Aerosol Effects on Clouds and Climate

Aerosols affect the climate system by changing cloud characteristics in many ways. They act as cloud condensation and ice nuclei, they may inhibit freezing and they could have an influence on the hydrological cycle. While the cloud albedo enhancement (Twomey effect) of warm clouds received most attention so far and traditionally is the only indirect aerosol forcing considered in transient climate simulations, here I discuss the multitude of effect

Prediction of the number of cloud droplets in the ECHAM GCM

In this paper a prognostic equation for the number of cloud droplets (CDNC) is introduced into the ECHAM general circulation model. The initial CDNC is based on the mechanistic model of Chuang and Penner [1995], providing a more realistical prediction of CDNC than the empirical method previously used. Cloud droplet nucleation is parameterized as a function of total aerosol number concentration, updraft velocity, and a shape parameter, which takes the aerosol composition and size distribution into account. The total number of aerosol particles is obtained as the sum of marine sulfate aerosols produced from dimethyl sulfide, hydrophylic organic and black carbon, submicron dust, and sea-salt aerosols. Anthropogenic sulfate aerosols only add mass to the preexisting aerosols but do not form new particles. The simulated annual mean liquid water path, column CDNC, and effective radius agree well with observations, as does the frequency distributions of column CDNC for clouds over oceans and the variations of cloud optical depth with effective radius

Influence of Giant CCN on warm rain processes in the ECHAM5 GCM

International audienceIncreased Cloud Condensation Nuclei (CCN) load due to anthropogenic activity might lead to non-precipitating clouds because the cloud drops become smaller (for a constant liquid water content) and, therefore, less efficient in rain formation (aerosol indirect effect). Adding giant CCN (GCCN) into such a cloud can initiate precipitation (namely, drizzle) and, therefore, might counteract the aerosol indirect effect. The effect of GCCN on global climate, especially on clouds and precipitation, within a General Circulation Model (GCM) is investigated. GCCN are aerosol particles larger than 5?10 ?m in radius that can act as cloud condensation nuclei. One prominent GCCN species is sea salt. Sea salt concentrations depend mainly on wind speed but also on relative humidity, stability and precipitation history. Natural variability is much larger than the simulated one because sea salt emissions within ECHAM5 are a function of wind speed only. Giant sea salt concentrations in ECHAM5 are determined by using the tail of the coarse mode aerosol distribution with cutoff radii of 5 ?m or 10 ?m. It is assumed that activated GCCN particles directly form rain drops (of 25 ?m size). Thereby, the added rain water mass and number stems from the redistribution of the condensed water into cloud and rain water according to the number of activated GCCN. As the formed precipitation is most likely drizzle with rather small drops a prognostic rain scheme is applied to account for the lower fall speeds and, therefore, slower sedimentation of the drizzle drops. The ECHAM5 simulations with incorporated GCCN show that precipitation is affected only locally. Cloud properties like liquid water and cloud drop number show a larger sensitivity to GCCN. On the one hand, the increased rain water mass causes an increase in the accretion rate and, therefore, in the rain production. On the other hand, very high GCCN concentrations can lead to an artificially exaggerated transfer of cloud water to the rain class which then results in a strong decrease of the conversion rate and the rain production. The introduction of the GCCN reduces the anthropogenic increase of liquid water in the atmosphere from pre-industrial to present day because clouds are precipitating faster in the presence of the GCCN. Hence, the accumulation of liquid water in the atmosphere is reduced. According to those changes in the cloud properties, the radiative budget is also changing. The GCCN cause a reduction of the anthropogenic aerosol indirect effect of about 0.1?0.25 W m?2 which corresponds to 5?10% of the total effect. Thus, the GCCN in ECHAM5 partly offset the anthropogenic aerosol indirect effect

Impact of sulfate aerosols on albedo and lifetime of clouds: A sensitivity study with the ECHAM4 GCM

