Simulating Mars D/H and atmospheric chemistry during the 2018 Global Dust Storm and comparing with NOMAD observations

2020 ◽  
Author(s):  
Frank Daerden ◽  
Lori Neary ◽  
Geronimo Villanueva ◽  
Shohei Aoki ◽  
Sebastien Viscardy ◽  
...  
Keyword(s):  
Water Vapor ◽  
Atmospheric Chemistry ◽  
Dust Storm ◽  
General Circulation ◽  
Circulation Model ◽  
Cloud Formation ◽  
Vertical Profiles ◽  
Considerable Impact ◽  
Physical And Chemical ◽  
The Impact

<p>The NOMAD instrument suite on the ESA-Roskosmos ExoMars Trace Gas Orbiter (TGO) observes the physical and chemical composition of the Martian atmosphere with highly resolved vertical profiles and nadir sounding in the IR and UV-vis domains. Vertically resolved profiles of, amongst other species, water vapor, HDO, ozone, CO, CO<sub>2</sub>, oxygen airglow, dust and clouds were obtained for more than one Martian year [1-5]. During its first year of operations, NOMAD witnessed the 2018 Global Dust Storm (GDS) during its onset, peak and decline. The redistribution of water vapor to high altitudes and latitudes observed during the GDS was explained using the GEM-Mars General Circulation Model (GCM) [6-8]. The GCM was driven by the dust optical depths for Mars Year 34 provided by [9]. The photolysis products of water vapor are a major driver for the atmospheric chemistry on Mars. As water vapor is redistributed over the atmosphere, it is expected to have considerable impact on many other species. GEM-Mars contains routines for atmospheric chemistry and here we present some results of the simulated impact of the GDS on atmospheric chemistry and on several of the observed species. GEM-Mars now also includes the simulation of HDO and the fractionation of water vapor upon cloud formation. The simulations will be compared with the vertical profiles of the D/H ratio obtained from NOMAD observations. The impact of the GDS on D/H can be estimated from these simulations.</p><p>  </p><p>References</p><p> </p><p>[1] Vandaele, A. C. et al. (2019), Nature, 568, 7753, 521-525, doi: 10.1038/s41586-019-1097-3.</p><p>[2] Aoki, S. et al. (2019), J. Geophys. Res.: Planets, 124, 3482–3497. https://doi.org/10.1029/2019JE006109</p><p>[3] Gérard et al. (2020), Nature Astronomy, https://doi.org/10.1038/s41550-020-1123-2</p><p>[4] Villanueva et al., submitted.</p><p>[5] Korablev et al., 2020, in rev.</p><p>[6] Neary, L. and F. Daerden (2018), Icarus, 300, 458–476, https://doi.org/10.1016/j.icarus.2017.09.028</p><p>[7] Daerden, F. et al. (2019), Icarus, 326, 197-224, doi: 10.1016/j.icarus.2019.02.030.</p><p>[8] Neary, L. et al. (2020), Geophys. Res. Lett., 47, e2019GL084354. https://doi.org/10.1029/2019GL084354</p><p>[9] Montabone, L. et al. (2019), J. Geophys. Res.: Planets. doi: 10.1029/2019JE006111.</p><p> </p> <div>2.11.0.0</div><!-- COMO-HTML-CONTENT-END --> <div> <div>BIRA-IASB NOMAD team (continued):</div> <p>S. Robert (1), L. Trompet (1), A. Mahieux (1), C. Depiesse (1), E. Neefs (1) and B. Ristic (1).</p> </div> <!-- COMO-HTML-CONTENT-END --> <div class="co_mto_htmlabstract-teamMembers d-none d-md-block"> <div class="co_mto_htmlabstract-teamMembers-name h1-special journal-contentHeaderColor header-element color-primary">BIRA-IASB NOMAD team (continued):</div> <p>S. Robert (1), L. Trompet (1), A. Mahieux (1), C. Depiesse (1), E. Neefs (1) and B. Ristic (1).</p> </div> <p class="co_mto_htmlabstract-citationHeader"> <strong class="co_mto_htmlabstract-citationHeader-intro">How to cite:</strong> Daerden, F., Neary, L., Villanueva, G., Aoki, S., Viscardy, S., Thomas, I., Vandaele, A. C., Liuzzi, G., Crismani, M., Khayat, A., Smith, M. D., Clancy, R. T., Wolff, M. J., Sandor, B. J., Whiteway, J. A., Mumma, M. J., Erwin, J., Willame, Y., and Piccialli, A. and the BIRA-IASB NOMAD team (continued): Simulating Mars D/H and atmospheric chemistry during the 2018 Global Dust Storm and comparing with NOMAD observations , Europlanet Science Congress 2020, online, 21 September–9 Oct 2020, EPSC2020-371, 2020 </p>

scholarly journals Evaluation of CLaMS, KASIMA and ECHAM5/MESSy1 simulations in the lower stratosphere using observations of Odin/SMR and ILAS/ILAS-II

