bluuebunny/crossref_metadata_2025 huggingface dataset:
Significant changes between the ISCCP C and D cloud climatologies
Authors: Doutriaux‐Boucher Marie , Sèze Geneviève
Published: February 2004

We analyse one year of cloud data from the ISCCP C and D datasets. The two datasets differ by their retrieval algorithms and their definitions of the cloud types defined from the cloud top pressure and cloud optical depth. The differences between the two datasets are first described in terms of the total cloud cover, as well as its repartition in low, middle, and high level cloudiness. We also project the ISCCP C cloud classes into the ISCCP D cloud types to circumvent the problem of different cloud type definitions in the two datasets. The differences between the two datasets are then also investigated in terms of the most frequent cloud type.
Comment on “Empirical determination of depth‐distance corrections for mb and Mw from Global Seismograph Network Stations” by G. Nolet et al.
Authors: Veith Karl F.
Published: February 2004

This paper looks at the bases for the cited depth‐distance corrections by Guust Nolet, Steve Krueger, and Robert M. Clouser (Paper 98GL01094, GRL, Vol. 25, No. 9, pp. 1451–1454, May 1, 1998), the historic curves of Gutenberg and Richter, and those given by Veith and Clawson (1972). It discusses the some of the problems associated with the establishment of such curves and suggests modes of strengthening both the current work and potential future work.
Unusual longitude modification of the night‐time midlatitude F2 region ionosphere in July 1980 over the array of tectonic faults in the Andes area: Observations and interpretation
Authors: Pulinets S. A. , Kim V. P. , Hegai V. V. , Depuev V. Kh. , Radicella S. M.
Published: February 2004

Ionosphere topside sounding data from the INTERCOSMOS‐19 satellite have been utilized to study longitude distribution of the night‐time midlatitude F2 region peak electron density NmF2 in the Southern hemisphere over the array of tectonic faults in the Andes area for low geomagnetic activity periods in July 1979 and in July 1980 when solar activity was high and nearly the same, however, in July 1980 there was intensified tectonic activity in the Andes area, and in July 1979 the tectonic activity was lower. The results show that in July 1980 the observed value of NmF2 as a function of longitude decreased by a factor of ∼3 with the change of longitude from 280° to 295°E over the latitude range 30°–45°S, whereas the appropriate longitude profiles of NmF2 observed in July 1979 and reproduced by the ionospheric model IRI‐90 do not reveal any appreciable longitude variations above the Andes area. Using model simulation we interpret the observed longitude anomaly of NmF2 in July 1980 as a result of the F2 region modification caused by a hypothetical large‐scale long‐living perturbation of the vertical electrostatic field on the Earth's surface associated with intensified tectonic activity.
Surface bidirectional reflectance distribution function observed at global scale by POLDER/ADEOS
Authors: Hautecœur Olivier , Leroy Marc M.
Published: February 2004

The spaceborne POLDER instrument presents the unique capability of sampling the surface Bidirectional Reflectance Distribution Function (BRDF) up to about 60° viewing angle for the full azimuth range of every point on Earth at 6 km resolution, when atmospheric conditions are favorable. This paper presents examples of BRDF signatures acquired at this resolution on several terrestrial biomes (desert, steppe, grassland, boreal forest, savanna, wetland). Well identified directional signatures for all azimuths are obtained and shown to be different for each biome. Specific directional effects in the hot spot and specular directions are well observed in the data.
Plasma waves in the dayside polar cap boundary layer: Bipolar and monopolar electric pulses and whistler mode waves
Authors: Tsurutani B. T. , Arballo J. K. , Lakhina G. S. , Ho C. M. , Buti B. , Pickett J. S. , Gurnett D. A.
Published: February 2004

We report four different types of plasma waves detected in and near the dayside polar cap boundary layer (PCBL) region at high altitudes (>6 RE). One wave type is narrowband whistler‐mode emission at frequencies just below fce (5.5 kHz). These emissions could be locally generated by resonant wave‐particle interactions involving an electron beam of ∼100 eV energy. A second type is a low frequency (200–300 Hz) whistler mode wave, which may be locally generated by ∼25 keV electrons or ∼45 keV ions. It is also possible that these latter waves are generated at low altitudes near the ionosphere and then converted from the ion cyclotron mode into whistler‐mode during propagation from the generation region to the spacecraft. Two further types of waves are large‐amplitude bipolar and monopolar solitary “electrostatic” waves. The bipolar wave structures are possibly generated all along the magnetic field lines in the field‐aligned current regions (at all local times). The monopolar structures could be evolved bipolar solitary waves. A one‐d schematic is presented to explain the paired monopolar structures as a result of splitting of an electron hole into two parts.
A reexamination of the “stratospheric fountain” hypothesis
Authors: Dessler A. E.
Published: February 2004

We reexamine the “stratospheric fountain” hypothesis by comparing estimates of the annually and zonally averaged volume mixing ratio (vmr) of water vapor entering the stratosphere to annually and zonally averaged estimates of the saturation vmr of the tropical tropopause‐region. We find that the vmr of water vapor entering the stratosphere (3.8±0.3 ppmv) agrees well with the saturation vmr of the tropical tropopause‐region (4.0±0.8 ppmv). Consequently, our analysis provides no support for the “stratospheric fountain” hypothesis, which required troposphere‐to‐stratosphere transport to occur preferentially in regions where the tropical tropopause is colder than average.
Theoretical Study of the stability of MgSiO3‐perovskite in the deep mantle
Authors: Dubrovinsky L. , Saxena S. K. , Ahuja R. , Johansson B.
Published: February 2004

