equivalent potential temperature
Gisele Zepka
gzepka at DGE.INPE.BR
Tue Jan 26 11:36:11 EST 2010
I will use temperature and relative humidity at surface from wrf model
(TMPsfc and RHsfc).
I think that I need to find the surface pressure from the variable pressfc.
Gisele
Em 26/1/2010 14:23, Jeffrey Duda escreveu:
> Which model data are you using? American models should have data for
> surface pressure. It's usually called pressfc.
>
> Jeff Duda
>
> On Tue, Jan 26, 2010 at 10:08 AM, Gisele Zepka <gzepka at dge.inpe.br
> <mailto:gzepka at dge.inpe.br>> wrote:
>
> Well I have a problem then.
> I run the wrf model and it has 42 levels. The surface pressure is
> defined as 1013. This is my lowest level when I set z=1.
> I really don't know how to get this Mb.
>
> Gisele
>
>
> Em 26/1/2010 13:59, Andrew Revering escreveu:
>
> If you're using GRIB data, you should find a SFC level. You
> don't want to
> set it to 1013 because that isn't necessarily the suface. In
> many cases that
> will be an imaginary, extrapolation below ground (in the
> mountains for
> example).
>
> Look for 'SFC' in the inventory of your GRIB data for the
> proper level. You
> should be able to find Tc, Td, RH for the 'SFC' level in there
> to do the
> calculations.
>
> So to clarify... MB would be the MB at the Surface. How that’s
> defined
> exactly in your data set you'll have to figure out, but you
> don’t want it to
> calculate it for 1013, unless you wanted a geopotential height
> like 850mb
> done.
>
> Andrew Revering
> Convective Development, Inc.
> http://www.convectivedevelopment.com/
>
>
> -----Original Message-----
> From: GRADSUSR at LIST.CINECA.IT <mailto:GRADSUSR at LIST.CINECA.IT>
> [mailto:GRADSUSR at LIST.CINECA.IT
> <mailto:GRADSUSR at LIST.CINECA.IT>] On Behalf Of
> Gisele Zepka
> Sent: Tuesday, January 26, 2010 9:50 AM
> To: GRADSUSR at LIST.CINECA.IT <mailto:GRADSUSR at LIST.CINECA.IT>
> Subject: Re: equivalent potential temperature
>
> 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>
> [mailto: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 <mailto: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
>
>
>
>
> --
> Jeff Duda
> Iowa State University
> Meteorology Graduate Student
> 3134 Agronomy Hall
> www.meteor.iastate.edu/~jdduda <http://www.meteor.iastate.edu/%7Ejdduda>
--
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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