scholarly journals Stratospheric dryness

2006 ◽  
Vol 6 (6) ◽  
pp. 11247-11298 ◽  
Author(s):  
J. Lelieveld ◽  
C. Brühl ◽  
P. Jöckel ◽  
B. Steil ◽  
P. J. Crutzen ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Radiative Heating ◽  
Mixing Ratios ◽  
Tropical Tropopause ◽  
Dehydration Mechanism ◽  
Radiation Processes ◽  
Stratospheric Clouds

Abstract. The mechanisms responsible for the extreme dryness of the stratosphere have been debated for decades. A key difficulty has been the lack of models which are able to reproduce the observations. Here we examine results from a new atmospheric chemistry general circulation model (ECHAM5/MESSy1) together with satellite observations. Our model results match observed temperatures in the tropical lower stratosphere and realistically represent recurrent features such as the semi-annual oscillation (SAO) and the quasi-biennual oscillation (QBO), indicating that dynamical and radiation processes are simulated accurately. The model reproduces the very low water vapor mixing ratios (1–2 ppmv) periodically observed at the tropical tropopause near 100 hPa, as well as the characteristic tape recorder signal up to about 10 hPa, providing evidence that the dehydration mechanism is well-captured, albeit that the model underestimates convective overshooting and consequent moistening events. Our results show that the entry of tropospheric air into the stratosphere at low latitudes is forced by large-scale wave dynamics; however, radiative cooling can regionally limit the upwelling or even cause downwelling. In the cold air above cumulonimbus anvils thin cirrus desiccates the air through the sedimentation of ice particles, similar to polar stratospheric clouds. Transport deeper into the stratosphere occurs in regions where radiative heating becomes dominant, to a large extent in the subtropics. During summer the stratosphere is moistened by the monsoon, most strongly over Southeast Asia.

scholarly journals Stratospheric dryness: model simulations and satellite observations

2007 ◽  
Vol 7 (5) ◽  
pp. 1313-1332 ◽  
Author(s):  
J. Lelieveld ◽  
C. Brühl ◽  
P. Jöckel ◽  
B. Steil ◽  
P. J. Crutzen ◽  
...  
Keyword(s):  
Water Vapor ◽  
General Circulation ◽  
Large Scale ◽  
Middle Atmosphere ◽  
Circulation Model ◽  
Satellite Observations ◽  
Radiative Heating ◽  
Mixing Ratios ◽  
Tropical Tropopause ◽  
Mass Fluxes

Abstract. The mechanisms responsible for the extreme dryness of the stratosphere have been debated for decades. A key difficulty has been the lack of comprehensive models which are able to reproduce the observations. Here we examine results from the coupled lower-middle atmosphere chemistry general circulation model ECHAM5/MESSy1 together with satellite observations. Our model results match observed temperatures in the tropical lower stratosphere and realistically represent the seasonal and inter-annual variability of water vapor. The model reproduces the very low water vapor mixing ratios (below 2 ppmv) periodically observed at the tropical tropopause near 100 hPa, as well as the characteristic tape recorder signal up to about 10 hPa, providing evidence that the dehydration mechanism is well-captured. Our results confirm that the entry of tropospheric air into the tropical stratosphere is forced by large-scale wave dynamics, whereas radiative cooling regionally decelerates upwelling and can even cause downwelling. Thin cirrus forms in the cold air above cumulonimbus clouds, and the associated sedimentation of ice particles between 100 and 200 hPa reduces water mass fluxes by nearly two orders of magnitude compared to air mass fluxes. Transport into the stratosphere is supported by regional net radiative heating, to a large extent in the outer tropics. During summer very deep monsoon convection over Southeast Asia, centered over Tibet, moistens the stratosphere.

scholarly journals Consistent simulation of bromine chemistry from the marine boundary layer to the stratosphere – Part 2: Bromocarbons

2008 ◽  
Vol 8 (3) ◽  
pp. 9477-9530 ◽  
Author(s):  
A. Kerkweg ◽  
P. Jöckel ◽  
N. Warwick ◽  
S. Gebhardt ◽  
C.A.M. Brenninkmeijer ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Chemistry ◽  
General Circulation ◽  
Marine Boundary Layer ◽  
Circulation Model ◽  
Degradation Process ◽  
Limited Information ◽  
Mixing Ratios ◽  
Emission Fluxes ◽  
Surface Mixing

