The Natal pulse: An extreme transient on the Agulhas Current


  • J. R. E. Lutjeharms,

  • H. R. Roberts


An analysis of satellite data collected over a period of 9 years as well as historic hydrographic data show that the northern Agulhas Current is subject to large, intermittent, and solitary meanders. These transient events, collectively named the Natal pulse, progress downstream at consistent rates of 21 cm/s. Upon reaching the area where the shelf broadens, their rate of progression slackens to 5 cm/s. They are present in some stages of development at least 17% of the time, extend offshore by about 170 km on average, and show a continuous lateral growth on moving downstream. With few exceptions the pulses are spawned as cold core, cyclonic, trapped lee eddies in the Natal Bight. They are held responsible for the intermittent coastal counter currents observed inshore of the Agulhas Current along the southern African coast and may play a crucial role in sediment distribution on the shelf.