The fraction of sunlight retained as net radiation in Hawaii

Abstract

Abst•'act. Both estimated and measured values of net radiation over several different surfaces established the retention of appro,ximately two-thirds of the sunlight as net radiation for stations at low elevations in Hawaii. This high retention of sunlight was a consequence of both low reflectance and a very low heating coefficient (change of long-wave net radiation with change in total net radiation). The persistent high elevation of the sun and the efficient convective heat sink formed by the maritime air helped to account for this large retention of sunlight as net radiation. The mineralogic composition of the soil and the leaf habit of the vegetative cover contributed to the low reflectance from these surfaces. Since this net radiation can be used to heat the soil, plants, and air, and to evaporate water, the heat and moisture budgets of a surface in the maritime tropics may differ markedly from those of a surface in the temperate latitudes under similar solar radiation. Net radiation is an important meteorological parameter for any area since its effect upon the heat and moisture budgets of the soil, crop, and air has been amply demonstrated [Tanner, 1960; Tanner and Pelton, 1960; Chang, 1961; Tanner and Lemon, 1962]. The fraction of sunlight retained as net radiation can be measured directly or can be closely approximated from the reflectance of the short-wave radiation and an estimated long-wave radiation balance [Monteith and Szeicz, 1962; Swinba.nk, 1963]. Net radiation was measured with a Beckman and Whitley model N-188 radiometer [Portman and Dias, 1959; Gates, 1962] over a pineapple field at the Pineapple Research Institute field station (Wahiawa, Oahu, 21ø28'N lat.; 216 m elev.; index 820.2) ITalia.retro, 1961]. The instrument was shaded for a field check of the

Radiation balance over a salt marsh

“…Equation (5) is in fair agreement with the relationship found by Ekern (1965) for a sugar cane field in Hawaii. His regression coefficient is 0.83 and Lo = -105 W me2.…”

“…On 4 of the 6 days, thundershowers occurred, usually in the early afternoon, with durations from 1 to 2 h, resulting in severe reduction of incoming radiation for these time periods. The daily average of total solar radiation was 380 ly (15.9X lo6 J mm2) as compared to 750 ly for total solar radiation received on clear summer days on Hawaii (Ekern, 1965). Ekern's regression fit includes only data from clear days, which explains his higher Lo value as compared to our analysis.…”

“…The radiation balance has been studied by many investigators over a variety of natural and agricultural surfaces (Stanhill er al., 1966;Szeicz, 1961, 1962;Ekern, 1965;Davies, 1967;Polavarapu, 1970;and others). In general, it may be expressed as…”

“…Ekern (1965) and Davies (1967) showed that this linear relationship yields a correlation coefficient better than 0.9 for many surfaces. The regression coefficient, b = (1 -(w)/( 1 -p), varies equally much with (Y and p according to Monteith and Szeicz (1962).…”

Evapotranspiration of Pineapple in Hawaii

“…The design of the leaf array and the persistent, small, zenith angles of the noonl sun in the subtropics make the net radiationl hurden on the pineapple very great (7,8). The thick suiccnilenit pilleapple leaf was reported (18) …”