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Showing papers on "Convective available potential energy published in 1997"


Journal ArticleDOI
TL;DR: In this article, a comparison study of four cumulus parameterization schemes (CPSs), the Anthes-Kuo, Betts-Miller, Grell, and Kain-Fritsch schemes, is conducted using The Pennsylvania State University-National Center for Atmospheric Research mesoscale model.
Abstract: A comparison study of four cumulus parameterization schemes (CPSs), the Anthes‐Kuo, Betts‐Miller, Grell, and Kain‐Fritsch schemes, is conducted using The Pennsylvania State University‐National Center for Atmospheric Research mesoscale model. Performance of these CPSs is examined using six precipitation events over the continental United States for both cold and warm seasons. Grid resolutions of 36 and 12 km are chosen to represent current mesoscale research models and future operational models. The key parameters used to evaluate skill include precipitation, sea level pressure, wind, and temperature predictions. Precipitation is evaluated statistically using conventional skill scores (such as threat and bias scores) for different threshold values based on hourly rainfall observations. Rainfall and other mesoscale features are also evaluated by careful examination of analyzed and simulated fields, which are discussed in the context of timing, evolution, intensity, and structure of the precipitation systems. It is found that the general 6-h precipitation forecast skill for these schemes is fairly good in predicting four out of six cases examined in this study, even for higher thresholds. The forecast skill is generally higher for cold-season events than for warm-season events. There is an increase in the forecast skill in the 12-km model, and the gain is most obvious in predicting heavier rainfall amounts. The model’s precipitation forecast skill is better in rainfall volume than in either the areal coverage or the peak amount. The scheme with the convective available potential energy‐based closure assumption (Kain‐Fritsch scheme) appears to perform better. Some systematic behaviors associated with various schemes are also noted wherever possible. The partition of rainfall into subgrid scale and grid scale is sensitive to the particular parameterization scheme chosen, but relatively insensitive to either the model grid sizes or the convective environments. The prediction of mesoscale surface features in warm-season cases, such as mesoscale pressure centers, windshift lines (gust fronts), and temperature fields, strongly suggests that the CPSs with moist downdrafts are able to predict these surface features more accurately.

305 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the environmental characteristics associated with 313 significant convective events in the western Mediterranean using radiosonde ascents made in Mallorca (Spain) and separated them into five groups, based on the observed event (hail, heavy rain, dry, storms with heavy rain and tornadoes). Classic stability indices, as well as values of convective available potential energy and helicity, are considered for each group.
Abstract: The environmental characteristics associated with 313 significant convective events in the western Mediterranean are investigated using radiosonde ascents made in Mallorca (Spain). The events are separated into five groups, based on the observed event (hail, heavy rain, “dry” storms, storms with heavy rain, and tornadoes). Classic stability indices, as well as values of convective available potential energy and helicity, are considered for each group. These traditional convective indices appear not to provide good guidance for discriminating environments associated with each group of events. In order to classify the environments, each sounding is defined by means of 34 variables that describe the thermal and humidity vertical structure, instability, precipitable water, and helicity. A cluster analysis shows that four different vertical structures appear. Each kind of event shows preference for the environments defined by a cluster. A simple method is presented for sounding classification using th...

92 citations


Book ChapterDOI
01 Jan 1997
TL;DR: In this article, the authors highlight the distinction between processes which supply moisture or available energy over the depth of the convecting layer (equilibrium control), versus inhibition and initiation processes at low levels (activation control).
Abstract: What processes control large-scale variations of deep convection (LSVDC) in the tropics? Here ‘large-scale’ is taken to mean any coherent variations, in either space or time, comprised of statistical populations of separate convective cloud systems. This essay highlights the distinction between processes which supply moisture or available energy over the depth of the convecting layer (equilibrium control), versus inhibition and initiation processes at low levels (activation control), as hypotheses for explaining LSVDC.

70 citations


Journal ArticleDOI
TL;DR: In this article, the ability to discriminate between tornadic and nontornadic thunderstorms using a mesoscale model was investigated using a simulation of nine severe weather events: four events are tornadic supercell thunderstorm outbreaks that occur in conjunction with strong large-scale forcing for upward motion, three events are bow-echo outbreaks that also occur in conjunctious conditions, and two are isolated supercell storms that occur under much weaker large scale forcing.
Abstract: The ability to discriminate between tornadic and nontornadic thunderstorms is investigated using a mesoscale model. Nine severe weather events are simulated: four events are tornadic supercell thunderstorm outbreaks that occur in conjunction with strong large-scale forcing for upward motion, three events are bow-echo outbreaks that also occur in conjunction with strong large-scale forcing for upward motion, and two are isolated tornadic supercell thunderstorms that occur under much weaker large-scale forcing. Examination of the mesoscale model simulations suggests that it is possible to discriminate between tornadic and nontornadic thunderstorms by using the locations of model-produced convective activity and values of convective available potential energy to highlight regions of likely thunderstorm development, and then using the values of storm-relative environmental helicity (SREH) and bulk Richardson number shear (BRNSHR) to indicate whether or not tornadic supercell thunderstorms are likely....

