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- Author or Editor: Deanna A. Hence x
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Abstract
Statistical analysis of the vertical structure of radar echoes in the eyewalls of tropical cyclones, shown by the Tropical Rainfall Measurement Mission (TRMM) Precipitation Radar (PR), shows that the eyewall contains high reflectivities and high echo tops, with deeper and more intense but highly intermittent echo perturbations superimposed on the basic structure. The overall echo strength, height of echo top, and presence of intense echo perturbations all increase with vortex strength. Intense echo perturbations decrease in frequency with low sea surface temperatures. When the PR data are normalized by the amount of radar echo in each sample and examined quadrant by quadrant relative to the direction of the environmental shear, the nature of convective processes in different parts of the eyewall becomes apparent. The normalized statistics of the echo intensity, brightband structure, and maximum echo-top height show that processes generating convective precipitation are generally favored in the downshear-right region of the eyewall, while the nonnormalized statistics indicate that the vertical wind shear determines the placement of precipitation particles downwind of the generation zone such that the precipitation maximum occurs about one quadrant downwind of the convective generation zone. When the track speed exceeds the magnitude of the shear vector, this pattern modifies such that the asymmetry rotates one quadrant to the right. The statistics, moreover, indicate that vertical wind shear is the factor determining the placement of precipitation particles around the storm, while other factors determine the location, intensity, and means of their generation.
Abstract
Statistical analysis of the vertical structure of radar echoes in the eyewalls of tropical cyclones, shown by the Tropical Rainfall Measurement Mission (TRMM) Precipitation Radar (PR), shows that the eyewall contains high reflectivities and high echo tops, with deeper and more intense but highly intermittent echo perturbations superimposed on the basic structure. The overall echo strength, height of echo top, and presence of intense echo perturbations all increase with vortex strength. Intense echo perturbations decrease in frequency with low sea surface temperatures. When the PR data are normalized by the amount of radar echo in each sample and examined quadrant by quadrant relative to the direction of the environmental shear, the nature of convective processes in different parts of the eyewall becomes apparent. The normalized statistics of the echo intensity, brightband structure, and maximum echo-top height show that processes generating convective precipitation are generally favored in the downshear-right region of the eyewall, while the nonnormalized statistics indicate that the vertical wind shear determines the placement of precipitation particles downwind of the generation zone such that the precipitation maximum occurs about one quadrant downwind of the convective generation zone. When the track speed exceeds the magnitude of the shear vector, this pattern modifies such that the asymmetry rotates one quadrant to the right. The statistics, moreover, indicate that vertical wind shear is the factor determining the placement of precipitation particles around the storm, while other factors determine the location, intensity, and means of their generation.
Abstract
Ten years of data from the Tropical Rainfall Measurement Mission satellite’s Precipitation Radar are analyzed to determine the typical vertical structure of the concentric eyewalls of tropical cyclones undergoing eyewall replacement. The vertical structure of the secondary (outer) eyewall is different from the primary (inner) eyewall and also different from the eyewall of single eyewall storms. The upper-troposphere portions of the outer eyewalls are like the rainbands from which they evolve. Their lower-tropospheric portions are more intense and more uniform than rainbands of single eyewall storms, suggesting that these secondary eyewalls are forming from rainbands undergoing axisymmetrization and building from below. The inner concentric eyewalls are more strongly affected by shear than are the eyewalls of single eyewall storms, while the outer eyewalls are relatively unaffected by shear, which suggests the outer eyewall is amplifying the shear-induced asymmetry of the inner eyewall.
Abstract
Ten years of data from the Tropical Rainfall Measurement Mission satellite’s Precipitation Radar are analyzed to determine the typical vertical structure of the concentric eyewalls of tropical cyclones undergoing eyewall replacement. The vertical structure of the secondary (outer) eyewall is different from the primary (inner) eyewall and also different from the eyewall of single eyewall storms. The upper-troposphere portions of the outer eyewalls are like the rainbands from which they evolve. Their lower-tropospheric portions are more intense and more uniform than rainbands of single eyewall storms, suggesting that these secondary eyewalls are forming from rainbands undergoing axisymmetrization and building from below. The inner concentric eyewalls are more strongly affected by shear than are the eyewalls of single eyewall storms, while the outer eyewalls are relatively unaffected by shear, which suggests the outer eyewall is amplifying the shear-induced asymmetry of the inner eyewall.
Abstract
Ten years of data from the Tropical Rainfall Measurement Mission satellite’s Precipitation Radar (TRMM PR) show the vertical structure of tropical cyclone rainbands. Radar-echo statistics show that rainbands have a two-layered structure, with distinct modes separated by the melting layer. The ice layer is a combination of particles imported from the eyewall and ice left aloft as convective cells collapse. This layering is most pronounced in the inner region of the storm, and the layering is enhanced by storm strength. The inner-region rainbands are vertically confined by outflow from the eyewall but nevertheless are a combination of strong embedded convective cells and robust stratiform precipitation, both of which become more pronounced in stronger cyclones.
Changes in rainband coverage, vertical structure, and the amount of active convection indicate a change in the nature of rainbands between the regions inward and outward of a radius of approximately 200 km. Beyond this radius, rainbands consist of more sparsely distributed precipitation that is more convective in nature than that of the inner-region rainbands, and the outer-region rainband structures are relatively insensitive to changes in storm intensity. The rainbands in both inner and outer regions are organized with respect to the environmental wind shear vector. The right-of-shear quadrants contain newer convection while in the left-of-shear quadrants the radar echoes are predominantly stratiform. This asymmetric distribution of rainband structures strengthens with environmental wind shear. Cool sea surfaces discourage rainband convection uniformly.
Abstract
Ten years of data from the Tropical Rainfall Measurement Mission satellite’s Precipitation Radar (TRMM PR) show the vertical structure of tropical cyclone rainbands. Radar-echo statistics show that rainbands have a two-layered structure, with distinct modes separated by the melting layer. The ice layer is a combination of particles imported from the eyewall and ice left aloft as convective cells collapse. This layering is most pronounced in the inner region of the storm, and the layering is enhanced by storm strength. The inner-region rainbands are vertically confined by outflow from the eyewall but nevertheless are a combination of strong embedded convective cells and robust stratiform precipitation, both of which become more pronounced in stronger cyclones.
Changes in rainband coverage, vertical structure, and the amount of active convection indicate a change in the nature of rainbands between the regions inward and outward of a radius of approximately 200 km. Beyond this radius, rainbands consist of more sparsely distributed precipitation that is more convective in nature than that of the inner-region rainbands, and the outer-region rainband structures are relatively insensitive to changes in storm intensity. The rainbands in both inner and outer regions are organized with respect to the environmental wind shear vector. The right-of-shear quadrants contain newer convection while in the left-of-shear quadrants the radar echoes are predominantly stratiform. This asymmetric distribution of rainband structures strengthens with environmental wind shear. Cool sea surfaces discourage rainband convection uniformly.
