_iL.-^_&, 



and +/- 16cm/sec respectively. In 

 comparing the melts due to forced 

 convection between the "master" 

 and "modified" currents, the real- 

 time input serves to reduce the 

 daily differences for each iceberg 

 by nearly half. The meteorologi- 

 cal conditions during the study 

 also helped to reduce the daily 

 differences in melt between using 

 the shallow- and deep-drogued 

 drifter velocities. Rapid changes 

 in the weather prevented wind 

 direction from remaining constant 

 (within a 60° arc of the compass) 

 for periods longer than 27 hours; 

 wind shifts averaged every 12 

 hours. Consequently, the sum of 

 the differences for each iceberg 

 never exceeded +1- 70cm for the 

 study period, or an averaged error 

 of +/- 21 cm/day. 



These statistics probably repre- 

 sent the minimum errors. In the 

 IIP region 5- to 7-day wind events 

 occur. An effort to control the 

 growth of these errors may be ap- 

 propriate. Wind-induced compo- 

 nents of the current could be 

 extracted from the dynamic 

 iceberg drift model and substi- 

 tuted for the existing input. This is 

 perceived to be a nnoderate level 

 of effort for the IIP. 



WAVE EROSION: 

 GLOBAL VS REGIONAL SCALE 

 PRODUCTS 



Wave erosion, which is induced 

 by heat convection from the 

 turbulent maximum orbital velocity 

 caused by the wave field sur- 

 rounding the iceberg, is computed 

 by the model. This convection is 

 124 



proportional to wave height (H) 

 times relative temperature (T), and 

 inversely proportional to wave 

 period (P). The model assumes 

 the effects of the wave field are 

 non-directional, implying that the 

 iceberg is melted uniformly from 

 all directions (White et al, 1980). 

 This assumption probably overes- 

 timates melt due to wave erosion. 

 Regardless, its melt contribution is 

 up to ten times greater than melt 

 by forced convection, and around 

 100 times greater than buoyant 

 convection. The applicability and 

 accuracy of the environmental 

 parameters used to model wave 

 erosion thus greatly affect the 

 daily melt rate estimated by the 

 model. 



The model computes T from sea 

 surface temperature. Significant 

 wave height and a primary wave 

 period, which is that period 

 associated with peak energy 

 observed in the full wave spec- 

 trum, are currently used by the 

 model for H and P respectively. 

 Sea surface temperature is as- 

 sumed to be the best parameter 

 from which the relative tempera- 

 ture term for wave erosion is 

 calculated, and it is readily avail- 

 able from data centers. Data 

 center products representing H 

 are significant wave height, sea 

 height, or swell height, and 

 products representing P are peal< 

 periods for the full, sea, or swell 

 energy spectra (Clancy, 1987). 

 When the model was implemented 

 in 1983, the wave parameters 

 currently used were the only ones 

 available. 



Table E-4 shows the differences 

 between our observations and 

 those analysis values produced by 

 operational data centers: U. S. 

 Navy Fleet Numerical Oceanogra- 

 phy Center, Monterey, CA (FLE- 

 NUMOCEANCEN); and Canadian 

 Forces Meteorological and 

 Oceanographic Center, Halifax, 

 Nova Scotia (METOC). The 

 global-scale (250km grid-spacing) 

 analyses were produced by FLE- 

 NUMOCEANCEN using its 

 computerized Expanded Ocean 

 Thermal Structure (EOTS) analysis 

 and Global Spectral Ocean Wave 

 Model (GSOWM) (COMNAVO- 

 CEANCOM, 1986). The regional- 

 scale (estimated from 50 to 1 00km 

 grid-spacing) analyses were 

 produced by METOC Halifax. 

 METOC depends on human 

 interpretation of surface thermal 

 observations and uses a paramet- 

 ric ocean-wave model (MacDonald 

 et al, 1987) which is qualitatively 

 blended with ship observations. All 

 data center values were interpo- 

 lated to each iceberg's OOOOZ 

 position. All values are for OOOOZ, 

 except for the METOC sea state 

 analyses, which were analyzed at 

 1800Z. The METOC 1800Z sea 

 state analysis normally contains 

 more ship observations than the 

 METOC OOOOZ analysis, thereby 

 improving the quality of the 1800Z 

 analysis. 



FLENUMOCEANCEN and METOC 

 sea surface temperature products 

 differed. The FLE- 

 NUMOCEANCEN-produced 

 temperatures averaged 1.3°C 

 colder than the observed values for 

 the cluster; the METOC-produced 



