Bulk Meteorological Parameters for Diagnosing Cloudiness in the Stochastic Cloud Forecast Model PDF Download
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Author: Publisher: ISBN: Category : Cloud forecasting Languages : en Pages : 59
Book Description
The three dimensional distribution of clouds is of great interest to the Air Force, and to the aviation community in general. The Stochastic Cloud Forecast Model (SCFM) is a novel, global cloud model currently operated at the Air Force Weather Agency (AFWA) which diagnoses cloud cover statistically using a minimal set of predictors from global numerical forecasts. Currently the four predictors are pressure, temperature, vertical velocity, and relative humidity. In this thesis, 330 sets of predictors are compared in the SCFM-R, a research version of the model programmed for this thesis. There are some differences in the SCFM and the SCFM-R that yield important information. It is found that the SCFM is very sensitive to how cloud cover in the boundary layer is diagnosed. An analysis of the diagnosis method used to initialize the model revealed a bias for over-diagnosing cloud at lower levels and under-diagnosing cloud at upper levels. Also, it is recommended that AFWA consider exchanging temperature for another predictor more related to moisture, such as cloud water, and that relative humidity is included as relative humidity to the fourth power. Other recommendations include improving the method for diagnosing cloud cover in the boundary layer and improving the model initial condition.
Author: Publisher: ISBN: Category : Cloud forecasting Languages : en Pages : 59
Book Description
The three dimensional distribution of clouds is of great interest to the Air Force, and to the aviation community in general. The Stochastic Cloud Forecast Model (SCFM) is a novel, global cloud model currently operated at the Air Force Weather Agency (AFWA) which diagnoses cloud cover statistically using a minimal set of predictors from global numerical forecasts. Currently the four predictors are pressure, temperature, vertical velocity, and relative humidity. In this thesis, 330 sets of predictors are compared in the SCFM-R, a research version of the model programmed for this thesis. There are some differences in the SCFM and the SCFM-R that yield important information. It is found that the SCFM is very sensitive to how cloud cover in the boundary layer is diagnosed. An analysis of the diagnosis method used to initialize the model revealed a bias for over-diagnosing cloud at lower levels and under-diagnosing cloud at upper levels. Also, it is recommended that AFWA consider exchanging temperature for another predictor more related to moisture, such as cloud water, and that relative humidity is included as relative humidity to the fourth power. Other recommendations include improving the method for diagnosing cloud cover in the boundary layer and improving the model initial condition.
Author: Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
The functional relationship between cloud cover and relative humidity (Rh) averaged over areas comparable to grid dimensions of numerical weather models was quantified using RTNEPH and 3DNEFH observations. Cloud cover in any atmospheric level decreases exponentially as layer averaged Rh tails below 100%, and no observations support critical Rhs below which cloud cover is zero. Small cloud amounts occur at all Rhs. Therefore, current weather models probably underestimate cloud coverage, especially at Rhs below the critical humidities used by most models. At the same Rh, convection enhances cloud coverage in the upper troposphere. and decreases cloud coverage in the lower troposphere. Developed a simplified and innovative mass flux convective parameterization that was evaluated using atmospheric radon profiles, and was also used to simulate the redistribution of heat and moisture by combining the approach of stochastic mixing with detraining plumes. A public domain cloud resolving model (ARPS) was used to further refine the 1-D parameterization. Both the cloud resolving models and the convective parameterization were evaluated using GATE observations. However the ARPS model employs an advection algorithm that does not conserve water mass, making it unreliable to use for refining cloud parameterizations.
Author: Jerry M. Straka Publisher: Cambridge University Press ISBN: 1139478834 Category : Science Languages : en Pages : 407
Book Description
This book focuses specifically on bin and bulk parameterizations for the prediction of cloud and precipitation at various scales - the cloud scale, mesoscale, synoptic scale, and the global climate scale. It provides a background to the fundamental principles of parameterization physics, including processes involved in the production of clouds, ice particles, liquid water, snow aggregate, graupel and hail. It presents full derivations of the parameterizations, allowing readers to build parameterization packages, with varying levels of complexity based on information in the book. Architectures for a range of dynamical models are given, in which parameterizations form a significant tool for investigating large non-linear numerical systems. Model codes are available online at www.cambridge.org/9780521883382. Written for researchers and advanced students of cloud and precipitation microphysics, this book is also a valuable reference for all atmospheric scientists involved in models of numerical weather prediction.
