The Turkana Jet is an equatorial low-level jet forming in East Africa. It is one of five major easterly low-level jets forming across the East African Rift System (Munday et al. 2021). Several papers have highlighted the importance of the Turkana Jet for the hydroclimate of East Africa. This page gives a brief history of work on the Turkana Jet, and explains the motivation for the RIFTJet observations.
Early Observations and Modelling
The Turkana Jet was first identified by officers of the Kenya Meteorological Department working out of Marsabit in northwest Kenya. They were regularly releasing pilot balloons at the time, and were returning abnormally high wind speed measurements to the central office in Nairobi. Joseph Hiri Kinuthia worked in Nairobi at the time and came to check out the readings.
After confirming the high wind speeds, he wrote the first paper on the Turkana Jet (Kinuthia and Asnani 1982). Measuring windspeeds only in daylight hours, he documented a southeasterly jet with pilot balloon windspeeds occassionally reaching in excess of 50 m/s. He hypothesised that orographic channeling (Bernoulli effect) was responsible for the fast winds. The Turkana Jet forms in the Turkana Channel, between the Ethiopian Highlands to the northeast and Kenya Highlands to the southwest.
To test this orographic channelling hypothesis, Kinuthia then designed a intensive field period involving multiple sites releasing pilot ballons in February 1983 and in June-July 1984. He found that the wind speeds tended to be fastest where the Turkana Channel was narrowest, and were especially fast near Marsabit. By analysing wind speeds for simultaneous releases, he confirmed presence of divergence along the major jet axis. He proposed that the divergence (and related subsidence) was a key cause of the low rainfall totals in northwest Kenya – possibly responsible for formation of the Chalbi Desert (Kinuthia 1992)
After these two initial papers, not much was written about the Turkana Jet until 2001. Matayo Indeje and colleagues, including Fred Semazzi at North Carolina State University, studied the dynamics of the Turkana Jet using a regional model (RegCM3) with grid spacing of 60 km. For a simulation running in October and November, they confirmed the first order importance of orographic channeling in causing fast jet wind speeds and showed how the depth of the channel influences the height of the jet core. They also computed jet-related moisture divergence, and linked the divergence to the low regional rainfall – in support of Kinuthia’s (1992) hypothesis.
Advent of new reanalysis and model simulations
In the 1990s, observations of the Turkana Jet via pilot balloon stations in the Turkana Channel all but ceased. The advent of reanalysis data offered a new route into understanding the jet and its role in regional climate.
Nicholson (2016) took up this task. Using ERA-Interim renalysis she provided a first full climatology of the Turkana Jet covering the full annual cycle. She found the jet to be a semi-permanent feature throughout the annual cycle. In ERA-Interim, the jet peaks in strength during the July-September dry season. While pilot balloon studied had been limited to daylight hours, when the balloons could be tracked, Nicholson confirmed that the fastest wind speeds occurred at night, as the boundary layer turbulence diminishes. In contrast to the pilot balloon measurements, however, the jet was weak and not present during the afternoon. Nicholson suggests that the strong jet-related divergence in June-September prevents development of a summer rainfall season in parts of Kenya.
Several model or reanalysis based studies followed Nicholson’s work. Hartman (2018) analysed NCEP and MERRA2 reanalysis data to demonstrate a primary role for horizontal temperature (pressure) gradients along the Turkana Channel in forcing the high wind speeds. Vizy and Cook (2019) analyse the jet in August, and link high pressure anomalies – and enhanced height gradient – along the East African coast to stronger phases of the Turkana Jet. Phases when the Turkana Jet is strong are associated with lower rainfall over East African highlands and South Sudan. The opposite is true for weak jet cases (Vizy and Cook 2019).
In the main rainy season, in October-November and March-May, variability in the jet is also linked with altered pressure gradients (King et al. 2021). At intraseasonal timescales, such anomalies have been linked with the MJO, and are amplified surface-atmosphere feedbacks (Talib et al. 2023). A stronger jet normally occurs in MJO phases 6-8, which are associated with enhanced subsidence and dry conditions over East Africa (Talib et al. 2023).
The performance of climate models forming part of the Coupled Model Intercomparison Projects at lower resolution, CMIP5 and CMIP6, is not great. They generally struggle to capture the complex topography of the region and therefore do not represent the Turkana Jet very well (Munday et al., 2021, King et al., 2021, Lino et al., 2022). These modelling errors may limit the value of CMIP projections of future rainfall changes in the region, especially on small scales of analysis.
The future change in the Turkana Jet is uncertain. Results from two high resolution model simulations (25 km and 4.5 km) from the UK Met Office suggest the jet will strengthen in response to an enhanced across channel pressure gradient (Misiani et al., 2021). This future strengthening, however, is at odds with reanalysis data suggest that the jet has been slowing down in recent decades as the channel pressure gradient has decreased (King et al., 2021).
