scholarly journals In situ observation of new particle formation (NPF) in the tropical tropopause layer of the 2017 Asian monsoon anticyclone – Part 1: Summary of StratoClim results

2021 ◽  
Vol 21 (15) ◽  
pp. 11689-11722
Author(s):  
Ralf Weigel ◽  
Christoph Mahnke ◽  
Manuel Baumgartner ◽  
Antonis Dragoneas ◽  
Bärbel Vogel ◽  
...  
Keyword(s):  
Asian Monsoon ◽  
Particle Formation ◽  
In Situ Observation ◽  
Aerosol Layer ◽  
New Particle Formation ◽  
Tropical Tropopause Layer ◽  
Temperature Anomalies ◽  
Nucleation Mode ◽  
Tropical Tropopause

Abstract. During the monsoon season of the year 2017 the airborne StratoClim mission took place in Kathmandu, Nepal, with eight mission flights of the M-55 Geophysica in the upper troposphere–lower stratosphere (UTLS) of the Asian monsoon anticyclone (AMA) over northern India, Nepal, and Bangladesh. More than 100 events of new particle formation (NPF) were observed. In total, more than 2 h of flight time was spent under NPF conditions as indicated by the abundant presence of nucleation-mode aerosols, i.e. with particle diameters dp smaller than 15 nm, which were detected in situ by means of condensation nuclei counting techniques. Mixing ratios of nucleation-mode particles (nnm) of up to ∼ 50 000 mg−1 were measured at heights of 15–16 km (θ ≈ 370 K). NPF was most frequently observed at ∼ 12–16 km altitude (θ ≈ 355–380 K) and mainly below the tropopause. Resulting nnm remained elevated (∼ 300–2000 mg−1) up to altitudes of ∼ 17.5 km (θ ≈ 400 K), while under NPF conditions the fraction (f) of sub-micrometre-sized non-volatile residues (dp > 10 nm) remained below 50 %. At ∼ 12–14 km (θ ≈ 355–365 K) the minimum of f (< 15 %) was found, and underneath, the median f generally remains below 25 %. The persistence of particles at nucleation-mode sizes is limited to a few hours, mainly due to coagulation, as demonstrated by a numerical simulation. The frequency of NPF events observed during StratoClim 2017 underlines the importance of the AMA as a source region for UTLS aerosols and for the formation and maintenance of the Asian tropopause aerosol layer (ATAL). The observed abundance of NPF-produced nucleation-mode particles within the AMA is not unambiguously attributable to (a) specific source regions in the boundary layer (according to backward trajectory analyses), or (b) the direct supply with precursor material by convective updraught (from correlations of NPF with carbon monoxide), or (c) the recent release of NPF-capable material from the convective outflow (according to air mass transport times in the tropical tropopause layer, TTL). Temperature anomalies with ΔT of 2 K (peak-to-peak amplitude), as observed at a horizontal wavelength of ∼ 70–100 km during a level flight of several hours, match with NPF detections and represent an additional mechanism for local increases in supersaturation of the NPF precursors. Effective precursor supply and widely distributed temperature anomalies within the AMA can explain the higher frequency of intense NPF observed during StratoClim 2017 than all previous NPF detections with COPAS (COndensation PArticle counting System) at TTL levels over Brazil, northern Australia, or West Africa.

scholarly journals In situ observation of new particle formation (NPF) in the tropical tropopause layer of the 2017 Asian monsoon anticyclone – Part 2: NPF inside ice clouds

2021 ◽  
Vol 21 (17) ◽  
pp. 13455-13481 ◽  
Author(s):  
Ralf Weigel ◽  
Christoph Mahnke ◽  
Manuel Baumgartner ◽  
Martina Krämer ◽  
Peter Spichtinger ◽  
...  
Keyword(s):  
Asian Monsoon ◽  
Deep Convection ◽  
Particle Formation ◽  
In Situ Observation ◽  
New Particle Formation ◽  
Nucleation Mode ◽  
Ice Particles ◽  
Cloud Ice ◽  
The Impact

