Editorial Type:
Article
Article Type:
Research Article

Passive Suppression of South African Rainfall by the Agulhas Current

Mark R. Jury University of Zululand, KwaDlangezwa, South Africa, and Physics Department, University of Puerto Rico Mayagüez, Mayagüez, Puerto Rico

Search for other papers by Mark R. Jury in
Current site
Google Scholar
PubMed Close
Print Publication:
01 Oct 2015
DOI:
https://doi.org/10.1175/EI-D-15-0017.1
Page(s):
1–14
Restricted access

Abstract

This study reconsiders the role of the Agulhas Current in South African climate variability. Here, the Agulhas Current is delimited by its anticyclonic looping flow and cluster analysis of detrended SST anomalies that lead to an area 28°–37°S, 18°–35°E, poleward of South Africa. Regression of detrended Agulhas SST with rainfall anomaly fields in the years 1950–2012 yields a surprising negative influence over the interior. In summer, the negative regression exhibits a northwest axis consistent with reduced cloud band activity. Positive influence is confined to the eastern escarpment in the September–November season when cutoff lows are prevalent. The overall negative influence of the Agulhas SST is confirmed by regression with the vegetation fraction and latent heat flux in the satellite era.

Mechanisms of South African rainfall suppression were investigated. The Agulhas SST index is positively related to the multivariate ENSO index at the 1–3-month lead time. Hence, warm years in the Agulhas Current follow Pacific El Niño. Composite ocean analysis shows enhanced westerly winds offshore and a westward extension of warm salty water from the anticyclonic south Indian Ocean gyre. Composite atmospheric analysis exhibits moist uplifted air over the Agulhas Current folding into an equatorward circulation that sinks over the interior plateau. Because Agulhas SST partially follows ENSO, its suppression of interior rainfall is concluded to be passive.

Corresponding author address: Mark R. Jury, Physics Dept., University of Puerto Rico Mayagüez, P.O. Box 9000, Mayagüez, Puerto Rico, 00681. E-mail address: mark.jury@upr.edu

Abstract

This study reconsiders the role of the Agulhas Current in South African climate variability. Here, the Agulhas Current is delimited by its anticyclonic looping flow and cluster analysis of detrended SST anomalies that lead to an area 28°–37°S, 18°–35°E, poleward of South Africa. Regression of detrended Agulhas SST with rainfall anomaly fields in the years 1950–2012 yields a surprising negative influence over the interior. In summer, the negative regression exhibits a northwest axis consistent with reduced cloud band activity. Positive influence is confined to the eastern escarpment in the September–November season when cutoff lows are prevalent. The overall negative influence of the Agulhas SST is confirmed by regression with the vegetation fraction and latent heat flux in the satellite era.

Mechanisms of South African rainfall suppression were investigated. The Agulhas SST index is positively related to the multivariate ENSO index at the 1–3-month lead time. Hence, warm years in the Agulhas Current follow Pacific El Niño. Composite ocean analysis shows enhanced westerly winds offshore and a westward extension of warm salty water from the anticyclonic south Indian Ocean gyre. Composite atmospheric analysis exhibits moist uplifted air over the Agulhas Current folding into an equatorward circulation that sinks over the interior plateau. Because Agulhas SST partially follows ENSO, its suppression of interior rainfall is concluded to be passive.

Corresponding author address: Mark R. Jury, Physics Dept., University of Puerto Rico Mayagüez, P.O. Box 9000, Mayagüez, Puerto Rico, 00681. E-mail address: mark.jury@upr.edu
Save
Cover Earth Interactions
Earth Interactions

  • Barclay, J. J., M. R. Jury, and W. Landman, 1993: Climatological and structural differences between wet and dry troughs over southern Africa in the early summer. Meteor. Atmos. Phys., 51, 41–54, doi:10.1007/BF01080879.

    • Search Google Scholar
    • Export Citation

  • Beal, L. M., T. K. Chereskin, Y. D. Lenn, and S. Elipot, 2006: The sources and mixing characteristics of the Agulhas Current. J. Phys. Oceanogr., 36, 2060–2074, doi:10.1175/JPO2964.1.

    • Search Google Scholar
    • Export Citation

  • Behringer, D. W., 2007: The Global Ocean Data Assimilation System (GODAS) at NCEP. Proc. 11th Symp. on Integrated Observing and Assimilation Systems for the Atmosphere, Oceans, and Land Surface, San Antonio, TX, Amer. Meteor. Soc., 3.3. [Available online at https://ams.confex.com/ams/87ANNUAL/webprogram/Paper119541.html.]

