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The Digital Atmosphere Page

If you're really interested in the weather, grab a copy of Digital Atmosphere (DA) and begin exploring. Digital Atmosphere is the program used by Australian Weather News to construct all of its world weather maps.

Digital Atmosphere is Tim Vasquez's excellent and inexpensive program for plotting and analysing real-time raw weather data freely available on the Net. Visit Tim's site at Weather Graphics, or participate in the Weather Graphics Forum where you'll find many like-minded people from around the globe who use DA to satisfy their fascination with weather, or in connection with their professional or recreational activities.

Here are some notes and links to help Australian DA users.

What is the difference between METAR and SYNOP data:

These two terms will come up often, so it's best to get them sorted at the start.

METAR appears to be an abbreviation of MÉTéorologique Aviation Régulière and is a report designed for aviation from an Automatic Weather Station (AWS) or manned station.

  • The METAR code is managed by the World Meteorological Organisation (WMO). For more information see Wikipedia.
  • In Australia, METARs are made from all AWSs hourly and from many AWSs half-hourly.
  • If conditions change significantly since the last METAR, the AWS will automatically transmit a SPECI, or special weather report.
  • SPECIs are sent to report heavy rain, sudden increase or direction change of wind, strong gusts, or sudden temperature variations.
  • An increasing number of AWSs at airports are fitted with instruments to measure horizontal visibility and cloud amounts and base heights, so any sudden reduction in visibility or cloud base may generate a SPECI as well.

SYNOP is an abbreviation of surface SYNOPtic observation and is a code that has been used for decades as the main means of transmitting weather information around the world. Unlike METARs which are designed to serve the aviation industry, SYNOPs exist to serve weather forecasters and those with a specific interest in weather.

  • The code is managed by the WMO and here is a summary of what it means.
  • SYNOPs carry more information about the weather than METARs (except in the USA) and there is a denser observation network.
  • In most countries, SYNOP observations are made and transmitted each 3 hours at 00, 03, 06, 09, 12, 15, 18 and 21 Universal Time (UTC) with 00, 06, 12 and 18 often carrying more information.
  • Australia is one of the very few countries that is non-standard. Our main synoptic hours are based on local clock time, with 9am being the most important. So during daylight saving time our major observation is at 2200, 2230, 2300, 2300 and 0100 UTC, depending on which state you're in.

Decoded METAR, SPECI and SYNOP data is all rolled into the same human-readable tables on the Bureau of Meteorology site where they are called "Observations". AWN splits them up with decoded METARs and SPECIs under Current > AWS obs and detailed decoded SYNOPS under Current > Synoptic Obs.

While global data sources will give you a thin coverage of Australia, you should use data from all available Bureau of Meteorology stations. These are available from the Bureau of Meteorology, but we think our own Australian Weather News implementation of the data works better with DA. Full details of both are given below, and you can make your own choice.

Australian data from the Bureau:

The Bureau codes the METAR/SPECIs and SYNOPs in its own AXF format which can be read by the current version of DA. Here are the details:

  • The axf files are in the directory at ftp://ftp2.bom.gov.au/anon/gen/fwo/.
  • File names look like this: IDY03100.201110042100.axf. The 5 digits after IDY indicate which file it is and everything after the first dot is the date and time for the file in UTC. And, of course, it's an axf file.
  • There are a LOT of other files in this directory. It's only the axf ones you need.
  • The axf files are updated about 8 minutes behind their nominal times.
  • There is a 24-hour archive.
  • There are four types of axf files:
    • IDY03000 - SYNOP files with data that came in in the past 15 minutes.
    • IDY03010 - SYNOP files with data that came in in the past hour.
    • IDY03100 - METAR/SPECI files with data that came in in the past 15 minutes.
    • IDY03101 - METAR/SPECI files with data that came in in the past hour.
  • Each file may contain data from previous times.
  • Full details of the axf codes are available in Word documents for the METAR/SPECI codes and SYNOP codes.

You can forget most of the above and let DA do it for you. You just need to check that it's set up properly. The following works with the latest DA Version 2.09

  1. Open DA and click on the antenna dish symbol on the bar under the menu bar, or using the menu bar click Data > Retrieve Data.
  2. In the Data Retrieval Window, scroll down to find METAR from Australia BOM (AXF format via FTP).
  3. Highlight this and click Edit Site
  4. Confirm Enter URL for this site reads ftp://ftp2.bom.gov.au/anon/gen/fwo/IDY03101.20@Y@M@D@H00.axf or cut and paste this URL into the box.
  5. Scroll down to find SYNOP from Australia BOM (AXF format via FTP).
  6. Highlight this and click Edit Site
  7. Confirm Enter URL for this site reads ftp://ftp2.bom.gov.au/anon/gen/fwo/IDY03010.20@Y@M@D@H00.axf or cut and paste this URL into the box.
  8. The two URLs above grab the full hour files. You can change IDY03101 to IDY03100 and IDY03010 to IDY03000 if you want to minimise getting mixed-hour observations.

After doing all this, you may be a little disappointed with the results. There is quite a lot of information that DA doesn't extract from the axf files. For this reason, I have created this different implementation.

Australian data from AWN:

AWN converts the data into standard SYNOP files, with an archive going back to 2004. SYNOP code is even human-readable with a little practice; e.g.

