The resolution dependence of cloud effects and ship‐induced aerosol‐cloud interactions in marine stratocumulus

Possner, Anna; Zubler, Elias; Lohmann, Ulrike; Schär, Christoph

doi:10.1002/2015jd024685

Cited by 22 publications

(24 citation statements)

References 79 publications

(107 reference statements)

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“…Ghan et al, 2001;Adams and Seinfeld, 2002;Spracklen et al, 2005) and several have explored aerosol-cloud interactions in regional-scale models (e.g. Bangert et al, 2011;Zubler et al, 2011;Yang et al, 2012), only a few studies (Ekman et al, 2004(Ekman et al, , 2006Wang et al, 2011;Archer-Nicholls et al, 2016;Possner et al, 2016;Weigum et al, 2016) have explored the microphysical properties of aerosols, and their potential interactions with clouds, at resolutions of ∼ 1 km where convection is resolved.…”

Section: Introductionmentioning

confidence: 99%

Spatial and temporal CCN variations in convection-permitting aerosol microphysics simulations in an idealised marine tropical domain

et al. 2017

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Abstract. A convection-permitting limited area model with periodic lateral boundary conditions and prognostic aerosol microphysics is applied to investigate how concentrations of cloud condensation nuclei (CCN) in the marine boundary layer are affected by high-resolution dynamical and thermodynamic fields. The high-resolution aerosol microphysicsdynamics model, which resolves differential particle growth and aerosol composition across the particle size range, is applied to a domain designed to match approximately a single grid square of a climate model. We find that, during strongly convective conditions with high wind-speed conditions, CCN concentrations vary by more than a factor of 8 across the domain (5-95th percentile range), and a factor of ∼ 3 at more moderate wind speed. One reason for these large subclimate-grid-scale variations in CCN is that emissions of sea salt and dimethyl sulfide (DMS) are much higher when spatial and temporal wind-speed fluctuations become resolved at this convection-permitting resolution (making peak wind speeds higher). By analysing how the model evolves during spin-up, we gain new insight into the way primary sea salt and secondary sulfate particles contribute to the overall CCN variance in these realistic conditions, and find a marked difference in the variability of super-micron and sub-micron CCN. Whereas the super-micron CCN are highly variable, dominated by strongly fluctuating sea spray emitted, the submicron CCN tend to be steadier, mainly produced on longer timescales following growth after new particle formation in the free troposphere, with fluctuations inherently buffered by the fact that coagulation is faster at higher particle concentrations. We also find that sub-micron CCN are less variable in particle size, the accumulation-mode mean size varying by ∼ 20 % (0.101 to 0.123 µm diameter) compared to ∼ 35 % (0.75 to 1.10 µm diameter) for coarse-mode particles at this resolution. We explore how the CCN variability changes in the vertical and at different points in the spin-up, showing how CCN concentrations are introduced both by the emissions close to the surface and at higher altitudes during strong wind-speed conditions associated to the intense convective period. We also explore how the non-linear variation of seasalt emissions with wind speed propagates into variations in sea-salt mass mixing ratio and CCN concentrations, finding less variation in the latter two quantities due to the longer transport timescales inherent with finer CCN, which sediment more slowly. The complex mix of sources and diverse community of processes involved makes sub-grid parameterisation of CCN variations difficult. However, the results presented here illustrate the limitations of predictions with largescale models and the high-resolution aerosol microphysicsdynamics modelling system shows promise for future studies where the aerosol variations will propagate through to modified cloud microphysical evolution.

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Section: Introductionmentioning

confidence: 99%

Spatial and temporal CCN variations in convection-permitting aerosol microphysics simulations in an idealised marine tropical domain

et al. 2017

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“…when simulating aerosol-cloud interactions. Furthermore, models of different resolutions generally have problems reproducing the structure of mixed-phase clouds prevalent in the Arctic (Morrison et al, 2009;Klein et al, 2009;Fan et al, 2011;Morrison et al, 2011;Possner et al, 2017), and the future sea ice extent, as well as the prescribed aerosol emissions, is highly uncertain (Collins et al, 2013). To gain a better understanding of the robustness of our results, we compare them with other studies, both concerning relative and absolute changes.…”

Section: Resultsmentioning

confidence: 94%

How important are future marine and shipping aerosol emissions in a warming Arctic summer and autumn?

Gilgen¹,

Huang²,

Ickes

et al. 2018

Atmos. Chem. Phys.

