bluuebunny/crossref_metadata_2025 huggingface dataset:
Frequency domain interferometry of polar mesosphere summer echoes with the EISCAT VHF radar: A case study
Authors: Franke S. J. , Röttger J. , LaHoz C. , Liu C. H.
Published: February 2008

During the polar mesosphere summer echo (PMSE) campaign in 1988 the first multiple‐frequency mesospheric measurements were carried out using the European incoherent scatter (EISCAT) 224‐MHz radar. A case study of nearly simultaneous measurements of coherent backscatter, collected on two closely spaced frequencies on July 3, 1988, is presented in this paper. The data are used to investigate the frequency coherence of the radar echoes and to perform frequency domain interferometry (FDI) analysis. The FDI technique provides precise information about the thickness and relative position of isolated scattering layers. The results indicate that scattering layers with thicknesses in the range 85–120 m are sometimes present in the polar summer mesosphere. Such a layer is shown to exist for a period of approximately 10 min, and its position is tracked as it descends over more than 1 km in altitude and transits from one range gate to the next. In addition, the FDI technique is used to study a case where a sudden frequency jump is observed in the Doppler spectrum. Spectral jumps appear to be a characteristic of the 224‐MHz PMSE echoes observed at EISCAT. The FDI analysis and Doppler sorting are employed to study the coherence spectrum of the two‐frequency data before, during, and after the jump. The frequency jump as well as the signatures that are observed in the coherence spectrum can be explained if the radar is observing a thin scattering layer which has been rippled by a steepened gravity wave.
On the spectral analysis and interpretation of incoherent scatter plasma line echoes
Authors: Heinselman C. J. , Vickrey J. F.
Published: February 2008

This paper describes a model of the physical interactions involved in incoherent scatter that result in specific plasma line spectral shapes as a function of range and frequency. This model is quite successful in duplicating the naturally occurring plasma line spectra observed at high latitudes. Moreover, the inherent sensitivity of the data collection method suggests a much more general applicability. For example, we will demonstrate a sensitivity of the method to plasma density irregularities in the medium that rivals or exceeds that possible with radio wave scintillation techniques. Unlike height‐integrated scintillation measurements, however, this new method can range resolve the fluctuations in plasma density. We are able to determine the altitude of the F layer peak to an accuracy of ∼ ± 1 km even with a probing pulse of 72 km in length. Our density fluctuation measurements indicate a residual level of ∼ 1% fluctuations after a linear‐temporal trend is removed. This indicates spatial variations in plasma density of this order within our relatively narrow (0.5°) antenna beam. These spatial variations are enhanced during periods when the F layer peak cutoff frequency is decreasing. Such behavior is consistent with increased plasma structure on the trailing edge of F region plasma blobs. Our technique involves not only model fitting but also a data collection method that minimizes range smearing. This data collection mode has already been successfully implemented at the Sondrestrom, Greenland, incoherent scatter radar facility.
The propagation of mixed polarization VLF (f ≤5 kHz) radio waves in the Antarctic Earth‐ionosphere waveguide
Authors: Cotton P. D. , Smith A. J. , Wolf T. G. , Poulsen W. L. , Carpenter D. L.
Published: February 2008

During 1986, a series of special VLF transmissions at ∼3 kHz and ∼5 kHz were made from the crossed dipole antenna at Siple Station, Antarctica, which simulated transmissions from a single horizontal dipole at a number of different orientations. The subionospheric signals thus excited were recorded at four Antarctic stations: Faraday, Halley, South Pole and Arrival Heights (McMurdo Sound). The signals excited broadside to the dipole were seen to exhibit characteristics notably different from those of signals excited along the axis of the antenna, showing a minimum in received power (the depth of the minimum decreasing for the more highly attenuating paths) and increases in apparent arrival azimuth error and elevation angle. A simple computer model for mode propagation close to 5 kHz in the Antarctic Earth‐ionosphere waveguide showed that these variations were the consequence of two effects: the preferential excitation of quasi‐transverse magnetic (QTM) modes along the axis of the antenna and the lower attenuation of quasi‐transverse electric (QTE) modes (with respect to QTM modes) over the Antarctic ice sheet. These results have important implications for studies involving the subionospheric propagation of signals with frequencies at the lower end of the VLF band and over highly attenuating surfaces, showing that QTE modes play a significant and sometimes dominant role. The propagation characteristics derived from the model may be applied to studies of the effect of burst energetic electron precipitation on subionospheric VLF signals (the Trimpi effect). Furthermore, the mode structure of subionospheric VLF signals radiated from the Siple transmitter, or a similar facility in Antarctica, may be controlled through the appropriate choice of signal frequency and antenna arrangement.
Propagation of dipole waves through the anisotropic ionosphere in equatorial regions
Authors: Ledinegg E. , Schürrer F. , Griehsnig P.
Published: February 2008

The Earth's magnetic field influences electromagnetic waves passing through the ionosphere. Dipole fields emitted from satellites above equatorial regions generate ground signals of different strength, depending on whether the waves propagate in east‐west or west‐east direction. This effect is investigated analytically within a plane three‐layer model consisting of the near‐Earth space, a homogeneous ionosphere, and the atmosphere. The obtained quotient of the “east‐west” and “west‐east” ground field strengths increases with increasing electron density of the ionosphere and decreases with increasing collision frequency of the electrons. Beyond that, this quotient shows an interesting frequency dependence caused by the anisotropy and the waveguide effect of the ionosphere. It could be proved that the gained results are also valid for short‐term fluctuations of the ionosphere.
Stresses in an overthrust sheet and propagation of thrusting: An Airy stress function solution
Authors: Liu J. Y. , Ranalli G.
Published: February 2008

