**Experiments**

**1.Tropical Cyclogenesis Experiment**

**[Program Significance and Background]{.underline}**

While forecasts of tropical cyclone track have shown significant
improvements in recent years (Aberson 2001), corresponding improvements
in forecasts of tropical cyclone intensity have been much slower
(DeMaria and Gross 2003). The lack of improvement in intensity
forecasting is the result of deficiencies in the numerical models (e.g.,
resolution limitation and parameterization inadequacies), deficiencies
in the observations, and deficiencies in our basic understanding of the
physical processes involved. The problem becomes even more acute for
forecasting tropical cyclogenesis. While global models have shown some
skill in recent years in predicting tropical cyclogenesis, our
understanding of the physical processes involved remains limited,
largely because observing genesis events is a difficult task. However, a
key aspect of the NOAA Intensity Forecasting Experiment (IFEX) is the
collection of observations during all portions of a tropical cyclone's
lifecycle. This emphasis on all stages of the lifecycle, including the
genesis stage, will provide an opportunity to observe several genesis
events and improve our understanding of this key process.

Tropical cyclogenesis can be viewed as a rapid increase of low-level
cyclonic vorticity organized on the mesoscale within a region of
enhanced convective activity. Numerous hypotheses have been advanced in
the literature to explain how this vorticity develops and amplifies. One
set of theories places primary focus on the dynamical fields as playing
the dominant role in genesis. For example, observations of multiple
midlevel vortices prior to genesis have led some to view the genesis
process as a stochastic one whereby chance merger and axisymmetrization
of these midlevel vortices leads to growth of the circulation to the
surface (Ritchie et al reference?). Another theory emphasizes the role
of a parent midlevel vortex in axisymmetrizing nearby low-level
convectively-generated cyclonic vorticity, leading to spin-up of the
surface circulation (Montgomery and Enagonio 1998; Davis and Bosart
2001; Montgomery et al 2004). Another set of theories emphasizes the
importance of changes in the thermodynamic fields in explaining genesis.
These theories focus on the reduction of the effective static stability
to low values in the core of the incipient cyclone. Suppression of
convectively-induced downdrafts is one means of accomplishing this
(Emanuel 1995; Raymond, Lopez, and Lopez 1998). Eliminating low-level
outflows produced by the downdrafts allows the inflow of updraft air to
spin up the low-level circulation, leading to the development of the
warm-core characteristic of the tropical cyclone. In another theory
related to the role of downdrafts in determining genesis potential,
downdrafts driven by evaporational cooling advect the vorticity of the
midlevel vortex downward, enhancing convection and low-level vorticity
production (Bister and Emanuel 1997). A third group of theories
highlights the combined importance of the dynamic and thermodynamic
fields by emphasizing the role the midlevel vortex and high midlevel
humidity play in providing a favorably-reduced local Rossby radius of
deformation to retain the heating from convective bursts and spin up
low-level vorticity through low-level stretching caused by the
convective heating (Chen and Frank 1993; Rogers and Fritsch 2001). The
purpose of the proposed experiment is to elucidate what role the dynamic
(e.g., low- and mid-level vortices) and thermodynamic (e.g., static
stability, humidity profiles) fields play in governing tropical
cyclogenesis.

Recent observations from airborne Doppler radar have identified
important processes on the mesoscale that contribute to tropical
cyclogenesis. For example, results obtained from a WP-3D aircraft
investigation of Dolly (1996) indicate its genesis was strongly
influenced by persistent, deep convection in the form of mesoscale
convective systems (MCSs) that developed in association with an easterly
wave over the Caribbean. Within this deep convection an eye-like feature
formed, after which time the system was declared a depression. The
initial development of the low-level circulation in both Dolly (1996)
and Guillermo (1991) occurred in the presence of multiple midlevel
vortices. The close proximity of the low- and mid-level vorticity maxima
(often within 50-100 km horizontally) observed in these two genesis
cases supports a further examination of the aforementioned vortex merger
ideas. To adequately diagnose the role of these vortices, it is vital
that they be sampled in their entirety (which will invariably depend on
the distribution of precipitation scatterers) and with a temporal
resolution that allows time continuity of the vortices to be established
when possible.

