Effects of regional-scale and convective transports on tropospheric ozone chemistry revealed by aircraft observations during the wet season of the AMMA campaign

Abstract. The African Monsoon Multidisciplinary Analyses (AMMA) fourth airborne campaign was conducted in July–August 2006 to study the chemical composition of the middle and upper troposphere in West Africa with the major objective to better understand the processing of chemical emissions by the West African Monsoon (WAM) and its associated regional-scale and vertical transports. In particular, the french airborne experiment was organized around two goals. The first was to characterize the impact of Mesoscale Convective Systems (MCSs) on the ozone budget in the upper troposphere and the evolution of the chemical composition of these convective plumes as they move westward toward the Atlantic Ocean. The second objective was to discriminate the impact of remote sources of pollution over West Africa, including transport from the middle east, Europe, Asia and from southern hemispheric fires. Observations of O3, CO, NOx, H2O and hydroperoxide above West Africa along repeated meridional transects were coupled with transport analysis based on the FLEXPART lagrangian model. The cross analysis of trace gas concentrations and transport pathways revealed 5 types of air masses: convective uplift of industrial and urban emissions, convective uplift of biogenic emissions, slow advection from Cotonou polluted plumes near the coast, meridional transport of upper tropospheric air from the subtropical barrier region, and meridional transport of Southern Hemisphere (SH) biomass burning emissions. O3/CO correlation plots and the correlation plots of H2O2 with a OH proxy revealed not only a control of the trace gas variability by transport processes but also significant photochemical reactivity in the mid- and upper troposphere. The study of four MCSs outflow showed contrasted chemical composition and air mass origins depending on the MCSs lifetime and latitudinal position. Favorables conditions for ozone production were found for MCSs with increased MCS lifetime (>1.5 days), which allowed for more H2O2 formation, and with trajectories crossing the 10° N latitude, which increased CO transport to the upper troposphere. The upper tropospheric concentrations sampled in the MCS outflow regions showed mixed origins including local vertical convective transport, and uplifting of air from the low troposphere over the middle-east related to the summer Asian low pressure system or from the southern hemispheric fires.

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The impact of overshooting deep convection on local transport and mixing in the tropical upper troposphere/lower stratosphere (UTLS)

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-6467-2015 ◽

2015 ◽

Vol 15 (11) ◽

pp. 6467-6486 ◽

Cited By ~ 21

Author(s):

W. Frey ◽

R. Schofield ◽

P. Hoor ◽

D. Kunkel ◽

F. Ravegnani ◽

...

Keyword(s):

Lower Stratosphere ◽

Deep Convection ◽

Horizontal Resolution ◽

Transport Processes ◽

Convective System ◽

Upper Troposphere ◽

Tropical Tropopause Layer ◽

Tropical Tropopause ◽

Transport And Mixing ◽

The Impact

Abstract. In this study we examine the simulated downward transport and mixing of stratospheric air into the upper tropical troposphere as observed on a research flight during the SCOUT-O3 campaign in connection with a deep convective system. We use the Advanced Research Weather and Research Forecasting (WRF-ARW) model with a horizontal resolution of 333 m to examine this downward transport. The simulation reproduces the deep convective system, its timing and overshooting altitudes reasonably well compared to radar and aircraft observations. Passive tracers initialised at pre-storm times indicate the downward transport of air from the stratosphere to the upper troposphere as well as upward transport from the boundary layer into the cloud anvils and overshooting tops. For example, a passive ozone tracer (i.e. a tracer not undergoing chemical processing) shows an enhancement in the upper troposphere of up to about 30 ppbv locally in the cloud, while the in situ measurements show an increase of 50 ppbv. However, the passive carbon monoxide tracer exhibits an increase, while the observations show a decrease of about 10 ppbv, indicative of an erroneous model representation of the transport processes in the tropical tropopause layer. Furthermore, it could point to insufficient entrainment and detrainment in the model. The simulation shows a general moistening of air in the lower stratosphere, but it also exhibits local dehydration features. Here we use the model to explain the processes causing the transport and also expose areas of inconsistencies between the model and observations.

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How might climate change affect river flows across West Africa?

