AUSTRALIAN DAILY RAINFALL

General Notes

All available Daily Rainfall observations until  a month prior to the compilation of data are included 
on this product, provided that the measuring site has a minimum of one month of data available.
Recent data may be available for those stations not included - contact the Bureau of Meteorology
(addresses provided in the readme.txt file).

Very few sites have a completely uninterrupted historical record, with no gaps.  Such gaps or
missing data may be due to many causes, ranging from illness of the observer to a broken
instrument. A site may have been closed, reopened, upgraded or downgraded during its existence,
possibly causing breaks in the record for a particular element. 

The majority of historical rainfall records have a resolution of 0.2mm although some more recent 
measurements are resolved to 0.1mm. A total that is less than 0.1 is referred to as a trace.

Accumulated Records

Many Australian observers 'accumulate' an observation over a period, often over a weekend.
In other words, the rainfall totals reported on a Monday morning may be those which occurred
over the period since the previous Friday morning, rather than the last 24 hours. There are fields
in the data file to indicate when this occurs, which are discussed in the file dr_formats.txt .

Time of Observation

Observations are made at 9am local time throughout the year. Daylight Saving has been used in some, 
but not all, states of Australia, since about 1973. The changeover occurs almost always in October 
and March but the exact dates vary from state to state and year to year. Thus the times that the 
rainfall totals were recorded are generally a combination of 8am and 9am standard times. This is 
discussed further in the file dr_formats.txt. 

Type of Precipitation

Observed precipitation can be classed as being of one of the types listed in the following table. In 
Australia precipitation predominantly occurs in the form of rain. When more than one type of 
precipitation has occurred the major contributor to the total is usually recorded. The type of
precipitation is noted by the site observer when recording precipitation totals.

     Precipitation Type                           Description

     Rain		Precipitation of liquid water drops greater than 0.5 mm in diameter.
               
     Fog		Precipitation from a suspension of very small water droplets in the air,
			reducing visibility at ground level to less than a kilometre. Mist is 
                        similar to fog, but visibility is between 1km and 10km.

     Frost		Deposit of soft white ice crystals or frozen dew drops formed when the
			surface temperature falls below freezing point. 

     Dew		Water condensed in the rain gauge when the overnight air temperature
			near the ground has fallen below the dew point temperature, but is still
			above freezing temperature. 

     Trace		Less than  0.1mm of precipitation. It is recorded as zero precipitation
			for the purposes of longer term totals. A day on which only a trace of 
			rainfall is reported is not considered to be a rainday.

     Snow		Precipitation in the form or small tabular and columnar white ice crystals
			formed directly from the water vapour of the air at a temperature of less
			than 0 degrees Celsius.

     Other		Other forms of precipitation such as hail.