Abstract 007

Abstract ID: 007

Surface drivers of sub-seasonal predictability across Africa

Lead Author: Joshua Talib
UK Centre for Ecology and Hydrology, United Kingdom

Keywords: Land, Drivers, Africa, Observations, Atmosphere dynamics

Abstract: Land surface characteristics are a key source of sub-seasonal predictability as they vary more slowly than atmospheric conditions but quicker than oceanic states. However, an understanding of the dynamical atmospheric response to sub-seasonal surface variability remains limited across Africa. Using earth observations and reanalysis data, in this presentation we will show how sub-seasonal precipitation variability across West and East Africa promotes a surface response which feeds back onto regional atmospheric conditions.
Surface soil moisture decreases across semi-arid regions during intraseasonal dry spells. This increases surface sensible heat fluxes and elevates land surface temperatures. During the West African monsoon for example, surface drying during an intraseasonal dry spell increases surface temperatures by approximately 1.5°C across the Sahel. This large-scale surface warming increases the depth of the planetary boundary layer, shifts low-level monsoon winds southwards by 1.5° latitude, and intensifies the African easterly jet. Across East Africa meanwhile, we conclude that surface-driven pressure fluctuations over the course of a single day are responsible for approximately 11% of the anomalous Turkana jet speed during a dry intraseasonal spell. Surface-induced jet variations impact the moisture budget across East Africa. To fully exploit predictability from sub-seasonal rainfall variability, forecast models must correctly represent surface processes and land-atmosphere feedbacks. Future work evaluating sub-seasonal forecast models and improving the representation of land-atmosphere interactions will enhance forecast skill across Africa.

Christopher M. Taylor (UK Centre for Ecology and Hydrology)
Bethan L. Harris (UK Centre for Ecology and Hydrology)
Cornelia Klein (UK Centre for Ecology and Hydrology)
Seonaid R. Anderson (UK Centre for Ecology and Hydrology)
Valiyaveetil S. Semeena (UK Centre for Ecology and Hydrology)
Caroline Wainwright (Imperial College London, U.K.)