Teleconnection Systems NAO AO PNA By: Michael Vuotto and Jake Mulholland

What is a Teleconnection System? - Are recurring and persistent, large-scale pattern of pressure and circulation anomalies that spans vast geographical areas. -What are the main systems that forecasters look at to determine what a season may be like?? There are several systems that meteorologists look at and the first is the NAO- North Atlantic Oscillation.

NAO- (North Atlantic Oscillation) Is a cycle that repeats itself. Can range anywhere from a few months to several years. What is the NAO? A fluctuation in the intensity of the Iceland low-pressure zones southeast of Greenland and the sub-tropical high-pressure zone northwest of Africa, over the Azores. Controls the strength and direction of the westerlies and storm tracks across the North Atlantic. Causes??

Causes Fluctuations and movements in this air pressure pattern control the strength and direction of the westerlies and storm tracks across the North Atlantic. Which?? Affects Temperature Affects Precipitation Where? New England, Western Europe, Siberia, eastern Mediterranean south to west africa.

Negative NAO phase

Positive NAO

NAO- North Atlantic Oscillation Forecast (Mid-to Late October)

PNA- Pacific/ North American Pattern Also can be positive or negative Relates atmospheric circulation pattern over the North Pacific Ocean with the one over the North American continent. Associated with strong fluctuations in the strength and location of the East Asian jet stream. Strongly influenced by the El-Nino-Southern Oscillation (ENSO) phenomenon.

Positive Phase Above-average barometric pressure heights near Hawaii and over the inter-mountain region of North America as well as below- average heights south of the Aleutians. Associated with and enhanced East Asian jet stream, eastward shift in the jet exit region toward the western United States. Look for above-average temps over Western Canada and the extreme western U.S as well as below normal temps in the south-central to southeast U.S. Little impact in the summer. Above-normal precip in Alaska to the Pacific Northwestern U.S. and below normal precip in the Midwest. (Negative phase has opposite effect) Tends to be associated with Pacific warm Episodes (El-Nino)

Negative Phase Associated with a westward retraction of the jet stream toward eastern Asia, blocks activity over high latitudes of Pacific. Strong-split flow configuration over the Central North Pacific. Pacific cold episodes (La Nina).

PNA- Pacific/ North American Pattern

Arctic Oscillation (AO) Also Northern Annular Mode/ Northern Hemisphere Annular Mode(NAM) Index of dominant pattern of non-seasonal sea-level pressure variations north of 20˚N latitude. Characterized by pressure anomalies of one sign in the Arctic with the opposite anomalies centered about 37-45N.

Arctic Oscillation in both phases

Positive Phase -Surface pressure is low in the polar region. -Helps the middle latitude jet stream to blow strongly and consistently from west to east, thus keeping cold Arctic air locked in the polar region . -drives ocean storms farther north, and changes the circulation pattern bring wetter weather to Alaska, Scotland, and Scandinavia and drier conditions to the western U.S and the Mediterranean. -frigid arctic air doesn’t extend as far into middle North America as would the negative phase. - East of Rockies warmer than normal and opposite in the negative phase.

Negative Phase Tends to be high pressure in the polar region, weaker zonal winds, and greater movement of frigid polar air into the middle latitudes.

EL-Nino- Southern Oscillation Is a quasiperiodic climate pattern tht occurs in the Pacific Ocean off of the Mexico, South America coastline about every 5 years . It refers to variations in temperature of the ocean surface temperature on Pacific Ocean surface. When the ocean is cooler than normal (Low pressure)in this area then we have La Nina which is the opposite of EL Nino When the ocean is warmer than normal (high pressure in the western Pacific) in this area then we have EL Nino which is the opposite of La Nina.

EL Nino-Signs Defined as prolonged differences in the Pacific ocean sea surface temperatures when compared with the average value. 1. Rise in surface pressure over the Indian Ocean , Indonesia and Australia. 2.Fall in air pressure over Tahiti and the rest of the central and eastern Pacific Ocean. 3. Trade winds in the South Pacific weaken or head east. 4. Warm air rises near Peru, causing rain in the northern Peruvian deserts. 5. Warm water spreads from the west Pacific and the Indian Ocean to the east Pacific. When this occurs rainfall becomes sparse and extensive drought in the western Pacifc and causes rainfall in the normally dry of the Pacific.

Southern Oscillation Oscillation in surface air pressure between the tropical Eastern and Western Pacific Ocean waters. Strength of the Southern Oscillation Index(SOI) is computed from the fluctuations in surface air pressure difference in Tahiti and Darwin, Australia. El-Nino- negative SOI La Nina- Positive SOI

Effects During an El-Nino, look for the winters in the United States to be warmer and drier than average across the Northeast, Midwest and the Northwest. Wetter winters in Northwest Mexico and southwest region of the U.S including southern and central California. Wetter and cooler than normal in Northeast Mexico and the southeast U.S.

Effects cont. La Nina Mostly the opposite of El-Nino above-average precipitation across the North Midwest, the Northern Rockies, Northern California, and the Pacific Northwest's southern and eastern regions. Meanwhile there is below-average precipitation in the southwestern and southeastern states.

EL-Nino in the Equatorial Pacific White shading warmer than normal temperatures.

Warm Episode relationships-Impacts

La-Nina Impacts- Cold Episode

Questions?? Hope y’all enjoyed it  Picture of the Blizzard of December 26-27 2010 during the approach of the La- Nina phase.