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تعداد نتایج: 16953589 فیلتر نتایج به سال:
The possibility that the tropopause could be lower during an ice-age cooling leads to an examination of the general sensitivity of global circulations to the tropopause height by altering a constant stratospheric temperature Ts in calculations with a dry, global, multilevel, spectral, primitive equation model subject to a simple Newtonian heating function. In general, lowering the tropopause by...
Introduction. The NASA Phoenix lander has provided a unique first-look at permafrost processes operating on the surface of the martian northern plains [1]. Critical results from the mission include the detection of an icy surface present beneath thin, overlying, dry sediments [1-3]; complex soil chemistry comparable to that observed in terrestrial cold and arid terrains [4, 5]; and weather/clim...
The pollination biology of the cactus Pachycereus pecten-aboriginum was studied in a tropical location in western Mexico (ca. 18° N latitude) to compare with data from a northern population (ca. 28° N latitude). Throughout this range, the nectar-feeding bat Leptonycteris curasoae is resident within the tropics but migratory in its northern range. The hypothesis was tested that if a predictable ...
Observations by the Ulysses SWOOPS plasma experiment are used to investigate spatial and temporal gradients during the mission, with emphasis on more recent high latitude observations including the recent South Pole to North Pole passage during solar minimum. Compared to lower latitudes, the high latitude solar wind had higher average speed, proton temperature, and momentum flux, and lower numb...
About 34 million years ago, Earth's climate shifted from a relatively ice-free world to one with glacial conditions on Antarctica characterized by substantial ice sheets. How Earth's temperature changed during this climate transition remains poorly understood, and evidence for Northern Hemisphere polar ice is controversial. Here, we report proxy records of sea surface temperatures from multiple...
Titanium and iron concentration data from the anoxic Cariaco Basin, off the Venezuelan coast, can be used to infer variations in the hydrological cycle over northern South America during the past 14,000 years with subdecadal resolution. Following a dry Younger Dryas, a period of increased precipitation and riverine discharge occurred during the Holocene "thermal maximum." Since approximately 54...
The increasing breast, colorectal and prostate cancer mortality rates found with increasinglatitude by ecological studies in the USA and in Europe has been equated to lower vitamin D statuswith increasing latitude. We examined in Western, Northern and Southern Europe the associationbetween latitude of residence and serum 25-hydroxyvitamin D levels. We performed a systematicsearc...
In this paper, the spatial correlations of ionospheric day-to-day variability are investigated by statistical analysis on GPS and Incoherent Scatter Radar observations. The meridional correlations show significant (>0.8) correlations in the latitudinal blocks of about 6 degrees size on average. Relative larger correlations of TEC’s day-to-day variabilities can be found between magnetic conjugat...
Before the magnetic storm sudden commencement during the November 2, 1967, solar particle event, the access of 1.2to 40-Mev protons into the high-latitude portion of the northern polar region was delayed by ~20 hours. At the same time the access delay for 10to 40-Mev protons was •1 hour in the southern polar region a•d at middle northern latitudes. The implications of the north-south asymmetry ...
Two atmospheric circulation systems, the mid-latitude Westerlies and the Asian summer monsoon (ASM), play key roles in northern-hemisphere climatic changes. However, the variability of the Westerlies in Asia and their relationship to the ASM remain unclear. Here, we present the longest and highest-resolution drill core from Lake Qinghai on the northeastern Tibetan Plateau (TP), which uniquely r...
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