67 citations


Journal ArticleDOI
TL;DR: In this paper, the authors test the strict quasi-equilibrium hypothesis over convecting regions of the tropical oceans using microwave sounding unit tropospheric temperature and precipitation fields, along with COADS surface data, on timescales of a month and longer and on space scales ranging upward from O(300 km).
Abstract: Quasi-equilibrium convective parameterizations share the common assumption that in regions of sustained deep convection rates of change in convective available potential energy (CAPE) are small compared to the magnitude of the large-scale and boundary layer forcings that act to modify CAPE. The more restrictive strict quasi-equilibrium hypothesis (SQE) is that changes in CAPE are dynamically negligible. Under this assumption, tropospheric temperature and thickness variations largely follow a moist adiabat associated with variations in the boundary layer θe. SQE is an attractive simplification for theories of large-scale circulation in the Tropics but has been inadequately tested to date. In this paper, we test the SQE hypothesis over convecting regions of the tropical oceans using microwave sounding unit tropospheric temperature and precipitation fields, along with COADS surface data, on timescales of a month and longer and on space scales ranging upward from O(300 km). One prediction of SQE, tha...

66 citations


Book ChapterDOI
01 Jan 1997
Abstract: Boundary layer quasi-equilibrium (BLQ) is a theory of how moist convection is controlled over the warm tropical oceans. Theories of convective control fall into two categories, those which postulate that convection is controlled by the large scale convergence of moisture, and those which insist that convection is controlled by the production and destruction of convective instability. BLQ falls in the latter category and pays particular attention to the role of the subcloud or boundary layer in determining instability. This presentation is based on work published by Raymond [16] and Emanuel [6].

19 citations


Journal ArticleDOI
Qi Hu1
TL;DR: In this article, the authors presented a cumulus parameterization that uses a cloud model that describes atmospheric convection as consisting of a sequence of intermittently rising thermals, and the total mass of thermals in a convection event is determined by the amount of convective available potential energy in local soundings.
Abstract: The author presents a cumulus parameterization that uses a cloud model that describes atmospheric convection as consisting of a sequence of intermittently rising thermals. The total mass of thermals in a convection event is determined by the amount of convective available potential energy in local soundings. In the cloud model, it is assumed that a thermal entrains environmental air only at a thin layer around the top frontier of its rising body. The entrained air mass mixes with the thermal’s air and produces “mixtures” that then detach themselves from the thermal. This limited mixing prevents deep erosion to the thermal’s buoyancy by entrainment and mixing processes. The remainder of the thermal continues rising to higher levels and forming more mixtures on its way to its own level of neutral buoyancy. The mixtures also rise or sink from the levels where they form to their level of neutral buoyancy. Evaluation of this scheme using Global Atmospheric Research Program Atlantic Tropical Experiment...

17 citations


Book ChapterDOI
01 Jan 1997
TL;DR: A detailed description of the ensemble and individual properties of convective clouds remains an elusive but compelling frontier in atmospheric research, and one with profound consequences for weather and climate prediction as mentioned in this paper.
Abstract: Winston Churchill’s description of Russia—a mystery inside a riddle, wrapped in an enigma—might equally apply to moist convection. Almost one hundred and fifty years have passed since James Pollard Espy [1] first correctly inferred that cumulus clouds are driven by the release of latent heat when water vapor condenses, yet very fundamental aspects of moist convection—for example, the profiles of temperature and water vapor in moist convecting atmospheres—remain poorly understood. A satisfying description of the ensemble and individual properties of convective clouds remains an elusive but compelling frontier in atmospheric research, and one with profound consequences for weather and climate prediction.

10 citations


Book ChapterDOI
01 Jan 1997
TL;DR: The mass flux approach to convection was formulated in the 1970s and formed the basis for the well known Arakawa-Schubert scheme (Arakawa and Schubert) as discussed by the authors.
Abstract: Although the principles of the mass flux approach to convection were formulated in the 1970s and formed the basis for the well known “Arakawa-Schubert” scheme (Arakawa and Schubert’) it has only been recently that such schemes have been used in many GCMs due to their expense compared to simpler schemes (moist convective adjustment and Kuo-type schemes). The approach has a stronger physical basis than these earlier methods and provides an understanding of how convection affects the large-scale atmosphere. It also allows more physically based microphysical treatments to be employed and vertical transports of tracers by convection to be estimated, of importance when considering the impact that aerosols have upon climate.

7 citations


01 Jan 1997
TL;DR: In this article, the authors present an alternative formula for convective available potential energy (CAPE) using the same closure assumptions as RI, and show that the predictions of CAPE by RI are not inconsistent with the numerical experiments presented in EB.
Abstract: Recently, both Renno and Ingersoll (1996, hereafter RI) and Emanuel and Bister (1996, hereafter EB) derive theoretical formulas for the convective available potential energy (CAPE), the fractional area covered by active updrafts, and the vertical velocity in the active updrafts for atmospheres in radiative–convective equilibrium. The theories of RI and EB differ primarily in the means of closure for the mass flux of cumulus convection. Emanuel and Bister state that ‘‘the predictions of our theory differ considerably from those of Renno and Ingersoll; for example, the buoyancy and velocity scales are independent of the magnitude of the radiative forcing.’’ The numerical experiments EB present support this notion that CAPE is relatively insensitive to the magnitude of the radiative forcing of the atmosphere. The quote above and the inference of EB’s paper is that the RI theory for CAPE will not satisfy these numerical experiments and therefore is invalid. In this comment, we present an alternative formula for CAPE using the same closure assumptions as RI. Furthermore, we will show that the predictions of CAPE by RI are not inconsistent with the numerical experiments presented in EB. Thus we will conclude it is inappropriate for EB to dismiss the theory of RI based upon the evidence presented by EB to date. Renno and Ingersoll derive the following expression for the CAPE of an atmosphere in radiative–convective equilibrium: