date: Fri Nov  6 08:43:19 1998
from: Mike Hulme <m.hulme@uea.ac.uk>
subject: Re: Inquiries
to: diane@moe.gov.lb

Diane,  

Answers to your two questions:

1. You are right in idenitfying box (32.5-35N,33.75-37.5E) as the closest HadCM2 box for Lebanon (NOTE: this definition defines the edges of *one* box).

This box is row 23 and column 11 in the HadCM2 grid layout, but remember that each row has 96 gridboxes (360/3.75).

To identify the actual box number in the 7008 member array, you need to multiply 22(rows) by 96 = 2112 and then add 11 (i.e, the 11th column in row 23) which gives you 2123.

If you use the *four* boxes you identified (and you might argue that for Lebanon that you should) then you need box numbers 2122, 2123, 2218, 2219.
But you should note that boxes 2122 and 2218 are 'ocean' and the other two are 'land' in HadCM2.  Your climate responses in the model will be quite different between ocean and land and really you only want the land response.

2. The choice of what forcing (0.5% or 1% pa) is just that - a choice.  And who knows which rate of GHG will be realised.  The IS92a scenario is about 1% pa. but IPCC never said IS92a was a best guess scenario - just one of 6 possibilities they identified.  Current GHG concentration increase is about 0.7% to 0.8% p.a.

My preference in any scenario and impatc study would be to choose both, i.e., explore the impacts of a low growth *and* and a high growth scenario.

By the way, I am not aware that IPCC have ever said that GHG doubling by 2100 is the most likely.  

Regards,

Mike

At 14:55 05/11/98 +0200, you wrote:
>Dear Dr. Hulme,
>I thank you for your prompt response. However, your explanation was not
>very clear. I am here informing you of the steps we have followed to
>identify GCM values relevant to Lebanon:
>- Lebanon's coordinates are:
>  33deg3' - 34deg41' N and 35deg6'-36deg37' E
>- The closest to these in the HADCM2 grid are:
>  32.5 -35 N and 33.75 -37.5 E
>- They correspond to HADCM2 coordinates :
>  24-23 N and 10-11 E
>- Since 96 longitudes x 73 latitudes = 7008 GCM output results, the
>relevant grid box numbers have been obtained by multiplying x by y:
>10x23=230
>10x24=240
>11x23=253
>11x24=264
>Therefore Lebanon lies at the corners of 4 boxes on the grid.
>
>The box number 2123 you proposed is way out of range according to my
>method.
>Please list the steps you followed to get this number or let me know
>wether my method is correct.
>
>Another thing, we have chosen 1% CO2 increase which implies a doubling
>of CO2 by the year 2070 but we have found unreasonnably high values of
>temperature increase. ex:October minimal T increase listed values up to
>8deg centigrade by the year 2020.
>Would it be more suitable to choose 0.5 % CO2 increase with doubling
>around the year 2130 bearing in mind that the doubling date specified by
>IPCC guidelines is the year 2100?
>
>Thank you
>Diane
>
>