High Quality weather station audit

Perth Airport 9021 raw temperature audit

Station opened 3 June 1944 audit to 31 December 2011

(See also Perth Regional Office 9034)

(See also Perth Metro 9225)

Perth Airport 9021 maximum temperature audit

At Perth Airport 9021 from 3 June 1944 to September 1972, whole .0 Fahrenheit degrees represented 13.2% of all maximum temperatures recorded and .5 Fahrenheit degrees represented 7% of all maximum temperatures recorded.

1944-1972 represented 42.6% of the time span and had 30.5% of .0C and 24.1% of .5C maximum temperatures within the entire temperature record.

From 1972-2011, maximum temperature recordings of .0 Celsius degrees represented 10.7% of the total and .5C recordings represented 10.3% of the total of all fractions since 1972. Together, .0C and .5C represented 21% of all maximum temperatures recorded since metrication.

Perth Airport 9021 BoM maxima raw data feed

Perth Airport BoM High Quality adjusted anomalies above

Perth Airport unadjusted raw temperatures below

Perth Airport 9021 minimum temperature audit

At Perth Airport 9021 from 3 June 1944 to September 1972, whole .0 Fahrenheit degrees represented 16.1% of all minimum temperatures recorded and .5 Fahrenheit degrees represented 7.6% of all minimum temperatures recorded.

1944-1972 represented 42.6% of the time span and had 28.6% of .0C and 23.7% of .5C minimum temperatures within the entire temperature record.

From 1972-2011, minimum temperature recordings of .0 Celsius degrees represented 11.7% of the total and .5C recordings represented 10% of the total of all fractions since 1972. Together, .0C and .5C represented 21.7% of all minimum temperatures recorded since metrication.

Perth Airport 9021 BoM minima raw data feed

Perth Airport BoM High Quality adjusted anomalies above

Perth Airport unadjusted raw temperatures below

Perth Regional Office 9034 raw temperature audit

Station opened 1 January 1897 audit to 29 April 1992

Perth Regional Office 9034 maximum temperature audit

At Perth Regional Office 9034 from 1 January 1897 to September 1972, whole .0 Fahrenheit degrees represented 13.7% of all maximum temperatures recorded and .5 Fahrenheit degrees represented 7.6% of all maximum temperatures recorded.

1897-1972 represented 79.6% of the time span and had 68% of .0C and 64.5% of .5C maximum temperatures within the entire temperature record.

From 1972-1992, maximum temperature recordings of .0 Celsius degrees represented 11% of the total and .5C recordings represented 10% of the total of all fractions since 1972. Together, .0C and .5C represented 21.1% of all maximum temperatures recorded since metrication.

Perth Regional Office 9034 BoM maxima raw data feed

Perth Regional Office 9034 minimum temperature audit

At Perth Regional Office 9034 from 1 January 1897 to September 1972, whole .0 Fahrenheit degrees represented 17.1% of all minimum temperatures recorded and .5 Fahrenheit degrees represented 7.1% of all minimum temperatures recorded.

1897-1972 represented 79.6% of the time span and had 65.7% of .0C and 60% of .5C minimum temperatures within the entire temperature record.

From 1972-1992, minimum temperature recordings of .0 Celsius degrees represented 12.7% of the total and .5C recordings represented 11.6% of the total of all fractions since 1972. Together, .0C and .5C represented 24.3% of all minimum temperatures recorded since metrication.

Perth Regional Office 9034 BoM minima raw data feed

Perth Metro 9225 raw temperature audit

Station opened 1 January 1994 audit to 31 December 2011

Perth Metro 9225 maximum temperature audit

At Perth Metro 9225 from 1 January 1994 to 31 December 2011, maximum temperature recordings of .0 Celsius degrees represented 10.3% of the total and .5C recordings represented 10.6% of the total of all fractions since 1972. Together, .0C and .5C represented 20.9% of all maximum temperatures recorded since 1 January 1994.

Perth Metro 9225 BoM maxima raw data feed

Perth Metro 9225 minimum temperature audit

At Perth Metro 9225 from 1 January 1994 to 31 December 2011, minimum temperature recordings of .0 Celsius degrees represented 17.6% of the total and .5C recordings represented 8.8% of the total of all fractions since 1972. Together, .0C and .5C represented 26.4% of all minimum temperatures recorded since 1 January 1994.

