Isobaric Surfaces Research Articles

Wind Energy Resource Estimation of the Upper Atmosphere over Southern Africa

On the basis of daily ECMWF data over the period 1982–89, the mean seasonal and mean annual wind energy resource fields on the isobaric surfaces 1000, 850, 700, 500, 300, 200, and 100 hPa, within the latitude–longitudinal zone 0°–50°S and 0°–45°E, have been calculated and analyzed. Generally, maximum wind energy is recorded on the 3OO-hPa surface, and the intensities are greater by about 25%–30% in winter than in summer. The greatest continental wind energy resources are experienced over the southern tip of the southern African subcontinent, where it was established that the free atmospheric resources exceed those near the surface by at least an order of magnitude. The two-dimensional Gaussian distribution of the wind vector has been used to provide an indirect estimate of the wind energy resource. Good agreement between this measure and the direct estimate of wind energy was obtained, demonstrating the potential usefulness of the two-dimensional Gaussian distribution in estimating upper-air wind energy resources.

Phase diagrams of molar volume against mole fractions at given temperatures and pressures for { xAAr + xBXe + (1 − xA− xB)NH 3}

The phase behaviour of (argon + xenon + ammonia) was investigated at the temperatures T= 273.15 K, 298.15 K, 323.15 K, 348.15 K, and 373.15 K and pressure pfrom 5.0 MPa up to 200.0 MPa. The results are given in a table and are shown as molar volume against mole fraction ( V m, x A, x B) diagrams. The measurements were carried out in a cylindrical autoclave with a moveable piston and a window allowing adjustment and observation of phase equilibria at given pand T. Samples were taken from the coexisting phases and were analysed to obtain their molar volumes and compositions. For given pand Tthe ends of the corresponding tie lines lie on isobaric and isothermal curves. Isothermal surfaces were drawn containing several isobars. Also isobaric surfaces with different isothermal curves were drawn. It is shown how isothermal surfaces can be combined with isobaric ones. The resulting intersection curves represent again the geometrical locus of all tie lines for given pressures and temperatures. In the ( V m, x A, x B) diagram the isothermal surfaces at T= 373.15 K and 348.15 K stretch between the gas and liquid molar volumes of pure NH 3. The corresponding binary isotherms, which are not interrupted, are their boundary curves. At lower temperatures one or two of the binary isotherms are interrupted. Due to this behaviour the isothermal surfaces at those temperatures are more complex. The five investigated isothermal surfaces are, however, closely related to one another and the shape of an isothermal surface is strongly dependent on the shape of the corresponding binary isotherm. The isobaric surfaces at higher pressures behave similarly. However, at lower pressures their shapes become very complex. In comparison the critical surface shows no great variation in shape or molar volume at the investigated temperatures and pressures, but consists of two separate parts.

Summertime atmospheric circulation in the vicinity of a blue ice area in Queen Maud Land, Antarctica

The surface wind field is an important factor controlling the surface mass balance of Antarctica. This paper focuses on the observed atmospheric circulation during summer of an Antarctic blue ice area in Queen Maud Land. Blue ice areas are characterised by a negative surface mass balance and henceforth provide an interesting location to study the influence of meteorological processes on large local mass balance gradients. During lapse conditions, synoptic forcing determines the surface-layer flow. No significant horizontal temperature gradient with coastal stations could be detected along isobaric surfaces, indicating weak or absent thermal wind. Observations performed at the coastal stations Halley and Georg von Neumayer show the pronounced effects of synoptic forcing. The surface winds in the valley of the blue ice area could be divided into two distinct flow patterns, occurring with about equal frequency during the experiment. Flow type I is associated with cyclonic activity at the coast, resulting in strong easterly winds, precipitation and drifting snow. Flow characteristics inside and outside of the valley are similar during these conditions. Flow type II occurs when a high pressure system develops in the Weddell Sea, weakening the free atmosphere geostrophic winds. A local circulation is able to develop inside the valley of the blue ice area during these tranquil conditions. The transition from flow type II to flow type I is associated with front-like phenomena inside the valley. Some simple theoretical considerations show that surface-layer stability and the upper air geostrophic wind determine the surface flow direction in the valley. Finally, the influence of the observed circulation on the energy and mass balance of the blue ice area is discussed.