An Airy stress function solution is derived for the stress field in an elastic wedge‐shaped overthrust sheet subject to horizontal forces at the rear and at the front. From this stress solution the state of stress on the basal thrust (lower boundary of the sheet) is obtained. Both normal and shear stresses on the basal thrust are affected by the rear pushing and front buttressing forces and by the slopes of the upper and lower boundaries of the wedge‐shaped block. For (1) nonlinear components of external horizontal forces exerted on the vertical edges of the block and/or (2) nonzero slopes of the upper and lower boundaries the normal and shear stresses vary systematically with position along the basal thrust. The ratio of shear and normal stresses along this plane (the “frictional function” of the thrust) can be compared with the friction coefficient to determine where slippage is likely to occur. Since the frictional function is a function of position, the strength is exceeded only on part of the thrust (near the rear for most values of the parameters). The assumption of simultaneous displacement of the whole thrust sheet on the basal plane is therefore not realistic. Even simple static models such as the present one indicate that the motion on thrust faults must be envisaged in terms of progressive, consecutive “dislocation‐type” slippage.
Evidence for cenozoic crustal extension in the Bering Sea region
Authors: Cooper A. K. , Marlow M. S. , Scholl D. W. , Stevenson A. J.
Published: February 2008

Geophysical and regional geologic data provide evidence that parts of the oceanic crust in the abyssal basins of the Bering Sea have been created or altered by crustal extension and back‐arc spreading. These processes have occurred during and since early Eocene time when the Aleutian Ridge developed and isolated oceanic crust within parts of the Bering Sea. The crust in the Aleutian Basin, previously noted as presumably Early Cretaceous in age (M1–M13 anomalies), is still uncertain. Some crust may be younger. Vitus arch, a buried 100‐ to 200‐km‐wide extensionally deformed zone with linear basement structures and geophysical anomalies, crosses the entire west central Aleutian Basin. We suggest that the arch and the inferred fracture zones in the Aleutian Basin are early Cenozoic structures related to the early entrapment history of the Bering Sea. These structures lie on trend with known early Cenozoic structures near the Bowers‐Shirshov‐Aleutian ridge junction and on the Beringian continental margin (with possible continuation into Alaska); the structures may have coeval and cogenetic(?) histories for early Cenozoic and possibly younger times. Cenozoic deformation within parts of the Bering Sea region is principally extensional, although the total amount of extension is not known. As examples, the Komandorsky basin formed by back‐arc seafloor spreading, the Aleutian Ridge has been extensively sheared, and extensional block faulting is common. Sedimentary basins of the Bering shelf have formed by extension associated with wrench faulting. The Cenozoic deformation throughout the Bering Sea region probably results from the interaction of major lithospheric plates and associated regional strike‐slip faults. We present models for the Bering Sea over the past 55 m.y. that show oceanic plate entrapment, back‐arc faulting and spreading along Vitus arch, breakup of the oceanic crust in the Aleutian Basin at fracture zones, and back‐arc spreading in Bowers Basin.
Upper Proterozoic rift‐related rocks in the Pensacola Mountains, Antarctica: Precursors to supercontinent breakup?
Authors: Storey Bryan C. , Alabaster Tony , Macdonald David I. M. , Millar Ian L. , Pankhurst Robert J. , Dalziel Ian W. D.
Published: February 2008

Sedimentological and structural studies in the Pensacola Mountains, Antarctica, suggest that upper Precambrian clastic sedimentary rocks of the Patuxent Formation and associated bimodal volcanic rocks formed in an intracontinental rift setting. The turbidites of the Patuxent Formation are part of a large depositional system, derived from a continental source. Interbedded pillow basalts and basaltic sills have trace and rare earth element signatures enriched relative to mid‐ocean ridge basalt and similar to some rift‐related tholeiitic suites. Nd and Sr isotopic values are compatible with derivation from a lithospheric mantle source in a continental setting. Associated felsic volcanic rocks have crustal trace element and isotopic characteristics. The rifting may have been a prelude to the fragmentation of a supercontinent and, according to recent hypotheses, the separation of Laurentia from Antarctica. Comparisons between the late Precambrian and Cambrian records of western North America and Antarctica suggest that, if these were conjugate margins, separation must have been Neoproterozoic rather than Cambrian in age.
Geology of the Idonnappu Belt, central Hokkaido, Japan: Evolution of a Cretaceous Accretionary Complex
Authors: Kiyokawa Shoichi
Published: February 2008

