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- Author or Editor: RICHARD A. ANTHES x
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Abstract
This paper investigates the problem of initializing operational hurricane models with several types of real data. Imbalances in real data generate inertia-gravity waves with periods that vary strongly in different regions of the hurricane domain. The energy of these waves is removed by propagation out of the domain, by the horizontal diffusion process, and by the truncation errors associated with the Matsuno time-differencing scheme. Several initialization schemes are tested with a symmetric hurricane model. Random and bias errors superimposed on perfect data produce imbalances that lend to significant errors in short-range forecasts. A general dynamic initialization scheme that is suitable for diabatic, viscous models yields very promising results.
The dynamic initialization technique is utilized in an effort to determine the types of data that will be most useful in initializing operational hurricane models. In general, observations are most useful near the center of the storm at low levels. Temperature and wind observations are about equally effective in reducing initial analysis errors. Specific humidity observations, on the other hand, seem less important. Finally, the sensitivity of the initialization method is tested with observations that include rather large bias errors.
Abstract
This paper investigates the problem of initializing operational hurricane models with several types of real data. Imbalances in real data generate inertia-gravity waves with periods that vary strongly in different regions of the hurricane domain. The energy of these waves is removed by propagation out of the domain, by the horizontal diffusion process, and by the truncation errors associated with the Matsuno time-differencing scheme. Several initialization schemes are tested with a symmetric hurricane model. Random and bias errors superimposed on perfect data produce imbalances that lend to significant errors in short-range forecasts. A general dynamic initialization scheme that is suitable for diabatic, viscous models yields very promising results.
The dynamic initialization technique is utilized in an effort to determine the types of data that will be most useful in initializing operational hurricane models. In general, observations are most useful near the center of the storm at low levels. Temperature and wind observations are about equally effective in reducing initial analysis errors. Specific humidity observations, on the other hand, seem less important. Finally, the sensitivity of the initialization method is tested with observations that include rather large bias errors.
Abstract
A two-dimensional mesoscale model is applied to study the evolution of a strong sea breeze on a stagnant base state. In contrast to previous studies, this paper considers the relationship of the planetary boundary layer (PBL), the thermodynamic structure and the vertical circulation associated with the sea breeze in detail.
The development of the sea breeze circulation is studied quantitatively using the circulation theorem. The circulation in the vertical plane normal to the coast develops as a result of the solenoid term. The vertical diffusion of momentum acts as the most important brake on the developing circulation in agreement with previous theoretical results. The Coriolis term is small until 6 h after the beating cycle. Late in the cycle, however, it reaches a value of 45% that of the solenoid term. Horizontal and vertical advective effects are small.
Under zero geostrophic wind conditions, the return flow occurs entirely above the PBL. Therefore, neutrally buoyant pollutants emitted at the surface can only enter the return flow through the narrow zone of upward motion at the sea breeze front. Trajectories indicate that considerable recirculation toward the shore of these pollutants as well as pollutants left over in the previous day's mixed layer may occur. For the time and space scale of the sea breeze considered here, Coriolis forces are important in causing significant transports along the coast.
The depth of the circulation and the trajectories are sensitive to the rate of heating over land and the initial static stability. For strong heating in a relatively unstable environment, a significant component to the return circulation exists up to 5 km. For moderate heating in a more stable environment, there is very little return circulation above 3 km.
Abstract
A two-dimensional mesoscale model is applied to study the evolution of a strong sea breeze on a stagnant base state. In contrast to previous studies, this paper considers the relationship of the planetary boundary layer (PBL), the thermodynamic structure and the vertical circulation associated with the sea breeze in detail.
The development of the sea breeze circulation is studied quantitatively using the circulation theorem. The circulation in the vertical plane normal to the coast develops as a result of the solenoid term. The vertical diffusion of momentum acts as the most important brake on the developing circulation in agreement with previous theoretical results. The Coriolis term is small until 6 h after the beating cycle. Late in the cycle, however, it reaches a value of 45% that of the solenoid term. Horizontal and vertical advective effects are small.
