scholarly journals Reduced effective radiative forcing from cloud–aerosol interactions (ERF<sub>aci</sub>) with improved treatment of early aerosol growth in an Earth system model

2021 ◽  
Vol 21 (23) ◽  
pp. 17243-17265
Author(s):  
Sara Marie Blichner ◽  
Moa Kristina Sporre ◽  
Terje Koren Berntsen
Keyword(s):  
Radiative Forcing ◽  
Cloud Droplet ◽  
Early Growth ◽  
Earth System Model ◽  
Aerosol Concentration ◽  
System Model ◽  
Earth System ◽  
Secondary Aerosols ◽  
Effective Radiative Forcing ◽  
Droplet Activation

Abstract. Historically, aerosols of anthropogenic origin have offset some of the warming from increased atmospheric greenhouse gas concentrations. The strength of this negative aerosol forcing, however, is highly uncertain – especially the part originating from cloud–aerosol interactions. An important part of this uncertainty originates from our lack of knowledge about pre-industrial aerosols and how many of these would have acted as cloud condensation nuclei (CCN). In order to simulate CCN concentrations in models, we must adequately model secondary aerosols, including new particle formation (NPF) and early growth, which contributes a large part of atmospheric CCN. In this study, we investigate the effective radiative forcing (ERF) from cloud–aerosol interactions (ERFaci) with an improved treatment of early particle growth, as presented in Blichner et al. (2021). We compare the improved scheme to the default scheme, OsloAero, which are both embedded in the atmospheric component of the Norwegian Earth System Model v2 (NorESM2). The improved scheme, OsloAeroSec, includes a sectional scheme that treats the growth of particles from 5–39.6 nm in diameter, which thereafter inputs the particles to the smallest mode in the pre-existing modal aerosol scheme. The default scheme parameterizes the growth of particles from nucleation up to the smallest mode, a process that can take several hours. The explicit treatment of early growth in OsloAeroSec, on the other hand, captures the changes in atmospheric conditions during this growth time in terms of air mass mixing, transport, and condensation and coagulation. We find that the ERFaci with the sectional scheme is −1.16 W m−2, which is 0.13 W m−2 weaker compared to the default scheme. This reduction originates from OsloAeroSec producing more particles than the default scheme in pristine, low-aerosol-concentration areas and fewer NPF particles in high-aerosol areas. We find, perhaps surprisingly, that NPF inhibits cloud droplet activation in polluted and/or high-aerosol-concentration regions because the NPF particles increase the condensation sink and reduce the growth of the larger particles which may otherwise activate. This means that in these high-aerosol regions, the model with the lowest NPF – OsloAeroSec – will have the highest cloud droplet activation and thus more reflective clouds. In pristine and/or low-aerosol regions, however, NPF enhances cloud droplet activation because the NPF particles themselves tend to activate. Lastly, we find that sulfate emissions in the present-day simulations increase the hygroscopicity of secondary aerosols compared to pre-industrial simulations. This makes NPF particles more relevant for cloud droplet activation in the present day than the pre-industrial atmosphere because increased hygroscopicity means they can activate at smaller sizes.

scholarly journals Reduced effective radiative forcing from cloud-aerosol interactions (ERF<sub>aci</sub>) with improved treatment of early aerosol growth in an Earth System Model

2021 ◽  
Author(s):  
Sara Marie Blichner ◽  
Moa Kristina Sporre ◽  
Terje Koren Berntsen
Keyword(s):  
Radiative Forcing ◽  
Cloud Droplet ◽  
Early Growth ◽  
Earth System Model ◽  
Aerosol Concentration ◽  
System Model ◽  
Earth System ◽  
Secondary Aerosols ◽  
Effective Radiative Forcing ◽  
Droplet Activation

