equivalent potential temperature
Gisele Zepka
gzepka at DGE.INPE.BR
Tue Jan 26 11:51:51 EST 2010
Arw_post from version 2.2
Gisele
Em 26/1/2010 14:44, Jeffrey Duda escreveu:
> What are you using to post-process the data?
>
> Jeff
>
> On Tue, Jan 26, 2010 at 10:42 AM, Gisele Zepka <gzepka at dge.inpe.br
> <mailto:gzepka at dge.inpe.br>> wrote:
>
> 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
>
>
>
>
> --
> 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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