Browsing by Author "Mahongo, Shigalla B."

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    Biophysical modelling of coastal upwelling variability and circulation along the Tanzanian and Kenyan coasts
    (Western Indian Ocean Marine Science Association, 2020) Halo, Issufo; Sagero, Philip; Manyilizu, Majuto; Mahongo, Shigalla B.
    Ocean circulation, upwelling phenomena and chlorophyll-a concentrations were investigated within the framework of numerical model simulations with 1/12 nested horizontal grid-size, in the tropical western Indian Ocean, along the coasts of Tanzania and Kenya. Ekman driven upwelling exhibited high levels of spatial and temporal variability in the region, characterized by a more vigorous occurrence/intensification during the Northeast than the Southwest Monsoon season. A similar trend was observed for chlorophyll-a distribution, but with an additional strong contribution during the inter-monsoon period from March to April. Trend analysis of a SST-derived coastal upwelling index (CUI) computed over the Pemba Channel and offshore of the East African Coastal Current (EACC), for 24 years (1990-2013), revealed a general linear relation of the form CUI (yr)= 2.4 x10-7 yr–285, with a steady small annual increase of the upwelling phenomena by 0.0024/year≃ 4% during the whole period of the simulation, which could be attributed to documented increasing trends of wind intensity and water volume transport in the region. The CUI exhibited the two most dominant peaks of variabilities on the range of annual and semi-annual timescales. The wind-stress southward component and the easting/westing veering of the northward EACC at 6 S revealed that these parameters were moderate and significantly correlated with the CUI (r=-0.53 and 0.52, p< 0.05) respectively, further suggesting its intensification during the Northeast Monsoon season.
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    A comparative study of ocean surface interannual variability in Northern Tanzania and the Northern Kenya bank
    (WIOMSA, 2020) Manyilizu, Majuto; Sagero, Philip; Halo, Issufo; Mahongo, Shigalla B.
    The livelihoods of most residents of Tanga (Northern Tanzania) and Malindi (Northern Kenya), rely strongly on fish¬ing activities in the East African shelf region. Thus, understanding variations in sea surface temperature (SST) and its related parameters such as thermocline depths and upper ocean circulation are crucial. This study applies a regional model to understand interannual spatial relationships between ocean circulation and SST off Northern Tanzania and on the Northern Kenya Bank. The results indicate slight differences in variations off the Northern Tanzanian shelf region and the Northern Kenya Bank. Such small variations might have local impacts on the human popula¬tion through influencing primary productivity and fisheries. The coastal waters off Malindi indicate stronger varia¬tions, particularly in 1997 (cold SST) and 1998 (warm SST), than those off Tanga region. The SST anomalies seem to be associated with thermocline and sea surface height (SSH) off Malindi, while off Tanga they relate only to SSH. This information provides further understanding of parameters that may affect fishing activities in these regions and can be used for planning and management processes.