Dynamical and Thermal Effects of Gravity Waves in the Terrestrial Thermosphere-Ionosphere

Transcription

1 1/25 Dynamical and Thermal Effects of Gravity Waves in the Terrestrial Thermosphere-Ionosphere Erdal Yiğit 1,3, Alexander S. Medvedev 2, and Aaron J. Ridley 1 1 University of Michigan, Ann Arbor, USA 2 Max Planck Institute for Solar System Research, K.-Lindau, Germany 3 University College London, London, UK erdal@umich.edu Chapman Conference: Atmospheric Gravity Waves and Their Effects on General Circulation and Climate Honolulu, Hawaii, USA, 28 February - 4 March 2011

2 Contents 1 Introduction - Science Question 3 2 Introduction - Gravity Waves 4 2/25 3 GWs in the Thermosphere 7 4 Parameterization of GWs 8 5 The Extended Spectral Nonlinear Gravity Wave Parameterization 9 6 Linear vs. Nolinear 13 7 Dynamical Effects of Gravity Waves 14 8 Thermal Effects of Gravity Waves 18 9 Variations with Solar Flux Summary and Conclusion 23

3 Introduction - Science Question This Study How do gravity waves propagate from the lower atmosphere to the thermosphere-ionosphere system & what are the resulting thermal and dynamical effects on the general circulation? 3/25

4 Introduction - Gravity Waves Small-scale GWs are unresolved by GCMs Parameterization. Shape the dynamical structure of the middle atmosphere departure from radiative equilibrium. 4/25 What was missing in GW dynamics in GCMs? The effects of GWs of lower atmospheric origin has been ignored in the studies of the thermosphere-ionosphere. Why? missing physics in GW schemes and/or limitations of GCMs. Impact of the problem on our understanding of variability; the energy and momentum budget of TI. vertical coupling

5 Research Strategy & Outcome This study A General Circulation Model that extends into the thermosphere + A Gravity Wave parameterization that accounts for GW thermospheric dissipation GW effects in the thermosphere-ionosphere 5/25

6 Motivation Significance of Modeling! Is there a true motivation of modeling of GW effects in the thermosphere-ionosphere? 6/25

7 GWs in the Thermosphere Earlier observations of disturbances in N e (Munro, 1950). Large-scale GWs are routinely observed in the thermosphere (e.g., Oliver et al., 1997; Djuth et al., 2004) Some medium-scale GWs, being independent of auroral processes, are thought to be of lower atmospheric origin. GWs from deep convective events can produce secondary GWs and large-scale TIDs in the thermosphere (Vadas and Liu, 2009) GW propagation in the thermosphere: wave-induced diffusion, thermal diffusivity, kinematic molecular viscosity, ion drag, and nonlinear wavewave interactions (Vadas and Fritts, 2005; Miyoshi and Fujiwara, 2008; Yiğit et al., 2008) dissipation 7/25

8 Parameterization of GWs What has been the problem with most GW parameterizations? Most GW schemes either cut off or exponentially decay wave effects above the turbopause They use either some intermittancy factors or fudge factors Gravity wave heating and/or cooling are not properly accounted for Nonlinearity is often ignored. 8/25

9 The Extended Spectral Nonlinear Gravity Wave Parameterization Effects of subgrid-scale GWs in GCMs Neither intermittancy factors nor fudge factors are used! Input : Initial gravity wave activity at a given source level Output: GW induced dynamical and thermal effects Further developments of the works by Weinstock (1982); Medvedev and Klaassen (1995, 2000) Accounts for the dissipation of GWs of lower atmospheric origin in the thermosphere: Nonlinear diffusion β non, ion drag β ion, radiative damping β new, molecular viscosity and thermal conduction β mol, eddy viscosity β eddy. 9/25

10 Wave Dissipation Impact of transmissivity τ on the vertical evolution of wave activity u w i = u w (z = z 0 )ρ(z 0 )/ρ(z)τ(z). (1) τ = 1 conservative τ < 1 dissipative 10/25 Estimate τ in terms of β, where β i c i ū x Assumptions: Single column, m 1 < H Details in Yiğit et al. (2008) N β tot = β i (2) i

