The combination of strong swirling winds, high inertial stability, and organized, deep convection distinguish the hurricane eyewall as among the most esoteric of the earth's weather systems. Although the eyewall has been extensively analyzed using in-situ aircraft observations since the 1950's and, in more recent decades, remotely by land-based and airborne Doppler radars, aspects of the structure, thermodynamics, and kinematics of the eyewall remain enigmatic.
The convective structure of the eyewall was once thought to consist of "hot towers" of cumulonimbus clouds embedded with strong updrafts that carry moisture-laden air from near the sea-surface to the upper troposphere. The latent-heat released in these vertically-aligned clouds is thought to be partially responsible for the warm core of the tropical cyclone and extremely low surface pressure near the center.
A more current paradigm considers the eyewall as a ring of convection surrounding the rain-free eye. Within this ring, updrafts are maintained by the latent heat transfer from low-level, inflowing air and exhibit a pronounced outward slope with height, roughly along angular momentum surfaces. The ring model describes the salient, axisymmetric, features of the eyewall including condensational heat sources in the updrafts near the radius of maximum winds that allow the convective ring to contract and, subsequently, lead to storm intensification. In this model, downdrafts are weaker and shallower than the updrafts and are generally located within the high precipitation region beneath the sloping updrafts. Downward motion within the eyewall is thought to contribute little to the intensity changes of a mature storm.
Recent observations of the hurricane eyewall, primarily from airborne Doppler radars and high-resolution dropwindsondes, reveal structure that does not fit the axisymmetric ring model. Among these features are strong, systematic asymmetries in the vertical motion field, shelf-clouds protruding from the eyewall into the eye with dipoles of strong vertical motion, mesovortices, strong and deep downdrafts that originate near the tropopause, and updrafts whose slopes may vary from being nearly upright to as much as 70° from vertical. The purpose of this work is to present some of these unusual and complex features so as to lead toward the goal of a more complete paradigm of the hurricane eyewall.