Abstract. Historically, aerosols of anthropogenic origin have offset some of the warming from increased atmospheric green- house gas concentrations. The strength of this negative aerosol forcing is, however, highly uncertain – especially the part originating from cloud-aerosol interactions. An important part of this uncertainty originates from our lack of knowledge about the pre-industrial aerosols and how many of these would have acted as cloud condensation nuclei (CCN). In order to simulate CCN concentrations in models, we must adequately model secondary aerosols, including new particle formation (NPF) and early growth, which contributes with a large part of atmospheric CCN. In this study, we investigate the effective radiative forcing (ERF) from cloud–aerosol interactions (ERFaci ) with an improved treatment of early particle growth, presented in Blichner et al. (2020). We compare the improved scheme to the default scheme, OsloAero, both part of the atmospheric component of the Norwegian Earth System Model v2 (NorESM2). The improved scheme, OsloAeroSec, includes a sectional scheme that treats the growth of the particles from 5–39.6 nm which thereafter inputs the particles to the smallest mode in the pre-existing, modal aerosol scheme. The default scheme parameterizes the growth of particles from nucleation and up to the smallest mode, a process that can take several hours. The explicit treatment of the early growth in OsloAeroSec on the other hand, captures the changes in atmospheric condition during this growth time both in terms of air mass mixing, transport and condensation and coagulation.We find that the ERF aci with the sectional scheme is −1.16 Wm−2 , which is 0.13 Wm−2 weaker compared to the default scheme. This reduction originates from OsloAeroSec producing more particles than the default scheme in pristine, low-aerosol- concentration areas and less NPF particles in high-aerosol areas. We find, perhaps surprisingly, that NPF inhibits cloud droplet activation in polluted/high-aerosol-concentration regions because the NPF particles increase the condensation sink and reduces the growth of the larger particles which may otherwise activate. This means that in these high-aerosol regions, the model with lowest NPF – OsloAeroSec – will have highest cloud droplet activation and thus more reflective clouds. In pristine/low aerosol regions however, NPF enhances cloud droplet activation, because the NPF particles themselves tend to activate.Lastly, we find that sulphate emissions in the present day simulations increase the hygroscopicity of the secondary aerosols compared to the pre-industrial simulations. This makes NPF particles more relevant for cloud droplet activation in the present day than the pre-industrial atmosphere, because the increased hygroscopicity means they can activate at smaller sizes.

Reduced effective radiative forcing from cloud-aerosol interactions with improved modelling of early aerosol growth in an Earth System Model

2021 ◽  
Author(s):  
Sara Marie Blichner ◽  
Moa Kristina Sporre ◽  
Terje Koren Berntsen
Keyword(s):  
Radiative Forcing ◽  
Particle Growth ◽  
Particle Formation ◽  
Climate Impacts ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
New Particle Formation ◽  
Secondary Aerosol ◽  
Effective Radiative Forcing

&lt;p&gt;Cloud-aerosol interactions are responsible for much of the uncertainty in forcing estimates from pre-industrial times and thus also climate sensitivity and future projections. Maybe the most important factor in this is our lack of knowledge about pre-industrial aerosols, their sources and their ability to act as cloud condensation nuclei (CCN). The number of CCN is highly dependent on secondary aerosol formation and in particular how much of this secondary aerosol mass that goes to new particle formation (NPF) and early particle growth, versus growing already large particles even larger.&amp;#160;&lt;br&gt;Earth system models which seek to model this, face a challenge because we need to represent processes at a very fine scale (nanometers) to a sufficient accuracy, while simultaneously keeping computational costs low. A common approach is to use log-normal modes to represent the sizedistribution, while more computationally expensive sectional schemes are considered closer to first principles.&amp;#160;&lt;/p&gt;&lt;p&gt;In this study, we investigate the effect of a newly developed scheme for early particle growth on the effective radiative forcing from cloud-aerosol interactions (ERF&lt;sub&gt;aci&lt;/sub&gt;) &amp;#160;in the Norwegian Earth System Model v2 (NorESMv2). The new scheme, referred to as OsloAeroSec, presented in &amp;#160;Blichner et al. (2020), combines a sectional scheme for the growth of the smallest particles (5 - 39.6 nm), with the original semi-modal aerosol scheme which would simply parameterize the growth up to the smallest mode with Lehtinen et al. (2007). This was shown to to improve the representation of CCN relevant particle concentrations, when compared to measurement data. &amp;#160;&lt;/p&gt;&lt;p&gt;We find that ERF&lt;sub&gt;aci&lt;/sub&gt; is weakened by approximately 10 % with the new scheme (from -1.29 &amp;#160;to -1.16 Wm&lt;sup&gt;-2&lt;/sup&gt;). The weakening originates from OsloAeroSec (the new scheme) reducing particle formation in regions with high aerosol concentrations while increasing it in very pristine regions. We find, perhaps surprisingly, that an important factor for the overall forcing, is that &amp;#160;NPF inhibits aerosol activation into cloud droplets in high-aerosol-concentration regions, while the opposite is true in pristine regions.&amp;#160;&lt;br&gt;This is because the NPF particles act as a condensation sink, and if they cannot activate directly themselves, they may reduce the growth of the larger particles which would otherwise activate.&amp;#160;&lt;br&gt;Furthermore, we find that the increase in particle hygroscopicity with present day emissions of sulphate pre-cursors, decreases the size of the activated particles, and thus makes NPF particles more relevant for cloud droplet activation.&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References:&amp;#160;&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Lehtinen, Kari E. J., Miikka Dal Maso, Markku Kulmala, and Veli-Matti Kerminen. &amp;#8220;Estimating Nucleation Rates from Apparent Particle Formation Rates and Vice Versa: Revised Formulation of the Kerminen&amp;#8211;Kulmala Equation.&amp;#8221; Journal of Aerosol Science (2007): https://doi.org/10.1016/j.jaerosci.2007.06.009.&lt;/p&gt;&lt;p&gt;Blichner, Sara M., Moa K. Sporre, Risto Makkonen, and Terje K. Berntsen. &amp;#8220;Implementing a sectional scheme for early aerosol growth from new particle formation in the Norwegian Earth System Model v2: comparison to observations and climate impacts.&amp;#8221; Geoscientific Model Development Discussions (2020): https://doi.org/10.5194/gmd-2020-357&lt;/p&gt;

