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- Author or Editor: RICHARD A. ANTHES x
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Abstract
An asymmetric nonlinear ocean model is employed to investigate the oceanic response to moving hurricanes. A turbulent kinetic energy budget is used to parameterize the stress-induced vertical mixing. The results show that the ocean's response to a symmetric storm is stronger on the right of the storm track. Although the maximum speed of the induced current under the storm is not sensitive to the storm's translation speed, the speed does have a large influence on the temperature structure and the thermocline depth in the wake. Vertical motions associated with the inertia-gravity oscillations persist in the wake of the storm. A narrow ridge in the thermocline is left in the storm track for fast-moving storms. The results in many respects agree with Geisler's linear solutions. However, vertical mixing produces significant differences in the depth of the thermocline behind the storm.
Abstract
An asymmetric nonlinear ocean model is employed to investigate the oceanic response to moving hurricanes. A turbulent kinetic energy budget is used to parameterize the stress-induced vertical mixing. The results show that the ocean's response to a symmetric storm is stronger on the right of the storm track. Although the maximum speed of the induced current under the storm is not sensitive to the storm's translation speed, the speed does have a large influence on the temperature structure and the thermocline depth in the wake. Vertical motions associated with the inertia-gravity oscillations persist in the wake of the storm. A narrow ridge in the thermocline is left in the storm track for fast-moving storms. The results in many respects agree with Geisler's linear solutions. However, vertical mixing produces significant differences in the depth of the thermocline behind the storm.
Abstract
An axisymmetric hurricane model and an axisymmetric ocean model are integrated simultaneously for 24 h to investigate the mutual response of the two systems. The feedbacks between the hurricane and the ocean are negative. The weakening of the hurricane in response to the cooling of the ocean's surface by upwelling and mixing results in a lessened response of the ocean. The results suggest that appreciable weakening of a hurricane due to the cooling of the oceanic surface will not occur if it is translating at typical speed.
Abstract
An axisymmetric hurricane model and an axisymmetric ocean model are integrated simultaneously for 24 h to investigate the mutual response of the two systems. The feedbacks between the hurricane and the ocean are negative. The weakening of the hurricane in response to the cooling of the ocean's surface by upwelling and mixing results in a lessened response of the ocean. The results suggest that appreciable weakening of a hurricane due to the cooling of the oceanic surface will not occur if it is translating at typical speed.
A few examples of scientific accomplishments in tropical meteorology and hurricane research are presented. Tropical field experiments such as GATE have greatly influenced observational studies of convection and tropical easterly waves. One application of the study of convection is the attempt to estimate precipitation from satellite platforms.
Research in tropical cyclones has further improved the definition of large-scale structure and the environment in which the hurricane grows. Radiation, convection, and air-sea interaction studies are directed at the forcing and possible feedback of the hurricane with its environment. With this improved physical understanding, numerical modeling of hurricanes can now produce position forecasts of reasonable accuracy that are becoming competitive with current statistical-dynamical methods. There is a continuing effort to attempt hurricane modification experiments in conjunction with an adequate measurement program.
A few examples of scientific accomplishments in tropical meteorology and hurricane research are presented. Tropical field experiments such as GATE have greatly influenced observational studies of convection and tropical easterly waves. One application of the study of convection is the attempt to estimate precipitation from satellite platforms.
Research in tropical cyclones has further improved the definition of large-scale structure and the environment in which the hurricane grows. Radiation, convection, and air-sea interaction studies are directed at the forcing and possible feedback of the hurricane with its environment. With this improved physical understanding, numerical modeling of hurricanes can now produce position forecasts of reasonable accuracy that are becoming competitive with current statistical-dynamical methods. There is a continuing effort to attempt hurricane modification experiments in conjunction with an adequate measurement program.
Abstract
In this paper a simple model of the planetary boundary layer (PBL) is proposed. The surface layer is modeled according to established similarity theory. Above the surface layer a prognostic equation for the mixing length is introduced. The time-dependent mixing length is a function of the PBL characteristics, including the height of the capping inversion, the local friction velocity and the surface heat flux. In a preliminary experiment, the behavior of the PBL is compared with observations from the Great Plains Experiment.
