scholarly journals Role of the stratospheric chemistry-climate interactions in the hot climate conditions of the Eocene

2018 ◽  
Author(s):  
Sophie Szopa ◽  
Rémi Thiéblemont ◽  
Slimane Bekki ◽  
Svetlana Botsyun ◽  
Pierre Sepulchre
Keyword(s):  
Thermal Structure ◽  
Stratospheric Ozone ◽  
Ozone Layer ◽  
Atmospheric Composition ◽  
Total Column Ozone ◽  
Climate Conditions ◽  
Ozone Distribution ◽  
Hot Climate ◽  
Ozone Column

Abstract. The stratospheric ozone layer plays a key role in atmospheric thermal structure and circulation. Although stratospheric ozone distribution is sensitive to changes in composition and climate, the modifications of stratospheric ozone are not usually considered in climate studies at geological time scales. Here, we evaluate with a chemical-climate model the potential role of stratospheric ozone chemistry in the case of the Eocene hot conditions. We show that the structure of the ozone layer is significantly different under these conditions (4×CO2 climate and high concentrations of tropospheric N2O and CH4). While at mid and high latitudes, the total column ozone is found to be enhanced, the tropical ozone column remains more or less unchanged. These ozone changes are related to the stratospheric cooling and an acceleration of stratospheric Brewer-Dobson circulation simulated under Eocene climate. The meridional distribution of the total ozone column appears also to be strongly modified, showing particularly pronounced mid-latitudes maxima and steeper negative poleward gradient from these maxima. These anomalies are consistent with changes in the seasonal evolution of the polar vortex during the winter, especially in the Northern Hemisphere. Compared to a pre-industrial atmospheric composition, the changes in local ozone concentration reach up to 40 % for zonal annual mean and affect temperature by a few Kelvins in the middle stratosphere. As inter-model differences in simulating the deep past temperatures are quite high, the consideration of atmospheric chemistry, which is computationally demanding in Earth system models, may seem superfluous. However, our results suggest that using stratospheric ozone calculated by the model (and hence more physically consistent with Eocene conditions) instead of the commonly specified preindustrial ozone distribution can change the simulated global surface air temperature by 14 %. This error is of the same order as the effect of non-CO2 boundary conditions (topography, bathymetry, solar constant & vegetation). Moreover, the results highlight the sensitivity of stratospheric ozone to hot climate conditions. Since the climate sensitivity to stratospheric ozone feedback largely differs between models, it must be better constrained not only for deep past conditions but also for future climates.

scholarly journals Role of the stratospheric chemistry–climate interactions in the hot climate conditions of the Eocene

2019 ◽  
Vol 15 (4) ◽  
pp. 1187-1203 ◽  
Author(s):  
Sophie Szopa ◽  
Rémi Thiéblemont ◽  
Slimane Bekki ◽  
Svetlana Botsyun ◽  
Pierre Sepulchre
Keyword(s):  
Atmospheric Chemistry ◽  
Thermal Structure ◽  
Stratospheric Ozone ◽  
Ozone Layer ◽  
Atmospheric Composition ◽  
Total Column Ozone ◽  
Climate Conditions ◽  
Ozone Distribution ◽  
Hot Climate

Abstract. The stratospheric ozone layer plays a key role in atmospheric thermal structure and circulation. Although stratospheric ozone distribution is sensitive to changes in trace gases concentrations and climate, the modifications of stratospheric ozone are not usually considered in climate studies at geological timescales. Here, we evaluate the potential role of stratospheric ozone chemistry in the case of the Eocene hot conditions. Using a chemistry–climate model, we show that the structure of the ozone layer is significantly different under these conditions (4×CO2 climate and high concentrations of tropospheric N2O and CH4). The total column ozone (TCO) remains more or less unchanged in the tropics whereas it is found to be enhanced at mid- and high latitudes. These ozone changes are related to the stratospheric cooling and an acceleration of stratospheric Brewer–Dobson circulation simulated under Eocene climate. As a consequence, the meridional distribution of the TCO appears to be modified, showing particularly pronounced midlatitude maxima and a steeper negative poleward gradient from these maxima. These anomalies are consistent with changes in the seasonal evolution of the polar vortex during winter, especially in the Northern Hemisphere, found to be mainly driven by seasonal changes in planetary wave activity and stratospheric wave-drag. Compared to a preindustrial atmospheric composition, the changes in local ozone concentration reach up to 40 % for zonal annual mean and affect temperature by a few kelvins in the middle stratosphere. As inter-model differences in simulating deep-past temperatures are quite high, the consideration of atmospheric chemistry, which is computationally demanding in Earth system models, may seem superfluous. However, our results suggest that using stratospheric ozone calculated by the model (and hence more physically consistent with Eocene conditions) instead of the commonly specified preindustrial ozone distribution could change the simulated global surface air temperature by as much as 14 %. This error is of the same order as the effect of non-CO2 boundary conditions (topography, bathymetry, solar constant and vegetation). Moreover, the results highlight the sensitivity of stratospheric ozone to hot climate conditions. Since the climate sensitivity to stratospheric ozone feedback largely differs between models, it must be better constrained not only for deep-past conditions but also for future climates.

