Stratosphere-troposphere exchange processes are responsible for controlling the distribution of chemically and radiatively important trace gases in the upper troposphere and lower stratosphere. Extensive characterization of exchange processes is critical to the development of our understanding and prediction of the climate system. This study examines the occurrence and dynamical and chemical characteristics related to two primary stratosphere-troposphere exchange processes: Rossby wavebreaking and moist convection. Intrusions of air from the tropical upper troposphere into the extratropical stratosphere above the subtropical jet via Rossby wavebreaking potentially have a significant impact on the composition of the lowermost stratosphere (the stratospheric part of the "middleworld"). We first present an analysis of tropospheric intrusion events observed in aircraft observations using kinematic and chemical diagnostics. The transport processes operating during each event are discussed using high-resolution model analyses and backward trajectory calculations. In situ chemical observations of the tropospheric intrusions are used to estimate the mixing timescales of the observed intrusions through use of a simple box model and trace species with different photo-chemical lifetimes. We estimate that the timescale for an intrusion to mix with the background stratospheric air is 5 to 6 days. Detailed analysis of small-scale features with tropospheric characteristics observed in the stratosphere suggests frequent irreversible transport associated with tropospheric intrusions. We also present a 30-year climatology (1981-2010) of anticyclonically and cyclonically sheared Rossby wave-breaking events along the boundary of the tropics in the 350-500 K potential temperature range from ECMWF ERA-Interim reanalyses. Lagrangian transport analyses show poleward transport at altitudes below and above the 370-390 K layer. Poleward transport at lower levels is in disagreement with previous studies and is shown to be largely dependent on the choice of tropical boundary. In addition, transport analyses reveal three modes of transport for anticyclonic wavebreaking events near the tropical tropopause (380 K): poleward, equatorward, and bidirectional. These transport modes are associated with distinct characteristics in the geometry of the mean flow. Stratospheric intrusions (tropopause folds) are known to be major contributors to stratosphere-troposphere exchange. The specific mixing processes that lead to irreversible exchange between stratospheric intrusions and the surrounding troposphere, however, are not entirely understood. This study presents direct observations of moist convection penetrating into stratospheric intrusions. The characteristics of convective injection are shown by using in situ aircraft measurements, radar reflectivities, and model analyses. Convective injection is observed at altitudes up to 5 km above the bottom of a stratospheric intrusion. Aircraft measurements show that convective injection in stratospheric intrusions can be uniquely identified by coincident observations of water vapor greater than about 100 ppmv and ozone greater than about 125 ppbv. Trajectory analyses show that convective injection can impact transport in both directions: from troposphere to stratosphere and from stratosphere to troposphere. We present a conceptual model of the synoptic meteorological conditions conducive to convective injection in stratospheric intrusions. In particular, convective injection is found to be associated with a "split front" where the upper-level frontal boundary outruns the surface cold front.

Stratosphere Troposphere exchange (STE) is important to study as it controls the chemical composition of the upper troposphere/lower stratosphere (UTLS) and thus the radiative balance of this region. STE also controls the transport of chemicals into the stratosphere which are vital to ozone depletion. The troposphere and the stratosphere have specific chemical characteristics and the transition region between these regions displays characteristics of both. Ozone and water vapour concentrations can be used as tracers for the characteristics of the troposphere and stratosphere. This thesis develops measures in tracer space, which allow the determination of the strength and depth of atmospheric mixing between the troposphere and the stratosphere in extratropical regions. The application of entropy as a measure of atmospheric mixing as introduced by Patmore and Toumi [2006], is improved in this study. This is a measure of how the ozone and water vapour mixing ratios vary as a result of mixing. An additional metric to give further information on the form of the mixing line in tracer space is also developed. This measure uses the ozone and water vapour mixing ratios at the boundaries of the transition region (BO3 and BH2O). This study uses data from ozonesondes and hygrometers, along with satellite data from the Atmospheric Infrared Sounder (AIRS). The ozone product from AIRS is also validated as part of this study. The entropy, BO3 and BH2O measures from this study, are successfully shown to detect regions of enhanced mixing in comparison studies. A key comparison shows that the measures developed in this study are able to produce comparable conclusions to higher resolution aircraft data, with regards to mixing. The separation of entropy, BO3 and BH2O, into different categories allows mixing processes to be assigned to some of the categories. Mixing is shown to have geographic preference, with some regions having significantly more mixing. Some categories have preference with regards to their location either poleward or equatorward of the jet stream. In addition, some information as to the direction of the vertical transport, whether stratosphere to troposphere or vice versa, is obtained.

