Dependence of NAO variability on coupling with sea ice

Abstract

The variance of the North Atlantic Oscillation index (denoted N) is shown to depend on its coupling with area-averaged sea ice concentration anomalies in and around the Barents Sea (index denoted B). The observed form of this coupling is a negative feedback whereby positive N tends to produce negative B, which in turn forces negative N. The effects of this feedback in the system are examined by modifying the feedback in two modeling frameworks: a statistical vector autoregressive model (F VAR ) and an atmospheric global climate model (F CAM ) customized so that sea ice anomalies on the lower boundary are stochastic with adjustable sensitivity to the model's evolving N. Experiments show that the variance of N decreases nearly linearly with the sensitivity of B to N, where the sensitivity is a measure of the negative feedback strength. Given that the sea ice concentration field has anomalies, the variance of N goes down as these anomalies become more sensitive to N. If the sea ice concentration anomalies are entirely absent, the variance of N is even smaller than the experiment with the most sensitive anomalies. Quantifying how the variance of N depends on the presence and sensitivity of sea ice anomalies to N has implications for the simulation of N in global climate models. In the physical system, projected changes in sea ice thickness or extent could alter the sensitivity of B to N, impacting the within-season variability and hence predictability of N.

The Impact of Regional Arctic Sea Ice Loss on Atmospheric Circulation and the NAO

“…The link between the NAO and sea ice cover has been investigated by several other studies Deser et al 2004;Kvamstø et al 2004;Seierstad and Bader 2009;Strong and Magnusdottir 2011;Jaiser et al 2012;Peings and Magnusdottir 2014). Despite varying conclusions, there seems to be widespread agreement that Arctic sea ice loss favors the negative mode of the NAO (Vihma 2014).…”

Drivers and potential predictability of summer time North Atlantic polar front jet variability

“…Woollings et al 2010;Woollings and Blackburn 2012;Strong and Magnusdottir 2011). The mean summer Atlantic atmospheric circulation is characterized by a weaker, poleward shifted jet (Woollings 2010), and an NAO pattern that shows weaker nodes, shifted in location and identified as the summer NAO (SNAO; e.g.…”

“…Wu and Zhang 2010;Strong and Magnusdottir 2011;Kim et al 2014). However, evidence for a link with summer North Atlantic atmospheric variability is much sparser.…”

Simple Statistical Probabilistic Forecasts of the Winter NAO

“…Folland et al (2012) use a regression approach to forecast European winter temperatures based on a range of predictors, and recent work with dynamical forecast models (Riddle et al 2013; concludes that important aspects of winter climate and the NAO are predictable months ahead, with a high proportion of the variance being accounted for by the models . A number of potential predictors have been identified: El Niño-Southern Oscillation (ENSO; e.g., Bell et al 2009), spring North Atlantic sea surface temperatures (SSTs; e.g., Rodwell and Folland 2002), tropical volcanic eruptions (e.g., Robock and Mao 1995), Arctic sea ice extent (e.g., Strong and Magnusdottir 2011), the stratospheric quasi-biennial oscillation (QBO;Ebdon 1975), and autumn Eurasian snow cover (e.g., Cohen and Jones 2011) have all been linked with North Atlantic atmospheric circulation variability (Hall et al 2015). Links have also been suggested between tropical SST anomalies and extratropical seasonal variability (e.g., Bader and Latif 2003;Hoerling et al 2004;Li et al 2010), where the upward trend in the NAO from 1950 to 1999 is attributed to increased SST over the Indian Ocean.…”