Cloud components of the Intertropical Convergence Zone

Guojun Gu, Chidong Zhang

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

This study explores the roles of different synoptic-scale cloud systems in the making of the Intertropical Convergence Zone (ITCZ). Outgoing longwave radiation (OLR) data are used to represent both the mean ITCZ and cloud systems. An OLR threshold of 205 W m-2 is used to distinguish daily mean deep convective clouds from nondeep clouds. Zonally moving synoptic-scale cloud systems are identified through a cloud-tracking method. Mean OLR of the ITCZ is decomposed into five components: westward and eastward moving synoptic-scale deep convective clouds, random (nonpropagating) deep convective clouds, nondeep clouds, and clear-sky backgrounds. Hypothetical ITCZ, each composed of one of the cloud components and the clear-sky background, are constructed and compared. The largest synoptic-scale cloud constituents of the LTCZ are nondeep clouds and deep clouds with no persistent tendency of zonal propagation. Each of the two comprises about 40-45% of total cloud signals in the ITCZ. A weak ITCZ could exist solely because of westward propagating, synoptic-scale, deep-convective clouds. In reality, these westward propagating clouds contribute 25-40% of deep convective clouds and 10-20% of total clouds in the ITCZ. Contributions from eastward propagating synoptic-scale clouds are much smaller (8% of the deep convective clouds and less than 5% of total clouds in the ITCZ). An ITCZ without any zonally propagating synoptic-scale deep convective clouds would be diffused in latitude. The cloud compositions in the ITCZ and other tropical convective zones are compared. Their discrepancies indicate fundamental characteristics in large-scale environments for the cloud components in different regions.

Original languageEnglish (US)
JournalJournal of Geophysical Research C: Oceans
Volume107
Issue number21
DOIs
StatePublished - 2002

Fingerprint

intertropical convergence zone
Radiation
convective cloud
longwave radiation
Chemical analysis
clear sky
sky
radiation

Keywords

  • 3314 Meteorology arid Atmospheric Dynamics: Convective processes
  • 3319 Meteorology and Atmospheric Dynamics: General circulation
  • 3364 Meteorology and Atmospheric Dynamics: Synoptic-scale meteorology

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Atmospheric Science
  • Astronomy and Astrophysics
  • Oceanography

Cite this

Cloud components of the Intertropical Convergence Zone. / Gu, Guojun; Zhang, Chidong.

In: Journal of Geophysical Research C: Oceans, Vol. 107, No. 21, 2002.

Research output: Contribution to journalArticle

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abstract = "This study explores the roles of different synoptic-scale cloud systems in the making of the Intertropical Convergence Zone (ITCZ). Outgoing longwave radiation (OLR) data are used to represent both the mean ITCZ and cloud systems. An OLR threshold of 205 W m-2 is used to distinguish daily mean deep convective clouds from nondeep clouds. Zonally moving synoptic-scale cloud systems are identified through a cloud-tracking method. Mean OLR of the ITCZ is decomposed into five components: westward and eastward moving synoptic-scale deep convective clouds, random (nonpropagating) deep convective clouds, nondeep clouds, and clear-sky backgrounds. Hypothetical ITCZ, each composed of one of the cloud components and the clear-sky background, are constructed and compared. The largest synoptic-scale cloud constituents of the LTCZ are nondeep clouds and deep clouds with no persistent tendency of zonal propagation. Each of the two comprises about 40-45{\%} of total cloud signals in the ITCZ. A weak ITCZ could exist solely because of westward propagating, synoptic-scale, deep-convective clouds. In reality, these westward propagating clouds contribute 25-40{\%} of deep convective clouds and 10-20{\%} of total clouds in the ITCZ. Contributions from eastward propagating synoptic-scale clouds are much smaller (8{\%} of the deep convective clouds and less than 5{\%} of total clouds in the ITCZ). An ITCZ without any zonally propagating synoptic-scale deep convective clouds would be diffused in latitude. The cloud compositions in the ITCZ and other tropical convective zones are compared. Their discrepancies indicate fundamental characteristics in large-scale environments for the cloud components in different regions.",
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