Surface Temperature and Albedo from ERA-interim reanalysis

This post is just a quick update on my first foray into the ERA-interim reanalysis data, in preparation for some work using the radiative kernels.  The free data that I’m using is available  at http://data-portal.ecmwf.int/data/d/interim_moda/levtype=sfc/, as long as you register.

Basically, to do a quick sanity check I was going to calculate the feedback for the easier 2D monthly parameters – skin temperature and albedo (both available at the above link).  I believe I’ll actually need to use the daily data to calculate monthly clear-sky vs. all-sky averages for these, but the monthly is a lot less data to work with while I download the other data.  The script and data available here simply read the downloaded data and performs a global spatial average.

For skin temperature the data looks good.  It matches the reanalysis temperature graph shown in figure 1C of Dessler10 (see previous post) very closely (note that my picture below is Jan 2000-Dec 2010):

I used the same spatial average on the gridded surface albedo data per month.  Technically, this average isn’t showing the true amount of surface reflectivity; because the effect of a particular cell on shortwave flux per month will depend on its latitude (e.g. arctic albedo is going to have a much greater impact in January than in June).  However, this should give us a general idea about the albedo data:

So far it looks okay, but when we remove the seasonal cycle it begins to look odd:

I’m not sure what’s going on here…it may be that albedo is estimated in such a way that it doesn’t really capture year-to-year variations.  If that’s the case, however, if will not likely be much use in calculating the feedback, nor as an input into calculating changes in clear-sky shortwave flux.  I’ll need to look into this further.