  • Derber, J. C., and A. Rosati, 1989: A global oceanic data assimilation system. J. Phys. Oceanogr., 19, 1333–1347, doi:10.1175/1520-0485(1989)019<1333:AGODAS>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Fauchereau, N., B. Pohl, C. J. C. Reason, M. Rouault, and Y. Richard, 2009: Recurrent daily OLR patterns in the southern Africa/southwest Indian Ocean region, implications for South African rainfall and teleconnections. Climate Dyn., 32, 575–591, doi:10.1007/s00382-008-0426-2.

    • Search Google Scholar
    • Export Citation

  • Funk, C. C., and Coauthors, 2014: A quasi-global precipitation time series for drought monitoring. U.S. Geological Survey Data Series 832, 4 pp., doi:10.3133/ds832.

  • Harrison, M. S. J., 1984: A generalized classification of South African summer rain-bearing synoptic systems. J. Climatol., 4, 547–560, doi:10.1002/joc.3370040510.

    • Search Google Scholar
    • Export Citation

  • Hart, N. C. G., C. J. C. Reason, and N. Fauchereau, 2013: Cloud bands over southern Africa: Seasonality, contribution to rainfall variability and modulation by the MJO. Climate Dyn., 41, 1199–1212, doi:10.1007/s00382-012-1589-4.

    • Search Google Scholar
    • Export Citation

  • Hermes, J. C., C. J. C. Reason, and J. R. E. Lutjeharms, 2007: Modeling the variability of the greater Agulhas Current system. J. Climate, 20, 3131–3146, doi:10.1175/JCLI4154.1.

    • Search Google Scholar
    • Export Citation

  • Hoell, A., C. Funk, T. Magadzire, J. Zinke, and G. Husak, 2014: El Niño–Southern Oscillation diversity and southern Africa teleconnections during austral summer. Climate Dyn., 45, 1583–1599, doi:10.1007/s00382-014-2414-z.

    • Search Google Scholar
    • Export Citation

  • Huang, B., Y. Xue, and D. W. Behringer, 2008: Impacts of Argo salinity in NCEP Global Ocean Data Assimilation System: The tropical Indian Ocean. J. Geophys. Res., 113, C08002, doi:10.1029/2007JC004388.

    • Search Google Scholar
    • Export Citation

  • Hulme, M., D. Conway, A. M. Joyce, and H. M. Mulenga, 1996: A 1961–90 climatology for Africa south of the equator and a comparison of potential evapotranspiration estimates. S. Afr. J. Sci., 92, 334–343.

    • Search Google Scholar
    • Export Citation

  • Jimenez, C., and Coauthors, 2011: Global intercomparison of 12 land surface heat flux estimates. J. Geophys. Res., 116, D02102, doi:10.1029/2010JD014545.

    • Search Google Scholar
    • Export Citation

  • Jury, M. R., H. R. Valentine, and J. R. E. Lutjeharms, 1993: Influence of the Agulhas Current on summer rainfall along the southeast coast of South Africa. J. Appl. Meteor., 32, 1282–1287, doi:10.1175/1520-0450(1993)032<1282:IOTACO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Jury, M. R., M. Rouault, S. Weeks, and M. Schormann, 1997: Atmospheric boundary layer fluxes and structure across a land-sea transition zone in southeastern Africa. Bound.-Layer Meteor., 83, 311–330, doi:10.1023/A:1000295700599.

    • Search Google Scholar
    • Export Citation

  • Jury, M. R., 2002: Economic impacts of climate variability in South Africa and development of resource prediction models. J. Appl. Meteor., 41, 46–55, doi:10.1175/1520-0450(2002)041<0046:EIOCVI>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Kanamitsu, M., W. Ebisuzaki, J. Woollen, S. K. Yang, J. J. Hnilo, M. Fiorino, and G. L. Potter, 2002: NCEP–DOE AMIP-II Reanalysis (R-2). Bull. Amer. Meteor. Soc., 83, 1631–1643, doi:10.1175/BAMS-83-11-1631.

    • Search Google Scholar
    • Export Citation

  • Kennedy, J. J., N. A. Rayner, R. O. Smith, M. Saunby, and D. E. Parker, 2011: Reassessing biases and other uncertainties in sea-surface temperature observations since 1850: 1. Measurement and sampling errors. J. Geophys. Res., 116, D14103, doi:10.1029/2010JD015218.

    • Search Google Scholar
    • Export Citation

  • Mason, S. J., and M. R. Jury, 1997: Climate change and variability over southern Africa: A reflection on underlying processes. Prog. Phys. Geogr., 21, 23–50, doi:10.1177/030913339702100103.