The Cretaceous Idonnappu Belt, located along the western Hidaka Mountains of central Hokkaido Island in Japan, records evidence of west to northwest directed underthrusting of oceanic crust. The Idonnappu fault divides the Idonnappu Belt into two subbelts; the western Oku‐niikappu (ON) subbelt and the eastern Koiboku (KO) subbelt. The ON subbelt is dominated by a melange facies. It includes various thicknesses of pillow basalts, bedded radiolarian cherts, limestones, and greenish siliceous shales, all of which are intermixed with a highly sheared shaley matrix that displays a scaly cleavage. The KO subbelt is dominated by a thick flysch sequence and alternations of sandstone and shale with thin tectonic melange. The stratigraphic sequences within these belts usually young toward the west and display westward vergent structures. Outcrop‐ to microscopic‐scale structures in the melange zone of the Idonnappu Belt, however, suggest eastward vergence. Detailed biostratigraphic studies show that structural packages young toward the east ranging in age from Lower to Upper Cretaceous. These observations are consistent with an accretionary prism model in which oceanic crust is underthrust toward the west or north west. In the middle Miocene, a change to westward vergence was caused by uplift of the Hidaka Mountains.
Effects of oceanic ridge subduction on accretionary wedges: Experimental modeling and marine observations
Authors: Lallemand Serge E. , Malavieille Jacques , Calassou Sylvain
Published: February 2008

Sandbox modeling is used to study the deformation of accretionary wedges caused by the subduction of oceanic ridges. The first experiment incorporates a massive ridge within a sand wedge. The wedge thickens and shortens when the forward propagation of the basal decollement ceases. The wedge thickening results in taper change, reactivation of preexisting thrusts, and retreat of the frontal part of the sand wedge. Similar mechanisms may have affected some margins that have undergone ridge subduction such as the Tonga margin after the subduction of the oblique Louisville oceanic ridge. The second experiment shows the effects of an active basement thrust slice as it enters a subduction zone. This process may have happened in the eastern Nankai accretionary wedge. Initially, the wedge in this experiment behaved similarly to that of the first experiment. Rapidly the topographic slope changed, the wedge thickened above the basement slice generating a slope break in the topography; a deeper propagating accretionary wedge again characterized by a small taper developed. These results, when compared with observations made in the Eastern Nankai Trench, are in agreement with the past subduction of a basement thrust slice in this area.
Duplexing and intraprism deformation of the Paleogene Shimanto Supergroup in western Shikoku, southwest Japan
Authors: Tokunaga Tomochika
Published: February 2008

The Kurusuno Formation belongs to the late Eocene to early Oligocene Shimanto Belt, and crops out in the Hata Peninsula, Shikoku, Japan. Detailed structural analysis reveals that the Kurusuno Formation was deposited as a trench fan formed mainly by transverse currents. Part of these thick trench sediments was underthrust and underplated to form a foreland‐dipping duplex. Steeply plunging folds were formed at a relatively early stage of the deformation, and a pervasive slaty cleavage formed after the folding. Temperatures locally exceeded 350°C during slaty cleavage development; abnormally high geothermal gradients may have been caused by a relatively young oceanic plate subducting at about 30 Ma. Underplating of younger trench fill sediments below previously accreted material is probably an important mechanism for the uplift of the shallow level rock bodies in an accretionary complex, and high‐temperature/low‐pressure metamorphism occurs in the lower part of an accretionary complex when young oceanic lithosphere is subducting.
Host rock rheology controls on the emplacement of tabular intrusions: Implications for underplating of extending crust
Authors: Parsons Tom , Sleep Norman H. , Thompson George A.
Published: February 2008

The pooling, ponding, and horizontal intrusion of basaltic magma at various depths into the crystalline crust is paradoxical because the stress conditions favoring such intrusions do not favor the opening of vertical feeder conduits necessary for their formation. The most rigid zones of the crust and upper mantle tend to behave elastically and store stress when subjected to tectonic forces, while the more ductile zones flow under stress. These rheological differences within the crust and upper mantle allow variation in the magnitude of deviatoric stress, and such variation has a profound effect on tabular intrusions. A vertical dike intruding into extending crust increases the horizontal least principal stress of the host rock when it is emplaced, and that effect is magnified in rheologically ductile zones where the pre‐existing deviatoric stress has been partially relaxed. Subsequent dikes intruding into the ductile zone may encounter stress conditions that have been altered to the extent that the local least principal stress has become vertical, and horizontal intrusion initiates. Multiple geological and geophysical observations of horizontal intrusions in extending crust indicate that such principal stress interchanges occur commonly.
Age and evolution of Western Brooks Range ophiolites, Alaska: Results from 40Ar/39Ar thermochronometry
Authors: Wirth Karl R. , Bird John M. , Blythe Ann E. , Harding David J. , Heizler Matthew T.
Published: February 2008

Basalt, gabbro, and peridotite in the western Brooks Range structurally overlie Mississippian through Late Jurassic platform sediments that were deformed during Late Jurassic ‐ Cretaceous time. 40Ar/39Ar step‐heating experiments on hornblende, biotite, plagioclase, and potassium feldspar from gabbro, diorite, plagiogranite, and granite yielded complex release spectra. On isotope correlation diagrams, the incremental‐heating data indicate that gabbro, diorite, and plagiogranite cooled below the closure‐temperature for argon in amphibole between 187 and 184 Ma. Because the closure temperature of argon retention in amphibole is relatively high, these ages are interpreted to be the time since crystallization. Biotite and hornblende from metamorphic rock exposed along faults separating peridotite and gabbro from underlying basalt yielded plateau and isochron dates of 169 – 163 Ma; these dates are interpreted to record postmetamorphic cooling following intraoceanic detachment and transport of “hot” peridotite and gabbro over “cold” basalt and sediment. Detachment and faulting of the gabbros and peridotites is interpreted to have occurred approximately 20 Ma after crystallization, and is longer than the 5–10 Ma interval commonly observed in studies of other ophiolites. Fossils in flysch underlying the ophiolites indicate that the ophiolites were emplaced onto the continental margin during the Tithonian, approximately 15–20 Ma after initial detachment. The ages of feldspars (149 – 137 Ma) in the ophiolites and associated volcanic rocks are similar to the fossil ages of the underlying flysch and might record uplift during emplacement of the ophiolites onto the continental margin. A fission‐track age of apatite implies that the ophiolitic rocks were overlain by >4 km of rock until ∼59 Ma ago, the time of regional uplift in the Brooks Range.

