Transcript The New Pacific Decadal Oscillation

Northern Hemispheric flow
Indices that may influence the
Flow
Richard H. Grumm
National Weather Service Office
State College PA
PSU 497A Lecture Series
Version 3.0
NWS-State College
Introduction
• Large scale Indices that affect the flow and
climatology over North America and Eurasia
–
–
–
–
North Atlantic Oscillation (NAO)
Pacific Decadal Oscillation (PDO)
Pacific North American pattern (PNA)
East Pacific Index (EP)
• Definitions
• Impacts on weather
• …and a tad of history…..
NWS-State College
North Atlantic Oscillation
NAO-flow Index
• A measure of the flow over the Atlantic
Basin
• Typically, the value is computed using MSLP
departures
– over Iceland and the Azores
– high NAO associated with deep Icelandic low
– low or negative NAO associated with ridge over
Iceland and Norway
• Periods of low NAO have been linked to cold
in Northern Europe and North America
– the Little Ice age ~1300-1860
NWS-State College
NAO
http://www.cru.uea.ac.uk/tiempo/floor2/data/nao.htmNAO
• Strictly the index should only be applied in the cold
season
• Recent low/negative NAO
– the winter of 1995-96
– Winter Oct-Jan 2002-2003
• Historically:
– NAO use to fluctuate more then in recent times
– we know this from history:
• wine harvest dates (later was a cold year)
• wheat harvests and periods of European Famine
– wheat and other grains failed or produced bad crops in cold wet
years.
• shipping and fishing industries back to Nordic and Basque
fishing times.
NWS-State College
– They followed the water-temperature
sensitive Cod fish
NAO-Positive Phase
• Stronger than usual subtropical high pressure center
and a deeper than normal Icelandic low
• The increased pressure difference results in more and
stronger winter storms crossing the Atlantic Ocean on
a more northerly track.
– Wetter in western Europe
– keeps cold air out of Europe
– Stronger Atlantic Jet into Western Europe (similar to EP in Pacific!)
• North American Weather
– in cold and dry winters in northern Canada and Greenland
– The eastern US experiences mild and wet winter conditions
NWS-State College
NAO-Positive Phase
NWS-State College
NAO-Negative Phase
• shows a weak subtropical high and a weak Icelandic
low.
• A reduced pressure gradient results in fewer and
weaker winter storms crossing on a more west-east
pathway.
– Moist Atlantic air moves into the Mediterranean
– cold air to northern Europe
– associated with many record cold European winters
– US east coast experiences more cold air outbreaks and snowy
weather conditions.
– Greenland, has milder winter temperatures
• during the warm conditions 800-1250 AD negative NAO's
NWS-State College
may have allowed farming
and fishing in Greenland
NAO-Negative Phase
NWS-State College
NAO in recent history
NWS-State College
Recent NAO 2002-03
NWS-State College
Positive Phase
NAO height
anomalies
Trough/Ridge
Enhances Atlantic
Jet (Green)
NWS-State College
Pacific Decadal Oscillation
PDA/NPO Oceanic Index
• The Pacific Decadal Oscillation (PDO) is an
index of long-term variability of the seasurface temperatures of the North Pacific
Ocean.
– reflects the dominant mode of SST over the North Pacific
Ocean.
– The PDO can impact the climate.
– A characteristic that distinguishes the PDO from ENSO is that
20th century PDO events have tended to persist for 20-to-30
years, while ENSO events have typically persisted for 6 to 18
months.
– also known as the North Pacific Oscillation (NPO) and the
terms can be used interchangeably.
NWS-State College
Phases of the PDO/NPO
– the high phase of the NPO is the term used to
describe a warm PDO and the low phase of the
NPO is the term used to describe the cold PDO.
– Recent research suggests a clear link of the
PDO to the ENSO. Some believe the sign of the
PDO may be linked or driven by the longer term
ENSO cycle.
NWS-State College
PDO SST Examples
Figure 2 The warm phase (left) and cold phase (right) of the PDO. The warm phase is also known as
a high NPO while the cold phase is also known as a low NPO. Similar to an El Nino event, note the
warm water in the eastern Pacific.
