资源环境科技发展态势分析平台

Tropospheric planetary waves, often linked to asymmetries in lower boundary forcing, significantly modulate atmospheric blocking and storm track structures that are, in turn, linked to extreme surface weather events. Day-to-day variability in the planetary scale circulation, taken as wave numbers 1 to 5 in the daily 500 hPa geopotential heights, and the associated impact on storm tracks and regional weather are studied for the period 1950-2005. Six boreal cold-season distinct planetary wave patterns are identified via hierarchical cluster analysis. The first, second, and sixth patterns feature a prominent zonal wave number 1 structure, while the fourth and fifth patterns resemble the negative and positive phases of northern annular mode, respectively. The second pattern represents an amplification of the climatological mean wave structure, while the third pattern resembles the zonal wave number 3 pattern. A multitaper spectral analysis of the daily projection indices indicates that the planetary wave patterns are primarily intraseasonal in nature. The first (sixth) pattern combines the positive (negative) phase of the Pacific-North American teleconnection pattern and negative (positive) phase of the North Atlantic Oscillation, inducing poleward (equatorward) shifts in the Pacific storm track and a weakened (strengthened) Atlantic storm track. In contrast, the fourth (fifth) pattern results in a simultaneous equatorward (poleward) displacement of both storm tracks. Extreme cold waves over the continental United States (U.S.) are favored during occurrences of the fourth and sixth patterns. During episodes of the first pattern, increased rainfall prevails over much of the U. S., while precipitation anomalies induced by the other patterns are more regional in nature.