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A main source of regional climate change uncertainty is the large disparity across models in simulating the atmospheric circulation response to global warming. Using the latest suite of global climate models from the sixth phase of the Coupled Model Intercomparison Project (CMIP6), a storyline approach is adopted to derive physically plausible scenarios of Antarctic climate change for 2070–99, according to Shared Socioeconomic Pathway SSP5-8.5. These storylines correspond to differences in the simulated amount of seasonal sea ice loss and either (i) the delay in the summertime stratospheric polar vortex (SPV) breakdown or (ii) wintertime SPV strengthening, which together constitute robust drivers of the response pattern to future climate change. Such changes combined are known to exert a strong control over the Southern Hemisphere midlatitude jet stream, which we quantify as collectively explaining up to 70% of the variance in jet response in summer and 35% in winter. For summer, the expected strengthening and displacement of the tropospheric jet stream varies between a;1 and 2 m s21 increase and;28–48 poleward shift, respectively, across storylines. In both seasons, a larger strengthening of the jet is correlated with less Antarctic warming. By contrast, the response in precipitation is more consistent but still strongly attenuated by large-scale dynamics. We find that an increase in high-latitude precipitation around Antarctica is more pronounced for storylines characterized by a greater poleward jet shift, particularly in summer. Our results highlight the usefulness of the storyline approach in illustrating model uncertainty and understanding the processes that determine the spread in projected Antarctic regional climate response. SIGNIFICANCE STATEMENT: Uncertainty in future climate predictions for the Antarctic is dominated by the unknown response of the large-scale (global) atmospheric circulation. In characterizing such uncertainty, plausible ou

In this study we provide a systematic characterization of Rossby wave activity during the 25 sudden stratospheric warming (SSW) and 31 strong polar vortex (SPV) events that occurred in the period 1979–2021, identifying the specific tropospheric and stratospheric waves displaying anomalous behaviour during such events. Space–time spectral analysis is applied to ERA5 data for this purpose, so that both the wavenumber and the zonal phase speed of the waves can be assessed. We find that SSW events are associated with a reduction in the phase speed of Rossby waves, first in the stratosphere and then in the troposphere; SPV events are tied to a simultaneous increase of phase speed across vertical levels. Phase speed anomalies become significant around the event and persist for 2–3 weeks afterwards. Changes of Rossby wave properties in the stratosphere during SSW and SPV events are dominated by changes in the background flow, with a systematic reduction or increase, respectively, in eastward propagation of the waves across most wavenumbers. In the troposphere, on the other hand, the effect of the background flow is also complemented by changes in wave properties, with a shift towards higher wavenumbers during SSW events and towards lower wavenumbers for SPV events. The opposite response between SSW and SPV events is also visible in the meridional heat and momentum flux co-spectra, which highlight from a novel perspective the connection between stratospheric Rossby waves and upward propagation of waves.

In this study we provide a systematic characterization of Rossby wave activity during the 25 sudden stratospheric warming (SSW) and 31 strong polar vortex (SPV) events that occurred in the period 1979–2021, identifying the specific tropospheric and stratospheric waves displaying anomalous behaviour during such events. Space–time spectral analysis is applied to ERA5 data for this purpose, so that both the wavenumber and the zonal phase speed of the waves can be assessed. We find that SSW events are associated with a reduction in the phase speed of Rossby waves, first in the stratosphere and then in the troposphere; SPV events are tied to a simultaneous increase of phase speed across vertical levels. Phase speed anomalies become significant around the event and persist for 2–3 weeks afterwards. Changes of Rossby wave properties in the stratosphere during SSW and SPV events are dominated by changes in the background flow, with a systematic reduction or increase, respectively, in eastward propagation of the waves across most wavenumbers. In the troposphere, on the other hand, the effect of the background flow is also complemented by changes in wave properties, with a shift towards higher wavenumbers during SSW events and towards lower wavenumbers for SPV events. The opposite response between SSW and SPV events is also visible in the meridional heat and momentum flux co-spectra, which highlight from a novel perspective the connection between stratospheric Rossby waves and upward propagation of waves.

In this study we provide a systematic characterization of Rossby wave activity during the 25 sudden stratospheric warming (SSW) and 31 strong polar vortex (SPV) events that occurred in the period 1979–2021, identifying the specific tropospheric and stratospheric waves displaying anomalous behaviour during such events. Space–time spectral analysis is applied to ERA5 data for this purpose, so that both the wavenumber and the zonal phase speed of the waves can be assessed. We find that SSW events are associated with a reduction in the phase speed of Rossby waves, first in the stratosphere and then in the troposphere; SPV events are tied to a simultaneous increase of phase speed across vertical levels. Phase speed anomalies become significant around the event and persist for 2–3 weeks afterwards. Changes of Rossby wave properties in the stratosphere during SSW and SPV events are dominated by changes in the background flow, with a systematic reduction or increase, respectively, in eastward propagation of the waves across most wavenumbers. In the troposphere, on the other hand, the effect of the background flow is also complemented by changes in wave properties, with a shift towards higher wavenumbers during SSW events and towards lower wavenumbers for SPV events. The opposite response between SSW and SPV events is also visible in the meridional heat and momentum flux co-spectra, which highlight from a novel perspective the connection between stratospheric Rossby waves and upward propagation of waves.

In this study we provide a systematic characterization of Rossby wave activity during the 25 sudden stratospheric warming (SSW) and 31 strong polar vortex (SPV) events that occurred in the period 1979–2021, identifying the specific tropospheric and stratospheric waves displaying anomalous behaviour during such events. Space–time spectral analysis is applied to ERA5 data for this purpose, so that both the wavenumber and the zonal phase speed of the waves can be assessed. We find that SSW events are associated with a reduction in the phase speed of Rossby waves, first in the stratosphere and then in the troposphere; SPV events are tied to a simultaneous increase of phase speed across vertical levels. Phase speed anomalies become significant around the event and persist for 2–3 weeks afterwards. Changes of Rossby wave properties in the stratosphere during SSW and SPV events are dominated by changes in the background flow, with a systematic reduction or increase, respectively, in eastward propagation of the waves across most wavenumbers. In the troposphere, on the other hand, the effect of the background flow is also complemented by changes in wave properties, with a shift towards higher wavenumbers during SSW events and towards lower wavenumbers for SPV events. The opposite response between SSW and SPV events is also visible in the meridional heat and momentum flux co-spectra, which highlight from a novel perspective the connection between stratospheric Rossby waves and upward propagation of waves.

At speeds roughly between five and ten thousand km/h, hypersonic aircraft offer the promise of an extremely fast means of transport. Growing concerns about climate warming, however, direct attention to sustainability. This thesis focuses on atmospheric composition and radiation changes by considering a range of individual hypersonic aircraft designs on trajectory and route network level. State-of-the-art Earth system models are used for simulations, and results calculated with the EMAC model are subsequently compared with simulations performed elsewhere with the LMDZ-INCA model. The comparison to a third model, i.e. WACCM, with a very similar – but independent – model setup allows even further clarification. For model validation satellite measurements (ozone, water vapor) and aircraft measurements (ozone, water vapor, temperature) are taken into account. After the introduction in the first chapter, the second chapter is a general description of the Earth system including anthropogenic perturbations, in particular perturbations from subsonic, supersonic and hypersonic aircraft emissions followed by a detailed explanation of methods and the EMAC model setup in the third chapter. A new research finding in the context of middle atmospheric chemistry is the increased methane and nitric acid oxidation following hypersonic emissions. This effect results in a (photo-)chemical net production of water vapor and eventually increases water vapor perturbations further, which is described in detail in chapter 4. In chapter 5 an analysis of atmospheric dynamics and transport of emitted trace gases in the middle atmosphere underlines the importance of the Brewer-Dobson circulation and shows the impact of polar stratospheric clouds on water vapor perturbations during polar winter. The evaluation of multiple hypersonic aircraft designed for different cruise altitudes shows that their climate impact increases with cruise altitude and can be approximately 10-20 time, Aircraft Noise and Climate Effects

In this study we provide a systematic characterization of Rossby wave activity during the 25 sudden stratospheric warming (SSW) and 31 strong polar vortex (SPV) events that occurred in the period 1979–2021, identifying the specific tropospheric and stratospheric waves displaying anomalous behaviour during such events. Space–time spectral analysis is applied to ERA5 data for this purpose, so that both the wavenumber and the zonal phase speed of the waves can be assessed. We find that SSW events are associated with a reduction in the phase speed of Rossby waves, first in the stratosphere and then in the troposphere; SPV events are tied to a simultaneous increase of phase speed across vertical levels. Phase speed anomalies become significant around the event and persist for 2–3 weeks afterwards. Changes of Rossby wave properties in the stratosphere during SSW and SPV events are dominated by changes in the background flow, with a systematic reduction or increase, respectively, in eastward propagation of the waves across most wavenumbers. In the troposphere, on the other hand, the effect of the background flow is also complemented by changes in wave properties, with a shift towards higher wavenumbers during SSW events and towards lower wavenumbers for SPV events. The opposite response between SSW and SPV events is also visible in the meridional heat and momentum flux co-spectra, which highlight from a novel perspective the connection between stratospheric Rossby waves and upward propagation of waves.

