Dynamics of the Atmosphere. General circulation of the atmosphere

Transcription

1 Dynamics of the Atmosphere General circulation of the atmosphere 1

2 Spinup of the general circulation in an idealized model Fig. 1 Schneider, General circulation of the atmosphere,

3 Sigma Mean zonal wind (m/s) in latitude-height plane Midlatitude jets with surface westerlies in addition to subtropical jets DJF Sigma JJA Fig (ERA40 reanalysis ) 3

4 2 Both Hadley and Ferrel cells Eulerian mean meridional streamfunction (10 10 kg s -1 ) 0.2 DJF 0.2 MAM 12 2 Sigma Sigma Sigma JJA SON 2 Sigma Fig (ERA40 reanalysis ) 4

5 General circulation of the atmosphere: subtopics 1. The generation of midlatitude westerlies 2. Effect of eddies on the Hadley Cell 3. Transformed Eulerian mean 4. Downward control and the stratospheric circulation 5

6 Eddy meridional heat flux: poleward in both hemispheres Sigma Fig. 4 Zonal and time mean of v θ cos(lat) in ms -1 K Red line indicates the tropopause (ERA40 reanalysis ) 6

7 Eddy meridional heat flux: poleward in both hemispheres Sigma Fig. 4 Zonal and time mean of v θ cos(lat) in ms -1 K Red line indicates the tropopause (ERA40 reanalysis ) 7

8 Eddy momentum flux: converges at midlatitudes (mostly poleward) Sigma Fig. 5 Zonal and time mean of u v cos(lat) in m 2 /s 2 (ERA40 reanalysis ) 8

9 Eddy momentum flux: converges at midlatitudes (mostly poleward) Sigma Fig. 5 Zonal and time mean of u v cos(lat) in m 2 /s 2 (ERA40 reanalysis ) 9

10 Eliassen-Palm fluxes: upwards and then equatorward 200 hpa 2.7e hpa 200 hpa 2.7e+9 4.2e hpa 400 hpa Fig hpa 600 hpa ucosφ s] [m/s] hpa S 30 S 0 30 N 60 N EP fluxes (arrows); orange is divergence, blue is convergence The reference arrow has units m 3 s -2. The contour interval is 75 m 2 s -2. Red line is the tropopause. Based on ERA-interim DJF Figure courtesy John Dwyer. 3.2e+9 ERA Interim JJA: (d) Dry 60 S 30 S 0 4.6e+9 (e) Effec 10

11 Linear phase (start) Nonlinear (early) E-P fluxes and their divergence in baroclinic lifecycle Nonlinear (late) Time average Fig. 7 Edmon et al

12 Tilts in Rossby waves leads to poleward flux of eastward momentum u v >0 u v <0 Fig. 8 Oort,

13 Eddy momentum fluxes and and theet strength of the RG3001 Schneider al.: WATER VAPOR AND RG3001 Schneider et al.: WATER VAPOR AND CLIMATE CHANGE RG3001C Hadley cells Figure 5. Earth s Hadley circulation over the course of the seasonal cycle. Black contours show the mass flux stream function, with dashed (negative) contours indicating clockwise motion and solid (positive) contours indicating counterclockwise motion (contour interval is kg s 1). Colors indicate horizontal eddy momentum flux divergence div(u0 v0 cos!), with the overbar denoting the seasonal and zonal mean and primes denoting deviations therefrom (contour interval m s 2, with red tones for positive and blue tones for negative values). Gray shading indicates regions in which Ro > 0.5. The 0 0 vertical coordinate s = p/ps is pressure p normalized by surface pressure ps. Computed from reanalysis data for the years provided by the European Centre for Medium Range Weather Forecasts [Kållberg et al., 2004; Uppala et al., 2005]. Schneider et al, Rev. Geophysics, 2010 Figure 5. Earth s Hadley circulation over the course of the mass flux stream function, with dashed (negative) contour (positive) contours indicating counterclockwise motion (contou cate horizontal eddy momentum flux divergence div(u v cos! and zonal mean and primes denoting deviations therefrom (con Fig. 9 for positive and blue tones for negative values). Gray shading climate changes only via changes in the eddy momentum the Hadley cells, a 10% increase in the strength of the mean 13

14 and theet strength of the RG3001 Eddy momentum fluxes and Schneider al.: WATER VAPOR AND C Hadley cells Colors: eddy momentum flux divergence (red positive) Figure 5. Earth s Hadley circulation over the course of the masseulerian flux meridional stream streamfunction function, with dashed (negative) contour Lines: (positive) contours indicating counterclockwise motion (contou Gray shading: Magnitude of local Rossby number > cate horizontal eddy momentum flux divergence div(u v cos! and zonal mean and primes denoting deviations therefrom (con Schneider et al, Rev. Geophysics, 2010 Fig. 9 for positive and blue tones for negative values). Gray shading 14

