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>• Rotated EOF

• 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

Iceland

S. Greenland

• 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

• Less important under high solar activity

• Oriented meridionally (wave-like)

• In solar max, more zonal

• No clear dependence of the variance it explains on the phase of solar cycle.

• Under solar max, British center is shifted westward

• Zonally oriented 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

• 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.

• Least pronounced effects of solar variations

• Kamchatka center extends more westward

• Southern center tends to move eastward

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) EU2 patterns. 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.

Part 2. BLOCKING EVENTS

Enhanced signature of solar variability in

Eurasian winter climate

T. Woollings et al. (2010)<Data>

• ERA40• Wolf sunspot numbers &

F10.7

Solar modulation of Northern Hemisphere

winter blocking

Barriopedro et al. (2008)<Data>

• NCEP reanalysis • Wolf sunspot numbers &

F10.7

T. Woollings et al. (2010)

Extend deeper

nolinear

T. Woollings et al. (2010)

Colder and extend eastward

Both weaker

Several of the coldest periods in Europe during the 2009/10 winter were associated with blocking events, in which the mild prevailing westerlies were replaced withcold northerly and easterly winds.

high solar

low solar

moderate solar

%age of days when the longitude was

blocked by a blocking event lasting more

than 5 days

Barriopedro et al. (2008)

Blocking frequency

Barriopedro et al. (2008)

Persist longerCenter locate further east

Barriopedro et al. (2008)

high solar

low solar Under LS, Europe experiences very cold temperatures and warm temperatures are detected in south Greenland and the Labrador Sea.

Extremely persistent blocking episodes (longer than 15 days) are more prone to occur during LS.

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.