May 23 - July 29
Arctic Weather and Abrupt Sea Ice Loss
Uriel Gutierrez, Steven Cavallo, and Nicholas Szapirol
What is already known:
- The long term climate trend for Arctic sea ice is well established with the ice-albedo effect as a main driver.
- Wind patterns from inter-seasonal oscillations (such as Arctic oscillation) have effects on sea ice motion and extent.
- Abrupt sea ice loss events have been observed on time scales of days and coincide with surface cyclones.
- A better understanding of year-to-year variability is important for improving future predictions of sea ice.
What this study adds:
- Oscillations in change of sea ice extent (1979-2014) at synoptic time scales were shown to be statistically significant.
- Synoptic time scale reductions in sea ice extent occur most frequently in July and December.
- Composite of top 1% of abrupt loss in sea ice extent events revealed strong winds over loss area.
- These conditions always occurred with a nearby surface cyclone; enhancement from anticyclones could sometimes also occur.
Abstract:
September Arctic sea ice extent is decreasing rapidly, especially over the past few decades. While the mechanisms contributing to this climate trend are relatively-well understood, the year-to-year variability is not. This study examines 2-d decreases in summer sea ice extent to quantify the year-to-year variability that is due to synoptic time-scale processes and isolate its possible source. It is hypothesized that the abrupt reductions in sea ice are a consequence of synoptic–scale cyclones, and in particular the anomalously strong surface winds over the periphery of the cyclones from a strong pressure gradient.
A spectral analysis of two-day changes in sea ice extent is performed to determine whether events at synoptic time-scales have significant contributions to sea ice loss with respect to red noise. Several significant periods are found at synoptic time-scales, at 5, 6, 8, 10, and 16 days. A Butterworth filter is then applied to high-pass periods shorter than 18 days to isolate the abrupt sea ice loss events corresponding to these high frequencies and compile a set of significant events. Defining the top 1% of the high-pass filtered two-day decrease in sea ice extent, there is found to be two annual maxima: July and December, and only summer cases (June-August) are retained for the present study. Composite sea level pressure of the 25 cases reveals the presence of a 998 hPa mean surface cyclone, which varies in strength from 999 to 978 hPa. While there is always a cyclone, there is often, but not always, a nearby anticyclone that can further enhance the pressure gradient over the sea ice loss region.