2. The Mixed Water Region to the east of Honshu
The Iwate Fisheries Technology Center has conducted oceanic observation along the 4 observation lines shown in Fig.2, on monthly base from 1963. All observed values of temperature (left) and of salinity (right) observed in the period from 1971 to 1995 are plotted against depth in Fig.3. The curves consist of vertical and horizontal lines indicate the permissible ranges adopted by NODC. Though the distribution ranges in the region under consideration are considerably wide in this region, the ranges used by NODC is clearly too wide to make a high quality-control. We calculated the means (m) and the standard deviations(σ) for each standard depth, and m and m±3σ are plotted with white triangles and white circles in Fig.3. If the distribution is Gaussian, 99.7% of the data would lie in the range of m±3σ. However, the cluster of the data points of temperature (Fig.3, left) is located much higher than m・3σ, and it extends continuously beyond the line of m+3σ.
The skewed nature is most conspicuous for temperature near 300 m depth. The frequency of the temperature values at 300 m is shown in Fig.4. No data exist below 0C, and significant frequency can be seen even for the value of m+9σ. Thus, m+3σ criterion cannot be applied in this region. If the distribution is skewed in the same manner for variable depths, we may determine the range by considering the values of skewness, kurtosis and so on. However, the distribution pattern is changeable with depth and with season. The distribution patterns of temperature for variable depth are shown in Fig.5. As seen in this figure the distribution pattern for shallower depths than 150 m depth is quite different to those for deeper depth than 150 m depth. Further investigation is needed to set the reasonable range parameter.
