scholarly journals Effects of the 2006 El Niño on tropospheric ozone and carbon monoxide: implications for dynamics and biomass burning

2009 ◽  
Vol 9 (1) ◽  
pp. 2735-2761
Author(s):  
S. Chandra ◽  
J. R. Ziemke ◽  
B. N. Duncan ◽  
T. L. Diehl ◽  
N. J. Livesey ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Atmospheric Chemistry ◽  
Forest Fires ◽  
El Niño ◽  
Tropospheric Ozone ◽  
Large Scale ◽  
El Nino ◽  
Global Burden ◽  
The North ◽  
Tropospheric O3

Abstract. We have studied the effects of the 2006 El Niño on tropospheric O3 and CO at tropical and sub-tropical latitudes measured from the OMI and MLS instruments on the Aura satellite. The 2006 El Niño-induced drought allowed forest fires set to clear land to burn out of control during October and November in the Indonesian region. The effects of these fires are clearly seen in the enhancement of CO concentration measured from the MLS instrument. We have used a global model of atmospheric chemistry and transport (GMI CTM) to quantify the relative importance of biomass burning and large scale transport in producing observed changes in tropospheric O3 and CO. The model results show that during October and November both biomass burning and meteorological changes contributed almost equally to the observed increase in tropospheric O3 in the Indonesian region. The biomass component was 4–6 DU but it was limited to the Indonesian region where the fires were most intense. The dynamical component was 4–8 DU but it covered a much larger area in the Indian Ocean extending from South East Asia in the north to western Australia in the south. By December 2006, the effect of biomass burning was reduced to zero and the observed changes in tropospheric O3 were mostly due to dynamical effects. The model results show an increase of 2–3% in the global burden of tropospheric ozone. In comparison, the global burden of CO increased by 8–12%.

scholarly journals Effects of the 2006 El Niño on tropospheric ozone and carbon monoxide: implications for dynamics and biomass burning

2009 ◽  
Vol 9 (13) ◽  
pp. 4239-4249 ◽  
Author(s):  
S. Chandra ◽  
J. R. Ziemke ◽  
B. N. Duncan ◽  
T. L. Diehl ◽  
N. J. Livesey ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Atmospheric Chemistry ◽  
Forest Fires ◽  
El Niño ◽  
Tropospheric Ozone ◽  
Large Scale ◽  
El Nino ◽  
Global Burden ◽  
The North ◽  
Tropospheric O3

Abstract. We have studied the effects of the 2006 El Niño on tropospheric O3 and CO at tropical and sub-tropical latitudes measured from the OMI and MLS instruments on the Aura satellite. The 2006 El Niño-induced drought caused forest fires (largely set to clear land) to burn out of control during October and November in the Indonesian region. The effects of these fires are clearly seen in the enhancement of CO concentration measured from the MLS instrument. We have used a global model of atmospheric chemistry and transport (GMI CTM) to quantify the relative importance of biomass burning and large scale transport in producing observed changes in tropospheric O3 and CO. The model results show that during October and November biomass burning and meteorological changes contributed almost equally to the observed increase in tropospheric O3 in the Indonesian region. The biomass component was 4–6 DU but it was limited to the Indonesian region where the fires were most intense. The dynamical component was 4–8 DU but it covered a much larger area in the Indian Ocean extending from South East Asia in the north to western Australia in the south. By December 2006, the effect of biomass burning was reduced to zero and the observed changes in tropospheric O3 were mostly due to dynamical effects. The model results show an increase of 2–3% in the global burden of tropospheric ozone. In comparison, the global burden of CO increased by 8–12%.

scholarly journals Atmospheric CH<sub>4</sub> and CO<sub>2</sub> enhancements and biomass burning emission ratios derived from satellite observations of the 2015 Indonesian fire plumes

2016 ◽  
Vol 16 (15) ◽  
pp. 10111-10131 ◽  
Author(s):  
Robert J. Parker ◽  
Hartmut Boesch ◽  
Martin J. Wooster ◽  
David P. Moore ◽  
Alex J. Webb ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Atmospheric Chemistry ◽  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Satellite Observations ◽  
Fire Plumes ◽  
Fire Activity ◽  
First Time ◽  
Smouldering Combustion

