bluuebunny/crossref_metadata_2025 huggingface dataset:
Tomographic images of a mantle circulation model
Authors: Bunge Hans‐Peter , Davies J. Huw
Published: February 2004

Sampling convection in the Earth's mantle by seismic tomography is difficult as evidenced by the uneven distribution of seismic stations and events with some regions being well imaged compared to others. Here we quantitatively explore tomographic filtering on Earth structure by tracing ISC P‐body‐wave data through a computer simulation of mantle circulation which accounts for internal heating of the mantle by radioactive decay, heatflux from the core, a depthwise increase in viscosity, and plate motion history of the past 120 million years. The travel time residuals are inverted by solving jointly for structure and hypocentral parameters with explicit damping and smoothing. We recover the Farallon and Tethys slabs as well as some low velocity anomalies associated with hot upwelling flow suggesting that tomographic filtering is probably minor in areas of high ray density.
Accretion of interplanetary dust in polar ice
Authors: Brook Edward J. , Kurz Mark D. , Curtice Joshua , Cowburn Stuart
Published: February 2004

Measurements of helium isotopes in particles separated from polar ice demonstrate that extraterrestrial ³He dominates the ³He flux at the GISP2 (Greenland) and Vostok (Antarctica) ice core sites. Replicate measurements of late Holocene ice samples yield ³He fluxes of 0.62±0.27×10−12 cm³ STP cm−2 ka−1 (GISP2) and 0.77 ± 0.25 × 10−12 cm³ STP cm−2 ka−1 (Vostok), similar to results from marine sediments. These are the first detailed measurements of ³He in particles from ice core samples, and they demonstrate the utility of the ice core record for evaluating the temporal history of the extraterrestrial dust flux. Results from Vostok samples from 1096–1403 m depth (75–97 ka B.P.) are similar to the late Holocene data, with the exception of two highly anomalous results from 1307 m. The latter probably indicate the presence of rare, large or gas‐rich extraterrestrial particles.
ENSO and eddies on the southwest coast of Mexico
Authors: Zamudio Luis , Leonardi Alan P. , Meyers Steven D. , O'Brien James J.
Published: February 2004

TOPEX/POSEIDON and ERS‐2 (T/ERS) sea surface height altimeter observations and the Naval Research Laboratory Layered Ocean Model (NLOM) are used to study the circulation along the southwest coast of Mexico. The results of this research indicate that strong El Niño/Southern Oscillation (ENSO) warm phase Kelvin waves (KW) destabilize the upper ocean circulation. The effect of ENSO appears as three distinct stages. First, a coastal jet characterized by strong vertical shear flow develops. Second, the shear flow strengthens, increasing its horizontal dimension and the amplitude of its oscillations. Finally, the jet becomes unstable and breaks into anticyclonic eddies, which separate from the coast and drift southwestward. The genesis and strengthening of the jet is due to the simultaneous occurrence of the poleward‐flowing currents along the southwest coast of Mexico and the poleward circulation associated with ENSO downwelling KW.
Climate and interior coupled evolution on Venus
Authors: Phillips Roger J. , Bullock Mark A. , Hauck Steven A.
Published: February 2004

Climate‐interior coupled evolution is investigated for Venus by merging a partial‐melting/parameterized mantle convection model with a gray radiative‐convective atmospheric model. A positive feedback process can operate by the release of water to the atmosphere via mantle melting, leading to an increase in atmospheric opacity and the radiative temperature gradient. The resulting amplification of the greenhouse surface temperature raises the mantle temperature leading to an increase in the partial‐melting rate. Using thin‐lid convection, a coupled model for Venus running over an interval of 3 to 1 Ga shows a significant increase in surface temperature, partial‐melting extent, and extrusive magma flux compared to a model where there is no communication between greenhouse‐modulated surface temperature and partial‐melting in the interior. Coupled and uncoupled models that transition (with variable timing) to stagnant‐lid convection either shut down partial melting via lithospheric thickening, or evolve to large amounts of melt due to increased interior temperatures.
A new DOAS parameterization for retrieval of trace gases with highly‐structured absorption spectra
Authors: Maurellis Ahilleas N. , Lang Rüdiger , van der Zande Wim J.
Published: February 2004

