[gradsusr] Help: Extent

[Davide Sacchetti]

actually I don't know, just a detail:

the method for calculating GRID area is correct (but in km2, not Mk2):
area = (dx*dy)/1000000 is in Mk2

define xx=tloop(asum(ones*area,lon=0,lon=360,lat=-90,lat=0))/1000000

it seems correct (I've not checked against your data)

bye bye
Davide


On Tue, 2013-04-23 at 14:20 +0000, Fernanda Casagrande wrote:
> Dear All,
> 
> I have a problem with the calculation of the area (million km2).
> 
> I have a file of sea ice (ice concentration data from 0-100%) and I
> need to create a time series with a total extension of sea ice in the
> arctic and antartica (million km2). For this calculation, usually
> consider only areas with ice concentration equal to or above 15%, so I
> used the function maskout.
> 
> The. gs is running but the values ​​for the Arctic are wrong, can
> someone help me? Some other method to calculate the area (million km2)
> 
> these data are from satellite.
> 
> 
> 'sdfopen X172.16.9.158.108.11.23.58.nc'
> *calculate area (million km2)
> 'dx=2*3.1416*6371*cos(lat*3.1416/180)/360.0*cdiff(lon,x)/2 '
> 'dy=2*3.1416*6371/360.0*cdiff(lat,y)/2'
> 'area=(dx*dy)'  
> 'fracao=area*(icec/100)'
> 
> 
> say 'calcula a area'
> 
> 'set lon 0 360'
> 'set lat -90 90'
> 'set t 1 last'
> 
> 'define ones = const(const(maskout(icec,icec-15),1),0,-u)' 
> 'set x 1'
> 'set y 1'
> 
> 
> 
> 'define xx=tloop(asum(ones*area,lon=0,lon=360,lat=-90,lat=0))'
> 'd xx'
> 
> 'ltrend xx a b c'
> 'set ccolor 2'
> 'd a';'d b'
> trend=subwrd(result,4)
>  say 'trend='trend
> ' d c'
> rmse=subwrd(result,4)
>  say 'rmse='rmse
> 
> 'draw title Antarctic Sea Ice obs incl.'trend' rmse. 'rmse' '
> 
> 
> regards
> 
> 
> 
> 
> 
> 
> Fernanda 
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-- 
--> Attenzione cambio indirizzo: davide.sacchetti at arpal.gov.it
--
Davide Sacchetti
Centro Funzionale Meteo Idrologico di Protezione Civile della Regione Liguria
ARPAL Unità Tecnica Complessa di livello Regionale
V.le Brigare Partigiane 2 16121 Genova (I)
tel: +39 010 6437535                    fax: +39 010 6437520
mail: davide.sacchetti at arpal.gov.it     web: www.meteoliguria.it