Transcript Document

Climate Variables used in Dendrochronology
Tree-ring data are just one type of many proxies of past climate.
Tree-ring data are extremely valuable for evaluating past
changes in temperature, for example. Why is past information
needed?
To better understand trends in future climate, whether humanforced or natural.
Trends in reconstructed Northern Hemisphere temperatures.
Trends in reconstructed precipitation for the American Southwest.
Recent research emphasizes relationships between trends in treering data and long-term climate oscillations.
Which climate variables can we analyze from the tree-ring
record?
Precipitation:
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Monthly
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Seasonal
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Water Year
Temperature:
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Monthly
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Seasonal
Palmer Drought Severity Index (PDSI)
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Monthly
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Seasonal
Palmer Hydrological Drought Index (PHDI)
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Monthly
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Seasonal
Where do these data come from?
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National Climatic Data Center
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FTP site for monthly divisional data:
ftp://ftp.ncdc.noaa.gov/pub/data/cirs/
Climate Data Row Header:
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Example: 0101011895
State
code
Division Climate
number Type
Year
0101011895
Climate Data Types:
01 = Precipitation
02 = Temperature
03 = Heating Degree Days
04 = Cooling Degree Days
05 = PDSI
06 = PHDI
07 = Z-Index
08 = PMDI
71 = SP01
72 = SP02
73 = SP03
74 = SP06
75 = SP09
76 = SP12
77 = SP24
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El Niño-Southern Oscillation
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Changes in pressure patterns, wind patterns, and
oceanic circulation
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Mainly concentrated in the Pacific Ocean
Measured using Southern Oscillation Index
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Differences in pressure observed in Tahiti and
Darwin, Australia
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SOI = 10 x ((average Tahiti MSLP for month) (average Darwin MSLP for month) - long term
average difference for month) / long term standard
deviation of difference for month)
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Combined to form ENSO phenomenon
Brings drastic changes in weather to affected areas
Different El Niño-Southern Oscillation Indices based on
region of the Pacific Ocean:
The Niño 3 Region is bounded by 90°W-150°W and 5°S5°N. The Niño 3.4 Region is bounded by 120°W-170°W and
5°S- 5°N.
Normal ocean temperatures
The big slosh of warm ocean temps to the eastern Pacific.
Warm ocean
temps where
they should be.
What changes in
climate can be
expected?
Much colder
temps now in
eastern Pacific.
The NINO 3.4 Index is “the departure in monthly sea surface
temperature from its long-term mean averaged over the
NINO 3.4 region.”
In this method, an El Niño or La Niña event is identified if the
5-month running-average of the NINO 3.4 Index exceeds
+0.4 °C (for El Niño; -0.4 °C for La Niña) for at least 6
consecutive months.
Pacific Decadal Oscillation
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Discovered late 1990s by salmon fisheries experts
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Long-lived El Niño-like pattern of Pacific climate
variability
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Operates on longer 20 to 30 year periods
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Note when regime shifts occurred…
Pacific Decadal Oscillation
Warm phase PDO
Pacific Decadal Oscillation
Cool phase PDO
Climate during positive (warm) PDO phase:
Mantua, N.J. 1999. The Pacific
Decadal Oscillation and climate
forecasting for North America. In
Maryam Golnaraghi (ed), Climate
Risk Solutions 1(1): 10-13.
http://www.atmos.washington.edu/~mantua/REPORTS/PDO/PDO_cs.htm
Climate during positive (warm) PDO phase
Mechanisms:
• Warm ocean waters in the eastern Pacific.
• These give rise to development of low pressure troughs.
• Jet stream allowed to track further south.
• Brings moisture to southern tier of U.S., especially southwestern U.S.
• Causes dry, warm (drought) conditions in northwestern U.S.
• Note “polar” relationship between the two western regions.
• Fire weather enhanced in northwestern U.S. during +PDO phase
(“fires tended to occur during El Niño and positive PDO years.”)
• Wet, mild weather in southwest = rapid growth of fuels
• La Niña phase causes drying of fuels = fire weather in southwest.
Table 1: Summary of North American climate anomalies associated with extreme
phases of the PDO (from Mantua 1999):
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
Although the PDO exhibits several patterns of behavior, the most
significant one seems to be in regime shifts between "warm" and
"cool" patterns which last 20 to 30 years.
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1750: PDO displays an unusually strong oscillation.
1905: After a strong swing, PDO changed to a weak warm phase.
1925: Warm phase significantly strengthens.
1946: PDO changed to a cool phase.
1977: PDO changed to a warm phase.
