Analysis of stratospheric ozone depletion in the Arctic using a data assimilation technique

Serious ozone depletion has been measured every Antarctic spring since the early 80’s. This ozone depletion is considered to be a result of photo chemical reactions and cat- alytic cycles resulting from anthropogenic halogen containing gases. In addition, the formation of Polar Stratospheric Clouds (PSCs) facilitates ozone loss because reac- tive halogen species are released by heterogeneous reactions on the surface of a PSC particle.Generally, Arctic ozone depletion is less severe and show larger variability than Antarctic loss because of the unstable and warmer condition. However, the Arctic stratosphere has been becoming colder during past decades and the Arctic ozone loss in the 2011 winter was comparable to Antarctic losses. Ozone depletion is di- rectly/indirectly linked to the climate because the absorption of UV radiation changes the temperature field. It is therefore important to quantify the loss for future climate prediction.The aim of this thesis is to quantify Arctic ozone depletion in several winters by using the data assimilation technique which is generally used in numerical weather prediction. The DIAMOND (Dynamical Isentropic Assimilation Model for Odin Data) is used in this thesis. This thesis includes two articles. The first paper fo- cuses on the specific northern winter (2009/2010) when SMILES (Superconducting Submillimeter-Wave Limb-Emission Sounder) observed stratospheric species. In Ad- dition, a new vertical transport scheme was implemented into the DIAMOND model to account for the diabatic descent inside the polar vortex during the polar night. The comparison shows that the ozone loss estimation from the assimilation of SMILES agrees with the loss from Odin/SMR (sub-millimeter microwave radiometer) measure- ment. Two different chemical mechanisms, the Cl catalytic cycle with PSC formation and NOx related chemistry, can explain losses at different altitudes that occurred in the 2009/2010 winter. The second paper presents the extension of the assimilation analysis for the entire SMR observation period. The ozone depletions during each of the Arctic winters from 2002 to 2012 were quantified using SMR data. The results indicate that the loss can be categorized into 3 types of winters based on the stability of the stratosphere, cold winters (stable, related to PSC formation), warm winters (unstable, NOx induced loss) and intermediate winters

Decadal analysis of stratospheric ozone depletion using data assimilation and Odin/SMR measurements

Serious ozone depletion has been measured every Antarctic spring since the early 80’s. This ozone depletion is considered to be a result of photo-chemical reactions and catalytic cycles resulting from anthropogenic halogen containing gases. facilitated by the formation of Polar Stratospheric Clouds (PSCs). The reactive halogen species are released through heterogeneous reactions on the surface of the particles. Currently, global ozone is recovering during past decades as a result of the Montreal Protocol (1987) on the control of ozone depleting substances (ODSs).Arctic ozone depletion is, on the other hand, less severe and show larger variability than Antarctic loss because of the unstable and warmer condition. However, the Arctic stratosphere has been becoming colder and the Arctic ozone loss in the 2011 winter was comparable to Antarctic losses. Ozone depletion is directly/indirectly linked to the climate because the absorption of UV radiation changes the temperature field. It is therefore important to quantify the loss for future climate prediction.The aim of this thesis is to quantify ozone depletions in several Arctic and Antarctic winters using ozone profiles measured by Odin/SMR and a data assimilation tech- nique which is generally used in numerical weather prediction. The DIAMOND (Dynamical Isentropic Assimilation Model for Odin Data) is used in this thesis. A new vertical transport scheme was implemented into the DIAMOND model to account for the diabatic descent inside the polar vortex during the polar night. The new version of the DIAMOND model was examined for the specific northern winter (2009/2010) when SMILES (Superconducting Submillimeter-Wave Limb-Emission Sounder) ob- served stratospheric species as well as SMR. A decadal record of ozone depletion has been determined by comparing the assimilated fields to passively transported fields initialized by assimilation of SMR ozone data. Ozone retrieved from the emission line at 544GHz has been demonstrated for use in ozone depletion studies in the thesis. Two different chemical mechanisms, the Cl catalytic cycle with PSC formation and NOx related chemistry, can explain losses at different altitudes that occurred in the polar winters. This thesis also propose an other methodology to quantify ozone depletion utilising assimilation information

Decadal analysis of stratospheric ozone depletion using data assimilation and Odin/SMR measurements

Serious ozone depletion has been measured every Antarctic spring since the early 80’s. This ozone depletion is considered to be a result of photo-chemical reactions and catalytic cycles resulting from anthropogenic halogen containing gases. facilitated by the formation of Polar Stratospheric Clouds (PSCs). The reactive halogen species are released through heterogeneous reactions on the surface of the particles. Currently, global ozone is recovering during past decades as a result of the Montreal Protocol (1987) on the control of ozone depleting substances (ODSs).Arctic ozone depletion is, on the other hand, less severe and show larger variability than Antarctic loss because of the unstable and warmer condition. However, the Arctic stratosphere has been becoming colder and the Arctic ozone loss in the 2011 winter was comparable to Antarctic losses. Ozone depletion is directly/indirectly linked to the climate because the absorption of UV radiation changes the temperature field. It is therefore important to quantify the loss for future climate prediction.The aim of this thesis is to quantify ozone depletions in several Arctic and Antarctic winters using ozone profiles measured by Odin/SMR and a data assimilation tech- nique which is generally used in numerical weather prediction. The DIAMOND (Dynamical Isentropic Assimilation Model for Odin Data) is used in this thesis. A new vertical transport scheme was implemented into the DIAMOND model to account for the diabatic descent inside the polar vortex during the polar night. The new version of the DIAMOND model was examined for the specific northern winter (2009/2010) when SMILES (Superconducting Submillimeter-Wave Limb-Emission Sounder) ob- served stratospheric species as well as SMR. A decadal record of ozone depletion has been determined by comparing the assimilated fields to passively transported fields initialized by assimilation of SMR ozone data. Ozone retrieved from the emission line at 544GHz has been demonstrated for use in ozone depletion studies in the thesis. Two different chemical mechanisms, the Cl catalytic cycle with PSC formation and NOx related chemistry, can explain losses at different altitudes that occurred in the polar winters. This thesis also propose an other methodology to quantify ozone depletion utilising assimilation information

