Lagrangian temperature and vertical velocity fluctuations due to gravity waves in the lower stratosphere

International audienceWave-induced Lagrangian fluctuations of temperature and vertical velocity in the lower stratosphere are quantified using measurements from superpressure balloons (SPBs). Observations recorded every minute along SPB flights allow the whole gravity wave spectrum to be described and provide unprecedented information on both the intrinsic frequency spectrum and the probability distribution function of wave fluctuations. The data set has been collected during two campaigns coordinated by the French Space Agency in 2010, involving 19 balloons over Antarctica and 3 in the deep tropics. In both regions, the vertical velocity distributions depart significantly from a Gaussian behavior. Knowledge on such wave fluctuations is essential for modeling microphysical processes along Lagrangian trajectories. We propose a new simple parameterization that reproduces both the non-Gaussian distribution of vertical velocities (or heating/cooling rates) and their observed intrinsic frequency spectrum

Observations of Tropical Tropopause Layer clouds from a balloon-borne lidar

Tropical Tropopause Layer (TTL) clouds have a significant impact on the Earth’s radiative budget and regulate the amount of water vapor entering the stratosphere. During the Strateole-2 observation campaign, three microlidars were flown onboard stratospheric superpressure balloons from October 2021 to late January 2022, slowly drifting only a few kilometers above the TTL. These measurements have unprecedented sensitivity to thin cirrus and provide a fine-scale description of cloudy structures both in time and space. Case studies of collocated observations with the space-borne lidar Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) show a very good agreement between the instruments and highlight the unique ability of the microlidar to detect optically very thin clouds below CALIOP detection capacity (optical depth τ < 2 · 10−3). Statistics on cloud occurrence show that TTL cirrus appear in more than 50 % of the microlidar profiles and have a mean geometrical depth of 1 km. Ultrathin TTL cirrus (τ < 2 · 10−3) have a significant coverage (16 % of the profiles) and their mean geometrical depth is below 500 m

Waves and turbulence at the tropical tropopause and their impacts on tropical tropopause layer cirrus

Cette thèse s’intéresse aux ondes de gravité et à la turbulence dans la région de la tropopause tropicale (TTL pour tropical tropopause layer, entre 14 et 18 km d’altitude), et à leurs impacts sur les cirrus.Dans un premier temps, les fluctuations de température et de vent vertical induites dans la TTL par les ondes de gravité sont quantifiées et caractérisées à partir de mesures provenant de vols de ballons stratosphériques longue durée. Les perturbations observées sont comparées aux champs de fluctuations résolues par différents modèles atmosphériques globaux. À la lumière des observations, différentes méthodes de paramétrisation des fluctuations de température sont discutées.Dans un second temps, l’influence des ondes équatoriales et de gravité sur la microphysique des cirrus est étudiée. On considère d’abord l’impact des ondes de gravité de haute fréquence sur la nucléation des cristaux de glace. La question du rôle des anomalies de vent vertical induites par les ondes de basse fréquence sur le transport de la glace est ensuite abordée et son impact quantifié à l’aide d’observations in situ. Enfin, on étudie la formation et l’évolution d’un cirrus de grande échelle à l’aide de simulations numériques. Parmi les différents processus en jeu (radiatifs,...), on montre l’importance d’une onde équatoriale de grande échelle dans la structuration et l’évolution du champ nuageux.Dans une dernière partie, les fluctuations de vents de petite échelle dans la TTL, interprétées comme de la turbulence, sont étudiées à partirdes observations avion de la campagne ATTREX au-dessus de l’océan Pacifique. Leur impact sur le transport vertical de différents traceurs est quantifié. Il est inférieur à l’impact de l’upwelling équatorial de grande échelle mais néanmoins significatif.Atmospheric waves and turbulence and their impacts on cirrus clouds in the Tropical Tropopause Layer (TTL, 14-18 km altitude) are studied using in situ observations, numerical simulations and theoretical approaches.First, long-duration stratospheric balloon measurements are used to analyze Lagrangian temperature and vertical wind fluctuations induced by gravity waves at the tropical tropopause. The amplitude and intermittency of wave fluctuations are assessed, and the observations are compared with resolved wave fluctuations in atmospheric models. Methods to parameterize Lagrangian temperature fluctuations are then discussed.Then, some impacts of waves on cirrus clouds microphysics are examined. We first consider the influence of high frequency gravity waves on the ice nucleation process. Next, we explore the interplay between ice crystal sedimentation and advection by the wind perturbations induced by low frequency waves. At last, we use numerical simulations to investigate the formation of a large-scale cirrus in the TTL. We demonstrate the role of large-scale equatorial waves and quantify the relevance of different processes (dynamics, radiative heating,...) in the cloud evolution.Finally, small-scale wind fluctuations, interpreted as turbulent bursts, are characterized using aircraft measurements from the ATTREX campaign in the tropical Pacific. The impact of the fluctuations on vertical mixing and on the TTL tracer budget is quantified. The vertical transport induced by turbulent mixing is found to be smaller than that induced by mean tropical upwelling, but nonetheless significant