1998: PDO index showed several years of cool values, but did
not remain in that pattern.
• 2008: The early stages of a cool phase of the PDO??
• Current: PDO appears to be transitioning!
• During the 1900s, PDO regime shifts were related to many
different environmental changes in the Pacific Ocean.
Pacific Decadal Oscillation
PDO reconstructed from tree-ring data.
Pacific Decadal Oscillation
PDO reconstructed from tree-ring data.
Pacific Decadal Oscillation
PDO-SOI reconstructed from tree-ring data.
“We also observed that CPYs became more numerous during the 20th
century (beginning with the severe drought year of 1924) after a long
absence of severe regional drought years between 1717 and 1923. This
relationship possibly suggests that the influence of the PDO was
nonexistent or minimal during the period 1717–1923, ” – Paul Knapp,
Henri Grissino-Mayer, and Peter Soule, 2002, Quaternary Research.
El Malpais trees recording PDO? What the… ?
North Atlantic Oscillation
• Large scale seesaw in
atmospheric mass between
the subtropical high and the
polar low
• Dominant mode of winter
climate variability in the North
Atlantic region ranging from
central North America to
Europe
• Again, note where shifts
occurred…
North Atlantic Oscillation
North Atlantic Oscillation: Positive Phase
Strong Atlantic pressure gradient
North Atlantic Oscillation: Negative Phase
Weak Atlantic Pressure Gradient
North Atlantic Oscillation
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Positive Phase:
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More frequent and stronger winter storms crossing
Atlantic on a more northerly track
Results in warm and wet winters in Europe and in cold
and dry winters in northern Canada and Greenland
Eastern US experiences mild and wet winter conditions
Negative Phase:
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Fewer and weaker storms on a more southerly track
Brings moist air into the Mediterranean and cold air to
northern Europe
Eastern US experiences more cold air outbreaks and
snowy weather conditions
E. Cook, R. D’Arrigo, and M. Mann, 2002. A well-verified, multiproxy
reconstruction of the winter North Atlantic Oscillation Index since A.D. 1400.
Journal of Climate 15: 1754-1764.
0.6
Precip
Temp
PDSI
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0.5
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0.4
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0.3
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0.1
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Aug
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July
0.2
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0
-0.1
-0.2
Dec
Nov
Oct
Sept
June
May
April
March
Feb
Jan
Prev. Dec
Prev. Nov
Prev. Oct
Prev. Sept
Prev. Aug
Prev. July
Prev. June
Prev. May
-0.3
Figure 2. Correlation coefficients between the shortleaf pine standard
chronology and precipitation, temperature, and PDSI (* p < 0.05, ** p < 0.01,
*** p < 0.001).
Figure 7. Correlation coefficients between the shortleaf pine standard
chronology and PDO, NAO, and SSTA (* p < 0.05, ** p < 0.01, *** p < 0.001).
Atlantic Multidecadal Oscillation
• A multidecadal (20-40 yrs) pattern of North Atlantic sea surface
temperature variability between the equator and Greenland.
• When the AMO is positive (warm Atlantic), rainfall is lower than
average over most of the United States.
• During warm phases of the AMO, the number of tropical storms that
mature into severe hurricanes is much greater than during cool
phases.
• Since the mid-1990s, we have been in a warm phase.
• Appears related to the past occurrence of major droughts in the
Midwest and the Southwest. Positive AMO = more frequent and
severe droughts, and vice-versa.
• Two of the most severe droughts of the 20th century occurred during
the positive AMO between 1925 and 1965: The Dust Bowl of the
1930s and the 1950s drought.
Atlantic Multidecadal Oscillation
Atlantic Multidecadal Oscillation
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Rainfall in central and south Florida becomes more
plentiful during a warm phase AMO, and droughts and
wildfires are more frequent in the cool phase.
Atlantic Multidecadal Oscillation
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52% of drought variability in the lower U.S. can be attributed
to the AMO and PDO! (Blue = wet, red = drought)
+ PDO - AMO
+ PDO + AMO
(Drought frequency in percent of years.)
- PDO - AMO
- PDO + AMO
Atlantic Multidecadal Oscillation
Accumulated Cyclone Energy by Year
Atlantic Multidecadal Oscillation
AMO reconstructed from tree-ring data.
One final note on oscillations:
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“Some feature of the atmosphere can always be found that
will oscillate in accordance with your hypothesis.”
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“Shortly after its discovery the oscillation will disappear.”
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Peter B. Wright, 1971. Quasi-biennial oscillations in the
atmosphere. Weather 26: 69–76.
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In 2007, Grissino-Mayer et al. discover “NAFO.”