scholarly journals Key drivers of ozone change and its radiative forcing over the 21st century

2018 ◽  
Vol 18 (9) ◽  
pp. 6121-6139 ◽  
Author(s):  
Fernando Iglesias-Suarez ◽  
Douglas E. Kinnison ◽  
Alexandru Rap ◽  
Amanda C. Maycock ◽  
Oliver Wild ◽  
...  
Keyword(s):  
Climate Change ◽  
21St Century ◽  
Radiative Forcing ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Atmospheric Composition ◽  
Climate Conditions ◽  
Radiative Balance ◽  
Radiative Forcings ◽  
Year 2000

Abstract. Over the 21st century changes in both tropospheric and stratospheric ozone are likely to have important consequences for the Earth's radiative balance. In this study, we investigate the radiative forcing from future ozone changes using the Community Earth System Model (CESM1), with the Whole Atmosphere Community Climate Model (WACCM), and including fully coupled radiation and chemistry schemes. Using year 2100 conditions from the Representative Concentration Pathway 8.5 (RCP8.5) scenario, we quantify the individual contributions to ozone radiative forcing of (1) climate change, (2) reduced concentrations of ozone depleting substances (ODSs), and (3) methane increases. We calculate future ozone radiative forcings and their standard error (SE; associated with inter-annual variability of ozone) relative to year 2000 of (1) 33 ± 104 m Wm−2, (2) 163 ± 109 m Wm−2, and (3) 238 ± 113 m Wm−2 due to climate change, ODSs, and methane, respectively. Our best estimate of net ozone forcing in this set of simulations is 430 ± 130 m Wm−2 relative to year 2000 and 760 ± 230 m Wm−2 relative to year 1750, with the 95 % confidence interval given by ±30 %. We find that the overall long-term tropospheric ozone forcing from methane chemistry–climate feedbacks related to OH and methane lifetime is relatively small (46 m Wm−2). Ozone radiative forcing associated with climate change and stratospheric ozone recovery are robust with regard to background climate conditions, even though the ozone response is sensitive to both changes in atmospheric composition and climate. Changes in stratospheric-produced ozone account for ∼ 50 % of the overall radiative forcing for the 2000–2100 period in this set of simulations, highlighting the key role of the stratosphere in determining future ozone radiative forcing.

The response of the ozone layer under abrupt 4xCO2 in CMIP6

2021 ◽  
Author(s):  
Gabriel Chiodo ◽  
William T. Ball ◽  
Peer Nowack ◽  
Clara Orbe ◽  
James Keeble ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Climate Models ◽  
Stratospheric Ozone ◽  
Ozone Layer ◽  
Cmip5 Models ◽  
Radiative Efficiency ◽  
Tropospheric Circulation ◽  
Column Ozone ◽  
The Relationship

