APPENDIX B 



LABRADOR CURRENT COMPUTER MODEL 



A report on completion of size expansion and suggested operational implementation 

 by Captain Ronald C. Kollmeyer, Ph.D., USCG 



A hydrodynamic numerical predictive com- 

 puter model of the Labrador Current off the 

 Grand Banks of Newfoundland was completed 

 and tested against collected data in 1974. This 

 model had 4 layers with an area of one degree 

 square of latitude. The region modeled was lo- 

 cated at 43°51'N, 49°20'W. This model was 

 further tested in June 1975. For these tests, the 

 model successfully predicted the current induced 

 environmental changes in temperature and salin- 

 ity distribution for an eight day period. 



Further work has been completed on the model 

 (January- July 1977) in the form of larger area 

 coverage, two degree square of latitude, and an 

 increase to six layers. In addition, the model 

 has be«n made ready for operational testing and 

 use by International Ice Patrol by development 

 of a data handling system that allows direct in- 

 put of the vertical distribution of temperature 

 and salinity from hydrographic casts. This 

 work is reported on herein. 



Successful predictions through model operation 

 depend on the quantity of the collected input 

 data points together with the degree of synoptic- 

 ity. The more closely spaced the hydrographic 

 casts are in both space and time, the more correct 

 will be the output results. For the newly devel- 

 oped larger area model, data collection from a 

 surface vessel in the traditional manner (STD 

 casts) is not sufficiently fast to provide for either 

 the desired sampling density or the required 

 synopticity. It is expected that eventual devel- 

 opment by the Navy (NORDA, Bay St. Louis, 

 Miss.) of the air deployable, expendable salinity 

 temperature/depth sensors will provide the suit- 

 able data suite required by the model. Prototype 

 sensing probes are expected to be available by 

 1980/81 and possibly earlier. 



The model predicts currents relative to the 

 1000 decibar isobaric surface (approximately 

 1000 meters depth). This isobaric level has been 

 used for current calculations by IIP for the past 

 50 years. Evidence exists that the 1000 decibar 

 level is itself in motion, and thus knowledge of 

 this motion is needed as a model input to provide 

 for absolute motion drift prediction. Data con- 

 cerning the sea surface slope in the modeled area 

 would provide the necessary information on 

 which the model could base these absolute motion 

 calculations. Eventually, the SEASAT B satel- 

 lite may give us that information to the accept- 

 able accuracy of 1 centimeter of elevation per 1 

 kilometer in the horizontal. 



The Labrador Current Model now covers any 

 selected area of the Grand Banks of Newfound- 

 land. The model size compared to the overall 

 problem area is shown in Figure B-l. The cov- 

 erage is 120 x 120 nautical miles. There are six 

 layers in the model, with thickness of 30, 40, 80, 

 150, 200 and 500 meters. The model is initiated 

 by introducing a processed data set which is the 

 output of a newly developed data handling pro- 

 gram described in later paragraphs. This data 

 set consists of 24,300 layer averaged temperature 

 and salinitj' data points, 2025 points describing 

 the bathymetry of the area modeled, the wind 

 field (both present and expected during the 

 model's predictive period), the position of the 

 southwesternmost corner of the area modeled, 

 and the commencement time of the predictive 

 period. Upon commencement of model opera- 

 tion, the initial conditions of the current field are 

 calculated and then recalculated each hour as 

 time advances. The recalculations are based on 

 the advection (movement) of the water and the 

 mixing (interaction). These provide the steer- 

 ing mechanism that alters both the velocity and 



B-l 



