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Thermal Front Parameter (TFP)

"Is a widely used parameter for frontal analysis. It is computed from the second derivative of temperature in space" (da EUMETRAIN).

"In this unit we will calculate the so-called thermal front parameter and see how it is a measure of the location of fronts in a developing system. We will observe the connection between this quantity and satellite images (Meteosat) of the system. The purpose of this unit is to show the value and possibilities of combining satellite data and dynamic fields".

 * nomefile tfp.gs'
* program to calculate the Thermal Front Parameter
* using the 1000-850 thickness for temperature
  
 'set display color white'  
 'c'  
 'map europe'  
 'run constants.gs'File contenente la definizione di alcune costanti comuni. Il file si trova generalmente nella cartella degli scripts. 
 'define tcos = cos(lat*d2r)'d2r definita in constants.gs come segue:

"define d2r = 3.1415/180"

 'define thick=hgtprs(lev=850)-hgtprs(lev=1000)' 
 'set gxout contour'  
 'define tave1=grav*thick/(log(1000/850)*rdry)' 

Acceleration of gravity (m/s2):
"define grav = 9.81"

Gasconstant for dry air (J kg-1 K-1):
"define rdry = 287.04"

 

 *Correction for moisture (specific humidity)
*Use Equivalent temperature definition
  
 'define q1=75*(spfhprs(lev=1000)+spfhprs(lev=925))/2' 
 'define q2=75*(spfhprs(lev=925)+spfhprs(lev=850))/2' 
 'define qave=(q1+q2)/150' 
 'define tave=tave1+(2.5e+6/cp)*qave'Specific heat of air at constant pressure (J kg-1 K-1)
"define cp = 1004"
 'define eqth=tave*log(1000/850)*rdry/grav'eqth = equivalent thickness

Lo spessore equivalente (eqth, equivalent thickness) si basa sull'aumento di temperatura che si avrebbe se tutta l'acqua contenuta condensasse. Il vantaggio che si ottiene usando questo parametro modificato consiste in una maggiore definizione dei gradienti frontali.

Vedi anche: carta degli spessori equivalenti.

 'set gxout contour'  
 "set clevs 0 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 7 8 9 10"  
 "set ccols 4 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2"  
 'set cthick 8'  
 *set ccolor 2  
 'set cint 1'  
Horizontal increments*Horizontal increments  
'define dTy = cdiff(tave,y)'  
'define dTx = cdiff(tave,x)'  
'define dy = cdiff(lat,y)*d2r*rearth'  
'define dx = cdiff(lon,x)*d2r*rearth*tcos'  
Temperature Gradient* Temperature Gradient  
'define Txgrad = (dTx/dx)'  
'define Tygrad = (dTy/dy)'  
Magnitude Temperature Gradient* Magnitude Temperature Gradient  
'define Tmagrad = mag(Txgrad,Tygrad)'  
Inflection Points* Inflection Points  
'define d2tx = cdiff(tmagrad,x)'  
'define d2ty = cdiff(tmagrad,y)'  
'define Txmagrad = -1*(d2tx/dx)'  
'define Tymagrad = -1*(d2ty/dy)'  
 Direction Projection* Direction Projection  
'define Txdir = (Txgrad/Tmagrad)'  
'define Tydir = (Tygrad/Tmagrad)'  
 say 'Ready script TFP4.gs'   
 say 'Calculated TFP at level: 1000-850 mb'  
 say ' '  
 'define TFP = ((Txmagrad*Txdir)+(Tymagrad*Tydir))'  
    
    
 'd TFP*1e+11'  
 'draw title Thermal Front Parameter (1000-850 hPa)' 

 

 

Riferimenti e bibliografia:


Questa pagina stata realizzata da Vittorio Villasmunta

Ultimo aggiornamento: 14/05/16