Investigation of transport in the northern lowermost stratosphere between spring and fall using airborne in situ tracer measurements

2020 ◽  
Author(s):  
Andrea Rau ◽  
Valentin Lauther ◽  
Johannes Wintel ◽  
Emil Gehardt ◽  
Peter Hoor ◽  
...  
Keyword(s):  
Time Scales ◽  
Asian Monsoon ◽  
Lagrangian Model ◽  
Mixing Ratios ◽  
Tropical Tropopause ◽  
Research Aircraft ◽  
Transport And Mixing ◽  
The University

<p>Over the course of the summer, when the subtropical jet is weakest, quasi-isentropic transport of young air from the troposphere and the tropical tropopause layer into the northern hemisphere (NH) lowermost stratosphere (LMS) is increased resulting in a drastic change of LMS chemical composition between spring and fall. The focus of this work is on the role of different transport paths into the NH LMS, including outflow from the Asian Monsoon, and their associated time scales of transport and mixing.<br><br>We present and analyse in situ measurements of CO<sub>2</sub> and various long-lived tracers obtained during three recent aircraft campaigns encompassing over 40 research flights in the NH UTLS during winter/spring, summer, and fall. The POLSTRACC/GW-LCYCLE/SALSA campaign probed the northern high latitude LMS in winter/spring 2016, deploying the German research aircraft HALO from Kiruna (Sweden) and from Germany. The second campaign deployed the M55 Geophysica research aircraft in July/August 2017 from Kathmandu, Nepal, in the frame of the EU-funded project StratoClim (Stratospheric and upper tropospheric processes for better Climate predications) in order to probe in situ for the first time the inside of the Asian Monsoon anticyclone. Roughly two months later the WISE (Wave-driven ISentropic Exchange) campaign deployed again HALO from Shannon (Ireland) in September and October 2017 to investigate isentropic transport and mixing in the NH LMS.<br><br>The University of Wuppertal measured CO<sub>2</sub> and a suite of long-lived tracers on each aircraft. On the Geophysica, the measurements were made with the HAGAR (High Altitude Gas AnalyzeR) instrument. On HALO, a recently developed extended 5-channel version, HAGAR-V, was flown, which in addition measured a suite of short-lived tracers by GC coupled with a mass spectrometer. The University of Mainz measured N2O and CO on HALO using laser absorption techniques. For our analysis we use mixing ratios of CO<sub>2</sub>, SF<sub>6</sub>, CFC-11, CFC-12, and N<sub>2</sub>O.<br><br>Owing to their different lifetimes, tropospheric growth (for SF<sub>6</sub>) and a seasonal cycle (for CO<sub>2</sub>), the LMS distributions of these long-lived trace gases and their development between spring and fall contain key information about the origin and mean stratospheric age of LMS air as well as time scales of rapid isentropic transport and mixing. The analysis of tracer measurements is complemented by simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) providing information on age of air spectra and fractions of origin from specific surface regions, allowing in particular to assess the role of the Asian Monsoon in determining the composition of the NH LMS in fall.</p>

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 Annual cycle of ozone at and above the tropical tropopause: observations versus simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS)

2010 ◽  
Vol 10 (1) ◽  
pp. 121-132 ◽  
Author(s):  
P. Konopka ◽  
J.-U. Grooß ◽  
G. Günther ◽  
F. Ploeger ◽  
R. Pommrich ◽  
...  
Keyword(s):  
Annual Cycle ◽  
Potential Temperature ◽  
Early Spring ◽  
Lagrangian Model ◽  
Boreal Summer ◽  
Tropical Tropopause Layer ◽  
Mixing Ratios ◽  
Tropical Tropopause ◽  
In Situ Observations