We have used theoretical methods (Full‐Potential Linear‐muffin‐tin‐orbital, FPLMTO, and lattice dynamics) to calculate the Gibbs free energy of the phases, perovskite (MgSiO3), SBAD (SiO2), stishovite (SiO2) and periclase (MgO). At 300 K, perovskite is found to be stable at all pressures up to 150 GPa. As the temperature is increased, the free energy difference between the oxide mixture and perovskite decreases and at 3000 K and at pressures between 105 and 115 GPa, the oxide mixture becomes more stable. The calculated equilibrium pressure is much higher than the observed experimental pressure which may be due to stress in the sample and/or due to the inadequacy of the applied theoretical models not accounting for anharmonicity effects.
The changing relationship between ENSO variability and moisture balance in the continental United States
Authors: Cole Julia E. , Cook Edward R.
Published: February 2004

The El Niño‐Southern Oscillation (ENSO) system orchestrates a well‐documented suite of climate anomalies worldwide. The details of ENSO's extratropical influence vary among events, but this variability has not been described or diagnosed beyond the past few decades, and previous descriptions have looked at inter‐event differences rather than decadal patterns. We use a new tree‐ring based drought reconstruction for the continental U.S. and instrumental ENSO indices to document systematic decadal changes in the U.S. drought‐ENSO relationship since the late 19th century. Significant ENSO‐drought correlation occurs consistently in the southwest U.S., but the strength of penetration of moisture anomalies into the continent varies substantially. The most striking change over the past 130 years is the initiation of a “bipolar” ENSO‐drought signature around 1920, producing opposite‐sign moisture anomalies in the southwest and mid‐Atlantic states. Shifts in teleconnection patterns coincide with variations in the strength of ENSO and in a North Pacific mode.
A 25‐year record of 10 kHz sferics noise in Antarctica: Implications for tropical lightning levels
Authors: Watkins Nicholas W. , Clilverd Mark A. , Smith Andy J. , Yearby Keith H.
Published: February 2004

We report measured levels of very low frequency (VLF) radio noise at ∼10 kHz, due to lightning sferics, observed at Halley Station, Antarctica (76°S, 27°W) between 1971 and 1996. The observed VLF noise levels at Halley are a product of the thunderstorm source function and the transfer function for propagation to the receiver in the waveguide formed by the Earth's surface and the ionosphere. Least squares fitting enables us to confirm the characteristic diurnal, annual and semi‐annual periodicities found by the present authors in a separate paper. That method and also cross correlation of annual averaged 10 kHz VLF power with sunspot number shows a ∼4 dB peak‐to‐peak fluctuation at the ∼11‐year solar cycle period, believed to be due to the influence of EUV flux on the the ionospheric D region. Finally we constrain any linear trend to 1.4±2.6 dB in 25 years. If a positive trend is present and is interpreted as a change in tropical South American lightning flash rate, it is less than 10%.
Crustal transition between continental and oceanic domains along the North Iberian Margin from wide angle seismic and gravity data
Authors: Fernéndez‐Viejo G. , Gallart J. , Pulgar J. A. , Gallastegui J. , Dañobeitia J. J. , Córdoba D.
Published: February 2004

Deep crustal features of the transition between the North Iberian mainland and the Bay of Biscay are constrained from new wide‐angle seismic and gravity data. Velocity‐depth models are derived from far‐offset recordings onshore of two N‐S marine profiles, complemented with new refraction data inland and tested against models that fit the gravity anomalies. Important lateral variations are inferred along the North Iberian margin. In the western transect, a Variscan crust is documented from the mainland across the continental shelf, and a rapid crustal thinning beneath the slope marks the transition to the oceanic domain. The eastern transect shows an outstanding crustal thickening beneath the coastline (Moho depths around 50 km) and a gradual thinning across the shelf. Differences are related to the V‐shape of the Bay of Biscay that causes a W‐E transition along the margin, from a short‐lived oceanic subduction to continental collision during the Tertiary oblique convergence between Europe and Iberia.
A numerical study of the contrail‐to‐cirrus transition
Authors: Gierens Klaus , Jensen Eric
Published: February 2004

A numerical 2D‐simulation of the transformation of a contrail in its vortex phase to a cirrus‐like cloud during the dispersion phase has been performed using a model that handles both wake dynamics and ice micro‐physics. The contrail is located in an environment characterized by measured profiles of wind and temperature. The ambient humidity at cruise level slightly exceeds ice‐saturation. The thermal structure of the atmosphere causes a strong vertical growth of the contrail cloud, even into a dry layer, until a stably stratified layer is reached. Thereafter the cloud expands mainly horizontally and after 30 min it eventually disappears because of entrainment of dry ambient air.
Theoretical modeling of seismic noise propagation in firn at the South Pole, Antarctica
Authors: Albert Donald G.
Published: February 2004

