Pacific–North American teleconnection pattern
The Pacific–North American teleconnection pattern (PNA) is a large-scale
On average, the
Indices
The PNA is typically quantified using an index using
where describes the normalized 500-hPa height anomaly as a function of location. The subtropical center at (20°N, 160°W) can be excluded, though the difference between the resulting index and the index is small.[3]
Applying rotated principal component analysis to the 500-hPa geopotential height anomaly field in the Northern Hemisphere can also provide a quantification of the PNA (), with the canonical PNA pattern emerging as the second-leading principal component. This methodology is used by the U.S. Climate Prediction Center to compute its PNA index.[4][5][6]
Dynamics
Although the PNA is usually defined based on anomalies relative to monthly or seasonal averages, the PNA often varies at weekly timescales. However, as a pattern of internal climate variability, the state of the PNA occasionally changes without a clear and identifiable cause. This reduces the predictability of the PNA and can complicate long-range seasonal weather forecasts. Predictability of the PNA is limited to roughly within 10 days.
Storms over the tropical Pacific and Indian oceans may play a role in exciting the positive and negative phases of the PNA by influencing the East Asian jet. Tropical convection can induce a low-amplitude PNA pattern that amplifies to its peak strength after 8–12 days. Atmospheric eddies and Rossby waves can further intensify the PNA pattern. Positive PNA is correlated with increased convective activity over western tropical Pacific and reduced convective activity over the tropical Indian Ocean, while negative PNA is correlated with the opposite convective anomalies. The Rossby waves associated with positive PNA tend to track eastward and undergo cyclonic wavebreaking, while those associated with negative PNA tend to track equatorward towards the subtropics and break anticyclonically; the wavebreaking behavior of the Rossby waves is determined by the meridional gradient of potential vorticity and the magnitude and orientation of wind shear, which in turn are modulated by variations in the East Asian jet stream. In either case, positive feedbacks associated with the wavebreaking sustain amplified PNA patterns.[8]
Other teleconnections can modulate the PNA by modifying the jet stream.
Effects on weather
The regional variations in weather associated with the PNA are generally the result of the PNA's influence on the East Asian jet.
Correlations between precipitation patterns and the PNA are weaker than temperature patterns, but are nonetheless evident.[3] Anomalously high precipitation over the Gulf of Alaska and Pacific Northwest accompany the positive phase, along with below-average precipitation totals over the Pacific Northwest, Northern Rocky Mountains, and Ohio and Tennessee river valleys.[2] The negative PNA phase exhibits the opposite departures from average.[1]
See also
- Teleconnection
- Arctic dipole anomaly
- Kuroshio Current
- North Pacific Gyre
- Pacific Decadal Oscillation
- Pineapple Express
- Walker circulation
References
- ^ a b c d e f g h "Pacific/North American (PNA)". Teleconnection Pattern. Climate Prediction Center. January 10, 2012. Retrieved December 23, 2023.
- ^ a b c d e f g h L'Heureux, Michelle (April 23, 2019). "The Pacific-North American Pattern: the stomach sleeper of the atmosphere". ENSO Blog. Climate.gov. Retrieved December 23, 2023.
- ^ a b c d e Rodionov & Assel 2001, p. 1519.
- ^ Rodionov & Assel 2001, p. 1520.
- ^ "Pacific-North American (PNA)". National Centers for Environmental Information. Retrieved December 27, 2023.
- ^ "Teleconnection Pattern Calculation Procedures". Climate Prediction Center. December 12, 2005. Retrieved December 27, 2023.
- ^ a b Dahlman, Luann (September 1, 2009). "Climate Variability: Pacific–North American Pattern". Understanding Cliamte. Climate.gov. Retrieved December 23, 2023.
- ^ Franzke, Feldstein & Lee 2011, p. 329.
Sources
- Franzke, Christian; Feldstein, Steven B.; Lee, Sukyoung (January 2011). "Synoptic analysis of the Pacific–North American teleconnection pattern". Quarterly Journal of the Royal Meteorological Society. 137 (655). Royal Meteorological Society: 329–346. S2CID 55883064.
- Rodionov, Sergei; Assel, Raymond (April 15, 2001). "A new look at the Pacific/North American Index". Geophysical Research Letters. 28 (8): 1519–1522. .