Meteorology and Climate Dynamics
Ryuichi KAWAMURA, Professor
Tetsuya KAWANO, Assistant Professor
http://fujin.geo.kyushu-u.ac.jp/tropo-labo/
Meteorology and Climate Dynamics Laboratory (MCDL) has a long history at Kyushu
University, encompassing a broad range of observational, theoretical and numericalexperimental research on dynamic meteorology and climate system. The MCDL highlights
fundamental issues of cloud physics, mesoscale and synoptic meteorology, large-scale
dynamical processes in the atmosphere, and ocean and climate dynamics. We also pay
particular attention to the mechanisms of severe local storm, tropical cyclone and winter storm
to contribute to disaster reduction in Monsoon Asia. The following topics are part of recent
work from MCDL.
1. Rapid intensification of winter storm
It is well known that explosively developing extratropical cyclones frequently appear over thenorthwestern Pacific Ocean and the northwestern Atlantic Ocean during boreal winter. More recently,
we highlighted an explosive cyclone migrating along the southern periphery of the Kuroshio/Kuroshio
Extension in January 2013 and investigated the manner in which vapor evaporating from the warm
currents influences the rapid growth of the cyclone. We stressed that active roles of the cold conveyor
belt (CCB) were key factors in the explosive development of the cyclone over warm currents. The CCB
is a low-level easterly flow with cold and dry air that prevails along the northern side of the cyclone’scenter. The CCB plays a vital role not only in stimulating surface evaporation from the warm currents
but also in importing the evaporated vapor into the vicinity of the cyclone’s center. The importedmoisture converges at the bent-back front within the cyclone system and induces latent heat release,
eventually accelerating the cyclone’s development. The cyclone’s deepening further intensifies the CCB.
We suggested that this positive feedback process leads to rapid intensification of cyclones over warm
currents.
We are also trying to reproduce
the mesoscale structure in winterstorm, together with the Japan
Agency for Marine-Earth ScienceandTechnology(JAMSTEC).
Using the Earth Simulator ofJAMSTEC, we are able to perform
very high-resolution simulations
with a horizontal scale of about 2km. We expect that such a study
contributes a great deal to proper
understanding of the developing
Comparison of simulated rainfall distribution within an extratropicalmechanism of the winter storm andcyclone system between low- and high-resolution regional models.
the associated severe local storm.
2. Development and maintenance of tropical cyclone via moisture conveyor belt
The role of remote ocean sea surface temperature (SST) in regulating tropical cyclone (TC)characteristics has been examined by performing numerical experiments with a regional scale model.
Model simulations have been carried out to simulate typhoon Man-yi (July 2007), in our case study,
under a range of SST conditions over the Indian Ocean and the South China Sea. The intensity andtrack of the cyclone have been systematically changed in sensitivity simulations of cool and warm SSTs
over that region, following its peak phase. Warm oceans can substantially reduce the intensification ofwestern North Pacific cyclones, whereas cool oceans can enhance their strength. This is intimately

Typhoon Man-yi (2007) and moisture conveyor belt.

associated with the enhancement/weakening of
the moisture supply through the moisture
conveyor belt (MCB) in the lower troposphere,
from the Indian Ocean and South China Sea into
the vicinity of the cyclone center. When the MCB
is interrupted over the South China Sea in warm
SST occurrences, the large-scale transport ofmoisture into the cyclone system is significantlyreduced, leading to the weakening of the cyclone
intensity and to the eastward shift of its track. This
study shows that changes in remote tropicalocean SST can also modulate TCs and thus canhelp in improving the forecasting of TC intensities
and tracks.

3. Numerical simulation of supercell
tornadogenesis
A tornado is one of the most violent
meteorological phenomena causing fatal
damage. Most strong tornadoes arespawned by supercells, which arecumulonimbi with a strong vertical vortex.
Tornadogenesis in association withsupercells, however, is not completelyunderstood. We focused on theinteraction between a supercell and an
outflow boundary, which is often made bya preexisting cumulonimbus, because
many tornadoes occur in the vicinity ofoutflow boundaries.
To investigate tornadogenesis related tothe interaction, we performed numericalsimulations. As a highly idealized outflow
boundary approached a developed
supercell having a strong surface vortex,
the surface vortex in the supercell
markedly intensified. This intensification
was associated with the enhancement of
the near-surface horizontal convergenceby the outflow boundary.

Three-dimensional view of the updraft (gray isosurface),
potential temperature perturbation (bottom colors and blue
isosurface), and cyclonic vorticity (red isosurface) field at(a) 122 min, (b) 135 min, and (c) 140.5 min of a simulationwith a highly idealized outflow boundary, and (d) 140.5
min of a simulation without any outflow boundary.

4. Videosonde observations of snow clouds on the Japan Sea
side of central Japan
Videosondes, which are balloon-borne equipment that canmeasure sizes and electric charges of each precipitation particle
in cloud, are very useful for understanding precipitation
processes. We carried out observation campaigns withvideosondes in the Hokuriku district in winter, collaborating withCentral Research Institute of Electric Power Industry andYamaguchi University and are trying to clarify precipitationprocesses in wintertime Hokuriku snow clouds through a detailed
analysis of the videosonde observations.

Launching of a videosonde withtwo balloons into a snow cloud.