What: マッデンジュリアン振動の東進機構の仮説 CINDY2011期間で最初に発生した10月下旬のMJOの事例解析から、その東進機構について仮説を提案する。 その仮説とは、南インド洋上を東進する温帯低気圧がMJOを牽引して東進させる、というものである。 このMJO対流は、南緯40−10度を東進する温帯低気圧とほぼ完全に同期して赤道インド洋から海大陸に東進していた。 温帯低気圧は、その西側に気圧傾度力によって生じる地表の西風偏差域を伴い、東風偏差域との境界では、南北に伸びる東西風収束帯が形成される。 すなわち、南インド洋上の温帯低気圧から南北に伸びる寒冷前線の収束帯が赤道域にまで伸び、MJO対流を牽引したため、両者は完全に同じ速度(­〜6 m/s)で東進した。 このMJO東進機構の概念図をFigure 4に示す。 この提案されたMJO東進シナリオは、3つの図（OLR、JRA55によるSLP、地表西風偏差、地表収束）に基いて簡潔に説明される。 Hypothesis on the mechanism of eastward propagation of the Madden-Julian Oscillation This study proposes a new hypothesis on the eastward propagation mechanism of the Madden Julian Oscillation (MJO) from a case study of the first MJO generated in the late October during CINDY2011. The hypothesis is that the MJO convection is pulled by an eastward-propagating extratropical cyclone over the southern Indian Ocean. The eastward propagation of the MJO convection from the equatorial Indian Ocean to the Maritime Continent was found to be completely synchronized with that of the extratropical cyclone from the analyses of OLR and SLP with the JRA55. The extratropical cyclone was accompanied by the anomalous westerlies to the west, which was due to the pressure gradient force. Schematic illustrations for the eastward-propagation mechanism of the MJO is shown in Figure 4 (see URL). Thus, the surface convergence zone extending from the extratropical cyclone to the equator pulled the MJO convection eastward and the both propagated at the same speed (­〜6 m/s). The proposed scenario of the eastward propagation of the MJO is simply explained by three figures of OLR, SLP, anomalous surface winds, and surface convergence with JRA55. Figure 1: http://bit.ly/1OBUU6o Figure 2: http://bit.ly/1NkR79X Figure 3: http://bit.ly/1D4chd5 Figure 4: http://bit.ly/1CSWAUg

1. MJO
東進機構の仮説
茂木耕作
の

2. MJOの東進機構の概念図

4. 正規化した偏差の定義
normalized anomaly =
X − 30daysX
30daysσ
変動の緯度依存性を除去

5. 北半球の低圧偏差

6. 赤道域の低圧偏差の東進

7. 南半球の低圧偏差の東進

14. MJOの南北構造
ZA:RH UA:U
西部
中心部

15. ZA:RH
西部
中心部

16. UA:U
西部
中心部

17. MJOの東進機構の概念図

18. MJO西部の南北構造

19. MJO中心部の南北構造

21. 惑星規模中緯度ロスビー波

22. 惑星規模中緯度ロスビー波

24. 東西風収束と西風偏差

43. 低気圧偏差

62. Anti-symmetric features
of the October MJO
during CINDY2011
Qoosaku MOTEKI
(the JMSJ article under review)

63. suppressed
just before
onset
just after
onset
mature

64. suppressed

65. just before onset

66. just after onset

67. mature

69. Period separation based on the schematic
illustration from Madden and Julian (1976)
suppressed
just before
onset
just after
onset
mature
eastward
propagating

70. Period separation based on the schematic
illustration from Madden and Julian (1976)
suppressed
just before
onset
just after
onset
mature
eastward
propagating

71. Convective area separation
based on features during each period
suppressed
just before
onset
just after
onset
mature
eastward
propagating
WPDSCCWC

73. Transition from double-ITCZ to MJO in the
time-latitude cross section
suppressed just before
onset
just after
onset
mature eastward
propagating

74. Transition from double-ITCZ to MJO as
weakening the Mascarene High
suppressed
just before
onset
just after
onset
mature

75. suppressed

76. just before onset

77. just after onset

78. mature