temperature structure within the first few fathoma of water is closely related tc windspeed. With winds in excess of 10-15 knots there is vigorous mixing and the structure is isothermal. Otherwise, the temperature tends to be isothermal at night (with surface cooling) and to increase upward only very slightly by day, with the temperature difference between the surface and the 2-fathom depth belng a small fraction of a degree Fahrenheit. 5. TOPOGRAPHY® As indicated in the introduction, weather observations during the Eniwetok Microclimatic Project were made at seven different sites in the atoll. These sites were on the lslets of FRED, ELMER, BRUCE, YVONNE, JANET, KEITH and also in the lagoon at MACK (Figure 1). It is the purpose of this section to describe the local topography of each of these observation points. 6Miost of the detailed reef descriptions given in this section were obtained from "Geology of Bikini and Nearby Atolls" by Emery, Tracy, Ladd et al, USGS Prof. Paper No. 260-A, Part I, 1954. The reader is referred to this publication for more detailed information. FRED, one of the principal islets of the atoll, is located at its southern- most extremity, immediately adjacent to the east side of Wide Passage. crescent-shaped islet 1s oriented approximately northeast-southwest and measures arm ae Nae he a some 2.6 miles long by 0.4 miles wide. of dry land. This The islet comprises some 0.8 square miles The development of FRED as the principal permanent operational base has removed essentially all of its natural topographic features. of an essentially flat, graded, It now consists table some 11 feet above mean sea level. Only in the extreme northeastern portion of the islet are remnants of original relief Still observed. An aircraft runway, numerous taxiways, alrcraft parking areas and buildings occupy more than 90% of the western two-thirds of the islet. The eastern one-third of the islet is principally used for housing facilities for personnel. (See Figure 7,) The seaward reef along the southeastern face of the islet is composed of four principal parts: (1) An Algal Ridge made up of small moderately well developed buttresses with small relatively straight and regular surge channels. 10