equivalent potential temperature

Tue Jan 26 11:44:37 EST 2010

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> 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> 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>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] On
>>>> Behalf Of
>>>> Gisele Zepka
>>>> Sent: Tuesday, January 26, 2010 9:50 AM
>>>> To: 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] 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
>>>
>>
>>
>>
>> --
>> 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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://gradsusr.org/pipermail/gradsusr/attachments/20100126/888317d1/attachment.html 