Query: monthly tropospheric aerosol

title: An aerosol climatology for global models based on the tropospheric aerosol scheme in the Integrated Forecasting System of ECMWF
abstract: An aerosol climatology to represent aerosols in the radiation schemes of Global Atmospheric Models was recently developed. We derived the climatology from a reanalysis of atmospheric composition produced by the Copernicus Atmosphere Monitoring Service (CAMS) As an example of application into a global atmospheric model, we discuss the technical aspects of the implementation in the Integrated Forecasting System of European Centre for Medium Range Weather Forecasts (ECMWF IFS) and the impact of the new climatology on the medium range weather forecasts and one year simulations. The new aerosol climatology was derived by combining a set of model simulation with constrained meteorological conditions and an atmospheric composition reanalysis for the period 2003 2014 produced by the IFS. The aerosol fields of the re analysis are constrained by assimilating Aerosol optical thickness (AOT) retrievals product by the MODIS instruments. In a further step, we used modelled aerosol fields to correct the aerosol speciation and the vertical profiles of the aerosol reanalysis fields. The new climatology provides the monthly mean mass mixing ratio of five aerosol species constrained by assimilated MODIS AOT. Using the new climatology in the ECMWF IFS leads to changes in direct aerosol radiative effect compared to the climatology previously implemented, which have a small, but non negligible impact on the forecast skill of large scale weather patterns in the medium range. However, details of the regional distribution of aerosol radiative forcing can have a large local impact. This is the case for the area of the Arabian Peninsula and the northern Indian Ocean. Here changes in the radiative forcing of the mineral dust significantly improve the Summer Monsoon circulation.

title: Improved aerosol correction for OMI tropospheric NO2 retrieval over East Asia Constraint from CALIOP aerosol vertical profile
abstract: Satellite retrieval of vertical column densities (VCDs) of tropospheric nitrogen dioxide NO2 is critical for NOx pollution and impact evaluation. For regions with high aerosol loadings, the retrieval accuracy is greatly affected by whether aerosol optical effects are treated implicitly (as additional "effective" clouds) or explicitly, among other factors. Our previous POMINO algorithm explicitly accounts for aerosol effects to improve the retrieval, especially in polluted situations over China, by using aerosol information from GEOS Chem simulations with further monthly constraints by MODIS/Aqua aerosol optical depth (AOD) data. Here we present a major algorithm update, POMINO v1.1, by constructing a monthly climatological dataset of aerosol extinction profiles, based on level 2 CALIOP/CALIPSO data over 2007 2015, to better constrain the modeled aerosol vertical profiles. We find that GEOS Chem captures the month to month variation in CALIOP aerosol layer height (ALH) but with a systematic underestimate by about 300 600 m (season and location dependent) due to a too strong negative vertical gradient of extinction above 1 km. Correcting the model aerosol extinction profiles results in small changes in retrieved cloud fraction, increases in cloud top pressure (within 2 6 in most cases) and increases in tropospheric NO2 VCD by 4 16 over China on a monthly basis in 2012. The improved NO2 VCDs (in POMINO v1.1) are more consistent with independent ground based MAX DOAS observations R2=0.80 NMB 3.4 for 162 pixels in 49 days) than POMINO R2=0.80 NMB 9.6 DOMINO v2 R2=0.68 NMB 2.1 and QA4ECV R2=0.75 NMB 22.0 are. Especially on haze days, R2 reaches 0.76 for POMINO v1.1, much higher than that for POMINO (0.68) DOMINO v2 (0.38) and QA4ECV (0.34) Furthermore, the increase in cloud pressure likely reveals a more realistic vertical relationship between cloud and aerosol layers, with aerosols situated above the clouds in certain months instead of always below the clouds. The POMINO v1.1 algorithm is a core step towards our next public release of the data product (POMINO v2) and it will also be applied to the recently launched S5P TROPOMI sensor.

