1. ATMS 373C.C. Hennon, UNC Asheville Tropical Oscillations Madden-Julian Oscillation (MJO)

2. ATMS 373C.C. Hennon, UNC Asheville Introduction MJO is an intraseasonal oscillation –Longer than synoptic-scale (2-5 days), shorter than a season (~90 days) –Generally have periods of 7-70 days MJO is the primary intraseasonal oscillation in the tropics –Others have been identified

3. ATMS 373C.C. Hennon, UNC Asheville Real-time MJO Monitoring http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/OLR_modes/amaps.all.50to20.gif

4. ATMS 373C.C. Hennon, UNC Asheville Introduction Early 1970’s: Roland Madden and Paul Julian (NCAR) discovered a 40-50 day oscillation in the tropical zonal wind MJO (as it came to be known) is an easterly propagating wave in the atmosphere

5. ATMS 373C.C. Hennon, UNC Asheville Characteristics of the MJO Wavenumber 1 –Symmetrical and circular in shape Amplitude varies as wave travels around the globe –Has been observed to extend as much as 20°-30° away from the equator Can be identified by a maximum in the upper level divergence field (200 mb) Frequently accompanied by convection –East of the Dateline, convection becomes uncoupled from the wave Average phase speed = 10 m/s –Moves slower (5 m/s) between 60°E and the Dateline

6. ATMS 373C.C. Hennon, UNC Asheville Characteristics of the MJO Dipole of upper level divergence between Indian Ocean (60°E - 120°E) and the central Pacific/SPCZ region Upper level divergence field moves around the globe –Convection tends to maximize in the Indian Ocean, dissipate, then reform near 160°E

7. ATMS 373C.C. Hennon, UNC Asheville Schematic of OLR evolution for 28-72 day time scales. A cycle of cloudiness goes from 1 to 2 to 3 to 4 to 1. OLR anomalies at 1/3 and 2/4 tend to be out-of-phase (From Weickmann et al. 1985 – Copyright American Meteorological Society)

8. ATMS 373C.C. Hennon, UNC Asheville Observed Structure of MJO As wave approaches, easterly trades enhanced After passage of convection, westerly wind anomalies weaken or reverse easterly trades Convection dissipates over Pacific

9. ATMS 373C.C. Hennon, UNC Asheville Example of MJO passage in OLR Time-longitude section of the OLR anomalies for the MJO-filtered band averaged for the latitudes from 10°S to 2.5°N. The zero contour has been omitted. Light shading for positive anomalies and dark shading for negative anomalies (From Wheeler and Kiladis 1999 – Copyright American Meteorological Society ~40 day spacing between waves

10. ATMS 373C.C. Hennon, UNC Asheville Importance of MJO Affects weather across the tropics –wind, SST, cloudiness, rainfall, oceanic effects Has been connected to enhanced or suppressed times for tropical cyclogenesis, esp. in the eastern Pacific

11. ATMS 373C.C. Hennon, UNC Asheville MJO and Tropical Cyclones Maloney and Hartmann (2001) found that tropical cyclone formation in the EPAC was enhanced during the westerly wind phase of the MJO –Positive phase (westerly 850 mb zonal wind anomalies Strength of EPAC tropical cyclones was also higher during the MJO positive phase

12. ATMS 373C.C. Hennon, UNC Asheville

13. ATMS 373C.C. Hennon, UNC Asheville Negative phase Positive phase

14. ATMS 373C.C. Hennon, UNC Asheville MJO and Tropical Cyclones Why are TCs enhanced during positive MJO phase? –Enhanced cyclonic vorticity north of westerly wind anomalies –Enhanced convective activity –Enhanced low-level convergence –Near zero vertical wind shear Easterly MJO phase creates enhanced low-level divergence and higher shear

15. ATMS 373C.C. Hennon, UNC Asheville Maloney and Hartmann (2000) Journal of Climate

16. ATMS 373C.C. Hennon, UNC Asheville Enhanced convective activity

17. ATMS 373C.C. Hennon, UNC Asheville Enhanced Low-level Convergence

18. ATMS 373C.C. Hennon, UNC Asheville Enhanced Cyclonic Vorticity Note anomalous cyclonic circulation

19. ATMS 373C.C. Hennon, UNC Asheville Zero shear line farther south during negative MJO phase Less north-south shear gradient in negative MJO phase (shown to be more unfavorable for genesis)

20. ATMS 373C.C. Hennon, UNC Asheville Creation of Eddy Kinetic Energy (EKE) by MJO phase (Maloney and Hartmann 2001) Allows for growth of disturbances

21. ATMS 373C.C. Hennon, UNC Asheville MJO and North American Monsoon June – September precipitation in normally arid regions

22. ATMS 373C.C. Hennon, UNC Asheville MJO and North American Monsoon Lorenz and Hartmann (2006) found that positive zonal wind anomalies (more westerly) lead to above-normal precipitation in northwest Mexico and Arizona up to a week later MJO contributes moisture surges up Gulf of California –Westerly MJO phase amplifies easterly waves off coast of Mexico

23. ATMS 373C.C. Hennon, UNC Asheville Simulation of MJO in Climate Models Previous climate models (Community Climate Model 3 (CCM3)) could only simulate a weak MJO that moved in the opposite direction –Weakness in convective scheme? Recent research (Zhang and Mu 2005) has resulted in a more accurate simulation –zonal wind, precipitation, OLR match closely –Period of oscillation shorter (~30 days) than observed MJO (30-60 day)