P. Konopka

Forschungszentrum Jülich, Jülich, North Rhine-Westphalia, Germany

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Publications (131)304.07 Total impact

  • C. M. Hoppe · F. Ploeger · P. Konopka · R. Müller
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    ABSTRACT: The representation of vertical velocity in chemistry climate models is a key element for the representation of the large scale Brewer–Dobson-Circulation in the stratosphere. Here, we diagnose and compare the kinematic and diabatic vertical velocities in the ECHAM/Messy Atmospheric Chemistry (EMAC) model. The calculation of kinematic vertical velocity is based on the continuity equation, whereas diabatic vertical velocity is computed using diabatic heating rates. Annual and monthly zonal mean climatologies of vertical velocity from a 10 year simulation are provided for both, kinematic and diabatic vertical velocity representations. In general, both vertical velocity patterns show the main features of the stratospheric circulation, namely upwelling at low latitudes and downwelling at high latitudes. The main difference in the vertical velocity pattern is a more uniform structure for diabatic and a noisier structure for kinematic vertical velocity. Diabatic vertical velocities show higher absolute values both in the upwelling branch in the inner tropics and in the downwelling regions in the polar vortices. Further, there is a latitudinal shift of the tropical upwelling branch in boreal summer between the two vertical velocity representations with the tropical upwelling region in the diabatic representation shifted southward compared to the kinematic case. Furthermore, we present mean age of air climatologies from two transport schemes in EMAC using these different vertical velocities. The age of air distributions show a hemispheric difference pattern in the stratosphere with younger air in the Southern Hemisphere and older air in the Northern Hemisphere using the transport scheme with diabatic vertical velocities. Further, the age of air climatology from the transport scheme using diabatic vertical velocities shows younger mean age of air in the inner tropical upwelling branch and older mean age in the extratopical tropopause region.
    No preview · Article · Nov 2015 · Atmospheric Chemistry and Physics
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    ABSTRACT: The variation in tropospheric ozone over East Asia was analyzed using tropospheric column ozone data measured by the Global Ozone Monitoring Experiment (GOME) satellite. An empirical orthogonal function (EOF) analysis was carried out to derive the dominant modes of the variation in the tropospheric ozone volume-mixing ratio (TOVMR). The EOF1 mode, which explained 61.5% of the total variance, showed a same-sign distribution over all of East Asia, with a belt of enhanced ozone concentrations around 40°N. The principal component of EOF1 (PC1) suggested that photochemical ozone production together with Brewer-Dobson circulation and subtropical westerly jet plays important roles in modulating the seasonal variation of the TOVMR; ozone-rich air produced by photochemical processes was transported from the stratosphere to the troposphere by BD circulation and this ozone-rich air was then blocked by the subtropical westerly jet and accumulated north of the jet. The EOF2 mode explained 29.2% of the total variance with an opposite-sign pattern on the north and south side of 35°N. When anticyclonic circulation transported ozone-poor air from the upwelling area over the Bay of Bengal towards the Tibetan Plateau during the onset of the Asian summer monsoon, tropospheric ozone in this region decreased dramatically.
    Full-text · Article · Sep 2015 · Advances in Meteorology
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    ABSTRACT: Based on simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) for the 1979–2013 period, driven by the ECMWF ERA-Interim reanalysis, we analyse the impact of the quasi-biennial oscillation (QBO) and of Major Stratospheric Warmings (MWs) on the amount of water vapor entering the stratosphere during boreal winter. The amplitude of H2O variation related to the QBO amounts to 0.5 ppmv. The additional effect of MWs reaches its maximum about 2–4 weeks after the central date of the MW, and strongly depends on the QBO-phase. Whereas during the easterly QBO phase there is a pronounced drying of about 0.3 ppmv about 3 weeks after the MW, the impact of the MW during the westerly QBO phase is smaller (about 0.2 ppmv) and more diffusely spread over time. We suggest that the MW-associated enhanced dehydration combined with a higher frequency of MWs after the year 2000 may have contributed to the lower stratospheric water vapor after 2000.
