Cloud Top Heights of Cumulonimbi, Cloud Top Heights of Cumulonimbi, Thermodynamically Estimated from Thermodynamically Estimated from

Objective Analysis Data Objective Analysis Data during the Baiu Seasonduring the Baiu Season

Teruyuki KATOTeruyuki KATO（（ Meteorological Research Institute / Meteorological Research Institute /

JMAJMA））

3/11/2006: 3/11/2006: 5th International Conference on Mesoscale Meteorology and Typhoon5th International Conference on Mesoscale Meteorology and Typhoon

Purposes of today’s presented studyPurposes of today’s presented study

• to clarify the to clarify the thermodynamically atmospheric conditionsthermodynamically atmospheric conditions around the Baiu Frontal Zonearound the Baiu Frontal Zone

in relation to the development of cumulonimbi.in relation to the development of cumulonimbi.

• to examine the condition under which to examine the condition under which convection with cloud tops less than the melting levelconvection with cloud tops less than the melting level ca ca

n form, and its cause.n form, and its cause.

Such convection was often observed around the Baiu frSuch convection was often observed around the Baiu frontal Zone (e.g., Zhang et al. 2006).ontal Zone (e.g., Zhang et al. 2006).

By using objective analysis data,By using objective analysis data,

Objective analysis data and statistical areaObjective analysis data and statistical area

Data used in this studyData used in this study

Regional Analysis data Regional Analysis data of the JMAof the JMA

Resolution:Resolution: 20 km 20 km

Vertical grids:Vertical grids: -p plane-p plane p planep plane

Available:Available: 6 hourly 6 hourly

Period:Period: June & July June & July in 2001-2005in 2001-2005

Statistical areaStatistical area

JULYJULY

JUNEJUNE

Cloud top heights of cumulonimbi, Cloud top heights of cumulonimbi, thermodynamically estimated in this studythermodynamically estimated in this study

Heig

ht

Dry Adiabat Originating LevelLifting Condensation Level

Profile of TemperatureProfile of Temperaturein the environmental fieldin the environmental field

Neutral Buoyancy Neutral Buoyancy LevelLevel (LNB) (LNB)

Moist Adiabat

Level of FreeConvection (LFC)

Temperature

e e is conseis conse

rved.rved.

Equivalent potential temperature e

Profile Profile of of ee**

~ Level of Neutral Buoyancy (LNB) of an air with the m~ Level of Neutral Buoyancy (LNB) of an air with the maximum aximum ee at the low level, except the surface at the low level, except the surface

NOTE: NOTE: Originating level - LFC Originating level - LFC < 200 hPa< 200 hPa

Appearance frequency of LNB around the Japan IslandsAppearance frequency of LNB around the Japan Islands

First half (June)First half (June) Second half (July)Second half (July)Upper-air sounding dataUpper-air sounding data

Appearance frequency of LNB Appearance frequency of LNB overover Northwestern Pacific Northwestern Pacific

Upper-air sounding dataUpper-air sounding data

Appearance Appearance frequency of LNB frequency of LNB

over the over the other areasother areasaround the around the

Baiu frontal zoneBaiu frontal zone

②②

③③

④④

⑤⑤

Dependency of LNB on Atmospheric StabilityDependency of LNB on Atmospheric Stability

LLee**minmin

LNBLNBmaxmax

Lapse rateLapse rateLarge ← stability → Small

Saturated equivalent Saturated equivalent potential temperaturepotential temperature

Equivalent Equivalent potential potential temperaturetemperature

1000hPa-level temperature of Celsius 25 degrees

相当温位相当温位

1000hPa-level Temperature

LLee**minmin

LNBLNBmaxmax

Dependency of LNB on low-level temperatureDependency of LNB on low-level temperature

JUNE JULY

Over the SeaOver the Sea

On the landOn the land

JUNEJUNE JULYJULY

JUNEJUNE JULYJULY

DomainDomain ::Around Japan Islands:Around Japan Islands:

Appearance Appearance rate of LNBrate of LNB

toto

MaxiumMaxiumequivalentequivalentpotential potential

temperaturetemperatureat the low-levelat the low-level

DomainDomain ::Around Japan Islands:Around Japan Islands:

JUNEJUNE JULYJULY

JUNEJUNE JULYJULY

Over the SeaOver the Sea

On the landOn the land

Appearance Appearance rate of LNBrate of LNB

toto

Lapse rateLapse rateBetweenBetween

500500mm-altitude-altitudeandand

700700hPa-levelhPa-level

5K/km5K/km

5K/km5K/km

5K/km5K/km

5K/km5K/km

ConclusionsConclusionsIn the appearance rate of LNB during the Baiu season,In the appearance rate of LNB during the Baiu season, >> Upper and middle peaks are found on the land. Upper and middle peaks are found on the land. (~ 150hPa) (~ 700hPa) (~ 150hPa) (~ 700hPa) >> Another peak (~ 900hPa) is also found over the sea. Another peak (~ 900hPa) is also found over the sea.

CauseCause：： Stabilization of atmospheric conditions around the Japan Stabilization of atmospheric conditions around the Japan Islands, brought from the inflow of middle-level airs warmed by Islands, brought from the inflow of middle-level airs warmed by convective activities convective activities overover upstream areas, upstream areas, especiallyespecially China Continent China Continent

Factor to divide LNB into upper and middle peaks isFactor to divide LNB into upper and middle peaks is （（ ~ ~ 150150hPahPa ）（）（ ~ ~ 700700hPahPa ））

For For > about 5K/km and large > about 5K/km and large ee of lifted air, LNB appears at the of lifted air, LNB appears at the upper level. For the other, LNB appears at the middle level.upper level. For the other, LNB appears at the middle level.

dependent mainly on mean lapse late dependent mainly on mean lapse late below the middle level. below the middle level.

Pre

ssur

e (h

Pa)

e (K)

Profile of e

*

600

200hPa

700

500

200

U ~ 6 K km-1

L > 5 K km-1

Tropopause

Middle-level Peak

Profile of e

*

Upper-level Peak

Formation mechanism of Formation mechanism of Upper- and Middle-level Peaks of LNBUpper- and Middle-level Peaks of LNB

Adiabatic Adiabatic heatingheating

Upper-level Peak

L < 5 K km-1

Originating Level