Kim, H. M., D. Kim, F. Vitart, V. E. Toma, J. S. Kug, and P. J. Webster, 2016:
MJO Propagation across the Maritime Continent in the ECMWF Ensemble Prediction System.
J. Climate, 29, 3973-3988.
15A.5 Drastic Thickening of the Barrier Layer Off the Western Coast of Sumatr...耕作 茂木
Qoosaku Moteki, Japan Agency for Marine Earth Science and Technology, Yokosuka city, Japan; and K. Yoneyama, M. Katsumata, K. Ando, and T. Hasegawa
The drastic thickening of the barrier layer in the marginal sea off the western coast of Sumatra during the passage of the Madden Julian Oscillation (MJO) observed during December 2015 is investigated. Before the MJO arrival, the halocline above 20 m depth was very strong and the barrier layer thickness was 5-10 m from based on R/V Mirai observations. During the MJO forcing of 13-16 December, the isothermal layer was drastically deepened from 20 m to 100 m. Meanwhile, the mixed layer deepening was lagged behind the isothermal layer deepening by 1 day, and the barrier layer underwent dramatic thickening to 60 m within 24 hours. An evaluation of the vertical salinity gradient tendency showed that the dramatic thickening of the barrier layer was due to the vertical oceanic mixing by the atmospheric MJO forcing and the vertical stretching by the oceanic downwelling coastal Kelvin wave intruding from the open ocean. One of the important factors in the drastic barrier layer thickening was concluded to be the atmospheric external forcing and the oceanic internal wave being in-phase. The downwelling oceanic Kelvin wave continuously lowered the thermocline from the middle of November to the end of December, and the salinity stratification in the vicinity of the thermocline was continuously mitigated by the vertical stretching. Under such conditions, the MJO forcing caused vertical mixing of the freshwater with the strong salinity stratification and temperature stratification near the surface. The combination of the two distinct processes caused the drastic thickening of the barrier layer, and the barrier layer thickness reached a maximum of 85 m 5 days after the MJO arrival.
The document discusses how the barrier layer off the western coast of Sumatra drastically deepened due to the passage of a Madden-Julian Oscillation (MJO) during the Pre-YMC period. The barrier layer thickness increased from 5m to 60m within one day and up to 85m over five days, which had never been observed before. This drastic deepening was caused by vertical mixing from the MJO forcing and downwelling of the thermocline by an oceanic Kelvin wave occurring in phase with the MJO. High-frequency observations are needed to better understand the ocean's response and role in rainfall formation during MJO events.
15A.5 Drastic Thickening of the Barrier Layer Off the Western Coast of Sumatr...耕作 茂木
Qoosaku Moteki, Japan Agency for Marine Earth Science and Technology, Yokosuka city, Japan; and K. Yoneyama, M. Katsumata, K. Ando, and T. Hasegawa
The drastic thickening of the barrier layer in the marginal sea off the western coast of Sumatra during the passage of the Madden Julian Oscillation (MJO) observed during December 2015 is investigated. Before the MJO arrival, the halocline above 20 m depth was very strong and the barrier layer thickness was 5-10 m from based on R/V Mirai observations. During the MJO forcing of 13-16 December, the isothermal layer was drastically deepened from 20 m to 100 m. Meanwhile, the mixed layer deepening was lagged behind the isothermal layer deepening by 1 day, and the barrier layer underwent dramatic thickening to 60 m within 24 hours. An evaluation of the vertical salinity gradient tendency showed that the dramatic thickening of the barrier layer was due to the vertical oceanic mixing by the atmospheric MJO forcing and the vertical stretching by the oceanic downwelling coastal Kelvin wave intruding from the open ocean. One of the important factors in the drastic barrier layer thickening was concluded to be the atmospheric external forcing and the oceanic internal wave being in-phase. The downwelling oceanic Kelvin wave continuously lowered the thermocline from the middle of November to the end of December, and the salinity stratification in the vicinity of the thermocline was continuously mitigated by the vertical stretching. Under such conditions, the MJO forcing caused vertical mixing of the freshwater with the strong salinity stratification and temperature stratification near the surface. The combination of the two distinct processes caused the drastic thickening of the barrier layer, and the barrier layer thickness reached a maximum of 85 m 5 days after the MJO arrival.