title: The MACv2 aerosol climatology
abstract: The MAC aerosol climatology defines monthly global maps for aerosol properties. The definition of mid visible optical and microphysical properties is strongly linked to multi year statistics of observations by sun photometers of the AERONET and MAN ground networks. As available statistics are spatially sparse, context from bottom up global modelling is added. Now in its second version, oceanic MAN reference data are included, a different lower anthropogenic fraction is assumed and the merging of the data statistics is improved. Hereby, now only absolute properties are merged and trusted photometer data are given stronger weights via regional corrections in place of local domain limited corrections. Global average mid visible (550 mn) aerosol properties are 0.12 for the aerosol optical depth (AOD) 0.94 for the single scattering albedo (SSA) and 0.7 for the asymmetry factor (ASY) Averages for sub micrometer (fine mode) and super micrometer (coarse mode) aerosol sizes are 0.063 (AODf) and 0.058 (AODc) 0.92 (SSAf) and 0.965 (SSAc) and 0.64 (ASYf) and 0.77 (ASYc) respectively. A new element is the separation of aerosol absorption (AAOD) by sky /sun photometers into fine mode and coarse mode contributions. These properties as well as the fine mode effective radii were merged with background data from global modelling yielding global averages of 0.0051 (AAODf) 0.0021 (AAODc) and 0.18 mm (RE,f) Local monthly mode detail now allows (in a 'top down' approach) to extract global distributions for aerosol component amounts and sizes. As the considered components for soot (BC) organics (OC) non absorbing fine mode (SU) sea salt (SS) and mineral dust (DU) have pre defined spectrally resolved properties, optical properties at other than mid visible wavelengths are automatically defined as required in broadband radiative transfer applications. With component information (e.g. amount, composition and size) also MAC estimates for CCN and IN concentrations are possible and also a simple MAC based aerosol retrieval model for satellite sensor data is suggested.

title: The role of chlorine in global tropospheric chemistry
abstract: We present a comprehensive simulation of tropospheric chlorine within the GEOS Chem global 3 D model of oxidant aerosol halogen atmospheric chemistry. The simulation includes explicit accounting of chloride mobilization from sea salt aerosol by acid displacement of HCl and by other heterogeneous processes. Additional small sources of tropospheric chlorine (combustion, organochlorines, transport from stratosphere) are also included. Reactive gas phase chlorine Cl* including Cl, ClO, Cl2, BrCl, ICl, HOCl, ClNO3, ClNO2, and minor species, is produced by the HCl+OH reaction and by heterogeneous conversion of sea salt aerosol chloride to BrCl, ClNO2, Cl2, and ICl. The model successfully simulates the observed mixing ratios of HCl in marine air (highest at northern midlatitudes) and the associated HNO3 decrease from acid displacement. It captures the high ClNO2 mixing ratios observed in continental surface air at night and attributes the chlorine to HCl volatilized from sea salt aerosol and transported inland following uptake by fine aerosol. The model successfully simulates the vertical profiles of HCl measured from aircraft, where enhancements in the continental boundary layer can again be largely explained by transport inland of the marine source. It does not reproduce the boundary layer Cl2 mixing ratios measured in the WINTER aircraft campaign (1 5 ppt in the daytime, low at night) the model is too high at night, which could be due to uncertainty in the rate of the ClNO2+Cl reaction, but we have no explanation for the high observed Cl2 in daytime. The global mean tropospheric concentration of Cl atoms in the model is 620 cm 3 and contributes 1.0 of the global oxidation of methane, 20 of ethane, 14 of propane, and 4 of methanol. Chlorine chemistry increases global mean tropospheric BrO by 85 mainly through the HOBr+Cl reaction, and decreases global burdens of tropospheric ozone by 7 and OH by 3 through the associated bromine radical chemistry. ClNO2 chemistry drives increases in ozone of up to 8 ppb over polluted continents in winter.

