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- Author or Editor: Edgar G. Pavía x
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Abstract
In this note, a procedure to construct predictors is suggested that could take advantage of the increasing predictive skill of ENSO models. These so-called secondary forecast models (SFM) attempt to produce a forecast for a particular object application based on independent forecasts of ENSO. Although their predictive skill may be modest, these models can provide an alternate and objective forecast to the entirely subjective schemes more widely used. An example of the application of SFM to the forecast of the seasonal precipitation of a typical station of the Mediterranean Californias shows promising results.
Abstract
In this note, a procedure to construct predictors is suggested that could take advantage of the increasing predictive skill of ENSO models. These so-called secondary forecast models (SFM) attempt to produce a forecast for a particular object application based on independent forecasts of ENSO. Although their predictive skill may be modest, these models can provide an alternate and objective forecast to the entirely subjective schemes more widely used. An example of the application of SFM to the forecast of the seasonal precipitation of a typical station of the Mediterranean Californias shows promising results.
Abstract
Unstable, infinitely long filaments, with a front at each side delimiting their width, are studied with the aid of a particle-in-cell numerical model. Two dynamical systems are considered: the shallow-water primitive equations and the frontal-geostrophic approximation. Invariably, the filaments break into a series of disconnected vortices. A case with zero potential vorticity (integrated with the primitive equations) yields a set of elongated eddies, which slightly depart from the main axis. Shape and dealignment from the axis are both due to a surplus in angular momentum, which results from the transition from filament to eddies. Integration with the frontal-geostrophic equations (nonzero potential vorticity) gives qualitatively similar results, but the eddies are less eccentric, and the departure from the axis is more notorious. This latter case is also investigated analytically, verifying the numerical results.
Abstract
Unstable, infinitely long filaments, with a front at each side delimiting their width, are studied with the aid of a particle-in-cell numerical model. Two dynamical systems are considered: the shallow-water primitive equations and the frontal-geostrophic approximation. Invariably, the filaments break into a series of disconnected vortices. A case with zero potential vorticity (integrated with the primitive equations) yields a set of elongated eddies, which slightly depart from the main axis. Shape and dealignment from the axis are both due to a surplus in angular momentum, which results from the transition from filament to eddies. Integration with the frontal-geostrophic equations (nonzero potential vorticity) gives qualitatively similar results, but the eddies are less eccentric, and the departure from the axis is more notorious. This latter case is also investigated analytically, verifying the numerical results.
Abstract
In this work, recent (1948–2001) rainfall data in a southwestern California station (San Diego) and a northwestern Baja California station (Ensenada) within a region called Mediterranean California, around 33°N, 117°W, are studied. Cumulative annual means are used as indicators of climatological variability; but the entire datasets are analyzed by modeling the histogram of each set as a Weibull distribution probability density function, f. The climatology of both stations, defined simply as the arithmetic average, is compared with their theoretical mean; that is, the first moment of f. It is assumed that this comparison would be indicative of the reliability of the available rainfall climatologies.
If these assumptions hold, in particular if the data is indeed Weibull distributed, it can be concluded that the climatological annual mean precipitation in this region is slightly overestimated at this time.
Abstract
In this work, recent (1948–2001) rainfall data in a southwestern California station (San Diego) and a northwestern Baja California station (Ensenada) within a region called Mediterranean California, around 33°N, 117°W, are studied. Cumulative annual means are used as indicators of climatological variability; but the entire datasets are analyzed by modeling the histogram of each set as a Weibull distribution probability density function, f. The climatology of both stations, defined simply as the arithmetic average, is compared with their theoretical mean; that is, the first moment of f. It is assumed that this comparison would be indicative of the reliability of the available rainfall climatologies.
If these assumptions hold, in particular if the data is indeed Weibull distributed, it can be concluded that the climatological annual mean precipitation in this region is slightly overestimated at this time.
Abstract
The purpose of this research is to investigate the evolution of elongated warm eddies. A shallow-water, reduced-gravity, primitive equation model is used to perform a multicase numerical experiment, which includes vortices of very different eccentricities and strengths. The above is partly motivated by the increased number of oceanic observations, performed in recent years, that show the wide variety of warm eddies. Under the assumption that an eddy can be approximately described as a solid-body rotating elliptical vortex, the evolution is followed using a least-squares fitting procedure. Results indicate that the majority of these eddies evolve toward less eccentric states, a process called axisymmetrization. A few of the most elongated eddies break up, and some of the less eccentric ones remain unchanged. Axisymmetrization seems to be triggered by instability and, in the space of the parameters that describe the elliptical vortex, the trajectories followed in each of the cases fairly approximate contours of the conserved quantity q 0 V 1/2, where q 0 is the potential vorticity at the center of the elliptical vortex and V its total volume.
Abstract
The purpose of this research is to investigate the evolution of elongated warm eddies. A shallow-water, reduced-gravity, primitive equation model is used to perform a multicase numerical experiment, which includes vortices of very different eccentricities and strengths. The above is partly motivated by the increased number of oceanic observations, performed in recent years, that show the wide variety of warm eddies. Under the assumption that an eddy can be approximately described as a solid-body rotating elliptical vortex, the evolution is followed using a least-squares fitting procedure. Results indicate that the majority of these eddies evolve toward less eccentric states, a process called axisymmetrization. A few of the most elongated eddies break up, and some of the less eccentric ones remain unchanged. Axisymmetrization seems to be triggered by instability and, in the space of the parameters that describe the elliptical vortex, the trajectories followed in each of the cases fairly approximate contours of the conserved quantity q 0 V 1/2, where q 0 is the potential vorticity at the center of the elliptical vortex and V its total volume.