Abstract. From 27 July to 10 August 2017, the airborne StratoClim mission took place in Kathmandu, Nepal, where eight mission flights were conducted with the M-55 Geophysica up to altitudes of 20 km. New particle formation (NPF) was identified by the abundant presence of nucleation-mode aerosols, with particle diameters dp smaller than 15 nm, which were in-situ-detected by means of condensation nuclei (CN) counter techniques. NPF fields in clear skies as well as in the presence of cloud ice particles (dp > 3 µm) were encountered at upper troposphere–lowermost stratosphere (UTLS) levels and within the Asian monsoon anticyclone (AMA). NPF-generated nucleation-mode particles in elevated concentrations (Nnm) were frequently found together with cloud ice (in number concentrations Nice of up to 3 cm−3) at heights between ∼ 11 and 16 km. From a total measurement time of ∼ 22.5 h above 10 km altitude, in-cloud NPF was in sum detected over ∼ 1.3 h (∼ 50 % of all NPF records throughout StratoClim). Maximum Nnm of up to ∼ 11 000 cm−3 was detected coincidently with intermediate ice particle concentrations Nice of 0.05–0.1 cm−3 at comparatively moderate carbon monoxide (CO) contents of ∼ 90–100 nmol mol−1. Neither under clear-sky nor during in-cloud NPF do the highest Nnm concentrations correlate with the highest CO mixing ratios, suggesting that an elevated pollutant load is not a prerequisite for NPF. Under clear-air conditions, NPF with elevated Nnm (> 8000 cm−3) occurred slightly less often than within clouds. In the presence of cloud ice, NPF with Nnm between 1500–4000 cm−3 was observed about twice as often as under clear-air conditions. NPF was not found when ice water contents exceeded 1000 µmol mol−1 in very cold air (< 195 K) at tropopause levels. This indicates a reduction in NPF once deep convection is prevalent together with the presence of mainly liquid-origin ice particles. Within in situ cirrus near the cold point tropopause, recent NPF or intense events with mixing ration nnm larger than 5000 mg−1 were observed only in about 6 % of the in-cloud NPF data. In determining whether the cloud-internal NPF is attenuated or prevented by the microphysical properties of cloud elements, the integral radius (IR) of the ice cloud population turned out to be indicative. Neither the number of ice particles nor the free distance between the ice particles is clearly related to the NPF rate detected. While the increase in ice particles' mass per time dmdt is proportional to the IR and mainly due to the condensation of water vapour, additional condensation of NPF precursors proceeds at the expense of the NPF rate as the precursor's saturation ratio declines. Numerical simulations show the impact of the IR on the supersaturation of a condensable vapour, such as sulfuric acid, and furthermore illustrate that the IR of the cloud ice determines the effective limitation of NPF rates.

scholarly journals New particle formation inside ice clouds: In-situ observations in the tropical tropopause layer of the 2017 Asian Monsoon Anticyclone

2021 ◽  
Author(s):  
Ralf Weigel ◽  
Christoph Mahnke ◽  
Manuel Baumgartner ◽  
Martina Krämer ◽  
Peter Spichtinger ◽  
...  
Keyword(s):  
Ultrafine Particles ◽  
Asian Monsoon ◽  
Particle Formation ◽  
New Particle Formation ◽  
Mixing Ratios ◽  
Microphysical Properties ◽  
Tropical Tropopause ◽  
Ice Particles ◽  
Cloud Ice

