Hi Linda,
thanks for the feedback.
There is no monthly mean data for December 1988 in the geostationary surface radiation data set due to too few satellite observations.
The performance of some of the Meteosat satellites was not as good as expected (I believe especially Meteosat 3 and 4 had some problems.) so there are data gaps in the original satellite data. For the calculation of the monthly averages we require to have at least 20 daily averages available to ensure the high quality of the data set. This conditions was fulfilled for every month from 1983 to 2005, except for December 1988. So the data entry for this monthy mean is set to NA.
For the daily (and, of course, hourly) averages, there are even more missing data...
We are about to prepare a list of missing averages for the data set, which will be made available through the CM SAF Webpage.
Regarding the time series plot, please have a closer look into December 1988 (e.g., by printing out the values of the variable 'field'), there should also be a missing value in the time series..
Regards,
Jörg
P.S. The subject of this post is slightly misleading, I assume you are referring to the Meteosat surface radiation data set, not the CLARA data set, which is available globally derived from the AVHRR instruments.