Deep convective influence on the UTLS composition in the Asian Monsoon Anticyclone region: 2017 StratoClim campaign results

2020 ◽  
Author(s):  
Silvia Bucci ◽  
Bernard Legras ◽  
Pasquale Sellitto ◽  
Francesco D'Amato ◽  
Silvia Viciani ◽  
...  
Keyword(s):  
Asian Monsoon ◽  
Deep Convection ◽  
Direct Injection ◽  
Trace Gases ◽  
Convective Cloud ◽  
Air Masses ◽  
The North ◽  
Transport Condition ◽  
Trajectory System

<p>The StratoClim stratospheric aircraft campaign, taking place in summer over the Nepalese region, provided a wide dataset of observations of air composition inside the Asian Monsoon Anticyclone (AMA). To improve the understanding of the role of penetrating overshoot in the AMA region, we exploit the TRACZILLA Lagrangian simulations, computed on meteorological fields from ECMWF (ERA-Interim and ERA5) at 3h and 1h resolution and using both kinematic and diabatic vertical velocity approaches. The synergy with high-resolution observations of convective cloud top from the MSG1 and Himawari geostationary satellites is used to individuate the convective sources.</p><p>To evaluate the capability of the trajectory system to reproduce the transport in the UTLS we compare the simulations with the observed trace gases concentration. The ERA5 simulations appear to provide a higher consistency with observed data than ERA-Interim and show a better agreement between the diabatic and kinematic results. The best performance is given by the ERA5 with diabatic transport and, adopting this setting, we analyze the transport condition during the 8 flights of the campaign.</p><p>The aircraft sampled different convective plumes, often carrying pollutant compounds up to the UTLS level. The highest observed concentration of trace gases had been linked to fresh convective air (younger than a few days) coming from China, Pakistan and the North Indian region.</p><p>A vertical stratification is observed in the age of air: up to 15 km, the age of air is less than 3 days and these fresh air masses make up nearly the entire totality of the air composition. Above, a transition layer is identified between 15 km and 17 km (close to the tropopause), where the convective influence is still dominant and the ages range from one week to two. Finally, above this layer, the convective influence rapidly decreases toward zero and the mean air age increase to 20 days and more.</p><p>This study quantifies the contribution of direct injection of deep convection on the UTLS composition based on the aircraft measurements. Preliminary results of the upscale analysis based on the trajectories-satellites system will also be presented.</p>

scholarly journals The role of the retention coefficient for the scavenging and redistribution of highly soluble trace gases by deep convective cloud systems: model sensitivity studies

2006 ◽  
Vol 6 (5) ◽  
pp. 10773-10809
Author(s):  
M. Salzmann ◽  
M. G. Lawrence ◽  
V. T. J. Phillips ◽  
L. J. Donner
Keyword(s):  
Deep Convection ◽  
Trace Gases ◽  
Convective Cloud ◽  
Upper Troposphere ◽  
Cloud Systems ◽  
Retention Coefficient ◽  
Systems Model ◽  
Toga Coare ◽  
Deep Convective Cloud

Abstract. The role of the retention coefficient (i.e. the fraction of a dissolved trace gas which is retained in hydrometeors during freezing) for the scavenging and redistribution of highly soluble trace gases by deep convective cloud systems is investigated using a modified version of the Weather Research and Forecasting (WRF) model. Results from cloud system resolving model runs (in which deep convection is initiated by small random perturbations in association with so-called "large scale forcings (LSF)") for a tropical oceanic (TOGA COARE) and a mid-latitude continental case (ARM) are compared to two runs in which bubbles are used to initiate deep convection (STERAO, ARM). In the LSF runs scavenging is found to almost entirely prevent a highly soluble tracer initially located in the lowest 1.5 km of the troposphere from reaching the upper troposphere, independent of the retention coefficient. The release of gases from freezing hydrometeors leads to mixing ratio increases in the upper troposphere comparable to those calculated for insoluble trace gases only in runs in which bubbles are used to initiate deep convection. This result indicates that previous cloud resolving model studies using bubbles to initiate deep convection may possibly have over-estimated the influence of the retention coefficient on the vertical transport of highly soluble tracers. The retention coefficient is, however, found to play an important role for the scavenging and redistribution of highly soluble trace gases with a (chemical) source in the free troposphere and also for trace gases for which even relatively inefficient transport may be important.

