Subcloud Layer Inflow Dynamics Experimental Options
This document is divided into SEVEN sections:
Primary Experiment: Hurricane PBL
This option requires
penetration of convective rainbands at altitudes as low as 450 ft (150 m),
and in regions free of precipitation, flight legs as low as 300 ft (100 m)
may be requested. To meet this requirement all flights must occur in
daylight.
Initial survey
Operation conditions permitting, the first aircraft (AC 1)
departs the base of operations 1 hour before the second aircraft (AC 2).
AC 1 performs the storm survey. The nominal survey pattern is a figure 4
pattern, where the aircraft finds the storm center, passing directly
through the storm to the opposite side on the same heading. Mini-drifting
buoys, GPS-sondes and AXBTs are dropped as indicated in Fig. 12.
The
survey pattern extends 60-90 nmi (110-165 km) from the storm center, and
preferably beyond any suitable rainband targets. AC 1 then turns downwind,
as in Fig. 12. At 3, the aircraft heads through the storm to the opposite
side at 4. By this time, the rainband target should be selected. The
figure-4 survey should be completed even if the target can be selected
after one pass through the storm. On each pass into and out of the storm,
an AXBT and an GPS-sonde are dropped between any rainbands and the eyewall,
preferably in a precipitation-free region. AXBTs are dropped on the
outside of any rainbands encountered in the survey.
Rainband structure
After the target has been chosen, AC 1 proceeds to the
initial point of the second phase, indicated by 5 in Fig. 12, along the
upwind and outside end of the rainband target. At 5, AC 1 performs a
box-sounding (Fig. 13a), clear of most cloud and precipitation, climbing
from 500 to 20,000 ft (150 m to 6 km), or as high as the aircraft can
climb.
After the sounding the aircraft descends to 5,000 ft (1.5 km)
altitude to begin a simultaneous stepped-descent pattern, as illustrated in
Figs. 13b and 14. During this time, AC 2 is approaching the storm, fixing
the storm center if it is between the base of operations and the target
rainband. GPS-sondes should be dropped between the rainband and the
eyewall. The second aircraft should arrive at the rainband by the end of
the AC 1 stepped-descent pattern. AC 2 should attempt a box-sounding (Fig.
13a) on the inner side of the rainband from 500 to 10,000 ft (150 m to 3
km) if it arrives early. Both aircraft then assemble at 5 (AC 1) and 7 (AC
2) for the simultaneous stepped descent pattern as shown in Figs. 13b and
14. Both aircraft should set airborne Doppler radars in F/AST mode and
maintain a distance 5 nmi (10 km) from the edge of the 25-dBZ radar
reflectivity contour.
PBL Structure and Recovery
In some cases, the region between the eyewall
and the major convective rainband may be characterized by suppressed
convective activity, characterized by light precipitation from the anvil of
the eyewall and rainband. If such a region exists on a cross-wind scale of
22 nmi (40 km), AC 1 and AC 2 will conduct detailed cross-wind (CW)
profiles at 30 nmi (55 km) separation, as depicted in Figs. 15 and 16.
These measurements will detect low qe air and map its recovery. The
profile locations should maintain a fixed position relative to the storm
center, but may be changed to stay in the clear.
If secondary rainbands exist in this region such that well-defined
clear regions of 22 nmi (40 km) scale are not present, AC 1 will identify
one or two target convective cells within the band for repeated Doppler box
patterns as given in Fig. 17, with leg lengths of 18 nmi (33 km). The
cells should be followed as they evolve along the band. A box-sounding
(Fig. 13a) from the surface to 500 mb should be executed at 10 after the
Doppler pattern. Upon completion, AC 1 should return home through the
storm center at 5,000 ft (1.5 km).
To complement the rainband momentum transport measurements of AC 1,
AC 2 conducts a high density GPS-sonde sampling pattern between rainbands
in sequence 7-8-9-8-7-8-9, as shown in Fig. 17. Upon completion, AC 2
returns home through the storm center at 5,000 ft (1.5 km) altitude.
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Secondary Experiment: PBL in a decaying EPAC
hurricane
The
objective of the surface wind calibration option is to obtain in-situ
surface wind measurements to compare with the airborne remote-sensing
estimates of surface wind from the SFMR and C-SCAT. These comparisons
should be made under various air-sea temperature difference conditions and
under various wave conditions (fully developed and fetch-limited).
This option involves one aircraft that is equipped with the SFMR
and C-SCAT deploying to La Paz on the Baja Peninsula of Mexico and then
flying a series of three missions into an EPAC hurricane beginning near the
26_C isotherm. Each flight involves a figure-4 pattern, similar to Fig.
12, flown at 5,000 ft (1.5 km) and at 1,000 ft (300 m) AXBTs are dropped
while at 5,000 ft (1.5 km).
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Tertiary Experiment: Calibration of surface wind estimation
techniques
The wind calibration option of this experiment requires one
flight off the east coast of the United States over NOAA buoys prior to the
start of the hurricane season, preferably during the winter in February or
March. One flight should be in strong winds with an easterly component and
fully developed seas, and one flight should be in moderate, off-shore winds
with fetch-limited seas. These flights require one aircraft to depart the
AOC base of operations and pass over selected buoy locations offshore from
Florida to New England and back with options for an overnight stay between
legs.
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Mission Notes
- Operations will be executed in a TC in the Atlantic or
eastern Pacific Oceans, the Caribbean Sea, or the Gulf of Mexico,
preferably within 1 hour (300 nmi [550 km]) of the base of operations.
- The wind calibration option of this experiment would
require one flight off the U.S. east coast over NOAA buoys prior to the
start of the hurricane season, preferably during the winter in February or
March. One flight should be in strong winds with an easterly component and
fully developed seas and one flight should be in moderate, off-shore winds
with fetch-limited seas.
- The primary atmospheric experiment requires penetration of
convective rainbands at altitudes as low as 1,500 ft (450 m), and in
regions free of precipitation, as low as 300 ft (100 m). If this
requirement is to be met, most or all of the flight must occur in daylight.
- To conduct this experiment, both aircraft should have
working lower fuselage, tail, and tail Doppler radars. The standard
flight-level data instrumentation, the SFMR and C-SCAT on 42RF, and the
GPS-sondes and AXBT instrumentation should be operational. Sufficient
GPS-sondes and AXBT's must be carried to perform the drops noted in Figs.
12, 13, and 14. Nose and side-looking video cameras are required.
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