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  • 1
    Publication Date: 2016-02-01
    Description: This paper presents a set of observations by the CRISTA infrared limb sounder in low-earth orbit taken in August 1997 and analyses of trace-gases in the Asian Summer Monsoon (ASM) region. The spatially highly-resolved measurements of peroxyacetyl nitrate (PAN) and O3 allow a detailed analysis of an eddy-shedding event of the ASM anticyclone.We identify enhanced PAN volume mixing ratios (VMRs) within the main anticyclone and within the eddy, which are suitable as a tracer for polluted air within the ASM originating in India and China. Comparing the retrieved PAN VMRs with potential vorticity (PV) on isentropes reveals that the PAN VMRs exhibit the strongest decrease at each isentrope for an increasing value of PV which may be used to identify the extent of the ASM. Using temperature values also derived from CRISTA measurements, we also computed the location of the thermal tropopause according to the WMO criterion and find that its location agrees well with the limits of the area of increased PAN VMRs both horizontally on isentropes and vertically within the anticyclone. In contrast, the shed eddy exhibits enhanced PAN VMRs for 1 to 2 km above the thermal tropopause. Using the relationship between PAN as a tropospheric tracer and O3 as a stratospheric tracer to identify mixed air parcels, we further found the anticyclone to contain few such parcels, whereas the region in between the anticyclone and the eddy contains many mixed parcels. In combination, this implies that while the anticyclone confines polluted air masses well, eddy shedding provides a very rapid horizontal transport pathway of Asian pollution into the extratropical lowermost stratosphere with a time scale of only a few days.
    Electronic ISSN: 1680-7375
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union (EGU).
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  • 2
    Publication Date: 2015-04-13
    Description: 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.
    Electronic ISSN: 1680-7375
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union (EGU).
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  • 3
    Publication Date: 2015-04-02
    Description: The impact of different boundary layer source regions in Asia on the chemical composition of the Asian monsoon anticyclone, considering its intraseasonal variability in 2012, is analysed by CLaMS simulations using artificial emission tracers. Our simulations show that the Asian monsoon anticyclone is highly variable in location and shape and oscillates between 2 states: first a symmetric anticyclone and second, an asymmetric anticyclone either elongated or split in two smaller anticyclones. A maximum in the distribution of air originating from Indian/Chinese boundary layer sources is usually found in the core of the symmetric anticyclone, in contrast the asymmetric state is characterised by a double peak structure in the horizontal distribution of air originating from India and China. The simulated horizontal distribution of artificial emission tracers for India/China is in agreement with patterns found in satellite measurements of O3 and CO by the Aura Microwave Limb Sounder (MLS). The contribution of different boundary source regions to the Asian monsoon anticyclone strongly depends on its intraseasonal variability and is therefore more complex than hitherto believed, but in general the highest contributions are from North India and Southeast Asia at 380 K. In the early (June to mid-July) and late (mid-August to October) period of the monsoon 2012, contributions of emissions from Southeast Asia are highest and in the intervening period (≈ mid-July to mid-August) emissions from North India have the largest impact. Further, our simulations confirm that the thermal tropopause above the anticyclone constitutes a vertical transport barrier. Enhanced contributions of emission tracers for Asia are found at the northern flank of the Asian monsoon anticyclone between double tropopauses indicating an isentropic transport from the anticyclone into the lowermost stratosphere. After the breakup of the anticyclone, significant contributions of air masses originating in India/China are sill found over Asia in September/October. In addition, these air masses spread out within the mid-latitudes of the Northern Hemisphere and in the tropics at around 380 K. Moreover, air masses from Southeast Asia experienced diabatic upward transport in the tropics and subsequently isentropic poleward transport occurs at around 380 K with the result that the extratropical lowermost stratosphere is flooded by end of September with air masses originating in Southeast Asia. Our results demonstrate that emissions from Asia have a significant impact on the chemical compositions of the lowermost stratosphere of the Northern Hemisphere in particular after the end of the monsoon season in September/October 2012.
    Electronic ISSN: 1680-7375
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union (EGU).
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  • 4
    Publication Date: 2015-11-27
    Description: 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 a local maximum in the gradient of potential vorticity (PV), following methods developed for the polar vortex (e.g., Nash et al., 1996). The monsoon anticyclone is dynamically highly variable and the maximum in the PV gradient is weak, such that additional constraints are needed (e.g., time averaging). Nevertheless, 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 satellite observations from the Microwave Limb Sounder (MLS) instrument. Hence, the PV-based transport barrier reflects the separation between air inside the core of the anticyclone 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.
    Print ISSN: 1680-7316
    Electronic ISSN: 1680-7324
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union (EGU).
