Ice Microphysical Properties
in Stratiform Region of a Baiu Frontal Convective System
Observed by Hydrometeor Videosonde
1112T. Ohigashi , S. Miyai , K. Tsuboki , and E. Nakakita
1Hydrospheric Atmospheric Research Center, Nagoya University, Nagoya, Japan
2Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan

E-mail: ohigashi@rain.hyarc.nagoya-u.ac.jp
Introduction
Mesoscale convective systems (MCSs) developed in the Baiu frontal zone frequently form clusters of upper-level clouds with low
brightness temperature. The deep clouds extending from convective regions form stratiform precipitation. The upper-level clouds coolcloud-top layers through radiation, which can intensify or develop convections.
A numerical model which incorporates detailed cloud microphysical processes is a powerful tool to understand the processes suchas precipitation formations and dynamics of MCSs in the Baiu frontal zone. Although simulation results should be validated byobservations, observations of microphysical properties of upper-level ice clouds, which are related with precipitation formation anddynamical processes, are insufficient for MCSs in the Baiu frontal zone.
To examine microphysical quantitative properties of ice clouds of the Baiu frontal MCSs, we performed an observation at theOkinawa Island in Japan during a Baiu season using hydrometeor videosondes (HYVIS).

Hydrometeor videosonde (HYVIS) observation
Observation

Microphysical quantitative properties
Sounding

Number concentration

melting level: 4650 m

HYVIS and two camera images
closeup camera image

microscope camera image

5.5 mm

1.4 mm(Murakami and Matsuo 1990, JTECH)

Made by Meisei Electric Co., Japan

Particles more than ～10 μm on a film can be measured.

Water vapor density isnearly equal to or slightly
largerthansaturation
vapor density with respect
to ice. Ice supersaturationis less than 0.1.

Number concentrations of the particles
less than and more than 100 μm are105-106 m-3 and 104-105 m-3 ,respectively. “Plate” and “unknown”
particle types were predominant.

Particle size distribution

Convective system observed by HYVISBaiu front and development of a MCS
15 JST, 12 June 2008

A MCS developed at
12 June 2008 in theBaiu front. Around 15JST, the MCS was ata mature to decaying
stage.

Radar image
horizontal display of precipitation intensity(JMA radar)

Mixing ratio
NeedleColumnPlate
Column and Plate
Total (solid line)
Water vapor(dashed line)

stratiform region

convective region

vertical cross section (COBRA radar)
AZ=186°

Total mixing ratio was 10-2-10-1 g kg-1.
“Plate” and “Column and Plate” types
significantly contribute to the total mixing
ratio.

The modified gamma distributions are
more suitable than the exponentialdistributions. Its shape parameter
showed positive values, which indicate
the PSDs are convex upward.

Summary
A MCS developed at 12 June 2008 in the Baiu frontal zone. A HYVIS was released in
the stratiform region of the MCS which was at a mature to decaying stage. The layer
above a melting layer was examined.

bright band

A HYVIS was released in the stratiform
region at 1426 JST, 12 June 2008. The
ascending velocity was about 5.5 m s-1.

z Orders of number concentrations of ice particles less than 100 μm and morethan 100 μm were 105-106 m-3 and 104-105 m-3 , respectively.
z Mixing ratio was 10-2-10-1 g kg-1 except for the cloud top.
z Particle size distributions (PSDs) are approximated by the modified gamma
distribution. The PSDs’ shapes are convex upward.
z The dominant habit was “Plate” through the ice clouds with low ice supersaturation.
These facts provide references for future numerical simulations.