equivalent potential temperature

Tue Jan 26 11:40:16 EST 2010

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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://gradsusr.org/pipermail/gradsusr/attachments/20100126/f87b3ed3/attachment.html 