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The present study proposes improved multispectral methods for the detection of vegetation ® res and smoke plumes that are applied to south-eastern Africa and Madagascar. Data are provided by the AVHRR² sensor onboard the NOAA (11 and 14) satellites. Improvements of a multispectral methods address to ® re detection di culties arising from the low saturation level of AVHRR channel 3, from the presence of clouds and from contrasted vegetation and climate conditions. The methods are based on a multi-channel algorithm using AVHRR data, in visible and thermal ranges. Results are checked against other algorithm and ground concurrent data. It is shown that the presented multispectral methods are able to detect vegetation ® res and associated smoke plumes with an improved accuracy. The results evidence clearly the seasonal character of biomass burning. Two maxima are characterized in the reference zone: one in September in Mozambique and the other in October in Eastern Madagascar. We note that ® re intensity maxima were accompanied by well developed smoke plumes which could reach more than 50 km.

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Abstract. Since 1998, a ground-based tropospheric ozone lidar has been running at Reunion Island and has been involved with a daily measurement campaign that was performed in the latter part of the biomass burning season, during November-December 1999. The averaged ozone profile obtained during November-December 1999 agrees well with the averaged ozone profile obtained from the ozonesondes launch at Reunion during November-December (1992. Comparing weekly sonde launches (part of the Southern Hemisphere Additional Ozonesondes: SHADOZ program) with the daily ground-based lidar observations shows that some striking features of the day-to-day variability profiles are not observed in the sonde measurements. Ozone profiles respond to the nature of disturbances which vary from one day to the next.The vertical ozone distribution at Reunion is examined as a function of prevailing atmospheric circulation. Back trajectories show that most of the enhanced ozone crossed over biomass burning and convectively active regions in Madagascar and the southern African continent. The analyses of the meteorological data show that ozone stratification profiles are in agreement with the movement of the synoptic situations in November-December 1999. Three different sequences of transport are explained using wind fields. The first sequence from 23 to 25 November is characterized by northerly transport; during the second sequence from 26 to 30 November, the air masses are influenced by meridional transport. The third sequence from 2 to 6 December is characterized by westerly transport associated with the subtropical jet stream. The large, standard deviations of lidar profiles in the middle and upper troposphere are in agreement with the upper wind variabilities which evidence passing ridge and trough disturbances. During the transition period between the dry season and the wet season, multiple ozone sources including stratosphere-troposphere exchanges, convection and biomass burning contribute to troCorrespondence to: T. Randriambelo (randriam@univ-reunion.fr) pospheric ozone at Reunion Island through sporadic events characterized by a large spatial and temporal variability.