equivalent potential temperature
Gisele Zepka
gzepka at DGE.INPE.BR
Tue Jan 26 11:42:06 EST 2010
I am running my own wrf simulations.
Gisele
Em 26/1/2010 14:40, Jeffrey Duda escreveu:
> Are you performing your own WRF simulations or are you obtaining past
> data from operationally run models?
>
> Jeff
>
> On Tue, Jan 26, 2010 at 10:36 AM, Gisele Zepka <gzepka at dge.inpe.br
> <mailto:gzepka at dge.inpe.br>> wrote:
>
> 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
>
>
>
>
> --
> 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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