APPENDIX C 71 



180 150 120 90 60 



30 60 90 120 150 180 



180 150 120 90 60 30 



30 60 90 120 150 180 



Figure C-15. Percent of time gradient < —100 (N/km): May. 



Figure C-16. Percent of superrefractive layers thicker than 100 m: May. 