Abstract. From 27 July to 10 August 2017 the airborne StratoClim mission took place in Kathmandu, Nepal where eight mission flights were conducted with the M-55 Geophysica up to altitudes of 20 km. New Particle Formation (NPF) was identified by the abundant presence of ultrafine aerosols, with particle diameters dp smaller than 15 nm, which were in-situ detected by means of condensation nuclei counting techniques. NPF fields in clear-skies as well as in the presence of cloud ice particles (dp > 3 µm) were encountered at upper troposphere/lowermost stratosphere (UT/LS) levels and within the Asian Monsoon Anticyclone (AMA). NPF-generated ultrafine particles in elevated concentrations (Nuf) were frequently found together with cloud ice (in number concentrations Nice of up to 3 cm−3) at heights between ~ 11 km and 16 km. From a total measurement time of ~ 22.5 hours above 10 km altitude, in-cloud NPF was in sum detected over ~ 1.3 hours (~ 50 % of all NPF records throughout StratoClim). Maximum Nuf of up to ~ 11000 cm−3 were detected coincidently with intermediate ice particle concentrations Nice of 0.05–0.1 cm−3 at comparatively moderate carbon monoxide (CO) contents of ~ 90–100 nmol mol−1. Neither under clear-sky nor during in-cloud NPF do the highest Nuf concentrations correlate with the highest CO mixing ratios, suggesting that an elevated pollutant load is not a prerequisite for NPF. Under clear-air conditions, NPF with elevated Nuf (> 8000 cm−3) occurred slightly less often than within clouds. In the presence of cloud ice, NPF with Nuf between 1500–4000 cm−3 were observed about twice as often as under clear air conditions. When ice water contents exceeded 1000 µmol mol−1 in very cold air ( 5000 mg−1) were rarely observed (~ 6 % of in-cloud NPF data). For specifying the constraining mechanisms for NPF possibly imposed by the microphysical properties of the cloud elements, the integral radius (IR) of the ice cloud population was identified as the most practicable indicator. Neither of both, the number of ice particles or the free distance between the ice particles, is clearly related to the NPF-rate detected. The results of a numerical simulation indicates how the IR affects the supersaturation of a condensable vapour, such as sulphuric acid, and that IR determines the effective limitation of NPF rates due to cloud ice.

scholarly journals In-Situ observation of New Particle Formation in the upper troposphere/lower stratosphere of the Asian Monsoon Anticyclone

2020 ◽  
Author(s):  
Ralf Weigel ◽  
Christoph Mahnke ◽  
Manuel Baumgartner ◽  
Antonis Dragoneas ◽  
Bärbel Vogel ◽  
...  
Keyword(s):  
Ultrafine Particles ◽  
Asian Monsoon ◽  
Lower Stratosphere ◽  
Monsoon Season ◽  
Particle Formation ◽  
In Situ Observation ◽  
New Particle Formation ◽  
Upper Troposphere ◽  
Mixing Ratios

Abstract. During the monsoon season of the year 2017 the airborne StratoClim mission took place in Kathmandu, Nepal with eight mission flights of the M-55 Geophysica in the upper troposphere/lower stratosphere (UT/LS) of the Asian Monsoon Anticyclone (AMA) over northern India, Nepal and Bangladesh. More than hundred events of New Particle Formation (NPF) were observed. In total, more than two hours of flight time were spent under NPF conditions as indicated by the abundant presence of ultrafine aerosols, i.e. with particle diameters dp smaller than 15 nm, which were in-situ detected by means of condensation nuclei counting techniques. Mixing ratios of ultrafine particles (nuf) of up to ~ 50000 mg−1 were measured at heights of 15–16 km (θ ≈ 370 K). NPF was most frequently observed at ~ 12–16 km altitude (θ ≈ 355–380 K) and mainly below the tropopause , but nuf remained elevated (~ 300–2000 mg−1) up to altitudes of ~ 17.5 km (θ ≈ 400 K) while under NPF conditions the fraction (f) of submicrometre-sized non-volatile particle residues (dp > 10 nm) remained below 50 %. At ~ 12–14 km (θ ≈ 355–365 K) the minimum of f (

scholarly journals Characterization of satellite based proxies for estimating nucleation mode particles over South Africa