94517 16/// /1008 10181 20130 40159 69925 333 70006=

says at station 94517 (St George, QLD) the wind was from 100 degrees at 8 knots, temperature was 18.1, dew point 13.0, barometer 1015.9, rainfall 0.2mm in the past hour and 6mm since 9am.

The directories containing these files are:

Main points of difference from the Bureau's axf data:

  • The data in each file is for that hour only
  • Data is available about 14 minutes past the hour with updates through to 59 past the hour.
  • The DA/axf file implementation doesn't give visibility and cloud where available, pressure in SYNOPS(!), rainfall in past hour and since 9am, a readable WMO number which allows you to show name of station, and maximum and minimum temperatures.

How to set up DA to work with AWN data:

  1. Open DA and click on the antenna dish symbol on the bar under the menu bar, or using the menu bar click Data > Retrieve Data.
  2. In the Data Retrieval Window click Add Site to bring up the popup Internet Date Product Editor.
  3. In the Choose a name for this site box type: METAR from Australian Weather News (Australia)
  4. In the Enter the URL for this site box cut and paste: http://australianweathernews.com/digatm/met/@Y@M@D@H.MET
  5. Click OK. To add SYNOPs, click Add Site again
  6. In the Choose a name for this site box type: SYNOP from Australian Weather News (Australia)
  7. In the Enter the URL for this site box cut and paste: http://australianweathernews.com/digatm/syn/@Y@M@D@H.SYN
  8. Click OK. Close the Data Retrieval Window.

If you wish to plot rainfall, note that DA cannot plot 3-hourly rainfall but can plot 1-hourly rainfall. That's fine for METARs which give two rainfall figures (when there's been rain) - rain in last hour and rain since 9am. To get both or one of these in your station plots, select PCP01 and/or PCP24 under File > Preferences > Station Plots tab.

However, except at 9am, most Australian stations report 3-hourly rainfall in SYNOPs. As there is no way of plotting 3-hourly rainfall, AWN has cheated a bit and coded 3-hourly rainfall as 1-hourly rainfall. So in a SYNOP plot, selecting PCP01 on the File > Preferences > Station Plots tab will give you the 3-hourly rainfall.

Global data

A number of sites are available for global surface, upper air and other data which, of course, includes Australia. Some of these are listed below. Please note that they are mostly University sites, and they sometimes go offline for periods from a few hours to a few days due to technical hitches. If one site is down, try another.

These sites, and others, are listed in the Data Retrieval menu on DA which allows you to download data for the time you want automatically. Usually, synoptic surface reports for both land stations and ships are in the /syn directory, upper air reports in /upa, hourly metar reports in the /sao directory and drifting buoy report (and ships again) in the /boy directory.

Curiously, you'll find quite a lot of our Australian SYNOP reports at non-standard hours sitting in the /boy folder, in with the ships and drifting bouys down in the Southern Ocean.

In North America, METAR data is sometimes referred to as SAO (Surface Aviation Observation), although that code form dropped out of use in 1996. It's important to know that the United States uses METARs as its primary means of transmitting weather information, so the .sao files carry a lot more US information than the .syn files.

Station information

DA's station list is carried in the file location-identifier-list.csv (it has been changed from digatmos.stn which is still referred to in some help information). Stations change from time to time, and if you want to get the latest station information and edit your location-identifier-list.csv file***, you can do so from the following resources:

  • Australian station information - see this ftp directory on the Bureau of Meteorology's site. The latest file is named stations.txt. The other files in this directory are archives and station lists broken into states. The station lists are updated weekly. These lists are pretty large as they include all the Bureau stations, including rainfall only sites, that have ever operated.
  • Global station information - this is available from the World Meteorological Organisation in this ftp directory. Look for the file named Pub9volAYYMMDDx.flatfile, where YYMMDD is the latest date. Try to open this in Excel which brings up the Text import wizzard. Select Delimited in the first window and Tab in the second.
  • Another useful source of global station information that allows you to look up places by name, WMO number or ICAO aviation code is at Ogimet. Enter name, WMO number or ICAO code and the other two appear.

*** Take care in updating this file. Wally Mayo has been maintaining it - see this thread on the Weathergraphics Forum - but his updates are mostly for the US and, to a lesser extent, the rest of North America and Europe. The Australian stations have fallen behind, though my own copy is fairly up-to-date. I will post new Australian stations here after my next update, ready for incorporation into location-identifier-list.csv.

If you make changes or additions to the location-identifier-list.csv, these are the steps:

  1. BACKUP YOUR EXISTING location-identifier-list.csv FILE, CALLING IT SOMETHING LIKE location-identifier-list-YYYYMMDD.csv (YYYYMMDD = today's date backwards).
  2. Open location-identifier-list.csv in Excel. In my implementation, this file is in the C:\Documents and Settings\##MySystemFiles##\Local Settings\Application Data\DigitalAtmosphere directory. You may have to search for yours.
  3. Make your changes, additions, deletions.
  4. When finished, click Save as, name the file back to location-identifier-list.csv, and click Save.
  5. IMPORTANT. NOTHING HAPPENS UNTIL YOU DO THIS. In the File menu, select Station tables then Import default LIL location table. Click OK to start the process, and the status window will show lots of activity.