Abstract. Multi-annual simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) were conducted to study the seasonality of O3 within the stratospheric part of the tropical tropopause layer (TTL), i.e. above θ=360 K potential temperature level. In agreement with satellite (HALOE) and in-situ observations (SHADOZ), CLaMS simulations show a pronounced annual cycle in O3, at and above θ=380 K, with the highest mixing ratios in the late boreal summer. Within the model, this cycle is driven by the seasonality of both upwelling and in-mixing. The latter process occurs through enhanced horizontal transport from the extratropics into the TTL that is mainly driven by the meridional, isentropic winds. The strongest in-mixing occurs during the late boreal summer from the Northern Hemisphere in the potential temperature range between 370 and 420 K. Complementary, the strongest upwelling occurs in winter reducing O3 to the lowest values in early spring. Both CLaMS simulations and Aura MLS O3 observations consistently show that enhanced in-mixing in summer is mainly driven by the Asian monsoon anticyclone.

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 Central role of nitric oxide in ozone production in the upper tropical troposphere over the Atlantic Ocean and western Africa

2021 ◽  
Vol 21 (10) ◽  
pp. 8195-8211
Author(s):  
Ivan Tadic ◽  
Clara M. Nussbaumer ◽  
Birger Bohn ◽  
Hartwig Harder ◽  
Daniel Marno ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Atlantic Ocean ◽  
General Circulation ◽  
Simulated Data ◽  
Ozone Production ◽  
Mixing Ratios ◽  
Western Africa ◽  
Tropical Troposphere

Abstract. Mechanisms of tropospheric ozone (O3) formation are generally well understood. However, studies reporting on net ozone production rates (NOPRs) directly derived from in situ observations are challenging and are sparse in number. To analyze the role of nitric oxide (NO) in net ozone production in the upper tropical troposphere above the Atlantic Ocean and western Africa, we present in situ trace gas observations obtained during the CAFE-Africa (Chemistry of the Atmosphere: Field Experiment in Africa) campaign in August and September 2018. The vertical profile of in situ measured NO along the flight tracks reveals lowest NO mixing ratios of less than 20 pptv between 2 and 8 km altitude and highest mixing ratios of 0.15–0.2 ppbv above 12 km altitude. Spatial distribution of tropospheric NO above 12 km altitude shows that the sporadically enhanced local mixing ratios (>0.4 ppbv) occur over western Africa, which we attribute to episodic lightning events. Measured O3 shows little variability in mixing ratios at 60–70 ppbv, with slightly decreasing and increasing tendencies towards the boundary layer and stratosphere, respectively. Concurrent measurements of CO, CH4, OH, HO2 and H2O enable calculations of NOPRs along the flight tracks and reveal net ozone destruction at −0.6 to −0.2 ppbv h−1 below 6 km altitude and balance of production and destruction around 7–8 km altitude. We report vertical average NOPRs of 0.2–0.4 ppbv h−1 above 12 km altitude with NOPRs occasionally larger than 0.5 ppbv h−1 over western Africa coincident with enhanced NO. We compare the observational results to simulated data retrieved from the general circulation model ECHAM/MESSy Atmospheric Chemistry (EMAC). Although the comparison of mean vertical profiles of NO and O3 indicates good agreement, local deviations between measured and modeled NO are substantial. The vertical tendencies in NOPRs calculated from simulated data largely reproduce those from in situ experimental data. However, the simulation results do not agree well with NOPRs over western Africa. Both measurements and simulations indicate that ozone formation in the upper tropical troposphere is NOx limited.

scholarly journals Origins and characterization of CO and O<sub>3</sub> in the African upper troposphere

2021 ◽  
Author(s):  
Victor Lannuque ◽  
Bastien Sauvage ◽  
Brice Barret ◽  
Hannah Clark ◽  
Gilles Athier ◽  
...  
Keyword(s):  
Wind Shear ◽  
Asian Monsoon ◽  
Shear Zones ◽  
Hadley Cell ◽  
Trade Winds ◽  
Air Masses ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
Hadley Cells

