Global Radiation (global + radiation)

Distribution by Scientific Domains

Selected Abstracts

Stochastic modelling of global solar radiation measured in the state of Kuwait

S. A. Al-Awadhi
Abstract Two stochastic models that capture the main features of daily exposure of global radiation in Kuwait are proposed. The development of these models is based on removing the annual periodicity and seasonal variation of solar radiation. Thus the daily radiation is decomposed as the sum of the trend component and a stochastic component. In many situations, there are dramatic changes in the radiation series through the year due to the condition of the weather, as is the case of the data from Kuwait. This would affect the accuracy of the model, and therefore the series is divided into two regimes: one corresponds to clear days where the value of the global radiation would be normal and the other to non-clear days where the value of global radiation would be very low. Then the trend component is expressed as a Fourier series taking into account such apparent breaks in the series. The stochastic component is first tested for linearity and Gaussianity and it is found that it does not satisfy these assumptions. Therefore, a linear time series model (ARMA modeling) may not be adequate and, to overcome this problem, a bilinear time series is used to model the stochastic component of daily global radiation in Kuwait. The method proposed considers first fitting an AR model to the data and then seeing whether a further reduction in the mean sum of squares can be achieved by introducing extra bilinear terms. The Akaike Information Criterion (AIC) is used to select the best model. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Surface Heat Balance and Spatially Distributed Ablation Modelling at Koryto Glacier, Kamchatka Peninsula, Russia

Keiko Konya
Abstract To investigate the characteristics of ablation at Koryto Glacier, a mountain glacier under maritime climate in Kamchatka Peninsula, Russia, we made field observations from August to early September 2000. At a site near the equilibrium line, the 31-day average net radiation, sensible heat flux, and latent heat flux were 43, 59 and 31 W,2, respectively. We developed a new distributed ablation model, which only needs measurements of air temperature and global radiation at one site. Hourly ablation rates at this site obtained by the energy balance method are related to measured air temperature and global radiation by linear multiple regression. A different set of multiple regression coefficients is fitted for snow and ice surfaces. Better estimates of ablation rate can be obtained by this approach than by other temperature index models. These equations are then applied to each grid cell of a digital elevation model to estimate spatially distributed hourly melt. Air temperature is extrapolated using a constant temperature lapse rate and global radiation is distributed considering topographic effects. The model enables us to calculate the hourly spatial distribution of ablation rates within the glacier area and could well provide a realistic simulation of ablation over the whole glacier. [source]

Evaporative climate change in the British Isles

Gerald Stanhill
Abstract Evaporation measurements made at 16 sites in the British Isles were analysed for evidence of long-term changes. Half of the series were from sites in Ireland measured with Class A evaporation pans between 1963 and 2005 and half in England and Scotland measured with the British Meteorological Office (MO) sunken evaporation tank between 1885 and 1968. Four of the Irish series showed significant linear trends, three of increasing and one of decreasing evaporation. These significant changes ranged between , 0.1 and + 0.1 mm year,1 equivalent to annual changes between , 0.22 and + 0.15%. Five of the UK series showed statistically significant linear trends, three of them decrease and two increase: These ranged in size between , 3.7 and + 2.1 mm year,1, equivalent to annual changes of , 1.05 to + 0.40% of the mean. Curvilinear time trends accounted for twice the amount of inter-annual variation in evaporation as did the linear trends. Differences in sunshine duration (SD), used as a proxy for global radiation, were found to be the major factor explaining spatial as well as temporal changes in evaporation in the British Isles. The pooled Irish data, expressed as normalized anomalies, showed a small and significant linear increase in evaporation over the last 40 years. Similarly parameterized the UK measurements showed no significant trend up till 1968; the one UK series that did extend till 2004 indicated a marked increase during the last 20 years. The long-term changes found in annual evaporation were similar to those in air temperatures both in Ireland and England. The relevance of these findings to the hypothesis of an acceleration in the hydrological cycle is discussed. Copyright © 2007 Royal Meteorological Society [source]

