Abstract
ABSTRACTThe response of the Arctic atmosphere to low and high sea ice concentration phases based on European Center for Medium-Range Weather Forecast (ECMWF) Re-Analysis Interim (ERA-Interim) atmospheric data and Hadley Centre's sea ice dataset (HadISST1) from 1989 until 2010 has been studied. Time slices of winter atmospheric circulation with high (1990–2000) and low (2001–2010) sea ice concentration in the preceding August/September have been analysed with respect to tropospheric interactions between planetary and baroclinic waves. It is shown that a changed sea ice concentration over the Arctic Ocean impacts differently the development of synoptic and planetary atmospheric circulation systems. During the low ice phase, stronger heat release to the atmosphere over the Arctic Ocean reduces the atmospheric vertical static stability. This leads to an earlier onset of baroclinic instability that further modulates the non-linear interactions between baroclinic wave energy fluxes on time scales of 2.5–6 d and planetary scales of 10–90 d. Our analysis suggests that Arctic sea ice concentration changes exert a remote impact on the large-scale atmospheric circulation during winter, exhibiting a barotropic structure with similar patterns of pressure anomalies at the surface and in the mid-troposphere. These are connected to pronounced planetary wave train changes notably over the North Pacific.
Highlights
The observed decrease in Arctic summer sea ice cover over recent decades is likely due to a combination of decadalscale variability in the coupled iceÁoceanÁatmosphereÁ land system and radiative greenhouse gas forcing (Serreze et al, 2007). Stroeve et al (2007) analysed the Arctic sea ice cover changes in the Fourth IPCC Assessment Report model simulations and demonstrated that the observed sea ice retreat is much faster than in the model mean
We showed that the initial response of the atmosphere to reduced sea ice concentration in late summer is baroclinic in autumn, which changes to barotropic in winter and triggers changes in the large-scale planetary wave trains over the Pacific
We showed that Arctic heating anomalies due to low sea ice concentrations in late summer (August/September) trigger changes in baroclinic systems in autumn because of an earlier onset of baroclinic instability that influences the structure of large-scale planetary waves in the following winter
Summary
The observed decrease in Arctic summer sea ice cover over recent decades is likely due to a combination of decadalscale variability in the coupled iceÁoceanÁatmosphereÁ land system and radiative greenhouse gas forcing (Serreze et al, 2007). Stroeve et al (2007) analysed the Arctic sea ice cover changes in the Fourth IPCC Assessment Report model simulations and demonstrated that the observed sea ice retreat is much faster than in the model mean. Using more recent ERA-Interim data, we analyse the influence of Arctic sea ice on transient baroclinic activity and large-scale atmospheric circulation systems and their non-linear interactions during the winter season for a period with high ice concentration (1990Á2000) and a period of low ice concentration (2001Á2010). A main focus is on the scale separation between planetary waves and synoptic-scale changes during the atmospheric adjustment process with respect to high and low sea ice cover changes The results of this observational study are compared with a model study reported by Sokolova et al (2007), where two time slices with high and low sea ice cover have been analysed with respect to the non-linear atmospheric interactions between planetary and baroclinic waves. They found an increase in Eliassen-Palm (EP) fluxes on baroclinic scales, a decrease in planetary scales and preferred positive AO phases for high ice regimes
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