Technical note on correction of value for Waingawa, April 1910

This note outlines a correction made the NIWA seven-station temperature series relating to an incorrect value of monthly mean temperature for Waingawa for April 1910

An incorrect value of monthly mean temperature for Waingawa (agent 2473) has been picked up for April 1910. The previous (erroneous) value of 17.3°C has been replaced by the corrected 11.8°C.

This makes at most 0.01°C difference to the warming trend over the past 100 years shown in the seven-station temperature series.

Reason for correction

The previous April 1910 mean temperature of 17.3°C was a clear outlier (the warmest April ever at the site by a good margin) and was checked against the original paper records. The original value was recorded as 53.2°F, which converts to 11.8°C. The value of 53.2°F agrees with the average of the original monthly maximum and minimum. We suspect a data entry error, whereby the number was mis-read as 63.2°F (which converts to 17.3°C). The underlying daily temperatures have not been digitised for this site, and so some of the quality control checking procedures are disabled for the early years of the temperature record.

Consequence for seven-station series

This correction reduces the 1910 ‘Masterton’ annual temperature (and its associated anomaly from the 1971–2000 normal) by nearly 0.5°C.

It reduces the 1910 New Zealand average annual temperature by about 0.07°C in NIWA’s seven-station annual temperature data set.

There is minimal effect on the 100-year linear trend of the seven-station time series over 1909-2009. When rounded to two decimal places, the warming trend was previously calculated as +0.90°C; using the corrected value produces a warming trend of +0.91°C.

The Excel file of NIWA’s 7-station temperature series has been updated accordingly. This tempature series was replaced in December 2010.

Click here for the new temperature series.

Documentation of correction in database

The original (pre-correction) value is preserved in AUD_MTHLY_STATS on the NIWA Climate Database, with the time that the change was made. This table is a full record of audits and changes made to the “Monthly Stats” table where the monthly mean temperatures can be found.

Office spreadsheet icon NZT7_Data_updated2010-4.xls46 KB