The positive North Atlantic Oscillation with downstream blocking and Middle East snowstorms: Impacts of the North Atlantic jet

Yao Yao, Dehai Luo, Aiguo Dai, Steven B. Feldstein

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

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.

Original languageEnglish (US)
Pages (from-to)1853-1876
Number of pages24
JournalJournal of Climate
Volume29
Issue number5
DOIs
StatePublished - Jan 1 2016

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snowstorm
North Atlantic Oscillation
zonal wind
temperature anomaly
anomaly
advection
winter
energy

All Science Journal Classification (ASJC) codes

  • Atmospheric Science

Cite this

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title = "The positive North Atlantic Oscillation with downstream blocking and Middle East snowstorms: Impacts of the North Atlantic jet",
abstract = "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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The positive North Atlantic Oscillation with downstream blocking and Middle East snowstorms : Impacts of the North Atlantic jet. / Yao, Yao; Luo, Dehai; Dai, Aiguo; Feldstein, Steven B.

In: Journal of Climate, Vol. 29, No. 5, 01.01.2016, p. 1853-1876.

Research output: Contribution to journalArticle

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