Supplement Appendix 1 is available with entire article on microfiche. Order from the American Geophysical Union, 2000 Florida Avenue, N.W., Washington, D.C. 20009. document T92‐005; $2.50. Payment must accompany order.
Cenozoic crustal rotations in the Mojave Desert from paleomagnetic studies around Barstow, California
Authors: Valentine Michael J. , Brown Laurie L. , Golombek Matthew P.
Published: February 2008

Paleomagnetic data from the Mojave Desert around Barstow, California suggest 55° to 75° of clockwise rotation of this area in earliest Miocene time, followed by 23° of counterclockwise rotation in the Early Miocene, and no rotation after 18 Ma. Earliest Miocene clockwise rotation of the Barstow area is suggested by data from nine sites in the Oligocene‐Miocene Lane Mountain Quartz Latite and Jackhammer Formation and may be related to oroclinal bending of the southern Sierra Nevada batholith. Data from 13 sites in the Early Miocene Pickhandle Formation indicate counterclockwise rotation, which coincides with Early Miocene E‐NE‐W‐SW extension and detachment faulting in the Mojave Desert. Other parts of the Mojave Desert experienced variable senses and amounts of rotation at this time which may be related to drag along transfer zones within the upper plate, while the lower plate was not rotated. These results suggest that Miocene extension in the Mojave Desert is related to similarly oriented extension in the Colorado River extensional corridor. Early Miocene to Pliocene rocks of the Andesite and Dacite of the Calico Mountains, Barstow Formation, Andesite of Murphy's Well, and Black Mountain Basalt show no evidence for significant rotation of the Barstow area after 18 Ma. Most other paleomagnetic data from elsewhere in the Mojave are consistent with a lack of significant post‐18 Ma rotations, suggesting that post‐10 Ma right‐lateral faulting there has produced relatively little crustal rotation. The exception to this generalization is the northeast corner of the Mojave Desert which underwent substantial post‐18 Ma clockwise rotation. Paleomagnetic flattening data also indicate that post‐Oligocene N‐S translation of crustal blocks in the Mojave Desert has been insignificant.
CO2 and CH4 dynamics of a Sphagnum‐dominated peatland in West Virginia
Authors: Yavitt J. B. , Weider R. K. , Lang G. E.
Published: February 2008

Climatic change could bring about net release of carbon dioxide (CO2) and/or methane (CH4) from the deep peat deposits in northern peatlands into the atmosphere. To provide insight into this hypothesis, we studied net flux of CO2 and CH4 in Big Run Bog, West Virginia, which has a temperate climate, making it an analog to evaluate climatic change imposed on more northern counterparts. Net CO2 flux ranged from −564 to 300 mg C m−2 hr−l. Measurements made during the nighttime showed that net CO2 flux increased exponentially with increasing air temperature, whereas CO2 sequestration increased with increasing air temperature for daytime measurements. Net CH4 flux ranged from −2.3 to 70 mg C m−2 hr−l, showing no consistent relationship to temperature or water table level. Net efflux for both CO2 and CH4 was tenfold higher from peat cores incubated in a greenhouse compared to field measurements. Even cores drained and allowed to dry for 8 days showed moderately high flux for both CO2 and CH4. The enhanced efflux seemed to be due to altered hydrology rather than increased rates of bacterial production (measured in anoxic, in vitro incubations) which could account for only 50% of the whole‐core flux. Presumably the remainder was CO2 and CH4 stored in the peat cores at the time of collection. Overall, the results suggest that a temperate climate imposed on northern peatlands could mobilize stored carbon and increase CO2 and CH4 efflux into the troposphere. Studies involving peat cores must insure that CO2 and CH4 dynamics measured in vitro mimic those in situ.
Global sources and sinks of OCS and CS2and their distributions
Authors: Chin Mian , Davis D. D.
Published: February 2008

This study investigates the distribution and magnitudes of the global sources and sinks of OCS and CS2. From an analysis of the correlations between measured emission rates and environmental parameters, the sources of OCS and CS2are estimated to be 1.23 (0.83−1.71) Tg(OCS) yr−1and 0.57 (0.34−0.82) Tg(CS2) yr−1, respectively. Our results indicate that 30% of the atmospheric OCS source is derived from the oxidation of CS2, while emissions from the ocean and other natural terrestrial sources contribute 28% and 24%, respectively. In the case of CS2, the major source is from chemical industrial emissions (58%) while the ocean contributes about 34% to the total CS2source. Our estimate of the OCS and CS2emission rates suggests that anthropogenic activities contribute approximately 32% to the total OCS source. The major sink for CS2is oxidation by tropospheric OH, whereas, that for OCS appears to be uptake by vegetation.
Distribution of 32Si in the world ocean: Model compared to observation
Authors: Peng Tsung‐Hung , Maier‐Reimer Ernst , Broecker Wallace S.
Published: February 2008