Investigating model nudging as a novel technique to isolate aerosol radiative adjustment mechanisms

2021 ◽  
Author(s):  
Max Coleman ◽  
William Collins ◽  
Keith Shine ◽  
Nicolas Bellouin ◽  
Fiona O'Connor
Keyword(s):  
Black Carbon ◽  
Radiative Forcing ◽  
Potential Temperature ◽  
Atmospheric Temperature ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Aerosol Emission ◽  
Aerosol Emissions ◽  
Adjustment Mechanisms

&lt;p&gt;We investigate a novel use of model nudging to interrogate radiative rapid adjustment mechanisms and their magnitudes in response to aerosol emission perturbations in an earth system model. The radiative effects of a forcing agent can be quantified using the effective radiative forcing (ERF). ERF is the sum of the instantaneous radiative forcing, and radiative adjustments &amp;#8211; changes in the atmosphere&amp;#8217;s state in response to the initial forcing agent that cause a further radiative forcing. Radiative adjustments are particularly important for aerosols, which affect clouds both via microphysical interactions and changes in circulation, stratification and convection. Understanding the different adjustment mechanisms and their contribution to the total ERF of different aerosol emissions is necessary to better understand how their ERF may change with future changes in anthropogenic aerosol emissions. In this work we investigate radiative adjustments resulting from changes in atmospheric temperature (and the resulting changes in stratification and convection) due to anthropogenic sulphate and black carbon aerosol forcing.&lt;/p&gt;&lt;p&gt;We have conducted multiple global atmosphere-only time-slice experiments using the UK Earth System Model (UKESM1). Each experiment has either control, black carbon perturbed, or sulphur dioxide perturbed emissions; and either no nudging, nudged horizontal winds (uv), or nudged horizontal winds and potential temperature (uv&amp;#952;). The difference between nudged uv&amp;#952; minus nudged uv simulations determines the atmospheric temperature related adjustments arising from the aerosol perturbation. We have also conducted repeats of each simulation, varying the nudging setup to test sensitivity to different nudging parameters.&lt;/p&gt;&lt;p&gt;We find that nudging horizontal winds affects the resulting ERF very little, whereas nudging potential temperature as well can cause a significant difference from the non-nudged experiments, primarily in the cloud radiative effect. However, this difference is sensitive to the strength of the nudging applied, for which we consider the most appropriate value.&lt;/p&gt;

Coupling interactive fire with atmospheric composition and climate in the UK Earth System Model (UKESM)

2020 ◽  
Author(s):  
João Teixeira ◽  
Fiona O'Connor ◽  
Nadine Unger ◽  
Apostolos Voulgarakis
Keyword(s):  
Atmospheric Chemistry ◽  
Prescribed Fire ◽  
Radiative Forcing ◽  
Regional Scale ◽  
Earth System Model ◽  
System Model ◽  
Atmospheric Composition ◽  
Earth System ◽  
Fire Emissions ◽  
The Uk