<p>Previous studies indicate a possible role of stratospheric ozone chemistry feedbacks in the climate response to 4xCO2, either via a reduction in equilibrium climate sensitivity (ECS) or via changes in the tropospheric circulation (Nowack et al., 2015; Chiodo and Polvani, 2017). However, these effects are subject to uncertainty. Part of the uncertainty may stem from the dependency of the feedback on the pattern of the ozone response, as the radiative efficiency of ozone largely depends on its vertical distribution (Lacis et al., 1990). Here, an analysis is presented of the ozone layer response to 4xCO2 in chemistry–climate models (CCMs) which participated to CMIP inter-comparisons. In a previous study using CMIP5 models, it has been shown that under 4xCO2, ozone decreases in the tropical lower stratosphere, and increases over the high latitudes and throughout the upper stratosphere (Chiodo et al., 2018). It was also found that a substantial portion of the spread in the tropical column ozone is tied to inter-model spread in tropical upwelling, which is in turn tied to ECS. Here, we revisit this connection using 4xCO2 data from CMIP6, thereby exploiting the larger number of CCMs available than in CMIP5. In addition, we explore the linearity of the ozone response, by complementing the analysis with simulations using lower CO2 forcing levels (2xCO2). We show that the pattern of the ozone response is similar to CMIP5. In some models (e.g. WACCM), we find larger ozone responses in CMIP6 than in CMIP5, partly because of the larger ECS and thus larger upwelling response in the tropical pipe. In this presentation, we will discuss the relationship between radiative forcing, transport and ozone, as well as further implications for CMIP6 models.</p>

scholarly journals Evidence for a continuous decline in lower stratospheric ozone offsetting ozone layer recovery

2018 ◽  
Vol 18 (2) ◽  
pp. 1379-1394 ◽  
Author(s):  
William T. Ball ◽  
Justin Alsing ◽  
Daniel J. Mortlock ◽  
Johannes Staehelin ◽  
Joanna D. Haigh ◽  
...  
Keyword(s):  
Lower Stratosphere ◽  
Stratospheric Ozone ◽  
Ozone Layer ◽  
Montreal Protocol ◽  
Downward Trend ◽  
Polar Regions ◽  
Total Column Ozone ◽  
Ozone Depleting Substances ◽  
Column Ozone ◽  
Total Column

Abstract. Ozone forms in the Earth's atmosphere from the photodissociation of molecular oxygen, primarily in the tropical stratosphere. It is then transported to the extratropics by the Brewer–Dobson circulation (BDC), forming a protective ozone layer around the globe. Human emissions of halogen-containing ozone-depleting substances (hODSs) led to a decline in stratospheric ozone until they were banned by the Montreal Protocol, and since 1998 ozone in the upper stratosphere is rising again, likely the recovery from halogen-induced losses. Total column measurements of ozone between the Earth's surface and the top of the atmosphere indicate that the ozone layer has stopped declining across the globe, but no clear increase has been observed at latitudes between 60° S and 60° N outside the polar regions (60–90°). Here we report evidence from multiple satellite measurements that ozone in the lower stratosphere between 60° S and 60° N has indeed continued to decline since 1998. We find that, even though upper stratospheric ozone is recovering, the continuing downward trend in the lower stratosphere prevails, resulting in a downward trend in stratospheric column ozone between 60° S and 60° N. We find that total column ozone between 60° S and 60° N appears not to have decreased only because of increases in tropospheric column ozone that compensate for the stratospheric decreases. The reasons for the continued reduction of lower stratospheric ozone are not clear; models do not reproduce these trends, and thus the causes now urgently need to be established.

scholarly journals A comparative analysis of UV nadir-backscatter and infrared limb-emission ozone data assimilation

2016 ◽  
Author(s):  
Rossana Dragani
Keyword(s):  
Data Assimilation ◽  
Control Experiment ◽  
Stratospheric Ozone ◽  
Michelson Interferometer ◽  
European Space Agency ◽  
Ultra Violet ◽  
Total Column Ozone ◽  
Ozone Distribution ◽  
Ozone Data ◽  
Ozone Profile

Abstract. This paper presents a comparative assessment of ultra violet nadir-backscatter and infrared limb-emission ozone profile assimilation. The Meteorological Operational Satellite A (MetOp-A) Global Ozone Monitoring Experiment 2 (GOME-2) nadir and the ENVISAT Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) limb profiles, generated as part of the European Space Agency Climate Change Initiative, were individually added to a reference set of ozone observations and assimilated in the European Centre for Medium-Range Weather Forecasts (ECMWF) data assimilation system (DAS). The two sets of resulting analyses were compared with that from a control experiment, only constrained by the reference dataset, and independent, unassimilated observations. Comparisons with independent observations show that both datasets improve the stratospheric ozone distribution. The changes inferred by the limb-based observations are more localized and, in places, more important than those implied by the nadir profiles, albeit they have a much lower number of observations. A small degradation (up to 0.25 mg/kg for GOME-2 and 0.5 mg/kg for MIPAS) is found in the tropics between 20 and 30 hPa. In the lowermost troposphere below its vertical coverage, the limb data is found able to modify the ozone distribution with changes as large as 60 %. Comparisons of the ozone analyses with sonde data show that at those levels the assimilation of GOME-2 leads to about 1 Dobson Unit (DU) smaller root mean square error (RMSE) than that of MIPAS. However, the assimilation of MIPAS can still improve the quality of the ozone analyses, and – with a reduction in the RMSE up to about 2 DU – outperform the control experiment thanks to its synergistic assimilation with total column ozone data within the DAS. High vertical resolution ozone profile observations are essential to accurately monitor and forecast ozone concentrations in a DAS. This study demonstrates the potential and limitations of each dataset and instrument type, as well as the need for a balanced future availability of nadir and limb sensors, and long-term plans for limb-viewing instruments.

