[ferret_users] regarding box averaging for time series

Dear ferreters,

i am bit confused regarding the box averaging. i am having HadiSST monthly data from 1979-2014.

This is the data specification

sh da
     currently SET data sets:
    1> ./sst_1979_2014.nc (default)
name     title                                     I         J         K         L         M         N
SST_1979_2014
SST[T=1-JAN-1979:1-DEC-2014    1:290     1:120     ...       1:432     ...       ..

sh gr sst_1979_2014
    GRID GEQ1
name       axis             # pts           start                        end
LON201_490 LONGITUDE         290mr        20.5E                     50.5W
LAT31_150 LATITUDE               120 r         59.5S                   59.5N
normal    Z
TIME      TIME                          432 i 01-JAN-1979 00:00    01-DEC-2014 00:00
normal    E
normal    F

Now i created the monthly anomaly using the following script

use sst_1979_2014.nc
use climatological_axes
cancel data climatological_axes
let temp_cli_1979_2014=sst_1979_2014[gt=month_`sst_1979_2014,return=cal`@mod]
let sst_anm_1979_2014=sst_1979_2014-temp_cli_1979_2014[gt=sst_1979_2014]

now i want to calculate the box averages for the following regions for the whole time series i.e. from 1-jan-1979 to 1-dec-2014
Region 1: 25°N–45°N, 140°E–145°W
Region 2: 10°S–10°N, 170°E–90°W
Region 3: 50°S–15°S, 150°E–160°W

so i use this transformation on latitudes and longitudes

let ipo_1=sst_anm_1979_2014[x=145W:140E@ave,y=25:45@ave]
let ipo_2=sst_anm_1979_2014[x=90W:170E@ave,y=-10:10@ave]
let ipo_3=sst_anm_1979_2014[x=160W:150E@ave,y=-50:15@ave]

but if flip the values in x then the result is something else

let ipo_1=sst_anm_1979_2014[x=140E:145W@ave, y=25:45@ave]
let ipo_2=sst_anm_1979_2014[x=170E:90W@ave, y=-10:10@ave]
let ipo_3=sst_anm_1979_2014[x=150E:160W@ave, y=-50:15@ave]

or shall i proceed in this manner to get the box average

let ipo_1=sst_anm_1979_2014[x=140:215@ave, y=25:45@ave]
let ipo_2=sst_anm_1979_2014[x=170:270@ave, y=-10:10@ave]
let ipo_3=sst_anm_1979_2014[x=150:200@ave, y=-50:15@ave]

i getting 215 by 360-145, 270 by 360-90, 200 by 360-160

so i am confused that which one is correct box averaging method when we have the box expanding from east to west or vice versa.

i hope this is not be a bug of ferret. Any suggestion or help will be appreciated.

thanks

REGARDS

Saurabh Rathore

M.Tech (Earth System Sciences & Technology)

Centre For Oceans, Rivers, Atmosphere & Land Science Technology

Indian Institute Of Technology, Kharagpur

contact :- 91- 8345984434