Differential Optical Absorption Spectroscopy (DOAS) has proven to be an extremely useful technique for retrieving trace gas columns from atmospheric measurements of reflected solar irradiance. We show that the use of DOAS is strongly constrained by the complexity of the absorption spectral structure that may be sampled by individual pixels in a detector array (for example, in the vibration‐rotation bands of many species in the visible and infrared). To this end we introduce a Spectral Structure Parameterization (SSP) modification to DOAS which depends primarily on structure in the absorption cross‐section of the atmospheric species intended for retrieval. We show that DOAS‐SSP may be used to determine which absorption spectra are suitable, in terms of complexity of absorption structure, for use in DOAS retrievals as well as how to extend DOAS trace gas retrieval to those species with highly‐structured absorption spectra.
The motion and active deformation of India
Authors: Paul J. , Bürgmann R. , Gaur V. K. , Bilham R. , Larson K. M. , Ananda M. B. , Jade S. , Mukal M. , Anupama T. S. , Satyal G. , Kumar D.
Published: February 2004

Measurements of surface displacements using GPS constrain the motion and deformation of India and India‐Eurasia plate boundary deformation along the Himalaya. The GPS velocities of plate‐interior sites constrain the pole of the angular velocity vector of India with respect to Eurasia to lie at 25.6±1.0°N 11.1±9.0°E, approximately 6° west of the NUVEL‐1A pole of <3 Ma plate motion. The angular rotation rate of 0.44 ±0.03°Myr−1 is 14% slower than the long‐term rate of 0.51° Myr−1. Insignificant velocities between plate interior sites indicate that the exposed Indian plate is stable to within 7 · 10−9 yr−1. The observed contraction vector across the Himalaya (≤20 mm/yr) veers from ∼N20°E in the northwest Himalaya to ∼N25°W in east Nepal, consistent with east‐west extension of southern Tibet.
Upwelling along the coasts of Java and Sumatra and its relation to ENSO
Authors: Susanto R. Dwi , Gordon Arnold L. , Zheng Quanan
Published: February 2004

Upwelling along the Java‐Sumatra Indian Ocean coasts is a response to regional winds associated with the monsoon climate. The upwelling center with low sea surface temperature migrates westward and toward the equator during the southeast monsoon (June to October). The migration path depends on the seasonal evolution of alongshore winds and latitudinal changes in the Coriolis parameter. Upwelling is eventually terminated due to the reversal of winds associated with the onset of the northwest monsoon and impingement of Indian Ocean equatorial Kelvin waves. Significant interannual variability of the Java‐Sumatra upwelling is linked to ENSO through the Indonesian throughflow (ITF) and by anomalous easterly wind. During El Niño episodes, the Java‐Sumatra upwelling extends in both time (into November) and space (closer to the equator). During El Nino (La Niña), the ITF carries colder (warmer) water shallowing (deepening) thermocline depth and enhancing (reducing) upwelling strength.
Radiative forcing due to trends in stratospheric water vapour
Authors: Smith Claire A. , Haigh Joanna D. , Toumi Ralf
Published: February 2004

Trends derived from the latest version of Halogen Occultation Experiment (HALOE) data are used in a two‐dimensional atmospheric model to estimate their radiative effects over the last decade. The results show a stratospheric cooling in regions of H2O increase, of magnitude similar to that due to stratospheric ozone loss indicating a significant additional cause of observed stratospheric temperature decreases. Radiative forcings are derived and it is found that global average radiative forcing due to stratospheric water vapour changes probably lies in the range 0.12 to 0.20 Wm−2 decade−1. This could have more than compensated for the negative radiative forcing due to decadal ozone loss.
Variability in the tropical southeast Indian Ocean and links with southeast Australian winter rainfall
Authors: Ansell T. , Reason C. J. C. , Meyers G.
Published: February 2004

Variability in the southeast (SE) Indian Ocean is examined in relation to SE Australian winter rainfall. Analyses of sea surface temperature (SST), sea surface height (SSH), thermocline depth, wind, outgoing longwave radiation (OLR) and moisture flux data suggest, firstly, that SE Australian winter rainfall is influenced by SST in the tropical SE Indian Ocean and, secondly, that SST anomalies in this region are associated with local atmosphere‐ocean coupling. Based on these analyses, a mechanism for SE Australian interannual winter rainfall variability is proposed.
Satellite observations of formaldehyde over North America from GOME
Authors: Chance Kelly , Palmer Paul I. , Spurr Robert J. D. , Martin Randall V. , Kurosu Thomas P. , Jacob Daniel J.
Published: February 2004