Under zero geostrophic wind conditions, the return flow occurs entirely above the PBL. Therefore, neutrally buoyant pollutants emitted at the surface can only enter the return flow through the narrow zone of upward motion at the sea breeze front. Trajectories indicate that considerable recirculation toward the shore of these pollutants as well as pollutants left over in the previous day's mixed layer may occur. For the time and space scale of the sea breeze considered here, Coriolis forces are important in causing significant transports along the coast.
The depth of the circulation and the trajectories are sensitive to the rate of heating over land and the initial static stability. For strong heating in a relatively unstable environment, a significant component to the return circulation exists up to 5 km. For moderate heating in a more stable environment, there is very little return circulation above 3 km.
Abstract
ATS-III satellite data and conventional aerological data are used to construct detailed wind analyses of the outflow layer for four hurricanes and one tropical storm. Harmonic analysis of these data, and of the data for a mean Atlantic hurricane and a mean Pacific typhoon, shows that wave numbers 1 and 2 around the circumference of the storm account for most of the variance of momentum and kinetic energy. Subtraction of the symmetric part of the vortex circulation from the total flow to yield the “asymmetric wind” reveals two eddies located in preferred quadrants of the storm. An anticyclonic eddy is found to the right and a cyclonic eddy to the left of the storm motion. These eddies transport absolute vorticity inward, opposing the outward transport by the mean circulation. They also transport a significant amount of negative relative angular momentum outward.
The presence of inertial (or dynamic) instability is investigated. Although substantial areas of negative absolute vorticity and anomalous anticyclonic winds exist in all cases, these areas are correlated so well that the regions of dynamic instability are small.
Abstract
ATS-III satellite data and conventional aerological data are used to construct detailed wind analyses of the outflow layer for four hurricanes and one tropical storm. Harmonic analysis of these data, and of the data for a mean Atlantic hurricane and a mean Pacific typhoon, shows that wave numbers 1 and 2 around the circumference of the storm account for most of the variance of momentum and kinetic energy. Subtraction of the symmetric part of the vortex circulation from the total flow to yield the “asymmetric wind” reveals two eddies located in preferred quadrants of the storm. An anticyclonic eddy is found to the right and a cyclonic eddy to the left of the storm motion. These eddies transport absolute vorticity inward, opposing the outward transport by the mean circulation. They also transport a significant amount of negative relative angular momentum outward.
The presence of inertial (or dynamic) instability is investigated. Although substantial areas of negative absolute vorticity and anomalous anticyclonic winds exist in all cases, these areas are correlated so well that the regions of dynamic instability are small.
Abstract
Heat and moisture budgets are computed for the 40 km model simulations of moist frontogenesis described recently by Hsie and others. The apparent heat source and moisture sinks are dominated by the condensation term and have maxima in the middle troposphere. Both the large-scale (200 km) moisture convergence and the large-scale vertical motion are highly correlated with the mesoscale condensation rate.
Four alternative schemes for treating the effects of moist convection in primitive equation models are tested, and the results compared with those from the explicit scheme for calculating condensation and precipitation. A scheme in which only water vapor is predicted yields results similar to the explicit simulation, which included prediction equations for water vapor, cloud water and rainwater. The neglect of two opposing effects-water loading and evaporation-is apparently responsible for the similarity to the control. However, when both cloud water and water vapor are predicted, the presence of evaporation, but not water loading by rain, results in larger differences from the control. A third scheme, developed by Kessler, does not conserve total water, and the latent heat released is overestimated.
The cumulus parameterization proposed by Anthes is tested as the fourth scheme in a coarse-resolution (200 km) version of the model. The major deficiency with the coarse-mesh model is its failure to resolve a narrow, frictionally-driven updraft close to the surface cold front. The feedback of the moisture convergence and the cumulus heating parameterization produces large differences in the horizontal distribution of heating in the thermal and wind structure.
