Data Comparisons

Lower Tropospheric Divergence?

14 Comments
Figure 1: Was February warmer or cooler?
Figure 1: Was February warmer or cooler?

The torrential March rains in the Chicago area immersed my Comcast connection. When I got back on line, I discovered my readers had alerted me to the odd divergence in RSS and UAH temperatures. Here’s the scoop:

  • UAH says the temperature anomaly for the lower troposhpere rose from 0.304 C in Jan 2009 to 0.35 C in Feb 2009. This is shown in light blue above.
  • RSS says the it fell from 0.322 in Jan 2009 to 0.230 C in Feb 2009.
  • If we average the two, the average dropped roughly 0.02C. This probably doesn’t mean much.

The figure above shows the temperature anomalies reported by RSS and UAH, which measure the same thing, ordinarily move together as they should. (Note, I rebaseline to the average anomaly for the period shown.)

This month’s disagreement is odd. I anticipate some investigation to determine which record is mistaken.

14 thoughts on “Lower Tropospheric Divergence?”

  1. Both measurements have differred in the past by that much and maybe more. It seems rarer, though, that they “diverge”, in the sense that they go in opposite directions. But there also seem to have been a few such instances. I don’t think one should read too much into this. You might want to calculate the distribution of the difference between the two, and see how probable (or improbable) this instance is.

  2. Francois–
    I read an explanation by Roy Spencer posted at Anthony’s blog. Evidently, the difference in methods can cause more divergence this time of year. I may look at the differences– but bear in mind, we only have since 1979!

    Needless to say, I’m interested in reading the HadCrut and GISS when they come out.

  4. This is probably those darn diurnal corrections again. The different groups can’t seem to agree on how to adjust for satellite drift. UAH is now using AQUA which doesn’t need them (it doesn’t drift, apparently) but RSS is using NOAA 15 which apparently does need them. But RSS doesn’t seem to have sufficiently corrected for diurnal effects, at least according to some analyses. I think this is the paper I’m thinking of:
    Randall R. M. and B. M. Herman (2008) Using Limited Time Period Trends as a Means to Determine Attribution of Discrepancies in Microwave Sounding Unit . J. Geophs. Res – Atmospheres 113 D05105, doi:10.1029/2007JD008864.

    But I could be wrong. Maybe if I could figure out how to ask Roger Sr. he would no the paper to which I refer.

  5. There’s an item on the RSS page explaining an issue with RADCAL impacting the F15 sensor and them planning to correct the temps by April.

    Yes F15 is the same as the one that NSIDC gave Sea Ice reading problems… at least the identifier is the same.

  8. ZH,
    There seems to be a step change in your graph around 1992-93. Were adjustments made to one of the data sets around that time?

  13. I noticed that Simon commented with a link to my post on seasonal divergence in UAH.

    I’m working on a second post looking at monthly trends (should be out early next week). Meanwhile here’s a chart showing global trends in surface and tropospheric data sets by month.

    In recent years, UAH has typically been above RSS in February (resulting in a higher linear trend over the 30 year period), but well below in mid-year months. The UAH trends vary much more from month to month than RSS or the surface data sets.

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