Simulated Liquid Water Research Articles

Sensitivity of aerosol indirect effects to cloud nucleation and autoconversion parameterizations in short‐range weather forecasts during the May 2003 aerosol IOP

Aerosol‐cloud interactions begin with the direct involvement of aerosols in cloud nucleation followed by its indirect contribution to the formation of precipitation through autoconversion. Since the treatments of cloud microphysics in climate models are highly parameterized, a thorough study is needed to examine the range of simulations associated with different parameterizations of aerosol‐cloud interactions. Unlike previous studies focused on climate‐mode simulations, our interest is in short‐range model response before the development of model bias and the compensation of multiple feedback mechanisms. In this study, we modified CAM4 to explore model sensitivity to treatments of cloud nucleation and autoconversion over the Atmospheric Radiation Measurement Southern Great Plains (SGP) facility during the May 2003 Aerosol Intensive Operations Period (IOP) under the Cloud‐Associated Parameterizations Testbed framework. Simulated liquid water path and low cloud fraction were sensitive to the choice of parameterization; however, change of modeled precipitation was insignificant with varying parameterization in short‐range (∼3 day) simulation. In general, simulated cloud properties were more sensitive to the treatment of autoconversion than nucleation. Calculations of sulfate indirect effects indicate that the change of shortwave fluxes from cloud lifetime effect is much more sensitive to cloud parameterizations than cloud albedo effect. Microphysical feedbacks complicate the local response of the climate system and can yield a positive 2nd indirect sulfate forcing that counters the expectation that increases in aerosol concentration decrease the shortwave fluxes. As a result, the calculated total sulfate indirect forcing over SGP varies widely ranging from −0.1 to −2.1 W m−2 during the IOP.

J056026 格子ボルツマン法を用いた固体高分子形燃料電池ガス拡散層内での気液二相流解析

For practical use of a polymer electrolyte fuel cell (PEFC), a flooding phenomenon is one of the problems to be solved. The flooding is caused by liquid water accumulated in the gas diffusion layer (GDL) and the gas flow channels and deteriorates the performance of the PEFC. Therefore, it is necessary to clarify the gas and liquid flow in the PEFC and to control the liquid water behavior appropriately. Our research group applied the lattice Boltzmann method (LBM) for the two phase flow with high density ratio, considering the effect of wettability, and has carried out the analyses of gas and liquid water to propose optimal structures of the PEFC. Here, the LBM is a method to reproduce the macroscopic flow by considering fluid as an aggregate of a virtual particle and calculating those collisions and translation sequentially, and suitable for the two-phase flow simulation with complex boundary geometries. In this study, we simulated liquid water behavior inside of the GDL applying a low density ratio LBM with shorter computational time instead of the high density ratio model. It was confirmed that the effect of large density difference on the liquid water behavior is negligible because of the weak gas flow inside of the GDL. Using the LBM with low density ratio, we tried efficient large-scale analyses in the GDL to elucidate the effect of the GDL structure and wettability on the liquid water behavior inside of the GDL.

Estimating the Sensitivity of Radiative Impacts of Shallow, Broken Marine Clouds to Boundary Layer Aerosol Size Distribution Parameter Uncertainties for Evaluation of Satellite Retrieval Requirements

Abstract A proposed objective of the planned Aerosol–Cloud–Ecosystem (ACE) satellite mission is to provide constraints on climate model representation of aerosol effects on clouds by retrieving profiles of aerosol number concentration, effective variance, and effective radius over the 0.1–1-μm radius range under humidified ambient conditions with 500-m vertical resolution and uncertainties of 100%, 50%, and 10%, respectively. Shallow, broken marine clouds provide an example of conditions where boundary layer aerosol properties would be retrieved in clear-sky gaps. To quantify the degree of constraint that proposed retrievals might provide on cloud radiative forcing (CRF) simulated by climate models under such conditions, dry aerosol size distribution parameters are independently varied here in large-eddy simulations of three well-established modeling case studies. Using the rudimentary available aerosol specifications, it is found that relative changes of total dry aerosol properties in simulations can be used as a proxy for relative changes of ambient aerosol properties targeted by ACE retrievals. The sensitivity of simulated daytime shortwave CRF to the proposed uncertainty in retrieved aerosol number concentration is −15 W m−2 in the overcast limit, roughly a factor of 2 smaller than a simple analytic estimate owing primarily to aerosol-induced reductions in simulated liquid water path across this particular set of case studies. The CRF sensitivity to proposed uncertainties in retrieved aerosol effective variance and effective radius is typically far smaller, with no corresponding analytic estimate. Generalization of the results obtained here using only three case studies would require statistical analysis of relevant meteorological and aerosol observations and quantification of observational and model uncertainties and biases.

