Lagrangian Drifters stick to the boundary.

[wolfegg]

Hi all,

I am using Lagrangian drifters to study the residence time in an estuary. Initially, I release 1612 drifters to surface of the estuary at 20140301 00:00:00. The initial locations of the drifters are shown in figure(a). But I found that after a 4-month simulation (20140301-20140630), most of the drifters stick to the land/ocean boundary and do not move (figure(b), actually they move, but the distances are super tiny). At the end of the simulation there are 1123 (out of 1612) drifters left in the estuary (actually, adhere to the boundary). The estimated residence time is >= 120 days in the upper and middle estuary. This result is not consistent with previous study using FVCOM. Do anyone know about how to deal with the "non-moving" drifters?




Many thanks!

Dan

[wilkin]

Are you using the online #define FLOATS option in ROMS, or doing the particle tracking yourself from archived ROMS model output?

[wolfegg]

Are you using the online #define FLOATS option in ROMS, or doing the particle tracking yourself from archived ROMS model output?

Hi Wilkin,
I am using the #define FLOATS option in ROMS.

Thanks,
Dan

[wilkin]

Are the sticky floats always stuck? i.e. did they move at all?

It's hard to tell for sure from the images you posted, but I get a sense that many of the stuck floats are in one-cell wide bays or corners, and it is very hard to generate a flow inside a one-cell wide bay that will move a float out of it.

With online float tracking on every time step I would be surprised if floats entered a bay from outside and stuck there.

Also, you may have some one-cell wide land cells that "kiss" at the corners only, in which case you have the high order advection term finite-difference stencil stepping over land which is not recommended by possibly not actually wrong.

[wolfegg]

Are the sticky floats always stuck? i.e. did they move at all?

It's hard to tell for sure from the images you posted, but I get a sense that many of the stuck floats are in one-cell wide bays or corners, and it is very hard to generate a flow inside a one-cell wide bay that will move a float out of it.

With online float tracking on every time step I would be surprised if floats entered a bay from outside and stuck there.

Also, you may have some one-cell wide land cells that "kiss" at the corners only, in which case you have the high order advection term finite-difference stencil stepping over land which is not recommended by possibly not actually wrong.

Hi Wilkin,
The floats do move and will leave the estuary (the red dot area in Figure(a)) eventually after a quite long time. I ran a one-year simulation, most of the floats leave the estuary after 200 days, although I still have a considerable amount of floats staying in the estuary for the whole year. Such estimation is not "correct" or "reasonable" since some previous studies suggest that the maximum duration of time for the floats to leave the estuary is about 100 days.

I also extended my wet cells in the narrow channels for a more "energetic" dynamic field...But, I still got the similar results.
Typically, the momentum in the upper estuary (the uppermost three lakes) is low even for the waters in the central lake (the current velocity is at a magnitude of 0.01m/s), not to mention the edges of the lakes.

So, would it be possible to "kick" the stuck floats out when they get attached to the edges where the momentum is super low?

Thanks,
Dan