ttest in namelist_ice

Why set ttest? Shouldn't we be creating ice if sst is at freezing point of sea water?


namelist_ice

ttest       =  2.0      !  threshold water temperature for initial sea ice


Source: http://forge.ipsl.jussieu.fr/little_nemo/browser/vendor/nemo/current/NEMOGCM/NEMO/LIM_SRC_3/limistate.F90?rev=2

95

	t_bo(:,:) = tfreez( tsn(:,:,1,jp_sal) ) * tmask(:,:,1)       ! freezing/melting point of sea water [Celcius]
96
97	DO jj = 1, jpj                                       ! ice if sst <= t-freez + ttest
98	DO ji = 1, jpi
99	IF( tsn(ji,jj,1,jp_tem)  - t_bo(ji,jj) >= ttest ) THEN   ;   zidto(ji,jj) = 0.e0      ! no ice
100	ELSE                                                     ;   zidto(ji,jj) = 1.e0      !    ice
101	ENDIF
102	END DO
103	END DO