Climate Variability

1
ClimateVariability
Eric Salathé

• Climate Impacts GroupDepartment of Atmospheric
  SciencesUniversity of Washington

Thanks to Nathan Mantua
2
Northwest Climate the mean

• Factors that influence local/regional climate
• 1. Latitude
• day length, intensity of sunlight
• 2. Altitude
• 3. Mountain Barriers
• 4. Proximity to the ocean
• ocean currents
• 5. location relative to prevailing winds

3
Mean SLP fields

• the dominant feature shifts from the subtropical
  High in summer to the Aleutian Low in winter

4
(No Transcript)
5
Oregon Climate Service http//www.ocs.orst.edu
6
Northwest terrain maps the big-picture winds and
storms onto a complex landscape

• localized cold air outbreaks
• the Puget Sound Convergence Zone
• rain shadows

7
Arctic Blasts
8
The Puget Sound Convergence Zone
9
Annual average rainsnowfall 1961-1990
10
The predictable part seasonal rhythms
Puget Sound Precip
Insolation
Insolation
Oct Feb Jun
Upwelling winds at 48N
Oct Feb Jun
Jan May Sep
Amphitrite Pt SST
Oct Feb Jun
11
Year to year variations on the seasonal rhythms
Monthly Puget Sound Precip
Daily Upwelling winds
Monthly Amphitrite Pt SST
12
Northwest Climate Variability
13
Pollen records on the Olympic Peninsula Crocker
Lake
cedars
cool-wet
fires hot-dry
alder
df
cool
pines
McLachlan, J. S. and L. B. Brubaker. 1995 Local
and regional vegetation change on the
northeastern Olympic Peninsula during the
Holocene. Canadian J. of Botany.
14
The Dust Bowl (1929-1931) was probably not the
worst drought sequence in the past 250
years (based on Columbia Basin Tree-ring
chronologies)
red observed, blue reconstructed
Source Gedalof, Z., D.L. Peterson and Nathan J.
Mantua. (2004). Columbia River Flow and
Drought Since 1750. Journal of the American
Water Resources Association.
15
PNW climate variability
1. What does our regions climate history tell us
about natural variability? 2. How is climate
variability experienced in the Pacific
Northwest? are there patterns within the
region? are there preferred frequencies of
change (year to year, decade to decade,
etc.) 3. Why does our climate vary?
16
Warm and cool (or wet and dry) halves of the
year oct-mar versus apr-sep
17
Characteristics of variability?

• Lots of year-to-year variability in both halves
  of the year longer-term variations
• Multi-decadal cycles and century long trends
• temperatures and precipitation are more variable
  in cool season than in warm season

18
Washington State Oct-Sept Average Temperature
50
48
46
1987
1967
1947
1927
1907
2007
19
Riffe Lake, west slopes of the CascadesSpring
2001
20
March 15 Snow depth anomalies at Paradise, Mt
Rainier
Avg4 meters
Avg 4 meters (170 inches) January 5, 2005 48
inches January 6, 2007 130 inches
21
Water Year Columbia River streamflow
Average annual runoff at The Dalles, Oregon
150 Million Acre-Feet (MAF) Oct 2000-September
2001 100 MAF
22
NW Climate variability

• Why the strong climate changes?
• The chaotic nature of the climate system
• big volcanic eruptions
• natural modes of climate variability internal to
  the climate system
• in the Pacific sector, changes in ENSO and PDO
  are important factors

23
(No Transcript)
24

• Circulation changes are sensitive to the
  intensity of tropical El Nino events
• Contrast the average event with the extreme
  winters of 1982-83 and 1997-98

25
Oct 97-Mar 98 El Niño
Oct 98-Mar 99 La Niña
26
El Niño year precip anomalies Oct 1997- Mar 1998
La Niña year precip anomalies Oct 1998- Mar 1999
27
Regional patterns?

• Typically, cool-season (oct-mar) climate
  anomalies are coherent throughout most of the PNW
  region
• warm-season climate anomalies also tend to be
  regionally coherent, but to a lesser degree

28
Regional patterns?
Observations
Regional Simulation
Dry
wet
Leung et al 2003
29
Accumulated daily rainfall Oct 1 1998-Sept 20
1999 A very wet year everywhere but Yakima!
http//www.cpc.ncep.noaa.gov/products/analysis_mon
itoring/ensostuff/current_impacts/global_precip_ac
cum.html
30
(No Transcript)
31
composite avg PNW temperature and precipitation
during El Niño and La Niña (based on averages
of past centurys events)
EN-LN
32
The Pacific Decadal Oscillation

• an El Niño-like pattern of climate variability
• 20 to 30 year periods of persistence in North
  American and Pacific Basin climate
• warm extremes prevailed from 1925-46, and again
  from 1977-98 a prologed cold era spanned 1947-76

1925
1947
1977
1998?
Mantua et al. 1997, BAMS
33
October-March PDO Regression fields Maps show
typical warm PDO climate anomalies
Surface Air Temperature
Precipitation
dry
Strong Aleutian Low
Strong Aleutian Low
dry
wet
Warm
dry
dry
Figures produced by Todd Mitchell, UW/JISAO
34
A history of the PDO
A history of ENSO
warm
warm
cool
1900 1910 1920 1930 1940 1950
1960 1970 1980 1990 2000
1900 1910 1920 1930 1940 1950
1960 1970 1980 1990 2000
35
Real time nowcasts of the PDO?
Because we dont know how the PDO works (key
mechanisms for decadal patterns remain
mysterious), we cant be sure that the SST
pattern (and PDO index) is a good indicator for
where we are with this pattern. Recent years have
a variable PDO indexbut perhaps no moreso than
the late 1980s
Monthly PDO index 1900-Jan 2008
http//jisao.washington.edu/pdo
36
PDO and PNW monthly temperatures and precipitation
37
PDO and Cascades snowpack
38
Water year stream flow composites for Columbia
River natural flows at The Dalles, Oregon
39
PDO/ENSO and NW hydrology

• Because extremes in ENSO and PDO tend to favor
  either warm and wet or cool and dry
  conditions, these combinations lead to amplified
  responses in snowpack and streamflow
• Ex cold wet weather, lower snowline, more
  precipitation, more snow, less evaporation and
  more runoff

40
Cool/Warm PDO and Paradise snowdepth histograms
41
From the National Climate Data Center
www.ncdc.noaa.gov
42
A regionally averaged view of PNW cool season
Temps and precip
October-March OR-ID-WA Temperature and
Precipitation
2001
1994
1944

1977
Major drought years
43
Winter winds and pressure over the North Pacific
Summer winds and pressure over the North Pacific
L
L
H
H
Subtropical High
Aleutian Low
44
(No Transcript)