Abstract. In this second part of a series of articles dedicated to a detailed analysis of bromine chemistry in the atmosphere we address one (out of two) dominant natural sources of reactive bromine. The two main source categories are the release of bromine from sea salt and the decomposition of bromocarbons by photolysis and reaction with OH. Here, we focus on C1-bromocarbons. We show that the atmospheric chemistry general circulation model ECHAM5/MESSy realistically simulates their emission, transport and decomposition from the boundary layer up to the mesosphere. We included oceanic emission fluxes of the short-lived bromocarbons CH2Br2, CH2ClBr, CHClBr2, CHCl2Br, CHBr3 and of CH3Br. The vertical profiles and the surface mixing ratios of the bromocarbons are in general agreement with the (few available) observations, especially in view of the limited information available and the consequent coarseness of the emission fields. For CHBr3, CHCl2Br and CHClBr2 photolysis is the most important degradation process in the troposphere. In contrast to this, tropospheric CH2Br2, CH3Br and CH2ClBr are more efficiently decomposed by reaction with OH. In the free troposphere approximately one third of the C1-bromocarbons decomposes by reaction with OH. In the boundary layer the reaction with OH is relatively important, whereas it is negligible in the stratosphere. Our results indicate an approximately 50% longer lifetime of CH3Br (≈1 year) than assumed previously, implying a relatively strong contribution to stratospheric bromine and consequent ozone destruction.

scholarly journals Global atmospheric budget of simple monocyclic aromatic compounds

2016 ◽  
Author(s):  
David Cabrera-Perez ◽  
Domenico Taraborrelli ◽  
Rolf Sander ◽  
Andrea Pozzer
Keyword(s):  
Atmospheric Chemistry ◽  
Aromatic Compounds ◽  
General Circulation ◽  
Model Simulation ◽  
Circulation Model ◽  
Temporal Correlation ◽  
Chemical Production ◽  
Mixing Ratios ◽  
Photochemical Decomposition ◽  
Surface Mixing

Abstract. The global atmospheric budget and distribution of monocyclic aromatic compounds is estimated, using an atmospheric chemistry general circulation model. Simulation results are evaluated with an ensemble of surface and aircraft observations with the goal of understanding emission, production and removal of these compounds. Anthropogenic emissions represent the largest source of aromatics in the model (≃ 25 Tg/yr) and biomass burning the second largest (≃ 6 Tg/yr). The chemical production of aromatics accounts for ≃ 6 Tg/yr. The atmospheric burden of aromatics sums up to 0.3 Tg. The main removal process of aromatics is photochemical decomposition (≃ 32 Tg/yr), while wet and dry deposition are responsible for a removal of ≃ 4 Tg/yr. Simulated mixing ratios at the surface and elsewhere in the troposphere show good spatial and temporal agreement with the observations for benzene, although the model generally underestimates mixing ratios. Toluene is generally well reproduced by the model at the surface, but mixing ratios in the free troposphere are underestimated. Finally, larger discrepancies are found for xylenes: surface mixing ratios are not only overestimated but also a low temporal correlation is found with respect to in situ observations.

scholarly journals Formation of Jets and Equatorial Superrotation on Jupiter

2009 ◽  
Vol 66 (3) ◽  
pp. 579-601 ◽  
Author(s):  
Tapio Schneider ◽  
Junjun Liu
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Thermal Structure ◽  
Circulation Model ◽  
Zonal Flow ◽  
Heat Fluxes ◽  
Radiative Heating ◽  
Control Simulation ◽  
Deep Interior ◽  
Outer Atmosphere

Abstract The zonal flow in Jupiter’s upper troposphere is organized into alternating retrograde and prograde jets, with a prograde (superrotating) jet at the equator. Existing models posit as the driver of the flow either differential radiative heating of the atmosphere or intrinsic heat fluxes emanating from the deep interior; however, they do not reproduce all large-scale features of Jupiter’s jets and thermal structure. Here it is shown that the difficulties in accounting for Jupiter’s jets and thermal structure resolve if the effects of differential radiative heating and intrinsic heat fluxes are considered together, and if upper-tropospheric dynamics are linked to a magnetohydrodynamic (MHD) drag that acts deep in the atmosphere and affects the zonal flow away from but not near the equator. Baroclinic eddies generated by differential radiative heating can account for the off-equatorial jets; meridionally propagating equatorial Rossby waves generated by intrinsic convective heat fluxes can account for the equatorial superrotation. The zonal flow extends deeply into the atmosphere, with its speed changing with depth, away from the equator up to depths at which the MHD drag acts. The theory is supported by simulations with an energetically consistent general circulation model of Jupiter’s outer atmosphere. A simulation that incorporates differential radiative heating and intrinsic heat fluxes reproduces Jupiter’s observed jets and thermal structure and makes testable predictions about as yet unobserved aspects thereof. A control simulation that incorporates only differential radiative heating but not intrinsic heat fluxes produces off-equatorial jets but no equatorial superrotation; another control simulation that incorporates only intrinsic heat fluxes but not differential radiative heating produces equatorial superrotation but no off-equatorial jets. The proposed mechanisms for the formation of jets and equatorial superrotation likely act in the atmospheres of all giant planets.