Climatology of near-surface wind patterns over Switzerland

Rudolf O. Weber
Abstract Over complex, mountainous terrain the near-surface winds can form intricate patterns as large-scale winds and locally forced wind systems interplay. Switzerland, with its mountainous topography and dense meteorological network of 115 automated surface stations, ideally serves as a study area for such wind system interactions. Applying an automated classification scheme to the wind data of one single year (1995), 16 distinct near-surface flow patterns were found. These patterns also show characteristic distributions in magnitude and areal extent of temperature, global radiation and precipitation. An 18-year climatology of flow patterns was created with an identification method for fewer stations. This allowed the determination of annual and diurnal variations in the frequencies of occurrence of the different flow patterns, revealing pronounced daytime and night-time classes characterized by thermally forced winds. Transition probabilities between the flow patterns were computed as well. The relationship between the near-surface wind patterns and the synoptic flow situation was investigated with a comparison with synoptic weather types defined for the Alpine region. The results show clear but not unequivocal interdependencies between the synoptic weather type and the near-surface flow pattern. Copyright © 2001 Royal Meteorological Society [source]

Forecasting migration of cereal aphids (Hemiptera: Aphididae) in autumn and spring

A. M. Klueken
Abstract The migration of cereal aphids and the time of their arrival on winter cereal crops in autumn and spring are of particular importance for plant disease (e.g. barley yellow dwarf virus infection) and related yield losses. In order to identify days with migration potentials in autumn and spring, suction trap data from 29 and 45 case studies (locations and years), respectively, were set-off against meteorological parameters, focusing on the early immigration periods in autumn (22 September to 1 November) and spring (1 May to 9 June). The number of cereal aphids caught in a suction trap increased with increasing temperature, global radiation and duration of sunshine and decreased with increasing precipitation, relative humidity and wind speed. According to linear regression analyses, the temperature, global radiation and wind speed were most frequently and significantly associated with migration, suggesting that they have a major impact on flight activity. For subsequent model development, suction trap catches from different case studies were pooled and binarily classified as days with or without migration as defined by a certain number of migrating cereal aphids. Linear discriminant analyses of several predictor variables (assessed during light hours of a given day) were then performed based on the binary response variables. Three models were used to predict days with suction trap catches ,1, ,4 or ,10 migrating cereal aphids in autumn. Due to the predominance of Rhopalosiphum padi individuals (99.3% of total cereal aphid catch), no distinction between species (R. padi and Sitobion avenae) was made in autumn. As the suction trap catches were lower and species dominance changed in spring, three further models were developed for analysis of all cereal aphid species, R. padi only, and Metopolophium dirhodum and S. avenae combined in spring. The empirical, cross-classification and receiver operating characteristic analyses performed for model validation showed different levels of prediction accuracy. Additional datasets selected at random before model construction and parameterization showed that predictions by the six migration models were 33,81% correct. The models are useful for determining when to start field evaluations. Furthermore, they provide information on the size of the migrating aphid population and, thus, on the importance of immigration for early aphid population development in cereal crops in a given season. [source]

Feeding by the pine weevil Hylobius abietis in relation to sun exposure and distance to forest edges

Göran Nordlander
Abstract, 1,The intensity of feeding by adult pine weevils Hylobius abietis (L.) on the stem bark of Norway spruce Picea abies (L.) Karst. seedlings planted in rows with a north,south orientation across a clear-cutting, was measured throughout a growth season. The feeding was then correlated to light interception, soil temperature and distance to the nearest forest edge. 2,Feeding was at least twice as intense on seedlings in the central part of the clear-cutting compared to those at the edges. The decline began approximatety 15 m from the edge and was of similar proportions on both the sun-exposed and shaded sides. 3,Measures of global radiation and soil temperature correlated well with consumption on the shaded side. However, on the sun-exposed side, there were no apparent correlations with global radiation or soil temperature that could explain the decline in consumed bark area. 4,We conclude that the decline in feeding towards the forest edges was mainly due to factors other than the microclimate variables we monitored. We suggest that the presence of roots of living trees along the forest edge may reduce damage to seedlings, since they provide an alternative source of food for the weevils. This alternative-food hypothesis may also explain why seedlings in shelterwoods usually suffer less damage from pine weevils than seedlings in clear-cuttings. [source]