Circulation P... Ocean Dipole_Chibuike Chie...ozie IBEBUCHI.pdf

Circulation Patterns Linked to the Positive Sub-TropicalIndian Ocean DipoleChibuike Chiedozie IBEBUCHI*Institute of Geography and Geology,University of Wrzburg,Am Hubland 97074 Wrzburg,Germany(Received 29 January 2022;revised 14 April 2022;accepted 18 May 2022)ABSTRACTThe positive phase of the subtropical Indian Ocean dipole(SIOD)is one of the climatic modes in the subtropicalsouthern Indian Ocean that influences the austral summer inter-annual rainfall variability in parts of southern Africa.Thispaper examines austral summer rain-bearing circulation types(CTs)in Africa south of the equator that are related to thepositive SIOD and the dynamics through which specific rainfall regions in southern Africa can be influenced by thisrelationship.Four austral summer rain-bearing CTs were obtained.Among the four CTs,the CT that featured(i)enhancedcyclonic activity in the southwest Indian Ocean;(ii)positive widespread rainfall anomaly in the southwest Indian Ocean;and(iii)low-level convergence of moisture fluxes from the tropical South Atlantic Ocean,tropical Indian Ocean,and thesouthwest Indian Ocean,over the south-central landmass of Africa,was found to be related to the positive SIOD climaticmode.The relationship also implies that positive SIOD can be expected to increase the amplitude and frequency ofoccurrence of the aforementioned CT.The linkage between the CT related to the positive SIOD and austral summerhomogeneous regions of rainfall anomalies in Africa south of the equator showed that it is the principal CT that is related tothe inter-annual rainfall variability of the south-central regions of Africa,where the SIOD is already known to significantlyinfluence its rainfall variability.Hence,through the large-scale patterns of atmospheric circulation associated with the CT,the SIOD can influence the spatial distribution and intensity of rainfall over the preferred landmass through enhancedmoisture convergence.Key words:subtropical Indian Ocean dipole,circulation types,rainfall,South Indian Ocean,moisture convergenceCitation:Ibebuchi,C.C.,2023:Circulation patterns linked to the positive sub-tropical Indian Ocean dipole.Adv.Atmos.Sci.,40(1),110128,https:/doi.org/10.1007/s00376-022-2017-2.Article Highlights:The positive phase of the subtropical Indian Ocean dipole modulates circulation patterns in Africa south of the equator.Through the modulation of circulation patterns,summer rainfall variability at the south-central parts of Africa areimpacted.Enhanced convective activity in parts of the southwest Indian Ocean contribute to above-average rainfall at the south-central parts of Africa.1.IntroductionThe inter-annual variability of rainfall in southernAfrica during austral summer is to a large extent related tosea surface temperature(SST)anomalies in the southwestIndian Ocean(Reason and Mulenga,1999).According to Rap-olaki et al.(2020),from January to April,the tropical north-west Indian Ocean and the northern Agulhas current are themajor sources of moisture to southern Africa.Climaticmodes in the south Indian Ocean are known to be associatedwith extreme events in southern Africa such as floods anddrought(Reason,2001;Manatsa et al.,2008),influence thespatial pattern and frequency of tropical cyclones in thesouth Indian Ocean(Ho et al.,2006;Ibebuchi,2022a),andeven modulate the southern Africa precipitation response tothe El Nio Southern Oscillation(ENSO)signal(Hoell etal.,2017).The primary inter-annual climatic modes in theIndian Ocean are the tropical Indian Ocean dipole(Saji etal.,1999),and the subtropical Indian Ocean dipole(SIOD)(Behera and Yamagata,2001),with ENSO having rather aremote influence(Meehl,1987;Hermes and Reason,2005;Ibebuchi,2021c).These climatic modes,through the modula-tion of regional atmospheric circulation patterns,can influ-ence the intensity and spatial distribution of rainfall in south-ern Africa (Xue et al.,2003;Reason and Jagadheesha,*Corresponding author:Chibuike Chiedozie IBEBUCHIEmail:chibuike.ibebuchiuni-wuerzburg.deADVANCES IN ATMOSPHERIC SCIENCES,VOL.40,JANUARY 2023,110128 Original Paper The Author(s)2023.This article is published with open access at .2005;Manatsa et al.,2008;Lim and Hendon,2017;Ibebuchi,2021a,c).The SIOD is phase-locked in the growingseason of southern Africa(Behera and Yamagata,2001)andits positive phase has been linked to above-average australsummer rainfall over parts of southern Africa (Reason,2002),which can impact food security and agricultural activi-ties.This study is dedicated to extending the understandingof the relationship between the positive SIOD climaticmode and the austral summer rain-bearing circulation types(CTs)in Africa south of the equator,and how this relationshipmight explain the large-scale patterns of atmospheric circula-tion through which the positive SIOD might influence theintensity and spatial distribution of rainfall at specificregions in Africa south of the equator.Generally,the hydroclimate of southern Africa can bemodulated by clim