South Atlantic circulation in a world ocean model

Abstract. The circulation in the South Atlantic Ocean has been simulated within a global ocean general circulation model. Preliminary analysis of the modelled ocean circulation in the region indicates a rather close agreement of the simulated upper ocean flows with conventional notions of the large-scale geostrophic currents in the region. The modelled South Atlantic Ocean witnesses the return flow and export of North Atlantic Deep Water (NADW) at its northern boundary, the inflow of a rather barotropic Antarctic Circumpolar Current (ACC) through the Drake Passage, and the inflow of warm saline Agulhas water around the Cape of Good Hope. The Agulhas leakage amounts to 8.7 Sv, within recent estimates of the mass transport shed westward at the Agulhas retroflection. Topographic steering of the ACC dominates the structure of flow in the circumpolar ocean. The Benguela Current is seen to be fed by a mixture of saline Indian Ocean water (originating from the Agulhas Current) and fresher Subantarctic surface water (originating in the ACC). The Benguela Current is seen to modify its flow and fate with depth; near the surface it flows north-westwards bifurcating most of its transport northward into the North Atlantic Ocean (for ultimate replacement of North Atlantic surface waters lost to the NADW conveyor). Deeper in the water column, more of the Benguela Current is destined to return with the Brazil Current, though northward flows are still generated where the Benguela Current extension encounters the coast of South America. At intermediate levels, these northward currents trace the flow of Antarctic Intermediate Water (AAIW) equatorward, though even more AAIW is seen to recirculate poleward in the subtropical gyre. In spite of the model's rather coarse resolution, some subtle features of the Brazil-Malvinas Confluence are simulated rather well, including the latitude at which the two currents meet. Conceptual diagrams of the recirculation and interocean exchange of thermocline, intermediate and deep waters are constructed from an analysis of flows bound between isothermal and isobaric surfaces. This analysis shows how the return path of NADW is partitioned between a cold water route through the Drake Passage (6.5 Sv), a warm water route involving the Agulhas Current sheeding thermocline water westward (2.5 Sv), and a recirculation of intermediate water originating in the Indian Ocean (1.6 Sv).

Diagnosing Climate Change and Ocean Ventilation Using Hydrographic Data

Changes in atmospheric forcing can affect the subsurface water column of the ocean by three different mechanisms. First, warmed mixed-layer water that is subducted into the ocean interior will cause subsurface warming; second, the subducted surface water can be freshened through changes in evaporation and precipitation; and third, the properties at a given depth may be changed by the vertical displacement of isotherms and isohalines without changes of water masses. These vertical displacements of the water column can be caused either by changes in the rates of renewal of water masses or by dynamical changes (such as changes in wind stress). A method for analysing the subsurface temporal changes in hydrographic data is described in terms of these three processes: “pure warming,” “pure freshening,” and “pure heave.” Linear relations are derived for the relative strength of each process in terms of the observed changes of potential temperature and salinity in two different coordinate frames: (i) constant density surfaces, and (ii) isobaric surfaces. Inverse methods are applied to three realizations of the SCORPIO section at 43°S in the Tasman Sea. These sections were obtained in 1967, and in the austral winter and summer of 1989 and 1990, respectively. This data is used to explore the relative strengths of surface warming, surface freshening, and heave of the water column. The six-month differences for this region show small changes in Sub-Antarctic mode water (SAMW) and are not characterized by any one process, whereas below the mode waters the observed differences are well described by the heave process. In contrast, the 23-year differences show significant changes in the properties of the water that flows into the Tasman Sea: SAMW (300-700 db) is well described by pure warming of near- surface waters, while the changes observed at the depth of the salinity minimum are consistent with pure freshening. The observed changes in the interior of the ocean between adjacent seasons do not exhibit significant changes of water masses, consistent with the distance of this section from the outcrop region of the density surfaces of interest. For the 23-year differences, changed surface waters subducted into the ocean interior have sufficient time to influence the temperature-salinity correlations. The skill of our approach in discriminating between short-term changes (almost exclusively heave) and long-term changes associated with the subduction of changed surface waters is particularly encouraging. Although the observed changes could equally well be natural variability, they are qualitatively consistent with coupled numerical models of climate change in which surface waters are warmed and increased precipitation occurs south of the Sub-Antarctic Front.