When the cumulus heating in the coarse-mesh simulation is specified from the average distribution given by the explicit scheme in the fine-mesh simulation, the coarse-mesh simulation is much closer to the large-scale average of the fine-mesh simulation.
Abstract
Heat and moisture budgets are computed for the 40 km model simulations of moist frontogenesis described recently by Hsie and others. The apparent heat source and moisture sinks are dominated by the condensation term and have maxima in the middle troposphere. Both the large-scale (200 km) moisture convergence and the large-scale vertical motion are highly correlated with the mesoscale condensation rate.
Four alternative schemes for treating the effects of moist convection in primitive equation models are tested, and the results compared with those from the explicit scheme for calculating condensation and precipitation. A scheme in which only water vapor is predicted yields results similar to the explicit simulation, which included prediction equations for water vapor, cloud water and rainwater. The neglect of two opposing effects-water loading and evaporation-is apparently responsible for the similarity to the control. However, when both cloud water and water vapor are predicted, the presence of evaporation, but not water loading by rain, results in larger differences from the control. A third scheme, developed by Kessler, does not conserve total water, and the latent heat released is overestimated.
The cumulus parameterization proposed by Anthes is tested as the fourth scheme in a coarse-resolution (200 km) version of the model. The major deficiency with the coarse-mesh model is its failure to resolve a narrow, frictionally-driven updraft close to the surface cold front. The feedback of the moisture convergence and the cumulus heating parameterization produces large differences in the horizontal distribution of heating in the thermal and wind structure.
When the cumulus heating in the coarse-mesh simulation is specified from the average distribution given by the explicit scheme in the fine-mesh simulation, the coarse-mesh simulation is much closer to the large-scale average of the fine-mesh simulation.
Abstract
Abstract not available.
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Abstract
A series of numerical experiments with the Hoskins-Bretherton horizontal shear model of frontogenesis in an, amplifying, two-dimensional baroclinic wave is performed. The analytic solutions from the Boussinesq, semi-geostrophic model provide initial conditions for numerical integrations with a two-dimensional, dry version of the fully compressible, hydrostatic primitive equation (PE) model of Anthes and Warner with 40 km horizontal resolution. The PE model is integrated 1) without planetary boundary layer (PBL) physics; 2) with a one-layer bulk-drag scheme; and 3) with a high-vertical-resolution PBL model. The lower boundary is thermally insulated in order to isolate the effect of the internal mixing of heat in the PBL.
The simulation with the high-resolution PBL physics resolves several realistic features including 1) a narrow updraft at the top of the PBL above the sea-level pressure trough at the warm edge of the frontal zone; 2) a stable layer capping the PBL to the rear of the frontal zone; and 3) slightly unstable or neutral lapse rates in the PBL behind the front and stable lapse rates in the PBL ahead of the front. A diagnostic analysis of the frontogenesis indicates that the fine structure resulting from adding PBL physics can be attributed to the frictionally driven, ageostrophic inflow in the PBL toward the surface pressure trough in which the frontal zone is located. A finding of particular interest is that the stability patterns in the PBL on either side of the front evolve independently of sensible heating at the surface.
Abstract
A series of numerical experiments with the Hoskins-Bretherton horizontal shear model of frontogenesis in an, amplifying, two-dimensional baroclinic wave is performed. The analytic solutions from the Boussinesq, semi-geostrophic model provide initial conditions for numerical integrations with a two-dimensional, dry version of the fully compressible, hydrostatic primitive equation (PE) model of Anthes and Warner with 40 km horizontal resolution. The PE model is integrated 1) without planetary boundary layer (PBL) physics; 2) with a one-layer bulk-drag scheme; and 3) with a high-vertical-resolution PBL model. The lower boundary is thermally insulated in order to isolate the effect of the internal mixing of heat in the PBL.