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Abstract. Future sea ice retreat in the Arctic in summer and autumn is expected to affect both natural and anthropogenic aerosol emissions: sea ice acts as a barrier between the ocean and the atmosphere, and reducing it increases dimethyl sulfide and sea salt emissions. Additionally, a decrease in the area and thickness of sea ice could lead to enhanced Arctic ship traffic, for example due to shorter routes of cargo ships. Changes in the emissions of aerosol particles can then influence cloud properties, precipitation, surface albedo, and radiation. Next to changes in aerosol emissions, clouds will also be affected by increases in Arctic temperatures and humidities. In this study, we quantify how future aerosol radiative forcings and cloud radiative effects might change in the Arctic in late summer (July–August) and early autumn (September–October). Simulations were conducted for the years 2004 and 2050 with the global aerosol–climate model ECHAM6-HAM2. For 2050, simulations with and without additional ship emissions in the Arctic were carried out to quantify the impact of these emissions on the Arctic climate. In the future, sea salt as well as dimethyl sulfide emissions and burdens will increase in the Arctic. The increase in cloud condensation nuclei, which is due to changes in aerosol particles and meteorology, will enhance cloud droplet number concentrations over the Arctic Ocean (+10 % in late summer and +29 % in early autumn; in-cloud values averaged between 75 and 90∘ N). Furthermore, both liquid and total water path will increase (+10 % and +8 % in late summer; +34 % and +26 % in early autumn) since the specific humidity will be enhanced due to higher temperatures and the exposure of the ocean's surface. Changes in both aerosol radiative forcings and cloud radiative effects at the top of the atmosphere will not be dominated by the aerosol particles and clouds themselves but by the decrease in surface albedo (and by the increase in surface temperature for the longwave cloud radiative effect in early autumn). Mainly due to the reduction in sea ice, the aerosol radiative forcing will become less positive (decreasing from 0.53 to 0.36 W m−2 in late summer and from 0.15 to 0.11 W m−2 in early autumn). The decrease in sea ice is also mainly responsible for changes in the net cloud radiative effect, which will become more negative in late summer (changing from −36 to −46 W m−2). Therefore, the cooling component of both aerosols and clouds will gain importance in the future. We found that future Arctic ship emissions related to transport and oil and gas extraction (Peters et al., 2011) will not have a large impact on clouds and radiation: changes in aerosols only become significant when we increase these ship emissions by a factor of 10. However, even with 10-fold ship emissions, the net aerosol radiative forcing shows no significant changes. Enhanced black carbon deposition on snow leads to a locally significant but very small increase in radiative forcing over the central Arctic Ocean in early autumn (no significant increase for average between 75 and 90∘ N). Furthermore, the 10-fold higher ship emissions increase the optical thickness and lifetime of clouds in late summer (net cloud radiative effect changing from −48 to −52 W m−2). These aerosol–cloud effects have a considerably larger influence on the radiative forcing than the direct effects of particles (both aerosol particles in the atmosphere and particles deposited on snow). In summary, future ship emissions of aerosols and their precursor gases might have a net cooling effect, which is small compared to other changes in future Arctic climate such as those caused by the decrease in surface albedo.

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“…As discussed in Giglio et al (2010) and van der Werf et al 2010, emissions in GFED3 have increased compared to GFED2 due to an improved mapping approach of burned areas using MODIS and a higher resolution of 0.5°compared to GFED2 with 1°resolution. Previous studies have also pointed at the importance of the spatial (Possner et al, 2016) and temporal resolution (Dentener et al, 2006) of aerosol emissions.…”

Section: Discussionmentioning

confidence: 99%

Investigating processes that control the vertical distribution of aerosol in five subtropical marine stratocumulus regions – A sensitivity study using the climate model NorESM1-M

Frey

Bender

Svensson

2019

Preprint

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<p><strong>Abstract.</strong> The vertical distribution of aerosols plays an important role in determining the effective radiative forcing from aerosol&#8211;radiation and aerosol&#8211;cloud interactions. Here, a number of processes controlling the vertical distribution of aerosol in five subtropical marine stratocumulus regions in the climate model NorESM1-M are investigated, with a focus on the total aerosol extinction. A comparison with satellite lidar data (CALIOP, Cloud-Aerosol Lidar with Orthogonal Polarization) shows that the model underestimates aerosol extinction throughout the troposphere, especially elevated aerosol layers in the two regions where they are seen in observations. It is found that the shape of the vertical aerosol distribution is largely determined by the aerosol emissions and removal processes in the model, primarily through the injection height, emitted particle size, and wet scavenging. In addition, the representation of vertical transport related to shallow convection and entrainment are found to be important, whereas alterations in aerosol optical properties and cloud microphysics parameterizations have smaller effects on the vertical aerosol extinction distribution. However, none of the alterations made are sufficient for reproducing the observed vertical distribution of aerosol extinction, neither in magnitude nor in shape. Interpolating the vertical levels of CALIOP to the corresponding model levels, leads to a better agreement in the boundary layer and highlights the importance of the vertical resolution.</p>

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The resolution dependence of cloud effects and ship‐induced aerosol‐cloud interactions in marine stratocumulus

Cited by 22 publications

References 79 publications

Spatial and temporal CCN variations in convection-permitting aerosol microphysics simulations in an idealised marine tropical domain

Spatial and temporal CCN variations in convection-permitting aerosol microphysics simulations in an idealised marine tropical domain

How important are future marine and shipping aerosol emissions in a warming Arctic summer and autumn?

Investigating processes that control the vertical distribution of aerosol in five subtropical marine stratocumulus regions – A sensitivity study using the climate model NorESM1-M

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