The Indian Ocean Dipole and its Impact on East African Short Rains in Two CMIP5 Historical Scenarios With and Without Anthropogenic Influence

• Published in: Journal of geophysical research. Atmospheres 2020-08, Vol.125 (16), p.n/a
• Main Authors: Blau, M. T., Ha, K.‐J.
• Format: Article
• Language: English
• Subjects: Anthropogenic factors; Atmosphere; Climate change; Climate models; CMIP5 models; Computer simulation; Convergence; Convergence zones; Dipoles; East African precipitation; Emissions; Environmental impact; Geophysics; Hadley circulation; human impact detection; Human influences; Hydroclimate; Indian Ocean dipole mode; Intercomparison; Intertropical convergence zone; Moisture; Oceans; Precipitation; Precipitation regime; short rains; Temperature; Tropical circulation; Tropical climate; Variability; Walker circulation; Water vapor; Water vapour
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1029/2020JD033121

The Indian Ocean dipole mode impacts the atmosphere and hydroclimate in areas surrounding the Indian Ocean. The Coupled Model Intercomparison Project 5 output was used in this study to reveal new aspects of the relationship between the dipole mode and East African “short rains” (occurring from September to November). Furthermore, the impact of human activity on the ocean‐atmosphere system was investigated using two scenarios, one with and one without human forcings from 1960 to 1999. The Indian Ocean dipole and its teleconnection were simulated, and the impact of the dipole mode on the atmosphere displayed a similar pattern and strength under both scenarios. However, the dipole peak was slightly delayed from September to October under the scenario with anthropogenic warming. Further, increased moisture convergence over East Africa was found to enhance the local monsoon system during boreal autumn in the scenario considering anthropogenic forcing. More intense Walker and Hadley circulations were found with the presence of anthropogenic influences and the dipole mode had a significant impact on both. Positive Indian Ocean dipole events were found to temporarily weaken Walker circulation and strengthen Hadley circulation. Plain Language Summary The Indian Ocean significantly affects the precipitation regime of East Africa during the “short rains” in September, October, and November. The precipitation amount in this season is determined by the variability of the neighboring ocean, namely, the Indian Ocean dipole mode. In this study, the interaction between the Indian Ocean and short rains and the impact of climate change were investigated, yielding new insights. To evaluate changes in the system due to human emissions, two scenarios, one including and one excluding anthropogenic impacts on climate, were considered. The results showed that peak variability was delayed from September to October due to human impacts. Between 1960 and 1999, tropical circulations (namely, Walker and Hadley circulations) and the intertropical convergence zone were stronger under anthropogenic influences. Further, the ability of the air to hold water vapor and the moisture convergence over East Africa was enhanced, leading to increasingly frequent wet years with enhanced anthropogenic emissions. Key Points Human influence enhanced the tropical circulation of the western Indian Ocean between 1960 and 1999 Human influence historically delays the peak phase of the dipole mode and easter