A coupled sulfur chemistry-cloud microphysics scheme (COUPL) is used to study the impact of sulfate aerosols on cloud lifetime and albedo. The cloud microphysics scheme includes precipitation formation, which depends on the cloud droplet number concentration (CDNC) and on the liquid water content. On the basis of different observational data sets, CDNC is proportional to the sulfate aerosol mass, which is calculated by the model. Cloud cover is a function of relative humidity only. Additional sensitivity experiments with another cloud cover parameterization (COUPL-CC), which also depends on cloud water, and with a different autoconversion rate of cloud droplets (COUPL-CC-Aut) are conducted to investigate the range of the indirect effect due to uncertainties in cloud physics. For each experiment, two simulations, one using present-day and one using preindustrial sulfur emissions are carried out. The increase in liquid water path, cloud cover, and shortwave cloud forcing due to anthropogenic sulfur emissions depends crucially upon the parameterization of cloud cover and autoconversion of cloud droplets. In COUPL the liquid water path increases by 17 and cloud cover increases by 1 because of anthropogenic sulfur emissions, yielding an increase in shortwave cloud forcing of-1.4 W m-2. In COUPL-CC the liquid water path increases by 32, cloud cover increases by 3 and thus shortwave cloud forcing increases by -4.8 W m-2. This large effect is caused by the strong dependence of cloud cover on cloud water and of the autoconversion rate on CDNC, cloud water, and cloud cover. Choosing a different autoconversion rate (COUPL-CC-Aut) with a reduced dependence on CDNC and cloud water results in an increase of liquid water path by only 11 and of cloud cover by 1 , and the increase in shortwave cloud forcing amounts to -2.2 W m-2. These results clearly show that the uncertainties linked to the indirect aerosol effect are higher than was previously suggested. Copyright 1997 by the American Geophysical Union

Influence of Giant CCN on warm rain processes in the ECHAM5 GCM

Predmet rada je detektirati i analizirati kanale distribucije proizvoda za njegu kose. U tu svrhu su obrađeni dostupni sekundarni izvori informacija te je provedeno empirijsko istraživanje na uzorku poznavatelja metodom dubinskog intervjua. Kanali distribucije proizvoda za njegu kose u Hrvatskoj su u većini slučajeva neizravni s jednim ili više posrednika. Posrednici mogu biti distributeri, veleprodaje, maloprodaje, ljekarne, frizerski saloni, drogerije, internet prodaja itd. Izbor posrednika ovisi o segmentu u kojem se proizvodi za kosu prodaju, a on može biti luksuzne, dermatološke, profesionalne prirode ili za masovnu potrošnju. Kod proizvoda za njegu kose se tržište značajno izmijenilo razvojem digitalne tehnologije. Kako bi pojedina marka uspjela, mora prije svega osluškivati postojeće i nadolazeće trendove, biti inovativna u razvoju proizvoda, pružiti prirodnost barem u dijelu svog asortimana, poznavati svoju ciljanu skupinu potrošača te njihove potrebe, navike i preferencije i na temelju toga pronaći dodanu vrijednost proizvoda koju im može ponuditi. Nakon toga mora pomno odabrati kanale distribucije, ali i tu treba biti vrlo fleksibilna i prilagođavati se čestim promjenama. Svakako mora biti prisutna online, imati svoju web stranicu, Facebook i Instagram profil, You Tube i IGTV kanal i mrežu influencera. Oni moraju biti pažljivo odabrani da svojim modnim, verbalnim i osobnim izričajem odgovaraju vrijednostima marke jer samo tako mogu biti vjerodostojni. Osim toga, vrlo je bitno da pratitelji influencera čine ciljanu skupinu marke kako bi se osiguralo doticanje pravih potencijalnih kupaca. U svim segmentima obraćanja publici, marka mora prenositi istu poruku jer je sve više kupaca koji informacije o proizvodima prikupljaju iz više različitih izvora. U porastu je prodaja putem interneta na koju se kupci odlučuju nakon što su se informirali na samom prodajnom mjestu ili također online. Zato je vrlo važno da svi sudionici kanala budu educirani o proizvodima, ali i da poznaju svoje kupce. No, to više nije dovoljno, oni moraju biti i i vrsni prodavači. Stoga se sve više ulaže u edukacije i načine motiviranja posrednika između proizvođača i potrošača jer su ovi potonji postali dosta zahtjevni i upućeni u ono što žele, kako mogu do toga doći i uz koje uvjete. Ni najbolji proizvodi za kosu se ne mogu uspješno prodati ukoliko se ne omogući dostupnost tih proizvoda na mjestima gdje i kada ju potrošači žele kupiti.The subject of this thesis is to detect and analyze distribution channels of hair care products. For this purpose, available secondary sources of information were processed and empirical research on a sample of experts was conducted through a deep interview method. Distribution channels of hair care products in Croatia are in most cases indirect with one or more intermediaries. Intermediary can be distributors, wholesalers, retailers, pharmacies, hairdressers, drugstores, internet sales, etc. The selection of mediators depends on the segment in which hair products are sold and it can be of luxurious nature, dermatologic, professional or mass market. Regarding hair care products, the market has significantly changed with the development of digital technology. In order for each brand to succeed, it must primarily listen to existing and upcoming trends, be innovative in product development, provide naturalness in at least part of its range, know its target consumer group and their needs, habits and preferences and find added value of products to offer them. Thereafter, it is necessary to carefully select distribution channels, but also be very flexible and adapt them to the frequent changes. Brand must be present online, have its website, Facebook and Instagram profiles, You Tube and IGTV channels and influencers network. They have to be carefully selected and present the brand's values by their personal, fashion and verbal expressions to ensure their credibility. Additionally, it is very important that influencer's followers are part of brand's target group to ensure that they are touching the right potential buyers. In all segments of addressing the audience, the brand has to deliver the same message because customers receive product information from a variety of sources. Online sales is growing and buyers buy online after they have been informed about products at the point of sale or online. That is why it is very important for all channel participants to be educated about products, but also to know their customers. That is not enough anymore; they must be excellent sellers as well. Therefore, investment in education and ways of motivating intermediaries between producers and consumers are rising, because the latter have become highly demanding and acquainted to what they want, how they can get it and under what conditions. Even the best hair products cannot be successfully sold unless you ensure that these products are available in places where and when consumers want to buy it