The response of stratospheric ozone and dynamics to changes in atmospheric oxygen

2021 ◽  
Author(s):  
Iga Józefiak ◽  
Timofei Sukhodolov ◽  
Tatiana Egorova ◽  
Eugene Rozanov ◽  
Gabriel Chiodo ◽  
...  
Keyword(s):  
Molecular Oxygen ◽  
Climate Model ◽  
Atmospheric Oxygen ◽  
Stratospheric Ozone ◽  
Ozone Layer ◽  
Self Healing ◽  
Oxygen Level ◽  
Meridional Transport ◽  
Regional Patterns ◽  
Total Column Ozone

<p>Photolysis of molecular oxygen (O<sub>2</sub>) maintains the stratospheric ozone layer, protecting living organisms on Earth by absorbing harmful ultraviolet radiation. The atmospheric oxygen level has not always been constant, and has been held responsible for species extinctions via a thinning of the ozone layer in the past. On paleo-climate timescales, it ranged between 10 and 35% depending on the level of photosynthetic activity of plants and oceans. Previous estimates, however, showed highly uncertain ozone (O<sub>3</sub>) <sub></sub>responses to atmospheric O<sub>2</sub> changes, including monotonic positive or negative correlations, or displaying a maximum in O<sub>3 </sub>column around a certain oxygen level. Motivated by these discrepancies we reviewed how the ozone layer responds to atmospheric oxygen changes by means of a state-of-the-art chemistry-climate model (CCM). We used the CCM SOCOL-AERv2 to assess the ozone layer sensitivity to past and potential future concentrations of atmospheric oxygen varying from 5 to 40 %. Our findings are at odds with previous studies: we find that the current mixing ratio of O<sub>2</sub>, 21 %, indeed maximizes the O<sub>3</sub> layer thickness and, thus, represents an optimal state for life on Earth. In the model, any alteration in atmospheric oxygen would result globally in less total column ozone and, therefore, more UV reaching the troposphere. Total ozone column in low-latitude regions is less sensitive to the changes, because of the “self-healing” effect, i.e. more UV entering lower levels, where O<sub>2</sub> photolyzes, can partly compensate the O<sub>3</sub> lack higher up. Mid- and high-latitudes, however, are characterized by ±20 DU ozone hemispheric redistributions even for small (±5 %) variations in O<sub>2</sub> content. Additional regional patterns result from the hemispheric asymmetry of meridional transport pathways via the Brewer-Dobson circulation (BDC). We will discuss the different ozone responses resulting from changes in the BDC. These effects are further modulated by the influence of ozone on stratospheric temperatures and thus on the BDC. Lower O<sub>2 </sub>cases result in a deceleration of the BDC. This renders the relation between ozone and molecular oxygen changes non-linear on both global and regional scales.</p>

scholarly journals Inconsistencies between chemistry climate model and observed lower stratospheric trends since 1998

2019 ◽  
Author(s):  
William T. Ball ◽  
Gabriel Chiodo ◽  
Marta Abalos ◽  
Justin Alsing
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Ozone Layer ◽  
Montreal Protocol ◽  
Total Column Ozone ◽  
Temperature Trends ◽  
Ozone Depleting Substances ◽  
The Tropics