The stratosphere can have a significant impact on winter surface weather on subseasonal to seasonal (S2S) timescales. This study evaluates the ability of current operational S2S prediction systems to capture two important links between the stratosphere and troposphere: (1) changes in probabilistic prediction skill in the extratropical stratosphere by precursors in the tropics and the extratropical troposphere and (2) changes in surface predictability in the extratropics after stratospheric weak and strong vortex events. Probabilistic skill exists for stratospheric events when including extratropical tropospheric precursors over the North Pacific and Eurasia, though only a limited set of models captures the Eurasian precursors. Tropical teleconnections such as the Madden‐Julian Oscillation, the Quasi‐Biennial Oscillation, and El Niño–Southern Oscillation increase the probabilistic skill of the polar vortex strength, though these are only captured by a limited set of models. At the surface, predictability is increased over the United States, Russia, and the Middle East for weak vortex events, but not for Europe, and the change in predictability is smaller for strong vortex events for all prediction systems. Prediction systems with poorly resolved stratospheric processes represent this skill to a lesser degree. Altogether, the analyses indicate that correctly simulating stratospheric variability and stratosphere‐troposphere dynamical coupling are critical elements for skillful S2S wintertime predictions., Academy of Finland (Suomen Akatemia), European Council, JSPS, National Research Foundation of Korea, National Science Foundation (NSF), Swiss National Science Foundation, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

The Hunga Tonga–Hunga Ha'apai volcano eruption was a unique event that caused many atmospheric phenomena around the globe. In this study, we investigate the atmospheric gravity waves in the mesosphere/lower thermosphere (MLT) launched by the volcanic explosion in the Pacific, leveraging multistatic meteor radar observations from the Chilean Observation Network De Meteor Radars (CONDOR) and the Nordic Meteor Radar Cluster in Fennoscandia. MLT winds are computed using a recently developed 3DVAR+DIV algorithm. We found eastward- and westward-traveling gravity waves in the CONDOR zonal and meridional wind measurements, which arrived 12 and 48 h after the eruption, and we found one in the Nordic Meteor Radar Cluster that arrived 27.5 h after the volcanic detonation. We obtained observed phase speeds for the eastward great circle path at both locations of about 250ms^-1, and they were 170–150ms^-1 for the opposite propagation direction. The intrinsic phase speed was estimated to be 200–212ms^-1. Furthermore, we identified a potential lamb wave signature in the MLT winds using 5 min resolved 3DVAR+DIV retrievals.

In this study, the excitation and propagation of non-orographic gravity waves (NOGWs) above tropopause depressions usually associated with propagating Rossby waves is investigated. Observations and analysis of NOGWs in the upper strato- sphere during research flight 25 of the 2014 DEEPWAVE campaign show hydrostatic wave patterns above a tropopause depression comparable to waves excited by orography at the surface. These gravity waves (GWs) stay above the depression as the depression travels east with the phase speed of the Rossby wave. In austral winter, the polar night jet (PNJ) develops in the Southern Hemisphere, leading to a much faster zonal stratospheric flow than the Rossby wave’s phase speed. Therefore, the source of these GWs could simply be the vertical displacement of the airflow above the tropopause mimicking an obstacle to the flow above. The goal was to evaluate this potential NOGW source through idealized numerical simulations with the geophysical flow solver EULAG. Typical shapes of tropopause depressions and typical stratospheric winter conditions suggest the excitation of low-frequency or inertia-gravity waves (IGWs). To account for their oscillation in the vertical and horizontal plane, all simulations were conducted in 3D. Preliminary studies were performed to assess the reliability of the model by comparing its numerical solutions to analytical solutions of different mountain wave regimes. In particular, comparisons of the gravity wave drag and surface momentum fluxes were instructive and guided the setup of the following simulations. Within the framework of this thesis, the simulations are constrained to the stratosphere, with the tropopause represented as a transient, impermeable, and frictionless lower boundary. Multiple simulations with different idealized tropopause shapes and different idealized background conditions were carried out to characterise the sensitivity of the waves’ momentum and energy fluxes and to identify scenarios which re, by Michael Binder, Masterarbeit University of Innsbruck 2023

© 2016 American Meteorological Society. TL would like to thank Han-Li Liu and Chengyun Yang for helpful discussion. TL and XD are supported by the National Natural Science Foundation of China Grants 41225017 and 41421063 and the National Basic Research Program of China Grant 2012CB825605. TL's visit to ERAU is partially supported by the NSF Grants AGS-1115249 and AGS-1110199. NC acknowledges partial support from the Spanish Ministry of Economy and Competitiveness through the PALEOSTRAT project (Paleomodelización desde una perspectiva estratoférica; Ref. CGL2015-69699-R) and the European Project 603557-STRATOCLIM under program FP7-ENV.2013.6.1-2. JY is supported by the NASA AIM and TIMED satellite missions. JMR is supported under NASA SABER Grant NNX15AD22G. MGM is supported by the NASA TIMED satellite project. AZL is supported by National Science Foundation Grants AGS-1115249 and AGS-1110199. The WACCM 3.5 results were obtained from the Atmospheric Chemistry Division at the National Center for Atmospheric Research. The radiosonde dataset is downloaded from http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/qbo/index.html. We want to thank Bodil Karlsson and two other anonymous reviewers for their constructive comments on this paper., In the Southern Hemisphere (SH) polar region, satellite observations reveal a significant upper-mesosphere cooling and a lower-thermosphere warming during warm ENSO events in December. An opposite pattern is observed in the tropical mesopause region. The observed upper-mesosphere cooling agrees with a climate model simulation. Analysis of the simulation suggests that enhanced planetary wave (PW) dissipation in the Northern Hemisphere (NH) high-latitude stratosphere during El Nino strengthens the Brewer-Dobson circulation and cools the equatorial stratosphere. This increases the magnitude of the SH stratosphere meridional temperature gradient and thus causes the anomalous stratospheric easterly zonal wind and early breakdown of the SH stratospheric polar vortex. The resulting perturbation to gravity wave (GW) filtering causes anomalous SH mesospheric eastward GW forcing and polar upwelling and cooling. In addition, constructive inference of ENSO and quasi-biennial oscillation (QBO) could lead to stronger stratospheric easterly zonal wind anomalies at the SH high latitudes in November and December and early breakdown of the SH stratospheric polar vortex during warm ENSO events in the easterly QBO phase (defined by the equatorial zonal wind at similar to 25 hPa). This would in turn cause much more SH mesospheric eastward GW forcing and much colder polar temperatures, and hence it would induce an early onset time of SH summer polar mesospheric clouds (PMCs). The opposite mechanism occurs during cold ENSO events in the westerly QBO phase. This implies that ENSO together with QBO could significantly modulate the breakdown time of SH stratospheric polar vortex and the onset time of SH PMC., Unión Europea. FP7, National Aeronautics and Space Administration (NASA), National Natural Science Foundation of China (NSFC), National Basic Research Program of China, National Science Foundation (NSF), Stratospheric and upper tropospheric processes for better climate predictions (STRATOCLIM), UE, Ministerio de Economía y Competitividad (MINECO), España, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2009 by the American Geophysical Union. N. Calvo was supported by the visitor program of the Max Planck Institute for Meteorology in Hamburg, the Spanish Ministry of Education and Science, and the Fulbright Commission in Spain. The simulations described here were carried out on the NEC-SX6 computer at the German Climate Computing Center (DKRZ). We thank Rolando R. García and Daniel Marsh for their helpful comments and suggestions., The influence of the quasi-biennial oscillation (QBO) on the Northern Hemisphere (NH) polar vortex response to warm El Nino-Southern Oscillation (ENSO) events and the impact of the warm ENSO events on the QBO signal in the NH polar stratosphere have been analyzed using the Middle Atmosphere ECHAM5 model. The experiment setup was designed to include simulations of extended NH winter seasons for either strong easterly or strong westerly phases of the tropical QBO, forced with either sea surface temperatures (SSTs) from the strong ENSO event that occurred in 1997/1998 or with climatological SSTs. It has been found that the weakening and warming of the polar vortex associated with a warm ENSO are intensified at the end of the winter during both QBO phases. In addition, the westerly QBO phase delays the onset of the warm ENSO signal, while the easterly QBO phase advances it. Warm ENSO events also impact the extratropical signal of the QBO by intensifying ( weakening) the QBO effects in early ( late) winter. Therefore, it appears that during warm ENSO events the duration of QBO signal in the northern extratropics is shortened while its downward propagation accelerated. Our dynamical analysis has revealed that these results are due to changes in the background flow caused by the QBO combined with changes in the anomalous propagation and dissipation of extratropical waves generated by warm ENSO. In both cases, a nonlinear behavior in the response of the polar vortex is observed when both warm ENSO and the easterly phase of the QBO operate together. These results suggest that the Arctic polar vortex response to combined forcing factors, in our case warm ENSO and the QBO phenomena, is expected to be nonlinear also for other coexistent forcing factors able to affect the variability of the vortex in the stratosphere., Max Planck Institute for Meteorology (Hamburgo), Ministerio de Educación y Cultura (MEC), España, Programa Fulbright Comisión de España, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2009 Royal Meteorological Society. This work is supported jointly by the National Natural Science Foundation of China (Grant 40775035) and City University of Hong Kong (Grants 7002136 and 9610021)., Blocking variability over the Ural Mountain region in the boreal winter and its relationship with the East Asian winter climate is investigated. The climate shift around mid 1970s has been shown to exert a significant influence on the blocking pattern. In contrast with the years before 1976/1977, the Ural blocking signal after 1976/1977 is found to propagate less into the stratosphere and more eastward in the troposphere to East Asia, which therefore exerts more influence on the East Asian winter climate. This enhanced Ural blocking-East Asian climate relationship amplifies the impact of Ural blocking on East Asia and, with the background of decreasing Ural blocking, contributes to the higher frequency of warm winters in this region. Further analyses suggest that the NAM-related stratospheric polar vortex strength and its modulation on the propagation of atmospheric stationary waves can account for this change, with the key area being located in the North Atlantic region., National Natural Science Foundation of China, City University of Hong Kong, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2004 by the American Geophysical Union., The quasi-biennial oscillation (QBO) signal in stratospheric zonal and meridional wind, temperature, and geopotential height fields is analyzed based on the use of the National Centers for Environmental Prediction (NCEP) reanalysis (1958-2001). The multitaper method-singular value decomposition (MTM-SVD), a multivariate frequency domain analysis method, is used to detect significant and spatially coherent narrowband oscillations. The QBO is found as the most intense signal in the stratospheric zonal wind. Then, the MTM-SVD method is used to determine the patterns induced by the QBO at every stratospheric level and data field. The secondary meridional circulation associated with the QBO is identified in the obtained patterns. This circulation can be characterized by negative (positive) temperature anomalies associated with adiabatic rising (sinking) motions over zones of easterly (westerly) wind shear and over the subtropics and midlatitudes, while meridional convergence and divergence levels are found separated by a level of maximum zonal wind shear. These vertical and meridional motions form quasi-symmetric circulation cells over both hemispheres, though less intense in the Southern Hemisphere., Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2009 by the American Geophysical Union. N. Calvo was supported by the visitor program of the Max Planck Institute for Meteorology in Hamburg, the Spanish Ministry of Education and Science, and the Fulbright Commission in Spain. The simulations described here were carried out on the NEC-SX6 computer at the German Climate Computing Center (DKRZ). We thank Rolando R. Garcia and Daniel Marsh for their helpful comments and suggestions., The influence of the quasi-biennial oscillation (QBO) on the Northern Hemisphere (NH) polar vortex response to warm El Nino-Southern Oscillation (ENSO) events and the impact of the warm ENSO events on the QBO signal in the NH polar stratosphere have been analyzed using the Middle Atmosphere ECHAM5 model. The experiment setup was designed to include simulations of extended NH winter seasons for either strong easterly or strong westerly phases of the tropical QBO, forced with either sea surface temperatures (SSTs) from the strong ENSO event that occurred in 1997/1998 or with climatological SSTs. It has been found that the weakening and warming of the polar vortex associated with a warm ENSO are intensified at the end of the winter during both QBO phases. In addition, the westerly QBO phase delays the onset of the warm ENSO signal, while the easterly QBO phase advances it. Warm ENSO events also impact the extratropical signal of the QBO by intensifying ( weakening) the QBO effects in early ( late) winter. Therefore, it appears that during warm ENSO events the duration of QBO signal in the northern extratropics is shortened while its downward propagation accelerated. Our dynamical analysis has revealed that these results are due to changes in the background flow caused by the QBO combined with changes in the anomalous propagation and dissipation of extratropical waves generated by warm ENSO. In both cases, a nonlinear behavior in the response of the polar vortex is observed when both warm ENSO and the easterly phase of the QBO operate together. These results suggest that the Arctic polar vortex response to combined forcing factors, in our case warm ENSO and the QBO phenomena, is expected to be nonlinear also for other coexistent forcing factors able to affect the variability of the vortex in the stratosphere., Max Planck Institute for Meteorology in Hamburg, Spanish Ministry of Education and Science, Fulbright Commission in Spain, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