The problem of interfering noise (produced by ground vehicles) on teleseismic arrivals recorded by Global Seismic Network sensors at South Pole Station is addressed. Using the wavenumber integration method, theoretically calculated seismograms show that installing the GSN sensors in a borehole 200 to 300 m deep, 10 km away from the Station, will significantly reduce the vehicle‐generated noise and improve signal quality. Because the intrinsic attenuation of seismic waves propagating in the polar firn is low, most of the predicted noise reduction results from wavefront spreading, Rayleigh wave amplitude decay with depth, and from placing the sensors below the refractive waveguide that traps much of the seismic energy in the near surface layers.
Seasonal variability in the Agulhas Retroflection Region
Authors: Matano R. P. , Simionato C. G. , de Ruijter W. P. , van Leeuween P. J. , Strub P. T. , Chelton D. B. , Schlax M. G.
Published: February 2004

The objective of this article is to present evidence for the existence of seasonal variability in sea surface height (SSH) anomaly in the Agulhas Retroflection region. TOPEX/POSEIDON altimeter data are used to estimate seasonal changes in the mesoscale SSH variability. There is a seasonal oscillation of SSH variability characterized by a maximum during the austral summer and a minimum during the austral winter. The amplitude of this seasonal change is approximately 30% of its mean value. During the winter season the spatial distribution of SSH variability resembles that of the annual mean variability, with relative maxima centered at approximately 18°E, 27°E and 38°E. During the summer there is an additional maximum which extends from approximately 20°E to 25°E and from 40° to 42°S. Analysis of longitude‐time diagrams reveals that at low latitudes planetary waves propagate freely throughout the basin. Along the latitude of the Agulhas Retroflection region, the East Madagascar Ridge hampers the westward propagation of planetary waves. It is speculated that the difference between summer and winter patterns is caused by an inertially driven bifurcation of the Agulhas Current.
Conamara Chaos Region, Europa: Reconstruction of mobile polygonal ice blocks
Authors: Spaun N. A. , Head J. W. , Collins G. C. , Prockter L. M. , Pappalardo R. T.
Published: February 2004

New Galileo images of Europa reveal regions of chaotic terrain in otherwise highly‐lineated background plains. Examination of Conamara Chaos shows that 59% of the region is composed of fine‐textured matrix material lying at low elevations and formed by destruction of lineated plains, while the remainder consists of 139 fragmented polygons of linear‐textured background plains. Using through‐trending linear features, we reconstruct the original positions of chaos polygons and find that significant lateral translation and rotation have occurred: 78% of the polygons have undergone horizontal translations with most moving between 1 and 5 km, and 81% have rotated (average rotation of ∼11°). Movement of polygons appears to be inward from the chaos margins and clockwise in the center, while polygon rotation is evenly clockwise and counterclockwise. Chaos formation in this region thus involves destruction of over half of the pre‐existing terrain, and mobilization, translation, and rotation of the remaining polygons, implying elevated near‐surface temperatures and a highly mobile substrate over lateral scales of ∼100 km.
Modeling the radiative transfer properties of media containing particles of moderately and highly elongated shape
Authors: Schulz F. M. , Stamnes K. , Stamnes J. J.
Published: February 2004

The transfer of polarized radiation in a medium containing size‐shape distributions of randomly oriented nonspherical particles is modeled by employing a prolate spheroidal particle model. The parameter characterizing the mean departure from sphericity of the shape‐distribution is the effective aspect ratio of the particle ensemble. The radiance, the degree of linear polarization and the degree of circular polarization are strongly sensitive to a variation of the effective aspect ratio. This shape‐sensitivity is observed consistently from size‐shape distributions containing mainly moderately aspherical particles to those containing predominantly highly aspherical particles. When the effective aspect ratio varies between 4 and 12, the degree of linear polarization changes by as much as 0.15. At certain angles from the sun, the radiance changes by as much as 60% within the same range of effective aspect ratios.
Near and far offset impedances: Seismic attributes for identifying lithofacies and pore fluids
Authors: Mukerji Tapan , Jørstad Arild , Mavko Gary , Granli John Reidar
Published: February 2004

Reliably predicting lithologic and saturation heterogeneities is a key problem in reservoir characterization. This study shows how near and far offset seismic impedance can be used to classify lithologies and pore fluids. The near offset seismic stack approximates a zero offset section, giving an estimate of the normal incidence acoustic impedance (AI = ρV). The far offset stack gives an estimate of a Vp/VS related elastic impedance (EI) attribute, equivalent to the acoustic impedance for non‐normal incidence. These attributes can be computed from log data. Well data can be used, prior to seismic inversions, to test the feasibility of using AI‐EI attributes for lithofacies identification. Bi‐variate AI‐EI probability distribution functions can be estimated from logs to obtain classification success rate for each facies. Success rate is a measure of the value of far‐offset data for reservoir characterization. Examples are presented from North Sea, Gulf of Mexico, and Australia.
Short‐wavelength lateral variation of a D′ P‐wave reflector beneath the southwestern Pacific
Authors: Yamada A. , Nakanishi I.
Published: February 2004