Stratosphere Troposphere exchange (STE) is important to study as it controls the chemical composition of the upper troposphere/lower stratosphere (UTLS) and thus the radiative balance of this region. STE also controls the transport of chemicals into the stratosphere which are vital to ozone depletion. The troposphere and the stratosphere have specific chemical characteristics and the transition region between these regions displays characteristics of both. Ozone and water vapour concentrations can be used as tracers for the characteristics of the troposphere and stratosphere. This thesis develops measures in tracer space, which allow the determination of the strength and depth of atmospheric mixing between the troposphere and the stratosphere in extratropical regions. The application of entropy as a measure of atmospheric mixing as introduced by Patmore and Toumi [2006], is improved in this study. This is a measure of how the ozone and water vapour mixing ratios vary as a result of mixing. An additional metric to give further information on the form of the mixing line in tracer space is also developed. This measure uses the ozone and water vapour mixing ratios at the boundaries of the transition region (BO3 and BH2O). This study uses data from ozonesondes and hygrometers, along with satellite data from the Atmospheric Infrared Sounder (AIRS). The ozone product from AIRS is also validated as part of this study. The entropy, BO3 and BH2O measures from this study, are successfully shown to detect regions of enhanced mixing in comparison studies. A key comparison shows that the measures developed in this study are able to produce comparable conclusions to higher resolution aircraft data, with regards to mixing. The separation of entropy, BO3 and BH2O, into different categories allows mixing processes to be assigned to some of the categories. Mixing is shown to have geographic preference, with some regions having significantly more mixing. Some categories have preference with regards to their location either poleward or equatorward of the jet stream. In addition, some information as to the direction of the vertical transport, whether stratosphere to troposphere or vice versa, is obtained.

A lack of quality data on high clouds has led to inadequate representations within global weather and climate models. Recent advances in spaceborne measurements of the Earth’s atmosphere have provided complementary information on the interior of these clouds. This study demonstrate how an array of space-borne measurements can be used and combined, by close co-located comparisons in space and time, to form a more complete representation of high cloud processes and properties. High clouds are found in the upper atmosphere, where sub-zero temperatures frequently result in the formation of cloud particles that are composed of ice. Weather and climate models characterise the bulk properties of these ice particles to describe the current state of the cloud-sky atmosphere. By directly comparing measurements with simulations undertaken at the same place and time, this study demonstrates how improvements can be made to the representation of cloud properties. The results from this study will assist in the design of future cloud missions to provide a better quality input. These improvements will also help improve weather predictions and lower the uncertainty in cloud feedback response to increasing atmospheric temperature. Most clouds are difficult to monitor by more than one instrument due to continuous changes in: large-scale and sub-cloud scale circulation features, microphysical properties and processes and characteristic chemical signatures. This study undertakes co-located comparisons of high cloud data with a cloud ice dataset reported from the Microwave Limb Sounder (MLS) instrument onboard the Aura satellite that forms part of the A-train constellation. Data from the MLS science team include vertical profiles of temperature, ice water content (IWC) and the mixing ratios of several trace gases. Their vertical resolutions are 3 to 6 km. Initial investigations explore the link between cloud-top properties and the longwave radiation budget, developing methods for estimating cloud top heights using; longwave radiative fluxes, and IWC profiles. Synergistic trios of direct and indirect high cloud measurements were used to validate detections from the MLS by direct comparisons with two different A-train instruments; the NASA Moderate-resolution Imaging Spectroradiometer (MODIS) and the Clouds and the Earth’s Radiant Energy System (CERES) onboard on the Aqua satellite. This finding focuses later studies on two high cloud scene types that are well detected by the MLS; deep convective plumes that form from moist ascent, and their adjacent outflows that emanate outwards several hundred kilometres. The second part of the thesis identifies and characterises two different high cloud scenes in the tropics. Direct observational data is used to refine calculations of the climate sensitivity to upper tropospheric humidity and high cloud in different conditions. The data reveals several discernible features of convective outflows are identified using a large sample of MLS data. The key finding, facilitated by the use of co-location, reveals that deep convective plumes exert a large longwave warming effect on the local climate of 52 ± 28Wm−2, with their adjacent outflows presenting a more modest warming of 33 ± 20Wm−2.

