As a warm-core vortex, the cyclonic circulation of a tropical cyclone weakens with height. In a mature tropical cyclone, the peak winds occur in the lowest kilometer of the atmosphere. The intensity and areal extent of the cyclonic wind field decreases with altitude. In most text-book illustrations, the cyclonic flow region of the tropical cyclone is shown to decrease in size as one ascends to the upper troposphere, and in the outflow layer (above 200 hPa) the flow is depicted as predominantly anticyclonic.
An examination of soundings from islands of the western North Pacific, vertical wind profiles in tropical cyclones obtained from Doppler radars located on Guam and Kwajalein, and water-vapror winds from the University of Wisconsin, have been collected during the lifetimes of several very intense tropical cyclones occurring in the western North Pacific. These data reveal that the extent of cyclonic circulation at upper levels is far more extensive than is commonly depicted, and that the signature bands and plumes of anticyclonically curved cirrus surrounding these tropical cyclones (which are usually interpreted as evidence of anticyclonic outflow aloft) are not indicative of anticyclonic flow; but rather, they exist in cyclonically curved flow for several hundered kilometers outward from the tropical cyclone core. They propagate outward and derive their curvature from horizontal shear.
Outflow jets -- often referred to as outflow channels -- (another feature commonly thought to exist in the upper tropospheric flow surrounding tropical cyclones) are not found in our data set. Rather, broad areas of flow with an outward-directed radial component (with respect to the cyclone center) nearly encircle the tropical cyclone and may be enhanced somewhat in regions no smaller than a full quadrant of azimuth (in earth-relative coordinates). In storm-relative coordinates, the radially directed outward flow is more symmetrical, and exhibits even less azimuthal concentrations of outflow.
High-speed jet streaks existing at the periphery of tropical cyclones (usually marked by long plumes of cirrus) have no concentrated links to the tropical cyclone's core. Indeed, all air flow directed outward at upper levels from the tropical cyclone core must cross a velocity minimum before it accelerates and enters these peripheral jets.
Some common tropical cyclone outflow patterns emerge from our data. They show that common operational estimation of tropical cyclone outflow from satellite imagery (e.g., the regions of good or poor outflow, and the location of outflow jets (or channels)) is flawed