15 RG3001 Eddy momentum fluxes and and the strength of the Schneider et al.: WATER VAPOR AND CLIMATE CHANGE Hadley cells RG3001 Figure 5. Earth s Hadley circulation over the course of the seasonal cycle. Black contours show the Colors: eddy momentum flux divergence (red positive) mass flux stream function, with dashed (negative) contours indicating clockwise motion and solid (positive) contours indicating counterclockwise motion (contour interval is kg s 1). Colors indilines: Eulerian meridional cate horizontal eddy momentum flux streamfunction divergence div(u0 v0 cos!), with the overbar denoting the seasonal and zonal mean and primes denoting deviations therefrom (contour interval m s 2, with red tones for positive blue tonesmagnitude for negativeofvalues). Gray shading indicates Grayand shading: local Rossby number > 0.5regions in which Ro > 0.5. The vertical coordinate s = p/ps is pressure p normalized by surface pressure ps. Computed from reanalysis data for the years provided by the European Centre for Medium Range Weather Forecasts [Kållberg et al., 2004; Uppala et al., 2005]. Schneider et al, Rev. Geophysics, 2010 climate changes only via changes in the eddy momentum Fig. 9 the Hadley cells, a 10% increase in the strength of the mean 15

16 Transformed Eulerian mean (TEM) circulation (10 9 kg s -1 ) 0.2 Sigma Fig (ERA ) 16

17 Transformed Eulerian mean (TEM) circulation (10 9 kg s -1 ) 0.2 Sigma Fig (ERA ) 17

18 Dry-isentropic mean meridional streamfunction (10 10 kg s -1 ) Potential temperature [K] Fig Red: Tropopause Magenta: 10, 50, 90 percentiles of surface potential temperature distribution (ERA40 reanalysis ) 18

19 0.2 Sigma Transformed Eulerian mean circulation (10 9 kg s -1 ) Sigma Dry isentropic circulation interpolated to sigma coordinates (10 9 kg s -1 ) Fig. 12 (ERA ) 19

20 0.2 Sigma Transformed Eulerian mean circulation (10 9 kg s -1 ) Very similar except near lower boundary Sigma Dry isentropic circulation interpolated to sigma coordinates (10 9 kg s -1 ) Fig. 12 (ERA ) 20

21 Mean meridional circulation on dry and moist isentropes: averaging on θe surfaces (moist isentropes) gives simplest circulation (Pauluis et al, Science, 2008) Fig

22 Mean meridional circulation on dry and moist isentropes: averaging on θe surfaces (moist isentropes) gives simplest circulation Moist isentropes give very simple circulation (Pauluis et al, Science, 2008) Fig

23 Vertical structure of the atmosphere Fig

24 Zonal wind (m/s) and temperature (K): zonal mean for January Fig. 15 Holton&Hakim 24

25 Zonal wind (m/s) and temperature (K): zonal mean for January Temperature maximum at summer pole Easterlies in summer hemisphere Westerlies in winter hemisphere Fig. 15 Holton&Hakim 25

26 Zonal wind (m/s) and temperature (K): zonal mean for July Fig. 16 Holton&Hakim 26

27 Compare radiative-equilibrium and actual temperature Fig. 17 Holton&Hakim 27

28 Compare radiative-equilibrium and actual temperature Radiative-equilibrium much colder here Fig. 17 Holton&Hakim 28

29 Residual circulation Height (km) Jan in the stratosphere (sometimes called Brewer-Dobson circulation) (A) 90 S 60 S 30 S 0 30 N 60 N 90 N 50 7 Height (km) Jul Streamfunction units are kg/m/s Unlike earlier streamfunctions based on zonal average rather than zonal integral (B) 90 S 60 S 30 S 0 30 N 60 N 90 N Figure 3 Average ( ) residual mean meridional streamfunction calculated from UK Meterological Office UARS assimilation winds and temperatures for (A) January and (B) July. Fig. 18 W. Norton 29

30 Wave-driving of the residual circulation Fig. 19 FIGURE 12.8 Schematic cross-section of the wave-driven circulation in the middle atmosphere and its role in transport. Thin dashed lines denote potential temperature surfaces. Dotted line is the tropopause. Solid lines are contours of the TEM meridional circulation driven by the wave-induced forcing (shaded region). Wavy double-headed arrows denote meridional transport and mixing by eddy motions. Heavy dashed line shows an isopleth of mixing ratio for a long-lived tracer. Holton and Hakim 30

31 Downward control: response to steady zonal force at 45N, 45km Fig. 20 Streamfunction after 100 days; clockwise for a westward force Haynes et al,

32 60 Height (km) Relevance of residual circulation for transport of tracers Trajectory over two years: starts at equator at 25km (red, green, blue, black) (A) S 60 S 30 S 0 30 N 60 N 90 N Starting at other longitudes gives different behavior (e.g. other hemisphere, lower branch) Fig. 21 Figure 4 Two-year trajectories calculated from UK Meterological Office UARS assimilation winds started in April 1996 on the Equator at 25 km at four different longitudes. The first 6 months are colored red, the second 6 months green, the third 6 months blue, and last 6 months black. W. Norton 32

33 Relevance of residual circulation: Zonal-mean methane concentration Height (km) S 60 S 30 S 0 30 N 60 N 90 N Figure 5 Zonally averaged mixing ratio of methane for October ( ) as measured by Halogen Occultation Experiment (HALOE) on the UARS. Contour interval is 0.2 ppmv. Fig. 22 W. Norton 33

34 Relevance of residual circulation: Zonal-mean methane concentration 50 Quasi-horizontal mixing by eddies Height (km) Descent Ascent Descent S 60 S 30 S 0 30 N 60 N 90 N Figure 5 Zonally averaged mixing ratio of methane for October ( ) as measured by Halogen Occultation Experiment (HALOE) on the UARS. Contour interval is 0.2 ppmv. Fig. 22 W. Norton 34