South Atlantic circulation in a world ocean model

The circulation in the South Atlantic Ocean has been simulated within a global ocean general circulation model. Preliminary analysis of the modelled ocean circulation in the region indicates a rather close agreement of the simulated upper ocean flows with conventional notions of the large-scale geostrophic currents in the region. The modelled South Atlantic Ocean witnesses the return flow and export of North Atlantic Deep Water (NADW) at its northern boundary, the inflow of a rather barotropic Antarctic Circumpolar Current (ACC) through the Drake Passage, and the inflow of warm saline Agulhas water around the Cape of Good Hope. The Agulhas leakage amounts to 8.7 Sv, within recent estimates of the mass transport shed westward at the Agulhas retroflection. Topographic steering of the ACC dominates the structure of flow in the circumpolar ocean. The Benguela Current is seen to be fed by a mixture of saline Indian Ocean water (originating from the Agulhas Current) and fresher Subantarctic surface water (originating in the ACC). The Benguela Current is seen to modify its flow and fate with depth; near the surface it flows north-westwards bifurcating most of its transport northward into the North Atlantic Ocean (for ultimate replacement of North Atlantic surface waters lost to the NADW conveyor). Deeper in the water column, more of the Benguela Current is destined to return with the Brazil Current, though northward flows are still generated where the Benguela Current extension encounters the coast of South America. At intermediate levels, these northward currents trace the flow of Antarctic Intermediate Water (AAIW) equatorward, though even more AAIW is seen to recirculate poleward in the subtropical gyre. In spite of the model's rather coarse resolution, some subtle features of the Brazil-Malvinas Confluence are simulated rather well, including the latitude at which the two currents meet. Conceptual diagrams of the recirculation and interocean exchange of thermocline, intermediate and deep waters are constructed from an analysis of flows bound between isothermal and isobaric surfaces. This analysis shows how the return path of NADW is partitioned between a cold water route through the Drake Passage (6.5 Sv), a warm water route involving the Agulhas Current sheeding thermocline water westward (2.5 Sv), and a recirculation of intermediate water originating in the Indian Ocean (1.6 Sv).

The generation of available potential energy, according to Lorenz’ exact and approximate equations

The generation of available potential energy (APE) in the atmosphere according to Lorenz′ (1955a, b) exact and approximate equations is investigated in the space-time domain. The generation is determined from the fields of diabatic heating and temperature. The heating is evaluated by the residual method, using 4 × daily ECMWF-(European Centre for Medium-Range Weather Forecasts) initialised analyses for the January months of 1986–1992 and the July months of 1985–1991. The contributions of different parts of the atmosphere to the exact and approximate generation are investigated, and the differences between these contributions are explained. In the derivation of the equation of the approximate generation, Lorenz made several approximations. The most serious one appears to be that the average pressure on an isentropic surface is approximately equal to the pressure of the isobaric surface, for which the average potential temperature is equal to the potential temperature of the isentropic surface. Our results show that the largest differences between the contributions to the exact and approximate generation occur in the extratropical low troposphere. Here the contribution to the exact generation of eddy APE is up to 10 × smaller than in the approximation, and the contribution to the exact generation of zonal- and time-mean APE is weakly positive, whereas for the approximation it is strongly negative. Other main differences occur in the tropical middle troposphere where the contribution to the exact generation of mean APE is about two times as small as the approximate value. Despite these large differences, the globally averaged exact generation of mean APE, which is 2.29 W/m 2 in January and 1.88 W/m 2 in July, differs less than 3% from its approximation. The globally averaged exact generation of stationary eddy APE, which is 0.26 W/m 2 in January and 0.45 W/m 2 in July, is about 25% smaller than its approximation. In most individual months the globally averaged exact generation of transient eddy APE is weakly positive (about 0.01 W/m 2 ), whereas the approximation is weakly negative (about – 0.08 W/m 2 ). The globally averaged generation of mean APE is not sensitive to the period and kind of the circulation data. The sensitivity of the globally averaged generation of stationary and transient eddy APE is about 0.1 W/m 2 . DOI: 10.1034/j.1600-0870.1994.t01-3-00002.x