2014 ◽  
Vol 14 (18) ◽  
pp. 25825-25867
Author(s):  
A.-M. Sundström ◽  
A. Nikandrova ◽  
K. Atlaskina ◽  
T. Nieminen ◽  
V. Vakkari ◽  
...  
Keyword(s):  
South Africa ◽  
Industrial Area ◽  
Particle Formation ◽  
Point Sources ◽  
New Particle Formation ◽  
Factors Affecting ◽  
Nucleation Mode ◽  
Sink Term ◽  
Major Factors

Abstract. In this work satellite observations from the NASA's A-Train constellation were used to derive the values of primary emission and regional nucleation proxies over South Africa to estimate the potential for new particle formation. As derived in Kulmala et al. (2011), the satellite based proxies consist of source terms (NO2, SO2 and UV-B radiation), and a sink term describing the pre-existing aerosols. The first goal of this work was to study in detail the use of satellite aerosol optical depth (AOD) as a substitute to the in situ based condensation sink (CS). One of the major factors affecting the agreement of CS and AOD was the elevated aerosol layers that increased the value of column integrated AOD but not affected the in situ CS. However, when the AOD in the proxy sink was replaced by an estimate from linear bivariate fit between AOD and CS, the agreement with the actual nucleation mode number concentration improved somewhat. The second goal of the work was to estimate how well the satellite based proxies can predict the potential for new particle formation. For each proxy the highest potential for new particle formation were observed over the Highveld industrial area, where the emissions were high but the sink due to pre-existing aerosols was relatively low. Best agreement between the satellite and in situ based proxies were obtained for NO2/AOD and UV-B/AOD2, whereas proxies including SO2 in the source term had lower correlation. Even though the OMI SO2 boundary layer product showed reasonable spatial pattern and detected the major sources over the study area, some of the known minor point sources were not detected. When defining the satellite proxies only for days when new particle formation event was observed, it was seen that for all the satellite based proxies the event day medians were higher than the entire measurement period median.

scholarly journals In situ observations of new particle formation in the tropical upper troposphere: the role of clouds and the nucleation mechanism

2011 ◽  
Vol 11 (18) ◽  
pp. 9983-10010 ◽  
Author(s):  
R. Weigel ◽  
S. Borrmann ◽  
J. Kazil ◽  
A. Minikin ◽  
A. Stohl ◽  
...  
Keyword(s):  
South America ◽  
West Africa ◽  
Central America ◽  
Particle Formation ◽  
Tropical Convection ◽  
New Particle Formation ◽  
Upper Troposphere ◽  
Nucleation Mode ◽  
In Situ Observations

Abstract. New particle formation (NPF), which generates nucleation mode aerosol, was observed in the tropical Upper Troposphere (UT) and Tropical Tropopause Layer (TTL) by in situ airborne measurements over South America (January–March 2005), Australia (November–December 2005), West Africa (August 2006) and Central America (2004–2007). Particularly intense NPF was found at the bottom of the TTL. Measurements with a set of condensation particle counters (CPCs) with different dp50 (50% lower size detection efficiency diameter or "cut-off diameter") were conducted on board the M-55 Geophysica in the altitude range of 12.0–20.5 km and on board the DLR Falcon-20 at up to 11.5 km altitude. On board the NASA WB-57F size distributions were measured over Central America in the 4 to 1000 nm diameter range with a system of nucleation mode aerosol spectrometers. Nucleation mode particle concentrations (NNM) were derived from these measurements which allow for identifying many NPF events with NNM in the range of thousands of particles per cm3. Over Australia and West Africa, we identified NPF in the outflow of tropical convection, in particular of a Mesoscale Convective System (MCS). Newly formed particles with NNM > 1000 cm−3 were found to coexist with ice cloud particles (dp > 2 μm) as long as cloud particle concentrations remained below 2 cm−3. The occurrence of NPF within the upper troposphere and the TTL was generally confined within 340 K to 380 K potential temperature, but NPF was of particular strength between 350 K and 370 K (i.e. ~1–4 km below the cold point tropopause). Analyses of the aerosol volatility (at 250 °C) show that in the TTL on average 75–90% of the particles were volatile, compared to typically only 50% in the extra-tropical UT, indicative for the particles to mainly consist of H2SO4-H2O and possibly organic compounds. Along two flight segments over Central and South America (24 February 2005 and 7 August 2006, at 12.5 km altitude) in cloud free air, above thin cirrus, particularly high NNM were observed. Recent lifting had influenced the probed air masses, and NNM reached up to 16 000 particles cm−3 (ambient concentration). A sensitivity study using an aerosol model, which includes neutral and ion induced nucleation processes, simulates NNM in reasonable agreement with the in situ observations of clear-air NPF. Based on new, stringent multi-CPC criteria, our measurements corroborate the hypothesis that the tropical UT and the TTL are regions supplying freshly nucleated particles. Our findings narrow the altitude of the main source region to the bottom TTL, i.e. to the level of main tropical convection outflow, and, by means of measurements of carbon monoxide, they indicate the importance of anthropogenic emissions in NPF. After growth and/or coalescence the nucleation mode particles may act as cloud condensation nuclei in the tropical UT, or, upon ascent into the stratosphere, contribute to maintain the stratospheric background aerosol.

