Hemispherical asymmetry of tropical precipitation in ECHAM5/MPI-OM during El Niño and under global warming

Chia Chou, Jien Yu Tu

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

Similarities and differences between El Niño and global warming are examined in hemispherical and zonal tropical precipitation changes of the ECHAM5/Max Planck Institute Ocean Model (MPI-OM) simulations. Similarities include hemispherical asymmetry of tropical precipitation changes. This precipitation asymmetry varies with season. In the boreal summer and autumn (winter and spring), positive precipitation anomalies are found over the Northern (Southern) Hemisphere and negative precipitation anomalies are found over the Southern (Northern) Hemisphere. This precipitation asymmetry in both the El Niño and global warming cases is associated with the seasonal migration of the Hadley circulation; however, their causes are different. In El Niño, a meridional moisture gradient between convective and subsidence regions is the fundamental basis for inducing the asymmetry. Over the ascending branch of the Hadley circulation, convection is enhanced by less effective static stability. Over the margins of the ascending branch, convection is suppressed by the import of dry air from the descending branch. In global warming, low-level moisture is enhanced significantly due to warmer tropospheric temperatures. This enhances vertical moisture transport over the ascending branch of the Hadley circulation, so convection is strengthened. Over the descending branch the mean Hadley circulation tends to transport relatively drier air downward, so convection is reduced.

Original languageEnglish
Pages (from-to)1309-1332
Number of pages24
JournalJournal of Climate
Volume21
Issue number6
DOIs
Publication statusPublished - 2008 Mar 15

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global warming
asymmetry
convection
moisture
ocean
anomaly
air
Southern Hemisphere
import
Northern Hemisphere
subsidence
autumn
winter
summer
simulation
temperature

All Science Journal Classification (ASJC) codes

  • Atmospheric Science

Cite this

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abstract = "Similarities and differences between El Ni{\~n}o and global warming are examined in hemispherical and zonal tropical precipitation changes of the ECHAM5/Max Planck Institute Ocean Model (MPI-OM) simulations. Similarities include hemispherical asymmetry of tropical precipitation changes. This precipitation asymmetry varies with season. In the boreal summer and autumn (winter and spring), positive precipitation anomalies are found over the Northern (Southern) Hemisphere and negative precipitation anomalies are found over the Southern (Northern) Hemisphere. This precipitation asymmetry in both the El Ni{\~n}o and global warming cases is associated with the seasonal migration of the Hadley circulation; however, their causes are different. In El Ni{\~n}o, a meridional moisture gradient between convective and subsidence regions is the fundamental basis for inducing the asymmetry. Over the ascending branch of the Hadley circulation, convection is enhanced by less effective static stability. Over the margins of the ascending branch, convection is suppressed by the import of dry air from the descending branch. In global warming, low-level moisture is enhanced significantly due to warmer tropospheric temperatures. This enhances vertical moisture transport over the ascending branch of the Hadley circulation, so convection is strengthened. Over the descending branch the mean Hadley circulation tends to transport relatively drier air downward, so convection is reduced.",
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Hemispherical asymmetry of tropical precipitation in ECHAM5/MPI-OM during El Niño and under global warming. / Chou, Chia; Tu, Jien Yu.

In: Journal of Climate, Vol. 21, No. 6, 15.03.2008, p. 1309-1332.

Research output: Contribution to journalArticle

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