When South Atlantic Pressure Systems Tango

All ocean scientists show a special interest in the atmosphere. Most of the ocean’s currents are forced by the winds, the heating from the sun and the difference between rainfall and evaporation. Those who go to sea on research vessels have an even larger interest in the atmospheric weather. Calm winds and dry weather allows for efficient working conditions. Strong winds and rough seas slow down the vessel and may lead to a complete halt of the planned research activities.


The South Atlantic Ocean is marked by a quasi permanent high pressure system, lets call her Maria, in the middle of the ocean basin. Over the South West African continent, however, the hot daytime temperatures are responsible for the development of a low surface pressure system, lets call him Carlos. The winds encircle Maria in a counter clockwise direction (note we are in the Southern hemisphere) while the air masses swirl clockwise around Carlos. Every once in a while Maria feels attracted by Carlos and moves closer to land. Her high pressure gets dangerously close to Carlos’ low pressure. The gradient between them grows rapidly. The swirling of the air masses speed up dramatically. And all of a sudden gale force winds hit the ocean of the coast of Namibia and South Africa from the south. Several hours later Maria takes Carlos by the hand and swirls him around to the south and east out of the South Atlantic towards the Indian Ocean. He loses his high pressure slowly and the hot Tango dance is finally over.


The METEOR on its 100th expedition witnessed this stormy love affair between the two atmospheric pressure systems. Gale force winds from the south with up to 5 meter tall waves battered METEOR’s bow as she was trying to make headway towards the south. For more than two days all science had to be stopped and progress towards the Cape of Good Hope was slow. Finally Maria swirled around Carlos, the wind slacked and the voyage of the METEOR resumed its normal operation. What was fascinating to all of us is, that blue skies and bright sunshine were rarely disrupted by the powerful Tango dance. The sunrays caused plenty of small rainbows in the white water flying behind braking surface waves.