Spatially inhomogeneous bimodal inherent structure of simulated liquid water

In the supercooled regime at elevated pressure two forms of liquid water, high-density (HDL) and low-density (LDL), have been proposed to be separated by a coexistence line ending at a critical point, but a connection to water at ambient conditions has been lacking. Here we perform large-scale molecular dynamics simulations and demonstrate that the underlying potential energy surface gives a strictly bimodal characterization of the molecules at all temperatures and pressures, including the biologically and technologically important ambient regime, as spatially inhomogeneous either LDL- or HDL-like with a 3 : 1 predominance for HDL under ambient conditions. The Widom line in the supercooled regime, where maximal structural fluctuations take place, coincides with a 1 : 1 distribution. Although our results are based on molecular dynamics force-field simulations the close agreement with recent analyses of experimental X-ray spectroscopy and scattering data indicates a unified description also of real liquid water covering supercooled to ambient conditions.

Estimating the sensitivity of radiative impacts of shallow, broken marine clouds to boundary-layer aerosol size distribution parameter uncertainties for evaluation of satellite retrieval requirements

A proposed objective of the planned Aerosol–Cloud–Ecosystem (ACE) satellite mission is to provide constraints on climate model representation of aerosol effects on clouds by retrieving profiles of aerosol number concentration, effective variance, and effective radius over the 0.1–1-μm radius range under humidified ambient conditions with 500-m vertical resolution and uncertainties of 100%, 50%, and 10%, respectively. Shallow, broken marine clouds provide an example of conditions where boundary layer aerosol properties would be retrieved in clear-sky gaps. To quantify the degree of constraint that proposed retrievals might provide on cloud radiative forcing (CRF) simulated by climate models under such conditions, dry aerosol size distribution parameters are independently varied here in large-eddy simulations of three well-established modeling case studies. Using the rudimentary available aerosol specifications, it is found that relative changes of total dry aerosol properties in simulations can be used as a proxy for relative changes of ambient aerosol properties targeted by ACE retrievals. The sensitivity of simulated daytime shortwave CRF to the proposed uncertainty in retrieved aerosol number concentration is −15 W m−2 in the overcast limit, roughly a factor of 2 smaller than a simple analytic estimate owing primarily to aerosol-induced reductions in simulated liquid water path across this particular set of case studies. The CRF sensitivity to proposed uncertainties in retrieved aerosol effective variance and effective radius is typically far smaller, with no corresponding analytic estimate. Generalization of the results obtained here using only three case studies would require statistical analysis of relevant meteorological and aerosol observations and quantification of observational and model uncertainties and biases.

Analysis of an extremely dense regional fog event in Eastern China using a mesoscale model

An unusually dense regional advection-radiation fog event over Anhui and the surrounding provinces in eastern China during Dec. 25–27, 2006, was investigated. At its mature stage, the fog covered most Anhui and parts of the surrounding provinces, reducing visibility to 100 m or less. It lasted more than 36 consecutive hours in some places. A mesoscale meteorological model (MM5), together with back-trajectory analysis, was used to investigate this fog event. The observations from a field station as well as hundreds of routine stations, along with two sets of visibility computing methods, were used to quantitatively and objectively validate the MM5 simulated liquid water content (LWC) and visibility. The verifications demonstrate that MM5 has a better fog predictability for the first day compared to the second day forecast, and better fog predictability compared to dense fog predictability with regard to the probability of detection (POD) and the threat score (TS). The new visibility algorithm that uses both LWC and number density of fog droplets significantly outperforms the conventional LWC-only based one in the fog prediction in terms of the POD score, especially for dense fog prediction. The objective verification in this work is the first time conducted for MM5 fog prediction, with which we can better understand the performance of simulated temporal and spatial fog coverage. The back-trajectory and sensitivity experiments confirm that subsidence and the steady warm and moist advections from southeast and southwest maintained the dense fog while the northwesterly dry wind resulted in dissipation of the fog.

