The East Pacific Wavetrain: Its variability and impact on the atmospheric circulation in the boreal winter

Abstract

The East Pacific wavetrain (EPW) refers to here the intense stationary wave activity detected in the troposphere over the East Pacific and North America in 45 northern winters from 1958 to 2002. The EPW is generated in the lower troposphere over the East Pacific, propagating predominantly eastward into North America and slightly upward then eventually into the stratosphere. The intensity of the EPW varies from year to year and exhibits apparent decadal variability. For the period 1958-1964, the EPW was in its second maximum, and it was weakest for the period 1965-1975, then it was strongest for the period 1976-1987. After 1987, the EPW weakened again.The intensity and position of the members (i.e., the Aleutian low, the North American trough, and the North American ridge) of the EPW oscillate from time to time. For an active EPW versus a weak EPW, the Aleutian low deepens abnormally and shifts its center from the west to the east of the date line, in the middle and upper troposphere the East Asian trough extends eastward, and the Canadian ridge intensifies at the same time. The opposite is true for a weak EPW. Even in the lower stratosphere, significant changes in the stationary wave pattern are also observed.Interestingly the spatial variability of the EPW assumes a Pacific-North American (PNA)-like teleconnection pattern. It is likely that the PNA low-frequency oscillation is a reflection of the oscillations of intensity and position of the members of the EPW in horizontal direction.

Responses of Planetary Waves to Global Warming: Implications from CMIP3 4×CO2 Experiments

“…vectors turns slightly equator-ward. The largest west-east momentum fluxes over Siberia change the least, which is also supported by the diagnostics for the past decades in observations (Zhou et al, 2012). The strong semi-permanent pressure systems, such as the Siberia high and Aleutian low, stabilize the variability of the planetary wave activity's surroundings.…”

“…The vertical component of waves, also called wave heat fluxes, also decrease, varying from -8.1% to -28.6%, with the maximum decrease occurring over the Eastern North Pacific. The diagnostics for the past several dec-ades from the reanalysis data also support the conclusion that the vertical component of wave fluxes over the Eastern North Pacific has the largest sensitivity to climate change among the three centers (Zhou et al, 2012), which is partly attributed to the influences of the internal mode of the air-sea system from low latitudes, such as El Niño and the Southern Oscillation (ENSO) and the Pacific North America (PNA) teleconnection pattern.…”

Mechanism of the wintertime Aleutian Low–Icelandic Low seesaw

“…[12] Next, we explore the relationship between the AL-IL seesaw, the EPWs, and the polar vortex. Zhou et al [2012] found that the AL and the EPWs are closely related. For a weak (strong) AL, the vertical component of the stationary wave activity flux over the eastern Pacific is weak (strong), and the associated EPW is also weak (strong).…”

“…Zhou et al . [] suggested that the EPWs and the PNA are the same phenomenon as revealed in different variables. The EPWs correspond to wave activity fluxes, while the PNA is in the form of a wave train of geopotential height anomalies.…”

Recent Strengthened Impact of the Winter Arctic Oscillation on the Southeast Asian Surface Air Temperature Variation

“…An issue remains to be further explored in the future is the possible factors for the change in the spatial structure of the winter AO. Studies have demonstrated that structure of the winter AO can be impacted by several factors, such as the solar cycle [46], polar vortex [47,48], the Aleutian Low-Aleutian Low oscillator [49], and the eastern Pacific atmospheric wave train [50,51]. Individual and combined roles of the above factors in modulating the spatial structure of the winter AO need to be investigated in the future.…”