Back to Intensity Change projects
|
Back to Main Projects Page
Real-Time Doppler Winds
Principal Investigator
John Gamache
Team Members:
Peter Dodge (HRD)
Nancy Griffin (HRD)
Joe Griffin (HRD)
Paul Leighton (HRD)
Frank Marks (HRD)
Sundararaman.G.Gopalakrishnan (HRD)
Collaborating Scientists
Naomi Surgi (NCEP/EMC)
Qingfu Liu (NCEP/EMC)
Objectives:
- To control the quality of airborne Doppler radar data.
- To analyze the quality-controlled data in real time.
- To deliver the data and analyses in 'real time' to
the Environmental Modeling Center and National Hurricane Center.
- To examine how these data may be incorporated into numerical simulations.
- To determine the best flight strategies for obtaining
data that will initialize the simulations.
Rationale and Methodology:
As operational hurricane forecasts attain finer resolution, the models must be
initialized with finer-resolution data. Airborne Doppler radar observations
provide the most widespread observations of the hurricane core at a 1.5 km or
better horizontal resolution. At the Hurricane Research Division we have been
developing methods to produce research-quality analyses from the P-3 airborne
Doppler radar for over 20 years. Within the last decade we have been refining
a three-dimensional variational method to produce three-dimensional wind
analyses, as well as analyses of winds in a vertical cross-section defined by
the flight track of the aircraft. The three-dimensional analysis scheme was
described by Gamache et al. (1997), and has been modified in such a way as to
be nearly identical to the method described by Gao et al. (1999). The
variational scheme simultaneously minimizes
- the difference between the projection of the wind analysis on the
Doppler radial direction cosines, and the observed Doppler radial velocities,
- the error in the 4-th order discretized three-dimensional mass divergence
of the wind field, and
- the various second derivatives of wind components.
The third term acts as a filter of 2 delta x noise resulting from solving the
discretized mass-continuity equation, and is kept as small as practically
possible. Although this method of solution is computationally expensive it
works best in situations where the aircraft must fly through the middle of the
feature it is observing, as in aircraft penetrations of the hurricane eyewall.
Until 2004, the data analyzed in the aforementioned method were manually
quality controlled, which is a time consuming process, although possible when
doing research. To quality control an hour of airborne Doppler data can take
one person approximately 2-4 weeks. To produce analyses in 'real time,' that is
within minutes to an hour of the observations, quality control must be
performed automatically, and methods were developed in 2003 and 2004 to perform
such quality-control tasks as, 1) to remove noisy data, 2) to remove
reflections of the main and side lobes by the sea surface, and 3) to correct
improperly de-aliased Doppler radial velocities. Because of present
limitations of the airborne Doppler radar signal processing, a three-step
process is used. In the first step, the single-PRF (single pulse repetition
frequency) data are de-aliased using a single-radial method developed by
Bargen and Brown (1980), followed by a two-dimensional method developed at HRD.
Any data beyond a radial gap of 1 km or greater are discarded, since the
Bargen-Brown method can be unreliable with greater gaps in the high-gradient
eyewalls of hurricanes.Those data left are analyzed in a cylindrical analysis
centered on the storm center, but with wavenumber 0 and 1 Fourier components
in the azimuthal direction. This low-wavenumber analysis is then used to
improve the de-aliasing in a second pass through the Doppler data, where a
three-dimensional Cartesian analysis of the wind is produced. The lowest
levels of this analysis are then transmitted back to the National Hurricane
Center. A second type of analysis uses the same quality-controlled data, but
incorporates Doppler data well upwind and downwind of the flight track, and
looking both fore and aft of the flight track, to produce higher resolution
vertical cross-sections of wind speed, radial wind (wind component toward or
away from storm center), vertical wind, and reflectivity.Examples of both the
three-dimensional analysis and the vertical profiles are shown below.
Starting in 2008, the data used in the analysis will be transmitted to the
Environmental Modeling Center for assimilation into the operational hurricane
model (HWRF-Hurricane Weather Research and Forecasting). In 2008, the data may
still only be assimilated into a 'parallel' run at EMC. Efforts continue in
2007 at HRD to make the actual running of the real-time quality control aboard
the aircraft, and the transmission of data from the aircraft, as automatic
(with as little onboard human interaction) as possible. Further development
and improvement will occur in 2008, when the Sigmet RVP-8 Doppler-radar
processing will be operating on 2 NOAA P-3s (N42RF and N43RF) and the NOAA
Gulfstream-IV (N49RF) aircraft.We also hope to examine independently how data
could best be collected to meet the model needs (in OSSEs).
A new modeling effort is starting up at HRD to test different procedures in
hurricane simulations.One such effort will involve studying different methods
in which the Doppler radials or Doppler wind analyses may be used to initilize
numerical simulations.
Accomplishments:
- Method tested successfully on NOAA WP-3D aircraft in 2004.
- Doppler analyses transmitted to NHC in real time in
2005 (in particular in Wilma of October 2005)
- Real-time quality controlled analyses of airborne
Doppler radar data accepted by JHT (NHC) for operational use.
- Real-time analyses transmitted in real time from
Tropical Storm Ernesto and Hurricane Helene of 2006.
- New more automatic determinations of storm center, and
some quality control parameters developed in spring 2007.
- A simple GUI menu was developed to help set up
parameters for automatic quality control and analysis
- Real-time analyses transmitted in real time from
Tropical Storm Erin, Hurricane Felix, Tropical Storm Ingrid, Tropical
Depression 10, and Hurricane Karen
Goals for FY 2008:
- Develop I/O software for RVP-8 Sigmet data in quality
control/analysis software
- Develop and test a completely automatic quality control
program and try it in 2008 hurricane field season
References:
Bargen, D. W., and R. C. Brown, 1980:Interactive radar velocity unfolding.
Proc. 19th Conference on Radar Meteorology, Miami,
Amer. Meteor. Soc., 278-283.
Gamache,
J. F., 1997: Evaluation of a fully three-dimensional variational Doppler
analysis technique. Preprints, 28th Conf. On Radar Meteorology
, 9-13 Sept. 1997, Austin, AMS.
Gamache, J. F., 2005:Final report on JHT project entitled: Real-Time
Dissemination of Hurricane Wind Fields Determined from Airborne Doppler Radar.
http://www.nhc.noaa.gov/jht/2003-2005reports/DOPLRgamache_JHTfinalreport.pdf
Gao Jidong, Ming Xue, Alan Shapiro, Kelvin K. Droegemeier, 1999: A
Variational Method for the Analysis of Three-Dimensional Wind Fields from Two
Doppler Radars. Mon. Wea. Rev: 127, 2128-2142.
Total wind-speed vertical cross-section
Radial wind vertical cross-section
Total wind speed at 500 meters
Examples of analyses produced from automatically quality-controlled airborne
Doppler observations collected in Hurricane Katrina on 28 August 2005, when it
was a category 5 hurricane. Top and bottom panels on left are total wind speed
and radial wind, respectively at 1725-1818 UTC, while the analysis on the right
is of the total wind speed at 500 meters above sea level.
http://www.aoml.noaa.gov/hrd/Storm_pages/katrina2005/radar.html
Last modified: 10/24/2007
|