Calculations of the 32Si/SiO2 ratio obtained in ocean models are compared with measurements of this ratio made as part of the GEOSECS program (Somayajulu et al., 1987, 1991). A major difference is found; while the models predict threefold to fivefold higher ratios in the deep Atlantic Ocean than in the deep Pacific and Indian oceans, no such difference is seen in the measurements. This points to a flaw in the measurements. Our modeling results suggest that the most interesting application for this 120‐year half‐life cosmogenic isotope is as a monitor of upwelling. However, considering the expense and difficulty associated with 32Si measurements, such studies may prove impractical.
Methane flux from drained northern peatlands: Effect of a persistent water table lowering on flux
Authors: Roulet Nigel T. , Ash R. , Quinton W. , Moore Tim
Published: February 2008

Measurements of CH4 flux from drained and undrained sites in three northern Ontario peatlands (a treed fen, a forested bog, and a treed bog) were made from the beginning of May to the end of October 1991. In the drained portions, the water table had been lowered between 0.1 and 0.5 m, compared to the water table of the undrained portion of the peatlands. The mean seasonal CH4 flux from the undrained portions of three peatlands was small, ranging from 0 to 8 mg m−2d−1, but similar to the CH4 flux from other treed and forested northern peatlands. The mean seasonal CH4 flux from the drained portion of the peatlands was either near zero or slightly negative (i.e.,uptake): fluxes ranged from 0.1 to −0.4 mg m−2 d−1. Profiles of CH4 in the air‐filled pores in the unsaturated zone, and the water‐filled pores of the saturated zone of the peat at the undrained sites, showed that all the CH4 produced at depth was consumed within 0.2 m of the water table and that atmospheric CH4 was consumed in the upper 0.15 m of the peatland. On the basis of laboratory incubations of peat slurries to determine CH4 production and consumption potentials, the lowering of the water table eliminated the near‐surface zone of CH4 production that existed in the undrained peatland. However, drainage did not alter significantly the potential for CH4 oxidation between the water table and peatland surface but increased the thickness of the layer over which CH4 oxidation could take place. These changes occurred with a drop in the mean summer water table of only 0.1 m (from −0.2 to −0.3 m) suggesting that only a small negative change in soil moisture would be required to significantly reduce CH4 flux from northern peatlands.
The biosphere as an increasing sink for atmospheric carbon: Estimates from increased nitrogen depostion
Authors: Schindler D. W. , Bayley S. E.
Published: February 2008

Estimates of carbon uptake and storage based on global nitrogen deposition, C:N ratios for typical terrestrial ecosystems, and recent ecosystem‐scale nutrient studies indicate that 1.0‐2.3 Gt C yr−l of carbon storage may be stimulated by anthropogenically caused increases in nitrogen deposition in the past century. Sixty four to eighty four percent of global nitrogen uptake appears to occur on northern continents, with the remainder largely in northern coastal oceans. Increased nitrogen input by terrestrial ecosystems causes increased accumulation of carbon as plant tissue, with C:N ratios generally 50 to 200:1. Calculations suggest that northern continents are a major sink for carbon and that nitrogen‐stimulated carbon uptake may more or less balance global carbon losses to the atmosphere from deforestation and agriculture. Much of the uptake appears to occur in aggrading forests, and the question of how long it can continue has important consequences for global carbon budgets.
Terrestrial ecosystem production: A process model based on global satellite and surface data
Authors: Potter Christopher S. , Randerson James T. , Field Christopher B. , Matson Pamela A. , Vitousek Peter M. , Mooney Harold A. , Klooster Steven A.
Published: February 2008

This paper presents a modeling approach aimed at seasonal resolution of global climatic and edaphic controls on patterns of terrestrial ecosystem production and soil microbial respiration. We use satellite imagery (Advanced Very High Resolution Radiometer and International Satellite Cloud Climatology Project solar radiation), along with historical climate (monthly temperature and precipitation) and soil attributes (texture, C and N contents) from global (1°) data sets as model inputs. The Carnegie‐Ames‐Stanford approach (CASA) Biosphere model runs on a monthly time interval to simulate seasonal patterns in net plant carbon fixation, biomass and nutrient allocation, litterfall, soil nitrogen mineralization, and microbial CO2 production. The model estimate of global terrestrial net primary production is 48 Pg C yr−1 with a maximum light use efficiency of 0.39 g C MJ−1PAR. Over 70% of terrestrial net production takes place between 30°N and 30°S latitude. Steady state pools of standing litter represent global storage of around 174 Pg C (94 and 80 Pg C in nonwoody and woody pools, respectively), whereas the pool of soil C in the top 0.3 m that is turning over on decadal time scales comprises 300 Pg C. Seasonal variations in atmospheric CO2 concentrations from three stations in the Geophysical Monitoring for Climate Change Flask Sampling Network correlate significantly with estimated net ecosystem production values averaged over 50°–80° N, 10°–30° N, and 0°–10° N.
Some aspects of satellite spin effects on spherical probe measurements in a magnetized plasma
Authors: Hilgers A. , Holback B.
Published: February 2008

We analyze the spin modulation of the current of a boom‐mounted positive biased spherical Langmuir probe observed with the Viking experiment. The satellite perturbs the probe current by two distinct effects: (1) photoelectrons emitted by the low potential part of the satellite, (2) capture of ambient electrons. These two effects are shown to be strongly dependent on the magnetic field orientation with respect to the probe‐satellite axis. We quantify experimentally and theoretically the range of such effects. We then deduce some basic rules for electron energy and density measurements and for the design of satellite‐borne Langmuir probe experiments.
A comparison between patterns of temperature trends and sulfate aerosol pollution
Authors: Engardt Magnuz , Rodhe Henning
Published: February 2008

