Atmospheric Variability
 Why was it so cold winter 2010-2011 or
winter 2013-2014?
 Why was it so hot summer 2010?
 Why was it so dry in 2007?
 Why was it so wet in 1998, 2009 (fall)?
 Are these extremes becoming more
common? Why or why not?
 Does variability in atmospheric flow patterns
fully answer these questions?
Atmospheric Variability
 Temporal

weekly, monthly, seasonal, annual, decadal
 Spatial (x,y)

Global, synoptic, regional, mesoscale,
microscale, sub-micro
 Vertical (z)

Surface, 1000mb, 925, 850, 700, 500, 300
 Trends?

Natural or anomalous
What is a teleconnection
 AMS:
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1. A linkage between weather changes occurring in widely
separated regions of the globe. 2. A significant positive or
negative correlation in the fluctuations of a field at widely
separated points. Most commonly applied to variability on
monthly and longer timescales, the name refers to the fact
that such correlations suggest that information is
propagating between the distant points through the
atmosphere.”
Pressure fluctuations
SST
Height anomalies (700, 500mb)
Associations with circulation indices
http://www.esrl.noaa.gov/psd/data/climateindices/list/
The North Atlantic Oscillation (NAO)
 Pressure dipole in North Atlantic centered near
Iceland/Greenland and over the Azores


Icelandic Low vs Azores High
Tendency for either both weak or both strong
 Dominant mode of Variability in Atlantic
 Winter
 The NAO index is obtained by projecting the NAO loading
pattern to the daily anomaly 500 millibar height field over 090°N. The NAO loading pattern has been chosen as the first
mode of a Rotated Empirical Orthogonal Function (EOF)
analysis using monthly mean 500 millibar height anomaly data
from 1950 to 2000 over 0-90°N latitude. (NCDC)
The North Atlantic Oscillation
The North Atlantic Oscillation
Dec – March Temp correlations
Dec – March Precip correlations
58.0
Bama state averaged
temp Dec-Feb
53.0
48.0
43.0
38.0
2009
2004
1999
1994
1989
1984
1979
1974
1969
1964
1959
1954
1949
Arctic Oscillation (AO) or NHam
 Cyclonic circulation of upper level winds
around the Arctic

Latitude poleward of 55°N

Positive = stronger winds- confines Arctic air
 More zonal

Negative = relaxed winds- Arctic air oozes
southward
 AO index is obtained by projecting the AO loading pattern to the
daily anomaly 1000 millibar height field over 20°N-90°N latitude
Winter AO
58.0
Bama state averaged
temp Dec-Feb
53.0
48.0
43.0
38.0
2009
2004
1999
1994
1989
1984
1979
1974
1969
1964
1959
1954
1949
Current Phase
Pacific North American (PNA)
 Quadripole pattern of 500mb height anomalies
 All months except June and July
 winter
 Center locations
 Similar signs south of Aleutians and over SE U.S.
 Hawaii and InterMountain U.S. and Canada
 The PNA index is obtained by projecting the PNA loading
pattern to the daily anomaly 500 millibar height field over 090°N. The PNA loading pattern has been chosen as the second
mode of a Rotated EOF analysis using monthly mean 500
millibar height anomaly data from 1950 to 2000 over 0-90°N
latitude.
PNA
58.0
Bama state averaged
temp Dec-Feb
53.0
48.0
43.0
38.0
2009
2004
1999
1994
1989
1984
1979
1974
1969
1964
1959
1954
1949
El Nino Southern Oscillation (ENSO)
 Both a SST and pressure fluctuation in the
tropical Pacific
 ~ 5-7 year periodicity
 Most significant atmospheric/oceanic
coupling in the world
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El Nino = warmer than normal SST
La Nina = colder than normal SST
Southern oscillation= pressure flip-flop
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_update/sstanim.shtml
Southern Oscillation Index (SOI)
 Standardized difference in MSLP between
Darwin Australia and Tahiti (T-D)
 Pressure normally higher over Tahiti and
lower over Darwin

Slow east to west flow of tropical water
Nino Regions
Oceanic Nino Index
 Running mean of the Nino
3.4 region

At least 5 consecutive
overlapping months above
(below) 0.5°C sst anomaly
ENSO Impacts
Alabama Impacts
http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ENSO/box_whiskers/index.php
Pacific Decadal Oscillation (PDO)
 Discovered 1996 (Hare and Mantua)

Leading principal component of Northern
Pacific SST variability
 Similar to ENSO


Long-lived ENSO
Greater SST variability in mid latitiude Pacific
Pacific Decadal Oscillation (PDO)
Positive
Negative
El Nino vs positive PDO
Table 1: summary of North American climate anomalies associated with extreme phases
of the PDO.
climate anomalies
Warm Phase PDO
Cool Phase PDO
Ocean surface temperatures
in the northeastern and
tropical Pacific
Above average
Below average
October-March
northwestern North
American air
temperatures
Above average
Below average
October-March
Southeastern US air
temperatures
Below average
Above average
October-March southern
US/Northern Mexico
precipitation
Above average
Below average
October-March
Northwestern North
America and Great
Lakes precipitation
Below average
Above average
Northwestern North
American spring time
snow pack
Below average
Above average
Winter and spring time flood
risk in the Pacific
Northwest
Below average
Above average
Thermohaline Circulation
Atlantic Multidecadal Oscillation
(AMO)
 Fluctuation in detrended SST in north Atlantic (0 –
70°N)
 AMO index 10 year running mean
 Relationships to speed of thermohaline circulation
AMO and
hurricane activity
AMO and
hurricane activity
PDO and AMO
drought
Quasi Biennial Oscillation (QBO)
 Oscillating (E-W) stratospheric winds 10 –
100 mb above the equator
 20 – 36 month periodicity

Impacts

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Spike in ATL hurricane activity during west
(positive) zonal flow
May impact Asian monsoon and ENSO
Quasi Biennial
Oscillation
(QBO)
Madden Julian Oscillation
 30 – 60 day oscillation, Tropical Indo-Pacific
 Eastward wave propagation of anomlaous rainfall low
OLR

4-8 m/s
 Impacts trop and subtrop, precip, temp, and
circulation
 Most prominent NH winter
 U.S. Impacts

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Increase frequency/intensity west coast precip
Eastern cold air outbreaks
 http://web.archive.org/web/20070612204448/http://w
ww.apsru.gov.au/mjo/index.asp
Madden Julian Oscillation
MJO- OLR and pressure
MJO Phase Diagram
http://www.cpc.ncep.noaa.gov/
products/precip/CWlink/MJO/C
omposites/Precipitation/
MJO and Atlantic Hurricanes
 Phase 1 and 2 support a more active regime
of Atlantic convection
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ACE > 76
91.5 major hurricane days (1974 – 2007)
 Phase 6 and 7 less active
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ACE < 36
20.5 major hurricane days (1974 – 2007)