    Full-text · Article · May 2015 · Geophysical Research Letters
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    ABSTRACT: Dehydration in the Antarctic winter stratosphere is a well-known phenomenon and occasionally observed by ballon-borne and satellite measurements. However, in-situ measurements of dehydration in the Antarctic vortex are very rare. Here, we present detailed in-situ observations with the FISH, HAI, FAIRO, TRIHOP, and GLORIA payload aboard the new German aircraft HALO. Strongly dehydrated air masses down to 1.6 ppmv were observed in a region up to 47 • S and at 12 to 13 km altitude only, which has never been observed by satellites before. The dehydration can be traced back to individual ice formation events, where ice crystals sedimented out and water vapor was irreversibly removed. Within these dehydrated stratospheric air masses, filaments of moister air down to the tropopause are detected with the high resolution limb sounder GLORIA.
    Full-text · Conference Paper · Apr 2015
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    ABSTRACT: The Asian summer monsoon provides an important pathway of tropospheric source gases and pollution into the lower stratosphere. This transport is characterized by deep convection and steady upwelling, combined with confinement inside a large-scale anticyclonic circulation in the upper troposphere and lower stratosphere (UTLS). In this paper, we show that a barrier to horizontal transport along the 380 K isentrope in the monsoon anticyclone can be determined from the potential vorticity (PV) field, following the polar vortex criterion by Nash et al. (1996). Due to large dynamic variability of the anticyclone, the corresponding maximum in the PV gradient is weak and additional constraints are needed (e.g., time averaging). Notwithstanding, PV contours in the monsoon anticyclone agree well with contours of trace gas mixing ratios (CO, O3) and mean age from model simulations with a Lagrangian chemistry transport model (CLaMS) and MLS satellite observations. Hence, the PV-based transport barrier reflects the separation between air inside the anticyclone core and the background atmosphere well. For the summer season 2011 we find an average PV value of 3.6 PVU for the transport barrier in the anticyclone on the 380 K isentrope.
    No preview · Article · Apr 2015 · Atmospheric Chemistry and Physics
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    ABSTRACT: Dehydration in the Antarctic winter stratosphere is a well-known phenomenon that is occasionally observed by balloon-borne and satellite measurements. However, in-situ measurements of dehydration in the Antarctic vortex are very rare. Here, we present detailed observations with the in-situ and GLORIA remote sensing instrument payload aboard the new German aircraft HALO. Strongly dehydrated air masses down to 1.6 ppmv of water vapor were observed as far north as 47° S and between 12 and 13 km in altitude, which has never been observed by satellites. The dehydration can be traced back to individual ice formation events, where ice crystals sedimented out and water vapor was irreversibly removed. Within these dehydrated stratospheric air masses, filaments of moister air reaching down to the tropopause are detected with the high resolution limb sounder, GLORIA. Furthermore, dehydrated air masses are observed with GLORIA in the Antarctic troposphere down to 7 km. With the help of a backward trajectory analysis, a tropospheric origin of the moist filaments in the vortex can be identified, while the dry air masses in the troposphere have stratospheric origins. The transport pathways of Antarctic stratosphere/troposphere exchange are investigated and the irrelevant role of the Antarctic thermal tropopause as a transport barrier is confirmed. Further, it is shown that the exchange process can be attributed to several successive Rossby wave events in combination with an isentropic interchange of air masses across the weak tropopause and subsequent subsidence due to radiative cooling. Once transported to the troposphere, air masses with stratospheric origin are able to reach near-surface levels within 1–2 months. http://www.atmos-chem-phys-discuss.net/15/7895/2015/acpd-15-7895-2015.html
