Multilayered feed forward Artificial Neural Network model to predict the average summer-monsoon rainfall in India

In the present research, possibility of predicting average summer-monsoon rainfall over India has been analyzed through Artificial Neural Network models. In formulating the Artificial Neural Network based predictive model, three layered networks have been constructed with sigmoid non-linearity. The models under study are different in the number of hidden neurons. After a thorough training and test procedure, neural net with three nodes in the hidden layer is found to be the best predictive model.Comment: 19 pages, 1 table, 3 figure

Molecular biogeography of planktonic and benthic diatoms in the Yangtze River

Background: Diatoms are of great significance to primary productivity in oceans, yet little is known about their biogeographic distribution in oligotrophic rivers. Results: With the help of metabarcoding analysis of 279 samples from the Yangtze River, we provided the first integral biogeographic pattern of planktonic and benthic diatoms over a 6030 km continuum along the world's third largest river. Our study revealed spatial dissimilarity of diatoms under varying landforms, including plateau, mountain, foothill, basin, foothill-mountain, and plain regions, from the river source to the estuary. Environmental drivers of diatom communities were interpreted in terms of photosynthetically active radiation, temperature, channel slope and nutrients, and human interference. Typical benthic diatoms, such as Pinnularia, Paralia, and Aulacoseira, experienced considerable reduction in relative abundance downstream of the Three Gorges Dam and the Xiluodu Dam, two of the world's largest dams. Conclusions: Our study revealed that benthic diatoms are of particular significance in characterizing motile guild in riverine environments, which provides insights into diatom biogeography and biogeochemical cycles in large river ecosystems

Model comparison for the calculation of linke's turbidity factor

Pyrheliometric mesurements of direct solar radiation performed at Athens Observatory (NOA) from 1954 to 1992, were used to test the applicability of several models which compute the Link's turbidity factor, TL. The models used in this analysis belong to two categories: the direct, or the so-called pyrheliometric, formula and the indirect, or parameterized, method. The statistical indicators, mean bias (MBE) and root-mean-square (RMSE) error in combination with the t statistic are proposed for the evaluation and comparison of TL as produced by various models. The direct method is presented using three different parameterized algorithms for δR(λ), proposed by Louche et al., Granier et al. and Kasten; whereas the indirect schemes were Dogniaux's and Valko's parameterized models. Based on the comparison against the early pyrheliometric method, Grenier et al.'s model performed the best with respect to R2, MBE, and RMSE, whereas adjusted Louche et al.'s, Louche et al.'s, Valko's, and Dogniaux's II and I models follow in that order. It is significant that Valko's model performed the best with respect to the t statistic. Dogniaux's scheme was found to depend strongly on the acrosol's microphysics loading in the atmosphere, whereas Valko's scheme did not show such a dependence. Finally, the probable dependence on the water vapour content of the relationship linking TL to Ångstrom's turbidity coefficient β, is discussed. © 1997 by the Royal Moteorological Society

An underground pipe system as an energy source for cooling/heating purposes

A complete numerical model for the prediction of air and soil temperature fields under a building is developed. The model describes the simultaneous heat and mass transfer inside an earth-tube system and into the soil, taking into account the soil's natural thermal stratification. The proposed model is validated against two experimental data sets and is found accurate. The proposed algorithms were developed within the TRNSYS environment and can be easily coupled with building or greenhouse simulation codes for the description of earth-tube heat exchangers' determinant parameters. © 1995

Statistical procedures for the evaluation of evapotranspiration computing models

The widely used mean bias error (MBE) and root mean square error (RMSE) in combination with the t-statistic are proposed as statistical indicators for the evaluation and comparison of evapotranspiration computing models. Using data published in Jacovides et al. (1988) it was demonstrated that the use of MBE and RMSE separately can lead to a wrong decision in selecting the best model from a suite of candidate models. The t-statistic should be used in conjunction with the MBE and RMSE errors to better evaluate a model's performance. Finally, the t-statistic indicator can be viewed as a supplement of the MBE and RMSE errors in aiding modellers to determine whether or not a model's estimates are statistically significant at a particular confidence level. © 1995

Broad-band turbidity parameters and spectral band resolution of solar radiation for the period 1954-1991, in Athens, Greece

In the present analysis broad-band turbidity parameters, which depend upon the attenuation over the entire solar spectrum and which can be determined from unfiltered pyrheliometric measurements of direct beam solar irradiance, are presented. Unsworth-Monteith attenuation coefficient TUM, Linke factor TL and Ångstrom turbidity coefficient β (in parameterized form), were calculated from mid-day observations at the National Observatory of Athens, Greece for the period 1954-1991. Values of Angstrom turbidity coefficient β compare well with those obtained directly through the so-called pyrheliometric formula β0. Summertime turbidity levels were found to be higher than winter values. The long-term variation of the turbidity parameters in conjunction with their frequency distribution depicts the deterioration of air quality in the Athens basin during the period under study. The dependence on the aerosol amount of the fraction of the various spectral bands to direct total irradiance as well as the ratio of diffuse to total global irradiation, are also discussed

The effect of moist layer location on the stability of trapped gravity waves in an almost saturated atmosphere

