Teleconnections Zach Hiris/Phil Pascarelli

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1 Teleconnections Zach Hiris/Phil Pascarelli
Images Provided by Jeff Haby & NC State Climate Office

2 What is a Teleconnection?
A teleconnection is a recurring and persistent, large-scale pattern of pressure and circulation anomalies that spans vast geographical areas. A few teleconnections El Nino Southern Oscillation (ENSO) North Atlantic Oscillation (NAO) Pacific/North American pattern (PNA) Arctic Oscillation (AO) East Pacific Oscillation (EPO)

3 El Nino Southern Oscillation
Measure of equatorial sea surface temperature anomalies from the South American coast to approximately 160° E It is also a measure of pressure anomalies between Darwin, Australia and Tahiti (Southern Oscillation Index) El Nino- Positive SST anomalies in these regions La Nina- Negative SST anomalies in the same regions El Nino/La Nina both occur approximately once every 5 years Currently in one of the strongest El Ninos on record

4 El Nino- Cause & Effects
El Ninos generally feature a rise in surface pressures over the Indian Ocean, with lower pressures near Tahiti and the Central/East Pacific Weak trade winds in the South Pacific The weakening of easterly trades allows warm water to spread east towards the South American coast Strong Westerly Wind Bursts (WWB) can help “push” these warmer waters east

5 El Nino SST Pattern

6 El Nino Effects The general pattern for an El Nino features warmer temperatures over Alaska and Western Canada, with cooler temperatures over the Southeast U.S. Portions of California through the southern Plains receive above average rainfall as part of the “Pineapple Express”

7 La Nina Generally opposite of El Nino, with stronger trade winds and cooler water over the central and eastern equatorial Pacific Stronger trade winds also suppress convection across the Pacific, leading to a weaker southern jet and less precipitation for the southern portion of the U.S.

8 La Nina Effects

9 North atlantic Oscillation (NAO)
Consists of a High Pressure over the Azores and a Low Pressure over Iceland Phase of the NAO depends on the pressure difference between the systems During the positive phase the individual pressure systems increase in strength and this increases the strength of the westerlies This corresponds to a warmer and wetter pattern in the eastern United States During the negative phase the individual pressure systems weaken and the westerlies weaken. This corresponds to a colder pattern over the eastern United States When the low pressure is near 50 N and 50 W, there is increased likelihood of East Coast Storms

10 NAO Examples

11 NAO Correlation During Winter
Correlation between NAO and surface temperatures During a +NAO, there is a strong correlation to above normal temperatures over the East During a -NAO, the opposite is true

12 Arctic Oscillation (AO)
Measure of the state of the atmospheric circulation over the Arctic Positive Phase Below normal geopotential heights (Lower than normal pressures) Polar Vortex becomes much stronger Increases wind speeds, which does not allow cold air to drift south away from the Arctic Negative Above normal geopotential heights (higher than normal pressure) Polar Vortex becomes weaker, easily displaced Arctic air more likely to drift into US/Europe

13 Arctic Oscillation Positive Phase

14 Arctic Oscillation Negative Phase

15 Dr. Cohen & The Snow Advance Index (SAI)
Dr. Judah Cohen has created a new climate index called the Snow Advance Index (SAI) The SAI measures the advance of snowcover in Eurasia during the month of October Theorizes that rapid snow growth amplifies the jet stream, allowing warmer air into the poles Leads to a -AO!

16 Pacific/North American Oscillation (PNA)
One of the most significant oscillations in the Northern Hemisphere The PNA pattern reflects a quadripole pattern of 500 millibar height anomalies, with anomalies of similar sign located south of the Aleutian Islands and over the southeastern United States. Anomalies with sign opposite to the Aleutian center are located in the vicinity of Hawaii, and over the intermountain region of North America (central Canada) during the winter and fall. (NCDC) If there is lower Geopotential heights (negative anomalies) over the Aleutians, this leads to positive anomalies (Ridge) over the West, and negative anomalies (Trough) over the southeast U.S. Relates the atmospheric circulations over the North Pacific Ocean with the North American continental circulation

17 PNA- Positive Phase

18 PNA- Negative Phase

19 Eastern Pacific Oscillation (EPO)
Similar to the PNA, but with a different specific region of focus Generally speaking, a +EPO features a strong low over Alaska, with High Pressure to the south Leads to above normal heights and temperature over most of the U.S. -EPO features a strong ridge over Alaska, with cooler temperatures over most of the United States Generally not a big player unless other teleconnections are not particularly strong, or if the EPO is significantly strong (values >2.00)

20 EPO - Negative Phase

21 EPO Case Study During the second half of February, into early March of last year, the EPO was strongly negative This -EPO flooded the CONUS with very cold air!

22 EPO Case Study

23 Things to Know About Teleconnections
Very easy to find forecasts for nearly ever teleconnection (AO/NAO/PNA/EPO) Most forecasts are derived from computer forecast models like the GFS and ECMWF Aren’t a “perfect guidance” Although a +NAO/AO favors warm weather for the eastern U.S., we can still see cold temperatures and snowstorms depending on other factors Generally the strength of these teleconnections is to show the pattern- NOT the individual storm forecasts Give a general idea of the upcoming forecasts for the next couple weeks Long range forecasters typically use teleconnections as the basis for their forecasts -NAO/+PNA pattern will likely lead to cold temps here, but the opposite is true for a +NAO/-PNA

24 Helpful links/Sources of info
AO/NAO/PNA/EPO Daily Forecasts (ESRL) NC State’s Global Patterns Page Extremely helpful link, also includes forecasts and topics not discussed in this lecture Climate Prediction Center- Teleconnections General Teleconnection Information