A comparison of simulated monsoon circulations and snow accumulation in Asia during the mid-Holocene and at the Last Glacial Maximum

Tropical climatology through the last glacial cycle is believed to have ranged from colder, windier conditions at the Last Glacial Maximum (LGM) to relatively warm, stable conditions during the Holocene. Changes in strength of the South Asian monsoon have previously been determined from a variety of proxy data and have been attributed primarily to changes in radiative forcing, although tropical sea surface temperature (SST) is known to play a fundamental role in regulating monsoon strength and is also believed to have changed throughout the late Quaternary.In this study, the monsoons simulated in a coupled atmosphere–ocean general circulation model (GCM) configured for the mid-Holocene (6000 years B.P.) and for the LGM (21,000 years B.P.) are compared. The colder and windier conditions simulated for the LGM produced a summer monsoon whose westerly winds are stronger and whose precipitation and snowfall into the eastern Himalaya are increased, with drier conditions over the rest of the Indian subcontinent and over most of southwest Asia.The mid-Holocene monsoon circulation is stronger than today, and annual mean snow accumulation is increased over the northwestern Himalaya. These changes in precipitation and snow accumulation are analyzed in terms of the altered atmospheric circulations, which are in turn driven by changes in radiative forcing, sea surface temperatures, and sea surface height. All of these factors are therefore demonstrated to be important in governing the spatial distribution of snow and ice deposition in the Himalaya during the late Quaternary, and are likely to have contributed to the observed asynchroneity of Himalayan glaciation and Northern Hemisphere ice sheet volume.     

Analysing the New Saturnian Rings, R/2004 S1 and R/2004 S2

The Cassini-Huygens arrival into the Saturnian system brought a large amount of data about the satellites and rings. Two diffuse rings were found in the region between the A ring and Prometheus. R/2004 S1 is coorbital to Atlas and R/2004 S2 is close to Prometheus. In this work we analysed the closest approach between Prometheus and both rings. As a result we found that the satellite removes particles from R/2004 S2 ring. Long-term numerical simulations showed that some particles can cross the F ring region . The well known region of the F ring, where small satellites are present and particles are being taking from the ring, gains a new insight with the presence of particles from R/2004 S2 ring. The computation of the Lyapunov Characteristic Exponent reveled that the R/2004 S2 ring lies in a chaotic region while R/2004 S1 ring and Atlas are in a stable region. Atlas is responsible for the formation of three regimes in the R/2004 S1 ring, as expected for a satellite embedded in a ring.     

Modeling non-Darcy flows in realistic pore-scale proppant geometries

The ability to evaluate the effective permeability of proppant packs is useful in predicting the efficiency of hydraulic fracture installations. In this paper we propose a computational approach combining microimaging data from X-ray computed microtomography, the simulations of flow at pore-scale, and an upscaling process which identifies the effective model parameters at the core-scale. With this computational approach applied to proppant pack we confirm the reduction in the fracture conductivity and subsequent reduction in the productivity of a hydraulically fractured reservoir due to the high flow rates and to the migration of fine particles resulting in pore throat bridging.