Dear ferret users
I have precipitation data for the period 1979-2010 from GPCP
I have make the camposit of JJAS for EL Nini Modoki years. (from the anomaly)
I
want to check 95% signifinat from the JJAS camposit for the El Nino
modoki by using significant at 90% confidence level from a 2-tailed
Student’s t-test. i have tried like this
use "/home/abhishek/
gpcp_precipitation_1979_2010.nc"
set region/x=30E:60W/y=-50:50
set mem/size=900
SET WINDOW/ASPECT=0.55
! <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< Calculation for 95% confidencde level<<<<<<<
!let alpha = 0.025 ! alpha= 1%-95% = 5% = 0.05, alpha/2=0.025
let alpha = 0.01 ! alpha= 1%-90% = 10% = 0.01, alpha/2=0.005
!
<<<<<<<<<<<<<< calculation
for degree of freedom
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
let df = 384-1 ! total number of points-1, n=384 in my case
!<<<<<<<<<<<<<Now we see the t table for the t(1-alpha,n-1)
let t_sta = 2.330 !from the student t table alpha=0.01
!<<<<<<<<<<<<<<<<<Calculation
for standatd error
<<<<<<<<<<<<<<<<<<<<<<<<<<<<
let p = t[gt=precip] ! before doing i have detrended the data
let q = precip
go regresst
let myline=p*slope+intercep ! Here myline=qhat
let precip_detrend = precip-myline
let var_detrend=precip_detrend[l=@var]
let sd_detrend=var_detrend^0.5
let S_E=(sd_detrend/df^0.5) ! calculation for standard error S.E= standard_deviation/n^.05
!<<<<<<<<Calulation
for critical value
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<!
let t_crit = t_sta*S_E ! calculation for critical value Standard_error*t_sta
!<<<<<<<<<<<<<calculation
for 90% of significant level
<<<<<<<<<<<<<<<<<<<<<<<<<<<!
!<<<<<<<<<<<<<Calculation
for
mean<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<!
use climatological_axes
cancel data climatological_axes
let precip_detr_cli=precip_detrend[gt=month_`precip_detrend,return=cal`@mod]
let precip_detr_anm=precip_detrend-precip_detr_cli[gt=precip_detrend]
!<<<<<<<<<<<<Calculation
for confidence interval
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<!
let precip_90_u = precip_detr_cli[gt=t_crit] + t_crit ! (mean+t_crit)
let precip_90_l = precip_detr_cli[gt=t_crit] - t_crit ! (mean-t_crit)
!<<<<<<<<<<<<<<<<<<Calculation
for precipitation 95 signifivant
<<<<<<<<<<<<<<<<<<
let var_sig = if precip_detr_anm ge precip_95_l and precip_detr_anm le precip_95_u then 1
let pre_95 = var_sig*precip_detr_anm
!<<<<<<<<<<<<<<<<<Camposit
for JJAS during the canonical years
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<!
let var1=pre_95[t=15-jun-1986:15-sep-1986]
let var2 =pre_95[t=15-jun-1990:15-sep-1990]
let var3= pre_95 [t=15-jun-1991:15-sep-1991]
let var4= pre_95 [t=15-jun-1992:15-sep-1992]
let var5= pre_95 [t=15-jun-1994:15-sep-1994]
let var6= pre_95 [t=15-jun-2002:15-sep-2002]
let var7= pre_95 [t=15-jun-2004:15-sep-2004]
let precip_summer_jjas=(var1+var2+var3+var4+var5+var6+var7)/7