Gravity-Wave-Driven Seasonal Variability of Temperature Differences between ECMWF IFS and Rayleigh Lidar Measurements in the Lee of the Southern Andes

Abstract

Even now with a growing understanding of stratospheric processes, highly developed numerical models, and increasing computational resources, middle atmosphere temperature (re)analyses have a larger uncertainty than their tropospheric counterparts. Improving the representation of the past (reanalysis), current (analysis), and future (forecast) state of the middle atmosphere in general circulation models (GCMs) is important for the validation and forecasting of tropospheric weather and future climate. It is known that the circulation in the middle and upper atmosphere is strongly influenced by internal gravity waves (GWs) triggered for example, by flow over mountains (Fritts & Alexander, 2003). At the same time, processes in the stratosphere such as anomalies in the winter-and spring-time stratospheric polar vortex impact the tropospheric circulation (Baldwin & Dunkerton, 2001;Byrne & Shepherd, 2018;Garfinkel & Hartmann, 2011).One issue when modeling the middle atmosphere is that there is a limited amount of observations to constrain the current model state (e.g., Eckermann et al., 2018). Above 10 hPa, most of the observations assimilated into the Integrated Forecasting System (IFS) of the European Center for Medium-Range Weather Forecasts (ECMWF) are from satellites and have limited spatial and temporal resolutions. They mainly provide temperature-related data (e.g., Global Navigation Satellite System Radio Occultation (GNSS-RO), Atmospheric Infrared Sounder (AIRS), Advanced Microwave Sounding Unit (AMSU-A)) and the topmost radiances assimilated peak at approximately 1-2 hPa. The range of sensitivity of the satellite observations to certain horizontal and vertical scales of GWs depends on the instrument and viewing geometry (observational filter, see Alexander, 1998) as can be seen in for example, Figure 9 of Preusse et al. (2008). To produce the most accurate representation of the atmospheric state, all the observations irregularly distributed in time and space and each having their limitations and uncertainties are combined with the numerical weather prediction model on a global grid. For the (re)analyses at ECMWF, this is achieved by 4-dimensional variational data assimilation (4D-Var).

The Relationship between Stratospheric Gravity Wave Potential Energy and Tropospheric Parameters over South America inferred from COSMIC-2 and METOP Radio Occultation Measurements

“…Tropopause parameters height and temperature uctuations show seasonal and inter-annual variability (Zhou and Holton 2002;Randel et al 2003;Seidel and Randel 2006) The relationship between the tropospheric parameters and the stratospheric gravity wave (SGW) potential energy (E p ) has become an important subject since the launch of the Radio Occultation (RO) satellites, especially the Constellation Observing System for Meteorology, Ionosphere, and Climate (COS-MIC) satellites. The GW E p is an important parameter to measure the GW impacts in the atmosphere due to it dependency on only atmospheric temperature pro le for the derivation of GWs in the atmosphere (Cai et al 2017;Baumgarten et al 2018;Yang et al 2021;Strelnikova et al 2021;Gisinger et al 2022). South America continent comprises different sources of gravity waves and the peculiar characteristics of these sources with their link with the SGWs have received lesser attention.…”