Two Hundred Years of Thunderstorms in Oxford
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Two hundred years of thunderstorms in Oxford Article Published Version Creative Commons: Attribution 4.0 (CC-BY) Open access Burt, S. (2021) Two hundred years of thunderstorms in Oxford. Weather. ISSN 0043-1656 doi: https://doi.org/10.1002/wea.3884 Available at http://centaur.reading.ac.uk/94545/ It is advisable to refer to the publisher’s version if you intend to cite from the work. See Guidance on citing . To link to this article DOI: http://dx.doi.org/10.1002/wea.3884 Publisher: Wiley All outputs in CentAUR are protected by Intellectual Property Rights law, including copyright law. Copyright and IPR is retained by the creators or other copyright holders. Terms and conditions for use of this material are defined in the End User Agreement . www.reading.ac.uk/centaur CentAUR Central Archive at the University of Reading Reading’s research outputs online Two hundred years of thunderstorms in Oxford Stephen Burt Geography at the University of Oxford, is 1853–1935 99 99, No. Vol. 9999, – Month Weather shown in Figure 1. From 1840, the astronomical observa- Department of Meteorology, tions and tabulations from the Radcliffe University of Reading, UK 1828–1852 Observatory were published in (initially) The format of the Radcliffe Observatory’s annual volumes entitled Astronomical obser- The long instrumental meteorological meteorological register was expanded in vations made at the Radcliffe Observatory in records from the Radcliffe Observatory site January 1828 to permit more details of the year [x], volumes hereafter referred to as in Oxford (where records commenced in the day’s weather to be included. For this the Radcliffe Results. Some later years were 1772) are well known, and have recently project, dates with thunder were extracted amalgamated into multiyear volumes; from been documented to 2018 by Burt and manually by careful eye examination of the the 1900–1905 volume, the meteorological Burt (2019). Less well-known, and still largely daily weather entries from high-resolution observations were published in their own in manuscript or paper format, are the non- photographic copies of the monthly manu- binding until the 1931–1935 volume, the instrumental records also maintained by the script observation registers, the originals of last in the series following the move of the Observatory which documented the occur- which are held in the School of Geography (astronomical) observatory to South Africa rence of fog, snowfall, thunderstorms and at the University of Oxford. The period and the transfer of responsibility for the the like. Records of thunderstorm occur- 1828–1840 was examined by myself, and meteorological records to the University. rence at the Radcliffe Observatory, by date, 1841–1852 by Tim Burt; a random series of Meteorological summaries began to be are complete between 1828 and 1986, months within each period was checked by included from the 1853 Radcliffe Results excluding the years 1936 to 1970 for which us both to minimise the risk of one of us volume, and a more-or-less standard for- only monthly totals are available. Since missing an entry, although it is possible that mat quickly evolved, whereby from 1859 1986, a reliable private record of thunder some obscure or illegible entries may have and in most years the dates of various frequency from Oxford, very close to the been missed. phenomena including thunderstorms were Radcliffe Observatory site, has been used to extend the record to 2019, forming a record of almost 200 years of thunderstorm frequency for the city – a record probably unique anywhere in the world. This newly digitised record, made available for the first time, is examined for long-term (decadal) trends in thunderstorm frequency, and by Lamb Weather Type. Comparisons are made with other long-period records from west London, around 75km southeast of Oxford. Reasons to account for the marked reduc- tion in thunderstorm frequency in the last decade are suggested. The observational record – details and sources Sources Full details of the Radcliffe Observatory site and instrumental records are given in Burt and Burt (2019). An almost unbroken daily temperature record has been maintained since November 1813, although the earli- est surviving thunderstorm records are for 1828. The Radcliffe Observatory site is at 51.761°N, 1.264°W, at 63m above mean sea level; the location of the observatory site, Figure 1. The Oxford area, showing the city, the River Thames and the 60 and 100m contours. The known today as the Radcliffe Meteorological central square shows the Radcliffe Observatory quarter in North Oxford. (Map courtesy of Chris Station (RMS) and run by the School of Orton, University of Durham.) 