Low Pressure System Responsible For Lower Antarctic Sea Ice Extent Last Month
By Paul Homewood
A reader, (sorry, forgot who!), pointed out last month the sharp drop in Antarctic sea ice early in September.
It turns out that weather was to blame. From the NSIDC report for September:
Antarctic sea ice extent reached 18.44 million square kilometers (7.12 million square miles) on August 31, 2016, and this appears to be the maximum extent for this year. This is the earliest maximum in the satellite record since 1979, and the first time the maximum has occurred in August. The maximum was 240,000 square kilometers (93,000 square miles) greater than the average extent for this date of 18.20 million square kilometers (7.03 million square miles). It is the tenth lowest maximum extent on record. On average, the maximum occurs much later (September 23 to 24).
The early maximum appears to be the result of an intense wind pattern in September, spanning nearly half of the continent from the Wilkes Land area to the Weddell Sea, and centered on the Amundsen Sea. Stronger than average low pressure in this area, coupled with high pressure near the Falkland Islands, and near the southern tip of New Zealand in the Pacific Ocean, created two regions of persistent northwesterly winds. Sea ice extent decreased in the areas where the northwesterly winds reached the ice front.
A comparison of sea ice extent from the date of the maximum (August 31) and the last day of September (one month later) shows that sea ice extent decreased through the month along a broad region west and east of the Antarctic Peninsula. It also decreased on the other side of the continent north of Wilkes Land. By comparison, this was partly offset by increases in the northern Amundsen Sea and north of Dronning Maud Land.