Formaldehyde (HCHO) is an important indicator of tropospheric hydrocarbon emissions and photochemical activity. We present HCHO observations over North America for July 1996 from the GOME instrument on‐board the ESA ERS‐2 satellite. Slant columns are determined to < 4 × 1015 molecules cm−2 sensitivity by directly fitting GOME radiance measurements. These show a distinct enhancement over the southeastern United States, consistent with a large regional source from oxidation of non‐methane hydrocarbons including in particular isoprene. Conversion of slant to vertical columns is done by combining species vertical distribution information from the GEOS‐CHEM 3‐D tropospheric chemistry and transport model with scattering weights from the Smithsonian Astrophysical Observatory LIDORT multiple scattering radiative transfer model. The results demonstrate the ability to measure HCHO from space in typical continental atmospheres, and imply that space‐based measurements of HCHO may provide valuable information on emission fluxes of reactive hydrocarbons.
Listening to sounds from an exploding meteor and oceanic waves
Authors: Evers L. G. , Haak H. W.
Published: February 2004

Low frequency sound (infrasound) measurements have been selected within the Comprehensive Nuclear‐Test‐Ban Treaty (CTBT) as a technique to detect and identify possible nuclear explosions. The Seismology Division of the Royal Netherlands Meteorological Institute (KNMI) operates since 1999 an experimental infrasound array of 16 micro‐barometers. Here we show the rare detection and identification of an exploding meteor above Northern Germany on November 8th, 1999 with data from the Deelen Infrasound Array (DIA). At the same time, sound was radiated from the Atlantic Ocean, South of Iceland, due to the atmospheric coupling of standing ocean waves, called microbaroms. Occurring with only 0.04 Hz difference in dominant frequency, DIA proved to be able to discriminate between the physically different sources of infrasound through its unique lay‐out and instruments. The explosive power of the meteor being 1.5 kT TNT is in the range of nuclear explosions and therefore relevant to the CTBT.
Correlations between patterns of 19th and 20th century surface temperature change and HadCM2 Climate Model ensembles
Authors: Johns T. C. , Gregory J. M. , Stott P. A. , Mitchell J. F. B.
Published: February 2004

We examine the similarity between patterns of changes in decadally‐averaged surface air temperature simulated by ensemble experiments with the HadCM2 coupled climate model and observed patterns over the period 1860–1999, using a spatial pattern correlation method. The analysis is conducted for two anthropogenic (greenhouse gases with/without sulphate aerosols) and two natural (solar and volcanic) modelled forcing histories. For each scenario an ensemble of at least four model runs is used. We compare transient model signal and observed patterns at corresponding times, and establish significance using a 1000 year model control run to construct sampling distributions for random noise patterns. We find evidence of an anthropogenic signal in observed surface temperature patterns emerging over recent decades, particularly in northern winter and spring seasons. Signals from greenhouse gas forcing alone or in combination with sulphate aerosols are both plausible in our analysis, but the highest significance is achieved using seasonally‐defined greenhouse gas plus aerosol signals. There is little evidence of any detectable solar signal, but we do find two periods (late 19th century; 1960s–90s) during which a weak volcanic signal is detectable. Using ensemble simulations makes the conclusions quite robust, but the somewhat different interpretations from this analysis compared to optimal fingerprint analysis of the same simulations reveals some sensitivity to the choice of methodology.
Non‐adiabaticity in mantle convection
Authors: Bunge Hans‐Peter , Ricard Yanick , Matas Jan
Published: February 2004

Seismic observations indicate that Earth's lower mantle is homogeneous as revealed by smooth depth variations of the bulk sound velocity and Bullen's inhomogeneity parameter η being close to one. Here we show with 3D spherical convection simulations that it should also be non‐adiabatic because a significant proportion of mantle heat sources is internal. The computer simulations predict non‐adiabaticity of 100–300 degrees for the lower mantle geotherm, with η ∼ 1.01 implying that the temperature drop across the Core Mantle Boundary exceeds 1000 degrees.
Geometrical constraints of the 1980 Mount St. Helens intrusion from analogue models
Authors: Donnadieu Franck , Merle Olivier
Published: February 2004