Abstract. The stratospheric ozone layer shields surface life from harmful ultraviolet radiation. Following the Montreal Protocol ban of long-lived ozone depleting substances (ODSs), rapid depletion of total column ozone (TCO) ceased in the late 1990s and ozone above 32 km now enjoys a clear recovery. However, there is still no confirmation of TCO recovery, and evidence has emerged that ongoing quasi-global (60° S–60° N) lower stratospheric ozone decreases may be responsible, dominated by low latitudes (30° S–30° N). Chemistry climate models (CCMs) used to project future changes predict that lower stratospheric ozone will decrease in the tropics by 2100, but not at mid-latitudes (30°–60°). Here, we show that CCMs display an ozone decline similar to that observed in the tropics over 1998–2016, likely driven by a increase of tropical upwelling. On the other hand, mid-latitude lower stratospheric ozone is observed to decrease, while CCMs show an increase. Despite opposing lower stratospheric ozone changes, which should induce opposite temperature trends, CCM and observed temperature trends agree; we demonstrate that opposing model-observation stratospheric water vapour (SWV) trends, and their associated radiative effects, explain why temperature changes agree in spite of opposing ozone trends. We provide new evidence that the observed mid-latitude trends can be explained by enhanced mixing between the tropics and extratropics. We further show that the temperature trends are consistent with the observed mid-latitude ozone decrease. Together, our results suggest that large scale circulation changes expected in the future from increased greenhouse gases (GHGs) may now already be underway, but that most CCMs are not simulating well mid-latitude ozone layer changes. The reason CCMs do not exhibit the observed changes urgently needs to be understood to improve confidence in future projections of the ozone layer.

scholarly journals The MACC reanalysis: an 8-yr data set of atmospheric composition

2012 ◽  
Vol 12 (12) ◽  
pp. 31247-31347 ◽  
Author(s):  
A. Inness ◽  
F. Baier ◽  
A. Benedetti ◽  
I. Bouarar ◽  
S. Chabrillat ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Satellite Data ◽  
Urban Areas ◽  
Stratospheric Ozone ◽  
Anthropogenic Pollution ◽  
Atmospheric Composition ◽  
Data Set ◽  
Total Column Ozone ◽  
Reactive Gases ◽  
Assimilation System

Abstract. An eight-year long reanalysis of atmospheric composition data covering the period 2003–2010 was constructed as part of the FP7 funded Monitoring Atmospheric Composition and Climate project by assimilating satellite data into a global model and data assimilation system. This reanalysis provides fields of chemically reactive gases, namely carbon monoxide, ozone, nitrogen oxides, and formaldehyde, as well as aerosols and greenhouse gases globally at a resolution of about 80 km for both the troposphere and the stratosphere. This paper describes the assimilation system for the reactive gases and presents validation results for the reactive gases analysis fields to document the dataset and to give a first indication of its quality. Tropospheric CO values from the MACC reanalysis are on average 10–20% lower than routine observations from commercial aircrafts over airports through most of the troposphere, and have larger negative biases in the boundary layer at urban sites affected by air pollution, possibly due to an underestimation of CO or precursor emissions. Stratospheric ozone fields from the MACC reanalysis agree with ozone sondes and ACE-FTS data to within ±10% in most situations. In the troposphere the reanalysis shows biases of −5% to +10% with respect to ozone sondes and aircraft data in the extratropics, but has larger negative biases in the tropics. Area averaged total column ozone agrees with ozone fields from a multi sensor reanalysis data set to within a few percent. NO2 fields from the reanalysis show the right seasonality over polluted urban areas of the NH and over tropical biomass burning areas, but underestimate wintertime NO2 maxima over anthropogenic pollution regions and overestimate NO2 in Northern and Southern Africa during the tropical biomass burning seasons. Tropospheric HCHO is well simulated in the MACC reanalysis even though no satellite data are assimilated. It shows good agreement with independent SCIAMACHY retrievals over regions dominated by biogenic emissions with some anthropogenic input, such as the Eastern US and China, and also over African regions influenced by biogenic sources and biomass burning.

scholarly journals The MACC reanalysis: an 8 yr data set of atmospheric composition

2013 ◽  
Vol 13 (8) ◽  
pp. 4073-4109 ◽  
Author(s):  
A. Inness ◽  
F. Baier ◽  
A. Benedetti ◽  
I. Bouarar ◽  
S. Chabrillat ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Satellite Data ◽  
Urban Areas ◽  
Stratospheric Ozone ◽  
Horizontal Resolution ◽  
Atmospheric Composition ◽  
Data Set ◽  
Total Column Ozone ◽  
Reactive Gases ◽  
Assimilation System

