East Asia and Western Pacific METEOROLOGY AND CLIMATE

226
A CLOUD WAVE THEORY AND ITS APPLICATION TO THE
30-50 DAY OSCILLATION IN THE EQUATORIAL ATMOSPHERE
Qiu-shi Chen
Department of Geophysics
Peking University
Beijing, China
and
Kuo-Nan Liou
Department of Meteorology/CARSS
University of Utah
Salt Lake City, Utah 84112, U.S.A.
1. Introduction and the Basic Idea for the Cloud Wave
The 30-50 day oscillation has recently been investigated by Murakami and
Nakazawa (1985), Lau and Chan (1985), and Knutson et al. (1986) using the
outgoing longwave radiation (OLR) dataset.
From the analysis of the observed
OLR, the most dominant patterns consist of an east-west oriented dipole that
propagates eastward at a speed of about 4-5 m/s over the equatorial Indian and
western Pacific Oceans.
The half wavelength of the OLR patterns is about
6000-7000 km. The strongest OLR pattern is primarily developed in the Indian
and western Pacific Oceans, while the wind pattern appears to have a global
influence.
The variations of the u-wind at 850 mb and 150 mb levels at Truk
(152°E, 7°N) are out of phase on both levels.
The 30-50 day oscillation can
be clearly observed in the u-wind at this station (Madden, 1986).
What is the physical implication of the observed OLR patterns in the
tropics
The smaller OLR values imply the presence of high tropospheric