Abstract
Along with significant changes in the Arctic climate system, the largest year-to-year variation in sea-ice extent (SIE) has occurred in the Laptev, East Siberian, and Chukchi seas (defined here as the area of focus, AOF), among which the two highly contrasting extreme events were observed in the summers of 2007 and 1996 during the period 1979–2012. Although most efforts have been devoted to understanding the 2007 low, a contrasting high September SIE in 1996 might share some related but opposing forcing mechanisms. In this study, we investigate the mechanisms for the formation of these two extremes and quantitatively estimate the cloud-radiation-water vapor feedback to the sea-ice-concentration (SIC) variation utilizing satellite-observed sea-ice products and the NASA MERRA reanalysis. The low SIE in 2007 was associated with a persistent anticyclone over the Beaufort Sea coupled with low pressure over Eurasia, which induced anomalous southerly winds. Ample warm and moist air from the North Pacific was transported to the AOF and resulted in positive anomalies of cloud fraction (CF), precipitable water vapor (PWV), surface LWnet (down-up), total surface energy and temperature. In contrast, the high SIE event in 1996 was associated with a persistent low pressure over the central Arctic coupled with high pressure along the Eastern Arctic coasts, which generated anomalous northerly winds and resulted in negative anomalies of above mentioned atmospheric parameters. In addition to their immediate impacts on sea ice reduction, CF, PWV and radiation can interplay to lead to a positive feedback loop among them, which plays a critical role in reinforcing sea ice to a great low value in 2007. During the summer of 2007, the minimum SIC is 31 % below the climatic mean, while the maximum CF, LWnet and PWV can be up to 15 %, 20 Wm−2, and 4 kg m−3 above. The high anti-correlations (−0.79, −0.61, −0.61) between the SIC and CF, PWV, and LWnet indicate that CF, PWV and LW radiation are indeed having significant impacts on the SIC variation. A new record low occurred in the summer of 2012 was mainly triggered by a super storm over the central Arctic Ocean in early August that caused substantial mechanical ice deformation on top of the long-term thinning of an Arctic ice pack that had become more dominated by seasonal ice.
Highlights
The global mean surface temperature has increased 0.6–0.7 °C since the mid-1960s (Kennedy et al 2007), and during the same period the temperature over the Arctic region has risen by 1.9–2.0 °C, even more during the winter and spring months (RichterMenge et al 2008; Graversen et al 2008)
In this study we explore in detail the underlying processes driving the 2007 and 1996 extreme events, and identify similarities and differences between these 2 years with respect to the major factors and atmospheric conditions contributing to the formation of the sea-ice extent (SIE) extremes
We examine two highly contrasting extreme events (2007 and 1996) in the September Arctic sea-ice extent using satellite observed sea-ice extent/concentration and the Modern-Era Retrospective Analysis for Research and Applications (MERRA) reanalysis
Summary
The global mean surface temperature has increased 0.6–0.7 °C since the mid-1960s (Kennedy et al 2007), and during the same period the temperature over the Arctic region (north of 60°) has risen by 1.9–2.0 °C, even more during the winter and spring months (RichterMenge et al 2008; Graversen et al 2008). Schweiger et al (2008) demonstrated with an ice-ocean model that reduced CF and enhanced downwelling SW flux had contributed little to the 2007 low They argued that the impact of enhanced downwelling SW flux was small and largely confined to areas north of the ice edge, where surface albedo remained high and additional absorption of solar radiation by the surface was minimal. We further investigate the mechanisms for triggering and causing the 2007 low, such as the onset was triggered by a persistent large-scale atmospheric circulation anomaly during spring, and later on the sea ice melting was accelerated by a positive cloud-radiation-PWV (precipitable water vapor) feedback over the AOF during summer and early autumn
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