The 1980 Mount St. Helens cryptodome intrusion has been simulated by scaled experiments. Silicone, used as a magma analogue, was intruded into a cohesive cone that models the edifice. Measuring surface deformation features associated with variations of injection rate and depth of cryptodome initiation revealed linear relationships with the intrusion characteristics. Scaled to Mount St. Helens dimensions, the 1980 cryptodome is found to have had a maximum E‐W width of 850 m, an initial depth of 680 to 835 m. It had an ascending velocity of 5.7–7.3 m/day that corresponds to a vertical displacement of 330–380 m toward the surface within the two months of deformation. This brought the intrusion to less than 250 m below the crater floor at the point when the north flank failed on May 18, 1980.
Negative ion mass spectrometry and the detection of carbonyls and HCN from clover
Authors: Custer Thomas G. , Kato Shuji , Fall Ray , Bierbaum Veronica M.
Published: February 2004

We have demonstrated that negative ion‐chemical ionization mass spectrometry (NI‐CIMS) can be used to distinguish several isomeric volatile organic compounds (VOCs) that are emitted from wounded plants. Reaction chemistry with HO−, hydrogen/deuterium exchange patterns, and collision‐induced dissociation spectra allow identification of the isomers. Laboratory studies of emissions from wounded clover using NI‐CIMS show several previously detected VOCs, but also clearly demonstrate the emission of HCN. This compound is presumably formed by the decomposition of cyanogenic glycosides which also form aldehyde and ketone byproducts. These results suggest that NI‐CIMS may be a valuable tool for investigating VOCs and HCN release from vegetation.
Monthly fractional green vegetation cover associated with land cover classes of the conterminous USA
Authors: Gallo Kevin , Tarpley Dan , Mitchell Ken , Csiszar Ivan , Owen Timothy , Reed Brad
Published: February 2004

The land cover classes developed under the coordination of the International Geosphere‐Biosphere Programme Data and Information System (IGBP‐DIS) have been analyzed for a study area that includes the Conterminous United States and portions of Mexico and Canada. The 1‐km resolution data have been analyzed to produce a gridded data set that includes within each 20‐km grid cell: 1) the three most dominant land cover classes, 2) the fractional area associated with each of the three dominant classes, and 3) the fractional area covered by water. Additionally, the monthly fraction of green vegetation cover (fgreen) associated with each of the three dominant land cover classes per grid cell was derived from a 5‐year climatology of 1‐km resolution NOAA‐AVHRR data. The variables derived in this study provide a potential improvement over the use of monthly fgreen linked to a single land cover class per model grid cell.
MORB emplacement and structure: Insights from the Semail Ophiolite, Oman
Authors: Pezard Philippe A. , Einaudi Florence , Hermitte Daniel , Cochemé Jean‐Jacques , Coulon Christian , Laverne Christine
Published: February 2004

As opposed to discontinuous seafloor dredging and coring, ophiolites and downhole geophysical measurements provide continuous sections along which high frequency accretion processes at mid‐ocean ridges may be studied. A multidisciplinary study carried out on a volcanic section of the Semail ophiolite with MORB‐like chemical composition reveals two main petrological and geochemical members. The boundary between the two is marked by the presence of a massive flow equating to the most primitive lava sampled, and across which significant changes are obtained. Petrophysical profiles are correlated to geochemical variations and provide thus a description of the magmatic activity through time. These temporal variations may be compared to those derived from crustal drilling and continuous logging measurements.
Fault dynamic rupture simulation of the hypocenter area of the thrust fault of the 1999 Chi‐Chi (Taiwan) Earthquake
Authors: Dalguer L. A. , Irikura K. , Riera J. D. , Chiu H. C.
Published: February 2004

A 2D Discrete Element Model was employed to simulate the rupture propagation and near‐source ground motion in the epicentral area of the 1999 Chi‐Chi (Taiwan) earthquake. The observations show that the hanging wall side is characterized by larger particle motions than the footwall side. The simulation results reproduce the main features of the recorded ground motion and show that the particle velocity on the hanging wall side and on the footwall side are symmetric in the deeper fault region, however, as the crack approaches the free surface, the hanging wall side is characterized by larger particle motions than the footwall side. These results suggest that the difference in the particle motion on the hanging wall and on the footwall is due mainly to the asymmetric geometry of hanging wall and footwall. Thus, the model used leads to good approximations in the vicinity of the epicenter.
Collisionless model of the solar wind in a spiral magnetic field
Authors: Pierrard V. , Issautier K. , Meyer‐Vernet N. , Lemaire J.
Published: February 2004

