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