Horizontal and vertical structure of easterly waves in the Pacific ITCZ

Yolande Serra, George N. Kiladis, Meghan F. Cronin

Research output: Contribution to journalArticle

55 Citations (Scopus)

Abstract

Outgoing longwave radiation (OLR) and low-level wind fields in the Atlantic and Pacific intertropical convergence zone (ITCZ) are dominated by variability on synoptic time scales primarily associated with easterly waves during boreal summer and fall. This study uses spectral filtering of observed OLR data to capture the convective variability coupled to Pacific easterly waves. Filtered OLR is then used as an independent variable to isolate easterly wave structure in wind, temperature, and humidity fields from open-ocean buoys, radiosondes, and gridded reanalysis products. The analysis shows that while some Pacific easterly waves originate in the Atlantic, most of the waves appear to form and strengthen within the Pacific. Pacific easterly waves have wavelengths of 4200-5900 km, westward phase speeds of 11.3-13.6 m s-1, and maximum meridional wind anomalies at about 600 hPa. A warm, moist boundary layer is observed ahead of the waves, with moisture lofted quickly through the troposphere by deep convection, followed by a cold, dry signal behind the wave. The waves are accompanied by substantial cloud forcing and surface latent heat flux fluctuations in buoy observations. In the central Pacific the horizontal structure of the waves appears as meridionally oriented inverted troughs, while in the east Pacific the waves are oriented southwest-northeast. Both are tilted slightly eastward with height. Although these tilts are consistent with adiabatic barotropic and baroclinic conversions to eddy energy, energetics calculations imply that Pacific easterly waves are driven primarily by convective heating. This differs from African easterly waves, where the barotropic and baroclinic conversions dominate.

Original languageEnglish (US)
Pages (from-to)1266-1284
Number of pages19
JournalJournal of the Atmospheric Sciences
Volume65
Issue number4
DOIs
StatePublished - Apr 2008

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easterly wave
intertropical convergence zone
longwave radiation
latent heat flux
radiosonde
open ocean
wind field
tilt
troposphere
humidity
eddy
trough
energetics
boundary layer
convection
moisture
heating
wavelength
timescale
anomaly

ASJC Scopus subject areas

  • Atmospheric Science

Cite this

Horizontal and vertical structure of easterly waves in the Pacific ITCZ. / Serra, Yolande; Kiladis, George N.; Cronin, Meghan F.

In: Journal of the Atmospheric Sciences, Vol. 65, No. 4, 04.2008, p. 1266-1284.

Research output: Contribution to journalArticle

Serra, Yolande ; Kiladis, George N. ; Cronin, Meghan F. / Horizontal and vertical structure of easterly waves in the Pacific ITCZ. In: Journal of the Atmospheric Sciences. 2008 ; Vol. 65, No. 4. pp. 1266-1284.
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