&lt;p&gt;Fires constitutes a key process in the Earth system (ES), being driven by climate as well as affecting the climate by changing atmospheric composition and its impact on the terrestrial carbon cycle. However, global modelling studies on the effects of fires on atmospheric composition, radiative forcing and climate have been very limited to date. The aim of this work is the development and application of a fully coupled vegetation-fire-chemistry-climate ES model in order to quantify the impacts of fire variability on atmospheric composition-climate interactions in the present day. For this, the INFERNO fire model is coupled to the atmosphere-only configuration of the UK&amp;#8217;s Earth System Model (UKESM). This fire-atmosphere interaction through atmospheric chemistry and aerosols allows for fire emissions to feedback on radiation and clouds changing weather which can consequently feedback on the atmospheric drivers of fire. Additionally, INFERNO was updated based on recent developments in the literature to improve the representation of human/economic factors in the anthropogenic ignition and suppression of fire. This work presents an assessment of the effects of interactive fire coupling on atmospheric composition and climate compared to the standard UKESM1 configuration which has prescribed fire emissions. Results show a satisfactory performance when using the fire-atmosphere coupling (the &amp;#8220;online&amp;#8221; version of the model) when compared to the offline UKESM that uses prescribed fire. The model can reproduce observed present day global fire emissions of carbon monoxide (CO) and aerosols, despite underestimating the global average burnt area. However, at a regional scale there is an overestimation of fire emissions over Africa due to the miss-representation of the underlying vegetation types and an underestimation over Equatorial Asia due to a lack of representation of peat fires.&lt;/p&gt;

scholarly journals Aviation 2006 NO<sub>x</sub>-induced effects on atmospheric ozone and HO<sub>x</sub> in Community Earth System Model (CESM)

2014 ◽  
Vol 14 (18) ◽  
pp. 9925-9939 ◽  
Author(s):  
A. Khodayari ◽  
S. Tilmes ◽  
S. C. Olsen ◽  
D. B. Phoenix ◽  
D. J. Wuebbles ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Radiative Forcing ◽  
Photochemical Reactions ◽  
Earth System Model ◽  
Design Tool ◽  
System Model ◽  
Nox Emissions ◽  
Earth System ◽  
Community Earth System Model ◽  
Aerosol Module

Abstract. The interaction between atmospheric chemistry and ozone (O3) in the upper troposphere–lower stratosphere (UTLS) presents a major uncertainty in understanding the effects of aviation on climate. In this study, two configurations of the atmospheric model from the Community Earth System Model (CESM), Community Atmosphere Model with Chemistry, Version 4 (CAM4) and Version 5 (CAM5), are used to evaluate the effects of aircraft nitrogen oxide (NOx = NO + NO2) emissions on ozone and the background chemistry in the UTLS. CAM4 and CAM5 simulations were both performed with extensive tropospheric and stratospheric chemistry including 133 species and 330 photochemical reactions. CAM5 includes direct and indirect aerosol effects on clouds using a modal aerosol module (MAM), whereby CAM4 uses a bulk aerosol module, which can only simulate the direct effect. To examine the accuracy of the aviation NOx-induced ozone distribution in the two models, results from the CAM5 and CAM4 simulations are compared to ozonesonde data. Aviation NOx emissions for 2006 were obtained from the AEDT (Aviation Environmental Design Tool) global commercial aircraft emissions inventory. Differences between simulated O3 concentrations and ozonesonde measurements averaged at representative levels in the troposphere and different regions are 13% in CAM5 and 18% in CAM4. Results show a localized increase in aviation-induced O3 concentrations at aviation cruise altitudes that stretches from 40° N to the North Pole. The results indicate a greater and more disperse production of aviation NOx-induced ozone in CAM5, with the annual tropospheric mean O3 perturbation of 1.2 ppb (2.4%) for CAM5 and 1.0 ppb (1.9%) for CAM4. The annual mean O3 perturbation peaks at about 8.2 ppb (6.4%) and 8.8 ppb (5.2%) in CAM5 and CAM4, respectively. Aviation emissions also result in increased hydroxyl radical (OH) concentrations and methane (CH4) loss rates, reducing the tropospheric methane lifetime in CAM5 and CAM4 by 1.69 and 1.40%, respectively. Aviation NOx emissions are associated with an instantaneous change in global mean short-term O3 radiative forcing (RF) of 40.3 and 36.5 mWm−2 in CAM5 and CAM4, respectively.

scholarly journals Implementing a sectional scheme for early aerosol growth from new particle formation in the Norwegian Earth System Model v2: comparison to observations and climate impacts

2020 ◽  
Author(s):  
Sara M. Blichner ◽  
Moa K. Sporre ◽  
Risto Makkonen ◽  
Terje K. Berntsen
Keyword(s):  
Size Distribution ◽  
Large Scale ◽  
Particle Formation ◽  
Early Growth ◽  
Number Concentration ◽  
Climate Impacts ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
New Particle Formation