Characteristics and direct radiative effect of mid-latitude continental aerosols: the ARM case

International audienceA multi-year field measurement analysis of the characteristics and direct radiative effect of aerosols at the Southern Great Plains (SGP) central facility of the Atmospheric Radiation Measurement (ARM) Program is presented. Inter-annual mean and standard deviation of submicrometer scattering fraction (at 550 nm) and Ångström exponent å (450 nm, 700 nm) at the mid-latitude continental site are indicative of the scattering dominance of fine mode aerosol particles, being 0.84±0.03 and 2.25±0.09, respectively. We attribute the diurnal variation of submicron aerosol concentration to coagulation, photochemistry and the evolution of the boundary layer. Precipitation does not seem to play a role in the observed afternoon maximum in aerosol concentration. Submicron aerosol mass at the site peaks in the summer (12.1±6.7mg m-3), with the summer value being twice that in the winter. Of the chemically analyzed ionic components (which exclude carbonaceous aerosols), SO4= and NH4+ constitute the dominant species at the SGP seasonally, contributing 23-30% and 9-12% of the submicron aerosol mass, respectively. Although a minor species, there is a notable rise in NO3- mass fraction in winter. We contrast the optical properties of dust and smoke haze. The single scattering albedo w0 shows the most remarkable distinction between the two aerosol constituents. We also present aircraft measurements of vertical profiles of aerosol optical properties at the site. Annually, the lowest 1.2 km contributes 70% to the column total light scattering coefficient. Column-averaged and surface annual mean values of hemispheric backscatter fraction (at 550 nm), w0 (at 550 nm) and å (450 nm, 700 nm) agree to within 5% in 2001. Aerosols produce a net cooling (most pronounced in the spring) at the ARM sit

Characteristics, impacts and direct radiative forcing of aerosols at the ARM Southern Great Plains Central Facility

International audienceBased on the analysis of five years of field measurements of aerosol and meteorological variables, we present the characteristics, impacts and direct radiative forcing of aerosols at the Southern Great Plains (SGP) Central Facility (CF) of the Atmospheric Radiation Measurement (ARM) Program. Annual means of total submicron aerosol concentration for particles with aerodynamic diameter (Dp) Np) for aerosols with 0.1 Dp?2, 654&olusmn;290 cm?3, 2.0±0.7 Mm?1 and 0.94±0.02, respectively, while those of submicron total scattering coefficient, hemispheric backscatter fraction, submicrometer scattering fraction (Rsp), Angström exponent, hygroscopic growth factor and visibility at 550 nm are 36±2 Mm?1, 0.12± 0.01, 0.84±0.03, 2.25±0.09 and 1.84±0.10, 38±2 km, respectively. Although they exhibit a considerable year-to-year variability, ,i>Rsp, ?p, Np and ozone show some increase over the period examined here. This increase is accompanied by a decline in annual precipitation, column integrated water vapor, relative humidity, and cloud cover (particularly from 1998 to 2001) at the site. In particular, the marked precipitation deficit at the SGP CF in 2000 and 2001 is evident of drought associated with La Nina conditions. We compare the diabatic impacts and optical characteristics for smoke and dust aerosols. In general, aerosols at the ARM site produce a net diabatic cooling, with an estimated direct radiative forcing ranging from about ?0.7 W m?2 in winter to ?2.4 W m?2 in summer

