The Global Monsoon as Seen through the Divergent Atmospheric Circulation

Trenberth, Kevin E.; Stepaniak, David P.; Caron, Julie M.

doi:10.1175/1520-0442(2000)013<3969:tgmast>2.0.co;2

Cited by 457 publications

(370 citation statements)

References 30 publications

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“…The vertical structure of this Hadley-type circulation for the Horn of Africa (30-50°E) bears a strong resemblance to that of the July meridional overturning circulation of the divergent flow for Africa (10-40°E) identified by Trenberth et al (2000) the equator with rising northerlies near 10°N, subsiding air to the south, and shallow overturning below 600 hPa. Also, our inclusion of the desert-like and subsident region of the Horn (Figure 4(a), 43-50°E) is a principal reason that the ascending motion near 10°N in Figure 4(b) is weaker than that obtained from the divergent meridional flow analysis of Trenberth et al (2000).…”

Section: Large-scale Atmospheric Circulation Climatologymentioning

confidence: 71%

“…Also, our inclusion of the desert-like and subsident region of the Horn (Figure 4(a), 43-50°E) is a principal reason that the ascending motion near 10°N in Figure 4(b) is weaker than that obtained from the divergent meridional flow analysis of Trenberth et al (2000). When the vertical and meridional winds were averaged over 30-42.5°E, we obtained much stronger ascending motion between 5 and 15°N in the mid-to upper-troposphere and a more organized lower-level overturning cell below 600 hPa (not shown) that compare well with the results of Trenberth et al (2000).…”

Section: Large-scale Atmospheric Circulation Climatologymentioning

confidence: 87%

“…Trenberth et al, 2000;Hastenrath, 2001;Zhao and Moore, 2008). However, Krishnamurthy and Goswami (2000) and Raicich et al (2003) employed counterpart analyses of the observed (total) horizontal wind and vertical velocity fields for this purpose, presumably because of their computational simplicity and qualitatively acceptable results.…”

Section: Large-scale Atmospheric Circulation Climatologymentioning

confidence: 99%

“…Owing to the large magnitude of disparity between horizontal and vertical velocity fields, Trenberth et al (2000) noted that vertical circulation cross-sections can be deceptive and cautioned against using arbitrary scales to depict regional vertical circulation cells. Therefore, the two-dimensional wind vectors in Figure 4 were obtained by dividing the actual values of the horizontal winds and vertical velocity by their respective standard deviation for the entire cross-sectional domain represented in Figure 4 (30°N-20°S/30°W-90°E, 1000-100 hPa).…”

Section: Large-scale Atmospheric Circulation Climatologymentioning

confidence: 99%

See 3 more Smart Citations

Large‐scale atmospheric circulation and global sea surface temperature associations with Horn of Africa June–September rainfall

Segele

Lamb

Leslie

2008

Intl Journal of Climatology

142

171

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This study uses correlation, regression, and composite analyses for the period 1970-1999 to explore the relationships between the June-September rainfall in the Horn of Africa (especially Ethiopian) and large-scale regional atmospheric circulation patterns across Africa and the Atlantic and Indian Oceans, and global sea surface temperature (SST) anomalies. Abundant rainfall in the Horn of Africa is associated with enhanced westerlies across western and central Africa. These westerlies are produced by a stronger north-east directed mean sea level pressure (MSLP) gradient resulting from MSLP intensification over the Gulf of Guinea and deepening of the monsoon trough across the Arabian Peninsula. This is reflected by a strong correlation (−0.71) between 5-day (pentad) Ethiopian rainfall and the Gulf of Guinea minus the Arabian Peninsula MSLP difference. This correlation decreases to −0.39 when the seasonal cycles are removed from both time series. A wet Horn of Africa monsoon is also associated with deep moist air extending up to mid-troposphere and large water vapour transport convergence across much of Ethiopia, a strong Somali low-level jet, and a strong tropical easterly jet (TEJ). Although there are large changes in TEJ strength, the position of the jet axis shows little variation between wet and dry events. Associated with the TEJ, the strongest upper level divergence occurs at 100 hPa, where the raw/de-seasonalized zonal wind speed correlates negatively (−0.71/−0.23) with the corresponding Ethiopian rainfall at the pentad time-scale. Furthermore, SSTs over the equatorial Pacific, Indian, and southern Atlantic Oceans correlate strongly with contemporary Ethiopian summer rainfall. In general, Ethiopian rainfall is suppressed during El Niño and enhanced during La Niña. This identification and documentation of the regional atmospheric circulation patterns and global SST anomalies directly linked to rainfall variability over Ethiopia/Horn of Africa, are crucial for developing statistical prediction schemes and designing climate model simulations for the region on intra-seasonal to inter-annual time-scales.