scholarly journals Model sensitivity studies regarding the role of the retention coefficient for the scavenging and redistribution of highly soluble trace gases by deep convective cloud systems

2007 ◽  
Vol 7 (8) ◽  
pp. 2027-2045 ◽  
Author(s):  
M. Salzmann ◽  
M. G. Lawrence ◽  
V. T. J. Phillips ◽  
L. J. Donner
Keyword(s):  
Deep Convection ◽  
Trace Gases ◽  
Convective Cloud ◽  
Upper Troposphere ◽  
Cloud Systems ◽  
Retention Coefficient ◽  
Toga Coare ◽  
Model Setup ◽  
Deep Convective Cloud

Abstract. The role of the retention coefficient (i.e. the fraction of a dissolved trace gas which is retained in hydrometeors during freezing) for the scavenging and redistribution of highly soluble trace gases by deep convective cloud systems is investigated using a modified version of the Weather Research and Forecasting (WRF) model. Results from cloud system resolving model runs (in which deep convection is initiated by small random perturbations in association with so-called "large scale forcings (LSF)") for a tropical oceanic (TOGA COARE) and a mid-latitude continental case (ARM) are compared to two runs in which bubbles are used to initiate deep convection (STERAO, ARM). In the LSF runs, scavenging is found to almost entirely prevent a highly soluble tracer initially located in the lowest 1.5 km of the troposphere from reaching the upper troposphere, independent of the retention coefficient. The release of gases from freezing hydrometeors leads to mixing ratio increases in the upper troposphere comparable to those calculated for insoluble trace gases only in the two runs in which bubbles are used to initiate deep convection. A comparison of the two ARM runs indicates that using bubbles to initiate deep convection may result in an overestimate of the influence of the retention coefficient on the vertical transport of highly soluble tracers. It is, however, found that the retention coefficient plays an important role for the scavenging and redistribution of highly soluble trace gases with a (chemical) source in the free troposphere and also for trace gases for which even relatively inefficient transport may be important. The large difference between LSF and bubble runs is attributed to differences in dynamics and microphysics in the inflow regions of the storms. The dependence of the results on the model setup indicates the need for additional model studies with a more realistic initiation of deep convection, e.g., considering effects of orography in a nested model setup.

The North Pacific Pacemaker Effect on Historical ENSO and Its Mechanisms

2019 ◽  
Vol 32 (22) ◽  
pp. 7643-7661 ◽  
Author(s):  
Dillon J. Amaya ◽  
Yu Kosaka ◽  
Wenyu Zhou ◽  
Yu Zhang ◽  
Shang-Ping Xie ◽  
...  
Keyword(s):  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Southern Oscillation ◽  
Deep Convection ◽  
Boreal Summer ◽  
Enso Events ◽  
The North ◽  
The North Pacific

Abstract Studies have indicated that North Pacific sea surface temperature (SST) variability can significantly modulate El Niño–Southern Oscillation (ENSO), but there has been little effort to put extratropical–tropical interactions into the context of historical events. To quantify the role of the North Pacific in pacing the timing and magnitude of observed ENSO, we use a fully coupled climate model to produce an ensemble of North Pacific Ocean–Global Atmosphere (nPOGA) SST pacemaker simulations. In nPOGA, SST anomalies are restored back to observations in the North Pacific (>15°N) but are free to evolve throughout the rest of the globe. We find that the North Pacific SST has significantly influenced observed ENSO variability, accounting for approximately 15% of the total variance in boreal fall and winter. The connection between the North and tropical Pacific arises from two physical pathways: 1) a wind–evaporation–SST (WES) propagating mechanism, and 2) a Gill-like atmospheric response associated with anomalous deep convection in boreal summer and fall, which we refer to as the summer deep convection (SDC) response. The SDC response accounts for 25% of the observed zonal wind variability around the equatorial date line. On an event-by-event basis, nPOGA most closely reproduces the 2014/15 and the 2015/16 El Niños. In particular, we show that the 2015 Pacific meridional mode event increased wind forcing along the equator by 20%, potentially contributing to the extreme nature of the 2015/16 El Niño. Our results illustrate the significant role of extratropical noise in pacing the initiation and magnitude of ENSO events and may improve the predictability of ENSO on seasonal time scales.

