Generation mechanismsof convections
by gravity waves
Hiromu Seko, Syugo Hayashi and Kazuo Saito(Meteorological Research Institute /Japan Meteorological Agency)

Contents

1.Motivation
2.Ideal experiment of the 2-dimensional
model
3.Generation mechanisms of convections
by gravity waves
4.Summary1. Motivation-I believe that it is important to understand thegeneration and development mechanisms ofthe convections because convective storms
sometime cause mud slides or floods.
-Reducing the damage of disasters has always
been top priority. Further investigation of thegeneration mechanisms of the convections isnecessary.

2. Ideal experiment of the 2-dimensional model• To understand the generation process ofconvections, ideal experiments using the2-dimensional model was performed by Yamasaki
and Seko (1992).
• Typical profiles of temperature and humidity in thetropical atmosphere were used as the basic fields.
• Two sets of four babbles were placed in thedomain of numerical model.
References
Yamasaki, M., and H. Seko, Effect of the gravity wave on the convections, 1992,
Proceedings of Spring meeting of Meteorological Society of Japan, A108 (in Japanese).

Temporal variations of vertical velocity at z=1.2km
ADETime（hr）

BFGCH
J

Updraft （1.2km）

Time sequence of updraft at z=1.2km (After Yamasaki and Seko,1992）．

-GWs were generated at the convections and propagated to bothdirections.
-Convection F was generated at the overlapped area of GWs from theconvections A and C. Convection F was developed when GWs fromthe convections B and E arrived.

Temporal variations of vertical velocity at z=1.2km
ADETime（hr）

BFGCH
J

Updraft （1.2km）

Time sequence of updraft at z=1.2km (After Yamasaki and Seko,1992）．

-Convection J was also generated when the GWs from the convection Garrived, and was developed when GW from the convection H arrived.
-When GWs approached, temperature was decreased and moistened (notshown). Updraft and these changes were caused by GWs and werefavorable conditions for the generation of convections.

Temporal variations of temperature at z=150 m

Time（hr）

AD

BCJE

F

G

H

Temperature （150m）
Time sequence of temperature at 150m (After Yamasaki and Seko,1992）．

-There were no cold pools where convections F and J were generated.
This distribution supports that GWs generate and develop theconvections.

3. Generation mechanisms of convections bygravity waves• Numerical simulations of NHM with the gridinterval of 20 km were performed.
• Initial and boundary conditions were produced
from JRA25 data.
• Initial time was 12UTC 28 2008.
• Downscale experiments were performed with thegrid intervals of 5 kms and 1 km.

Rainfall distribution reproduced by 5km-NHM

10m/s∆x=5kmRainfall region reproduced by 5km-NHM. Initial time is18UTC 28 Jan..

-A convective band that extended southeastward wasgenerated at the eastern side of Sumatra island.
-Westerly and northwesterly flows were converged near theconvective band.

Rainfall and temperature distributionsat P=1000hPa, reproduced by 1km-NHM∆x=1km（a）A∆x=5km（b）∆x=1kmB（c）(a) Rainfall region reproduced by 5km-NHM. Initial time is 18UTC 28 Jan. 2008. Rainfall
region and temperature at 1000hPa at (b) 22:30UTC 29 and (c) 23:20UTC reproduced by1km-NHM. Domains of (b) and (c) are indicated by rectangle in (a). Initial time of 1kmNHM is 15UTC 29.

-Convections ‘A’ were successively generated on the easternside of the convective band where cold pools did not exist.

Rainfall and temperature distributionsat P=1000hPa, reproduced by 1km-NHM∆x=1km（a）A∆x=5km（b）∆x=1kmB（c）(a) Rainfall region reproduced by 5km-NHM. Initial time is 18UTC 28 Jan. 2008. Rainfall
region and temperature at 1000hPa at (b) 22:30UTC 29 and (c) 23:20UTC reproduced by1km-NHM. Domains of (b) and (c) are indicated by rectangle in (a). Initial time of 1kmNHM is 15UTC 29.

-Next, time sequences along the brokenlines are shown.

