Example 05: CENTRAL ENGLAND Tavg

This post documents a reconstruction of monthly average mean temperature (Tavg) variations back to 1760 for Central England, shown schematically in the figure above. Data was averaged democratically across the region, excluding periods deemed to be distorted by non-climatic influences such as station moves and equipment changes.

Some more distant temperature records were examined and (not) used as follows:

• Valley (NW coast of Wales) was examined, but not used due to weather fluctuations and trend being significantly different to those of Central England
• Armagh Observatory (Northern Ireland) was examined, but not used due to weather fluctuations being significantly different to those of Central England
• Bournemouth Airport (South coast of England) was examined, but not used due to inconsistent trends (probably caused by station changes)

Temperature Data Sources:

• UK Met Office long-term monthly records (see the Data page (UK) for the link). Tavg was obtained by averaging Tmax and Tmin.
• CET monthly Tavg data: https://www.metoffice.gov.uk/hadobs/hadcet/
• GHCNMv3 and GHCNMv4 (see the GHCN page for links)
• Armagh Observatory website (see the Data page (UK) for the link)

Metadata Sources: None used due to lack of availability.

Methodology: The standard methodology of this website was used, see the pages above, starting with OUTLINE. A small deviation from the ideal methodology was that the Central England Temperature (CET) data was treated as a single station record, due to the non-availability of some of its constituent parts.

RESULTS

The following figure shows the 12-month moving average of regional-average Tavg variations, together with its 15-year moving average:

The seasonal dependence of the Tavg variations is shown in the following figure:

Finally, the Tavg variations for each separate month are shown in the following two figures:

VALIDATION

The following set of figures show 12-month and 15-year moving averages of “regional weather-corrected” Tavg data for all 35 stations examined, in order of increasing start date. Regional-weather-correction is simply the subtraction from a temperature record of the estimated regional average temperature fluctuations.

The bold lines are the station regional-weather-corrected moving averages used to obtain the regional moving average, shown as the dashed black lines. Validation follows from the identification and clean exclusion of periods of anomalous temperature change.

SAMPLE STATION ANALYSIS: CET

Each station record underwent visual inspections to detect/confirm/mark inhomogeneities. The following two figures show the main visual analysis plots for an example record: The Central England (mean) Temperature series.

The following figure shows 12-month and 15-year moving averages, for the regional-weather-corrected CET Tavg data and for the regional average:

CET has somewhat of a trend inconsistency with the regional average, and a step change in 2004, which corresponds to a date when there was a change in the station composition of monthly mean CET (see Parker and Horton 2005, available here: https://www.metoffice.gov.uk/hadobs/hadcet/ ).

The following figure shows the recent monthly data for January to August, revealing that the step change was more prominent in Summer than in the other seasons:

STATION DATA USED

The following figure shows the “nominal” number of stations being averaged in each year of the reconstruction, the actual number of stations in the average is somewhat lower because some periods of data were omitted:

The list of stations used, together with the periods excluded from regional averaging, is given in the following list, copied and pasted from the configuration file for the region.

NOTES

• TR = transition, the name given to all periods excluded from regional averaging
• W = 1 means this station record was included in regional averaging of weather fluctuations (slow transitions, such as gradual urban heating, or shading from growing vegetation, might be included in weather averaging, but excluded from averaging of station moving averages)
• M = 1 means this station record was included in the regional moving averages
• The first flag  in transition definitions allows temperature fluctuations to be included in regional weather averaging, 1 means exclude, 0 means include.
• The other transition parameters are the start year/month then the end year/month
• QC NaNs are data that were deemed to be invalid, set to NaN (Not a Number) by the software, triggering their automatic infilling using valid data either side and the regional average weather fluctuations
• The information below is ALL the configuration for this region, allowing reproduction of the results shown, given the software (available on request)

