The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
Piers M. Forster - One of the best experts on this subject based on the ideXlab platform.
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The semi‐direct aerosol effect: Impact of absorbing Aerosols on marine stratocumulus
Quarterly Journal of the Royal Meteorological Society, 2004Co-Authors: Ben Johnson, Keith P. Shine, Piers M. ForsterAbstract:SUMMARY Aerosols that absorb solar radiation may lead to a decrease of low-cloud cover and liquid-water path (LWP), leading to a positive radiative forcing. A large-eddy model was used to investigate this ‘semi-direct effect’ for marine stratocumulus and examine the dependency on the vertical distribution of the aerosol. In this study, the Aerosols influenced clouds by directly altering the short-wave heating rate (the semi-direct effect), but did not interact with the cloud microphysics (i.e. indirect aerosol effects are excluded). Absorbing Aerosols within the boundary layer (BL) decreased LWP by 10 g m −2 , leading to a positive semi-direct forcing. Even for mildly absorbing Aerosols (mid-visible single-scattering albedo of 0.96), the semi-direct forcing was three times stronger, and opposite in sign, to the aerosol direct forcing. The semi-direct forcing was found to be proportional to aerosol single-scattering co-albedo (tested to a value of 0.12). Conversely, with the absorbing aerosol layer above the cloud, the LWP increased by 5 to 10 g m −2 , leading to a negative semi-direct forcing. Absorbing Aerosols located in the BL heat the cloud layer, enhancing the daytime decoupling and thinning of the stratocumulus layer. Absorbing Aerosols immediately above the BL increased the contrast in potential temperature across the inversion, leading to a lower cloud-top entrainment rate. With aerosol both within and above the BL, the semidirect forcing was positive but half the magnitude of that experienced when aerosol was only in the BL. As marine stratocumulus covers about 20% of the globe, the semi-direct effect could significantly influence the radiative forcing by absorbing Aerosols.
Makiko Sato - One of the best experts on this subject based on the ideXlab platform.
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Climate forcing by stratospheric Aerosols
Geophysical Research Letters, 1992Co-Authors: Andrew A Lacis, James Hansen, Makiko SatoAbstract:We illustrate how climate forcing by stratospheric Aerosols depends on aerosol properties. The climate forcing is a function of aerosol size distribution, but the size dependence can be described well by a single parameter: the area-weighted mean radius, reff.If reff is greater than about 2 μm, the global average greenhouse effect of the Aerosols exceeds the albedo effect, causing a surface heating. The aerosol climate forcing is less sensitive to other characteristics of the size distribution, the aerosol composition, and the altitude of the Aerosols. Thus stratospheric aerosol forcing can be defined accurately from measurements of aerosol, extinction over a broad wavelength range.
A. Da Silva - One of the best experts on this subject based on the ideXlab platform.
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Direct and semi‐direct aerosol effects in the NASA GEOS‐5 AGCM: aerosol‐climate interactions due to prognostic versus prescribed Aerosols
Journal of Geophysical Research: Atmospheres, 2013Co-Authors: Cynthia A. Randles, P. R. Colarco, A. Da SilvaAbstract:[1] The present-day climate response to aerosol direct and semi-direct effects is investigated using the NASA Goddard Earth Observing System version 5 (GEOS-5) atmospheric general circulation model. We focus our investigation on aerosol-climate interactions by using either prognostic Aerosols from an online aerosol module or Aerosols from a climatology based on the prognostic Aerosols. As found in previous studies, forcing from all Aerosols cools the land surface, warms the troposphere, and impacts global mean circulation, affecting both the strength of the Hadley cell and the zonal mean wind. Less absorbing natural aerosol alone tends to have weaker impacts on global climate. We find that removing the feedback of meteorology on aerosol distributions can significantly impact the climate response depending on the parameter, region, and season considered. Much of the differing climate response to prognostic and prescribed Aerosols occurs in regions remote from direct aerosol forcing, such as in the stratosphere and the northern and southern high latitudes. This suggests that aerosol-climate interactions may induce remote dynamical responses to aerosol forcing in global models. The largest effect of removing coupling is to enhance the aerosol optical depth globally over the oceans. This enhancement is due to the removal of the co-variability between aerosol mass and relative humidity on sub-monthly timescales in the high humidity oceanic environment.