In addition to the wind and rainfall measurements provided by the
Doppler radars, measurements of temperature and moisture are vital to
address the thermodynamic issues described above. Dropsondes released in
a regular grid will enable the determination of thermodynamic fields in
the vicinity of the incipient system, as well as enable the calculation
of mean divergence and vorticity fields around the system, important in
determining the strength and depth of the downdrafts (provided time
aliasing is minimized). The dropsondes should be released from as high
an altitude as possible to provide observations of mid-level humidity
and winds where scatterers are not present. The tail radars on the P-3's
will also enable a determination of the presence of saturation when
scatterers are observed.

Since both tropical cyclogenesis and tropical cyclone intensity change
can be defined by changes in low- and mid-level vorticity, knowledge of
the processes that play a significant role in genesis will also advance
our understanding of intensity change. A better understanding of the
processes that lead to an increase in low- and mid-level cyclonic
vorticity will also allow NHC to better monitor and forecast tropical
cyclogenesis and intensity change, improvements that would be especially
valuable for those events that threaten coastal areas. Data obtained by
aircraft investigating potential genesis events will positively impact
operations and research in other ways as well. The collection of
three-dimensional data at all stages in a tropical cyclone's lifecycle
is one of the key requirements for NCEP as a part of the IFEX
experiment. Such data will provide information that will guide the
development of balance assumptions and error covariance matrices
important in the development of data assimilation schemes for models
(i.e., HWRF) that will be used in these environments. They will also
provide important datasets for evaluating the performance of HWRF. In
addition to improving the understanding and forecasting of tropical
cyclogenesis and intensity change, the proposed experiment will yield
useful insight into the structure, growth and ultimately the
predictability of the systems responsible for almost all of the
weather-related destruction in the tropical Atlantic and East Pacific.
Investigation of systems that fail to complete the genesis process will
also result in a better understanding and prediction of easterly
disturbances in general so that distinction can be better made between
developing and non-developing tropical disturbances.

**[Objectives]{.underline}**

In keeping with the discussions above, the objectives of this experiment
are as follows:

-   Develop means for identifying likely candidates for tropical
    cyclogenesis and techniques for finding and tracking low- and
    mid-level vortices within these candidates.

-   Investigate role, if any, that midlevel vortex plays in organizing
    deep convection.

-   Document the development of low-level vorticity in the presence of a
    midlevel vortex center.

-   Study the interactions between low- and mid-level vortices in
    pre-genesis environments.

-   Determine the importance of static stability decreases through
    downdraft suppression in tropical cyclogenesis.

-   Study the role of humidity profiles and static stability in
    governing downdraft morphology and vortex response to convective
    heating.

**[Mission Description]{.underline}**

This experiment may be executed with aircraft from NOAA alone, or NOAA
in cooperation with the NASA ER-2 aircraft flying into pre-genesis and
incipient tropical disturbances over the western Caribbean Sea, Gulf of
Mexico, and tropical eastern North Pacific Ocean. The P-3's will be
based in San Jose, Costa Rica and Acapulco, Mexico. For missions flown
in conjunction with the NASA ER-2, the P-3's will operate out of San
Jose. The systems flown here will primarily be incipient systems. If a
system undergoes genesis and continues to develop, however, the P-3's my
fly the system from San Jose and recover in Acapulco. Flights into the
system will continue from Acapulco while it is still in range for the
P-3's. When the system reaches its mature stage, it will fly the
single-aircraft mature storm pattern (see Mature Storm Experiment in
this Field Program Plan) out of Acapulco. If the system has the
potential for decaying over the sea-surface temperature front in the
East Pacific, the Decay Experiment will be flown (see Decay Experiment
in this Field Program Plan).

The primary mission will require two WP-3Ds flying back-to-back
missions. They will fly mesoscale survey patterns designed to document
any suspected low- and mid-level vortices and sample any changes in the
low- and mid-level thermodynamic fields associated with the incipient
systems. Crucial to a complete understanding of the genesis process is
the collection of observations with high temporal and spatial
resolution. Therefore, the staggered WP-3D missions are designed to
commence on station at midnight (12 AM) local and again on station at
noon (12 PM) local.

