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Direct Solar Radiation (direct + solar_radiation)
Selected AbstractsTHE RESPONSE OF PARTIALLY DEBRIS-COVERED VALLEY GLACIERS TO CLIMATE CHANGE: THE EXAMPLE OF THE PASTERZE GLACIER (AUSTRIA) IN THE PERIOD 1964 TO 2006GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 4 2008ANDREAS KELLERER-PIRKLBAUER ABSTRACT. Long-term observations of partly debris-covered glaciers have allowed us to assess the impact of supra-glacial debris on volumetric changes. In this paper, the behaviour of the partially debris-covered, 3.6 km2 tongue of Pasterze Glacier (47°05,N, 12°44,E) was studied in the context of ongoing climate changes. The right part of the glacier tongue is covered by a continuous supra-glacial debris mantle with variable thicknesses (a few centimetres to about 1 m). For the period 1964,2000 three digital elevation models (1964, 1981, 2000) and related debris-cover distributions were analysed. These datasets were compared with long-term series of glaciological field data (displacement, elevation change, glacier terminus behaviour) from the 1960s to 2006. Differences between the debriscovered and the clean ice parts were emphasised. Results show that volumetric losses increased by 2.3 times between the periods 1964,1981 and 1981,2000 with significant regional variations at the glacier tongue. Such variations are controlled by the glacier emergence velocity pattern, existence and thickness of supra-glacial debris, direct solar radiation, counter-radiation from the valley sides and their changes over time. The downward-increasing debris thickness is counteracting to a compensational stage against the common decrease of ablation with elevation. A continuous debris cover not less than 15 cm in thickness reduces ablation rates by 30,35%. No relationship exists between glacier retreat rates and summer air temperatures. Substantial and varying differences of the two different terminus parts occurred. Our findings clearly underline the importance of supra-glacial debris on mass balance and glacier tongue morphology. [source] Evaporation estimation on Lake Titicaca: a synthesis review and modellingHYDROLOGICAL PROCESSES, Issue 13 2007François Delclaux Abstract The aim of this study was to validate evaporation models that can be used for palaeo-reconstructions of large lake water levels. Lake Titicaca, located in a high-altitude semi-arid tropical area in the northern Andean Altiplano, was the object of this case study. As annual evaporation is about 90% of lake output, the lake water balance depends heavily on the yearly and monthly evaporation flux. At the interannual scale, evaporation estimation presents great variability, ranging from 1350 to 1900 mm year,1. It has been found that evaporation is closely related to lake rainfall by a decreasing relationship integrating the implicit effect of nebulosity and humidity. At the seasonal scale, two monthly evaporation data sets were used: pan observations and estimations derived from the lake energy budget. Comparison between these data sets shows that (i) there is one maximum per year for pan evaporation and two maxima per year for lake evaporation, and (ii) pan evaporation is greater than lake evaporation by about 100 mm year,1. These differences, mainly due to a water depth scale factor, have been simulated with a simple thermal model ,w(h, t) of a free-surface water column. This shows that pan evaporation (h = 0·20 m) is strongly correlated with direct solar radiation, whereas the additional maximum of lake evaporation (h = 40 m) is related to the heat restitution towards the atmosphere from the water body at the end of summer. Finally, five monthly evaporation models were tested in order to obtain the optimal efficiency/complexity ratio. When the forcing variables are limited to those that are most readily available in the past, i.e. air temperature and solar radiation, the best results are obtained with the radiative Abtew model (r = 0·70) and with the Makkink radiative/air temperature model (r = 0·67). Copyright © 2007 John Wiley & Sons, Ltd. [source] The influence of tree canopies and elephants on sub-canopy vegetation in a savannahAFRICAN JOURNAL OF ECOLOGY, Issue 1 2010Robert Guldemond Abstract The apparent influence of elephants on the structure of savannahs in Africa may be enhanced by management activities, fire and other herbivores. We separated the effect elephants have on grasses, woody seedlings (<0.5 m) and saplings (0.5,2 m) from the effect of tree canopies (canopy effect), and herbivory (park effect). We defined the canopy effect as the differences between plant abundances and diversity indices under tree canopies and 20 m away from these. Our testing of the park effect relied on the differences in the sub-canopy plant indices inside and outside a protected area that supported a range of herbivores. We based our assessment of the elephant effect on sub-canopy vegetation indices associated with elephant induced reductions in tree canopies. The park and canopy effects were more pronounced than the elephant effect. The park effect suppressed the development of woody seedlings into saplings. Conditions associated with tree canopies benefited woody plants, but not the grasses, as their indices were lower under trees. Elephants reducing canopies facilitated grass species tolerant of direct solar radiation. We concluded that management should consider other agents operating in the system when deciding on reducing the impact that elephants may have on vegetation. Résumé L'influence apparente des éléphants sur la structure des savanes africaines pourrait bien être accentuée par les activités de gestion, les feux et les autres herbivores. Nous avons séparé l'effet que les éléphants ont sur les herbes, les jeunes plants ligneux (<0,5 m) et les arbustes (0,5,2 m) de ceux de la canopée des arbres (effet canopée) et de la présence d'herbivores (effet parc). Nous avons défini l'effet canopée comme la différence entre les indices d'abondance et de diversité des plantes sous la canopée des arbres et à 20 m de ceux-ci. Notre expérimentation de l'effet parc se basait sur la différence des indices de végétation sous canopée à l'intérieur et à l'extérieur d'une aire protégée qui accueille toute une gamme d'herbivores. Nous avons fondé notre évaluation de l'effet éléphants sur les indices de végétation sous canopée, associés aux réductions induites par les éléphants dans la canopée des arbres. Les effets parc et canopée étaient plus prononcés que l'effet éléphants. L'effet parc supprimait le développement des jeunes plants ligneux en arbustes. Les conditions liées à la canopée des arbres bénéficiaient aux plantes ligneuses mais pas aux herbes, car leurs indices étaient inférieurs sous les arbres. Les canopées réduites par les éléphants favorisaient les espèces d'herbes tolérantes à la lumière directe du soleil. Nous en avons conclu que toute gestion devrait considérer l'impact d'autres agents dans le système lorsqu'il s'agit de réduire l'impact que les éléphants peuvent avoir sur la végétation. [source] Latitude and Incidence of Ocular MelanomaPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2006Guo-Pei Yu We investigated the associations between latitude and the incidence of two different types of ocular melanoma, external ocular melanoma (exposed to sunlight) and internal melanoma (not exposed to sunlight), separately. Using 1992,2002 data from the Surveillance, Epidemiology, and End Results (SEER) Program of National Cancer Institute, we identified 2142 ocular melanoma cases in non-Hispanic whites, and then regressed the incidences of various types of ocular melanomas with latitude. Our analysis indicated that the higher the latitude (away from the equator, the less sun exposure), the lower the risk of external ocular melanoma (eyelid and conjunctival melanomas) among non-Hispanic whites (P for trend = 0.018). The incidence increased 2.48 fold from 47,48° to 20,22°. This trend is very similar to that of skin melanoma. The incidence of internal ocular melanoma (uveal melanoma) increased significantly with increasing latitudes (the less sun exposure, P for trend < 0.0001), it increased 4.91 fold from 20,22° to 47,48°. The latitudinal patterns of ocular melanomas may reflect the dual effects of sunlight exposure, i.e. a mutagenic effect of direct solar radiation on external ocular melanomas and a protective effect for internal uveal melanoma, which is similar to the sun radiation protective effects for various internal malignant tumors that are not exposed to the sunlight. [source] | ||||||||||