Daylight Saving Time

Observing Practices under Daylight Saving Time

The observation practices used during World War I and World War II are not fully documented. Evidence from available observations and other information suggests that:

  • During WW2, the general practices at Bureau-staffed stations were to take observations at a uniform local clock time, so in summer observations were 1 hour earlier UTC (Coordinated Universal Time, which is equivalent to GMT). Supplementary observations were made at 0900 and 1500 Local Standard Time (LST), or 0830/1430 LST in SA. There were numerous local variations to this - for example, Darwin did not take supplementary observations, at Launceston Airport the observations at 0900 and 1500 replaced, rather than supplemented, the 0800/1400 ones, whilst at Sydney Airport, at some points in the record supplementary observations are made at times other than 0900/1500, whilst at other points (particularly early 1942) observations are made at a uniform UTC time (not clock time).
  • In 1917, it appears that daily observations (maximum and minimum temperatures, and rainfall) were made at the same local clock time, but fixed-hour observations (at 0900, 1500, 2100) at stations which made more than one observation per day were one hour later in clock time (uniform standard/UTC time).

In the 1967/68 season, all Tasmanian surface and upper air observations were made at the same UTC times which meant that the nominal 9am observation was taken at 10am DST. The same practice was adopted in the 1968/69 season, with the exception that the evening Hobart radiosonde flight was made at 1000 UTC instead of 1100 UTC. Synoptic weather reports continued to show EST times in their message preamble. The same pattern continued in the 1969/70 and 1970/71 seasons.

In the 1971/72 season, DST was to be trialled in all States and territories except the Northern Territory and also in Papua New Guinea (PNG), which at that time was still a Territory of Australia. However, the State parliament in WA temporarily stopped sitting that year and DST was not implemented in that State. For this season, the following observational practices were adopted in all states which operated DST.

  • Synoptic and Climatological stations' surface and upper air observations were maintained at the same UTC time, hence they were taken at 1 hour later by the DST clock
  • Rainfall only and river height stations reported at 9am by the DST clock (i.e. one hour earlier in UTC time)
  • Observations were entered in field books at the hour closest to the clock time i.e. the 10am DST observation was entered against the space for the 9am observation, and the preamble of synoptic messages assumed the nominal time (e.g. 0900)
  • At synoptic and climatological stations all autographic instruments were changed at 10am DST but the pen was set on the 9am time line on the chart, to prevent the pen from running off the chart, and the chart was endorsed LST. However pluviographs operated at rainfall only stations were endorsed DST after setting time
  • Some evening upper air soundings were made one hour earlier for operational purposes and some cooperative observations were of necessity taken at the nominal time by the clock (e.g. 9am DST)

Comprehensive changes to procedures applied in the 1972/73 season. Essentially the major points are as follows:

  • Surface observations at synoptic and climatological stations in States with DST were made by the clock set to DST, so that observations were actually taken one hour earlier with respect to UTC time. Where DST was not implemented the following occurred:
    • In Queensland, Willis Island and the Northern Territory, Bureau staffed observations made observations one hour earlier, i.e. 0200, 0800, 1400 and 2000 Eastern Standard Time (EST) or Central Standard Time (CST).
    • An additional observation was made (workload permitting) at 0300, 0900, 1500 and 2100. Non Bureau sites reported at their normal observation times. At 0000, 0600, 1200 and 1800 EST or CST all sites conducted their normal observations.
    • In WA all observations continued to be performed in accordance with their normal schedules.
  • Rainfall and river height observations were taken by the clock time of 9am (i.e. making them one hour ahead of normal by UTC time where DST was introduced)
  • Upper air observations were made one hour ahead of normal by UTC, except in PNG, the British Solomon Islands Province, Cocos, Christmas, Norfolk and Macquarie Islands and Antarctic stations.
  • Bureau sites with autographic instruments were to change charts by clock time, whether DST or not, and where applicable the original records should have been marked DST. However in Queensland and NT those Bureau staffed stations which made observations at both 0800 and 0900 attended to the autographic instruments at 0900 (EST or CST). If no 0900 observations were made the charts were changed at 0800. All charts were boldly marked "LST". Non Bureau staffed stations in Qld and the NT, and all sites in WA, PNG and British Solomon Islands Province were to change charts at the usual times and marked them "LST".

Procedures were simplified in 1973/74 and remained in effect until 1997/98:

  • All surface observations were carried out by clock time in all States (so that 9am DST observation, for example, was made one hour earlier according to UTC)
  • Upper air observations were made one hour (UTC) earlier in all States. No changes were made to the observation program at Cocos Island, Christmas Island, Norfolk Island, Macquarie Island or the Antarctic stations.

This practice has been followed in general since then with occasional variations to suit staffing arrangements. In general, the dates on which the upper air observation times were changed were the starting and finishing dates of DST in the state/territory concerned, with those states not observing DST following the NSW changeover dates. The exceptions to these were as follows:

  • In 1991-92, Northern Territory followed the South Australian changeover dates
  • In 1990-91, all stations throughout Australia followed the Victorian changeover dates.
  • In 1985-86, Western Australia, Northern Territory and Queensland followed the Tasmanian changeover dates.
  • In 1981-82 and 1982-83, all stations throughout Australia followed the Victorian changeover dates

Solar Radiation measurements use local mean time or local standard time, depending on the site involved. Ozone measurements use local standard time.

Last modified 8 November 2012