    Full-text · Article · Mar 2015 · Atmospheric Chemistry and Physics
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    ABSTRACT: In a case study of a remarkable Major stratospheric sudden Warming (MW) during the boreal winter 2008/09, we investigate how transport and mixing triggered by this event affect the composition of the whole stratosphere in the Northern Hemisphere. We simulate this event with the Chemical Lagrangian Model of the Stratosphere (CLaMS), with optimized mixing parameters and with no mixing, i.e. with transport occurring only along the Lagrangian trajectories. The results are investigated by using the tracer–tracer correlation technique and by applying the Transformed Eulerian Mean formalism. The CLaMS simulation of N2O and O3 with optimized mixing parameters shows good agreement with the Aura Microwave Limb Sounder (MLS) data. The spatial distribution of mixing intensity in CLaMS correlates fairly well with the Eliassen–Palm flux convergence and illustrates how planetary waves drive mixing. By comparing the simulations with and without mixing, we find that after the MW poleward transport of air increases not only across the vortex edge but also across the subtropical transport barrier. Moreover, the MW event also accelerates polar descent and tropical ascent of the Brewer–Dobson circulation. The accelerated ascent in the tropics and descent at high latitudes firstly occurs in the upper stratosphere and then propagates downward to the lower stratosphere. This downward propagation takes over one month from the potential temperature level of 1000 to 400 K.
    Full-text · Article · Feb 2015 · Atmospheric Chemistry and Physics
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    ABSTRACT: Based on multi-annual simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS), driven by ECMWF ERA-Interim reanalysis, we discuss hemispheric asymmetries and the seasonality of the mean age of air (AoA) in the lower stratosphere. First, the planetary wave forcing of the Brewer-Dobson (BD) circulation is quantified in terms of Eliassen Palm (EP) flux divergence calculated by using the isentropic coordinate θ. While the forcing of the deep branch at θ = 1000 K (around 10 hPa) has a clear maximum in each hemisphere during the respective winter, the shallow branch of the BD circulation, i.e. between 100 and 70 hPa (380 < θ < 420 K), shows almost opposite seasonality in both hemispheres with a pronounced minimum between June and September in the SH. Second, we decompose the time-tendency of AoA into the contributions of the residual circulation and of eddy mixing by analyzing the zonally averaged tracer continuity equation. In the tropical lower stratosphere between ± 30∘, the air becomes younger during boreal winter and older during boreal summer. During boreal winter, the decrease of AoA due to tropical upwelling outweighs aging by isentropic mixing. In contrast, weaker isentropic mixing outweighs an even weaker upwelling in boreal summer and fall making the air older during these seasons. Poleward of 60∘, the deep branch locally increases AoA and eddy mixing locally decreases AoA with the strongest net decrease during spring. Eddy mixing in the NH outweighs that in the SH throughout the year.
    Full-text · Article · Feb 2015
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    ABSTRACT: It is an outstanding issue to what degree trends in stratospheric mean age of air reflect changes in the (slow) residual circulation and how they are affected by (fast) eddy mixing. We present a method to quantify the effects of mixing and residual circulation on mean age trends, based on simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) driven by ERA-Interim reanalysis and on the integrated tracer continuity equation. During 1990–2013, mean age decreases throughout most of the stratosphere, qualitatively consistent with results based on climate model simulations. During 2002–2012, age changes show a clear hemispheric asymmetry in agreement with satellite observations. We find that changes in the residual circulation transit time cannot explain the mean age trends, and including the integrated effect of mixing is crucial. Above about 550K (about 22km), trends in the mixing effect on mean age appear to be coupled to residual circulation changes.
