[gradsusr] converting omega to vertical velocity

[Rowell, Mason D.]

Hello,

You would really need high resolution (temporally and spatially) reanaliyis data that utilized some type of LES simulation for that I would think. NNRP data and surely NARR data as well will not resolve vertical velocity for phenomenon smaller than the synoptic scale. Also, the conversion formula you are using assumes the vertical equation of motion is in hydrostatic balance, and more often than not, appreciable vertical accelerations that then yield large values of W are usually within non-hydostatic environments.

Mason
________________________________
From: gradsusr-bounces at gradsusr.org [gradsusr-bounces at gradsusr.org] on behalf of Alireza Azargoun [alireza.azargoun at gmail.com]
Sent: Tuesday, November 15, 2011 8:48 PM
To: GrADS Users Forum
Subject: Re: [gradsusr] converting omega to vertical velocity

Dear Mai, Mason and Ricardo
I really appreciate your help since I'm not familiar with the subject. now i understand the trends in the equation. i had checked out the results in different levels ( including 700mb). but all these values were about the same order ( 10^-3 (m/s) ). I'm using reanalysis data of NCEP from the following link:

html<http://dss.ucar.edu/pub/cfsr.html>http://dss.ucar.edu/pub/cfsr.html

I'm trying to use this data to compute vertical velocities of air which affect the airplanes passing through these air parcels. (I don't think values below 1 (m/s) have any effects on airliners) . but it seems either I used a wrong datasets which cannot simulate reality conditions or these  downwash and upwash streams are local and rapid changes which can't be found in any datasets!
Regards,
Alireza


On Wed, Nov 16, 2011 at 4:51 AM, Ricardo Hallak <hallak at model.iag.usp.br<mailto:hallak at model.iag.usp.br>> wrote:
Hi Alireza,

next to surface, where the air density (rho) is about 1.2 kg/m^3, a w=1 m/s gives omg=11.8 Pa/s.
In your example, your omg~0.1 Pa/s, so it is a low value. In large-scale, the vertical motion is actually low.

In thunderstorms (and clusters of thunderstorms as well, which are mesoscale in temporal and spatial range), however, w can frequently be > 20 m/s. If you are dealing with large-scale (synoptic scale) data, your data will not be able to "see" thunderstorms.

What are the dx and dy intervals of your data? Probably your data can not explicitly resolve big vertical motions. Try to compute w in a region where there is a cold front in activity at, for example, 700 mb level.

Hope this helps,
Ricardo

On Wed, 16 Nov 2011 04:32:43 +0330, Alireza Azargoun wrote
> thnx Tereza
>
> but I don't understand it. did you mean that my answer [W=0.00912 (m/s)]  is not (m/s) and it's in (cm/sec)!? supposing that isn't a 0.912 cm/sec a low speed vertical velocity airflow!? if there's any reference on this subject I'll be glad if you anyone notify me about it.
>
> On Wed, Nov 16, 2011 at 4:18 AM, <tcavazos at cicese.mx<mailto:tcavazos at cicese.mx>> wrote:
>
Hi
>
> The usual unit (magnitude) of vertical velocity is in cm/seg.
> So, it is fine.
>
> Cheers,
> Tereza
>
> > Dear GrADS users
> > Hi
> >
> > I'm recently working on a project about the vertical speed of air in
> > different elevations. I'm using CFSR data in grb2 format. these data sets
> > have omega (Pa/s) instead . I tried to convert them to vertical velocity
> > (m/s) using this equation:
> > omega=  - rho * g * w  ( or omega=- (P/RT) *g * w )
> > but the results in (m/s ) are in the order of 10^-3. I know it's not a
> > Grads problem. but I'm an aerospace student and I need to find out if
> > anything is wrong with this equation or the results or not. ( I'm not
> > really familiar with meteorology!)
> >
> > for example:
> > if  omega= 0.10595
> > & g=9.807
> > & R=287
> > & P= 100000 Pa
> > & T=294.27
> > resulted value is W=0.00912 (m/s)
> >
> >
> > Thanks in advance,
> > Alireza
> > _______________________________________________
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> > gradsusr at gradsusr.org<mailto:gradsusr at gradsusr.org>
> > http://gradsusr.org/mailman/listinfo/gradsusr
> >
>
>
> --
> Tereza Cavazos
> Departamento de Oceanografia Fisica
> CICESE
> Ensenada, Baja California, MEXICO
> http://usuario.cicese.mx/~tcavazos/<http://usuario.cicese.mx/%7Etcavazos/>
>
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> gradsusr at gradsusr.org<mailto:gradsusr at gradsusr.org>
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>

>

> --
> Alireza Azargoun

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--
Alireza Azargoun
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