Aerosol size-dependent below-cloud scavenging by rain and snow in the ECHAM5-HAM

Abstract. Wet deposition processes are highly efficient in the removal of aerosols from the atmosphere, and thus strongly influence global aerosol concentrations, and clouds, and their respective radiative forcings. In this study, physically detailed size-dependent below-cloud scavenging parameterizations for rain and snow are implemented in the ECHAM5-HAM global aerosol-climate model. Previously, below-cloud scavenging by rain in the ECHAM5-HAM was simply a function of the aerosol mode, and then scaled by the rainfall rate. The below-cloud scavenging by snow was a function of the snowfall rate alone. The global mean aerosol optical depth, and sea salt burden are sensitive to the below-cloud scavenging coefficients, with reductions near to 15% when the more vigorous size-dependent below-cloud scavenging by rain and snow is implemented. The inclusion of a prognostic rain scheme significantly reduces the fractional importance of below-cloud scavenging since there is higher evaporation in the lower troposphere, increasing the global mean sea salt burden by almost 15%. Thermophoretic effects are shown to produce increases in the global and annual mean number removal of Aitken size particles of near to 10%, but very small increases (near 1%) in the global mean below-cloud mass scavenging of carbonaceous and sulfate aerosols. Changes in the assumptions about the below-cloud scavenging by rain of particles with radius smaller than 10 nm do not cause any significant changes to the global and annual mean aerosol mass or number burdens, despite a change in the below-cloud number removal rate for nucleation mode particles by near to five-fold. Annual and zonal mean nucleation mode number concentrations are enhanced by up to 30% in the lower troposphere with the more vigourous size-dependent below-cloud scavenging. Closer agreement with different observations is found when the more physically detailed below-cloud scavenging parameterization is employed in the ECHAM5-HAM model.

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Aerosol size-dependent below-cloud scavenging by rain and snow in the ECHAM5-HAM

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-7873-2009 ◽

2009 ◽

Vol 9 (2) ◽

pp. 7873-7925 ◽

Cited By ~ 5

Author(s):

B. Croft ◽

U. Lohmann ◽

R. V. Martin ◽

P. Stier ◽

S. Wurzler ◽

...

Keyword(s):

Climate Model ◽

Fine Particles ◽

Removal Rate ◽

Lower Troposphere ◽

Sea Salt ◽

Radiative Forcings ◽

Nucleation Mode ◽

Size Dependent ◽

Cloud Scavenging ◽

Global Mean

Abstract. Wet deposition processes are highly efficient in the removal of aerosols from the atmosphere, and thus strongly influence global aerosol concentrations, and clouds, and their respective radiative forcings. In this study, physically detailed size-dependent below-cloud scavenging parameterizations for rain and snow are implemented in the ECHAM5-HAM global aerosol-climate model. Previously, below-cloud scavenging by rain in the ECHAM5-HAM was simply a function of the aerosol mode, and then scaled by the rainfall rate. The below-cloud scavenging by snow was a function of the snowfall rate alone. The global mean aerosol optical depth, and sea salt burden are sensitive to the below-cloud scavenging coefficients, with reductions near to 15% when the more vigorous size-dependent below-cloud scavenging by rain and snow is implemented. The inclusion of a prognostic rain scheme significantly reduces the fractional importance of below-cloud scavenging since there is higher evaporation in the lower troposphere, increasing the global mean sea salt burden by almost 15%. Thermophoretic effects are shown to produce increases in the global and annual mean below-cloud number removal of Aitken size particles of near to 15%, but very small increases (near 1%) in the global mean below-cloud mass scavenging of carbonaceous and sulfate aerosols. Changes in the assumptions about the below-cloud scavenging of ultra-fine particles by rain do not cause any significant changes to the global mean aerosol mass or number burdens, despite a change in the below-cloud number removal rate for nucleation mode particles by near to 10%. For nucleation mode particles, changes to the assumptions about the below-cloud scavenging by snow produce a greater change in the number removal rate, in excess of one order of magnitude. Closer agreement with different observations is found when the more physically detailed below-cloud scavenging parameterization is employed in the ECHAM5-HAM model.