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  • 5
    Publication Date: 2015-08-07
    Description: In a case study of a remarkable major sudden stratospheric warming (SSW) during the boreal winter 2008/09, we investigate how transport and mixing triggered by this event affected the composition of the entire stratosphere in the Northern Hemisphere. We simulate this event with the Chemical Lagrangian Model of the Stratosphere (CLaMS), both with optimized mixing parameters and with no mixing, i.e. with transport occurring only along the Lagrangian trajectories. The results are investigated by using tracer–tracer correlations and by applying the transformed Eulerian-mean formalism. The CLaMS simulation of N2O and O3, and in particular of the O3–N2O tracer correlations 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. This correlation illustrates how planetary waves drive mixing. By comparing simulations with and without mixing, we find that after the SSW, poleward transport of air increases, not only across the vortex edge but also across the subtropical transport barrier. Moreover, the SSW event, at the same time, accelerates polar descent and tropical ascent of the Brewer–Dobson circulation. The accelerated ascent in the tropics and descent at high latitudes first occurs in the upper stratosphere and then propagates downward to the lower stratosphere. This downward propagation takes over 1 month from the potential temperature level of 1000 to 400 K.
    Print ISSN: 1680-7316
    Electronic ISSN: 1680-7324
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union (EGU).
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  • 6
    Publication Date: 2015-02-24
    Description: Heterogeneous reactions in the Antarctic stratosphere are the cause of chlorine activation and ozone depletion, but the relative roles of different types of polar stratospheric clouds (PSCs) in chlorine activation is an open question. We use multi-year simulations of the chemistry-climate model ECHAM5/MESSy for Atmospheric Chemistry (EMAC) to investigate the impact that the various types of PSCs have on Antarctic chlorine activation and ozone loss. One standard and three sensitivity EMAC simulations have been performed. In all simulations a Newtonian relaxation technique using the ERA-Interim reanalysis was applied to simulate realistic synoptic conditions. In the three sensitivity simulations, we only changed the heterogeneous chemistry on PSC particles by switching the chemistry on liquid, nitric acid trihydrate (NAT) and ice particles on and off. The results of these simulations show that the significance of heterogeneous reactions on NAT and ice particles for chlorine activation and ozone depletion in Antarctic winter and spring is small in comparison to the significance of heterogeneous reactions on liquid particles. Liquid particles alone are sufficient to activate almost all of the available chlorine, with the exception of the upper PSC regions between 10 and 30 hPa, where temporarily ice particles show a relevant contribution. Shortly after the first PSC occurrence, NAT particles contribute a small fraction to chlorine activation. Heterogeneous chemistry on liquid particles is responsible for more than 90% of the ozone depletion in Antarctic spring in the model simulations. In high southern latitudes, heterogeneous chemistry on ice particles causes only up to 5 DU of additional ozone depletion in the column and heterogeneous chemistry on NAT particles less than 0.5 DU. The simulated HNO3, ClO and O3 results agree closely with observations from the Microwave Limb Sounder (MLS) onboard NASA's Aura satellite.
    Print ISSN: 1680-7316
    Electronic ISSN: 1680-7324
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union (EGU).
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  • 7
    Publication Date: 2017-09-19
    Description: Carbon dioxide (CO2) liberated at arc volcanoes that intersect buried carbonate platforms plays a larger role in influencing atmospheric CO2 than those active margins lacking buried carbonate platforms. This study investigates the contribution of carbonate-intersecting arc activity on palaeo-atmospheric CO2 levels over the past 410 million years by integrating a plate motion model with an evolving carbonate platform development model. Our modelled subduction zone lengths and carbonate-intersecting arc lengths approximate arc activity with time, and can be used as input into fully-coupled models of CO2 flux between deep and shallow reservoirs. Continuous and cross-wavelet as well as wavelet coherence analyses were used to evaluate trends between carbonate-intersecting arc activity, non-carbonate-intersecting arc activity and total global subduction zone lengths and the proxy-CO2 record between 410 Ma and the present. Wavelet analysis revealed significant linked periodic behaviour between 75–50 Ma, where global carbonate-intersecting arc activity is relatively high and where peaks in palaeo-atmospheric CO2 is correlated with peaks in global carbonate-intersecting arc activity, characterised by a ~ 32 Myr periodicity and a 10 Myr lag of CO2 peaks after carbonate-intersecting arc length peaks. The linked behaviour may suggest that the relative abundance of carbonate-intersecting arcs played a role in affecting global climate during the Late Cretaceous to Early Paleogene greenhouse. At all other times, atmospheric CO2 emissions from carbonate-intersecting arcs were not correlated with the proxy-CO2 record. Our analysis did not support the idea that carbonate-intersecting arc activity is more important than non-carbonate intersecting arc activity in driving changes in palaeo-atmospheric CO2 levels. This suggests that tectonic controls are more elaborate than the subduction-related volcanic emissions component or that other feedback mechanisms between the geosphere, atmosphere and biosphere played larger roles in modulating climate in the Phanerozoic.
