for T measurements (AMTM) and a meteor radar (SAAMER) are alsoavailable. A major objective at this hotspot region is a better understandingof GW sources, vertical and horizontal refraction, mean flow interaction andenergy and momentum transport from the lower to the upper atmosphere. This preliminary experiment will constitute a testexercise to gain experience in preparation for a more complete field program,to be held during the southern spring of 2019 (SouthTRAC Experiment). Followingprevious results, we will show that the combination of simultaneousmeasurements at constant pressure levels provided by 2 lidars and twoindependent profiles (e.g. a radiosounding, a radio occultation event, etc)constitutes a possible method to derive non stationary and stationary GWparameters. In the distinction between stationary and non stationary GWstructures, airglow images and an analysis of the possible imbalance of theflow will be considered as well.