The Experts below are selected from a list of 234 Experts worldwide ranked by ideXlab platform

Yi Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Performance of CAMS-CSM in Simulating the Shortwave Cloud Radiative Effect over Global Stratus Cloud Regions: Baseline Evaluation and Sensitivity Test
    Journal of Meteorological Research, 2019
    Co-Authors: Yihui Zhou, Yi Zhang, Xinyao Rong
    Abstract:

    The ability of climate models to correctly reproduce Clouds and the radiative effects of Clouds is vitally important in climate simulations and projections. In this study, simulations of the shortwave cloud radiative effect (SWCRE) using the Chinese Academy of Meteorological Sciences Climate System Model (CAMS-CSM) are evaluated. The relationships between SWCRE and dynamic-thermodynamic regimes are examined to understand whether the model can simulate realistic processes that are responsible for the generation and maintenance of Stratus Clouds. Over eastern China, CAMS-CSM well simulates the SWCRE climatological state and Stratus cloud distribution. The model captures the strong dependence of SWCRE on the dynamic conditions. Over the marine boundary layer regions, the simulated SWCRE magnitude is weaker than that in the observations due to the lack of low-level Stratus Clouds in the model. The model fails to simulate the close relationship between SWCRE and local stability over these regions. A sensitivity numerical experiment using a specifically designed parameterization scheme for the stratocumulus cloud cover confirms this assertion. Parameterization schemes that directly depict the relationship between the Stratus cloud amount and stability are beneficial for improving the model performance.

  • Simulations of Stratus Clouds over Eastern China in CAM5: Sources of Errors
    Journal of Climate, 2014
    Co-Authors: Yi Zhang, Haoming Chen
    Abstract:

    AbstractA previous study by Zhang et al. suggested two biases of the high-resolution configured Community Atmosphere Model, version 5 (CAM5), in simulating Stratus Clouds over eastern China, including an underestimation of Stratus occurrence frequency and a spurious low Stratus amount when present (AWP) value center over the Sichuan basin. In this study, the causes for these two problems are further explored.The underestimate of Stratus occurrence frequency in the model is attributed to the bias in large-scale ambient environmental fields. This is confirmed by investigating the differences between two climate counterparts. Results suggest that when the environmental fields in the climate ensemble become more realistic, the simulations of Stratus cloud radiative forcing and cloud fraction are enhanced, mainly caused by a corresponding increase in the Stratus occurrence frequency. The specific sources of the cloud changes between these two ambient climates are then investigated.The presence of a low Stratus...

  • Simulations of Stratus Clouds over Eastern China in CAM5: Sensitivity to Horizontal Resolution
    Journal of Climate, 2014
    Co-Authors: Yi Zhang, Haoming Chen
    Abstract:

    This paper evaluates the simulations of Stratus Clouds over eastern China (EC) in the Community Atmosphere Model, version 5 (CAM5), with an emphasis on the impact of changing horizontal resolutions on the performance.CAM5inallexperimentsgenerallysatisfactorilysimulatesthecloudradiativefeaturesoverEC, including the spatial distributions of the continental shortwave cloud radiative forcing (SWCF) and Stratus regimes, the responses of SWCF to the dynamic and thermodynamic ambient environment, and several relations in the environmental fields that are favorable to the Stratus formation. Meanwhile, all experiments suffer from similar biases. Models tend to underestimate the Stratus amount because of a corresponding underestimate of Stratus occurrence frequency, while the Stratus amount when present (AWP) is generally higher than that in the observation. Models also simulate similar errors in the environmental fields. The differencesbetweenlow-andhigh-resolutionexperimentsaredistinct. Anincreaseofresolutionenhancesthe SWCF in southern China, but the skill deteriorates in the Sichuan basin. Correspondingly, the Stratus amount increases in southern China from low- to high-resolution experiments, mainly because of more Stratus occurrences, which are found to be related to the better represented environmental fields in the high-resolution experiments, especially the dynamic component. Several relations in the ambient environment are also slightly improved in the high-resolution experiments. Meanwhile, the reason for the decrease of Stratus AWP within the Sichuan basin, which is mainly responsible for the decreased Stratus amounts and weaker SWCF from low- to high-resolution experiments, is also discussed.

