[gradsusr] Fwd: Socorrooooo/ HELP

Wed Apr 6 13:34:47 EDT 2011

RafaelCB,

Please find attached a copy of script plot_hurricane_center3.gs (and 
cbar_line.gs, cbar_line_box.gs, and a script function pause.gsf used by 
it), and let me know if you have any questions about it.

The script is designed to be run interactively, and prompts the user to 
define a rectangle box around the feature of choice, and finds the 
minimum value of a "sea-level pressure variable" (which could be changed 
to another variable like surface pressure, or geopotential height, 
etc...).  Currently, the script does not check that the pressure or the 
mean pressure gradient satisfy certain criteria, but this could be added 
in the script after the coordinates of the possible center are 
identified.  Some ideas: First, use the GrADS maskout function to make a 
modified sea-level pressure variable with defined points for sea-level 
pressures <= 1015 hPa (or conversely, undefined points for sea-level 
pressures > 1015 hPa), if I correctly understand your first requirement 
(see also http://grads.iges.org/grads/gadoc/gradfuncmaskout.html).  
Then, use the modified sea-level pressure variable to calculate the 
pressure gradient over the entire domain which is a vector quantity... 
could use "cdiff" (http://grads.iges.org/grads/gadoc/gradfunccdiff.html 
and/or the code in post to the GrADS Users Forum by Eric Altshuler from 
10/19/2010 "Re: [gradsusr] CDIFF Versus HDIVG?") to define GrADS field 
variables dpdx = ..., dpdy = ..., and then use the GrADS "mag()" 
function (http://grads.iges.org/grads/gadoc/gradfuncmag.html) to define 
a field variable of the magnitude of the pressure gradient (say pgmag = 
mag(dpdx,dpdy)) (pressure gradient and pressure gradient magnitude 
reference: Dynamical and Physical Meteorology by Haltiner and Martin, 
1957, page 6, and for the magnitude of a vector, Calculus and Analytic 
Geometry by Thomas, 1972, page 587).  These variables would be defined 
prior to doing the search for the coordinates of the minimum value of 
the modified sea-level pressure variable.  Then, define a the desired 
rectangle around the identified minimum sea-level pressure point and use 
the GrADS "aave()" function 
(http://grads.iges.org/grads/gadoc/gradfuncaave.html) to calculate the 
area-averaged mean sea-level pressure gradient within this rectangle.  
Then use GrADS "if" command to check whether the identified minimum 
sea-level pressure point satisfies the pressure gradient requirement 
before writing it out to the coordinates text file in the script.  
Please let me know if you have any questions about the above ideas.

Thanks,
Chuck

RafaelCB wrote:
>
>
> ---------- Forwarded message ----------
> From: *Venize Teixeira* <nizeteixeira at gmail.com 
> <mailto:nizeteixeira at gmail.com>>
> Date: 2011/4/5
> Subject: Socorrooooo/ HELP
> To: RafaelCB <rafael.ciram at gmail.com <mailto:rafael.ciram at gmail.com>>
>
>
> I have data level pressure at sea and would like to create a script 
> that generates a text file that selects only the cyclones with the 
> following characteristics:
>
> The suggestion is as follows:
>
> Create a script that, within the area of lat -80 -20 and lon -100 
> -80, finds the minimum value of pressure and then check if this value is:
>
> -  the central sea level pressure cannot be higher than
> 1,015 hPa; and
>
> -  the mean pressure gradient, estimated for an area of 5°lat×
> 7°lon around the minimum pressure, has to be of at least 0.55 hPa/250 km.
>
>
> if the condition is satisfied, write to a file. "txt" latitude, 
> longitude, date, time, months.
>
> if the condition is not met, run the scan in the next "t".
>
>
> You could give me a hint how to do this?
>
> Thank you for your attention
> -- 
> Venize A. Teixeira
> Meteorologista
> Msc: Ciência Ambientais
>
>
> ------------------------------------------------------------------------
>
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> gradsusr at gradsusr.org
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>   

-- 

Please note that Charles.Seman at noaa.gov should be considered my NOAA
email address, not cjs at gfdl.noaa.gov.

********************************************************************
 Charles Seman                                Charles.Seman at noaa.gov
 U.S. Department of Commerce / NOAA / OAR
 Geophysical Fluid Dynamics Laboratory         voice: (609) 452-6547
 201 Forrestal Road                              fax: (609) 987-5063
 Princeton, NJ  08540-6649            http://www.gfdl.noaa.gov/~cjs/
********************************************************************

"The contents of this message are mine personally and do not reflect any
official or unofficial position of the United States Federal Government,
the United States Department of Commerce, or NOAA."

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