BATAL: The Balloon Measurement Campaigns of the Asian Tropopause Aerosol Layer
Jean‐Paul VernierT. D. FairlieTerry DeshlerM. Venkat RatnamHarish GadhaviB. Suneel KumarM. NatarajanAmit Kumar PanditSivan Thankamani Akhil RajA. Hemanth KumarA. JayaramanA. K. SinghNeeraj RastogiP. R. SinhaSarvan KumarS. TiwariTobias WegnerNoël BakerDamien VignellesGeorgiy StenchikovIllia ShevchenkoJ. SmithKristopher M. BedkaAmit P. KesarkarVikas SinghJyoti BhateV. RavikiranM. Durga RaoSaginela Ravindra BabuAnil PatelHazel VernierFrank G. WienholdHongyu LiuTravis N. KneppL. W. ThomasonJ. H. CrawfordLuke D. ZiembaJohn R. MooreSuzanne CrumeyrolleMatthew A. WilliamsonGwenaël BerthetFabrice JégouJean‐Baptiste Renard
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Abstract We describe and show results from a series of field campaigns that used balloonborne instruments launched from India and Saudi Arabia during the summers 2014–17 to study the nature, formation, and impacts of the Asian Tropopause Aerosol Layer (ATAL). The campaign goals were to i) characterize the optical, physical, and chemical properties of the ATAL; ii) assess its impacts on water vapor and ozone; and iii) understand the role of convection in its formation. To address these objectives, we launched 68 balloons from four locations, one in Saudi Arabia and three in India, with payload weights ranging from 1.5 to 50 kg. We measured meteorological parameters; ozone; water vapor; and aerosol backscatter, concentration, volatility, and composition in the upper troposphere and lower stratosphere (UTLS) region. We found peaks in aerosol concentrations of up to 25 cm –3 for radii > 94 nm, associated with a scattering ratio at 940 nm of ∼1.9 near the cold-point tropopause. During medium-duration balloon flights near the tropopause, we collected aerosols and found, after offline ion chromatography analysis, the dominant presence of nitrate ions with a concentration of about 100 ng m –3 . Deep convection was found to influence aerosol loadings 1 km above the cold-point tropopause. The Balloon Measurements of the Asian Tropopause Aerosol Layer (BATAL) project will continue for the next 3–4 years, and the results gathered will be used to formulate a future National Aeronautics and Space Administration–Indian Space Research Organisation (NASA–ISRO) airborne campaign with NASA high-altitude aircraft.Keywords:
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Abstract. Large-scale cross-tropopause mass fluxes are diagnosed globally from 1979 to 1989 for Northern Hemisphere winter conditions (December, January, and February). Results of different methods of approaches with regard to the definition of the tropopause and the way to calculate the mass fluxes are compared and discussed. The general pattern of the mass exchange from the tropopause into the stratosphere and vice versa agrees fairly well when using different methods, but the absolute values can differ up to 100%. An inspection of the temporal development of the mass fluxes for solstice conditions indicates a complex picture. Whereas a permanent significant downward flux from the stratosphere into the troposphere is detected for latitude regions nearly between 25°N and 40°N and between 30°S and 50°S (initiated by the poleward branches of the Hadley cells), a non-uniform behaviour is observed at higher latitude bands. Periods of strong mass exchange from the troposphere into the stratosphere are disrupted by periods of an opposite mass exchange. A comparison of the stratoshere-troposphere (ST) exchange with the exchange at higher altitudes through surfaces, quasi-parallel to the tropopause, excludes a general connection. Only a few strong upward directed ST mass exchange events have counterparts at higher altitudes. The composition of the stratosphere may be influenced directly by the ST exchange only in a thin layer above the tropopause.
