Role of Indian and Atlantic Oceans on Southern African Climatic Variability

A Makarau

Department of Physics

University of Zimbabwe

Intercorrelations (99% sig level)

Byo N Zim NWSA Lusaka Maun NWMg

Byo 1 0.74 0.69 0.70 0.66 0.66

N Zim 1 0.75 0.92 0.76 0.86

NWSA 1 0.68 0.74 0.74

Lusaka 1 0.72 0.81

Maun 1 0.77

NWMg 1

Atlantic Ocean Influence

Direct influence- Sub-tropical high pressure belt and associated wave- trains- cold upwelling (west coasts of S Africa, Namibia, Angola, DRC)- westerly waves (S Africa, Namibia, Botswana, Zimbabwe)

OUTGOING LONG WAVE RADIATION (OLR)

SEP

NOV

JAN

Atlantic Ocean Influence

Indirect influence- Botswana Anticyclone (Namibia, Botswana, South

Africa, Zimbabwe, Zambia)

- Tropical-sub-tropical troughs (Namibia, South Africa, Lesotho, Angola, Botswana, Zimbabwe)

- Reinforcement of the Indian Ocean Anticyclone

Indian Ocean Influence Direct influence

- Tropical cyclones (islands, Tanzania, Malawi, Mozambique, Zimbabwe, Swaziland, South Africa)

- Monsoons and easterly waves (Tanzania, DRC, Zambia, Malawi, Mozambique, islands)

- Inter-Tropical Convergence Zone (ITCZ)

Correlations : Zimbabwe rainfall with SSTs

MAM

JJA

SON

DJF

Summary: The Atlantic Ocean Correlations between Atlantic Ocean SSTs and area-

averaged rainfall in Southern Africa have been relatively weak for operational usage (e.g., Walker, Pathack, Landman, Rocha, Mason, Makarau, Zhakata)

Central Atlantic SST are however positively correlated with early summer rainfall over western South Africa, Namibia, Angola and DRC

Summary: The Indian Ocean Negative correlations (up to –0.6) exist between area-

averaged rainfall in southern Africa and central equatorial Indian Ocean SSTs (Makarau, Rocha, Jury, Pathack, Mason, Zhakata, Landman). The window comprising the equator-10°S and 60-70 ° E offers useful forecast guidance at 3-6 months prior to austral summer.

At –9 months, rainfall is positively correlated with SSTs in the South Indian Ocean (r=+0.42 near 35 ° S, 65 ° E)

Summary: The Indian Ocean

Central Equatorial Indian Ocean is the source of moisture and energy variability over northeastern southern Africa (Islands, Tanzania, DRC, Zambia, Malawi, Mozambique, Zimbabwe, northeastern South Africa and Swaziland) modulating the ITCZ, monsoons, low-level jet and related easterly waves and tropical cyclones