Letteratura scientifica selezionata sul tema "Tropical tropopause (TTL)"
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Articoli di riviste sul tema "Tropical tropopause (TTL)":
1
Gettelman, A., T. Birner, V. Eyring, H. Akiyoshi, D. A. Plummer, M. Dameris, S. Bekki et al. "The Tropical Tropopause Layer 1960–2100". Atmospheric Chemistry and Physics Discussions 8, n. 1 (29 gennaio 2008): 1367–413. http://dx.doi.org/10.5194/acpd-8-1367-2008.
Abstract (sommario):
Abstract. The representation of the Tropical Tropopause Layer in 13 different Chemistry Climate Models designed to represent the stratosphere is analyzed. Simulations for 1960–present and 1980–2100 are analyzed and compared to reanalysis model output. Results indicate that the models are able to reproduce the basic structure of the TTL. There is a large spread in cold point tropopause temperatures that may be linked to variation in TTL ozone values. The models are generally able to reproduce historical trends in tropopause pressure obtained from reanalysis products. Simulated historical trends in cold point tropopause temperatures and in the meridional extent of the TTL are not consistent across models. The pressure of both the tropical tropopause and the level of main convective outflow appear to be decreasing (increasing altitude) in historical runs. Similar trends are seen in the future. Models consistently predict decreasing tropopause and convective outflow pressure, by several hPa/decade. Tropical cold point temperatures increase by 0.2 K/decade. This indicates that tropospheric warming dominates stratospheric cooling at the tropical tropopause. Stratospheric water vapor at 100 hPa increases by up to 0.5–1 ppmv by 2100. This is less than implied directly by the temperature and methane increases, highlighting the correlation of tropopause temperatures with stratospheric water vapor, but also the complex nature of TTL transport.
2
Lei, Siliang, Xijuan Zhu, Yuxiang Ling, Shiwen Teng e Bin Yao. "Tropical Tropopause Layer Cloud Properties from Spaceborne Active Observations". Remote Sensing 15, n. 5 (22 febbraio 2023): 1223. http://dx.doi.org/10.3390/rs15051223.
Abstract (sommario):
A significant part of clouds in the tropics appears over the tropopause due to intense convections and in situ condensation activity. These tropical tropopause layer (TTL) clouds not only play an important role in the radiation budget over the tropics, but also in water vapor and other chemical material transport from the troposphere to the stratosphere. This study quantifies and analyzes the properties of TTL clouds based on spaceborne active observations, which provide one of the most reliable sources of information on cloud vertical distributions. We use four years (2007–2010) of observations from the joint Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and CloudSat and consider all cloudy pixels with top height above the tropopause as TTL clouds. The occurrence frequency of TTL clouds during the nighttime is found to be almost 13% and can reach ~50–60% in areas with frequent convections. The annual averages of tropical tropopause height, tropopause temperature, and cloud top height are 16.2 km, −80.7 °C, and 16.6 km, respectively, and the average cloud top exceeds tropopause by approximately 500 m. More importantly, the presence of TTL clouds causes tropopause temperature to be ~3–4 °C colder than in the all-sky condition. It also lifts the tropopause heights ~160 m during the nighttime and lowers the heights ~84 m during the daytime. From a cloud type aspect, ~91% and ~4% of the TTL clouds are high clouds and altostratus, and only ~5% of them are associated with convections (i.e., nimbostratus and deep convective clouds). Approximately 30% of the TTL clouds are single-layer clouds, and multi-layer clouds are dominated by those with 2–3 separated layers.
3
Tegtmeier, Susann, James Anstey, Sean Davis, Rossana Dragani, Yayoi Harada, Ioana Ivanciu, Robin Pilch Kedzierski et al. "Temperature and tropopause characteristics from reanalyses data in the tropical tropopause layer". Atmospheric Chemistry and Physics 20, n. 2 (22 gennaio 2020): 753–70. http://dx.doi.org/10.5194/acp-20-753-2020.
