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Hugh Morrison - One of the best experts on this subject based on the ideXlab platform.
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modeling of Cloud Microphysics can we do better
Bulletin of the American Meteorological Society, 2019Co-Authors: Wojciech W Grabowski, Hugh Morrison, Shinichiro Shima, Gustavo C Abade, Piotr Dziekan, Hanna PawlowskaAbstract:AbstractRepresentation of Cloud Microphysics is a key aspect of simulating Clouds. From the early days of Cloud modeling, numerical models have relied on an Eulerian approach for all Cloud and ther...
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advection of coupled hydrometeor quantities in bulk Cloud Microphysics schemes
Monthly Weather Review, 2016Co-Authors: Hugh Morrison, Anders A Jensen, Jerry Y Harrington, Jason A MilbrandtAbstract:AbstractThis paper discusses the advection of coupled hydrometeor quantities by air motion in atmospheric models. It is shown that any bulk property derived from a set of advected microphysical variables must meet certain conditions in order to be preserved during transport using linear or semilinear advection schemes when the property is initially uniform, with implications for physical consistency of the property. A new, efficient flux-based method for calculating hydrometeor advection, similar to vector transport applied previously in aerosol modeling, is also presented. In this method, called scaled flux vector transport (SFVT), lead scalars (the mass mixing ratios) are advected using the host model’s unmodified advection scheme and secondary scalars (e.g., number mixing ratios) are advected by appropriately scaling the lead scalar fluxes. By design, SFVT retains linear relationships between the advected scalars. Analytic tests reveal that mean errors using SFVT are similar to those incurred using the...
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development of two moment Cloud Microphysics for liquid and ice within the nasa goddard earth observing system model geos 5
Geoscientific Model Development, 2014Co-Authors: Donifan Barahona, Hugh Morrison, Andrew Gettelman, Andrea Molod, Julio T Bacmeister, Athanasios Nenes, Vaughan T J Phillips, Andrew F EichmannAbstract:Abstract. This work presents the development of a two-moment 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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modeling convective stratiform precipitation processes on a mei yu front with the weather research and forecasting model comparison with observations and sensitivity to Cloud Microphysics parameterizations
Journal of Geophysical Research, 2010Co-Authors: Yali Luo, Yanjie Wang, Hongyan Wang, Yongjun Zheng, Hugh MorrisonAbstract:[1] Deep convective-scale simulations of the linear mesoscale convective systems (MCSs) formed on a Mei-Yu front over the Huai River basin in China on 7–8 July 2007 were conducted using the Advanced Research Weather Research and Forecasting model to investigate impacts of Cloud Microphysics parameterizations on simulated convective-stratiform precipitation processes. Eight simulations were performed with identical configurations, except for differences in the Cloud Microphysics parameterizations. Measurements from rain gauges, ground-based weather radars, and the Tropical Rainfall Measuring Mission satellite Precipitation Radar were used to quantitatively evaluate the model results. While all of the simulations largely capture the observed large-scale characteristics of the precipitation event, notable differences among the simulations are found in the morphology and evolution of the MCSs at mesoscale and Cloud scale. Significant influences on the coupling between dynamical and microphysical processes at the resolved deep convective scale by the various microphysical parameterizations are evident. On the one hand, the different microphysical schemes produce not only substantial differences in intensity of convective precipitation but also distinguishable vertical distributions of latent heating and condensate loading in the deep convective regions, which in turn results in significant differences in the vertical distributions of vertical air velocity and in the heights and strength of detrainment from deep convective regions. Consequently, detrainment of hydrometeors and positively buoyant air from the deep convective regions to the stratiform regions is significantly different, which impacts the formation and growth of ice-phase hydrometeors at the upper levels and thus surface rainfall rates in the stratiform regions. On the other hand, prediction of rain size distribution significantly impacts the simulated rain evaporation rates and mass-weighted rain fall speeds, and hence rain flux. Improper determination of the intercept parameter of rain size distribution can result in unrealistic features in the morphology of the storm and can have substantial impacts on precipitation distribution and evolution.
