Advancing Tropical Cyclone Forecasts Using Aircraft Observations - Monitoring and Prediction of Tropical Cyclones in the Indian Ocean and Climate Change - page 168

The aircraft had three main data systems: one for navigational and flight-
level meteorological data, one for radar data, and a third for cloud microphysics
data. Observations were recorded on magnetic tapes, a capability that greatly
aided timely data processing and analysis.
As electronic equipment and expendable probes became more accurate,
smaller, faster, and lighter, new instrumentation enhanced the potential to gather
comprehensive TC research datasets. For example, P-3 instruments now include
the airborne infrared radiation thermometer (AIRT) for remotely determining
flight-level temperature in clear air (Barnes et al., 1991), a stepped frequency
microwave radiometer (SFMR) for estimating surface wind speed (Uhlhorn
and Black, 2003), and Global Positioning System (GPS) navigation. Omega
dropwindsondes (ODWs) (Govind, 1975) were used first in 1982, primarily to
study the TC environment. The GPS dropwindsonde (Hock and Franklin, 1999),
first used in 1996, provided reliable wind and thermodynamic profiles in the
TC eyewall for the first time. Each aircraft also carries a workstation for airborne
data processing and can now transmit crucial data via satellite to the Global
Telecommunications System (Griffin et al., 1992). All of this makes the two
P-3s the most advanced and comprehensive of all meteorological research
aircraft currently in use.
At the beginning of the P-3 era, the TC was considered to be an
axisymmetric vortex with convergence at low levels and divergence high in
the eyewall and rainbands, upward motion within these features, and
compensating subsidence in the eye and outside the vortex. The eyewall was
assumed to be nearly vertical, and horizontal winds were assumed to be constant,
up to midlevels (Simpson, 1952). Observations obtained from the P-3 allowed
for refinement of descriptions of the axisymmetric structure of TCs, and also
for the first understanding of higher-wavenumber features.
Using airborne radar reflectivity data, Jorgensen (1984a, b) provided a
more accurate description of the symmetric eyewall and rainband structure
than was previously available. The largest updrafts were located radially inward
from the wind and reflectivity maxima in the eyewall that slope radially outward
with height (Jorgensen, 1984a). Adjacent rainbands were more cellular than
the eyewall and lacked consistent updrafts and distinct wind speed maxima at
flight level (Jorgensen, 1984a). Jorgensen (1984b) documented the TC eyewall
structural evolution during coordinated eyewall penetrations by the P-3s and a
NOAA C-130. An eyewall radius-height schematic (Fig. 1) from these studies
depicted the eyewall and its associated wind speed maximum, the relative
positions of clouds and radar features, the regions of in- and outflow, and the
location and strength of up- and downdrafts. Although the schematic did not
describe asymmetries, and Marks and Houze (1987) subsequently showed that
the maximum tangential wind was not inside the reflectivity maximum at all
levels, the diagram still is representative of mean mature axisymmetric TC
structure.