Improved hydrograph prediction through subsurface characterization: conditional stochastic hillslope simulations     

Steven B. Meyerhoff  Reed M. Maxwell  Wendy D. Graham  John L. Williams III 《Hydrogeology Journal》2014,22(6):1329-1343

Subsurface heterogeneity is one of the largest sources of uncertainty associated with saturated hydraulic conductivity. Recent work has demonstrated that uncertainty in hydraulic conductivity can impart significant uncertainty in runoff generation processes and surface-water flow. Here, the role of site characterization in reducing hydrograph prediction bias and uncertainty is demonstrated. A fully integrated hydrologic model is used to conduct two sets of stochastic, transient simulation experiments comprising different overland flow mechanisms: Dunne and Hortonian. Conditioning hydraulic conductivity fields using values drawn from a simulated synthetic control case are shown to reduce both mean bias and variance in an ensemble of conditional hydrograph predictions when compared with the control case. The ensemble simulations show a greater reduction in uncertainty in the hydrographs for Hortonian flow. The conditional simulations predict surface ponding and surface pressure distributions with reduced mean error and reduced root mean square error compared with unconditional simulations. Uncertainty reduction in Hortonian and Dunne flow cases demonstrates different temporal signals, with more substantial reduction achieved for Hortonian flow.  相似文献   

Two new eucrite breccias from Northwest Africa     

Sheryl A. SINGERLING  Aubrey L. MODI  Blake MCFERRIN  Emily A. WORSHAM  Harry Y. MCSWEEN JR.  Douglas RUMBLE III  Ryoji TANAKA  Lawrence A. TAYLOR 《Meteoritics & planetary science》2013,48(2):E1-E9

Abstract– This work describes two newly discovered eucrite breccias: three presumably paired meteorites, all named Northwest Africa (NWA) 6105, and NWA 6106. For each meteorite, major‐ and minor‐element compositions of minerals were determined using the electron microprobe. Pyroxene Fe‐Mn co‐variations and bulk‐rock oxygen isotope compositions confirm their classification as eucrites. Variations in mineral compositions and textures are attributed to differences in clast types present (i.e., basaltic or cumulate eucrite). The pyroxene compositions support the hypothesis that samples NWA 6105,1; 6105,2; and 6105,3 are paired polymict eucritic breccias, whereas sample NWA 6106 is a monomict basaltic eucritic breccia. Two‐pyroxene geothermometry yields temperatures too low for igneous crystallization. The variation in temperatures among samples suggests that metamorphism occurred prior to brecciation.  相似文献   

A lake in Uzboi Vallis and implications for Late Noachian-Early Hesperian climate on Mars     

J.A. Grant  R.P. Irwin III  D. Buczkowski 《Icarus》2011,212(1):110-122

Uzboi Vallis (centered at ∼28°S, 323°E) is ∼400 km long and comprises the southernmost segment of the northward-draining Uzboi-Ladon-Morava (ULM) meso-scale outflow system that emerges from Argyre basin. Bond and Holden craters blocked the valley to the south and north, respectively, forming a Late Noachian-to-Hesperian paleolake basin that exceeded 4000 km³. Limited CRISM data suggest lake deposits in Uzboi and underlying basin floor incorporate relatively more Mg-clays and more Fe-clays, respectively. The short-lived lake overflowed and breached Holden crater’s rim at an elevation of −350 m and rapidly drained into the crater. Fan deltas in Holden extend 25 km from the breach and incorporate meter-sized blocks, and longitudinal grooves along the Uzboi basin floor are hundreds of meters long and average 60 m wide, suggesting high-discharge drainage of the lake. Precipitation-derived runoff rather than regional groundwater or overflow from Argyre dominated contributions to the Uzboi lake, although the failure of most tributaries to respond to a lowering of base level indicates their incision largely ended when the lake drained. The Uzboi lake may have coincided with alluvial and/or lacustrine activity in Holden, Eberswalde, and other craters in southern Margaritifer Terra, where fluvial/lacustrine activity may have required widespread, synoptic precipitation (rain or snow), perhaps associated with an ephemeral, global hydrologic system during the Late Noachian into the Hesperian on Mars.  相似文献