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Maritime Continent Monsoon

This study examines the interactions between the maritime continent monsoon, intraseasonal and synoptic motions, and the influence of the Borneo vortex during the winter season. It also analyzes the impact of the Madden-Julian Oscillation (MJO) on these motions.

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Maritime Continent Monsoon

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  1. Maritime Continent Monsoon Intraseasonal and Synoptic Motions (Winter) Chang, C.-P., P. A. Harr, and H. J. Chen, 2005: Mon. Wea. Rev. - Typhoon Vamei Chang, C.-P., C. H. Liu, and H. C. Kuo, 2003:. Geophys. Res. Let. Annual Cycle Chang, C.-P., Z. Wang, J. McBride and C. Liu, 2005. J. Climate Interannual Variations Chang, C.-P., Z. Wang, J. Ju and T. Li, 2004. J. Climate

  2. Intraseasonal and Synoptic Motions during Asian Winter Monsoon

  3. Cold Surges Subtropical High Borneo Vortex MJO East Asian Winter Monsoon SMH

  4. (a) CI, Dec (c) CI, Feb (b) CI, Jan (d) V&Div, Dec (e) V&Div, Jan (f) V&Div, Feb Monthly Convection, 925 hPa V and Divergence

  5. Vortex Center Frequency 628 of 1895 days have at least one vortex center in 5S-10N, 105E-115E

  6. Seasonal Vortex Centers

  7. Distribution of days with presence of asurgeand avortex Days of vortex cases vs. surge cases Cold Surge: 20% of the days B Vortex: 33% of the daysB. Vortex during Surge: 40%

  8. CONVECTIVE INDEX No Surge / No Vortex No Surge / Vortex Surge / No Vortex Surge / Vortex 925 hPa Winds and Divergence No Surge / No Vortex No Surge / Vortex Surge / No Vortex Surge / Vortex

  9. Strong Surge / No Vortex Strong Surge / Vortex Convective Index Impact of Borneo vortex during strong surges

  10. (a) MJO Dry Phase (b) MJO Dry-to-Wet Phase (c) MJO Wet Phase (d) MJO Wet-to-Dry Phase 850 hPa winds and anomalous OLR (SVD 30-60d filter)

  11. Surge Cases with Respect to MJO and Its Phases MJO suppresses surge Vortex Cases with Respect to MJO and Its Phases MJO suppresses B. Vortex

  12. Vortex CI Composite MJO Dry Phase MJO Dry-to-Wet MJO Wet Phase MJO Wet-to-Dry 925 hPa Winds and Divergence

  13. No MJO MJO

  14. Intraseasonal/Synoptic Summary • Presence of Borneo vortex during surge deflects low-level winds and convergence to the west in SCS. • Over southern SCS, surges tend to enhance the Borneo vortex. • Shift of vortex location eastward to Borneo. • Strong interaction between surge winds and terrain. • Surges frequency tends to decrease during MJO. • MJO-scale circulation pattern tends to oppose surge wind pattern. • MJO impacts Borneo vortex: • Primarily when MJO circulation interrupts cold surges. • Secondary impact when wet phase enhances the cyclonic shear of the vortex.

  15. Typhoon Vamei GMS V 12/27/2001 0232 UTC 5N 5N KUALA LUMPUR   BORNEO ISLAND SINGAPORE EQ EQ SUMATRA ISLAND 105E 110E (Wong T.S., Meteorol. Services Singapore)

  16. Typhoon Vamei - QuikSCAT 12N 12/26/2001 22:32 UTC 10N 8N 6N MALAYPENNINSULA 4N 2N + BORNEO ISLAND EQ SUMATRA ISLAND 2S 102E 104E 106E 108E 110E 112E (Liu, T., JPL)

  17. Day 3 Day 4 Day 6 Day 9 Wind and geopotential response to p(t) forcing 30N Lim and Chang (1981 JAS)

  18. Theory and Observations Day 6 Day 3 EQUATORIAL WAVE THEORY (A) D day (B) D+3 30N 15N EQ EQ EQ NOGAPS 850 hPa WIND ANALYSIS 15S (D)12/22 0000 (C)12/19 0000 +L 0 +L -L -L 0

  19. NOGAPS 850hPa Wind and Vorticity (red+,green-)

  20. Frequency of Vortex Centers 13/214 3/66 4d=6 20/438 6/222 3d=21 52-yr NCEP/NCAR 925 hPa counterclockwise centers; Frequency of persistent (>96h) center / total # center days. Heavy dashed box : QuikSCAT NE surge index.

  21. QuikSCAT Surge Index Upstream surge at 00 and 12 UTC during Dec-Feb 1999/2000 – 2001/2002. Values  10 m s-1 are shaded.