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impact of Cloud Microphysics on the development of trailing stratiform precipitation in a simulated squall line comparison of one and two moment schemes
Monthly Weather Review, 2009Co-Authors: Hugh Morrison, G. Thompson, V. TatarskiiAbstract:A new two-moment Cloud Microphysics scheme predicting the mixing ratios and number concentrations of five species (i.e., Cloud droplets, Cloud ice, snow, rain, and graupel) has been implemented into the Weather Research and Forecasting model (WRF). This scheme is used to investigate the formation and evolution of trailing stratiform precipitation in an idealized two-dimensional squall line. Results are compared to those using a one-moment version of the scheme that predicts only the mixing ratios of the species, and diagnoses the number concentrations from the specified size distribution intercept parameter and predicted mixing ratio. The overall structure of the storm is similar using either the one- or two-moment schemes, although there are notable differences. The two-moment (2-M) scheme produces a widespread region of trailing stratiform precipitation within several hours of the storm formation. In contrast, there is negligible trailing stratiform precipitation using the one-moment (1-M) scheme. The primary reason for this difference are reduced rain evaporation rates in 2-M compared to 1-M in the trailing stratiform region, leading directly to greater rain mixing ratios and surface rainfall rates. Second, increased rain evaporation rates in 2-M compared to 1-M in the convective region at midlevels result in weaker convective updraft cells and increased midlevel detrainment and flux of positively buoyant air from the convective into the stratiform region. This flux is in turn associated with a stronger mesoscale updraft in the stratiform region and enhanced ice growth rates. The reduced (increased) rates of rain evaporation in the stratiform (convective) regions in 2-M are associated with differences in the predicted rain size distribution intercept parameter (which was specified as a constant in 1-M) between the two regions. This variability is consistent with surface disdrometer measurements in previous studies that show a rapid decrease of the rain intercept parameter during the transition from convective to stratiform rainfall.
Brian A. Tinsley - One of the best experts on this subject based on the ideXlab platform.
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solar wind atmospheric electricity Cloud Microphysics connections to weather and climate
Journal of Atmospheric and Solar-Terrestrial Physics, 2016Co-Authors: Mai Mai Lam, Brian A. TinsleyAbstract:Abstract We review recent research articles that present observations of the large-scale day-to-day dynamic tropospheric response to changes in the downward current density Jz of the global atmospheric electric circuit (GEC). The evidence for the global circuit downward current density, Jz, causing changes in atmospheric dynamics is now even stronger than as reviewed by Tinsley (2008) (Rep. Prog. Phys. 71, 066801). We consider proposed mechanisms for these responses, and suggest future directions for research.
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the global atmospheric electric circuit and its effects on Cloud Microphysics
Reports on Progress in Physics, 2008Co-Authors: Brian A. TinsleyAbstract:This review is an overview of progress in understanding the theory and observation of the global atmospheric electric circuit, with the focus on its dc aspects, and its short and long term variability. The effects of the downward ionosphere-earth current density, Jz, on Cloud Microphysics, with its variability as an explanation for small observed changes in weather and climate, will also be reviewed. The global circuit shows responses to external as well as internal forcing. External forcing arises from changes in the distribution of conductivity due to changes in the cosmic ray flux and other energetic space particle fluxes, and at high magnetic latitudes from solar wind electric fields. Internal forcing arises from changes in the generators and changes in volcanic and anthropogenic aerosols in the troposphere and stratosphere. All these result in spatial and temporal variation in Jz.Variations in Jz affect the production of space charge in layer Clouds, with the charges being transferred to droplets and aerosol particles. New observations and new analyses are consistent with non-negligible effects of the charges on the Microphysics of such Clouds. Observed effects are small, but of high statistical significance for Cloud cover and precipitation changes, with resulting atmospheric temperature, pressure and dynamics changes. These effects are detectable on the day-to-day timescale for repeated Jz changes of order 10%, and are thus second order electrical effects. The implicit first order effects have not, as yet, been incorporated into basic Cloud and aerosol physics. Long term (multidecadal through millennial) global circuit changes, due to solar activity modulating the galactic cosmic ray flux, are an order of magnitude greater at high latitudes and in the stratosphere, as can be inferred from geological cosmogenic isotope records. Proxies for climate change in the same stratified depositories show strong correlations of climate with the inferred global circuit variations.The theory for electrical effects on scavenging of aerosols in Clouds is reviewed, with several microphysical processes having consequences for contact ice nucleation; effects on droplet size distributions; precipitation and Cloud lifetimes. There are several pathways for resulting macroscopic Cloud changes that affect atmospheric circulation; including enhanced ice production and precipitation from Clouds in cyclonic storms, with latent heat release affecting cyclone vorticity; and Cloud cover changes in layer Clouds that affect the atmospheric radiation balance. These macroscopic consequences of global circuit variability affecting aerosols–Cloud interactions provide explanations for the many observations of short term and long term changes in Clouds and climate that correlate with measured or inferred Jz and cosmic ray flux changes due to external or internal forcing, and lead to predictions of additional effects.
