Influence of Indian Ocean SST regionality on the East African short rains

2020 ◽  
Vol 54 (11-12) ◽  
pp. 4991-5011 ◽  
Author(s):  
Weiran Liu ◽  
Kerry H. Cook ◽  
Edward K. Vizy
Keyword(s):  
Indian Ocean ◽  
East African ◽  
Short Rains

scholarly journals The Impact of Indian Ocean Mean-State Biases in Climate Models on the Representation of the East African Short Rains

2018 ◽  
Vol 31 (16) ◽  
pp. 6611-6631 ◽  
Author(s):  
Linda Hirons ◽  
Andrew Turner
Keyword(s):  
Indian Ocean ◽  
Wind Stress ◽  
Equatorial Indian Ocean ◽  
East African ◽  
Easterly Wind ◽  
Low Level ◽  
The Indian Ocean ◽  
Short Rains ◽  
The Impact ◽  
Mean State

The role of the Indian Ocean dipole (IOD) in controlling interannual variability in the East African short rains, from October to December, is examined in state-of-the-art models and in detail in one particular climate model. In observations, a wet short-rainy season is associated with the positive phase of the IOD and anomalous easterly low-level flow across the equatorial Indian Ocean. A model’s ability to capture the teleconnection to the positive IOD is closely related to its representation of the mean state. During the short-rains season, the observed low-level wind in the equatorial Indian Ocean is westerly. However, half of the models analyzed exhibit mean-state easterlies across the entire basin. Specifically, those models that exhibit mean-state low-level equatorial easterlies in the Indian Ocean, rather than the observed westerlies, are unable to capture the latitudinal structure of moisture advection into East Africa during a positive IOD. Furthermore, the associated anomalous easterly surface wind stress causes upwelling in the eastern Indian Ocean. This upwelling draws up cool subsurface waters, enhancing the zonal sea surface temperature gradient between west and east and strengthening the positive IOD pattern, further amplifying the easterly wind stress. This positive Bjerknes coupled feedback is stronger in easterly mean-state models, resulting in a wetter East African short-rain precipitation bias in those models.

scholarly journals The Moderate Impact of the 2015 El Niño over East Africa and Its Representation in Seasonal Reforecasts

2019 ◽  
Vol 32 (22) ◽  
pp. 7989-8001 ◽  
Author(s):  
David MacLeod ◽  
Cyril Caminade
Keyword(s):  
Indian Ocean ◽  
East Africa ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Lower Troposphere ◽  
Eastern Indian Ocean ◽  
East African ◽  
The Indian Ocean ◽  
Short Rains

Abstract El Niño–Southern Oscillation (ENSO) has large socioeconomic impacts worldwide. The positive phase of ENSO, El Niño, has been linked to intense rainfall over East Africa during the short rains season (October–December). However, we show here that during the extremely strong 2015 El Niño the precipitation anomaly over most of East Africa during the short rains season was less intense than experienced during previous El Niños, linked to less intense easterlies over the Indian Ocean. This moderate impact was not indicated by reforecasts from the ECMWF operational seasonal forecasting system, SEAS5, which instead forecast large probabilities of an extreme wet signal, with stronger easterly anomalies over the surface of the Indian Ocean and a colder eastern Indian Ocean/western Pacific than was observed. To confirm the relationship of the eastern Indian Ocean to East African rainfall in the forecast for 2015, atmospheric relaxation experiments are carried out that constrain the east Indian Ocean lower troposphere to reanalysis. By doing so the strong wet forecast signal is reduced. These results raise the possibility that link between ENSO and Indian Ocean dipole events is too strong in the ECMWF dynamical seasonal forecast system and that model predictions for the East African short rains rainfall during strong El Niño events may have a bias toward high probabilities of wet conditions.

scholarly journals Paramount Impact of the Indian Ocean Dipole on the East African Short Rains: A CGCM Study

2005 ◽  
Vol 18 (21) ◽  
pp. 4514-4530 ◽  
Author(s):  
Swadhin K. Behera ◽  
Jing-Jia Luo ◽  
Sebastien Masson ◽  
Pascale Delecluse ◽  
Silvio Gualdi ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Indian Ocean Dipole ◽  
General Circulation ◽  
Southern Oscillation ◽  
Circulation Model ◽  
Sea Surface ◽  
Driving Mechanism ◽  
East African ◽  
The Indian Ocean ◽  
Short Rains