2009 ◽  
Vol 9 (1) ◽  
pp. 1977-2020
Author(s):  
F. Khosrawi ◽  
R. Müller ◽  
M. H. Proffitt ◽  
R. Ruhnke ◽  
O. Kirner ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
General Circulation ◽  
Lower Stratosphere ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Circulation Model ◽  
Lagrangian Model ◽  
Data Sets ◽  
Data Set ◽  
The Impact

Abstract. 1-year data sets of monthly averaged nitrous oxide (N2O) and ozone (O3) derived from satellite measurements were used as a tool for the evaluation of atmospheric photochemical models. Two 1-year data sets, one derived from the Improved Limb Atmospheric Spectrometer (ILAS and ILAS-II) and one from the Odin Sub-Millimetre Radiometer (Odin/SMR) were employed. Here, these data sets are used for the evaluation of two Chemical Transport Models (CTMs), the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA) and the Chemical Lagrangian Model of the Stratosphere (CLaMS) as well as for one Chemistry-Climate Model (CCM), the atmospheric chemistry general circulation model ECHAM5/MESSy1 (E5M1) in the lower stratosphere with focus on the Northern Hemisphere. Since the Odin/SMR measurements cover the entire hemisphere, the evaluation is performed for the entire hemisphere as well as for the low latitudes, midlatitudes and high latitudes using the Odin/SMR 1-year data set as reference. To assess the impact of using different data sets for such an evaluation study we repeat the evaluation for the polar lower stratosphere using the ILAS/ILAS-II data set. Only small differences were found using ILAS/ILAS-II instead of Odin/SMR as a reference, thus, showing that the results are not influenced by the particular satellite data set used for the evaluation. The evaluation of CLaMS, KASIMA and E5M1 shows that all models are in good agreement with Odin/SMR and ILAS/ILAS-II. Differences are generally in the range of ±20%. Larger differences (up to −40%) are found in all models at 500±25 K for N2O mixing ratios greater than 200 ppb. Generally, the largest differences were found for the tropics and the lowest for the polar regions. However, an underestimation of polar winter ozone loss was found both in KASIMA and E5M1 both in the Northern and Southern Hemisphere.

scholarly journals Methane chemistry in a nutshell – The new submodels CH4 (v1.0) and TRSYNC (v1.0) in MESSy (v2.54.0)

2020 ◽  
Author(s):  
Franziska Winterstein ◽  
Patrick Jöckel
Keyword(s):  
Water Vapour ◽  
Atmospheric Chemistry ◽  
General Circulation ◽  
Hydrological Cycle ◽  
Circulation Model ◽  
Optimization Techniques ◽  
Specific Humidity ◽  
Climate Projections ◽  
Sensitivity Studies ◽  
The Impact

Abstract. Climate projections including chemical feedbacks rely on state-of-the-art chemistry-climate models (CCMs). Of particular importance is the role of methane (CH4) for the budget of stratospheric water vapor (SWV), which has an important climate impact. However, simulations with CCMs are, due to the large number of involved chemical species, computationally demanding, which limits the simulation of sensitivity studies. To allow for sensitivity studies and ensemble simulations with a reduced demand for computational resources, we introduce a simplified approach to simulate the core of methane chemistry in form of the new Modular Earth Submodel System (MESSy) submodel CH4. It involves an atmospheric chemistry mechanism reduced to the sink reactions of CH4 with predefined fields of the hydroxyl radical (OH), excited oxygen (O(1D)), and chlorine (Cl), as well as photolysis and the reaction products limited to water vapour (H2O). This chemical production of H2O is optionally feed back onto the specific humidity (q) of the connected General Circulation Model (GCM), to account for the impact onto SWV and its effect on radiation and stratospheric dynamics. The submodel CH4 is further capable of simulating the four most prevalent CH4 isotopologues for carbon and hydrogen (CH4 and CH3D as well as 12CH4 and 13CH4), respectively. Furthermore, the production of deuterated water vapour (HDO) is, similar to the production of H2O in the CH4 oxidation, optionally feed back to the isotopological hydrological cycle simulated by the submodel H2OISO, using the newly developed auxiliary submodel TRSYNC. Moreover, the simulation of a user defined number of diagnostic CH4 age- and emission classes is possible, which output can be used for offline inverse optimization techniques. The presented approach combines the most important chemical hydrological feedback including the isotopic signatures with the advantages concerning the computational simplicity of a GCM, in comparison to a full featured CCM.