title: Description and evaluation of the tropospheric aerosol scheme in the European Centre for Medium Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS AER, cycle 45R1)
abstract: This article describes the IFS AER aerosol module used operationally in the Integrated Forecasting System (IFS) cycle 45R1, operated by the European Centre for Medium Range Weather Forecasts (ECMWF) in the framework of the Copernicus Atmospheric Monitoring Services (CAMS) We describe the different parameterizations for aerosol sources, sinks, and its chemical production in IFS AER, as well as how the aerosols are integrated in the larger atmospheric composition forecasting system. The focus is on the entire 45R1 code base, including some components that are not used operationally, in which case this will be clearly specified. This paper is an update to the Morcrette et al. (2009) article that described aerosol forecasts at the ECMWF using cycle 32R2 of the IFS. Between cycles 32R2 and 45R1, a number of source and sink processes have been reviewed and/or added, notably increasing the complexity of IFS AER. A greater integration with the tropospheric chemistry scheme of the IFS has been achieved for the sulfur cycle and for nitrate production. Two new species, nitrate and ammonium, have also been included in the forecasting system. Global budgets and aerosol optical depth (AOD) fields are shown, as is an evaluation of the simulated particulate matter (PM) and AOD against observations, showing an increase in skill from cycle 40R2, used in the CAMS interim ReAnalysis (CAMSiRA) to cycle 45R1.

title: Aerosol radiative effects with MACv2
abstract: Monthly global maps for aerosol properties of the Max Planck Aerosol Climatology version 2 (MACv2) are applied in an offline radiative transfer model to determine aerosol radiative effects. This model setup cannot address rapid adjustments by clouds, but current evidence suggests their contribution to be small when compared to the instantaneous radiative forcing. Global maps are presented to detail the regional and seasonal variability associated with (annual) global averages. Radiative effects caused by the aerosol presence (direct effects) and by aerosol modified clouds (indirect effects) are examined. Direct effects are determined for total aerosol, anthropogenic aerosol and extracted individual aerosol components. Indirect effects cover the impact of reduced cloud drop sizes by anthropogenic aerosol. Present day global annual radiative effects for anthropogenic aerosol yield (1) a climate cooling of 1.0 W m 2 at the top of the atmosphere (TOA) (2) a surface net flux reduction of 2.1 W m 2; and, by difference; (3) an atmospheric effect of +1.1 W m 2. This atmospheric solar heating is almost entirely a direct effect. On a global basis, indirect effects 0.65 W m 2) dominate direct effects 0.35 W m 2) for the present day climate response at the TOA, whereas the present day surface radiative budget is more strongly reduced by direct effects 1.45 W m 2) than by indirect effects 0.65 W m 2) Natural aerosols are on average less absorbing and larger in size. However, their stronger solar TOA cooling efficiency is offset by a non negligible infrared (IR) greenhouse warming efficiency. In the sum the global average annual direct forcing efficiencies (per unit AOD) for natural and anthropogenic aerosol are similar: 12 W m 2 per unit AOD for all sky conditions and 24 W m 2 per unit AOD for clear sky conditions. The present day direct TOA impact by all soot (BC) is +0.55 W m 2, when globally and annually averaged. Between +0.25 and +0.45 W m 2 of that can be attributed to anthropogenic sources, depending on assumptions for the preindustrial BC reference state. Similarly, the preindustrial fine mode reference uncertainty has a strong influence not just on the direct effect but even more on the indirect effect. Present day aerosol TOA forcing is estimated to stay within the 0.7 to 1.6 W m 2 range (with the best estimate at 1.0 W m 2) Calculations with scaled temporal changes to anthropogenic AOD from global modeling indicate that the global annual aerosol forcing has not changed much over the last decades, despite strong shifts in regional maxima for anthropogenic AOD. These regional shifts explain most solar insolation (brightening or dimming) trends that have been observed by ground based radiation data.

