Structure and Properties of Synoptic-Scale Wave Disturbances in the Equatorial Western Pacific

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  • 1 Dept. of Atmospheric Sciences, University of Washington, Seattle
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Abstract

A compositing technique is used to obtain the average structure of 18 disturbances which traversed an area in the equatorial western Pacific during the wet season (July–September) of 1967. Principal emphasis is placed on the wave properties in the triangular area described by Ponape, Kwajalein and Eniwetok within which it was possible to measure divergence and vertical motion and to compute moisture and heat budgets.

Meridional wind maxima of nearly opposite phase occurred in the lower and upper troposphere. Negative temperature deviations were found in the vicinity of the wave trough at low and high levels; positive deviations were observed at intermediate levels. Highest relative humidities occurred in the trough region. This was also the region of strongest upward motion and greatest rainfall and cloud amount. The maximum upward velocity of 2.5 cm sec−1 was found at 300 mb. Convergence was strongest in the sub-cloud layer; divergence was concentrated near 175 mb. The maximum anticyclonic vorticity was also observed at that level.

The wave structure changed in a systematic fashion across the network. The change is attributed to the variation with longitude of the shear of the basic current.

The rainfall computed from the observed wind and moisture fields agreed well with observed amounts which varied from about 2 cm day−1 in the vicinity of the trough axis to about 0.5 cm day−1 near the ridge axis. The diabatic heating difference between trough and ridge regions was largest at 400 mb where it was estimated to be nearly 10C day−1.

Abstract

A compositing technique is used to obtain the average structure of 18 disturbances which traversed an area in the equatorial western Pacific during the wet season (July–September) of 1967. Principal emphasis is placed on the wave properties in the triangular area described by Ponape, Kwajalein and Eniwetok within which it was possible to measure divergence and vertical motion and to compute moisture and heat budgets.

Meridional wind maxima of nearly opposite phase occurred in the lower and upper troposphere. Negative temperature deviations were found in the vicinity of the wave trough at low and high levels; positive deviations were observed at intermediate levels. Highest relative humidities occurred in the trough region. This was also the region of strongest upward motion and greatest rainfall and cloud amount. The maximum upward velocity of 2.5 cm sec−1 was found at 300 mb. Convergence was strongest in the sub-cloud layer; divergence was concentrated near 175 mb. The maximum anticyclonic vorticity was also observed at that level.

The wave structure changed in a systematic fashion across the network. The change is attributed to the variation with longitude of the shear of the basic current.

The rainfall computed from the observed wind and moisture fields agreed well with observed amounts which varied from about 2 cm day−1 in the vicinity of the trough axis to about 0.5 cm day−1 near the ridge axis. The diabatic heating difference between trough and ridge regions was largest at 400 mb where it was estimated to be nearly 10C day−1.

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