The document discusses how the barrier layer off the western coast of Sumatra drastically deepened due to the passage of a Madden-Julian Oscillation (MJO) during the Pre-YMC period. The barrier layer thickness increased from 5m to 60m within one day and up to 85m over five days, which had never been observed before. This drastic deepening was caused by vertical mixing from the MJO forcing and downwelling of the thermocline by an oceanic Kelvin wave occurring in phase with the MJO. High-frequency observations are needed to better understand the ocean's response and role in rainfall formation during MJO events.
A triggering factor of the eastward propagation of the Madden–Julian oscillation (MJO) is proposed from a case study of the first MJO generated in late October during CINDY2011. The proposed scenario is that the eastward propagation of the MJO is triggered by an extratropical cyclone in the Southern Hemisphere. The ridge and trough pair meridionally extending between 30°S~15°N accompanied by the extratropical cyclone was found to be completely synchronized with the eastward propagating MJO convection. The ascending areas of the cold front extending from the extratropical cyclone partially combined with those of the MJO and the large-scale ridge and trough below 500 hPa were formed across the midlatitudes in the Southern Hemisphere and the tropics. The convection center of the MJO shifted eastward as a result of the westerly winds in the tropics, expanding eastward by the zonal pressure gradient force between the ridge and trough.
Moteki MJO seminar-150401 Hypothesis on eastward propagation mechanism of the...耕作 茂木
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
A triggering factor of the eastward propagation of the Madden–Julian oscillation (MJO) is proposed from a case study of the first MJO generated in late October during CINDY2011. The proposed scenario is that the eastward propagation of the MJO is triggered by an extratropical cyclone in the Southern Hemisphere. The ridge and trough pair meridionally extending between 30°S~15°N accompanied by the extratropical cyclone was found to be completely synchronized with the eastward propagating MJO convection. The ascending areas of the cold front extending from the extratropical cyclone partially combined with those of the MJO and the large-scale ridge and trough below 500 hPa were formed across the midlatitudes in the Southern Hemisphere and the tropics. The convection center of the MJO shifted eastward as a result of the westerly winds in the tropics, expanding eastward by the zonal pressure gradient force between the ridge and trough.
Moteki MJO seminar-150401 Hypothesis on eastward propagation mechanism of the...耕作 茂木
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. Kim, H. M., D. Kim, F. Vitart, V. E. Toma, J. S. Kug, and
P. J. Webster, 2016:
MJO Propagation across the Maritime Continent in the
ECMWF Ensemble Prediction System.
J. Climate, 29, 3973-3988.
2. ECMWF アンサンブル予報における MJO の海大陸横断
インド洋で MJO 初期発生したときに、西太平洋での対流抑制がハッキリしている
と海大陸をまたいだ東進が明瞭でなおかつ予報スキルも高くなる。
The MJO initiated over the IO under the situation with suppressed convection over the WP would tend to
propagate across the MC and its prediction skill would be higher than that for the other cases.
3. 1. Introduction
contents
2. Data and methodology
a. Data
b. MJO index (Fig. 1)
c. Measures of MJO prediction skill:
Collective and segment prediction skill
3. Identification of the high-skill and low-skill MJO events
a. MJO initial amplitude and prediction skill relationship(Fig. 2)
b. High-skill versus low-skill events(Figs. 3, 4)
4.Favorable initial conditions and key physical processes for
MJO propagation across the Maritime Continent a. Initial
condition and propagation characteristics(Figs. 5-7) b.
Ocean–atmosphere interaction(Fig. 8) c. Drawbacks of using
the RMM index(Fig. 9)
5. Systematic mean biases and the possible influence on MJO
prediction(Figs. 10-12)
6. Summary and discussion
13. (a) 高スキル事例の観測値、 (b) 高スキル事例の予報値、 (c) 低スキル事例の観
測値、 (d) 高スキル事例の予報値。 OLR( カラー ) 、 850hPa 東西風偏差
(0.4m/s 毎等値線 )
(a) よく組織化され、東進がはっ
きりしている観測事例は、
(b) 振幅がやや不明瞭になるもの
の 32 日後まで下層東西風偏差の
東進シグナルが予報できているが
、
(c) 位相速度が対流結合赤道 Kelvin
波のように速く、減衰する事例は
、
(d) 予報スキルが低い。
つまり、スキルの高低の差は、振
幅ではなく、初期条件における対
流分布の組織化度合いと東進の明
瞭さにある。
5m/s
9m/s
4.Favorable initial conditions and key physical processes for
MJO propagation across the Maritime Continent a. Initial
condition and propagation characteristics(Figs. 5-7)
well-organized propagation
fast propagation like CCKW
14. 初期振幅の強い事例・中程度の事例の全てに対する西太平洋の観測 OLR 偏
差 x と 32 日予報スキル y の関係。
予報スキルは、西太平洋上の OLR
に対する明瞭な関数とは言えない
が、高スキルのほとんどは、乾燥
偏差によっており、頻度として高
スキルになりやすいことは言える
。
西太平洋が乾いていることは、十
分条件ではないが、必要条件であ
る。
4.Favorable initial conditions and key physical processes for
MJO propagation across the Maritime Continent a. Initial
condition and propagation characteristics(Figs. 5-7)
15. Kim, D., J. S. Kug, and A. H. Sobel, 2014: Propagating
versus Nonpropagating Madden-Julian Oscillation
Events. J. Climate, 27, 111-125.