Intercomparison of model simulations of mixed‐phase clouds observed during the ARM Mixed‐Phase Arctic Cloud Experiment. I: single‐layer cloud

AbstractResults are presented from an intercomparison of single‐column and cloud‐resolving model simulations of a cold‐air outbreak mixed‐phase stratocumulus cloud observed during the Atmospheric Radiation Measurement (ARM) programme's Mixed‐Phase Arctic Cloud Experiment. The observed cloud occurred in a well‐mixed boundary layer with a cloud‐top temperature of − 15 °C. The average liquid water path of around 160 g m−2was about two‐thirds of the adiabatic value and far greater than the average mass of ice which when integrated from the surface to cloud top was around 15 g m−2.Simulations of 17 single‐column models (SCMs) and 9 cloud‐resolving models (CRMs) are compared. While the simulated ice water path is generally consistent with observed values, the median SCM and CRM liquid water path is a factor‐of‐three smaller than observed. Results from a sensitivity study in which models removed ice microphysics suggest that in many models the interaction between liquid and ice‐phase microphysics is responsible for the large model underestimate of liquid water path.Despite this underestimate, the simulated liquid and ice water paths of several models are consistent with observed values. Furthermore, models with more sophisticated microphysics simulate liquid and ice water paths that are in better agreement with the observed values, although considerable scatter exists. Although no single factor guarantees a good simulation, these results emphasize the need for improvement in the model representation of mixed‐phase microphysics. Copyright © 2009 Royal Meteorological Society

Large Eddy Simulation of the Diurnal Cycle in Southeast Pacific Stratocumulus

Abstract This paper describes a series of 6-day large eddy simulations of a deep, sometimes drizzling stratocumulus-topped boundary layer based on forcings from the East Pacific Investigation of Climate (EPIC) 2001 field campaign. The base simulation was found to reproduce the observed mean boundary layer properties quite well. The diurnal cycle of liquid water path was also well captured, although good agreement appears to result partially from compensating errors in the diurnal cycles of cloud base and cloud top due to overentrainment around midday. At all times of the day, entrainment is found to be proportional to the vertically integrated buoyancy flux. Model stratification matches observations well; turbulence profiles suggest that the boundary layer is always at least somewhat decoupled. Model drizzle appears to be too sensitive to liquid water path and subcloud evaporation appears to be too weak. Removing the diurnal cycle of subsidence had little effect on simulated liquid water path. Simulations with changed droplet concentration and drizzle susceptibility showed large liquid water path differences at night, but differences were quite small at midday. Droplet concentration also had a significant impact on entrainment, primarily through droplet sedimentation feedback rather than through drizzle processes.

Vertical cloud properties in the tropical western Pacific Ocean: Validation of the CCSR/NIES/FRCGC GCM by shipborne radar and lidar

This study examined the vertical cloud structure over the tropical western Pacific Ocean using 95‐GHz radar and lidar data observed from September to December 2001 during the MR01‐K05 cruise of the research vessel Mirai. The cloud vertical structure was homogeneous between 6 and 10 km, and the maximum cloud occurrence was 20% and located at 12 km. The mean precipitation occurrence was 11.5% at 1 km. The cloud fraction, radar reflectivity factor, and lidar backscattering coefficient were simulated along the Mirai cruise track using the output from the Center for Climate System Research, University of Tokyo; National Institute for Environmental Studies; and Frontier Research Center for Global Change (CCSR/NIES/FRCGC) general circulation model (GCM). The original output showed the maximum cloud fraction at 15 km; however, after considering attenuation and the minimum sensitivity of the radar, the maximum shifted to 12 km. The model overestimated the cloud fraction above 8 km, with the simulated fraction more than twice as large as the observed fraction. The model overpredicted the frequency of deep convection reaching the upper atmosphere above 12 km. Further, it overestimated precipitation frequency. Simulated radar reflectivity was underestimated throughout the entire altitude range, whereas simulated and observed lidar backscattering were in good agreement above 12 km with subgrid‐scale treatment. The ice effective radius of 40 μm and ice water content were reasonable in thin clouds, but the radius was underestimated in other regions. The simulated liquid water content was overestimated.

