index showalter

[Ivana Stiperski]

Hi Jose
I just wrote a script for showalter index calculation (using formulas from 
USA Noaa's AWIPS) but the problem is that it still hasn't been fully 
tested. as far as i have seen (in comparison with our sounding) it gives a 
bit bigger values than it should. try it and see if it performs well in 
your conditions.
t is temperature in kelvin, r relative humidity in %.
i have another script, a bit more refined or better to say not so empirical 
but i am still working on it. so if you see that this one is not good 
enough for you let me know and i will send you the other (a bit dubious) one.
good luck!
ivana





At 21:05 04. 03. 05, you wrote:
>Hi,
>
>I´m needing a script to calculate the index showalter. Something like a 
>indexshowater.gs?
>
>Thanks
>
>Pesquero
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'open data.ctl'


************* AWIPS-SHOWALTER INDEX ********************

* calculates Showalter Index by a forumla used at AWIPS


'define Rd=287'
'define Cp=1004'
'define k1=0.0091379024'
'define k2=6106.396'
'define k3=223.1986'
'define k4=0.0182758048'
'define k5=-0.37329638'
'define k6=41.178204'
'define k7=0.0015945203'
'define k10=0.1419709'
'define k11=20.746475'
'define k12=6672.5713'
'define k13=0.000036336427'
'define k15=26.66082'

'set lev 850'

* calculation of temperature and pressure at LCL
* water vapour pressure epres , saturated espres, dew point temp dewtemp
* temperature at LCL tcp, pressure at LCL pcp
'define espres=exp(k15-k1*t-k2/t)'
'define epres=r/100*espres'
'define pom=k15-log(epres)'
'define dewtemp=(pom-sqrt(pom*pom-k3))/k4'
'define tcp=dewtemp-(t-dewtemp)*(k5+k6/t+k7*t)'
'define pcp=850*pow((tcp/t),(Cp/Rd))'
'define ww=epres/(850-epres)'


* Showalter index calculation
'set lev 500'
'define pd=(pcp-500+abs(pcp-500))/(2*abs(pcp-500))'
if(pd=1)
     'define awshowalter=t-t(lev=850)*pow((500/850),(Rd/Cp))'
  else
     'define awshowalter=t-tcp+(pcp-500)*(k10+k11*ww-k12*ww/tcp-k13*pcp)'
endif
'd awshowalter'





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