Synoptic Dendroclimatology : Establishing Mechanistic Linkages between TreeRings, Climate and Atmosp

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Synoptic Dendroclimatology Establishing
Mechanistic Linkages between Tree-Rings, Climate
and Atmospheric Circulation  Katherine K.
HirschboeckDavid M. Meko Fenbiao
Ni Laboratory of Tree-Ring Research University
of Arizona
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• PURPOSE
• To explore and establish mechanistic linkages
  between
• tree-rings
• climate
• atmospheric circulation

Synoptic Dendroclimatology Approach
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BASIC PREMISE Climatic changes may manifest
themselves as temperature (T) and precipitation
(P) changes, but T P are delivered by synoptic
atmospheric circulation processes

• Critical missing link in dendroclimatology
• Circulation-based methods underutilized
• Wide array of weather-related variables (e.g.,
  dewpoint temperatures, frontal passages, etc.)
  may be linked to tree growth

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Synoptic dendroclimatology using dated tree
rings to study and reconstruct present and past
climates from the viewpoint of the climates
constituent weather components and the way in
which these components are related to atmospheric
circulation at all scales" (Hirschboeck et
al., 1996)
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Climate Variable
Time Series
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PROJECT Synoptic Dendroclimatology in Western
United States
Rawindsonde measurements at 700 mb
Elevation of 700 mb surface 2700 - 3000 meters
(winter)
7 Sites in Western U.S.
Elevation of trees 1100 3000 meters
Funding from NOAA Paleoclimate Program GC96-188
Katie Hirschboeck, Dave Meko, Fenbiao Ni,
Gregg Garfin, Matt Salzer (Bob Maddox)
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METHODS

• Seasonally- and annually-dated tree-ring time
  series
• 7 climatically sensitive geographically
  diverse sites in western United States
• Linked with variables derived from observed
  meteorological data

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• Large-scale circulation patterns defined using
  spatial correlation fields

Correlation fields
Correlation Fields
Tree-ring series
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• Composite maps of 700 mb geopotential heights
  compiled for key growth-sensitive seasons during
• narrow-ring years
• wide-ring years
• average-width years -- for each site

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Mid-tropospheric SOUNDING DATA (nearest upstream
rawinsonde station)

• Threshold criteria established to identify the
  passage of short-wave 700 mb troughs and ridges
• 700 mb heights
• 700 mb temperature
• Relative humidity
• Dewpoint temperature observations
• Variables created by calculating the of days
  above or below specified thresholds from the
  long-term daily mean (e.g., of 700 mb troughs,
  days w/ low 700 mb R.H., days w/ cold 700 mb
  temps)

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Optimal tree-ring/climate window (i.e., "season")
defined for use in linking atmospheric sounding
data with the ring-width series at each site
Output error (OE), linear dynamic time series
model, (adapted by Meko, 1995 based on Ljung,
1987)
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• Correlated frequency-based meteorological
  variables w/ ring-width series, using each site's
  optimal climatic window

• Surface climate variables (temp precip) ?
  traditional response functions

Keen Camp Summit
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Keen CampNarrow ring 1961
700 mb height(m)
Wide ring 1973
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Responding to winter spring precipitation
Reno Gulch, SD Site
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More frequent persistent ridges
Reno GulchNarrow ring 1985
Rapid City Sounding data 700 mb heights
Deep, persistent trough frequent recurrence of
troughs
Wide ring 1990
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Reno Gulch Narrow ring 1985
Wide ring 1990
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Reno Gulch, S.D.
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Growth positively correlated with Rapid City
of 700 mb troughssounding days with high
relative humidity of days with cold 700 mb
temps
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Reno Gulch, S.D.
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Composite Map
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Growth inversely correlated with Rapid City
of 700 mb ridgessounding days with low
relative humidity of days with warm 700 mb
temps
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H
Horse Ridge, OR
Growth inversely correlated with Boise of
700 mb ridgessounding of days with warm 700
mb temps
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Horse Ridge, OR
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Boise sounding Growth positively correlated with
of 700 mb troughs in Fall / Winter
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L
H
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RESULTS

• (1) Spatial correlation fields and composite
  maps show distinct seasonal "signature"
  circulation patterns at each site.
• These patterns are
• consistent
• physically plausible
• meteorologically coherent
• explainable by tree-ring/climate response
  functions

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(3) Spatial correlation fields similar in
pattern to the composites of wide-ring years (4)
Narrow ring-width composites resemble inverse
of wide-ring composites correlation
fields. (5) Average growth year composites
unique -- different from both wide narrow ring
composites (suggesting circulation patterns
typical of non-extreme meteorological conditions )
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• Significant correlations between
  rawinsonde-based variables ring-width
  variations varied from site to site
• Each suite of significant variables
  explainable from a process-based perspective
• Daily mid-tropospheric sounding data CAN be
  linked to ring-width variations

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(9) Mid-tropospheric observations, taken in the
"free atmosphere" via atmospheric soundings, may
be better indicators of the weather climate
conditions directly affecting mid- to high-
elevation sites than observations from the
nearest surface climate stations . . . . . .
which are often at much lower elevations often
not very representative of the daily variations
in climate at the tree-ring site -- especially in
regions of complex terrain
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How useful for CLIMATE CHANGE studies? . . .
toward Mechanistic Climatic Reconstructions
Eagle, CO
Fenbiao Ni (2000)
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CIRCULATION ANOMALY CENTER (CAC)
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Reconstructed CAC Index
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Keen CampNarrow ring 1961
Wide ring 1973