Search Results
You are looking at 1 - 3 of 3 items for
- Author or Editor: C. P. Jacovides x
- Refine by Access: All Content x
Abstract
The effectiveness of a number of forecasting indices for non-frontal thunderstorm activity has been investigated for the Greater Cyprus area. The indices include the humidity index (HI), the Pickup index (PI), the K-stability index, the Yonetani index in its original II and modified IIc, form, and the Showalter stability index (SSI) for the Mediterranean area. Combinations of some of these indices with information of the flow curvature are also considered.
Two data sets, representative of coastal and inland locations are used to evaluate the accuracy of these indices. Verification statistics indicate that Yonetani's indices II and IIc, are more successful than the HI, PI, and K indices in the forecast of air mass thunderstorms. The addition of the flow curvature at 500 hPa improves the effectiveness of most indices and its inclusion should be seriously considered for the Eastern Mediterranean area.
Abstract
The effectiveness of a number of forecasting indices for non-frontal thunderstorm activity has been investigated for the Greater Cyprus area. The indices include the humidity index (HI), the Pickup index (PI), the K-stability index, the Yonetani index in its original II and modified IIc, form, and the Showalter stability index (SSI) for the Mediterranean area. Combinations of some of these indices with information of the flow curvature are also considered.
Two data sets, representative of coastal and inland locations are used to evaluate the accuracy of these indices. Verification statistics indicate that Yonetani's indices II and IIc, are more successful than the HI, PI, and K indices in the forecast of air mass thunderstorms. The addition of the flow curvature at 500 hPa improves the effectiveness of most indices and its inclusion should be seriously considered for the Eastern Mediterranean area.
Abstract
This paper investigates the influence of gaseous pollutants and aerosol on the spectral composition of various segments of the solar spectrum in cloudless conditions. This investigation is done by using data of the spectral energy distribution of global and diffuse solar irradiances collected during a field experiment in Athens. The authors found that the Ångström turbidity coefficient β always shows a temporal pattern with high values in the morning and the afternoon and low values at midday, and the wavelength exponent α widely varies over 1.02–1.4.
Atmospheric turbidity produced a measurable but variable effect on spectral solar irradiances. The authors found that the relative attenuations caused by high urban aerosol can exceed 36% ± 7.5%, 30% ± 5.8%, and 26% ± 4.1% in the ultraviolet, visible, and near-infrared portions of the solar spectrum, respectively, as compared with “background” values. On the other hand, the relative increase in scattered irradiance was greater in the near-infrared band (40% ± 4.8%), and in visible and ultraviolet bands the relative increase reached 31% ± 5.5% and 18% ± 6.5%, respectively.
Spectrally reduced (Rayleigh corrected) and aerosol (Ångström) optical depths were retrieved, representing different aerosol loadings over the Athens atmosphere. The effects of altitude and the temporal and spatial variability of spectral optical depth values were analyzed. The overall results suggest that the shortest wavelengths are very sensitive to aerosol loading.
Abstract
This paper investigates the influence of gaseous pollutants and aerosol on the spectral composition of various segments of the solar spectrum in cloudless conditions. This investigation is done by using data of the spectral energy distribution of global and diffuse solar irradiances collected during a field experiment in Athens. The authors found that the Ångström turbidity coefficient β always shows a temporal pattern with high values in the morning and the afternoon and low values at midday, and the wavelength exponent α widely varies over 1.02–1.4.
Atmospheric turbidity produced a measurable but variable effect on spectral solar irradiances. The authors found that the relative attenuations caused by high urban aerosol can exceed 36% ± 7.5%, 30% ± 5.8%, and 26% ± 4.1% in the ultraviolet, visible, and near-infrared portions of the solar spectrum, respectively, as compared with “background” values. On the other hand, the relative increase in scattered irradiance was greater in the near-infrared band (40% ± 4.8%), and in visible and ultraviolet bands the relative increase reached 31% ± 5.5% and 18% ± 6.5%, respectively.
Spectrally reduced (Rayleigh corrected) and aerosol (Ångström) optical depths were retrieved, representing different aerosol loadings over the Athens atmosphere. The effects of altitude and the temporal and spatial variability of spectral optical depth values were analyzed. The overall results suggest that the shortest wavelengths are very sensitive to aerosol loading.
Abstract
Unsworth and Monteith's attenuation coefficient T UM was calculated from midday cloudless sky data in Athens, Greece, for the period 1954 to 1991. An interdependence between T UM and the Linke factor T L was found and is expressed as a mathematical function. It was also shown that the minimum turbidity levels occur during the winter and maximum levels occur during summer. An analysis of the long-term variation of the attenuation coefficients depicts the deterioration of air quality during the same period. The dependence of the ratio of diffuse to global radiation on the attenuation coefficient T UM, is also presented.
Abstract
Unsworth and Monteith's attenuation coefficient T UM was calculated from midday cloudless sky data in Athens, Greece, for the period 1954 to 1991. An interdependence between T UM and the Linke factor T L was found and is expressed as a mathematical function. It was also shown that the minimum turbidity levels occur during the winter and maximum levels occur during summer. An analysis of the long-term variation of the attenuation coefficients depicts the deterioration of air quality during the same period. The dependence of the ratio of diffuse to global radiation on the attenuation coefficient T UM, is also presented.
