OBSGRID segfault in "obs_sort_module.F90"

[greent12]

This is an issue opened in the obsgrid forum: https://forum.mmm.ucar.edu/threads/obsgrid-exe-fails-after-a-few-seconds.13474/

Summary of the problem: In certain scenarios, obsgrid segfaults in "obs_sort_module.F90" around line 3158. This segfault has to do with the pointer variable "next." Admittedly, my knowledge of pointers in fortran is very limited, so I will refrain from making a judgement on exactly what is happening with this pointer.

To reproduce this error with the current version of the source code, you can use a single sounding in little R format. I am attaching my namelist.oa(linked as namelist.oa.txt) and little R file, obs:2021-01-01_00(linked as obs.txt) containing a sounding. The user will have to create the metgrid file, as it won't let me upload that file. My domain is centered over Oklahoma City for 0000 UTC Jan 01, 2021. After trying obsgrid with the single sounding, try cutting down the sounding to a single data record (making sure to change the appropriate fields in header record and tail integers to indicate just one data record). Obsgrid will still fail with a segfault. Finally, using the little R file with the single data record, change the "sounding" logical from "T" to "F". Obsgrid will now run to completion without the segfault error. These different scenarios are mentioned for use in debugging and trying to isolate the source of the problem, and I am not considering these to be an actual workaround.

Here are my namelist and sounding little R files for input to obsgrid.exe. Note, I've added the '.txt' extension so that they can be included in this issue description:

namelist.oa.txt
obs.txt