scholarly journals Terrestrial sources and distribution of atmospheric sulphur

1997 ◽  
Vol 352 (1350) ◽  
pp. 149-158 ◽  
Author(s):  
J. Lelieveld ◽  
G.–J. Roelofs ◽  
L. Ganzeveld ◽  
J. Feichter ◽  
H. Rodhe
Keyword(s):  
Aqueous Phase ◽  
General Circulation ◽  
Heterogeneous Reaction ◽  
Circulation Model ◽  
Anthropogenic Emissions ◽  
Natural Emissions ◽  
Global Estimates ◽  
Deposition Processes ◽  
The Impact ◽  
Sulphur Species

The general circulation model ECHAM has been coupled to a chemistry and sulphur cycle model to study the impact of terrestrial, i.e. mostly anthropogenic sulphur dioxide (SO 2 ), sources on global distributions of sulphur species in the atmosphere. We briefly address currently available source inventories. It appears that global estimates of natural emissions are associated with uncertainties up to a factor of 2, while anthropogenic emissions have uncertainty ranges of about +/− 30 per cent. Further, some recent improvements in the model descriptions of multiphase chemistry and deposition processes are presented. Dry deposition is modelled consistently with meteorological processes and surface properties. The results indicate that surface removal of SO 2 is less efficient than previously assumed, and that the SO 2 lifetime is thus longer. Coupling of the photochemistry and sulphur chemistry schemes in the model improves the treatment of multiphase processes such as oxidant (hydrogen peroxide) supply in aqueous phase SO 2 oxidation. The results suggest that SO 2 oxidation by ozone (O 3 ) in the aqueous phase is more important than indicated in earlier work. However, it appears that we still overestimate atmospheric SO 2 concentrations near the surface in the relatively polluted Northern Hemisphere. On the other hand, we somewhat underestimate sulphate levels in these regions, which suggests that additional heterogeneous reaction mechanisms, e.g. on aerosols, enhance SO 2 oxidation.

scholarly journals Ozone impacts of gas–aerosol uptake in global chemistry transport models

2018 ◽  
Vol 18 (5) ◽  
pp. 3147-3171 ◽  
Author(s):  
Scarlet Stadtler ◽  
David Simpson ◽  
Sabine Schröder ◽  
Domenico Taraborrelli ◽  
Andreas Bott ◽  
...  
Keyword(s):  
East Asia ◽  
Surface Area ◽  
General Circulation ◽  
Heterogeneous Reaction ◽  
Circulation Model ◽  
Photochemical Reactions ◽  
Heterogeneous Reactions ◽  
Transport Models ◽  
Global Pattern ◽  
The Impact

Abstract. The impact of six heterogeneous gas–aerosol uptake reactions on tropospheric ozone and nitrogen species was studied using two chemical transport models, the Meteorological Synthesizing Centre-West of the European Monitoring and Evaluation Programme (EMEP MSC-W) and the European Centre Hamburg general circulation model combined with versions of the Hamburg Aerosol Model and Model for Ozone and Related chemical Tracers (ECHAM-HAMMOZ). Species undergoing heterogeneous reactions in both models include N2O5, NO3, NO2, O3, HNO3, and HO2. Since heterogeneous reactions take place at the aerosol surface area, the modelled surface area density (Sa) of both models was compared to a satellite product retrieving the surface area. This comparison shows a good agreement in global pattern and especially the capability of both models to capture the extreme aerosol loadings in east Asia. The impact of the heterogeneous reactions was evaluated by the simulation of a reference run containing all heterogeneous reactions and several sensitivity runs. One reaction was turned off in each sensitivity run to compare it with the reference run. The analysis of the sensitivity runs confirms that the globally most important heterogeneous reaction is the one of N2O5. Nevertheless, NO2, HNO3, and HO2 heterogeneous reactions gain relevance particularly in east Asia due to the presence of high NOx concentrations and high Sa in the same region. The heterogeneous reaction of O3 itself on dust is of minor relevance compared to the other heterogeneous reactions. The impacts of the N2O5 reactions show strong seasonal variations, with the biggest impacts on O3 in springtime when photochemical reactions are active and N2O5 levels still high. Evaluation of the models with northern hemispheric ozone surface observations yields a better agreement of the models with observations in terms of concentration levels, variability, and temporal correlations at most sites when the heterogeneous reactions are incorporated. Our results are loosely consistent with results from earlier studies, although the magnitude of changes induced by N2O5 reaction is at the low end of estimates, which seems to fit a trend, whereby the more recent the study the lower the impacts of these reactions.

