NCL is getting slower when I call "user defined function" many times

Dear NCL users

I'm calculating the tropopause for temperature profiles using NCL's "do
loop" and a user-defined function.
The user-defined function works for a single temperature profile, and do
loop call the function for each temperature profiles.
There is an exactly same calculation ("just calling of a function I
defined") in the do loop, so each step is expected to take a same time.
However the do loop takes longer and longer time as it progresses.

Here is the example
(elapsed time (time1-time0) for each step keeps increasing)
[joowan@rossby ttl_joowan]$ ncl *main.ncl*
 Copyright (C) 1995-2011 - All Rights Reserved
 University Corporation for Atmospheric Research
 NCAR Command Language Version 6.0.0
 The use of this software is governed by a License Agreement.
 See http://www.ncl.ucar.edu/ for more details.
(0) loop i = 1 elapsed time: 4
(0) loop i = 2 elapsed time: 5
(0) loop i = 3 elapsed time: 7
(0) loop i = 4 elapsed time: 9
(0) loop i = 5 elapsed time: 10
(0) loop i = 6 elapsed time: 11
(0) loop i = 7 elapsed time: 13
(0) loop i = 8 elapsed time: 14
(0) loop i = 9 elapsed time: 15
(0) loop i = 10 elapsed time: 17
(0) loop i = 11 elapsed time: 19
(0) loop i = 12 elapsed time: 20
...
...
(0) loop i = 31 elapsed time: 52
(0) loop i = 32 elapsed time: 54

I tested this with the newest version 6.1.2, but it has the same problem.
It is very strange because I never met this problem with NCL before.
One thing I found is memory use keeps increase until unreasonable size. I
guess "user defined function" doesn't return memory, so lots of calling it
takes bigger memory and longer time. (If I directly do the calculation in
the code, not using a user-defined function, that slow down does NOT
happen.) But it is just my crude guess...
It is a serious problem for me, because the do loop goes up to 3000 for
model analysis, and the computation time grows exponentially.
Is there any Known issue for this problem or treatment?
Any comment will be appreciated.

Thanks so much

Best!
Just in case, I attached my script and data

Joowan

P.S.
I'm using
Linux rossby.meteo.mcgill.ca 2.6.34.9-69.fc13.x86_64 #1 SMP Tue May 3
09:23:03 UTC 2011 x86_64 x86_64 x86_64 GNU/Linux
GCC version is "gcc version 4.4.5 20101112 (Red Hat 4.4.5-2) (GCC)"

-- 
Joowan Kim
Atmospheric and Oceanic Sciences
McGill University
e-mail : joowan.kim@mail.mcgill.ca
                joowan.k@gmail.com

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