Abstract
In this paper a simple model of the planetary boundary layer (PBL) is proposed. The surface layer is modeled according to established similarity theory. Above the surface layer a prognostic equation for the mixing length is introduced. The time-dependent mixing length is a function of the PBL characteristics, including the height of the capping inversion, the local friction velocity and the surface heat flux. In a preliminary experiment, the behavior of the PBL is compared with observations from the Great Plains Experiment.
Abstract
This paper describes the effect of condensation and evaporation on mesoscale frontal circulations in a two-dimensional numerical model. Utilizing an explicit scheme for the prediction of water vapor, cloud water and rainwater, the model is used to investigate the interactions between convection and the larger-scale environment. The model results are qualitatively compared with results of theoretical and observational studies, including those from the recent Severe Environmental Storms and Mesoscale Experiment-Atmospheric Variability Experiment (SESAME-AVE).
Three major differences are observed in a comparison of the moist and dry simulations: 1) The speed of the upper- and lower-level jets was significantly higher in the moist case, 2) The intensity of the ageostrophic circulations in the moist simulation was much stronger, 3) The vertical velocity field in the moist case was characterized by a banded structure not present in the dry case.
Abstract
This paper describes the effect of condensation and evaporation on mesoscale frontal circulations in a two-dimensional numerical model. Utilizing an explicit scheme for the prediction of water vapor, cloud water and rainwater, the model is used to investigate the interactions between convection and the larger-scale environment. The model results are qualitatively compared with results of theoretical and observational studies, including those from the recent Severe Environmental Storms and Mesoscale Experiment-Atmospheric Variability Experiment (SESAME-AVE).
Three major differences are observed in a comparison of the moist and dry simulations: 1) The speed of the upper- and lower-level jets was significantly higher in the moist case, 2) The intensity of the ageostrophic circulations in the moist simulation was much stronger, 3) The vertical velocity field in the moist case was characterized by a banded structure not present in the dry case.
Abstract
The two-dimensional model simulation of frontogenesis in a moist atmosphere discussed by Hsie and others is used to provide dynamically consistent data for diagnostic calculations to quantify the physical process important in the frontogenesis. The terms in the prognostic equations for the horizontal gradient of potential vorticity, relative vorticity, and static stability are evaluated to indicate the relative importance of confluence, shear, tilting, and frictional and diabatic process in generating these properties of the front. An evaluation of the potential vorticity and equivalent potential vorticity fields and their budgets indicates that symmetric instability is not present in the dry simulation, but occurs in the moist simulation and is associated with the formation of rainbands.
The effect of condensation on the energetics of the frontgenesis is studied by evaluation of the kinetic energy budget. The latent heat of condensation generates available potential energy on the mesoscale and enhances the conversion of zonal available potential energy to eddy available potential energy by enhancing the north-south component of flow across the front. It also enhances the conversion of eddy available potential energy to eddy kinetic energy by producing a stronger direct secondary circulation in the moist simulation.
The diagnostic Sawyer-Eliassen equation is used to partition the forcing responsible for the generation of the ageostrophic secondary circulation. The process that produce this circulation are geostrophic shearing deformation, vertical exchange of heat and momentum, and latent heat release.
The Sawyer-Eliassen diagnostic studies revealed a number of facts concerning the generation of the secondary circulation. The major findings are: 1) The lame-scale features of both the moist and dry ageostrophic circulations are generated by geostrophic deformational forcing; 2) a jet of vertical velocity observed ahead of the surface cold front in the dry simulation is the result of forcing by both deformational and frictional process; 3) the magnitude and structure of the vertical motion field in the moist case are produced primarily by latent heat release; 4) the increase in the horizontal ageostrophic circulation observed in the moist case is due to combined effects of deformation and latent heating; and 5) the turbulent exchange of heat had very little influence on the generation of secondary circulation because of a thermally insulated lower boundary.