Abstract (sommario):
Abstract. The tropical tropopause layer (TTL) is the transition region between the well-mixed convective troposphere and the radiatively controlled stratosphere with air masses showing chemical and dynamical properties of both regions. The representation of the TTL in meteorological reanalysis data sets is important for studying the complex interactions of circulation, convection, trace gases, clouds, and radiation. In this paper, we present the evaluation of climatological and long-term TTL temperature and tropopause characteristics in the reanalysis data sets ERA-Interim, ERA5, JRA-25, JRA-55, MERRA, MERRA-2, NCEP-NCAR (R1), and CFSR. The evaluation has been performed as part of the SPARC (Stratosphere–troposphere Processes and their Role in Climate) Reanalysis Intercomparison Project (S-RIP). The most recent atmospheric reanalysis data sets (ERA-Interim, ERA5, JRA-55, MERRA-2, and CFSR) all provide realistic representations of the major characteristics of the temperature structure within the TTL. There is good agreement between reanalysis estimates of tropical mean temperatures and radio occultation data, with relatively small cold biases for most data sets. Temperatures at the cold point and lapse rate tropopause levels, on the other hand, show warm biases in reanalyses when compared to observations. This tropopause-level warm bias is related to the vertical resolution of the reanalysis data, with the smallest bias found for data sets with the highest vertical resolution around the tropopause. Differences in the cold point temperature maximize over equatorial Africa, related to Kelvin wave activity and associated disturbances in TTL temperatures. Interannual variability in reanalysis temperatures is best constrained in the upper TTL, with larger differences at levels below the cold point. The reanalyses reproduce the temperature responses to major dynamical and radiative signals such as volcanic eruptions and the quasi-biennial oscillation (QBO). Long-term reanalysis trends in temperature in the upper TTL show good agreement with trends derived from adjusted radiosonde data sets indicating significant stratospheric cooling of around −0.5 to −1 K per decade. At 100 hPa and the cold point, most of the reanalyses suggest small but significant cooling trends of −0.3 to −0.6 K per decade that are statistically consistent with trends based on the adjusted radiosonde data sets. Advances of the reanalysis and observational systems over the last decades have led to a clear improvement in the TTL reanalysis products over time. Biases of the temperature profiles and differences in interannual variability clearly decreased in 2006, when densely sampled radio occultation data started being assimilated by the reanalyses. While there is an overall good agreement, different reanalyses offer different advantages in the TTL such as realistic profile and cold point temperature, continuous time series, or a realistic representation of signals of interannual variability. Their use in model simulations and in comparisons with climate model output should be tailored to their specific strengths and weaknesses.
4
Dzambo, Andrew M., Matthew H. Hitchman e Kai-Wei Chang. "The Influence of Gravity Waves on Ice Saturation in the Tropical Tropopause Layer over Darwin, Australia". Atmosphere 10, n. 12 (5 dicembre 2019): 778. http://dx.doi.org/10.3390/atmos10120778.
Abstract (sommario):
Gravity waves (GWs) in the tropical tropopause layer (TTL) can help dehydrate the lower stratosphere through rapid cooling events, but observational studies of GWs in the TTL are limited. Using a long-term, high-resolution radiosonde temperature dataset, an atmospheric state classification technique, and wavelet analysis, we characterize temperature perturbations generated by GWs in the TTL over Darwin, Australia across eight atmospheric states. We find a peak in GW power just above the tropical tropopause and a climatological maximum during peak monsoon season. While accounting for a chronic negative temperature bias near the tropical tropopause, we estimate that, in the upper troposphere, GWs impose a 2 K temperature perturbation during non-monsoon states and a 3 K temperature perturbation during the monsoon states, with corresponding values of 5 K and 6 K in the upper TTL. A 3 K negative temperature perturbation will lead to significant perturbations in relative humidity with respect to ice, which has implications for environmental ice number concentrations and TTL cloud fraction.
5
Gettelman, A., T. Birner, V. Eyring, H. Akiyoshi, S. Bekki, C. Brühl, M. Dameris et al. "The Tropical Tropopause Layer 1960–2100". Atmospheric Chemistry and Physics 9, n. 5 (4 marzo 2009): 1621–37. http://dx.doi.org/10.5194/acp-9-1621-2009.