title: Observationally constrained aerosol cloud semi direct effects
abstract: Absorbing aerosols, like black carbon (BC) give rise to rapid adjustments, and the associated perturbation to the atmospheric temperature structure alters the cloud distribution. The level of scientific understanding of these rapid cloud adjustments otherwise known as semi direct effects (SDEs) is considered low, with models indicating a likely negative 0.44 to +0.1 Wm 2) forcing. Recent studies suggest this negative SDE is primarily driven by decreases in high level clouds and enhanced longwave cooling. Here, we investigate the SDE using multiple models driven by observationally constrained fine mode aerosol forcing without dust and sea salt. Unlike aerosol simulations, which yield a relatively vertically uniform aerosol atmospheric heating profile with significant upper tropospheric heating, observation based heating peaks in the lower troposphere and then decays to zero in the mid troposphere. We find a significant global annual mean decrease in low and mid level clouds, and weaker decreases in high level clouds, which leads to a positive SDE dominated by shortwave radiation. Thus, in contrast to most studies, we find a robust positive SDE, implying cloud adjustments act to warm the climate system. Sensitivity tests with identical average, but vertically uniform observationally constrained aerosol atmospheric heating result in a negative SDE, due to enhanced longwave cooling as a result of large reductions in high level clouds. Our results therefore suggest that model simulations lead to a negatively biased SDE, due to an aerosol atmospheric heating profile that is too vertically uniform. Aerosol cloud interactionsObservationally constrained modelling reveals aerosol cloud semi direct effects (SDE) are likely positive, contrasting with what was once thought. SDE describe aerosol related changes in cloud distribution and their corresponding radiative forcing. While previous studies indicate SDE are negative, these estimates are associated with large uncertainty, due, in part, to limitations in aerosol observations, specifically inadequate representation of their vertical variability. Robert Allen from the University of California Riverside, USA, and colleagues therefore constrain three climate models with complete aerosol profiles from CALIOP retrievals. The simulations reveal aerosol cloud SDE act to warm the climate system thus representing a positive forcing in response to an increase in shortwave radiation resulting from reductions in low and mid level clouds. These results emphasise the importance of correctly representing vertical aerosol profiles when quantifying aerosol cloud interactions and their subsequent radiative effects.

title: Impact of El Nino Southern Oscillation on the interannual variability of methane and tropospheric ozone
abstract: The interannual variability of the greenhouse gases methane (CH4) and tropospheric ozone (O3) is largely driven by natural variations in global emissions and meteorology. The El Nino Southern Oscillation (ENSO) is known to influence fire occurrence, wetland emission and atmospheric circulation, affecting sources and sinks of CH4 and tropospheric O3, but there are still important uncertainties associated with the exact mechanism and magnitude of this effect. Here we use a modelling approach to investigate how fires and meteorology control the interannual variability of global carbon monoxide (CO) CH4 and O3 concentrations, particularly during large El Nino events. Using a three dimensional chemical transport model (TOMCAT) coupled to a sophisticated aerosol microphysics scheme (GLOMAP) we simulate changes to CO, hydroxyl radical (OH) and O3 for the period 1997 2014. We then use an offline radiative transfer model to quantify the climate impact of changes to atmospheric composition as a result of specific drivers. During the El Nino event of 1997 1998, there were increased emissions from biomass burning globally, causing global CO concentrations to increase by more than 40 This resulted in decreased global mass weighted tropospheric OH concentrations of up to 9 and a consequent 4 increase in the CH4 atmospheric lifetime. The change in CH4 lifetime led to a 7.5 ppb yr 1 increase in the global mean CH4 growth rate in 1998. Therefore, biomass burning emission of CO could account for 72 of the total effect of fire emissions on CH4 growth rate in 1998. Our simulations indicate that variations in fire emissions and meteorology associated with El Nino have opposing impacts on tropospheric O3 burden. El Nino related changes in atmospheric transport and humidity decrease global tropospheric O3 concentrations leading to a 0.03 W m 2 change in the O3 radiative effect (RE) However, enhanced fire emission of precursors such as nitrogen oxides (NOx) and CO increase O3 and lead to an O3 RE of 0.03 W m 2. While globally the two mechanisms nearly cancel out, causing only a small change in global mean O3 RE, the regional changes are large up to 0.33 W m 2 with potentially important consequences for atmospheric heating and dynamics.