Copyright 2008 by the American Geophysical Union. This work was partly funded by the Spanish National Research Project TRODIM MEC-CGL2007-65891-C05-04-CLI., The seasonality of the quasi-biennial oscillation (QBO) and its secondary circulation is analyzed in the European Reanalysis (ERA-40) and Middle Atmosphere European Centre Hamburg Model (MAECHAM5) general circulation model data sets through the multitaper method-singular value decomposition (MTM-SVD). In agreement with previous studies, the results reveal a strong seasonal dependence of the QBO secondary circulation. This is characterized by a two-cell structure symmetric about the equator during autumn and spring. However, anomalies strongly weaken in the summer hemisphere and strengthen in the winter hemisphere, leading to an asymmetric QBO secondary circulation characterized by a single-cell structure displaced into the winter hemisphere during the solstices. In ERA-40, this asymmetry is more pronounced during the northern than during the southern winter. These results provide the first observation of the QBO secondary circulation asymmetries in the ERA-40 reanalysis data set across the full stratosphere and the lower mesosphere, up to 0.1 hPa. The MTM-SVD reconstruction of the seasonal QBO signals in the residual circulation and the QBO signals in Eliassen Palm (EP) flux divergences suggest a particular mechanism for the seasonal asymmetries of the QBO secondary circulation and its extension across the midlatitudes. The analysis shows that the QBO modulates the EP flux in the winter hemispheric surf zone poleward of the QBO jets. The zonal wind forcing by EP flux divergence is transformed by the Coriolis effect into a meridional wind signal. The seasonality in the stratospheric EP flux and the hemispheric differences in planetary wave forcing cause the observed seasonality in the QBO secondary circulation and its hemispheric differences., Proyecto TRODIM (Diagnosis y modelización de la tropopausa extratropical), MEC, Ministerio de Educación y Ciencia (MEC), España, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2006 by the American Geophysical Union. This paper has been partially funded by NCAR and MPI, which, additionally, kindly provided the data from the models. Furthermore, we want to thank the National Institute of Meteorology (INM) in Spain and the ECMWF for facilitating the accessto the ERA-40 data., The vertical propagation of the El Nino-Southern Oscillation (ENSO) temperature signal has been analyzed in two general circulation models, the Whole Atmosphere Community Climate Model and the Middle Atmosphere European Center - Hamburg Model, and in the ERA-40 reanalysis data set. Monthly mean data have been used, and composite differences ( El Nino - La Nina) have been computed. Our results show that the ENSO signal propagates into the middle atmosphere by means of planetary Rossby waves. Significant wave-like anomalies are observed up to around 40 km. This propagation is strongly influenced by the zonal mean zonal winds, being most effective in midlatitudes of the Northern Hemisphere because ENSO events tend to peak in northern winter, when stratospheric winds are westerly in the Northern Hemisphere, and allow vertical propagation of Rossby waves. In addition, zonal mean temperature anomalies are observed in the middle atmosphere in the tropics and at polar latitudes of the Northern Hemisphere. These anomalies are the result of changes in the residual mean meridional circulation: Our analysis reveals that during an El Nino event, vertical wave propagation and divergence of Eliassen-Palm flux are enhanced, forcing a stronger residual circulation in the stratosphere, which cools the tropics and warms the higher latitudes. This pattern is highly significant in the models during certain months but much less in the ERA-40 data, where other sources of variability ( in particular the quasi-biennial oscillation) also influence the residual circulation., NCAR, MPI, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

This study presents a comprehensive analysis of 40 stellar occultations observed during the Cassini Grand Finale mission, providing unprecedented insights into Saturn's atmosphere. By offering simultaneous latitude coverage and seasonal constraints, these observations enable a detailed exploration of composition and temperature variations across the middle and upper atmosphere. This work has produced the first 2D temperature map of the thermosphere with latitude and pressure, which reveals a temperature distribution that differs in important ways from model predictions. The Saturn Thermosphere Ionosphere Model (STIM) predicted that temperatures would peak around 630 K near 10^-8 bar at the poles. Contrary to these predictions, the observed temperature map indicates that peak temperatures are around 550 K, concentrated near auroral latitudes around 10^-12 bar. This observation suggests that auroral heating plays a pivotal role in determining thermospheric temperatures, highlighting the importance of equatorward transport, which requires further investigation. In-depth analysis using pressure-temperature profiles and H2 density data enabled the derivation of kronopotential and wind fields. These results revealed robust westward zonal jets, slower (peaking at 800 m/s) and closer to the equator (30 to 85 degrees latitude at 0.1 microbar) than predicted. Meridional winds generated by ion drag showed peak equatorward speeds of 20–40 m/s. Gravity wave signatures in the thermosphere were analyzed to derive 2D fields of gravity wave drag. The addition of gravity wave drag reduced the speed of zonal jets and increased the meridional winds by 20 to 50 m/s in the southern and northern hemispheres, respectively, demonstrating their role in enhancing meridional wind speeds. These findings align with model predictions by the Saturn Thermosphere Ionosphere model based on wave drag parameterized from near-equatorial observations by the Cassini Ion Neutral Mass Spectrometer and under

In this study, the excitation and propagation of non-orographic gravity waves (NOGWs) above tropopause depressions usually associated with propagating Rossby waves is investigated. Observations and analysis of NOGWs in the upper strato- sphere during research flight 25 of the 2014 DEEPWAVE campaign show hydrostatic wave patterns above a tropopause depression comparable to waves excited by orography at the surface. These gravity waves (GWs) stay above the depression as the depression travels east with the phase speed of the Rossby wave. In austral winter, the polar night jet (PNJ) develops in the Southern Hemisphere, leading to a much faster zonal stratospheric flow than the Rossby wave’s phase speed. Therefore, the source of these GWs could simply be the vertical displacement of the airflow above the tropopause mimicking an obstacle to the flow above. The goal was to evaluate this potential NOGW source through idealized numerical simulations with the geophysical flow solver EULAG. Typical shapes of tropopause depressions and typical stratospheric winter conditions suggest the excitation of low-frequency or inertia-gravity waves (IGWs). To account for their oscillation in the vertical and horizontal plane, all simulations were conducted in 3D. Preliminary studies were performed to assess the reliability of the model by comparing its numerical solutions to analytical solutions of different mountain wave regimes. In particular, comparisons of the gravity wave drag and surface momentum fluxes were instructive and guided the setup of the following simulations. Within the framework of this thesis, the simulations are constrained to the stratosphere, with the tropopause represented as a transient, impermeable, and frictionless lower boundary. Multiple simulations with different idealized tropopause shapes and different idealized background conditions were carried out to characterise the sensitivity of the waves’ momentum and energy fluxes and to identify scenarios which re, by Michael Binder, Masterarbeit University of Innsbruck 2023

There is growing recognition of the stratosphere's role in modulating tropospheric processes, yet due to the computational costs of detailed parameterizations and refined model domains, most standard climate models include simplified stratospheres with coarse vertical resolution. To evaluate the skill of these computationally efficient ``low-top'' models at replicating stratosphere/troposphere coupling processes, we compare the expression of simulated sudden stratospheric warming events (SSWs) between two versions of the Community Earth system model version 2's atmosphere; ``low top'' CAM6 (Community Atmosphere Model, v. 6) and ``high top'' WACCM6 (Whole Atmosphere Community Climate Model, v. 6). Our results illustrate distinct differences in SSW characteristics between configurations, including decreased frequency and enhanced intensity of events in the low-top model. These results illustrate the prominent role vertical resolution and parameterization schemes play in replicating SSW climatology and underscore the need to improve theoretical frameworks of processes driving stratospheric variability and its downward influence.

