• Date applied: data prior to this date was adjusted for the reason (cause) cited. Adjustments are superimposed on each other; for example, if two adjustments are shown, one for 1/1/2000 and one for 1/1/1988, data prior to 1/1/1988 has both adjustments applied to it, data between 1/1/1988 and 1/1/2000 only has the first adjustment applied, and data after 1/1/2000 is not adjusted at all.
• Temperature variable: this describes which aspect of the temperature record was adjusted—daily maximum or daily minimum temperature.
• Cause: this describes why an adjustment was required.
  • Merge: data from two different station numbers are being merged, with overlap.
  • Move: a documented site move.
  • Move (n): a documented site move, together with a change of station number.
  • Screen: a change or repair to the Stevenson screen, including changes from a large to a small screen.
  • Obs time: a change in observation time (most often the 1964 change at some stations from a midnight to 9 am observation time).
  • Site: a change has occurred in the local site environment (e.g. addition/removal of building nearby, change in vegetation).
  • Statistical: a change found by statistical methods without specific documentary support.
• Impact: an estimate of the overall impact of the daily adjustments made for the particular reason (cause) cited. This is stated as an annual mean and is calculated using the mean difference between the adjusted and unadjusted data over the five years prior to the adjustment. Seasonal adjustments are shown only where the adjustment is made on the basis of seasonal (rather than annual) criteria (see below). The impact shown is for that specific adjustment, and is not cumulative.
• Seasonal adjustments apply where the adjustment was made on the basis of seasonal, rather than annual, criteria. In general the minimum threshold for adjustment is a 0.3 °C difference in the annual mean. Exceptions include:
  • where seasonal criteria are met (0.3 °C in two seasons, or 0.5 °C in a single season), in which case details are given; or
  • for the 1964 observation time change, which standardised the time for taking all observations to 9.00 am and changes from large to small screens.
• Comparative stations: stations against which the location’s data was compared statistically, for that breakpoint.
• All comparison stations: full list of all stations against which the location’s data was compared statistically, across all breakpoints.

The station catalogue includes values for the impact of adjustment on annual and/or seasonal values, for each breakpoint at which an adjustment has been made for the timeseries for that location. 

Adjustments are not normally made as a single flat value added or subtracted from all temperature observations for the relevant period.

The exact "amount" of adjustment on each daily temperature observation will vary where transfer functions have been used - see an example in the FAQ "An example of the adjustment process", or section 3.2 of the ACORN-SAT v2 technical report, which describes the adjustment process in more detail.

The ACORN-SAT data is maintained and kept separately from the unadjusted data in our national climate database. Raw unadjusted observations remain available through Climate Data Online