A decadal satellite record of gravity wave activity in the lower stratosphere to study polar stratospheric cloud formation

Abstract

Abstract. Atmospheric gravity waves yield substantial small-scale temperature fluctuations that can trigger the formation of polar stratospheric clouds (PSCs). This paper introduces a new satellite record of gravity wave activity in the polar lower stratosphere to investigate this process. The record is comprised of observations of the Atmospheric Infrared Sounder (AIRS) aboard NASA's Aqua satellite from January 2003 to December 2012. Gravity wave activity is measured in terms of detrended and noise-corrected 15 µm brightness temperature variances, which are calculated from AIRS channels that are the most sensitive to temperature fluctuations at about 17-32 km of altitude. The analysis of temporal patterns in the data set revealed a strong seasonal cycle in wave activity with wintertime maxima at mid-and high latitudes. The analysis of spatial patterns indicated that orography as well as jet and storm sources are the main causes of the observed waves. Wave activity is closely correlated with 30 hPa zonal winds, which is attributed to the AIRS observational filter. We used the new data set to evaluate explicitly resolved temperature fluctuations due to gravity waves in the European Centre for Medium-Range Weather Forecasts (ECMWF) operational analysis. It was found that the analysis reproduces orographic and non-orographic wave patterns in the right places, but that wave amplitudes are typically underestimated by a factor of 2-3. Furthermore, in a first survey of joint AIRS and Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) satellite observations, nearly 50 gravity-wave-induced PSC formation events were identified. The survey shows that the new AIRS data set can help to better identify such events and more generally highlights the importance of the process for polar ozone chemistry.

Accuracy and precision of polar lower stratospheric temperatures from reanalyses evaluated from A-Train CALIOP and MLS, COSMIC GPS RO, and the equilibrium thermodynamics of supercooled ternary solutions and ice clouds

“…Similarly, in the Arctic, a slight increase in variance can be seen along the east coast of Greenland. These spatial imprints of gravity wave activity are largely consistent with the patterns identified by the AIRS 15 µm brightness temperature variations (Hoffmann et al, 2017b) and the Antarctic winter monthly-mean E p patterns also derived from COSMIC GPS-RO (Hindley et al, 2015). However, since any kind of wave activity giving rise to vertical temperature fluctuations will increase the calculated variance, non-orographic features are also visible in these COSMIC temperature variance maps.…”

“…For example, a study of superpressure balloon measurements by Hoffmann et al (2017a) found that ERA-I, MERRA, and MERRA-2 reproduced about 30 % of the standard deviation of the balloon temperature fluctuations, whereas the lower spatial resolution NCEP/NCAR reanalysis reproduced only 15 % and the higher-resolution ECMWF operational analysis reproduced 60 %. ECMWF analyses also underestimate both gravity wave momentum fluxes derived from the balloon measurements (Jewtoukoff et al, 2015) and wave amplitudes derived from Aqua AIRS (Hoffmann et al, 2017b). Similarly, the COSMIC data should perform better than the reanalyses because of their higher resolution.…”

Polar stratospheric cloud climatology based on CALIPSO spaceborne lidar measurements from 2006–2017

“…This work is part of a larger effort to compile 25 new reference PSC climatologies based on the contemporary CALIOP, MIPAS, and MLS datasets that is being performed under the auspices of the Stratospheric-tropospheric Processes and their Role in Climate (SPARC) Polar Stratospheric Cloud initiative (PSCi: http://www.sparc-climate.org/activities/polar-stratospheric-clouds/). A separate MIPAS PSC climatology has been compiled by Spang et al (2017). These new climatologies represent the first observational-based records of PSC occurrence, composition, and particle characteristics on vortex-wide spatial scales covering decadal time scales and are a 30 valuable resource for testing and validating current and future global models.…”

Connections Between Stratospheric Ozone Concentrations Over the Arctic and Sea Surface Temperatures in the North Pacific

“…The residual term in equation (4) may be an approximation of the net chemical production term. Some previous studies have suggested that gravity waves could affect polar stratospheric clouds via small-scale temperature fluctuations and that the polar stratospheric clouds induced by gravity waves in the northern hemisphere are nonuniform in the meridional direction (Alexander et al, 2013;Hoffmann et al, 2017;Zhao et al, 2019). The meridional structure of the residual term in Figure 9d is therefore possibly related to the modulation of stratospheric ozone concentrations by gravity waves and molecular diffusion.…”