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A New Method of Comparing Forcing Agents in Climate Models*

Journal of Climate ◽

10.1175/jcli-d-14-00663.1 ◽

2015 ◽

Vol 28 (20) ◽

pp. 8203-8218 ◽

Cited By ~ 11

Author(s):

Ben Kravitz ◽

Douglas G. MacMartin ◽

Philip J. Rasch ◽

Andrew J. Jarvis

Keyword(s):

Solar Irradiance ◽

Feedback Loop ◽

Climate Models ◽

Climate Model ◽

Co2 Concentration ◽

Total Solar Irradiance ◽

New Method ◽

Convergence Time ◽

Radiative Forcings ◽

Global Mean

Abstract The authors describe a new method of comparing different climate forcing agents (e.g., CO2 concentration, CH4 concentration, and total solar irradiance) in climate models that circumvents many of the difficulties associated with explicit calculations of efficacy. This is achieved by introducing an explicit feedback loop external to a climate model that adjusts one forcing agent to balance another while keeping global-mean surface temperature constant. The convergence time of this feedback loop can be adjusted, allowing for comparisons of forcing agents to be achieved with relatively short simulations. Comparisons between forcing agents are highly linear in concordance with predicted scaling relationships; for example, the global-mean climate response to a doubling of the CO2 concentration is equivalent to that of a 2.1% change in total solar irradiance. This result is independent of the magnitude of the forcing agent (within the range of radiative forcings considered here) and is consistent across two different climate models.

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Modelling sea salt aerosol and its direct and indirect effects on climate

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-7-14939-2007 ◽

2007 ◽

Vol 7 (5) ◽

pp. 14939-14987 ◽

Cited By ~ 1

Author(s):

X. Ma ◽

K. von Salzen ◽

J. Li

Keyword(s):

Radiative Forcing ◽

Climate Model ◽

Global Climate ◽

Global Climate Model ◽

Sea Salt ◽

Size Distributions ◽

Size Dependent ◽

Sea Salt Aerosol ◽

Direct Forcing ◽

Log Normal

Abstract. A size-dependent sea salt aerosol parameterization was developed based on the piecewise log-normal approximation (PLA) for aerosol size distributions. Results of this parameterization from simulations with a global climate model produce good agreement with observations at the surface and for vertically-integrated volume size distributions. The global and annual mean of the sea salt burden is 10.1 mg m−2. The direct radiative forcing is calculated to be −1.52 and −0.60 W m−2 for clear sky and all sky, respectively. The first indirect radiative forcing is about twice as large as the direct forcing for all-sky (−1.34 W m−2). The results also show that the total indirect forcing of sea salt is −2.9 W m−2 if climatic feedbacks are taken into account. The sensitivity of the forcings to changes in the burdens and sizes of sea salt particles was also investigated based on additional simulations with a different sea salt source function.

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Effects of heterogeneous reactions on tropospheric chemistry: a global simulation with the chemistry–climate model CHASER V4.0

Geoscientific Model Development ◽

10.5194/gmd-14-3813-2021 ◽

2021 ◽

Vol 14 (6) ◽

pp. 3813-3841

Author(s):

Phuc T. M. Ha ◽

Ryoki Matsuda ◽

Yugo Kanaya ◽

Fumikazu Taketani ◽

Kengo Sudo

Keyword(s):

