On the yearly phase delay of winter intraseasonal mode in the western United States
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In the western United States, persistent and recurrent flow patterns not only modulate precipitation events but also result in prolonged surface inversion episodes. In this region, the frequency of persistent ridge/trough events ranges between 20 and 40 days, well within the intraseasonal timescale. Based on NCEP reanalysis data starting at 1949, with a focus on the interior West, we observed that episodes of prolonged ridge/trough events appear to occur about a week later every year and resets every 5–7 years—a previously undocumented phenomenon examined herein. Diagnostic analyses indicate that the interplay between regional intraseasonal flow patterns and the North Atlantic Oscillation (NAO) alternates the preferred timeframe for the persistent ridge/trough events to occur. This may result from different phases of the NAO shifting the winter mean ridge and such shifts modulate the occurrence and timing of persistent ridge/trough events. When the timing changes evolve around the quasi-6 years cycle of the NAO, the resultant evolution forms what appears to be a steady phase delay in the ridge/trough events year after year. These results are a further step in disclosing the multiple-scale interaction between intraseasonal and interannual modes and its regional climate/weather impact.
KeywordsRossby Wave Empirical Orthogonal Function Pacific Decadal Oscillation North Atlantic Oscillation North Atlantic Oscillation Index
This research was supported by NASA Grant NNX13AC37G, Bureau of Reclamation Project R11AC81456, and the Utah Agricultural Experiment Station, Utah State University approved as journal paper number 8529.
- Hurrell JW (2003) The North Atlantic oscillation: climatic significance and environmental impact. Am Geophys Union 134:279Google Scholar
- Lau K-M (2005) El Nino and southern oscillation connection (Chp. 9). In: Lau K-M, Waliser DE (eds) Intraseasonal variability in the atmosphere-ocean climate system. Praxis Publishing Ltd, Dordrecht, Netherlands, pp 271–300Google Scholar
- Nakamura H, Miyasaka T, Kosaka Y, Takaya K, Honda M (2010) Northern hemisphere extratropical tropospheric planetary waves and their low-frequency variability: their vertical structure and interactin with transient eddies and surface thermal contrasts. In: Sun D-Z, Bryan F (eds) Climate dynamics: why does climate vary? American Geophysical Union, pp 149–180Google Scholar
- Wang S-Y, Gillies RR, Martin R, Davies RE, Booth MR (2012) Connecting subseasonal movements of the winter mean ridge in western North America to inversion climatology in cache valley, Utah. J Appl Meteorol Climatol 51:617–627Google Scholar