If available, the G-IV aircraft would fly simultaneously at upper levels
(42,000 ft or 175 mb) and collect observations to a distance of \~1500
km from the center of the disturbance. This G-IV mission would only
occur if operations happened in the Western Caribbean and there were
indications of mid- or low-level dry air in the vicinity of the
disturbance. The G-IV would operate coincident with the afternoon P-3
flight. The ER-2 can fly at very high altitudes (around 65,000 ft or
less than 100 mb), measuring Doppler vertical velocities, reflectivity,
temperature, and humidity along flight legs sometimes coordinated with
the P-3's.

The main aircraft for the mesoscale flights will be the two WP-3Ds.
Doppler radar observations, GPS-sondes, and flight level observations
obtained during these flights will help locate low- and mid-level
vortices and help document their structures and life cycles. Primary
aspects of this experiment will be to observe the complete life cycle
and interaction of low- and mid-level vortices, understand how these
vortices are influenced by the diurnal cycle of convection, and observe
the evolution of the thermodynamic fields as the incipient system
evolves. The location of persistent areas of deep convection and
candidate vortices will be determined using high-resolution visible and
infrared GOES-winds produced available online. Additionally, favorable
large-scale environments for deep convection and vortex development,
such as those described in the Introduction, will be identified using
water vapor loops, model analysis fields enhanced by satellite winds,
and QuikScat imagery, also available online. \[\[\[\[OTHER PRODUCTS FOR
DETERMINING THIS?\]\]\]\]

Staggered missions with the two WP-3D aircraft will begin with the
aircraft flying one of two survey patterns at 14,000 ft (4 km). The
primary purpose of these patterns will be to collect F/AST Doppler radar
and GPS-sonde data in the area of deep convection in order to map the
evolution of the three-dimensional wind and thermodynamic structure of
the deep convection and incipient vortex. Two possible patterns can be
flown, with the decision of which pattern determined by the degree of
organization of the system. For incipient systems that are relatively
disorganized, a sawtooth pattern is flown (Fig. 1) along the axis of an
easterly wave. Leg lengths will be 150-200 nmi (250-300 km), with some
variability dependent on the size of the system and the time available
on station. The pattern will be centered approximately on any
discernible circulation, if identifiable, or on a dominant area of
convective activity. After the circulation center or convective area is
passed, the sawtooth pattern is mirrored and the aircraft completes a
return trip, creating a series of diamond shapes to complete the
pattern. This return trip will provide some greater temporal continuity
to the observations.

As a system becomes better organized, a second survey pattern is flown
(Fig. 2), consisting of a square-spiral configuration centered on a
broad low- or mid-level circulation center. If multiple mesoscale
convective systems exist embedded within a parent circulation, the
pattern will be centered on the parent circulation. Dropsondes are
released at regular intervals to create a near uniform grid covering the
circulation and including any MCS's, if possible. The spacing between
the outer spiral and the inner box pattern is nominally set for 60 nm
(111 km), but it can be varied to ensure optimal representation of the
convective and mesoscale features.

Once a persistent low-level vortex is identified, subsequent missions
will fly a pattern centered on the vortex. This pattern will be a
rotating figure-4 pattern (Fig. 3). Flight legs for the figure-4 pattern
will be 60-120 nm (111-225 km) to allow for the collection of data with
high temporal and spatial resolution in the vicinity of the vortex. The
length of these flight legs is designed to completely include the
low-level vortex and convection associated with it. Depending on the leg
lengths and the time available on station, the pattern may consist of
higher azimuthal resolution (cf. Fig. 3a and Fig. 3b). The tail radar
will operate in F/AST mode during the entirety of these patterns. For
the P-3 using the NOAA antenna, the tail radar will operate in
continuous mode for portions of the legs that are coordinated with the
NASA ER-2 and during modules where the aircraft is flying a coordinated
pattern with the ER-2 (see Microphysics Module below).