Ondes et turbulence à la tropopause tropicale et impacts sur les cirrus

Atmospheric waves and turbulence and their impacts on cirrus clouds in the Tropical Tropopause Layer (TTL, 14-18 km altitude) are studied using in situ observations, numerical simulations and theoretical approaches.First, long-duration stratospheric balloon measurements are used to analyze Lagrangian temperature and vertical wind fluctuations induced by gravity waves at the tropical tropopause. The amplitude and intermittency of wave fluctuations are assessed, and the observations are compared with resolved wave fluctuations in atmospheric models. Methods to parameterize Lagrangian temperature fluctuations are then discussed.Then, some impacts of waves on cirrus clouds microphysics are examined. We first consider the influence of high frequency gravity waves on the ice nucleation process. Next, we explore the interplay between ice crystal sedimentation and advection by the wind perturbations induced by low frequency waves. At last, we use numerical simulations to investigate the formation of a large-scale cirrus in the TTL. We demonstrate the role of large-scale equatorial waves and quantify the relevance of different processes (dynamics, radiative heating,...) in the cloud evolution.Finally, small-scale wind fluctuations, interpreted as turbulent bursts, are characterized using aircraft measurements from the ATTREX campaign in the tropical Pacific. The impact of the fluctuations on vertical mixing and on the TTL tracer budget is quantified. The vertical transport induced by turbulent mixing is found to be smaller than that induced by mean tropical upwelling, but nonetheless significant.Cette thèse s’intéresse aux ondes de gravité et à la turbulence dans la région de la tropopause tropicale (TTL pour tropical tropopause layer, entre 14 et 18 km d’altitude), et à leurs impacts sur les cirrus.Dans un premier temps, les fluctuations de température et de vent vertical induites dans la TTL par les ondes de gravité sont quantifiées et caractérisées à partir de mesures provenant de vols de ballons stratosphériques longue durée. Les perturbations observées sont comparées aux champs de fluctuations résolues par différents modèles atmosphériques globaux. À la lumière des observations, différentes méthodes de paramétrisation des fluctuations de température sont discutées.Dans un second temps, l’influence des ondes équatoriales et de gravité sur la microphysique des cirrus est étudiée. On considère d’abord l’impact des ondes de gravité de haute fréquence sur la nucléation des cristaux de glace. La question du rôle des anomalies de vent vertical induites par les ondes de basse fréquence sur le transport de la glace est ensuite abordée et son impact quantifié à l’aide d’observations in situ. Enfin, on étudie la formation et l’évolution d’un cirrus de grande échelle à l’aide de simulations numériques. Parmi les différents processus en jeu (radiatifs,...), on montre l’importance d’une onde équatoriale de grande échelle dans la structuration et l’évolution du champ nuageux.Dans une dernière partie, les fluctuations de vents de petite échelle dans la TTL, interprétées comme de la turbulence, sont étudiées à partirdes observations avion de la campagne ATTREX au-dessus de l’océan Pacifique. Leur impact sur le transport vertical de différents traceurs est quantifié. Il est inférieur à l’impact de l’upwelling équatorial de grande échelle mais néanmoins significatif