Climate Model ◽

Model Simulation ◽

Model Performance ◽

Lower Troposphere ◽

Heterogeneous Reactions ◽

Tropospheric Chemistry ◽

Small Contribution ◽

Modeling Framework ◽

Positive Tendency ◽

Global Mean

Abstract. This study uses a chemistry–climate model CHASER (MIROC) to explore the roles of heterogeneous reactions (HRs) in global tropospheric chemistry. Three distinct HRs of N2O5, HO2, and RO2 are considered for surfaces of aerosols and cloud particles. The model simulation is verified with EANET and EMEP stationary observations; R/V Mirai ship-based data; ATom1 aircraft measurements; satellite observations by OMI, ISCCP, and CALIPSO-GOCCP; and reanalysis data JRA55. The heterogeneous chemistry facilitates improvement of model performance with respect to observations for NO2, OH, CO, and O3, especially in the lower troposphere. The calculated effects of heterogeneous reactions cause marked changes in global abundances of O3 (−2.96 %), NOx (−2.19 %), CO (+3.28 %), and global mean CH4 lifetime (+5.91 %). These global effects were contributed mostly by N2O5 uptake onto aerosols in the middle troposphere. At the surface, HO2 uptake gives the largest contributions, with a particularly significant effect in the North Pacific region (−24 % O3, +68 % NOx, +8 % CO, and −70 % OH), mainly attributable to its uptake onto clouds. The RO2 reaction has a small contribution, but its global mean negative effects on O3 and CO are not negligible. In general, the uptakes onto ice crystals and cloud droplets that occur mainly by HO2 and RO2 radicals cause smaller global effects than the aerosol-uptake effects by N2O5 radicals (+1.34 % CH4 lifetime, +1.71 % NOx, −0.56 % O3, +0.63 % CO abundances). Nonlinear responses of tropospheric O3, NOx, and OH to the N2O5 and HO2 uptakes are found in the same modeling framework of this study (R>0.93). Although all HRs showed negative tendencies for OH and O3 levels, the effects of HR(HO2) on the tropospheric abundance of O3 showed a small increment with an increasing loss rate. However, this positive tendency turns to reduction at higher rates (>5 times). Our results demonstrate that the HRs affect not only polluted areas but also remote areas such as the mid-latitude sea boundary layer and upper troposphere. Furthermore, HR(HO2) can bring challenges to pollution reduction efforts because it causes opposite effects between NOx (increase) and surface O3 (decrease).

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The global aerosol-climate model ECHAM-HAM, version 2: sensitivity to improvements in process representations

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-8911-2012 ◽

2012 ◽

Vol 12 (19) ◽

pp. 8911-8949 ◽

Cited By ~ 225

Author(s):

K. Zhang ◽

D. O'Donnell ◽

J. Kazil ◽

P. Stier ◽

S. Kinne ◽

...

Keyword(s):

