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Strat-trop de-coupling


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Hi. Can the more learned on this forum possibly explain why the Trop and lower Strat has been so de-coupled from the Upper Strat since Sept ? And set to continue for much of Dec by the looks of latest Ens and weekly fcasts (ECM46). I expect phases of this but it seems unusual to see such longevity in the winter half of the year. I'm trying to understand what may be driving the perpetual Arctic blocking and -AO signature in the absence of any sig downwelling from the upper Strat. Are we looking at a greater influence from the reduced Arctic sea ice or SAI this season, perhaps ? I do wonder if a split SSW (as I'm expecting this Jan) would break the Strat-Trop de-coupling we're currently seeing, though of course this is likely to induce further Arctic blocking for the second half of the winter. Any suggestions appreciated - with the ultimate aim of improving seasonal guidance !

GPH anomaly.JPG

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