November 21, 2012
New Method Uses Ocean Currents To Predict Arctic Sea Ice Forecast
Lee Rannals for redOrbit.com - Your Universe Online
Researchers at MIT have developed a new method for optimally combining models and observations of the Arctic Ocean to accurately simulate the seasonal extent of the ice change and the ocean circulation beneath.
The Arctic Ocean freezes each winter to form sheets of sea ice that spread over millions of square miles. This ice then acts as a massive sun visor for the Earth and helps to reflect solar radiation and shield the planet from warming too much.
Over the last three decades, this winter ice cap has shrunk, and its annual maximum reached record lows in 2007 and again in 2011.
Understanding the processes that drive sea-ice formation and advancement may help scientists predict the future extent of Arctic ice coverage. However, the models being used today vary in their predictions for how sea ice will evolve.
In order to make a more accurate prediction, the team applied its synthesis method to produce a simulation of the Labrador Sea that matched actual satellite and ship-based observations in the area.
The researchers were able to identify an interaction between sea ice and ocean currents that is important for determining what is known as "sea ice extent." This is where winds and ocean currents push newly formed ice into warmer waters, which helps to grow the ice sheet.
Patrick Heimbach, a principal researcher in MIT´s Department of Earth, Atmospheric and Planetary Sciences (EAPS), said that accounting for this feedback is an important piece in the puzzle to predict sea-ice extent.
“Until a few years ago, people thought we might have a seasonal ice-free Arctic by 2050,” Heimbach said in a press release. “But recent observations of sustained ice loss make scientists wonder whether this ice-free Arctic might occur much sooner than any models predict “¦ and people want to understand what physical processes are implicated in sea-ice growth and decline.”
The team constructed a model to simulate ice cover, thickness and transport in response to atmospheric and ocean circulation. They developed a method known in computational science and engineering as "optical state and parameter estimation" to plug in a variety of observations to improve the simulations.
They tested out their method on data taken in 1996 and 1997 in the Labrador Sea. They included satellite observations of ice cover, as well as local readings of wind, speed, water and air temperature, and water salinity. Their approach helped to gain an accurate simulation compared to observed sea-ice and ocean conditions in the Labrador Sea.
The model and observations revealed not just where ice forms, but also how ocean currents transport ice flows within and between seasons. Through their simulations the team found that as new ice forms in northern regions of the Arctic, ocean currents push this ice to the south in a process known as advection.
As ice migrates farther south, it creates a fresh layer of ocean water that eventually insulates more incoming ice from warmer sub-surface waters of subtropical Atlantic origin.
The researchers may use the method of model-data synthesis to predict sea-ice growth and transport in the future.
“The Northwest Passage has for centuries been considered a shortcut shipping route between Asia and North America – if it was navigable,” Heimbach says. “But it´s very difficult to predict. You can just change the wind pattern a bit and push ice, and suddenly it´s closed. So it´s a tricky business, and needs to be better understood.”
Martin Losch, a research scientist at the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany said that the feedback mechanism identified by the researchers is important to help predict sea-ice extent on a regional scale.
“The dynamics of climate are complicated and nonlinear, and are due to many different feedback processes,” said Losch, who was not involved with the research. “Identifying these feedbacks and their impact on the system is at the heart of climate research.”
The researchers published their paper "Hydrographic Preconditioning for Seasonal Sea Ice Anomalies in the Labrador Sea" in the Journal of Physical Oceanography.