Abstract. Between December 2005 and 2013, the In-service Aircraft for a Global Observing System (IAGOS) program produced almost daily in situ measurements of CO and O3 between Europe and southern Africa. IAGOS data combined with measurements from the IASI instrument onboard the Metop-A satellite (2008–2013) are used to characterize meridional distributions and seasonality of CO and O3 in the African upper troposphere (UT). The FLEXPART particle dispersion model and the SOFT-IO model which combines the FLEXPART model with CO emission inventories are used to explore the sources and origins of the observed transects of CO and O3. We focus our analysis on two main seasons: December to March (DJFM) and June to October (JJASO). These seasons have been defined according to the position of Intertropical Convergence Zone (ITCZ), determined using in situ measurements from IAGOS. During both seasons, the UT CO meridional transects are characterized by maximum mixing ratios located 10° from the position of the ITCZ above the dry regions inside the hemisphere of the strongest Hadley cell (132 to 165 ppb at 0–5° N in DJFM and 128 to 149 ppb at 3–7° S in JJASO), and decreasing values south- and north-ward. The O3 meridional transects are characterized by mixing ratio minima of ~ 42–54 ppb at the ITCZ (10–16° S in DJFM and 5–8° N in JJASO) framed by local maxima (~ 53–71 ppb) coincident with the wind shear zones North and South of the ITCZ. O3 gradients are strongest in the hemisphere of the strongest Hadley cell. IASI UT O3 distributions in DJFM have revealed that the maxima are a part of a crescent-shaped O3 plume above the Atlantic Ocean around the Gulf of Guinea. CO emitted at the surface is transported towards the ITCZ by the trade winds and then convectively uplifted. Once in the upper troposphere, CO enriched air masses are transported away from the ITCZ by the upper branches of the Hadley cells and accumulate within the zonal wind shear zones where the maximum CO mixing ratios are found. Anthropogenic and fires both contribute, by the same order of magnitude, to the CO budget of the African upper troposphere. Local fires have the highest contribution, drive the location of the observed UT CO maxima, and are related to the following transport pathway: CO emitted at the surface is transported towards the ITCZ by the trade winds and further convectively uplifted. Then UT CO enriched air masses are transported away from the ITCZ by the upper branches of the Hadley cells and accumulate within the zonal wind shear zones where the maxima are located. Anthropogenic CO contribution is mostly from Africa during the entire year, with a low seasonal variability, and is related to similar transport circulation than fire air masses. There is also a large contribution from Asia in JJASO related to the fast convective uplift of polluted air masses in the Asian monsoon region which are further westward transported by the tropical easterly jet (TEJ) and the Asian monsoon anticyclone (AMA). O3 minima correspond to air masses that were recently uplifted from the surface where mixing ratios are low at the ITCZ. The O3 maxima correspond to old high altitude air masses uplifted from either local or long distance area of high O3 precursor emissions (Africa and South America during all the year, South Asia mainly in JJASO), and must be created during transport by photochemistry. This analysis of meridional transects contribute to a better understanding of distributions of CO and O3 in the intertropical African upper troposphere and the processes which drive these distributions. Therefore, it provides a solid basis for comparison and improvement of models and satellite products in order to get the good O3 for the good reasons.

scholarly journals Intercomparison of midlatitude tropospheric and lower-stratospheric water vapor measurements and comparison to ECMWF humidity data

2018 ◽  
Vol 18 (22) ◽  
pp. 16729-16745 ◽  
Author(s):  
Stefan Kaufmann ◽  
Christiane Voigt ◽  
Romy Heller ◽  
Tina Jurkat-Witschas ◽  
Martina Krämer ◽  
...  
Keyword(s):  
Water Vapor ◽  
Climate Impact ◽  
Cloud Formation ◽  
Mean Values ◽  
Stratospheric Water Vapor ◽  
Mixing Ratios ◽  
Quality Of Water ◽  
Research Aircraft ◽  
German Aerospace