scholarly journals Methane chemistry in a nutshell – the new submodels CH4 (v1.0) and TRSYNC (v1.0) in MESSy (v2.54.0)

2021 ◽  
Vol 14 (2) ◽  
pp. 661-674
Author(s):  
Franziska Winterstein ◽  
Patrick Jöckel
Keyword(s):  
Water Vapour ◽  
Atmospheric Chemistry ◽  
General Circulation ◽  
Hydrological Cycle ◽  
Circulation Model ◽  
Optimization Techniques ◽  
Specific Humidity ◽  
Climate Projections ◽  
Sensitivity Studies ◽  
The Impact

Abstract. Climate projections including chemical feedbacks rely on state-of-the-art chemistry–climate models (CCMs). Of particular importance is the role of methane (CH4) for the budget of stratospheric water vapour (SWV), which has an important climate impact. However, simulations with CCMs are, due to the large number of involved chemical species, computationally demanding, which limits the simulation of sensitivity studies. To allow for sensitivity studies and ensemble simulations with a reduced demand for computational resources, we introduce a simplified approach to simulate the core of methane chemistry in form of the new Modular Earth Submodel System (MESSy) submodel CH4. It involves an atmospheric chemistry mechanism reduced to the sink reactions of CH4 with predefined fields of the hydroxyl radical (OH), excited oxygen (O(1D)), and chlorine (Cl), as well as photolysis and the reaction products limited to water vapour (H2O). This chemical production of H2O is optionally fed back onto the specific humidity (q) of the connected general circulation model (GCM), to account for the impact onto SWV and its effect on radiation and stratospheric dynamics. The submodel CH4 is further capable of simulating the four most prevalent CH4 isotopologues for carbon and hydrogen (CH4 and CH3D, as well as 12CH4 and 13CH4). Furthermore, the production of deuterated water vapour (HDO) is, similar to the production of H2O in the CH4 oxidation, optionally passed back to the isotopological hydrological cycle simulated by the submodel H2OISO, using the newly developed auxiliary submodel TRSYNC. Moreover, the simulation of a user-defined number of diagnostic CH4 age and emission classes is possible, the output of which can be used for offline inverse optimization techniques. The presented approach combines the most important chemical hydrological feedback including the isotopic signatures with the advantages concerning the computational simplicity of a GCM, in comparison to a full-featured CCM.

scholarly journals Influence of aromatics on tropospheric gas-phase composition

2020 ◽  
Author(s):  
Domenico Taraborrelli ◽  
David Cabrera-Perez ◽  
Sara Bacer ◽  
Sergey Gromov ◽  
Jos Lelieveld ◽  
...  
Keyword(s):  
East Asia ◽  
Gas Phase ◽  
Atmospheric Chemistry ◽  
General Circulation ◽  
Anthropogenic Activities ◽  
Regional Scale ◽  
Circulation Model ◽  
Significant Loss ◽  
Tropospheric Chemistry ◽  
The Impact

