Table 1 shows that the stations with the largest 

 fractions of missing data are the weather ships, partly 

 because of the exclusion of temperatures if the ships are 

 off station. Data may also be missing at either weather 

 ships or shore locations because of bad weather or equipment 

 failure. As an indication of the nature of occurrence of the 

 missing data for stations with fairly large fractions of 

 missing data, consider figure 4. Shown are histograms of 

 the frequency of missing temperature sequences for 7 years 

 of PAPA data and 21 years of St. James Island data. Sta- 

 tion PAPA was selected from the two open ocean locations 

 since the bathythermograph observations were made by 

 oceanographers and were considered to be more accurate 

 than for station ECHO. St. James Island was chosen from 

 among the island and coastal locations since it had the 

 largest fraction of missing data of these stations. 



Except for a few long periods of missing data for each 

 station, as indicated in figure 4, the missing data days are 

 distributed very much as though at random. That is, given 

 the appropriate probability of there being data on a day, the 

 distributions by length of data-present sequences and data- 

 missing sequences are like those expected. More specifi- 

 cally, the computed histograms shown in figure 4 result 

 from randomly generated time series with two controlling 

 conditional probabilities. The first conditional probability 

 used for figure 4A is 0. 76, which is the probability that a 

 temperature will be observed, given that a temperature 

 was observed the previous day. The second conditional 

 probability used is 0. 51, which is the probability that a 

 temperature will be observed, given that a temperature was 

 not observed the previous day. The corresponding probabil- 

 ities for figure 4B are 0.89 and 0.59. These conditional 

 probabilities agree quite well with the physical situation 

 that missing data sequences occur infrequently, but once 

 they occur they persist longer than can be explained by a 

 single probability. 



16 



