Surprisingly, the study of history is increasingly becoming an important area of investigation in weather and climate change. Frequently, scientists who take part in the WMO Commission for Climatology (CCl) special ad hoc weather extremes committee must become quasi-historians. These committees are created on an “as-needed” basis to assess potential world and regional weather extreme records, such as maximum and minimum temperatures, highest and lowest pressures and precipitation levels.
While many investigations are evaluations of new and recent weather extreme observations, several have involved examination of older records whose existence have just come to light or whose validity have been questioned. Such is the case in the recent evaluation of the “new” cold extreme for WMO Region V (South-west Pacific).
An international evaluation committee recently completed its assessment of a cold temperature extreme for the region. This assessment was initiated when the National Institute of Water and Atmospheric Research (NIWA) identified a “new” record for New Zealand’s coldest temperature: −25.6°C (actually −14°F), recorded at Ranfurly on 17 July 1903. Consequently, WMO CCl organized a panel of climate experts to investigate the claim.
This discovery of the 1903 extreme cold temperature record resulted from an ongoing effort to digitize old paper daily records and enter the data into NIWA’s climate database. For such old records, the CCl evaluation committee’s role becomes one of ascertaining whether there are irregularities in the record. Often, the committee has to determine whether there were specific problems and/or errors with the equipment, procedures or siting locations associated with the record under investigation. The committee evaluated the NIWA report of findings, including images of the original weather observation logs, hand-drawn synoptic weather maps and even local newspapers from 1903.
Many of the committee felt that there was a need to explore the sheltering of the New Zealand thermometers at that time. Proper station sheltering is a critical aspect of temperature monitoring. For example, an exposed thermometer can record very different temperatures, often more extreme, compared to a thermometer properly sheltered from direct sun, wind and precipitation. Consequently, WMO has set guidelines for temperature observation practices, and current temperature measurements should adhere to these standards.
However, the New Zealand 1903 temperature observation occurred so long ago that it becomes difficult to ascertain if the current WMO sheltering guidelines had been met. Was there documentation dating that far back in time to indicate that adequate sheltering of the Ranfurly thermometer occurred in 1903? A document was discovered that suggested some form of standardized weather shelter was in use in New Zealand at that time. As a result, the committee’s unanimous opinion was that a new WMO Region V (South-west Pacific) record for coldest temperature had been set.
By Gregor Macara (NIWA New Zealand)
Randall S. Cerveny (Arizona State University, U.S.)
Thomas C. Peterson (WMO Commission for Climatology President, U.S.)
Manola Brunet (Dept. of Geography, University Rovira i
Fatima Driouech (Climate Studies Service, Direction de la Météorologie nationale of Morocco)
Pierre Bessemoulin (METEO-FRANCE)
Andrew Tait (NIWA New Zealand)
Andrew Harper (NIWA New Zealand)
Ali Eddenjal (Libyan National Meteorological Center, Libya)
Alexander Sterin (Russian Research Institute for Hydrometeorological Information- World Data Center, Russia)
Blair Trewin (Climate Information Services, Australian Bureau of Meteorology, Australia]
Dushmanta R. Pattanaik (India Meteorological Department, India]