1 / 40

INTRASEASONAL Oscillations—the Heartbeat of 14-100 Day Weather Variability

INTRASEASONAL Oscillations—the Heartbeat of 14-100 Day Weather Variability. Paul E. Roundy. Cold Air Outbreak Timeline. Active convective anomaly amplified in Indian ocean (mid February 2003)

craig
Download Presentation

INTRASEASONAL Oscillations—the Heartbeat of 14-100 Day Weather Variability

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. INTRASEASONAL Oscillations—the Heartbeat of 14-100 Day Weather Variability Paul E. Roundy

  2. Cold Air Outbreak Timeline • Active convective anomaly amplified in Indian ocean (mid February 2003) • Anomaly approached maritime continent (around February 20)—heating deflected pacific jet stream pattern

  3. Cold Air Outbreak • Large edge wave formed (late February), propagated poleward • Cold air stream enhanced by strengthened west-coast ridge

  4. Convective Anomaly Pattern26 February, 2003 From BMRC, Matthew Wheeler, Australia

  5. Cold Air Outbreak, February 27, 2003 From NCEP Reanalysis

  6. The Large-Scale ConvectiveDisturbance • Tropical Intraseasonal or Madden-Julian Oscillation

  7. What IS the MJO? • Large-scale disturbance of deep convection and winds that controls up to half of the variance of tropical convection in some regions • Brief history

  8. Simplified Madden-Julian Oscillation Composite OLR from A.J. Matthews, 2000.

  9. MJO Statistics • Eastward propagation, 4 +/- 2 ms-1. Also has standing wave behavior • 30-60 day period • Wavenumber 1-4 (planetary scale) • Interacts with midlatitudes, but some of this is nonlinear and hard to quantify

  10. Schematic of Mature MJO

  11. How Does It Propagate? • Is a matter of debate, but, probably involves • interactions with equatorial waves • Kelvin wave • Equatorial Rossby wave • Feedbacks from convection • Sea surface temperatures—air-sea interaction • Land interactions

  12. Kelvin Wave • Equatorial zonal wind disturbance L L H H

  13. Kelvin Wave • Propagation mechanism: H L Pressure Fall Pressure Fall Pressure Rise Dry wave propagates eastward at greater than 40 ms-1

  14. Convective Kelvin Wave z Convection removes Some of the accumulating mass, slows propagation H L x Propagation speed: less than 20 ms-1

  15. Equatorial Rossby Wave H L Pressure Rises Pressure Falls Pressure Rises L H

  16. Wave Cooperation • Kelvin and Rossby waves linked by convection, land, and air-sea interaction combine to produce the observed disturbance.

  17. Decay Region Formation Region

  18. Active Convection

  19. Enhanced Easterlies Active Convection

  20. Deflected Jet Stream Active Convection Energy Build-up

  21. Cold air outbreak enhancement Active Convection

  22. Effect of Background • Intraseasonal oscillations are modified by convective coupling, so they must be modified by • The annual cycle • Interannual processes like ENSO

  23. Prediction of MJO • Global weather models predict it with some skill to about 7 or 8 days • Filtering methods allow prediction up to 20 days (Wheeler and Weikmann, 2001) • Statistical schemes may allow prediction for more than 40 or 50 day lead times

More Related