Organic Matter ◽

Water Uptake ◽

Climate Model ◽

Organic Aerosols ◽

Lower Troposphere ◽

Cloud Microphysics ◽

Number Concentration ◽

Sea Salt ◽

Microphysics Scheme ◽

Aerosol Mass

Abstract. This paper introduces and evaluates the second version of the global aerosol-climate model ECHAM-HAM. Major changes have been brought into the model, including new parameterizations for aerosol nucleation and water uptake, an explicit treatment of secondary organic aerosols, modified emission calculations for sea salt and mineral dust, the coupling of aerosol microphysics to a two-moment stratiform cloud microphysics scheme, and alternative wet scavenging parameterizations. These revisions extend the model's capability to represent details of the aerosol lifecycle and its interaction with climate. Nudged simulations of the year 2000 are carried out to compare the aerosol properties and global distribution in HAM1 and HAM2, and to evaluate them against various observations. Sensitivity experiments are performed to help identify the impact of each individual update in model formulation. Results indicate that from HAM1 to HAM2 there is a marked weakening of aerosol water uptake in the lower troposphere, reducing the total aerosol water burden from 75 Tg to 51 Tg. The main reason is the newly introduced κ-Köhler-theory-based water uptake scheme uses a lower value for the maximum relative humidity cutoff. Particulate organic matter loading in HAM2 is considerably higher in the upper troposphere, because the explicit treatment of secondary organic aerosols allows highly volatile oxidation products of the precursors to be vertically transported to regions of very low temperature and to form aerosols there. Sulfate, black carbon, particulate organic matter and mineral dust in HAM2 have longer lifetimes than in HAM1 because of weaker in-cloud scavenging, which is in turn related to lower autoconversion efficiency in the newly introduced two-moment cloud microphysics scheme. Modification in the sea salt emission scheme causes a significant increase in the ratio (from 1.6 to 7.7) between accumulation mode and coarse mode emission fluxes of aerosol number concentration. This leads to a general increase in the number concentration of smaller particles over the oceans in HAM2, as reflected by the higher Ångström parameters. Evaluation against observation reveals that in terms of model performance, main improvements in HAM2 include a marked decrease of the systematic negative bias in the absorption aerosol optical depth, as well as smaller biases over the oceans in Ångström parameter and in the accumulation mode number concentration. The simulated geographical distribution of aerosol optical depth (AOD) is better correlated with the MODIS data, while the surface aerosol mass concentrations are very similar to those in the old version. The total aerosol water content in HAM2 is considerably closer to the multi-model average from Phase I of the AeroCom intercomparison project. Model deficiencies that require further efforts in the future include (i) positive biases in AOD over the ocean, (ii) negative biases in AOD and aerosol mass concentration in high-latitude regions, and (iii) negative biases in particle number concentration, especially that of the Aitken mode, in the lower troposphere in heavily polluted regions.

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Modelling sea salt aerosol and its direct and indirect effects on climate

Atmospheric Chemistry and Physics ◽

10.5194/acp-8-1311-2008 ◽

2008 ◽

Vol 8 (5) ◽

pp. 1311-1327 ◽

Cited By ~ 69

Author(s):

X. Ma ◽

K. von Salzen ◽

J. Li

Keyword(s):

Radiative Forcing ◽

Climate Model ◽

Global Climate ◽

Global Climate Model ◽

Sea Salt ◽

Size Distributions ◽

Size Dependent ◽

Sea Salt Aerosol ◽

Direct Forcing ◽

Log Normal

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Tropospheric ozone changes, radiative forcing and attribution to emissions in the Atmospheric Chemistry and Climate Model Inter-comparison Project (ACCMIP)

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-26047-2012 ◽

2012 ◽

Vol 12 (10) ◽

pp. 26047-26097 ◽

Cited By ~ 8

Author(s):

D. S. Stevenson ◽

P. J. Young ◽

V. Naik ◽

J.-F. Lamarque ◽

D. T. Shindell ◽

...

Keyword(s):

Nitrogen Oxides ◽

Atmospheric Chemistry ◽

Tropospheric Ozone ◽

Radiative Forcing ◽

Climate Model ◽

Lower Troposphere ◽

Radiative Forcings ◽

A Value ◽

Intercomparison Project ◽

Column Ozone

Abstract. Ozone (O3) from 17 atmospheric chemistry models taking part in the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) has been used to calculate tropospheric ozone radiative forcings (RFs). We calculate a~value for the pre-industrial (1750) to present-day (2010) tropospheric ozone RF of 0.40 W m−2. The model range of pre-industrial to present-day changes in O3 produces a spread (±1 standard deviation) in RFs of ±17%. Three different radiation schemes were used – we find differences in RFs between schemes (for the same ozone fields) of ±10%. Applying two different tropopause definitions gives differences in RFs of ±3%. Given additional (unquantified) uncertainties associated with emissions, climate-chemistry interactions and land-use change, we estimate an overall uncertainty of ±30% for the tropospheric ozone RF. Experiments carried out by a subset of six models attribute tropospheric ozone RF to increased emissions of methane (47%), nitrogen oxides (29%), carbon monoxide (15%) and non-methane volatile organic compounds (9%); earlier studies attributed more of the tropospheric ozone RF to methane and less to nitrogen oxides. Normalising RFs to changes in tropospheric column ozone, we find a global mean normalised RF of 0.042 W m−2 DU−1, a value similar to previous work. Using normalised RFs and future tropospheric column ozone projections we calculate future tropospheric ozone RFs (W m−2; relative to 1850 – add 0.04 W m−2 to make relative to 1750) for the Representative Concentration Pathways in 2030 (2100) of: RCP2.6: 0.31 (0.16); RCP4.5: 0.38 (0.26); RCP6.0: 0.33 (0.24); and RCP8.5: 0.42 (0.56). Models show some coherent responses of ozone to climate change: decreases in the tropical lower troposphere, associated with increases in water vapour; and increases in the sub-tropical to mid-latitude upper troposphere, associated with increases in lightning and stratosphere-to-troposphere transport.