Abstract (sommario):
Abstract. The representation of the Tropical Tropopause Layer (TTL) in 13 different Chemistry Climate Models (CCMs) designed to represent the stratosphere is analyzed. Simulations for 1960–2005 and 1980–2100 are analyzed. Simulations for 1960–2005 are compared to reanalysis model output. CCMs are able to reproduce the basic structure of the TTL. There is a large (10 K) spread in annual mean tropical cold point tropopause temperatures. CCMs are able to reproduce historical trends in tropopause pressure obtained from reanalysis products. Simulated historical trends in cold point tropopause temperatures are not consistent across models or reanalyses. The pressure of both the tropical tropopause and the level of main convective outflow appear to have decreased (increased altitude) in historical runs as well as in reanalyses. Decreasing pressure trends in the tropical tropopause and level of main convective outflow are also seen in the future. Models consistently predict decreasing tropopause and convective outflow pressure, by several hPa/decade. Tropical cold point temperatures are projected to increase by 0.09 K/decade. Tropopause anomalies are highly correlated with tropical surface temperature anomalies and with tropopause level ozone anomalies, less so with stratospheric temperature anomalies. Simulated stratospheric water vapor at 90 hPa increases by up to 0.5–1 ppmv by 2100. The result is consistent with the simulated increase in temperature, highlighting the correlation of tropopause temperatures with stratospheric water vapor.
6
Schiller, C., J. U. Grooß, P. Konopka, F. Plöger, F. H. Silva dos Santos e N. Spelten. "Hydration and dehydration at the tropical tropopause". Atmospheric Chemistry and Physics Discussions 9, n. 4 (24 agosto 2009): 17495–529. http://dx.doi.org/10.5194/acpd-9-17495-2009.
Abstract (sommario):
Abstract. High-resolution water measurements from three tropical airborne missions in Northern Australia, Southern Brazil and West Africa in different seasons are analysed to study the transport and transformation of water in the tropical tropopause layer (TTL) and its impact on the stratosphere. The mean profiles are quite different according to the season and location of the campaigns, with lowest mixing ratios below 2 ppmv at the cold point tropopause during the Australian mission in November/December and high TTL mixing ratios during the African measurements in August. We present backward trajectory calculations considering freeze-drying of the air to the minimum saturation mixing ratio and initialised with climatological satellite data. This trajectory-based reconstruction of water agrees well with the observed H2O average profiles and therefore demonstrates that the water vapour set point in the TTL is primarily determined by the Lagrangian saturation history. Deep convection was found to moisten the TTL, in several events even above the cold point up to 420 K potential temperatures. However, our study does not provide evidence for a larger impact of these highly-localised events on global scales.
7
Schiller, C., J. U. Grooß, P. Konopka, F. Plöger, F. H. Silva dos Santos e N. Spelten. "Hydration and dehydration at the tropical tropopause". Atmospheric Chemistry and Physics 9, n. 24 (23 dicembre 2009): 9647–60. http://dx.doi.org/10.5194/acp-9-9647-2009.
Abstract (sommario):
Abstract. High-resolution water measurements from three tropical airborne missions in Northern Australia, Southern Brazil and West Africa in different seasons are analysed to study the transport and transformation of water in the tropical tropopause layer (TTL) and its impact on the stratosphere. The mean profiles are quite different according to the season and location of the campaigns, with lowest mixing ratios below 2 ppmv at the cold point tropopause during the Australian mission in November/December and high TTL mixing ratios during the African measurements in August. We present backward trajectory calculations considering freeze-drying of the air to the minimum saturation mixing ratio and initialised with climatological satellite data. This trajectory-based reconstruction of water agrees well with the observed H2O average profiles and therefore demonstrates that the water vapour set point in the TTL is primarily determined by the Lagrangian saturation history. Deep convection was found to moisten the TTL, in several events even above the cold point up to 420 K potential temperatures. However, our study does not provide evidence for a larger impact of these highly-localised events on global scales.
8
Ryu, Jung-Hee, e Sukyoung Lee. "Effect of Tropical Waves on the Tropical Tropopause Transition Layer Upwelling". Journal of the Atmospheric Sciences 67, n. 10 (1 ottobre 2010): 3130–48. http://dx.doi.org/10.1175/2010jas3434.1.