Abstract. The 2015–2016 strong El Niño event has had a dramatic impact on the amount of Indonesian biomass burning, with the El Niño-driven drought further desiccating the already-drier-than-normal landscapes that are the result of decades of peatland draining, widespread deforestation, anthropogenically driven forest degradation and previous large fire events. It is expected that the 2015–2016 Indonesian fires will have emitted globally significant quantities of greenhouse gases (GHGs) to the atmosphere, as did previous El Niño-driven fires in the region. The form which the carbon released from the combustion of the vegetation and peat soils takes has a strong bearing on its atmospheric chemistry and climatological impacts. Typically, burning in tropical forests and especially in peatlands is expected to involve a much higher proportion of smouldering combustion than the more flaming-characterised fires that occur in fine-fuel-dominated environments such as grasslands, consequently producing significantly more CH4 (and CO) per unit of fuel burned. However, currently there have been no aircraft campaigns sampling Indonesian fire plumes, and very few ground-based field campaigns (none during El Niño), so our understanding of the large-scale chemical composition of these extremely significant fire plumes is surprisingly poor compared to, for example, those of southern Africa or the Amazon.Here, for the first time, we use satellite observations of CH4 and CO2 from the Greenhouse gases Observing SATellite (GOSAT) made in large-scale plumes from the 2015 El Niño-driven Indonesian fires to probe aspects of their chemical composition. We demonstrate significant modifications in the concentration of these species in the regional atmosphere around Indonesia, due to the fire emissions.Using CO and fire radiative power (FRP) data from the Copernicus Atmosphere Service, we identify fire-affected GOSAT soundings and show that peaks in fire activity are followed by subsequent large increases in regional greenhouse gas concentrations. CH4 is particularly enhanced, due to the dominance of smouldering combustion in peatland fires, with CH4 total column values typically exceeding 35 ppb above those of background “clean air” soundings. By examining the CH4 and CO2 excess concentrations in the fire-affected GOSAT observations, we determine the CH4 to CO2 (CH4 ∕ CO2) fire emission ratio for the entire 2-month period of the most extreme burning (September–October 2015), and also for individual shorter periods where the fire activity temporarily peaks. We demonstrate that the overall CH4 to CO2 emission ratio (ER) for fires occurring in Indonesia over this time is 6.2 ppb ppm−1. This is higher than that found over both the Amazon (5.1 ppb ppm−1) and southern Africa (4.4 ppb ppm−1), consistent with the Indonesian fires being characterised by an increased amount of smouldering combustion due to the large amount of organic soil (peat) burning involved. We find the range of our satellite-derived Indonesian ERs (6.18–13.6 ppb ppm−1) to be relatively closely matched to that of a series of close-to-source, ground-based sampling measurements made on Kalimantan at the height of the fire event (7.53–19.67 ppb ppm−1), although typically the satellite-derived quantities are slightly lower on average. This seems likely because our field sampling mostly intersected smaller-scale peat-burning plumes, whereas the large-scale plumes intersected by the GOSAT Thermal And Near infrared Sensor for carbon Observation – Fourier Transform Spectrometer (TANSO-FTS) footprints would very likely come from burning that was occurring in a mixture of fuels that included peat, tropical forest and already-cleared areas of forest characterised by more fire-prone vegetation types than the natural rainforest biome (e.g. post-fire areas of ferns and scrubland, along with agricultural vegetation).The ability to determine large-scale ERs from satellite data allows the combustion behaviour of very large regions of burning to be characterised and understood in a way not possible with ground-based studies, and which can be logistically difficult and very costly to consider using aircraft observations. We therefore believe the method demonstrated here provides a further important tool for characterising biomass burning emissions, and that the GHG ERs derived for the first time for these large-scale Indonesian fire plumes during an El Niño event point to more routinely assessing spatiotemporal variations in biomass burning ERs using future satellite missions. These will have more complete spatial sampling than GOSAT and will enable the contributions of these fires to the regional atmospheric chemistry and climate to be better understood.

scholarly journals Atmospheric CH<sub>4</sub> and CO<sub>2</sub> enhancements and biomass burning emission ratios derived from satellite observations of the 2015 Indonesian fire plumes

2016 ◽  
Author(s):  
Robert J. Parker ◽  
Hartmut Boesch ◽  
Martin J. Wooster ◽  
David P. Moore ◽  
Alex J. Webb ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Atmospheric Chemistry ◽  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Satellite Observations ◽  
Fire Plumes ◽  
First Time ◽  
Smouldering Combustion ◽  
Emission Ratios