Water vapour transport
The Turkana Jet is an inland branch of the large scale flow in the equatorial Indian Ocean. As a consequence, it transports a great deal of water vapour inland towards the African interior, mainly during the night (Vizy and Cook 2019; Viste and Sorteberg 2013; Munday et al., 2021).
Recent model experiments by Munday et al., (2023) which prevent the Turkana Jet related water vapour transport by blocking the Turkana Channel, show profound changes to African hydroclimate. With the jet blocked off, more water vapour becomes available over East Africa – dramatically increasing rainfall totals across arid regions. In the same experiments, rainfall decreases over the Congo Basin, suggesting a trade off between rainfall between East and Central Africa.
RIFTJet observations
The inconsistensies between reanalysis data, model simulations and pilot balloons, and the recognition of the importance of water vapour transport via the Turkana Jet motivated the RIFTJet field campaign.
New science following the field campaign has emphasised reanalysis underestimation of Turkana Jet winds (Munday et al. 2022, Munday et al. 2023), the influence of elevated subsidence inversions on the diurnal cycle of low-level jet winds, including the daytime persistence of the jet (Munday et al. 2023), instances of extreme water vapour transport associated with the jet (Munday et al. 2022), the role of model resolution in jet wind speed (Warner et al. 2024), and the influence of soil moisture anomalies at amplifying or reducing jet wind speeds (Talib et al. 2025).
See publications for full list of paper emanating from the project.
Bibliography
Hartman, A.T., 2018. An analysis of the effects of temperatures and circulations on the strength of the low-level jet in the Turkana Channel in East Africa. Theoretical and Applied Climatology, 132, pp.1003-1017.
Indeje, M., Semazzi, F.H., Xie, L. and Ogallo, L.J., 2001. Mechanistic model simulations of the East African climate using NCAR regional climate model: influence of large-scale orography on the Turkana low-level jet. Journal of Climate, 14(12), pp.2710-2724.
King, J.A., Engelstaedter, S., Washington, R. and Munday, C., 2021. Variability of the Turkana low‐level jet in reanalysis and models: Implications for rainfall. Journal of Geophysical Research: Atmospheres, 126(10), p.e2020JD034154.
Kinuthia, J.H., 1992. Horizontal and vertical structure of the Lake Turkana jet. Journal of Applied Meteorology and Climatology, 31(11), pp.1248-1274.
Kinuthia, J.H. and Asnani, G.C., 1982. A newly found jet in North Kenya (Turkana Channel). Monthly Weather Review, 110(11), pp.1722-1728.
Misiani, H.O., Finney, D.L., Segele, Z.T., Marsham, J.H., Tadege, A., Artan, G. and Atheru, Z., 2020. Circulation patterns associated with current and future rainfall over Ethiopia and South Sudan from a convection-permitting model. Atmosphere, 11(12), p.1352.
Munday, C., Washington, R. and Hart, N., 2021. African low‐level jets and their importance for water vapor transport and rainfall. Geophysical Research Letters, 48(1), p.e2020GL090999.
Munday, C., Engelstaedter, S., Ouma, G., Ogutu, G., Olago, D., Ong’ech, D., Lees, T., Wanguba, B., Nkatha, R., Ogalo, C. and Gàlgalo, R.A., 2022. Observations of the Turkana Jet and the East African dry tropics: the RIFTJet field campaign. Bulletin of the American Meteorological Society, 103(8), pp.E1828-E1842.
Nicholson, S., 2016. The Turkana low‐level jet: Mean climatology and association with regional aridity. International Journal of Climatology, 36(6), pp.2598-2614.
Oscar, L., Nzau, M.J., Ellen, D. et al. Characteristics of the Turkana low-level jet stream and the associated rainfall in CMIP6 models. Clim Dyn (2022). https://doi.org/10.1007/s00382-022-06499-4
Talib, J., Taylor, C.M., Harris, B.L. & Wainwright, C.M.(2023) Surface-driven amplification of Madden–Julian oscillation circulation anomalies across East Africa and its influence on the Turkana jet. Quarterly Journal of the Royal Meteorological Society, 149(754), 1890–1912. Available from: https://doi.org/10.1002/qj.4487
Talib, J., Taylor, C.M., Klein, C., Warner, J., Munday, C., Folwell, S., et al. (2025) Modelling the influence of soil moisture on the Turkana jet. Quarterly Journal of the Royal Meteorological Society, e4972. Available from: https://doi.org/10.1002/qj.4972
Warner, J. L., Munday, C., & Engelstaedter, S. (2024). Resolving the Turkana Jet—Impact of model resolution in simulating channel flow and inversions. Journal of Geophysical Research: Atmospheres, 129, e2023JD040299. https://doi.org/10.1029/2023JD040299
Vizy, E.K. and Cook, K.H., 2019. Observed relationship between the Turkana low-level jet and boreal summer convection. Climate Dynamics, 53, pp.4037-4058.
RIFTJet field campaign 