CRUE-CSIC (Acuerdos Transformativos 2022), The stratospheric polar vortex is a cyclonic circulation that forms over the winter pole, whose edge is characterized by a strong westerly jet (also called polar night jet, PNJ). The PNJ plays a key role in processes such as the distribution of atmospheric constituents in the polar stratosphere or the wave propagation. Further, variations in PNJ can also affect the troposphere, being behind the occurrence of extreme events near the Earth’s surface. Thus, it is important to correctly characterize the mean state of the PNJ and its variability. Already existing algorithms, although working, may present several issues. The simplest ones, those based on zonal mean wind, can miss important information. In contrast, the 2-dimensional ones usually involve multiple calculations with several fields, some of them not always included in typical datasets. In this study, we describe a new artificial intelligence technique to characterize the PNJ. The algorithm only requires data of zonal wind that is classified each time step with a decision trees algorithm with 95.5% accuracy, trained with images processed by a climate science researcher. The classifier is applied to JRA-55 reanalysis data and the output of simulations of three climate models and is found to perform reasonably well when validated against traditional zonal-mean methods. Indeed, it provides more information about the PNJ, as it offers in one step the PNJ region, averaged magnitudes and even identify if the PNJ is under perturbed conditions. We have explored two examples of potential applications of the classifier such as the study of the influence of climate change on the PNJ and the variability of the PNJ on monthly and daily scales. In both cases, our algorithm has produced coherent results with those produced with previous studies, but with more detail obtained at a single step., Ministerio de Ciencia e Innovación (MICINN)/FEDER, Depto. de Física de la Tierra y Astrofísica, Depto. de Arquitectura de Computadores y Automática, Fac. de Ciencias Físicas, Fac. de Informática, TRUE, pub

The investigation of weather properties and clouds distribution in the stratosphere is rare, but essential for science. In this research, twenty years of satellite recordings showed the properties of stratospheric clouds approved by GIS (Geographical Information System) and Remote sensing (RS) techniques. This type of clouds covered a small area in the analyzed period, but the results were important for meteorological and climatological condition in the atmosphere. A very tiny layer of water vapor and their low concentration produces a small number of clouds throughout the year. The average altitude of the stratosphere varied between 12 km and 50 km. The stratosphere is very dry; only polar stratospheric clouds (PSCCl) may be found. This type of clouds appears near the poles in the winter season. This research provides the explanation on the climate properties of clouds (water content) in this layer of the atmosphere. The layers of this type of clouds present stable factor of meteorological stability, but have recently been influenced by climate change effects. The new findings of water in the stratosphere were made possible by precise analysis of satellite recordings. The estimated amount of water in the clouds in the stratosphere may be significant for potential cloud seeding in the future.

Understanding atmospheric impacts of solar energetic particle precipitation (EPP) remains challenging, from quantification of the response in ozone, to implications on temperature. Both are necessary to understand links between EPP and regional climate variability. Here we use a chemistry-climate model to assess the importance of EPP on late winter/spring polar stratosphere. In transient simulations, the impact on NOy, ozone, and temperature is underestimated when using EPP forcing from the current recommendation of the Coupled Model Intercomparison Project (CMIP6). The resulting temperature response is largely masked by overall dynamical variability. An idealised experiment with EPP forcing that reproduces observed levels of NOy results in a significant reduction of ozone (up to 25%), cooling the stratosphere (up to 3 K) during late winter/spring. Our results unravel the inconsistency regarding the temperature response to EPP-driven springtime ozone decrease, and highlight the need for an improved EPP forcing in climate simulations.

Stratospheric ozone is a trace gas of great importance as it filters harmful ultraviolet radiations reaching the earth surface. Since ozone influences temperature and dynamics of the stratosphere, it is also a climate-relevant gas by modifyimg the tropospheric temperature. Significant changes in the stratospheric ozone are, therefore, a concern for human health and climate. India has a dedicated polar research programme with two stations in Antarctica; Maitri (70.4° S, 11.4° E, since 1989) and Bharati (69.2° S, 76.2° E, since 2012). Semi-regular measurements of total column ozone (TCO) are carried out to monitor the changes in the ozone layer there. Here, we use the available TCO measurements from Maitri in the winters of 1999–2003 and 2006, to estimate the chemical ozone depletion for the first time there. We estimate the largest ozone loss (59% or 180 DU) in 2006, and smallest in 2002 and 1999 (44% or 160 DU) among the winters; consistent with the meteorology, as the winter 2006 was the coldest and 2002 was the warmest with the first-ever major sudden stratospheric warming over Antarctica. The Maitri ozone loss analysis is found to be representative for the whole Antarctica as assessed from the comparisons with the average TCO from all Antarctic stations and satellite overpass TCO observations. The study, henceforth, demonstrates the value and significance of continuous monitoring of the ozone hole at Maitri to assist the policy decisions such as the Montreal Protocol and its amendments and adjustments.

This dissertation comprises multiple studies surrounding the middle atmosphere's chemistry, composition, and dynamics. The middle atmosphere refers to the region from ~ 10 km to ~ 100 km and consists of the Stratosphere, Mesosphere, and Lower Thermosphere. The Stratosphere, Mesosphere, and Thermosphere are bounded by pauses where the strongest changes in chemical composition, movement, density, and thermal behavior take place. While several studies in the past have investigated the chemical composition of the middle atmosphere and quantified the distribution of various species from the stratosphere to the lower thermosphere, seasonal variations and redistribution of species resulting from transport events make it important to continuously monitor the middle atmosphere. Dynamic events such as Sudden Stratospheric Warmings (SSW) impact the temperature gradient and the zonal mean wind pattern in the stratopause. Descent events triggered by SSWs result in enhanced transport of species from the lower thermosphere to the stratosphere. Temperature increments during SSWs have an important impact on Polar Stratospheric Clouds (PSCs), resulting in Antarctic ozone enhancement and a smaller ozone hole. The middle atmosphere is, thus, home to a diverse range of dynamics and chemistry, making it a critical subject that warrants attention from the science community. The continuous monitoring of the middle atmosphere is important to this end. Several satellite missions in the past have been dedicated to monitoring the middle atmosphere and collecting data for decades. However, continual revisions and revaluations of measurement approaches and the introduction of novel space instruments are necessary to compensate for the limitations associated with existing missions, expand the extant specimen database, and improve phenomenon-centric observations. The Solar Occultation for Ice Experiment (SOFIE) is one of the two instruments on the Aeronomy of Ice in the Mesosphere (AIM) spacecraft

This thesis studies the effect of energetic electron precipitation (EEP) on the Earth’s atmosphere, focusing on the northern wintertime stratosphere. EEP is driven by the interaction between the Earth’s magnetosphere and solar wind, a plasma stream from the Sun. Energetic electrons precipitate constantly from the near-Earth space to the high-latitude upper atmosphere. In the northern hemisphere, EEP has been found to affect in the lower atmosphere during the winter, most notably on the polar vortex, a wind system dominating winter stratosphere. Variations in polar vortex also extend to the surface, where EEP has been observed to affect large-scale weather modes. The aim of this thesis is to clarify the EEP effect on wintertime middle atmosphere and its dependence on atmospheric conditions. The EEP effect is also studied together with the other solar-related driver, solar radiation, and internal drivers of the atmosphere. This work utilizes newly calibrated and corrected satellite measurements of precipitating electron fluxes and surface measurements of geomagnetic activity to quantify EEP activity. The atmosphere is studied by using reanalysis datasets which are based on comprehensive observations and cover the whole globe from the surface to about 50 kilometer altitude. In this work we use different statistical methods to reliably distinguish the atmospheric variability related to EEP. Results of this thesis confirm the earlier findings that EEP significantly enhances the northern polar vortex. We also show that EEP is the main solar-related driver of the wintertime northern stratosphere. The EEP effect on the polar vortex is found to be particularly significant if the quasi-biennial oscillation (QBO), a wind mode in the equatorial stratosphere, is in the easterly phase. A remarkable interdependence is revealed between the EEP effect on the polar vortex and an extreme event of wintertime stratosphere, the sudden stratospheric warming (SSW). This thesis sho

The predictability of the Northern Hemisphere stratosphere and its underlying dynamics are investigated in five state-of-the-art seasonal prediction systems from the Copernicus Climate Change Service (C3S) multi-model database. Special attention is devoted to the connection between the stratospheric polar vortex (SPV) and lower-stratosphere wave activity (LSWA). We find that in winter (December to February) dynamical forecasts initialised on the first of November are considerably more skilful than empirical forecasts based on October anomalies. Moreover, the coupling of the SPV with mid-latitude LSWA (i.e., meridional eddy heat flux) is generally well reproduced by the forecast systems, allowing for the identification of a robust link between the predictability of wave activity above the tropopause and the SPV skill. Our results highlight the importance of November-to-February LSWA, in particular in the Eurasian sector, for forecasts of the winter stratosphere. Finally, the role of potential sources of seasonal stratospheric predictability is considered: we find that the C3S multi-model overestimates the stratospheric response to El Niño–Southern Oscillation (ENSO) and underestimates the influence of the Quasi–Biennial Oscillation (QBO).