Author: Martin Fox Publisher: ISBN: Category : Languages : en Pages : 81
Book Description
A stochastic model is proposed for the evolution of cloud cover. In this model each of the four observable states (clear, partially cloudy, cloudy, and overcast) is assumed to be the image under some function of two states of an eight state Markov chain. Estimates are given of transition probabilities in the observable four state process. Tables which allow assessment of the accuracy of the estimates and of the goodness of fit of the model are also provided. (Author).
Author: David Collins Publisher: ISBN: Category : Languages : en Pages :
Book Description
We propose a mathematical procedure to derive a stochastic parameterization for the bulk warm cloud micro-physical properties of collision and coalescence. Unlike previous bulk parameterizations, the stochastic parameterization does not assume any particular droplet size distribution, all parameters have physical meanings which are recoverable from data, all equations are independently derived making conservation of mass intrinsic, the auto conversion parameter is finely controllable, and the resultant parameterization has the flexibility to utilize a variety of collision kernels. This new approach to modelling the kinetic collection equation (KCE) decouples the choice of a droplet size distribution and a collision kernel from a cloud microphysical parameterization employed by the governing climate model. In essence, a climate model utilizing this new parameterization of cloud microphysics could have different distributions and different kernels in different climate model cells, yet employ a single parameterization scheme.This stochastic bulk model is validated theoretically and empirically against an existing bulk model that contains a simple enough (toy) collision kernel such that the KCE can be solved analytically. Theoretically, the stochastic model reproduces all the terms of each equation in the existing model and precisely reproduces the power law dependence for all of the evolving cloud properties. Empirically, values of stochastic parameters can be chosen graphically which will precisely reproduce the coefficients of the existing model, save for some ad-hoc non-dimensional time functions. Furthermore values of stochastic parameters are chosen graphically. The values selected for the stochastic parameters effect the conversion rate of mass cloud to rain. This conversion rate is compared against (i) an existing bulk model, and (ii) a detailed solution that is used as a benchmark.The utility of the stochastic bulk model is extended to include hydrodynamic and turbulent collision kernels for both clean and polluted clouds. The validation and extension compares the time required to convert 50\% of cloud mass to rain mass, compares the mean rain radius at that time, and used detailed simulations as benchmarks. Stochastic parameters can be chosen graphically to replicate the 50\% conversion time in all cases. The curves showing the evolution of mass conversion that are generated by the stochastic model with realistic kernels do not match corresponding benchmark curves at all times during the evolution for constant parameter values. The degree to which the benchmark curves represent ground truth, i.e. atmospheric observations, is unknown. Finally, among alternate methods of acquiring parameter values, getting a set of sequential values for a single parameter has a stronger physical foundation than getting one value per parameter, and a stochastic simulation is preferable to a higher order detailed method due to the presence of bias in the latter.
Author: Publisher: ISBN: Category : Languages : en Pages : 5
Book Description
This research program utilizes satellite and surface-derived cloud observations together with standard meteorological measurements to evaluate and improve our ability to accurately diagnose cloud coverage. Results of this research will be used to compliment existing or future parameterizations of cloud effects in general circulation models, since nearly all cloud parameterizations must specify a fractional area of cloud coverage when calculating radiative or dynamic cloud effects, and current parameterizations rely on rather crude cloud cover estimates. During the first phase of this research program, our goal is to evaluate and improve the methods for calculating cloud cover within a mesoscale meteorology model. To accomplish this, a mesoscale meteorology model will be quantitatively evaluated using available cloud cover databases, including the US Air Force 3DNEPH and RTNEPH satellite-derived cloud fields, as well as CART data as they become available. During the second phase of this research, the cloud cover data and improved parameterizations of cloud coverage developed during the first phase will be incorporated into a mesoscale meteorology model. Model forecasts which utilize the observed cloud coverage and depth should be improved relative to forecasts which crudely specify cloud properties.
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Author: Nils G. Kvamstoe
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Author: Donald C. Norquist
Author: Jerry M. Straka
Author: Martin Fox
Author: David Collins
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