We present a kinetic collisionless model of the solar wind generalized to take into account the spiral structure of the interplanetary magnetic field. This model, which also includes Kappa velocity distributions, calculates self‐consistently the electric potential profile and derives the solar wind speed and the temperatures of the medium. We study how the inclusion of the spiral geometry changes the plasma parameters compared to the case of a radial magnetic field. Whereas the interplanetary electric potential, the wind density and bulk speed are not significantly changed, we show that the electron and proton temperatures are modified; in particular, we find a decrease of the proton temperature and of its anisotropy, and an increase of the electron temperature. We discuss these results and the validity of the model.
Synoptic storms and the development of the 1997 warming and freshening event in the Beaufort Sea
Authors: Yang Jiayan , Comiso Josefino , Krishfield Richard , Honjo Susumu
Published: February 2004

The climatic state in the Beaufort Sea in 1997 was characterized by warmer atmosphere, smaller areal coverage of sea ice in summer than average, and an oceanic mixed layer with a relatively low salinity that persisted into fall and and early winter. The most remarkable change occurred near the end of 1997 when both salinity and temperature in the upper layer varied dramatically in a short‐time period. The evolution of the air‐sea‐ice condition was observed by an autonomous buoy. The buoy observation revealed that deep mixing that penetrated through the Arctic halocline occurred in response to enhanced wind‐stress forcing associated with an intense storm and was mainly responsible for the abrupt change of temperature and salinity in the mixed layer near the end of 1997. Similar events were inferred from storms in the Eurasian basin in 1994. We postulate that synoptic storms plays a very important role in the variations of the heat and salt budgets in the upper Arctic Ocean.
Long‐term infrared surveillance of Lascar Volcano: Contrasting activity cycles and cooling pyroclastics
Authors: Wooster Martin J.
Published: February 2004

Lascar Volcano (Chile) erupted on 20 July 2000, generating a >10 km high ash column. Satellite infrared data have previously indicated that Lascar's large vulcanian explosions are preceded by significant cooling within the active crater, suggesting that characteristic thermal radiance trends can act as remotely detectable eruption precursors. New analyses and data extend the Lascar's thermal history to cover all five large vulcanian eruptions occurring over the last 15 years. The 2000 eruption follows a formerly undocumented style of infrared radiance variation and indicates that Lascar may have modified its activity since 1993, the year of its greatest historical eruption. Therefore such patterns, evident for over a decade at Lascar, can be unexpectedly modified and this has implications for the way apparent thermal precursors should be treated. The largest 1993 eruption produced 8.5 km long pyroclastic flows which the infrared data indicate exhibited exponential cooling over an 8–12 months period.
Evaluating space weather forecasts of geomagnetic activity from a user perspective
Authors: Thomson A. W. P.
Published: February 2004

Decision Theory can be used as a tool for discussing the relative costs of complacency and false alarms with users of space weather forecasts. We describe a new metric for the value of space weather forecasts, derived from Decision Theory. In particular we give equations for the level of accuracy that a forecast must exceed in order to be useful to a specific customer. The technique is illustrated by simplified example forecasts for global geomagnetic activity and for geophysical exploration and power grid management in the British Isles.
The utility of remotely sensed CO2 concentration data in surface source inversions
Authors: Rayner P. J. , O'Brien D. M.
Published: February 2004

This paper aims to establish the required precision for column‐integrated CO2 concentration data to be useful in constraining surface sources. We use the method of synthesis inversion and compare the uncertainties in regional sources calculated from a moderate‐sized surface network and either global or oceanic coverage of column‐integrated pseudodata. With a simple measure of total uncertainty, we require precision of monthly averaged column data better than 2.5 ppmv on a 8° × 10° footprint for comparable performance with the existing surface network. If coverage is only oceanic we require 1.5 ppmv precision. We recommend more detailed studies on the feasibility of obtaining such observations from current and future satellite instruments.
The atmospheric impact of boreal forest fires in far eastern Siberia on the seasonal variation of carbon monoxide: Observations at Rishiri, A northern remote island in Japan
Authors: Tanimoto Hiroshi , Kajii Yoshizumi , Hirokawa Jun , Akimoto Hajime , Minko Nikolay P.
Published: February 2004