Dans le contexte du réchauffement et du changement climatique, il est important d’étudier les distributions, les cycles saisonniers et les tendances des gaz à l’état de trace dans l’atmosphère tels que la vapeur d’eau. L'Observatoire de Physique du Globe de Clermont-Ferrand a en charge plusieurs dispositifs d’observation dont le site instrumenté Cézeaux, Opme et Puy de Dôme (CO-PDD) situés dans le centre de la France (45◦ N, 3◦ E). Le site des Cézeaux dispose d’un LIDAR Rayleigh – Mie - Raman fournissant en routine des profils verticaux de vapeur d’eau et de paramètres optiques caractérisant les cirrus. Le site du puy de Dôme est équipé d’un spectroscope à cavité optique (CRDS-Picarro). Des mesures de colonnes totales de vapeur d’eau sont disponibles sur tous ces sites par GPS. Le site d’Opme est équipé d’un pluviomètre. Enfin Météo-France effectue le travail de contrôle qualité des données météorologiques sur les stations de mesure en France et ces données ont été utilisées dans cette thèse. La validation des données sur le site du puy de Dôme a été la première la première exploitation dans cette thèse. Des comparaisons des données sur le puy de Dôme ont montré un très bon accord entre les données de vapeur d’eau extraites de la station météorologique du puy de Dôme, de Météo France et les donnes CRDS du puy de Dôme, avec une corrélation de 0.94 et 0.98 respectivement. Les profils verticaux obtenus par LIDAR ont permis de sélectionner une anomalie de vapeur d’eau et d’identifier une intrusion stratosphère-troposphère en analysant les processus dynamique associés à cette anomalie. Les données OLR ont montré que cette intrusion est accompagnée de convection profonde et enfin LACYTRAJ confirme l'origine stratosphérique d’une partie de la masse d'air présente au-dessus de Clermont-Ferrand au cours de l’anomalie. Les longues séries d’observations (ex : Puy de Dôme 1995-2015) et des ré-analyse ECMWF ERA-Interim (1979-2017) et la diversité des sources de données (ex : satellites AIRS et COSMIC), nous permettent de documenter, analyser et comparer la variabilité, les cycles et la tendance de la vapeur d'eau à la surface et dans la troposphère, à différentes échelles de temps et déterminer les processus géophysiques responsables des distributions de vapeur d'eau sur le site CO-PDD. Le cycle annuel de la vapeur d'eau est clairement établi pour les deux sites de différentes altitudes et pour tous les types de mesure. Les sites de Cézeaux et du puy de Dôme ne présentent presque aucun cycle diurne, suggérant que la variabilité de la vapeur d'eau à la surface sur ces deux sites est plus influencée par les systèmes météorologique sporadiques que par les variations diurnes régulières. Les données LIDAR montrent une plus grande variabilité mensuelle de la distribution verticale que les produits satellites COSMIC et AIRS. La colonne totale de vapeur d'eau GPS sur le site des Cézeaux présente une tendance positive (0,42 ± 0,45 g/kg*décade entre 2006-2017). L'analyse par régressions multi-linéaires montre que les forçages continentaux (East Atlantic, East Atlantic-West Russia) ont une plus grande influence que le forçage océanique (Nord Atlantic Oscillation) sur les variations de vapeur d'eau. / In the context of global warming and climate change, it is important to study the distributions, seasonal cycles and trends of trace gases in the atmosphere such as water vapor. of the Observatoire de Physique du Globe de Clermont-Ferrand is in charge of several observation devices including the instrumented site Cézeaux, Opme and Puy de Dôme (CO-PDD) located near the center of France (45◦ N, 3◦ E). The site of Cézeaux is instrumented by a Rayleigh - Mie–LIDAR Raman providing routine vertical profiles of water vapor mixing ratio and optical parameters characterizing cirrus clouds. The puy de Dôme site is equipped with an optical cavity spectroscope (CRDS-Picarro). Measurements of total water vapor columns are available on all these sites by GPS. The Opme site is equipped with rain gauges. Finally, Météo-France performs the quality control work and of data on meteorological stations in France and these data were used in this thesis. The validation of the puy de Dôme data was the first the first task in this thesis. Comparisons between the puy de Dôme data sets showed a very good agreement between the water vapor datafrom the OPGC meteorological station of Puy de Dôme, Météo France and CRDS data with a correlation of 0.94 and 0.98 respectively. The vertical profiles deduced from the LIDAR allowed to identify a water vapor anomaly and a stratosphere-troposphere intrusion associated with this anomaly. OLR data showed that this intrusion could be linked with deep convection and LACYTRAJ confirms the stratospheric origin of a part of the air mass present above Clermont-Ferrand. Long series of observations (eg Puy de Dôme 1995-2015) and ECMWF ERA-Interim re-analysis (1979-2017) and the diversity of data sources (eg AIRS and COSMIC satellites), allowed us to document, analyze and compare the variability, cycles and trend of surface and tropospheric water vapor at different time scales and determine the geophysical processes responsible for water vapor distributions at the site of CO-PDD. The annual cycle of water vapor is clearly established for the two sites of different altitudes and for all types of measurement. Cézeaux and puy de Dôme present almost no diurnal cycle, suggesting that the variability of surface water vapor at this site is more influenced by a sporadic meteorological system than by regular diurnal variations. The LIDAR dataset shows a greater monthly variability of the vertical distribution than the COSMIC and AIRS satellite products. The Cézeaux site presents a positive trend for the GPS water vapor total column (0.42 ± 0.45 g/kg*decade during 2006–2017) and a significant negative trend for the surface water vapor mixing ratio (−0.16 ± 0.09 mm/decade during 2002–2017). The multi-linear regression analysis shows that continental forcings (East Atlantic Pattern and East Atlantic-West Russia Pattern) have a larger influence than oceanic forcing (North Atlantic Oscillation) on the water vapor variations.