Abstract The variability in the East African short rains is investigated using 41-yr data from the observation and 200-yr data from a coupled general circulation model known as the Scale Interaction Experiment-Frontier Research Center for Global Change, version 1 (SINTEX-F1). The model-simulated data provide a scope to understand the climate variability in the region with a better statistical confidence. Most of the variability in the model short rains is linked to the basinwide large-scale coupled mode, that is, the Indian Ocean dipole (IOD) in the tropical Indian Ocean. The analysis of observed data and model results reveals that the influence of the IOD on short rains is overwhelming as compared to that of the El Niño–Southern Oscillation (ENSO); the correlation between ENSO and short rains is insignificant when the IOD influence is excluded. The IOD–short rains relationship does not change significantly in a model experiment in which the ENSO influence is removed by decoupling the ocean and atmosphere in the tropical Pacific. The partial correlation analysis of the model data demonstrates that a secondary influence comes from a regional mode located near the African coast. Inconsistent with the observational findings, the model results show a steady evolution of IOD prior to extreme events of short rains. Dynamically consistent evolution of correlations is found in anomalies of the surface winds, currents, sea surface height, and sea surface temperature. Anomalous changes of the Walker circulation provide a necessary driving mechanism for anomalous moisture transport and convection over the coastal East Africa. The model results nicely augment the observational findings and provide us with a physical basis to consider IOD as a predictor for variations of the short rains. This is demonstrated in detail using the statistical analysis method. The prediction skill of the dipole mode SST index in July and August is 92% for the observation, which scales slightly higher for the model index (96%) in August. As observed in data, the model results show decadal weakening in the relationship between IOD and short rains owing to weakening in the IOD activity.

scholarly journals The Ends of the Indian Ocean: Tracing Coastlines in the Tanzanian “Hinterland”

2019 ◽  
Vol 46 ◽  
pp. 359-383
Author(s):  
Julia Verne
Keyword(s):  
Indian Ocean ◽  
Central Africa ◽  
East African ◽  
Relational Thinking ◽  
East African Coast ◽  
East Central ◽  
Trade Routes ◽  
Empirical Ground ◽  
The Indian Ocean ◽  
Spatial Entity

Abstract:In recent years, several attempts to revitalize Area Studies have concentrated on oceans as the unifying force to create regions. In this respect, the Indian Ocean has become a prime example to show how economic as well as cultural flows across the sea have contributed to close connections between its shores. However, by doing so, they not only seem to create a certain, rather homogeneous, Indian Ocean space, they often also lead to a conceptual separation between “coast” and “hinterland,” similar to earlier distinctions between “African/Arab” or “East/Central Africa.” In this contribution, so-called “Arab” traders who settled along trade routes connecting the East African coast to its hinterland will serve as an empirical ground to explore and challenge these boundaries. Tracing maritime imaginaries and related materialities in the Tanzanian interior, it will reflect on the ends of the Indian Ocean and the nature of such maritime conceptualizations of space more generally. By taking the relational thinking that lies at the ground of maritimity inland, it wishes to encourage a re-conceptualization of areas that not only replaces a terrestrial spatial entity with a maritime one, but that genuinely breaks with such “container-thinking” and, instead, foregrounds the meandering, fluid character of regions and their complex and highly dynamic entanglements.

scholarly journals A 17-My-old whale constrains onset of uplift and climate change in east Africa

2015 ◽  
Vol 112 (13) ◽  
pp. 3910-3915 ◽  
Author(s):  
Henry Wichura ◽  
Louis L. Jacobs ◽  
Andrew Lin ◽  
Michael J. Polcyn ◽  
Fredrick K. Manthi ◽  
...  
Keyword(s):  
Indian Ocean ◽  
East Africa ◽  
Sea Level ◽  
Drainage System ◽  
Beaked Whale ◽  
East African ◽  
Surface Uplift ◽  
The Indian Ocean ◽  
Mantle Processes ◽  
The Impact

Timing and magnitude of surface uplift are key to understanding the impact of crustal deformation and topographic growth on atmospheric circulation, environmental conditions, and surface processes. Uplift of the East African Plateau is linked to mantle processes, but paleoaltimetry data are too scarce to constrain plateau evolution and subsequent vertical motions associated with rifting. Here, we assess the paleotopographic implications of a beaked whale fossil (Ziphiidae) from the Turkana region of Kenya found 740 km inland from the present-day coastline of the Indian Ocean at an elevation of 620 m. The specimen is ∼17 My old and represents the oldest derived beaked whale known, consistent with molecular estimates of the emergence of modern strap-toothed whales (Mesoplodon). The whale traveled from the Indian Ocean inland along an eastward-directed drainage system controlled by the Cretaceous Anza Graben and was stranded slightly above sea level. Surface uplift from near sea level coincides with paleoclimatic change from a humid environment to highly variable and much drier conditions, which altered biotic communities and drove evolution in east Africa, including that of primates.

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