Hi,
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Because the question did not go to the list, I will just answer. The longitude axis is a modulo axis, so your different box specifications wrap around the earth differently. Longitudes are always given from west to east. Often it's easy to use Ferret itself to see what is going on. Compare these two plots with your data:
shade/L=1 sst_anm_1979_2014[x=145W:140E,y=25:45]; go fland
shade/L=1 sst_anm_1979_2014[x=140E:145W, y=25:45]; go fland
In the first, you'll see land masses. That is because 145W:140E starts in the eastern Pacific and wraps across north America, the Atlantic Ocean, Europe and Asia, ending in the West Pacific. 140E:145W is entirely in the Pacific Ocean. It crosses 180. If E or W is not specified, then East longitude is assumed, so 140:215 is the same as 140E:45W.
A prettier script:
yes? use coads_climatology
yes? go basemap x=160w:160e y=0:90
yes? shade/over/L=1 sst[x=145W:140E,y=25:45]; pause
yes? go basemap x=120e:120w y=0:90
yes? shade/over/L=1 sst[x=140E:145W,y=25:45]; pause
yes? go basemap x=120e:120w y=0:90
yes? shade/over/L=1 sst[x=140:215,y=25:45]
Ansley
On 3/17/2016 2:06 AM, saurabh rathore wrote:
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 RathoreM.Tech (Earth System Sciences & Technology)Centre For Oceans, Rivers, Atmosphere & Land Science TechnologyIndian Institute Of Technology, Kharagpurcontact :- 91- 8345984434