Stratosphere–Troposphere Coupling and Links with Eurasian Land Surface Variability

Abstract

A diagnostic of Northern Hemisphere winter extratropical stratosphere-troposphere interactions is presented to facilitate the study of stratosphere-troposphere coupling and to examine what might influence these interactions. The diagnostic is a multivariate EOF combining lower-stratospheric planetary wave activity flux in December with sea level pressure in January. This EOF analysis captures a strong linkage between the vertical component of lower-stratospheric wave activity over Eurasia and the subsequent development of hemisphere-wide surface circulation anomalies, which are strongly related to the Arctic Oscillation. Wintertime stratosphere-troposphere events picked out by this diagnostic often have a precursor in autumn: years with large October snow extent over Eurasia feature strong wintertime upwardpropagating planetary wave pulses, a weaker wintertime polar vortex, and high geopotential heights in the wintertime polar troposphere. This provides further evidence for predictability of wintertime circulation based on autumnal snow extent over Eurasia. These results also raise the question of how the atmosphere will respond to a modified snow cover in a changing climate.

The Influence of the AMOC Variability on the Atmosphere in CCSM3

“…Because of the stochastic character of the intrinsic atmospheric variability, the lagged MCA has been extensively used to detect oceanic influence on the atmosphere since the relationships between oceanic and atmospheric fields are indicative of the influence of the ocean on the atmosphere when the ocean leads by more than the atmospheric persistence (Frankignoul et al 1998). However, other boundary forcing such as sea ice (e.g., Alexander et al 2004) or continental snow cover (Cohen et al 2007) may also play a role. To establish whether the MCA modes are meaningful, statistical significance was estimated using a moving blocks bootstrap approach as in Czaja and Frankignoul (2002): each MCA was repeated 100 times, linking the original oceanic anomalies with randomly scrambled atmospheric ones based on blocks of two successive years to reduce the influence of possible serial correlation in the atmosphere.…”

Winter 2015/16: A Turning Point in ENSO-Based Seasonal Forecasts

“…A strong polar vortex is a plausible explanation for the poleward-displaced jet stream during winter 2015/16, despite a record strong El Niño that favors just the opposite response. Two of the proposed Arctic boundary influences on weather patterns in lower latitudes are changes in Arctic sea ice coverage (Honda et al, 2009;Overland et al, 2011;Vihma, 2014) and in Eurasian snow cover (Cohen and Entekhabi, 1999;Cohen et al, 2007;Allen and Zender, 2011). The atmospheric response most closely associated with these factors is variability in the strength of the Siberian high (Cohen et al, 2014a).…”

“…Another important atmospheric response attributed to amplified Arctic warming is a weakened polar vortex during middle to late winter (Cohen et al, 2014b;Kim et al, 2014). The weakened polar vortex is caused by increased poleward heat and equatorward momentum transport related to increased upward vertical wave activity flux (WAFz) and is associated with a stronger Siberian high (Cohen et al, 2007;Jaiser et al, 2012). The winter began with an anomalously strong polar vortex (Figure 5a, contours).…”

“…Through a chain of physical linkages, this leads to an increased net poleward heat flux and a weakened polar vortex, culminating in an extended period when the Arctic Oscillation (AO) resides predominantly in its negative phase (Cohen and Entekhabi, 1999;Cohen et al, 2007).…”

Multi-annual variations in winter westerly disturbance activity affecting the Himalaya

“…The AO, SH, and PE exhibit documented feedbacks between each mode that greatly complicate large-scale circulation (Cohen et al 2007). Furthermore, High Mountain Asia lies in a unique region where climate is influenced by complex interactions with these modes (Bothe et al 2012).…”