A PRELIMINARY-STUDY OF THE TRANSPORT OF AIR FROM AFRICA AND AUSTRALIATO NEW-ZEALAND

Kinematic trajectory modelling is used in a preliminary examination of inter-regional transport of air within the Southern Hemisphere. In pa rticular, the westerly zonal transport of air in the lower troposphere from southern Africa and Australia to New Zealand is determined for J anuary and July, using both forward and backward trajectories originat ing or ending up in the 850-800 hPa layer respectively. Mean transport plumes are derived from swarms of individual trajectories, and the re sults show that in winter around 22% of air originating over the centr al interior of South Africa reaches the central Tasman Sea south of Ne w Zealand. In summer the amount is insignificant owing to seasonal cha nges in the position of major circulation features. In contrast, both summer and winter low-level air transport from southeastern and southw estern Australia and adjacent oceans to New Zealand is substantial, wi th 83% of all low-level air parcels from the Sydney area in summer pas sing over central New Zealand 5 days later. In winter the transport pl ume passes over the northern part of the North Island within 3 days. B ack trajectories show that in some seasons two distinct paths are foll owed by air arriving at Christchurch and Auckland, from the west-north west and southwest. Analysis of the vertical structure of the transpor t plumes arriving in New Zealand shows that the westerly air reaching Auckland in the 850-800 hPa layer does so in a subsiding airstream thr oughout the year, whereas that arriving in the same layer over Christc hurch experiences only minor subsidence en route from Australia and th e ocean to the south. This descending motion is related to the dominan ce of anticyclonic circulation, particularly over the northern section of the New Zealand region.