The stability characteristics of trapped gravity waves, generated by an isothermal bounded tanh (z) velocity profile in the presence of a saturated finite layer, are studied. The saturated layer is introduced at different levels above the inlection point and the variations of moisture content, layer thickness and distance from the origin are examined. The growthyrates and phase speeds of the unstable modes are obtained by solving numerically the equations of motion in the linear, inviscid, Boussinesq limit, via the technique of Lalas and Einaudi (1976). It is shown that the presence of the saturated layer can significantly affect the stability characteristics of the waves. inereases in moisture, layer thickness and distance of the layer from the inflection point are found to amplify the wave response because the saturated layer behaves as a top boundtry to the shear flow. The presence of such effective boundaries is found to stabilize short wavelengths and destabilize longer wavelengths. Finally, an application of the results to a rainband case produces values of the wave parameters in good agreement with the observed ones. © 1991 Springer-Verlag

The effect of moist layer location on the stability of trapped gravity waves in an almost saturated atmosphere

The stability characteristics of trapped gravity waves, generated by an isothermal bounded tanh (z) velocity profile in the presence of a saturated finite layer, are studied. The saturated layer is introduced at different levels above the inlection point and the variations of moisture content, layer thickness and distance from the origin are examined. The growthyrates and phase speeds of the unstable modes are obtained by solving numerically the equations of motion in the linear, inviscid, Boussinesq limit, via the technique of Lalas and Einaudi (1976). It is shown that the presence of the saturated layer can significantly affect the stability characteristics of the waves. inereases in moisture, layer thickness and distance of the layer from the inflection point are found to amplify the wave response because the saturated layer behaves as a top boundtry to the shear flow. The presence of such effective boundaries is found to stabilize short wavelengths and destabilize longer wavelengths. Finally, an application of the results to a rainband case produces values of the wave parameters in good agreement with the observed ones. © 1991 Springer-Verlag

Spectral solar irradiance and some optical properties for various polluted atmospheres

Using ground-based spectroradiometric measurements taken over the Athens atmosphere during May 1995, the influence of gaseous pollutants and aerosol on the spectral radiant energy distribution was investigated. It was found that spectral measurements exhibited variations based on various polluted urban atmospheric conditions as determined via gaseous pollutants record analysis. The relative attenuations caused by gaseous pollutants and aerosol can exceed 27%, 17% and 16% in the global ultraviolet, visible and near-infrared portions of the solar spectrum respectively, as compared to 'background' values. In contrast, an enhancement of the near-infrared diffuse component by 66%, was observed, while in visible and ultraviolet bands the relative increases reached 54% and 21% respectively. Experimental total Rayleigh-corrected and spectral aerosol optical depths were retrieved, representing differences in polluted air over the Athens atmosphere. The diffuse component accounts for more than 80% of the total radiation field under high polluted atmosphere. The observed differences of solar radiation between the Athens center and at a nearby suburban site are a manifestation of contrasting air properties provided mainly by automotive traffic. (C) 2000 Elsevier Science Ltd. All rights reserved. Using ground-based spectroradiometric measurements taken over the Athens atmosphere during May 1995, the influence of gaseous pollutants and aerosol on the spectral radiant energy distribution was investigated. It was found that spectral measurements exhibited variations based on various polluted urban atmospheric conditions as determined via gaseous pollutants record analysis. The relative attenuations caused by gaseous pollutants and aerosol can exceed 27%, 17% and 16% in the global ultraviolet, visible and near-infrared portions of the solar spectrum respectively, as compared to `background' values. In contrast, an enhancement of the near-infrared diffuse component by 66%, was observed, while in visible and ultraviolet bands the relative increases reached 54% and 21% respectively. Experimental total Rayleigh-corrected and spectral aerosol optical depths were retrieved, representing differences in polluted air over the Athens atmosphere. The diffuse component accounts for more than 80% of the total radiation field under high polluted atmosphere. The observed differences of solar radiation between the Athens center and at a nearby suburban site are a manifestation of contrasting air properties provided mainly by automotive traffic

Spectral band resolution of solar radiation in Athens, Greece

A 14‐year (1977–1990) record of global solar radiation measurements performed in Athens, Greece, has been utilized to determine the distribution of radiant energy in the various wavelength bands. The monthly mean values of the irradiation ratios in the spectral intervals, blue (0·380–0·525 μm), green‐orange (0·525–0·630 μm), red (0·630–0·710 μm), and photosynthetically active radiation (PAR) (0·380–0·710 μm) and the global irradiation (0·3–2·8 μm) compare favourably with values reported in the literature for different locations over a wide geographical area. The irradiation ratios exhibit seasonal variations attributable to changes in local air‐mass climatology. It is observed that the proportion of the radiant energy in the various spectral bands relative to the global solar irradiation increases as sky conditions change from ‘clear’ to ‘partly cloudy’. Finally, the observed seasonal dependence of the broad‐band spectral energy distribution is essentially caused by changes in the composition of the air masses (turbidity, airborne pollutants, clouds) in residence at the measurement site in the course of the year. Copyright © 1993 John Wiley & Sons, Lt