Abstract
AbstractThe role of the Indian Ocean dipole (IOD) in controlling interannual variability in the East African short rains, from October to December, is examined in state-of-the-art models and in detail in one particular climate model. In observations, a wet short-rainy season is associated with the positive phase of the IOD and anomalous easterly low-level flow across the equatorial Indian Ocean. A model’s ability to capture the teleconnection to the positive IOD is closely related to its representation of the mean state. During the short-rains season, the observed low-level wind in the equatorial Indian Ocean is westerly. However, half of the models analyzed exhibit mean-state easterlies across the entire basin. Specifically, those models that exhibit mean-state low-level equatorial easterlies in the Indian Ocean, rather than the observed westerlies, are unable to capture the latitudinal structure of moisture advection into East Africa during a positive IOD. Furthermore, the associated anomalous easterly surface wind stress causes upwelling in the eastern Indian Ocean. This upwelling draws up cool subsurface waters, enhancing the zonal sea surface temperature gradient between west and east and strengthening the positive IOD pattern, further amplifying the easterly wind stress. This positive Bjerknes coupled feedback is stronger in easterly mean-state models, resulting in a wetter East African short-rain precipitation bias in those models.
Highlights
Eastern Africa comprises the countries Tanzania, Burundi, Rwanda, Uganda, Kenya, Somalia, Ethiopia, South Sudan, Djibouti, and Eritrea
This leads to several outstanding questions: (i) How is the wet bias over East Africa (EA) related to larger-scale mean-state biases in the Indian Ocean (IO), and are these consistent across models? (ii) What influence do such large-scale biases in the IO have on the interaction between the Indian Ocean dipole (IOD) and East African short rains (EASR)? (iii) What is the role of ocean–atmosphere coupling? This study will address these questions by comparing teleconnections between the IOD and EASR in a range of coupled and atmosphereonly global climate models
It is well known that large-scale patterns of sea surface temperatures (SSTs) in the Pacific (e.g., Hoell and Funk 2014) and Indian (e.g., Bahaga et al 2015) Oceans drive interannual variability in the East African short rains (EASR) from October to December (OND)
Summary
National Centre for Atmospheric Science, University of Reading, Reading, United Kingdom.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.