Is there correlation between the AQUA channel 5 data and ENSO?
To answer that we must first do something about the annual cycle which is present in the channel 5 data. Global surface temperature cycles over a year, with the global peak during the boreal summer, apparently due to variation in the amount of landfalling insolation. Here’s a plot of the annual cycle:
This is created by averaging the 2003-2010 temperatures for each date of the calendar. For example, the average for January 22 is created by averaging the January 22 readings recorded for 2003, 2004, 2005, 2006, 2007, 2008, 2009 and 2010.
The difference between an actual daily value (say, for January 22, 2010) and the 2003-2010 average for January 22 is what I define as the “daily temperature anomaly”. By tataking these differences one can effectively remove the annual cycle.
Here is the time series of the daily temperature anomalies from January, 2003 through mid-2011:
It’s an interesting pattern, with little net change from 2003 to late 2007 then several sizeable changes, up and down, thereafter.
How does that compare with ENSO, the best-known driver of global temperature anomalies on interannual and intraannual timescales? Here’s the same anomaly plot along with the “ONI” (Oceanic Nino Index). In this plot ONI leads the channel 5 data by three months:
ONI and the daily anomalies have an r-squared value of 0.37 over the period January 2003 thru June 2011. The relationship is significant. As expected, channel 5 data shows that the tropospheric temperature varies with ENSO.