The Positive North Atlantic Oscillation with downstream blocking and Middle East snowstorms: Impacts of the North Atlantic Jet

A recent study revealed that cold winter outbreaks over the Middle East and southeastern Europe are caused mainly by the northeast-southwest (NE-SW) tilting of European blocking (EB) associated with the positive-phase North Atlantic Oscillation (NAO+). Here, the North Atlantic conditions are examined that determine the EB tilting direction, defined as being perpendicular to the dipole anomaly orientation. Using daily reanalysis data, the NAO+ events are classified into strong (SJN) and weak (WJN) North Atlantic jet types. A composite analysis shows that the EB is generally stronger and located more westward and southward during SJN events than during WJN events. During SJN events, the NAO+ and EB dipoles exhibit NE-SW tilting, which leads to strong cold advection and large negative temperature anomalies over the Middle East and southeastern Europe. In contrast, northwest-southeast (NW-SE) tilting without strong negative temperature anomalies over the Middle East is seen during WJN events. A nonlinear multiscale interaction model is modified to investigate the physical mechanism through which the North Atlantic jet (NAJ) affects EB with the NAO+ event. It is shown that, when the NAJ is stronger, an amplified EB event forms because of enhanced NAO+ energy dispersion. For a strong (weak) NAJ, the EB tends to occur in a relatively low-latitude (high latitude) region because of the suppressive (favorable) role of intensified (reduced) zonal wind in high latitudes. It exhibits NE–SW (NW-SE) tilting because the blocking region corresponds to negative-over-positive (opposite) zonal wind anomalies. The results suggest that the NAJ can modulate the tilting direction of EB, leading to different effects over the Middle East.

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Author Yao, Yao
Luo, Dehai
Dai, Aiguo
Feldstein, Steven
Publisher UCAR/NCAR - Library
Publication Date 2016-03-01T00:00:00
Digital Object Identifier (DOI) Not Assigned
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Topic Category geoscientificInformation
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Metadata Date 2023-04-14T21:07:25.478819
Metadata Record Identifier edu.ucar.opensky::articles:18273
Metadata Language eng; USA
Suggested Citation Yao, Yao, Luo, Dehai, Dai, Aiguo, Feldstein, Steven. (2016). The Positive North Atlantic Oscillation with downstream blocking and Middle East snowstorms: Impacts of the North Atlantic Jet. UCAR/NCAR - Library. Accessed 10 June 2023.

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