    Full-text · Article · Feb 2015 · Geophysical Research Letters
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    F. Ploeger · M. Riese · F. Haenel · P. Konopka · R. Müller · G. Stiller
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    ABSTRACT: We analyze the variability of mean age of air (AoA) and of the local effects of the stratospheric residual circulation and eddy mixing on AoA within the framework of the isentropic zonal mean continuity equation. AoA for the period 1988–2013 has been simulated with the Lagrangian chemistry transport model CLaMS driven by ERA-Interim winds and diabatic heating rates. Model simulated AoA in the lower stratosphere shows good agreement with both in-situ observations and satellite observations from MIPAS (Michelson Interferometer for Passive Atmospheric Sounding), even regarding interannual variability and changes during the last decade. The interannual variability throughout the lower stratosphere is largely affected by the QBO-induced circulation and mixing anomalies, with year-to-year AoA changes of about 0.5 years. The decadal 2002–2012 change shows decreasing AoA in the lowest stratosphere, below about 450 K. Above, AoA increases in the NH and decreases in the SH. Mixing appears to be crucial for understanding AoA variability, with local AoA changes resulting from a close balance between residual circulation and mixing effects. Locally, mixing increases AoA at low latitudes (40S-40N) and decreases AoA at higher latitudes. Strongest mixing occurs below about 500 K, consistent with the separation between shallow and deep circulation branches. The effect of mixing integrated along the air parcel path, however, significantly increases AoA globally, except in the polar lower stratosphere. Changes of local effects of residual circulation and mixing during the last decade are supportive of a strengthening shallow circulation branch in the lowest stratosphere and a southward shifting circulation pattern above.
    Full-text · Article · Dec 2014
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    A. Kunz · N. Spelten · P. Konopka · R. Müller · R. M. Forbes · H. Wernli
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    ABSTRACT: An evaluation of water vapor in the upper troposphere and lower stratosphere (UTLS) of the ERA-Interim, the global atmospheric reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF), is presented. Water vapor measurements are derived from the Fast In situ Stratospheric Hygrometer (FISH) during a large set of airborne measurement campaigns from 2001 to 2011 in the tropics, midlatitudes and polar regions, covering isentropic layers from 300 to 400K (5–18km). The comparison shows around 87% of the reanalysis data are within a factor of 2 of the FISH water vapor measurements and around 30% have a nearly perfect agreement with an over- and underestimation lower than 10%. Nevertheless, strong over- and underestimations can occur both in the UT and LS, in particularly in the extratropical LS and in the tropical UT, where severe over- and underestimations up to 10 times can occur. The analysis data from the evolving ECMWF operational system is also evaluated, and the FISH measurements are divided into time periods representing different cycles of the Integrated Forecast System (IFS). The agreement with FISH improves over the time, in particular when comparing water vapor fields for time periods before 2004 and after 2010. It appears that influences of tropical tropospheric and extratropical UTLS processes, e.g., convective and quasi-isentropic exchange processes, are particularly challenging for the simulation of the UTLS water vapor distribution. Both the reanalysis and operational analysis data show the tendency of an overestimation of low water vapor mixing ratio (⪅10ppmv) in the LS and underestimation of high water vapor mixing ratio (⪆300ppmv) in the UT.
    Full-text · Article · Oct 2014 · Atmospheric Chemistry and Physics
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    ABSTRACT: Variations in the mixing ratio of trace gases of tropospheric origin entering the stratosphere in the tropics are of interest for assessing both troposphere to stratosphere transport fluxes in the tropics and the impact of these transport fluxes on the composition of the tropical lower stratosphere. Anomaly patterns of carbon monoxide (CO) and long-lived tracers in the lower tropical stratosphere allow conclusions about the rate and the variability of tropical upwelling to be drawn. Here, we present a simplified chemistry scheme for the Chemical Lagrangian Model of the Stratosphere (CLaMS) for the simulation, at comparatively low numerical cost, of CO, ozone, and long-lived trace substances (CH4, N2O, CCl3F (CFC-11), CCl2F2 (CFC-12), and CO2) in the lower tropical stratosphere.