Abstract. The 2015–2016 strong El Niño event has had a dramatic impact on the amount of Indonesian biomass burning, with the El Niño driven drought further desiccating the already drier than normal landscapes that are the result of decades of peatland draining, widespread deforestation, anthropogenically-driven forest degradation, and previous large fire events. It is expected that the 2015–16 Indonesian fires will have emitted globally significant quantities of greenhouse gases (GHGs) to the atmosphere, as did previous El Niño driven fires in the region. The form which the carbon released from the combustion of the vegetation and peat soils takes has a strong bearing on its atmospheric chemistry and climatological impacts. Typically, burning in tropical forests and especially in peatlands is expected to involve a much higher proportion of smouldering combustion than the more flaming-characterised fires that occur in fine-fuel dominated environments such as grasslands, consequently producing significantly more CH4 (and CO) per unit of fuel burned. However, currently there have been no aircraft campaigns sampling Indonesian fire plumes, and very few ground-based field campaigns (none during El Niño), so our understanding of the large-scale chemical composition of these extremely significant fire plumes is surprisingly poor compared to, for example, those of southern Africa or the Amazon. Here, for the first time, we use satellite observations of CH4 and CO2 from the Greenhouse gases Observing SATellite (GOSAT) made in large scale plumes from the 2015 El Niño-driven Indonesian fires to probe aspects of their chemical composition. We demonstrate significant modifications in the concentration of these species in the regional atmosphere around Indonesia, due to the fire emissions. Using CO and fire radiative power (FRP) data from the Copernicus Atmosphere Service, we identify fire-affected GOSAT soundings and show that peaks in fire activity are followed by subsequent large increases in regional greenhouse gas concentrations. CH4 is particularly enhanced, due to the dominance of smouldering combustion in peatland fires, with CH4 total column values typically exceeding 35 ppb above that of background "clean air" soundings. By examining the CH4 and CO2 excess concentrations in the fire-affected GOSAT observations, we determine the CH4/CO2 fire emission ratio for the entire 2-month period of the most extreme burning (September–October 2015), and also for individual shorter periods where the fire activity temporarily peaks. We demonstrate that the overall CH4 to CO2 emission ratio (ER) for fires occurring in Indonesia over this time is 6.2 ppb/ppm. This is higher than that found over both the Amazon (5.1 ppb/ppm) and southern Africa (4.4 ppb/ppm), consistent with the Indonesian fires being characterised by an increased amount of smouldering combustion due to the large amount of organic soil (peat) burning involved. We find the range of our satellite-derived Indonesian ERs (6.18 ppb/ppm to 13.6 ppb/ppm) to be relatively closely matched to that of a series of "close-to-source" ground-based sampling measurements made on Kalimantan at the height of the fire event (7.53 to 19.67 ppb/ppm), although typically the satellite-derived quantities are slightly lower on average. This seems likely to be because our field sampling mostly intersected smaller-scale peat burning plumes, whereas the large-scale plumes intersected by the GOSAT TANSO-FTS footprints would very likely come from burning that was occurring in a mixture of fuels that included peat, tropical forest and already cleared areas of forest characterised by vegetation types that are more fire-prone than the natural rainforest biome (e.g. post-fire areas of ferns and scrubland, along with agricultural vegetation). The ability to determine large-scale emission ratios from satellite data allows the combustion behaviour of very large regions of burning to be characterised and understood in a way not possible with ground-based studies, and which can be logistically difficult and very costly to consider using aircraft observations. We therefore believe the method demonstrated here provides a further important tool for characterising biomass burning emissions, and that the GHG emission ratios derived for the first time for these large-scale Indonesian fire plumes during an El Niño event, points the way to more routinely assessing spatio-temporal variations in biomass burning emission ratios using future satellite missions that will have more complete spatial sampling than GOSAT, and that will enable the contributions of these fires to the regional atmospheric chemistry and climate to be better understood.

scholarly journals Impact of El Niño–Southern Oscillation on the interannual variability of methane and tropospheric ozone

2019 ◽  
Vol 19 (13) ◽  
pp. 8669-8686 ◽  
Author(s):  
Matthew J. Rowlinson ◽  
Alexandru Rap ◽  
Stephen R. Arnold ◽  
Richard J. Pope ◽  
Martyn P. Chipperfield ◽  
...  
Keyword(s):  
Growth Rate ◽  
Interannual Variability ◽  
Biomass Burning ◽  
El Niño ◽  
Tropospheric Ozone ◽  
El Nino ◽  
Southern Oscillation ◽  
Fire Emissions ◽  
Tropospheric O3 ◽  
Global Mean

