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| JMA operates an array of observation networks to monitor weather, climate and the environment around the clock on a nationwide scale. |
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Surface observation is carried out at about 1,300 stations using automatic observation equipment collectively known as the Automated Meteorological Data Acquisition System (AMeDAS).
Stations are laid out at average intervals of 17 km throughout the country, with about 1,200 of them unmanned.
Observation at manned stations covers weather, wind direction/speed, amount of precipitation, type and base height of cloud, visibility, air temperature, humidity and atmospheric pressure. Data other than those relating to weather, visibility and cloud-related elements are automatically sent every ten seconds from manned stations and some unmanned stations, and every ten minutes from the remaining unmanned stations, of which about 700 observe four elements (precipitation, air temperature, wind direction/speed and sunshine duration) and about 300 observe precipitation. In addition to these elements, snow depth is also observed at stations in areas of heavy snowfall. All observational data are transmitted to JMA Headquarters via dedicated lines. - Latest weather (Maps / Tables) - Analysis and Forecasting of Precipitation |
 Observational sites of AMeDAS |
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JMA's network of 20 C-band radars (with a wavelength of 5.6 cm) covers most of Japan's territory and observes rainfall intensity and distribution.
Radar data are digitized to produce special radar-echo composite maps every five minutes for the purpose of monitoring precipitation throughout the country. The data are also calibrated with AMeDAS in-situ data and rain gauge data from related authorities for use as initial values in Very Short-Range Forecasting of Precipitation. JMA has been replacing its radars with Doppler units that can measure not only precipitation intensity but also the radial velocity of raindrops. As of the end of March 2010, 16 out of the 20 units in the network had been replaced with Doppler radars. - Radar and Precipitation Nowcast |
 JMA Radar Observation Network |
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Upper-air observation is performed through two different networks: the radiosonde observation network (16 stations) and the wind profiler observation network (31 stations).
The radiosonde (a balloon-borne instrument platform with a radio-transmitting device) covers the upper air up to a maximum of 30 km from the surface, measuring temperature, pressure, humidity and wind. Radiosonde observation is carried out twice a day at 0000 and 1200 UTC, and JMA's research vessel occasionally performs such observation in the western North Pacific and the seas adjacent to Japan. The wind profiler - a ground-based multiple-beam Doppler radar unit - covers a range up to 5 km from the surface and automatically measures wind every ten minutes. The observed data are collected at JMA Headquarters on a real-time basis. |  JMA Upper-air Observation |
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In 1977, Japan launched the first geostationary meteorological satellite (GMS) into geostationary orbit (about 36,000 km above the equator at a longitude of 140 degrees east) mainly to cover the western Pacific and East Asia as part of a space-based component of the Global Observation System (GOS) under the WMO World Weather Watch (WWW) programme.
Since then, continuous efforts have been made to maintain and enhance the observational capabilities of meteorological satellites.
Satellite observation provides a wealth of information, including data on cloud height and distribution, upper-air wind, and sea surface temperature distribution. The observational data received from the spacecraft allow JMA and other National Meteorological and Hydrological Services (NMHSs) to continuously monitor significant meteorological phenomena such as typhoons, fronts and low-pressure systems. The data are also directly assimilated into the numerical weather prediction system, which in turn contributes to the timely issuance of disaster prevention information and weather forecasts from JMA and NMHSs. Currently, the Multi-functional Transport Satellite (MTSAT-1R) launched in 2005 is in operation, performing observation every 30 minutes with imaging channels consisting of a visible band and four infrared bands. MTSAT-2 (launched in 2006 and currently in a state of standby in geostationary orbit) is scheduled to take over the imaging functions of MTSAT-1R in summer 2010. MTSAT-2 has the same imaging channels as MTSAT-1R, and will provide similar observation data. Along with information from MTSAT, JMA utilizes data from various polar orbiting satellites such as the NOAA series operated by the US, Metop operated by Europe, and earth observation satellites such as TRMM and AQUA. Data from these satellites are indispensable in observing typhoons, monitoring the global and marine environment and producing initial fields for numerical weather prediction. |
 Current and planned space-based component of the Global Observation System (picture from the WMO website) |
| The lightning monitoring system pinpoints the time and location of lightning occurrences by detecting radio waves caused by lightning flashes. Data from individual detectors located at 30 airports are gathered and processed by the Data Processing Center at JMA. The results are delivered immediately to airlines for purposes such as securing ground operations at airports and managing aircraft in Japan's airspace. |
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Geomagnetic observation is carried out around the clock by the Magnetic Observatory in Ishioka and its two branch offices in Ozora and Kanoya.
The results of observation are distributed not only to the relevant domestic institutes and laboratories but also to international organizations such as the World Data Center for Geomagnetism - an organization within the framework of the International Council for Science (ICSU). |  JMA Geomagnetic Observation sites |
| In addition to the aforementioned comprehensive observation network operated by JMA itself, the Agency also actively exchanges meteorological observational data with relevant central governmental and local authorities on a real-time basis. The integrated usage of such rain-gauge and radar data with those of JMA plays a vital role in the forecasting of torrential rain. |