scholarly journals Iodine speciation and size distribution in ambient aerosols at a coastal new particle formation hotspot in China

2019 ◽  
Vol 19 (6) ◽  
pp. 4025-4039 ◽  
Author(s):  
Huan Yu ◽  
Lili Ren ◽  
Xiangpeng Huang ◽  
Mingjie Xie ◽  
Jun He ◽  
...  
Keyword(s):  
Particle Formation ◽  
Coastal Areas ◽  
Aerosol Sample ◽  
Size Distributions ◽  
New Particle Formation ◽  
Nucleation Mode ◽  
Iodine Species ◽  
Organic Iodine ◽  
Iodine Compounds ◽  
Iodine Speciation

Abstract. Intense new particle formation (NPF) events were observed in the coastal atmosphere during algae growth and farming season at Xiangshan gulf of the east China coast. High nucleation-mode iodine concentrations measured by ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF-MS) confirmed that the NPF events were induced by iodine species. Our study provides important information on iodine speciation, size distributions, and its role in NPF in the context of heavy air pollution in China's coastal areas. For the first time, we identified 5 inorganic iodine species, 45 organic iodine compounds (35 molecular formulas), and a group of iodide–organic adducts in aerosols. The concentrations and size distributions of iodine species down to 10 nm were measured during the iodine-induced NPF, continental NPF, and non-NPF days at the coastal site and compared to those at an inland site. The iodine in the above four aerosol sample types were characterized by iodate, aromatic iodine compounds, iodoacetic acid or iodopropenoic acid, and iodide–organic adducts, respectively. Iodide and organic iodine compounds were found in the nucleation-mode particles; however, it is still not clear whether they contributed to nucleation or just new particle growth. Wild algae, as well as farmed algae, could be an important NPF source in China's coastal areas.

scholarly journals Tracer measurements in the tropical tropopause layer during the AMMA/SCOUT-O3 aircraft campaign

2010 ◽  
Vol 10 (8) ◽  
pp. 3615-3627 ◽  
Author(s):  
C. D. Homan ◽  
C. M. Volk ◽  
A. C. Kuhn ◽  
A. Werner ◽  
J. Baehr ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Deep Convection ◽  
Transport Processes ◽  
Gradual Transition ◽  
Tropical Tropopause Layer ◽  
Mixing Ratios ◽  
Tropical Tropopause ◽  
Multidisciplinary Analysis ◽  
The Tropics