    Full-text · Article · Aug 2014 · Geoscientific Model Development
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    ABSTRACT: Lagrangian transport schemes have proven to be useful tools for modelling stratospheric trace gas transport since they are less diffusive than classical Eulerian schemes and therefore especially well suited for maintaining steep tracer gradients. Here, we present the implementation of the full-Lagrangian transport core of the Chemical Lagrangian Model of the Stratosphere (CLaMS) into the ECHAM/MESSy Atmospheric Chemistry model (EMAC). We performed a ten-year time-slice simulation to evaluate the coupled model system EMAC/CLaMS. Simulated zonal mean age of air distributions are compared to age of air derived from airborne measurements, showing a good overall representation of the stratospheric circulation. Results from the new Lagrangian transport scheme are compared to tracer distributions calculated with the standard flux-form semi-Lagrangian (FFSL) transport scheme in EMAC. The differences in the resulting tracer distributions are most pronounced in the regions of strong transport barriers. The polar vortices are presented as an example and simulated trace gas distributions are compared to satellite measurements. The analysis of CFC-11, N2O, CH4, and age of air in the polar vortex regions shows that the CLaMS Lagrangian transport scheme produces a stronger, more realistic transport barrier at the edge of the polar vortex than the FFSL transport scheme of EMAC. Differences in simulated age of air range up to one year in the Arctic polar vortex in late winter/early spring. The new coupled model system EMAC/CLaMS thus constitutes a suitable tool for future model studies of stratospheric tracer transport.
    No preview · Article · Feb 2014 · Geoscientific Model Development
  • A. Kunz · N. Spelten · P. Konopka · R. Müller · R. M. Forbes · H. Wernli

    No preview · Article · Jan 2014 · Atmospheric Chemistry and Physics
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    M. Abalos · F. Ploeger · P. Konopka · W. J. Randel · E. Serrano
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    ABSTRACT: We aim to reconcile the recently published, apparently contrasting results regarding the relative importance of tropical upwelling versus horizontal transport for the seasonality of ozone above the tropical tropopause. Different analysis methods in the literature (Lagrangian versus Eulerian, and isentropic versus pressure vertical coordinates) yield different perspectives of ozone transport, and the results must be carefully compared in equivalent terms to avoid misinterpretation. By examining the Lagrangian calculations in the Eulerian formulation, we show here that the results are in fact consistent with each other and with a common understanding of the ozone transport processes near and above the tropical tropopause. We further emphasize that the complementary approaches are suited for answering two different scientific questions: (1) what drives the observed seasonal cycle in ozone at a particular level above the tropical tropopause? and (2) how important is horizontal transport from mid-latitudes for ozone concentrations in the tropical lower stratosphere? Regarding the first question, the analysis of the transformed Eulerian mean (TEM) ozone budget shows that the annual cycle in tropical upwelling is the main forcing of the ozone seasonality at altitudes with large vertical gradients in the tropical lower stratosphere. To answer the second question a Lagrangian framework must be used, and the results show that a large fraction (∼50%) of the ozone molecules ascending through the tropical lower stratosphere is of extra-tropical origin and has been in-mixed from mid-latitudes.
    Full-text · Article · Nov 2013 · ATMOSPHERIC CHEMISTRY AND PHYSICS
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    ABSTRACT: We compare global water vapor observations from Microwave Limb Sounder (MLS) and simulations with the Lagrangian chemical transport model CLaMS (Chemical Lagrangian Model of the Stratosphere) to investigate the pathways of water vapor into the lower stratosphere during Northern Hemisphere (NH) summer. We find good agreement between the simulation and observations, with an effect of the satellite averaging kernel especially at high latitudes. The Asian and American monsoons emerge as regions of particularly high water vapor mixing ratios in the lower stratosphere during boreal summer. In NH midlatitudes and high latitudes, a clear anticorrelation between water vapor and ozone daily tendencies reveals a large region influenced by frequent horizontal transport from low latitudes, extending up to about 450K during summer and fall. Analysis of the zonal mean tracer continuity equation shows that close to the subtropics, this horizontal transport is mainly caused by the residual circulation. In contrast, at higher latitudes, poleward of about 50°N, eddy mixing dominates the horizontal water vapor transport. Model simulations with transport barriers confirm that almost the entire annual cycle of water vapor in NH midlatitudes above about 360K, with maximum mixing ratios during summer and fall, is caused by horizontal transport from low latitudes. In the model, highest water vapor mixing ratios in this region are clearly linked to horizontal transport from the subtropics.