1 set out by month in a supplementary table ing mainly at night, largely in the era before 1971–1986 entitled ‘Summary [or ‘Characteristics …’] of extensive urban street lighting. Dates of ‘thunder heard’ were extracted the weather and remarkable phenomena, Monthly and annual totals of ‘days from the Met Office Integrated Data Archive for each month [year]’. An example, for the with thunder heard’ for Oxford were System (MIDAS) climate archives held within month of August 1878 (the most thun- published in the Monthly Weather Report the Natural Environment Research Council’s dery month on the record), is included as (MWR) 1884–1993 (when the MWR ceased Data Repository for Atmospheric Science Figure 2. In addition, the published monthly publication), and these together with and Earth Observation (CEDA – http:// data tables often include notes of thun- other sites were analysed by Valdivieso archive.ceda.ac.uk/), and monthly and der, etc., although the annual ‘Summary/ et al. (2019). However, monthly values annual totals tabulated. Characteristics’ table is generally the more extracted from the MWR were normally complete. Some of the Radcliffe Results lower than those taken from the Radcliffe volumes have already been scanned and Results. Examination of the discrepancies 1987–2019 Two hundred years of thunderstorms in Oxford of thunderstorms years hundred Two a number are available online; the relevant suggested that the ‘thunder day’ totals From late 1986, RMS authorities chose not to (meteorological) pages from the others were reported by the Observatory and subse- submit records of snow falling and thunder photographed from the partial set held quently published in the MWR were (often, in their monthly observational returns to the within the School of Geography, the remain- but not always) ‘thunderstorm days’ alone, Met Office, because it was felt that the vigi- ing volumes being consulted and photo- and days where thunder was heard but lance required for a good record was becom- graphed in the Bodleian Library to assemble no lightning was observed were excluded, ing impossible to maintain. From January the complete series as PDF files. (These are resulting in a lower total. 1987 onwards, RMS records of thunder are available on Figshare - https://www.doi. mostly missing, and the Radcliffe Observatory org/10.6084/m9.figshare.13333925.) These 1936–1970 records effectively cease at this point. PDF files were converted to computer- Monthly and annual totals of ‘thunder days’ To complete the series to date, a high- readable text using Optical Character for this period were extracted from manu- quality personal record kept in central Recognition software, and dates of thun- script tabulations held within the School of Oxford (mostly within 4km of the Radcliffe Weather – Month 9999, Vol. 99, No. 99 99, No. Vol. 9999, – Month Weather der events were then extracted by search- Geography. Unfortunately, dates of occur- Observatory) since 1983 by Jonathan ing for the string ‘thun’ (the abbreviation rence could not be traced within the Webb, a director of the Tornado and Storm allowing for hyphenation, abbreviations, School’s archive for this period, although Research Organisation (TORRO), has been etc.). Most entries also carried information the original monthly manuscript climato- used. Accuracy and continuity of record on the timing and sometimes the severity logical returns are believed to exist in the was assessed by comparison with the of the storms, although these details were Met Office climatological archive1. record from the Met Office staffed air- not extracted. field at Brize Norton, 21km to the west. For much of the published record, thunder- Figure 3 shows the annual thunder day storm records were separately categorised 1The author planned to visit the Met Office totals, and Table 1 the annual averages, into ‘thunderstorm’ (thunder and lightning archives during spring 2020 to obtain daily from Brize Norton, from the commence- observed), ‘thunder’ (thunder heard, pre- thunder day dates for this period and thereby ment of records in 1968 through to 2019, sumably without lightning seen) and ‘light- eliminate this gap, but was unable to do so once compared with the record for the Radcliffe ning’ (only). The first two were counted as the facility closed to visitors in mid-March 2020 site for 1968–1986 and the Webb record a ‘thunder day’ record, only one per day if owing to the coronavirus lockdown. Completion for ‘central Oxford’ for 1987–2019. There is both were reported on the same date, while of this paper was delayed for six months good temporal correlation between Oxford ‘lightning only’ events were not included in awaiting re-opening. Rather than delay Radcliffe and Brize Norton annual thunder these analyses. The frequency of lightning publication indefinitely, this paper was resubmit- day totals 1968–1986 (correlation coeffi- ted without the dates for 1936–1970 in late at the Radcliffe Observatory was surprisingly cient R2 = 0.54) and Brize Norton and central September 2020 as the archive remains closed 2 high, sometimes twice or more the annual for the foreseeable future. Monthly and annual Oxford 1987–2019 (R = 0.55), although the frequency of thunder heard; it should be totals are complete: the online dataset will be more comprehensive Kolmogorov–Smirnov remembered that this was an astronomical updated with the 1936–1970 dates once access test (Massey, 1951) on the two distributions observatory with a staff of observers, work- to the Met Office archives is available once more.