Latitudinal variations of the convective source and propagation condition of inertio-gravity waves in the tropics

Hye-Yeong Chun, Jung Suk Goh, In Sun Song, Lucrezia Ricciardulli

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

Latitudinal variations of the convective source and vertical propagation condition of inertio-gravity waves (IGWs) in the tropical region (30°S-30°N) are examined using high-resolution Global Cloud Imagery (GCI) and 6-hourly NCEP-NCAR reanalysis data, respectively, for 1 yr (March 1985-February 1986). The convective source is estimated by calculating the deep convective heating (DCH) rate using the brightness temperature of the GCI data. The latitudinal variation of DCH is found to be significant throughout the year. The ratio of the maximum to minimum values of DCH in the annual mean is 3.2 and it is much larger in the June-August (JJA) and December-February (DJF) means. Spectral analyses show that DCH has a dominant period of 1 day, a zonal wavelength of about 1600 km, and a Gaussian-type phase-speed spectrum with a peak at the zero phase speed. The vertical propagation condition of IGWs is determined, in the zonal wavenumber and frequency domain, by two factors: (i) latitude, which determines the Coriolis parameter, and (ii) the basic-state wind structure in the target height range of wave propagation. It was found that the basic-state wind significantly influences the wave propagation condition in the lower stratosphere between 150 and 30 hPa, and accordingly a large portion of the source spectrum is filtered out. This is prominent not only in the latitudes higher than 15° where strong negative shear exists, but also near the equator where strong positive shear associated with the westerly phase of the quasi-biennial oscillation (QBO) filters out large portions of the low-frequency components of the convective source. There is no simple relationship between the ground-based frequency and latitude; lower latitudes are not always favorable for low-frequency IGWs to be observed in the stratosphere. The basic-state wind in the Tropics, which has seasonal, annual, and interannual variations, plays a major role not only in determining the wave propagation condition in the stratosphere but also in producing convective sources in the troposphere.

Original languageEnglish
Pages (from-to)1603-1618
Number of pages16
JournalJournal of the Atmospheric Sciences
Volume64
Issue number5
DOIs
Publication statusPublished - 2007 May 1

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gravity wave
wave propagation
heating
stratosphere
annual variation
imagery
quasi-biennial oscillation
tropical region
brightness temperature
westerly
troposphere
seasonal variation
filter
wavelength
tropics
speed

All Science Journal Classification (ASJC) codes

  • Atmospheric Science

Cite this

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title = "Latitudinal variations of the convective source and propagation condition of inertio-gravity waves in the tropics",
abstract = "Latitudinal variations of the convective source and vertical propagation condition of inertio-gravity waves (IGWs) in the tropical region (30°S-30°N) are examined using high-resolution Global Cloud Imagery (GCI) and 6-hourly NCEP-NCAR reanalysis data, respectively, for 1 yr (March 1985-February 1986). The convective source is estimated by calculating the deep convective heating (DCH) rate using the brightness temperature of the GCI data. The latitudinal variation of DCH is found to be significant throughout the year. The ratio of the maximum to minimum values of DCH in the annual mean is 3.2 and it is much larger in the June-August (JJA) and December-February (DJF) means. Spectral analyses show that DCH has a dominant period of 1 day, a zonal wavelength of about 1600 km, and a Gaussian-type phase-speed spectrum with a peak at the zero phase speed. The vertical propagation condition of IGWs is determined, in the zonal wavenumber and frequency domain, by two factors: (i) latitude, which determines the Coriolis parameter, and (ii) the basic-state wind structure in the target height range of wave propagation. It was found that the basic-state wind significantly influences the wave propagation condition in the lower stratosphere between 150 and 30 hPa, and accordingly a large portion of the source spectrum is filtered out. This is prominent not only in the latitudes higher than 15° where strong negative shear exists, but also near the equator where strong positive shear associated with the westerly phase of the quasi-biennial oscillation (QBO) filters out large portions of the low-frequency components of the convective source. There is no simple relationship between the ground-based frequency and latitude; lower latitudes are not always favorable for low-frequency IGWs to be observed in the stratosphere. The basic-state wind in the Tropics, which has seasonal, annual, and interannual variations, plays a major role not only in determining the wave propagation condition in the stratosphere but also in producing convective sources in the troposphere.",
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Latitudinal variations of the convective source and propagation condition of inertio-gravity waves in the tropics. / Chun, Hye-Yeong; Goh, Jung Suk; Song, In Sun; Ricciardulli, Lucrezia.

In: Journal of the Atmospheric Sciences, Vol. 64, No. 5, 01.05.2007, p. 1603-1618.

Research output: Contribution to journalArticle

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