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are stratospheric aerosols the missing link between tropospheric vorticity and earth transits of the heliospheric current sheet
Journal of Geophysical Research, 1996Co-Authors: Matt W Kirkland, Brian A. Tinsley, Todd J HoeksemaAbstract:Evidence has accumulated for the past two decades demonstrating a correlation between Earth transits of the heliospheric current sheet (HCS) and changes in winter tropospheric vorticity. These correlations persisted for a few years following the Agung and El Chichon volcanic eruptions, but were significantly weaker at other times. This suggests that the missing link in a physical mechanism explaining the correlation may involve volcanic aerosols and their effect on Cloud Microphysics, via atmospheric electricity. An analysis of 500-mbar northern hemispheric vorticity for the 1991-1994 winter periods following the Pinatubo eruption shows a similar correlation between tropospheric vorticity and Earth transits of the HCS, supporting the previous interpretation.
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correlations of atmospheric dynamics with solar activity evidence for a connection via the solar wind atmospheric electricity and Cloud Microphysics
Journal of Geophysical Research, 1993Co-Authors: Brian A. Tinsley, R A HeelisAbstract:We respond to several criticisms of the view that there is a physical linkage between solar activity and the dynamics of the troposphere and lower stratosphere, and we provide further evidence in support of a mechanism for such a linkage involving atmospheric electricity and Cloud Microphysics. The main criticisms are (1) that the decadal time scale variations in stratified data result from aliasing introduced by the sampling process and are not responses to a decadal time scale physical input; (2) that the observed correlations are due to chance coincidence or an atmospheric periodicity that is not uniquely related to solar variability; and (3) that there are no plausible mechanisms that can amplify one of the weak solar-varying inputs in the region where the correlations are found. We show that the aliasing criticism is inadequate because the real quasi-biennial oscillation departs from an ideal sine wave in a way that reduces aliasing effects to insignificant levels. The nonuniqueness of identification of the 11-year solar cycle as the period of the arctic forcing for the Arctic winter stratospheric temperatures is a problem only for the short 33-year record of polar temperatures; in much longer time series of unstratified climate data the periods of 11 and 22 years are prominent. Highly unique signatures of solar wind forcing of tropospheric dynamics exist on the day-to-day time scale via two independent inputs to atmospheric electricity. These are (1) through changes in tropospheric ion production as a result of solar wind modulation of galactic cosmic rays and (2) through changes in the potential difference between the polar ionospheres and the surface, forced by the solar wind By component. The product of the cosmic ray flux and the ionospheric potential determines the vertical air-earth electrical current. In the presence of Clouds of large horizontal extent, this current determines the rate of polarization charging of the Clouds via the accumulation of positive electrostatic charges on droplets near Cloud tops. The observed correlations, and theoretical and laboratory results for the effects of electrostatic charges on droplets and aerosols on the rates of ice nucleation, are consistent with the postulate that for certain regions and seasons and atmospheric levels the large-scale atmospheric electrical parameters have significant effects on the rates of initial ice nucleation. In such cases the chain of consequences includes changes in the rates of precipitation, net latent heat release, vertical motions, atmospheric vorticity, and ultimately in the general circulation. Much more work is required before the mechanism can be considered to have a secure basis in laboratory experiment and quantitative atmospheric modeling.
Steven J Ghan - One of the best experts on this subject based on the ideXlab platform.