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Aircraft measurements of aerosol particles and trace gases were performed in the upper free troposphere and lower stratosphere during the Stratosphere and Troposphere Experiment by Aircraft Measurements (STREAM‐96) campaign from Shannon airport, Ireland. During one measurement flight, ultrafine particle number densities up to 10 4 cm −3 (STP) were observed in the lowermost stratosphere. Concurrent with these very high number densities of ultrafine particles, high accumulation mode particle number densities were observed over the same geographical location in the free troposphere, which were attributed to convective transport in the troposphere. The observations suggest that adiabatic cooling of the stratospheric air, as a result of the convective transport in the troposphere that lifted the tropopause and the air in the lowermost stratosphere, was responsible for triggering the formation of new particles. However, also aircraft emissions could have contributed to the enhancement in ultrafine particles.
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The behavior of air parcel transport between hemispheres and between the troposphere and stratosphere is studied by directly calculating 180-day trajectories based on observed data. It is shown that air parcels from the extra-tropical troposphere of one hemisphere are transported to the other hemisphere through the upper troposphere. The estimated inter-heimispheric exchange time is about one year. The main pathway from the troposphere to the stratosphere is the tropical tropopause. The flow from the equatorial lower stratosphere branches off in two directions, i, e., one is the return flow to the troposphere through the sub-tropical tropopause gaps and the other is the poleward flow in the lower stratosphere.
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The tropopause is the boundary between the troposphere and the stratosphere, so its height determines the nature of processes in the atmosphere and depends on them. The criterion for determining the height of the tropopause is a decrease in the vertical temperature gradient in a layer above 5 km and at least 2 km thick. Consequently, the uncertainty in determining the height of the section between the troposphere and the stratosphere is 2 km or more. In addition, the temperature profile changes due to the influence of many reasons, so sometimes the height of the tropopause cannot even be determined. The optical properties of air in the troposphere and stratosphere differ, which makes it possible to measure the height of the section with high accuracy using a radiosonde with an optical sensor. The launches of radiosondes with optical sensors made it possible to measure the height of the tropopause by changing the attenuation coefficient of visible light. It turned out that the lower edge of the tropopause corresponds to a sharp change in the attenuation coefficient. The repeatability of the results was confirmed by the simultaneous launch of radiosondes. The results of the work will be useful for the tasks of weather forecasting and climate research.
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The stratosphere‐troposphere (ST) mode operation of the Indian mesosphere‐stratosphere‐troposphere (MST) radar provided evidence of multiple stable layer structures near the tropopause and also of its “weakening” during late night hours on several occasions. Mass exchange can take place between the troposphere and the stratosphere during periods of such weakening. To examine whether there is any transport of ozone from the stratosphere to the troposphere at the time of tropopause weakening at tropical latitudes, simultaneous observations were carried out using the Indian MST radar located at Gadanki (13.5°N, 79.2°E), now fully operational in MST mode, and ozonesonde flights from Trivandrum (8.9°N, 76.6°E). Four campaigns of simultaneous observations were conducted during January 3–8, November 9–16, and December 5–10, 1994, and June 7–24, 1995. The results show occurrence of the tropopause weakening several times during January 3–8, November 9–16, and December 5–10, 1994. Simultaneous observations of ozone profiles, particularly on January 7–8, November 10 and 16, and December 7–8, 1994, the days of tropopause weakening, show evidence of a decrease in stratospheric ozone and a corresponding increase in tropospheric ozone after this event, the total ozone remaining essentially constant on these days with respect to other days. Tropopause weakening on January 4–5, 1994, however, does not show any considerable change in the ozone profiles. The results are presented here relating the degree of tropopause weakening to the extent of vertical mass exchange between the troposphere and the stratosphere. An effort has been made to examine the role of horizontal advection of ozone in increasing tropospheric ozone at the region of interest; the geographical distribution of tropospheric ozone residual (TOR) has been analyzed by the two data sets obtained independently from Meteor 3 total ozone mapping spectrometers (Meteor 3 TOMS) and the Upper Air Research Satellite (UARS). Simultaneously, the possibility of horizontal transport of ozone from the areas surrounding Tirupati and Trivandrum in increasing tropospheric ozone due to synoptic scale circulation has also been verified by close inspection of synoptic weather charts at 1000, 700, 500, and 300 hPa obtained from the National Center for Medium‐Range Weather Forecasting general circulation model at 0000 and 1200 UTC on January 7 and 0000 and 1200 UTC on January 8, 1994.
