SUMMARYResults are presented from six micrometeorological studies conducted over a grass turf at Davis, California, in 1066 and 1967. Highly reliable surface drag and evaporation data from very sensitive lysimeters of 6.1 m diameter afforded excellent opportunity to evaluate several parameters important to aerodynamicprediction equations.For the six studies the mean von Kirman constant, k, ranged from 0-40 to 0 4 4 , strongly supporting continued acceptance of k at around 0.42.The Monin-Obukhov (1954) universal 4 '~ function was found to vary as IRij-*/3 under near-free convection, indicating significantly greater diabatic profile effects than suggested in the form of the KEYPS profile as given by Sellers (1965).Empirical relationships providing excellent fit to experimental data for the range -3.5 < Ri < 0.3, were 4~ = (1-16 Ri)-1'3 and $M = (1+16 Ri)1/3 respectively for unstable and stable conditions. For +W corresponding expressions were 4w = .885 (1-22 Ri)-.40 and $w = .885 ( l f 3 4 Ri).40.The ratio Kw/KM showed a systematic drop from 1.13 at neutral to a value around 0.75 under strongly

No abstract

No abstract

Very little basic work has been done within the USA on the energy balance of a rice crop (Oryza sativa L.) as affected by surface and climatic conditions. During 1968 and 1969, energy‐balance studies were conducted in the middle of a very large rice field 40.2 km (25 mi) north of Davis, California. Evapotranspiration data obtained were compared with data from a large weighing lysimeter at Davis, planted to grass. From daily ratios thus obtained, estimates of normal monthly evapotranspiration for rice were obtained, using data from the long‐term lysimeter study at Davis. For a May 1 to October 1 period, a normal seasonal use for rice of 920 mm (36.2 in) was indicated, a value only 3.5% greater than the 10‐year mean of 889 mm of water used by fescue (Festuca eliator L.) at Davis during the same period. Air temperature differences between the rice site and the Davis lysimeter were rather minor, but humidities were markedly higher over the rice. Lower wind speed at the rice site, no doubt, contributed to the higher humidity, although the very extensive up‐wind fetch of rice (2 km or greater) was probably a more important factor. The much higher humidities and somewhat lower wind speeds at the rice site are believed to have reduced the evaporation potential by as much as 20 to 25% below that at Davis. Although in this study evapotranspiration by rice and by grass was very similar, it is estimated that losses by rice, in a plot similar in size to the grass plot, would have exceeded the loss by grass by as much as 20 to 25% if the two crops had been grown at Davis.

Rain gage data were compared with ground level precipitation as determined with a highly sensitive weighing lysimeter 20 feet in diameter. Rain gages of various types were tested in the Central Valley of California during twenty‐four storms in the 1966–1968 rainfall seasons. Rainfall totals for each storm as measured by the lysimeter and by several rain gages in its vicinity were compared by regression analysis. Wind effects on a standing gage seemed unimportant, since agreement was close between a standard 8‐inch rain gage mounted in the normal standing position and a USSR 3000‐square‐centimeter rain gage mounted at ground level. Storm totals from these two gages spaced about ten feet apart averaged 4% higher than catches measured 450 feet away by the lysimeter and a Fischer and Porter digitizing rain gage spaced about 10 feet apart. Fischer and Porter gage storm catch values varied generally about the mean value of the lysimeter data. The coinciding means of all of the data from these two instruments suggest that wind effects compensate over the period of storms studied.