scholarly journals Global atmospheric budget of simple monocyclic aromatic compounds

2016 ◽  
Vol 16 (11) ◽  
pp. 6931-6947 ◽  
Author(s):  
David Cabrera-Perez ◽  
Domenico Taraborrelli ◽  
Rolf Sander ◽  
Andrea Pozzer
Keyword(s):  
Atmospheric Chemistry ◽  
Aromatic Compounds ◽  
General Circulation ◽  
Model Simulation ◽  
Circulation Model ◽  
Temporal Correlation ◽  
Chemical Production ◽  
Mixing Ratios ◽  
Photochemical Decomposition ◽  
Surface Mixing

Abstract. The global atmospheric budget and distribution of monocyclic aromatic compounds is estimated, using an atmospheric chemistry general circulation model. Simulation results are evaluated with an ensemble of surface and aircraft observations with the goal of understanding emission, production and removal of these compounds.Anthropogenic emissions provided by the RCP database represent the largest source of aromatics in the model (≃ 23 TgC year−1) and biomass burning from the GFAS inventory the second largest (≃ 5 TgC year−1). The simulated chemical production of aromatics accounts for  ≃ 5 TgC year−1. The atmospheric burden of aromatics sums up to 0.3 TgC. The main removal process of aromatics is photochemical decomposition (≃ 27 TgC  year−1), while wet and dry deposition are responsible for a removal of  ≃ 4 TgC year−1.Simulated mixing ratios at the surface and elsewhere in the troposphere show good spatial and temporal agreement with the observations for benzene, although the model generally underestimates mixing ratios. Toluene is generally well reproduced by the model at the surface, but mixing ratios in the free troposphere are underestimated. Finally, larger discrepancies are found for xylenes: surface mixing ratios are not only overestimated but also a low temporal correlation is found with respect to in situ observations.

scholarly journals Effects of model configuration for superparametrised long-term simulations – Implementation of a cloud resolving model in EMAC (v2.50)

2019 ◽  
Author(s):  
Harald Rybka ◽  
Holger Tost
Keyword(s):  
Diurnal Cycle ◽  
Atmospheric Chemistry ◽  
General Circulation ◽  
Cloud Cover ◽  
Large Scale ◽  
Current Model ◽  
Sensible Heat Flux ◽  
Circulation Model ◽  
Cloud Amount ◽  
Model Configuration

Abstract. A new module has been implemented in the ECHAM5/MESSy Atmospheric Chemistry (EMAC) Model that simulates cloud related processes on a much smaller grid. This so called superparametrisation acts as a replacement for the convection parametrisation and large-scale cloud scheme. The concept of embedding an ensemble of cloud resolving models (CRMs) inside of each grid box of a general circulation model leads to an explicit representation of cloud dynamics. The new model component is evaluated against observations and the conventional usage of EMAC using a convection parametrisation. In particular, effects of applying different configurations of the superparametrisation are analyzed in a systematical way. Consequences of changing the CRMs orientation, cell size and number of cells range from regional differences in cloud amount up to global impacts on precipitation distribution and its variability. For some edge case setups the analysed climate state of superparametrised simulations even deteriorates from the mean observed energy budget. In the current model configuration different climate regimes can be formed that are mainly driven by some of the parameters of the CRM. Presently, the simulated cloud cover is at the lower edge of the CMIP5 model ensemble indicating that the hydrological overturning is too efficient. However, certain "tuning" of the current model configuration could improve the currently underestimated cloud cover, which will result in a shift of the climate. The simulation results show that especially tropical precipitation is better represented with the superparamerisation in the EMAC model configuration. Furthermore, the diurnal cycle of precipitation is heavily affected by the choice of the CRM parameters. However, despite an improvement of the representation of the continental diurnal cycle in some configurations, other parameter choices result in a deterioration compared to the reference simulation using a conventional convection parameterisation. The ability of the superparametrisation to represent latent and sensible heat flux climatology is dependent on the chosen CRM setup. Further interactions of the planetary boundary layer and the free troposphere can significantly influence cloud development on the large-scale. Therefore a careful selection of the CRM setup is recommended to compensate for computational expenses.