The short‐period vertical‐component data from the Fiji Is. earthquakes recorded by three seismological networks in Japan are analysed to investigate short‐wavelength lateral heterogeneities in D′ layer. A double‐array stacking method, which allows us to combine event and receiver arrays, is applied to the records of each network. Three regions in the D′ layer sampled by the three networks are located at horizontal intervals of a few hundred kilometers. In all three regions, the D′ reflectors are detected. The height of the D′ reflector above the CMB, which is estimated by the differential travel time between PdP (D′ reflection) and P, changes from 270 km to 170 km. This result may suggest that some strong short‐wavelength lateral heterogeneities exist in the D′ layer beneath the southwestern Pacific.
Sound velocities in MgSiO3‐garnet to 8 GPa
Authors: Gwanmesia Gabriel D. , Chen Ganglin , Liebermann Robert C.
Published: February 2004

Velocities of acoustic compressional (P) and shear (S) waves were measured to 8 GPa at room temperature for dense (99.7% of theoretical density), isotropic polycrystalline specimens of MgSiO3‐majorite garnet using the phase comparison method of ultrasonic interferometry in a 1000‐ton split‐cylinder apparatus (USCA‐1000). The pressure derivatives of the adiabatic bulk modulus (KS) and the shear modulus (G) are Ko′ = (∂Ks/∂P)T =6.7±0.4 and Go′ = (∂G/∂P)T =1.9±0.1. Substitution of Si for Mg and Al in these garnets increase Ko′ by 26%, and Go′ by 16%, from Mg3Al2Si3O12‐pyrope to majorite. The high values of Ko′ and Go′ from this study lead to much steeper velocity‐depth profiles in the transition zone (400–700 km) than those calculated from the Ko′ and Go′ estimates from elasticity systematics by Duffy and Anderson (1989).
Heterogeneous nucleation of a common atmospheric aerosol: Ammonium sulfate
Authors: Oatis Susan , Imre Dan , McGraw Robert , Xu Jun
Published: February 2004

Natural and anthropogenic aerosols have a direct impact on the earth's radiative balance. Many of the common atmospheric aerosols contain hygroscopic salts and therefore their physical state and composition are sensitive to the relative humidity. The phase of the aerosol particle will dramatically affect the relative rates of atmospheric reactions, and radiative properties such as scattering and optical activity. In order to understand these atmospheric processes and provide accurate input for global modeling, it is imperative that these phase transitions be well defined. It is thought that the degree of metastability is influenced by the presence of foreign particulate matter. These solid impurities are predicted to reduce the barrier of nucleation by providing a surface upon which heterogeneous nucleation can be catalyzed. We report the results of CaCO3 and BaSO4 solid impurities on the efflorescence of (NH4)2SO4‐H2O micro‐droplets. The results show that both solid impurities act as catalysts for heterogeneous nucleation by causing a decrease in the degree of metastability at the efflorescence point. BaSO4 does not prove to be significantly more efficient than CaCO3 in spite of having the same crystalline structure and similar lattice parameters as in (NH4)2SO4.
An interpretation of the cross‐phase spectrum of geomagnetic pulsations by the field line resonance theory
Authors: Chi P. J. , Russell C. T.
Published: February 2004

The cross‐phase spectrum of the magnetic fields at two closely spaced stations located on the same meridian can be used to determine the field line resonance frequencies in the magnetosphere. The model of two harmonic oscillators previously proposed in the literature to interpret this technique, however, deviates from the traditional field line resonance model and it fails to interpret the cross‐phase spectrum for the Z component. We show that the cross‐phase spectrum can be interpreted by traditional field line resonance theory with consideration of ionospheric effects even in the presense of a continuum of non‐interacting resonating field lines.
On tide propagation in convergent estuaries
Authors: Lanzoni Stefano , Seminara Giovanni
Published: February 2004

We revisit the problem of one‐dimensional tide propagation in convergent estuaries considering four limiting cases defined by the relative intensity of dissipation versus local inertia in the momentum equation and by the role of channel convergence in the mass balance. In weakly dissipative estuaries, tide propagation is essentially a weakly nonlinear phenomenon where overtides are generated in a cascade process such that higher harmonics have increasingly smaller amplitudes. Furthermore, nonlinearity gives rise to a seaward directed residual current. As channel convergence increases, the distortion of the tidal wave is enhanced and both tidal wave speed and wave lenght increase. The solution loses its wavy character when the estuary reaches its “critical convergence”; above such convergence the weakly dissipative limit becomes meaningless. Finally, when channel convergence is strong or moderate, weakly dissipative estuaries turn out to be ebb dominated. In strongly dissipative estuaries, tide propagation becomes a strongly nonlinear phenomenon that displays peaking and sharp distortion of the current profile, and that invariably leads to flood dominance. As the role of channel convergence is increasingly counteracted by the diffusive effect of spatial variations of the current velocity on flow continuity, tidal amplitude experiences a progressively decreasing amplification while tidal wave speed increases. We develop a nonlinear parabolic approximation of the full de Saint Venant equations able to describe this behaviour. Finally, strongly convergent and moderately dissipative estuaries enhance wave peaking as the effect of local inertia is increased. The full de Saint Venant equations are the appropriate model to treat this case.
A new calculation of chemical eddy transport for several middle atmospheric tracers
Authors: Siskind David E. , Bacmeister J. T. , Summers M. E.
Published: February 2004

