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The Role of Environmental Shear and Thermodynamic conditionin Determining the Structure and Evolution of
Mesoscale Convective Systems during TOGA COARE
M. A. LeMone, E. J. Zipser and S. B. Trier
発表者: 清水 慎吾Shingo SHIMIZU
1 線状 MCS の論文のレビュー (Histrocal Reviews of line-shaped MCS )2 LeMone の論文紹介 ( Introduction of LeMone’s paper )3 自分の研究との関わり合い (Future work of my study)
Mon. Wea. Rev. 1998
Today’s contents
線状メソ対流系の特徴
•2~10個の対流セルがある決まった方向に並んだ強い雨域 ( convective line )•104km2以上の広い面積をもつ弱い雨域( stratiform region )
線状 MCS 全体としての研究課題 (common subject)
•三次元構造(対流域と層状域)、気流構造の解明
•発生・発達・組織化・維持の mechanism の解明
•より大きな場との相互作用(環境場、大きな場へのフィードバック)(運動量輸送、熱輸送、放射特性)
はじめに
①②
③
(Houze,1990)
convective line
stratiform region
Characteristic of linear MCS
Large area of Weak rain region
Area of several Convective cells
線状 MCS の研究年表 ① structure ② mechanism ③ environment
Moncrieff 1976,78,81
Weisman 1986,92,93Rottuno 1985,88
Fovell 1988
数値実験
②
Thorpe 1982②
②
時間
Zipser 1977
Bluestein 1985,87
Smull 1985,87a,87b
Houze 1990
Newton 1950
Schiesser 1995
LeMene 1998
観測解析
Barns 1984
Wang 1990
①①
①
③③
③
③
Biggerstaff 1991 ①
Keenan 1992Alexander 1992
③①
線状 MCS の内部構造( Reflectivity )(対流性と層状性の雨域の特徴)
線状 MCS と環境風の関係(下層、中層鉛直シアー)移動方向、走向、組織化過程
線状 MCS の気流構造上昇流の維持過程
線状 MCS の地域特性
地域特性の比較線状 MCS と環境場( UV,T,RH )
Moncrieff 1976,78,81
Weisman 1986,92,93Rottuno 1985,88
Fovell 1988
数値実験
②
Thorpe 1982②
②
二次元モデル鉛直シアーと cold pool の関係(上昇流の維持過程)
三次元モデル鉛直シアーと cold pool の関係(上昇流の維持過程)
二次元モデル鉛直シアーと cold pool の関係(組織化過程)
環境風に対して、ライン状対流域がどのような走向をもつのか? (the relation between environmental wind and line orientation)
GATE の観測結果から
Alexander and Young(1992)
EMEX の観測結果から
Main theme 1
~ Review of past studies ~
900~500 hPa のラインに直交 shear :大 → fast-moving小 → slow-moving( ただし、ライン平行 shear :中 )(more or less than 7 m/s )
950~750 hPa に5m / s以上の風速差YES→ shear 直交型 (shear-perpendicular)
NO→ shear 平行型( parallel to 800 ~ 400 hPa shear )
Barnes and Sieckman(1984)
TOGA-COARE の観測概要と観測領域
TOGA-COARE の HP より
Toropical Ocean Global Atmosphere(TOGA)-
Coupled Atmosphere-Ocean Response Experiment(COARE) (1992-1993 年 )
Five category (Lemone,98)
①shear 直交型②shear 平行型③ 小規模 scale 対流群④shear 無縁型⑤ 非組織化型
①
①② ②
⑤①shear 直交型
下層(1000~800 hPa )shear に直交
② shear 平行型
中層(800~400 hPa )shear に平行
① ② 混合型は?