Climatic Change ◽

10.1007/s10584-021-03256-0 ◽

2021 ◽

Vol 169 (3-4) ◽

Author(s):

Ponnambalam Rameshwaran ◽

Victoria A. Bell ◽

Helen N. Davies ◽

Alison L. Kay

Keyword(s):

Climate Change ◽

West Africa ◽

Regional Scale ◽

Weather Data ◽

Eastern Region ◽

Water Shortages ◽

River Flows ◽

Considerable Uncertainty ◽

Modelling Framework ◽

The Impact

AbstractWest Africa and its semi-arid Sahelian region are one of the world’s most vulnerable regions to climate change with a history of extreme climate variability. There is still considerable uncertainty as to how projected climate change will affect precipitation at local and regional scales and the consequent impact on river flows and water resources across West Africa. Here, we aim to address this uncertainty by configuring a regional-scale hydrological model to West Africa. The model (hydrological modelling framework for West Africa—HMF-WA) simulates spatially consistent river flows on a 0.1° × 0.1° grid (approximately 10 km × 10 km) continuously across the whole domain and includes estimates of anthropogenic water use, wetland inundation, and local hydrological features such as endorheic regions. Regional-scale hydrological simulations driven by observed weather data are assessed against observed flows before undertaking an analysis of the impact of projected future climate scenarios from the CMIP5 on river flows up to the end of the twenty-first century. The results indicate that projected future changes in river flows are highly spatially variable across West Africa, particularly across the Sahelian region where the predicted changes are more pronounced. The study shows that median peak flows are projected to decrease by 23% in the west (e.g. Senegal) and increase by 80% in the eastern region (e.g. Chad) by the 2050s. The projected reductions in river flows in western Sahel lead to future droughts and water shortages more likely, while in the eastern Sahel, projected increases lead to future frequent floods.

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Impact of Lagrangian transport on lower-stratospheric transport timescales in a climate model

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-15227-2020 ◽

2020 ◽

Vol 20 (23) ◽

pp. 15227-15245

Author(s):

Edward J. Charlesworth ◽

Ann-Kristin Dugstad ◽

Frauke Fritsch ◽

Patrick Jöckel ◽

Felix Plöger

Keyword(s):

Atmospheric Chemistry ◽

Large Scale ◽

Climate Model ◽

Polar Vortex ◽

Transport Processes ◽

Lagrangian Model ◽

Trace Gas ◽

Lagrangian Transport ◽

Transport Barriers ◽

The Impact

Abstract. We investigate the impact of model trace gas transport schemes on the representation of transport processes in the upper troposphere and lower stratosphere. Towards this end, the Chemical Lagrangian Model of the Stratosphere (CLaMS) was coupled to the ECHAM/MESSy Atmospheric Chemistry (EMAC) model and results from the two transport schemes (Lagrangian critical Lyapunov scheme and flux-form semi-Lagrangian, respectively) were compared. Advection in CLaMS was driven by the EMAC simulation winds, and thereby the only differences in transport between the two sets of results were caused by differences in the transport schemes. To analyze the timescales of large-scale transport, multiple tropical-surface-emitted tracer pulses were performed to calculate age of air spectra, while smaller-scale transport was analyzed via idealized, radioactively decaying tracers emitted in smaller regions (nine grid cells) within the stratosphere. The results show that stratospheric transport barriers are significantly stronger for Lagrangian EMAC-CLaMS transport due to reduced numerical diffusion. In particular, stronger tracer gradients emerge around the polar vortex, at the subtropical jets, and at the edge of the tropical pipe. Inside the polar vortex, the more diffusive EMAC flux-form semi-Lagrangian transport scheme results in a substantially higher amount of air with ages from 0 to 2 years (up to a factor of 5 higher). In the lowermost stratosphere, mean age of air is much smaller in EMAC, owing to stronger diffusive cross-tropopause transport. Conversely, EMAC-CLaMS shows a summertime lowermost stratosphere age inversion – a layer of older air residing below younger air (an “eave”). This pattern is caused by strong poleward transport above the subtropical jet and is entirely blurred by diffusive cross-tropopause transport in EMAC. Potential consequences from the choice of the transport scheme on chemistry–climate and geoengineering simulations are discussed.

