The Australian Climate Observations Reference Network ...

The Australian Climate Observations Reference Network ¨C

Surface Air Temperature (ACORN-SAT) version 2

Blair Trewin

October 2018

Bureau Research Report - 032

THE AUSTRALIAN CLIMATE OBSERVATIONS REFERENCE NETWORK ¨C SURFACE AIR TEMPERATURE (ACORN-SAT) VERSION 2

THE AUSTRALIAN CLIMATE OBSERVATIONS REFERENCE NETWORK ¨C SURFACE AIR TEMPERATURE (ACORN-SAT) VERSION 2

The Australian Climate Observations Reference

Network ¨C Surface Air Temperature (ACORN-SAT)

version 2

Blair Trewin

Bureau Research Report No. 032

October 2018

National Library of Australia Cataloguing-in-Publication entry

Author: Blair Trewin

Title: The Australian Climate Observations Reference Network ¨C Surface Air Temperature (ACORNSAT) version 2

ISBN: XXX-X-XXX-XXXXX-X

Series: Bureau Research Report ¨C BRR032

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THE AUSTRALIAN CLIMATE OBSERVATIONS REFERENCE NETWORK ¨C SURFACE AIR TEMPERATURE (ACORN-SAT) VERSION 2

Enquiries should be addressed to:

Blair Trewin:

Bureau of Meteorology

GPO Box 1289, Melbourne

Victoria 3001, Australia

b.trewin@.au:

Copyright and Disclaimer

? 2018 Bureau of Meteorology. To the extent permitted by law, all rights are reserved and no part of

this publication covered by copyright may be reproduced or copied in any form or by any means except

with the written permission of the Bureau of Meteorology.

The Bureau of Meteorology advise that the information contained in this publication comprises general

statements based on scientific research. The reader is advised and needs to be aware that such

information may be incomplete or unable to be used in any specific situation. No reliance or actions

must therefore be made on that information without seeking prior expert professional, scientific and

technical advice. To the extent permitted by law and the Bureau of Meteorology (including each of its

employees and consultants) excludes all liability to any person for any consequences, including but not

limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly

from using this publication (in part or in whole) and any information or material contained in it.

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THE AUSTRALIAN CLIMATE OBSERVATIONS REFERENCE NETWORK ¨C SURFACE AIR TEMPERATURE (ACORN-SAT) VERSION 2

Contents

Preface ........................................................................................................................... 1

1.

2.

Introduction .......................................................................................................... 1

Data and metadata ............................................................................................... 3

2.1

2.2

3.

Data .......................................................................................................................... 3

Metadata ................................................................................................................... 5

Homogenisation methods ................................................................................... 5

3.1

3.2

Detection of inhomogeneities - use of multiple detection methods in parallel.......... 5

The adjustment procedure in ACORN-SAT.............................................................. 7

3.2.1

3.2.2

3.2.3

3.2.4

3.2.5

3.2.6

3.2.7

3.3

Adjustment methodological changes in ACORN-SAT version 2 ............................ 16

3.3.1

3.3.2

3.3.3

3.3.4

4.

Removal of rounding biases ............................................................................... 16

Detection of date shifts ....................................................................................... 16

Adjustment of negative diurnal ranges ................................................................ 17

Transition from large to small thermometer screens ........................................... 17

Evaluation of other potential systematic issues ............................................ 19

4.1

4.2

5.

The percentile-matching (PM) algorithm ¨C overlap case ....................................... 8

The percentile-matching algorithm ¨C non-overlap case ...................................... 10

Monthly adjustments ........................................................................................... 13

'Spike' adjustments ............................................................................................. 13

Overall summary of adjustments......................................................................... 14

Second round of homogenisation ....................................................................... 14

Observation time adjustments............................................................................. 15

The transition to automatic weather stations .......................................................... 19

Potential changes in response times with changes in automatic weather station

probes ..................................................................................................................... 21

Sensitivity and uncertainty testing .................................................................. 22

5.1

5.2

5.3

5.4

5.5

Parallel station sets used in uncertainty testing ..................................................... 22

Sensitivity of adjustments to choice of reference stations ...................................... 23

Sensitivity of adjustment to number of reference stations used ............................. 24

Sensitivity of adjustment to choice of reference period .......................................... 25

Comparison of daily and monthly adjustments ....................................................... 27

6.

Magnitude of adjustments ................................................................................ 27

7.

Comparison of version 1, version 2 and AWAP.............................................. 29

8.

Case studies ....................................................................................................... 33

8.1

8.2

Unrepresentativeness of overlap periods ............................................................... 33

Variable inter-site relationships during high-rainfall periods in arid regions ........... 34

9.

Conclusion ......................................................................................................... 35

10.

References ......................................................................................................... 36

Appendix 1 ...................................................................................................................38

Appendix 2. ..................................................................................................................45

Appendix 3 ...................................................................................................................57

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