scholarly journals Impact of convection on the upper-tropospheric composition (water vapor/ozone) over a subtropical site (Réunion Island, 21.1° S–55.5° E) in the Indian Ocean

2020 ◽  
Author(s):  
Damien Héron ◽  
Stephanie Evan ◽  
Jerome Brioude ◽  
Karen Rosenlof ◽  
Françoise Posny ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Local Maximum ◽  
Reunion Island ◽  
Mixing Ratio ◽  
Air Masses ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
South West Indian Ocean ◽  
Réunion Island ◽  
The Impact

Abstract. Observations of ozonesonde measurements of the NDACC/SHADOZ program and humidity profiles from the daily Météeo-France radiosondes at Réunion Island (21.1° S, 55.5° E) from November 2013 to April 2016 are analyzed to identify the origin of wet upper tropospheric air masses with low ozone mixing ratio observed above the island, located in the South West Indian Ocean (SWIO). A seasonal variability in hydration events in the upper troposphere was found and linked to the convective activity within the SWIO basin. In the upper troposphere, ozone mixing ratios were lower (mean of 57 ppbv) in humid air masses (RH > 50 %) compared to the background mean ozone mixing ratio (73.8 ppbv). A convective signature was identified in the ozone profile dataset by studying the probability of occurrence of different ozone thresholds. It was found that ozone mixing ratios lower than 45 to 50 ppbv had a local maximum of occurrence between 10 and 13 km in altitude, indicative of the mean level of convective outflow. Combining FLEXPART Lagrangian backtrajectories with METEOSAT 7 infrared brightness temperature products, we established the origin of convective influence on the upper troposphere above Réunion island. It has been found that the upper troposphere above Réunion island is impacted by convective outflows in austral summer. Most of the time, deep convection is not observed in the direct vicinity of the island, but more than a thousand of kilometers away from the island, in the tropics, either from tropical storms or the Inter Tropical Convective Zone. In November and December, the air masses above Réunion Island originate, on average, from Central Africa and the Mozambique channel. During January, February the source region is the North-east of Mozambique and Madagascar. Those results improve our understanding of the impact of the ITCZ and tropical cyclones hydration of the upper troposphere in the subtropics in the SWIO.

scholarly journals Impact of convection on the upper-tropospheric composition (water vapor and ozone) over a subtropical site (Réunion island; 21.1° S, 55.5° E) in the Indian Ocean

2020 ◽  
Vol 20 (14) ◽  
pp. 8611-8626 ◽  
Author(s):  
Damien Héron ◽  
Stéphanie Evan ◽  
Jérôme Brioude ◽  
Karen Rosenlof ◽  
Françoise Posny ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Local Maximum ◽  
Reunion Island ◽  
Mixing Ratio ◽  
Southwest Indian Ocean ◽  
Air Masses ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
Réunion Island ◽  
The Impact

Abstract. Observations of ozonesonde measurements of the NDACC/SHADOZ (Network for the Detection of Atmospheric Composition Change and the Southern Hemisphere ADditional OZonesondes) program and humidity profiles from the daily Météo-France radiosondes at Réunion island (21.1∘ S, 55.5∘ E) from November 2013 to April 2016 were analyzed to identify the origin of wet upper-tropospheric air masses with low ozone mixing ratio observed above the island, located in the southwest Indian Ocean (SWIO). A seasonal variability in hydration events in the upper troposphere was found and linked to the convective activity within the SWIO basin. In the upper troposphere, ozone mixing ratios were lower (mean of 57 ppbv) in humid air masses (RH > 50 %) compared to the background mean ozone mixing ratio (73.8 ppbv). A convective signature was identified in the ozone profile dataset by studying the probability of occurrence of different ozone thresholds. It was found that ozone mixing ratios lower than 45 to 50 ppbv had a local maximum of occurrence between 10 and 13 km in altitude, indicative of the mean level of convective outflow. Combining FLEXPART Lagrangian back trajectories with METEOSAT-7 infrared brightness temperature products, we established the origin of convective influence on the upper troposphere above Réunion island. It has been found that the upper troposphere above Réunion island is impacted by convective outflows in austral summer. Most of the time, deep convection is not observed in the direct vicinity of the island, but it is observed more than 1000 km away from the island, in the tropics, either from tropical storms or the Intertropical Convection Zone (ITCZ). In November and December, the air masses above Réunion island originate, on average, from central Africa and the Mozambique Channel. During January and February the source region is the northeast of Mozambique and Madagascar. Those results improve our understanding of the impact of the ITCZ and tropical cyclones on the hydration of the upper troposphere in the subtropics in the SWIO.