Global temperature records over the past century are compared to estimated atmospheric loading of anthropogenic aerosol sulfate, in order to investigate the possible cooling effect of such pollutants. Between the 1940s and the 1980s south‐eastern Europe, China, and the northern Atlantic have experienced a summertime cooling. The first two of these regions agree well with those where anthropogenic sulfur emissions have increased during the same period. During winter, the two former regions experienced a substantial warming while the northern Atlantic and south‐eastern US exhibited a cooling. The results are qualitatively consistent with theoretical calculations which indicate that anthropogenic sulfate aerosols cause a substantial cooling. However, because of large natural variations in the temperature records, the statistical significance of this conclusion is low.
The effects of the October 1989 solar proton events on the stratosphere as computed using a three‐dimensional model
Authors: Jackman Charles H. , Nielsen J. Eric , Allen Dale J. , Cerniglia Mark C. , McPeters Richard D. , Douglass Anne R. , Rood Richard B.
Published: February 2008

Very large solar proton events (SPEs) occurred from October 19–27, 1989. These SPEs are predicted to produce short‐lived increases in HOx and long‐lived increases in NOx species, which both can lead to ozone destruction. December 1989 SBUV/2 measurements of upper stratospheric ozone show substantially more ozone depletion in the Northern than in the Southern Hemisphere even though the amount of HOx and NOx produced in both hemispheres should be similar from these SPEs. Our two‐dimensional (2D) model simulations predict only a modest interhemispheric difference in the ozone depletion in December caused by the October 1989 SPEs. In an attempt to better understand the interhemispheric difference in the observed ozone depletion, we have used the GSFC three‐dimensional (3D) chemistry and transport model to simulate the distribution of NOx and ozone after the SPEs. Our 3D model computations of ozone and NOx behavior for two months after the October 1989 SPEs indicate differences in the constituent behavior in the two hemispheres during the October–November–December 1989 time period which are qualitatively consistent with SBUV/2 ozone observations. These differences are caused by: 1) Substantial mixing of perturbed air in the Southern Hemisphere from the polar region with unperturbed lower latitude air during the November final warming; and 2) Significant confinement of the photochemically perturbed air in the Northern Hemisphere in the winter‐time polar vortex.
Tomographic study of upper mantle atttenuation in the Pacific Ocean
Authors: Bussy Martine , Montagner Jean‐Paul , Romanowicz Barbara
Published: February 2008

The quality factor Q has been measured in the Pacific ocean along many paths using long period seismograms of the Geoscope and IDA networks. The Love and Rayleigh phase velocity and QR−1 have been regionalised in the period range 60s to 200s, and then simultaneously inverted at depth to obtain 3D images of S‐wave velocity and attenuation Qβ−1 in the depth range 60–300km. Up to 100s, three very attenuating zones appear, one under the East Pacific Rise (E.P.R), another one around Hawaii, a third one east of Kermadec. By inversion, those three anomalies are found stable down to 160km. Below 200km, lateral variations are less intense and differently distributed; the maximum attenuation seems to concentrate along a northeast trend in the North Central Pacific.
Heat flow across the toe of accretionary prisms — The role of fluid flux
Authors: Wang Chi‐yuen , Liang Guoping , Shi Yaolin
Published: February 2008

Compaction‐driven fluid flow in accretionary prisms is ineffective in changing heat flow across the lower slope, even when the rate of fluid flow is greatly enhanced by hydrofracturing, as results of numerical analysis show. For most faults which are long relative to their thickness, conductive heat loss to the wall rock is much more effective in heat transport than advective transport along the faults.
Universal multifractal indices for the ocean surface at far red wavelengths
Authors: Tessier Y. , Lovejoy S. , Schertzer D. , Lavallée D. , Kerman B.
Published: February 2008

For some time, ocean wave breaking has been conceptualized as a cascade process in which the large scale wind energy flux driving the system is dissipated by wave breaking at small scales, the two seperated by the “equilibrium” scaling range. Cascades are now known to generically lead to multifractals; with special “universal” multifractals theoretically predicted. In this paper we use far red (0.95 μm) radiances at 1m resolution obtained from aircraft to test the multifractal behavior of the ocean surface and estimate the corresponding universal multifractal parameters of the radiance field.
Moment‐ration imaging of seismic regions for earthquake prediction
Authors: Lomnitz Cinna
Published: February 2008

An algorithm for predicting large earthquakes is proposed. The reciprocal ratio (mri) of the residual seismic moment to the total moment release in a region is used for imaging seismic moment precursors. Peaks in mri predict recent major earthquakes, including the 1985 Michoacán, 1985 central Chile, and 1992 Eureka, California earthquakes.
Well log‐derived estimates of thermal conductivity in crystalline rocks penetrated by the 4‐KM deep KTB Vorbohrung
Authors: Pribnow Daniel , Williams Colin F. , Burkhardt Hans
Published: February 2008