NWS-State College
The cold phase
• Cold PDO regimes prevailed from 1890-1950
– cold phase index is positive
– the PDO was higher then average from 1920 to
1950.
– cold phase may behave like a weak La Nina
• note colder water in tropical Pacific dominates
• may enhance impacts of La Nina when they are in phase
– The cold phase occurs when there is warmer water
over the western and central Pacific associated with
a deepened Aleutian low.
– Colder water over eastern and tropical Pacific
NWS-State College
The warm phase
• Warm PDO regimes dominated from 1950
through the 1980’s.
• During the warm phase, the PDO is
negative.
• On a 30 year time scale, the PDO was lower
than average from 1950 to 1980.
• A negative PDO may act like an El Nino.
• The warm phase occurs when there is colder
water over the western and central Pacific.
NWS-State College
The warm phase
• Warmer and drier winters in the northern
and wetter and cooler winters observed in
the southern in the United States.
• El Nino is associated with a negative SOI,
weak tropical easterlies and warm ENSO3
SST’s.
NWS-State College
PDO
SST/wind vectors/MSLP anomalies
Figure 2 The warm phase (left) and cold phase (right) of the PDO. The warm phase is also known as
a high/positive NPO while the cold phase is also known as a low/negative NPO. Similar to an El Nino
event, note the warm water in the eastern Pacific.
NWS-State College
PDO-ENSO Similarities
SST/wind vectors/MSLP anomalies
NWS-State College
PDO values 1900-2000
NWS-State College
East Pacific Index (EP)
• Pattern is evident all months except August
and September
• A north-south dipole of height anomalies
over the eastern North Pacific.
– The northern center is located in the vicinity of
Alaska and the west coast of Canada
– the southern center is of opposite sign and is
found near/east of Hawaii.
• May have a link to the PDO and ENSO
– Weak correlation with the PNA pattern too.
NWS-State College
Positive EP
• Deeper than normal trough near the vicinity
of the Gulf of Alaska/ western North
America, and
– positive height anomalies are observed farther
south.
– a pronounced northeastward extension of the
Pacific jet stream toward western North America,
– enhanced westerlies over the Pacific northwestern
US, northern California, and sometimes
southwestern British Columbia.
• Last persistent positive phase of the EP from
1973-1975.
NWS-State College
Positive EP Maps
NWS-State College
Negative phase of the EP
• split-flow over the eastern North Pacific,
• reduced westerlies throughout the region.
• a confinement of the climatological mean
Pacific trough to the western North Pacific
• May result in a blocking flow configuration
farther east.
• Persistent negative phase occurred early
1992 to mid-1993.
– A period dominated by ENSO warm episode in
the equatorial Pacific,
– two distinct periods of mature ENSO conditions.
NWS-State College
EP in recent history
NWS-State College
EP and PNA in recent time
Courtesy of the cpc website
Month-Year
EP
PNA
Dec 2002
0.40
1.1
Nov 2002
-0.7
1.6
Oct 2002
-1.4
0.8
Mar 2002
0.4
-2.1
Feb 2002
0.6
-0.7
Jan 2002
0.5
-0.3
Dec 2001
1.4
0.3
NWS-State College
Pacific North American Patten
• Flow Pattern over North America and
adjacent pacific ocean
• referred to as the PNA
• The standard one is from Wallace and
Gutzler (1981) where they defined the index
as being: z=zonal component of wind
time(year)=[z(20N,160W)z(45N,165W)+z(55N,115W)+z(30N,85W)]/ 4
NWS-State College
PNA Description
• The PNA pattern is one of the most prominent
modes of low-frequency variability in the Northern
Hemispheric extra-tropics
– appearing in all months except June and July.
• The PNA pattern reflects a quadripole pattern of
height anomalies,
– anomalies of similar sign located south of the Aleutian
Islands and over the southeastern United States.
