Solar radiation and the duration of sunshine

Abstract

SHORTER CONTRIBUTIONS 231moved to the front of the apparatus and its chamber supplied with a cover (not shown on the photograph). T h e pen arm is fitted on to a gate which allows the pressure exerted on the chart by the pen to be finely adjusted. DrscussroNThis apparatus was constructed with the limited object of determining the length of time leaves were wet, but it could be used for other purposes such as measuring the amount of dew deposited, which would be valuable to agricultural meteorologists, particularly in arid zones. By measuring the surface area of the shoot and calibrating the deflection of the beam, the weight of water per unit area can be estimated. In 1953, one shoot was measured, and it; surface area found to be 1,480 cm2. Rain to ' run-off ' added 14.2 g, or 9-6 x l W 3 g cm-2. The maximum increase in weight during the three dew nights while this shoot was exposed were 4.7 g, 7.0 g and 10.2 g. The weights of dew per unit of total surface area were 3.2,4.7 and 6.9 x g cm-2, and the rate of deposition ranged from 6 to 8 x lo-' g cm-* hr-I in the period between the start of dew formation and the time when it reached its greatest weight. Estimates of the mean weight of water over the total surface area of the shoot obscure the differences of distribution and persistence of water deposits at different levels, on the stems and petioles compared to the leaf surfaces, and on different parts of the leaf. These differences are probably very important to pathology; for instance, the frequent potato blight lesions on the tip of the leaflets are often associated with large persistent water droplets. They are more common after rain than after dew, which rarely approaches run-off under English conditions. Interesting observations might be made on these differences by the use of several balances bearing variously dissected shoots. (11) on a monthly basis have been collected for 32 stations and regression equations relating the data calculated in the form Q = QA (a + bn/N) where QA is the mmimum possible ndiation in the absence of an atmosphere, and A! is the maximum possible duration of bright sunshine. For five of these stations records for long series of individual months have been examined and for all stations mean monthly values. In the overall regression equation a = 0.23 and b = 0.48. SUMMARY Records of solar radiation (Q) and of duration of sunshine

The vegetation of Greek fir (Abies cephalonica Loudon) forests on the Oxia – North Vardousia mountain system, central Greece, in relation to drought

“…The coefficients a s and b s were considered constants for the whole region with values of 0.22 and 0.52 respectively (Glover and McCulloch, 1958;Koutsoyiannis and Xanthopoulos, 1999). The above values are close to the values given by Black et al (1954) and Flocas (1980). For the weather stations Lefkada and Nafpaktos, the above formula could not be used because relative sunshine duration data were missing.…”

Selection of cloudless sky conditions by applying solar global ultraviolet irradiance measurements

“…The dimensionless parameter clearness index, k t , was defined as the ratio of global horizontal irradiance at the Earth's surface over extraterrestrial horizontal irradiance and it describes insolation conditions at a given point in time when only global broadband irradiance is known (Black et al 1954). …”

“…Con formato: Subíndice Glossary k t clearness index: defined as the ratio of global irradiance at the Earth's surface over extraterrestrial irradiance, defined by Black et al 1954.…”

Water Balance and Level Change of Lake Babati, Tanzania: Sensitivity to Hydroclimatic Forcings

“…The net shortwave radiation, which is the radiant flux resulting directly from solar radiation was estimated from [43] as:…”

“…α being the albedo of the water surface (α ≈ 0.66 [33]) and R TOA is the solar radiation at the top of the atmosphere, which is a function of latitude [43]. R TOA was estimated to be 416.4 W/m 2 at Lake Babati.…”