'. . ' 1 .2,.3 ' I L. Test No. z (m) Ax (m)-k =. The coherence of winds a t two points separated by a horizontal distance i n the atmos-: ,. A: - .-1. t pheric boundary layer was the subject of two L d-' I c. .-recent papers: Ropelewski, e t al., (1973) and-Panofalry, e t al., (1973). From these papers, it !*-is found that the coherence of wind component , , , variations may be modeled as decaying exponen- , .-. t i a l functions of separation distance accord-&ng t o I I' , .-I-L k J. ;-, v 8 1 *-:#: ;cohii-(n) = exp. (aikn~&/W. , , In (1) Coh refers t o the coherency spectrum, n is frequency, a i s a coherency decay factor, Ax i s a separation distance, and a i s ' the mean wind speed. The subscript i = 1, 2, 3 refers t o the turbulence components u' , v' , and w', while the superscript k = 1, 2, 3 refers t o alongwind, crosswind, and vertical separations.. Thus cohiik(n) i s the coherence between ui measured st eac of two locations separated by a distance 9, and uik i s the associated coher-ency decay factor. A small numerical value of aik indicates high coherence. The above mentioned papers s t a t e that the decw factors a l l and aB1 are increasing functions of stability, roughness and tur-I/ bulence intensity. I'he present paper i s based on data that pruvliicrs comparison of the decay factors for alongwind separations for all three wind components. 2. SITE, llPSTRUMWTATION AND DATA The data were dl taken from sonic and G i l l anemometers mounted on tower arrays a t the Hanford meteorological s i t e , which i s located on a broad level expanse of desert with sege-brush and clump grass vegetation. Data from several t e s t s have been analyzed which include several separation distances established by logarithmic spacing of towers i n an dongwind line. Analyses of two of these t e s t s , for which the azimuth angle between the tower l i n e and the mean wind direction was l e s s than lo0, are presented here. I : ; .-.. :I , &rJmw,,x;,,;-.. 1.1 '1' .I-The separation distances Ax between consecutive towers and the heights a t which the instruments were located were: The separlration distances of t e s t s V-6 and T603 were i n the order shown, with the long separation distances being on the upwind end of the line. A l l the data from t e s t V-6 ware taken by G i l l anemometers. The data from t e s t 6 0 3 were taken by four G i l l anemometers and three sonic anemaeters. The sonic anemom-eters enclosed the 4-and 8-m separation distances. The G i l l anemometers enclosed the larger separation distances. Other sgecifics for these t e s t s are given i n Table 1.
