scholarly journals Diagnosing the Droughts and Floods in Equatorial East Africa during Boreal Autumn 2005–08

2010 ◽  
Vol 23 (3) ◽  
pp. 813-817 ◽  
Author(s):  
Stefan Hastenrath ◽  
Dierk Polzin ◽  
Charles Mutai
Keyword(s):  
Indian Ocean ◽  
East Africa ◽  
Short Note ◽  
Vertical Circulation ◽  
Circulation Cell ◽  
Droughts And Floods ◽  
The Indian Ocean ◽  
Short Rains ◽  
Surface Manifestation

Abstract Building on an earlier report on the 2005 drought in equatorial East Africa, this short note examines the circulation mechanisms of the anomalies in the boreal autumn “short rains” season in the subsequent three years. Westerlies during this season are the surface manifestation of a powerful zonal–vertical circulation cell along the Indian Ocean equator. The surface equatorial westerlies were fast during the 2005 and 2008 droughts, near average during the near-average 2007 short rains, and slack during the 2006 floods, consistent with the known circulation diagnostics.

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 Diagnosing the 2005 Drought in Equatorial East Africa

2007 ◽  
Vol 20 (18) ◽  
pp. 4628-4637 ◽  
Author(s):  
Stefan Hastenrath ◽  
Dierk Polzin ◽  
Charles Mutai
Keyword(s):  
Indian Ocean ◽  
Pressure Gradient ◽  
East Africa ◽  
Equatorial Indian Ocean ◽  
Ocean Basin ◽  
Severe Drought ◽  
The West ◽  
Zonal Circulation ◽  
Circulation Cell ◽  
Short Rains

Abstract Equatorial East Africa suffered severe drought during its 2005 “short rains,” centered on October–November. The circulation mechanisms of such precipitation anomalies are examined, using long-term upper-air and surface datasets, and based on diagnostic findings from earlier empirical investigations. The steep eastward pressure gradient is conducive to fast westerlies over the central-equatorial Indian Ocean, surface manifestation of a powerful zonal circulation cell with subsidence over East Africa, and ascending motion over Indonesia. With fast westerlies, rainfall in East Africa is deficient and they tend to be accompanied by anomalously cold waters in the northwestern and warm anomalies in the southeastern extremity of the equatorial Indian Ocean Basin, without any seesaw between these domains. In October–November 2005, pressure in the west was anomalously high, entailing a steep eastward pressure gradient along the equator, conducive to fast westerlies and, further symptomatic of the zonal circulation cell, subsidence in the west and ascending motion in the east were enhanced. Overall, the chain of causalities can be traced to anomalously high pressure in the west.

scholarly journals Customization and Validation of a Regional Climate Model Using Satellite Data Over East Africa

Atmosphere ◽  
2019 ◽  
Vol 10 (6) ◽  
pp. 317
Author(s):  
Masilin Gudoshava ◽  
Fredrick H. M. Semazzi
Keyword(s):  
Indian Ocean ◽  
Surface Temperature ◽  
East Africa ◽  
Climate Model ◽  
Lake Victoria ◽  
Regional Climate ◽  
Sea Surface ◽  
Modes Of Variability ◽  
The Indian Ocean ◽  
Short Rains

This study focused on the customization of the fourth generation International Center for Theoretical Physics Regional Climate Model version 4.4 and its ability to reproduce the mean climate and most dominant modes of variability over East Africa. The simulations were performed at a spatial resolution of 25 km for the period 1998–2013. The model was driven by ERA-Interim reanalysis. The customization focus was on cumulus and microphysics schemes during the Short Rains for the year 2000. The best physics combinations were then utilized for the validation studies. The East Africa region and Lake Victoria Basin region are adapted to carry out empirical orthogonal function analysis, during the Short and Long Rains. Tropical Rainfall Measuring Mission data was utilized in the validation of the model. The first mode of variability from the model and observational data during the Short Rains was associated with the warming of the Pacific Ocean and the sea surface temperature gradients over the Indian Ocean. During the Long rains, the inter-annual rainfall variability over the Lake Victoria region was associated with the sea surface temperature anomaly over the Indian Ocean and for the East Africa region the associations were weak. The drivers during the Long Rains over East Africa region were then further investigated by splitting the season to the March–April and May periods. The March–April period was positively correlated to the West Pacific and Indian Ocean dipole index, while May was associated with the Quasi-Biennial Oscillation. In conclusion, although the model can reproduce the dominant modes of variability as in the observational data sets during the Short Rains, skill was lower during the Long Rains.