Abstract. Aromatics contribute a significant fraction to organic compounds in the troposphere and are mainly emitted by anthropogenic activities and biomass burning. Their oxidation in lab experiments is known to lead to the formation of ozone and aerosol precursors. However, their overall impact on tropospheric composition is uncertain as it depends on transport, multiphase chemistry, and removal processes of the oxidation intermediates. Representation of aromatics in global atmospheric models has been either neglected or highly simplified. Here, we present an assessment of their impact on the gas-phase chemistry, using the general circulation model EMAC (ECHAM5/MESSy Atmospheric Chemistry). We employ a comprehensive kinetic model to represent the oxidation of the following monocyclic aromatics: benzene, toluene, xylenes, phenol, styrene, ethylbenzene, trimethylbenzenes, benzaldehyde, and lumped higher aromatics that contain more than 9 C atoms. Significant regional changes are identified for several species. For instance, glyoxal increases by 130 % in Europe and 260 % in East Asia, respectively. Large increases in HCHO are also predicted in these regions. In general, the influence of aromatics is particularly evident in areas with high concentrations of NOx, with increases up to 12 % in O3 and 17 % in OH. On a global scale, the estimated net changes are minor when aromatic compounds are included in our model. For instance, the tropospheric burden of CO increases by about 6 %, while the burdens of OH, O3, and NOx (NO + NO2) decrease between 3 % and 9 %. The global mean changes are small, partially because of compensating effects between high- and low-NOx regions. The largest change is predicted for the important aerosol precursor glyoxal, which increases globally by 36 %. In contrast to other studies, the net change in tropospheric ozone is predicted to be negative, −3 % globally. This change is larger in the northern hemisphere where global models usually show positive biases. We find that the reaction with phenoxy radicals is a significant loss for ozone, of the order of 200–300 Tg/yr, which is similar to the estimated ozone loss due to bromine chemistry. Although the net global impact of aromatics is limited, our results indicate that aromatics can strongly influence tropospheric chemistry on a regional scale, most significantly in East Asia. An analysis of the main model uncertainties related to oxidation and emissions suggests that the impact of aromatics may even be significantly larger.

scholarly journals Influence of aromatics on tropospheric gas-phase composition

2021 ◽  
Vol 21 (4) ◽  
pp. 2615-2636
Author(s):  
Domenico Taraborrelli ◽  
David Cabrera-Perez ◽  
Sara Bacer ◽  
Sergey Gromov ◽  
Jos Lelieveld ◽  
...  
Keyword(s):  
East Asia ◽  
Gas Phase ◽  
Atmospheric Chemistry ◽  
General Circulation ◽  
Anthropogenic Activities ◽  
Regional Scale ◽  
Circulation Model ◽  
Significant Loss ◽  
Tropospheric Chemistry ◽  
The Impact

Abstract. Aromatics contribute a significant fraction to organic compounds in the troposphere and are mainly emitted by anthropogenic activities and biomass burning. Their oxidation in lab experiments is known to lead to the formation of ozone and aerosol precursors. However, their overall impact on tropospheric composition is uncertain as it depends on transport, multiphase chemistry, and removal processes of the oxidation intermediates. Representation of aromatics in global atmospheric models has been either neglected or highly simplified. Here, we present an assessment of their impact on gas-phase chemistry, using the general circulation model EMAC (ECHAM5/MESSy Atmospheric Chemistry). We employ a comprehensive kinetic model to represent the oxidation of the following monocyclic aromatics: benzene, toluene, xylenes, phenol, styrene, ethylbenzene, trimethylbenzenes, benzaldehyde, and lumped higher aromatics that contain more than nine C atoms. Significant regional changes are identified for several species. For instance, glyoxal increases by 130 % in Europe and 260 % in East Asia, respectively. Large increases in HCHO are also predicted in these regions. In general, the influence of aromatics is particularly evident in areas with high concentrations of NOx, with increases up to 12 % in O3 and 17 % in OH. On a global scale, the estimated net changes of trace gas levels are minor when aromatic compounds are included in our model. For instance, the tropospheric burden of CO increases by about 6 %, while the burdens of OH, O3, and NOx (NO+NO2) decrease between 3 % and 9 %. The global mean changes are small, partially because of compensating effects between high- and low-NOx regions. The largest change is predicted for the important aerosol precursor glyoxal, which increases globally by 36 %. In contrast to other studies, the net change in tropospheric ozone is predicted to be negative, −3 % globally. This change is larger in the Northern Hemisphere where global models usually show positive biases. We find that the reaction with phenoxy radicals is a significant loss for ozone, on the order of 200–300 Tg yr−1, which is similar to the estimated ozone loss due to bromine chemistry. Although the net global impact of aromatics is limited, our results indicate that aromatics can strongly influence tropospheric chemistry on a regional scale, most significantly in East Asia. An analysis of the main model uncertainties related to oxidation and emissions suggests that the impact of aromatics may even be significantly larger.

scholarly journals Effects of business-as-usual anthropogenic emissions on air quality