• Anomalies with sign opposite to the Aleutian center
are located in the vicinity of Hawaii, and over the
intermountain region of North America (central
Canada) during the Winter and Fall (Spring).
NWS-State College
NWS-State College
Positive PNA-January
Deep
troughs
Ridges
NWS-State College
Conclusions
• Several large scale Indices affect the flow and
climatology over North America:
–
–
–
–
North Atlantic Oscillation (NAO)
Pacific Decadal Oscillation (PDO)
Pacific North American pattern (PNA)
East Pacific Index (EP)
• The NAO relates to the flow over the Atlantic Ocean
– Modulates Atlantic jet stream into Europe
– This relates to the storm track
• The EP relates to the flow over the Pacific
– Modulates the Pacific Jet stream into North America
– This relates to the storm track
NWS-State College
Conclusions-PNA
• Pacific North American pattern (PNA)
– Quardripole over Pacific/North America
– Positive PNA is associated with
• trough over the North Pacific and southern US
• Also, a strong ridge over western North America
• Cold in eastern US
– Negative Phase
• Trough over western North America and central pacific
• Ridge over southern US and Gulf of Alaska
• Warm in eastern US
NWS-State College
PDO Summary
• Relates to ENSO cycles
– Frequency of El Nino can be related to PDO phase during the
past 30-40 years.
– PDO can interfere both constructively and destructively with
ENSO.
– PDO may not be independent of ENSO
• High NPO (warm phase)
– Cold water in north/central Pacific
– Warm water along west coast NOAM (fishing industry
named phases so obvious name is not obvious!)
– May act like a Positive El Nino trough in eastern US
• Low NPO (cold phase)
– Warm water in north/central Pacific
– La Nina like impact connect with weaker storm tracks,
farther north [dry-nation]
NWS-State College
Web resources/Credits
• NAO
• http://www.ldeo.columbia.edu/NAO/
• http://www.cru.uea.ac.uk/tiempo/floor2/data/nao.htm
• http://www.cpc.noaa.gov/data/teledoc/nao.html
• http://www.cdc.noaa.gov/USclimate/pna.html
• http://www.cpc.ncep.noaa.gov/data/teledo
c/ep.html
• http://tao.atmos.washington.edu/pdo/grap
hics.html
NWS-State College
Climatic Indices
italics-NAO Bold EP
•
•
•
•
•
•
•
•
•
•
2002
2002
2002
2002
2002
2002
2002
2002
2002
2002
1
2
3
4
5
6
7
10
11
12
0.4 1.5 -9.9 0.1
1.6 1.2 -9.9 0.8
0.5 0.5 -9.9 1.0
2.2 -0.4 0.2 -0.1
-0.7 -9.9 0.3 -0.3
0.4 -9.9 2.0 0.4
0.7 -9.9 0.6 -0.5
-1.4 1.6 -9.9 2.5
-0.5 2.0 -9.9 0.6
-1.3 1.0 -9.9 1.4
0.5
0.6
0.4
0.9
0.3
0.6
1.0
-1.4
-0.7
0.4
NWS-State College
Referemces
Rogers, J.C., 1997: North Atlantic storm track variability and its association to
the North Atlantic Oscillation and climate variability of Northern Europe.
Journal of Climate 10(7), 1635-1647.
Hurrell, J.W., 1995: Decadal trends in the North Atlantic Oscillation and
relationships to regional temperature and precipitation. Science 269, 676679.
Wallace, J.M. and David S. Gutzler, 1981:"Teleconnections in the Geopotential
Height Field during the Northern Hemisphere Winter" Mon. Wea.
Review,109,784-812.
Teleconnections Linking Wolrdwide Climate Anomalies. ed. M.H. Glantz, R.W.
Katz and N. Nicholls, Cambridge University Press, 1991.
Rogers, J.C. and H. Van Loon, 1979: "The Sea-Saw in winter temperatures
between Greenland and Northern Europe. Part II. Some atmospheric and
oceanic effectes in middle and high latitudes." Mon Wea. Rev. ,107, 509-519.
NWS-State College