  • Vertical Structures and Physical Properties of the Cold-Season Stratus Clouds Downstream of the Tibetan Plateau: Differences between Daytime and Nighttime
    Journal of Climate, 2014
    Co-Authors: Yi Zhang, Haoming Chen
    Abstract:

    AbstractThis study compares the daytime–nighttime (DN) differences in the occurrence frequencies and macrophysical, microphysical, and radiative vertical structures of the single-layer Stratus Clouds downstream of the Tibetan Plateau (TP) during the boreal cold season (November–April) using four Cloudsat products. The Stratus cloudy profiles are selected and the midtopped Stratus profiles are further classified into nimboStratus (NI) and altoStratus (AS) according to the cloud-top height and column-integrated optical depth. It is found that the entire Stratus and NI profiles tend to occur more frequently in the daytime, while the AS cloud occurs more frequently in the nighttime. Consistent with the DN differences in the occurrence frequencies, the AS tends to be much thicker with larger cloud fraction in the nighttime, while the NI becomes slightly thicker with larger cloud fraction in the daytime. An analysis of the ambient dynamic and thermodynamic fields associated with Stratus formation suggests that ...

  • Dynamic and Thermodynamic Relations of Distinctive Stratus Clouds on the Lee Side of the Tibetan Plateau in the Cold Season
    Journal of Climate, 2013
    Co-Authors: Yi Zhang, Weihua Yuan, Minghua Zhang
    Abstract:

    AbstractGiven the large discrepancies that exist in climate models for shortwave cloud forcing over eastern China (EC), the dynamic (vertical motion and horizontal circulation) and thermodynamic (stability) relations of Stratus Clouds and the associated cloud radiative forcing in the cold season are examined. Unlike the Stratus Clouds over the southeastern Pacific Ocean (as a representative of marine boundary Stratus), where thermodynamic forcing plays a primary role, the Stratus Clouds over EC are affected by both dynamic and thermodynamic factors. The Tibetan Plateau (TP)-forced low-level large-scale lifting and high stability over EC favor the accumulation of abundant saturated moist air, which contributes to the formation of Stratus Clouds. The TP slows down the westerly overflow through a frictional effect, resulting in midlevel divergence, and forces the low-level surrounding flows, resulting in convergence. Both midlevel divergence and low-level convergence sustain a rising motion and vertical wate...

Minghua Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Dynamic and Thermodynamic Relations of Distinctive Stratus Clouds on the Lee Side of the Tibetan Plateau in the Cold Season
    Journal of Climate, 2013
    Co-Authors: Yi Zhang, Weihua Yuan, Minghua Zhang
    Abstract:

    AbstractGiven the large discrepancies that exist in climate models for shortwave cloud forcing over eastern China (EC), the dynamic (vertical motion and horizontal circulation) and thermodynamic (stability) relations of Stratus Clouds and the associated cloud radiative forcing in the cold season are examined. Unlike the Stratus Clouds over the southeastern Pacific Ocean (as a representative of marine boundary Stratus), where thermodynamic forcing plays a primary role, the Stratus Clouds over EC are affected by both dynamic and thermodynamic factors. The Tibetan Plateau (TP)-forced low-level large-scale lifting and high stability over EC favor the accumulation of abundant saturated moist air, which contributes to the formation of Stratus Clouds. The TP slows down the westerly overflow through a frictional effect, resulting in midlevel divergence, and forces the low-level surrounding flows, resulting in convergence. Both midlevel divergence and low-level convergence sustain a rising motion and vertical wate...

