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On the coupling between polar and tropical regions during springtime: variability of tropical intrusion and Frozen In Anticyclones.

Huret, N.; Thiéblemont, R.; Hauchecorne, A.; Orsolini, Y.J.; Matthes. K.

Publication details

Presented at Our Common Future Under Climate Change, International Scientific Coference, 7-10 July 2015, Paris, France.

Link: http://www.commonfuture-paris2015.org/

Summary: Abstract : Recent observational and modeling transport studies of Arctic stratospheric final warming have shown that tropical/subtropical air masses can be transported to high latitudes and remain confined within a long-lived ¿frozen- in¿ anticyclone (FriaC), embedded in the summer easterlies for several months. We first present a climatology of these sporadic events over the period 1960-2011 using era-40 and era interim reanalyses. this study highlights stratospheric favorable preconditioning for FrIACs occurrence, that is: i) early and abrupt final warming, ii) no stratospheric major warming during the previous winter, and iii) east phase of the Quasi-Biennial Oscillation. We will present in detail the FriaC in spring 2011, which was the largest ever recorded. Our climatology further suggests that the frequency of occurrence of FriaCs has increased over the last decade (among the nine cases detected over the period 1960- 2011, five occurred between 2002 and 2011). A chemistry climate model is then used for the first time to investigate FriaCs characteristics and variability. simulations were performed with the nCar¿s Community earth system Model (CesM, version 1.0.2), a coupled model system including the Whole Atmosphere Community Climate Model (WACCM). FrIACs characteristics (i.e. spatial extent and duration), are overall consistent by comparing with FriaCs detected era-40 meteorological reanalyses. Dynamical analysis reveals that FriaCs are associated with an abrupt and early winter-to-summer stratospheric circulation transition, characterized by an amplification of planetary wave activity. Furthermore, our model results confirm that FrIACs occur preferentially under the easterly phase of the QBO and in absence of MSW during the preceding