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<<  QNEG4 WARNING from TPHYSAC, http://bb.cgd.ucar.edu//viewtopic.php?t=133 >>

PosterpjrPostedMon Mar 07, 2005 3:58 pm MST, http://bb.cgd.ucar.edu//viewtopic.php?p=397#397
Message: Hi,
<br />
<br />I am new to CAM3. Its an Altix - Itanium machine that I am working on. I have used Intel compilers V 8.0 for building CAM. I get the below error message while running CAM3. 
<br />
<br /> QNEG4 WARNING from TPHYSAC , lchnk =   5; Max possible LH flx exceeded at    1 points.  Worst excess =  -2.9597E-06 at i =  121
<br /> QNEG4 WARNING from TPHYSAC , lchnk =   5; Max possible LH flx exceeded at    1 points.  Worst excess =  -5.4597E-08 at i =  122
<br />.
<br />.
<br />.
<br /> QNEG4 WARNING from TPHYSAC , lchnk =   4; Max possible LH flx exceeded at    1 points.  Worst excess =  -1.4211E-06 at i =  125
<br /> QNEG4 WARNING from TPHYSAC , lchnk =   4; Max possible LH flx exceeded at    1 points.  Worst excess =  -4.2685E-09 at i =  126
<br />
<br />MPI: MPI_COMM_WORLD rank 0 has terminated without calling MPI_Finalize()
<br />MPI: aborting job
<br />MPI: Received signal 11
<br />
<br />Any pointers in this regard will be of great help.
<br />
<br />T!
 hanks,
<br />rpb
<br />The QNEG4 errors are usually generated at the beginning of a model run when there are inconsistencies between the model initial conditions for land and atmosphere. I wouldnt worry about them unless they persist.
<br />
<br />The MPI errors is obviously more serious. I would first try running the
<br />model single tasked, single threaded, and see if problems still occur.
<br />
<br />One of the fundamental tests we do to see whether the model is
<br />correctly implemented is to run it in a variety of configurations and assure ourselves that the simulations differ at an acceptable level. So, for
<br />example, I would check:
<br />1) does the model run for an extended length (at least a few days)
<br />without MPI or OPENMP turned on?
<br />2) does the model give the similar answers when MPI and OPENMP are turned on?
<br />3) does the model give the exact same answer when run with a given
<br />set of compiler options (eg OPENMP and MPI choice) but a !
 different number of processors.
<br />
<br />There are other p!
 osts on 
the forum that discuss these issues in more detail, and the appropriate testing procedures, but it is worth noting that
<br />just getting the model to compiler is no guarantee that you are going to 
<br />get the right answer.
<br />
<br />Phil

------------------------------

<<  time step in CCM3, http://bb.cgd.ucar.edu//viewtopic.php?t=117 >>

PosterpjrPostedMon Mar 07, 2005 4:04 pm MST, http://bb.cgd.ucar.edu//viewtopic.php?p=398#398
Message: Dear CCM and CAM users,
<br />
<br />I am using the CCM3.6.6. within Paleo-CCSM simulations with continents different from today. With some
<br />continental geometries everything worked fine, but now I tried a new one, and then the atmosphere model
<br />crashes at some point with the error message:
<br />
<br />CUBYDR: Departure point out of bounds: jcen,icount,pgls= 39,  1726,  1728
<br />
<br />which seems to have to do with the length of the time step.
<br />I use the T31 resolution with a time step
<br />
<br />DTIME=1800
<br />
<br />as it should be for this resolution. The problem seems to be solved by just setting the time step to 1200
<br />seconds as is recomended for the T42 resolution. However, then physical parametrizations also change, and I
<br />don't know what I have to expect from that. Can I just change the time step without changing other
<br />parameters?
<br />
<br />It would be nice if I could get some help with that.
<br />
<br />Best regard!
 s,
<br />
<br />Anna
<br />
<br />--------------------------------
<br />Dr. Anna von der Heydt 
<br />Institute for Marine and Atmospheric Research
<br />Utrecht University
<br />The Netherlands
<br />
<br />The nominal time step to use with the model is really controlled by
<br />the strength of the wind field, in relation to a CFL criterion. For present day conditions the strongest winds occur in the northern hemisphere polar night in the middle atmosphere, and it is this wind speed that
<br />controls the required time step length. Shifting the continents etc will
<br />obviously change the wind behavior and it is no surprise to me that
<br />you require a smaller time step.  My response to your question about
<br />the possible need for retuning is that it depends on your experimental setup. If you are going to compare to a present day simulation you would want to run both simulations with the same (shorter) time step length.
<br />Then, depending on how far off your p!
 resent day simulation is, you will need to consider the need f!
 or a ret
uning exercise.
<br />
<br />Phil

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