    Print ISSN: 1814-9340
    Electronic ISSN: 1814-9359
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union (EGU).
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  • 8
    Publication Date: 2019-01-15
    Description: Traditional approaches to develop 3D geological models employ a mix of quantitative and qualitative scientific techniques, which do not fully provide quantification of uncertainty in the constructed models and fail to optimally weight geological field observations against constraints from geophysical data. Here, we demonstrate a Bayesian methodology to fuse geological field observations with aeromagnetic and gravity data to build robust 3D models in a 13.5 × 13.5 km region of the Gascoyne Province, Western Australia. Our approach is validated by comparing model results to independently-constrained geological maps and cross-sections produced by the Geological Survey of Western Australia. By fusing geological field data with magnetics and gravity surveys, we show that at 89 % of the modelled region has 〉 95 % certainty. The boundaries between geological units are characterized by narrow regions with
    Electronic ISSN: 1869-9537
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union (EGU).
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  • 9
    Publication Date: 2018-06-21
    Description: The CO2 liberated along subduction zones through intrusive/extrusive magmatic activity and the resulting active and diffuse outgassing influences global atmospheric CO2. However, when melts derived from subduction zones intersect buried carbonate platforms, decarbonation reactions may cause the contribution to atmospheric CO2 to be far greater than segments of the active margin that lacks buried carbon-rich rocks and carbonate platforms. This study investigates the contribution of carbonate-intersecting subduction zones (CISZs) to palaeo-atmospheric CO2 levels over the past 410 million years by integrating a plate motion and plate boundary evolution model with carbonate platform development through time. Our model of carbonate platform development has the potential to capture a broader range of degassing mechanisms than approaches that only account for continental arcs. Continuous and cross-wavelet analyses as well as wavelet coherence are used to evaluate trends between the evolving lengths of carbonate-intersecting subduction zones, non-carbonate-intersecting subduction zones and global subduction zones, and are examined for periodic, linked behaviour with the proxy CO2 record between 410 Ma and the present. Wavelet analysis reveals significant linked periodic behaviour between 60 and 40 Ma, when CISZ lengths are relatively high and are correlated with peaks in palaeo-atmospheric CO2, characterised by a 32–48 Myr periodicity and a ∼ 8–12 Myr lag of CO2 peaks following CISZ length peaks. The linked behaviour suggests that the relative abundance of CISZs played a role in affecting global climate during the Palaeogene. In the 200–100 Ma period, peaks in CISZ lengths align with peaks in palaeo-atmospheric CO2, but CISZ lengths alone cannot be determined as the cause of a warmer Cretaceous–Jurassic climate. Nevertheless, across the majority of the Phanerozoic, feedback mechanisms between the geosphere, atmosphere and biosphere likely played dominant roles in modulating climate. Our modelled subduction zone lengths and carbonate-intersecting subduction zone lengths approximate magmatic activity through time, and can be used as input into fully coupled models of CO2 flux between deep and shallow carbon reservoirs.
    Print ISSN: 1814-9324
    Electronic ISSN: 1814-9332
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union (EGU).
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  • 10
    Publication Date: 2018-10-26
    Description: Movements of tectonic plates often induce oblique deformation at divergent plate boundaries. This is in striking contrast with traditional conceptual models of rifting and rifted margin formation, which often assume 2-D deformation where the rift velocity is oriented perpendicular to the plate boundary. Here we quantify the validity of this assumption by analysing the kinematics of major continent-scale rift systems in a global plate tectonic reconstruction from the onset of Pangea breakup until the present day. We evaluate rift obliquity by joint examination of relative extension velocity and local rift trend using the script-based plate reconstruction software pyGPlates. Our results show that the global mean rift obliquity since 230Ma amounts to 34° with a standard deviation of 24°, using the convention that the angle of obliquity is spanned by extension direction and rift trend normal. We find that more than  ∼ 70% of all rift segments exceeded an obliquity of 20° demonstrating that oblique rifting should be considered the rule, not the exception. In many cases, rift obliquity and extension velocity increase during rift evolution (e.g. Australia-Antarctica, Gulf of California, South Atlantic, India-Antarctica), which suggests an underlying geodynamic correlation via obliquity-dependent rift strength. Oblique rifting produces 3-D stress and strain fields that cannot be accounted for in simplified 2-D plane strain analysis. We therefore highlight the importance of 3-D approaches in modelling, surveying, and interpretation of most rift segments on Earth where oblique rifting is the dominant mode of deformation.
    Print ISSN: 1869-9510
    Electronic ISSN: 1869-9529
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union (EGU).
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