The Quasi-Biennial Oscillation Analysis of the Resolved Wave Forcing

Transcription

1 The Quasi-Biennial Oscillation Analysis of the Resolved Wave Forcing Thomas Krismer, Marco Giorgetta Max Planck Institute for Meteorology Hamburg

2 Introduction 1) The Quasi Biennial Oscillation is driven by: equatorial trapped, convectively triggered planetary waves and small scale (convectively triggered) gravity waves 2) Resent Studies focused on increasing the resolution of global climate models to resolve small scale waves and the forcing of the QBO (T42 L62 T42 L90, Giorgetta et al., 2006, T106L152 T213 L256, Kawatani et al., 2010a). 3) The challenges are resolving the scales important for the QBO forcing using realistic boundary conditions over various cycles to investigate the causes of the variability of the QBO 4) In the presented work we analyze: the climatological distribution of the resolved wave forcing during 10 cycles of the westerly phase of the QBO, simulated with a T127L95 resolution, using observed boundary conditions

3 The Quasi Biennial Oscillation in ECHAM6 ECHAM6: General Atmospheric Circulation Model Resolution: T127 L95 Boundary Conditions: AMIP (observed SST, Ozone, Solar Radiation, Greenhouse Gases, Aerosols, Volcanic Aerosols) GravWaveDrag: Hines scheme, 5% enhancement of rms from 10 S to 5 N Reference: Roeckner et al., 2006, Giorgetta et al.,2006

4 The QBO in ECHAM6 T127 L95: Statistics

5 The QBO in ECHAM6 T127 L95: Statistics Spectral Power

6 The QBO in ECHAM6 T127 L95: Comparison with ERA 40 Spectral Power

7 The QBO in ECHAM6 T127 L95: Comparison with ERA 40 Spectral Power

8 The QBO in ECHAM6 T127 L95: mean Conditions

9 The QBO in ECHAM6 T127 L95: mean Conditions Zonal Mean Zonal Wind [m/s]

10 The QBO in ECHAM6 T127 L95: mean Conditions Zonal Mean Zonal Wind [m/s]

11 The Resolved Wave Field in the Westerly Shear Zone IG Ro Kelvin 2

12 The Resolved Wave Field in the Westerly Shear Zone IG 2000 IG 90 Ro Kelvin 2 2

13 The Resolved Wave Field in the Westerly Shear Zone IG 2000 IG 90 Ro Kelvin 2 2

14 Latitudinal and Vertical Distribution of the Wave Forcing

15 Latitudinal and Vertical Distribution of the Wave Forcing

16 Latitudinal and Vertical Distribution of the Wave Forcing

17 Latitudinal and Vertical Distribution of the Wave Forcing

18 Seasonal Difference of the Wave Forcing

19 Seasonal Difference of the Wave Forcing

20 Summary and Outlook 1) A QBO with a realistic, variable period and structure could be modeled with ECHAM6/ T127L95 for 20 years. 2) Kelvin waves dominate the climatological wave spectrum. The sum over the contributions from resolved gravity waves is about equal. 3) Fast and slow Kelvin waves are a dominant forcing in the westerly shear zone. 4) Resolved gravity waves are absorbed at the edges of the westerly shear zone. Their tropospheric sources and vertical propagation shows a seasonal depended latitudinal structure. Future Work: => Investigate the influence of the horizontal model resolution on planetary waves => Illustrate the dependance of the momentum balances of waves on atmospheric conditions (Aerosols, SST CO2) => Try to explain the observed variance of the period of the QBO

21 Appendix I: Resolved Wave Forcing of the Easterly Phase

22 Momentum Balance with different resolutions T42L90 T127L95