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Hurricane Olivia on radar Radar reflectivity patterns in hurricanes provide a good means for flow visualization even though they represent precipitation, mostly rain, not winds. Descending motion occupies precipitation--free areas, such as the eye. The axis of the cyclone's rotation, here denoted by the hurricane symbol, lies near the center of the eye. The eyewall surrounds the eye. In intense hurricanes, it may contain reflectivities as high as 50 dB(Z), magenta in this picture, equivalent to rainfall rates of 74 mm/h (2.9 in/hr). Less extreme reflectivities--40 dB(Z), red here--characterize most convective rainfall in the eyewall and spiral bands where rainfall rates are 13 mm/h (0.5 in/h). The vertical velocities (both up and downdrafts, although the downdrafts are a little weaker) in convection with highest reflectivity may reach 25 m/s (5000 ft/min), but typical vertical velocities are less than 5 m/s (1000 ft/min). Such intense convection occupies only a small fraction of the hurricane's area. Outside convection, reflectivities are still weaker--30 dB(Z), yellow here--equivalent to 2.4 mm/h (a little less than 0.1 in/h) rain rate. This "stratiform rain" falls out of the anvil cloud that grows from the convection. The spiral bands tend to lie along the friction-layer wind that spirals inward toward the eyewall. The more-circular swirling wind above the friction layer (magenta arrow) blows through the spirals, spreading convective debris downwind.
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