The Role of Background Cloud Microphysics in the Radiative Formation of Ship Tracks

Platnick, S.; Durkee, Philip A.; Nielsen, K.; Taylor, Jonathan P.; King, Michael D.; Ferek, Ronald J.; Rottman, James W.

doi:10.1175/1520-0469(2000)057<2607:trobcm>2.0.co;2

Cited by 67 publications

(44 citation statements)

References 43 publications

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“…However, one remaining problem is that most climate models suggest an increase in liquid water when adding anthropogenic aerosols, whereas newer ship track studies show that polluted marine water clouds can have less liquid water than clean clouds (Platnick et al, 2000;Coakley Jr. and Walsh, 2002;Ackerman et al, 2004). …”

Section: Aerosol Effects On the Hydrological Cyclementioning

confidence: 99%

Global indirect aerosol effects: a review

2005

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Abstract. 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 we discuss the multitude of effects. Different approaches how the climatic implications of these aerosol effects can be estimated globally as well as improvements that are needed in global climate models in order to better represent indirect aerosol effects are discussed in this paper.

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Section: Aerosol Effects On the Hydrological Cyclementioning

confidence: 99%

Global indirect aerosol effects: a review

2005

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“…It uses a temperature difference of 4 K between the cloud and the maximum temperature, which usually corresponds to the sea surface temperature. Clouds susceptible for ship tracks are very low Platnick et al, 2000] and assuming a wet adiabatic lapse rate of À0.6 K/100 m, a maximum temperature difference of about 4 K between cloud top temperature and sea surface temperature results in a cloud top height of $700 m. If 256 successive lines fulfill criteria 1 and 2 by more than 20%, this part of the orbit (plus additional 256 lines on both ends) is selected as VLC scene for further analysis. Our automated selection of scenes is verified by a thorough analysis of 1% of the complete satellite data (4 days, one for each season), showing a ship track detection efficiency of 70% when reducing the original data by 98%.…”

Section: Global Coverage Of Low Marine Cloudsmentioning

confidence: 99%

“…Emissions of aerosols and their precursors by ships result in a high amount of additional CCNs and can possibly lead to a change of the optical and microphysical properties of clouds Platnick et al, 2000]. This results in an increased backscattering of the cloud layer, known as indirect aerosol effect [Twomey et al, 1968;Albrecht, 1989;Rosenfeld et al, 2006].…”

Section: Introductionmentioning

confidence: 99%

Global ship track distribution and radiative forcing from 1 year of AATSR data

Schreier¹,

Mannstein²,

Eyring³

et al. 2007

Geophysical Research Letters

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One year of ENVISAT‐AATSR (Advanced Along Track Scanning Radiometer) satellite data is analyzed to derive a global distribution of ship tracks and their radiative forcing (RF). Ship tracks are changes in cloud reflectance, visible in satellite data, and result from the emission of aerosols and their precursors by ships into the clean marine boundary layer. An algorithm is presented that extracts scenes dominated by low clouds over the oceans that are susceptible to be affected by ship emissions. These selected cloud scenes are used to examine ship tracks on a global scale via visual analysis. The results show a high temporal variability of ship track occurrence with peak values in July. They also show a high spatial variability with peak values in the North Pacific Ocean and on the west coast of southern Africa, correlated with high ship traffic and frequent low cloud occurrence in regions of cold upwelling ocean currents. The analysis of backscattered radiation at top of the atmosphere (TOA) compared to the surrounding area reveals enhanced backscattering with values between 0 and 100 Wm−2. For particular regions on the west coast of North America, the annual mean RF due to ship tracks estimated by the changes in backscattered radiation at TOA can be up to −50 mWm−2. The global annual mean RF due to ship tracks is small (−0.4 to −0.6 mWm−2) and negligible compared to previous global model estimates on the total indirect aerosol effect and RF contributions of other ship emissions.

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“…In most GCMs, it is assumed that, because of less efficient coalescence and collection among cloud droplets, increasing cloud droplet number concentrations from anthropogenic aerosols always slow formation of precipitation and increases liquid water path (LWP) and cloud lifetime (Albrecht, 1989). However, observations show evidence of both decreasing and increasing LWP with increasing aerosols (Platnick et al, 2000;Coakley and Walsh, 2002;Kaufman et al, 2005;Matsui et al, 2006), and cloud resolving model (CRM) studies show that changes in LWP depend on meteorological conditions (Ackerman et al, 2004;Xue et al, 2008;Small et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

Aerosol indirect effects in a multi-scale aerosol-climate model PNNL-MMF

et al. 2011

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Abstract. Much of the large uncertainty in estimates of anthropogenic aerosol effects on climate arises from the multiscale nature of the interactions between aerosols, clouds and dynamics, which are difficult to represent in conventional general circulation models (GCMs). In this study, we use a multi-scale aerosol-climate model that treats aerosols and clouds across multiple scales to study aerosol indirect effects. This multi-scale aerosol-climate model is an extension of a multi-scale modeling framework (MMF) model that embeds a cloud-resolving model (CRM) within each vertical column of a GCM grid. The extension allows a more physicallybased treatment of aerosol-cloud interactions in both stratiform and convective clouds on the global scale in a computationally feasible way. Simulated model fields, including liquid water path (LWP), ice water path, cloud fraction, shortwave and longwave cloud forcing, precipitation, water vapor, and cloud droplet number concentration are in reasonable agreement with observations. The new model performs quantitatively similar to the previous version of the MMF model in terms of simulated cloud fraction and precipitation. The simulated change in shortwave cloud forcing from anthropogenic aerosols is −0.77 W m −2 , which is less than half of that (−1.79 W m −2 ) calculated by the host GCM (NCAR CAM5) with traditional cloud parameterizations and is also at the low end of the estimates of other conventional global aerosol-climate models. The smaller forcing in the MMF model is attributed to a smaller (3.9 %) increase in LWP from preindustrial conditions (PI) to present day (PD) compared with 15.6 % increase in LWP in stratiform clouds in CAM5. The difference is caused by a much smaller response in LWP to a given perturbation in cloud condensation nuclei (CCN) concentrations from PI to PD in the MMF (about one-third of that in CAM5), and, to a lesser

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The Role of Background Cloud Microphysics in the Radiative Formation of Ship Tracks

Cited by 67 publications

References 43 publications

Global indirect aerosol effects: a review

Global indirect aerosol effects: a review

Global ship track distribution and radiative forcing from 1 year of AATSR data

Aerosol indirect effects in a multi-scale aerosol-climate model PNNL-MMF

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