A novel ELF radar for major oil deposits

This letter proposes a novel extremely low frequency (ELF) radar for major oil deposits. Using our recently developed whole-Earth electromagnetic wave propagation model based upon the finite-difference time-domain method, we have determined that detection of the radial (vertical) component of the scattered H-field provides a sensitive means to detect oil fields that are located within several kilometers of the Earth's surface. As an example, we provide numerical simulations of ELF radar returns from a hypothetical Alaskan oil field excited by a 20-Hz pulse emitted from the former U.S. Navy site in Wisconsin. The proposed method would potentially provide means to rapidly and inexpensively conduct aerial surveys of thousands of square kilometers for significant oil deposits.     

Fabric development in brittle-to-ductile shear zones

Brittle-to-ductile shear zones from two separate geological settings are shown to have nucleated on zones of predominantly brittle deformation. The shear zones are not simply foliated cataclasites, since they contain abundant evidence of dynamic recrystallization of constituent minerals. A small quartz diorite lens in the Borrego Springs shear zone, southern California, contains centimeter-scale cataclasite zones that exhibit a gradual transition into foliated rock. Alteration of magnesiohornblende to actinolite, feldspar to white mica plus quartz, and biotite to chlorite, produced elongate minerals that define the foliation. During the later stages of deformation, intracrystalline slip and dynamic recrystallization of quartz and feldspar were important deformation mechanisms.The widespread occurrence of mineralized dilatant cracks predated the development of meter-to-decimeter-scale ductile shear zones in the Striped Rock granite, southern Virginia. Again, important deformation mechanisms in the final stages of deformation were intracrystalline slip and dynamic recrystallization of quartz.In both field areas the role of fluids has been important from the onset of brittle deformation. Fluids may have enhanced early fracturing in addition to causing the alteration and hydrolytic weakening of host rock minerals and the introduction of new mineral species. Each of these processes is thought to have contributed to the later localization of crystal plastic deformation in the rocks.     

Design and Implementation of Evapotranspiration Measuring Equipment for Owens Valley, California

As part of a plant survivability and ground water study in Owens Valley, California, semipermanent installations are used to measure continuous range-land evapotranspiration in the valley's phreatophyte community. A proposed mobile installation also has been designed. The semipermanent micrometeoro-logical station collects continuous data for solution of the Bowen ratio/energy budget equation and the Penman combination equation. Three sites were chosen for this type of installation to provide a representative sampling of Owens Valley. The proposed mobile aerodynamic installation should be capable of calculating evapotranspiration by the eddy correlation method. This instrumentation will be used throughout the valley for short periods of time (up to five days). Many problems with equipment operation, calibration and design have been identified and resolved by means of improved calibration techniques, systematic error-removal techniques, reduced cycle times, modified equipment design and proper observer training. The collected evapotranspiration data will be instrumental in developing a one-dimensional evapotranspiration flux algorithm for a model of valleywide ground water flow.     

Cumulus mergers in the maritime continent region

Summary We examine a family of tall (up to 20 km) cumulonimbus complexes that develop almost daily over an adjacent pair of flat islands in the Maritime Continent region north of Darwin, Australia, and that are known locally as Hectors. Nine cases observed by a rawinsonde network, surface observations (including radiation and soil measurements), the TRMM/TOGA radar, and one day of aircraft photography are used to analyse the development, rainfall, surface energy budgets, and vertical structure of these convective systems.The systems undergo convective merging which is similar to that observed in previous Florida studies and is multiplicative in terms of rainfall. About 90% of the total rainfall comes from the merged systems, which comprise less than 10% of convective systems, and this has implications for the manner in which tropical rainfall is parameterised in largerscale numerical models. By comparison to the West Indies, GATE, and Florida, the Hector environment contains a weaker basic flow, with less vertical shear. The main thermodynamic difference is that the Darwin area has an unstable upper troposphere and very high tropopause. Numerical modelling results support earlier observations of updraughts in excess of 30 ms^–1 in this region, but show that only modest convective drafts are experienced below the freezing level (5 km).The surface fluxes over the islands are estimated from a Monash University study to be mainly in latent form from evapotranspiration, with a Bowen ratio only slightly larger than that commonly observed over oceans. These surface fluxes are crucial to the development of a suitable mixed layer to support deep convection. The flux estimates agree with the observed changes below the cloud base and provide sufficient information for calculations of the bounds on precipitation efficiency. Of particular interest are the observations of Hector development on a day when the islands were under a dense cirrus overcast. We find that the islands still provide sufficient net sensible and latent heat fluxes to initiate convection.With 10 Figures     