Twelve years of Arctic ozone loss observed by the Odin satellite

In 2011, several groups reported dramatic ozone depletion over the arctic polar region approaching that of the Antarctic ozone hole. Odin, The Swedish-led satellite project in collaboration with Canada, France and Finland, was launched in February 2001 and continues to produce profiles of chemical species relevant to understanding the middle and upper atmosphere.This study concerns ozone loss over the northern pole utilizing the 12 years of ozone data from Odin/SMR.The unstable nature of the arctic vortex due to the propagation of planetary waves from troposphere makes quantifying chemical ozone loss in the arctic more difficult. The assimilation technique using a transport model is useful for separating the dynamical and chemical changes in the ozone amount as demonstrated earlier by Roseval et al (2007) . We have applied this method with a number of improvements to study the inter-annual variability during the entire Odin period

Twelve years of Arctic ozone loss observed by the Odin satellite

In 2011, several groups reported dramatic ozone depletion over the arctic polar region approaching that of the Antarctic ozone hole. Odin, The Swedish-led satellite project in collaboration with Canada, France and Finland, was launched in February 2001 and continues to produce profiles of chemical species relevant to understanding the middle and upper atmosphere.This study concerns ozone loss over the northern pole utilizing the 12 years of ozone data from Odin/SMR.The unstable nature of the arctic vortex due to the propagation of planetary waves from troposphere makes quantifying chemical ozone loss in the arctic more difficult. The assimilation technique using a transport model is useful for separating the dynamical and chemical changes in the ozone amount as demonstrated earlier by Roseval et al (2007) . We have applied this method with a number of improvements to study the inter-annual variability during the entire Odin period

Two mechanisms of stratospheric ozone loss in the Northern Hemisphere, studied using data assimilation of Odin/SMR atmospheric observations

Observations from the Odin/Sub-Millimetre Radiometer (SMR) instrument have been assimilated into the DIAMOND model (Dynamic Isentropic Assimilation Model for OdiN Data), in order to estimate the chemical ozone (O3) loss in the stratosphere. This data assimilation technique is described in Sagi and Murtagh (2016), in which it was used to study the inter-annual variability in ozone depletion during the entire Odin operational time and in both hemispheres. Our study focuses on the Arctic region, where two O3 destruction mechanisms play an important role, involving halogen and nitrogen chemical families (i.e. NOx  =  NO and NO2), respectively. The temporal evolution and geographical distribution of O3 loss in the low and middle stratosphere have been investigated between 2002 and 2013. For the first time, this has been done based on the study of a series of winter–spring seasons over more than a decade, spanning very different dynamical conditions. The chemical mechanisms involved in O3 depletion are very sensitive to thermal conditions and dynamical activity, which are extremely variable in the Arctic stratosphere. We have focused our analysis on particularly cold and warm winters, in order to study the influence this has on ozone loss. The winter 2010/11 is considered as an example for cold conditions. This case, which has been the subject of many studies, was characterised by a very stable vortex associated with particularly low temperatures, which led to an important halogen-induced O3 loss occurring inside the vortex in the lower stratosphere. We found a loss of 2.1 ppmv at an altitude of 450 K in the end of March 2011, which corresponds to the largest ozone depletion in the Northern Hemisphere observed during the last decade. This result is consistent with other studies. A similar situation was observed during the winters 2004/05 and 2007/08, although the amplitude of the O3 destruction was lower. To study the opposite situation, corresponding to a warm and unstable winter in the stratosphere, we performed a composite calculation of four selected cases, 2003/04, 2005/06, 2008/09 and 2012/13, which were all affected by a major mid-winter sudden stratospheric warming event, related to particularly high dynamical activity. We have shown that such conditions were associated with low O3 loss below 500 K (approximately 20 km), while O3 depletion in the middle stratosphere, where the role of NOx-induced destruction processes prevails, was particularly important. This can mainly be explained by the horizontal mixing of NOx-rich air from lower latitudes with vortex air that takes place in case of strongly disturbed dynamical situation. In this manuscript, we show that the relative contribution of O3 depletion mechanisms occurring in the lower or in the middle stratosphere is significantly influenced by dynamical and thermal conditions. We provide confirmation that the O3 loss driven by nitrogen oxides and triggered by stratospheric warmings can outweigh the effects of halogens in the case of a dynamically unstable Arctic winter. This is the first time that such a study has been performed over a long period of time, covering more than 10 years of observations