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Abstract
A two-dimensional wind field analysis technique based upon the objective analyses of vorticity and divergence obtained by the Bellamy method is defined. Point values of vorticity and divergence are approximated from line integrals around triangles (neighboring wind observations define vertices of the triangles). A one-scan anisotropic influence radius is incorporated to obtain grid-point estimates of vorticity and divergence. Streamfunction (ψ) and velocity potential (χ) are relaxed from vorticity and divergence fields and the total wind vector is defined by the derivatives of ψ and χ. In situations where temperature and wind are in quasi-balance, temperature fields may also be obtained by solving the balance equation.
By analyzing vorticity and divergence, this procedure has the advantage of explicitly defining perturbations in the wind field. Constraints upon the first derivatives of wind velocity are not required since the differentiated quantities are analyzed. The technique has maximum applicability in the tropics or under other weak geopotential gradient conditions where the relative error of observed temperature typically is large.
The technique is applied to a summertime weak-gradient situation over the United States and the results are compared to those obtained from a subjective analysis. A second case, for the extraordinary severe weather situation of 3 April 1974, is also examined. Results indicate the technique is capable of resolving subsynoptic-scale systems that likely play an important role in organizing convection.
Abstract
A two-dimensional wind field analysis technique based upon the objective analyses of vorticity and divergence obtained by the Bellamy method is defined. Point values of vorticity and divergence are approximated from line integrals around triangles (neighboring wind observations define vertices of the triangles). A one-scan anisotropic influence radius is incorporated to obtain grid-point estimates of vorticity and divergence. Streamfunction (ψ) and velocity potential (χ) are relaxed from vorticity and divergence fields and the total wind vector is defined by the derivatives of ψ and χ. In situations where temperature and wind are in quasi-balance, temperature fields may also be obtained by solving the balance equation.
By analyzing vorticity and divergence, this procedure has the advantage of explicitly defining perturbations in the wind field. Constraints upon the first derivatives of wind velocity are not required since the differentiated quantities are analyzed. The technique has maximum applicability in the tropics or under other weak geopotential gradient conditions where the relative error of observed temperature typically is large.
The technique is applied to a summertime weak-gradient situation over the United States and the results are compared to those obtained from a subjective analysis. A second case, for the extraordinary severe weather situation of 3 April 1974, is also examined. Results indicate the technique is capable of resolving subsynoptic-scale systems that likely play an important role in organizing convection.
Nimbus IV radiance measurements in the 10.5–12.5-μm window channel from the tropical Atlantic during July and August 1970 are studied. The relative frequency of cold, and presumably high clouds, is determined. The average spatial distribution of equivalent black-body temperatures associated with 38 cloud clusters is reported. Ship cloud and weather observations are studied in conjunction with the satellite data. By combining the evidence provided by the satellite and ship observations, a model of typical clouds and weather associated with cloud clusters is proposed for further study.
Nimbus IV radiance measurements in the 10.5–12.5-μm window channel from the tropical Atlantic during July and August 1970 are studied. The relative frequency of cold, and presumably high clouds, is determined. The average spatial distribution of equivalent black-body temperatures associated with 38 cloud clusters is reported. Ship cloud and weather observations are studied in conjunction with the satellite data. By combining the evidence provided by the satellite and ship observations, a model of typical clouds and weather associated with cloud clusters is proposed for further study.
Abstract
In Part 1 of the two-part paper, we present an analysis of a portion of a tropical wave in the BOMEX Phase IV ship network on a much smaller sale than normally attempted using conventional observations and data from a number of research aircraft. The results indicate the existence of a strong mesoscale cyclone with a lifetime of less than 12 h within the synoptic-scale wave. At the time of maximum data density, the analysis time, the system was near its maximum intensity.
Abstract
In Part 1 of the two-part paper, we present an analysis of a portion of a tropical wave in the BOMEX Phase IV ship network on a much smaller sale than normally attempted using conventional observations and data from a number of research aircraft. The results indicate the existence of a strong mesoscale cyclone with a lifetime of less than 12 h within the synoptic-scale wave. At the time of maximum data density, the analysis time, the system was near its maximum intensity.
Abstract
In Part 2 of the two-part paper, scale interaction between the large-scale wave and the BOMEX 26 July 1969 mesoscale system, is examined, primarily through the means of divergence, vertical motion, and mass flux computations.
The mesoscale system was the dominant feature of most of the computational area. Vertical motions in the mesoscale system were an order of magnitude greater than those associated with the synoptic-scale wave. Compensatory sinking around the mesoscale system overwhelmed the synoptic-scale ascent. The integrated vertical mass flux in the mesoscale system was comparable to that produced by the synoptic-scale wave.
A comparison is drawn between the 26 July mesoscale system and previously described tropical systems of similar short lifetimes. It is suggested that for small-scale systems to continue to intensify, a correspondingly strong concurrent large-scale forcing is a prerequisite.
Abstract
In Part 2 of the two-part paper, scale interaction between the large-scale wave and the BOMEX 26 July 1969 mesoscale system, is examined, primarily through the means of divergence, vertical motion, and mass flux computations.
The mesoscale system was the dominant feature of most of the computational area. Vertical motions in the mesoscale system were an order of magnitude greater than those associated with the synoptic-scale wave. Compensatory sinking around the mesoscale system overwhelmed the synoptic-scale ascent. The integrated vertical mass flux in the mesoscale system was comparable to that produced by the synoptic-scale wave.
A comparison is drawn between the 26 July mesoscale system and previously described tropical systems of similar short lifetimes. It is suggested that for small-scale systems to continue to intensify, a correspondingly strong concurrent large-scale forcing is a prerequisite.
