Characteristics of vertical velocity in marine stratocumulus: comparison of large eddy simulations with observations

Guo, Huan; Liu, Yangang; Daum, P. H.; Senum, G.; Tao, Wei‐Kuo

doi:10.1088/1748-9326/3/4/045020

Cited by 31 publications

(38 citation statements)

References 31 publications

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“…The range of σ w shown in Fig. 4 is in good agreement with in situ measurements of vertical velocity at cloud base in marine stratocumulus (Peng et al, 2005;Guo et al, 2008), and continental regions (Fountoukis et al, 2007;Tonttila et al, 2011), showing σ w mostly between 0.2 and 1 m s −1 . However, global measurements of σ w have not been reported.…”

Section: Subgrid-scale Vertical Velocitysupporting

confidence: 83%

Development of two-moment cloud microphysics for liquid and ice within the NASA Goddard Earth Observing System Model (GEOS-5)

et al. 2014

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Abstract. This work presents the development of a twomoment cloud microphysics scheme within version 5 of the NASA Goddard Earth Observing System (GEOS-5). The scheme includes the implementation of a comprehensive stratiform microphysics module, a new cloud coverage scheme that allows ice supersaturation, and a new microphysics module embedded within the moist convection parameterization of GEOS-5. Comprehensive physically based descriptions of ice nucleation, including homogeneous and heterogeneous freezing, and liquid droplet activation are implemented to describe the formation of cloud particles in stratiform clouds and convective cumulus. The effect of preexisting ice crystals on the formation of cirrus clouds is also accounted for. A new parameterization of the subgrid-scale vertical velocity distribution accounting for turbulence and gravity wave motion is also implemented. The new microphysics significantly improves the representation of liquid water and ice in GEOS-5. Evaluation of the model against satellite retrievals and in situ observations shows agreement of the simulated droplet and ice crystal effective radius, the ice mass mixing ratio and number concentration, and the relative humidity with respect to ice. When using the new microphysics, the fraction of condensate that remains as liquid follows a sigmoidal dependency with temperature, which is in agreement with observations and which fundamentally differs from the linear increase assumed in most models. The performance of the new microphysics in reproducing the observed total cloud fraction, longwave and shortwave cloud forcing, and total precipitation is similar to the operational version of GEOS-5 and in agreement with satellite retrievals. The new microphysics tends to underestimate the coverage of persistent low-level stratocumulus. Sensitivity studies showed that the simulated cloud properties are robust to moderate variation in cloud microphysical parameters. Significant sensitivity remains to variation in the dispersion of the ice crystal size distribution and the critical size for ice autoconversion. Despite these issues, the implementation of the new microphysics leads to a considerably improved and more realistic representation of cloud processes in GEOS-5, and allows the linkage of cloud properties to aerosol emissions.

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Section: Subgrid-scale Vertical Velocitysupporting

confidence: 83%

Development of two-moment cloud microphysics for liquid and ice within the NASA Goddard Earth Observing System Model (GEOS-5)

et al. 2014

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“…Moreover, it has been noted that also the vertical resolution of a model has an effect on the representation of vertical velocities. Guo et al (2008) suggested that a vertical resolution of about 10 m is needed to robustly resolve the higher order statistical moments of vertical velocities.…”

Section: Discussionmentioning

confidence: 99%

“…Measuring vertical velocities in the atmosphere is difficult, mostly because of their relatively small magnitude. In-situ measurements are, in practice, only possible with research aircraft (Duynkerke et al, 1999;Rodts et al, 2003;Snider et al, 2003;Guo et al, 2008;Lu et al, 2009;Ghate et al, 2010), although mast measurements can be made in layers close to the surface (up to an altitude of a few hundred meters). The aircraft measurements are usually related to intensive field campaigns with limited spatial and temporal coverage, which restricts their usability.…”

