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Impacts of the ENSO Modoki and other Tropical Indo-Pacific Climate-Drivers on African Rainfall.

Preethi B, Sabin TP, Adedoyin JA, Ashok K - Sci Rep (2015)

Bottom Line: However, both the El Niño flavours anomalously reduce the northern hemispheric rainfall during June-September.During boreal summer, the El Niño Modoki and canonical El Niño (positive IOD) tend to weaken (strengthen) the tropical easterly jet, and result in strengthening (weakening) and southward shift of African easterly jet.This anomalously reduces (enhances) rainfall in the tropical north, including Sahelian Africa.

View Article: PubMed Central - PubMed

Affiliation: Indian Institute of Tropical Meteorology, Pune 411008, India.

ABSTRACT
The study diagnoses the relative impacts of the four known tropical Indo-Pacific drivers, namely, El Niño Southern Oscillation (ENSO), ENSO Modoki, Indian Ocean Dipole (IOD), and Indian Ocean Basin-wide mode (IOBM) on African seasonal rainfall variability. The canonical El Niño and El Niño Modoki are in general associated with anomalous reduction (enhancement) of rainfall in southern (northern) hemispheric regions during March-May season. However, both the El Niño flavours anomalously reduce the northern hemispheric rainfall during June-September. Interestingly, during boreal spring and summer, in many regions, the Indian Ocean drivers have influences opposite to those from tropical Pacific drivers. On the other hand, during the October-December season, the canonical El Niño and/or positive IOD are associated with an anomalous enhancement of rainfall in the Eastern Africa, while the El Niño Modoki events are associated with an opposite impact. In addition to the Walker circulation changes, the Indo-Pacific drivers influence the African rainfall through modulating jet streams. During boreal summer, the El Niño Modoki and canonical El Niño (positive IOD) tend to weaken (strengthen) the tropical easterly jet, and result in strengthening (weakening) and southward shift of African easterly jet. This anomalously reduces (enhances) rainfall in the tropical north, including Sahelian Africa.

No MeSH data available.


Related in: MedlinePlus

Partial correlations between EMI and velocity potential at 850 hPa (shadings).Correlations significant at 85%, 90% and 95% confidence level based on Student’s t-test are provided for different seasons (a) MAM, (b) JJAS, (c) OND and (d) JF. Partial correlations between EMI and 850 hPa divergent wind components (vectors), significant at 95% confidence level is also given for each season. [Figure created using the COLA/GrADS software].
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f3: Partial correlations between EMI and velocity potential at 850 hPa (shadings).Correlations significant at 85%, 90% and 95% confidence level based on Student’s t-test are provided for different seasons (a) MAM, (b) JJAS, (c) OND and (d) JF. Partial correlations between EMI and 850 hPa divergent wind components (vectors), significant at 95% confidence level is also given for each season. [Figure created using the COLA/GrADS software].

Mentions: The ENSO Modoki events influence the tropical and subtropical African rainfall significantly by inducing anomalous changes in Walker Circulation. The partial correlations of the EMI with divergent wind at 850 hPa and those with velocity potential at 850 hPa are presented in Fig. 3. These indicate that the enhanced rainfall activity over north Madagascar and tropical regions of Africa (Fig. 2a, A2a) in MAM season during an El Niño Modoki is associated with an anomalous zone of large scale convergence over southwest Indian Ocean and the east coast of Africa (Fig. 3a). The northwest Africa receives a significant part of its spring rainfall through synoptic systems associated with baroclinic instability40. Interestingly, we find that El Niño Modoki events are associated with strengthening of the subtropical jet stream over the northern regions of Africa (Fig. 4a) during MAM season. This suggests that the anomalous increase in rainfall during the El Niño Modoki (Fig. 2a) is manifested through strengthening of interactions between the mean flow and synoptic activity.


Impacts of the ENSO Modoki and other Tropical Indo-Pacific Climate-Drivers on African Rainfall.

Preethi B, Sabin TP, Adedoyin JA, Ashok K - Sci Rep (2015)

Partial correlations between EMI and velocity potential at 850 hPa (shadings).Correlations significant at 85%, 90% and 95% confidence level based on Student’s t-test are provided for different seasons (a) MAM, (b) JJAS, (c) OND and (d) JF. Partial correlations between EMI and 850 hPa divergent wind components (vectors), significant at 95% confidence level is also given for each season. [Figure created using the COLA/GrADS software].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4645176&req=5

f3: Partial correlations between EMI and velocity potential at 850 hPa (shadings).Correlations significant at 85%, 90% and 95% confidence level based on Student’s t-test are provided for different seasons (a) MAM, (b) JJAS, (c) OND and (d) JF. Partial correlations between EMI and 850 hPa divergent wind components (vectors), significant at 95% confidence level is also given for each season. [Figure created using the COLA/GrADS software].
Mentions: The ENSO Modoki events influence the tropical and subtropical African rainfall significantly by inducing anomalous changes in Walker Circulation. The partial correlations of the EMI with divergent wind at 850 hPa and those with velocity potential at 850 hPa are presented in Fig. 3. These indicate that the enhanced rainfall activity over north Madagascar and tropical regions of Africa (Fig. 2a, A2a) in MAM season during an El Niño Modoki is associated with an anomalous zone of large scale convergence over southwest Indian Ocean and the east coast of Africa (Fig. 3a). The northwest Africa receives a significant part of its spring rainfall through synoptic systems associated with baroclinic instability40. Interestingly, we find that El Niño Modoki events are associated with strengthening of the subtropical jet stream over the northern regions of Africa (Fig. 4a) during MAM season. This suggests that the anomalous increase in rainfall during the El Niño Modoki (Fig. 2a) is manifested through strengthening of interactions between the mean flow and synoptic activity.

Bottom Line: However, both the El Niño flavours anomalously reduce the northern hemispheric rainfall during June-September.During boreal summer, the El Niño Modoki and canonical El Niño (positive IOD) tend to weaken (strengthen) the tropical easterly jet, and result in strengthening (weakening) and southward shift of African easterly jet.This anomalously reduces (enhances) rainfall in the tropical north, including Sahelian Africa.

View Article: PubMed Central - PubMed

Affiliation: Indian Institute of Tropical Meteorology, Pune 411008, India.

ABSTRACT
The study diagnoses the relative impacts of the four known tropical Indo-Pacific drivers, namely, El Niño Southern Oscillation (ENSO), ENSO Modoki, Indian Ocean Dipole (IOD), and Indian Ocean Basin-wide mode (IOBM) on African seasonal rainfall variability. The canonical El Niño and El Niño Modoki are in general associated with anomalous reduction (enhancement) of rainfall in southern (northern) hemispheric regions during March-May season. However, both the El Niño flavours anomalously reduce the northern hemispheric rainfall during June-September. Interestingly, during boreal spring and summer, in many regions, the Indian Ocean drivers have influences opposite to those from tropical Pacific drivers. On the other hand, during the October-December season, the canonical El Niño and/or positive IOD are associated with an anomalous enhancement of rainfall in the Eastern Africa, while the El Niño Modoki events are associated with an opposite impact. In addition to the Walker circulation changes, the Indo-Pacific drivers influence the African rainfall through modulating jet streams. During boreal summer, the El Niño Modoki and canonical El Niño (positive IOD) tend to weaken (strengthen) the tropical easterly jet, and result in strengthening (weakening) and southward shift of African easterly jet. This anomalously reduces (enhances) rainfall in the tropical north, including Sahelian Africa.

No MeSH data available.


Related in: MedlinePlus