JMA User Guide

Comprehensive user guide for the JMA Explorer, detailing how to navigate the map, filter Japanese stations, and visualize high-resolution weather data.

Access the Application: Return to Explorer

1. Introduction

The JMA Explorer is an interactive dashboard for exploring historical and recent weather data from the Japan Meteorological Agency (JMA). It allows you to visualize meteorological records from stations across Japan, including AMeDAS (Automated Meteorological Data Acquisition System) and manned stations. Data is available in four resolutions: 10-Minute, Hourly, Daily, and Monthly.

1.1 Station Types

The explorer distinguishes between two main types of observation stations:

Manned Stations (Synoptic): These are premium stations (historically staffed) that collect the most comprehensive data, including cloud cover, visibility, detailed weather codes, and humidity.
AMeDAS (Automated Meteorological Data Acquisition System): A high-density network of automated stations. While they provide excellent coverage for core parameters like temperature, precipitation, and wind, they typically do not record visual observations like cloud cover or visibility.

2. Global Navigation (Sidebar)

The sidebar on the left controls the global view of the application.

Time Resolution: Toggle between 10 Minutes, Hourly, Daily, and Monthly data modes. This filters the available stations and determines the granularity of the data visualized.
Find Station: A searchable dropdown to quickly locate a specific station by name (English).
Select Date Range: Filter stations based on their operational periods.
- Note: The application automatically limits the date range request to prevent overloading (e.g., 1 year for daily data, 3 months for hourly).
Visible Stations: Displays the count of stations that match your current resolution and date filters.

3. Main Navigation Tabs

The application features three main tabs at the top:

Map View

The default view is an interactive map showing available Japanese weather stations.

Markers: Blue dots represent available stations.
Selection: Click any marker to highlight the station (red ring) and view its summary.
- Popup Info: Display name, ID, Type (AMeDAS or Manned), and period of record.
Home Button: A “Home” icon is overlaid on the map to reset the view to the Japan archipelago.

Station Info

A tabular listing of all filtered stations. This view is useful for browsing the full station catalog or filtering by specific attributes.

Double-Click: Double-click any row to load that station’s data and navigate directly to the Dashboard.

Dashboard

The Dashboard displays detailed data for a selected station. It becomes active after selecting a station from the map or table.

Dashboard Sub-Tabs

Plots: Specialized visualization tabs for different weather parameters:
- Temperature: Timeline of Mean, Max, and Min temperatures.
- Precipitation: Bar charts of precipitation accumulation.
- Wind: Wind speed timeline and Wind Rose (for Hourly data).
- Solar/Clouds: Solar radiation, Sunshine duration, and Cloud cover (where available).
- Humidity/Pressure: Relative Humidity and Pressure trends.
- Snow: Snowfall and Snow Depth (where available).
Data: Provides raw data access for the selected station and period.

Dashboard Data
- The table displays the parsed data ready for export.
- Export CSV: Use the download buttons to save the currently loaded dataset.

4. Parameter Reference

The following tables list the parameters available in the JMA Explorer for each resolution. Note that not all stations measure all parameters.

10-Minute & Hourly Parameters

[!NOTE] All timestamps for 10-Minute and Hourly resolutions are in Japan Standard Time (JST), which is UTC+9.

Column Name	Definition	Unit
`Year`, `Month`, `Day`	Date Components	-
`Hour`	Hour of Observation	1-24
`Time`	Time of Observation (10-min resolution)	HH:MM
`Temperature`	Air Temperature	°C
`Precipitation`	Precipitation Amount	mm
`Wind_Speed`	Mean Wind Speed	m/s
`Wind_Direction`	Wind Direction	16-point Compass / Degrees
`Wind_Direction_Deg`	Wind Direction	Degrees (0-360)
`Sunshine_Minutes`	Sunshine Duration (10-min)	min
`Sunshine_Hours`	Sunshine Duration (Hourly)	hours
`Pressure`	Station Level Pressure	hPa
`Pressure_Sea_Level`	Sea Level Pressure	hPa
`Humidity`	Relative Humidity	%
`Dew_Point`	Dew Point Temperature	°C
`Vapor_Pressure`	Vapor Pressure	hPa
`Solar_Radiation`	Global Solar Radiation	MJ/m²
`Cloud_Cover`	Cloud Cover (0-10)	1/10
`Visibility`	Visibility	km
`Snowfall`	Snowfall Amount	cm
`Snow_Depth`	Snow Depth	cm

Daily Parameters

Column Name	Definition	Unit
`Year`, `Month`, `Day`	Date Components	-
`Temp_Mean`	Daily Mean Temperature	°C
`Temp_Max`	Daily Maximum Temperature	°C
`Temp_Min`	Daily Minimum Temperature	°C
`Precipitation`	Total Precipitation	mm
`Precipitation_Max_1h`	Max 1-Hour Precipitation	mm
`Precipitation_Max_10min`	Max 10-Minute Precipitation	mm
`Wind_Speed`	Mean Wind Speed	m/s
`Wind_Max_Speed`	Maximum Wind Speed	m/s
`Wind_Gust_Speed`	Maximum Gust Speed	m/s
`Humidity`	Mean Relative Humidity	%
`Humidity_Min`	Minimum Relative Humidity	%
`Pressure`	Mean Station Pressure	hPa
`Pressure_Sea_Level`	Mean Sea Level Pressure	hPa
`Sunshine_Hours`	Total Sunshine Duration	hours
`Snowfall`	Total Snowfall	cm
`Snow_Depth`	Maximum Snow Depth	cm

Monthly Parameters

Column Name	Definition	Unit
`Year`, `Month`	Date Components	-
`Temp_Mean`	Monthly Mean Temperature	°C
`Temp_Max`	Monthly Mean Daily Maximum	°C
`Temp_Min`	Monthly Mean Daily Minimum	°C
`Precipitation`	Total Precipitation	mm
`Wind_Speed`	Monthly Mean Wind Speed	m/s
`Wind_Speed_Max`	Maximum Wind Speed	m/s
`Pressure`	Monthly Mean Station Pressure	hPa
`Pressure_Sea_Level`	Monthly Mean Sea Level Pressure	hPa
`Humidity`	Monthly Mean Humidity	%
`Sunshine_Hours`	Total Sunshine Duration	hours
`Snowfall`	Total Snowfall	cm
`Snow_Depth`	Max Snow Depth	cm
`Snow_Days`	Number of Days with Snow	days
`Fog_Days`	Number of Days with Fog	days
`Thunder_Days`	Number of Days with Thunder	days

5. Data Source

Original data is sourced from the Japan Meteorological Agency (JMA) website.

Source URL: JMA Historical Weather Data Search
Note: The application dynamically scrapes and parses these tables to provide a unified dataset.