problem in plotting trajectory using global data

From: Ufuk Utku Turuncoglu <u.utku.turuncoglu_at_nyahnyahspammersnyahnyah>
Date: Mon Dec 28 2009 - 00:30:42 MST

Hi,

I try to plot trajectories using ECMWF ERA40 dataset and gsn_polyline
function. The problem is NCL plots artificial parallel lines to connect
trajectory path that passes from 0 longitude. I attach two different
plot that shows the problem. The track_raw is plotted without any
modification over longitude variable. In this case, NCL does not draw
trajectory correctly (see around 0 longitude) but if trajectory continue
from right side of the map to left one, the trajectory looks good. The
gsn_polyline function takes account the cyclic point. To correct the
problem, i try to modify longitude based on following criteria,

if (lon .gt. 180.0) then
  lon = lon-360.0
end if

and you can see the plot in track_lon-360 file. In this case, NCL draws
the trajectory correctly in 0 longitude but other one is wrong. Is there
any solution for it? How can i draw both one in the same plot? May be i
could draw to split them into two different plot and i can use overlay
function after that but there could be easier solution.

Example track data:

TRACK_ID 421
POINT_NUM 28
44 0.502097 73.913086 2.791847e+00
45 1.147323 73.242691 6.004342e+00
46 1.515933 71.030869 8.055365e+00
47 1.298914 68.667351 8.317214e+00
48 359.402008 64.137444 6.039263e+00
49 357.505035 59.299000 5.366868e+00
50 357.192780 55.944424 3.733113e+00
51 356.532043 53.748260 3.187781e+00
52 357.106659 50.272743 4.486194e+00
53 358.536896 47.064690 7.892114e+00
54 1.560772 44.485828 1.053436e+01
55 3.515971 42.982204 1.313965e+01
56 4.783206 41.885006 1.440779e+01
57 5.995381 41.050323 1.705493e+01
58 6.665836 39.986656 1.876119e+01
59 8.133615 39.737965 1.857688e+01
60 10.046181 39.868969 1.736890e+01
61 11.255802 40.183357 1.643047e+01
62 13.257846 40.473854 1.531118e+01
63 14.234121 40.869377 1.190000e+01
64 11.396882 41.550262 9.673411e+00
65 8.818160 40.083595 7.746586e+00
66 9.923666 39.717323 1.048592e+01
67 10.582663 40.126450 1.282651e+01
68 13.352924 39.639008 1.332119e+01
69 15.406126 39.694725 1.596746e+01
70 17.604263 40.084320 1.627496e+01
71 20.176548 40.460274 1.413614e+01

TRACK_ID 535
POINT_NUM 16
84 152.471680 40.310097 1.126093e+01
85 156.280151 40.776115 1.342023e+01
86 160.719894 40.529774 1.639741e+01
87 164.660049 40.821220 1.767797e+01
88 168.426666 41.405369 1.843181e+01
89 172.029724 42.594719 2.017140e+01
90 176.103165 43.760841 2.256382e+01
91 179.600800 45.465179 2.235561e+01
92 182.329681 47.291069 2.268816e+01
93 183.897781 49.648006 2.256968e+01
94 185.061844 52.251072 2.102557e+01
95 185.301468 55.234501 2.045463e+01
96 182.694244 58.037880 2.110939e+01
97 179.180893 59.926064 2.139341e+01
98 179.564819 61.041470 1.708533e+01
99 181.582291 61.607300 1.346206e+01

Thanks,

--ufuk

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Received on Mon Dec 28 00:30:59 2009

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