Gary M. Barnes

On 1 October 1986, two NOAA WP-3D aircraft were flown in Hurricane Paine as it passed just south of the Baja California Peninsula, providing an opportunity to observe how the category-1 hurricane responded to the presence of a 1200-m-high ridge. Ten fixes of the circulation center and 25 passes through the eyewall show no apparent impact by the peninsula on the track and intensity of Paine. Reflectivity fields reveal a subtle response with a distortion of the eyewall shape and the development of a weak reflectivity zone downwind of the ridge. The minimal response of the hurricane is hypothesized to be due to the large-scale trough in which the hurricane is embedded. Southwest winds inhibit the development of downslope flow from the Baja ridge and the subsequent introduction of this drier air into Paine's inner core.

On 26 August 1998, a NOAA WP-3D aircraft executed a curved track that mimics an inflow trajectory to the eyewall of Hurricane Bonnie. Global positioning system (GPS) sondes and airborne expendable bathythermographs jettisoned along the trajectory provide the observations to conduct an energy budget for the 1600-m-deep inflow to the eyewall. Surface fluxes are estimated via the bulk aerodynamic equations and the flux at the top of the inflow is solved as a residual. From 170- to 125-km radial distance from the circulation center the mean θe of the inflow remains constant despite combined sensible and latent surface fluxes in excess of 500 W m−2. Convective cells remove energy from the inflow boundary layer at a rate similar to the inputs from the sea. From 125 to 100 km, in the annulus adjacent to the eyewall, mean θe increases 4.5 K in response to higher surface fluxes and little loss through the inflow top. Energy balance may be achieved by either entrainment of higher θe through the top of the inflow layer, or by inclusion of just half the estimated heat from viscous dissipation. The authors infer that the secondary circulation of the eyewall inhibits convective cells from forming in this region and thus facilitates the rapid increase of energy in the inflow. The results support hypotheses that hurricane intensity appears to be strongly modulated by energy exchange in a meso-β region adjacent to and under the eyewall.

The evolution of the wind field beyond the radius of maximum winds is studied for 18 Atlantic tropical cyclones (TCs) with 989 research and reconnaissance flight legs. Inner core strength, defined as the storm relative mean tangential wind from 65 to 140 km from the circulation center for a given flight leg, is shown to be linearly correlated with tropical cyclone intensity. Inner core strengthening coincides with deepening, but as a hurricane decays, the inner core may exhibit a wider range of behavior. During an eyewall replacement cycle inner core strength and intensity become out of phase. Inner core strength tends to be axisymmetric as no quadrant maintains a higher inner core strength than the other quadrants for more than a day. Increases of inner core strength occur throughout the entire 65–140-km radial distance and, thus, are not due to the higher winds found in rainbands alone. The authors speculate that inner core strength, being relatively close to the circulation center, responds ef... Abstract The evolution of the wind field beyond the radius of maximum winds is studied for 18 Atlantic tropical cyclones (TCs) with 989 research and reconnaissance flight legs. Inner core strength, defined as the storm relative mean tangential wind from 65 to 140 km from the circulation center for a given flight leg, is shown to be linearly correlated with tropical cyclone intensity. Inner core strengthening coincides with deepening, but as a hurricane decays, the inner core may exhibit a wider range of behavior. During an eyewall replacement cycle inner core strength and intensity become out of phase. Inner core strength tends to be axisymmetric as no quadrant maintains a higher inner core strength than the other quadrants for more than a day. Increases of inner core strength occur throughout the entire 65–140-km radial distance and, thus, are not due to the higher winds found in rainbands alone. The authors speculate that inner core strength, being relatively close to the circulation center, responds ef...

One hundred and thirty Omega dropwindsondes deployed within 500-km radius of the eye of six North Atlantic hurricanes are used to determine the magnitudes and trends in convective available potential energy, and 10–1500-m and 0–6-km shear of the horizontal wind as a function of radius, quadrant, and hurricane intensity. The moist convective instability found at large radii (400–500 km) decreases to near neutral stability by 75 km from the eyewall. Vertical shears increase as radius decreases, but maximum shear values are only one-half of those found over land. Scatter for both the conditional instability and the shear is influenced chiefly by hurricane intensity, but proximity to reflectivity features does modulate the pattern. The ratio of the conditional instability to the shear (bulk Richardson number) indicates that supercell formation is favored within 250 km of the circulation center, but helicity values are below the threshold to support strong waterspouts. The difference between these oce... Abstract One hundred and thirty Omega dropwindsondes deployed within 500-km radius of the eye of six North Atlantic hurricanes are used to determine the magnitudes and trends in convective available potential energy, and 10–1500-m and 0–6-km shear of the horizontal wind as a function of radius, quadrant, and hurricane intensity. The moist convective instability found at large radii (400–500 km) decreases to near neutral stability by 75 km from the eyewall. Vertical shears increase as radius decreases, but maximum shear values are only one-half of those found over land. Scatter for both the conditional instability and the shear is influenced chiefly by hurricane intensity, but proximity to reflectivity features does modulate the pattern. The ratio of the conditional instability to the shear (bulk Richardson number) indicates that supercell formation is favored within 250 km of the circulation center, but helicity values are below the threshold to support strong waterspouts. The difference between these oce...

Heavy rain events (>100 mm day−1) over the southeast flank of Mauna Loa volcano on the island of Hawaii are examined using surface, rawinsonde, rain gauge, and satellite data. The events occur in the presence of four types of synoptic-scale disturbances that include Kona storms, cold fronts, upper-tropospheric troughs, and tropical systems. The heaviest rainfall occurs at elevations above 0.5 km over the volcano slopes facing the prevailing low-level flow with the leeside slopes experiencing considerably smaller amounts. Rainfall duration and patterns demonstrate that the rains and flash floods are the result of more than one convective cell. Soundings prior to the heavy rain events show only modest instability, with only the K index serving as a useful predictor for heavy rain among the standard stability indices. There is an increase in both the moisture content of the midlevels (750–450 mb) and the onshore flow normal to the terrain gradient prior to the heavy rain. The lack of the trade winds... Abstract Heavy rain events (>100 mm day−1) over the southeast flank of Mauna Loa volcano on the island of Hawaii are examined using surface, rawinsonde, rain gauge, and satellite data. The events occur in the presence of four types of synoptic-scale disturbances that include Kona storms, cold fronts, upper-tropospheric troughs, and tropical systems. The heaviest rainfall occurs at elevations above 0.5 km over the volcano slopes facing the prevailing low-level flow with the leeside slopes experiencing considerably smaller amounts. Rainfall duration and patterns demonstrate that the rains and flash floods are the result of more than one convective cell. Soundings prior to the heavy rain events show only modest instability, with only the K index serving as a useful predictor for heavy rain among the standard stability indices. There is an increase in both the moisture content of the midlevels (750–450 mb) and the onshore flow normal to the terrain gradient prior to the heavy rain. The lack of the trade winds...