the Air Vent

Because the world needs another opinion

Sat vs Ground Difference Plots

Posted by Jeff Id on March 26, 2009

Just a short post where I plotted the difference between the surface station data and sat data as per a request by Kenneth Fritsch. The main thing I notice is the noise level in these graphs is large enough to dominate any minor ‘real’ slope signal. These plots again use the NSIDC raw data and do not use Steig’s unavailable data.

This is a continuation of my other post Know Your Data and it uses the 1400 ‘day’ version of the data.



5 Responses to “Sat vs Ground Difference Plots”

  1. Amundsen_Scott is the South Pole data set and is one of only a few interior datasets. Those are very large differences.

  2. Jeff Id said

    I think its cloud masking that causes the problem but am not sure. The odd part is that the way the data is collected the instrument scans the pole point 14 times a day so it should be pretty well known.

  3. Kenneth Fritsch said

    Jeff, thanks much for the difference and trend line plots. Like you say, on first look it is very noisy. Now that the “official” cloud mask data are available from Steig, we can look again.

    Rather OT, but I did want to comment here that I have really appreciated the efforts made by the two Jeffs (I have identical twin granddaughters 6 1/2 years old that insist they be called by their given names and not referred to as the “twins”), Ryan, RomanM, Hu M, Steve M and a host of others from whom I have learned a substantial amount, and including more efficient uses of R. To me the main issue is what the sensitivity tests reveal about the substance of the Steig et al. (2009) conclusion and/or the conclusions that were ignored.

    My simple-minded analyses have convinced me that the conclusions about Antarctica temperature trends (given that the reconstructions are valid) are very sensitive to start times, that the TIR and AWS reconstructions diverge going forward in time and that the warming of West Antarctica in recent times in the TIR reconstruction could well be an artifact of the methods used in that reconstruction.

    I realize that there remain a number of questions, that analyses have raised, about the applications of RegEM and PCA by Steig et al., but in this layperson’s view, I would judge that the cloud masking procedures and the sensitivity to potential variations of that procedure might well lead to the greater uncertainties in these reconstructions.

  4. Layman Lurker said

    Jeff, not sure how much you have researched on avhrr / surface station calibration literature, but here is one paper from JOC 1996 that sheds light on the sources of discrepencies:

    some of the highlights I noted:
    1. Seasonal differences between winter and summer where winter months have greater proportion of temperature inversion (neg lapse rate) and summer is more isothermal. The implication is that winter AVHRR temps are warmer relative to surface while summer temps the differences are smaller.
    2. Seasonal and geographical differences in cloud microphysics (like water vapor vs. ice), which in turn affect cloud emisivity.
    3. Volcanic aerosols
    4. The effect of polar stratospheric clouds (psc’s) in winter where it is suggested that psc’s may be picked up as clouds when there is only starlight to work with.

  5. Layman Lurker said

    Jeff, now that you have Steig’s AVHRR data, could you re-run grid vs. surface station and differences on that? Just curious to see how well Steig took care of the data discrepencies with surface stations.

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