Abstract. The interannual variability of the greenhouse gases methane (CH4) and tropospheric ozone (O3) is largely driven by natural variations in global emissions and meteorology. The El Niño–Southern Oscillation (ENSO) is known to influence fire occurrence, wetland emission and atmospheric circulation, affecting sources and sinks of CH4 and tropospheric O3, but there are still important uncertainties associated with the exact mechanism and magnitude of this effect. Here we use a modelling approach to investigate how fires and meteorology control the interannual variability of global carbon monoxide (CO), CH4 and O3 concentrations, particularly during large El Niño events. Using a three-dimensional chemical transport model (TOMCAT) coupled to a sophisticated aerosol microphysics scheme (GLOMAP) we simulate changes to CO, hydroxyl radical (OH) and O3 for the period 1997–2014. We then use an offline radiative transfer model to quantify the climate impact of changes to atmospheric composition as a result of specific drivers. During the El Niño event of 1997–1998, there were increased emissions from biomass burning globally, causing global CO concentrations to increase by more than 40 %. This resulted in decreased global mass-weighted tropospheric OH concentrations of up to 9 % and a consequent 4 % increase in the CH4 atmospheric lifetime. The change in CH4 lifetime led to a 7.5 ppb yr−1 increase in the global mean CH4 growth rate in 1998. Therefore, biomass burning emission of CO could account for 72 % of the total effect of fire emissions on CH4 growth rate in 1998. Our simulations indicate that variations in fire emissions and meteorology associated with El Niño have opposing impacts on tropospheric O3 burden. El Niño-related changes in atmospheric transport and humidity decrease global tropospheric O3 concentrations leading to a −0.03 W m−2 change in the O3 radiative effect (RE). However, enhanced fire emission of precursors such as nitrogen oxides (NOx) and CO increase O3 and lead to an O3 RE of 0.03 W m−2. While globally the two mechanisms nearly cancel out, causing only a small change in global mean O3 RE, the regional changes are large – up to −0.33 W m−2 with potentially important consequences for atmospheric heating and dynamics.

Using Satellite Altimeter and SST Observations of the 1997-1998 El Nino to Check the Key Ocean Processes Involved in a Strong El Nino.

2021 ◽  
Author(s):  
David Webb ◽  
Andrew Coward ◽  
Helen Snaith
Keyword(s):  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Ocean Model ◽  
Satellite Altimeter ◽  
The North ◽  
Satellite Sst ◽  
Model Study ◽  
North Equatorial Counter Current ◽  
Equatorial Current

&lt;p&gt;A recent high-resolution ocean model study of the strong El Ninos of 1982-1983 and 1997-1998 highlighted a previously neglected ocean mechanism which was active during their growth. &amp;#160; The mechanism involved a weakening of both the Equatorial Current and the tropical instability eddies in mid-ocean. &amp;#160;It also involved an increase in the strength of the North Equatorial Counter Current due to the passage of the annual Rossby wave.&lt;/p&gt;&lt;p&gt;&amp;#160; &amp;#160; &amp;#160; This presentation reports how satellite altimeter and satellite SST data was used to validate the model results the key areas, confirming the changes in the current and eddy fields and the resulting eastward extension of the region of highest SST values. &amp;#160;The SST changes were sufficient to trigger new regions deep-atmospheric convection and so had the potential to have a significant impact on the development of the El Nino and the resulting changes in the large scale atmospheric circulation.&lt;/p&gt;

scholarly journals Impact of El Niño Southern Oscillation on the interannual variability of methane and tropospheric ozone

2019 ◽  
Author(s):  
Matthew J. Rowlinson ◽  
Alexandru Rap ◽  
Stephen R. Arnold ◽  
Richard J. Pope ◽  
Martyn P. Chipperfield ◽  
...  
Keyword(s):  
Growth Rate ◽  
Interannual Variability ◽  
Biomass Burning ◽  
El Niño ◽  
Atmospheric Transport ◽  
El Nino ◽  
Southern Oscillation ◽  
Fire Emissions ◽  
Tropospheric O3 ◽  
Global Mean