Fast-movingslow-moving
目的 (objective)
データ (data)
① 環境風に対して、ライン状対流域がどのような走向をもつのか? ( The relation between environmental vertical wind shear and convective line orientation )② ライン状対流域が維持に、重要な環境場の熱力学パラメータは?( What environmental thermodynamical factor determinesthe maintenance of convective line ? ) ~ 観測計画間の比較( GATE,EMEX との比較) ~飛行機搭載 radar による反射強度分布データ
( radar reflectivity observed by three airplanes.)(20 cases during 1992 – 1993 in TOGA-COARE)
3 台の飛行機による (three airplane observation)•直接観測 (potential theta, specific humidity,winds)•飛行機からのドロップゾンデ (dropsonde)
ゾンデデータ (radiosonde)
データ( analysis method )
Definition of “inflow environment”
storm-relative inflow の風上 150 km ×150 km の領域において•高度 300m 以下で混合層がよく発達した場 ( qv,θ 一様場)•高度 400m 以下で降水がない (no liquid water)
走向の評価
飛行機によるradar 観測
環境場の評価
Radiosonde( 6km ~)dropsonde( 1km ~ 6km )In situ measurement( 1km ~ 6km )(30m ~ 1km)
目的1
環境風に対して、ライン状対流域がどのような走向をもつのか?
Objective 1
The relation between environmental vertical wind shear And
Orientaion of Line-shaped MCS
データ( Case selection )
20 cases ofline-MCS
Each case studieswere reported by
(Observation)
Jorgensen(97)Lewis(98)
(Numerical simulation)
Trier(96,98)
low-level shear : Large
①Shear 直交型
下層(1000~800 hPa )shear に直交
15 dBZ が outline25 dBZ が shade
CAPE
高度300mの
ラインの走向と
移動速度の走向に直交す
る成分
Fast-moving (7 m/s) (perpendicular to convective line)
Reflectivity and hodograph
Definition of “Large shear”2 (1.25) m/s per 100 hPa4 m/s (1000-800 hPa)5 m/s (800-400 hPa)
②Shear 平行型中層 shear に平行
mid-level shear : Strong
low-level shear : Small
Slow-moving(almost stationary)
Reflectivity and hodograph
20 dBZ が outline30 dBZ が shade
①② 混合型
下層 shear に直交中層 shear に平行
mid-level shear : Strong
low-level shear : Strong
Fast-moving
Reflectivity and hodograph
20 dBZ が outline30 dBZ が shade
Primary
band
Primary band
Secondary band
Secondary band
Time evolution of orientation
30分後After 30 min
20 dBZ が outline30 dBZ が shade
mid-level shear : Strong
low-level shear : Strong
Fast-moving(except for 6 Feb)
Reflectivity and hodograph
①② 混合型
下層 shear に直交中層 shear に平行
20 dBZ が outline30 dBZ が shade
mid-level shear : Strong
low-level shear : Strong
Fast-moving
Reflectivity and hodograph
①② 混合型
下層 shear に直交中層 shear に平行
20 dBZ が outline30 dBZ が shade
Summary of objective 1
1) If strong low-level shear exists,→ shear-perpendicular type
2 ) If strong mid-level shear exists without strong low-level shear,→ shear-parallel type
3 ) If strong both low- and mid-level shear exists,→ primary bands first form perpendicular to low-level shear→After that, secondary bands form trailing or leading primary band parallel to mid-level shear
The relation between vertical shear and Line orientation
目的2
ライン状対流域が維持に重要な環境場の熱力学パラメータ
は?
What environmental thermodynamical parameter determines the maintenance of line-shaped MCS ?