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influence of superparameterization and a higher order turbulence closure on rainfall bias over amazonia in community atmosphere model version 5
Journal of Geophysical Research, 2017Co-Authors: Kai Zhang, Steven J Ghan, Ruby L Leung, Minghuai Wang, Muhammad Shaikh, Robert E Dickinson, Jose A MarengoAbstract:We evaluate the Community Atmosphere Model Version 5 (CAM5) with a higher-order turbulence closure scheme, named Cloud Layers Unified By Binomials (CLUBB), and a Multiscale Modeling Framework, referred as the “super-parameterization” (SP) with two different Microphysics configurations to investigate their influences on rainfall simulations over Southern Amazonia. The two different Microphysics configurations in SP are the one-moment Cloud Microphysics without aerosol treatment (SP1) and two-moment Cloud Microphysics coupled with aerosol treatment (SP2). Results show that both SP2 and CLUBB effectively reduce the low biases of rainfall, mainly during the wet season, and reduce low biases of humidity in the lower troposphere with further reduced shallow Clouds and increased surface solar flux. These changes increase moist static energy in the lower atmosphere, contribute to stronger convection and more rainfall. SP2 appears to realistically capture the observed increase of relative humidity prior to deep convection and it significantly increases rainfall in the afternoon; CLUBB significantly delays the afternoon peak rainfall and produces more precipitation in the early morning, due to more gradual transition between shallow and deep convection. In CAM5 and CAM5 with CLUBB, occurrence of more deep convection appears to be a result of stronger heating rather than higher relative humidity.
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coupling spectral bin Cloud Microphysics with the mosaic aerosol model in wrf chem methodology and results for marine stratocumulus Clouds
Journal of Advances in Modeling Earth Systems, 2016Co-Authors: Wenhua Gao, Jiwen Fan, Richard C Easter, Qing Yang, Chun Zhao, Steven J GhanAbstract:Aerosol-Cloud interaction processes can be represented more physically with bin Cloud Microphysics relative to bulk microphysical parameterizations. However, due to computational power limitations in the past, bin Cloud Microphysics was often run with very simple aerosol treatments. The purpose of this study is to represent better aerosol-Cloud interaction processes in the Chemistry version of Weather Research and Forecast model (WRF-Chem) at convection-permitting scales by coupling spectral-bin Cloud Microphysics (SBM) with the MOSAIC sectional aerosol model. A flexible interface is built that exchanges Cloud and aerosol information between them. The interface contains a new bin aerosol activation approach, which replaces the treatments in the original SBM. It also includes the modified aerosol resuspension and in-Cloud wet removal processes with the droplet loss tendencies and precipitation fluxes from SBM. The newly coupled system is evaluated for two marine stratocumulus cases over the Southeast Pacific Ocean with either a simplified aerosol setup or full-chemistry. We compare the aerosol activation process in the newly coupled SBM-MOSAIC against the SBM simulation without chemistry using a simplified aerosol setup, and the results show consistent activation rates. A longer time simulation reinforces that aerosol resuspension through Cloud drop evaporation plays an important role in replenishing aerosols and impacts Cloud and precipitation in marine stratocumulus Clouds. Evaluation of the coupled SBM-MOSAIC with full-chemistry using aircraft measurements suggests that the new model works realistically for the marine stratocumulus Clouds, and improves the simulation of Cloud microphysical properties compared to a simulation using MOSAIC coupled with the Morrison two-moment Microphysics.
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a multiscale modeling framework model superparameterized cam5 with a higher order turbulence closure model description and low Cloud simulations
Journal of Advances in Modeling Earth Systems, 2015Co-Authors: Minghuai Wang, Steven J Ghan, Xiaohong Liu, Vincent E Larson, Mikhail Ovchinnikov, David P Schanen, Heng Xiao, Philip J Rasch, Zhun GuoAbstract:In this study, a higher-order turbulence closure scheme, called Cloud Layers Unified By Binormals (CLUBB), is implemented into a Multiscale Modeling Framework (MMF) model to improve low-Cloud simulations. The performance of CLUBB in MMF simulations with two different Microphysics configurations (one-moment Cloud Microphysics without aerosol treatment and two-moment Cloud Microphysics coupled with aerosol treatment) is evaluated against observations and further compared with results from the Community Atmosphere Model, Version 5 (CAM5) with conventional Cloud parameterizations. CLUBB is found to improve low-Cloud simulations in the MMF, and the improvement is particularly evident in the stratocumulus-to-cumulus transition regions. Compared to the single-moment Cloud Microphysics, CLUBB with two-moment Microphysics produces Clouds that are closer to the coast and agrees better with observations. In the stratocumulus-to-cumulus transition regions, CLUBB with two-moment Cloud Microphysics produces short-wave Cloud forcing in better agreement with observations, while CLUBB with single-moment Cloud Microphysics overestimates short-wave Cloud forcing. CLUBB is further found to produce quantitatively similar improvements in the MMF and CAM5, with slightly better performance in the MMF simulations (e.g., MMF with CLUBB generally produces low Clouds that are closer to the coast than CAM5 with CLUBB). Improved low-Cloud simulations in MMF make it an even more attractive tool for studying aerosol-Cloud-precipitation interactions.