The simulation with the high-resolution PBL physics resolves several realistic features including 1) a narrow updraft at the top of the PBL above the sea-level pressure trough at the warm edge of the frontal zone; 2) a stable layer capping the PBL to the rear of the frontal zone; and 3) slightly unstable or neutral lapse rates in the PBL behind the front and stable lapse rates in the PBL ahead of the front. A diagnostic analysis of the frontogenesis indicates that the fine structure resulting from adding PBL physics can be attributed to the frictionally driven, ageostrophic inflow in the PBL toward the surface pressure trough in which the frontal zone is located. A finding of particular interest is that the stability patterns in the PBL on either side of the front evolve independently of sensible heating at the surface.
Abstract
The energetics of Eady's (1949) model of baroclinic instability are used to express the wavenumber-dependent disturbance growth rate in terms of upward and northward fluxes of heat and momentum. This formulation leads to simple physical interpretations for the existence of the wavelength of maximum growth rate and the shortwave cutoff.
Abstract
The energetics of Eady's (1949) model of baroclinic instability are used to express the wavenumber-dependent disturbance growth rate in terms of upward and northward fluxes of heat and momentum. This formulation leads to simple physical interpretations for the existence of the wavelength of maximum growth rate and the shortwave cutoff.
Abstract
This paper investigates the generation and propagation of spiral bands on an axisymmetric base-state vortex. A linear model is used to study the formation of bands from internal gravity-inertia waves in a barotropic atmosphere. Spiral bands form random perturbations placed on a vortex with unstable static stability that is equal for ascending and descending motion. This growing mode assumes the characteristics of pseudoadiabatic motion in a conditionally unstable atmosphere due to the coarse vertical resolution of the linear model. Implicit diffusion from the centered finite-difference scheme shifts the preferred growth modes from infinite wavenumbers, characteristic of inviscid analytical solutions, to 4Δλ and 4Δr,ar wavelengths in numerical experiments. Here Δλ and Δr are the angular and radial distances between grid points. Explicit diffusion representing subgrid-scale eddies shifts preferred modes to longer wavelengths. Rotation in the basic state is a necessary condition before the unstable gravity-inertia waves form spiral bands. Rotation also organizes stable perturbations into a banded pattern. Inertial instability and the Coriolis parameter are unimportant for band formation in these linear experiments. The distance between bands increases and the growth rate decreases in experiments in which adiabatic warming occurs with descent and warming due to latent heat release occurs with ascending motion.
Abstract
This paper investigates the generation and propagation of spiral bands on an axisymmetric base-state vortex. A linear model is used to study the formation of bands from internal gravity-inertia waves in a barotropic atmosphere. Spiral bands form random perturbations placed on a vortex with unstable static stability that is equal for ascending and descending motion. This growing mode assumes the characteristics of pseudoadiabatic motion in a conditionally unstable atmosphere due to the coarse vertical resolution of the linear model. Implicit diffusion from the centered finite-difference scheme shifts the preferred growth modes from infinite wavenumbers, characteristic of inviscid analytical solutions, to 4Δλ and 4Δr,ar wavelengths in numerical experiments. Here Δλ and Δr are the angular and radial distances between grid points. Explicit diffusion representing subgrid-scale eddies shifts preferred modes to longer wavelengths. Rotation in the basic state is a necessary condition before the unstable gravity-inertia waves form spiral bands. Rotation also organizes stable perturbations into a banded pattern. Inertial instability and the Coriolis parameter are unimportant for band formation in these linear experiments. The distance between bands increases and the growth rate decreases in experiments in which adiabatic warming occurs with descent and warming due to latent heat release occurs with ascending motion.
