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What is the difference between 'cyclic' and 'fixed' type of time interpolation?

mlevy

Michael Levy
CSEG and Liaisons
Staff member
I assume you are seeing these values in either an XML file or a namelist file? Could you please let me know which variable and file you are looking at and I'll make sure someone familiar with that component of the model sees your question.
 
I assume you are seeing these values in either an XML file or a namelist file? Could you please let me know which variable and file you are looking at and I'll make sure someone familiar with that component of the model sees your question.
Hi Michael!
These are the values of type of time interpolation for boundary data in the atm_in file.For example-
ext_frc_type=Type of time interpolation for fixed lower boundary data.
Srf_emis_type=Type of time interpolation of emission datasets specified.
Can be set to 'CYCLICAL', 'SERIAL', 'INTERP_MISSING_MONTHS', or 'FIXED'.
 

nusbaume

Jesse Nusbaumer
CSEG and Liaisons
Staff member
Hi Anushree,

In the context you referenced, I believe the term FIXED means that the emissions will repeat the specified day/time regardless of the model date, whereas CYCLICAL will go through the full annual cycle of the specified year, meaning that every day/time is different inside that year, but then every year will have the same emissions cycle.

To summarize: FIXED = constant emissions, CYCLICAL = constant annual cycle of emissions

Hope that helps, and if you are still unsure about anything please let us know.

Thanks, and have a great day!

Jesse
 
Hi Anushree,

In the context you referenced, I believe the term FIXED means that the emissions will repeat the specified day/time regardless of the model date, whereas CYCLICAL will go through the full annual cycle of the specified year, meaning that every day/time is different inside that year, but then every year will have the same emissions cycle.

To summarize: FIXED = constant emissions, CYCLICAL = constant annual cycle of emissions

Hope that helps, and if you are still unsure about anything please let us know.

Thanks, and have a great day!

Jesse
Thank you for your answer!
As a follow-up question w.r.t 'fixed' emissions for ext_frc_type and srf_emis_type to get a more clear picture-
Suppose the model run_startdate is 01/01/2014 and i want to run transiently for the next two years till 31/12/2016, and i want to prescribe 'fixed' emissions,does it mean that it will only read the january 2014 emission for the whole simulation period (2014-2016)?
Also,if i want to prescribed 'fixed' emissions of any other date,different from the model start date,say emissions of the month of january,2010(assuming the emissions of Jan,2010 is there in the emissions file) for the simulation period of 2014-2016,is it possible to tell the model via namelist settings/xml changes to take this emission start date of jan,2010(keeping all other forcings to start from model run_start_date)?
 

nusbaume

Jesse Nusbaumer
CSEG and Liaisons
Staff member
Hi Anushree,

I believe you can specify which date the emissions are fixed at by setting the namelist variables:

Code:
ext_frc_fixed_ymd
srf_emis_fixed_ymd

which are both in YYYYMMDD format. You can also specify which time of day (if needed) by setting the namelist variables:

Code:
ext_frc_fixed_tod
srf_emis_fixed_tod

which has units of seconds (e.g. the time of day in XXX seconds). Setting those namelist values will set the date of emissions, as specified in your emissions file, regardless of whatever the internal model date is.

So, if you wanted to set the emissions so that they are for January, 2010 (assuming your emissions file only contains monthly values), then you would just need to look up the date/time associated with that month, and then set the ymd variables accordingly. For example, if that date was January 1st, 2010, then you would just need to add the lines:

Code:
ext_frc_fixed_ymd = 20100101
srf_emis_fixed_ymd = 20100101

to your user_nl_cam file and you should then have constant January 2010 (or at least January 1st, 2010) emissions throughout your run.

Does that make sense? If you are still confused about anything please let us know. Also, I realized that I should move this thread to the CAM-Chem forum, as they are likely to know how to properly handle emissions and other chemical forcing mechanisms better then I do, and might correct me if I gave any incorrect info.

Thanks, and hope that helps!

Jesse
 
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