Abstract
Merging of two anticyclonic vortices is studied in the context of a reduced-gravity model and with emphasis on frontal dynamics. Using a particle-in-cell method, numerical experiments illustrate the merging process and the accompanying Lagrangian motions. In any merger event, three stages can be distinguished. In the first stage, intrusions from each eddy wrap around the other eventually substituting particles of one eddy almost completely with those of the other. The second and rapid stage is the merging per se, leaving a new, elongated eddy. In a prolonged third stage, stabilization of this eddy proceeds with axisymmetrization and rejection of fluid to the surroundings. Such rejection of fluid, which is demonstrated to be essential for the conservation of potential vorticity, energy and angular momentum, proceeds with the formation not of filaments, as in Euler's dynamics, but of satellite vortices. The center eddy may or may not axisymmetric completely, but, in all cases, consists of a thorough mixture of particles from both original eddies.
Other numerical experiments with cyclones and zero–potential-vorticity anticyclones indicate that these vortices are resistant to merging. The impacts of the planetary beta effect and of eddy pulsation on merging are also considered.
Abstract
Merging of two anticyclonic vortices is studied in the context of a reduced-gravity model and with emphasis on frontal dynamics. Using a particle-in-cell method, numerical experiments illustrate the merging process and the accompanying Lagrangian motions. In any merger event, three stages can be distinguished. In the first stage, intrusions from each eddy wrap around the other eventually substituting particles of one eddy almost completely with those of the other. The second and rapid stage is the merging per se, leaving a new, elongated eddy. In a prolonged third stage, stabilization of this eddy proceeds with axisymmetrization and rejection of fluid to the surroundings. Such rejection of fluid, which is demonstrated to be essential for the conservation of potential vorticity, energy and angular momentum, proceeds with the formation not of filaments, as in Euler's dynamics, but of satellite vortices. The center eddy may or may not axisymmetric completely, but, in all cases, consists of a thorough mixture of particles from both original eddies.
Other numerical experiments with cyclones and zero–potential-vorticity anticyclones indicate that these vortices are resistant to merging. The impacts of the planetary beta effect and of eddy pulsation on merging are also considered.
Abstract
The probability distribution of wind speed data over the world's oceans is studied using a two-parameter Weibull distribution. The parameters are estimated following a linearized least-squares approach. The seasonal and latitudinal variation are described. A bootstrap statistical stability criterion is developed to select the appropriate method to estimate the Weibull parameters A and C. The method with the most stable estimate of parameters gives acceptable goodness-of-fit values. The Kolmogorov–Smirnov test also shows that the distribution adequately fits the data.
The seasonal and latitudinal variations are presented using Hovmöller diagrams of the Weibull parameters. In general, these diagrams showed a seasonal change in fair agreement with other independent estimates of wind speed statistics. The results are more reliable in the Northern Hemisphere because more adequate data are available. The uneven geographical distribution and the scarcity of data at high latitudes and the Southern Hemisphere do not permit precise determination of Weibull statistics and remain unsolved problems.
Abstract
The probability distribution of wind speed data over the world's oceans is studied using a two-parameter Weibull distribution. The parameters are estimated following a linearized least-squares approach. The seasonal and latitudinal variation are described. A bootstrap statistical stability criterion is developed to select the appropriate method to estimate the Weibull parameters A and C. The method with the most stable estimate of parameters gives acceptable goodness-of-fit values. The Kolmogorov–Smirnov test also shows that the distribution adequately fits the data.
The seasonal and latitudinal variations are presented using Hovmöller diagrams of the Weibull parameters. In general, these diagrams showed a seasonal change in fair agreement with other independent estimates of wind speed statistics. The results are more reliable in the Northern Hemisphere because more adequate data are available. The uneven geographical distribution and the scarcity of data at high latitudes and the Southern Hemisphere do not permit precise determination of Weibull statistics and remain unsolved problems.
Abstract
The role of the Pacific decadal oscillation (PDO) in El Niño–Southern Oscillation (ENSO)-related Mexican climate anomalies during winter and summer is investigated. The precipitation and mean temperature data of approximately 1000 stations throughout Mexico are considered. After sorting ENSO events by warm phase (El Niño) and cold phase (La Niña) and prevailing PDO phase: warm or high (HiPDO) and cold or low (LoPDO), the authors found the following: 1) For precipitation, El Niño favors wet conditions during summers of LoPDO and during winters of HiPDO. 2) For mean temperature, cooler conditions are favored during La Niña summers and during El Niño winters, regardless of the PDO phase; however, warmer conditions are favored by the HiPDO during El Niño summers.
Abstract
The role of the Pacific decadal oscillation (PDO) in El Niño–Southern Oscillation (ENSO)-related Mexican climate anomalies during winter and summer is investigated. The precipitation and mean temperature data of approximately 1000 stations throughout Mexico are considered. After sorting ENSO events by warm phase (El Niño) and cold phase (La Niña) and prevailing PDO phase: warm or high (HiPDO) and cold or low (LoPDO), the authors found the following: 1) For precipitation, El Niño favors wet conditions during summers of LoPDO and during winters of HiPDO. 2) For mean temperature, cooler conditions are favored during La Niña summers and during El Niño winters, regardless of the PDO phase; however, warmer conditions are favored by the HiPDO during El Niño summers.