Tropical Tropospheric-Only Responses to Absorbing Aerosols

2012 ◽  
Vol 25 (7) ◽  
pp. 2471-2480 ◽  
Author(s):  
Geeta G. Persad ◽  
Yi Ming ◽  
V. Ramaswamy
Keyword(s):  
Black Carbon ◽  
General Circulation Model ◽  
General Circulation ◽  
Large Scale ◽  
Substantial Reduction ◽  
Circulation Model ◽  
Cloud Amount ◽  
Radiative Heating ◽  
Physically Based ◽  
Absorbing Aerosols

Abstract Absorbing aerosols affect the earth’s climate through direct radiative heating of the troposphere. This study analyzes the tropical tropospheric-only response to a globally uniform increase in black carbon, simulated with an atmospheric general circulation model, to gain insight into the interactions that determine the radiative flux perturbation. Over the convective regions, heating in the free troposphere hinders the vertical development of deep cumulus clouds, resulting in the detrainment of more cloudy air into the large-scale environment and stronger cloud reflection. A different mechanism operates over the subsidence regions, where heating near the boundary layer top causes a substantial reduction in low cloud amount thermodynamically by decreasing relative humidity and dynamically by lowering cloud top. These findings, which align well with previous general circulation model and large-eddy simulation calculations for black carbon, provide physically based explanations for the main characteristics of the tropical tropospheric adjustment. The implications for quantifying the climate perturbation posed by absorbing aerosols are discussed.

scholarly journals Consistent simulation of bromine chemistry from the marine boundary layer to the stratosphere – Part 2: Bromocarbons

2008 ◽  
Vol 8 (19) ◽  
pp. 5919-5939 ◽  
Author(s):  
A. Kerkweg ◽  
P. Jöckel ◽  
N. Warwick ◽  
S. Gebhardt ◽  
C. A. M. Brenninkmeijer ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Chemistry ◽  
General Circulation ◽  
Marine Boundary Layer ◽  
Circulation Model ◽  
Degradation Process ◽  
Limited Information ◽  
Mixing Ratios ◽  
Emission Fluxes ◽  
Surface Mixing

Abstract. In this second part of a series of articles dedicated to a detailed analysis of bromine chemistry in the atmosphere we address one (out of two) dominant natural sources of reactive bromine. The two main source categories are the release of bromine from sea salt and the decomposition of bromocarbons by photolysis and reaction with OH. Here, we focus on C1-bromocarbons. We show that the atmospheric chemistry general circulation model ECHAM5/MESSy realistically simulates their emission, transport and decomposition from the boundary layer up to the mesosphere. We included oceanic emission fluxes of the short-lived bromocarbons CH2Br2, CH2ClBr, CHClBr2, CHCl2Br, CHBr3 and of CH3Br. The vertical profiles and the surface mixing ratios of the bromocarbons are in general agreement with the (few available) observations, especially in view of the limited information available and the consequent coarseness of the emission fields. For CHBr3, CHCl2Br and CHClBr2 photolysis is the most important degradation process in the troposphere. In contrast to this, tropospheric CH2Br2, CH3Br and CH2ClBr are more efficiently decomposed by reaction with OH. In the free troposphere approximately 40% of the C1-bromocarbons decompose by reaction with OH. Our results indicate that bromoform contributes substantial amounts of reactive bromine to the lower stratosphere and thus should not be neglected in stratospheric simulations.

scholarly journals A climatology of surface ozone in the extra tropics: cluster analysis of observations and model results

2007 ◽  
Vol 7 (24) ◽  
pp. 6099-6117 ◽  
Author(s):  
O. A. Tarasova ◽  
C. A. M. Brenninkmeijer ◽  
P. Jöckel ◽  
A. M. Zvyagintsev ◽  
G. I. Kuznetsov
Keyword(s):  
Atmospheric Chemistry ◽  
Seasonal Variations ◽  
General Circulation ◽  
Surface Ozone ◽  
Circulation Model ◽  
Transport Processes ◽  
Mixing Ratios ◽  
Seasonal Maximum ◽  
Summer Maximum ◽  
Spring Maximum

