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See ChangeLog CAM5_3_69 and CAM5_3_85, and Jira AG-290. Bug fix available from github branch on github provided by Balwinder: singhbalwinder/cam/rrtmg-limiters
CAM5_3_69 (by bsander, santos, and cacraig)" A “bug fix for exponentials in rrtmg_sw_reftra" "to replace the lookup table by double precision exponentials". This is to prevent “the rare occurrences of extreme hot surface temperatures (exceeding 100 C)”, which is due to “the use of low precision LUT”. Performance slowdown is in the run-time noise and “Rich Neale who inspected the 5 year comparison runs says the simulations look pretty near identical”.
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Po-Lun's 5-yr runs on Cori indicates that the impact on the overall climate is negligible. The only noticeable difference is that the bug fix produces a colder stratosphere (temperature near model top (above 70km, only seen in the WACCM plot). See AMWG diagnostics (flx01a: control simulation with v1b tuning; v1b_rrtmg_bugfix: with the rrtmg bug fix).
Balwinder's 5-yr runs on EOS gives the same conclusion that the impact of the bug on the overall climate is negligible.
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