Intraseasonal Circulation and Outgoing Longwave Radiation Modes During Northern Hemisphere Winter

Abstract

An eigenvector analysis is used to characterize global-scale, intraseasonal variability in satellite-derived outgoing longwave radiation fields and NMC analyzed circulation fields. Five-day average covering November-March of 1974–75 through 1979–80 comprise the data sample. The results show that circulation eigenvector 2 and 3 (CEV2 and CEV3) describe wavenumber 1 and wavenumber 2 index cycles of the extratropical windfield, while radiation eigenvectors 2 and 4 describe large-scale fluctuations in tropical cloudiness In most winters studied, the tropical cloudiness fluctuations display a tendency for eastward propagation in the region from Africa to the central equatorial Pacific. In some winters, the intraseasonal fluctuations in the extratropical windfield are closely coupled to the propagating feature in tropical cloudiness. The “period” displayed by the fluctuations in different winters (November-March) ranges from 35 to 80 days.