On the impact of sea ice in a global ocean circulation model

1997 ◽  
Vol 25 ◽  
pp. 111-115 ◽  
Author(s):  
Achim Stössel
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Ocean Circulation ◽  
General Circulation ◽  
Thermohaline Circulation ◽  
Circulation Model ◽  
Deep Ocean ◽  
Global Ocean ◽  
Convective Activity ◽  
The Impact

This paper investigates the long-term impact of sea ice on global climate using a global sea-ice–ocean general circulation model (OGCM). The sea-ice component involves state-of-the-art dynamics; the ocean component consists of a 3.5° × 3.5° × 11 layer primitive-equation model. Depending on the physical description of sea ice, significant changes are detected in the convective activity, in the hydrographic properties and in the thermohaline circulation of the ocean model. Most of these changes originate in the Southern Ocean, emphasizing the crucial role of sea ice in this marginally stably stratified region of the world's oceans. Specifically, if the effect of brine release is neglected, the deep layers of the Southern Ocean warm up considerably; this is associated with a weakening of the Southern Hemisphere overturning cell. The removal of the commonly used “salinity enhancement” leads to a similar effect. The deep-ocean salinity is almost unaffected in both experiments. Introducing explicit new-ice thickness growth in partially ice-covered gridcells leads to a substantial increase in convective activity, especially in the Southern Ocean, with a concomitant significant cooling and salinification of the deep ocean. Possible mechanisms for the resulting interactions between sea-ice processes and deep-ocean characteristics are suggested.

scholarly journals The Rossby radius in the Arctic Ocean

Ocean Science ◽  
2014 ◽  
Vol 10 (6) ◽  
pp. 967-975 ◽  
Author(s):  
A. J. G. Nurser ◽  
S. Bacon
Keyword(s):  
Arctic Ocean ◽  
General Circulation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
High Arctic ◽  
The Arctic ◽  
Hudson Bay ◽  
Ocean Eddies ◽  
Shelf Seas ◽  
The Impact

Abstract. The first (and second) baroclinic deformation (or Rossby) radii are presented north of ~60° N, focusing on deep basins and shelf seas in the high Arctic Ocean, the Nordic seas, Baffin Bay, Hudson Bay and the Canadian Arctic Archipelago, derived from climatological ocean data. In the high Arctic Ocean, the first Rossby radius increases from ~5 km in the Nansen Basin to ~15 km in the central Canadian Basin. In the shelf seas and elsewhere, values are low (1–7 km), reflecting weak density stratification, shallow water, or both. Seasonality strongly impacts the Rossby radius only in shallow seas, where winter homogenization of the water column can reduce it to below 1 km. Greater detail is seen in the output from an ice–ocean general circulation model, of higher resolution than the climatology. To assess the impact of secular variability, 10 years (2003–2012) of hydrographic stations along 150° W in the Beaufort Gyre are also analysed. The first-mode Rossby radius increases over this period by ~20%. Finally, we review the observed scales of Arctic Ocean eddies.

scholarly journals Impact of precipitation intermittency on NAO-temperature signals in proxy records

2013 ◽  
Vol 9 (2) ◽  
pp. 871-886 ◽  
Author(s):  
M. Casado ◽  
P. Ortega ◽  
V. Masson-Delmotte ◽  
C. Risi ◽  
D. Swingedouw ◽  
...  
Keyword(s):  
General Circulation ◽  
Ice Core ◽  
Circulation Model ◽  
Ice Cores ◽  
Stable Isotope Ratio ◽  
Global Network ◽  
Temporal Correlations ◽  
The North ◽  
The North Atlantic Oscillation ◽  
The Impact

Abstract. In mid and high latitudes, the stable isotope ratio in precipitation is driven by changes in temperature, which control atmospheric distillation. This relationship forms the basis for many continental paleoclimatic reconstructions using direct (e.g. ice cores) or indirect (e.g. tree ring cellulose, speleothem calcite) archives of past precipitation. However, the archiving process is inherently biased by intermittency of precipitation. Here, we use two sets of atmospheric reanalyses (NCEP (National Centers for Environmental Prediction) and ERA-interim) to quantify this precipitation intermittency bias, by comparing seasonal (winter and summer) temperatures estimated with and without precipitation weighting. We show that this bias reaches up to 10 °C and has large interannual variability. We then assess the impact of precipitation intermittency on the strength and stability of temporal correlations between seasonal temperatures and the North Atlantic Oscillation (NAO). Precipitation weighting reduces the correlation between winter NAO and temperature in some areas (e.g. Québec, South-East USA, East Greenland, East Siberia, Mediterranean sector) but does not alter the main patterns of correlation. The correlations between NAO, δ18O in precipitation, temperature and precipitation weighted temperature are investigated using outputs of an atmospheric general circulation model enabled with stable isotopes and nudged using reanalyses (LMDZiso (Laboratoire de Météorologie Dynamique Zoom)). In winter, LMDZiso shows similar correlation values between the NAO and both the precipitation weighted temperature and δ18O in precipitation, thus suggesting limited impacts of moisture origin. Correlations of comparable magnitude are obtained for the available observational evidence (GNIP (Global Network of Isotopes in Precipitation) and Greenland ice core data). Our findings support the use of archives of past δ18O for NAO reconstructions.

