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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

First column (a–c) shows, respectively, simulated rainfall (mm/month), 200 hPa zonal winds (m/s) and 700 hPa zonal winds (m/s) during JJAS season from the control experiment. The simulated differences for the El Niño Modoki experiment (obtained by subtracting the control simulation from the El Niño Modoki simulation) are shown in second column (d–f represent rainfall, 200 hPa and 700 hPa zonal winds respectively). The corresponding differences for the El Niño experiment and positive IOD experiment are shown in third (g–i) and fourth columns (j–l) respectively. Significant values at 85%, 90% and 95% confidence level based on Student’s t-test are shown in shadings. [Figure created using the COLA/GrADS software].
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f7: First column (a–c) shows, respectively, simulated rainfall (mm/month), 200 hPa zonal winds (m/s) and 700 hPa zonal winds (m/s) during JJAS season from the control experiment. The simulated differences for the El Niño Modoki experiment (obtained by subtracting the control simulation from the El Niño Modoki simulation) are shown in second column (d–f represent rainfall, 200 hPa and 700 hPa zonal winds respectively). The corresponding differences for the El Niño experiment and positive IOD experiment are shown in third (g–i) and fourth columns (j–l) respectively. Significant values at 85%, 90% and 95% confidence level based on Student’s t-test are shown in shadings. [Figure created using the COLA/GrADS software].

Mentions: To confirm that such an attributed change in zonal winds during the boreal summer is indeed due to the forcing from Indo-Pacific events, we perform the following several sensitivity experiments using the LMDZ (Laboratoire de Meteorologie Dynamique and Z stands for Zoom) Atmospheric General Circulation Model (AGCM), (a) a control experiment with climatological SST, and experiments in which the AGCM is forced with SSTs representative of a typical (b) El Niño Modoki, (c) canonical El Niño and (d) positive IOD. Before analysing the results, we ascertain the ability of the LMDZ model in simulating the climatological rainfall and zonal winds over Africa. A comparison between the observations (Fig. 6a–c) and model-simulations obtained from the control run (Fig. 7a–c), demonstrates that the model, in general, simulates a reasonable spatial distribution of the JJAS rainfall and zonal winds over Africa. Intensity and general position of core axis of the TEJ and AEJ are also in good agreement with the observations.


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)

First column (a–c) shows, respectively, simulated rainfall (mm/month), 200 hPa zonal winds (m/s) and 700 hPa zonal winds (m/s) during JJAS season from the control experiment. The simulated differences for the El Niño Modoki experiment (obtained by subtracting the control simulation from the El Niño Modoki simulation) are shown in second column (d–f represent rainfall, 200 hPa and 700 hPa zonal winds respectively). The corresponding differences for the El Niño experiment and positive IOD experiment are shown in third (g–i) and fourth columns (j–l) respectively. Significant values at 85%, 90% and 95% confidence level based on Student’s t-test are shown in shadings. [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

f7: First column (a–c) shows, respectively, simulated rainfall (mm/month), 200 hPa zonal winds (m/s) and 700 hPa zonal winds (m/s) during JJAS season from the control experiment. The simulated differences for the El Niño Modoki experiment (obtained by subtracting the control simulation from the El Niño Modoki simulation) are shown in second column (d–f represent rainfall, 200 hPa and 700 hPa zonal winds respectively). The corresponding differences for the El Niño experiment and positive IOD experiment are shown in third (g–i) and fourth columns (j–l) respectively. Significant values at 85%, 90% and 95% confidence level based on Student’s t-test are shown in shadings. [Figure created using the COLA/GrADS software].
Mentions: To confirm that such an attributed change in zonal winds during the boreal summer is indeed due to the forcing from Indo-Pacific events, we perform the following several sensitivity experiments using the LMDZ (Laboratoire de Meteorologie Dynamique and Z stands for Zoom) Atmospheric General Circulation Model (AGCM), (a) a control experiment with climatological SST, and experiments in which the AGCM is forced with SSTs representative of a typical (b) El Niño Modoki, (c) canonical El Niño and (d) positive IOD. Before analysing the results, we ascertain the ability of the LMDZ model in simulating the climatological rainfall and zonal winds over Africa. A comparison between the observations (Fig. 6a–c) and model-simulations obtained from the control run (Fig. 7a–c), demonstrates that the model, in general, simulates a reasonable spatial distribution of the JJAS rainfall and zonal winds over Africa. Intensity and general position of core axis of the TEJ and AEJ are also in good agreement with the observations.

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