150 DISCOVERY REPORTS 



The Berg winds are extremely hot, dry winds which blow seawards across the desert, carrying much 

 sand and dust. They may last from a few hours to several days. A temperature of 1 1 5 F. was recorded 

 at Port Nolloth one day during a Berg wind. The highest recorded at Walvis is 104 F. but the average 

 lies about 90 F. These winds are most frequent in winter, but can occur whenever the pressure 

 gradient and heating of the surface air inland is suitable. When the ' William Scoresby ' visited Walvis 

 Bay on 5 October 1950, a typical Berg wind was encountered. It blew for 4 or 5 hr. at 17-21 knots 

 and produced a fine deposit of sand all over the ship. The air temperature reached 99 F. and the 

 wind was uncomfortably dry. The Berg wind does not have much effect over the sea, for coming up 

 against the cool dense air over the water the light hot air diverges upward, away from the sea surface. 



In the coastal region, then, the principal wind of force is the sea-breeze, or 'soo-oop-wa' (as the 

 natives call it), S.S.W. in the north and more southerly in the south. Jackson (personal communication) 

 reckons that the sea-breeze probably has a fetch of some 80-100 miles over the sea, that is from its 

 divergence from the south-east trade. 



Weather preceding and during the surveys 

 There are not very many settlements along the desert coast of South-west Africa, and consequently 

 the number of stations which make regular climatological observations is very small. Fortunately, 

 however, records are maintained at Walvis Bay, Luderitz Bay, and Alexander Bay and these are used 

 by the South African Weather Bureau in the construction of synoptic charts of the South Atlantic 

 and South African region. Although we have not had access to the original data we have seen the 

 synoptic charts published at Pretoria and have extracted the data for these three coastal stations as 

 accurately as possible. 



While shore observations are useful up to a point, observations at sea would have been much more 

 desirable, but the sparsity of observing ships in the region during the survey makes it impossible to 

 construct a complete enough picture. Most of the observations at sea are made on the main shipping 

 route from Capetown to Sierra Leone, well outside the area of our survey. Such observations as there 

 are, however, have been listed in Table 2, and do serve to show the constancy of the offshore winds, 

 nearly all the observations, at least during survey II, lying in the south to east quadrant. 



The only estimate, therefore, of the weather conditions preceding the surveys must be based on the 

 observations made at the three coastal stations ; and although the importance of the diurnal variations 

 of the inshore winds has already been explained, all the synoptic charts are based on observations 

 made once daily, at 08.00 s.a.s.t. These shortcomings of the records at our disposal have to be accepted, 

 but must be borne in mind in interpreting the data. 



The observations from the three shore stations for the periods preceding and during the surveys 

 are given in Table 3. It can be seen that before survey I the weather at Walvis Bay had been calm 

 or northerly, while at Luderitz Bay, right up to the time the ship visited the locality, the winds had 

 mainly been southerly. At Orange river there had been very little wind for the whole month pre- 

 ceding and during the Survey. 



Prior to Survey II, however, conditions were very different. Both Walvis Bay and Luderitz Bay 

 had experienced much stronger winds, mainly from between south and west. As on the first survey, 

 Orange river experienced comparatively calm weather. 



So much for conditions on the coast. The constancy of the trade wind has already been shown from 

 the observations at sea (Table 2). From the synoptic charts we can get some further information upon 

 the state of these winds. It has not been considered advisable to calculate the vectors and velocities 

 of the oceanic winds from the isobars, as they are based on so few recording stations. Regular observa- 

 tions come from the South African coastal stations, Tristan da Cunha and St Helena, and the observa- 