scholarly journals Effect of Lockdown on Pollutant Levels in the Delhi Megacity: Role of Local Emission Sources and Chemical Lifetimes

2021 ◽  
Vol 9 ◽  
Author(s):  
Chinmay Mallik ◽  
Harish Gadhavi ◽  
Shyam Lal ◽  
Rahul Kant Yadav ◽  
R. Boopathy ◽  
...  
Keyword(s):  
Seasonal Changes ◽  
Trace Gases ◽  
Emission Sources ◽  
Air Masses ◽  
The World ◽  
Local Emission ◽  
Maximum Decrease ◽  
Emission Changes

The COVID-19 pandemic resulted in changed emission regimes all over the world. India also imposed complete lockdown on all modes of travel and industrial activities for about 2 months from 25-March-2020 and later unlocked these activities in a phased manner. Here, we study signatures of emissions changes on levels of atmospheric trace gases and aerosols contributing to air pollution over multiple sites in India’s capital Delhi covering various lockdown and unlock phases using satellite data and in-situ observations. The resulting changes in the levels of these species were compared with respect to their average of 2015–2019 to attribute for year to year and seasonal changes. A clear impact of lockdown was observed for AOD, PM, NO2, CO, and SO2 as a result of emission changes, while changed precursor levels led to a change in O3 chemical regimes impacting its concentrations. A detailed analysis of FLEXPART trajectories revealed increased PM levels over Delhi in north-westerly air masses sourced to Punjab region all the way up to Pakistan. Changes in aerosols and NO2 were not only restricted to the surface but transcended the total tropospheric column. The maximum decrease in PM, NO2, CO, and SO2 was observed during the month of total lockdown in April. The lockdown impact varied with species e.g., PM10 and PM2.5 as well as locations even within the periphery of Delhi. While surface level aerosols and NO2 showed significant and almost similar changes, AOD showed much lower decrease than tropospheric column NO2.

scholarly journals Deep-convective influence on the upper troposphere–lower stratosphere composition in the Asian monsoon anticyclone region: 2017 StratoClim campaign results

2020 ◽  
Vol 20 (20) ◽  
pp. 12193-12210
Author(s):  
Silvia Bucci ◽  
Bernard Legras ◽  
Pasquale Sellitto ◽  
Francesco D'Amato ◽  
Silvia Viciani ◽  
...  
Keyword(s):  
Asian Monsoon ◽  
Lower Stratosphere ◽  
Trace Gases ◽  
Vertical Motion ◽  
Back Trajectory ◽  
Convective System ◽  
Small Contribution ◽  
Back Trajectories ◽  
Air Masses ◽  
Upper Troposphere

Abstract. The StratoClim stratospheric aircraft campaign took place in summer 2017 in Nepal (27 July–10 August) and provided for the first time a wide dataset of observations of air composition inside the Asian monsoon anticyclone (AMA). In the framework of this project, with the purpose of modelling the injection of pollutants and natural compounds into the stratosphere, we performed a series of diffusive back trajectory runs along the flights' tracks. The availability of in situ measurements of trace gases has been exploited to evaluate the capability of the trajectory system to reproduce the transport in the upper troposphere–lower stratosphere (UTLS) region. The diagnostics of the convective sources and mixing in the air parcel samples have been derived by integrating the trajectory output with high-resolution observations of cloud tops from the Meteosat Second Generation (MSG1) and Himawari geostationary satellites. Back trajectories have been calculated using meteorological fields from European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA-Interim and ERA5) at 3 and 1 h resolution, using both kinematic and diabatic vertical motion. The comparison among the different trajectory runs shows, in general, a higher consistency with observed data as well as a better agreement between the diabatic and kinematic version when using ERA5-based runs with respect to ERA-Interim. Overall, a better capacity in reproducing the pollution features is finally found in the diabatic version of the ERA5 runs. We therefore adopt this setting to analyse the convective influence in the UTLS starting from the StratoClim observations. A large variety of transport conditions have been individuated during the eight flights of the campaign. The larger influence by convective injections is found from the continental sources of China and India. Only a small contribution appears to be originated from maritime regions, in particular the South Pacific and the Bay of Bengal, which, unexpectedly, was not particularly active during the period of the campaign. In addition, a mass of clean air injected from a typhoon has also been detected at around 18 km. Thin filamentary structures of polluted air, characterized by peaks in CO, are observed, mostly associated with young convective air (age less than a few days) and with a predominant South China origin. The analysis revealed a case of direct injection of highly polluted air close to the level of the tropopause (anomalies of around 80 ppbv injected at 16 km) that then kept rising inside the anticyclonic circulation. Due to the location of the campaign, air from continental India, in contrast, has been only observed to be linked to air masses that recirculated within the anticyclone for 10 to 20 d, resulting in a lower concentration of the trace gas. The analysis of a flight overpassing an intense convective system close to the southern Nepalese border revealed the injection of very young air (few hours of age) directly in the tropopause region (∼18 km), visible in the trace gases as an enhancement in CO and a depletion in the O3 one. From the whole campaign, a vertical stratification in the age of air is observed: up to 15 km, the age is less than 3 d, and these fresh air masses constitute almost the totality of the air composition. A transition layer is then individuated between 15 and 17 km, where the convective contribution is still dominant, and the ages vary between 1 and 2 weeks. Above this level, the mean age of the air sampled by the aircraft is estimated to be 20 d. There, the convective contribution rapidly decreases with height and finally becomes negligible around 20 km.

