# equivalent potential temperature

Gisele Zepka gzepka at DGE.INPE.BR
Tue Jan 26 10:50:14 EST 2010

```Thanks a lot Andrew.

As I said before, I will use model data to calculate theta-e. If I set
the surface in the model, it is 1013 hPa. Is this the level that I need
to consider in Mb (station pressure). If not, what is Mb? All Tc, Td and
RH are catch in Mb level, aren't they?

Gisele

Em 26/1/2010 12:59, Andrew Revering escreveu:
> You can calculate the Theta-E from ANY level. The typical levels of interest
> for severe weather are 850mb and the surface. Values of 330K or greater are
> usually indicative of instability great enough for severe weather. If you're
> looking at severe weather, I probably would use the surface. Likewise, you
> can use the gradient you get from Theta-E, overlay wind barbs at the level
> you're calculating (surface or 850) and you get a real nice idea of where
> the boundaries are at that level.
>
> The disclaimer is there are a LOT of other parameters needed to really
> identify a situation as severe-worthy though.
>
> I don't know if GrADS has a function for it, but the 'saturated' potential
> temperature (Theta-E) can be calculated with either of the following:
>
> Tc= temperature in degrees C
> Td = dew point temperature in degrees C (if needed)
> Mb = station pressure (be careful to note this is not sea level pressure or
> altimeter, they are all different)
> M = Mixing Ratio (calculations below if needed)
> RH = relative humidity
> Ms = Saturation Mixing Ratio (if needed, calculations below)
> Es = Dry Saturation Vapor Pressure (calculations below if needed)
>
> ThetaE = (Tc + 273.15) * ( 1000 / Mb ) ^ 0.286 + (3 * M)
>
> OR
>
> ThetaE = (273.15 + Tc) * ( 1000 / Mb ) ^ 0.286 + (3 * (RH * (3.884266 * 10 ^
> (( 7.5 * Tc ) / ( 237.7 + Tc )) ) /100 ))
>
>
> M= RH*Ms/100
> OR
> M= ((0.622*E)/(Mb-E))*1000
>
> Ms = ((Val(RH) / 100) / Val(M)) * 100
> OR MORE ACCURATELY
> Ms = 0.622 * Es/(P - Es)
>
> Es = 6.1078 * exp([(9.5939 * Td) - 307.004]/[(0.556 * Td) + 219.522])
>
> Andrew Revering
> Convective Development, Inc.
> http://www.convectivedevelopment.com/
>
> -----Original Message-----
> From: GRADSUSR at LIST.CINECA.IT [mailto:GRADSUSR at LIST.CINECA.IT] On Behalf Of
> Gisele Zepka
> Sent: Tuesday, January 26, 2010 8:40 AM
> To: GRADSUSR at LIST.CINECA.IT
> Subject: equivalent potential temperature
>
> Dear all,
>
> I am interested to analyse the atmospheric instability when a storm
> occurrs using equivalent potential temperature from mesoscale model.
> What atmospheric level do I need to check to get an idea of instability?
> I don't have a theta_e output, so I will calculate it from temperature
> and humidity data from model.
>
> Please, any help will be nice.
>
> Thanks.
> Gisele
>
>

--
Msc. Gisele dos Santos Zepka
Atmospheric Electricity Group (ELAT)
National Institute for Space Research (INPE)
Av. dos Astronautas, 1758
São José dos Campos/ SP/ Brazil CEP 12227-010
Phone ++55(12)39456841

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