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Large-scale transient variations of tropical deep convection forced with zonally symmetric SSTs

Large-scale transient variations of tropical deep convection forced with zonally symmetric SSTs. Zhiming Kuang Dept. Earth and Planetary Sciences and School of Engineering and Applied Sciences Harvard University. Zonally symmetric SST cases can be interesting. Log(Power).

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Large-scale transient variations of tropical deep convection forced with zonally symmetric SSTs

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  1. Large-scale transient variations of tropical deep convection forced with zonally symmetric SSTs Zhiming Kuang Dept. Earth and Planetary Sciences and School of Engineering and Applied Sciences Harvard University

  2. Zonally symmetric SST cases can be interesting Log(Power) SPCAM experiment modeled after earlier experiments by Marat Khairoutdinov

  3. A simple model of convectively coupled waves Zonally symmetric double-ITCZ Kuang, 2008; Andersen and Kuang, 2008

  4. A moisture-stratiform instability

  5. Question • Is the intraseasonal signal a moisture mode that differs fundamentally from convectively coupled waves? Moisture mode: Growth comes from negative effective gross moist stability. The disturbance will propagate through column MSE sources and sinks (e.g. Yu and Neelin, 1994; Sobel et al. 2001; Fuchs and Raymond, 2002, 2005, 2007; Sugiyama, 2009ab)

  6. Decay time of T, q anomalies of an isolated moist convecting atmosphere column Kuang, JAS, In press

  7. The most slowly decaying eigenmode Column MSE excess is expressed in terms of a shift in the reference profile of the Betts-Miller scheme Decay time is ~15days, the time for surface flux to remove the column MSE anomaly (radiation is fixed in this case)

  8. This slowly decaying mode could provide the memory that reddens the spectrum in frequency. • The decay time will be modified by diabatic sources, export of column MSE, which could lead to growth. The disturbance will propagate through column MSE sources and sinks (e.g. Yu and Neelin, 1994; Sobel et al. 2001; Fuchs and Raymond, 2002, 2005, 2007; Sugiyama, 2009ab) • The above moisture modes are either stationary or propagate by horizontal moisture advection

  9. Is horizontal moisture advection key to the propagation of the intraseasonal signal seen in the simulation? • Use zonally rotated u,v fields to compute horizontal moisture advection longitude normal u1,v1,q1 u2,v2,q2 u3,v3,q3 u4,v4,q4 Rotate wind for q advection u1+i,v1+i,q1 u2+i,v2+i,q2 u3+i,v3+i,q3 u4+i,v4+i,q4 i is chosen randomly each day

  10. This disrupts the coherence between u,v and q thus removes phase dependent horizontal moisture advection on time scales longer than a day • But preserves the mean horizontal q advection and allows some coherent sub-daily horizontal q advection

  11. Check climatology is not greatly changed

  12. Normalized spectra Phase dependent horizontal moisture advection is removed Control 0.4 0.3 0.2 0.1

  13. Horizontal moisture advection is key to the propagation of the intraseasonal signal but not that of convectively coupled waves

  14. Zonally homogenize surface heat fluxes Control Homogenized sfc hflx latitude Control

  15. Zonally homogenize radiative heating Control

  16. Column MSE budgets Work by Joe Andersen

  17. Why does radiative feedback weaken convectively coupled Kelvin waves? Radiative heating anomaly Temperature anomaly Work by Joe Andersen

  18. An illustration with column CRM experiments No anomalous radiative heating Anomalous radiative heating applied more in the lower troposphere

  19. Vertical distribution of the anomalous radiativeheating can affect the gross moist stability

  20. Conclusions • The intraseasonal signals appear to be moisture modes as they depend on diabatic sources and their propagation depends on horizontal moisture advection • Effects of radiative feedback on both convectively coupled waves and the intraseasonal variabilities can depend on the vertical structure of the anomalous radiative heating

  21. Width of the ITCZ

  22. Medium Width of the ITCZ Narrower Wider

  23. 80km global raveWRF rainfall climatology Observations Kuang, Walker, Andersen, Boos, Nie, in preparation

  24. Rainfall Spectra (γ=1)

  25. Rainfall Spectra (γ=20)

  26. Normalized rainfall Spectra (γ=20)

  27. OLR Spectra (γ=20)

  28. Normalized OLR Spectra (γ=20)

  29. Realistic WRF run without sub-seasonal surface flux variations Kuang, Walker, Andersen, Boos, Nie, in preparation

  30. Realistic WRF run without sub-seasonal surface flux variations: OLR spectra Kuang, Walker, Andersen, Boos, Nie, in preparation

  31. Aquaplanet warm pool

  32. Aquaplanet warm pool rainfall spectra

  33. Normalized

  34. A zonally symmetric case

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