bug: the ncep error module crashes for obs with pressures < 1 mb if debug flags on

🐛 the ncep error module crashes for obs at pressures < 1 mb if debug flags on

Describe the bug

0. check out the ncep_errors branch
1. copy over the main branch observations/obs_converters/obs_error/ncep_obs_err_mod.f90
2. build developer_tests/obs_converters/obs_error/work/obs_ncep_error_test WITH DEBUGGING FLAGS!!
3. with the original ncep obs_error_mod.f90 it crashes when the pressure is < 1.0 when taking log(0)
4. check out the ncep_obs_err_mod.f90 from this branch
5. with the fixed ncep_obs_err_mod it doesn't crash

Error Message

it crashes when taking the log of 0 if debugging flags are on. it silently computes log(0) == 0 with the optimized flags which is why this probably hasn't been caught before. that happens to return a valid value, so this hasn't been a numerical problem. but if you turn on debugging flags to debug something else, you crash here instead.

Version of DART

the bug is on the main branch (and all others)

Have you modified the DART code?

Yes, the fixes are on the ncep_errors branch

Start with observations/obs_converters/obs_error/ncep_obs_err_mod.f90 and compare it with the version on the ncep_errors branch. Build developer_tests/obs_converters/obs_error/work/obs_ncep_error_test with debugging flags and reproduce the case using observation pressures below 1 mb. Done means the test no longer crashes in that case.