11 Model Description (CMAT2) University College London (UCL) 3-D first principle hydrostatic finite difference general circulation model (GCM) described in the works by Yiğit et al. (2009) Vertical extent: to 600 km, depending on the heliospheric activity Time step 30 s. NCEP lower boundary Planetary waves GSWM tidal forcing PIM 11/25

12 Framework This study A General Circulation Model that extends into the thermosphere A Gravity Wave Parameterization that accounts for thermospheric dissipation of GWs GW effects in the thermosphere-ionosphere + 12/25

13 favor the vertical propagation of GWs, which are absorbed rapidly below 130 km. The difference between the linear and nonlinear saturation schemes is significant in the SH i where the peak value of the drag computed with b lin (above Linear vs. Nolinear 13/25 the source level denotes the S1 s 1, u 0 w 0 max = ed line is for c s = r c s = 10 m s m s 1. Figure 1: Comparison of linear scheme with the nonlinear scheme. Adopted from Yiğit et al. -type parameterutions (2008, of the Figure flux6). solid line shows of the spectrum m s 1, c s = 0, 0 =0ms 1, k h =

14 Dynamical Effects of Gravity Waves I Zonal mean zonal winds 14/25 Figure 2: Zonal mean zonal wind in m s 1 for June solstice: a) HWM; b) Rayleigh drag run; c) gravity wave drag run with cut-off; and d) allowing GW propagation into the thermosphere. Adopted from Yiğit et al. (2009, Figure 2).

15 Dynamical Effects of Gravity Waves II Zonal mean zonal GW drag 15/25 Figure 3: Zonal mean zonal gravity wave drag in m s 1 day 1 and comparison with ion drag: a) GW drag in the cut-off run; and b) full GW drag; c) and d) are the associated ion drag. Adopted from Yiğit et al. (2009, Figure 3).

16 Dynamical Effects of Gravity Waves III Temporal Variations 16/25 Figure 4: Zonal gravity wave drag and winds at three representative latitudes in the extended simulation. Adopted from Yiğit et al. (2009, Figure 7).

17 Dynamical Effects of Gravity Waves IV 17/25 Figure 5: Zonal gravity wave drag in m s 1 day 1 and comparison with ion drag: Zonal wind in a) cut-off and b) extended simulation; c) Gravity wave drag and d) ion drag in the extended simulation. Adopted from Yiğit et al. (2009, Figure 6).

18 GW Thermal Effects I YIĞIT AND MEDVEDEV: GRAVITY WAVE HEATING IN THE THERMOSPHERE L /25 igure day averaged zonal mean heating/cooling rates simulated with CMAT2 (in K d 1 ): (a) irreversible GW eating (E); (b) total GW heating/cooling (E + Q); (c) Joule heating; (b) cooling due to molecular thermal conduction. haded are the positive values. Figure 6: Mean Gravity wave heating/cooling ( K day 1 ) in the thermosphere. Adopted from Yiğit and Medvedev (2009, Figure 1).

19 GW Thermal Effects II 19/25 Figure 7: Gravity wave heating/cooling ( K day 1 ) in the thermosphere. Adopted from Yiğit and Medvedev (2009, Figure 3). Compare with Q J (Yiğit and Ridley, 2010).

20 Variations with Solar Flux How do the effects of GWs vary with the variation of the solar activity? 20/25 Solar activity Variations in thermospheric parameters (T, u, ρ, N, v mol, etc.) Two GCM simulations at low (F 10.7 = W m 2 Hz 1 ) and high (F 10.7 = W m 2 Hz 1 ) solar activity for solstice conditions.

21 Variations with Solar Flux 21/25 Figure 8: GCM results at solstice: Zonal mean zonal GW drag (1st row) and heating/cooling (2nd row) at low (1st column) and high (2nd column) solar activity. Adopted from Yiğit and Medvedev (2010, Figure 10).