Mercury, a global contaminant, enters the stratosphere through convective uplift, but its chemical cycling in the stratosphere is unknown. We report the first model of stratospheric mercury chemistry based on a novel photosensitized oxidation mechanism. We find two very distinct Hg chemical regimes in the stratosphere: in the upper stratosphere, above the ozone maximum concentration, Hg0 oxidation is initiated by photosensitized reactions, followed by second-step chlorine chemistry. In the lower stratosphere, ground-state Hg0 is oxidized by thermal reactions at much slower rates. This dichotomy arises due to the coincidence of the mercury absorption at 253.7 nm with the ozone Hartley band maximum at 254 nm. We also find that stratospheric Hg oxidation, controlled by chlorine and hydroxyl radicals, is much faster than previously assumed, but moderated by efficient photo-reduction of mercury compounds. Mercury lifetime shows a steep increase from hours in the upper-middle stratosphere to years in the lower stratosphere. © 2022. The Authors.

This study provides a long-term (1891–2014) global assessment of precipitation trends using data from two station-based gridded datasets and climate model outputs evolved through the fifth and sixth phases of the Coupled Model Intercomparison Project (CMIP5 and CMIP6, respectively). Our analysis employs a variety of modeling groups that incorporate low- and high-top level members, with the aim of assessing the possible effects of including a well-resolved stratosphere on the model’s ability to reproduce long-term observed annual precipitation trends. Results demonstrate that only a few regions show statistically significant differences in precipitation trends between observations and models. Nevertheless, this pattern is mostly caused by the strong interannual variability of precipitation in most of the world regions. Thus, statistically significant model-observation differences on trends (1891–2014) are found at the zonal mean scale. The different model groups clearly fail to reproduce the spatial patterns of annual precipitation trends and the regions where stronger increases or decreases are recorded. This study also stresses that there are no significant differences between low- and high-top models in capturing observed precipitation trends, indicating that having a well-resolved stratosphere has a low impact on the accuracy of precipitation projections.

In the last years the S5Lab (Sapienza Space Systems and Space Surveillance Laboratory) from Sapienza University of Rome has given to the students the opportunity to gather knowledge on stratospheric payloads by supporting the design and development of two experiments selected for the participation in the REXUS/BEXUS educational Programme, managed by three european space institutions. The insights and lessons learned gathered during the participations in the REXUS/BEXUS educational programme gave the possibility to the student to take part in the development of a third experiment in the frame of the professional research programme HEMERA and complete it successfully. STRATONAV (STRATOspheric NAVigation experiment) was a stratospheric experiment based on Software Defined Radios (SDRs) technology whose aim was the testing of the VOR (VHF Omnidirectional Range) navigation system, evaluating its performance above the standard service volume, which was launched on BEXUS 22 in October 2016. TARDIS (Tracking and Attitude Radio-based Determination In Stratosphere) was developed as a follow up of STRATONAV between 2018 and 2019. Similarly to its predecessor TARDIS was a stratospheric experiment aimed at exploiting the VOR signal, with the aid of SDRs, to perform in-flight attitude and position determination, and was launched on BEXUS 28 in October 2019. After the launch of TARDIS, a team composed both by former STRATONAV and TARDIS students was formed for the development of a third stratospheric experiment going by the name of STRAINS (Stratospheric Tracking Innovative Systems), conceived by Sapienza University of Rome and ALTEC and supported by ASI. STRAINS main objective was the proof of concept of the possibility of achieving the Time Difference of Arrival (TDOA) and the Frequency Difference of Arrival (FDOA) for navigation purposes with the aid of SDRs. The experiment was developed between 2020 and 2021 exploiting the lessons learned from the former team members of the tw

Recent studies show that the Asian summer monsoon anticyclone (ASMA) transports emissions from the rapidly industrializing nations in Asia into the tropical upper troposphere. Here, we present a unique set of measurements on over 100 air samples collected on multiple flights of the M55 Geophysica high altitude research aircraft over the Mediterranean, Nepal, and Northern India during the summers of 2016 and 2017 as part of the European Union project StratoClim. These air samples were measured for 27 ozone-depleting substances (ODSs), many of which were enhanced above expected levels, including the chlorinated very short-lived substances, dichloromethane (CH2Cl2), 1,2-dichloroethane (CH2ClCH2Cl), and chloroform (CHCl3). CH2Cl2 mixing ratios in the tropopause region were 65–136 parts per trillion (ppt) in comparison to previous estimates of mixing ratios in the tropical tropopause layer of 30–44 ppt in 2013–2014. Backward trajectories, calculated with the trajectory module of the chemistry-transport model CLaMS and driven by the ERA5 reanalysis, indicate possible source regions of CH2Cl2 in South Asia. We derived total equivalent chlorine (ECl), and equivalent effective stratospheric chlorine (EESC) and found that these quantities were substantially higher than previous estimates in the literature. EESC at mean age-of-air of 3 years based on the 2016 measurements was 1,861–1,872 ppt in comparison to a previously estimated EESC of 1,646 ppt. Our findings show that the ASMA transports larger than expected mixing ratios of long-lived and very short-lived ODSs into the upper troposphere and lower stratosphere, likely leading to an impact on the stratospheric ozone layer.

This work was supported by the research projects CGL2017-82216-R, PID2019-108589RA-I00 and PCI2019-103631 financed by the Spanish Commission of Science and Technology and FEDER and CROSSDRO project financed by the AXIS (Assessment of Cross(X)-sectoral climate Impacts and pathways for Sustainable transformation), JPI-Climate co-funded call of the European Commission. This study is also supported by "Unidad Asociada CSIC-Universidad de Vigo: Grupo de Física de la Atmósfera y del Oceano". CM acknowledges funding from the Irish Environmental Protection Agency (2019-CCRP-MS.60). LG and RN received partial support from the Xunta de Galicia under the Project ED431C 2017/64-GRC Programa de Consolidación e Estructuración de Unidades de Investigación Competitivas (Grupos de Referencia Competitiva) and Consellería de Educación e Ordenación Universitaria. Previous funders received cofounding from the ERDF, in the agenda of the Operational Program Galicia 2014-2020.", This study provides a long-term (1891-2014) global assessment of precipitation trends using data from two station-based gridded datasets and climate model outputs evolved through the fifth and sixth phases of the Coupled Model Intercomparison Project (CMIP5 and CMIP6, respectively). Our analysis employs a variety of modeling groups that incorporate low- and high-top level members, with the aim of assessing the possible effects of including a well-resolved stratosphere on the model's ability to reproduce long-term observed annual precipitation trends. Results demonstrate that only a few regions show statistically significant differences in precipitation trends between observations and models. Nevertheless, this pattern is mostly caused by the strong interannual variability of precipitation in most of the world regions. Thus, statistically significant model-observation differences on trends (1891-2014) are found at the zonal mean scale. The different model groups clearly fail to reproduce the spatial patterns of annual precipitation trends and the regions where stronger increases or decreases are recorded. This study also stresses that there are no significant differences between low- and high-top models in capturing observed precipitation trends, indicating that having a well-resolved stratosphere has a low impact on the accuracy of precipitation projections., Ministerio de Ciencia e Innovación (MICINN)/FEDER, CROSSDRO project - AXIS (Assessment of Cross(X)-sectoral climate Impacts and pathways for Sustainable transformation), JPI-Climate - call of the European Commission, Unidad Asociada CSIC-Universidad de Vigo: Grupo de Física de la Atmósfera y del Océano, Irish Environmental Protection Agency, Xunta de Galicia, Conselleria de Educacion e Ordenacion Universitaria, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

©2020 American Geophysical Union. Artículo firmado por 13 autores. We thank Jian Rao for producing Table 4. BA acknowledges support from the Spanish Ministry of Science and Innovation through the JeDiS (RTI-2018-096402-B-I00) project. MPB was supported by the Natural Environment Research Council (grant number NE/M006123/1). TB and HG acknowledge support by the Transregional Collaborative Research Center SFB/TRR 165 Waves to Weather (www.wavestoweather.de) funded by the German Research Foundation (DFG). Funding by the Swiss National Science Foundation to D.D. through project PP00P2_170523 is gratefully acknowledged. EPG acknowledges support from the US NSF through grant AGS-1852727. CIG acknowledges the support of a European Research Council starting grant under the European Union Horizon 2020 research and innovation programme (grant agreement number 677756). NB was supported by the Met Office Hadley Centre Programme funded by BEIS and Defra. Part of the material is based upon work supported by the National Center for Atmospheric Research, which is a major facility sponsored by the U.S. National Science Foundation under Cooperative Agreement 1852977. NP acknowledges support from NASA grant 80NSSC18K1046., Sudden stratospheric warmings (SSWs) are impressive fluid dynamical events in which large and rapid temperature increases in the winter polar stratosphere (∼10–50 km) are associated with a complete reversal of the climatological wintertime westerly winds. SSWs are caused by the breaking of planetary-scale waves that propagate upwards from the troposphere. During an SSW, the polar vortex breaks down, accompanied by rapid descent and warming of air in polar latitudes, mirrored by ascent and cooling above the warming. The rapid warming and descent of the polar air column affect tropospheric weather, shifting jet streams, storm tracks, and the Northern Annular Mode, making cold air outbreaks over North America and Eurasia more likely. SSWs affect the atmosphere above the stratosphere, producing widespread effects on atmospheric chemistry, temperatures, winds, neutral (nonionized) particles and electron densities, and electric fields. These effects span both hemispheres. Given their crucial role in the whole atmosphere, SSWs are also seen as a key process to analyze in climate change studies and subseasonal to seasonal prediction. This work reviews the current knowledge on the most important aspects of SSWs, from the historical background to dynamical processes, modeling, chemistry, and impact on other atmospheric layers., Unión Europea. Horizonte 2020, Ministerio de Ciencia e Innovación (MICINN), Natural Environment Research Council, Transregional Collaborative Research Center SFB/TRR 165 Waves to Weather funded by the German Research Foundation (DFG), Swiss National Science Foundatio, US NSF, Met Office Hadley Centre Programme funded by BEIS and Defra, National Center for Atmospheric Research, U.S. National Science Foundation under Cooperative, NASA, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

