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  1. Article ; Online: An Intercomparison of Large‐Eddy Simulations of a Convection Cloud Chamber Using Haze‐Capable Bin and Lagrangian Cloud Microphysics Schemes

    Fan Yang / Fabian Hoffmann / Raymond A. Shaw / Mikhail Ovchinnikov / Andrew M. Vogelmann

    Journal of Advances in Modeling Earth Systems, Vol 15, Iss 5, Pp n/a-n/a (2023)

    2023  

    Abstract: Abstract Recent in situ observations show that haze particles exist in a convection cloud chamber. The microphysics schemes previously used for large‐eddy simulations of the cloud chamber could not fully resolve haze particles and the associated ... ...

    Abstract Abstract Recent in situ observations show that haze particles exist in a convection cloud chamber. The microphysics schemes previously used for large‐eddy simulations of the cloud chamber could not fully resolve haze particles and the associated processes, including their activation and deactivation. Specifically, cloud droplet activation was modeled based on Twomey‐type parameterizations, wherein cloud droplets were formed when a critical supersaturation for the available cloud condensation nuclei (CCN) was exceeded and haze particles were not explicitly resolved. Here, we develop and adapt haze‐capable bin and Lagrangian microphysics schemes to properly resolve the activation and deactivation processes. Results are compared with the Twomey‐type CCN‐based bin microphysics scheme in which haze particles are not fully resolved. We find that results from the haze‐capable bin microphysics scheme agree well with those from the Lagrangian microphysics scheme. However, both schemes significantly differ from those from a CCN‐based bin microphysics scheme unless CCN recycling is considered. Haze particles from the recycling of deactivated cloud droplets can strongly enhance cloud droplet number concentration due to a positive feedback in haze‐cloud interactions in the cloud chamber. Haze particle size distributions are more realistic when considering solute and curvature effects that enable representing the complete physics of the activation process. Our study suggests that haze particles and their interactions with cloud droplets may have a strong impact on cloud properties when supersaturation fluctuations are comparable to mean supersaturation, as is the case in the cloud chamber and likely is the case in the atmosphere, especially in polluted conditions.
    Keywords large‐eddy simulation ; bin microphysics ; Lagrangian microphysics ; haze‐cloud interaction ; cloud chamber ; Physical geography ; GB3-5030 ; Oceanography ; GC1-1581
    Subject code 520
    Language English
    Publishing date 2023-05-01T00:00:00Z
    Publisher American Geophysical Union (AGU)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  2. Article ; Online: Large‐Eddy Simulations of a Convection Cloud Chamber

    Fan Yang / Mikhail Ovchinnikov / Subin Thomas / Alexander Khain / Robert McGraw / Raymond A. Shaw / Andrew M. Vogelmann

    Journal of Advances in Modeling Earth Systems, Vol 14, Iss 5, Pp n/a-n/a (2022)

    Sensitivity to Bin Microphysics and Advection

    2022  

    Abstract: Abstract Bin microphysics schemes are useful tools for cloud simulations and are often considered to provide a benchmark for model intercomparison. However, they may experience issues with numerical diffusion, which are not well quantified, and the ... ...

    Abstract Abstract Bin microphysics schemes are useful tools for cloud simulations and are often considered to provide a benchmark for model intercomparison. However, they may experience issues with numerical diffusion, which are not well quantified, and the transport of hydrometeors depends on the choice of advection scheme, which can also change cloud simulation results. Here, an atmospheric large‐eddy simulation model is adapted to simulate a statistically steady‐state cloud in a convection cloud chamber under well‐constrained conditions. Two bin microphysics schemes, a spectral bin method and the method of moments, as well as several advection methods for the transport of the microphysical variables are employed for model intercomparison. Results show that different combinations of microphysics and advection schemes can lead to considerable differences in simulated cloud properties, such as cloud droplet number concentration. We find that simulations using the advection scheme that suffers more from numerical diffusion tends to have a smaller droplet number concentration and liquid water content, while simulation with the microphysics scheme that suffers more from numerical diffusion tends to have a broader size distribution and thus larger mean droplet sizes. Sensitivities of simulations to bin resolution, spatial resolution, and temporal resolution are also tested. We find that refining the microphysical bin resolution leads to a broader cloud droplet size distribution due to the advection of hydrometeors. Our results provide insight for using different advection and microphysics schemes in cloud chamber simulations, which might also help understand the uncertainties of the schemes used in atmospheric cloud simulations.
    Keywords large eddy simulation ; cloud chamber ; microphysics scheme ; advection scheme ; Physical geography ; GB3-5030 ; Oceanography ; GC1-1581
    Subject code 518
    Language English
    Publishing date 2022-05-01T00:00:00Z
    Publisher American Geophysical Union (AGU)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  3. Article ; Online: A Time-Gated, Time-Correlated Single-Photon-Counting Lidar to Observe Atmospheric Clouds at Submeter Resolution

    Fan Yang / Yong Meng Sua / Alexandros Louridas / Katia Lamer / Zeen Zhu / Edward Luke / Yu-Ping Huang / Pavlos Kollias / Andrew M. Vogelmann / Allison McComiskey

    Remote Sensing, Vol 15, Iss 1500, p

    2023  Volume 1500

    Abstract: Most lidars used for cloud observations have the range resolution of about 10 m, so they are incapable of resolving submeter-scale processes that are crucial to cloud evolution. This article describes a prototype of a ground-based, vertically pointing, ... ...

