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- Author or Editor: Raúl Erlando López x
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Abstract
Results of a preliminary experiment are described in which a lidar-acoustic sounder system was used to measure plume and cloud width and depth. These parameters are shown to be lognormally distributed. By applying the theory of the genesis of the lognormal to the formation process of convective cells it is suggested that clear air plumes and small cumulus clouds grow by the merger or agglomeration of smaller elements.
Abstract
Results of a preliminary experiment are described in which a lidar-acoustic sounder system was used to measure plume and cloud width and depth. These parameters are shown to be lognormally distributed. By applying the theory of the genesis of the lognormal to the formation process of convective cells it is suggested that clear air plumes and small cumulus clouds grow by the merger or agglomeration of smaller elements.
Abstract
The interaction of cumulus convection with larger scale systems is perhaps the most fundamental problem confronting meteorology today. The main obstacle to the clarification of this problem, however, is the lack of understanding of the dynamics of individual cumulus clouds and of the processes by which they impart heat and mass to their surroundings. As a tool in the investigation of these subjects, a one-dimensional, time-dependent model has been developed. Although the model is fundamentally one-dimensional, the clouds are assumed to consist of two regions—a protected core and an exposed surrounding shell. The entire depth of the cloud is numerically simulated for each of these mutually interacting regions. The mixing between cloud and environment is parameterized in the model in terms of the turbulence intensity of the interior and exterior of the cloud. In this way, the commonly used but physically invalid assumption of similarity is avoided. Additional equations have been introduced in the model to predict the turbulence level of the cloud at all times. The internal circulation of the clouds and the attending redistribution of mass between levels is parameterized in the model in terms of the one-dimensional velocity field of the core. Laboratory and theoretical information about spherical vortices is used in the parameterization.
Results of a typical cloud simulation are presented. The model has shown to be successful in simulating the entire life cycle of cumulus clouds subject to different initial conditions. Although a strict comparison with particular real cases has not been attempted, the computed values for the different variables compare reasonably well with the values commonly observed for tropical clouds. In addition, the model has proven successful in avoiding the unrealistic large radii developed in the early stages of those clouds that were simulated with previous one-dimensional models.
Abstract
The interaction of cumulus convection with larger scale systems is perhaps the most fundamental problem confronting meteorology today. The main obstacle to the clarification of this problem, however, is the lack of understanding of the dynamics of individual cumulus clouds and of the processes by which they impart heat and mass to their surroundings. As a tool in the investigation of these subjects, a one-dimensional, time-dependent model has been developed. Although the model is fundamentally one-dimensional, the clouds are assumed to consist of two regions—a protected core and an exposed surrounding shell. The entire depth of the cloud is numerically simulated for each of these mutually interacting regions. The mixing between cloud and environment is parameterized in the model in terms of the turbulence intensity of the interior and exterior of the cloud. In this way, the commonly used but physically invalid assumption of similarity is avoided. Additional equations have been introduced in the model to predict the turbulence level of the cloud at all times. The internal circulation of the clouds and the attending redistribution of mass between levels is parameterized in the model in terms of the one-dimensional velocity field of the core. Laboratory and theoretical information about spherical vortices is used in the parameterization.
Results of a typical cloud simulation are presented. The model has shown to be successful in simulating the entire life cycle of cumulus clouds subject to different initial conditions. Although a strict comparison with particular real cases has not been attempted, the computed values for the different variables compare reasonably well with the values commonly observed for tropical clouds. In addition, the model has proven successful in avoiding the unrealistic large radii developed in the early stages of those clouds that were simulated with previous one-dimensional models.
Abstract
It is shown that the lognormal distribution describes the frequency distributions of height, horizontal size, and duration of cloud and radar echo populations in many different regions and convective situations. Two hypotheses are suggested to explain this phenomenon. The first postulates a growth process of cloud parcels, in which growth by entrainment of environmental air occurs by a random process that obeys the law of proportionate effects. The second postulates a formation process for clouds, in which the clouds are formed by the merger of random boundary-layer convective elements.
The information presented in this paper should be useful for the parameterization of cumulus convection in larger scale models, and for the understanding and modeling of cloud formation and development.
Abstract
It is shown that the lognormal distribution describes the frequency distributions of height, horizontal size, and duration of cloud and radar echo populations in many different regions and convective situations. Two hypotheses are suggested to explain this phenomenon. The first postulates a growth process of cloud parcels, in which growth by entrainment of environmental air occurs by a random process that obeys the law of proportionate effects. The second postulates a formation process for clouds, in which the clouds are formed by the merger of random boundary-layer convective elements.
The information presented in this paper should be useful for the parameterization of cumulus convection in larger scale models, and for the understanding and modeling of cloud formation and development.
Abstract
This paper (part II) is the second of two papers dealing with cumulus and broader scale flow interaction. The first (part I) is a companion paper that deals with this topic from broad-scale considerations. The second (part II) deals with this topic from the cumulus scale point of view.
A numerical model of individual convective clouds has been used to investigate the effects of a typical population of cumulus clouds on the large-scale features of a tropical disturbance or cloud cluster. The typical cloud population has been determined from U.S. Navy aircraft reconnaissance radar data in the tropical Atlantic Ocean.
This study shows that the detrainment of cloud mass from the population produces net cooling of the air around the clouds. This occurs because the cooling produced by the evaporation of the detrained cloud liquid water over-compensates for the detrainment of sensible heat excess. A heat and moisture budget for a steady-state tropical cloud cluster has been computed using the typical cloud population. A mass budget of the cluster reveals that the vertical circulation required to explain typically observed rainfall rates has a magnitude many times larger than the synoptic mass circulation. The synoptic scale vertical mass circulation is, in fact, a small residual between both the much larger upward mass transport by the clouds and the downward mass transport induced in the cloud-free region around the clouds.
Abstract
This paper (part II) is the second of two papers dealing with cumulus and broader scale flow interaction. The first (part I) is a companion paper that deals with this topic from broad-scale considerations. The second (part II) deals with this topic from the cumulus scale point of view.
A numerical model of individual convective clouds has been used to investigate the effects of a typical population of cumulus clouds on the large-scale features of a tropical disturbance or cloud cluster. The typical cloud population has been determined from U.S. Navy aircraft reconnaissance radar data in the tropical Atlantic Ocean.
This study shows that the detrainment of cloud mass from the population produces net cooling of the air around the clouds. This occurs because the cooling produced by the evaporation of the detrained cloud liquid water over-compensates for the detrainment of sensible heat excess. A heat and moisture budget for a steady-state tropical cloud cluster has been computed using the typical cloud population. A mass budget of the cluster reveals that the vertical circulation required to explain typically observed rainfall rates has a magnitude many times larger than the synoptic mass circulation. The synoptic scale vertical mass circulation is, in fact, a small residual between both the much larger upward mass transport by the clouds and the downward mass transport induced in the cloud-free region around the clouds.