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a new two moment bulk stratiform Cloud Microphysics scheme in the community atmosphere model version 3 cam3 part ii single column and global results
Journal of Climate, 2008Co-Authors: Andrew Gettelman, Hugh Morrison, Steven J GhanAbstract:The global performance of a new two-moment Cloud Microphysics scheme for a general circulation model (GCM) is presented and evaluated relative to observations. The scheme produces reasonable representations of Cloud particle size and number concentration when compared to observations, and it represents expected and observed spatial variations in Cloud microphysical quantities. The scheme has smaller particles and higher number concentrations over land than the standard bulk Microphysics in the GCM and is able to balance the top-of-atmosphere radiation budget with 60% the liquid water of the standard scheme, in better agreement with retrieved values. The new scheme diagnostically treats both the mixing ratio and number concentration of rain and snow, and it is therefore able to differentiate the two key regimes, consisting of drizzle in shallow, warm Clouds and larger rain drops in deeper Cloud systems. The modeled rain and snow size distributions are consistent with observations.
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application of Cloud Microphysics to ncar community climate model
Journal of Geophysical Research, 1997Co-Authors: Steven J Ghan, Ruby L LeungAbstract:The Colorado State University Regional Atmospheric Modeling System bulk Cloud Microphysics parameterization has been applied to the treatment of stratiform Clouds in the National Center for Atmospheric Research community climate model. Predicted Cloud properties are mass concentrations of Cloud water, Cloud ice, rain, and snow and number concentration of ice. Microphysical processes treated include condensation of water vapor and evaporation of Cloud water and rain, nucleation of ice crystals, vapor deposition and sublimation of Cloud ice and snow, autoconversion and accretion of Cloud water, aggregation and collection of Cloud ice, melting of ice and snow, riming on ice and snow, and gravitational settling of ice, rain, and snow. Although the parameterization is more detailed and hence more computationally demanding than other Cloud Microphysics parameterizations in climate models, it treats the Bergeron-Findeisen process explicitly and hence does not require an ad hoc parameterization to distinguish liquid water and ice. A variety of simulations were performed, testing sensitivity to horizontal and vertical resolution, the treatment of ice number, droplet number, and parameterization of cumulus convection. The simulated planetary radiation balance is found to be particularly sensitive to the treatment of ice number and cumulus convection.
Andrew Gettelman - One of the best experts on this subject based on the ideXlab platform.
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development of two moment Cloud Microphysics for liquid and ice within the nasa goddard earth observing system model geos 5
Geoscientific Model Development, 2014Co-Authors: Donifan Barahona, Hugh Morrison, Andrew Gettelman, Andrea Molod, Julio T Bacmeister, Athanasios Nenes, Vaughan T J Phillips, Andrew F EichmannAbstract:Abstract. This work presents the development of a two-moment 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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a new two moment bulk stratiform Cloud Microphysics scheme in the community atmosphere model version 3 cam3 part ii single column and global results
Journal of Climate, 2008Co-Authors: Andrew Gettelman, Hugh Morrison, Steven J GhanAbstract:The global performance of a new two-moment Cloud Microphysics scheme for a general circulation model (GCM) is presented and evaluated relative to observations. The scheme produces reasonable representations of Cloud particle size and number concentration when compared to observations, and it represents expected and observed spatial variations in Cloud microphysical quantities. The scheme has smaller particles and higher number concentrations over land than the standard bulk Microphysics in the GCM and is able to balance the top-of-atmosphere radiation budget with 60% the liquid water of the standard scheme, in better agreement with retrieved values. The new scheme diagnostically treats both the mixing ratio and number concentration of rain and snow, and it is therefore able to differentiate the two key regimes, consisting of drizzle in shallow, warm Clouds and larger rain drops in deeper Cloud systems. The modeled rain and snow size distributions are consistent with observations.