    Abstract Most lidars used for cloud observations have the range resolution of about 10 m, so they are incapable of resolving submeter-scale processes that are crucial to cloud evolution. This article describes a prototype of a ground-based, vertically pointing, time-gated, time-correlated single-photon-counting lidar (referred to as the T2 lidar) developed to explore atmospheric clouds at range resolution two orders of magnitude finer than traditional atmospheric lidars. The T2 lidar emits green-light pulses (532 nm) at a repetition rate of 20.6 kHz and a pulse width of ∼650 ps, which enables the observation of aerosol and cloud layers at heights from a few hundred meters to 7.28 km above the ground level at range resolution down to 10 cm. In addition, a digital delay pulse generator controls the detector to only receive photons for a short period after each laser pulse. This time-gated technique blocks photons arriving from regions outside the target zone, thus significantly reducing the noise level and allowing observation even inside clouds. Initial observations show that the T2 lidar can detect sharp cloud boundaries and fine structures near the cloud base. Such refined measurements of cloud structure could lead to an improved understanding of microphysical processes such as droplet activation, entrainment and mixing, and precipitation.
    Keywords remote sensing ; lidar ; clouds ; atmospheric science ; time-gated and time-correlated ; Science ; Q
    Subject code 520
    Language English
    Publishing date 2023-03-01T00:00:00Z
    Publisher MDPI AG
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  4. Article ; Online: Improving Convection Trigger Functions in Deep Convective Parameterization Schemes Using Machine Learning

    Tao Zhang / Wuyin Lin / Andrew M. Vogelmann / Minghua Zhang / Shaocheng Xie / Yi Qin / Jean‐Christophe Golaz

    Journal of Advances in Modeling Earth Systems, Vol 13, Iss 5, Pp n/a-n/a (2021)

    2021  

    Abstract: Abstract Deficiencies in convection trigger functions, used in deep convection parameterizations in General Circulation Models (GCMs), have critical impacts on climate simulations. A novel convection trigger function is developed using the machine ... ...

    Abstract Abstract Deficiencies in convection trigger functions, used in deep convection parameterizations in General Circulation Models (GCMs), have critical impacts on climate simulations. A novel convection trigger function is developed using the machine learning (ML) classification model XGBoost. The large‐scale environmental information associated with convective events is obtained from the long‐term constrained variational analysis forcing data from the Atmospheric Radiation Measurement (ARM) program at its Southern Great Plains (SGP) and Manaus (MAO) sites representing, respectively, continental mid‐latitude and tropical convection. The ML trigger is separately trained and evaluated per site, and jointly trained and evaluated at both sites as a unified trigger. The performance of the ML trigger is compared with four convective trigger functions commonly used in GCMs: dilute convective available potential energy (CAPE), undilute CAPE, dilute dynamic CAPE (dCAPE), and undilute dCAPE. The ML trigger substantially outperforms the four CAPE‐based triggers in terms of the F1 score metric, widely used to estimate the performance of ML methods. The site‐specific ML trigger functions can achieve, respectively, 91% and 93% F1 scores at SGP and MAO. The unified trigger also has a 91% F1 score, with virtually no degradation from the site‐specific training, suggesting the potential of a global ML trigger function. The ML trigger alleviates a GCM deficiency regarding the overprediction of convection occurrence, offering a promising improvement to the simulation of the diurnal cycle of precipitation. Furthermore, to overcome the black box issue of the ML methods, insights derived from the ML model are discussed, which may be leveraged to improve traditional CAPE‐based triggers.
    Keywords Physical geography ; GB3-5030 ; Oceanography ; GC1-1581
    Subject code 551
    Language English
    Publishing date 2021-05-01T00:00:00Z
    Publisher American Geophysical Union (AGU)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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    Inter-library loan at ZB MED

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  5. Article ; Online: January 2016 extensive summer melt in West Antarctica favoured by strong El Niño

    Julien P. Nicolas / Andrew M. Vogelmann / Ryan C. Scott / Aaron B. Wilson / Maria P. Cadeddu / David H. Bromwich / Johannes Verlinde / Dan Lubin / Lynn M. Russell / Colin Jenkinson / Heath H. Powers / Maciej Ryczek / Gregory Stone / Jonathan D. Wille

    Nature Communications, Vol 8, Iss 1, Pp 1-

    2017  Volume 10

    Abstract: Sporadic surface melt over the West Antarctic Ice Sheet is not fully understood. Here, the authors report on an extensive melting episode in the Ross Ice Shelf area in 2016 and use comprehensivein situobservations and model simulations to highlight the ... ...

    Abstract Sporadic surface melt over the West Antarctic Ice Sheet is not fully understood. Here, the authors report on an extensive melting episode in the Ross Ice Shelf area in 2016 and use comprehensivein situobservations and model simulations to highlight the role of the strong El Niño event.
    Keywords Science ; Q
    Language English
    Publishing date 2017-06-01T00:00:00Z
    Publisher Nature Portfolio
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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    Inter-library loan at ZB MED

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