The understanding of transient forcing

alain

Hello，everyone:

For a transient simulation, we need a some forcings as input and i.e

 md.smb.mass_balance` = [ smb smb-1];
 md.smb.mass_balance = [ md.smb.mass_balance; [10 20]];
 md.timestepping.time_step=1;
 md.timestepping.final_time=20;  % 200

We add a the variable (smb) to be forced value at the end of simulation (time=20). It's a time series and sometimes it just need only one value. Will it get more precise simulation results if we have more observation and input more time series value.
md.smb.mass_balance = [ smb; 1]

I find that some example final_time always have a forcing, but if I want to simulate and predict the results of 200 year in future. Must we need impose a forcing at time=200? In general, how long is most robust to simulation duration?
Thanks advance

mathieumorlighem

Hi Alain,

I am not sure to fully understand your question. What ISSM does is a linear interpolation between the dates for which you prescribed an SMB. In your case, you have smb10 for year 10 and smb20 for year 20:

for all time steps before 10, ISSM will use "smb10",
for all time steps between 10 and 20, ISSM will use "alphasmb10 + (1-alpha)(smb20) " where alpha = (20-time)/10
for all time steps after 20, ISSM will use smb20

If you only provide SMB until year 20, ISSM will use the SMB of year 20 for all time steps after 20, so keep this in mind because this may not be what you would like to do.
I hope this answers your question?
Mathieu

alain

mathieumorlighem
Very thankful to your timely reply. It's not reasonal that using the SMB of year 20 to simulated the results after year 20 from your reply. So if we want to get the transinent results of year 200, but we don't have the smb of year 200. In genaeral we need to take which forcing as assumption input in order to make some prediction in the future.
That is to say that we would like to get transient solution at later time, we must prescribe a coresponding forcing.

mathieumorlighem

Yes exactly, you need to prescribe a scenario for the future SMB...