22 Extended GWs Scheme: Mars From the Earth... Parameterization of the effects of vertically propagating gravity waves for thermosphere general circulation models: Sensitivity study, Yiğit, E., Medvedev, et al., JGR, /25 to Mars modeling: Estimates of gravity wave drag on Mars: Indication of a possible lower thermospheric wind reversal, Medvedev, E. Yiğit, P. Hartogh, Icarus, Poster by Alexander S. Medvedev: Gravity Wave Drag in the Mesosphere of Mars

23 Summary and Conclusion GW propagation and saturation is a nonlinear process The extended scheme: First nonlinear scheme that extends systematically into the thermosphere-ionosphere and successfully works in a 3-D GCM. The linear schemes produce unrealistically larger GW drag artificially imposed intermittancy factor. Significance of wave-wave interactions 23/25 Gravity waves are important for TI Gravity waves penetration up to F region altitudes Gravity wave drag (> 150 m s 1 day 1 ) Ion drag Gravity wave heating/cooling (> 150 K day 1 ) Joule heating GW anisotropy Possible penetration mechanism into TI.

24 Summary and Conclusion (cont d) Gravity wave effects depend highly on solar variations GWs penetrate higher into the thermosphere at high solar activity, generating weaker dynamical and thermal effects. 24/25 Importance of GW effects in GCMs Effects of GWs should be accounted for in GCMs extending from the lower to the upper atmosphere in order to better simulate vertical coupling.

25 References Medvedev, A. S., and G. P. Klaassen (1995), Vertical evolution of gravity wave spectra and the parameterization of associated wave drag, J. Geophys. Res., 100, 25,841 25, /25 Medvedev, A. S., and G. P. Klaassen (2000), Parameterization of gravity wave momentum deposition based on nonlinear wave interactions: Basic formulation and sensitivity tests, J. Atmos. Sol.-Terr. Phys., 62, Miyoshi, Y., and H. Fujiwara (2008), Gravity waves in the thermosphere simulated by a general circulation model, J. Geophys. Res., 113, D011101, doi: /2007jd Munro (1950), Traveling disturbances in the ionosphere, Proc. Roy. Soc. London, A, 202 (1069), Vadas, S., and H. Liu (2009), Generation of large-scale gravity waves and neutral winds in the thermosphere from the dissipation of convectively generated gravity waves, J. Geophys. Res., 114, A10310, doi: /2009ja Vadas, S. L., and D. C. Fritts (2005), Thermospheric responses to gravity waves: Influences of increasing viscosity and thermal diffusivity, J. Geophys. Res., 110, D15103, doi: /2004jd Weinstock, J. (1982), Nonlinear theory of gravity waves: Momentum deposition, generalized rayleigh friction, and diffusion, J. Atmos. Sci., 39, 1,698 1,710. Yiğit, E., and A. S. Medvedev (2009), Heating and cooling of the thermosphere by internal gravity waves, Geophys. Res. Lett., 36, L14807, doi: /2009gl Yiğit, E., and A. S. Medvedev (2010), Internal gravity waves in the thermosphere during low and high solar activity: Simulation study., J. Geophys. Res., 115, A00G02, doi: /2009ja Yiğit, E., and A. J. Ridley (2010), Tidal effects on the upper atmosphere in a non-hydrostatic general circulation model, J. Atmos. Sol.-Terr. Phys., ATP2574, submitted for publication. Yiğit, E., A. D. Aylward, and A. S. Medvedev (2008), Parameterization of the effects of vertically propagating gravity waves for thermosphere general circulation models: Sensitivity study, J. Geophys. Res., 113, D19106, doi: / 2008JD Yiğit, E., A. S. Medvedev, A. D. Aylward, P. Hartogh, and M. J. Harris (2009), Modeling the effects of gravity wave momentum deposition on the general circulation above the turbopause, J. Geophys. Res., 114, D07101, doi: / 2008JD