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David P. Jorgensen
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David P. Jorgensen
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David P. Jorgensen
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David P. Jorgensen
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David P. Jorgensen
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David P. Jorgensen
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David P. Jorgensen
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David P. Jorgensen
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David P. Jorgensen

Abstract

The eyewall structure of Hurricane Alien is examined from analyses of multiple aircraft data on two days, 5 and 8 August 1980. These data sets are unique in that, for the first time, three instrumented aircraft executed coordinated radial penetrations of the eyewall at multiple levels. The data collected on 5 August illustrate the persistence of various features on horizontal scales > 10 km over several hours. Composite cross sections constructed from the 8 August data show similar structure, although the eye diameter had decreased to less than half that of 5 August.

The convergence of air in the eyewall was highly two-dimensional. This convergence supported organized ascent that was along the inner edge of the high reflectivity region and displaced inward several kilometers from the radius of maximum wind (RMW). A mean eyewall updraft of 5–6 m s−1 is computed from integration of the two-dimensional continuity equation. Embedded within the two-dimensional eyewall were cores of high reflectivity that were 2–5 km in diameter, three-dimensional, and generally not traceable from pass to pass (∼20 min intervals). These convective-scale entities had highest updraft velocities of 7–9 m s−1. Upward mass flux in the eyewall was 4–5 times greater than that diagnosed by Zipser and others for a GATE slow-moving convective line. This greater mass flux was accomplished not through larger vertical velocities within convective cares, but by a greater area covered by active updrafts within the low-level convergence zone.

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Nick Guy and David P. Jorgensen

Abstract

This study presents characteristics of convective systems observed during the Dynamics of the Madden–Julian oscillation (DYNAMO) experiment by the instrumented NOAA WP-3D aircraft. Nine separate missions, with a focus on observing mesoscale convective systems (MCSs), were executed to obtain data in the active and inactive phase of a Madden–Julian oscillation (MJO) in the Indian Ocean. Doppler radar and in situ thermodynamic data are used to contrast the convective system characteristics during the evolution of the MJO. Isolated convection was prominent during the inactive phases of the MJO, with deepening convection during the onset of the MJO. During the MJO peak, convection and stratiform precipitation became more widespread. A larger population of deep convective elements led to a larger area of stratiform precipitation. As the MJO decayed, convective system top heights increased, though the number of convective systems decreased, eventually transitioning back to isolated convection. A distinct shift of echo top heights and contoured frequency-by-altitude diagram distributions of radar reflectivity and vertical wind speed indicated that some mesoscale characteristics were coupled to the MJO phase. Convective characteristics in the climatological initiation region (Indian Ocean) were also apparent. Comparison to results from the Tropical Ocean and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) in the western Pacific indicated that DYNAMO MCSs were linearly organized more parallel to the low-level shear and without strong cold pools than in TOGA COARE. Three-dimensional MCS airflow also showed a different dynamical structure, with a lack of the descending rear inflow present in shear perpendicularly organized TOGA COARE MCSs. Weaker, but deeper updrafts were observed in DYNAMO.

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