Equatorial Waves, Diurnal Tides and Small Scale Thermal Variability in the Tropical Lower Stratosphere From COSMIC 2 Radio Occultation

International audienceA new constellation of radio occultation satellites called COSMIC 2 (Constellation Observing System for Meteorology, Ionosphere, and Climate 2) is providing unprecedented dense measurements of the tropical atmosphere, with on average more than 4,000 high quality observations per day over 40°N-S. We use these data to evaluate large and small scale thermal variability in the tropical lower stratosphere during October 2019 - April 2020. Space time spectral analysis of 6 hourly gridded COSMIC 2 data reveals a rich spectrum of traveling planetary scale waves, including Kelvin waves, mixed Rossby gravity waves and inertia gravity waves, in addition to propagating diurnal tides. These coherent modes show enhanced amplitudes from the tropical tropopause through the lower stratosphere (∼17-25 km). Characteristics of small scale temperature variances, calculated as deviations from the gridded fields, reveal systematic spatial patterns including time average maxima over Africa and South America overlying frequent deep convection. Small scale variances also exhibit transient maxima in the equatorial lower stratosphere tied to local variations in static stability, associated with large scale Kelvin waves. The new COSMIC 2 observations provide novel details on the rich spectrum of large and small scale waves near and above the tropical tropopause

Smoke-charged vortices in the stratosphere generated by wildfires and their behaviour in both hemispheres: comparing Australia 2020 to Canada 2017

The two most intense wildfires of the last decade that took place in Canada in 2017 and Australia in 2019-2020 were followed by large injections of smoke in the stratosphere due to pyroconvection. It was discovered by Khaykin et al. (2020) and Kablick et al. (2020) that, after the Australian event, part of this smoke self-organized as anticyclonic confined vortices that rose in the mid-latitude stratosphere up to 35 km. Based on CALIOP observations and the ERA5 reanalysis, this new study analyzes the Canadian case and find, similarly, that a large plume penetrated the stratosphere by 12 August 2017 and got trapped within a meso-scale anticyclonic structure which travelled across the Atlantic. It then broke into three offsprings that could be followed until mid-October performing three round the world journeys and rising up to 23 km. We analyze the dynamical structure of the vortices produced by these two wildfires and demonstrate how they are maintained by the assimilation of data from instruments measuring the signature of the vortices in the temperature and ozone field. We propose that these vortices can be seen as bubbles of low absolute potential vorticity and smoke carried vertically across the stratification from the troposphere inside the middle stratosphere by their internal heating, against the descending flux of the Brewer-Dobson circulation

Quantification of water vapour transport from the Asian monsoon to the stratosphere

Numerous studies have presented evidence that the Asian summer monsoon anticyclone substantially influences the distribution of trace gases – including water vapour – in the upper troposphere and lower stratosphere (e.g. Santee et al., 2017). Stratospheric water vapour in turn strongly affects surface climate (see e.g. Solomon et al., 2010). Here, we analyse the characteristics of water vapour transport from the upper troposphere in the Asian monsoon region to the stratosphere employing a multiannual simulation with the chemistry-transport model CLaMS (Chemical Lagrangian Model of the Stratosphere). This simulation is driven by meteorological data from ERA-Interim and features a water vapour tagging that allows us to assess the contributions of different upper tropospheric source regions to the stratospheric water vapour budget. Our results complement the analysis of air mass transport through the Asian monsoon anticyclone by Ploeger et al. (2017). The results show that the transport characteristics for water vapour are mainly determined by the bulk mass transport from the Asian monsoon region. Further, we find that, although the relative contribution from the Asian monsoon region to water vapour in the deep tropics is rather small (average peak contribution of 14 % at 450 K), the Asian monsoon region is very efficient in transporting water vapour to this region (when judged according to its comparatively small spatial extent). With respect to the Northern Hemisphere extratropics, the Asian monsoon region is much more impactful and efficient regarding water vapour transport than e.g. the North American monsoon region (averaged maximum contributions at 400 K of 29 % versus 6.4 %)

