The following describes seven basic flight scenarios (which address
the goals of the TEFLUN-A campaigns.
TEFLUN-A had two aircraft [ER-2 and SPEC Learjet cloud physics
aircraft (CP)] and
flight plans are shown in following seven Flight Scenarios:
The intent here is
to provide a set of flight scenarios
which satisfy the TRMM objectives, but also which operate within the
flight
safety constraints of the aircraft. The flight scenarios presented
are for
three aircraft, with the expectation of situations where ony one or
two
aircraft are available. The three aircraft flight scenarios presented
can be
adjusted for fewer aircraft.
Note that Scenarios 1 to 5 are strongly tied to a precipitation event,
with
effort to maximize coordination with the ground-based measurements,
and
TRMM overpasses. Of highest priority for TRMM FCs is to maximize
coincidence between the satellite, aircraft, and ground-based
measurements. It is
clear that the probability of obtaining ALL these measurements during
a
precipitation event and over the enhanced Texas GV network during
TEFLUN-A.
Decisions will have to be made
on a case by case basis as to whether the available resources will
provide
scientifically important data. Thus, the ER-2 and
CP aircraft may at times be operated independently of a TRMM overpass.
Scenario 6 requires coincidence of the ER-2 and TRMM;
coincidence with other facilities such as the CP and ground-based
radars is
highly desirable. Scenario 7 is radar dependent, i.e., the ER-2
and CP will fly radar radials. For TEFLUN-A, the possible radars are
the
Houston WSR-88D, NOAA AL profiler, X-POL, combination, ADRAD, or if
necessary, another WSR-88D (Corpus Christi, Lake Charles, New
Braunfels, or
Granger).
Safety Concerns:
The flight scenarios presented are
conceptual
and their implementation depends on real-time decisions concerning
aircraft
safety. While TRMM desires measurements within convective and
stratiform
precipitation regions, the CP will not be directed through any
cells with indications of high reflectivities, hail, or strong
updrafts.
The ER-2 may still be directed over intense convection depending on
the
particular case.
Flight Clearances:
Flight clearances may be difficult to
obtain for
some of the flight scenarios, patricularly ones focusing on lower
altitudes.
If flight clearances are not given, then the flight profile may have
to be
modified significantly from that shown in the flight scenario. These
decisions will be made on a real-time basis and may prebent close
coordination
of the aircraft.
Squall Line and Trailing Stratiform
(Scenario 1)
Objectives:
Many MCS's appear as a leading convective line and a trailing
stratiform reagion,
sometines with a transition zone between them. These systems are of
particular
interest to TRMM because the latent heating profiles differ greatly
between
stratiform, convective, and transition regions. Climatology suggests
that this
type of MCS is more common during TEFLUN-A . Combination of
diverse aircraft and surface data sets will help improve model physics
and
understanding the comples relations between clou microphysics,
microwave radiances,
and latent heating. Also, the measurements will enable examination of
issues such
as the relation between cloud electrification, ice mass, updraft
strength,
and 85 GHz grightness tempratures.
The goal of this flight scenario is to provide coverage of the
evolution of the 3-D
structure of a squall line system for model validation, with as many
of the available
supporting observations as possible. The ER-2 will perform lines
normal to the squall
line, covering the convective and stratiform regions. The CP will
perform
coordinated flight lines with the ER-2 when possible due to safety
considerations.
This will most likely involve weak squall lines. CP will collect
microphysical information under the ER-2 . At other times when the
convection is too
strong for safe aircraft operation, the CP will fly a racetrack in the
trailing stratiform reagion. The CP will fly this pattern descending
to lower
altitudes in the stratiform region to collect vertical profiles of
microphysical
information.
Vertical Structure of Stratiform
Rain (Scenario 2)
Objectives:
To determine the microwave emission from the
radar bright band.
The radar and the radiometer communities currently model the
absorption (and
concomitant emission) of the bright band differently. These modeling
approaches are important for physically-based raingall retrievals from
either
the radiometer or the radar on TRMM. But the merit of the different
approaches are not well validated against observations. This flight
module is
aimed at stratiform regions with rain rates of 2-10 mm/hr.
The ER-2 could also participate since it would provide a broader
picture of
the precipitation region.
MCSs with Disorganized Convection
(Scenario 3)
Objectives:
MCSs are often observed which are more complex
than linear squall line
systems. We can expect these in TEFLUN. The goals of
this flight scenario are similar to Scenario 1. The three aircraft
would be
stacked and perform flight lines along the convective cells. The
intensity of
the cells will vary from system to system. There will be situations
where
the convective cells are weak and present no danger to the CP. These
are the preferred situations. There will be other cases where the
individual
convective storms will be too strong for the CP. In these
situations, alternative, safer flight plans will be given for the CP.
The ER-2 may still be requested to fly over the active convective
regions, since
both the radar and radiometer measurements would be most userful.