Well log measurements of compressional and shear velocity (Vp, Vs), density, and temperature from the 4 km‐deep KTB Vorbohrung (pilot hole) were applied in a phonon conduction model for the thermal conductivity of a crystalline solid. The resulting conductivity estimates were compared with conductivities (kLAB) measured on the nearly continuous (91% recovery) core. Previous studies have shown the log‐derived conductivity (kLOG) to be within ±15% of kLAB in isotropic or flat‐lying anisotropic crystalline rocks. The section penetrated by the KTB pilot hole includes both predominantly isotropic metabasites and highly anisotropic gneisses with foliation dips ranging from horizontal to vertical. The predictions of the phonon model were accurate within ±4% in the metabasites but inaccurate by as much as 23% in the gneisses. The accuracy of the model in the metabasites confirms the utility of the phonon conduction approach in isotropic or weakly anisotropic rocks, but the discrepancies in the anisotropic gneisses remain unexplained. These relatively large discrepancies between kLOG and kLAB correspond to depths at which laboratory measurements of Vs under in situ conditions deviate from the sonic log Vs. This suggests that sonic log determinations of Vs may not be reliable in dipping, anisotropic rocks. Alternatively, the laboratory Vs measurements may not constitute a representative sample, or there may be errors in the phonon conduction model. If the discrepancies can be tied to errors in sonic log Vs measurements, the phonon conduction model may provide a tool for deriving thermal conductivity profiles of the Earth's crust from seismic studies of Vp and Vs.
Thermal distributions of hot volcanic surfaces constrained using three infrared bands of remote sensing data
Authors: Oppenheimer Clive
Published: February 2008

Infrared remote sensing provides a means for radiometry of hot volcanic features. Previously, two spectral band measurements have been combined to solve simple 2‐component models of lava surface temperatures. However, pixel dimensions often exceed the widths of lava bodies. In such cases, 3‐component models are more realistic. Here, a procedure for solving such a model from three infrared observations is presented. It is then demonstrated using Thematic Mapper Simulator data recorded over Mount Etna, Italy, in 1991. By constraining temperatures and pixel‐filling fractions of the three different thermal components in this way, improved estimates of radiant emittance can be obtained. The techniques described could be applied to satellite data of volcanic, and other, hot spots (including fires).
Artificial auroras in the upper atmosphere: 2. Imaging results
Authors: Mende S. B. , Burch J. L. , Swenson G. R. , Aamodt E. K. , Geller S. P. , Rairden R. L. , Hassler P. L.
Published: February 2008

On the ATLAS 1 mission (STS‐45, launched March 24, 1992) two experiments, AEPI (Atmospheric Emissions Photometric Imaging) and SEPAC (Space Experiments with Particle Accelerators) performed the first experiment in a series of active experiments intended to probe the atmosphere, ionosphere and magnetosphere with electron beams. The luminous artificial aurora generated by the electron beam interaction was detected and measured by AEPI both in white light and in a narrow wavelength band at 427.8 nm (peak intensity 5 kR). Modelling calculation showed that there was a significant contribution from emissions originating near the spacecraft. The spatial intensity distribution of the observed auroral patch is consistent with emission contribution from both high and low altitude regions. An extended tail in the direction of the shuttle wake was observed in the 427.8 nm channel, consistent with a decay time associated with the dissipation of the hot electron plasma.
Sharpness of the mantle discontinuities
Authors: Petersen N. , Vinnik L. , Kosarev G. , Kind R. , Oreshin S. , Stammler K.
Published: February 2008

Seismic estimates of sharpness of the mantle discontinuities are important for constraining models of composition and temperature in the deep Earth but these data are difficult to obtain. We explore a possibility to determine sharpness of the major mantle discontinuities (those at depths around 400 and 650 km) from the broad‐band records of phases converted from P to S underneath the receiver. Our estimates are obtained from a comparative analysis of waveforms of the converted phases and those of the P waves in the teleseismic records of BRV (Kazakhstan), GRF (Germany), NRE0 (Norway) and YKW (Canada). The data indicate that the shape of the pulse converted at the 400‐km discontinuity is close to that of the P wave whereas the pulse of the 650‐km conversion is substantially broader. We infer from this comparison that the 400‐km discontinuity is sharp (width of the transition zone is less than 5–7 km). The 650‐km transition is modelled by a linear gradient zone 20–30 km thick.
A test of the Great Circle Approximation in the analysis of surface waves
Authors: Alsina Dolors , Snieder Roel , Maupin Valerie
Published: February 2008

A new way of reconstructing wave fronts is developed for testing the validity of the great circle approximation in dispersion analysis of surface waves. Phase and time delays between pairs of stations of an array are used to reconstruct the wave fronts or surfaces of equal phase. This technique is applied to fundamental mode Rayleigh waves recorded at the NARS stations during the ILIHA (Iberian Lithosphere Heterogeneity and Anisotropy) project. The resulting wave fronts are compared with the theoretical ones, i.e. calculated assuming that the waves have traveled along the great circle path with a constant phase velocity, and the angle between both fronts is calculated. Waves traveling mostly through a laterally homogeneous oceanic path before arriving to the Iberian Peninsula are analyzed for the frequency range of 10 to 60 mHz. These show angles up to 8 degrees between the theoretical wave fronts and the wave fronts reconstructed using the delay data. This implies that we make a relative error less than 1% when calculating path‐averaged phase velocities ignoring the deviation of the arrival of the wave from the great circle direction.
Stratospheric dryness: Antiphased desiccation over Micronesia and Antarctica
Authors: Tuck A. F. , Russell James M. , Harries John E.
Published: February 2008

