Longitude

About: Longitude is a research topic. Over the lifetime, 2260 publications have been published within this topic receiving 54988 citations. The topic is also known as: angle of longitude.

Climate Cycles and Climate Transitions as a Response to Astronomical and CO2 Forcings

Abstract: The natural variability of climate occurs on a wide range of time scales, ranging from decades to millions of years. The time scales of importance to the ice ages of the late Cenozoic are of the order of 10 to 1000 ka. On these time scales, the so-called astronomical theory of paleoclimates and in particular its Milan-kovitch version have become the almost universally accepted basis of research (Berger 1992). In its traditional form, the astronomical theory states that changes in high-latitude summer insolation cause the waxing and waning of the continental ice sheets. This was first quantitatively formulated by Milanko-vitch (Berger 1988; Milankovitch 1995), who calculated how the incoming radiation at the top of the atmosphere varies as a function of latitude and the orbital parameters e, ∈ and e sin ῶ, where e denotes the eccentricity of the Earth’s orbit around the Sun, ∈ is the obliquity and e sin ῶ is the precessional effect, with ῶ being the longitude of the perihelion as measured from the moving equinox. Each of the orbital parameters can be expressed as a quasi-periodic function of time. According to the astronomical theory, low summer insolation could prevent the winter snow from melting. The high albedo of snow- and ice-covered areas would initiate a further cooling of the Earth. Eventually, this positive feedback would result in the build-up of the continental ice sheets.

Topography effects on small-scale precipitation variability in the Swiss pre-Alps

Abstract: Long-term precipitation and snow-cover measurements were carried out to estimate the areal pattern of precipitation in a small, rugged Swiss pre-Alpine basin. The dense networks used consisted of 34 storage gauges and 32 pit gauges with orifice parallel with slope, the latter being corrected for wetting losses. Consequently, the corrected data was very near to the true precipitation at a particular point. In the winter season also snow-cover characteristics were measured at 11 locations. Altitude turned out to be the best overall predictor for corrected data (R 2 = 0.67) and longitude for uncorrected data (R 2 = 0.67 vs only 0.58 for altitude!). The combination of altitude, longitude and latitude explains almost 75% of the spatial variance of summer season precipitation and snow-cover characteristics. However, the three variables used in the analysis were found to be interrelated, particularly in networks of storage gauges and snow-cover measurements (R 2 = 0.40-0.70).

Supercooled ion temperatures observed in the topside ionosphere at dawn meridian during storm periods

Abstract: [1] A few rare events of supercooled ion temperature near the magnetic equator at dawn meridian have been observed by the first satellite of the Republic of China, ROCSAT-1, at 600 km altitude. The ion cooling event occurs within a narrow longitude region where a large density reduction together with a large downward, eastward, and field-aligned flow is observed. Although ion temperature troughs around the magnetic equator have been observed by many satellites before, and the interhemispheric plasma transport of adiabatic cooling effect for ions near the equator has been modeled to explain the past observations, the current observation enunciates some new facts of the ion cooling effect that have not been reported. First, ion cooling events are observed by ROCSAT at an unprecedented low altitude of 600 km during the solar maximum years of 2000 and 2001. Second, the ion temperature trough is observed, together with a large density reduction and a large downward and eastward drift that were absent in the past observations. Third, the present events are only observed near the dawn meridian during the disturbed periods. Comparing the observational facts with the existing models, we conclude that the model of interhemispheric plasma transport [Bailey et al., 1973; Heelis et al., 1978; Bailey and Heelis, 1980] seems to fit best with the current observations. However, instead of resorting to the quiet time neutral wind to induce the quasi steady state plasma transport as modeled before, a storm time transient dynamical process could have occurred within a limited longitude region where ions at high latitudes are forced to move along the field lines to the dip equator to cause ion cooling observed at 600 km lower than predicted in the model. This storm time ionospheric process could be related to the creation of a westward electric field in the inner magnetosphere near the dawn meridian from a sudden enhancement of the convection field during a disturbed period modeled in the comprehensive ring current model [Fok et al., 2003].