    Full-text · Article · Jul 2013 · Journal of Geophysical Research Atmospheres
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    ABSTRACT: A review of Lagrangian methods was presented along with proposals for improving the accuracy of atmospheric Lagrangian models through better access to meteorological analysis and forecast products. The review specifically focused on kinematic Lagrangian models, which computed the trajectories of air particles given the Eulerian velocity field. The kinematic equation of motion comprised of a set of coupled, first-order, ordinary differential equations for each component of motion. Lagrangian dispersion models augmented pure trajectory models by including parameterizations of the effects of unresolved scales of motion on the path of a particle. Dispersion model applications ranged from the microscale, such as the emission from an automobile tailpipe to the global scale, such as the transport of a cloud of volcanic ash. Dispersion models required additional information, such as wind shear, stability, and turbulence parameters to estimate the properties of the unresolved flow.
    Preview · Article · Jul 2013 · Bulletin of the American Meteorological Society
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    ABSTRACT: Based on OSIRIS satellite observations, Bourassa et al. (2012) suggested that the June 2011 eruption of the Nabro volcano had the strongest impact on stratospheric aerosol since Pinatubo. Based on a reported visible plume height of 13 km, they claimed that no direct stratospheric injection of ash, sulfate and SO2 occurred, and that volcanic material was transported to the stratosphere exclusively via the Asian summer monsoon anticyclone. In contrast, Sawamura et al. (2012) and Vernier et al. (2012) present undisputable evidence for a direct injection contribution using back trajectory calculations from ground based lidar and space-borne CALIOP observations within the first few days after the eruption. To assess which pathway - direct injection (DI) or uplift via the Asian monsoon (AMU) - dominated transport of Nabro sulfur and aerosol to the stratosphere, we use a trajectory ensemble approach. Forward trajectories were started from Nabro at the time of eruption, and the distribution of air parcels in the stratosphere was monitored separately for trajectories initial-ized in the stratosphere (corresponding to DI) and in the troposphere (some of which reaching the stratosphere by AMU). While the path of a single trajectory tends to become rather uncertain after several days, the ensemble approach allows for a statistical analysis where random errors are expected to average out. During the first week after the eruption, only DI air parcels are found in the stratosphere, in agreement with satellite observations of SO2 (MIPAS) and aerosols (MIPAS, CALIOP). About a week after the eruption, the first trajectories initialized in the troposphere reach the stratosphere inside the Asian monsoon anticyclone. By the end of July, the pattern of the AMU air parcels resembles the observed distribution of stratospheric aerosol much more closely than the pattern of the DI air parcels does. The simulations further show that some of the air parcels that entered the stratospheric part of the TTL rise further when upwelling intensifies with the onset of boreal winter. The observation of stronger aerosol signatures in MIPAS spectra for tangent altitudes above 20 km in the tropics in winter 2011/12 compared to other years suggests that aerosol originating from Nabro may enter the upper branch of the BD-circulation. This study has implications beyond revealing the transport pathway of a stratospheric aerosol plume from the Nabro volcano. Because the aerosol signal is readily picked up by satellites, it represents an ideal case study to investigate the efficiency of the Asian monsoon as a transport pathway to the stratosphere in general, e.g. for anthropogenic SO2 and other pollutants. Bourassa, A. E., et al.: Large Volcanic Aerosol Load in the Stratosphere Linked to Asian Monsoon Transport, Science, 337, 78-81, 2012. Sawamura, P., et al.: Stratospheric AOD after the 2011 eruption of Nabro volcano measured by lidars over the Northern Hemisphere, Environ. Res. Lett., 7, 2012. Vernier, J.-P., et al.: Comment on "Large volcanic aerosol load in the stratosphere linked to Asian Monsoon Transport" by Bourassa and co-authors. Accepted for publication Science (December 2012).