  • dynamic and thermodynamic relations of distinctive Stratus Clouds on the lee side of the tibetan plateau in the cold season
    Journal of Climate, 2013
    Co-Authors: Yi Zhang, Weihua Yuan, Minghua Zhang
    Abstract:

    Given the large discrepancies that exist in climate models for shortwave cloud forcing over eastern China (EC), the dynamic (vertical motion and horizontal circulation) and thermodynamic (stability) relations of Stratus Clouds and the associated cloud radiative forcing in the cold season are examined. Unlike the Stratus Clouds over the southeastern Pacific Ocean (as a representative of marine boundary Stratus), where thermodynamic forcing plays a primary role, the Stratus Clouds over EC are affected by both dynamic and thermodynamicfactors.TheTibetanPlateau(TP)-forcedlow-levellarge-scaleliftingandhighstabilityoverEC favor the accumulation of abundant saturated moist air, which contributes to the formation of Stratus Clouds. TheTPslowsdownthewesterlyoverflowthroughafrictionaleffect,resultinginmidleveldivergence,andforces the low-level surroundingflows, resulting in convergence. Both midlevel divergence and low-level convergence sustain a rising motion and vertical water vapor transport over EC. The surface cold air is advected from the Siberianhighbythesurroundingnortherlyflow,causinglow-levelcooling.Thecoolingeffectisenhancedbythe blockingoftheYunGuiPlateau.Thesouthwesterlywindcarryingwarm,moistairfromtheeastBayofBengalis uplifted by the HengDuan Mountains via topographical forcing; the midtropospheric westerly flow further advects the warmair downstream ofthe TP, moistening andwarmingthemiddletroposphereontheleesideofthe TP. The low-level cooling and midlevel warming together increase the stability. The favorable dynamic and thermodynamiclarge-scaleenvironmentallows for the formation of StratusCloudsover ECduring the cold season.

James W. Telford - One of the best experts on this subject based on the ideXlab platform.

  • Marine Stratus Clouds: Changing liquid‐water and temperature structure
    Quarterly Journal of the Royal Meteorological Society, 2010
    Co-Authors: James W. Telford
    Abstract:

    Aircraft measurements with the Wyoming King Air investigated the response of marine Stratus Clouds off the north California coast, advected to regions with changed sea surface temperature in coastal upwelling. Cloud and associated clear-air observations were made before and near sunrise to eliminate any role of solar heating. Repeated vertical soundings followed temporal advected air. Subcloud structure was observed for the presence of moist convection, reported below Clouds in some conditions. The atmospheric structure in the clear air above the marine Stratus cloud layer showed shallow layers having large temperature gradients with height, apparently remaining from an earlier decoupled overlying cloud layer. Such gradients appear to be associated with thermal radiative-heat transfer in the clear air. Cloud tops were observed to be mostly warmer than the cloud just below. It is suggested that a large temperature increase over a small height difference at the cloud-top inversion may serve to neutralize radiative cooling of the cloud drops below, occurring through the atmospheric thermal radiative window. Observations show that subcloud air is often stable to dry convection. This is not evidence that there is decoupling from the sea surface, since there is no wind shear in the layer and moisture continually moves upwards. Subcloud convection from the sea appears to continue everywhere, demonstrated by the rise of intermittent patches of condensation. Such Clouds are found below the Stratus deck after passage over cooler water, and are clearly responsible for the upward transport of moisture. These transfer processes have been shown to influence cloud-drop spectra and liquid-water content in the Clouds as well as the growth and dissipation of Stratus Clouds. It is concluded that high spatial-resolution (less than a few metres) measurements of vertical radiative-flux divergence are required to confirm the importance of the overlying warmer region in the overall heat balance of a stratiform cloud.