The NASA ER-2 will fly primarily at night, concurrent with the nighttime
P-3. The ER-2 patterns will consist of .... \[\[\[NEED INPUT FROM NASA
ON THIS\]\]\]. For most of the missions strict coordination between the
P-3 and the ER-2 is not needed. For the Microphysics Module, however,
the ER-2 will fly legs coordinated with the P-3 (below and Fig. 5)

If available, the G-IV will be most beneficial flying a synoptic-scale
pattern. It will fly at maximum altitude observing the upper and lower
troposphere with GPS-sondes in the pre-genesis and incipient tropical
disturbance environment. \[\[\[\[NEED TO PUT IN A SAMPLE G-IV TRACK FOR
THE WESTERN CARIBBEAN\]\]\]\]

The possible availability of multiple aircraft during this experiment
leads to several different scenarios. A summary of the potential
combinations of aircraft during genesis experiments follows:

-   **Option 1 (primary experiment):**

The two NOAA WP-3D aircraft alone will fly, in the East Pacific, Gulf of
Mexico, or western Caribbean basins, either diamond or square-spiral
survery patterns to locate low- and mid-level vortices (Figs. 1 or 2).
Once a persistent mid-level vortex is located, either rotating figure-4
(Fig. 3) or square-spiral patterns will be flown over a 2-4 day period.

-   **Option 2 (optimal experiments):**

A\) Option 1 augmented with high-altitude measurements obtained by the
NASA ER-2 aircraft operating out of San Jose, Costa Rica.

B\) Option 2A augmented with large-scale upper- and lower-tropospheric
observations obtained by the G-IV aircraft flying patterns similar to
those given in Fig. 7 in the western Caribbean basin.

**Auxiliary Storm Modules:** These are stand-alone "plug-in" modules
that are one hour or less in duration and can be executed after the
selected primary storm module. Execution is dependent on system
attributes, aircraft fuel and weight restrictions, and proximity to
operations base.

(1) **Microphysics Module:** This module can be flown as a combination
    P-3/ER-2 mission or by a P-3 alone. It is intended to collect both
    *in situ* and remotely-sensed microphysics data, including water and
    ice concentrations, reflectivity, and vertical and horizontal motion
    fields. While the primary pattern is flown, locations of active
    mesoscale convective systems are determined. Once the primary
    pattern is complete, the aircraft will target one mesoscale
    convective system, provided an extensive stratiform anvil is
    present. Due to the possibility of aircraft electrification, this
    module can only be performed after the primary pattern is completed.
    The P-3 will penetrate the stratiform rain region from the rear of
    the convective system at an altitude of 14,000 ft (Fig. 5a). Once
    within the anvil, the aircraft will conduct a box-survey pattern,
    with the tail radar in Fore/Aft scanning mode. The dimensions of the
    box should be up to 40 nm, or whatever size will ensure the aircraft
    stays within the stratiform rain shield and does not reach the
    leading line of deep convective cores. Once the box is completed,
    the P-3 will head into the anvil, where it will begin a series of
    slanted ascents whose leg lengths should not exceed 15 nm (Fig. 5b).
    The P-3 will climb by 1000 ft during each leg. At the end of each
    leg, the P-3 will turn 180 degrees, return to the point at the end
    of the previous leg, and begin the next slanted ascent. The P-3 will
    again turn 180 degrees and repeat the process up to an altitude of
    18,000 ft, traversing the melting level and collecting microphysical
    data and vertical motion data during the pattern. During these
    stepped ascents the tail radar should be in continuous mode to
    provide vertical incidence data. If the tail radar is not able to
    run in continuous mode, the stepped-ascent pattern should still be
    flown to collect the *in situ* measurements.

> If available, the ER-2 will fly a pattern over the same system with
> the P-3. During the box survey the ER-2 will fly at altitude,
> conducting a butterfly pattern over the system and collecting
> remotely-sensed data. When the P-3 is prepared to perform the stepped
> ascents, the ER-2 will fly an extended leg along the same axis as the
> P-3, so that a portion of the P-3 pattern will be coincident with the
> ER-2. Once the ER-2 completes the leg, it will turn 180 degrees, and
> fly back to the beginning point to get two periods of coincident
> passes with the P-3. At the end of the return leg the pattern will be
> complete.