We describe a new approach to calculating transport of chemically active tracers by nonbreaking planetary waves (chemical eddy transport). This approach uses the horizontal displacements calculated from a planetary wave model to estimate the time variation of the photolysis rates experienced at each grid point. We contrast our method with a previously documented approach that assumes linear photochemical relaxation and calculates separate diffusion coefficients for each species. Our results are presented for five middle atmospheric tracers, O3, NO2, NO, CO, and H2. For O3, greater transport into the polar region is seen around 30 km. For mesospheric NO, the increased exposure of polar air to UV sunlight leads to more photodissociation and thus less net downward transport into the stratosphere. Mesospheric CO and H2 are less sensitive to chemical eddy transport because their chemical lifetimes are longer.
On the applicability of current land surface schemes for Arctic tundra: An intercomparison study
Authors: Tilley Jeffrey S. , Lynch Amanda H.
Published: February 2004

In this paper, we examine the performance of three land surface schemes—the Bio‐sphere‐Atmosphere Transfer Scheme (BATS1E), the NCAR Land Surface Model (LSM) and the Canadian Land Surface Scheme, (CLASS) for simulations at two sites on the Alaskan North Slope: Barrow and Imnavait Creek. These sites are characterized by similar large‐scale meteorological conditions but different land surface environments and soil characteristics. The simulations are driven by field data collected in several observational programs during the 1992 Arctic summer season; these programs also provide validation data for the schemes. Examination of the simulation results indicates that the schemes with three or more layers (LSM, CLASS) capture the basic seasonal behavior somewhat successfully, while BATS1E is less satisfactory. The details of the soil thermal and moisture field evolution vary substantially between LSM and CLASS. The results suggest that improvements in the treatment of Arctic biological processes, water and energy partitioning, and freeze‐thaw physics are needed before higher confidence in prediction from not only the land surface models but also their host climate models is possible for the Arctic regions.
Kelvin waves and the quasi‐biennial oscillation: An observational analysis
Authors: Canziani Pablo O , Holton James R.
Published: February 2004

A method is derived for estimating the Kelvin wave contribution to the vertical flux of westerly momentum in the equatorial stratosphere, which is based on temperature and geopotential perturbations. This method is used to estimate the momentum transfer due to Kelvin wave activity as derived from the cryogenic limb array etalon spectrophotometer (CLAES) temperature data set, for the onset of the westerly phase of the QBO during 1992 and the first few months of 1993, that is, during the first part of the Upper Atmosphere Research Satellite (UARS) mission. The results are compared with the zonal winds as observed by the high‐resolution Doppler imager (HRDI) also flown on board UARS, and the United Kingdom Meteorological Office (UKMO) data assimilation model product, a correlative data set to the UARS mission. The analysis shows that although the Kelvin wave momentum flux convergence is occasionally sufficient to account for the observed QBO westerly acceleration, the observed flux is sporadic in nature and virtually disappears during the second half of the sample, when the westerly vertical shear zone approaches the 100 hPa level. An estimate of the total westerly momentum flux necessary to produce the observed descent of the westerly phase of the QBO is made using the transformed Eulerian mean (TEM) formalism. The results suggest that Kelvin waves are not sufficient to force the descent of the westerly phase of the QBO. There appears to be a need for enhanced westerly forcing throughout the descent of the westerly phase of the QBO. This enhanced forcing is most likely provided by gravity waves that are unresolved by the satellite observations. These results are in agreement with the results derived from general circulation models.
Momentum transport in the solar wind erosion of the Mars ionosphere
Authors: Pérez‐de‐Tejada H.
Published: February 2004

Measurements in the Mars plasma environment indicate that a friction layer develops between the solar wind and that planet's ionosphere. The observed features include a velocity boundary layer in the solar wind that streams around the flanks of the Mars ionosphere and enhanced planetary particle fluxes detected when the solar wind speed decreases to low values within the boundary layer. It is suggested that a cold plasma flow is present in the tenuous Mars upper ionosphere and that its momentum is provided by the solar wind within the adjacent velocity boundary layer. Calculations are presented to estimate the momentum flux that is delivered to the Mars upper ionosphere. It is argued that an ionospheric flow can be driven by solar wind momentum transferred from a velocity boundary layer whose thickness is 100–200 km around the terminator. By comparison a dense early Mars ionosphere could have been eroded by the momentum flux delivered from a ∼1000 km thick boundary layer which would be comparable to that present around the Venus ionosphere. The total mass loss eroded by this process through Martian history should have not been larger than that of a few meters‐deep global layer of water. It is further suggested that the erosion of the Mars ionosphere is not axially symmetric around the terminator but should preferably occur over the magnetic polar regions of the ionosphere.
Characterization of auroral radar power spectra and autocorrelation functions
Authors: Jackel Brian J.
Published: February 2004

Radar backscatter is a commonly used tool for studying plasma instabilities in the auroral E region. Analysis of the received signals typically involves moments of the scattered power spectrum such as total power, mean Doppler shift, and spectral width; in some cases the spectral asymmetry may also be of interest. This paper presents the steps required to estimate spectral moments directly from the autocorrelation function, and some advantages and limitations of working in the lag domain are discussed. Recent measurements of auroral spectra at UHF (440 and 933 MHz) are used to motivate the discussion and as test cases. The utility of parametric models is also studied with an emphasis on determining whether spectra are more nearly Gaussian or Lorentzian. A model autocorrelation function is introduced, with spectral characteristics similar to a Voigt distribution but a more convenient functional form.
Paleomagnetism and geochronology of the Late Cretaceous‐Paleogene island arc complex of the Kronotsky Peninsula, Kamchatka, Russia: Kinematic implications
Authors: Levashova Natalia M. , Shapiro Mikhail N. , Beniamovsky Vladimir N. , Bazhenov Mikhail L.
Published: February 2004

