portion of the systems. depths between feet, The lowest of these, extending from the surface up to about 20,000 is the well known trade wind current. The Trades are deepest and strong- tographs show est during the winter months, December through February, iy at the surface of about 19 knots from an east-northeasterly direction. Halimeda with an average strength Maximum speeds occur at about the four to five thousand foot level, where speeds greater ‘eet in depth. than 25 knots are not uncommon. The top of the current during this season may he surface, often extend to 30,000 feet or more, C per mile, become gradually weaker and more variable. Ik Atoll. most typical direction veers from east~northeasterly to easterly. During August an and in 1930 | and September the average surface wind is 1]1 knots from the east. During these coconuts, and two months, niwetok Atoll southeast, nd because of rent becomes shallowest, often not extending above the 8,000 or 9,000-foot level. At the same time their average or frequent periods of very light winds, During March, are often observed. especially coming from the April and May the trade wind cur- Figure 4, on which is plotted the zonal or east-west component of the wind as a At masses, During the spring and summer the Trades 10 natives function of height and of month, shows these different changes. ‘with Ameri. statistics by month are given in Table I. persong Surface wind Above the trades and extending up to the tropopause, which is generally veral hun- located between 55,000 and 60,000 feet, purposes called the Upper Westeriies. are westerly winds which are usually This wind stream may be thought of as the southward ' On FRED extension of the strong circumpolar jet stream of mid-latitudes. ding from of Eniwetok this southward extension of the polar westerlies overlies the trade es, wind current. At the latitude The Upper Westerlies are quite variable due to the presence of numerous cyclonic and anticyclonic vortices which are typically carried along in the basic current. lands area The upper westerly current, whose core is normally located at about the 40,000- f the foot level, fent a hE othaataa Se in h of the tC wind is strongest in the spring, deepest and most well developed. autumn, at from the month of March through May, which time average velocities reach 25 knots. ar with belt, in the proper position relative to Enlwetok, often produces east winds for periods of two to four days at these upper levels. x III), at , Such a vortex, At the same time this current is As the season progresses through summer into the thickness and strength of the current diminishes to average values of about 5 knots with extremely high variability. In mid-winter the Upper West- erlies often do not extend as far south aloft as Eniwetok. Above the tropopause and situated in the lower stratosphere is wind stream, which is an easterly and very steady current. the third These winds are Vo er oe rome