scholarly journals A new WRF-Chem treatment for studying regional-scale impacts of cloud processes on aerosol and trace gases in parameterized cumuli

2015 ◽  
Vol 8 (2) ◽  
pp. 409-429 ◽  
Author(s):  
L. K. Berg ◽  
M. Shrivastava ◽  
R. C. Easter ◽  
J. D. Fast ◽  
E. G. Chapman ◽  
...  
Keyword(s):  
Deep Convection ◽  
Trace Gases ◽  
Regional Scale ◽  
Cloud Droplet ◽  
Convective Cloud ◽  
Cumulus Parameterization ◽  
Sulfate Production ◽  
Shallow Clouds ◽  
The Impact ◽  
Wet Removal

Abstract. A new treatment of cloud effects on aerosol and trace gases within parameterized shallow and deep convection, and aerosol effects on cloud droplet number, has been implemented in the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) version 3.2.1 that can be used to better understand the aerosol life cycle over regional to synoptic scales. The modifications to the model include treatment of the cloud droplet number mixing ratio; key cloud microphysical and macrophysical parameters (including the updraft fractional area, updraft and downdraft mass fluxes, and entrainment) averaged over the population of shallow clouds, or a single deep convective cloud; and vertical transport, activation/resuspension, aqueous chemistry, and wet removal of aerosol and trace gases in warm clouds. These changes have been implemented in both the WRF-Chem chemistry packages as well as the Kain–Fritsch (KF) cumulus parameterization that has been modified to better represent shallow convective clouds. Testing of the modified WRF-Chem has been completed using observations from the Cumulus Humilis Aerosol Processing Study (CHAPS). The simulation results are used to investigate the impact of cloud–aerosol interactions on regional-scale transport of black carbon (BC), organic aerosol (OA), and sulfate aerosol. Based on the simulations presented here, changes in the column-integrated BC can be as large as −50% when cloud–aerosol interactions are considered (due largely to wet removal), or as large as +40% for sulfate under non-precipitating conditions due to sulfate production in the parameterized clouds. The modifications to WRF-Chem are found to account for changes in the cloud droplet number concentration (CDNC) and changes in the chemical composition of cloud droplet residuals in a way that is consistent with observations collected during CHAPS. Efforts are currently underway to port the changes described here to the latest version of WRF-Chem, and it is anticipated that they will be included in a future public release of WRF-Chem.

scholarly journals Southern Ocean convection amplified past Antarctic warming and atmospheric CO2 rise during Heinrich Stadial 4

2020 ◽  
Vol 1 (1) ◽  
Author(s):  
Luke Skinner ◽  
Laurie Menviel ◽  
Lauren Broadfield ◽  
Julia Gottschalk ◽  
Mervyn Greaves
Keyword(s):  
Southern Ocean ◽  
Temperature Change ◽  
North Atlantic ◽  
Deep Convection ◽  
Ice Cores ◽  
Distinct Pattern ◽  
The North ◽  
Rapid Changes ◽  
Ocean Convection