2012 ◽  
Vol 12 (15) ◽  
pp. 6915-6937 ◽  
Author(s):  
A. Pozzer ◽  
P. Zimmermann ◽  
U.M. Doering ◽  
J. van Aardenne ◽  
H. Tost ◽  
...  
Keyword(s):  
Air Pollution ◽  
Air Quality ◽  
East Asia ◽  
South Asia ◽  
Atmospheric Chemistry ◽  
General Circulation ◽  
Circulation Model ◽  
Business As Usual ◽  
The Impact ◽  
Very High

Abstract. The atmospheric chemistry general circulation model EMAC has been used to estimate the impact of anthropogenic emission changes on global and regional air quality in recent and future years (2005, 2010, 2025 and 2050). The emission scenario assumes that population and economic growth largely determine energy and food consumption and consequent pollution sources with the current technologies ("business as usual"). This scenario is chosen to show the effects of not implementing legislation to prevent additional climate change and growing air pollution, other than what is in place for the base year 2005, representing a pessimistic (but plausible) future. By comparing with recent observations, it is shown that the model reproduces the main features of regional air pollution distributions though with some imprecisions inherent to the coarse horizontal resolution (~100 km) and simplified bottom-up emission input. To identify possible future hot spots of poor air quality, a multi pollutant index (MPI), suited for global model output, has been applied. It appears that East and South Asia and the Middle East represent such hotspots due to very high pollutant concentrations, while a general increase of MPIs is observed in all populated regions in the Northern Hemisphere. In East Asia a range of pollutant gases and fine particulate matter (PM2.5) is projected to reach very high levels from 2005 onward, while in South Asia air pollution, including ozone, will grow rapidly towards the middle of the century. Around the Persian Gulf, where natural PM2.5 concentrations are already high (desert dust), ozone levels are expected to increase strongly. The population weighted MPI (PW-MPI), which combines demographic and pollutant concentration projections, shows that a rapidly increasing number of people worldwide will experience reduced air quality during the first half of the 21st century. Following this business as usual scenario, it is projected that air quality for the global average citizen in 2050 would be almost comparable to that for the average citizen in East Asia in the year 2005, which underscores the need to pursue emission reductions.

scholarly journals Effects of business-as-usual anthropogenic emissions on air quality

2012 ◽  
Vol 12 (4) ◽  
pp. 8617-8676
Author(s):  
A. Pozzer ◽  
P. Zimmermann ◽  
U.M. Doering ◽  
J. van Aardenne ◽  
H. Tost ◽  
...  
Keyword(s):  
Air Pollution ◽  
Air Quality ◽  
East Asia ◽  
South Asia ◽  
Atmospheric Chemistry ◽  
General Circulation ◽  
Circulation Model ◽  
Business As Usual ◽  
The Impact ◽  
Very High

Abstract. The atmospheric chemistry general circulation model EMAC has been used to estimate the impact of anthropogenic emission changes on global and regional air quality in recent and future years (2005, 2010, 2025 and 2050). The emission scenario assumes that population and economic growth largely determine energy and food consumption and consequent pollution sources with the current technologies ("business as usual"). This scenario is chosen to show the effects of not implementing legislation to prevent additional climate change and growing air pollution, other than what is in place for the base year 2005, representing a pessimistic (but feasible) future. By comparing with recent observations, it is shown that the model reproduces the main features of regional air pollution distributions though with some imprecisions inherent to the coarse horizontal resolution (~100 km) and simplified bottom-up emission input. To identify possible future hot spots of poor air quality, a multi pollutant index (MPI), suited for global model output, has been applied. It appears that East and South Asia and the Middle East represent such hotspots due to very high pollutant concentrations, although a general increase of MPIs is observed in all populated regions in the Northern Hemisphere. In East Asia a range of pollutant gases and fine particulate matter (PM2.5) is projected to reach very high levels from 2005 onward, while in South Asia air pollution, including ozone, will grow rapidly towards the middle of the century. Around the Arabian Gulf, where natural PM2.5 concentrations are already high (desert dust), ozone levels are expected to increase strongly. The per capita MPI (PCMPI), which combines demographic and pollutants concentrations projections, shows that a rapidly increasing number of people worldwide will experience reduced air quality during the first half of the 21st century. Following the business as usual scenario, it is projected that air quality for the global average citizen in 2050 would be almost comparable to that for the average citizen in the East Asia in the year 2005, which underscores the need to pursue emission reductions.

scholarly journals Evaluation of CLaMS, KASIMA and ECHAM5/MESSy1 simulations in the lower stratosphere using observations of Odin/SMR and ILAS/ILAS-II