Meteorological satellite TIROS—N TOVS remote sensing of atmospheric property and cloud

In this paper, a new retrieval method, i.e., the Statistical-Physical Retrieval Method (STPRM) has been developed. It is a combination of both statistical and physical method. On this basis, a retrieval system of temperature-humidity profiles and cloud parameters has been developed. By use of the developed TOVS STPRM the distribution of atmospheric temperature, humidity and geopotential height on isobaric surface can be obtained. In comparison with the statistical method and physical method, the TOVS STPRM system not only has the advantage of convenience in use, quickness in data processing and accuracy in retrieval result, but also can display cloud evolution on screen.

Age and origin of Late Jurassic and Paleocene granitoids, Nelson Batholith, southern British Columbia

In the Middle Jurassic Nelson Batholith, southern British Columbia, young 40Ar/39Ar ages (i.e., 50–60 Ma) and distorted isobaric surfaces in the batholith suggest the possibility of Paleocene granitic plutonism. We present the results of a study undertaken to evaluate this possibility. Geochemical criteria successfully distinguish a suite of granitoids within the Nelson Batholith that differ from Nelson granites of similar SiO2 content. The granitoid suite is composed of 71.6–75.7 wt.% SiO2 leucocratic biotite granite and quartz monzonite with strong enrichments in alkaline, alkaline earth, and rare earth elements. Nd and Pb isotopic compositions suggest that biotite granite and quartz monzonite are not related. Biotite granite yields a U–Pb age of 158.9 ± 0.6 Ma (concordant zircons). Quartz monzonite crystallized at 61 ± 1 Ma, based on interpretation of titanite and zircon analyses. Zircons from this sample lie along a line from 61 to 160 Ma and demonstrate the presence of Middle Jurassic inheritance. Based on its petrographic and isotopic similarity to other Middle Jurassic plutons in the Nelson Batholith – Valhalla Complex area, we include the 159 Ma biotite granite with the Jurassic plutonic suite. This result demonstrates that magmatism in southern British Columbia was active at least until the early Late Jurassic (Oxfordian). The Paleocene (61 Ma) quartz monzonite that intrudes the southern Nelson Batholith is the structurally highest occurrence of "Ladybird" granite yet documented in southern British Columbia. Comparison of new and published geochemical and isotopic data for Paleocene granitoids throughout the southern Omineca Belt, British Columbia, suggests that these granitoids were not derived from a single, old crustal source.

Computations of the vertical motion and atmospheric energetics using omega and thermodynamic equations for a case study of a depression (September 1985)

The vertical velocity and diabatic heating have been computed at 200 mb, 400 mb, 600 mb and 800 mb surfaces through the solution of omega and thermodynamic energy equations using real data of the depression (September 1985) over the Indian monsoon region and its vertical structure were presented. The contribution of vertical motion due to sensible and latent heat was observed to be the highest, and the least being the adiabatic vertical motion which was less than 4%. Generation, conversion and dissipation of available potential energy and kinetic energy have been computed at different isobaric surfaces. In the lower troposphere, eddy kinetic energy acted as a source to eddy available potential energy whereas eddy available potential energy acted as a source to eddy kinetic energy in the upper troposphere. Downward transfer of eddy kinetic energy from upper to lower troposphere may be associated with the cyclonic circulation. The intense phase of the cyclonic circulation resulted in an increase in destruction of eddy kinetic energy in the lower troposphere.

Experimental study of the high-pressure stability limit of osumilite in the system K2O-MgO-Al2O3-SiO2: implications for high-temperature granulites

In experiments on synthetic minerals in piston-cylinder solid-media apparatus Mg-osumilite breaks down to enstatite, sillimanite, K-feldspar and quartz at a pressure between 11 and 12 kbar over a temperature range of 950-1100°C. The reaction has a flat dP/dT slope. The reactions osumilite = cordierite + enstatite + K-feldspar + quartz and osumilite = sapphirine + enstatite + K-feldspar + quartz limit osumilite stability at lower and higher temperatures respectively. Because osumilite in nature is invariably more magnesian than other co-existing ferromagnesian minerals, the magnesian end-member can be predicted to have the greatest stability field. Osumilite, like cordierite, can thus only occur in normal thickness continental crust. The data indicate that in the Napier complex, Enderby Land, Antarctica, where osumilite occurs on a regional scale, an inferred «isograd», marking the disappearance of osumilite, is the trace of a nearly isobaric surface at a paleo-depth of ca. 35 km. On this surface osumilite breaks down to orthopyroxene, sillimanite, K-feldspar and quartz

