Variations in the Activity of the Madden-Julian Oscillation:Implications for the Southern Hemisphere
University of CaliforniaSanta Barbara*Collaboration: Leila Carvalho (USP)
Brief overview of the MJOExample of importance of the MJO for the midlatitudes of the southern hemisphereOutstanding issues about the MJO
The Madden-Julian OscillationPower spectrum of zonal winds at 850-hPa Originally discovered in early 1970s Most important mode of tropical intraseasonal variations Time scales of 30 to 60 days Anomalies propagate eastward along the tropical belt; phase speeds ~ 5 m s-1 Eastern hemisphere: strong interaction with clouds, rain, surface winds and large-scale circulation Western hemisphere: modest interaction with convection and large-scale circulation Significant case-to-case and interannual variability
*Modulate the variability of the monsoons in Asia-Australia, Africa and AmericasTeleconnections with extratropics in both hemispheresModulate thermocline variability in the tropical Pacific Ocean via westerly wind bursts; interaction with El Nio/Southern Oscillation (ENSO)Influence on forecast skills in the tropics and extratropics
*Madden-Julian Oscillation (MJO) Life CycleHendon and Salby (1994)
Anomalous upper level circulation (200-hPa)Enhanced Convection in the western PacificCoupled Forced Rossby-Kelvin wave responseRossby waves -+-+Midlatitude wave trainKelvin wave Madden-Julian Oscillation (MJO) Life Cycle
Identify variations in extratropical cyclones properties during distinct phases of the Antarctic Oscillation
Murray and Simmons (1991) tracking scheme was applied to track storms with origin south of 50oS during summer (DJF) 1979-2000.
*The Daily AAO Index 1979-2000The daily AAO index: leading mode of the EOF analysis of daily anomalies of 700hPa geopotential height (H700) from Reanalysis (20-90 S). Positive (negative) phases of the AAO : time coefficient of the first EOF is greater (less) than 1 standard deviation of the DJF time series.
Extratropical Cyclones properties Obtained from tracking scheme based on Murray and Simmonds (1991)Carvalho et al. 2005Minimum PressureMaximum latitudeLife cycle duration * 12 hAAO-AAO-AAO-AAO+AAO+AAO+
*What are the relationships between the MJO and AAO?
*Lag composites (Days) OLR anomalies (20-70 days)NEGATIVE AAOPOSITIVE AAOLAG 0LAG +5LAG +10LAG +15LAG +20LAG +25LAG 0LAG +5LAG +10LAG +15LAG +20LAG +25
*Indication that onset of negative phases of AAO is associated with eastward propagation of the MJO
*Case to CaseSeasonal VariationsInterannual VariationsLong-term BehaviorTime scales??????????Extensively studied over the years but no comprehensive theoryBehavior on time scales longer than interannual is unknown Long-term behavior of the MJO is unknown
*Has the MJO been more active (linear trend)?Does the MJO have a low-frequency mode of variability (decadal)?How will the continuous warming in tropical Indian and Pacific Oceans modify/interact with MJO?
DataDaily U200 and U850 (1948-2006), OLR (1979-2006)Subtract daily climatology; band-pass filtered (20-200 days)Average 15S-15NCombined EOF analysis (U200, U850)Use (EOF1, PC1), (EOF2, PC2) Phase angle (PC1,PC2) normalized*
MJO IdentificationCriteria:Systematic eastward propagation at least 1 4 Minimum amplitude: A = (PC12 + PC22)1/2 > 0.35Entire duration between 30-90 daysMean amplitude during event > 0.9227 MJO events in 1948-2006OLR Anomalies*
*Linear trends in amplitudes and number of events?Statistically significant trends in amplitudes and number of MJO events
*In progress: are linear trends in MJO activity real?
*Does the MJO have a low-frequency mode of variability?Low-Frequency diagram Consider XT, T=1, N pentads, XT=1 event, XT= 0 no eventDefine moving window SK and compute number of MJO events in SKSK odd number and varied from smallest (1 pentad) to largest possible N pentads)
*Low-frequency diagramCone of InfluenceCone of Influence
*Indication: MJO activity exhibits significant variations on decadal time scalesIn progress: stochastic and dynamical models Simulation with the IPRC University of Hawaii hybrid coupled model (Joshua Fu):Atmospheric model: ECHAMOceanic model: intermediate model, tropical Indian and Pacific Oceans200 years simulation
*Identification of model MJO as in observational analysisRealistic MJO simulationComposites of U200 anomalies
*Low-Frequency variations of the MJO200-yr model simulation
*Real time monitoring and forecasting of the MJOwww.icess.ucsb.edu/asr
Motivation*Lag composites show the life cycle of the MJO; time runs downwards. Composites show the eastward propagation of enhanced tropical convection.*Methodology: U850*