About GCM simulations in Southwestern US

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yongguang zhang

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Aug 27, 2010, 3:52:27 PM8/27/10
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Hi Everybody,

I got some questions about GCM simulations in the southwestern US. I am not sure if I could ask these here. Maybe somebody had some experiences about this.

I am working on a project about climate change impact in the southwestern US. My study area range 31°-34°N and 112° -108° W.  For the GCM models, the longitude are 248° -252°E.

I retrieved some GCM outputs of several GCM models (including HadCM3, ECHAM5, CCCma (T_63), GFDL_CM2.1, NCAR_PCM, NCAR_CCSM3) for this area from IPCC data center.  I compared the simulations of 20C3M experiment to the historical data, and found that the GCM models simulated more precipitation in winter  month than that in summer monsoon month. That's way too far from the observations. First, I thought maybe I retrieved the data from the wrong grid cell, and checked them out many times, it's still the same.

So I just wonder whether anybody have the same experiences and could share some information with me.

Thanks

John


John Sully

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Aug 27, 2010, 9:39:57 PM8/27/10
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It is well known that GCM simulations of regional climate on sub continental scales are poor.   It is probably better to look at region climate models driven by the forcings output by the GCMS.  This is a technique which has been used, for example, by Kerry Emmanuel in his more recent work looking at hurricane activity (which caused him to back off on some earlier predictions based on GCMs).

I would try to find papers looking at the SW US using RCMs.  This might provide a better look at what might happen.

--John

Date: Fri, 27 Aug 2010 12:52:27 -0700
Subject: [Global Change: 3810] About GCM simulations in Southwestern US
From: yongg...@gmail.com
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Alastair

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Aug 28, 2010, 11:17:09 AM8/28/10
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On Aug 27, 7:52 pm, yongguang zhang <yongguan...@gmail.com> wrote:
> Hi Everybody,
>
> I got some questions about GCM simulations in the southwestern US. I am not
> sure if I could ask these here. Maybe somebody had some experiences about
> this.
>
> I am working on a project about climate change impact in the southwestern
> US. My study area range *31°-34°**N* and 112° -108° ** *W*.  For the GCM
> models, the longitude are 248° -252°E.
>
> I retrieved some GCM outputs of several GCM models (including HadCM3,
> ECHAM5, CCCma (T_63), GFDL_CM2.1, NCAR_PCM, NCAR_CCSM3) for this area from
> IPCC data center.  I compared the simulations of 20C3M experiment to the
> historical data, and found that the GCM models simulated more precipitation
> in winter  month than that in summer monsoon month. That's way too far from
> the observations. First, I thought maybe I retrieved the data from the wrong
> grid cell, and checked them out many times, it's still the same.
>
> So I just wonder whether anybody have the same experiences and could share
> some information with me.
>
> Thanks
>
> John

When are these projections you are looking at for: 25 years, 50 year
or 100 years ahead? You really have to wait until then before you
dismiss them.

IMHO, climate, like weather, is Chaotic. So you can get 10 dry years
then ten monsoons. I believe therw are still some glaciers in SW USA,
so when they disappear the climate may switch then. Even if that
happens it may only affect the coastal strip, because a feature of the
Chaos of climate is that it is fractal, and while one region goes one
way the adjacent region does the opposite. Moreover within those
regions you will also get contrasts.

Mandelbrot got his inspiration for the fractal nature of nature from
the English meteorologist L. F. Richardson who wrote:

Big whirls have little whirls
that feed on their velocity,
and little whirls have lesser whirls
and so on to viscosity.

HTH,

Cheers, Alastair.

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