scholarly journals Reactive nitrogen, ozone and ozone production in the Arctic troposphere and the impact of stratosphere-troposphere exchange

2011 ◽  
Vol 11 (24) ◽  
pp. 13181-13199 ◽  
Author(s):  
Q. Liang ◽  
J. M. Rodriguez ◽  
A. R. Douglass ◽  
J. H. Crawford ◽  
J. R. Olson ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Stratospheric Ozone ◽  
Arctic Region ◽  
Ozone Production ◽  
The Arctic ◽  
Subsequent Formation ◽  
Air Masses ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
The Impact

Abstract. We use aircraft observations obtained during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission to examine the distributions and source attributions of O3 and NOy in the Arctic and sub-Arctic region. Using a number of marker tracers, we distinguish various air masses from the background troposphere and examine their contributions to NOx, O3, and O3 production in the Arctic troposphere. The background Arctic troposphere has a mean O3 of ~60 ppbv and NOx of ~25 pptv throughout spring and summer with CO decreasing from ~145 ppbv in spring to ~100 ppbv in summer. These observed mixing ratios are not notably different from the values measured during the 1988 ABLE-3A and the 2002 TOPSE field campaigns despite the significant changes in emissions and stratospheric ozone layer in the past two decades that influence Arctic tropospheric composition. Air masses associated with stratosphere-troposphere exchange are present throughout the mid and upper troposphere during spring and summer. These air masses, with mean O3 concentrations of 140–160 ppbv, are significant direct sources of O3 in the Arctic troposphere. In addition, air of stratospheric origin displays net O3 formation in the Arctic due to its sustainable, high NOx (75 pptv in spring and 110 pptv in summer) and NOy (~800 pptv in spring and ~1100 pptv in summer). The air masses influenced by the stratosphere sampled during ARCTAS-B also show conversion of HNO3 to PAN. This active production of PAN is the result of increased degradation of ethane in the stratosphere-troposphere mixed air mass to form CH3CHO, followed by subsequent formation of PAN under high NOx conditions. These findings imply that an adequate representation of stratospheric NOy input, in addition to stratospheric O3 influx, is essential to accurately simulate tropospheric Arctic O3, NOx and PAN in chemistry transport models. Plumes influenced by recent anthropogenic and biomass burning emissions observed during ARCTAS show highly elevated levels of hydrocarbons and NOy (mostly in the form of NOx and PAN), but do not contain O3 higher than that in the Arctic tropospheric background except some aged biomass burning plumes sampled during spring. Convection and/or lightning influences are negligible sources of O3 in the Arctic troposphere but can have significant impacts in the upper troposphere in the continental sub-Arctic during summer.

scholarly journals Reactive nitrogen, ozone and ozone production in the Arctic troposphere and the impact of stratosphere-troposphere exchange

2011 ◽  
Vol 11 (4) ◽  
pp. 10721-10767 ◽  
Author(s):  
Q. Liang ◽  
J. M. Rodriguez ◽  
A. R. Douglass ◽  
J. H. Crawford ◽  
E. Apel ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Arctic Region ◽  
Tropospheric Chemistry ◽  
Ozone Production ◽  
The Arctic ◽  
Source Attribution ◽  
Air Masses ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
The Impact

Abstract. We analyze the aircraft observations obtained during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellite (ARCTAS) mission together with the GEOS-5 CO simulation to examine O3 and NOy in the Arctic and sub-Arctic region and their source attribution. Using a number of marker tracers and their probability density distributions, we distinguish various air masses from the background troposphere and examine their contribution to NOx, O3, and O3 production in the Arctic troposphere. The background Arctic troposphere has mean O3 of ~60 ppbv and NOx of ~25 pptv throughout spring and summer with CO decreases from ~145 ppbv in spring to ~100 ppbv in summer. These observed CO, NOx and O3 mixing ratios are not notably different from the values measured during the 1988 ABLE-3A and the 2002 TOPSE field campaigns despite the significant changes in the past two decades in processes that could have changed the Arctic tropospheric composition. Air masses associated with stratosphere-troposphere exchange are present throughout the mid and upper troposphere during spring and summer. These air masses with mean O3 concentration of 140–160 ppbv are the most important direct sources of O3 in the Arctic troposphere. In addition, air of stratospheric origin is the only notable driver of net O3 formation in the Arctic due to its sustainable high NOx (75 pptv in spring and 110 pptv in summer) and NOy (~800 pptv in spring and ~1100 pptv in summer) levels. The ARCTAS measurements present observational evidence suggesting significant conversion of nitrogen from HNO3 to NOx and then to PAN (a net formation of ~120 pptv PAN) in summer when air of stratospheric origin is mixed with tropospheric background during stratosphere-to-troposphere transport. These findings imply that an adequate representation of stratospheric O3 and NOy input are essential in accurately simulating O3 and NOx photochemistry as well as the atmospheric budget of PAN in tropospheric chemistry transport models of the Arctic. Anthropogenic and biomass burning pollution plumes observed during ARCTAS show highly elevated hydrocarbons and NOy (mostly in the form of NOx and PAN), but do not contribute significantly to O3 in the Arctic troposphere except in some of the aged biomass burning plumes sampled during spring. Convection and/or lightning influences are negligible sources of O3 in the Arctic troposphere but can have significant impacts in the upper troposphere in the continental sub-Arctic during summer.