(2) **Convective Burst Module:**

**Tropical Cyclogenesis Experiment**

![](media/image1.jpeg){width="5.2875in" height="5.9430555555555555in"}

**Figure 1. P-3 Vortex survey pattern -- Diamond pattern**

-   Note 1: True airspeed calibration is required.

-   Note 2. The pattern is flown with respect to the wave axis,
    typically inclined at 30-40° from N, or relative to circulation or
    vorticity centers.

-   Note 3. Length of pattern (axis parallel to wave axis) should cover
    both low- and mid-level vortices, leg lengths range from 150 -- 200
    nm (275-375 km).

-   Note 4. Fly 1-2-3-4-5-6-7-8 at 14,000 ft (4 km) altitude, dropping
    sondes at all locations denoted by black circles.

-   Note 5. Set airborne Doppler radar to scan F/AST on all legs.

**Tropical Cyclogenesis Experiment**

![](media/image2.jpeg){width="4.979861111111111in"
height="5.9430555555555555in"}

**Figure 2. P-3 Vortex survey pattern -- Square-spiral pattern**

-   Note 1. True airspeed calibration is required.

-   Note 2. The pattern is flown with respect to the wave axis,
    typically inclined at 30-40° from N, or relative to circulation or
    vorticity centers.

-   Note 3. Drop sondes at all numbered points. Drops at intermediate
    points can be omitted if sonde supply is insufficient.

-   Note 4. The spacing between the outer spiral and inner box
    (nominally set to 60 nm (111 km)) can be increased or decreased
    depending on the size of the disturbance.

-   Note 5. Fly 1-2-3-4-5-6-7-8-9-10-11-12 at 14,000 ft (4.0 km)
    altitude.

-   Note 6. Set airborne Doppler radar to scan F/AST on all legs.

**Tropical Cyclogenesis Experiment**

![](media/image3.jpeg){width="5.0in" height="5.988194444444445in"}

**Figure 3a. P-3 Rotating Figure-4 pattern -- 8 leg**

-   Note 1: True airspeed calibration is required.

-   Note 2. The pattern may be entered along any compass heading.

-   Note 3. Fly 1-2-3-4-5-6-7-8 at 14,000 ft altitude, 60-120 nm
    (111-225 km) leg length.

-   Note 4 Set airborne Doppler radar to scan F/AST on all legs except
    for portions of those legs coordinated with NASA ER-2.

**Tropical Cyclogenesis Experiment**

![](media/image4.jpeg){width="5.363888888888889in"
height="5.839583333333334in"}

**Figure 3b. P-3 Rotating Figure-4 pattern -- 12 leg**

-   Note 1: True airspeed calibration is required.

-   Note 2. The pattern may be entered along any compass heading.

-   Note 3. Fly 1-2-3-4-5-6-7-8-9-10-11-12 at 14,000 ft altitude, 60-120
    nm (111-225 km) leg length.

-   Note 4 Set airborne Doppler radar to scan F/AST on all legs except
    for portions of those legs coordinated with NASA ER-2.

**Figure 4. ER-2 Flight Tracks**

![](media/image5.jpeg){width="4.99375in" height="6.623611111111111in"}

**Figure 5. Microphysics module**

-   Note 1: True airspeed calibration is required.

-   Note 2. The pattern may be entered along any compass heading.

-   Note 3. The P-3 flies box survey pattern at 14 kft, airborne Doppler
    set to scan F/AST.

-   Note 4. At completion of survey pattern, change airborne Doppler to
    continuous mode, if possible, and head into anvil. Complete series
    of slanted ascents, beginning at 14 kft and climbing 1 kft during
    each leg. Each leg not to exceed 15 nm. Stop ascents at 18 kft.

-   Note 5: ER-2 flies butterfly pattern at altitude while P-3 conducts
    survey pattern, then flies leg back and forth aligned with P-3
    during P-3 stepped ascents.

**Figure 6. Convective Burst module**

**Figure 7. G-IV flight track**