  • marine Stratus Clouds changing liquid water and temperature structure
    Quarterly Journal of the Royal Meteorological Society, 2010
    Co-Authors: James W. Telford
    Abstract:

    Aircraft measurements with the Wyoming King Air investigated the response of marine Stratus Clouds off the north California coast, advected to regions with changed sea surface temperature in coastal upwelling. Cloud and associated clear-air observations were made before and near sunrise to eliminate any role of solar heating. Repeated vertical soundings followed temporal advected air. Subcloud structure was observed for the presence of moist convection, reported below Clouds in some conditions. The atmospheric structure in the clear air above the marine Stratus cloud layer showed shallow layers having large temperature gradients with height, apparently remaining from an earlier decoupled overlying cloud layer. Such gradients appear to be associated with thermal radiative-heat transfer in the clear air. Cloud tops were observed to be mostly warmer than the cloud just below. It is suggested that a large temperature increase over a small height difference at the cloud-top inversion may serve to neutralize radiative cooling of the cloud drops below, occurring through the atmospheric thermal radiative window. Observations show that subcloud air is often stable to dry convection. This is not evidence that there is decoupling from the sea surface, since there is no wind shear in the layer and moisture continually moves upwards. Subcloud convection from the sea appears to continue everywhere, demonstrated by the rise of intermittent patches of condensation. Such Clouds are found below the Stratus deck after passage over cooler water, and are clearly responsible for the upward transport of moisture. These transfer processes have been shown to influence cloud-drop spectra and liquid-water content in the Clouds as well as the growth and dissipation of Stratus Clouds. It is concluded that high spatial-resolution (less than a few metres) measurements of vertical radiative-flux divergence are required to confirm the importance of the overlying warmer region in the overall heat balance of a stratiform cloud.

Jeroen C H Van Der Hage - One of the best experts on this subject based on the ideXlab platform.

  • surface and tethered balloon observations of actinic flux effects of arctic Stratus surface albedo and solar zenith angle
    Journal of Geophysical Research, 2001
    Co-Authors: Stephan R De Roode, W Boot, Peter G Duynkerke, Jeroen C H Van Der Hage
    Abstract:

    As part of the First ISCCP Regional Experiment (FIRE III) Arctic Cloud Experiment actinic flux measurements were made above the Arctic Sea ice during May 1998. The actinic flux, which is also referred to as the 4π radiative flux, is the relevant radiative parameter needed to determine photodissociation rates. It is shown that for a plane-parallel cloud the change in the net irradiance as a function of the optical depth is proportional to the magnitude of the actinic flux. Continuous actinic flux measurements were made just above the snow-covered ice surface by a UV-A and a visible 4π radiometer (wavelengths ∼365 and ∼550 nm, respectively). In addition, vertical profiles of the actinic flux through low arctic Stratus Clouds were obtained by means of a visible 4π radiometer suspended under a tethered balloon. The cloud thermodynamic and microphysical structure was determined from observations made by the National Center for Atmospheric Research C-130 aircraft. In addition, the phase and liquid water path of the cloud was assessed from microwave radiometer, lidar, and radar data. During clear-sky conditions the diurnal variation of the magnitude of actinic flux was controlled mainly by Rayleigh scattering and surface reflection. Above a Stratus cloud layer the actinic flux was found to be almost the same as during clear-sky conditions. This could be attributed to the fact that the effective albedo of the arctic sea ice and the cloud is only slightly higher than the ground albedo alone. In the arctic Stratus Clouds the actinic flux was found to be nearly constant with height, except in a shallow layer near the cloud top where the actinic flux increased significantly with height. The vertical profiles that were observed in arctic Stratus differed from those measured in Atlantic stratocumulus; in the latter the actinic flux was found to increase gradually from cloud base to cloud top. A delta-Eddington model is utilized to illustrate that the exact shape of the vertical profile is very sensitive to the solar zenith angle. During the arctic experiments the solar zenith angle was generally much larger than during the observations in Atlantic stratocumulus.

Haoming Chen - One of the best experts on this subject based on the ideXlab platform.