The remnants of ancient island arcs are exposed in the Achayvayam‐Valagina and East Peninsulas tectonic zones of the Olutor‐Kamchatka region, northeast Russia. Geochemically, Late Cretaceous to Paleogene island arc complexes of the East Peninsulas zone are similar to intraoceanic island arcs, and the East Peninsulas zone is regarded as the extinct Kronotsky island arc. Paleomagnetic and biostratigraphic studies of Late Cretaceous and Paleogene island arc rocks were carried out at 21 sites in the eastern part of the Kronotsky Peninsula, which belongs to the East Peninsulas zone. Characteristic remanent magnetizations of both polarities isolated from most sites pass reversal and fold tests; the Cretaceous result is also supported by a positive conglomerate test on lava boulders from an intraformational conglomerate. Mean inclinations of Late Cretaceous, Ypresian and Bartonian rocks correspond to paleolatitudes of 44.8° ± 8.0°N, 38.6° ± 3.5°N, and 45.1° ± 7.0°N, respectively. These values are ∼20° lower than the corresponding reference values for the North American plate for the Cretaceous and Ypresian and ∼14° lower for the Bartonian. Therefore northward transport of the Kronotsky island arc is indicated. Kinematic evolution of the Kronotsky island arc in the Late Cretaceous‐Paleogene was reconstructed using published kinematic parameters. In addition, we incorporated into analysis the geological and published paleomagnetic data for the Late Cretaceous and Tertiary island arc complexes of the Cape Kamchatka Peninsula from the East Peninsulas zone and the Late Cretaceous island‐arc complexes of the Achayvayam‐Valagina zone. As a result, two alternative scenarios of kinematic evolution for the Kronotsky island arc are proposed. According to both of them, the Kronotsky island arc was moving with the continental plate in Late Cretaceous time and with the Pacific plate from the beginning of the Paleocene until docking with the Eurasian margin in Miocene‐Pliocene time.
Trace gas exchange in a high‐Arctic valley: 3. Integrating and scaling CO2 fluxes from canopy to landscape using flux data, footprint modeling, and remote sensing
Authors: Soegaard Henrik , Nordstroem Claus , Friborg Thomas , Hansen Birger U. , Christensen Torben R , Bay Christian
Published: February 2004

Within the framework of the European Land Arctic Physical Processes project and as part of the Danish Research Council's Polar Program, a study on trace gas exchange in a high‐arctic ecosystem was conducted in NE Greenland, May‐August 1997. On the basis of carbon dioxide flux measurements from three dominant surface types, this paper reports on the upscaling of such measurements from canopy to landscape level. Over a three‐week period starting in mid‐July, the different surfaces revealed large differences in the CO2 flux with uptake rates ranging from 0.7 g C m−2 d−1 over the dwarf shrub heath to 3.0 g Cm−2 d−1 over denser parts of the fen, while willow snowbed revealed intermediate uptake rates. The carbon dioxide exchange could be simulated by a CO2 model, combining photosynthesis and soil respiration routines, for which the parametrization depended on the vegetation type. Results from the simulation were supported by a sensitivity analysis based on a three‐dimensional footprint model where it was shown that the CO2 uptake was strongly related to the measured leaf area index. The CO2 model was used to calculate the spatial distribution in Net Ecosystem Exchange (NEE) on the basis of Landsat satellite data acquired at the peak of the growing season and stratified according to vegetation type. It was found that there was a reasonable agreement between the satellite‐based flux estimate (‐0.77 g C m−2 d−1) and the CO2 flux found by areal weighting of the eddy correlation measurements (‐0.88 g C m−2 d−1) for the specific study day. Finally, the summer season NEE was calculated for the whole Zackenberg Valley bottom. In June, there was a valley‐wide carbon loss of 8.4±2.6 g C m−2 month−1, whereas the valley system accumulated 18.8±6.7 g C m−2 season−1 during the growing season (July‐August).
Testing the performance of a dynamic global ecosystem model: Water balance, carbon balance, and vegetation structure
Authors: Kucharik Christopher J. , Foley Jonathan A. , Delire Christine , Fisher Veronica A. , Coe Michael T. , Lenters John D. , Young‐Molling Christine , Ramankutty Navin , Norman John M. , Gower Stith T.
Published: February 2004