Perth Metro 9225 BoM minima raw data feed

Notes re Perth Metro 9225:

The BoM has explained the 19 months of minimum temperatures at Perth Metro 9225 in 1995/96 with all daily temperatures rounded to .0C:

"For the months in question, the Automatic Weather Station at Perth Metro was only sending 9am-to-9am minimum temperatures at a precision of 1 degree. ... Where rounding has occurred, our systems round to the nearest whole number, rounding 0.5 to odd. So 4.3 = 4, 4.4 = 4, 4.5 = 5, 4.6 = 5 ... 5.4 = 5, 5.5 = 5, 5.6 = 6, 5.7 = 6, etc"

This reply prompted further questions to the BoM in January 2012:

If the Mt Lawley AWS was only sending 9am-to-9am minimum temperatures at a precision of 1 degree, why didn't anybody notice at the time? Did the AWS produce obviously wrong minima results for 19 months and nothing was done about it?

"In the early days of the Bureau's automatic weather stations, they were programmed to report in an international code, which was limited to reporting maximum and minimum temperatures to the nearest degree Celsius. High precision data from the AWS was monitored in the Perth Regional Office and manual intervention forced some of the data to be sent to the database with its full precision, however this was a manually intensive task and for a period from 31 March 1995 to 1 December 1996, the less precise data was automatically forwarded to the climate database, though there are some exceptions during that period.  After this time, the software was altered to allow the full precision to be automatically transmitted. Thus the Bureau was fully aware of the inconsistency at the time, as you would expect. It is important to note that minimum temperature data to the nearest degree was not wrong, but simply less precise than the raw data."

"The precise minimum temperatures were recorded in a local database from the 009225 AWS and these form the basis of the official Perth Metro climate record that is reported via our climate monitoring products. The precise minimum temperatures can be provided if required."

Have the erroneous minimum data been in Perth Metro 9225 temperature records since 95/96 and why haven't they been previously corrected?

"As I pointed out above, the data are not erroneous, just less precise. A process is underway to have the more precise data entered into the national climate database, from our local database, however this is a slow process, particularly given the resources that are available for such tasks. Our desire is to have the most accurate data available to the public via our website."

Is there an estimate of how much these 19 months of incorrect minima influence Perth's Metro's mean temperature trend since 1995?

"A comparison of the monthly mean minimum temperatures between the precise values and those rounded to the nearest degree for the 1995/6 period suggest differences of between 0.0 C and 0.3 C. These values will have a negligible impact on the Perth mean temperature trend, though as I said above, the most precise data is used in our analysis and reporting of Perth Metro climate statistics.

The data on the CDO web pages is provided to the general public so they can access national climate records freely. However there are issues with a small proportion of the data in the database, as you have identified, and these are explained in general terms in the link at the top of the temperature data pages:

"For the reasons stated on this web page, it is very important for researchers to understand the background to the data they are using and they need to consult the Bureau to make sure that the data is suitable for their purpose. The Bureau maintains a high quality dataset for research purposes.

For the city's historic temperature trend, the BoM compares Perth Metro 9225 with Perth Regional Office 9034 which recorded temperatures atop Mt Eliza from 1897 to 1957 before being relocated to Wellington St where it functioned until 1992.

For more detail about the temperature recording history of "Perth", see Perth Temperature History.

Extracts from Simon Torok thesis The development of a high quality historical temperature data base for Australia (1996, vol 2) which first established Australia's High Quality temperature record:

Perth Airport 9021 station equipment history

Air Temperature
20/JUN/1994 INSTALL Temperature Probe - Dry Bulb (Type Rosemount S/N - 0265) Surface Observations
01/MAY/1944 INSTALL Thermograph (Type Fielden S/N - Unknown) Surface Observations
20/JUN/1994 REMOVE Thermograph (Type Fielden S/N - Unknown) Surface Observations
01/JUN/1944 INSTALL Thermometer, Mercury, Dry Bulb (Type Dobbie S/N - 14561) Surface Observations

