Mesoscale Structure of Tropical Cyclones
- Principal Investigator:
- Frank Marks
- Other Scientists:
- John Gamache
- Peter Dodge
Earlier studies of Hurricanes Norbert
and Gloria have shown that the
airborne radar data are one of the
most effective tools for describing the structure and
organization of mesoscale wind and precipitation features in
tropical cyclones. In particular, the
airborne Doppler radars are essential for studying how the
changes in organization and structure of the precipitation
features relate to changes in the storms wind field and track.
Analysis of the airborne Doppler
observations have revealed a number of common features of the
three dimensional kinematic structure
of the inner core of tropical cyclones. The inner core circulation
is dominated by three components
that vary on a time scale of 6-24 h; (1)
the mean azimuthal flow; (2) the mean
horizontal wind; and (3) a wave number
one asymmetry. The mean horizontal wind
is a measure of the environmental flow in the vicinity of
the cyclone, and is comparable in magnitude to the secondary
circulation. The vertical variation of this component provides an
estimate of the vertical wind shear or baroclinity of the
environmental flow. A vertical mass-weighted mean of the mean
horizontal wind provides an estimate of the mean cyclone motion.
The temporal variation of this component is a measure of the
changing environmental flow in which the cyclone is embedded
and is related to the cyclone motion.
The wave number one asymmetry,
characterized by cyclonic and anticyclonic gyres centered on
the radius of maximum wind, is comparable in magnitude to the
secondary circulation and mean horizontal wind. Observations of
this asymmetry indicate that the orientation of the gyres is
related to the shear of the mean horizontal wind, suggesting
that the gyres are related to changes in the environmental flow.
The Velocity Track Display (VTD)
algorithm is similar to the Velocity Azimuth Display (VAD)
technique developed for ground-based radars. The
VTD technique utilizes a harmonic
analyses of the Doppler velocities collected along a single
flight leg in a series of concentric rings about the storm
center at a number of altitudes. In this way, the cross-track
component of the mean flow, the mean tangential and radial
velocity components can be deduced for each ring when enough
Doppler velocities are available. An improved version of the
VTD algorithm, Extended Velocity
Track Display (EVTD) is proposed based on a different
mathematical formulation of the problem and on the simultaneous
consideration of Doppler data collected during successive legs
crossing the storm center. The improved algorithm permits the
solution of some uncertainties associated with VTD: i.e.,
non-uniqueness of the values for the mean flow on successive
rings; lack of wavenumbers higher than wavenumber 0 for the
radial wind component; and random variations of the different
coefficients for successive rings.
During the last 5 years, the two algorithms have been developed
to analyze airborne Doppler radar hurricane wind data on a
workstation on one of the NOAA P-3s. The
VTD algorithm derives a radius-height mean tangential wind field
from data collected during a single pass of the aircraft
through the center of a tropical cyclone. The
EVTD method uses Doppler
velocities from two or more flight legs to retrieve the
horizontal mean wind over the vortex core, the axisymmetric and
wave number one radial wind field, and the temporal evolution
of the tangential and radial components.
During 1993-95, Doppler wind sets were obtained in Hurricanes
Emily (93), Olivia (94),
Erin (95), Iris (95), Luis (95), and Marilyn (95). VTD and EVTD
analyses of these data depict the evolution of the horizontal
mean wind and the mean tangential wind as the storms evolved.
The efforts will focus on four activities:
- Continued testing of the real-time VTD
and EVTD airborne algorithms during hurricane research
flights, culminating with a plan to transmit data to NHC during
the 1996 season.
- Compare the EVTD wind analyses from
Emily, Erin, and Marilyn with the
mesoscale surface wind analyses to determine the usefulness of
the EVTD analyses in estimating the low level wind structure.
- Use the EVTD wind analyses over the two days in
Olivia together with dual-Doppler analyses
to study the storm structure and motion.
- Compare the vertical profile of the mean horizontal wind
produced by the EVTD wind analyses to that determined from the
ODW observations gathered in Iris and Luis to ascertain whether
the EVTD winds are useful in studies of storm motion.
- Burpee, R.W., S.D. Aberson, P.G.
Black. M. DeMaria, J.L. Franklin, J.S. Griffin, S.H. Houston,
J. Kaplan, S.J. Lord, F.D. Marks, M.D. Powell, and H.E.
Willoughby, 1994: Real-time guidance provided by NOAA's
Hurricane Research Division to forecasters during Hurricane
Emily of 1993. Bull. Amer. Meteor. Soc., 75,
- Franklin, J.L., S.J. Lord, S.E. Feuer,
and F.D. Marks, 1993: The kinematic structure of Hurricane
Gloria (1985) determined from nested analyses of
dropwindsonde and Doppler radar data. Mon. Wea. Rev.,
- Griffin, J.S., R.W. Burpee, F.D. Marks,
And J.L. Franklin, 1992: Real-time airborne analysis of
aircraft data supporting operational hurricane forecasting.
Wea. Forecasting, 7, 480-490.
- Lee, W.-C., F.D. Marks, and R.E. Carbone,
1994: Velocity Track Display, A technique to extract
real-time tropical cyclone circulations using a single airborne
Doppler radar. J. Atmos. and Ocean.Tech., 11,
- Marks, F.D., R.A. Houze, and J.F.
Gamache, 1992: Dual-Aircraft investigation of the inner core of
Hurricane Norbert: Part I: Kinematic structure. J.
Atmos. Sci., 49, 919-942.
- Roux, F. and F.D. Marks, 1995: Extended
velocity track display (EVTD): An improved processing
method for Doppler radar observation of tropical cyclones.
accepted for J. Atmos. Ocean. Tech..
- Dodge, P., F. Marks, and J. Gamache,
1995: The evolution of the inner core of Hurricane
Olivia (1994) from EVTD Doppler radar analysis.
Preprints of the 21st Conference on Hurricanes and Tropical
Meteorology, Miami, FL, AMS, 463-465.
- Marks, F., 1992: Kinematic structure of the
hurricane inner core as revealed by airborne Doppler radar.
Preprints of Fifth Conference on Mesoscale Processes.
Atlanta, GA, AMS, 127-132.
Return to HRD
Updated Tue, Nov 14, 1995