Development and validation of the frozen soil parameterization scheme in Common Land Model

In this paper, a frozen soil parameterization scheme is developed based on the Common Land Model. We modify a frozen soil parameterization scheme using soil matric potential to define maximum liquid water content when soil temperature is below the freezing point; the simulation performance is validated using the data from Maqu station on the Tibetan Plateau from 2005 to 2006. The simulated results indicate that the modified frozen soil parameterization scheme allows the liquid water to exist when the soil temperature is below the freezing point, and the simulated soil liquid water content is significantly improved. The simulated soil temperature is also improved because of the successful simulation of the soil liquid water content. The distribution of energy from the modified model is closer to the observed data. Also, the simulated latent heat flux from the modified model increases and the simulated soil heat flux descends compared with the original model.

Electron emission from foils and biological materials after proton impact

Electron emission spectra from thin metal foils with thin layers of water frozen on them (amorphous solid water) after fast proton impact have been measured and have been simulated in liquid water using the event-by-event track structure code PARTRAC. The electron transport model of PARTRAC has been extended to simulate electron transport down to 1 eV by including low-energy phonon, vibrational and electronic excitations as measured by Michaud et al. [Michaud, M., Wen, A., Sanche, L., 2003. Cross sections for low-energy (1–100 eV) electron elastic and inelastic scattering in amorphous ice. Radiat. Res. 159, 3–22] for amorphous ice. Simulated liquid water yields follow in general the amorphous solid water measurements at higher energies, but overestimate them significantly at energies below 50 eV.

Computational mechanics reveals nanosecond time correlations in molecular dynamics of liquid systems

Statistical complexity, a measure introduced in computational mechanics has been applied to MD simulated liquid water and other molecular systems. It has been found that statistical complexity does not converge in these systems but grows logarithmically without a limit. The coefficient of the growth has been introduced as a new molecular parameter which is invariant for a given liquid system. Using this new parameter extremely long time correlations in the system undetectable by traditional methods are elucidated. The existence of hundreds of picosecond and even nanosecond long correlations in bulk water has been demonstrated.

Cloud microphysics and aerosol indirect effects in the global climate model ECHAM5-HAM

Abstract. The double-moment cloud microphysics scheme from ECHAM4 that predicts both the mass mixing ratios and number concentrations of cloud droplets and ice crystals has been coupled to the size-resolved aerosol scheme ECHAM5-HAM. ECHAM5-HAM predicts the aerosol mass, number concentrations and mixing state. The simulated liquid, ice and total water content and the cloud droplet and ice crystal number concentrations as a function of temperature in stratiform mixed-phase clouds between 0 and −35° C agree much better with aircraft observations in the ECHAM5 simulations. ECHAM5 performs better because more realistic aerosol concentrations are available for cloud droplet nucleation and because the Bergeron-Findeisen process is parameterized as being more efficient. The total anthropogenic aerosol effect includes the direct, semi-direct and indirect effects and is defined as the difference in the top-of-the-atmosphere net radiation between present-day and pre-industrial times. It amounts to −1.9 W m−2 in ECHAM5, when a relative humidity dependent cloud cover scheme and aerosol emissions representative for the years 1750 and 2000 from the AeroCom emission inventory are used. The contribution of the cloud albedo effect amounts to −0.7 W m−2. The total anthropogenic aerosol effect is larger when either a statistical cloud cover scheme or a different aerosol emission inventory are employed because the cloud lifetime effect increases.