Abstract
The two-dimensional model simulation of frontogenesis in a moist atmosphere discussed by Hsie and others is used to provide dynamically consistent data for diagnostic calculations to quantify the physical process important in the frontogenesis. The terms in the prognostic equations for the horizontal gradient of potential vorticity, relative vorticity, and static stability are evaluated to indicate the relative importance of confluence, shear, tilting, and frictional and diabatic process in generating these properties of the front. An evaluation of the potential vorticity and equivalent potential vorticity fields and their budgets indicates that symmetric instability is not present in the dry simulation, but occurs in the moist simulation and is associated with the formation of rainbands.
The effect of condensation on the energetics of the frontgenesis is studied by evaluation of the kinetic energy budget. The latent heat of condensation generates available potential energy on the mesoscale and enhances the conversion of zonal available potential energy to eddy available potential energy by enhancing the north-south component of flow across the front. It also enhances the conversion of eddy available potential energy to eddy kinetic energy by producing a stronger direct secondary circulation in the moist simulation.
The diagnostic Sawyer-Eliassen equation is used to partition the forcing responsible for the generation of the ageostrophic secondary circulation. The process that produce this circulation are geostrophic shearing deformation, vertical exchange of heat and momentum, and latent heat release.
The Sawyer-Eliassen diagnostic studies revealed a number of facts concerning the generation of the secondary circulation. The major findings are: 1) The lame-scale features of both the moist and dry ageostrophic circulations are generated by geostrophic deformational forcing; 2) a jet of vertical velocity observed ahead of the surface cold front in the dry simulation is the result of forcing by both deformational and frictional process; 3) the magnitude and structure of the vertical motion field in the moist case are produced primarily by latent heat release; 4) the increase in the horizontal ageostrophic circulation observed in the moist case is due to combined effects of deformation and latent heating; and 5) the turbulent exchange of heat had very little influence on the generation of secondary circulation because of a thermally insulated lower boundary.
The Three-Cornered Hat Method for Estimating Error Variances of Three or More Atmospheric Datasets. Part I: Overview and EvaluationAbstract
The three-cornered hat (3CH) method, which was originally developed to assess the random errors of atomic clocks, is a means for estimating the error variances of three different datasets. Here we give an overview of the historical development of the 3CH and select other methods for estimating error variances that use either two or three datasets. We discuss similarities and differences between these methods and the 3CH method. This study assesses the sensitivity of the 3CH method to the factors that limit its accuracy, including sample size, outliers, different magnitudes of errors between the datasets, biases, and unknown error correlations. Using simulated datasets for which the errors and their correlations among the datasets are known, this analysis shows the conditions under which the 3CH method provides the most and least accurate estimates. The effect of representativeness errors caused by differences in vertical resolution of datasets is investigated. These representativeness errors are generally small relative to the magnitude of the random errors in the datasets, and the impact of this source of errors can be reduced by appropriate filtering.
Abstract
The three-cornered hat (3CH) method, which was originally developed to assess the random errors of atomic clocks, is a means for estimating the error variances of three different datasets. Here we give an overview of the historical development of the 3CH and select other methods for estimating error variances that use either two or three datasets. We discuss similarities and differences between these methods and the 3CH method. This study assesses the sensitivity of the 3CH method to the factors that limit its accuracy, including sample size, outliers, different magnitudes of errors between the datasets, biases, and unknown error correlations. Using simulated datasets for which the errors and their correlations among the datasets are known, this analysis shows the conditions under which the 3CH method provides the most and least accurate estimates. The effect of representativeness errors caused by differences in vertical resolution of datasets is investigated. These representativeness errors are generally small relative to the magnitude of the random errors in the datasets, and the impact of this source of errors can be reduced by appropriate filtering.
