The climatology of slow and fast air mass transport towards Rukomechi research station in northern Zimbabwe (16.1°S, 29.4°E) is examined through an analysis of 5-day kinematic back trajectories arriving at 1180 m above ground level (~850 hPa) for the period 1994-99. The trajectories are computed daily by the HYSPLIT 4 model using the National Oceanic and Atmospheric Administration's re-analysed wind fields as input. Objective classification of trajectories into different flow regimes is done using a non-hierarchical cluster algorithm that is applied to all the trajectories at once, to examine the temporal and spatial characteristics. The synoptic-scale atmospheric circulation associated with each cluster was also studied. Four major transport corridors and seven large-scale flows were found to provide an indication of source regions of the air masses and transport pathways influencing Rukomechi. The dominant transport features include (1) the late dry season to wet season eastern air flows that contribute 35% of the total flow and which are driven by an anticyclone that wraps around the subcontinent and stretches into the Mozambique Channel, (2) the late wet season to dry season southeastern pathway that accounts for 44% of the total flow and is associated with the South Atlantic anticyclone and the tropical depression in the Indian Ocean, (3) the fast (11 m s-1) dry season southern flow (contributes 8%) that is driven by a continental anticyclone over South Africa coupled to a South Atlantic anticyclone, and (4) the north-northwesterly flow that contributes 6% to the total flow and is associated with the Intertropical Convergence Zone. A further, very slow (1.8 m s-1) flow regime, consisting of regionally re-circulated air results from regional differential heating at the surface. Concentrations of particulate mass, measured during 1994-2000 at the Rukomechi site, are shown to be significantly correlated with the occurrence of those seven large-scale flows, which have been identified by objective trajectory classification. High particulate mass concentrations are associated only with air masses carried along the fast easterly flow, the slow southeasterly flow and the southerly flow (dry season flows); low particulate mass concentrations are exclusively found with wet season flows.

Mecanismos de vento local, tal como as brisas, influenciam o transporte e dispersão dos gases. Medidas da direção do vento e concentração de ozônio (O3) à 10 metros de altura foram realizadas durante a execução do projeto LBA/CLAIRE-2001 (Large Scale Biosphere-Atmosphere Experiment in Amazônia / Cooperative LBA Airbone Regional Experiment - 2001), no período de 02 a 28.07.2001, nas dependências do Laboratório de Limnologia (01º 55' S, 59º28' W, 174 m) pertencente à Usina Hidrelétrica de Balbina, Amazonas. O lago artificial tem uma área de 2.360 km², sendo suficientemente grande para estabelecer um regime de brisas. As brisas de lago e floresta apresentam-se de forma bem definidas, sendo que a brisa de lago fica melhor caracterizada no período mais quente do dia (10 às 14 horas), enquanto a brisa de floresta evidencia-se no período de 16 às 08 horas com o resfriamento radiativo mais intenso da floresta, o que acarreta um forte contraste térmico. Enquanto isso, a concentração média diária (24 h) de O3 foi de 8,7 ppbv com média de 10,6 ppbv no período diurno e 3,5 ppbv no período noturno. Os resultados também indicaram que quando a brisa é de lago, mesmo a noturna, a concentração de O3 é muito maior do que correspondente a concentração referente a brisa de floresta.

Local wind systems, such as sea or lake breezes, strongly affect the transport and dispersion of atmospheric trace gases. Based on its size and location, the artificial lake of Balbina in the Amazon - can be expected to give rise to a lake/forest breeze regime. During the period 2 to 28 July 2002, within the LBA/CLAIRE-2001 experiment, we have continually measured the ozone concentrations (O3) and the wind directions close to the Balbina dam. We found that there is indeed a well established breeze system, with lake breezes prevailing during mid-day (10 to 14 LT) while forest breezes prevail from the afternoon to early morning (16 to 8 LT). During the latter period radioactive cooling in the forest creates a strong local thermal contrast. The average daily ozone concentration was 8.7 ppbv, with an average of 10.6 ppbv during the day, and 3.5 ppbv at night. When local winds came from the lake, even at night, ozone concentrations were greater compared to breezes coming from the forest.