Normal-mode Rossby waves observed in the wavenumber 1-5 geopotential fields of the stratosphere and troposphere

Abstract

The geopotentials extend from the 850- to 2-mb levels and 85°N to 85°S latitudes, and describe four Northern Hemisphere winters. The analyses indicate that variations in geopotential are dominated by westward moving waves that resemble normal mode Rossby waves. Mode structures are found to agree in general with the predictions of theory and numerical models. Only the first symmetric modes are found to maintain their symmetry throughout the troposphere and lower stratosphere. Other modes are found to resemble their prodicted Hough function structures in the troposphere but, to varying degree, not in the stratosphere. The observations support the importance of thermal damping and critical lines as causes of this departure. Evidence is found that supports the increasing importance of lower tropospheric damping with increasing mode wavenumber and meridional index. -from Author