Ben Johnson - One of the best experts on this subject based on the ideXlab platform.
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The semi‐direct aerosol effect: Impact of absorbing Aerosols on marine stratocumulus
Quarterly Journal of the Royal Meteorological Society, 2004Co-Authors: Ben Johnson, Keith P. Shine, Piers M. ForsterAbstract:SUMMARY Aerosols that absorb solar radiation may lead to a decrease of low-cloud cover and liquid-water path (LWP), leading to a positive radiative forcing. A large-eddy model was used to investigate this ‘semi-direct effect’ for marine stratocumulus and examine the dependency on the vertical distribution of the aerosol. In this study, the Aerosols influenced clouds by directly altering the short-wave heating rate (the semi-direct effect), but did not interact with the cloud microphysics (i.e. indirect aerosol effects are excluded). Absorbing Aerosols within the boundary layer (BL) decreased LWP by 10 g m −2 , leading to a positive semi-direct forcing. Even for mildly absorbing Aerosols (mid-visible single-scattering albedo of 0.96), the semi-direct forcing was three times stronger, and opposite in sign, to the aerosol direct forcing. The semi-direct forcing was found to be proportional to aerosol single-scattering co-albedo (tested to a value of 0.12). Conversely, with the absorbing aerosol layer above the cloud, the LWP increased by 5 to 10 g m −2 , leading to a negative semi-direct forcing. Absorbing Aerosols located in the BL heat the cloud layer, enhancing the daytime decoupling and thinning of the stratocumulus layer. Absorbing Aerosols immediately above the BL increased the contrast in potential temperature across the inversion, leading to a lower cloud-top entrainment rate. With aerosol both within and above the BL, the semidirect forcing was positive but half the magnitude of that experienced when aerosol was only in the BL. As marine stratocumulus covers about 20% of the globe, the semi-direct effect could significantly influence the radiative forcing by absorbing Aerosols.
Kevin R Wilson - One of the best experts on this subject based on the ideXlab platform.
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real time in situ chemical characterization of sub micron organic Aerosols using direct analysis in real time mass spectrometry dart ms the effect of aerosol size and volatility
Analyst, 2013Co-Authors: Man Nin Chan, Kevin R WilsonAbstract:Direct Analysis in Real Time (DART) mass spectrometry is an atmospheric pressure ionization technique suitable for in situ chemical analysis of organic Aerosols. Here, mass spectra are obtained by introducing a stream of nanometer-sized Aerosols into the ionization region, which is an open space between the ion source and the atmospheric inlet of mass spectrometer. Model single component Aerosols are used to show how the aerosol size and volatility influence the measured ion signals at different DART gas temperatures. The results show that for equivalent aerosol mass concentrations, the ion signal scales with particle surface area, with smaller diameter oleic acid Aerosols yielding higher ion signals relative to larger diameter Aerosols. For the Aerosols of the same size, but different vapor pressures, the ion signal is larger for more volatile succinic acid Aerosols than less volatile adipic and suberic acid particles. From the measured changes in aerosol size, produced by the DART source, the radial probing depth for these model Aerosols range from 1 to 10 nm, the magnitude of which depends upon the physiochemical properties of the Aerosols and DART gas temperature. An aerosol evaporation model reveals that the ion signal is correlated with changes in aerosol size and depends upon the total quantity of evaporated aerosol mass, consistent with a mechanism in which gas-phase molecules are first desorbed from the aerosol surface prior to ionization. The results of this work serve as a basis for future investigations of the mass spectra, ionization pathways, and probing depth of the Aerosols using DART.
