About This Site

AMeDAS is the acronym of Automated Meteorological Acquisition System, and its meaning is that this is a system for observing meterological elements and collecting those data automatically.

This site summarizes the probability distribution of hourly observation based on AMeDAS dataset. The purpose of this site is to put thecurrent observation data into a historical context. The source of data is "Annual AMeDAS Report" before 2010, and "Monthly Meteorological Observation Report" after 2011, both published by Japan Meteorological Agency. After March 2008, the observation is gradually changed from every hour to every 10 minutes, so the hourly data is computed from the dataset for comparison. Information about AMeDAS stations is also extracted from those sources, including stations that are out of operation now. Hence the number of stations listed in this site is larger than that of currently active stations.

For searching individual AMeDAS data, Japan Meteorological Agency provides Meteorological data reference room (in Japanese). Base maps that are used for the map of AMeDAS stations are processed from NASA Blue Marble Data.

The site provides statistics data until February 2013, and the data is updated after a new monthly report is issued. Real-time AMeDAS after that is not included in the statistics, but is included in AMeRAS (AMeDAS Ranking Service) or AMeDAS Heavy Rains. Please note, however, that these data are provided for research purposes, and not for commercial purposes or life-and-death decision making.

AMeDAS Meteorological Elements

The site deals with statistics for the five of meteorological elements in the following, but does not deal with statistics for snow depth. Hence an AMeDAS station that only measures snow depth appears that their observations are missing, but please note that their observations on all meteorological observations may not be missing as a whole.

Precipitation amount One hour amount is measured. Statistics are 1mm in unit but measured 0.5mm in unit.
Wind direction and speed Wind direction is 10 minutes average of directions from 10 minutes before observation time and digitized in 16 levels. In case of calm (wind speed is less than 1 m/s) direction is not assigned. Wind speed is ten minutes average and 1 meter/second in unit.
Temperature Observation in Celsius degree
Sunshine Duration Observed by 0.1 hour in unit.

The location of AMeDAS stations is published in the unit of 0.1 minute. This means that the error of the location reaches at maximum 0.05 minute = 3 seconds. This amounts to about 120m in Tokyo, 115m in Sapporo, and 125m in Naha, so you should not believe that the AMeDAS station is located exactly at the location of latitude and longitude on the site, but understand that it is located somewhere around 100m from the location. And the movement of the station within this error bound is recorded as the movement between the same location. Finally this site uses decimal degrees, so it is a different representation from the published locations in degrees and minutes.

(Reference) AMeDAS annual report. Snow depth is omitted. More detail can be found in about using the statistics of meteorological observations (Japan Meteorological Agency) (in Japanese).

The moon age (phase) is computed as the 30th division of the moon phase based on approximately 29.53 days of a synodic month, starting from zero at the new moon, 0.5 at the full moon, and 1.0 at the next new moon. Hence the definition is a little different from an ordinary definition of the moon age.

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