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Paper review

Paper review. Speaker ： Pei-Yu Chueh Adviser ： Yu- Heng Tseng Date ： 2011/3/22. Part 1 . MODES OF LOW-FREQUENCY VARIABILITY. Solar cycle effects on modes of low-frequency circulation variability. Radan Huth et al. (2006 ). <Data> NCEP reanalysis Wolf sunspot numbers <Method>

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Paper review

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  1. Paper review Speaker：Pei-Yu Chueh Adviser：Yu-Heng Tseng Date：2011/3/22

  2. Part 1. MODES OF LOW-FREQUENCY VARIABILITY Solar cycle effects on modes of low-frequency circulation variability RadanHuth et al. (2006) • <Data> • NCEP reanalysis • Wolf sunspot numbers • <Method> • Rotated EOF

  3. Iceland • Explain much more variance under high solar activity • Icelandic center shift westward • Lack extension toward Alaska in solar max • Azores center separates into two centers • HS : more zonal S. Greenland

  4. Weaker under low solar activity • Pattern is similar to NAO→zonally oriented mode • In solar max, whole pattern is shifted slightly southward • North center becomes more zonally (extend westward) • separates into two centers

  5. Less important under high solar activity • Oriented meridionally (wave-like) • In solar max, more zonal

  6. No clear dependence of the variance it explains on the phase of solar cycle. • Under solar max, British center is shifted westward

  7. Zonallyoriented and located over central and eastern Asia • Weaken under solar average • Lack extension toward Alaska in solar max • A strong extension over eastern Canada appears

  8. It is weakest under solar max. • The Aleutian center eastward shift • The American center moves southward • The Florida center becomes weaker • Remote center over Siberia gets larger and intensifies.

  9. Least pronounced effects of solar variations • Kamchatka center extends more westward • Southern center tends to move eastward

  10. Summary I • The zonal (seesaw-like) patterns tend to be more/less active in solar maxima/minima: this applies to the NAO and EA patterns ; the WPO does not manifest any preference regarding the solar cycle. • The meridional (wave-like) patterns tend to be least active in solar maxima, which holds for the PNA, EU1, and (to a lesser extent) EU2patterns. The NAs pattern is neither clearly zonal nor clearly meridional. • Another common feature of the majority of modes is a southward shift of at least one of their action centers with increasing solar activity: This is observed for the NAO, EA, EU1, EU2, and PNA modes. • In general terms, the circulation variability modes in solar maxima tend to be more zonal, join remote action centers (i.e., the teleconnections span longer distances), and their action centers occupy a larger area, but tend to be weaker.

  11. Part 2. BLOCKING EVENTS • Enhanced signature of solar variability in Eurasian winter climate • Solar modulation of Northern Hemisphere winter blocking T. Woollingset al. (2010) Barriopedroet al. (2008) • <Data> • ERA40 • Wolf sunspot numbers & F10.7 • <Data> • NCEP reanalysis • Wolf sunspot numbers & F10.7

  12. nolinear Extend deeper T. Woollingset al. (2010)

  13. Colder and extend eastward Several of the coldest periods in Europe during the 2009/10 winter were associated with blocking events, in which the mild prevailing westerlieswere replaced with cold northerly and easterly winds. Both weaker T. Woollingset al. (2010)

  14. Blocking frequency high solar moderate solar low solar %age of days when the longitude was blocked by a blocking event lasting more than 5 days Barriopedroet al. (2008)

  15. Persist longer Center locate further east Barriopedroet al. (2008)

  16. Extremely persistent blocking episodes (longer than 15 days) are more prone to occur during LS. high solar low solar Under LS, Europe experiences very cold temperatures and warm temperatures are detected in south Greenland and the Labrador Sea. Barriopedroet al. (2008)

  17. Summary II • The circulation anomalies are particularly enhanced over the North Atlantic/Eurasian sector, where there are large changes in the occurrence of blocking and the winter mean surface temperature differs by several degrees between high‐ and low‐solar activity. • Blocking amplify under the QBO-west phases. • Low solar Atlantic blocking episodes last longer, are located further east and become more intense than high solar blocking events. • Our results suggest that the excessively cold conditions recorded in Europe during the Maunder Minimum may have arisen from an eastward shift of long-lasting blockings with near-normal frequencies.

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