Investigation of the short-time variability of tropical tropospheric ozone

Abstract

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.

Southern Hemisphere Additional Ozonesondes (SHADOZ) ozone climatology (2005–2009): Tropospheric and tropical tropopause layer (TTL) profiles with comparisons to OMI‐based ozone products

“…Seasonal influences on tropospheric and TTL ozone over Irene and Réunion (Figures 3c and 3d) include a sustained period of biomass burning impacts (August–November) [e.g., Baldy et al , 1996; Diab et al , 1996 ; Taupin et al , 1999; Randriambelo et al , 2000, 2003; Thompson et al , 2003a, 2003b; Diab et al , 2004; Clain et al , 2009]. Stratosphere‐troposphere exchange events over Irene [ Diab et al , 1996, 2004] and Réunion [ Baray et al , 1998, 1999], the latter frequent occurrences at the edge of the subtropical jet, are well‐documented.…”

Gravity and Rossby wave signatures in the tropical troposphere and lower stratosphere based on Southern Hemisphere Additional Ozonesondes (SHADOZ), 1998–2007

“…Ozone structure over La Réunion (Figure 2b) reflects a mixture of subsidence, entrainment of extratropical air and convection over the Indian Ocean. Evidence for these multiple influences is observed in satellite tropospheric O 3 data [ Chatfield et al , 2004, 2007] and in sonde‐lidar observations [ Randriambelo et al , 2003; Clain et al , 2009]. Stratospheric influences, in downward transport or as filaments from the extratropics, are frequent at La Réunion [ Baray et al , 1998, 1999; Leclair de Bellevue et al , 2006] and over Irene [ Diab et al , 1996; see Diab et al , 2004, Figure 4] and to a lesser degree, over San Cristóbal (green‐yellow shading above 12 km in Figure 2f [cf.…”

“…In the July–August 2007 sampling, the RW frequency over Alajuela reached 30% at 3 km [ Thompson et al , 2010, Figure 4]; localized pollution in an elevated basin may have contributed. Elevated RW in the TTL is expected at sites farther from the equator in austral spring, when stratospheric influence increases, i.e., over La Réunion (21°S) [ Baray et al , 1998, 2003; Portafaix et al , 2003; Randriambelo et al , 2003] and Irene (26°S) [ Diab et al , 1996; Thompson et al , 1996].…”

Tropospheric ozone climatology at two Southern Hemisphere tropical/subtropical sites, (Reunion Island and Irene, South Africa) from ozonesondes, LIDAR, and in situ aircraft measurements

“…The island meteorology is subject to subtropical, tropical and temperate influences of the general circulation. The South Indian Ocean anticyclone, and perturbations carried in the westerlies affect the island (Randriambelo et al, 2003). The influence of the subtropical jet stream on the island is at a maximum during winter.…”