The Wacky World of Weather Stations: No. 187- Cape Leeuwin (WA)

Tuesday 29/10/2019

Please refer back to my first post for site specifications and to No. 92- Logan City for 2018 specifications.  If you wish to check on this (or any) site for yourself, go to my post on how to check for yourself.

Station: Cape Leeuwin 9518

Opened: 1897

Daily Temperature data from: 1907

Data used to adjust Acorn sites at: Albany.

Location:   Co-ordinates  -34.3728 115.1358

275km south of Perth, in the extreme south-west corner of the continent.

BOM site plan 2018:

This looks to be not a bad site, although there is a bitumen road 15 metres away. Note for later the “Native Grasses” around the screen. This was noted exactly the same on site plans in 2008 and 2013.

The station was moved from the old site beside a bitumen road in 1999:

Google satellite image 2019:

Here we can see the bitumen road, and the bare rock to the west, admittedly a few metres below the screen. Note however the dark green patches close to the screen. Here is a street view photo taken by Henry Chik in April 2017:

The dark green patches on the satellite image can be seen to be coastal scrub to about a metre high or perhaps more. Some may say the satellite image is really from before March 2018 and the scrub has been cleared since then. If so, the site has been changed. It is still 15 metres from a bitumen road and 25 metres from a much wider area of bitumen: the recommended distance is 5 times the width.

As noted above, the screen was moved from right beside a bitumen road. BOM adjusted data in April 1999 for this move. The annual effect of moving away from the bitumen road to the new more exposed site was –0.31 degrees Celsius annually. That indicates that in many other sites where the screen is too close to bitumen or dirt, non-compliance can have a very large effect on temperatures.

Update 05/11/2019: Thanks to reader Brian who has supplied current photos. The first shows vegetation around the screen more than merely “native grasses” and NOT “trimmed to a few centimetres”:

And this one shows how bad the station was up to April 1999:

This Acorn station is/ has been non-compliant, with temperatures reported at Latest Weather Observations and used to adjust data at other Acorn sites.

FAIL

Percentage of all Australian sites not compliant: 25.83%.

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5 Responses to “The Wacky World of Weather Stations: No. 187- Cape Leeuwin (WA)”

  1. John in Oz Says:

    -.31 degrees would not seem to be sufficient to counter the heating effect of a bitumen road.

    Try standing on one with bare feet on a 35 degree (air temp) day.

    • kenskingdom Says:

      That’s -0.31 over a year in maxima; individual days would be much more than this on still hot days but who knows on windy wet days. Still I agree with your comment in general. Remember they made every previous year 0.31C cooler, even back before bitumen was laid.

  2. Bill In Oz Says:

    Ken your comments about this BOM site are very interesting. Yes, not compliant again !

    It’s especially interesting that the BOM adjusted the this site’s observations by 0.31 degrees when it was moved away from a bitumen road !
    As you say it gives an indication of how other BOM weather stations may be impacted by sealed & tarred roads close by.

    And added note : I just read this by Bill Johnston on Jo Nova’s blog about this BOM weather station at Cape Leeuin .It fills in the history a bit.

    October 28, 2019 at 4:39 pm ·
    “Hi Snoopy,

    The original Cape Leeuwin screen was up at the lighthouse where it was so over-exposed they reduced its height to 2-feet off the ground. Wind-shaking reset instruments which means that much of the early data is not much use. The screen moved to a new site, which according to a map and photograph was down off the point, where its performance improved but the Bureau don’t seem to know when that happened. From the start of the record to 1936 they used an old “observatory pattern screen” so it could have been that it moved when the screen was replaced in 1936 (or they may not know). By 1964, the screen was damaged; then it moved about 250 m south in October 1978 between two sheds (for protection) where the Bureau say they installed a small (60-litre) screen. The site was automated (using the same screen) in 1993 then in April 1999 they shifted to a new site in an updraft zone beside the cliff.

    From about 1942 to 1972, they mainly reported whole degrees-F,and the AWS also reported whole degrees-C from 1998 until 2002. Annual rainfall reduced markedly after the site moved to the up-draft zone in 1999. Further, the frequency of daily rainfalls greater than the wet-day median (2.5 mm) declined from 50 to about 35% of rain-days (and vice-versa for raindays above 2.5 mm/day), which indicates the current site on the side of the cliff is over-exposed.

    Although it is the longest continuous datset in WA, I don’t think it’s useful for determining trend or change; certainly not using naive Excel regression analysis.

    Cheers, Bill “

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