  • Simulations of Stratus Clouds over Eastern China in CAM5: Sources of Errors
    Journal of Climate, 2014
    Co-Authors: Yi Zhang, Haoming Chen
    Abstract:

    AbstractA previous study by Zhang et al. suggested two biases of the high-resolution configured Community Atmosphere Model, version 5 (CAM5), in simulating Stratus Clouds over eastern China, including an underestimation of Stratus occurrence frequency and a spurious low Stratus amount when present (AWP) value center over the Sichuan basin. In this study, the causes for these two problems are further explored.The underestimate of Stratus occurrence frequency in the model is attributed to the bias in large-scale ambient environmental fields. This is confirmed by investigating the differences between two climate counterparts. Results suggest that when the environmental fields in the climate ensemble become more realistic, the simulations of Stratus cloud radiative forcing and cloud fraction are enhanced, mainly caused by a corresponding increase in the Stratus occurrence frequency. The specific sources of the cloud changes between these two ambient climates are then investigated.The presence of a low Stratus...

  • Simulations of Stratus Clouds over Eastern China in CAM5: Sensitivity to Horizontal Resolution
    Journal of Climate, 2014
    Co-Authors: Yi Zhang, Haoming Chen
    Abstract:

    This paper evaluates the simulations of Stratus Clouds over eastern China (EC) in the Community Atmosphere Model, version 5 (CAM5), with an emphasis on the impact of changing horizontal resolutions on the performance.CAM5inallexperimentsgenerallysatisfactorilysimulatesthecloudradiativefeaturesoverEC, including the spatial distributions of the continental shortwave cloud radiative forcing (SWCF) and Stratus regimes, the responses of SWCF to the dynamic and thermodynamic ambient environment, and several relations in the environmental fields that are favorable to the Stratus formation. Meanwhile, all experiments suffer from similar biases. Models tend to underestimate the Stratus amount because of a corresponding underestimate of Stratus occurrence frequency, while the Stratus amount when present (AWP) is generally higher than that in the observation. Models also simulate similar errors in the environmental fields. The differencesbetweenlow-andhigh-resolutionexperimentsaredistinct. Anincreaseofresolutionenhancesthe SWCF in southern China, but the skill deteriorates in the Sichuan basin. Correspondingly, the Stratus amount increases in southern China from low- to high-resolution experiments, mainly because of more Stratus occurrences, which are found to be related to the better represented environmental fields in the high-resolution experiments, especially the dynamic component. Several relations in the ambient environment are also slightly improved in the high-resolution experiments. Meanwhile, the reason for the decrease of Stratus AWP within the Sichuan basin, which is mainly responsible for the decreased Stratus amounts and weaker SWCF from low- to high-resolution experiments, is also discussed.

  • Vertical Structures and Physical Properties of the Cold-Season Stratus Clouds Downstream of the Tibetan Plateau: Differences between Daytime and Nighttime
    Journal of Climate, 2014
    Co-Authors: Yi Zhang, Haoming Chen
    Abstract:

    AbstractThis study compares the daytime–nighttime (DN) differences in the occurrence frequencies and macrophysical, microphysical, and radiative vertical structures of the single-layer Stratus Clouds downstream of the Tibetan Plateau (TP) during the boreal cold season (November–April) using four Cloudsat products. The Stratus cloudy profiles are selected and the midtopped Stratus profiles are further classified into nimboStratus (NI) and altoStratus (AS) according to the cloud-top height and column-integrated optical depth. It is found that the entire Stratus and NI profiles tend to occur more frequently in the daytime, while the AS cloud occurs more frequently in the nighttime. Consistent with the DN differences in the occurrence frequencies, the AS tends to be much thicker with larger cloud fraction in the nighttime, while the NI becomes slightly thicker with larger cloud fraction in the daytime. An analysis of the ambient dynamic and thermodynamic fields associated with Stratus formation suggests that ...