Abstract
Results from diagnostic studies of a nonlinear hurricane model support the conclusion that internal gravity-inertia waves are responsible for hurricane rainbands. The mean relative vorticity differed little between the bands and their environment, a characteristic of gravity waves modified slightly by the earth's rotation. Small differences in mean radial and tangential velocity components, divergence, and the radial pressure gradient force were noted between the bands and their environment. The upper layers of the bands were responsible for a small increase in the model storm's kinetic energy due to a net convergence of kinetic energy flux from the environment into the bands. A large net convergence of cyclonic angular momentum flux into the bands occurred in the boundary layer. Conversion of available potential energy to kinetic energy was not significant in the model bands. Finally, latent heating in the bands did not play an important role in the maintenance or propagation of the bands at large radii.
Abstract
Results from diagnostic studies of a nonlinear hurricane model support the conclusion that internal gravity-inertia waves are responsible for hurricane rainbands. The mean relative vorticity differed little between the bands and their environment, a characteristic of gravity waves modified slightly by the earth's rotation. Small differences in mean radial and tangential velocity components, divergence, and the radial pressure gradient force were noted between the bands and their environment. The upper layers of the bands were responsible for a small increase in the model storm's kinetic energy due to a net convergence of kinetic energy flux from the environment into the bands. A large net convergence of cyclonic angular momentum flux into the bands occurred in the boundary layer. Conversion of available potential energy to kinetic energy was not significant in the model bands. Finally, latent heating in the bands did not play an important role in the maintenance or propagation of the bands at large radii.
Abstract
An axisymmetric, multilayer hurricane model is used to investigate the hurricane's response to sudden changes of sea surface temperature (SST). The model contains a parameterization of the planetary boundary layer (PBL) which includes matched formulations for the surface layer and the mixed layer. The heat, moisture and momentum fluxes are mutually dependent through Monin-Obukhov similarity theory.
The height of the model hurricane PEL is 400–500 m, below which the potential temperature and specific humidity are nearly invariant with height. The flow in the hurricane PBL is characterized by subgradient tangential velocities and nearly uniform cross-isobaric flow angles. The sensible heating from the ocean is insignificant, but the evaporation is large. The magnitudes of the equivalent drag coefficients are approximately one-third those of the exchange coefficients for heat and moisture.
As the SST is suddenly decreased (increased), the steady-state model hurricane experiences two stages of modification. The first stage consists of adjustments of the hurricane PBL featuring a weakened (enhanced) dynamic and thermodynamic coupling of the storm with the ocean. No important changes of intensity occur during this stage, which lasts several hours. The decrease (increase) of kinetic energy dissipation offsets part of the decrease (increase) of kinetic energy generation. The second stage is characterized by a steady modification of storm intensity. The fluctuations of intensity in these experiments are less pronounced than those shown by a similar model with a conventional bulk parameterization of the hurricane PBL.
Abstract
An axisymmetric, multilayer hurricane model is used to investigate the hurricane's response to sudden changes of sea surface temperature (SST). The model contains a parameterization of the planetary boundary layer (PBL) which includes matched formulations for the surface layer and the mixed layer. The heat, moisture and momentum fluxes are mutually dependent through Monin-Obukhov similarity theory.
The height of the model hurricane PEL is 400–500 m, below which the potential temperature and specific humidity are nearly invariant with height. The flow in the hurricane PBL is characterized by subgradient tangential velocities and nearly uniform cross-isobaric flow angles. The sensible heating from the ocean is insignificant, but the evaporation is large. The magnitudes of the equivalent drag coefficients are approximately one-third those of the exchange coefficients for heat and moisture.
As the SST is suddenly decreased (increased), the steady-state model hurricane experiences two stages of modification. The first stage consists of adjustments of the hurricane PBL featuring a weakened (enhanced) dynamic and thermodynamic coupling of the storm with the ocean. No important changes of intensity occur during this stage, which lasts several hours. The decrease (increase) of kinetic energy dissipation offsets part of the decrease (increase) of kinetic energy generation. The second stage is characterized by a steady modification of storm intensity. The fluctuations of intensity in these experiments are less pronounced than those shown by a similar model with a conventional bulk parameterization of the hurricane PBL.