Objective 2
Comparison of “convective line” lifetime between GATE and COARE
slow-moving line in GATE
•Typical lifetime of convective line is 4-5 hours•Continuous propagation
slow-moving line in COARE
•Longest lifetime was 3 hours (2/17 case), the others was < 2 hours•Discontinuously propagation (except for 2/17)
In a strong low-level vertical shear environment,Convective line tends to be long-lived (Rottuno,1988)
In this study, the impact of thermodynamical parameters on the lifetime.Slow-moving lines are focused.(they forms in a weak low-level vertical shear)
The comparison of RH profiles between GATE and COARE
Mid-level RH (top of BL and 500 hPa)is higher in slow-moving GATEthan that of COARE
The lifetime of Slow-moving lines in GATEis longer than those in COARE
Strength of cold poolEvaluated by
the deficit of temperature
Cold pool was weaker in both GATE and COARE than that ofmidlatitude
Cold pool of 2/17 is weaker than that of 2/18
Lifetime of line on 2/17Is longer than that on 2/18
The vertical profile of Relative Humidity(3 cases in COARE)
The RH in mid-level(top of BL and 500 hPa)on 17 Feb was higher thanthat on 18 Feb
A weaker cold pool on 2/17
Thermodynamical parameter
Conclusion
If strong both low- and mid-level shear exists,→ primary band first forms perpendicular to low-level shear→ After that, secondary convective line formed trailing or leading primary band parallel to mid-level shear
Convective inhibits in GATE and COARE (less than 10 J/kg)were smaller than those of midlatitude(60-100 J/kg)
The relation between shear and orientation was confirmed and extended
In a weak low-level shear environment,Humidity between top of boundary layer and 500 hPa determinesthe lifetime of convective line (more than 1 hour longer).
In small CIN, and high RH at mid-level environment,Convective line would be well-maintained.
Thermodynamical parameter to determine the lifetime of convective line
Moncrieff 1976,78,81
Weisman 1986,92,93Rottuno 1985,88
Fovell 1988
数値実験
②
Thorpe 1982②
②
時間
Zipser 1977
Bluestein 1985,87
Smull 1985,87a,87b
Houze 1990
Newton 1950
Schiesser 1995
LeMene 1998
観測解析
Barns 1984
Wang 1990
①①
①
③③
③
③
Biggerstaff 1991 ①
Keenan 1992Alexander 1992
③①
For my study・・・・ ① structure ② mechanism ③ environment
•In various places,•Observational or Numerical Studies•Could be conducted in high-resolution
For my study・・・・ ① structure ② mechanism ③ environment
Rottuno 1985,88 ②Fovell 1988 ②Bluestein 1985,87
LeMene 1998
③
③
Seko, 2002
Convective cell’s feature Linear MCS’s feature
Kato,1998 ② ③①② ③①
② ③①
環境場の特性
Yoshizaki,2000
dry
Barnes 1984 ③
Moist
対流セルとシステムの関係(対流セルの組織化過程)Vertical shear
Mid-level humidity
Instabilityinput (Environment) process (mechanism) output(structure)
•対流セル•MCSの特徴
Composite profiles of θe, Obtained in
GATE and COARE
It depends on the differenceof SST(1-2 K higher in COARE)
Equivalent PT of COAREis higher than that of GATE
The vertical gradient of EPT is Similar (17 K drop between600 hPa and surface)
Mean profiles of q,θ,θe within
boundary layer Obtained in COARE
Below 400 m,Mixing layer exists
Qv,PT,EPT of COARE are higher
(qv 18 g:PT: 301K:EPT : 355 K)
( GATE : 17 g : 298.5 K :348 K )
At surface
Smaller scale convection
(shallow convection and little stratiform region)
20 dBZ が outline30 dBZ が shade
shear 無縁型(他の MCS のOutflow によるもの)
20 dBZ が outline30 dBZ が shade
shear 無縁型
20 dBZ が outline30 dBZ が shade
非組織化型
鉛直シアーが小さい
20 dBZ が outline30 dBZ が shade
Orientation and wind shear 走向が鉛直シアーと30 ° 以内は太字
Modification of wind by convective lineDiscussion 1
Discussion 2 Frequency of linear MCS
GATE : mainly slow-moving (avarage speed 2.9 m/s) ( slow moving : 80 cases, fast moving: 6 cases 7% )COARE: more fast-moving can be observed relatively (fast moving : 30 % )
GATE : 90 % (Houze,96 ,Alkell 77)COARE: 66% (Rickenbanch , 1998)
Frequency of organization to line-shape
Frequency of slow or fast moving line