Maximum Temperature
01/JUN/1944 INSTALL Thermometer, Mercury, Max (Type Dobbie S/N - 15391) Surface Observations
04/OCT/2002 REPLACE Thermometer, Mercury, Max (Now Dobbie S/N - 17198) Surface Observations
25/JUN/2009 REPLACE Thermometer, Mercury, Max (Now WIKA S/N - 22072) Surface Observations
Minimum Temperature
01/JUN/1944 INSTALL Thermometer, Alcohol, Min (Type Dobbie S/N - 17031) Surface Observations
20/JUN/2009 REPLACE Thermometer, Alcohol, Min (Now Dobbie S/N - 29052) Surface Observations

Perth Regional Office 9034 station equipment history

Air Temperature
01/JAN/1876 INSTALL Thermograph (Type Fielden S/N - Unknown) Surface Observations
17/JUL/1985 REMOVE Thermograph (Type Fielden S/N - Unknown) Surface Observations
01/JAN/1947 INSTALL Thermometer, Mercury, Dry Bulb (Type Unknown S/N - Unknown) Surface Observations
30/APR/1992 REMOVE Thermometer, Mercury, Dry Bulb (Type Unknown S/N - Unknown) Surface Observations

Maximum Temperature
01/JAN/1947 INSTALL Thermometer, Mercury, Max (Type Unknown S/N - Unknown) Surface Observations
30/APR/1992 REMOVE Thermometer, Mercury, Max (Type Unknown S/N - Unknown) Surface Observations
Minimum Temperature
01/JAN/1947 INSTALL Thermometer, Alcohol, Min (Type Unknown S/N - Unknown) Surface Observations
30/APR/1992 REMOVE Thermometer, Alcohol, Min (Type Unknown S/N - Unknown) Surface Observations

Perth Metro 9225 station equipment history

Air Temperature
01/NOV/1993 INSTALL Temperature Probe - Dry Bulb (Type Rosemount S/N - NONE) Surface Observations
07/JUL/2011 REPLACE Temperature Probe - Dry Bulb (Now Rosemount S/N - 10319) Surface Observations
02/JAN/2001 INSTALL Thermometer, Mercury, Dry Bulb (Type Dobbie S/N - 1451) Surface Observations
18/DEC/2003 REMOVE Thermometer, Mercury, Dry Bulb (Type Dobbie S/N - 1451) Surface Observations

Maximum Temperature (No Electronic History)
Minimum Temperature (No Electronic History)

Perth Metro 9225 Station Detail Changes
01/NOV/1993 CLASSIFICATION Building (FBL)
10/JAN/2011 CLASSIFICATION Critical (ASOSCRIT)
01/AUG/2003 OBJECT Document/SKYLINE DATA
27/FEB/2008 OBJECT Document/SKYLINE DATA
05/FEB/1993 STATION - (nondb seeding) Opened
05/FEB/1993 STATION - (nondb seeding) bar_ht Changed to 25.4
05/FEB/1993 STATION - (nondb seeding) name Changed to PERTH METRO
05/FEB/1993 STATION - (nondb seeding) stn_ht Changed to 24.9
05/FEB/1993 STATION - (nondb seeding) stn_ht_deriv Changed to MAP 1:100 000
05/FEB/1993 STATION - (nondb seeding) wmo_num Changed to 94608
31/OCT/1997 STATION aviation_id Changed to PERT
05/FEB/1993 STATION latitude Changed to -31.9192Using WGS84
05/FEB/1993 STATION latlon_deriv Changed to GPS
05/FEB/1993 STATION longitude Changed to 115.8728Using WGS84
21/NOV/2000 STATION lu_0_100m Changed to City area, buildings < 10 metres (3 storey)
21/NOV/2000 STATION lu_100m_1km Changed to City area, buildings < 10 metres (3 storey)
21/NOV/2000 STATION lu_1km_10km Changed to City area, buildings < 10 metres (3 storey)
21/NOV/2000 STATION soil_type Changed to sand
01/AUG/2003 STATION surface_type Changed to fully covered by grass
13/DEC/2006 STATION surface_type Changed to mostly covered by grass
21/NOV/2000 STATION surface_type Changed to mostly covered by grass

This website produced by Scribeworks 2009/12