Isolated Convection (Scenario
4)
Objectives:
The FCs will ideally collect data from thunderstorms in different
stages of
evolution, intensity, and geographical locations. Isolated
thunderstorms may be
present during TEFLUN. Individual thunderstorms are simpler to model
numerically, and it is often easier to obtain representative
environmental
conditions. Often, isolated thunderstorms do not have well developed
anvils or
stratiform regions. Consequently, the latent heating profiles may be
different
than typical tropical systems which have considerable stratiform rain.
Because
thunderstorms often have small dimensions relative to TRMM footprints,
they
can present beamfilling problems for TRMM algorithms. This flight
scenario is
aimed at isolated thunderstorms that are identifiable by the ER-2
pilots and do
not have significant anvil ice present.
The main goal of this scenario is examine the relation between
thunderstorm
evolution, microwave brightness temperatures, vertical structure of
reflectivity
and updrafts, electrical activity, and relative amount of supercooled
water and
large ice aloft, and surface rainfall. This scenario requires
repeated bow tie
flight patterns with short flight legs, covering the evolution of the
thunderstorm.
The CP would fly similar patterns if entry into the convection was
within
safe limits.
Multicellular Convection With
Anvil (Scenario 5)
Objectives:
Multicell thunderstorms have cells in various stages of development
with the
growing cells on the upwind end, and the decaying cells on the
downwind end.
The individual cells have short lifetimes
(approximately 20 minutes), and are occasionally (butmost often not)
intense.
Flights over cells in varying stages of evolution are very important
for TRMM
objectives. The microwave brightness tempratures from which the
vertical
hydrometeor profiles are derived, are highly dependent on the stage of
development
of the cells. Young cells consist mostly of supercooled water above
the freezing
level without significant ice aloft, and rainfall is low. Mature
cells have
significant ice aloft and rainfall. Dissipating cells have highest
rainrates at
the surface with a reduction in ice aloft. And decayed cells move off
into the
anvil. Thus, there can be a time delay between the heaviest rainfall
and the
coldest 85 GHz microwave temperatures measured from above. The 85 GHz
ice
scattering-based channel, is the most useful channel for rain
detection over land.
Cloud microphysics measurements in the ice region are especially
important for
validation of model ice parameterizations, and for determining
radiometric responses.
The flight lines for this scenario are linear tracks over the cells
and anvil
associated with this relatively small system. The three aircraft are
stacked,
and the CP will fly at higher levels (7-10 km). If the cells are weak,
the CP
will fly at multiple altitudes to map out the vertical microphysical
structure.
Underflight of TRMM (Scenario
6)
Objectives:
This scenario is aimed at cordinating the ER-2, and CP with a TRMM
overpass.
Coordination of the aircraft and overpass may require locating away
from the
augmented surface observations and soundings, but possibly within
range of a
WSR-88D. The goal of this scenario is:
- to examine resolution and sensitivity limitations of the PR and
TML, and
- to validate the PR surface refrence (SRT) attenuation correction
(2A-25)
andvariability of the surface scattering cross section,
sigmao.
The EDOP-AMPR combination on the ER-2 provide high-resolution
measurements that can be used to examine (1).
EDPO is an X-band radar which is much less attenuated than ARMAR or
the PR and
it can be used as a reference for the PR corrections.
For this scenario, the aircraft would begin a track a few minutes
before the
projected time of the TRMM overpass at that point so that the time of
coincidence
would be roughly mid-point of the flight line. This is the best
coincidence that
can be obtained given that TRMM is traveling at such a rapid velocity
and the
aircraft are traveling relatively slowly. The TRMM PR swath is about
220 km so
that the flight line can be oriented along the precipitation region
rather than
the TRMM subpoint (the figure shows the aircraft track along the TRMM
subpoint).
The CP would perform an ascent or descent through the region. Both
land-based
and ocean cases are of interest for this scenario, and precipitation
systems which
cover both land and water background are of particular interest.
These measurements
would provide guidance for algorithm improvements for the difficult
case of
land backgrounds.
Range Dependence of GV Rain Rate
Relations (Scenario 7)
Objectives:
The Z-R relations used to convert radar reflectivity to rain rates
have
uncertainties due to their dependence on particle size distributions.
In addition,
the increase in radar beam size with distance from the radar,
introduces further
uncertainty. The size dependence issue will in part be addressed by
flight lines
of the type described in Scenario 2 which are not necessarily tied to
a GV radar.
The goal of the flight lines here are to examine the range dependence
of the Z-R
relations. This scenario will focus on ER-2 flight lines of about
200-300 km
in length directed along radar radials and crossing directly over the
radar. The
ADRAD, X-POL will provide RHIs coordinated with the ER-2 ;
or in the case of the WSR-88D, vertical structure will be
reconstructed along the
aircraft track from PPIs. The CP is highly desirable in the rain
layer at several
levels including the rain region, if possible. The
Doppler/polarization radars on
both the ER-2 can provide some information on the characteristics of
the
rain, but ideally the CP aircraft would provide information on the
particle size
distribution over the radar range interval.
