Mascarene High on Rainfall Anomalies over Rwanda – Abstract

Journal of Environmental and Agricultural Sciences (JEAS). Nkurunziza et al., 2019. Volume 20: 1-20

Open Access – Research Article

Influence of the Mascarene High on October-December Rainfall and their Associated Atmospheric Circulation Anomalies over Rwanda
Idrissa F. Nkurunziza 1 , Tan Guirong 2 , Jean Paul Ngarukiyimana 2,*, Celestin Sindikubwabo 3
1 Key Laboratory of the Atmospheric Composition & Optical Radiation, CAS, School of Earth & Space Sciences, University of Science & Technology, Hefei, China
2 Key Laboratory of Meteorological Disaster, Ministry of Education (KLME)/Joint International Research Laboratory of Climate & Environment Change (ILCBC)/Collaborative Disasters (CIC-FEMD), Nanjing 210044, China
3 Key Laboratory of Arid Climate Change & Disaster Reduction of Gansu Province, College of Atmospheric Sciences, Lanzhou University, Lanzhou, Gansu, China

Abstract: This study aims to understand the influence of the Mascarene High (MH) on October to December (OND) rainfall and their associated atmospheric circulation anomalies in East Africa (EA) region with a focus on Rwanda. The relationship between Mascarene high indices and rainfall over the study area was revealed. The Mascarene East Ridge index presented significant correlation (r=0.53) with OND rainfall. Further investigation indicated that MH moves eastwards from its normal position, the rainfall was abnormally increased while when MH moves westwards from its normal position the rainfall deficit were noted over the study region. Associated atmospheric circulation anomalies (wind, velocity potential, sea surface temperature) show a close relation with the zonal movement of the Mascarene eastern ridge. The region was dominated by westerly winds at a lower level (850hPa) and easterly wind at high level (200hPa) during eastwards movement of MH. As the MH moves to east it gets weakened; the southerlies wind advected moisture from western equatorial Indian Ocean and reached Rwanda after being deflected by mountain Kenya and Kilimanjaro as north easterlies and easterlies converging with westerlies from Congo airmass. While during the westward position, the reverse was observed. Wet years i.e. 1997, 2002 and 2006 occurred when the MH moves eastwards, peaking in 1997 where it extends up to 10°E of its normal position; while the dry years i.e. 1981, 1993, 1996, 1998, 2005 coincide with west MH movement. Sea surface temperature over Indian Ocean and Mascarene East Ridge were positively correlated with significance level higher than 0.05 level. It was noted that when the Mascarene East Ridge moves to the East position, the Sea surface temperature gets warmer (positive anomaly) and cooler (negative anomaly) during West position.

Keywords: Mascarene High, East ridge, rainfall, East Africa, Rwanda.

*Corresponding author: Jean Paul Ngarukiyimana:

Cite this article as:
Nkurunziza, I.F., T. Guirong, J.P. Ngarukiyimana and C. Sindikubwabo. 2019. Influence of the Mascarene High on October-December rainfall and their associated atmospheric circulation anomalies over Rwanda. Journal of Environmental & Agricultural Sciences. 20:1-20. [Abstract] [View Full-Text] [Citations]

Copyright © Nkurunziza et al., 2019. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium provided the original author and source are appropriately cited and credited.

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