scholarly journals Coupled Ocean–Atmosphere Response to Seasonal Modulation of Ocean Color: Impact on Interannual Climate Simulations in the Tropical Pacific

2007 ◽  
Vol 20 (2) ◽  
pp. 353-374 ◽  
Author(s):  
J. Ballabrera-Poy ◽  
R. Murtugudde ◽  
R-H. Zhang ◽  
A. J. Busalacchi
Keyword(s):  
Solar Radiation ◽  
Interannual Variability ◽  
Seasonal Cycle ◽  
General Circulation ◽  
Ocean Color ◽  
Circulation Model ◽  
Enso Events ◽  
Ocean Atmosphere ◽  
Atmosphere Model ◽  
The Impact

Abstract The ability to use remotely sensed ocean color data to parameterize biogenic heating in a coupled ocean–atmosphere model is investigated. The model used is a hybrid coupled model recently developed at the Earth System Science Interdisciplinary Center (ESSIC) by coupling an ocean general circulation model with a statistical atmosphere model for wind stress anomalies. The impact of the seasonal cycle of water turbidity on the annual mean, seasonal cycle, and interannual variability of the coupled system is investigated using three simulations differing in the parameterization of the vertical attenuation of downwelling solar radiation: (i) a control simulation using a constant 17-m attenuation depth, (ii) a simulation with the spatially varying annual mean of the satellite-derived attenuation depth, and (iii) a simulation accounting for the seasonal cycle of the attenuation depth. The results indicate that a more realistic attenuation of solar radiation slightly reduces the cold bias of the model. While a realistic attenuation of solar radiation hardly affects the annual mean and the seasonal cycle due to anomaly coupling, it significantly affects the interannual variability, especially when the seasonal cycle of the attenuation depth is used. The seasonal cycle of the attenuation depth interacts with the low-frequency equatorial dynamics to enhance warm and cold anomalies, which are further amplified via positive air–sea feedbacks. These results also indicate that interannual variability of the attenuation depths is required to capture the asymmetric biological feedbacks during cold and warm ENSO events.

scholarly journals Impact of climate change on sediment yield in the Mekong River basin: a case study of the Nam Ou basin, Lao PDR

2013 ◽  
Vol 17 (1) ◽  
pp. 1-20 ◽  
Author(s):  
B. Shrestha ◽  
M. S. Babel ◽  
S. Maskey ◽  
A. van Griensven ◽  
S. Uhlenbrook ◽  
...  
Keyword(s):  
Climate Change ◽  
Sediment Yield ◽  
General Circulation ◽  
Climate Models ◽  
Greenhouse Gas Emission ◽  
Circulation Model ◽  
Sediment Flux ◽  
Seasonal Temperature ◽  
Impact Of Climate Change ◽  
The Impact

Abstract. This paper evaluates the impact of climate change on sediment yield in the Nam Ou basin located in northern Laos. Future climate (temperature and precipitation) from four general circulation models (GCMs) that are found to perform well in the Mekong region and a regional circulation model (PRECIS) are downscaled using a delta change approach. The Soil and Water Assessment Tool (SWAT) is used to assess future changes in sediment flux attributable to climate change. Results indicate up to 3.0 °C shift in seasonal temperature and 27% (decrease) to 41% (increase) in seasonal precipitation. The largest increase in temperature is observed in the dry season while the largest change in precipitation is observed in the wet season. In general, temperature shows increasing trends but changes in precipitation are not unidirectional and vary depending on the greenhouse gas emission scenarios (GHGES), climate models, prediction period and season. The simulation results show that the changes in annual stream discharges are likely to range from a 17% decrease to 66% increase in the future, which will lead to predicted changes in annual sediment yield ranging from a 27% decrease to about 160% increase. Changes in intra-annual (monthly) discharge as well as sediment yield are even greater (−62 to 105% in discharge and −88 to 243% in sediment yield). A higher discharge and sediment flux are expected during the wet seasons, although the highest relative changes are observed during the dry months. The results indicate high uncertainties in the direction and magnitude of changes of discharge as well as sediment yields due to climate change. As the projected climate change impact on sediment varies remarkably between the different climate models, the uncertainty should be taken into account in both sediment management and climate change adaptation.

