The Weddell Sea polynya is an area of open water that sometimes appears in the Weddell Sea over a relatively shallow region called Maud Rise.
In the latest satellite imagery from the DMSP satellite you can see the lower concentration sea ice as the darker blue colour. If you look at the MODIS imagery for the same date you can clear see black which indicates open water in the pack ice.
Trying to understand the geographic nature of the very low Antarctic sea ice extent I made the following animation:
The highlight issues in the graphic are the clear lack of sea ice in the Amundsen/Ross Seas and the Southern Ocean off Dronning Maud land. (If you are not familiar with the names off the seas / locations see the map below).
The Weddell Sea is has a relatively compressed sea ice cover this year - but it's clear there is large inter-annual variability.
Off Wilkes Land the sea ice is heavier this year - and it's easy for this to get lost in the headline story around the very low extent. There are several Antarctic research stations along this coast:
I was asked “what is an easy way to get a satellite image into Google Earth?”. Once I explained how I do it I thought it may be of interest to others. NASA have provided a really excellent web interface to some of their visual data called Worldview.
The Worldview description puts into perspective how good it is.
The Worldview tool from NASA's EOSDIS provides the capability to interactively browse global, full-resolution satellite imagery and then download the underlying data. Most of the 200+ available products are updated within three hours of observation, essentially showing the entire Earth as it looks "right now"
More than 200 data products within three hours…
Open worldview and this is the screen you are greeted with. It is easy to use. The key regions are the projection / copy / link tool in the yellow square on the right, the date control in the yellow box on the bottom of the browser screen and the layers control in the yellow box on the left.
I do recommend following the tour to find your way around the data sets.
If you click the layers button (red on the left) this is just a part of the choice of real time data you can easily access.
So you select the data you want to see, and then you can zoom in and easily download areas of interest. For some reason I always seem to find my way at this view
This movie I made shows how you can get imagery from Worldview easily into Google Earth.
I hope you find this useful. It's easy to spend a lot of time looking at this data.
The plot shows the difference between the daily ice extent, in each grid cell, for the year to 21 November 2016, and the mean, for each day, based on historical data for the 5 year period 1989-93.
Blue shades imply more sea ice and reds imply decreased sea ice compared with the mean.
To make the plot for each day of the year and each grid cell I worked out the mean sea ice extent for 5-year period 1989-1993. I then used this calculated mean taken away from the 2016 data for the same day to derive the anomaly maps.
For example if the plot shows very dark blue that means that there is 100% sea ice cover in that grid cell in 2016 and none in the 1989-93 mean. A dark red means there is no sea ice in 2016 where we would expect 100% sea ice cover.
The original data come from the DMSP SMMI data set at the NSIDC.
The seasonal cycle of sea ice extent in Antarctica has been fairly stable over the length of the satellite record. There is a slow growth of sea ice from a minimum of ~3x106 km2 in February to a maximum of ~19 x106km2 in September, before there is a relatively rapid fall in the Antarctic spring.
But this year something different is happening.
Below is Tamino's image for the Southern Hemisphere sea ice extent, the red line is 2016 up to 16 November 2016.
From January up to September the sea ice extent in 2016 follows all previous data.
You can see that the polynya in the centre of the picture can be seen from the very beginning. This is forming in front of the Dotson Ice Shelf - and from the scale bar you can see it is big. This polynya really starts to develop as open water around 5 October 2016.
The coastal polynya on the northern land boundary appear in mid September - and develop throughout the record.
The image below was in my previous post and it shows the three polynya from a MODIS image on 9 October 2016.
Next diversion will be a area of open water / time plot.
The Amundsen Sea currently has some very large polynya. In front of the Dotson, Getz and Pine Island ice shelves they are clear in the satellite data.
A polynya is an area of open water in the winter pack ice.
These are likely latent heat polynya, and strong winds are pushing the sea ice away from the coasts to make the open water. In the open water there will be a lot of sea ice generation. I wouldn't be surprised if the weather that is keeping the sea ice compressed against the Antarctic Peninsula is also responsible for opening them.
Taking the MODIS data from the TERRA satellite and importing that into google earth, the open water shows up as black. At the top of the image in front of Pine Island Glacier the polynya are partially obscured by cloud.
In Google Earth you can measure the area quite easily.
If you look at the sea ice concentration on the western Antarctic Peninsula you can see the effect of these westerly winds.
Towards the end of September 2016 the ice edge is compacted as the sea ice is pushed against the Peninsula.
The westerly winds (from bottom left to top right) compress the sea ice against the land (left hand side of the Antarctic Peninsula). This also creates open water on the eastern (right hand side ) of the Peninsula as the sea ice is pushed away from the land.
You can see the very sharp ice edge on the west, and the open open water in the MODIS satellite imagery.
The sea ice concentration anomaly for September 2016 shows that on both sides of the Antarctic Peninsula the westerly winds have reduced the amount of ice we would expect to observe by up to ~40%. On the west side because the sea ice is compressed, on the east side because the sea ice is being pushed away from the land.
This is just late winter weather.
There are a lot of Antarctic research stations on the west of the Antarctic Peninsula, including Rothera, the largest British Base. If the winds maintain the westerly direction then I can imagine it could be slow to resupply the base this season. There is time for it to change. According to the published schedule the ship is not due to arrive until 27 November 2016.
A slow resupply is not uncommon and I have been on at least one unsuccessful resupply voyage in my career. I took the picture below on 11 December 2004 under similar conditions.
I noticed in a blog post last week that there was a finger of open water extending down the Western Weddell Sea. I've carried on watching this open water in the MODIS satellite data. Whilst it's been opening and closing, there is a lot of open water. It's clearly a major sea ice generating factory at the moment.
The open water is clear in the lower resolution passive microwave sea ice data too.
If you look at some model output there are air temperatures above this open water of between -10° to about -25°C.
What is really good is if you look at the temperature anomaly (i.e. the departure from the average with a 1979-2000 baseline), it is very warm over the Weddell Sea.
I think the reason it is warmer is because the Weddell Sea pack ice is looser this year. So (as you can see in the picture above) there is lots of open water. The atmosphere is being warmed by the ocean as the sea ice is being generated.
I think the Weddell Sea pack ice is more mobile this winter. This is also telling us something about the difference between sea ice extent and sea ice thickness. The sea ice extent is large and easy to measure in the Antarctic - but we don't know how thick it is.