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Hydrogeochemistry and Related Processes Controlling the Formation of the Chemical Composition of Thermal Water in Podhale Trough, Poland

Energies ◽

10.3390/en13215584 ◽

2020 ◽

Vol 13 (21) ◽

pp. 5584

Author(s):

Klaudia Sekuła ◽

Piotr Rusiniak ◽

Katarzyna Wątor ◽

Ewa Kmiecik

Keyword(s):

Chemical Composition ◽

Thermal Water ◽

Flow Direction ◽

Regional Scale ◽

Water Reservoir ◽

Major Elements ◽

Hydrogeochemical Modelling ◽

West Carpathians ◽

Physical And Chemical ◽

The Impact

The most promising Polish region in terms of its geothermal resource potential is the Podhale Trough in the Inner West Carpathians, where the thermal water occurs in the Eocene-Mesozoic strata. The origin and conditions of formation of the chemical composition of the thermal water are different in a regional scale due to the impact of infiltrating water on the chemical compounds present in nearby thermal intakes, chemical processes responsible for the concentration of major elements and residence time. The article presents the regional conceptual model in regard to the factors controlling the chemistry of thermal water from Podhale Trough and the conditions of its exchange. It was allowed by performing the hydrogeochemical characteristics of studied water and analyzing its changes according to flow direction from HCO3-Ca-Mg type to SO4-Cl-Na-Ca and SO4-Ca-Mg types. The hydrogeochemical modelling was also made allowing identification of the impact of reservoir rocks on the formation of the chemical composition. For confirmation of the theories formulated and for more accurate interpretation of the results obtained from hydrogeochemical modelling, hydrochemical indices were calculated, i.e., rHCO3−/rCl−, rNa+/rCl−, rCa2+/rMg2+, rCa2+/(rCa2+ + rSO42−) and rNa+/(rNa+ + rCl−). The results revealed the most important processes evolving the chemistry of thermal water are progressive freshening of the thermal water reservoir, which in the past was filled with salty water, dissolution of gypsum, and ongoing dolomitization. Conducted research presents the important factors that in the case of increased exploitation of thermal water in the Podhale Trough, may influence the quality of thermal water in terms of its physical and chemical parameters.

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Climate Simulations with an Isentropic Finite-Volume Dynamical Core

Journal of Climate ◽

10.1175/2011jcli4184.1 ◽

2012 ◽

Vol 25 (8) ◽

pp. 2843-2861 ◽

Cited By ~ 3

Author(s):

Chih-Chieh Chen ◽

Philip J. Rasch

Keyword(s):

Finite Volume ◽

Climate Models ◽

Transport Processes ◽

Climate Simulation ◽

Modeling Framework ◽

Dynamical Core ◽

Vertical Coordinate ◽

Upper Troposphere ◽

Isentropic Model ◽

The Impact

Abstract This paper discusses the impact of changing the vertical coordinate from a hybrid pressure to a hybrid-isentropic coordinate within the finite-volume (FV) dynamical core of the Community Atmosphere Model (CAM). Results from a 20-yr climate simulation using the new model coordinate configuration are compared to control simulations produced by the Eulerian spectral and FV dynamical cores of CAM, which both use a pressure-based (σ − P) coordinate. The same physical parameterization package is employed in all three dynamical cores. The isentropic modeling framework significantly alters the simulated climatology and has several desirable features. The revised model produces a better representation of heat transport processes in the atmosphere leading to much improved atmospheric temperatures. The authors show that the isentropic model is very effective in reducing the long-standing cold temperature bias in the upper troposphere and lower stratosphere, a deficiency shared among most climate models. The warmer upper troposphere and stratosphere seen in the isentropic model reduces the global coverage of high clouds, which is in better agreement with observations. The isentropic model also shows improvements in the simulated wintertime mean sea level pressure field in the Northern Hemisphere.

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Direct inversion of circulation from tracer measurements – Part 2: Sensitivity studies and model recovery tests

10.5194/acp-2020-72 ◽

2020 ◽

Author(s):

Thomas von Clarmann ◽

Udo Grabowski

Keyword(s):