Abstract. The growth rate of global methane (CH4) concentrations has a strong interannual variability which is believed to be driven largely by fluctuations in CH4 emissions from wetlands and wildfires, as well as changes to the atmospheric sink. The El Niño Southern Oscillation (ENSO) is known to influence fire occurrence, wetland emission and atmospheric transport, but there are still important uncertainties associated with the exact mechanism and magnitude of this influence. Here we use a modelling approach to investigate how fires and meteorology control the interannual variability of global carbon monoxide (CO), CH4 and ozone (O3) concentrations, particularly during large El Niño events. Using a three-dimensional chemical transport model (TOMCAT) coupled to a sophisticated aerosol microphysics scheme (GLOMAP) we simulate changes to CO, hydroxyl radical (OH) and O3 for the period 1997–2014. We then use an offline radiative transfer model to quantify the impact of changes to atmospheric composition as a result of specific drivers. During the El Niño event of 1997–1998, there were increased emissions from biomass burning globally. As a result, global CO concentrations increased by more than 40 %. This resulted in decreased global mass-weighted tropospheric OH concentrations of up to 9 % and a resulting 4 % increase in the CH4 atmospheric lifetime. The change in CH4 lifetime led to a 7.5 ppb yr−1 increase in global mean CH4 growth rate in 1998. Therefore biomass burning emission of CO could account for 72 % of the total effect of fire emissions on CH4 growth rate in 1998. Our simulations indicate variations in fire emissions and meteorology associated with El Niño have opposing impacts on tropospheric O3 burden. El Niño-related atmospheric transport changes decrease global tropospheric O3 concentrations leading to a −0.03 Wm−2 change in O3 radiative effect (RE). However, enhanced fire emission of precursors such as nitrous oxides (NOx) and CO increase O3 RE by 0.03 Wm−2. While globally the two mechanisms nearly cancel out, causing only a small change in global mean O3 RE, the regional changes are large   up to −0.33 Wm−2 with potentially important consequences for atmospheric heating and dynamics.

scholarly journals Toward Identifying Subseasonal Forecasts of Opportunity Using North American Weather Regimes

2020 ◽  
Vol 148 (5) ◽  
pp. 1861-1875
Author(s):  
Andrew W. Robertson ◽  
Nicolas Vigaud ◽  
Jing Yuan ◽  
Michael K. Tippett
Keyword(s):  
North American ◽  
El Niño ◽  
Geopotential Height ◽  
Large Scale ◽  
El Nino ◽  
Lead Times ◽  
Seasonal Forecasts ◽  
The North ◽  
The Pacific ◽  
Graphical Tool

Abstract Large-scale atmospheric circulation regime structures are used to diagnose subseasonal forecasts of wintertime geopotential height fields over the North American sector, from the NCEP CFSv2 model. Four large-scale daily circulation regimes derived from reanalysis 500-hPa geopotential height data using K-means clustering are used as a low-dimensional basis for diagnosing the model’s forecasts up to 45 days ahead. On average, hindcast skill in regime space is found to be limited to 10–15 days ahead, in terms of anomaly correlation of 5-day averages of regime counts, over the 1999–2010 period. However, skill up to 30 days ahead is identified in individual winters, and intraseasonal episodes of high skill are identified using a forecast-evolution graphical tool. A striking vacillation between the West Coast and Pacific ridge patterns during December–January 2008/09 is shown to be predicted 20–25 days in advance, illustrating the possibility to identify “forecasts of opportunity” when subseasonal forecast skill is much higher than the average. The forecast-evolution tool also provides insight into the poor seasonal forecasts of California precipitation by operational centers during the 2015/16 El Niño winter. The Pacific trough regime is shown to be greatly overpredicted beyond 1–2 weeks in advance during the 2015/16 winter, with weather-scale features dominating the forecast evolution at shorter lead times. A similar though less extreme situation took place during the weaker El Niño of 2009/10, with the Pacific trough overforecast at S2S lead times.

scholarly journals The Influence of Large-Scale Climate Variability on Winter Maximum Daily Precipitation over North America

2010 ◽  
Vol 23 (11) ◽  
pp. 2902-2915 ◽  
Author(s):  
Xuebin Zhang ◽  
Jiafeng Wang ◽  
Francis W. Zwiers ◽  
Pavel Ya Groisman
Keyword(s):  
North America ◽  
Climate Variability ◽  
El Niño ◽  
Extreme Precipitation ◽  
Large Scale ◽  
El Nino ◽  
Southern Oscillation ◽  
Statistical Significance ◽  
Winter Season ◽  
The North

