ANOMALOUS ANOMALIES IN AVERAGED HYDROGRAPHIC DATA

A comparison of a recently assembled hydrographic database for the Nor th Atlantic with the Levitus atlas shows striking differences in the v icinity of the Gulf Stream and the North Atlantic Current. On isopycna l surfaces in the main thermocline, isolated pools of warm, saline wat er are found in the Levitus database but are absent in the new databas e. Using synoptic data as a proxy for temporally avenged climatologica l data, it is shown that the anomalous features can be accounted for b y the differences in the averaging process. To produce a gridded datab ase from irregularly spaced station data, Levitus avenged the data on pressure surfaces while the new database was prepared with averaging o n potential density surfaces. it is shown that averaging on a pressure surface in an area of sharply sloping isopycnals produces a water mas s with a 0-S signature uncharacteristic of the local water mass(es). T he anomalous potential temperatures and salinities that result are com pared to the large-scale water mass anomalies of the North Atlantic an d are shown to be of comparable strength. Finally, the consequences of having sizable averaging artifacts are discussed.