Abstract The record of past climate highlights recurrent and intense millennial anomalies, characterised by a distinct pattern of inter-polar temperature change, termed the ‘thermal bipolar seesaw’, which is widely believed to arise from rapid changes in the Atlantic overturning circulation. By forcing a suppression of North Atlantic convection, models have been able to reproduce many of the general features of the thermal bipolar seesaw; however, they typically fail to capture the full magnitude of temperature change reconstructed using polar ice cores from both hemispheres. Here we use deep-water temperature reconstructions, combined with parallel oxygenation and radiocarbon ventilation records, to demonstrate the occurrence of enhanced deep convection in the Southern Ocean across the particularly intense millennial climate anomaly, Heinrich Stadial 4. Our results underline the important role of Southern Ocean convection as a potential amplifier of Antarctic warming, and atmospheric CO2 rise, that is responsive to triggers originating in the North Atlantic.

Transport processes in the lowermost stratosphere - interhemispheric differences from trace gas observations during WISE and SouthTRAC

2020 ◽  
Author(s):  
Vera Bense ◽  
Peter Hoor ◽  
Björn Kluschat ◽  
Heiko Bozem ◽  
Daniel Kunkel ◽  
...  
Keyword(s):  
Large Scale ◽  
Trace Gases ◽  
Potential Temperature ◽  
Chemical Species ◽  
Transport Processes ◽  
Spatial And Temporal Variability ◽  
Remarkable Change ◽  
Transport Pathways ◽  
Air Masses ◽  
The North

<p><span>The lowermost stratosphere (LMS) plays an important role in determining the Earth's energy budget. </span><span>The chemical species that absorb and re-emit radiation in the LMS have a large spatial and temporal variability, which is controlled by mixing and transport processes. </span><span>T</span><span>he troposphere </span><span>and</span><span> middle stratosphere </span><span>affect the </span><span>LMS through large scale isentropic transport across the tropopause or downwelling from higher altitudes.</span></p><p><span>The data presented </span><span>in this study</span><span> originates from two HALO measurement campaigns that allow an interhemispheric comparison of the composition of the lower stratosphere: First the WISE campaign which took place in September and October 2017 over Europe and the North Atlantic, and second the mission SouthTRAC (September and November 2019) where measurements focused on South America and the region around the Antarctic Peninsula.</span></p><p><span>We use high resolution in-situ measurements of different trace gases (N<sub>2</sub>O, O<sub>3</sub>, CO<sub>2</sub>, CO, </span><span>SF<sub>6</sub></span><span>) in order to quantify transport time scales, to estimate tracer fluxes and to examine the prevalent transport pathways. Particularly correlations of trace gases of different lifetime can </span><span>provide</span><span> insight in the origin of air masses in the lower stratos</span><span>p</span><span>here and their transport histories.</span></p><p><span>During WISE a remarkable change of the N<sub>2</sub>O-O<sub>3</sub> correlation at the 380 K potential temperature isentrope indicates a surprisingly strong distinction between the lowermost stratosphere and the stratosphere, suggesting two mixing regimes. Above 380 K, isentropic mixing occurs between stratospheric air masses from the tropics to</span><span>wards</span><span> high latitudes leading to a slope flattening effect. In the lowermost stratosphere isentropic mixing connects the stratosphere with the tropical tropopause layer (TTL). Based on CO observations we quantify the contribution of air from the TTL to reach 60 % - 80 % in the LMS. Using CO<sub>2</sub> measurements we estimate a typical time scale of less than 30 days for transport from the TTL into the LMS. </span></p><p><span>These methods are applied to the observations during SouthTRAC as well. </span><span>Preliminary CO budget calculations suggest a smaller contribution of TTL air to the LMS in the order of 50 %. This analysis along with correlation s</span><span>lope s</span><span>tudies</span><span> allow for an interhemispheric and interseasonal comparison of the transport processes that were observed during the two measurement periods.</span></p>

scholarly journals Deep convective influence on the UTLS composition in the Asian Monsoon Anticyclone region: 2017 StratoClim campaign results