The climatic effects of the stratospheric volcanic ash

The climatic effects of the stratospheric volcanic ash are simulated. The model we used is a primitive equation model with theP—σ incorporated coordinate system. The model has 5 layers in the atmosphere and 2 layers in the soil. The volcanic ash is introduced to the first (highest) model layer with a fixed optical thickness of 0.1275. Two comparative numerical experiments with and without the volcanic ash are made. Results show that the effects of the stratospheric volcanic ash on the formations of the mean climatic fields are much smaller than those of the land-sea distribution and the large scale topography. However, it does have contributions to the anomalies of the basic climatic states. The direct effect of the volcanic ash is to increase the temperature in the stratosphere. It can also influence the temperature and the height fields of isobaric surfaces, horizontal and vertical motions, precipitation and the surface climate through dynamic and thermodynamic processes in the atmosphere.

Liquid-crystalline side chain polysiloxanes with 4-amino-4'-stilbenecarboxylic ester mesogens

Abstract : The liquid crystalline phases of polysiloxanes have been characterized by DSC, optical microscopy, and powder X-ray diffraction. The polysiloxanes form monolayers at the air/water interface with molecular areas of 30 - 35 A(2), and the films do not collapse at pressures of about 40 mN/m. The monolayers of CPS-1 and -2 showed good stability on water compared to those of HPS-1 and -2 as measured by isobaric surface area changes as a function of time. Moreover, there was little hysteresis between isotherms obtained by compression and subsequent decompression below 40 mN/m for CPS-1 and -2.

フライトレベルの幾何学的高度の変化特性

This paper describes the annual variations of the geometric heights of flight levels used for aircraft. The height difference between the isobaric surface corresponding to the flight level and the nominal flight level value is estimated from the measured geometric height of an aircraft by a height finding radar and the Mode C reported pressure altitude by the Secondary Surveillance Radar (SSR). The observed differences indicate a periodical variation of approximately twelve months. The seasonal trend of the difference between the geometric height H and the flight level FL, i.e., H-FL, is modelled by H-FL=C_1sin {C_2 (t-C_3)}+C_4+ε where t is the data acquisition time, ε is the residual and C_i (i=1, 2, 3, 4) are the model parameters. Several characteristics of H-FL are discussed herein.

Restoration of Laramide right-lateral strike slip in northern New Mexico by using Proterozoic piercing points: Tectonic implications from the Proterozoic to the Cenozoic

Early Proterozoic rocks in northern New Mexico can be used to document 100-170 km of right-lateral slip along a network of north-striking Laramide (Late Cretaceous-early Tertiary) faults that formed the precursor of the Rio Grande rift. Piercing lines are defined by the intersection of a subborizontal 4 kbar isobaric surface with steeply dipping stratigraphic markers and regional structures. Restoration of slip provides new insight into the nature of Proterozoic orogenic and crustal province boundaries. The Yavapai crustal province (1.75-1.72 Ga juvenile volcanogenic rocks) is imbricated with overlying Hondo Group sedimentary cover in an originally east-trending ductile thrust belt that formed near the southern margin of the Yavapai province. A series of offset magnetic anomalies (Jemez lineament) is interpreted to mark the thrust-buried boundary between older (Yavapai province) and younger (Mazatzal province) crust. Our microplate tectonic model suggests that Laramide strike-slip movement (New Mexico) was kinematically linked with coeval extensional collapse (Arizona) and foreland shortening (Wyoming) during decoupling and northward movement of the rigid Colorado Plateau relative to the undeformed midcontinent. Crustal-scale strike-slip faults in New Mexico were reactivated during later Tertiary extension and continue to localize high heat flow in the Rio Grande rift and northward into Colorado.

