APPENDIX B 59 



180 150 120 90 60 



30 60 90 120 150 180 



Figure B-14. Annual mean of sea-level refractivity, N . 



180 150 120 90 60 



30 60 90 120 150 180 



180 150 120 90 60 



30 60 90 120 150 180 



FIGURE B-15. Annual mean of refractivity gradient between surface and 1 km, AN. 



