Pacific–North American teleconnection pattern
[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 (
During the positive phase of the PNA, the East Asian jet intensifies and extends eastward across the North Pacific towards the western U.S. During the negative phase, the jet stream is retracted over East Asia, producing a blocking weather pattern over the North Pacific.
[1][7] Some of the energy that drives the PNA originates from the barotropic instability produced by the jet, potentially exciting Rossby waves.
[2] 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.
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.
The MJO's influence on the PNA arises from the interaction between the enhanced convection and the Pacific jet stream.
The positive phase of the PNA is correlated with above-average temperatures over the U.S. Pacific Coast and Western Canada.
During the positive phase, an anomalously strong ridge of high pressure over Canada reduces the frequency of cold air outbreaks over western Northern America.
[2] Below-average temperatures over the South-Central U.S., Southeastern U.S., and U.S. East Coast are associated with the positive phase due to the presence of anomalously low pressure.
[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.