Abstract. We present airborne in situ measurements made during the AMMA (African Monsoon Multidisciplinary Analysis)/SCOUT-O3 campaign between 31 July and 17 August 2006 on board the M55 Geophysica aircraft, based in Ouagadougou, Burkina Faso. CO2 and N2O were measured with the High Altitude Gas Analyzer (HAGAR), CO was measured with the Cryogenically Operated Laser Diode (COLD) instrument, and O3 with the Fast Ozone ANalyzer (FOZAN). We analyse the data obtained during five local flights to study the dominant transport processes controlling the tropical tropopause layer (TTL, here ~350–375 K) and lower stratosphere above West-Africa: deep convection up to the level of main convective outflow, overshooting of deep convection, and horizontal inmixing across the subtropical tropopause. Besides, we examine the morphology of the stratospheric subtropical barrier. Except for the flight of 13 August, distinct minima in CO2 mixing ratios indicate convective outflow of boundary layer air in the TTL. The CO2 profiles show that the level of main convective outflow was mostly located at potential temperatures between 350 and 360 K, and for 11 August reached up to 370 K. While the CO2 minima indicate quite significant convective influence, the O3 profiles suggest that the observed convective signatures were mostly not fresh, but of older origin (several days or more). When compared with the mean O3 profile measured during a previous campaign over Darwin in November 2005, the O3 minimum at the main convective outflow level was less pronounced over Ouagadougou. Furthermore O3 mixing ratios were much higher throughout the whole TTL and, unlike over Darwin, rarely showed low values observed in the regional boundary layer. Signatures of irreversible mixing following overshooting of convective air were scarce in the tracer data. Some small signatures indicative of this process were found in CO2 profiles between 390 and 410 K during the flights of 4 and 8 August, and in CO data at 410 K on 7 August. However, the absence of expected corresponding signatures in other tracer data makes this evidence inconclusive, and overall there is little indication from the observations that overshooting convection has a profound impact on gas-phase tracer TTL composition during AMMA. We find the amount of photochemically aged air isentropically mixed into the TTL across the subtropical tropopause to be not significant. Using the N2O observations we estimate the fraction of aged extratropical stratospheric air in the TTL to be 0.0±0.1 up to 370 K during the local flights. Above the TTL this fraction increases to 0.3±0.1 at 390 K. The subtropical barrier, as indicated by the slope of the correlation between N2O and O3 between 415 and 490 K, does not appear as a sharp border between the tropics and extratropics, but rather as a gradual transition region between 10° N and 25° N where isentropic mixing between these two regions may occur.

scholarly journals Direct observation of molecular clusters and nucleation mode particles in the Amazon

2017 ◽  
Author(s):  
Daniela Wimmer ◽  
Stephany Buenrostro Mazon ◽  
Hanna Elina Manninen ◽  
Juha Kangasluoma ◽  
Alessandro Franchin ◽  
...  
Keyword(s):  
Growth Rates ◽  
Ground Level ◽  
Particle Formation ◽  
New Particle Formation ◽  
Wet Season ◽  
Ion Concentrations ◽  
Nucleation Mode ◽  
Rain Events ◽  
20 Nm ◽  
Spectrometer Data

Abstract. We investigated atmospheric new particle formation (NPF) in the Amazon rainforest using direct measurement methods. The occurrence of NPF on ground level in the Amazon region has not been observed previously in pristine conditions. Our measurements extended to two field sites and two tropical seasons (wet and dry). We measured the variability of air ion concentrations (0.8–20 nm) with an ion spectrometer between 2011 and 2014 at the T0t site and between February and October 2014 at the GoAmazon 2014/5 T3 site. The main difference between the two sites is their geographical location. Both sites are influenced by the Manaus pollution plume yet with different frequencies. T0t is reached by the pollution about 1 day in 7, where the T3 site is about 15 % of the time affected by Manaus. The sampling was performed at ground level at both sites. At T0t the instrumentation was located inside the rainforest, whereas the T3 site was an open pasture site. T0t site is mostly parallel wind to Manaus, whereas T3 site is downwind of Manaus. No NPF events were observed inside the rainforest canopy (site T0t) at ground level during the period Sep 2011–Jan 2014. However, rain-induced ion and particle bursts (hereafter, “rain events”) occurred frequently (306/529 days) at T0t throughout the year but most frequently between January and April (wet season). Rain events increased nucleation mode (2–20 nm) particle and ion concentrations on the order of 104 cm−3. We observed 8 NPF events at the pasture site during the wet season. We calculated the growth rates (GR) and formation rates of neutral particles and ions for the size ranges 2–3 nm, 3–7 nm and 7–20 nm using the ion spectrometer data. One explanation for the absence of new particle formation events at the T0t site could be a combination of cleaner airmasses and the rainforest canopy acting as an ‘umbrella’, hindering the mixing of the airmasses down to the measurement height. Neutral particle growth rates in the 3–7 nm regime showed two phenomena. Growth rates were either about 2 nm h−1 or about 14 nm h−1. There was no clear difference in the sulfuric acid concentrations for NPF days vs days without NPF. Back trajectory calculations show different airmass origin for the NPF days compared to non NPF days.