Ducting and Biases of GPS Radio Occultation Bending Angle and Refractivity in the Moist Lower TroposphereAbstract
Radio occultation (RO) can provide high-vertical-resolution thermodynamic soundings of the planetary boundary layer (PBL). However, sharp moisture gradients and strong temperature inversion lead to large gradients in refractivity N and often cause ducting. Ducting results in systematically negative RO N biases resulting from a nonunique Abel inversion problem. Using 8 years (2006–13) of Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) RO soundings and collocated European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-I) data, we confirm that the large lower-tropospheric negative N biases are mainly located in the subtropical eastern oceans and we quantify the contribution of ducting for the first time. The ducting-contributed N biases in the northeast Pacific Ocean (160°–110°W; 15°–45°N) are isolated from other sources of N biases using a two-step geometric-optics simulation. Negative bending angle biases in this region are also observed in COSMIC RO soundings. Both the negative refractivity and bending angle biases in COSMIC soundings mainly lie below ~2 km. Such bending angle biases introduce N biases that are in addition to those caused by ducting. Following the increasing PBL height from the southern California coast westward to Hawaii, centers of maxima bending angles and N biases tilt southwestward. In areas where ducting conditions prevail, ducting is the major cause of the RO N biases. Ducting-induced N biases with reference to ERA-I compose over 70% of the total negative N biases near the southern California coast, where strongest ducting conditions prevail, and decrease southwestward to less than 20% near Hawaii.
Abstract
Radio occultation (RO) can provide high-vertical-resolution thermodynamic soundings of the planetary boundary layer (PBL). However, sharp moisture gradients and strong temperature inversion lead to large gradients in refractivity N and often cause ducting. Ducting results in systematically negative RO N biases resulting from a nonunique Abel inversion problem. Using 8 years (2006–13) of Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) RO soundings and collocated European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-I) data, we confirm that the large lower-tropospheric negative N biases are mainly located in the subtropical eastern oceans and we quantify the contribution of ducting for the first time. The ducting-contributed N biases in the northeast Pacific Ocean (160°–110°W; 15°–45°N) are isolated from other sources of N biases using a two-step geometric-optics simulation. Negative bending angle biases in this region are also observed in COSMIC RO soundings. Both the negative refractivity and bending angle biases in COSMIC soundings mainly lie below ~2 km. Such bending angle biases introduce N biases that are in addition to those caused by ducting. Following the increasing PBL height from the southern California coast westward to Hawaii, centers of maxima bending angles and N biases tilt southwestward. In areas where ducting conditions prevail, ducting is the major cause of the RO N biases. Ducting-induced N biases with reference to ERA-I compose over 70% of the total negative N biases near the southern California coast, where strongest ducting conditions prevail, and decrease southwestward to less than 20% near Hawaii.
The Three-Cornered Hat Method for Estimating Error Variances of Three or More Atmospheric Datasets. Part II: Evaluating Radio Occultation and Radiosonde Observations, Global Model Forecasts, and ReanalysesAbstract
We apply the three-cornered hat (3CH) method to estimate refractivity, bending angle, and specific humidity error variances for a number of datasets widely used in research and/or operations: radiosondes, radio occultation (COSMIC, COSMIC-2), NCEP global forecasts, and nine reanalyses. We use a large number and combinations of datasets to obtain insights into the impact of the error correlations among different datasets that affect 3CH estimates. Error correlations may be caused by actual correlations of errors, representativeness differences, or imperfect collocation of the datasets. We show that the 3CH method discriminates among the datasets and how error statistics of observations compare to state-of-the-art reanalyses and forecasts, as well as reanalyses that do not assimilate satellite data. We explore results for October and November 2006 and 2019 over different latitudinal regions and show error growth of the NCEP forecasts with time. Because of the importance of tropospheric water vapor to weather and climate, we compare error estimates of refractivity for dry and moist atmospheric conditions.
Abstract
We apply the three-cornered hat (3CH) method to estimate refractivity, bending angle, and specific humidity error variances for a number of datasets widely used in research and/or operations: radiosondes, radio occultation (COSMIC, COSMIC-2), NCEP global forecasts, and nine reanalyses. We use a large number and combinations of datasets to obtain insights into the impact of the error correlations among different datasets that affect 3CH estimates. Error correlations may be caused by actual correlations of errors, representativeness differences, or imperfect collocation of the datasets. We show that the 3CH method discriminates among the datasets and how error statistics of observations compare to state-of-the-art reanalyses and forecasts, as well as reanalyses that do not assimilate satellite data. We explore results for October and November 2006 and 2019 over different latitudinal regions and show error growth of the NCEP forecasts with time. Because of the importance of tropospheric water vapor to weather and climate, we compare error estimates of refractivity for dry and moist atmospheric conditions.