title: Impacts of recent decadal changes in Asian aerosols on the East Asian summer monsoon: roles of aerosol radiation and aerosol cloud interactions
abstract: Anthropogenic aerosols (AA) can affect cloud and precipitation through aerosol radiation interaction (ARI) and aerosol cloud interaction (ACI) Over the past few decades, anthropogenic aerosol emissions have exhibited remarkable changes in the magnitude and in spatial pattern. The most significant changes are the increased emissions over both South Asia and East Asia. In this study, the atmospheric component of a state of the art climate model that includes eight species of tropospheric aerosols, coupled to a multi level mixed layer ocean model, has been used to investigate the impacts of Asian anthropogenic aerosol precursor emission changes from 1970s to 2000s on large scale circulation and precipitation in boreal summer over East Asia. Results reveal significant changes in circulation and clouds over East Asia and over the tropical and western North Pacific (WNP) Increased Asian AA emissions lead to anomalous cyclonic circulation over the Maritime continent (MC) and anomalous anticyclonic circulation over the WNP, resulting in anomalous moisture transport convergence over the MC and therefore increased precipitation. They also lead to anomalous moisture flux divergence over both the WNP and large land areas of East Asia, especially over northern China, and therefore decreased precipitation there. These large scale circulation anomalies over the adjacent oceans are related to aerosol change induced ocean feedbacks, predominantly through ACI. It is the slow responses over the adjacent oceans (e.g. SST changes) through coupled atmosphere ocean interaction in pre monsoon seasons and summer that shape the changes of the East Asian summer monsoon and local precipitation. The results in this study suggest that increased Asian AA emissions from 1970s to 2000s may have played an important role for the observed southward shift of the Pacific intertropical convergence zone and precipitation belt, weakening of East Asian summer monsoon and reduced precipitation over northern China in East Asia during the latter half of the twentieth century.

title: Isotopic constraint on the twentieth century increase in tropospheric ozone
abstract: Tropospheric ozone (O3) is a key component of air pollution and an important anthropogenic greenhouse gas1. During the twentieth century, the proliferation of the internal combustion engine, rapid industrialization and land use change led to a global scale increase in O3 concentrations2,3; however, the magnitude of this increase is uncertain. Atmospheric chemistry models typically predict4 7 an increase in the tropospheric O3 burden of between 25 and 50 per cent since 1900, whereas direct measurements made in the late nineteenth century indicate that surface O3 mixing ratios increased by up to 300 per cent8 10 over that time period. However, the accuracy and diagnostic power of these measurements remains controversial2. Here we use a record of the clumped isotope composition of molecular oxygen (18O18O in O2) trapped in polar firn and ice from 1590 to 2016 ad, as well as atmospheric chemistry model simulations, to constrain changes in tropospheric O3 concentrations. We find that during the second half of the twentieth century, the proportion of 18O18O in O2 decreased by 0.03 0.02 parts per thousand (95 per cent confidence interval) below its 1590 1958 ad mean, which implies that tropospheric O3 increased by less than 40 per cent during that time. These results corroborate model predictions of global scale increases in surface pollution and vegetative stress caused by increasing anthropogenic emissions of O3 precursors4,5,11. We also estimate that the radiative forcing of tropospheric O3 since 1850 ad is probably less than +0.4 watts per square metre, consistent with results from recent climate modelling studies12.Isotope data from polar firn and ice are used to constrain the increase in tropospheric ozone between 1850 and 2005 ad.