Arecibo radar observations of Mars surface characteristics in the northern hemisphere

Mars surface characteristics at and near the Viking Chryse and Tritonis Lacus landing areas were determined by radio scatter using the new 12.6 cm radar at the Arecibo Observatory during 1975–1976. Interpretation of each power spectrum suggests rms surface tilts of 4° at the final A1WNW (47.9°W, 22.5°N) site, 5° near the original A1 site, and 6° between the two. At the back-up site (A2) surface roughness estimates were about 4°. Striking changes in surface texture have been found near the eastern bases of Tharsis Montes and Albor Tholus, each volcanic feature marking the western boundary of very smooth surface units. The roughness sensed at 1 to 100 m scales by radar appears to be relatively independent of the surface units defined at large scale lengths by photogeologists. Radar properties thus provide an additional means by which planetary surfaces may be characterized.     

Calculating Groundwater Response Times for Flow in Heterogeneous Porous Media

Predicting the amount of time required for a transient groundwater response to take place is a practical question that is of interest in many situations. This time scale is often called the response time. In the groundwater hydrology literature, there are two main methods used to calculate the response time: (1) both the transient and steady‐state groundwater flow equations are solved, and the response time is taken to be amount of time required for the transient solution to approach the steady solution within some tolerance; and (2) simple scaling arguments are adopted. Certain limitations restrict both of these approaches. In this study, we outline a third method, based on the theory of mean action time. We derive the governing boundary value problem for both the mean and variance of action time for confined flow in two‐dimensional heterogeneous porous media. Importantly, we show that these boundary value problems can be solved using widely available software. Applying these methods to a test case reveals the advantages of the theory of mean action time relative to standard methods.     

The formation of farm mounds on the Island of Sanday,Orkney

A recent archaeological site survey of the island of Sanday on Orkney has identified a distinct concentration of 15 farm mounds. An immediate need is to determine the nature, age, and processes of formation of these very distinctive landform features. This paper reports a geoarchaeological investigation of three mounds at Westbrough, Langskaill, and Skelbrae. For the island as a whole, the mounds vary in diameter from 50 to 205 m, with deposits up to a thickness of 4.3 m. The mounds vary in their morphology, reflecting complex processes of accumulation, often intense disturbance, and in some cases, erosion by the sea. Sections at the three sites are described with analytical data also being given for particle size, percent loss-on-ignition, total phosphate, δ¹³C, and radiocarbon dating. The Westbrough and Skelbrae mounds were formed post-7th century A.D.; more detailed dating was possible for the Langskaill site, which was initiated in the early to mid 13th century. A steady and relatively rapid sedimentation rate (ca. 1.9 cm year⁻¹) took place over the 200 years following the initiation of the mound. The lower part of the Westbrough mound is distinguished by the presence of peat, interpreted as discarded bedding material, but the remainder of the investigated sections are composed dominantly of mineral sediments containing organic matter of terrestrial origin. It is suggested that these materials accumulated from the ash of domestic hearths as well as from the residues of bedding material from the byres (cattle sheds). Turves (vegetation plus some underlying soil) would have been cut, dried, and then used in the byres and such turves would have retained a significant mineral content. The implication is that the inherent fertility of the island made it unnecessary for the farmers to spread the dung over the fields. This may explain why there is the distinct concentration of these mounds on the island of Sanday, an island noted in earlier times for its fertile soils developed on calcareous sands.     

Sea-breeze-initiated rainfall over the east coast of India during the Indian southwest monsoon

Sea-breeze-initiated convection and precipitation have been investigated along the east coast of India during the Indian southwest monsoon season. Sea-breeze circulation was observed on approximately 70–80% of days during the summer months (June–August) along the Chennai coast. Average sea-breeze wind speeds are greater at rural locations than in the urban region of Chennai. Sea-breeze circulation was shown to be the dominant mechanism initiating rainfall during the Indian southwest monsoon season. Approximately 80% of the total rainfall observed during the southwest monsoon over Chennai is directly related to convection initiated by sea-breeze circulation.