open, European wintertime precipitation is known to be skilfully estimated in reanalysis data and model simulations since it is highly correlated with large scale, low frequency modes of variability, namely the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO). Since the NAO and AO are mainly a wintertime mode of variability, the skill of estimating precipitation becomes more limited in the other seasons, most importantly in the summer, in which precipitation is mainly a result of mesoscale convection. The first part of the study uses observational data, reanalysis data, and the output of Weather Research and Forecast (WRF) model to study the recent changes of extreme daily precipitation events over Europe. It is found that in summer and transition seasons, more regions recorded an increase of extreme precipitation events than regions that recorded a decreasing trend. This is consistent with the global warming trends with Clausius-Clapeyron relation. The added value of using a high resolution, convection-permitting model to estimate precipitation extremes is deduced. The results show that WRF succeeds to correct the failure of ERA-Interim reanalysis to capture the positive trends of European extreme precipitation in summer and transition seasons that are indicated by the observational data (EOBS) and previous literature. On the other hand, more regions in Europe recorded negative extreme precipitation trends than regions with positive trends. This is found to be a consequence of the recent positive trend of the NAO over the past decades, causing more frequent positive NAO events, reducing extreme precipitation outbreaks to more regions in Europe. As the NAO and the highly correlated AO are changing, further investigations to the nature of the two oscillations are carried out. Reanalysis data and climate model simulations of historical and warm climates are used to show that the relation between the two oscillations changes with climate warming. The two modes ar, È noto che le precipitazioni invernali europee sono ben stimate nei dati di rianalisi e nelle simulazioni dai modelli dato che sono altamente correlate con modi con variabilità su larga scala e a bassa frequenza come l'oscillazione del Nord Atlantico (NAO) e l'oscillazione artica (AO). Dal momento che NAO e AO sono principalmente modi di variabilità invernale, la capacità di stimare le precipitazioni è più limitata nelle altre stagioni, soprattutto in estate, in cui (quando) le precipitazioni sono principalmente dovute alla convezione a mesoscala. La prima parte dello studio utilizza dati osservativi, dati di rianalisi e l'output del modello WRF (Weather Research and Forecast) per studiare i cambiamenti recenti negli eventi estremi di precipitazione giornaliera in Europa. Si è stato riscontrato che nelle stagioni estive e di transizione, sono più le regioni che hanno registrato un aumento di eventi di precipitazioni estreme rispetto a quelle che hanno registrato una tendenza al ribasso. Questo è coerente con le tendenze del riscaldamento globale con per via della relazione di Clausius-Clapeyron. è stato studiato anche il valore aggiunto dell'utilizzo di un modello ad alta risoluzione che consenta la convezione per stimare gli estremi delle precipitazioni. I risultati mostrano che WRF riesca a correggere il fallimento della rianalisi ERA-Interim per I risultati mostrano che WRF riesce, al contrario di ERA-Interim, a catturare le tendenze positive delle precipitazioni estreme europee sia in estate che nelle stagioni di transizione indicate dai dati osservativi (EOBS) e dalla letteratura precedente. D'altra parte, sono di più le aree in Europa che hanno registrato tendenze negative nelle precipitazioni estreme rispetto alle aree con tendenze positive. Questo si tratta di una conseguenza del recente trend positivo)della NAO negli ultimi decenni, che ha causato eventi NAO positivi più frequenti, riducendo le precipitazioni estreme in più regioni in Europa. Dato che sia l, 0, open, Hamouda, M

Los globos estratosféricos, como herramienta de apoyo y obtención de datos meteorológicos o como plataforma de investigación tienen un gran potencial dado a las capacidades y ventajas que presentan respecto sus principales competidores como podrían ser los satélites o cohetes sonda, principalmente debido a su bajo coste y facilidad de uso en comparación con sus competidores. Esto ha hecho que los globos se hayan usado con diversos fines científicos desde el S. XX, y que en el S.XXI se comiencen a postular como una alternativa a los tradicionales sistemas de investigación de alta altitud y como uno de los pilares fundamentales dentro de la corriente NewSpace, debido a sus múltiples capacidades y usos. No obstante, en el presente artículo se indica la necesidad de hacer que estos sistemas sean aún más reutilizables si cabe para reducir costes y impacto medioambiental que pueda generar el uso de estos sistemas., Stratospheric balloons, as a tool to support and obtain meteorological data or as a research platform have a great potential given the capabilities and advantages they present over their main competitors such as satellites or probe rockets, mainly due to their low cost and ease of use compared to their competitors. These balloons have been used for various scientific purposes since the twentieth century, and in the twenty-first century begin to postulate as an alternative to traditional high-altitude research systems and as one of the fundamental pillars within the NewSpace current, due to its multiple capabilities and uses. However, this article indicates the need to make these systems even more reusable in order to reduce the costs and environmental impact that the use of these systems can generate.

We found a statistically significant relationship between the stratospheric quasi-biennial oscillation (QBO) and Antarctic sea ice concentration (SIC) in austral winter. SIC differences between the easterly phase of the QBO (EQBO) and westerly phase of the QBO (WQBO) show positive anomalies of SIC in the following regions: over the Ross Sea, Weddell Sea, and around 90 degrees E. This wave-3 pattern is clearly seen in June and July, and decays in August. The increased SIC regions correspond to anomalous offshore wind regions, and the reduced SIC regions correspond to onshore wind regions, indicating the atmospheric circulation anomaly produced the SIC anomaly. The atmospheric circulation anomaly is barotropic and closely related with the upper atmospheric flow. The upper circulation anomaly shows a stationary Rossby wave train propagating from Indian Ocean. We show the enhanced convection in the tropical Indian Ocean in EQBO can excite the Rossby wave train. In summary, the stratospheric QBO affects the tropical convection, then generating the Rossby wave train which propagates into southern high latitude, and finally affecting Antarctic sea ice. There exists a possibility to predict winter sea ice in one-year advance, because the QBO is a quasi-regular oscillation.

We found a statistically significant relationship between the stratospheric quasi-biennial oscillation (QBO) and Antarctic sea ice concentration (SIC) in austral winter. SIC differences between the easterly phase of the QBO (EQBO) and westerly phase of the QBO (WQBO) show positive anomalies of SIC in the following regions: over the Ross Sea, Weddell Sea, and around 90°E. This wave-3 pattern is clearly seen in June and July, and decays in August. The increased SIC regions correspond to anomalous offshore wind regions, and the reduced SIC regions correspond to onshore wind regions, indicating the atmospheric circulation anomaly produced the SIC anomaly. The atmospheric circulation anomaly is barotropic and closely related with the upper atmospheric flow. The upper circulation anomaly shows a stationary Rossby wave train propagating from Indian Ocean. We show the enhanced convection in the tropical Indian Ocean in EQBO can excite the Rossby wave train. In summary, the stratospheric QBO affects the tropical convection, then generating the Rossby wave train which propagates into southern high latitude, and finally affecting Antarctic sea ice. There exists a possibility to predict winter sea ice in one-year advance, because the QBO is a quasi-regular oscillation.

We found a statistically significant relationship between the stratospheric quasi-biennial oscillation (QBO) and Antarctic sea ice concentration (SIC) in austral winter. SIC differences between the easterly phase of the QBO (EQBO) and westerly phase of the QBO (WQBO) show positive anomalies of SIC in the following regions: over the Ross Sea, Weddell Sea, and around 90 degrees E. This wave-3 pattern is clearly seen in June and July, and decays in August. The increased SIC regions correspond to anomalous offshore wind regions, and the reduced SIC regions correspond to onshore wind regions, indicating the atmospheric circulation anomaly produced the SIC anomaly. The atmospheric circulation anomaly is barotropic and closely related with the upper atmospheric flow. The upper circulation anomaly shows a stationary Rossby wave train propagating from Indian Ocean. We show the enhanced convection in the tropical Indian Ocean in EQBO can excite the Rossby wave train. In summary, the stratospheric QBO affects the tropical convection, then generating the Rossby wave train which propagates into southern high latitude, and finally affecting Antarctic sea ice. There exists a possibility to predict winter sea ice in one-year advance, because the QBO is a quasi-regular oscillation.

The impact of El Niño-Southern Oscillation (ENSO) on the late-winter extra-tropical stratosphere (January–March) is assessed in a multi-model framework. Three state-of-the-art atmospheric models are run with prescribed SST anomalies representative of a strong ENSO event, with symmetric patterns for El Niño and La Niña. The well-known temperature perturbation in the lower stratosphere during El Niño is captured by two models, in which the anomalous warming at polar latitudes is accompanied by a positive geopotential height anomaly that extends over the polar cap. In the third model, which shows a lack of temperature anomalies over the pole, the anomalous anticyclone is confined over Canada and does not expand to the polar cap. This anomalous center of action emerges from the large-scale tropospheric Rossby wave train forced by ENSO, and shrinking/stretching around the polar vortex is invoked to link it to the temperature response. No disagreement across models is found in the lower stratosphere for La Niña, whose teleconnection is opposite in sign but weaker. In the middle-upper stratosphere (above 50 hPa) the geopotential height anomalies project on a wavenumber-1 (WN1) pattern for both El Niño and, more weakly, La Niña, and show a westward tilt with height up to the stratopause. It is suggested that this WN1 pattern arises from the high-latitude lower-stratospheric anomalies, and that the ENSO teleconnection to the polar stratosphere can be interpreted in terms of upward propagation of the stationary Rossby wave train and quasi-geostrophic balance, instead of wave breaking., This work was supported by the MEDSCOPE project. MEDSCOPE is part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by AEMET (ES), ANR (FR), BSC (ES), CMCC (IT), CNR (IT), IMR (BE) and Météo-France (FR), with co-funding by the European Union (Grant 690462). B.M. and J.G.-S. were supported by the “Contratos Predoctorales para la Formación de Doctores” (BES-2016-076431) and “Ramón y Cajal” (RYC-2016-21181) programmes, respectively. F.M.P. was partially supported by the Spanish DANAE (CGL2015-68342-R) and GRAVITOCAST (ERC2018-092835) projects. Technical support at BSC (Computational Earth Sciences group) is sincerely acknowledged. We also thank the two anonymous reviewers for their helpful feedback., Peer Reviewed, Postprint (published version)

