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Teleconnections and height patterns: Meteorology 415 Fall 2011
Snow in Israel-Snow in DC Late Feb 2003 is there a connection Jerusalem Washington to
Introduction • What are teleconnections? • Brief history of teleconnections • Using Teleconnections – long-term forecast aspects – short-term forecast aspects – Flow regimes • Good old fashion teleconnections • New concepts and applications – nodes and antinodes
Teleconnectons defined Wallace and Gutzler MWR 1981 • Definitionsignificant simultaneous : correlations between temporal fluctuations in meteorological parameters at widely separated points on the earth. – Provide evidence of transitory behavior of planetary waves – show evidence of fluctuations with times scales on order of weeks. – Suggest preferred region of standing wave nodes and antinodes. (nodes-similar sign)
Similar definition O’Connor 1969 • Definitionthe favored modes for coupling : large-scale abnormalities of the atmospheric circulation as determined statistically or empirically. – Rossby’s centers of action (1939) concept proved teleconnections had a physical basis. (nodes) – Found great use to improve forecasts based on patterns and centers of action (nodes) – developed teleconnection maps correlating an anomalous trough/ridge at a 10 x 10 Lat/Lon region to other anomalies and anti-anomalies around the hemisphere. (nodes and antinodes )
Teleconnection Map Example (O’Connor)30 N/40 W Negative in Winter
Teleconnection Map Example (O’Connor)30 N/50 W Negative in Winter
Teleconnection Map Example (O’Connor)30 N/60 W Negative in Winter
Teleconnection Map Example 40 N 70 W: Winter Positive (~PA) Trof Ridge
The well known El Nino Teleconnection the temporal fluctuation about globe associated with El Nino
How El Nino Teleconnects Walker Circulation impacts
Teleconnectons Wallace and Gutzler MWR 1981 • Implications: – A standing wave in one location favors the existence of a wave downstream at a known location. Therefore, – there exist, preferred trough/ridge locations • may be referred to as nodes and antinodes – Their existence allows the use of indices to quantify or measure flow patterns associated with these features. • The NAO correlates the flow over the Atlantic Basin • The ENSO sign has its own teleconnections the both in northern and southern hemispheres • other known indices (EP, AO etc, etc…)
Teleconnectons Wallace and Gutzler MWR 1981 • Things to consider: – wave patterns and flow can be measured and teleconnected. – ocean indices can be measured and teleconnected – the indices are teleconnected, typically by regression, to a favored mode of weather conditions at a location. – Not all correlations are one-to-one • negative correlations too, ANTINODES – These correlation’s have direct forecast applications, especially on the scale of weeks and months.
Teleconnection’s A History Perspective • Southern Oscillation (SO), identified and documented in 1897. – Connecting weather and long term wet/dry periods in India and Australia. • Walker and Bliss (1932) improved SO documentation. • Association of weather patterns in western Europe to eastern United States – trough in western Europe correlates well with trough in eastern North America. NODES – A ridge in western Europe ~ ridge in eastern North America
Northern Hemisphere Teleconnection Patterns • North Atlantic Oscillation (NAO) – Negative phase cold eastern NOAM/Europe : – Positive phase warm wet Europe / eastern NOAM : • North Pacific Oscillation (NPO) • Pacific North American Pattern (PNA) – PNA > 0 similar to NAO <0 • The zonally symmetric seesaw/ Quasi. Biennial Oscillation (QBO)
Cutting to the Chase anomaly correlation showing nodes and antinodes Correlation point
North Atlantic Oscillation (NAO) • Statistical correlation’s: – Negative correlation severity of winters in Greenland Labrador and northwestern Europe. – Negative correlation between MSLP at Iceland the eastern Atlantic – Winter temperatures were used to determine severity – Deep Icelandic Low: Positive NAO • cold advection over Labrador and Greenland • warm southwesterly flow into Europe and southern flow into eastern North America.
Pacific North American Pattern (PNA) • There are clearly two preferred flow patterns over North America • relate upper air pattern mid-Pacific to eastern North America with two preferred modes: – Positive Mode • • Ridge along west coast with negative nodes southeastern US (35 N/75 W) near 45 N in the mid-Pacific (40 N/150 W) so called Postive PNA – Negative Mode • more zonal flow across north America • lack of Pacific Ridge, can flood US with Pacific air.