HALOE observations of water vapor and methane during the period 21 September–15 October 1992 are used to examine the role of Antarctic drying in the lower stratosphere. Zonal mean cross‐sections of [2 CH4+H2O] show the probability of transport of Antarctic type dryness to latitudes as distant as 20°N, with major water vapor deficits evident between 10 and 100 mb to 10°S. Examination of monthly mean tropical 100 mb temperatures and of Antarctic temperatures suggests that the observations are consistent with stratospheric dryness being achieved by the combined effects of tropopause freeze‐drying over the Micronesia region during northern winter and drying through the influence of the very low temperatures over Antarctica during southern winter. This paper presents these intriguing new results, and offers a possible explanation.
Microwave limb sounder measurement of stratospheric SO2 from the Mt. Pinatubo Volcano
Authors: Read W. G. , Froidevaux L. , Waters J. W.
Published: February 2008

The Microwave Limb Sounder (MLS) experiment on the Upper Atmosphere Research Satellite (UARS) began atmospheric measurements on September 19, 1991. Residual SO2 from the Pinatubo eruption was detected immediately after instrument activation. The SO2 was located in a tropical band with peak mixing ratios of ∼15 ppbv near 26 km altitude. The observed decay of SO2 has provided an estimate of the OH concentration in the plume.
Geomagnetic activity during solar cycle 9 (1844–1856)
Authors: Nevanlinna H. , Ketola A. , Häkkinen L. , Viljanen A. , Ivory K.
Published: February 2008

Ten‐minute values of declination observations carried out at the Helsinki observatory were used to analyze magnetic activity and storminess during 1844–1856 spanning solar cycle 9. Three‐hour K‐indices and daily Ak‐amplitudes were derived numerically from the data and compared with corresponding indices from the present Nurmijärvi magnetic observatory nearby. Helsinki magnetic activity data are based on homogeneous and reliable observations being thus utilizable for extending long activity series (like aa since 1868 onwards) backwards in time. Magnetic activity during 1844–1856 has been, on the average, on the same level as the activity at Nurmijärvi during the last four sunspot cycles in 1953–1992 but the occurrence of very large magnetic storms has been more frequent at Nurmijärvi. There have been about 300 magnetic storm days (Ak ≥ 30) during cycle 9. The distribution of storm occurrence was double‐peaked within the cycle: in the rising (1847–48) and falling (1851–54) parts of the sunspot cycle substantially more magnetic storms appeared than during the years in between.
On the role of atomic oxygen in the dynamics and energy budget of the mesosphere and lower thermosphere
Authors: Ward William E. , Fomichev Victor I.
Published: February 2008

Atomic oxygen affects both the heating and cooling of the mesosphere and lower thermosphere through its recombination and collisional deactivation of CO2. Recent increases in the accepted value of the deactivation constant, ko in CO2‐O collisions enhance the role of the latter process in the dynamics and energy budget of this region. There are strong increases in the radiative cooling due to CO2 in the 90–120 km region. The sensitivity of the cooling rate in the 15 μm band to variations in atomic oxygen concentration, [O], is enhanced so that the atmosphere in this region is unstable to these variations in concentration. Convection appears possible thereby providing a vertical mixing mechanism which is ineffective in the diffusion of heat but is effective in mixing constituents, and some justification for the use of different eddy diffusivities for heat and constituents. Heating rate calculations are intrinsically more complicated because both the heating and the cooling processes involving atomic oxygen are nonlinear functions of its concentration. The damping of atmospheric waves will be affected because radiative damping will be stronger up to 100 km and the cooling rate dependence on the atomic oxygen mixing ratio affords a new mechanism for photochemical damping. It appears that the overall dynamics and energy budget of this region must be reconsidered.
Chemical and physical diversity of hydrothermal plumes along the East Pacific Rise, 8°45′N to 11°50′N
Authors: Lupton J. E. , Baker E. T. , Mottl M. J. , Sansone F. J. , Wheat C. G. , Resing J. A. , Massoth G. J. , Measures C. I. , Feely R. A.
Published: February 2008

We conducted a survey of water‐column hydrothermal plumes along a 350‐km long section of the East Pacific Rise (EPR) axis stretching from 8°45′N to 11°50′N, including the region at 9°45′–54′N where 1991 ALVIN dives found evidence for recent seafloor volcanic eruptions. Our survey included measurements of temperature anomaly, light attenuation (suspended particles), methane, hydrogen, iron, manganese, helium, and aluminum. We detected strong light attenuation plumes in two main regions: south of the Clipperton Transform Fault (CTF) from 9°27′N to 9°57′N and north of the CTF from 11°05′N to 11°35′N. However, the plumes at these two regions had very different physical and chemical characteristics. South of the CTF, where the ridge is thought to be magmatically robust, the plumes had very high ratios of ³He/heat, methane/Mn and S/Fe. Plumes north of the CTF had much lower ratios of ³He/heat, methane/Mn, and S/Fe. These striking differences in volatile/heat and volatile/metal ratios suggest that the plumes in the vicinity of 9°50′N were derived from a young, evolving hydrothermal system, while the activity at ∼11°10′N is from an older, stable system. This survey demonstrated that water‐column plume measurements can be used not only to accurately locate regions of hydrothermal activity, but also to determine the first‐order chemical and physical characteristics of the hydrothermal fluids exiting from the seafloor.