Lower Stratosphere ◽

Velocity Fields ◽

Trace Gas ◽

Meridional Transport ◽

Upper Troposphere ◽

Direct Inversion ◽

Circulation Patterns ◽

Sensitivity Studies ◽

Reference Fields ◽

Middle Stratosphere

Abstract. The direct inversion of the 2D continuity equation allows to infer the effective meridional transport of trace gases in the middle stratosphere. This methods exploits the information both given by the displacement of patterns in measured trace gas distributions and by the approximate balance between sinks and horizontal as well as vertical advection. Model recovery tests have shown that with the current setup of the algorithm, this method reliably reproduces the circulation patterns in the entire analysis domain from 6 to 66 km altitude. Due to the regularization of the inversion, velocities above about 30 km are more likely under- than overestimated. This is explained by the fact that the measured trace gas distributions at higher altitudes generally contain less information and that the regularization of the inversion pushes results towards zero. Weaker regularization would in some cases allow a more accurate recovery of the velocity fields. However, there is a price to pay in that the risk of convergence failure increases. No instance was found where the algorithm generated artificial patterns not present in the reference fields. Most information on effective velocities above 50 km is included in measurements of CH4, CO, H2O, and N2O, while CFC-11, HCFC-22, and CFC-12 constrain the inversion most efficiently in the middle stratosphere. H2O is a particularly important tracer in the upper troposphere/lower stratosphere. SF6 and CCl4 contain generally less information but still contribute to the reduction of the estimated uncertainties.

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Space-Time Variability of UTLS Chemical Distribution in the Asian Summer Monsoon Viewed by Limb and Nadir Satellite Sensors

10.5194/acp-2017-252 ◽

2017 ◽

Author(s):

Jiali Luo ◽

Laura L. Pan ◽

Shawn B. Honomichl ◽

John W. Bergman ◽

William J. Randel ◽

...

Keyword(s):

Information Content ◽

Summer Monsoon ◽

Seasonal Variability ◽

Asian Summer Monsoon ◽

Trace Gas ◽

Time Variability ◽

Dynamical Structure ◽

Upper Troposphere ◽

Asian Summer ◽

The Impact

Abstract. The Asian Summer Monsoon (ASM) creates a hemispheric scale signature in trace gas distributions in the upper troposphere and lower stratosphere (UTLS). Data from satellite retrievals are the best source of information for characterizing these large-scale signatures. Measurements from the Microwave Limb Sounder (MLS), a limb viewing satellite sensor, have been the most widely used retrieval products for these type of studies. This work explores the information content for the ASM upper troposphere from two nadir-viewing sensors, IASI and OMI. Day-to-day behaviour of carbon monoxide (CO) and ozone (O3) in the UTLS from these two nadir-viewing sensors are analysed in comparison to MLS to examine the information content for the ASM UTLS trace gas analyses. Day-to-day changes in tracer distributions in response to dynamical variability is explored, to assess whether these nadir viewing sensors provide useful information for investigating sub-seasonal variability. Our result shows that both nadir-viewing instruments capture the impact of ASM dynamics on spatial distribution of tracers in the UTLS. Despite the limited vertical resolution, tropospheric profiles from IASI are able to represent the upper tropospheric enhancement of CO in the region of ASM anticyclone. Similarly, the OMI O3 profile product is capable of distinguishing the tropospheric dominated air mass in the anticyclone from the stratospheric dominated background on a daily time scale. The high horizontal sampling density of IASI data show finer structures in the horizontal distribution of CO compared to the limb viewing MLS, including CO enhancement in the upper troposphere over the western Pacific resulting from the eastward eddy shedding of the ASM anticyclone. Sub-seasonal variability of tracers is correlated with the dynamical structure of the anticyclone as represented by the geopotential height (GPH) field, and systematic differences between the nadir and limb sounder results are discussed.

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Direct inversion of circulation from tracer measurements – Part 2: Sensitivity studies and model recovery tests

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-2509-2021 ◽

2021 ◽

Vol 21 (4) ◽

pp. 2509-2526

Author(s):

Thomas von Clarmann ◽

Udo Grabowski

Keyword(s):

Lower Stratosphere ◽

Velocity Fields ◽

Trace Gas ◽

Meridional Transport ◽

Upper Troposphere ◽

Direct Inversion ◽

Circulation Patterns ◽

Sensitivity Studies ◽

Reference Fields ◽

Middle Stratosphere

Abstract. The direct inversion of the 2D continuity equation allows for the inference of the effective meridional transport of trace gases in the middle stratosphere. This method exploits the information given by both the displacement of patterns in measured trace gas distributions and the approximate balance between sinks and horizontal as well as vertical advection. Model recovery tests show that with the current setup of the algorithm, this method reliably reproduces the circulation patterns in the entire analysis domain from 6 to 66 km altitude. Due to the regularization of the inversion, velocities above about 30 km are more likely under- than overestimated. This is explained by the fact that the measured trace gas distributions at higher altitudes generally contain less information and that the regularization of the inversion pushes results towards 0. Weaker regularization would in some cases allow a more accurate recovery of the velocity fields, but there is a price to pay in that the risk of convergence failure increases. No instance was found where the algorithm generated artificial patterns not present in the reference fields. Most information on effective velocities above 50 km is included in measurements of CH4, CO, H2O, and N2O, while CFC-11, HCFC-22, and CFC-12 constrain the inversion most efficiently in the middle stratosphere. H2O is a particularly important tracer in the upper troposphere or lower stratosphere. SF6 and CCl4 generally contain less information but still contribute to the reduction in the estimated uncertainties. With these tests, the reliability of the method has been established.