While a new class of Dynamic Global Ecosystem Models (DGEMs) has emerged in the past few years as an important tool for describing global biogeochemical cycles and atmosphere‐biosphere interactions, these models are still largely untested. Here we analyze the behavior of a new DGEM and compare the results to global‐scale observations of water balance, carbon balance, and vegetation structure. In this study, we use version 2 of the Integrated Biosphere Simulator (IBIS), which includes several major improvements and additions to the prototype model developed by Foley et al. [1996]. IBIS is designed to be a comprehensive model of the terrestrial biosphere; the model represents a wide range of processes, including land surface physics, canopy physiology, plant phenology, vegetation dynamics and competition, and carbon and nutrient cycling. The model generates global simulations of the surface water balance (e.g., runoff), the terrestrial carbon balance (e.g., net primary production, net ecosystem exchange, soil carbon, aboveground and belowground litter, and soil CO2 fluxes), and vegetation structure (e.g., biomass, leaf area index, and vegetation composition). In order to test the performance of the model, we have assembled a wide range of continental and global‐scale data, including measurements of river discharge, net primary production, vegetation structure, root biomass, soil carbon, litter carbon, and soil CO2 flux. Using these field data and model results for the contemporary biosphere (1965–1994), our evaluation shows that simulated patterns of runoff, NPP, biomass, leaf area index, soil carbon, and total soil CO2 flux agree reasonably well with measurements that have been compiled from numerous ecosystems. These results also compare favorably to other global model results.
Chemical weathering in a region of active orogeny: Pescadero Creek Watershed, California
Authors: Phillips R. D. , Rojstaczer S.
Published: February 2004

Base flow chemical signals were used to determine the weathering reactions that control the groundwater chemistry of a geologically heterogeneous, mountainous watershed. Major ion signatures result from cyclic salt and formation water inputs and from the weathering of easily oxidized or highly soluble minerals, such as pyrite, calcite, and dolomite. If montmorillonite is the dominant secondary mineral product, then the bulk of silicate weathering probably involves volcanic rocks. Spatial rates of base flow chemical denudation range from 0.0004 to 0.02 mm yr−1, and temporal rates range from 0.0006 to 0.6 mm yr−1. The mean chemical denudation rate for the watershed is 0.03 mm yr−1, which is comparable to some of the world's most rapidly weathering large drainage basins. Because highly soluble or easily oxidized minerals contribute the bulk of the chemical signal to basin waters, spatial and temporal rates of chemical denudation are constrained largely by recharge and discharge rather than local variations in lithology.
Vertical profiles, boundary layer budgets, and regional flux estimates for CO2 and its 13C/12C ratio and for water vapor above a forest/bog mosaic in central Siberia
Authors: Lloyd Jon , Francey Roger J. , Mollicone Danilo , Raupach Michael R. , Sogachev Andrej , Arneth Almut , Byers John N. , Kelliher Francis M. , Rebmann Corinna , Valentini Riccardo , Wong S.‐Chin , Bauer Guntram , Schulze E.‐Detlef
Published: February 2004

On July 15 and 16, 1996, profiles of temperature, water vapor, carbon dioxide concentration, and its carbon isotopic composition were made within and above the convective boundary layer (CBL), near the village of Zotino in central Siberia (60°N, 89°E). On both days the CBL grew to a height of around 1000 m at midday after which little further growth was observed. This was despite high rates of sensible heat flux into the CBL from the predominantly coniferous vegetation below and was attributable to a high subsidence velocity. For all flights, marked discontinuities across the top of the CBL were observed for water vapor and CO2 concentrations with differences between the CBL and the free troposphere above being as high as 10 mmol mol−1 and 13 μmol mol−1, respectively. Associated with the lower CO2 concentrations within the CBL was an enrichment of the δ 13C in CO2 of up to 0.7‰. Although for any one flight, fluctuations in CO2 and δ13C within the CBL were small (less than 3 μmol mol−1 and 0.1 ‰); they were well correlated and suggested a photosynthetic discrimination, Δ, by the vegetation below of ∼17‰. Estimates of regional Δ based on CBL budgeting techniques suggested values ranging from 14.8 to 20.4 ‰. CBL budgeting techniques were also used to estimate regional ecosystem carbon fluxes (−3 to −9 μmol m−2 s−1) and evaporation rates (1−3 mmol m−2 s−1). Agreement with ground‐based tower measurements was reasonable, but a bootstrap error analysis suggested that errors associated with the integral CBL technique were sometimes unacceptably large, especially for estimates of regional photosynthetic 13C discrimination and regional evaporation rates. Conditions under which CBL techniques should result in reasonably accurate estimations of regional fluxes and isotopic fractionations are evaluated.
Simulating the effects of climate change and climate variability on carbon dynamics in Arctic tundra
Authors: Stieglitz Marc , Giblin Anne , Hobbie John , Williams Matthew , Kling George
Published: February 2004

Through a simple modeling exercise, three mechanisms have been identified, each operating at a different timescale, that may govern carbon dynamics in Arctic tundra regions and partially explain observed CO2 flux variability. At short timescales the biosphere reacts to meteorological forcing. Drier conditions are associated with aerobic soil decomposition, a large CO2efflux, and a net ecosystem loss of carbon. Cooler and moister conditions favor slower anaerobic decomposition in soils, good growing conditions, and terrestrial carbon sequestration. At intermediate timescales, periods of terrestrial carbon loss are directly linked to periods of carbon sequestration by the ability of the ecosystem to retain labile nitrogen. Labile nitrogen released to the soil during periods when the tundra is a source of carbon (soil respiration > net primary productivity) is retained within the ecosystem and accessed during periods when carbon sequestration is favored (net primary productivity > soil respiration). Finally, the ability of vegetation to respond to long‐term changes in soil nutrient status via changes in leaf nitrogen and leaf area index modulates this dynamic at intermediate to long timescales.
A global monthly climatology of phosphate, nitrate, and silicate in the upper ocean: Spring‐summer export production and shallow remineralization
Authors: Louanchi Ferial , Najjar Raymond G.
Published: February 2004