  22. NCEP/NCAR 200hPa Divergence 5S-5N, 102.5E-112.5E at 00 and 12 UTC during winter 1999/2000 – 2001/2002. Units: 10-5 sec-1.

  23. Formation Mechanism X-equatorial monsoon winds:*cyclonic turning( effect, terrain deflection) background cyclonic vorticity. • Narrowing of South China Sea at equator:*strengthening of sustained cold surgeenhancement of background vorticity. • Winter surges, Borneo vortices common. Why rare? *open water region too small Borneo vortices difficult to remain over water. *sustained intense surges infrequent sustained collocation w/ vortex more rare.

  24. Surge Duration Frequency, (DJF,1951/12 to 2002/02) max of (00z 12z) 10 m/s

  25. Surge Duration Frequency, (DJF,1951/12 to 2002/02) max of (00z 12z) 10 m/s

  26. Probability Estimates • 61 strong surges lasting >1 week, total 582 days. Assuming vortex needs 3-day overlap with surge, sustained spinning effect presents at the equator for 582-(61x2) = 460 days /(51x90+13 = 4603). ~ 10% of winter days. • Frequency of a pre-existing Borneo vortex staying over water for  3 days is 21, or 21/51 years = 40% in a given year. • Development depends on du/dz, , upper div, etc. In W Pacific, 30% pre-disturbances develops into TC.  Probability .10x.40x.301% a year.

  27. ISSUES • Will more frequent development be observed with increased remote sensing? • Can equatorial formation occur elsewhere? (Surges are strongest in the South China Sea).

  28. Annual Cycle

  29. Migration of Monsoon Diabatic Heat Sourcesduring July-February (Lau and Chan 1983)

  30. Slow Annual Cycle (LinHo and Wang 2002)

  31. 5 6 4 3 4 3 4 3 Migration of Monsoon Diabatic Heat Sourcesduring July-February (Lau and Chan 1983)

  32. Seasonal Transition Issues • Annual cycles and monsoon regimes in SE Asia/MC: Geographic variations due to complex terrain. (Braak 1921; Wyrtki 1956; Ramage 1971) Local heating vs. wind-terrain interactions? • Seasonal march of max convection asymmetric:  SON: gradual SE march along SE Asia land bridge;MAM: stays south of 5°N before northward jump.(Lau & Chan 1983; Meehl 1987; Yasunari 1991; Matsumoto & Murakami 2002; Hung & Yanai 2003) • Data:  Historical station rainfall data; Recent remote sensing data (TRMM, QuikSCAT).

  33. Monthly Mean Rainfall

  34. JAN OCT APR JUL Annual Cycle Mode at Rainfall Stations

  35. JAN OCT APR JUL Analyzed Annual Cycle vs. Semiannual Cycle

  36. DJF and JJA QuikSCAT Winds

  37. DJF TRMM and QuikSCAT

  38. JJA TRMM and QuikSCAT

  39. DJF minusJJA TRMM and QuikSCAT

  40. SON TRMMand QuikSCAT

  41. SON TRMM [minus max(DJF,JJA)] & QuikSCAT

  42. MAM TRMM and QuikSCAT

  43. MAM TRMM [minus max(DJF,JJA)] & QuikSCAT

  44. MMA & SON TRMM [minus max(DJF,JJA)] & QSCAT

  45. Possibly Mechanisms • Walker circulation strength?E. Pac cold tongue peaks in boreal fall. (Li & Philander 1996) W. IO warmest in boreal spring. (Webster et al. 1998) • Rossby-wave response? Northward march of ITCZ in boreal spring blocked by subsidence in oceanic regions west of heat sources (India, Indochina, Philippines). (Hung and Yanai 2003) • Boundary Layer convergence?Tendency of Eastward Propagation

  46. MAM SON Anomalous Walker Cell INDIAN PACIFIC

  47. SON minusMAM SLP

  48. A B C D SON minus MAM SLP

  49. Annual Cycle Summary • AC is dominated by interactions between complex terrain and simple reversal of large-scale surface monsoonal winds. • Comparable Semi-AC over some equatorial landmasses, but very small area reflects twice-yearly crossing of the sun. • Boreal summer and winter regimes intertwine across the equator. Winter regime extends far northward along eastern flanks of major landmasses. (Exception: west coast of Borneo: winter vortices)

  50. Annual Cycle Summary (Continued) • Asymmetric seasonal march: Boreal Fall: Max. convection at midpoint of the SE-ward progression of Asian (summer to winter) monsoon. Boreal Spring: Max. convection stays near or south of EQ. • Hypothesis: Different thermal memories during spring and fall  mass redistribution between land and ocean areas:  Orientation of Asian-Australian landmasses  asymmetric SLP patterns  (1) asymmetric wind-terrain interactions, & (2) asymmetric low-level divergence.  Both promote SE-ward march of max. convection during boreal fall but oppose NW-ward march during spring.

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