The North Atlantic Oscillation (NAO) - PowerPoint PPT Presentation

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The North Atlantic Oscillation (NAO)

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  1. The North Atlantic Oscillation (NAO) Jenny Kafka

  2. What is the nao? • Discovered by Sir Gilbert Walker in early 20th century • Based upon the difference in surface sea-level pressure between the Subtropical High (Azores) and the Subpolar Low (Iceland) One of many teleconnection Indices • Describes a recurring and persistent large-scale pattern of pressure and circulation anomalies • Gives us an understanding of climate variability

  3. importance • Positive Phasevs. Negative Phase • The NAO shapes the weather patterns over much of the Northern Hemisphere (especially in winter) e.g. Negative phase associated with cold & snowy winters in Northeast

  4. Time Scale ~ 20 years ~ 20 years • Can switch between modes in a matter of weeks, but one mode tends to dominate over a given year • Multi-decadal trends tend to persist

  5. the naoand the ocean • HIGH FREQUENCY RESPONSE (Seasonal to interannual) • Correlation between NAO phase and SST temperature  “NAO SST tripole” • + NAO: - SST anomaly by Greenland; + SST anomaly off US coast • - NAO: + SST anomaly by Greenland; - SST anomaly off US coast Visbeck et al. 2003

  6. the naoand the ocean HIGH FREQUENCY RESPONSE (Seasonal to interannual) - Observed response of wind stress pattern changes + NAO: Stronger westerlies; slightly stronger easterlies - NAO: Weaker westerlies; slightly weaker easterlies Visbeck et al. 2003

  7. the naoand the ocean LOW FREQUENCY RESPONSE (SEVERAL YEARS TO DECADES) - Strength/position of boundary currents  0-3 years to adjust - Meridional Overturning Circulation (MOC)  10+ years to adjust - Downstream movement of +SST anomaly - Loss of -SST anomaly over sub polar gyre Visbeck et al. 2003

  8. REsources • "Climate Prediction Center - North Atlantic Oscillation (NAO)." Climate Prediction Center - North Atlantic Oscillation (NAO). National Weather Service, n.d. Web. 02 Dec. 2013. <http://www.cpc.ncep.noaa.gov/data/teledoc/nao.shtml>. • Henson, Bob. "Twisters and Teleconnections." AtmosNews. NCAR UCAR, n.d. Web. 03 Dec. 2013. <https://www2.ucar.edu/atmosnews/opinion/6717/twisters-and-teleconnections>. • "North Atlantic Oscillation." Columbia University, n.d. Web. 02 Dec. 2013. <http://www.ldeo.columbia.edu/res/pi/NAO/>. • "North Atlantic Oscillation (NAO)." National Climatic Data Center (NCDC). N.p., n.d. Web. 03 Dec. 2013. <http://www.ncdc.noaa.gov/teleconnections/nao.php>. • Visbeck, M., Chassignet, E. P., Curry, R. G., Delworth, T. L., Dickson, R. R. and Krahmann, G. (2013) The Ocean's Response to North Atlantic Oscillation Variability, in The North Atlantic Oscillation: Climatic Significance and Environmental Impact (eds J. W. Hurrell, Y. Kushnir, G. Ottersen and M. Visbeck), American Geophysical Union, Washington, D. C.. doi: 10.1029/134GM06