Abstract. Aerosol-cloud interactions contribute with a large portion of the spread in estimates of climate forcing, climate sensitivity and future projections. An important part of this uncertainty is how much new particle formation (NPF) contributes to cloud condensation nuclei (CCN), and furthermore, how this changes with changes in anthropogenic emissions. Incorporating NPF and early growth in Earth System Models (ESMs) is, however, challenging both due to uncertain parameters (e.g. participating vapours), structural challenges (numerical description of growth from ∼1 to ∼100 nm), and due to large scale of ESM grid compared to NPF scale.A common approach in ESMs is to represent the particle size distribution by a certain number of log-normal modes. Sectional schemes on the other hand, where the size distribution is represented by bins, are considered closer to first principles because they do not make an a priori assumption about the size distribution. In order to improve the representation of early growth, we have implemented a sectional scheme for the smallest particles (5–39.6 nm diameter) in the Norwegian Earth System Model (NorESM), feeding particles into the original aerosol scheme. This is, to our knowledge, the first time such an approach has been tried. We find that including the sectional scheme for early growth improves the aerosol number concentration in the model when comparing against observations, particularly in the 50–100 nm diameter range. Furthermore, we find that the model with the sectional scheme produces much less particles than the original scheme in polluted regions, while it produces more in remote regions and the free troposphere, indicating a potential impact on the estimated aerosol forcing. Finally, we analyse the effect on cloud-aerosol interactions and find that the effect of changes in NPF efficiency on clouds is highly heterogeneous in space. While in remote regions, more efficient NPF leads to higher cloud droplet number concentration (CDNC), in polluted regions the opposite is in fact the case.

scholarly journals Coupling interactive fire with atmospheric composition and climate in the UK Earth System Model

2021 ◽  
Vol 14 (10) ◽  
pp. 6515-6539
Author(s):  
João C. Teixeira ◽  
Gerd A. Folberth ◽  
Fiona M. O'Connor ◽  
Nadine Unger ◽  
Apostolos Voulgarakis
Keyword(s):  
Biomass Burning ◽  
Prescribed Fire ◽  
Radiative Forcing ◽  
Regional Scale ◽  
Earth System Model ◽  
System Model ◽  
Atmospheric Composition ◽  
Earth System ◽  
Fire Emissions ◽  
Similar Performance

Abstract. Fire constitutes a key process in the Earth system (ES), being driven by climate as well as affecting the climate by changing atmospheric composition and impacting the terrestrial carbon cycle. However, studies on the effects of fires on atmospheric composition, radiative forcing and climate have been limited to date, as the current generation of ES models (ESMs) does not include fully atmosphere–composition–vegetation coupled fires feedbacks. The aim of this work is to develop and evaluate a fully coupled fire–composition–climate ES model. For this, the INteractive Fires and Emissions algoRithm for Natural envirOnments (INFERNO) fire model is coupled to the atmosphere-only configuration of the UK's Earth System Model (UKESM1). This fire–atmosphere interaction through atmospheric chemistry and aerosols allows for fire emissions to influence radiation, clouds and generally weather, which can consequently influence the meteorological drivers of fire. Additionally, INFERNO is updated based on recent developments in the literature to improve the representation of human and/or economic factors in the anthropogenic ignition and suppression of fire. This work presents an assessment of the effects of interactive fire coupling on atmospheric composition and climate compared to the standard UKESM1 configuration that uses prescribed fire emissions. Results show a similar performance when using the fire–atmosphere coupling (the “online” version of the model) when compared to the offline UKESM1 that uses prescribed fire. The model can reproduce observed present-day global fire emissions of carbon monoxide (CO) and aerosols, despite underestimating the global average burnt area. However, at a regional scale, there is an overestimation of fire emissions over Africa due to the misrepresentation of the underlying vegetation types and an underestimation over equatorial Asia due to a lack of representation of peat fires. Despite this, comparing model results with observations of CO column mixing ratio and aerosol optical depth (AOD) show that the fire–atmosphere coupled configuration has a similar performance when compared to UKESM1. In fact, including the interactive biomass burning emissions improves the interannual CO atmospheric column variability and consequently its seasonality over the main biomass burning regions – Africa and South America. Similarly, for aerosols, the AOD results broadly agree with the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Aerosol Robotic Network (AERONET) observations.

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