northwest climate: the mean factors that influence local/regional climate: 1. latitude day length,...
Post on 20-Dec-2015
215 Views
Preview:
TRANSCRIPT
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
Winter windsand pressure over the North Pacific
Summer windsand pressure over the North Pacific
“Aleutian Low” “Subtropical High”
HH
LL
Northwest terrain maps the big-picture windsand storms onto a complex landscape
• localized cold air outbreaks
• the Puget Sound Convergence Zone
• rain shadows
The Puget Sound Convergence Zone
http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?atx_n0r+/12h/30m
The predictable part: seasonal rhythms
Puget Sound Precip
Upwelling winds at 48N
Amphitrite Pt SST
Oct Feb Jun
Oct Feb Jun
Oct Feb Jun Jan May Sep
InsolationInsolation
Year to year variations on the seasonal rhythms
Monthly Puget Sound Precip
Daily Upwelling winds
Monthly Amphitrite Pt SST
Pollen records on the Olympic Peninsula
Crocker Lake
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.
alder
cedars
pines
df
1750 1775 1800 1825 1850 1875 1900 1925 1950 1975 2000Year
5.0
5.1
5.2
5.3
5.4
5.5
Log10 mean flow, The Dalles, OR (cfs)
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.
The Dust Bowl (1929-1931) was probably not the worst drought sequence in the past 250 years
(based on Columbia Basin Tree-ring chronologies)(based on Columbia Basin Tree-ring chronologies)
red = observed, blue = reconstructed
PNW climate variability
1. What does our region’s 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?
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
Washington State Oct-Sept Average Temperature
35
38
19801960194019201900 2000
40
Washington State Oct-Sept Total Precip
4
6
19801960194019201900 2000
March 15 Snow depth anomalies at Paradise, Mt Rainier
Avg ~ 4 meters (170 inches)January 5, 2005: 48 inchesJanuary 6, 2007: 130 inches
Avg=4 meters
Water Year Columbia River streamflow
Average annual runoff at The Dalles, Oregon ~ 150 Million Acre-Feet (MAF);
Oct 2000-September 2001 ~ 100 MAF
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
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
Accumulated daily rainfall: Oct 1 1998-Sept 20 1999 A very wet year everywhere but Yakima!
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/current_impacts/global_precip_accum.html
“composite avg” PNW temperature and precipitation
during El Niño and La Niña
(based on averages of past century’s events)
EN-LN
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
1998?1925 1947 1977
Mantua et al. 1997, BAMS
Real time “nowcasts” of the PDO?
http://jisao.washington.edu/pdo
Monthly PDO index: 1982-2010
Because we don’t know how the PDO works (key mechanisms for decadal patterns remain mysterious), we can’t 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 index…
0
100000
200000
300000
400000
500000
600000
700000
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Month
Average Flow (cfs)
ColdPDO
WarmPDO
Water year stream flow composites for Columbia River “natural” flows at The Dalles, Oregon
PDO/ENSO and NW hydrology
• Because extremes in ENSO and PDO tend to favor states of the Aleutian Low that 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
The Latest Climate forecasts from the International Research Institute for Climate Prediction
iri.colombia.edu
The Latest Climate forecasts from the International Research Institute for Climate Prediction
iri.colombia.edu
Recent La Niña Year snowpack
http://www.skimountaineer.com/CascadeSki/ParadiseCraterLakeSnow.php
1998-99
Recent La Niña Year snowpack
http://www.skimountaineer.com/CascadeSki/ParadiseCraterLakeSnow.php
2000-01
Recent La Niña Year snowpack
http://www.skimountaineer.com/CascadeSki/ParadiseCraterLakeSnow.php
2005-06
top related