Mathieu Rouault et al: Top

Cloud lines above the Agulhas Current
Modification of the atmosphere by the high Agulhas Current SST has been observed above it as cloud lines aligned with the warm water edge (Lutjeharms et al. 1986, Lutjeharms and Rouault, 2000). During the ACASEX cruise (Lee-Thorp et al, 1998b) a transition in cumulus was observed above the Agulhas Current during a period of anticyclonic ridging. Clear conditions over the shelf were replaced by active, coupled cumuli above the current and partly cloudy conditions above the seaward border. Negligible or even downward heat exchanges occur over the shelf whilst strong atmospheric heat and moisture gains occur over the current. This sets up a transition in stability of the boundary layer and potential cumulus formation. During the 1998/1999 season of interest here, cloud bands above the Agulhas Current were prevalent both before and after the 14/15 December 1998 case study, consistent with the cloud behaviour observed during the various cruises (Lutjeharms and Rouault, 2000).

Cloud lines above the Agulhas Current

Modification of the atmosphere by the high Agulhas Current SST has been observed above it as cloud lines aligned with the warm water edge (Lutjeharms et al. 1986, Lutjeharms and Rouault, 2000). During the ACASEX cruise (Lee-Thorp et al, 1998b) a transition in cumulus was observed above the Agulhas Current during a period of anticyclonic ridging. Clear conditions over the shelf were replaced by active, coupled cumuli above the current and partly cloudy conditions above the seaward border. Negligible or even downward heat exchanges occur over the shelf whilst strong atmospheric heat and moisture gains occur over the current. This sets up a transition in stability of the boundary layer and potential cumulus formation. During the 1998/1999 season of interest here, cloud bands above the Agulhas Current were prevalent both before and after the 14/15 December 1998 case study, consistent with the cloud behaviour observed during the various cruises (Lutjeharms and Rouault, 2000).

Fig. 2: Figure: Satellite image in the visible frequency band for southern Africa and adjoining ocean regions for 18 December 1998. Clouds are in white. Cloud lines above the Agulhas show the intensity of the latent heat flux above the current

[ Abstract| Introduction | Agulhas Current | TRMM SST|

Email: rouault@physci.uct.ac.za

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