Persistence Hunga Tonga plume in the stratosphere and its journey around the Earth.

International audienceThe Hunga Tonga eruption has generated an atmospheric plume rising above 40 km, establishing an observational record. Due to the explosive nature of the eruption with a lot of water, the plume carried an unprecedented amount of water and a cloud of sulfated aerosols and possibly ultra-thin ashes was released. The aerosols have already persisted for four weeks with peak scatterring ratio initially above 200 that are still above 30 on many patches, as seen from CALIOP. These high values combined with low depolarization suggest a large amount of small sub-micronic spherical particles, confirmed by in situ balloon measurements. This is compatible with dominance of sulfated aerosols.As the stratospheric flow has been mostly zonal with no breaking wave during the period and region of interest, and the horizontal shear dominates, the plume has been mostly dispersed in longitude keeping a similar latitudinal vertical pattern from the early days. A part has migrated to the tropical band reaching 10°N. Several concentrated patches have been preserved in particular a "mushroom" like pattern at 20S which has already circulated once around the Earth. . We will discuss the stability of this pattern in relation with vortical and thermal structures that are detected from several instruments and the meteorological analysis.We will also discuss the likely impact on the stratospheric composition and the radiative effect on the yearly basis

Quantification of water vapour transport from the Asian monsoon to the stratosphere

We have performed multiannual simulations with the chemistry-transport model CLaMS (Chemical Lagrangian Model of the Stratosphere) to investigate water vapour transport from the Asian monsoon region to the stratosphere. We assess the transport pathways and efficiency of water vapour transport from the Asian monsoon region to the stratosphere and make comparisons with other source regions (e.g. the tropics). Our nalyses are related to the previously published work by Ploeger et al. (2017), who have analyzed mass transport from the Asian monsoon anticyclone to the stratosphere. The presented findings are related to the Final Meeting Sessions “Transport and dynamics” and “Global Implications” and have recently been published for discussion in Atmospheric Chemistry and Physics (Nützel et al., 2019)

Observation of Gravity Waves at the Tropical Tropopause Using Superpressure Balloons

International audienceTropical gravity wave activity is investigated using measurements of momentum fluxes gathered during Strateole-2 superpressure balloon flights. The data set consists of eight balloon flights performed in the deep tropics from November 2019 to February 2020. The flights lasted for 2–3 months each, and in-situ meteorological data were collected every 30 s. The relation between gravity waves and deep convection is investigated using geostationary satellite data from the NOAA/NCEP GPM_MERGIR satellite data product, at 1 h resolution. The amplitude of gravity wave momentum fluxes shows a clear dependence on the distance to the nearest convective system, with a strong decay as distance to convection increases. The largest momentum-flux values (>urn:x-wiley:2169897X:media:jgrd57204:jgrd57204-math-0001mPa) are only found less than 200 km away from deep convection. The sensitivity of the wave flux to distance from convection is stronger for high frequency gravity waves (periods shorter than 60 min). Lower frequency waves tend to a non-zero, background value away from convection, supporting some background value in gravity-wave drag parameterizations. On the other hand, the wide range of momentum flux values observed close to the convection emphasizes the intermittent nature of the gravity-wave source. The large scale variation of gravity-wave intermittency within the equatorial belt is also studied. The results highlight spatial variations of gravity wave activity, with the highest momentum flux recorded over land