Observations of carbon monoxide (CO) and ozone (O3) at the surface have been made at Rishiri, a northern remote island in Japan. O3 seasonal variation shows a spring maximum and summer minimum, which are typically observed at remote mid‐latitude regions in the Northern Hemisphere. The seasonal cycle of CO shows a baseline enhancement and episodic high concentrations during the period from summer to early fall 1998, indicating a strong source of CO nearby. Both Advanced Very High Resolution Radiometer and Earth Probe Total Ozone Mapping Spectrometer satellite images during the same period produce clear pictures illustrating severe forest fire events and widespread smoke plumes in far eastern Siberia. Back trajectory analyses suggest that boreal forest fires in far eastern Siberia had a significant impact on CO observed at the site from summer to early fall 1998.
Magnetotelluric signature of the western Cantabrian Mountains
Authors: Pous Jaume , Queralt Pilar , Marcuello Alex
Published: February 2004

The magnetotelluric signature of the Alpine part of the Cantabrian Mountains was investigated in a N‐S magnetotelluric profile, from the Duero basin to the Cantabrian shoreline. A two‐dimensional conductivity model was obtained from the joint inversion of TM, TE modes and the geomagnetic transfer functions. A shallow conductor associated with the sediments of the Duero basin, and three north‐dipping conductors in the upper and middle crust were detected. Of the latter, one is interpreted as the sole detachment of the Cantabrian Mountains, whereas the others correlate with the Cabuérniga and San Vicente de la Barquera faults. This geometry suggests that the Cantabrian Mountains comprise uplifted Variscan basement. A comparison with a seismic reflection profile shows a good correlation between these conductors and seismic features. The lower crust is characterised by high conductivities.
Experimental determination of subcritical crack growth parameters in sedimentary rock
Authors: Holder Jon , Olson Jon E. , Philip Zeno
Published: February 2004

Mounting evidence suggests that subcritical crack growth is an important mechanism for the development of natural fractures. Numerical simulations of fracture patterns are sensitive to the subcritical crack growth index, the exponent used to describe the power law dependence of crack velocity on stress intensity. Few measured values of subcritical indices in sedimentary rocks have been published, however, and no systematic studies of diagenetic controls of subcritical crack index behavior are available. Subcritical crack index measurements are especially difficult in weak, porous rock, primarily because non‐elastic material response can obscure fracture‐related behavior. We have carried out numerous subcritical crack index measurements with the widely used dual torsion beam test configuration and developed a modified test methodology for subcritical crack index measurements on porous rocks. The principal element of the methodology is a specimen pre‐loading procedure to minimize transient material response. Measurement reliability is documented in the study by documentation of reproducibility in three sets of sandstone and carbonate specimens.
Seasonal variation in the main tidal constituent from altimetry
Authors: Huess V. , Andersen O. B.
Published: February 2004

The existence of seasonal variations in the main tidal constituents has been known for a long time from coastal tide gauges. In this paper we extend the amount of observations from the relatively limited number of coastal tide gauge observations to also include the large amount of offshore information that have become available from altimetry. These observations are compared with results from a hydrodynamical model applied for the north‐west European shelf. The model clearly identifies the seasonal variation in the M2 constituent as a shallow water effect with a large part of the variation explained as a barotropic signal having high dependency on the meteorological field over the area.
Seasonal distributions of aeolian iron fluxes to the global ocean
Authors: Gao Y. , Kaufman Y. J. , Tanré D. , Kolber D. , Falkowski P. G.
Published: February 2004

