Advancing Tropical Cyclone Forecasts Using Aircraft Observations - Monitoring and Prediction of Tropical Cyclones in the Indian Ocean and Climate Change - page 167

circular, axisymmetric vortex with nearly constant wind speeds extending to
at least 400 hPa, and with deviations from axisymmetry considered to be gusts.
The eyewall was thought to be vertically aligned up to 5-10 km above the
surface and funnel-shaped above. The eye was observed to have warm, moist
air below an inversion, with clear, dry air above and ice clouds streaming inward
near the top. Both the eyewall and rainbands were understood to have convergent
airflow in low levels and outflow above. Rainbands were seen to move inward
toward the eye and to cause intensification of eyewall convection. Numerical
modelling of TCs was limited to idealized two-dimensional studies due to a
lack of adequate computer power and observations of the dynamic and
thermodynamic fields in three dimensions and primitive techniques to assimilate
the data into model initial conditions (Simpson and Riehl, 1981).
Partially as a result of observations from the P-3s, the description and
understanding of TC behaviour and structure has been revolutionized. The
National Hurricane Research Laboratory and its successor, the Hurricane
Research Division (HRD), in collaboration with other governmental, university,
and international partners, conducted missions in over 150 TCs in the Atlantic
and eastern Pacific Oceans and near Australia (Aberson, 2006). Data were
obtained on the micro to synoptic scale, and data analyses have led to many
new insights about TC structure, dynamics, thermodynamics, and environmental
interactions.
Sophisticated instrumentation installed on and developed for the P-3s is
unique among meteorological airborne platforms. At delivery, each P-3 was
outfitted with a wide variety of tools to observe the TC and its environment
(Jorgensen, 1984a). The most advanced meteorological equipment on the P-3s
consisted of three digital radars that are still used. Two record the reflectivity
signal: a 5.5-cm-wave-length [lower fuselage (LF)] radar extends below the
fuselage and measures the horizontal distribution at all azimuth angles; a 3-
cm-wavelength radar is in the tail (TA) and determines the reflectivity
distribution along rays oriented either perpendicular to the aircraft track or at
angles fore and aft within 25° of the aircraft heading. A third radar with a 3.1-
cm wavelength is in the nose and scans horizontally back and forth; the pilots
use it to avoid turbulent weather, and the data have not been recorded since
1987. Important additions to the radar systems first occurred in 1980 when a
prototype Doppler signal processing system was added to the TA radar on one
P-3 (Jorgensen et al., 1983) and again in 1988-89 when refined radar data
systems were installed on both aircraft.
Both P-3s measured flight-level temperature, pressure, and moisture and
had a state-of-the-art inertial navigation system allowing for flight-level wind
speed calculations with 0.1-0.3 m s -1 accuracy. Additionally, both P-3s had 24
chutes in the fuselage for external ejection of airborne expendable bathy-
thermographs (AXBTs) to measure ocean temperature to a depth of ~300 m.
The P-3s also were equipped with Particle Measuring System probes mounted
on the wingtips to distinguish between water and ice particles and estimate
particle size (Black and Hallett, 1986).