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Vertical traces at successive times
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Introduction
We present a suite of programs to perform
the vertical tracing of cyclones through a set of pressure levels. A typical
situation would be following cyclonic centres from the surface [mean sea level
pressure (MSLP)] to (say) 500 hPa or to as high as a
vertical trace extends. These programs will collectively be referred to as the
vertical tracing software.
The heart of the
VTS is the program vertr. This is designed to work on a pair of neighbouring
levels and tries to connect a cyclone on a lower level to that immediately
above. It is convenient to regard the initial lower level in the sequence as
the ‘base’ set of tracks that is to be vertically traced. We then take each
track point in the base set and attempt to match it to a track point on the
next level e.g. the lower level (base set) might be MSLP and the upper level is
925 hPa. The output from this process is a ‘trace’
file that contains the matching status of each track point in the base set. A
flag will be set if there is no match i.e. the cyclone does not extend to the
upper level (it has ‘ended’), otherwise the track information for the matched
cyclone will be listed. There is one-to-one correspondence between the base set
and the next level.
The
trace files (comma separated value or CSV) may be easily manipulated or
combined in a spreadsheet package like Excel or with UNIX commands like cut and paste. At this stage
there is not a comprehensive set of utilities to process the trace files.
However we include one to determine the tilt
of a cyclone based on its location at an upper level relative to a lower
level (tilt). The trace may be plotted with a suitable
graphics package. The example on this page uses NCAR Graphics but NCL could
also be employed.
Obtaining the
The vertical
trajectory software is freely available from our group. It is written in
Fortran 77 and should compile correctly on any platform with a suitable
compiler e.g. the GNU g77 compiler. To date it has been compiled successfully
on systems running Solaris and Linux. We also provide a Linux binary
version of the software which should work on many Linux systems. At this stage
there is no version suitable for Cygwin under
Microsoft Windows XP but in principle the software may be compiled for that
platform.
The present version is intended for MSLP and geopotential height data from the common reanalysis
projects. Furthermore the software will work on either a global or regional
grid. The input data are expected to be in a simple binary format that we refer
to as ‘conmap’ (CMP). Details of this format are
given in the software documentation.
We provide some additional Fortran 77 software (read_nc2cmp) to assist
in converting GRIB or NetCDF data to the CMP format. We include a utility based
on NCAR Graphics (kmapline). Note that the actual tracing software does not
require any graphics libraries: the only external libraries required for
compilation are NetCDF (version 3+) for read_nc2cmp if that utility is needed.
|
The
software may be obtained by contacting: Ian Simmonds |
Please
indicate the platform that you intend to run the software on. We recommend the
g77 compiler but the software should
compile with others but we can’t test these ourselves.
Documentation
A detailed description of the software package
including compilation and examples is given in the Documentation.
Some other useful resources are:
The University of
Melbourne Automatic Cyclone Tracking Home Page
and the PDF documents:
The
University of Melbourne cyclone tracking software
Cyclone
tracking of geopotential height fields
as well as the articles in the References
section.
Please direct any questions or report any problems to Kevin Keay.
An example of vertical
tracing
The plot
below shows an example of vertical tracing that was computed using six-hourly
MSLP and geopotential height fields from the ERA Interim
Reanalysis. The tracing is based on six pressure levels: MSLP, 925, 850,
700, 600 and 500 hPa, which is a small subset of
those available in the ERA Interim Reanalysis to illustrate the method.
The MSLP cyclone track (black line) begins on June 19
2001 06 UTC and ends on June 23 2001 00 UTC. The 16 cyclone positions at MSLP
are indicated by black circles. The vertical tracing is shown every six hours
i.e. at each time point. Since the 925 hPa positions
are very close to those at MSLP this level is omitted from the plot but is
included in the tracing analysis. The coloured
symbols indicate the location of the cyclone at the different traced levels as shown
in the key. For instance, a dark blue circle indicates the cyclone position at
the 850 hPa level. The vertical structure of the
cyclone changes over time and this evolution is reflected by the highest level
of the tracing. In the middle of its life the cyclone extends to 500 hPa (and possibly higher) and there is a westward tilt i.e.
the upper level centres are
located to the west of the surface cyclones. This is more evident for the 500 hPa location (red circles). As the cyclone decays it
becomes shallower with a much smaller tilt i.e. a barotropic
structure, in contrast to the baroclinic nature that
it displayed earlier on in its development.
MSLP 850 Pa 700 hPa 600 hPa 500 hPa
Copyright
and Disclaimer
We use the
vertical tracing software that is presented here in our published research.
Although every effort has been made to ensure that the software is correct we
can not guarantee it is free from errors. Hence we take no responsibility for
any negative consequences arising from its use by any party external to our
group at the
The output
of the vertical tracing software, as data files or images, may be freely used
for research and publications including journals and books. It would be
appreciated that you include an appropriate reference to this web site. For
instance:
The vertical tracing software was obtained from the
Lim,
E.-P., and I. Simmonds, 2007:
Southern Hemisphere winter extratropical cyclone characteristics and vertical organization
observed with the ERA-40 reanalysis data in 1979-2001. Journal of Climate,
20, 2675-2690.
Lim, E.-P., and I. Simmonds,
2007: Southern Hemisphere winter extratropical cyclone characteristics and
vertical organization observed with the ERA-40 reanalysis data in 1979-2001. Journal
of Climate, 20, 2675-2690.
Lim, E.-P., 2005: Global changes in
synoptic activity with increasing atmospheric CO2. PhD
Thesis,
Last
Update: September 22 2009
Maintained
by: Kevin Keay