Abstract (sommario):
Abstract An initial-value problem is employed with a GCM to investigate the role of the convectively driven Rossby and Kelvin waves for tropopause transition layer (TTL) upwelling in the tropics. The convective heating is mimicked with a prescribed heating field, and the Lagrangian upwelling is identified by examining the evolution of passive tracer fields whose initial distribution is identical to the initial heating field. This study shows that an overturning circulation, induced by the tropical Rossby waves, is capable of generating the TTL upwelling. Even when the heating is placed in the eastern Pacific, the TTL upwelling occurs only over the western tropical Pacific, indicating that the background flow plays a crucial role. The results from a Rossby wave source analysis suggest that a key feature of the background flow is the strong absolute vorticity gradient associated with the Asian subtropical jet. In addition, static stability is relatively weak over the western Pacific, suggesting that this may also contribute to the TTL upwelling in that region. The background flow also modulates the internal Kelvin waves in such a manner that the coldest region in the TTL (resembling the observed “cold trap”) occurs over the western tropical Pacific. As a consequence, the upwelling air, induced by the meridional momentum flux of the Rossby wave, passes through the cold trap generated by the Kelvin wave. Since in reality the background flow is shaped by the convective heating, the climatological western tropical Pacific heating is ultimately responsible for both the TTL upwelling and the cold trap; however, both processes are realized indirectly through its impact on the background flow and the generation of the tropical waves.
9
Lin, Pu, David Paynter, Yi Ming e V. Ramaswamy. "Changes of the Tropical Tropopause Layer under Global Warming". Journal of Climate 30, n. 4 (1 febbraio 2017): 1245–58. http://dx.doi.org/10.1175/jcli-d-16-0457.1.
Abstract (sommario):
Abstract This paper investigates changes in the tropical tropopause layer (TTL) in response to carbon dioxide increase and surface warming separately in an atmospheric general circulation model, finding that both effects lead to a warmer tropical tropopause. Surface warming also results in an upward shift of the tropopause. A detailed heat budget analysis is performed to quantify the contributions from different radiative and dynamic processes to changes in the TTL temperature. When carbon dioxide increases with fixed surface temperature, a warmer TTL mainly results from the direct radiative effect of carbon dioxide increase. With surface warming, the largest contribution to the TTL warming comes from the radiative effect of the warmer troposphere, which is partly canceled by the radiative effect of the moistening at the TTL. Strengthening of the stratospheric circulation following surface warming cools the lower stratosphere dynamically and radiatively via changes in ozone. These two effects are of comparable magnitudes. This circulation change is the main cause of temperature changes near 63 hPa but is weak near 100 hPa. Contributions from changes in convection and clouds are also quantified. These results illustrate the heat budget analysis as a useful tool to disentangle the radiative–dynamical–chemical–convective coupling at the TTL and to facilitate an understanding of intermodel difference.
10
Dessler, A. E., e S. C. Sherwood. "A model of HDO in the tropical tropopause layer". Atmospheric Chemistry and Physics Discussions 3, n. 4 (29 agosto 2003): 4489–513. http://dx.doi.org/10.5194/acpd-3-4489-2003.
Abstract (sommario):
Abstract. Any theory of water vapor in the tropical tropopause layer (TTL) must explain both the abundance and isotopic composition of water there. In a previous paper, we presented a model of the TTL that simulated the abundance of water vapor as well as the details of the vertical profile. That model included the effects of "overshooting" convection, which injects dry air directly into the TTL. Here, we present results for the model after modifying it to include water's stable isotopologue HDO (where D represents deuterium, 2H). We find that the model predicts a nearly uniform HDO depletion throughout the TTL, in agreement with recent measurements. This occurs because the model dehydrates by dilution, which does not fractionate, instead of by condensation. Our model shows that this dehydration by dilution is consistent with other physical constraints on the system. We also show the key role that lofted ice plays in determining the abundance of HDO in the TTL. Such lofted ice requires a complementary source of dry air in the TTL; without that, the TTL will rapidly saturate and the lofted ice will not evaporate.
Tesi sul tema "Tropical tropopause (TTL)":
1
Waddicor, David Alan. "Aerosol in the tropical tropopause layer". Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/aerosol-in-the-tropical-tropopause-layer(c68a4252-15dc-4a96-a890-0156719b3a9f).html.
