Typhoon Structural Evolution

Abstract : Typhoon flight data from 750 aircraft reconnaissance missions into 101 named tropical cyclones of the northwestern Pacific Ocean are examined to study its changing life cycle structure. Flights were conducted at 700 mb. Life cycle changes are typified by three phases: 1) the entire vortex wind field builds as the cyclone intensifies to maximum intensity; 2) cyclone central pressure fills and maximum winds decrease in association with an expanding cyclone size and strengthening of the outer core (1 degree to 2.5 degree radius) winds; and 3) the entire vortex windfield decays. Aircraft radar reports of eyewall diameter are used to augment analysis of the typhoon's life cycle. The eye's character and diameter appear to reflect the ease with which the maximum wind field intensifies. On average, the eye first appears with intensifying cyclones at 980 mb central pressure. Cyclones which obtain an eye at a pressure high than 980 mb intensify more rapidly, while those whose eye initially appears at lower pressures deepen at slower rates and typically do not achieve as deep a central pressure. The eye generally contracts with intensification and expands as the cyclone fills. By removing the symmetric portion of the tangential wind field of the vortex and the cyclone motion vector, the residual asymmetric wind flow in the cyclone's interior region (0-2.5 degree radius) can be studied for many different cyclone behavioral stratifications. Tropical cyclones are observed to move faster and to the left of the mean 700 mb current core wind field.