Determination of the absolute geopotential by satellite sounding data

Abstract A method for reconstruction of the absolute geopotential by satellite data SATEM is proposed. It is based on the presence of an “isopicnic level” in the troposphere at a height about 8 km. Using the method, geopotential heights of 500 and 300 hPa isobaric surfaces over the Europe and Mediterranean are computed. Gridding both the satellite and radiosonde data on isobaric surfaces, the degree of compatibility of the analyses are assessed.

Empirical Correlations of Saturated Steam Properties

Summary Both steamdrive and steam stimulation processes for EOR involve thermodynamic and transport properties of steam. These properties have roles in the fluid flow, heat transfer, and mass and heat balances of recovery processes. Hence, they affect, not only the operation of the process, but also the economics and management of the oil recovery project. This paper presents empirical correlations of thermodynamic and transport properties of saturated steam in dimensionless forms as functions of either reduced temperature or reduced pressure. The pressure range of the correlations extends from atmospheric to 3, 000 psia [20.7 MPa]. The properties include saturation temperature, saturation pressure, specific volume, specific enthalpy, specific entropy, isobaric specific heat, dynamic viscosity, thermal conductivity, dielectric constant, surface tension, and isentropic expansion exponents. Compared with values listed in current steam tables, the calculated properties are accurate within ±0.02 % for saturation temperature and pressure, within ±0.12 % for thermodynamic properties, and within ±0.27% for transport properties.

The atmosphere of Neptune - an analysis of radio occultation data acquired with Voyager 2

The vertical structure of Neptune's atmosphere is studied on the basis of recordings of the tracking signals received from Voyager 2 during its occultation by Neptune. The measurements began at a planetographic latitude of 62 deg north and ended near 45 deg south, and cover an altitude interval of about 5000 km. The 1-bar isobaric surface has equatorial and polar radii of 24,766 +/-15 km and 24,342 +/-30 km, respectively, and a corresponding oblateness of 0.0171 +/-0.0014. At this pressure, the temperature was 72 +/-2 K. The tropopause was detected approximately 40 km above the 1-bar level at a pressure of about 100 mbar. A comparison with IR observations indicates that the gas at the tropopause consists of 78-84-percent hydrogen by number density with the rest being mostly helium. The temperature in this region was 52 +/-2 K.

Comprehensive Hydrostatic Quality Control at the National Meteorological Center

Abstract The Comprehensive Hydrostatic Quality Control (CHQC) of rawinsonde data on height and temperature at mandatory isobaric surfaces designed and implemented at the National Meteorological Center in Washington is described in detail. Main principles of the quality control design are discussed, followed by a brief description of the CHQC design and implementation at NMC. The CHQC algorithm is presented with particular emphasis on the Decision Making Algorithm. Numerous examples taken from the operational CHQC outputs illustrate the CHQC performance in general as well as its reaction to errors of various types and to their combinations.

Metamorphism in the Solitude Range, southwestern Rocky Mountains, British Columbia: comparison with adjacent Omineca Belt rocks and tectonometamorphic implications for the Purcell Thrust

Rocks of the Solitude Range, British Columbia, have been metamorphosed from chloritoid–chorite-zone to kyanite-zone conditions. The grade of metamorphism increases southwestward toward the Rocky Mountain Trench (RMT) and the Omineca Belt. Isograds crosscut lithologies and trend more northerly than deformation 2 (D2) structures and the RMT. They are thought to have been quenched syn- to post-D2. Pelitic (Mahto Formation) and calc-pelitic (Tsar Creek unit) rocks contain assemblages that reflect the increase in metamorphic grade. Physical conditions of metamorphism are estimated to be approximately 450–540 °C from the garnet to the kyanite zone; pressures averaged 6–7 kbar (1 kbar = 100 MPa). The pressures, temperatures, and metamorphic assemblages are very similar to those of the Adamant Range, which lies across the Purcell Thrust, to the southwest. This is in contrast with the Big Bend area, to the northwest, where differences in pressure across the Purcell Thrust (PT) have been documented. Two possible models to explain these contrasting relationships are presented. One model suggests that there was post-movement heating on the PT, which reduced the metamorphic contrast across the PT. The second model suggests that a combination of thrust and normal faulting, including warping of isobaric surfaces, has produced an apparently unbroken metamorphic sequence across the PT.