    No preview · Article · Apr 2013
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    ABSTRACT: We compare global water vapor observations in the lower stratosphere from MLS with global simulations with the Lagrangian chemical transport model CLaMS to investigate the pathways of water vapor into the lower stratosphere during northern hemisphere (NH) summer. Model simulations and observations both show that the Asian and American monsoons are main regions of upward transport of water vapor into the upper troposphere during summer, moistening the NH subtropics. In NH mid- and high-latitudes, a clear anticorrelation between water vapor and ozone tendencies reveals a large region influenced by frequent horizontal transport from low latitudes, extending up to about 430-450K during summer and fall. Close to the subtropics, this horizontal transport is caused by the shallow Brewer-Dobson circulation branch. In contrast, at higher latitudes polewards of about 50°, horizontal transport is caused by eddy mixing, related to Rossby-wave breaking. Additional sensitivity simulations with transport barriers in the model confirm that the entire annual cycle of water vapor mixing ratios in NH extratropics at altitudes above the subtropical jet core is caused by horizontal transport from the subtropics. Hence, NH water vapor between about 370-430K during summer and fall appears to be `subtropically controlled'. In the model, highest water vapor mixing ratios in this region are closely linked to horizontal transport from the subtropics rather than to mid-latitude convection. Further, an asymmetry exists in lower stratospheric water vapor, with a significantly moister NH than SH. This asymmetry is largely caused by processes at high latitudes, like strong dehydration within the Antarctic vortex and hemispheric differences in downwelling, and is only weakly affected by horizontal transport from low latitudes.
    No preview · Article · Apr 2013
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    ABSTRACT: Intense vertical transport of air from the troposphere to the stratosphere occurs in the maritime continent-west Pacific in boreal winter (Fueglistaler et al., 2004). Convective uplift injects tropospheric air masses into the TTL, where strong radiative heating fosters further vertical transport to the stratosphere and the upper branch of the Brewer Dobson Circulation. Based on observations of very low tropospheric ozone made during the TransBrom-Cruise (Ridder et al., 2012), Rex et al. (2011) has hypothesized that tropospheric air in the western Pacific region should be rather depleted in OH - the main tropospheric oxidant - leading to significantly longer lifetimes of compounds carrying halogens (VSLS) and sulfur (SO2) in these air masses. We investigate this hypothesis and its possible impact on SO2 and VSLS transport to the stratosphere by looking at aircraft measurements made during the SCOUT-O3 field experiment in Darwin, Australia, in November and December 2005. Trajectory calculations show that tropospheric ozone mixing ratios below 15 ppb encountered during several flights are typically found in clean Pacific air masses that are also relatively low in CO. A slightly negative correlation between CO and SO2 in these air masses may indeed be caused by a longer lifetime due to low OH. However, the tropospheric SO2 concentrations observed during SCOUT-O3 are too low to represent a significant sulfur source to the stratosphere. Samples of several VSLS made in the TTL are also analyzed for a possible signature of enhanced tropospheric lifetimes. Fueglistaler, S., et al.: Tropical troposphere-to-stratosphere transport inferred from trajectory calculations, J. Geophys. Res., 109, 10.1029/2003jd004069, 2004. Rex, M., et al.: Is There a Hole in the Global OH Shield Over the Tropical Western Pacific Warm Pool?, NDACC symposium, Reunion Island, 2011. Ridder, T., et al.: Ship-borne FTIR measurements of CO and O3 in the Western Pacific from 43° N to 35° S: an evaluation of the sources, Atmos. Chem. Phys., 12, 815-828, 10.5194/acp-12-815-2012, 2012.
    No preview · Article · Apr 2013