    • Search Google Scholar
    • Export Citation

  • Matano, R. P., E. J. Beier, P. T. Strub, and R. Tokmakian, 2002: Large-scale forcing of the Agulhas variability: The seasonal cycle. J. Phys. Oceanogr., 32, 1228–1241, doi:10.1175/1520-0485(2002)032<1228:LSFOTA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Mo, K., and J. N. Paegle, 2001: The Pacific–South American modes and their downstream effects. Int. J. Climatol., 21, 1211–1229, doi:10.1002/joc.685.

    • Search Google Scholar
    • Export Citation

  • Nakamura, M., 2012: Impacts of SST anomalies in the Agulhas Current system on the regional climate variability. J. Climate, 25, 1213–1229, doi:10.1175/JCLI-D-11-00088.1.

    • Search Google Scholar
    • Export Citation

  • Reason, C. J. C., 2001: Evidence for the influence of the Agulhas Current on regional atmospheric circulation patterns. J. Climate, 14, 2769–2778, doi:10.1175/1520-0442(2001)014<2769:EFTIOT>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Rienecker, M. M., and Coauthors, 2011: MERRA: NASA’s Modern-Era Retrospective Analysis for Research and Applications. J. Climate, 24, 3624–3648, doi:10.1175/JCLI-D-11-00015.1.

    • Search Google Scholar
    • Export Citation

  • Roberts, J. B., F. R. Robertson, C. A. Clayson, and M. G. Bosilovich, 2012: Characterization of turbulent latent and sensible heat flux exchange between the atmosphere and ocean in MERRA. J. Climate, 25, 821–838, doi:10.1175/JCLI-D-11-00029.1.

    • Search Google Scholar
    • Export Citation

  • Rouault, M., S. A. White, C. J. C. Reason, J. R. E. Lutjeharms, and I. Jobard, 2002: Ocean–atmosphere interaction in the Agulhas Current region and a South African extreme weather event. Wea. Forecasting, 17, 655–669, doi:10.1175/1520-0434(2002)017<0655:OAIITA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Rouault, M., C. J. C. Reason, J. R. E. Lutjeharms, and A. C. M. Beljaars, 2003: Underestimation of latent and sensible heat fluxes above the Agulhas Current in NCEP and ECMWF analyses. J. Climate, 16, 776–782, doi:10.1175/1520-0442(2003)016<0776:UOLASH>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Rouault, M., B. Pohl, and P. Penven, 2010: Coastal oceanic climate change and variability from 1982 to 2009 around South Africa. Afr. J. Mar. Sci., 32, 237–246, doi:10.2989/1814232X.2010.501563.

    • Search Google Scholar
    • Export Citation

  • Schneider, U., A. Becker, P. Finger, A. Meyer-Christoffer, M. Ziese, and B. Rudolf, 2014: GPCC’s new land surface precipitation climatology based on quality-controlled in situ data and its role in quantifying the global water cycle. Theor. Appl. Climatol., 115, 15–40, doi:10.1007/s00704-013-0860-x.

    • Search Google Scholar
    • Export Citation

  • Schulze, R. E., G. A. Kiker, and R. P. Kunz, 1993: Global climate change and agricultural productivity in southern Africa. Global Environ. Change, 3, 330–349, doi:10.1016/0959-3780(93)90022-D.

    • Search Google Scholar
    • Export Citation

  • Tucker, C. J., J. E. Pinzon, M. E. Brown, D. Slayback, E. W. Pak, R. Mahoney, E. Vermote, and N. El Saleous, 2005: An extended AVHRR 8-km NDVI data set compatible with MODIS and SPOT vegetation NDVI data. Int. J. Remote Sens., 26, 4485–4498, doi:10.1080/01431160500168686.

    • Search Google Scholar
    • Export Citation

  • Walker, N. D., 1990: Links between South African summer rainfall and temperature variability of the Agulhas and Benguela Current systems. J. Geophys. Res., 95, 3297–3319, doi:10.1029/JC095iC03p03297.

    • Search Google Scholar
    • Export Citation

  • Walker, N. D., and R. D. Mey, 1988: Ocean–atmosphere heat fluxes within the Agulhas retroflection region. J. Geophys. Res., 93, 15 473–15 483, doi:10.1029/JC093iC12p15473.

    • Search Google Scholar
    • Export Citation

  • Wolter, K., and M. S. Timlin, 2011: El Niño/Southern Oscillation behaviour since 1871 as diagnosed in an extended multivariate ENSO index (MEI.ext). Int. J. Climatol., 31, 1074–1087, doi:10.1002/joc.2336.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 299 65 6
PDF Downloads 166 33 7