Time （hr）

Time （hr）

Time sequences of updraft andtemperature at P= 1000hPa and
850hPa along the line thatGWA
crosses the convections ‘A’.
(850hPa)-At 1000hPa, updraft produced+Qr（a）
by the convergence of westerly
and northwesterly flows (solidarrow) was seen on the easternside of the convections.
GW(1000hPa)
A -These is no cold pools before
the generation of convections+T(1000hPa)‘A’.
Warm（b）-Convections ‘A’ were generated
when the updraft at 850hPa
Time variation of updraft (colored region)
at P=850hPa along the broken line in Fig. (broken arrow) was propagated
2b, (a) rainfall and (b) temperature atfrom the east.
P=1000hPa.

+T-Td(dew-point
deficit)(850hPa)

GW(850hPa)+T(850hPa)AUp （a）
Down

Time （hr）(850hPa)Time （hr）

GW

A

Time sequence of updraft andtemperature and dew-point
deficit (T-Td) at 850 hPa
along the line, which crosses
the convections ‘A’.
-Temperature was gradually
decreased as time passed.
-Temperature was fluctuatedwhen the updrafts were
propagated from the east.

Up （b）-The relation of temperature
Down

Time variation of updraft (colored region) at
P=850hPa along the broken line in Fig. 2b,(a) dew-point deficit at P=850 hPa and (b)temperature at P=850hPa..

and updraft is checkedby showing the verticalcross section.

Deviations of temperature and vertical velocity
from the horizontal average
Height500(hPa)w +∆TTime （hr）

GW(850hPa)+Qrba600

A（a）
Time variation of updraft

700

800
9001000

a12UTCb20UTCTime (UTC)-Temperature was gradually decreased as time passed.
-Temperature was largely decreased after the passage of updraft.
-This phase relation indicates that these deviations wereproduced by GWs.

(850hPa)+T-Td(dew-pointdeficit)(850hPa)Time （hr）

GW

AWet
（a）

Time sequences of updraft,temperature and dew-point
deficit (T-Td) at 850 hPa along
the broken line, whichcrossed the convections ‘A’.

Time （hr）-When the GW was propagated,temperature was decreased
GWand the dew-point deficit(850hPa)A
became smaller.
+T-These changes are common toCold(850hPa)
ones that explained（b）with results ofTime variation of updraft (colored region) the 2-dimensional model.
at P=850hPa along the broken line inFig. 2b, (a) dew-point deficit at P=850hPa and (b) temperature at P=850hPa..

Rainfall and temperature distributions at
P=1000hPa, reproduced by 1km-NHM∆x=1km（a）

A∆x=5km（b）∆x=1kmB（c）(a) Rainfall region reproduced by 5km-NHM. Initial time is 18UTC 28 Jan. 2008. Rainfall
region and temperature at 1000hPa at (b) 22:30UTC 29 and (c) 23:20UTC reproduced by1km-NHM. Domains of (b) and (c) are indicated by rectangle in (a). Initial time of 1kmNHM is 15UTC 29.

-Convections ‘B’ were generated on the large gradient zone oftemperature.

(950hPa)+QrTime（hr）

GW

Time sequences of updraft andtemperature at P=1000 hPa
and 950hPa along the broken
line, which crossed theconvections ‘B’.

B-Convection ‘B’ was generated
along the edge of the coldpool.
GW-Low-level updraft was(975hPa)
Cold
B
produced by the outflow of+Tpool
the cold pool.
(1000hPa)-When the GW from the（b）
western side overlapped
the edge of cold pool, theTime variation of updraft (colored region) at (a) P=950hPa and (b) 975hPa along the line, (a) rainfall and (b)convention ‘B’ was generated.
temperature at P=1000hPa.
Time（hr）（a）Time sequences of updraft
and temperature at P=1000
hPa and 950hPa along thebroken line, which crossed
the convections ‘B’.

+T-Td

(dew-pointdeficit)(950hPa)

GW(950hPa)+T(950hPa)

Wet

B
（a）

Time（hr）(950hPa)Time（hr）

GW

Cold-When GW was propagated,temperature was decreased
and dew-point deficit
became smaller.
B-These variations oftemperature and dew-point（b）
deficit were common withthose of the convections ‘A’.

Time variation of updraft (colored region) at P=950 hPa
along the broken line, (a) dew-point deficit and (b)temperature at P=950hPa..

4. Summary-Updraft of GWs makes the atmosphere cool andmoist. Updraft and these changes generated theconvections in this study.
-The generation point and timing of the convection
was influenced by GW. When the cold pool wasweak, GW influenced the generation point andtiming of convection.

Thank you for your attention.