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Large Scale Effects of Tropical Convection and Madden-Julian Oscillation

Explore the large-scale effects of tropical convection and the Madden-Julian Oscillation (MJO) on rainfall using sounding array observations and column modeling. Understand the coupling between convection and large-scale dynamics to improve simulation and prediction of MJO events.

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Large Scale Effects of Tropical Convection and Madden-Julian Oscillation

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  1. Tropical Convection and MJO Shuguang Wang

  2. Super cloud cluster on Nov 24, 2011 24 Nov 2011, Meteo7 IR Tropical convection organize into large scale

  3. Tropical convection f = 1x10-4 s-1 f = 0.5x10-4 s-1 f = 0 Liu and Montcrieff 2004

  4. Taking spatial average over a large area, thermodynamic equation becomes : Large scale influence of convection Consider dry static energy: Qr: radiation c: condensation e: evaporation Eddy transport Large-scale vertical motion Heat effects of convection

  5. Convection: large scale effects Thermodynamic eqn Apparent heat source Apparent moisture sink Moisture eqn Apparent momentum source Momentum eqn These are “observables”

  6. Yanai et al., 1973, JAS

  7. Sounding array in tropical field programs • Radiosondes are released at the “polygon” network every 3-6 hours • Flux of humidity is calculated using sounding observations • Based on the measurement of all the sources and sinks, the budget of moisture and energy can be constructed. Large scale vertical motion can also be derived. • Large scale vertical motion • Horizontal advection of moisture and temperature • Sea surface temperature (SST) • Surface wind speed

  8. Sounding array observations in tropical field campaign TOGA-COARE (Western Pacific) GATE (Atlantic) DYNAMO (Indian ocean) • Sounding array: Continuous sampling of atmospheric states over several months • Products: areal average of budget terms for thermodynamic variables

  9. Sounding array observation: Column modeling • Precipitation fits well Obs, but other important fields may not • Temperature, moisture • Radiative fluxes • Reflectivity, or microphysics Dx = 1 km TOGA: Rain 22 km ~64 km ~64 km

  10. Column modeling with parameterized large scale dynamics Standard method Alternative modeling strategy • WTG or wave coupling (WPG) • Sea surface temperature (SST) • Relaxation to large scale winds • Free troposphere temperature • Radiation • Large scale vertical motion • Sea surface temperature (SST) • Relaxation to large scale winds • Horizontal advection of moisture Goal: Simulate cloud statistics Goal: Simulate rainfall

  11. Two methods: WTG and Gravity-wave coupling - WTG: - Gravity-wave coupling Θ Θ C R M climatology C R M relax : timescale k: wavenumber ε: momentum damping at1 days temperature variations LS vertical motion Both:

  12. Parameterizing large scale dynamics for TOGA-COARE Surface fluxes WTG Damped-wave

  13. Parameterizing large-scale vertical velocity for TOGA-COARE WTG Damped-wave - Rain is not specified by the large-scale forcing. Expect much less agreement. - Good agreement in rainfall for the 1st MJO event, less agreement for the 2nd MJO event

  14. Parameterized large scale vertical velocity obs Potential Temperature: model-obs WTG WTG Gravity-Wave Gravity-Wave

  15. Madden-Julian Oscillation (MJO) (Madden and Julian 1971, 1972) 30 to 90 day tropical weather cycle • No satisfying theory to explain all the features • Difficult for both global climate/operational • models and regional models

  16. Dynamical structure Rui and Wang (1990).

  17. Tropical convection organize into large scaleSuper cloud cluster on Nov 24, 2011 24 Nov 2011, Meteo7 IR • This super cloud cluster is Madden-Julian Oscillation (MJO) at its initialization phase • MJO: a global weather phenomenon • Influence rainfall over all the tropics and subtropics

  18. Outgoing Longwave Radiation 2.5S-2.5N Madden Julian Oscillation Kelvin wave Equatorial Rossby Wave Convection is coupled with a range of large scale dynamic processes: Madden Julian Oscillation (5 m/s eastward) Kelvin waves (13 m/s eastward) Equatorial Rossby waves (Westward propagation) Tracking the November 2011 cloud cluster Interaction between convection and large scale processes is the key. CAWCB/Bureau of Meteorology

  19. 200 hPa Velocity Potential Anomalies (10N-10S) Gottschalck et al 2013 Red dashed: eastward propagation of upper-level divergence

  20. DYNAMO: RMM index OLR, 850/200 hPa zonal wind (Wheeler and Hendon 2004)

  21. DYNAMO: RMM index Longitude Longitude

  22. DYNAMO: setup of large domain WRF simulations Continuous free run for > 2 months

  23. DYNAMO: large domain cloud-permitting WRF simulations Longitude

  24. DYNAMO: budget of moist static energy M = cpT+gZ+LQv Oct 1

  25. DYNAMO: Surface fluxes and radiative fluxes

  26. Concluding remark Large scale effects of tropical convection (Q1, Q2) are observable using the sounding network Column modeling offers insights to both physics (cloud microphysics, radiation, etc.) and dynamics (parameterized large scale dynamic) Understanding coupling between convection and large scales is the key for tropical dynamics Convection is crucial for MJO, and responsible for poor simulation and prediction of MJO events in numerical models High resolution WRF modeling shows some promising results for precipitation

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