Resolution Dependence of Nonhydrostatic Models in Simulating the Formation and Evolution of Low-Level Clouds during a "Yamase" Event

In this study, numerical simulations of ‘Yamase’ clouds were conducted using a nonhydrostatic model (NHM). Yamase clouds are typical maritime boundary-layer clouds that frequently appear over the sea off the east coast of the Sanriku District (northeast Honshu Island, Japan) during the summer season. The simulation period was from July to August 1993, when cool easterly winds (termed Yamase winds) prevailed. The NHM, with a horizontal grid of 40 km (NHM40) was integrated, nested within global objective analysis data, for one month by adopting sponge boundaries widely to lateral grids and upper layers, in order to reproduce a synoptic situation. The synoptic weather pattern is precisely reproduced in the long term integration.Then, in order to investigate the formation and evolution processes and structures of Yamase low-level clouds, multi-nesting simulations were conducted using the results of the one-month integration. The characteristic features of simulated Yamase clouds in terms of horizontal distribution, cloud shape and structures, and cloud water content, as well as the dominant mechanisms of cloud formation and evolution, strongly depend on the horizontal resolution of NHMs. The NHM with the high resolution of 100 m (NHM01), simulates convective structures similar to those observed from satellite images. Furthermore, the simulated liquid water path is close to the values observed in other Yamase cases. These results indicate that NHM01 reproduces the characteristic properties of the low-level clouds. In contrast, in simulations using the NHM with the low-resolution of 10 km (NHM10), the mixed layer is too moist and its height too low compared with observed data, and the liquid water path is overestimated. These errors are brought from the fact that the interaction between cloud radiation and formation at night time is too strong compared with the case of NHM01. Vertical heating profiles related to radiation, condensation, and evaporation in NHM10 are different from those generated by NHM01. This study suggests that improved parameterizations, such as a partial condensation scheme, and an adequate scheme of the buoyant production, should be introduced in low-resolution models such as NHM10.

A microphysical parameterization for convective clouds in the ECHAM5 climate model: Single‐column model results evaluated at the Oklahoma Atmospheric Radiation Measurement Program site

The microphysical parameterization used for stratiform clouds in the ECHAM5 climate model is now extended for simulations of convective clouds. The performance of the newly implemented parameterization in simulating midlatitude continental summertime convective cloud systems is evaluated in this paper at the Atmospheric Radiation Measurement Program (ARM) Southern Great Plains (SGP) site in Oklahoma using the single‐column mode (SCM) of ECHAM5. Three ARM intensive operating periods (IOPs), including two summer ones and a late spring one, are used for the evaluation. Results show that the SCM simulated cloud cover fraction agrees well with observations. The SCM also captures most of the precipitation events. With the new microphysical parameterization, the model performs at least as well as with the original model setup in simulating almost all the fields examined in this study. Significant improvement is shown in the simulations of outgoing longwave radiation and net incoming solar radiation at the top of the atmosphere revealing the feasibility of the new parameterization. Sensitivity studies show that a 10‐fold increase in cloud droplet number concentration significantly increases the simulated liquid water content. More interestingly, this increase in cloud droplet number leads to an increase in the total amount of precipitation in two of the three IOPs.

A Study of the Aerosol Effect on a Cloud Field with Simultaneous Use of GCM Modeling and Satellite Observation

The indirect effect of aerosols was simulated by a GCM for nonconvective water clouds and was compared with remote sensing results from the Advanced Very High Resolution Radiometer (AVHRR) satellite-borne sensor for January, April, July, and October of 1990. The simulated global distribution of cloud droplet radius showed a land‐sea contrast and a characteristic feature along the coastal region similar to the AVHRR results, although cloud droplet radii from GCM calculations and AVHRR retrievals were different over tropical marine regions due to a lack of calculation of cloud‐aerosol interaction for convective clouds in the present model and also due to a possible error in the satellite retrieval caused by cirrus and broken cloud contamination. The simulated dependence of the cloud properties on the column aerosol particle number was also consistent with the statistics obtained by the AVHRR remote sensing when a parameterization with the aerosol lifetime effect was incorporated in the simulation. The global average of the simulated liquid water path based on the parameterization with the aerosol lifetime effect showed an insignificant dependence on the aerosol particle number as a result of a global balance of the lifetime effect and the wash-out effect. This dependence was contrary to the results of simulations based on the Sundqvist’s parameterization without aerosol lifetime effect; that is, the simulated cloud liquid water path showed a decreasing tendency with the aerosol particle number reflecting only the wash-out effect.