Abstract The generalized extreme value (GEV) distribution is fitted to winter season daily maximum precipitation over North America, with indices representing El Niño–Southern Oscillation (ENSO), the Pacific decadal oscillation (PDO), and the North Atlantic Oscillation (NAO) as predictors. It was found that ENSO and PDO have spatially consistent and statistically significant influences on extreme precipitation, while the influence of NAO is regional and is not field significant. The spatial pattern of extreme precipitation response to large-scale climate variability is similar to that of total precipitation but somewhat weaker in terms of statistical significance. An El Niño condition or high phase of PDO corresponds to a substantially increased likelihood of extreme precipitation over a vast region of southern North America but a decreased likelihood of extreme precipitation in the north, especially in the Great Plains and Canadian prairies and the Great Lakes/Ohio River valley.

scholarly journals The Role of El Nino Variability and Peatland in Burnt Area and Emitted Carbon in Forest Fire Modeling

2022 ◽  
pp. 84-103
Author(s):  
Ida Bagus Mandhara Brasika
Keyword(s):  
Forest Fires ◽  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Natural Environments ◽  
Fire Occurrence ◽  
Burnt Area ◽  
Peat Fire ◽  
Ground Fire ◽  
Limited Input Data

This study was conducted to model fire occurrence within El Nino variability and peatland distribution. These climate and geographical factors have a significant impact on forest fires in tropical areas such as Indonesia. The re-analysis dataset from ECMWF was observed with respect to climate characteristics in Indonesian El Nino events. The INFERNO (INteractive Fire and Emission algoRithm for Natural envirOnments) was utilized to simulate fires over Borneo Island due to its capability to simulate large-scale fires with simplified parameters. There were some adjustments in this INFERNO model, especially for peat fire as peatland has a significant impact on fires. The first was the contribution of climate to the peat fire which is represented by long-term precipitation. The second was the combustion completeness of peat fire occurrence that is mainly affected by human-induced peat drainage. The result of the model shows that El Nino variability mainly affected peat fires but was unable to well simulate the above-ground fire. It increased the burnt area during strong El Nino but overestimated the fires during low/no El Nino season due to lack of peat fire ignition in the calculation. Moreover, as the model did not provide peat drainage simulation, it underestimated the carbon emission. This model has shown promising results by addressing key features in limited input data, but improving some simulations is necessary for regulating weak/no El Nino conditions and carbon combustion of peat fire.

scholarly journals Tropical tropospheric ozone column retrieval for GOME-2

2014 ◽  
Vol 7 (1) ◽  
pp. 727-768 ◽  
Author(s):  
P. Valks ◽  
N. Hao ◽  
S. Gimeno Garcia ◽  
D. Loyola ◽  
M. Dameris ◽  
...  
Keyword(s):  
South America ◽  
Atmospheric Chemistry ◽  
El Niño ◽  
Tropospheric Ozone ◽  
El Nino ◽  
Southern Oscillation ◽  
Model Systems ◽  
Strong Increase ◽  
Tropospheric No2 ◽  
Ozone Column

Abstract. This paper presents the operational retrieval of tropical tropospheric ozone columns (TOC) from the Second Global Ozone Monitoring Experiment (GOME-2) instruments using the convective-cloud-differential (CCD) method. The retrieval is based on total ozone and cloud property data provided by the GOME Data Processor (GDP) 4.7, and uses above-cloud and clear-sky ozone column measurements to derive a monthly mean TOC between 20° N and 20° S. Validation of the GOME-2 TOC with several tropical ozonesonde sites shows good agreement, with a high correlation between the GOME-2 and sonde measurements, and small biases within ~ 3 DU. The TOC data have been used in combination with tropospheric NO2 measurements from GOME-2 to analyse the effect of the 2009–2010 El Niño–Southern Oscillation (ENSO) on the tropospheric ozone distribution in the tropics. El-Niño induced dry conditions in September–October 2009 resulted in relatively high tropospheric ozone columns over the southern Indian Ocean and northern Australia, while La Niña conditions in September–October 2010 resulted in a strong increase in tropospheric NO2 in South America, and enhanced ozone in the eastern Pacific and South America. Comparisons of the GOME-2 tropospheric ozone data with simulations of the ECHAM/MESSy Atmospheric Chemistry (EMAC) model for 2009 El Nino conditions, illustrate the usefulness of the GOME-2 TOC measurements in evaluating chemistry climate models. Evaluation of CCMs with appropriate satellite observations helps to identify strengths and weaknesses of the model systems, providing a better understanding of driving mechanisms and adequate relations and feedbacks in the Earth atmosphere, and finally leading to improved models.

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