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An overview of the SCOUT-AMMA stratospheric aircraft, balloons and sondes campaign in West Africa, August 2006: rationale, roadmap and highlights

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-19713-2009 ◽

2009 ◽

Vol 9 (5) ◽

pp. 19713-19781 ◽

Cited By ~ 5

Author(s):

F. Cairo ◽

J. P. Pommereau ◽

K. S. Law ◽

H. Schlager ◽

A. Garnier ◽

...

Keyword(s):

West Africa ◽

Large Scale ◽

Lower Stratosphere ◽

Chemical Species ◽

Upper Troposphere ◽

Convective Systems ◽

Mesoscale Convective ◽

Aerosol Dust ◽

D 20 ◽

The Impact

Abstract. A multi-platform field measurement campaign involving aircraft and balloons took place over West Africa between 26 July and 25 August 2006, in the frame of the concomitant AMMA Special Observing Period and SCOUT-O3 African tropical activities. Specifically aiming at sampling the upper troposphere and lower stratosphere, the high-altitude research aircraft M55 Geophysica was deployed in Ouagadougou (12.3° N, 1.7° W), Burkina Faso, in conjunction with the German D-20 Falcon, while a series of stratospheric balloon and sonde flights were conducted from Niamey (13.5° N, 2.0° E), Niger. The stratospheric aircraft and balloon flights intended to gather experimental evidence for a better understanding of large scale transport, assessing the effect of lightning on NOx production, and studying the impact of intense mesoscale convective systems on water, aerosol, dust and chemical species in the upper troposphere and lower stratosphere. The M55 Geophysica carried out five local and four transfer flights between southern Europe and the Sahel and back, while eight stratospheric balloons and twenty-nine sondes were flown from Niamey. These experiments allowed a characterization of the tropopause and lower stratosphere of the region. We provide here an overview of the campaign activities together with a description of the general meteorological situation during the flights and a summary of the observations accomplished.

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An introduction to the SCOUT-AMMA stratospheric aircraft, balloons and sondes campaign in West Africa, August 2006: rationale and roadmap

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-2237-2010 ◽

2010 ◽

Vol 10 (5) ◽

pp. 2237-2256 ◽

Cited By ~ 55

Author(s):

F. Cairo ◽

J. P. Pommereau ◽

K. S. Law ◽

H. Schlager ◽

A. Garnier ◽

...

Keyword(s):

West Africa ◽

Large Scale ◽

Lower Stratosphere ◽

Chemical Species ◽

Upper Troposphere ◽

Convective Systems ◽

Mesoscale Convective ◽

Aerosol Dust ◽

D 20 ◽

The Impact

Abstract. A multi-platform field measurement campaign involving aircraft and balloons took place over West Africa between 26 July and 25 August 2006, in the frame of the concomitant AMMA Special Observing Period and SCOUT-O3 African tropical activities. Specifically aiming at sampling the upper troposphere and lower stratosphere, the high-altitude research aircraft M55 Geophysica was deployed in Ouagadougou (12.3° N, 1.7° W), Burkina Faso, in conjunction with the German D-20 Falcon, while a series of stratospheric balloons and sonde flights were conducted from Niamey (13.5° N, 2.0° E), Niger. Altogether, these measurements were intended to provide experimental evidence for a better understanding of large scale transport, assessing the effect of lightning on NOx production, and studying the impact of intense mesoscale convective systems on water, aerosol, dust and chemical species in the upper troposphere and lower stratosphere. The M55 Geophysica carried out five local and four transfer flights between southern Europe and the Sahel and back, while eight stratospheric balloons and twenty-nine sondes were flown from Niamey. These experiments allowed a characterization of the tropopause and lower stratosphere of the region. The paper provides an overview of SCOUT-AMMA campaign activities together with a description of the meteorology of the African monsoon and the situation prevailing during the flights and a brief summary of the observations accomplished.

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