By Bernard Gitau
Kenya’s scientists are delving into the mysteries of a powerful wind that shapes the climate across East Africa, known as the Turkana Low-Level Jet (LLJ). This wind is more than just a meteorological curiosity—it’s a driving force behind both flooding and droughts and plays a key role in powering Africa’s largest wind farm.
The Kenya Meteorological Department (KMD), supported by independent research, has been studying the Turkana LLJ to understand its far-reaching effects. Prof. Gilbert Ouma, a Senior Lecturer at the University of Nairobi’s Institute for Climate Change and Adaptation and Department of Meteorology, describes the jet as “an intrinsic part of the African climate system.”
“It is the principal conduit for water vapor transport to the African interior from the Indian Ocean, and droughts in East Africa tend to occur when the jet is strong,” Prof. Ouma explains.
A 2013 study by Sorteberg highlights that the Turkana LLJ is responsible for about a third of the water vapor that crosses the East African Rift System from the Indian Ocean to the heart of the continent. As Prof. Ouma points out, “You need moisture for rainfall, and if you look at Turkana and the eastern part of Kenya, there is hardly any source of moisture, except for Lake Turkana, but that’s minimal.”
The Turkana LLJ was first identified in the 1980s by Joseph Hiri Kinuthia, a Kenya Meteorological Department officer. His groundbreaking pilot weather balloon observations revealed the existence of a strong southeasterly low-level jet in the Turkana channel, separating the Ethiopian Highlands from the East African highlands.
Kinuthia’s studies showed that the jet exists year-round, with wind speeds sometimes exceeding 50 meters per second. Interestingly, morning winds tend to be stronger than those in the afternoon, likely due to stronger vertical mixing and dilution of the jet maximum later in the day.
Kenya meteorological Department Deputy Director Mr Charles Mugah during the weather balloon launch. | Photo by Bernard Gitau
However, modern reanalysis datasets have struggled to capture the true strength of the Turkana LLJ, underestimating it by as much as 75% compared to Kinuthia’s original balloon data. To address this, the Radiosonde Investigation for the Turkana Jet (RIFTJet) was conducted from March 26 to April 23, 2021. This study utilized modern technology to observe the jet’s full diurnal cycle and quantify the moisture it transports.
According to Prof. Ouma, the Radiosonde data confirmed the jet’s persistence, with an average low-level maximum wind speed of 16.8 meters per second. These measurements underscore the jet’s crucial role in transporting water vapor, with Marsabit recording a mean transport rate of 172 kg m s−1.
“This is important information for the area—Marsabit, Turkana, and the drylands; we know they have floods. Sometimes those floods come from heavy rainfall within that region and sometimes from Mt. Elgon, which is a source of most rivers,” Prof. Ouma notes.
Accurate forecasting of these intense rainfalls is vital for water harvesting, disaster preparedness, and drought mitigation in these vulnerable regions.
But how does this mighty wind form? Prof. Ouma explains that it’s all about the interplay between land and water. The Northern Hemisphere has more land, while the Southern Hemisphere has more water. “Land and water heat differently, and when the sun heats the north, the land surface heats much faster, creating an imbalance—higher temperatures in the north and lower temperatures in the south—that drives the wind system and, ultimately, the jet,” he says.
As the seasons change, so does the movement of the wind. “During the rainy season, the wind moves upwards, bringing moisture from the Indian Ocean. During the dry season—December, January, February, June, July, and August—it moves downwards, and since it’s coming from the dry continental areas, there’s no moisture, and thus, no rainfall. But if it’s moving up, it picks up moisture from the Indian Ocean, bringing significant rainfall, especially to the Ethiopian highlands,” Prof. Ouma adds.
The Turkana Low-Level Jet is more than just a scientific phenomenon; it’s a vital part of East Africa’s climate narrative, influencing weather patterns and the livelihoods of millions. As research continues, understanding this jet could be key to unlocking new strategies for managing water resources, mitigating disasters, and adapting to climate change in the region.