Pareto Optimization for Rossby Wave Pattern Impacts on MH370 Debris

2020 ◽  
pp. 251-280
Keyword(s):  
Indian Ocean ◽  
Rossby Waves ◽  
Wave Pattern ◽  
Pareto Optimization ◽  
Southern Indian Ocean ◽  
Reunion Island ◽  
Réunion Island ◽  
Ocean Gyres ◽  
Western Side ◽  
The Impact

This chapter censoriously appraises the comprehensive theories that specify that more concepts are needed to bridge the gap found between the dynamic of the Southern Indian Ocean and the actual MH370 vanishing mechanism. Thus, this chapter is devoted to the Rossby waves, which could attribute to the fact that the MH370 flaperon got to Réunion Island. In this view, Rossby waves generate growth of energy in the west of the ocean gyres and create the strengthening currents on the western side of the ocean basins. Pareto optimization algorithm of the impact power of Rossby waves proves that the flaperon could not drift across the Southern Indian Ocean and be positioned on Réunion Island.

Corrigendum to “Human-shark interactions: The case study of Reunion island in the south-west Indian Ocean”[Ocean Coast. Manag. 136C (2016) 73–82]

2018 ◽  
Vol 163 ◽  
pp. 537
Author(s):  
Anne Lemahieu ◽  
Antonin Blaison ◽  
Estelle Crochelet ◽  
Geoffrey Bertrand ◽  
Gwenaëlle Pennober ◽  
...  
Keyword(s):  
Indian Ocean ◽  
West Indian ◽  
Reunion Island ◽  
The South ◽  
South West Indian Ocean ◽  
South West ◽  
Réunion Island ◽  
West Indian Ocean

scholarly journals Chikungunya Fever: A Clinical and Virological Investigation of Outpatients on Reunion Island, South-West Indian Ocean

2013 ◽  
Vol 7 (1) ◽  
pp. e2004 ◽  
Author(s):  
Simon-Djamel Thiberville ◽  
Veronique Boisson ◽  
Jean Gaudart ◽  
Fabrice Simon ◽  
Antoine Flahault ◽  
...  
Keyword(s):  
Indian Ocean ◽  
West Indian ◽  
Reunion Island ◽  
Chikungunya Fever ◽  
South West Indian Ocean ◽  
South West ◽  
Réunion Island ◽  
West Indian Ocean

Human-shark interactions: The case study of Reunion island in the south-west Indian Ocean

2017 ◽  
Vol 136 ◽  
pp. 73-82 ◽  
Author(s):  
Anne Lemahieu ◽  
Antonin Blaison ◽  
Estelle Crochelet ◽  
Geoffrey Bertrand ◽  
Gwenaëlle Pennober ◽  
...  
Keyword(s):  
Indian Ocean ◽  
West Indian ◽  
Reunion Island ◽  
The South ◽  
South West Indian Ocean ◽  
South West ◽  
Réunion Island ◽  
West Indian Ocean

scholarly journals Characterisation of African biomass burning plumes and impacts on the atmospheric composition over the South-West Indian Ocean

2020 ◽  
Author(s):  
Bert Verreyken ◽  
Crist Amelynck ◽  
Jérôme Brioude ◽  
Jean-François Müller ◽  
Niels Schoon ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Biomass Burning ◽  
West Indian ◽  
Atmospheric Composition ◽  
The South ◽  
Mixing Ratios ◽  
South West Indian Ocean ◽  
South West ◽  
West Indian Ocean ◽  
The Impact

