Got it

Look, it's melting...

Noted 2011-08-30

Now close to the end of the season wind has most impact on sea ice extent. Depending on the average concentration of a region moving ice floes may compact again and overcome the 15% percent threshold of common extent algorithms to appear back on the radar - the opposite effect also happens.

The binary nature of this threshold explains most of the daily fluctuation of the extent, especially because sea ice concentration is lower compared to recent years.

Apart from that, the southward drift through Fram Strait is another cause of sea ice loss. Every year about 10% of the Arctic Basin’s area is exported into the Greenland Sea. Mainly MYI is transported that way southwards into warmer North Atlantic water.


As a rule of thumb ice floes drift along the direction of surface wind and while they speed up also more to the right, the latter is caused by Earth rotating anti-clockwise and is called the Coriolis effect.

The drift forecast model visualized here as an overlay on the Arctic mosaic implements this drift law. The model is rather simple, nevertheless the results are pretty good. It provides a forecast of 16 days, shown on the map are the 72 hours forecast vectors.

The National Weather Service's National Centers For Environmental Prediction's Environmental Modeling Center runs this model for decades and it is used by the Anchorage Weather Service Forecast Office and the National Ice Center (NIC).

The relevant science and math of the drift model is explained in this paper: Virtual Floe Ice Drift Forecast Model Intercomparison. I’d like to thank R. Grumbine for his help clearing out some roadblocks during the course of this project.

Also available as overlay are sea surface temperature conditions provided by the Danish DMI Centre for Ocean and Ice in the Arctic Ocean. This overlay is connected to the calendar and shows up to the last 30 days. Since it depicts sea ice extent it is quite useful in these days having to much clouds to see the retreating sea ice directly.

All overlays are activated or deactivated via the overlay menu as shown on the left. In case you'll see the drift vectors below the SST bitmap just switch them off and on again. Finally you need a modern browser which does not ignore latest standards.

Everybody is invited to use the comment section below and ask for more infos or help.

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