Abstract. Accurate measurement of water vapor in the climate-sensitive region near the tropopause is very challenging. Unexplained systematic discrepancies between measurements at low water vapor mixing ratios made by different instruments on airborne platforms have limited our ability to adequately address a number of relevant scientific questions on the humidity distribution, cloud formation and climate impact in that region. Therefore, during the past decade, the scientific community has undertaken substantial efforts to understand these discrepancies and improve the quality of water vapor measurements. This study presents a comprehensive intercomparison of airborne state-of-the-art in situ hygrometers deployed on board the DLR (German Aerospace Center) research aircraft HALO (High Altitude and LOng Range Research Aircraft) during the Midlatitude CIRRUS (ML-CIRRUS) campaign conducted in 2014 over central Europe. The instrument intercomparison shows that the hygrometer measurements agree within their combined accuracy (±10 % to 15 %, depending on the humidity regime); total mean values agree within 2.5 %. However, systematic differences on the order of 10 % and up to a maximum of 15 % are found for mixing ratios below 10 parts per million (ppm) H2O. A comparison of relative humidity within cirrus clouds does not indicate a systematic instrument bias in either water vapor or temperature measurements in the upper troposphere. Furthermore, in situ measurements are compared to model data from the European Centre for Medium-Range Weather Forecasts (ECMWF) which are interpolated along the ML-CIRRUS flight tracks. We find a mean agreement within ±10 % throughout the troposphere and a significant wet bias in the model on the order of 100 % to 150 % in the stratosphere close to the tropopause. Consistent with previous studies, this analysis indicates that the model deficit is mainly caused by too weak of a humidity gradient at the tropopause.

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 The SCOUT-O3 Darwin Aircraft Campaign: rationale and meteorology

2009 ◽  
Vol 9 (1) ◽  
pp. 93-117 ◽  
Author(s):  
D. Brunner ◽  
P. Siegmund ◽  
P. T. May ◽  
L. Chappel ◽  
C. Schiller ◽  
...  
Keyword(s):  
Large Scale ◽  
Monsoon Season ◽  
Deep Convection ◽  
Cirrus Clouds ◽  
Cold Trap ◽  
Kelvin Wave ◽  
Rossby Wave Breaking ◽  
Tropical Tropopause

Abstract. An aircraft measurement campaign involving the Russian high-altitude aircraft M55 Geophysica and the German DLR Falcon was conducted in Darwin, Australia in November and December 2005 as part of the European integrated project SCOUT-O3. The overall objectives of the campaign were to study the transport of trace gases through the tropical tropopause layer (TTL), mechanisms of dehydration close to the tropopause, and the role of deep convection in these processes. In this paper a detailed roadmap of the campaign is presented, including rationales for each flight, and an analysis of the local and large-scale meteorological context in which they were embedded. The campaign took place during the pre-monsoon season which is characterized by a pronounced diurnal evolution of deep convection including a mesoscale system over the Tiwi Islands north of Darwin known as "Hector". This allowed studying in detail the role of deep convection in structuring the tropical tropopause region, in situ sampling convective overshoots above storm anvils, and probing the structure of anvils and cirrus clouds by Lidar and a suite of in situ instruments onboard the two aircraft. The large-scale flow during the first half of the campaign was such that local flights, away from convection, sampled air masses downstream of the "cold trap" region over Indonesia. Abundant cirrus clouds enabled the study of active dehydration, in particular during two TTL survey flights. The campaign period also encompassed a Rossby wave breaking event transporting stratospheric air to the tropical middle troposphere and an equatorial Kelvin wave modulating tropopause temperatures and hence the conditions for dehydration.

scholarly journals Seasonality and extent of extratropical TST derived from in-situ CO measurements during SPURT

2004 ◽  
Vol 4 (5) ◽  
pp. 1427-1442 ◽  
Author(s):  
P. Hoor ◽  
C. Gurk ◽  
D. Brunner ◽  
M. I. Hegglin ◽  
H. Wernli ◽  
...  
Keyword(s):  
Potential Temperature ◽  
Mixing Layer ◽  
Trace Gas ◽  
Tropical Tropopause ◽  
Tropopause Region ◽  
Gas Measurements ◽  
Transport And Mixing ◽  
Extratropical Tropopause ◽  
Background Air