Abstract (sommario):
This thesis details the ACTIVE campaign in the tropics of northern Australia during 2005-2006 (based in Darwin). The focus of the campaign was to find the influence of tropical convection on the aerosol and chemical content of the Tropical Tropopause Layer [TTL] and the cirrus cloud cover in the area, which is important for the global energy budget. This study details the background climatology of the Darwin region with statistical categorisation of the trace gases and particles. The TTL had regions of extremely high aerosol number concentration, much higher than that of the PBL. The 10 to 1000 nm particle concentrations were as high as 25,000 cm-3 and 100 to 1000 nm were as high as 1000 cm-3. High aerosol concentrations were usually found in cloud-free conditions; cloudy regions were typically low in aerosol number. Wind data and trajectories (BADC) were used to find the origin of the high particle concentrations. Aerosols were found to be nucleating in outflow regions of convective anvils. SO2 oxidation to H2SO4 is a widely accepted mechanism for nucleation. A binary mechanism (H2O-H2SO4), with SO2 as the precursor, was found to be inadequate in explaining the nucleation and growth rates -- tested using an aerosol sectional model. However, it was found, via back trajectory analysis, that the climatology of Darwin was influenced by local and long-range sources, including advection from Indonesia and the Tropical Warm Pool. These distant sources could have introduced condensable matter, with aerosol precursor properties (certain organic compounds). The aerosol model found a condensable precursor concentration of at least 300 pptv was necessary to replicate the observations.
2
Newton, Richard. "Vertical profiling in the west Pacific warm pool". Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/vertical-profiling-in-the-west-pacific-warm-pool(8c89d0ef-dc88-44d6-ad49-81cc34d5e662).html.
Abstract (sommario):
This thesis consists of three distinct parts of CAST, CONTRAST and ATTREX, which were aircraft and field campaigns in the West Pacific in January-March 2014. The first section comprises of ozonesonde measurements from Manus Island, Papua New Guinea. A contamination issue affected the first 14 ozonesondes, and so particular care was required to characterize the background current, and as a result, a 'hybrid' background current correction was developed, which combines a constant correction with a pressure dependent correction. Collocated measurements with the CONTRAST aircraft - the NCAR Gulfsteam V - suggests the new hybrid correction produces better ozonesonde profiles than the other corrections that are found in the literature. The results of the ozonesonde measurements revealed a low-ozone event, with minimum ozone concentrations of ~12 ppbv, which was coincident with an easterly jet, and traced back to an area of deep convection: clean marine boundary layer air was uplifted into the tropical tropopause layer (TTL) and then advected in the easterly jet across to Manus Island. The second section attempted to find more examples of low-ozone conditions in the TTL from the aircraft data. The ATTREX aircraft - the NASA Northrop Grumman Global Hawk - observed ozone concentrations of ~10 ppbv in the Southern Hemisphere in proximity of tropical storm Lusi. Whole air samples from all three aircraft suggests the low-ozone air had recently encountered the boundary layer, with enhanced concentrations of surface-generated very short lived substances (VSLSs) compared to air with higher ozone concentrations. No low-ozone events were found in the Northern Hemisphere, even in the vicinity of tropical cyclone Faxai. The third section explores the low-ozone events in the WRF-Chem (Weather Research and Forecasting - with chemistry) in order to see whether the model was capable of recreating the low-ozone event measured by the ozonesondes on 21-23 February as a case study. The WRF-Chem simulation did correctly reproduce the large convective storm in a similar area to that observed by satellites, and surface tracers were uplifted in large quantities as hypothesized. However, no evidence of injection of air into the stratosphere was found in the simulation, and, rather than uplift directly from the surface, mixing of air in the boundary layer followed by uplift into the TTL was the main mechanism for producing the low-ozone event.
3
Plöger, Felix [Verfasser]. "Impact of different vertical transport representations on simulating processes in the tropical tropopause layer (TTL) / Felix Plöger". Wuppertal : Universitätsbibliothek Wuppertal, 2011. http://d-nb.info/1012468402/34.
4
Podglajen, Aurélien. "Ondes et turbulence à la tropopause tropicale et impacts sur les cirrus". Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEE013/document.
Abstract (sommario):
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 significatifAtmospheric 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
5
Podglajen, Aurélien. "Ondes et turbulence à la tropopause tropicale et impacts sur les cirrus". Electronic Thesis or Diss., Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEE013.
Abstract (sommario):
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 significatifAtmospheric 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
6
Corcos, Milena. "Processes affecting cirrus clouds life cycle at the tropical tropopause layer : contributions from the Stratéole-2 campaigns". Electronic Thesis or Diss., Sorbonne université, 2023. http://www.theses.fr/2023SORUS119.
