Air-sea interaction: climate variability · PDO drivers • changes in ocean surface heat fluxes...
Transcript of Air-sea interaction: climate variability · PDO drivers • changes in ocean surface heat fluxes...
Air-sea interaction: climate variability
ATM2106
Climate variability v.s. climate change
• “Climate variability” : natural variability
• Natural “modes” of variability
• “Climate change” : anthropogenic forcing
• Due to man-made changes in greenhouse gases, land surfaces, species distributions, etc.
Elements of the climate system
• Sun
• Atmosphere
• Ocean
• Cryosphere (ice, snow)
• Land surface
• Biological and chemical cycles
Climate forcing
• External forcing
• Earth orbit parameters (solar distance factors)
• Solar luminosity
• Moon orbit
• Volcanoes and other geothermal sources
• Greenhouse gases…
Climate forcing
• Internal forcing : forcing between each element of the climate system
• Wind forcing to the ocean
• Ice extent forcing to the atmosphere or the ocean
Natural climate modes with interannual to millennial time scales
• Interannual : 1 year to 10 years
• ENSO
• Decadal : 10 years to multiple decades
• Pacific Decadal Oscillation
• North Atlantic Oscillation
• Southern Annular Mode
• Centennial : multiple hundreds years
Mean sea level pressure
Aleutian Low
Mean sea level pressure
Coastal upwelling
From https://www.nwfsc.noaa.gov/research/divisions/fe/estuarine/oeip/db-coastal-upwelling-index.cfm
Coastal upwelling
Figure from Capone and Hutchins, (2013)
Empirical orthogonal function (EOF)
EOF using sea surface temperature anomaly in the N. Pacific
Teleconnection
Teleconnection
From https://ds.data.jma.go.jp/tcc/tcc/products/elnino/decadal/pdo_doc.html#PDO_SLP
W I N D - S S T I N L A R G E S C A L E
MIXING
MORE MIXING
W I N D - S S T I N L A R G E S C A L E
Correlation between wind speed and SST
2000-2009 satellite wind and SST data A credit to Dr. Hyodae Seo (WHOI)
Oceanic response to the atmosphere
Teleconnection
From https://ds.data.jma.go.jp/tcc/tcc/products/elnino/decadal/pdo_doc.html#PDO_SLP
Pacific Decadal Oscillation
From https://www.climate.gov/sites/default/files/HR_PDO2005-2008.jpg
Warm phase Cold phase
PDO v.s. ENSO
From http://ffden-2.phys.uaf.edu/645fall2003_web.dir/Jason_Amundson/enso.htm
PDO v.s. ENSO
• Time scale
• PDO events persist for 20 to 30 years
• ENSO events persist for 6 to 18 months
• The climate fingerprints
• PDO in the North Pacific / North American sector
• ENSO in the tropics
From http://research.jisao.washington.edu/pdo/
PDO index
From https://www.nwfsc.noaa.gov/research/divisions/fe/estuarine/oeip/ca-pdo.cfm
Impact of a warm phase of PDO on climate
L
1. Deepening of Aleutian low2. Stronger wind over the Pacific > Cooler water temperature 3. Stronger southerly wind in the Northwest N. America > Warmer climate4. Weakening of the equatorial wind along the California coast > poorer ocean
Impact of PDO on climate
Figure from http://the-mound-of-sound.blogspot.kr/2015/03/coming-soon-great-warming-spurt.htmlAnd https://www.climate.gov/sites/default/files/LosNinoshighpressure_0.jpg
El Nino
La Nina
PDO drivers
• changes in ocean surface heat fluxes and Ekman (wind-driven) transport related to the Aleutian low • local unpredictable weather noise • remote forcing from interannual to decadal tropical variability
(largely El Niño) via the “atmospheric bridge” • ocean memory, or processes determining oceanic thermal inertia
including “re-emergence”, that act to integrate this forcing and generate the decadal variability of the PDO
• decadal changes in the Kuroshio-Oyashio current system, forced by winds over the North Pacific driving westward propagating oceanic Rossby waves, manifested as SST anomalies along the subarctic front at about 40ºN in the western Pacific ocean
Impact of PDO on the climate of east Asia
From Zhao et al., 2016
Haze day
Impact of PDO on the climate of east Asia
From Zhao et al., 2016
Impact of PDO on the climate of east Asia
Sea surface temperature near the Korean Peninsula
Kim et al., 2011