伝播性 MJO と非伝播性 MJO の違
いの概念図。
伝播性 MJO は、西太平洋で対流抑
制に対するロスビー応答として赤
道から極向きの流れが形成され、
湿潤域の南北幅が広くなり、イン
ド洋の MJO が東進する道を開く。
4.Favorable initial conditions and key physical processes for
MJO propagation across the Maritime Continent a. Initial
condition and propagation characteristics(Figs. 5-7)
17. 4.Favorable initial conditions and key physical processes for
MJO propagation across the Maritime Continent c.
Drawbacks of using the RMM index(Fig. 9)
In the RMM phase-space diagram (Fig. 4), we showed that in
the high-skill events, the RMM-defined MJO signal shows
propagation even after day 15 (Fig. 4) and prediction maintains
high skill throughout (Fig. 3). However, even in high-skill
events, the convective signal becomes almost absent after lead
day 15 (Fig. 6). If the forecast convective signal is marginal after
day 15, then what causes such a high prediction skill until day
32? It has become apparent that the fractional contribution of
winds to the variance of RMMs is relatively larger than the
contribution of the convective fields.
高スキルは、 15 日以降も MJO の東進がよく予報されているかのように RMM では見えるが
、実際は、 15 日以降の対流域はほとんど消えていて、循環場だけが東進している。
これは RMM という指標において、対流活動よりも風の場の寄与が大きいことによって、
見かけ上のスキルが生じてしまうという問題点だ。
18. 4.Favorable initial conditions and key physical processes for
MJO propagation across the Maritime Continent c.
Drawbacks of using the RMM index(Fig. 9)
10S-10N 緯度平均 OLR( 灰色と黒 ) 、 U850( 青 ) 、 U200( 赤 ) の偏
差の経度分布。 (a) 高スキルと (b) 低スキルの 1 日予報、 (c) 高スキ
ルの 20-25 日予報。実線、灰色の陰影が観測、点線が予報。
予報 1 日目では、 (a) 高スキルと (b) 低スキルの
いずれにおいても、対流と風の偏差がよく捉え
られている。
(c) 高スキルの予報 20 〜 25 日目でみると、対流
偏差は、観測に比べてかなり減衰しきっている
が、風の偏差は、観測と同等の大きさを保って
いる。
RMM は、風のパターンが同じならば、対流の分
布が大きく異なっていても、似たような振幅に
なる。
positivepositive
normalnormal
23. 1. Introduction
contents
2. Data and methodology
a. Data
b. MJO index (Fig. 1)
c. Measures of MJO prediction skill:
Collective and segment prediction skill
3. Identification of the high-skill and low-skill MJO events
a. MJO initial amplitude and prediction skill relationship(Fig. 2)
b. High-skill versus low-skill events(Figs. 3, 4)
4.Favorable initial conditions and key physical processes for
MJO propagation across the Maritime Continent a. Initial
condition and propagation characteristics(Figs. 5-7) b.
Ocean–atmosphere interaction(Fig. 8) c. Drawbacks of using
the RMM index(Fig. 9)
5. Systematic mean biases and the possible influence on MJO
prediction(Figs. 10-12)
6. Summary and discussion
24. ECMWF アンサンブル予報における MJO の海大陸横断
インド洋で MJO 初期発生したときに、西太平洋での対流抑制がハッキリしている
と海大陸をまたいだ東進が明瞭でなおかつ予報スキルも高くなる。
The MJO initiated over the IO under the situation with suppressed convection over the WP would tend to
propagate across the MC and its prediction skill would be higher than that for the other cases.