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[ Japanese ]
Research Activities
Research on satellite data analysis and their processing
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To improve both data assimilation for numerical weather prediction
models and monitoring of earth environments, we are developing a fast,
radiative-transfer model to retrieve highly accurate vertical profiles
of temperature and moisture from onboard, advanced infrared sounders of new
generation satellites.
We are also developing computational methods to obtain scattering properties
of irregularly shaped particles, and algorithms to retrieve atmospheric and
surface characteristics from polarimeter and multi-directional radiometer
observations.
As an application of the results of our research to operational use, we have
developed an algorithm for monitoring yellow sand aerosols using visible data
observed by geostationary meteorological satellites.
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Fig.1-1. Expected accuracy of temperature retrieval inferred
from radiative transfer simulation, using 281 channels selected from 2378
channels of a new-generation advanced-infrared sounder.
Expected accuracy is less than 1℃, which is much better than 2-3℃
of currently used infrared sounders.
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Fig.1-2. Optical thickness of yellow sand aerosols over the Sea
of Japan on 9 April 2002, retrieved from GMS-5 visible data using a model of
a non-spherical particle. Pixels for land and cloud areas are shown in white.
Yellow- and brown-colored areas indicate high density of yellow sand.
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Doppler radar activity on severe disturbances
We have been developing algorithms for a single
Doppler radar to detect and nowcast severe mesoscale-disturbances
including tornadoes and downbursts; and to retrieve a wind field under a typhoon
environment. Some of the algorithms have been built into the operational
Doppler weather radar systems deployed at major international airports in Japan.
Therefore these radar systems can automatically detect low-level wind shear caused
by severe mesoscale disturbances, which are hazardous for landing and take-off of
aircrafts.
To improve our observation capabilities, we have extended the maximum
detection range of C-band Doppler radar from 125km to 250km, preserving the
unambiguous velocity interval of ±54m/s, using a new algorithm based on the
random-phase technique. This extension allows us a wider range observation of
the wind field of severe weather disturbances, including typhoons.
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| Fig.2-1. Downburst precursor |
(a) The area of strong convergence at the midlevel of the storm.
(b) Mean divergence above 4m/s/km near the ground of the storm. More than
ten minutes prior to the outbreak of remarkable divergences (D1, D2), increase
of the strong convergence area (P1, P2) is observed, which is regarded
as a precursor of the downburst occurrences.
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(c) Fine structure of downbursts observed by radial wind shear.
Yellow-to-red area means a strong divergence area, indicating the downbursts.
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Fig.2-2. The left figure shows a typhoon wind field, retrieved from a single
Doppler radar observation using our new algorithm.
The center of this typhoon is located at the lower left of the figure.
The circulatory wind field around the typhoon's center is well presented.
The figure at right shows the corresponding intensity of precipitation.
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Research on lidar observational technique for atmospheric minor constituents
Lidar is a superior technique for measuring vertical profiles of
atmospheric minor constituents including ozone, aerosols and water vapor that
affect global climate through their radiative properties.
In order to acquire better observational frequency, resolution, and precision
for the troposphere, we are developing a differential-absorption lidar using
multi-wavelength laser lights and Raman lidar techniques.
We are also improving algorithms to derive vertical distributions of
atmospheric minor constituents from lidar signals.
Vertical profiles of ozone and aerosols will be observable from near ground to
40km, combinded with an already established stratospheric-measurement technique.
Our research results are applied to the operational aerosol lidar
installed in Ryori Atmosphere Environment Observatory.
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Fig.3-1. Lidar observation of ozone and aerosols.
The green beam transmitted vertically is a laser light of 532nm.
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Fig.3-2. Temporal-height cross-section of ozone densities.
The density at an altitude above 11km fluctuates significantly,
which may be difficult to observe with conventional methods.
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Research on meteorological observation systems
We are facilitating research on various observation systems
including development of an algorithm for retrieving a vertical moisture
profile from wind profiler observation and an observation technique for
a vertical profile of wind and temperature using a wind profiler equipped
with acoustic sources (figure below).
We are also researching an
algorithm for highly accurate estimation of precipitation by the composite
use of radar reflectivity and drop-size distribution, as well as a photography
method that enables fog visibility and yields particle-size information
utilizing a digital camera and image processing techniques.
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Fig.4. Time series of vertical profile of wind and potential temperature
up to 600m above the ground (for the lowest 100m, data from
meteorological-tower observation
are used).
Northwesterly flow of cold air is displayed near the ground.
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