Pacific North American Patten • Flow Pattern over North America and adjacent pacific ocean • referred to as the PNA • The standard one is from Wallace and Gutzler (1981) where they defined the index as being: z=zonal component of wind time(year)=[z(20 N, 160 W)z(45 N, 165 W)+z(55 N, 115 W)+z(30 N, 85 W)]/ 4
PNA Description • The PNA pattern is one of the most prominent modes of low-frequency variability in the Northern Hemispheric extra-tropics – appearing in all months except June and July. • The PNA pattern reflects a quadripole pattern of height anomalies, – 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 (Spring).
PNA in recent times
Positive PNA-January Deep troughs Ridges
PNA > 0 Positve Yellow Negative Blue antinode Nodes/Antinode
Teleconnection Maps relate flow pattern • Initial teleconnection’s used operationally – maps of anomalies in 10 x 10 Lat/Lon bands – relate a known height anomaly (Lat/Lon) with other associated anomalies – For example • Compute height anomaly at 30 N and 40 W • see what the mean anomalies are around the hemisphere when this anomaly exists • often find centers of action – correlation centers – low off eastern US correlates well with ridge over northern Atlantic – negative nodes typically have downstream preferred location of next negative node
Nodes and Antinode • Centers of action from re-analysis data • Use eastern US to compare to previous 40/75 W box • Examine impacts on past three winters – Note how our PA node correlates well with the preferred nodes of the PNA and NAO. • A forecast tool?
Autocorrelation JA-FE-MA 01 correlation point 40 N/75 W Anti. Node European Node PA Node Pacific Node
Conclusions • Teleconnections ~ weather to flow – Rossby waves dictate location of troughs/ridges – specific mean wavelengths imply existence of preferred nodes and antinodes • these preferred locations led to some of the wellknown indices (PNA) • Can produce these for any Lat/lon box on globe – relate weather to anomalies of heights • mean trough~cold or mean ridge~warm • forecast tools on the order of weeks
Conclusion-Indices • NAO: – North-South Dipole – teleconnects well with weather in Europe, Greenland western North America • PNA – quadrapole (nodes and antinodes ) – teleconnects well with NOAM weather – Trough in eastern US correlates with trough in Europe-relates PNA to NAO
References • Namias, J. , 1978: Multiple Causes of the North American Abnormal Winter 1976 -77. Mon. Wea. Rev. , 106, 279 -295. • O’Connor, J. F. 1969: Hemispheric Teleconnections of Mean Circulation anomalies at 700 millibars. ESSA Technical report WB 10, US Dept. Commerce. • van Loon, H. , and J. C. Rogers, 1978: The seesaw in winter temperatures between Greenland northern Europe. Part I: General description. Mon. Wea. Rev. , 106, 296 -310. • Wallace, J. , and D. Gutzler, 1981: Teleconnections in the Geopotential Height Field during the Northern Hemisphere Winter. Mon. Wea. Rev. , 109, 784 -811. • Burroughs, W. J, 2002: Climate Change. Cambridge Univ. Press, 1 -298.
Computing the PNA know the sign of the anomaly at center of action • Base on Anomalies (nodes and antinodes ) – – – 4 Locations SMid. Pac (SMP) = 20 N/160 W NMid. Pac (NMP) = 45 N/165 W WNOAM (NNM) = 55/115 W SERNUS (SUS) = 30 N/85 – PNA= (SMP - NMP + NNM - SERNUS)/4 PNA > 0 : Strong Ridgealong western Canada PNA < 0 : Trough or zonal flow along western Canada
The zonal symmetric seesaw • Lorenz (1951) first identified this seesaw effect in the MSLP fields • A similar patten has been associated with the Quasi-biennial oscillation (QBO) – pressure changes associated with sudden warming’s (mainly in polar regions) – effect most notable in Stratosphere (20 -30 km) – QBO has been related to surface pressure changes too and may have long term forecast skill on monthly/seasonal level. – NH winters may be related to phase of QBO at 50 h. Pa in the tropics
Quasi-Biennial Oscillation (QBO) • 20 -30 km in Stratosphere • Measured near 30 h. Pa • Wind reversal over equatorial regions every ~27 months • Easterly to westerly • Teleconnects to weather patterns – Correlated to some temperature records – And behavior of ENSO, – Hurricane activity in the Atlantic • Related to upward propagating easterly Kelvin waves and westerly Rossby waves.