Abstract. We present airborne in-situ trace gas measurements which were performed on eight campaigns between November 2001 and July 2003 during the SPURT-project (SPURenstofftransport in der Tropopausenregion, trace gas transport in the tropopause region). The measurements on a quasi regular basis allowed an overview of the seasonal variations of the trace gas distribution in the tropopause region over Europe from 35°-75°N to investigate the influence of transport and mixing across the extratropical tropopause on the lowermost stratosphere. From the correlation of CO and O3 irreversible mixing of tropospheric air into the lowermost stratosphere is identified. The CO distribution indicates that transport and subsequent mixing of tropospheric air across the extratropical tropopause predominantly affects a layer, which closely follows the shape of the local tropopause. In addition, the seasonal cycle of CO2 illustrates the strong coupling of that layer to the extratropical troposphere. Both, horizontal gradients of CO on isentropes as well as the CO-O3-distribution in the lowermost stratosphere reveal that the influence of quasi-horizontal transport and subsequent mixing weakens with distance from the local tropopause. The mixing layer extends to about 25 K in potential temperature above the local tropopause exhibiting only a weak seasonality. However, at large distances from the tropopause a significant influence of tropospheric air is still evident. The relation between N2O and CO2 indicates that a significant contribution of air originating from the tropical tropopause contributes to the background air in the extratropical lowermost stratosphere.

scholarly journals In situ observations of greenhouse gases over Europe during the CoMet 1.0 campaign aboard the HALO aircraft

2020 ◽  
Author(s):  
Michał Gałkowski ◽  
Armin Jordan ◽  
Michael Rothe ◽  
Julia Marshall ◽  
Frank-Thomas Koch ◽  
...  
Keyword(s):  
Greenhouse Gases ◽  
Isotopic Signature ◽  
Standard Uncertainty ◽  
The European Union ◽  
Air Samples ◽  
Mixing Ratios ◽  
Regional Sources ◽  
Research Aircraft ◽  
In Situ Observations

Abstract. The intensive measurement campaign CoMet 1.0 (Carbon dioxide and Methane mission) took place during May and June 2018, with a focus on greenhouse gases over Europe. CoMet 1.0 aimed at characterising the distribution of CH4 and CO2 over significant regional sources with the use of a fleet of research aircraft, as well as validating remote sensing measurements from state-of-the-art instrumentation installed on-board against a set of independent in-situ observations. Here we present the results of over 55 hours of accurate and precise in situ measurements of CO2, CH4 and CO mixing ratios made during CoMet 1.0 flights with a cavity ring-down spectrometer aboard the German research aircraft HALO, together with results from analyses of 96 discrete air samples collected aboard the same platform. A careful in-flight calibration strategy together with post-flight quality assessment made it possible to determine both the single measurement precision as well as biases against respective WMO scales. We compare the result of greenhouse gas observations against two of the available global modelling systems, namely Jena CarboScope and CAMS (Copernicus Atmosphere Monitoring Service). We find overall good agreement between the global models and the observed mixing ratios in the free-tropospheric range, characterised by very low bias values for the CAMS CH4 and the CarboScope CO2 products, with a mean free tropospheric offset of 0 (14) ppb and 0.8 (1.3) ppm respectively, with the quoted number giving the standard uncertainty in the final digits for the numerical value. Higher bias is observed for CAMS CO2 (equal to 3.7 (1.5) ppm), and for CO the model-observation mismatch is variable with height (with offset equal to −1.0 (8.8)). We also present laboratory analyses of air samples collected throughout the flights, which include information on the isotopic composition of CH_4, and we demonstrate the potential of simultaneously measuring δ13C-CH4 and δ2H-CH4 from air to determine the sources of enhanced methane signals using even a limited amount of discrete samples. Using flasks collected during two flights over the Upper Silesian Coal Basin (USCB, southern Poland), one of the strongest methane-emitting regions in the European Union, we were able to use the Miller-Tans approach to derive the isotopic signature of the measured source, with values of δ2H equal to −224.7 (6.6) permil and δ13C to −50.9 (1.1) permil, giving significantly lower d2H values compared to previous studies in the area.

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