Abstract. Important aspects of the seasonal variations of surface ozone are discussed. The underlying analysis is based on the long-term (1990–2004) ozone records of the Co-operative Programme for Monitoring and Evaluation of the Long-range Transmission of Air Pollutants in Europe (EMEP) and the World Data Centre of Greenhouse Gases, which provide data mostly for the Northern Hemisphere. Seasonal variations are pronounced at most of the 114 locations at all times of the day. A seasonal-diurnal variations classification using hierarchical agglomeration clustering reveals 6 distinct clusters: clean background, rural, semi-polluted non-elevated, semi-polluted semi-elevated, elevated and polar/remote marine. For the "clean background" cluster the seasonal maximum is observed in March-April, both for night and day. For those sites with a double maximum or a wide spring-summer maximum, the spring maximum appears both for day and night, while the summer maximum is more pronounced for daytime and hence can be attributed to photochemical processes. The spring maximum is more likely caused by dynamical/transport processes than by photochemistry as it is observed in spring for all times of the day. We compare the identified clusters with corresponding data from the 3-D atmospheric chemistry general circulation model ECHAM5/MESSy1 covering the period of 1998–2005. For the model output as for the measurements 6 clusters are considered. The simulation shows at most of the sites a spring seasonal maximum or a broad spring-summer maximum (with higher summer mixing ratios). For southern hemispheric and polar remote locations the seasonal maximum in the simulation is shifted to spring, while the absolute mixing ratios are in good agreement with the measurements. The seasonality in the model cluster covering background locations is characterized by a pronounced spring (April–May) maximum. For the model clusters which cover rural and semi-polluted sites the role of the photochemical production/destruction seems to be overestimated. Taking into consideration the differences in the data sampling procedure, the comparison demonstrates the ability of the model to reproduce the main regimes of surface ozone variations quite well.

CO and O2 in the Martian atmosphere with ACS NIR onboard TGO.

2021 ◽  
Author(s):  
Anna Fedorova ◽  
Franck Lefèvre ◽  
Alexander Trokhimovskiy ◽  
Oleg Korablev ◽  
Franck Montmessin ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
General Circulation ◽  
Near Infrared ◽  
Circulation Model ◽  
Carbon Oxide ◽  
Martian Atmosphere ◽  
Resolving Power ◽  
Mixing Ratio ◽  
Mars Atmosphere ◽  
Mixing Ratios

<p>The molecular oxygen (O2) and carbon oxide (CO) are minor constituents of the Martian atmosphere with the annual mean mixing ratio of (1560 ± 60 ppm) and (673 ± 2.6 ppm), respectively (Krasnopolsky, 2017). Both are non-condensable species and their latitudinal variations are induced by condensation and sublimation of CO<sub>2</sub> from the polar caps that result in enrichment and depletion and seasonal variations are following the total CO<sub>2</sub> amount in the atmosphere.</p><p>The Atmospheric Chemistry Suite (ACS) is a set of three spectrometers (-NIR, -MIR, and -TIRVIM) intended to observe Mars atmosphere onboard the ESA-Roscosmos ExoMars 2016 Trace Gas Orbiter (TGO) mission (Korablev et al., 2018). The near infrared channel (NIR) is a compact spectrometer operating in the range of 0.7–1.7 µm with a resolving power of λ/Δλ ~ 25,000. It is designed to operate in nadir and in solar occultation modes. The simultaneous vertical profiling of the O<sub>2 </sub>and CO density at altitudes of 10-60 km based on 0.76 µm and 1.57 µm bands, respectively, is a unique feature of the ACS NIR science in occultation. In this work we present the seasonal and latitudional distribution of the O<sub>2</sub> and CO mixing ratios obtained for period of 2018-2020 (MY34 and35) and the comparison with the LMD General Circulation model. We report the averaged mixing ratio for CO of ~950 ppm and for O2 of~1800 ppm at low altitudes (~20 km). Also, we detected extremely enriched CO layer at 10-15 km in the southern polar region at Ls=100-200° both for MY34 and MY35.</p>

Sign in / Sign up

Export Citation Format

Share Document