The Quasi-biennial Oscillation (QBO) dominates the interannual variability of the tropical stratosphere and influences other regions of the atmosphere. The high predictability of the QBO implies that its teleconnections could lead to increased skill of seasonal and decadal forecasts provided the relevant mechanisms are accurately represented in models. Here modelling and sampling uncertainties of QBO teleconnections are examined using a multi-model ensemble of QBO-resolving atmospheric general circulation models that have carried out a set of coordinated experiments as part of the Stratosphere-troposphere Processes And their Role in Climate (SPARC) QBO initiative (QBOi). During Northern Hemisphere winter, the stratospheric polar vortex in most of these models strengthens when the QBO near 50 hPa is westerly and weakens when it is easterly, consistent with, but weaker than, the observed response. These weak responses are likely due to model errors, such as systematically weak QBO amplitudes near 50 hPa, affecting the teleconnection. The teleconnection to the North Atlantic Oscillation is less well captured overall, but of similar strength to the observed signal in the few models that do show it. The models do not show clear evidence of a QBO teleconnection to the Northern Hemisphere Pacific-sector subtropical jet., We acknowledge the UK's Centre for Environmental Data Analysis (CEDA) for hosting the QBOi data archive. This work was supported by the National Center for Atmospheric Research, which is a major facility sponsored by the National Science Foundation under Cooperative Agreement no. 1852977. Portions of this study were supported by the Regional and Global Model Analysis (RGMA) component of the Earth and Environmental System Modeling Program of the U.S. Department of Energy's Office of Biological & Environmental Research (BER) via National Science Foundation IA 1844590. NB was supported by the Met Office Hadley Centre Programme funded by BEIS and Defra. SO and LG were supported by the National Centre for Atmospheric Science and the Natural Environment Research Council (NE/P006779/1, NE/N018001/1). FL and SO were supported by the JPI-Climate/Belmont Forum 423 project GOTHAM (ANR-15-JCLI-0004-01, NERC NE/P006779/1). CC and FS were supported by the Copernicus Climate Change Service, funded by the EU and implemented by ECMWF. HN was supported by the Environment Research and Technology Development Fund (S-12) of the Environmental Restoration and Conservation Agency of Japan and by Grant-in-Aid (JP18K03748, JP20H05171) for Science Research (KAKENHI) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan. For the EMAC simulations, PB, TK, and SV acknowledge support by the state of Baden-Württemberg through bwHPC. YK was supported by the Japan Society for Promotion of Science (JSPS) KAKENHI (grant nos. JP15KK0178, JP17K18816, JP18H01286 and 19H05702) and by the Environment Research and Technology Development Fund (JPMEERF20192004) of the Environmental Restoration and Conservation Agency of Japan. YK and KH were supported by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) through its sponsorship of research at the International Pacific Research Center. SW and YK were partly supported by the “Integrated Research Program for Advancing, Peer Reviewed, "Article signat per 29 autors/es: James A. Anstey, Isla R. Simpson, Jadwiga H. Richter, Hiroaki Naoe, Masakazu Taguchi, Federico Serva, Lesley J. Gray, Neal Butchart, Kevin Hamilton, Scott Osprey, Omar Bellprat, Peter Braesicke, Andrew C. Bushell, Chiara Cagnazzo, Chih-Chieh Chen, Hye-Yeong Chun, Rolando R. Garcia, Laura Holt, Yoshio Kawatani, Tobias Kerzenmacher, Young-Ha Kim, Francois Lott, Charles McLandress, John Scinocca, Timothy N. Stockdale, Stefan Versick, Shingo Watanabe, Kohei Yoshida, Seiji Yukimoto", Postprint (published version)

We found a statistically significant relationship between the stratospheric quasi-biennial oscillation (QBO) and Antarctic sea ice concentration (SIC) in austral winter. SIC differences between the easterly phase of the QBO (EQBO) and westerly phase of the QBO (WQBO) show positive anomalies of SIC in the following regions: over the Ross Sea, Weddell Sea, and around 90 degrees E. This wave-3 pattern is clearly seen in June and July, and decays in August. The increased SIC regions correspond to anomalous offshore wind regions, and the reduced SIC regions correspond to onshore wind regions, indicating the atmospheric circulation anomaly produced the SIC anomaly. The atmospheric circulation anomaly is barotropic and closely related with the upper atmospheric flow. The upper circulation anomaly shows a stationary Rossby wave train propagating from Indian Ocean. We show the enhanced convection in the tropical Indian Ocean in EQBO can excite the Rossby wave train. In summary, the stratospheric QBO affects the tropical convection, then generating the Rossby wave train which propagates into southern high latitude, and finally affecting Antarctic sea ice. There exists a possibility to predict winter sea ice in one-year advance, because the QBO is a quasi-regular oscillation.

Los globos estratosféricos, como herramienta de apoyo y obtención de datos meteorológicos o como plataforma de investigación tienen un gran potencial dado a las capacidades y ventajas que presentan respecto sus principales competidores como podrían ser los satélites o cohetes sonda, principalmente debido a su bajo coste y facilidad de uso en comparación con sus competidores. Esto ha hecho que los globos se hayan usado con diversos fines científicos desde el S. XX, y que en el S.XXI se comiencen a postular como una alternativa a los tradicionales sistemas de investigación de alta altitud y como uno de los pilares fundamentales dentro de la corriente NewSpace, debido a sus múltiples capacidades y usos. No obstante, en el presente artículo se indica la necesidad de hacer que estos sistemas sean aún más reutilizables si cabe para reducir costes y impacto medioambiental que pueda generar el uso de estos sistemas., Stratospheric balloons, as a tool to support and obtain meteorological data or as a research platform have a great potential given the capabilities and advantages they present over their main competitors such as satellites or probe rockets, mainly due to their low cost and ease of use compared to their competitors. These balloons have been used for various scientific purposes since the twentieth century, and in the twenty-first century begin to postulate as an alternative to traditional high-altitude research systems and as one of the fundamental pillars within the NewSpace current, due to its multiple capabilities and uses. However, this article indicates the need to make these systems even more reusable in order to reduce the costs and environmental impact that the use of these systems can generate.

È noto che le precipitazioni invernali europee sono ben stimate nei dati di rianalisi e nelle simulazioni dai modelli dato che sono altamente correlate con modi con variabilità su larga scala e a bassa frequenza come l'oscillazione del Nord Atlantico (NAO) e l'oscillazione artica (AO). Dal momento che NAO e AO sono principalmente modi di variabilità invernale, la capacità di stimare le precipitazioni è più limitata nelle altre stagioni, soprattutto in estate, in cui (quando) le precipitazioni sono principalmente dovute alla convezione a mesoscala. La prima parte dello studio utilizza dati osservativi, dati di rianalisi e l'output del modello WRF (Weather Research and Forecast) per studiare i cambiamenti recenti negli eventi estremi di precipitazione giornaliera in Europa. Si è stato riscontrato che nelle stagioni estive e di transizione, sono più le regioni che hanno registrato un aumento di eventi di precipitazioni estreme rispetto a quelle che hanno registrato una tendenza al ribasso. Questo è coerente con le tendenze del riscaldamento globale con per via della relazione di Clausius-Clapeyron. è stato studiato anche il valore aggiunto dell'utilizzo di un modello ad alta risoluzione che consenta la convezione per stimare gli estremi delle precipitazioni. I risultati mostrano che WRF riesca a correggere il fallimento della rianalisi ERA-Interim per I risultati mostrano che WRF riesce, al contrario di ERA-Interim, a catturare le tendenze positive delle precipitazioni estreme europee sia in estate che nelle stagioni di transizione indicate dai dati osservativi (EOBS) e dalla letteratura precedente. D'altra parte, sono di più le aree in Europa che hanno registrato tendenze negative nelle precipitazioni estreme rispetto alle aree con tendenze positive. Questo si tratta di una conseguenza del recente trend positivo)della NAO negli ultimi decenni, che ha causato eventi NAO positivi più frequenti, riducendo le precipitazioni estreme in più regioni in Europa. D, European wintertime precipitation is known to be skilfully estimated in reanalysis data and model simulations since it is highly correlated with large scale, low frequency modes of variability, namely the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO). Since the NAO and AO are mainly a wintertime mode of variability, the skill of estimating precipitation becomes more limited in the other seasons, most importantly in the summer, in which precipitation is mainly a result of mesoscale convection. The first part of the study uses observational data, reanalysis data, and the output of Weather Research and Forecast (WRF) model to study the recent changes of extreme daily precipitation events over Europe. It is found that in summer and transition seasons, more regions recorded an increase of extreme precipitation events than regions that recorded a decreasing trend. This is consistent with the global warming trends with Clausius-Clapeyron relation. The added value of using a high resolution, convection-permitting model to estimate precipitation extremes is deduced. The results show that WRF succeeds to correct the failure of ERA-Interim reanalysis to capture the positive trends of European extreme precipitation in summer and transition seasons that are indicated by the observational data (EOBS) and previous literature. On the other hand, more regions in Europe recorded negative extreme precipitation trends than regions with positive trends. This is found to be a consequence of the recent positive trend of the NAO over the past decades, causing more frequent positive NAO events, reducing extreme precipitation outbreaks to more regions in Europe. As the NAO and the highly correlated AO are changing, further investigations to the nature of the two oscillations are carried out. Reanalysis data and climate model simulations of historical and warm climates are used to show that the relation between the two oscillations changes with climate warming. The two modes ar