Section: Introductionmentioning

confidence: 99%

Cloud base vertical velocity statistics: a comparison between an atmospheric mesoscale model and remote sensing observations

et al. 2011

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Abstract. The statistics of cloud base vertical velocity simulated by the non-hydrostatic mesoscale model AROME are compared with Cloudnet remote sensing observations at two locations: the ARM SGP site in central Oklahoma, and the DWD observatory at Lindenberg, Germany. The results show that AROME significantly underestimates the variability of vertical velocity at cloud base compared to observations at their nominal resolution; the standard deviation of vertical velocity in the model is typically 4-8 times smaller than observed, and even more during the winter at Lindenberg. Averaging the observations to the horizontal scale corresponding to the physical grid spacing of AROME (2.5 km) explains 70-80 % of the underestimation by the model. Further averaging of the observations in the horizontal is required to match the model values for the standard deviation in vertical velocity. This indicates an effective horizontal resolution for the AROME model of at least 10 km in the presented case. Adding a TKE-term on the resolved grid-point vertical velocity can compensate for the underestimation, but only for altitudes below approximately the boundary layer top height. The results illustrate the need for a careful consideration of the scales the model is able to accurately resolve, as well as for a special treatment of sub-grid scale variability of vertical velocities in kilometer-scale atmospheric models, if processes such as aerosol-cloud interactions are to be included in the future.

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“…Marine stratocumulus updraughts are generally quite low, for example Guo et al (2008) present PDFs of vertical velocity in marine stratocumulus clouds measured during the Marine Stratus/Stratocumulus Experiment (MASE), they found that characteristic updraughts (w) were always < 0.2 m s −1 at the middle and base of the cloud, but found slightly higher updraughts close to the cloud top. Guibert et al (2003) Table 3 shows frequency statistics for the updraught (w) simulated in the UK Met Office Large-Eddy Simulation Model (LEM, 3-D) for the ASTEX GCSS Sc-Cu transition case (Bretherton et al, 1999) (A.…”

Section: In-cloud Updraught Velocitymentioning

confidence: 99%

A multi-model assessment of the impact of sea spray geoengineering on cloud droplet number

et al. 2012

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Abstract. Artificially increasing the albedo of marine boundary layer clouds by the mechanical emission of sea spray aerosol has been proposed as a geoengineering technique to slow the warming caused by anthropogenic greenhouse gases. A previous global model study (Korhonen et al., 2010) found that only modest increases (< 20 %) and sometimes even decreases in cloud drop number (CDN) concentrations would result from emission scenarios calculated using a windspeed dependent geoengineering flux parameterisation. Here we extend that work to examine the conditions under which decreases in CDN can occur, and use three independent global models to quantify maximum achievable CDN changes. We find that decreases in CDN can occur when at least three of the following conditions are met: the injected particle number is < 100 cm −3 , the injected diameter is > 250-300 nm, the background aerosol loading is large (≥ 150 cm −3 ) and the in-cloud updraught velocity is low (< 0.2 m s −1 ). With lower background loadings and/or increased updraught velocity, significant increases in CDN can be achieved. None of the global models predict a decrease in CDN as a result of geoengineering, although there is considerable diversity in the calculated efficiency of geoengineering, which arises from the diversity in the simulated marine aerosol distributions. All three models show a small dependence of geoengineering efficiency on the injected particle size and the geometric standard deviation of the injected mode. However, the achievability of significant cloud drop enhancements is strongly dependent on the cloud updraught speed. With an updraught speed of 0.1 m s −1 a global mean CDN of 375 cm −3 (previously estimated to cancel the forcing caused by CO 2 doubling) is achievable in only about 50 % of grid boxes which have > 50 % cloud cover, irrespective of the amount of aerosol injected. But at stronger updraft speeds (0.2 m s −1 ), higher values of CDN are achievable due to the elevated in-cloud supersaturations. Achieving a value of 375 cm −3 in regions dominated by stratocumulus clouds with relatively weak updrafts cannot be attained regardless of the number of injected particles, thereby limiting the efficacy of sea spray geoengineering.

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Characteristics of vertical velocity in marine stratocumulus: comparison of large eddy simulations with observations

Cited by 31 publications

References 31 publications

Development of two-moment cloud microphysics for liquid and ice within the NASA Goddard Earth Observing System Model (GEOS-5)

Development of two-moment cloud microphysics for liquid and ice within the NASA Goddard Earth Observing System Model (GEOS-5)

Cloud base vertical velocity statistics: a comparison between an atmospheric mesoscale model and remote sensing observations

A multi-model assessment of the impact of sea spray geoengineering on cloud droplet number

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