[RegCNET] Stagnant upper atmosphere in RegCM?

[giorgi]

Hi Maurice

we just checked and it looks like the vertical velocity is set to 0 at the 
model top, i.e. the model has a rigid lid in sigma coordinates. This may 
affect the stagnant conditions in the upper atmosphere.

My sugegstion would be to raise the model top as high as possible (in the 
past we used up to 10hPa) and increase the resolution in the upper 
atmosphere, say above 200 mb, leaving the troposphere as in the standard 
version. maybe youc an add, just as an experiment, some 10 layers above 
say 250 mb, Also remember to have smooth transitions of layer depths, 
which actually seems like you have. You 
may 
also want to use relatively large domains to allow the model to work its 
internal physics. How large is your domain? and what resolution?


cheers,   F.


  > Filippo,
>
> Thank you for your email.  In our simulations, the model top is set at 44hPa so it's fairly close to the normal range.  We are using 23 levels, which we have redistributed to give more resolution toward the top of the model (see list of pressure levels below).  Would this cause any of the problems we are seeing?  Should we increase the number of levels (per the attached discussion), keeping the lower levels intact?  Would increasing the number of levels have any adverse effects on the model physics?
>
> The levels in the ICBC files are:
> 1005.74
> 983.45
> 941.93
> 878.52
> 797.89
> 705.67
> 608.05
> 516.75
> 439.21
> 373.37
> 317.48
> 270.07
> 229.88
> 195.85
> 167.03
> 142.58
> 121.79
> 104.12
> 89.10
> 76.26
> 65.24
> 55.80
> 47.72
>
>
> ----- Original Message -----
> From: GIORGI FILIPPO <giorgi at ictp.it>
> Date: Tuesday, May 17, 2011 3:46 am
> Subject: Re: [RegCNET] Stagnant upper atmosphere in RegCM?
> To: Maurice.McHugh at noaa.gov
> Cc: regcnet at lists.ictp.it
>
>
>> Dear Maurice
>>
>> I would say that at the moment RegCM is not really designed to do detailed
>> stratosphere studies, at least in its standard configuration. The model
>> top is usually between 50 and 100 hPa (you should check what you are using
>> as model top) and in its standard configuration there are only a few
>> levels above 200 hPa.
>>
>> It is great if you can test the model for stratospheric studies, but in
>> this case you probably need to substantially change its configuration
>> in
>> the upper troposphere/stratosphere, increase model top and use many more
>> layers.
>>
>> I would be itnerested in knowing your progress on this,
>>
>> cheers,   Filippo
>>
>>> Colleagues,
>>>
>>> I am trying to perform some ozone transport in RegCM3.  However,
>> ozone is
>>> not being transported below the upper atmosphere, even when the
>> input data
>>> has downwelling.  I believe this is because the atmosphere is basically
>>> stagnant above 200 hPa (omega ~= 0 hPa/s).  Has anyone else worked with
>>> RegCM in the upper atmosphere?  Is there something hard-coded within
>> the
>>> model that does this?  Or are there parameters I could change to
>> solve the
>>> problem?
>>>
>>> I’ve attached a GRADS plot that demonstrates the difference between
>> model
>>> input and output data for ozone.  The other plot is the difference between
>>> omega from the GCM and RegCM output.
>>>
>>> Many thanks for any ideas.
>>> _______________________________________________
>>> RegCNET mailing list
>>> RegCNET at lists.ictp.it
>>>
>>
>>
>

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# Filippo Giorgi, Head                                         #
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