multiplied by T and ZTIME to obtain the amount 

 of deterioration due to wind forced convection: 



WINFO = FC*T*ZTIME*0.5/100 



(8*) 



As can be seen in Table C-2, wave erosion is 

 the most important method of iceberg 

 deterioration. Since there is no realistic method 

 to model calving caused by wave erosion, 

 calving has been ignored. The equation 

 selected to model deterioration caused by 

 wave erosion is (White, et al., 1980): 



V m * t/H = 0.000146(E/H)**0.2 



(9*) 



where t is wave period in sec, H is wave height 

 in centimeters, E is the height of the roughness 

 on the iceberg wall in centimeters, and V m is 

 the melting in m/sec/°C. This equation is 

 solved for melting rate in meters per day: 



WAVE = (XAMP*0.000146*(2.0/XAMP)**0.2*24*3600 



*ZTIME*0.5/IPER*T/100 



(10*) 



Where XAMP is wave height in centimeters, 

 IPER is wave period in seconds. In order to use 

 the selected equation, a value for the 

 roughness on the iceberg wall had to be as- 

 sumed. A value of 2.0 cm was chosen. The ef- 

 fects of selecting another value for iceberg 

 roughness is shown in Figure C-4. The shape of 

 the curve between 1 and 3 cm does not change 

 significantly with wave height. 



The total melt for the time period between 

 the present analysis run and the previous run is 

 calculated: 



XMELT = BUOY + WINFO + WAVE + SUN (11*) 



and then a total melt percent is calculated: 



PERMELT = PERMELT + ((XMELT/CHARL)*100) (12*) 



where CHARL is the characteristic length of 

 the appropriate size of iceberg. These calcula- 

 tions are performed for each berg. When 

 PERMELT (the percent of the original length 

 that has melted) exceeds 175%, a flag is 

 printed on the output listing notifying the 

 operator that the berg should be considered for 

 deletion from the active berg file. 



Environmental Inputs 



Sea surface temperature (to nearest °C), 

 wave height (to nearest foot), and wave period 

 (to nearest two seconds) analysis for 0000Z and 

 1200Z are received daily from FNOC. The infor- 

 mation is interpolated by FNOC and is received 



by IIP on a 1° latitude by 2° longitude grid. 

 There are occasions when some of the points 

 on the grid are not determined (values are set to 

 zero) or one or more of the products are not 

 available. Setting a missing parameter (except 

 SST when the actual SST is below zero) to zero 

 will make an iceberg melt slower. If a parameter 

 file has not been updated, the latest available 

 information will be used when the deterioration 

 model is run. 



The most critical parameter received from 

 FNOC is sea surface temperature. Temperature 

 is a controlling factor in equations (3*), (8*), 

 and (10*). As can be seen in Table C-3, an error 

 in temperature, particularly when the overall 

 sea surface temperature is low, will have 

 significant effects on the melting rate of an 

 iceberg. 



The FNOC environmental inputs were 

 evaluated this spring during an IIP cruise and a 

 transit of the IIP area by USCGC NORTHWIND. 

 Hourly measurements of sea surface 

 temperature and wave height were taken over 

 the two periods, totalling about eight days. Dur- 

 ing a six day period in March, the actual sea 

 surface temperature compared well with the 

 predicted values from FNOC. The difference 

 was always less than 1 °C (maximum 

 temperature in area surveyed was 4.8°C). The 

 differences observed in a two day transit of the 

 area in June were higher, with a maximum dif- 

 ference of 3.3°C. In nearly all cases, the ob- 

 served temperature was more than the 

 predicted temperature. This error would cause 

 the actual rate of deterioration to be faster than 

 that predicted by the model. 



The observed wave height was consistently 

 less than that predicted by FNOC during the 

 eight-day period. The largest observed dif- 

 ference was 22 feet. The differences between 

 the observed and the predicted wave heights 

 appeared to increase with the height of the 

 predicted waves. This error would cause the 

 predicted deterioration rate to be faster than 

 the actual rate. 



Table C-3 



SST 



Number of Days 



Number of days required to melt a 100 meter 

 iceberg at a given Sea Surface Temperature 

 assuming: Wave height = 6', Wave period = 10 

 sec and Relative Velocity = 25 cm/sec. 



71 