2020 ◽  
Author(s):  
Silvia Bucci ◽  
Bernard Legras ◽  
Pasquale Sellitto ◽  
Francesco D'Amato ◽  
Silvia Viciani ◽  
...  
Keyword(s):  
Asian Monsoon ◽  
Vertical Motion ◽  
Trace Gas ◽  
Small Contribution ◽  
Back Trajectories ◽  
Air Masses ◽  
Weather Forecasts ◽  
Trajectory System ◽  
Cloud Tops

Abstract. The StratoClim stratospheric aircraft campaign took place in summer 2017 in Nepal (the 27th of July–10th of August) and provided a wide dataset of observations of air composition inside the Asian Monsoon Anticyclone. In the framework of this project, with the purpose of modelling the injection of pollutants and natural compounds into the stratosphere, we performed a series of diffusive back-trajectories runs along the flights' tracks. The availability of in-situ measurements of trace gases has been exploited to evaluate the capability of the trajectory system to reproduce the transport in the Upper Troposphere–Lower Stratosphere (UTLS) region. The diagnostics of the convective sources and mixing in the air parcel samples have been derived by integrating the trajectories output with high-resolution observations of cloud tops from the Meteosat Second Generation (MSG1) and Himawari geostationary satellites. Back-trajectories have been calculated using meteorological fields from European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA-Interim and ERA-5) at 3 h and 1 h resolution, using both kinematic and diabatic vertical motion. The comparison among the different trajectory runs shows, in general, a higher consistency with observed data, as well as a better agreement between the diabatic and kinematic version, when using ERA-5 based runs with respect to ERA-Interim. Overall, a better capacity in reproducing the pollution features is finally found in the diabatic version of the ERA-5 runs. Adopting this setting for the analysis, a large variety of transport conditions have been individuated during the 8 flights of the campaign. The larger influence by convective injections is found from the continental sources of China and India. Only a small contribution appears to be originated from maritime regions, in particular the South Pacific and the Bay of Bengal that, unexpectedly, was not particularly active during the period of the campaign. Thin filamentary structures of polluted air, characterized by peaks in CO, are observed, mostly associated with young convective air (age less than a few days) and a predominant South-China origin. Observed air from continental India, on the contrary, is often linked to a lower concentration of the trace gas and to air masses that recirculated within the anticyclone for 10 to 20 days. Vertical stratification in the age of air is observed: up to 15 km, the age is less than 3 days and these fresh air masses constitute almost the totality of the air composition. A transition layer is then individuated between 15 km and 17 km, where the convective contribution is still dominant and the ages vary between one and two weeks. Above this level, the mean age of the air sampled by the aircraft is estimated to be 20 days. There, the convective contribution rapidly decreases with height, and finally became negligible around 20 km.

scholarly journals The role of spring dry zonal advection in summer drought onset over the US Great Plains

2019 ◽  
Vol 19 (24) ◽  
pp. 15199-15216 ◽  
Author(s):  
Amir Erfanian ◽  
Rong Fu
Keyword(s):  
Great Plains ◽  
Deep Convection ◽  
Source Region ◽  
Summer Precipitation ◽  
Summer Drought ◽  
Sharp Drop ◽  
The North ◽  
Zonal Advection ◽  
Predictive Understanding

Abstract. This study addresses the role of the atmospheric moisture budget in determining the onset and development of summer droughts over the North American Great Plains (GP) using two state-of-the-art reanalysis datasets. We identified zonal moisture advection as the main cause of severe tropospheric drying during the extreme droughts in the southern GP in 2011 and northern GP in 2012. For both events, the eastward advection of anomalously dry and warm air in the free troposphere in spring set the stage for summer drought. This led to a sharp drop in relative humidity above the boundary layer, enhancing dry entrainment and suppressing deep convection. Further breakdown of the zonal advection into dynamic (caused by circulation anomalies) and thermodynamic (caused by moisture anomalies) contributions reveals dominance of thermodynamic advection in the tropospheric drying observed during the onset of both 2011 and 2012 droughts. The dependence of thermodynamic advection on the moisture gradient links springtime precipitation in the Rockies and southwestern US, the source region of the anomalous dry advection, to the GP summer precipitation (with correlations > 0.4 using gauge-based data). Identifying this previously overlooked precursor of the GP summer droughts improves our predictive understanding of drought onset mechanisms over the region.

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