Difference of station file and history file output

[xmuliuy]

Hi,I am using roms701 to simulate tidal current in an estuary.
I compare the model data with fields data,use both output from station file and history file.when I use the results in history file,model data agrees well with fields data, but results from station file NOT.

so I wonder whether there are some difference between history file results and station file result when there are the same (I,J).

I have set Flag to 0 in 'stations.in' to specify horizontal location for a particular station (I,J).Time between writing data into stations file are 1 min,and time between writing data into history file are 1 hour.

Fig 1 shows difference of current between stations file and history file with the same location.
Fig 2 shows difference of current(U_eastward) between stations file and history file with the same location.
Fig 3 shows difference of current(v_northward) between stations file and history file with the same location.
(Blue:station results,Red:his results,Green:difference between station and his results)
what is the reason this kind of difference comes from ?

I think when i set flag to 1 in 'stations.in',i can specify lon and lat of my station,then the model will do some Interpolation and write the results into station file ,But when my flag is 0, just specify (I,J),i guess the model will write the data of the specify (I,J) into station file,and without Interpolation, but it seems not.

hope you can help me.
thanks.

[wilkin]

Do you get precise agreement for other variables, such as the true velocity components u,v or tracers?

u_eastward and v_northward get special treatment because they are the cell face velocities u,v averaged to a vector at the rho-points cell center, then rotated to geographic coordinates using the grid angle, and separated out into east and north. The i,j coordinate in a stations file should thus correspond to the rho-points grid for these variables.

If other variables are in precise agreement, then we would know to look more closely at the handling of u_eastward and v_northward in the stations option.