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Effects of heterogeneous reactions on global tropospheric chemistry

10.5194/gmd-2020-335 ◽

2020 ◽

Author(s):

Phuc T. M. Ha ◽

Fumikazu Taketani ◽

Yugo Kanaya ◽

Ryoki Matsuda ◽

Kengo Sudo

Keyword(s):

Climate Model ◽

Model Simulation ◽

Model Performance ◽

Lower Troposphere ◽

Reanalysis Data ◽

Heterogeneous Reactions ◽

Tropospheric Chemistry ◽

Small Contribution ◽

Positive Tendency ◽

Global Mean

Abstract. This study uses a chemistry-climate model CHASER (MIROC) to explore the roles of heterogeneous reactions (HRs) in global tropospheric chemistry. Three distinct HRs of N2O5, HO2, and RO2 are considered for surfaces of aerosols and cloud particles. The model simulation is verified with EANET and EMEP stationary observations, R/V MIRAI ship-based data, ATOM1 aircraft measurements, satellite observations by OMI, ISCCP, and CALIPSO-GOCCP, and reanalysis data JRA55. The heterogeneous chemistry facilitates improvement of model performance with respect to observations for NO2, OH, CO, and O3, especially in the lower troposphere. The calculated effects of heterogeneous reactions cause marked changes in global abundances of O3 (−3 %), NOx (−2.2 %), CO (+3.3 %), and global mean CH4 lifetime (+5.9 %). These global effects were contributed mostly by N2O5 uptake onto aerosols in the middle troposphere. At the surface, HO2 uptake gives the largest contributions, with a particularly significant effect in the North Pacific region (−24% O3, +68 % NOx, +8 % CO, and −70 % OH), mainly attributable to its uptake onto clouds. The RO2 reaction has a small contribution, but its global-mean negative effect on O3 is not negligible. In general, the uptakes onto ice crystals and cloud droplets that occur mainly by HO2 and RO2 radicals cause smaller global effects than the aerosol-uptake effects by N2O5 radicals (+1.34 % CH4 lifetime, +1.71 % NOx, −0.56 % O3, +0.63 % CO abundances). Nonlinear responses of tropospheric O3, NOx, and OH to the N2O5 and HO2 uptakes are found in the same modelling framework of this study (R > 0.93). Although all HRs showed negative tendencies for OH and O3 levels, the effects of HR(HO2) on the tropospheric abundance of O3 showed a small increment with an increasing loss rate. However, this positive tendency turns to reduction at higher rates (> 5 times). Our results demonstrate that the HRs affect not only polluted areas but also remote areas such as the mid-latitude sea boundary layer and upper troposphere. Furthermore, HR(HO2) can bring challenges to pollution reduction efforts because it causes opposite effects between NOx (increase) and surface O3 (decrease).

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Description and evaluation of GLOMAP-mode: a modal global aerosol microphysics model for the UKCA composition-climate model

Geoscientific Model Development ◽

10.5194/gmd-3-519-2010 ◽

2010 ◽

Vol 3 (2) ◽

pp. 519-551 ◽

Cited By ~ 267

Author(s):

G. W. Mann ◽

K. S. Carslaw ◽

D. V. Spracklen ◽

D. A. Ridley ◽

P. T. Manktelow ◽

...