Calibration and Validation of a Regional Climate Model for Pan-Arctic Hydrologic Simulation

Abstract A number of polar datasets have recently been released involving in situ measurements, satellite retrievals, and reanalysis output that provide new opportunities to evaluate regional climate in the Arctic. These data have been used to assess a 1-yr pan-Arctic simulation (October 1985–September 1986) performed by a version of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) that incorporated the NCAR land surface model (LSM) and a simple thermodynamic sea ice model to investigate interactions between the land surface and atmosphere. The model's standard cloud scheme using relative humidity was replaced by one using simulated cloud liquid water and ice water after a set of short test simulations revealed excessive cloud cover. Model validation concentrates on factors relevant to the water cycle: atmospheric circulation, temperature, surface radiation fluxes, precipitation, and runoff. The model captures general patterns of ...

Entrainment Rate, Cloud Fraction, and Liquid Water Path of PBL Stratocumulus Clouds

Abstract The large eddy simulation technique is used to search for key factors in determining the entrainment rate, cloud fraction, and liquid water path in the stratocumulus-topped boundary layer (STBL), with the goal of developing simple schemes of calculating these important quantities in climate models. In this study an entrainment rate formula is proposed where the entrainment rate is determined by four variables—total jump of the liquid water potential temperature across the entrainment zone, surface heat flux, net radiative flux away from the top of the STBL, and liquid water path. This study also shows that buoyancy reversal, measured here as the ratio between the equivalent potential temperature jump and the total moisture jump across the cloud top, plays a major role in reducing the simulated cloud amount, both cloud fraction and liquid water path. For cases where no buoyancy reversal occurs, the simulated cloud fraction remains 100% and the liquid water path depends solely on the cloud height. ...

Structural complexity of hydrogen-bonded networks

The molecular shape of a network can be characterized in detail by using information on its geometry and topology. In the case of permanent networks (e.g., those formed by a polymer melt), the structural complexity is usually measured in terms of entanglements within a chain and between chains. In this work, we show that this viewpoint can also be extended to the structural analysis of transient networks (e.g., those found in liquids with hydrogen bonding). For the hydrogen-bonded networks within clusters of simulated liquid water, we show the existence of power-law scaling in the averaged entanglement complexity as a function of cluster size.

A Sensitivity Study Of The Subtropical Ocean Surface Energy Balance To The Parameterization Of Precipitation From Stratocumulus Clouds

In the `First Lagrangian' of the Atlantic Stratocumulus Experiment(ASTEX), a cloudy air mass was tracked as it was advected by thetrade winds toward higher sea surface temperatures. In this study,a full diurnal cycle observed during this experiment is simulated andthe impact of the precipitation parameterization is examined. The modelwe use is the one dimensional version of the hydrostatic primitiveequation model MAR (Modele Atmospherique Regional) developed at the Universite catholique de Louvain (UCL).It includes an E-∈ turbulence closure, a wide-band formulationof the radiative transfer, and a parameterized microphysical schemeallowing partial condensation. The model realistically reproducesthe diurnal clearing of the cloud layer as well as the formation ofcumulus clouds under the stratocumulus deck. Nevertheless, as thesurface warms and the boundary layer becomes more convective,the simulation progressively differs from the observed evolution.Further experiments are carried out with different precipitationparameterizations commonly used in mesoscale modelsand general circulation models (GCMs).A strong sensitivity of the simulated liquid water path evolution isfound. The impact on the surface energy flux and the solar fluxreflected by the cloud is also examined. For both fluxes averagedover 24 hours, differences as large as 20 W m-2 are obtainedbetween the various simulations. Low cloudiness covers large areasover the ocean and such errors on the reflected solar flux may stronglyaffect the Earth's radiative budget in GCM simulations. We estimatethat the impact on the globally averaged outgoing solar flux could beas large as 5 W m-2. Furthermore, when atmospheric models arecoupled to ocean models, errors in the surface energy exchanges mayinduce significant drift in the simulated climate.