The Arctic is a key indicator of global climate change. Annual surface temperatures are increasing at more than twice the rate of the global average, and passive microwave satellite observations of Arctic sea-ice extent show a loss of nearly 40% over the last few decades. Despite recent advances in climate models, availability of observations, and statistical analysis, our understanding of ice-ocean-atmosphere interactions, and the teleconnections between the Arctic and other regions, remains incomplete. Assessing the atmospheric response to the rapid changes in Arctic sea ice will help to determine future societal impacts from climate change, including extreme weather events in the densely populated mid-latitude regions.The broad objective of this thesis is to improve our understanding of Arctic climate variability. To be more specific, this dissertation will explore (i) the internal variability of Arctic sea-ice thickness (SIT), (ii) the atmospheric response to thinning sea ice, and (iii) the role of stratospheric and tropospheric pathways in modulating Arctic-mid-latitude teleconnections. SIT has an important effect on the Arctic energy budget, and therefore it is critical to represent it accurately in global climate models. However, limited observations of SIT (satellite-derived and in situ) have prevented a robust analysis of the atmospheric response to its spatial and temporal variability. Here, I use perturbation experiments in a high-top atmospheric global climate model to examine the importance of stratosphere-troposphere coupling and other causal pathways for teleconnections between Arctic sea ice and the mid-latitudes.Internal variability contributes to an uncertainty of 10-20 years in the timing of future mean SIT falling below 0.5 m in a large ensemble of simulations of a fully-coupled global climate model. This loss of SIT is found to reinforce the large-scale tropospheric response to Arctic sea-ice concentration and contributes up to one third of the

While water and sulfuric acid droplets are the main component of stratospheric aerosols, measurements performed for about 30 years have shown that non-sulfate particles (NSPs) are also present. Such particles, released from the Earth mainly through volcanic eruptions, pollution or biomass burning, or coming from space, present a wide variety of compositions, sizes, and shapes. To better understand the origin of NSPs, we have performed measurements with the Light Optical Aerosol Counter (LOAC) during 151 flights under weather balloons in the 2013–2019 period reaching altitudes up to 35 km. Coupled with previous counting measurements conducted over the 2004–2011 period, the LOAC measurements indicate the presence of stratospheric layers of enhanced concentrations associated with NSPs, with a bimodal vertical repartition ranging between 17 and 30 km altitude. Such enhancements are not correlated with permanent meteor shower events. They may be linked to dynamical and photophoretic effects lifting and sustaining particles coming from the Earth. Besides, large particles, up to several tens of µm, were detected and present decreasing concentrations with increasing altitudes. All these particles can originate from Earth but also from meteoroid disintegrations and from the interplanetary dust cloud and comets. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.

The Arctic is a key indicator of global climate change. Annual surface temperatures are increasing at more than twice the rate of the global average, and passive microwave satellite observations of Arctic sea-ice extent show a loss of nearly 40% over the last few decades. Despite recent advances in climate models, availability of observations, and statistical analysis, our understanding of ice-ocean-atmosphere interactions, and the teleconnections between the Arctic and other regions, remains incomplete. Assessing the atmospheric response to the rapid changes in Arctic sea ice will help to determine future societal impacts from climate change, including extreme weather events in the densely populated mid-latitude regions.The broad objective of this thesis is to improve our understanding of Arctic climate variability. To be more specific, this dissertation will explore (i) the internal variability of Arctic sea-ice thickness (SIT), (ii) the atmospheric response to thinning sea ice, and (iii) the role of stratospheric and tropospheric pathways in modulating Arctic-mid-latitude teleconnections. SIT has an important effect on the Arctic energy budget, and therefore it is critical to represent it accurately in global climate models. However, limited observations of SIT (satellite-derived and in situ) have prevented a robust analysis of the atmospheric response to its spatial and temporal variability. Here, I use perturbation experiments in a high-top atmospheric global climate model to examine the importance of stratosphere-troposphere coupling and other causal pathways for teleconnections between Arctic sea ice and the mid-latitudes.Internal variability contributes to an uncertainty of 10-20 years in the timing of future mean SIT falling below 0.5 m in a large ensemble of simulations of a fully-coupled global climate model. This loss of SIT is found to reinforce the large-scale tropospheric response to Arctic sea-ice concentration and contributes up to one third of the

In situ and remote sensing observations of water vapor are analyzed to assess the evidence for direct convective hydration of the lower stratosphere. We have examined several hundred balloon-borne and airborne in situ measurements of lower stratospheric humidity in the tropics and northern midlatitudes. We find that the tropical lower stratospheric H2O enhancements above the background occur quite infrequently, and the height of the enhancements is within about 1 km of the cold-point tropopause. Following Schwartz et al. (2013, https://doi.org/10.1002/grl.50421), we examine the anomalously high (above 8 ppmv) water vapor mixing ratios retrieved by the Aura Microwave Limb Sounder (MLS) at 100- and 82-hPa pressure levels, and we determine their vertical location relative to the local tropopause based on both Global Forecast System (GFS) operational analysis and the ERA5 reanalysis temperature data. We find that essentially all of the >8-ppmv MLS water vapor measurements over the extratropical North American monsoon region are above the relatively low lapse-rate tropopause in the region, and most are above the local cold-point tropopause. Over the Asian monsoon region, most (80/90%) of the high H2O values occur below the relatively high-altitude local lapse-rate/cold-point tropopause. Anomalously high MLS water vapor retrievals at 100 and 82 hPa almost never occur in the deep tropics. We show that this result is consistent with the in situ observations given the broad vertical averaging kernel of the MLS measurement. The available evidence suggests that direct hydration of the lower stratosphere is important over North America during the monsoon season but likely has limited impact in the tropics.

In situ and remote sensing observations of water vapor are analyzed to assess the evidence for direct convective hydration of the lower stratosphere. We have examined several hundred balloon-borne and airborne in situ measurements of lower stratospheric humidity in the tropics and northern midlatitudes. We find that the tropical lower stratospheric H2O enhancements above the background occur quite infrequently, and the height of the enhancements is within about 1 km of the cold-point tropopause. Following Schwartz et al. (2013, https://doi.org/10.1002/grl.50421), we examine the anomalously high (above 8 ppmv) water vapor mixing ratios retrieved by the Aura Microwave Limb Sounder (MLS) at 100- and 82-hPa pressure levels, and we determine their vertical location relative to the local tropopause based on both Global Forecast System (GFS) operational analysis and the ERA5 reanalysis temperature data. We find that essentially all of the >8-ppmv MLS water vapor measurements over the extratropical North American monsoon region are above the relatively low lapse-rate tropopause in the region, and most are above the local cold-point tropopause. Over the Asian monsoon region, most (80/90%) of the high H2O values occur below the relatively high-altitude local lapse-rate/cold-point tropopause. Anomalously high MLS water vapor retrievals at 100 and 82 hPa almost never occur in the deep tropics. We show that this result is consistent with the in situ observations given the broad vertical averaging kernel of the MLS measurement. The available evidence suggests that direct hydration of the lower stratosphere is important over North America during the monsoon season but likely has limited impact in the tropics.

The Northern polar vortex experiences considerable interannual variability, which is also reflected to tropospheric weather. Recent research has established a link between polar vortex variations and energetic electron precipitation (EEP) from the near‐Earth space into the polar atmosphere, which is mediated by EEP‐induced chemical changes causing ozone loss in the mesosphere and stratosphere. The most dramatic changes in the polar vortex are due to sudden stratospheric warmings (SSWs). Enhanced planetary wave convergence and meridional circulation may cause an SSW, a temporary breakdown of the polar vortex. Here we study the relation of SSWs to the atmospheric response to EEP in 1957–2017 using combined ERA‐40 and ERA‐Interim reanalysis data and geomagnetic activity as a proxy of EEP. We find that the EEP‐related enhancement of the polar vortex and other associated dynamical responses are seen only during winters when an SSW occurs and that the EEP‐related changes are observed systematically slightly before the SSW onset. We show that during these times, the planetary wave activity into the stratosphere is systematically increased, thus favoring enhanced wave‐mean‐flow interaction, which can dynamically amplify the initial polar vortex enhancement caused by ozone loss. These results highlight the importance of considering planetary wave activity as a necessary condition for observing the effects of EEP on the polar vortex.

In situ and remote sensing observations of water vapor are analyzed to assess the evidence for direct convective hydration of the lower stratosphere. We have examined several hundred balloon-borne and airborne in situ measurements of lower stratospheric humidity in the tropics and northern midlatitudes. We find that the tropical lower stratospheric H2O enhancements above the background occur quite infrequently, and the height of the enhancements is within about 1 km of the cold-point tropopause. Following Schwartz et al. (2013, https://doi.org/10.1002/grl.50421), we examine the anomalously high (above 8 ppmv) water vapor mixing ratios retrieved by the Aura Microwave Limb Sounder (MLS) at 100- and 82-hPa pressure levels, and we determine their vertical location relative to the local tropopause based on both Global Forecast System (GFS) operational analysis and the ERA5 reanalysis temperature data. We find that essentially all of the >8-ppmv MLS water vapor measurements over the extratropical North American monsoon region are above the relatively low lapse-rate tropopause in the region, and most are above the local cold-point tropopause. Over the Asian monsoon region, most (80/90%) of the high H2O values occur below the relatively high-altitude local lapse-rate/cold-point tropopause. Anomalously high MLS water vapor retrievals at 100 and 82 hPa almost never occur in the deep tropics. We show that this result is consistent with the in situ observations given the broad vertical averaging kernel of the MLS measurement. The available evidence suggests that direct hydration of the lower stratosphere is important over North America during the monsoon season but likely has limited impact in the tropics.