Keyword(s):

Climate Model ◽

Cloud Condensation Nuclei ◽

Particle Growth ◽

Particle Formation ◽

Sea Salt ◽

Condensation Nuclei ◽

Aerosol Dynamics ◽

Cloud Processing ◽

Cloud Scavenging ◽

Primary Emissions

Abstract. A new version of the Global Model of Aerosol Processes (GLOMAP) is described, which uses a two-moment pseudo-modal aerosol dynamics approach rather than the original two-moment bin scheme. GLOMAP-mode simulates the multi-component global aerosol, resolving sulfate, sea-salt, dust, black carbon (BC) and particulate organic matter (POM), the latter including primary and biogenic secondary POM. Aerosol processes are simulated in a size-resolved manner including primary emissions, secondary particle formation by binary homogeneous nucleation of sulfuric acid and water, particle growth by coagulation, condensation and cloud-processing and removal by dry deposition, in-cloud and below-cloud scavenging. A series of benchmark observational datasets are assembled against which the skill of the model is assessed in terms of normalised mean bias (b) and correlation coefficient (R). Overall, the model performs well against the datasets in simulating concentrations of aerosol precursor gases, chemically speciated particle mass, condensation nuclei (CN) and cloud condensation nuclei (CCN). Surface sulfate, sea-salt and dust mass concentrations are all captured well, while BC and POM are biased low (but correlate well). Surface CN concentrations compare reasonably well in free troposphere and marine sites, but are underestimated at continental and coastal sites related to underestimation of either primary particle emissions or new particle formation. The model compares well against a compilation of CCN observations covering a range of environments and against vertical profiles of size-resolved particle concentrations over Europe. The simulated global burden, lifetime and wet removal of each of the simulated aerosol components is also examined and each lies close to multi-model medians from the AEROCOM model intercomparison exercise.

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ENSO sensitivity to radiative forcing

10.5194/egusphere-egu2020-11931 ◽

2020 ◽

Author(s):

Evgeniya Predybaylo ◽

Georgiy Stenchikov ◽

Andrew Wittenberg ◽

Sergey Osipov

Keyword(s):

Radiative Forcing ◽

Climate Model ◽

Southern Oscillation ◽

Volcanic Eruptions ◽

Boreal Winter ◽

Unified Framework ◽

Surface Cooling ◽

Radiative Forcings ◽

Global Mean ◽

Eruption Magnitude

<p>To improve El Ni&#241;o / Southern Oscillation (ENSO) predictions and projections in a changing climate, it is essential to better understand ENSO&#8217;s sensitivities to external radiative forcings. Strong volcanic eruptions can help to clarify ENSO&#8217;s sensitivities, mechanisms, and feedbacks. Strong explosive volcanic eruptions inject millions of tons of sulfur dioxide into the stratosphere, where they are converted into sulfate aerosols. For equatorial volcanoes, these aerosols can spread globally, scattering and absorbing incoming sunlight, and inducing a global-mean surface cooling. Despite this global-mean cooling effect, paleo data confirm remarkable warming of the eastern equatorial Pacific in the two years after a tropical eruption, with a shift towards an El Ni&#241;o-like state. To illuminate this response and explain why it tends to occur during particular seasons and ENSO phases, we present a unified framework that includes the roles of the seasonal cycle, stochastic wind forcing, eruption magnitude, and various tropical Pacific climate feedbacks. Analyzing over 20,000 years of large-ensemble simulations from the GFDL-CM2.1 climate model forced by volcanic eruptions, we find that the ENSO response comprises both stochastic and deterministic components, which vary depending on the perturbation season and the ocean preconditioning. For boreal winter eruptions, stochastic dispersion largely obscures the deterministic response, being the largest for the strong El Ni&#241;o preconditioning. Deterministic El Ni&#241;o-like responses to summer eruptions are well seen on neutral ENSO and weak to moderate El Ni&#241;o preconditioning and grow with the eruption magnitude. The relative balance of these components determines the predictability and strength of the ENSO response. The results clarify why previous studies obtained seemingly conflicting results.</p>

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