Below is a plot of AQUA channel 5 daily data for 2005 and 2006, as provided at the UAH Website. There is nothing special about 2005 and 2006 – they are selected simply for illustration. This time series shows two annual cycles, cycles which are generally attributed to the effects of land mass differences between the northern and southern hemispheres. See here for a further discussion. The data also shows jagged higher-frequency variability. It is this higher-frequency, intraseasonal (20 to 90 day) variability which is of interest here.
Removal of the annual cycle should allow a better visualization of the higher-frequency variability. The removal can be accomplished, approximately, by subtracting the “climatologically normal temperature” ( plot here ) for a date from each daily reading on that date. The “climatological normal temperature” for a date, as defined by me, is the average channel 5 value for that date over 2003-2010. That indeed is a short period for such an application but AQUA data is available only since late 2002. The result of the annual cycle removal is here . The derived values (actual minus “climatological”) will be called “daily anomalies” in this post.
The annual cycle is only part of the tropospheric temperature variation. There is also intermediate-term (interseasonal) variability in the channel 5 data, mainly attributable to ENSO effects. Subtracting a moving average (say, a 45-day, 60-day or 90-day average) from the data should remove much of the interseasonal trend while leaving shorter-term (intraseasonal) variability.
The result of subtracting the 45-day moving average is shown below. I term these derived values (daily anomaly minus 45-day moving average) as “adjusted daily anomalies” or “ADA” for short. The “adjustment” is simply the (approximate) removal of ENSO variability.