Abstract (sommario):
Cette thèse s'intéresse à l'observation des ondes de gravité dans la tropopause tropicale (TTL pour tropical tropopause layer) par ballons pressurisés, et à leur impact sur les cirrus. Dans un premier temps, l'activité des ondes de gravité est quantifiée grâce aux observations in-situ des ballons pressurisés des deux premières campagnes de Stratéole-2. Le lien entre la convection profonde tropicale et l'activité des ondes est démontré à l'échelle synoptique par la diminution de l'amplitude des ondes avec la distance aux cellules convectives. La variabilité géographique de l'activité des ondes de gravité, de leur intermittence, ainsi que leur variabilité inter-annuelle sont également évaluées. Dans un second temps, l'impact des ondes de gravité sur les cirrus est étudié grâce à la combinaison des mesures lagrangiennes des fluctuations de températures avec un modèle de microphysique prenant en compte la nucléation homogène, la croissance et la sédimentation des cristaux de glace, ainsi qu'une représentation très simplifiée du cisaillement de vent. L'impact des ondes sur la population de glace et les conséquences sur l'évolution des cirrus ainsi que sur leur capacité à assécher les masses d'air lors de l'ascension dans la TTL est quantifié. Les résultats sont comparés avec les observations de la campagne ATTREX dans la TTL au-dessus de l'océan Pacifique, et démontrent l'importance de la représentation réaliste des ondes dans les simulations de microphysique. Enfin, une étude de sensibilité à l'amplitude des ondes de gravité est discutée pour la structure des cirrus et la population de cristauxThis thesis focuses on the observation of gravity waves at the tropical tropopause layer (TTL) by superpressure balloons, and their impact on cirrus clouds. First, the gravity wave activity is quantified thanks to in-situ observations of superpressure balloons from the first two Stratéole-2 campaigns. The link between tropical deep convection and wave activity is demonstrated at a synoptic scale by the decrease of wave amplitude with distance to convective cell. The geographical variability of gravity wave activity, its intermittency, as well as its interannual variability are also studied. In a second step, the impact of gravity waves on cirrus clouds is studied thanks to the combination of Lagrangian measurements of temperature fluctuations with a microphysics model representing the homogeneous nucleation, growth and sedimentation of ice crystals, as well as a very simplified representation of the wind shear. The impact of the waves on ice crystals population and the consequences on the evolution of cirrus clouds and their capacity to dehydrate the air masses during the ascent in the TTL is quantified. The results are compared with observations from the ATTREX campaign in the TTL over the Pacific Ocean, and demonstrate the importance of realistic representation of waves in microphysics simulations. Finally, a sensitivity study to the amplitude of gravity waves is discussed for the cirrus structure and ice crystal population
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Wang, Tao. "Analysis of the Tropical Tropopause Layer Cirrus in CALIPSO and MLS Data - A Water Perspective". Thesis, 2011. http://hdl.handle.net/1969.1/ETD-TAMU-2011-05-9273.
Abstract (sommario):
Two mechanisms appear to be primarily responsible for the formation of cirrus clouds in Tropical Tropopause Layer (TTL): detrainment from deep convective anvils and in situ initiation. Here we propose to identify TTL cirrus clouds by analyzing water content measurements from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and Aura Microwave Limb Sounder (MLS). Using ice water content (IWC) and water vapor (H2O) abundances we identify TTL cirrus clouds that contain too much ice to have been formed in situ — and therefore must be of convective origin. We use two methods to infer amounts of water vapor available for in situ formation. Clouds with IWC greater than this threshold are categorized as being of convective origin; clouds with IWC below the threshold are ambiguous — they could either form from in situ or still be of convective origin. Applying the thresholds from December 2008 to November 2009, we found that at least 19.2% of tropical cirrus were definitively of convective origin at the tropopause (375 K) during boreal winter. At each level, we found three maxima in the occurrence of convective cirrus: western Pacific, equatorial Africa, and South America. Averaged over the entire tropics (30oS to 30oN), we found convective cirrus occurs more frequently in boreal winter and less frequently in boreal summer, basically following the a decreasing trend from DJF, MAM, SON, to JJA. During boreal summer, we found that only 4.6% of tropical cirrus come from convection. Sensitivity tests show that the thresholds derived at 390 K have the largest uncertainty. At lower levels, especially 375 K, our thresholds are robust.