3. Z. 2 Temperature Gradient Criterion 



The second criterion for case selection in this study, that of significant 

 SST gradients, proved to be generally incompatible with the first. Areas of 

 significant SST gradients (where observable synoptic scale activity seems most 

 likely) usually are areas of persistent or recurring meteorological fronts, and 

 so of obscuring cloud cover. (The comparative locations of the Gulf Stream and 

 of the nnean position of the western North Atlantic frontal zone provide one illustration 

 of this problem, ) There are several such ocean areas, but only daily observations 

 over a period of several days to a fe'w weeks can be expected to show significant 

 SST changes. 



3. 2. 3 Conventional Data Criterion 



The third criterion of adequate conventional SST data could not in general be 

 met. (If it could, much of the need for satellite measurement of the world's SST 

 patterns would vanish. ) Even in the North Atlantic cases, the number of conventional 

 ship reports proved inadequate. The only area of significant SST gradients where 

 there appear to be sufficient available ship SST measurements is in the vicinity of 

 the Gulf Stream off the east coast of the United States. But it is precisely here 

 that there is seldom readily available IR data. 



Most of the data for this area, for the immediate west coast North Pacific 

 waters, and for much of the continental U.S. are the so-called "real time" TIROS IR 

 data and remain in undigitized form. These data are read out in "real time" concurrent 

 with the playback of the IR data for the remainder of the preceding orbit, using a 

 frequency multiplexing technique. The data for the remainder of the orbit are read 

 out at 30 times the record speed and frequency, and the automatic processing system 

 is designed to handle these data. Processing the "real tiine" data, whose sub- 

 carriers are thus one -thirtieth of those of the majority of the data, require an 

 accelerated rerecording, and considerably more time and nnanual attention than 

 does the conventional IR data. Moreover, timing errors of the order of seconds are 

 very likely to be introduced because of the manual determination of the "End of Tape" 

 time at the CDA stations. For these reasons, only three cases of "real time" data* 

 were included in our studies. We suggest that the reduction of a sizable sample of 



* Made specially available, through the courtesy of Messrs. William R. Bandeen 

 and Robert Hite of GSFC. 