Fundação de Amparo a Pesquisa no Estado do Rio Grande do Sul / It was identified Stratosphere-Troposphere Exchange (STE) events on Southern South America and their effects in the Ozone Total Column (OTC) above Central Region of Rio Grande do Sul (CRRS), Brazil, in the period between 2005 and 2014. To this end, it was developed a methodology able to verify the tropopause height and the descend mass flux in this region, using reanalysis 2 data provided by NCEP/DOE. Furthermore, these cases must have wind cores above 40m/s (Upper-level Jet Stream - ULJS) acting between 30 and 80°W and 20 and 50°S. The arrival confirmation of air parcels from the STE at the CRRS was made through HYSPLIT trajectory analysis model from NOAA. For cases that acted at the CRRS, it was computed the OTC variation in relation to five days prior to the STE effects, through daily OTC data obtained from the OMI instrument for Santa Maria city (29.72°S; 53.72°W). This methodology proved to be effective in identifying 755 STE events on Southern South America, from which 103 came to act on CRRS, with 65% of cases increasing and 35% reducing the OTC in this region. Seasonal analysis showed that most cases happens in winter, followed by spring and in less quantity in summer and fall. Averaged fields of the vertical wind profile, mass flux, temperature and potential vorticity, showed that STE events occur more often in post-frontal situations at the Bacia do Prata region. Moreover, it was analyzed the convergence role in relation to jet streak s vertical transversal circulations, demonstrating that, in STE cases, these circulations increase even more the stratospheric air intake into the troposphere by strong convergence in the ULJS level. In short, it was verified that STE events on Southern South America act as a stratospheric ozone-rich air source to the CRRS, having as an allied the ULJS, which increase the phenomena. / Foram identificados eventos de Troca Estratosfera-Troposfera (TET) sobre o Sul da América do Sul e seus efeitos na variação da Coluna Total de Ozônio (CTO) Região Central do Rio Grande do Sul (RCRS), Brasil, no período entre 2005 e 2014. Para este fim, desenvolveu-se uma metodologia capaz de verificar a altura da tropopausa e o fluxo de massa descendente nesta região, utilizando dados de reanálise 2 fornecidos pelo NCEP/DOE. Além disso, os casos deveriam possuir núcleos de vento acima de 40 m/s (Corrente de Jato em Altos Níveis - CJAN) atuando entre 30 e 80°O e 20 e 50°S. A confirmação da chegada das parcelas de ar provenientes da TET na RCRS deu-se através da análise das trajetórias do modelo Hysplit da NOAA. Para os casos que atuaram na RCRS, calculou-se a variação da CTO em relação aos cinco dias anteriores aos efeitos da TET, através de dados diários da CTO obtidos do instrumento OMI para a cidade de Santa Maria (29.72°S; 53.72°O). Esta metodologia mostrou-se eficaz na identificação de 755 eventos de TET sobre o Sul da América do Sul, dos quais 103 vieram a atuar na RCRS, com 65% dos casos aumentando e com 35% reduzindo a CTO nesta região. A análise sazonal mostrou que a maioria dos casos acontece no inverno, seguido da primavera e em menor quantidade no verão e outono. Campos médios do perfil vertical de vento, fluxo de massa, temperatura e vorticidade potencial, mostraram que os eventos de TET ocorrem com mais frequência em uma situação pós-frontal na região da Bacia do Prata. Além disso, analisou-se o papel da convergência relacionada às circulações verticais transversais do núcleo da CJAN, mostrando que, em casos de TET, estas circulações intensificam ainda mais a entrada de ar estratosférico para dentro da troposfera por intermédio da forte convergência no nível da CJAN. Em suma, verificou-se que os eventos de TET sobre o Sul da América do Sul atuam como uma fonte de ar estratosférico rico em Ozônio para a RCRS, tendo como um de seus aliados a CJAN, a qual intensifica o fenômeno.