Rapidly Intensifying Hurricane Guillermo (1997). Part I: Low-Wavenumber Structure and Evolution

The structure and evolution of rapidly intensifying Hurricane Guillermo (1997) is examined using airborne Doppler radar observations. In this first part, the low-azimuthal-wavenumber component of the vortex is presented. Guillermo’s intensification occurred in an environmental flow with 7–8 m s−1 of deep-layer vertical shear. As a consequence of the persistent vertical shear forcing of the vortex, convection was observed primarily in the downshear left quadrant of the storm. The greatest intensification during the ∼6-h Doppler observation period coincided with the formation and cyclonic rotation of several particularly strong convective bursts through the left-of-shear semicircle of the eyewall. Some of the strongest convective bursts were triggered by azimuthally propagating low-wavenumber vorticity asymmetries. Mesoscale budget analyses of axisymmetric angular momentum and relative vorticity within the eyewall are presented to elucidate the mechanisms contributing to Guillermo’s structural evolution during this period. The observations support a developing conceptual model of the rapidly intensifying, vertically sheared hurricane in which shear-forced mesoscale ascent in the downshear eyewall is modulated by internally generated vorticity asymmetries yielding episodes of anomalous intensification.

Stable mass ranges of ν Andromedae planetary system

Doppler observation of extrasolar planets through the radial velocity displacement of their host stars can only determine lower limits of planetary masses. We numerically integrate ν Andromedae planetary orbits with various initial conditions of masses and angle variables to investigate which initial configuration produces stable orbits during the timescale of host star's age. According to our preliminary results starting from Lick dataset, ν Andromedae planetary system seems to remain stable over the timescale of its host star's age if sin i > 0.7 where i is the unknown line-of-sight inclination of planetary orbits. In this case we may estimate that the upper limit masses of ν Andromedae planets in our model is about 1/0.7 ∽ 1.43 times larger than its minimum.