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DYNAMO workshop, April 13-14, Boulder, Colorado

Theoretical and Modeling Issues Related to ISO/MJO Tim Li Department of Meteorology and IPRC University of Hawaii. DYNAMO workshop, April 13-14, Boulder, Colorado. 1. MJO Initiation issue: Role of air-sea interaction. Observed OLR Composite in northern summer (1980-2005).

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DYNAMO workshop, April 13-14, Boulder, Colorado

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  1. Theoretical and Modeling Issues Related to ISO/MJOTim LiDepartment of Meteorology and IPRCUniversity of Hawaii DYNAMO workshop, April 13-14, Boulder, Colorado

  2. 1. MJO Initiation issue: Role of air-sea interaction

  3. Observed OLR Composite in northern summer (1980-2005) Seasonal difference in ISO propagation: Winter: continuous eastward propagation across the maritime continent Summer: northward bifurcation over the eastern IO/maritime continent

  4. Evolution of specific humidity (-2.5oS-2.5oN ) 0 is initiation date Precursor signals for initiation of an opposite phase of ISO in boreal summer occur in PBL moisture field. Jiang and Li 2005 J. Climate

  5. Ocean model simulation with ERA40 daily forcing (Li et al. 2008) TMI SST, Saji et al. 2006 OPEN ISSUE: Is the effect of air-sea interaction on initiation season-dependent? The response of SST to the previous convective phase of ISO may have a delayedimpact on initiation of a subsequent opposite phase of ISO in western IO.

  6. Seasonal dependence of intraseasonal SST variability is caused by • Summer-winter difference in the background zonal wind • Summer-winter difference in the ISO forcing • Summer-winter difference in the mixed layer depth Atmospheric ISO convection z EQ W E Seasonal mean wind in DJF Seasonal mean wind in JJA • SST tendency is mainly affected by • Short wave cloud forcing • Latent heat flux/ocean mixing Li et al. 2008

  7. 2. MJO prediction issue:Does air-sea coupling extend the predictability?

  8. UH Hybrid coupled GCM (UH_HcGCM) • Atmospheric component: • ECHAM-4 AGCM • (Roeckner et al. 1996) • Ocean component: • Wang-Li-Fu intermediate upper ocean model (0.5ox0.5o) • (Wang, Li, Chang 1995; Fu and Wang 2001) •  Wang, Li, and Chang (1995): upper-ocean thermodynamics • McCreary and Yu (1992): upper-ocean dynamics •  Jin (1997) : mean and ENSO (intermediate fully coupled model) Zebiak and Cane (1987): ENSO (intermediate anomaly coupled model) • Fully coupling without heat flux correction • Coupling domain: Tropical Indian and Pacific Oceans (30oS-30oN) • Coupling interval: Once per day

  9. Air-sea coupling increases the intensity of ISO Air-sea coupling reproduces observed rainfall-SST relationship Fu, Wang, Li, McCreary (2003)

  10. Air-Sea Coupling Extends the Predictability of Tropical Intraseasonal Variability ATM Forecast Error Signal CPL Forecast Error [ATM: 17 days; CPL: 24 days] Fu et al. (2007)

  11. A Real-Case MJO Forecast

  12. Wet Dry Wet Impact of ISO on Tropical Cyclones over western Pacific TC Genesis TC Rapid Intensification (RI) Year 2000 20-70-day filtered OLR at TC genesis location and time Horizontal axis: time (day) from June 1 to September 30, 2000 Each bar represents one TC genesis case in WNP Fu, Li, et al. 2007 The maximum occurrence of RI over the WNP lags the peak wet phase of ISO in the equatorial western Pacific by three phases (about 12 days). (Wang and Zhou 2008). Does a better ISO prediction improve short-range and extended-range typhoon forecast?

  13. 3. Scale interaction issue:How does ISO impact synoptic-scale variability?How does synoptic-scale variability feed back to ISO?

  14. Evolution of synoptic disturbances during ISO wet phase Day 0 Day -3 Day -2 Day 1 Day -1 Day 2 850hPa wind (vector) and vorticity (contour)

  15. Evolution of synoptic disturbances during ISO dry phase Day -3 Day 0 Day -2 Day 1 Day -1 Day 2 850hPa wind (vector) and vorticity (contour)

  16. ( ¯ ) : climatological mean annual cycle; ( ' ): synoptic (3-8d); ( ~ ) : intraseasonal (20-90d) STD (20-90d LH, based on 3-8d + mean u,v,dq) STD (20-90d LH, based on total u,v,dq)

  17. 4. MJO PBL structure issue

  18. AIRS data reveal a new observational feature: boundary layer dryness under MJO convection MJO Over eastern Indian Ocean SST-wind-LHF-q phase relation ? AIRS moisture Decrease in LHF  SST warming Decrease in LHF  Decrease in air specific humidity Red line: TMI SST Green line: Surface Convergence (from QuikSCAT wind) Blue line: TMI rainfall

  19. Summary of the issues: • PBL dryness, what is corresponding dynamic /thermodynamic structure? what cause the dryness, and what is its impact? What leads to complex phase relationships among SST, wind, moisture, LHF and SWR associated with MJO at air-sea interface? • Effect of air-sea interaction in ISO initiation – Is it season-dependent? • ISO prediction: does a better ISO prediction help short-range and extended-range typhoon forecast? • Multi-scale interaction: is the current model able to capture two-way interactions between ISO and synoptic-scale variability?

  20. Evolution of divergence (-2.5oS-2.5oN ) initiation Date: 0

  21. ECHAM4 Simulation What is the effect of the maritime continent? 1) friction, 2) moisture reduction, 3) diurnal cycle Idealized numerical experiments: removing the maritime continent with interpolated SSTs from the surrounding ocean

  22. Rainfall vs. SST (Coupled) Contour: SST (oC);Shading: Rainfall (mm day-1) UH_MD, Mar 17-19, 2009

  23. Rainfall vs. SST (Forced) Contour: SST (oC);Shading: Rainfall (mm day-1) UH_MD, Mar 17-19, 2009

  24. Experimental Design • 20 TISV events in 15-year coupled control run • 4 phases for each TISV event • “Twin” perturbed experiments starting from each phase (Lorenz 1963; Waliser et al. 2003)  For both the atmosphere-ocean coupled model and atmosphere-only model, each with 160 forecasts Methods to Measure ISV Predictability • Signal-to-forecast error ratio • ACC

  25. Phase relation between ISO convection(contour) and nonlinearly rectified (SSV-induced) intraseasonal latent heat flux (shaded) Color: wet – dry composite of LH (3-8d + mean u,v,dq) field projected into the ISO (20-90d) timescale (It represents SSV-induced intraseasonal LHF) Contour: 20-90d OLR wet-dry composite Implication: SSV-induced nonlinearly rectified surface latent heat flux may 1) enhance ISOand2) contribute to northwestward propagation of ISO in western North Pacific.

  26. Event-I Event-II Control cases Coupled forecasts (CPL) Ten-ensemble-mean Atmosphere-only forecasts (ATM) Rainfall averaged over (65oE-120oE)

  27. Heat budget: latent heat vs. short wave vs. vertical entrainment

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