Project 1.2 Changes in filtering

From CAWSES

• Project leaders: Elisa Manzini (Italy) and Stephen Eckermann (USA)
• Project members: Venkat Ratnam (India), Patrick Espy (Norway), Yoshio Kawatani (Japan), Erich Becker (Germany), Nili Harnik (Israel)

Contents 1 Introduction 2 Questions 3 References 4 Related meetings

Introduction

To reach the upper atmosphere, planetary and gravity waves generated in the lower atmosphere (see Project 1.1) must propagate through the intervening wind patterns of the lower and middle atmosphere. As these waves propagate obliquely upwards, background wind and temperature changes refract the waves, such that some are absorbed or reflected while others are transmitted to the upper atmosphere. In turn, planetary and gravity waves interact nonlinearly with the background flow, heavily impacting global wind patterns. For example, planetary-wave breaking drives sudden stratospheric warming (SSW) dynamics, while critical-level filtering of gravity waves by mean winds and planetary waves leads to anisotropic distributions of transmitted momentum flux in the upper atmosphere that drive the large-scale climate and circulation at these altitudes.

Climate modeling has revealed interesting simulated trends in these and other wave filtering characteristics that affect how these simulated future geospace environments respond to projected climate change. For example, most climate models predict secular increases in the strength of the Brewer-Dobson circulation and in the frequency of SSWs due to climate-induced changes in extratropical planetary-wave and orographic gravity-wave drag caused by an altered mean environment for wave propagation driven by CO₂ increases (Li et al. 2008; McLandress and Shepherd, 2009a, 2009b; Butchart et al., 2006 2010). The CO₂ effects also interact with stratospheric ozone loss and recovery both radiatively (Eyring et al., 2007) and dynamically through a modified Southern Annular Mode that shifts the jet stream and Southern Ocean storm tracks poleward (Gillett and Thompson, 2003; Son et al., 2009), further affecting the propagation environment that controls the morphology of waves transmitted to the upper atmosphere (see, e.g., Manzini et al. 2003).

Recent observations show that SSWs, for example, yield deep circulation responses that extend through the mesosphere and lower thermosphere (MLT; Siskind et al. 2007) and deep into the ionosphere (Goncharenko and Zhang, 2008). Modeling and observations both indicate that these MLT and ionospheric responses are driven by SSW-induced changes in both planetary-wave and gravity-wave transmission to high altitudes (Siskind et al., 2010; Pedatella and Forbes, 2010) which affect the local wave-driven climate. Similar wave coupling also communicates QBO-like signals to the tropical upper atmosphere through QBO-modulated wave transmission and filtering (Burrage et al. 1996; Hagan et al. 1999; Garcia and Sassi, 1999; Wu et al. 2009). How or if the changes in wave filtering characteristics in the lower and middle atmospheres, due to tropospheric CO₂ and stratospheric O₃ trends, can communicate related climate-change-induced responses to the upper atmosphere through wave coupling, remains unclear and largely uninvestigated. This project seeks to foster research and collaborations that cast light on these and related questions.

Questions

• Do the robust CO₂–induced changes in extratropical stratospheric planetary- and gravity-wave drag in GCMs (due to modified filtering and refraction) affect MLT and ionospheric climate through modified upper-atmospheric wave driving?

• Do the modifications in these simulated features due to stratospheric ozone loss and recovery also impact high-altitudes through modified wave driving?

• Do long-term observations of climatological wave properties at high altitudes show evidence of long-term change consistent with changes in the wave filtering environment?

• Do simpler models (e.g., ray tracing, quasi-geostrophic codes) show evidence of robust long-term changes in upper-atmospheric waves due to a changed wave filtering environment?

References

Burrage, M. D., R. A. Vincent, H. G. Mayr, W. R. Skinner, N. F. Arnold, and P. B. Hays (1996), Long-term variability of the equatorial middle atmosphere zonal wind, J. Geophys. Res., 101, 12,847–12,854.

Butchart, N., et al. (2006), Simulations of anthropogenic change in the strength of the Brewer–Dobson circulation. Climate Dynamics, 27, 727-741.

