I thought monthly averaging of AERONET point data using cis aggregate was working OK and so I wrote a short script and calculated July monthly averages for all of over 1000 stations over entire periods. This took about 8 hours last evening which I think is pretty good.
However, I found that the results are not always good. So I have been checking and testing lots of things, but I haven't been able to figure out what was wrong.
Like I wrote in yesterday's post, I did this;
cis aggregate -v AOT_500:920801_171209_Izana.lev20 t=[1997-06-01T00:00:00,1997-08,P30D] -o AOT_500_Izana_monthly_1997-0608.nc
this gave me a result like these: 0.0112922097186701, 0.0396474479087452, _ . These are similar to the values in monthly average data (0.011310, 0.042982, N/A). I repeated this today and got the same results.
But now I'm calculating monthly averages and storing the result for each month in a separate file. In AOT_500_Izana_monthly_1997-06.nc created last night, AOT_500 has no value. This is how it looks;
I repeated this today just like this;
cis aggregate -v AOT_500:920801_171209_Izana.lev20 t=[1997-06-01T00:00:00,1997-06,P30D] -o AOT_500_Izana_monthly_1997-06.nc
The result is the same and the netCDF file does not have a value.
This is strange because there are lots of valid measurements after 17th June 1997. I noticed the same thing at Abisko for July 2007. Measurements start on 23rd July 2007 at this station, and a few tens of measurements are available in this month. This is much fewer than typical number of measurements in a month but still a sample large enough to do statistical analyses. However cis aggregate gives no value. The downloaded monthly data show a value of 0.075950. I repeated cis aggregate just like above for Izana but the result was the same.
Here is another problem. In some cases downloaded and aggregated monthly averages have similar values. The values for July 1997 at Izana are 0.042982 and 0.0438219161585366 and these are very close to each other. But those for August 2007 at Abisko are 0.067408 and 0.0726925972222222 and these are slightly more different. At Abracos_Hill, aggregated values for July of 1999-2005 are
0.0948166771929825, 0.137734431818182, no value, no value, 0.257221920716113, 0.285831646551724, 0.15355733126935
some of which are very different from the values in the downloaded data;
0.174853, 0.138214, N/A, 0.241016, 0.234410, 0.302466, 0.248706 .
Now I calculated monthly average for July 1999 from the point data in Excel and got 0.168352892, which is close to the value in the downloaded monthly data. There are about 680 measurements covering the entire length of the month. I repeated the calculation one more time manually;
cis aggregate -q --force-overwrite AOT_500:920801_171209_Abracos_Hill.lev20 t=[1999-07-01T00:00:00,1999-07,P31D] -o AOT_500_Abracos_Hill_monthly_1999-07.nc
and I got 0.0978945903225806 . For some reason this is not exactly the same as the result from yesterday but still similar to it.
Can you see any problem or error in what I have done? Do you have any idea what went wrong? Can you think of anything else I could try and check?