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Abstract:
The changes in intensity and position of the Aleutian Low exert significant effects on the ocean-land-atmosphere interactions and climate over the Pacific, East Asia and North America. In this study, the interannual variations of the intensity and latitudinal and longitudinal positions of the Aleutian Low along with their dynamical processes and energy conversions are investigated using 70-year NCEP-NCAR reanalysis data. The intensity variation and eastward shift of the Aleutian Low appear clearly in autumn, strengthen in winter, and diminish slowly in the following spring, associated with sea surface temperature anomalies (SSTAs) in the central and eastern tropical Pacific. Conversely, the meridional movement and westward shift of the Aleutian Low are not accompanied with apparent SSTAs and significant signals in autumn and spring. This different seasonal behavior of interannual variations may be associated with the remote forcing of El Niño-Southern Oscillation. A detailed diagnostic analysis with the geopotential tendency equation reveals that the absolute vorticity advection plays a most important role in the formation and maintenance of the intensity variation of the Aleutian Low, while the high-frequency transient eddies contribute most to its meridional and zonal shifts, providing an explanation for the distinct seasonal evolutions of the low. Moreover, strong energy conversation of high-frequency transient eddies occurs mostly over the extratropical northwestern Pacific, causing an asymmetry of the circulation variations associated with the east-west movement of the Aleutian Low.