The potential influence of Asian and African mineral dust on ice, mixed-phase and liquid water clouds

This modelling study explores the availability of mineral dust particles as ice nuclei for interactions with ice, mixed-phase and liquid water clouds, also tracking the particles' history of cloud-processing. We performed 61 320 one-week forward trajectory calculations originating near the surface of major dust emitting regions in Africa and Asia using high-resolution meteorological analysis fields for the year 2007. Dust-bearing trajectories were assumed to be those coinciding with known dust emission seasons, without explicitly modelling dust emission and deposition processes. We found that dust emissions from Asian deserts lead to a higher potential for interactions with high ice clouds, despite being the climatologically much smaller dust emission source. This is due to Asian regions experiencing significantly more ascent than African regions, with strongest ascent in the Asian Taklimakan desert at ~25%, ~40% and 10% of trajectories ascending to 300 hPa in spring, summer and fall, respectively. The specific humidity at each trajectory's starting point was transported in a Lagrangian manner and relative humidities with respect to water and ice were calculated in 6-h steps downstream, allowing us to estimate the formation of liquid, mixed-phase and ice clouds. Downstream of the investigated dust sources, practically none of the simulated air parcels reached conditions of homogeneous ice nucleation (<i>T</i>≲−40 °C) along trajectories that have not experienced water saturation first. By far the largest fraction of cloud forming trajectories entered conditions of mixed-phase clouds, where mineral dust will potentially exert the biggest influence. The majority of trajectories also passed through atmospheric regions supersaturated with respect to ice but subsaturated with respect to water, where so-called "warm ice clouds" (<i>T</i>≳−40 °C) theoretically may form prior to supercooled water or mixed-phase clouds. The importance of "warm ice clouds" and the general influence of dust in the mixed-phase cloud region are highly uncertain due to both a considerable scatter in recent laboratory data from ice nucleation experiments, which we briefly review in this work, and due to uncertainties in sub-grid scale vertical transport processes unresolved by the present trajectory analysis. For "classical" cirrus-forming temperatures (<i>T</i>≲−40 °C), our results show that only mineral dust ice nuclei that underwent mixed-phase cloud-processing, most likely acquiring coatings of organic or inorganic material, are likely to be relevant. While the potential paucity of deposition ice nuclei shown in this work dimishes the possibility of deposition nucleation, the absence of liquid water droplets at <i>T</i>≲−40 °C makes the less explored contact freezing mechanism (involving droplet collisions with bare ice nuclei) highly inefficient. These factors together indicate the necessity of further systematic studies of immersion mode ice nucleation on mineral dust suspended in atmospherically relevant coatings

Orographic cirrus in a future climate

A cloud resolving model (CRM) is used to investigate the formation of orographic cirrus clouds in the current and future climate. The formation of cirrus clouds depends on a variety of dynamical and thermodynamical processes, which act on different scales. First, the capability of the CRM in realistically simulating orographic cirrus clouds has been tested by comparing the simulated results to aircraft measurements of an orographic cirrus cloud. The influence of a warmer climate on the microphysical and optical properties of cirrus clouds has been investigated by initializing the CRM with vertical profiles of horizontal wind, potential temperature and equivalent potential temperature, respectively. The vertical profiles are extracted from IPCC A1B simulations for the current climate and for the period 2090–2099 for two regions representative for North and South America. The influence of additional moisture in a future climate on the propagation of gravity waves and the formation of orographic cirrus could be estimated. In a future climate, the increase in moisture dampens the vertical propagation of gravity waves and the occurring vertical velocities in the moist simulations. Together with higher temperatures fewer ice crystals nucleate homogeneously. Assuming that the relative humidity does not change in a warmer climate the specific humidity in the model is increased. This increase in specific humidity in a warmer climate results in a higher ice water content. The net effect of a reduced ice crystal number concentration and a higher ice water content is an increased optical depth. However, in some moist simulations dynamical changes contribute to changes in the ice water content, ice crystal number concentration and optical depth. For the corresponding dry simulations dynamical changes are more pronounced leading to a decreased optical depth in a future climate in some cases