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Stratosphere-troposphere exchange (STE) and its effects on the stratospheric and tropospheric chemical compositions have been studied for the past two decades, but details on how mass is transported between the stratosphere and the troposphere are not well established. The goal of this study is to better describe global properties of cross tropopause trajectories, and to understand the processes related to transport of mass between the troposphere and the stratosphere. This understanding led us to build the simplest model which captures the most important properties of STE. To do this, nine-day extra-tropical stratosphere-troposphere exchange trajectories covering a period of 10 years, calculated using the ERA-15 re-analysis data, are investigated. The present study shows that the fraction of trajectories that reside in the stratosphere or in the troposphere does not depend on the direction of the exchange (stratosphere-to-troposphere transport, STT, or troposphere-to-stratosphere transport, TST). Trajectories are found to reside longer in the troposphere than in the stratosphere which suggests that they are driven down by asymmetric two-way motion. A random walk model is used to see whether this asymmetric transport is a result of a diffusive process. The transport of trajectories along isentropic coordinates is found to be compatible with a Brownian motion with higher probabilities to go downward. Since stratosphere-troposphere exchange reflects a differential motion of air masses and the tropopause, the potential temperature at the tropopause directly above or below the air mass is also investigated. The tropopause steps distributions are not stationary and they show some dynamical behaviors like the deformation of the tropopause at exchange time. Dispersion of trajectories in the atmosphere was furthermore investigated using several methods. They gave rise to three different transport mechanisms: diffusion, sub-diffusion and super-diffusion transports.%%%%Les echanges entre la stratosphere et la troposphere (STE) et leurs effets sur la composition chimique de la stratosphere et de la troposphere ont ete etudies intensivement, mais les details sur la maniere dont les masses d'air sont transportes entre la stratosphere et la troposphere ne sont pas bien etablis. Le but de cette etude est de decrire les proprietes globales des trajectoires qui traversent la tropopause, et de mieux comprendre les processus lies au transport de la matiere entre la troposphere et la stratosphere. Une fois ces details etablis, nous avons essaye de construire un modele simple qui capture les proprietes les plus importantes des STE. Pour ce faire, des trajectoires d'echanges entre la stratosphere et la troposphere (STE), couvrant les extra-tropiques durant une periode de 10 ans ont ete calculees en utilisant les donnees d'ERA-15. Dans cette etude on montre que la fraction de trajectoires qui resident dans la stratosphere ou dans la troposphere ne depend pas de la direction de l'echange (transport de la stratosphere a la …
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In this study, the authors focus on the cut-off low pressure systems (COLs) lingering over East Asia in late spring and early summer and quantify the two-way stratosphere–troposphere exchange (STE) by 3D trajectory integrations, achieved using a revised version of the UK Universities Global Atmospheric Modelling Programme Offline Trajectory Code (Version 3). By selecting 10 typical COLs and calculating the cross-tropopause air mass fluxes, it is found that stratosphere-to-troposphere transport (STT) fluxes exist in the center of COLs; and in the periphery of the COL center, troposphere-to-stratosphere transport (TST) fluxes and STT fluxes are distributed alternately. Net transport fluxes in COLs are from stratosphere to troposphere, and the magnitude is about 10−4 kg m−2 s−1. The ratio between the area-averaged STT and TST fluxes increases with increasing strength of the COLs. By adopting appropriate residence time, the spurious transports are effectively excluded. Finally, the authors compare the results with previous studies, and find that the cross-tropopause fluxes (CTFs) induced by COLs are about one to two orders of magnitude larger than global CTFs. COLs play a significant role in local, rapid air mass exchanges, although they may only be responsible for a fraction of the total STE.
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