Butchart, N., I. Cionni, V. Eyring, D.W.Waugh, H. Akiyoshi, J. Austin, C. Brühl, M. P. Chipperfield, E. Cordero, M. Dameris, R. Deckert, S. M. Frith, R. R. Garcia, A. Gettelman, M. A. Giorgetta, D. E. Kinnison, F. Li, E. Mancini, C. McLandress, S. Pawson, G. Pitari, D. A. Plummer, E. Rozanov, F. Sassi, J. F. Scinocca, T. G. Shepherd, K. Shibata, and W. Tian (2010) Chemistry-climate model simulations of 21st century stratospheric climate and circulation changes, J. Clim. (in press).

Eyring, V., et al. (2007), Multimodel projections of stratospheric ozone in the 21st century, J. Geophys. Res., 112, D16303, doi:10.1029/2006JD008332.

Garcia, R. R. and F. Sassi (1999), Modulation of the mesospheric semiannual oscillation by the quasibiennial oscillation, Earth Planets Space, 51, 563-569.

Gillett, N. P., and D. W. J. Thompson (2003), Simulation of recent Southern Hemisphere climate change, Science, 302, 273–275.

Goncharenko, L., and S.-R. Zhang (2008), Ionospheric signatures of sudden stratospheric warming: Ion temperature at middle latitude, Geophys. Res. Lett., 35, L21103, doi:10.1029/2008GL035684.

Hagan, M. E., M. D. Burrage, J. M. Forbes, J. Hackney, W. J. Randel, and X. Zhang (1999), QBO effects on the diurnal tide in the upper atmosphere, Earth Planets Space, 51, 571–578.

Li, F., J. Austin, and J. Wilson (2008), The strength of the Brewer–Dobson circulation in a changing climate: Coupled chemistry–climate model simulations. J. Climate, 21, 40-57.

Manzini, E., B. Steil, C. Brühl, M.A. Giorgetta, and K. Krüger (2003), A new interactive chemistry-climate model: 2. Sensitivity of the middle atmosphere to ozone depletion and increase in greenhouse gases and implications for recent stratospheric cooling. J. Geophys. Res., 108(D14), 4429.

McLandress, C. and T. G. Shepherd (2009a), Simulated anthropogenic changes in the Brewer-Dobson circulation, including its extension to high altitudes, J. Clim. 22, 1516-1540.

McLandress, C. and T. G. Shepherd (2009b), Impact of climate change on stratospheric sudden warmings as simulated by the Canadian Middle Atmosphere Model, J. Clim. 22, 5449-5463.

Pedatella , N. M. and J. M. Forbes (2010), Evidence for stratosphere sudden warming‐ionosphere coupling due to vertically propagating tides, Geophys. Res. Lett., 37, L11104, doi:10.1029/2010GL043560.

Siskind, D. E., S. D. Eckermann, L. Coy, J. P. McCormack, and C. E. Randall (2007), On recent interannual variability of the Arctic winter mesosphere: Implications for tracer descent, Geophys. Res. Lett., 34, L09806, doi:10.1029/2007GL029293.

Siskind, D. E., S. D. Eckermann, J. P. McCormack, L. Coy, K. W. Hoppel, and N. L. Baker (2010), Case studies of the mesospheric response to recent minor, major and extended stratospheric warmings, J. Geophys. Res., (in press).

Son, S.-W., N. F. Tandon, L. M. Polvani, and D. W. Waugh (2009), Ozone hole and Southern Hemisphere climate change, Geophys. Res. Lett., 36, L15705, doi:10.1029/2009GL038671.

Wu, Q., S. C. Solomon, Y.-H. Kuo, T. L. Killeen, and J. Xu (2009), Spectral analysis of ionospheric electron density and mesospheric neutral wind diurnal nonmigrating tides observed by COSMIC and TIMED satellites, Geophys. Res. Lett., 36, L14102, doi:10.1029/2009GL038933.

Related meetings

AGU Chapman Conference on Atmospheric Gravity Waves and Their Effects on General Circulation and Climate, Honolulu, Hawaii, 28 February – 4 March 2011. Abstract deadline 13 October 2010.