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Section: Large-scale Atmospheric Circulation Climatologymentioning

confidence: 71%

Section: Large-scale Atmospheric Circulation Climatologymentioning

confidence: 87%

Section: Large-scale Atmospheric Circulation Climatologymentioning

confidence: 99%

Section: Large-scale Atmospheric Circulation Climatologymentioning

confidence: 99%

See 2 more Smart Citations

Large‐scale atmospheric circulation and global sea surface temperature associations with Horn of Africa June–September rainfall

Segele

Lamb

Leslie

2008

Intl Journal of Climatology

142

171

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“…The changes in the global monsoon system as a whole have received less attention. As the annual variation in solar heating is a fundamental driver of monsoon development, Trenberth et al [2000] and Wang and Ding [2006] proposed the concept of the global monsoon to describe the strength of overall monsoon systems around the globe. From observations, global monsoon precipitation (GMP) has increased over the past three decades [Hsu et al, 2011;Wang et al, 2011].…”

Section: Introductionmentioning

confidence: 99%

Future change of the global monsoon revealed from 19 CMIP5 models

et al. 2013

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[1] The variability of global monsoon area (GMA), global monsoon precipitation (GMP), and global monsoon intensity (GMI) in the present climate and the future warmer climate under Representative Concentration Pathways 4.5 (RCP4.5) scenario was examined based on 19 Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations. In the present-day simulations, the ensemble mean precipitation reproduces the observed GMA, GMP, and GMI, although the spread of individual models is large. In the RCP4.5 simulations, most (17 of 19) of the CMIP5 models project enhanced global monsoon activity, with the increases of GMA, GMP, and GMI by 1.9%, 3.2%, and 1.3%, respectively, per 1 K of surface warming. The diagnosis of a column-integrated moisture budget indicates that the increase in GMP is primarily attributed to the increases of moisture convergence and surface evaporation, whereas horizontal moisture advection has little effect. A further separation of dynamic and thermodynamic factors shows that increase of the moisture convergence comes mainly from the increase of water vapor, but is partly offset by the convergence effect. The increase of the surface evaporation is caused by the increase of sea-air specific humidity difference, while the change in surface wind speed plays a minor role. The GMP experiences a great year-to-year variation, and it is significantly negatively correlated with the Niño3.4 index averaged over a typical monsoon year (defined from May to the following April) in the pre-industrial control and present-day simulations, similar to observations. Under the RCP4.5 warming, such rainfall variability is intensified, and the relationship between monsoon and El Niño strengthens. A large proportion of intensification in the year-to-year monsoon rainfall variability arises from the land monsoon region.Citation: Hsu, P.-c., T. Li, H. Murakami, and A. Kitoh (2013), Future change of the global monsoon revealed from 19 CMIP5 models,

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Variations of monsoon rainfall: A simple unified index

Nguyen

Renwick

McGregor

2014

Geophysical Research Letters

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A new objective approach is proposed to identify the seasonal cycle of rainfall for major monsoon regions of the globe. Mean sea level pressure and low-level zonal wind are combined to establish a standardized monsoon index. The index is able to determine the timing of the summer monsoon rainy season across all major monsoon regions in Asia-Australia, Africa, and the Americas. A detailed application of the index in detecting the monsoon onset-withdrawal phases is demonstrated for the Vietnam-South China Sea region. A significant advantage of the index is that it can be used both for studies of monsoon rainfall variability and for monsoon predictability at seasonal time scales.

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The Global Monsoon as Seen through the Divergent Atmospheric Circulation

Cited by 457 publications

References 30 publications

Large‐scale atmospheric circulation and global sea surface temperature associations with Horn of Africa June–September rainfall

Large‐scale atmospheric circulation and global sea surface temperature associations with Horn of Africa June–September rainfall

Future change of the global monsoon revealed from 19 CMIP5 models

Variations of monsoon rainfall: A simple unified index

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