scholarly journals Evidence of horizontal and vertical transport of water in the Southern Hemisphere tropical tropopause layer (TTL) from high-resolution balloon observations

2016 ◽  
Vol 16 (18) ◽  
pp. 12273-12286 ◽  
Author(s):  
Sergey M. Khaykin ◽  
Jean-Pierre Pommereau ◽  
Emmanuel D. Riviere ◽  
Gerhard Held ◽  
Felix Ploeger ◽  
...  
Keyword(s):  
High Resolution ◽  
Water Vapour ◽  
Southern Hemisphere ◽  
Water Budget ◽  
Lower Stratosphere ◽  
Vertical Profiles ◽  
Tropical Tropopause Layer ◽  
Horizontal Transport ◽  
Tropical Tropopause

Abstract. High-resolution in situ balloon measurements of water vapour, aerosol, methane and temperature in the upper tropical tropopause layer (TTL) and lower stratosphere are used to evaluate the processes affecting the stratospheric water budget: horizontal transport (in-mixing) and hydration by cross-tropopause overshooting updrafts. The obtained in situ evidence of these phenomena are analysed using satellite observations by Aura MLS (Microwave Limb Sounder) and CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) together with trajectory and transport modelling performed using CLaMS (Chemical Lagrangian Model of the Stratosphere) and HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) model. Balloon soundings were conducted during March 2012 in Bauru, Brazil (22.3° S) in the frame of the TRO-Pico campaign for studying the impact of convective overshooting on the stratospheric water budget. The balloon payloads included two stratospheric hygrometers: FLASH-B (Fluorescence Lyman-Alpha Stratospheric Hygrometer for Balloon) and Pico-SDLA instrument as well as COBALD (Compact Optical Backscatter Aerosol Detector) sondes, complemented by Vaisala RS92 radiosondes. Water vapour vertical profiles obtained independently by the two stratospheric hygrometers are in excellent agreement, ensuring credibility of the vertical structures observed. A signature of in-mixing is inferred from a series of vertical profiles, showing coincident enhancements in water vapour (of up to 0.5 ppmv) and aerosol at the 425 K (18.5 km) level. Trajectory analysis unambiguously links these features to intrusions from the Southern Hemisphere extratropical stratosphere, containing more water and aerosol, as demonstrated by MLS and CALIPSO global observations. The in-mixing is successfully reproduced by CLaMS simulations, showing a relatively moist filament extending to 20° S. A signature of local cross-tropopause transport of water is observed in a particular sounding, performed on a convective day and revealing water vapour enhancements of up to 0.6 ppmv as high as the 404 K (17.8 km) level. These are shown to originate from convective overshoots upwind detected by an S-band weather radar operating locally in Bauru. The accurate in situ observations uncover two independent moisture pathways into the tropical lower stratosphere, which are hardly detectable by space-borne sounders. We argue that the moistening by horizontal transport is limited by the weak meridional gradients of water, whereas the fast convective cross-tropopause transport, largely missed by global models, can have a substantial effect, at least at a regional scale.

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