Author: Dr. Michael Chase
Photo above: Kerang, Victoria, circa 1930
ACORN-SAT is the outcome of a “system” for detection and correction of non-climatic influences on surface air temperature data recorded in Australia. Previous posts have dealt with errors in the correction part of the process, and with false detections. This post deals with failure to detect what should be detected.
Many non-climatic influences on temperature measurements are transient in nature, so if an attempt is made to detect and correct, then both ends of the transient influence must be found. That fact alone makes the process rather risky, and this post shows examples of the risk being realised, with one end of transient perturbations not being detected, resulting in invalid correction of the data before the onset of the transient influence.
The following figure shows a transient warming influence on daily maximum temperatures at Kerang in Victoria. To make the transient warming easier to see the data from a nearby reference station (Echuca Aerodrome) has been subtracted from the Kerang data (black curve), removing most of the natural background variation in temperature. The figure also shows matching results for nearby Deniliquin (red) and Rutherglen (blue), for which transient perturbations (detected via ACORN-SAT, and verified visually by me) have been corrected.
ACORN-SAT has a detection for Kerang in 1957 at the end of the transient influence, but no detection for the start, therefore it falsely corrects the data all the way back to 1910. The right answer is to correct the data only back to 1943, the onset of the transient, or to make no correction at all.
This post will be updated with any further detection failures that are found.
NOTE: Missing months of data have been infilled by interpolation, following the temperature variations of neighbouring stations, and partial quality control adjustments have been made for anomalous spikes and dips, in particular at Rutherglen in 1925.