scholarly journals Circulation Mechanisms of Kenya Rainfall Anomalies

2011 ◽  
Vol 24 (2) ◽  
pp. 404-412 ◽  
Author(s):  
Stefan Hastenrath ◽  
Dierk Polzin ◽  
Charles Mutai
Keyword(s):  
Indian Ocean ◽  
East Africa ◽  
Rainfall Variability ◽  
Equatorial Indian Ocean ◽  
Vertical Circulation ◽  
Boreal Spring ◽  
Zonal Circulation ◽  
South Indian ◽  
Extreme Flood ◽  
Circulation Cell

Abstract Expanding earlier studies on the boreal spring and autumn rainy seasons in equatorial East Africa, pending challenges on the mechanisms of rainfall variability, are investigated. Eastward pressure gradient and slack south Indian Ocean trade winds allow surface equatorial westerlies in spring and autumn. Complementing that, upper-tropospheric easterlies are required for the development of a zonal vertical circulation cell along the Indian Ocean equator. Because of the summer warming and high stand of upper-tropospheric topography over South Asia, strong upper-tropospheric easterlies over the tropical northern and equatorial Indian Ocean persist from summer into autumn, thus allowing the development of a zonal vertical circulation cell. By contrast, the winter cooling entails low stand of upper-tropospheric topography in the north, thus hindering easterlies over the equator. Consequently, an equatorial zonal circulation cell does not develop in boreal spring. The equatorial zonal circulation cell, with subsidence over East Africa, strongly controls the boreal autumn rains, as evidenced in their tight correlation with the equatorial westerlies. In a related vein, rain gauge stations show much shared variance in boreal autumn as compared to spring. Plausibly consistent with this, boreal autumn rather than spring has brought the extreme flood and drought disasters in the course of the past half-century.

Shipping and Trade between Hamburg-Bremen and the Indian Ocean, 1870–1914

1982 ◽  
Vol 13 (2) ◽  
pp. 349-386
Author(s):  
Hermann Kellenbenz
Keyword(s):  
Indian Ocean ◽  
East Africa ◽  
First World War ◽  
The Philippines ◽  
Early Years ◽  
World War ◽  
Short Survey ◽  
The First World War ◽  
The Indian Ocean ◽  
First World

This study is intended to give a short survey on the development of shipping and trade between two main German ports and the Indian Ocean from the early years of the Bismarck period to the beginning of the First World War. The study deals with the area from East Africa to East India and from Indochina to Indonesia. China, the Philippines, and Australia will not be considered. It is based on an analysis of published material.

scholarly journals The Geology of Portuguese Nyasaland

1922 ◽  
Vol 59 (5) ◽  
pp. 200-212
Author(s):  
Robert R. Walls
Keyword(s):  
Indian Ocean ◽  
East Africa ◽  
The South ◽  
The North ◽  
Dark Continent ◽  
The Indian Ocean

Portuguese Nyasaland is the name given to the most northern part of Portuguese East Africa, lying between Lake Nyasa and the Indian Ocean. It is separated from the Tanganyika territory in the north by the River Rovuma and from the Portuguese province of Mozambique in the south by the River Lurio. The territory measures about 400 miles from east to west and 200 miles from north to south and has an area of nearly 90,000 square miles. This territory is now perhaps the least known part of the once Dark Continent, but while the writer was actually engaged in the exploration of this country in 1920–1, the Naval Intelligence Division of the British Admiralty published two handbooks, the Manual of Portuguese East Africa and the Handbook of Portuguese Nyasaland, which with their extensive bibliographies contained practically everything that was known of that country up to that date (1920). These handbooks make it unnecessary in this paper to give detailed accounts of the work of previous explorers.

Forty Years On

2019 ◽  
pp. 17-51
Author(s):  
Edward A. Alpers
Keyword(s):  
Indian Ocean ◽  
East Africa ◽  
African Diaspora ◽  
Eastern Africa ◽  
Modern Period ◽  
The Indian Ocean ◽  
Indian Ocean World

Almost forty years ago, the author published an article on Gujarat and East Africa from the sixteenth to the nineteenth centuries. Although several other scholars had written serious historical works either about or including Indian traders in eastern Africa in the modern period, at the time it was a pioneering piece for historians of East Africa. While the author has written and continues to write about the African diaspora in the Indian Ocean world and, more recently, the islands of this vast oceanic space now referred to as Indian Ocean Africa, he has not again written anything specifically about Gujarat and the Indian Ocean, nor about Gujarati traders in East Africa. This chapter attempts to review the last forty years of scholarship written in English on Gujarat and the Indian Ocean with a focus on transregional trade and traders. What is hoped from this overview is a sense of how current debates have developed over these decades and where further research is called for.

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