2009 ◽  
Vol 9 (15) ◽  
pp. 5759-5783 ◽  
Author(s):  
F. Khosrawi ◽  
R. Müller ◽  
M. H. Proffitt ◽  
R. Ruhnke ◽  
O. Kirner ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
General Circulation ◽  
Lower Stratosphere ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Circulation Model ◽  
Lagrangian Model ◽  
Data Sets ◽  
Data Set ◽  
The Impact

Abstract. 1-year data sets of monthly averaged nitrous oxide (N2O) and ozone (O3) derived from satellite measurements were used as a tool for the evaluation of atmospheric photochemical models. Two 1-year data sets, one solar occultation data set derived from the Improved Limb Atmospheric Spectrometer (ILAS and ILAS-II) and one limb sounding data set derived from the Odin Sub-Millimetre Radiometer (Odin/SMR) were employed. Here, these data sets are used for the evaluation of two Chemical Transport Models (CTMs), the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA) and the Chemical Lagrangian Model of the Stratosphere (CLaMS) as well as for one Chemistry-Climate Model (CCM), the atmospheric chemistry general circulation model ECHAM5/MESSy1 (E5M1) in the lower stratosphere with focus on the Northern Hemisphere. Since the Odin/SMR measurements cover the entire hemisphere, the evaluation is performed for the entire hemisphere as well as for the low latitudes, midlatitudes and high latitudes using the Odin/SMR 1-year data set as reference. To assess the impact of using different data sets for such an evaluation study we repeat the evaluation for the polar lower stratosphere using the ILAS/ILAS-II data set. Only small differences were found using ILAS/ILAS-II instead of Odin/SMR as a reference, thus, showing that the results are not influenced by the particular satellite data set used for the evaluation. The evaluation of CLaMS, KASIMA and E5M1 shows that all models are in agreement with Odin/SMR and ILAS/ILAS-II. Differences are generally in the range of ±20%. Larger differences (up to −40%) are found in all models at 500±25 K for N2O mixing ratios greater than 200 ppbv, thus in air masses of tropical character. Generally, the largest differences were found for the tropics and the lowest for the polar regions. However, an underestimation of polar winter ozone loss was found both in KASIMA and E5M1 both in the Northern and Southern Hemisphere.

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 Bacteria in the global atmosphere – Part 2: Modeling of emissions and transport between different ecosystems

2009 ◽  
Vol 9 (23) ◽  
pp. 9281-9297 ◽  
Author(s):  
S. M. Burrows ◽  
T. Butler ◽  
P. Jöckel ◽  
H. Tost ◽  
A. Kerkweg ◽  
...  
Keyword(s):  
Seasonal Variation ◽  
Residence Time ◽  
General Circulation ◽  
Bacterial Species ◽  
Circulation Model ◽  
Cloud Condensation Nucleus ◽  
Cloud Formation ◽  
Emission Region ◽  
Culturable Bacteria ◽  
Bacterial Cells

Abstract. Bacteria are constantly being transported through the atmosphere, which may have implications for human health, agriculture, cloud formation, and the dispersal of bacterial species. We simulate the global transport of bacteria, represented as 1 μm and 3 μm diameter spherical solid particle tracers in a general circulation model. We investigate factors influencing residence time and distribution of the particles, including emission region, cloud condensation nucleus activity and removal by ice-phase precipitation. The global distribution depends strongly on the assumptions made about uptake into cloud droplets and ice. The transport is also affected, to a lesser extent, by the emission region, particulate diameter, and season. We find that the seasonal variation in atmospheric residence time is insufficient to explain by itself the observed seasonal variation in concentrations of particulate airborne culturable bacteria, indicating that this variability is mainly driven by seasonal variations in culturability and/or emission strength. We examine the potential for exchange of bacteria between ecosystems and obtain rough estimates of the flux from each ecosystem by using a maximum likelihood estimation technique, together with a new compilation of available observations described in a companion paper. Globally, we estimate the total emissions of bacteria-containing particles to the atmosphere to be 7.6×1023–3.5×1024 a−1, originating mainly from grasslands, shrubs and crops. We estimate the mass of emitted bacteria- to be 40–1800 Gg a−1, depending on the mass fraction of bacterial cells in the particles. In order to improve understanding of this topic, more measurements of the bacterial content of the air and of the rate of surface-atmosphere exchange of bacteria will be necessary. Future observations in wetlands, hot deserts, tundra, remote glacial and coastal regions and over oceans will be of particular interest.

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