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[ Japanese ]
Observation Instruments
Meteorological Observation Tower
This 213m-tall tower for meteorological observation
was constructed in 1975. Since then it has been observing wind speed and
direction, temperature, and humidity at heights of 10m, 25m, 50m, 100m, 150m,
200m, and 213m. Observed data are saved and used for studies on such phenomena
as the atmospheric boundary layer and hazardous winds. An intake port of air is
installed at the upper part of the tower in order to monitor a greenhouse-gas
concentration.
The right figure shows time series of wind speed in a typhoon
environment. Traces of blue, sky-blue, red, and green show the wind speed
at the height of 10m, 50m, 100m, and 213m, respectively, indicating the
vicinity of a typhoon center at around 2140 JST.
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Doppler Weather Radar
MRI’s pulse-Doppler weather radar uses a single directional
antenna to transmit and receive the microwaves. The radar transmits microwave pulses and then receives the
return from raindrops, snow flakes, etc. in the path of the radar beam. Precipitation intensity is derived
from the amplitude of the returned signals, and wind behavior is determined by detecting the Doppler frequency
shift in the returned signals. During warm seasons, clear-air returns from drifting insects are received,
which allows us to observe wind behavior under fine weather.
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Parabolic antenna of 4m in diameter.
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Signal processing and display units.
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Radar specifications are set for a transmitting frequency of
5260MHz, peak power of 250kW, maximum detection ranges of 400km for precipitation
intensity and of 250km for Doppler velocity, and unambiguous Doppler-velocity
range of ±54m/s.
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Precipitation-intensity distribution(left) and Doppler-velocity distribution(right).
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Lidar
Lidar (Light Detection and Ranging) is a kind of radar using
laser light instead of radio waves. It transmits pulsed laser light to the atmosphere;
and collects the light reflected from the atmospheric molecules, clouds, and aerosols with
the help of the receiving telescope.
Distribution of the atmospheric minor constituents of water vapor, temperature,
aerosols, and clouds are derived from the intensity of the received light; and distribution
of wind is derived from the Doppler shift within an order of ten minutes. One of our lidar
systems can transmit three wavelengths from one laser. The three wavelengths are extremely
stable, with a fluctuation of wavelength less than 0.0015pm.
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The right figure shows a Raman lidar system for measuring water vapor and
aerosols. The green laser light of 532nm is being transmitted. Maximum
pulse energy of the laser light is 800mJ; the pulse repetition frequency
is 30Hz; and the receiving telescope is 1m in diameter. This system measures
water vapor and aerosols ranging from 100m to 10km in altitude with a vertical
resolution of 100m and temporal resolution of three minutes. These resolutions
are higher than those of any other observation instruments. Daytime measurement
of the water vapor will be realized soon.
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Temporal-altitude cross-section of water vapor distribution.
The red area indicates a denser mixing ratio. The water vapor is concentrated below an altitude of 5km;
and its density exhibits temporal variation.
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