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TC bogus: how to set rmax?

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Yue Wu

New member
Hi there. I am a bit confused about the setting of rmax when using tc.exe to remove a tropical cyclone.

The differences among different values of rmax are tiny in the distributions of PSFC, UU and VV, unless I set rmax to zero. And I also check RH fields, in which a high-value region would appear after removing tc. The larger rmax I set, the bigger high-RH region appears.

My questions are:
1) What does rmax mean on earth?
2) Why rmax does not have obvious effect on dynamic fields, but only on humidity?
3) How to confirm the value of rmax?

Looking forward to the reply!
 
Hi
I can answer questions 1. rmax is the maximum radius outward from the storm center. To attempt to answer question 3, I believe this will rely on the actual storm you're trying to remove. You'll need to figure that out, based on observations. As for question 2, I'm not certain, and this may be related to the known issue with the TC bogus option. This is an insert from the examples.namelist file that discusses good strategies for using this program, and please see #3 below, that discusses the known problem:

** for tc bogusing:
Helpful hints
1) The TC bogus *MUST* only be run with a single processor: serial
(with or without a nest build option), or as a DM build with np=1.
2) Run the TC program for only the initial model time. Remember to copy
your metgrid file to a safe location and then let the TC scheme
generate the auxiliary files.
3) The TC program does not handle soil moisture or soil temperature
correctly. After running the TC program, use an NCL script to put the
modified fields back into the original metgrid file (remember that you
are keeping a pristine copy elsewhere). The modified fields to copy
are: "RH", "TT", "UU", "VV", "GHT", "PRES", "PMSL", "PSFC".
4) The TC program runs quickly, only a few seconds. It is a good idea to
process multiple runs, and vary the TC initialization. It would be
reasonable to select the maximum wind speed (vmax_meters_per_second)
from 30 to 60 by 5, select the radius of maximum winds ((m), rmax) =
50000 to 200000 by 50000, and select a tuning parameter for the
vortex (vmax_ratio) = 0.5 to 0.9 by 0.1. Look at the resulting
bogus storms (sea level pressure, surface wind speeds, and
overall storm size), and choose the best.
5) Remember to also consider starting the TC program at a later or
earlier time during your parameter space exploration.
6) The bogus storm will organize better if the initialization of the
tropical storm is entirely over water, and if the storm is able to
develop over water for several days.
7) After the metgrid file is finalized, and the real program is run,
use DFI in WRF. Removing and then introducing an entire bogus typhoon
is the definition of unbalanced. Running DFI for 2-3 hours back and forth
will be a benefit. For a successful implementation of a TC bogus storm in
WRF, the storm should not oscillate in size, should not be radiating
massive amounts of gravity waves, and should not rapidly weaken.

&tc
insert_bogus_storm = .true.,
remove_storm = .false.,
num_storm = 1,
latc_loc = 15.,
lonc_loc = -90.,
vmax_meters_per_second = 30,
rmax = 50000,
vmax_ratio = 0.5,
/
 
kwerner said:
Hi
I can answer questions 1. rmax is the maximum radius outward from the storm center. To attempt to answer question 3, I believe this will rely on the actual storm you're trying to remove. You'll need to figure that out, based on observations. As for question 2, I'm not certain, and this may be related to the known issue with the TC bogus option. This is an insert from the examples.namelist file that discusses good strategies for using this program, and please see #3 below, that discusses the known problem:

** for tc bogusing:
Helpful hints
1) The TC bogus *MUST* only be run with a single processor: serial
(with or without a nest build option), or as a DM build with np=1.
2) Run the TC program for only the initial model time. Remember to copy
your metgrid file to a safe location and then let the TC scheme
generate the auxiliary files.
3) The TC program does not handle soil moisture or soil temperature
correctly. After running the TC program, use an NCL script to put the
modified fields back into the original metgrid file (remember that you
are keeping a pristine copy elsewhere). The modified fields to copy
are: "RH", "TT", "UU", "VV", "GHT", "PRES", "PMSL", "PSFC".
4) The TC program runs quickly, only a few seconds. It is a good idea to
process multiple runs, and vary the TC initialization. It would be
reasonable to select the maximum wind speed (vmax_meters_per_second)
from 30 to 60 by 5, select the radius of maximum winds ((m), rmax) =
50000 to 200000 by 50000, and select a tuning parameter for the
vortex (vmax_ratio) = 0.5 to 0.9 by 0.1. Look at the resulting
bogus storms (sea level pressure, surface wind speeds, and
overall storm size), and choose the best.
5) Remember to also consider starting the TC program at a later or
earlier time during your parameter space exploration.
6) The bogus storm will organize better if the initialization of the
tropical storm is entirely over water, and if the storm is able to
develop over water for several days.
7) After the metgrid file is finalized, and the real program is run,
use DFI in WRF. Removing and then introducing an entire bogus typhoon
is the definition of unbalanced. Running DFI for 2-3 hours back and forth
will be a benefit. For a successful implementation of a TC bogus storm in
WRF, the storm should not oscillate in size, should not be radiating
massive amounts of gravity waves, and should not rapidly weaken.

&tc
insert_bogus_storm = .true.,
remove_storm = .false.,
num_storm = 1,
latc_loc = 15.,
lonc_loc = -90.,
vmax_meters_per_second = 30,
rmax = 50000,
vmax_ratio = 0.5,
/

Thanks for your prompt reply!
I have a further question: what if the tropical cyclone to remove is not strong enough to have vmax_meters_per_second>30? Can TC bogus still work under this situation?
 
HI,
I don't have much experience with this program, but you could probably modify the settings for vmax_meters_per_second and run a quick trial simulation to test it out.
 
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