Abstract. We present an investigation of biomass burning (BB) plumes originating from Africa and Madagascar based on measurements of carbon monoxide (CO), ozone (O3), nitrogen dioxide (NO2) and a suite of volatile organic compounds (VOCs) obtained during the dry season of 2018 and 2019 at the high altitude Maïdo observatory (21.1° S, 55.4° E, 2250 m above sea level), located on the remote island of La Réunion in the South-West Indian Ocean (SWIO). Biomass burning plume episodes were identified from increased acetonitrile (CH3CN) mixing ratios. Enhancement ratios (EnRs) – relative to CO – were calculated from in situ measurements for CH3CN, acetone (CH3COCH3), formic acid (HCOOH), acetic acid (CH3COOH), benzene (C6H6), methanol (CH3OH) and O3. We compared the EnRs to emission ratios (ERs) – relative to CO – reported in literature in order to estimate loss/production of these compounds during transport. For CH3CN and CH3COOH, the calculated EnRs are similar to the ERs. For C6H6 and CH3OH, the EnR is lower than the ER, indicating a significant net sinks of these compounds. For CH3COCH3 and HCOOH, the calculated EnRs are larger than the ERs. The discrepancy reaches an order of magnitude for HCOOH (18–34 pptv ppbv−1 compared to 1.8–4.5 pptv ppbv−1). This points to significant secondary production of HCOOH during transport. The Copernicus Atmospheric Monitoring Service (CAMS) global model simulations reproduces well the temporal variation of CO mixing ratios at the observatory but underestimates O3 and NO2 mixing ratios in the plumes on average by 16 ppbv and 60 pptv respectively. This discrepancy between modelled and measured O3 mixing ratios was attributed to (i) large uncertainties in VOC and NOx (NO + NO2) emissions due to BB in CAMS and (ii) misrepresentation of NOx recycling in the model during transport. Finally, transport of pyrogenically emitted CO is calculated with FLEXPART in order to (i) determine the mean plume age during the intrusions at the observatory and (ii) estimate the impact of BB on the pristine marine boundary layer (MBL). By multiplying the excess CO in the MBL with inferred EnRs at the observatory, we calculated the expected impact of BB on CH3CN, CH3COCH3, CH3OH and C6H6 concentrations in the MBL. These excesses constitute increases of ~ 20 %–150 % compared to background measurements in the SWIO MBL reported in literature.

Aerosol characterization in an oceanic context around Reunion island (AEROMARINE field campaign)

2021 ◽  
Author(s):  
Faustine Mascaut ◽  
Olivier Pujol ◽  
Jérôme Brioude ◽  
Bert Verreyken ◽  
Raphaël Peroni ◽  
...  
Keyword(s):  
Indian Ocean ◽  
High Altitude ◽  
Atmospheric Environment ◽  
Reunion Island ◽  
Free Troposphere ◽  
Marine Aerosols ◽  
Field Campaign ◽  
Air Masses ◽  
Major Interest ◽  
Réunion Island

<p>We present the results of the AEROMARINE field campaign which took place in the boreal spring 2019 off the coast of Reunion island in the South West Indian Ocean basin. The southern Indian Ocean is of major interest for the study of marine aerosols, their distribution and variability <em>[1]</em>. Nine instrumented light plane flights and a ground-based microwave radiometer were used during the AEROMARINE field campaign. These measurements were compared with the long-term measurements of the AERONET sun-photometer (based in Saint Denis, Reunion Island) and various instruments of the high altitude Maido Observatory (2200m above sea level, Reunion island). These results were analyzed using different model outputs: (i) the AROME mesoscale weather forecast model to work on the thermodynamics of the boundary layer, (ii) the FLEXPART-AROME Lagrangian particle dispersion model to assess the geographical and vertical origin of air masses, and (iii) the chemical transport model CAMS (Copernicus Atmosphere Monitoring Service) to work on the aerosol chemical composition of air masses. These measurements allowed us to determine the background concentration of natural marine aerosols and to highlight that (1) the atmospheric layers above 1500m are in the free troposphere and are mainly composed of aerosols from the regional background and (2) that the local environment (ocean or island) has little impact on the measured concentrations. Marine aerosols emitted locally are mostly measured in the lower atmospheric layers (below 500m). The daytime marine aerosol distributions in the free troposphere measured by the aircraft were compared to the aerosol distribution measured at the high altitude Maido observatory at night when the observatory is located in the free troposphere.  We also found that the CAMS reanalyses overestimated the aerosol optical depth in this region. Finally, our study confirms, with no ambiguity, that the AERONET station in Saint Denis (Reunion island) can be considered as a representative marine station in the tropics <em>[2]</em>. </p><p><br><br>References<br><em>[1]</em>  I.  Koren,  G.  Dagan,  and  O.  Altaratz.   From  aerosol-limited  to  invigoration  of  warm  convective clouds. Science, 344 (6188) : 1143–1146, 2014.<br><em>[2] </em> P. Hamill, M. Giordano, C. Ward, D. Giles, and B. Holben.  An aeronet-based aerosol classification using the mahalanobis distance. Atmospheric Environment, 140 : 213–233,2016.</p>

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