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a new two moment bulk stratiform Cloud Microphysics scheme in the community atmosphere model version 3 cam3 part i description and numerical tests
Journal of Climate, 2008Co-Authors: Hugh Morrison, Andrew GettelmanAbstract:A new two-moment stratiform Cloud Microphysics scheme in a general circulation model is described. Prognostic variables include Cloud droplet and Cloud ice mass mixing ratios and number concentrations. The scheme treats several microphysical processes, including hydrometeor collection, condensation/ evaporation, freezing, melting, and sedimentation. The activation of droplets on aerosol is physically based and coupled to a subgrid vertical velocity. Unique aspects of the scheme, relative to existing two-moment schemes developed for general circulation models, are the diagnostic treatment of rain and snow number concentration and mixing ratio and the explicit treatment of subgrid Cloud water variability for calculation of the microphysical process rates. Numerical aspects of the scheme are described in detail using idealized one-dimensional offline tests of the Microphysics. Sensitivity of the scheme to time step, vertical resolution, and numerical method for diagnostic precipitation is investigated over a range of conditions. It is found that, in general, two substeps are required for numerical stability and reasonably small time truncation errors using a time step of 20 min; however, substepping is only required for the precipitation microphysical processes rather than the entire scheme. A new numerical approach for the diagnostic rain and snow produces reasonable results compared to a benchmark simulation, especially at low vertical resolution. Part II of this study details results of the scheme in single-column and global simulations, including comparison with observations.
R A Heelis - One of the best experts on this subject based on the ideXlab platform.
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correlations of atmospheric dynamics with solar activity evidence for a connection via the solar wind atmospheric electricity and Cloud Microphysics
Journal of Geophysical Research, 1993Co-Authors: Brian A. Tinsley, R A HeelisAbstract:We respond to several criticisms of the view that there is a physical linkage between solar activity and the dynamics of the troposphere and lower stratosphere, and we provide further evidence in support of a mechanism for such a linkage involving atmospheric electricity and Cloud Microphysics. The main criticisms are (1) that the decadal time scale variations in stratified data result from aliasing introduced by the sampling process and are not responses to a decadal time scale physical input; (2) that the observed correlations are due to chance coincidence or an atmospheric periodicity that is not uniquely related to solar variability; and (3) that there are no plausible mechanisms that can amplify one of the weak solar-varying inputs in the region where the correlations are found. We show that the aliasing criticism is inadequate because the real quasi-biennial oscillation departs from an ideal sine wave in a way that reduces aliasing effects to insignificant levels. The nonuniqueness of identification of the 11-year solar cycle as the period of the arctic forcing for the Arctic winter stratospheric temperatures is a problem only for the short 33-year record of polar temperatures; in much longer time series of unstratified climate data the periods of 11 and 22 years are prominent. Highly unique signatures of solar wind forcing of tropospheric dynamics exist on the day-to-day time scale via two independent inputs to atmospheric electricity. These are (1) through changes in tropospheric ion production as a result of solar wind modulation of galactic cosmic rays and (2) through changes in the potential difference between the polar ionospheres and the surface, forced by the solar wind By component. The product of the cosmic ray flux and the ionospheric potential determines the vertical air-earth electrical current. In the presence of Clouds of large horizontal extent, this current determines the rate of polarization charging of the Clouds via the accumulation of positive electrostatic charges on droplets near Cloud tops. The observed correlations, and theoretical and laboratory results for the effects of electrostatic charges on droplets and aerosols on the rates of ice nucleation, are consistent with the postulate that for certain regions and seasons and atmospheric levels the large-scale atmospheric electrical parameters have significant effects on the rates of initial ice nucleation. In such cases the chain of consequences includes changes in the rates of precipitation, net latent heat release, vertical motions, atmospheric vorticity, and ultimately in the general circulation. Much more work is required before the mechanism can be considered to have a secure basis in laboratory experiment and quantitative atmospheric modeling.