scholarly journals Theoretical aspects of the onset of Indian summer monsoon from perturbed orography simulations in a GCM

2006 ◽  
Vol 24 (8) ◽  
pp. 2075-2089 ◽  
Author(s):  
A. Chakraborty ◽  
R. S. Nanjundiah ◽  
J. Srinivasan
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
General Circulation ◽  
Large Scale ◽  
Vertical Motion ◽  
Circulation Model ◽  
Threshold Value ◽  
The Earth ◽  
Static Energy ◽  
The Impact

Abstract. A theory is proposed to determine the onset of the Indian Summer Monsoon (ISM) in an Atmospheric General Circulation Model (AGCM). The onset of ISM is delayed substantially in the absence of global orography. The impact of orography over different parts of the Earth on the onset of ISM has also been investigated using five additional perturbed simulations. The large difference in the date of onset of ISM in these simulations has been explained by a new theory based on the Surface Moist Static Energy (SMSE) and vertical velocity at the mid-troposphere. It is found that onset occurs only after SMSE crosses a threshold value and the large-scale vertical motion in the middle troposphere becomes upward. This study shows that both dynamics and thermodynamics play profound roles in the onset of the monsoon.

scholarly journals The impact of the planetary β-effect on the tilting vertical structure of a mesoscale eddy

2018 ◽  
Author(s):  
Shengmu Yang ◽  
Jiuxing Xing ◽  
Shengli Chen ◽  
Jiwei Tian ◽  
Daoyi Chen
Keyword(s):  
South China Sea ◽  
South China ◽  
General Circulation ◽  
Vertical Structure ◽  
Mesoscale Eddy ◽  
Maximum Velocity ◽  
Circulation Model ◽  
Mesoscale Eddies ◽  
China Sea ◽  
The Impact

Abstract. Tilting mesoscale eddies in the South China Sea have been reported recently from observed field data. The mechanism of the dynamic process of the tilt, however, is not well understood. In this study, the influence of planetary β on the vertical structure of mesoscale eddies and its mechanism is investigated using theoretical analysis and numerical model experiments based on the MIT General Circulation Model (MITgcm). The results of the both approaches show that vertical motion due to the planetary β effect and nonlinear dynamics causes a pressure anomaly in the horizontal domain which triggers the tilt of the eddy axis. The tilting distance extends to be the radius of the eddy maximum velocity. In addition, the vertical stratification is another key factor in controlling the tilt of a mesoscale eddy. External forcings such as wind and inflow current are not considered in this study, and topography is included only in a realistic South China Sea model. Therefore, mesoscale eddies with large vertical depth should have the similar axis tilt character in open oceans under the β-effect.

scholarly journals Simulation of Atmospheric Circulation over Tahiti and of Local Effects on the Transport of 210Pb

2009 ◽  
Vol 137 (6) ◽  
pp. 1863-1880 ◽  
Author(s):  
P. Heinrich ◽  
X. Blanchard
Keyword(s):  
Atmospheric Circulation ◽  
General Circulation ◽  
Transport Model ◽  
Mesoscale Model ◽  
Natural Radionuclide ◽  
Circulation Model ◽  
Spatial And Temporal Variability ◽  
Local Circulation ◽  
Meteorological Model ◽  
The Impact

Abstract Atmospheric transport of the natural radionuclide 210Pb is simulated by a general circulation model (GCM) and calculated surface concentrations are compared with those recorded at the Tahiti station on a daily scale. Numerical results for 2006 show the underestimation of concentrations for most recorded peaks. The purpose of this paper is to explain the observed discrepancies, to evaluate the GCM physical parameterizations, and to determine by numerical means the concentrations at Tahiti for a pollutant circulating across the South Pacific Ocean. Three meteorological situations in 2006 are further analyzed. Circulation over Tahiti for these periods is simulated by a mesoscale meteorological model using four nested grids with resolutions ranging from 27 to 1 km. The calculated wind fields are validated by those observed at two stations on the northwest coast of Tahiti, which is exposed both to topography-induced vortices and to thermally driven local breezes. Atmospheric dispersion of an offshore plume is then calculated by a particle Lagrangian transport model, driven by the mesoscale model at 1- and 81-km resolutions, representing local and global circulations, respectively. Simulations at 1-km resolution show the complex atmospheric circulation over Tahiti, which results in a large spatial and temporal variability of 210Pb surface concentrations on an hourly scale. The impact of local circulation is, however, limited when daily averaged concentrations at the station are considered. Under the studied regimes, transport simulations at the two resolutions lead to similar daily averaged concentrations. The deficiencies of the GCM in simulating daily averaged 210Pb concentrations could be attributable to the deep convection parameterization.

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