*************************************************

N_half = 7; % Moving average window size = 2*N_half + 1 = 15
stations = […
% id            W M From To (W/M are Weather/Moving-average flags, see NOTES above)
01 0000000 1 0 1942 2018;… % ABERPORTH UKMO (Tmax+Tmin)/2, * ANOMALOUS TREND
02 3501001 1 0 1889 1969;… % ABERYSTWYTH GHCNMv4_TAVG, * ANOMALOUS TREND
03 0000000 0 0 1796 2002;… % ARMAGH TAVG from Observatory website *** OMITTED
04 3316001 1 1 1870 1971;… % BIDSTON (GHCNMv4_TAVG)
% TR: 1 1897 12 1897 12, UNK
05 3862000 0 0 1961 2018;… % BOURNEMOUTH (GHCNMv3_TAVG) *** OMITTED
06 0000000 1 1 1908 2017;… % BRADFORD UKMO (Tmax+Tmin)/2, no TR
07 3683002 1 1 1871 1969;… % CAMBRIDGE (GHCNMv3_TAVG), no TR
08 0000000 1 1 1959 2016;… % CAMBRIDGE UKMO (Tmax+Tmin)/2, no TR
09 0000000 1 1 1659 2018;… % CET UKMO TAVG
% TR: 0 2004 10 2004 10, % SWITCH IN STATIONS AVERAGED (Parker-Horton IJC2005)
10 0000000 1 1 1964 2010;… % CWMYSTWYTH UKMO (Tmax+Tmin)/2, no TR
11 3534001 1 1 1887 1969;… % EDGBASTON (GHCNMv4_TAVG), no TR
12 3776000 1 0 1961 1998;… % GATWICK (GHCNMv3_TAVG), *** ANOMALOUS TREND
13 3715000 1 1 1961 1998;… % GLAMORGAN (GHCNMv3_TAVG), no TR
14 3715000 0 0 1931 1975;… % GORLESTON (GHCNMv4_TAVG), *** ANOMALOUS TREND
15 3779001 1 1 1763 1969;… % GREENWICH (GHCNMv4_TAVG)
% TR: 1 1950 01 1950 01, UNK
16 3672001 1 1 1871 1945;… % KEW (GHCNMv3_TAVG)
% TR: 1 1946 01 1980 12]; % ANOMALOUS AFTER 1945, MAJOR STEP IN 1970
17 3743000 1 1 1931 1960;… % LARKHILL (GHCNMv3_TAVG) no TR
18 3257000 0 0 1971 2018;… % LEEMING (GHCNMv3_TAVG) *** ANOMALOUS
19 0001855 1 1 1960 2008;… % MALVERN (GHCNMv4_TAVG) no TR
20 3334000 1 1 1951 2004;… % MANCHESTER AI (GHCNMv3_TAVG TO 2004) no TR
21 0000000 1 0 1959 2016;… % NEWTON RIGG (UKMO (Tmax+Tmin)/2) *** ANOMALOUS
22 3657001 1 1 1828 2015;… % OXFORD (GHCNMv4_TAVG) no TR
23 0000000 0 0 1853 2016;… % OXFORD (UKMO (Tmax+Tmin)/2)
24 0000000 1 1 1949 2004;… % RINGWAY (UKMO (Tmax+Tmin)/2) no TR
25 3521001 1 1 1877 2013;… % ROSS ON WYE (GHCNMv4)
% TR: 0 1914 07 1914 07, UNK
26 0000000 0 0 1931 2016;… % ROSS ON WYE (UKMO (Tmax+Tmin)/2)
27 3670001 1 1 1872 2011;… % ROTHAMSTEAD (GHCNMv4_TAVG)
% TR: 1 1915 01 1915 01, UNK
% TR: 1 1991 07 1991 07, UNK
28 0000000 1 1 1957 2016;… % SHAWBURY (UKMO (Tmax+Tmin)/2) no TR
29 3345001 0 0 1882 1978;… % SHEFFIELD (GHCNMv3_TAVG)
30 0000000 1 1 1883 2016;… % SHEFFIELD (UKMO (Tmax+Tmin)/2)
% TR: 1 1991 12 1995 01, UNK
31 0253770 1 1 1848 1969;… % STONYHURST (GHCNMv4_TAVG)
% TR: 0 1848 01 1860 01, UNK
32 0000000 1 0 1959 2016;… % SUTTON BONINGTON (UKMO (Tmax+Tmin)/2)
% ANOMALOUS TREND
33 0000000 0 0 1931 2016;… % VALLEY (UKMO (Tmax+Tmin)/2) *** OMITTED
% ANOMALOUS WEATHER AND TREND
34 0000000 1 1 1947 2016;… % WADDINGTON (UKMO (Tmax+Tmin)/2)
% TR: 0 1990 01 1990 01, UNK
35 3355001 1 1 1871 1959]; % YORK (GHCNMv4_TAVG TO 1959)
% TR: 0 1900 02 1900 02, UNK
% TR: 1 1960 01 1969 12, ANOMALOUS COOLING
%

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