We have created monthly climatologies of nutrients in the upper 500 m of the ocean using the 1998 release of the World Ocean Atlas from the Ocean Climate Laboratory at the National Oceanographic Data Center. The data processing is similar to that used by Najjar and Keeling [1997] to create an oxygen climatology. The spatial extrapolation of the nutrients exploits regional relationships between nutrients and temperature in the ocean. The annual mean horizontal and vertical distributions of the nutrients follow the large scale patterns of oceanic circulation as previously reported in the literature. Surface seasonal variations of nutrients are high in the high latitudes and some restricted upwelling areas, whereas in the subtropical oligotrophic gyres nutrients are low all year. Surface seasonal variations are characterized by high values in winter and low values in summer, consistent with the dominance of entrainment during the winter and biological production during the summer. Good agreement is found between the climatologies and the limited reports of seasonal nutrient variations in the literature. Weaker seasonal variations of opposite phasing are found below roughly 100 m and likely reflect the dominance of remineralization during the summer and ventilation during the winter. Spring‐summer export production derived from the seasonal nutrient drawdown in the upper 100 m is 4.2±0.6 Tmol P, 59±8 Tmol N, and 70±15 Tmol Si. The N:P drawdown ratio is, within the error, in agreement with the traditional value of 16. Similarly, the Si:N drawdown ratio is in agreement with the value of 1 expected for diatom growth in unstressed conditions. The export of organic carbon estimated from the phosphate drawdown is 5.3±0.8 Gt C. The shallow remineralization inferred from seasonal phosphate variation between 100 and 200 m is 2.6±1.1 Gt C. The carbon and silica fluxes, considering that they are lower bounds on global export production because they do not capture the production signal in advectively dominated systems, are in reasonable agreement with other large scale estimates of organic carbon and silica export. The computed f ratio (using satellite‐based estimates of primary production) and the ratio of shallow aphotic zone remineralization to new production tend to increase with increasing latitude, supporting an increase in respiration with temperature, as suggested in recent studies.
Radiocarbon and stable carbon isotopic evidence for transport and transformation of dissolved organic carbon, dissolved inorganic carbon, and CH4 in a northern Minnesota peatland
Authors: Chasar L. S. , Chanton J. P. , Glaser P. H. , Siegel D. I. , Rivers J. S.
Published: February 2004

To elucidate the roles of hydrology and vegetation in below ground carbon cycling within peatlands, radiocarbon values were obtained for pore water dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), CH4, and peat from the Glacial Lake Agassiz peatland. The major implication of this work is that the rate of microbial respiration within a peat column is greater than the peat decomposition rate. The radiocarbon content of DOC at both bog and fen was enriched relative to solid‐phase peat by ∼150‐300‰ consistent with the advection of recently photosynthesized DOC downward into the peat column. Fen Δ14C values for DIC and CH4 closely track the Δ14C of pore water DOC at depth, indicating that this recent plant production was the predominant substrate for microbial respiration. Aceticlastic methanogenesis apparently dominated the upper third of the peat column (α = 1.05), shifting toward CO2 reduction with depth (1.05 < α < 1.08). Upwelling groundwater contributed as much as 15% of the DIC to the bulk DIC pool at depth in the fen. The similarity of Δ14C values for DIC and CH4 suggests that methanogens utilized DIC from this source as well as DIC produced in situ. Bog Δ14C values for pore water DIC and CH4 differ by ≤ 15‰ at all depths and are depleted in 14C relative to DOC by ∼100‰, suggesting microbial utilization of a mixture of older and modern substrates. CO2 reduction was the primary pathway for methanogenesis at all depths in the bog (α = 1.08), and groundwater influence on bulk DIC was negligible. For both sites, Δ14C−DIC and Δ14C−CH4 are approximately equal at depths where stable isotope data indicate a predominance of CO2 reduction and dissimilar when acetate fermentation is indicated.
Interannual variability of net ecosystem CO2 exchange at a subarctic fen
Authors: Griffis T. J. , Rouse W. R. , Waddington J. M.
Published: February 2004

Landscape‐scale net ecosystem CO2 exchange (NEE) and the energy balance of a subarctic fen were studied during five growing seasons near Churchill, Manitoba. Interannual variability in NEE was large and ranged from a net sink of −235 g CO2 m−2 in 1996 to a net source of +76 g CO2 m−2 in 1994. Annual estimates of CO2exchange indicate that during the present period the fen is losing carbon nearly 3 times faster than its long‐term historical gain of about −11 g CO2 m−2 yr−1. Our estimates suggest that gross ecosystem photosynthesis may be more variable than ecosystem respiration on diurnal, seasonal, and interannual timescales. Our data strongly indicate that an early snowmelt combined with wet and warm conditions during the spring period lead to large carbon acquisition even when drier conditions were experienced over the majority of the growing season. The phenological stage of the vegetation relative to the climatic conditions experienced is an important cause of the interannual variability in NEE. An accurate representation of phenology in climate models is, therefore, critical to the success of forecasting the carbon budgets of northern wetlands.