Tropical Cyclone Image Artifact Removal/Smoothing

[haicyu]

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Spurious image artifacts are making the hazard intensity profiles for tropical cyclones unusable at a high resolution.
Tropical cyclone storm tracks are printed into hazard intensity profiles at high spatial resolution with low temporal resolution. This results in spatial artifacts instead of a smooth profile of a tropical cyclone traveling through space over time. Is there any way to plot a smoother intensity profile for a given tropical cyclone?

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I've increased the number of synthetic tracks generated to get more smoothness by having them overlap with each other, but I've reached the limits of my system. Currently my model takes 4 hours to build, and I am still seeing these image artifacts. Is there any other way to get some smoothing? We should get a smooth intensity profile for a tropical cyclone along the direction of tropical cyclone travel and in a general region.

To Reproduce
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1. Run CLIMADA at high resolution, with spacing between centroids less than 0.1 degrees.
2. View TropicalCyclone intensity map.

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From the view of Tokyo, we can see the expected versus actual intensity profiles along the direction of travel of the tropical cyclone, which is the red line. Because we seem to have large time steps between cyclone footprints, we have spatial artifacts in the form of these dips instead of a smooth profile. Is there any way to get continuity here?

When we look at the larger view of Japan, we have an area with lots of artifacts within a high intensity area. Is there any way to smooth out that whole region to be roughly even intensity, since the dips in intensity are accidental and not essential.

[peanutfun]

@haicyu Thank you for your report. As far as I am aware, smoothing out these profiles is a far from trivial task, which is why Climada does not provide a function for that. Nonetheless, you can extract the full wind field for every track from TropCyclone.windfields, and you can possibly apply a smoothing algorithm of your choice on that data.

To avoid such artifacts in general, it is a good practice to match temporal and spatial resolution in such a manner that each cyclone only traverses one or very few centroids between each time step. Depending on your spatial resolution, a time step of 4h might hence be too large. Since your computation already takes a while, I therefore suggest you lower the spatial resolution. Hope this helps!

[haicyu]

Hi @peanutfun,

Thanks for your thoughtful reply. Could you point me to where I can tune the temporal resolution? I am trying to get the maximum possible spatial resolution that I can.

[haicyu]

Also, is there any interest in adopting a smoothing algorithm into CLIMADA if it were made available?

[peanutfun]

@haicyu Equal time step interpolation can be achieved with TCTracks.equal_timestep, choosing the timestep parameter accordingly:

climada_python/climada/hazard/tc_tracks.py

Line 1064 in 8f89ce1

def equal_timestep(self, time_step_h=1, land_params=False, pool=None):

Yes, we would generally be interested in adopting a suitable smoothing algorithm. However, we would need to see some results first and discuss possible advantages, shortcomings, and the actual implementation into Climada. Do you have a particular algorithm in mind?

[haicyu]

Hi @peanutfun I have a background in this area and many approaches come to mind. I can give a few of them a try and if anything useful comes out of it, what would be a good way to share back with you? Here in this thread would be fine?

Do you have any high level considerations that would be helpful to take into account? I am currently working from a climate risk management perspective, which leans towards being conservative.

[peanutfun]

@haicyu That sounds fantastic! I'll try to convert this thread into a discussion. It should then be easier to have parallel discussion on particular topics.