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Messages - u300673

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Arctic sea ice / Re: MOSAiC news
« on: September 20, 2020, 10:15:47 AM »

EDIT: The speed of drift swings between 10% and 20% of normal walking speed. And the tidal swings are only a few hundred meters each way. The circular movement I guess has more to do with changing wind direction than anything else.

Great. As you guessed that one hopefully you will run the numbers to prove it. Hourly wind direction from PS is here   P169 is near if you need buoy data.
I suspect it is the combination of both since wind drift appears to be of the same order of magnitude as 'tidal drift' and it's a more likely explanation than continuous tight wind vortexes at multiples of walking speed. 
A guess does not need proof. Circular motion needs explanation, and I'm at a loss to see what else it could be. Some sort of ocean current turbulence is of course also a possibility, but less likely to my mind.

The drift speed is not at "multiples of walking speed" in normal parlance. Slow strolling is 1m/s, while brisk walking is nearer to 1.5 m/s. The buyos drift speed swings around 0.1 m/s. I'm not sure what you mean by "tidal drift", I don't think such a thing exists. But the sideways pulsation of water every 6 hours sems to be in the region of a few hundred meters each way every 6 hours, translating into a slow pendulum swing at 0.02 m/s.

Uniqorn's animation (repeated below) does not indicate any wind vortexes at any speed. The twoo loops at the center of the image can be seen as a result of slow drift closely aligned to the direcion of the tidal pulse. If we were to remove the tidal factor, the buoy movement would paint a circle with a radius of 1 or 2 km over a three day period. Changes in wind direction seems the most likely explanation, but it is of course the surrounding ice that is moving and the forces causing the changes in movement could just as well be found hundreds of kms distant.

Have you considered inertial oscillations (e.g. ?

Arctic sea ice / Re: The 2019 melting season
« on: August 21, 2019, 10:15:28 PM »
a forecast time not available over internet for IFS to my knowledge

ECMWF forecasts every 3 hours can be found here:

Arctic sea ice / Re: Arctic Image of the Day
« on: July 12, 2019, 09:51:27 AM »
Nice Helmholtz-like waves at the edge of the remaining ice in the Kara sea today

Arctic sea ice / Re: 2019 sea ice area and extent data
« on: July 10, 2019, 09:18:19 PM »
Applied the filter, these are all 5-day avg double century drops in NSIDC, so we'll see tomorrow
Careful with the data before 1987, as there is only data reported every two days. So the "five day average loss" is really a "ten day average two day loss".


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