Abstract. An eight-year long reanalysis of atmospheric composition data covering the period 2003–2010 was constructed as part of the FP7-funded Monitoring Atmospheric Composition and Climate project by assimilating satellite data into a global model and data assimilation system. This reanalysis provides fields of chemically reactive gases, namely carbon monoxide, ozone, nitrogen oxides, and formaldehyde, as well as aerosols and greenhouse gases globally at a horizontal resolution of about 80 km for both the troposphere and the stratosphere. This paper describes the assimilation system for the reactive gases and presents validation results for the reactive gas analysis fields to document the data set and to give a first indication of its quality. Tropospheric CO values from the MACC reanalysis are on average 10–20% lower than routine observations from commercial aircrafts over airports through most of the troposphere, and have larger negative biases in the boundary layer at urban sites affected by air pollution, possibly due to an underestimation of CO or precursor emissions. Stratospheric ozone fields from the MACC reanalysis agree with ozonesondes and ACE-FTS data to within ±10% in most seasons and regions. In the troposphere the reanalysis shows biases of −5% to +10% with respect to ozonesondes and aircraft data in the extratropics, but has larger negative biases in the tropics. Area-averaged total column ozone agrees with ozone fields from a multi-sensor reanalysis data set to within a few percent. NO2 fields from the reanalysis show the right seasonality over polluted urban areas of the NH and over tropical biomass burning areas, but underestimate wintertime NO2 maxima over anthropogenic pollution regions and overestimate NO2 in northern and southern Africa during the tropical biomass burning seasons. Tropospheric HCHO is well simulated in the MACC reanalysis even though no satellite data are assimilated. It shows good agreement with independent SCIAMACHY retrievals over regions dominated by biogenic emissions with some anthropogenic input, such as the eastern US and China, and also over African regions influenced by biogenic sources and biomass burning.

scholarly journals A comparative analysis of UV nadir-backscatter and infrared limb-emission ozone data assimilation

2016 ◽  
Vol 16 (13) ◽  
pp. 8539-8557 ◽  
Author(s):  
Rossana Dragani
Keyword(s):  
Data Assimilation ◽  
Control Experiment ◽  
Stratospheric Ozone ◽  
Michelson Interferometer ◽  
European Space Agency ◽  
Total Column Ozone ◽  
Ozone Distribution ◽  
Ozone Data ◽  
Instrument Type ◽  
Ozone Profile

Abstract. This paper presents a comparative assessment of ultraviolet nadir-backscatter and infrared limb-emission ozone profile assimilation. The Meteorological Operational Satellite A (MetOp-A) Global Ozone Monitoring Experiment 2 (GOME-2) nadir and the ENVISAT Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) limb profiles, generated by the ozone consortium of the European Space Agency Climate Change Initiative (ESA O3-CCI), were individually added to a reference set of ozone observations and assimilated in the European Centre for Medium-Range Weather Forecasts (ECMWF) data assimilation system (DAS). The two sets of resulting analyses were compared with that from a control experiment, only constrained by the reference dataset, and independent, unassimilated observations. Comparisons with independent observations show that both datasets improve the stratospheric ozone distribution. The changes inferred by the limb-based observations are more localized and, in places, more important than those implied by the nadir profiles, albeit they have a much lower number of observations. A small degradation (up to 0.25 mg kg−1 for GOME-2 and 0.5 mg kg−1 for MIPAS in the mass mixing ratio) is found in the tropics between 20 and 30 hPa. In the lowermost troposphere below its vertical coverage, the limb data are found to be able to modify the ozone distribution with changes as large as 60 %. Comparisons of the ozone analyses with sonde data show that at those levels the assimilation of GOME-2 leads to about 1 Dobson Unit (DU) smaller root mean square error (RMSE) than that of MIPAS. However, the assimilation of MIPAS can still improve the quality of the ozone analyses and – with a reduction in the RMSE of up to about 2 DU – outperform the control experiment thanks to its synergistic assimilation with total-column ozone data within the DAS. High vertical resolution ozone profile observations are essential to accurately monitor and forecast ozone concentrations in a DAS. This study demonstrates the potential and limitations of each dataset and instrument type, as well as the need for a balanced future availability of nadir and limb sensors and long-term plans for limb-viewing instruments.

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