Among the factors affecting the photosynthetic rate of marine phytoplankton, aeolian iron (Fe) fluxes appear to be critical in several large regions of the global ocean. Here we present an analysis of in situ aerosol iron data obtained from a wide variety of marine locations to quantify the seasonal Fe inputs to the global ocean. When extrapolated to the global ocean, our results indicate strong seasonal variations in aeolian Fe fluxes in different oceanic basins. The predominant fraction of the Fe inputs enters the oceans in the Northern Hemisphere, with the summer flux rates ca. twice those of winter. The high Fe fluxes in the Northern Hemisphere are concentrated in low and mid‐latitudes. With the promising new data from MODIS aboard the Terra satellite, the linkage between Fe fluxes and phytoplankton biomass and productivity may be soon further quantified.
The role of the Siberian high in northern hemisphere climate variability
Authors: Cohen Judah , Saito Kazuyuki , Entekhabi Dara
Published: February 2004

The dominant mode of sea level pressure (SLP) variability during the winter months in the Northern Hemisphere (NH) is characterized by a dipole with one anomaly center covering the Arctic with the opposite sign anomaly stretched across the mid‐latitudes. Associated with the SLP anomaly, is a surface temperature anomaly induced by the anomalous circulation. We will show that this anomaly pattern originates in the early fall, on a much more regional scale, in Siberia. As the season progresses this anomaly pattern propagates and amplifies to dominate much of the extratropical NH, making the Siberian high a dominant force in NH climate variability in winter. Also since the SLP and surface temperature anomalies originate in a region of maximum fall snow cover variability, we argue that snow cover partially forces the phase of winter variability and can potentially be used for the skillful prediction of winter climate.
Detection of water vapor variations driven by thermally‐induced local circulations using the Japanese Continuous GPS Array
Authors: Ohtani Ryu
Published: February 2004

I present the detailed variations of precipitable water vapor (PWV) for a summer day using the Japanese continuous Global Positioning System (GPS) array. Spatial and temporal PWV variations show good coherence with the development of thermally‐induced local circulations, which reflect the movement of water vapor over a spatial scale of a few tens of kilometers.
A Radiative Transfer Case Study for 3‐d cloud effects in the UV
Authors: Meerkötter Ralf , Degünther Markus
Published: February 2004

Satellite UV mapping is usually based on the independent pixel approximation (IPA) which neglects horizontal photon transport between adjacent columns. Horizontal inhomogeneity of cloud fields therefore causes uncertainties in the derived UV radiation fields. While these effects are small for large pixel satellites, the broken‐cloud errors increase as the pixel size decreases. By comparing results of 1‐d and 3‐d UV radiative transfer calculations for three selected cloud scenes that cover a rather broad range of cloud inhomogeneity the main 3‐d cloud effects on the atmospheric UV transmission are identified and quantified in their order of magnitude. With respect to the different spatial resolutions of satellite instruments it is further shown how 3‐d cloud effects average out with increasing spatial scale. It turns out that locally the IPA cause maximum uncertainties up to ±100% for a spatial resolution of about 1 × 1 km² (e.g., AVHRR), they are reduced to ±10% for a resolution of about 15 × 15 km² and below 5% for a resolution greater than 30 km (e.g., TOMS).
Inversion of GPS data for spatially variable slip‐rate on the San Andreas Fault near Parkfield, CA
Authors: Murray J. R. , Segall P. , Cervelli P. , Prescott W. , Svarc J.
Published: February 2004

We analyze GPS data collected from 1991–1998 at 35 sites near the Parkfield segment of the San Andreas Fault. Inverting the resultant site velocities for the distribution of interseismic slip‐rate on the San Andreas reveals an area of low slip‐rate on the fault extending from between Middle Mountain and Carr Hill to southeast of Gold Hill. This slip‐rate pattern is similar to that found by Harris and Segall [1987] using trilateration data collected between 1966 and 1984. We infer a deep slip‐rate (33 mm/yr) and depth of the transition between seismogenic and non‐seismogenic slip (14 km) that agree better with independent geologic evidence than those found in the 1987 study. In contrast to Harris and Segall [1987], we find no evidence of fault‐normal contraction.
Diagnosing the plasmapause with a network of closely spaced ground‐based magnetometers
Authors: Milling D. K. , Mann I. R. , Menk F. W.
Published: February 2004

Using cross‐phase analysis on data from the closely spaced magnetometers of the BEAR array, we have obtained meridional frequency‐latitude profiles of field line resonances (FLRs) from the inner plasmasphere, across the plasmapause and into the plasmatrough. The location of the plasmapause is indicated by the discontinuity in the frequency‐latitude profile and is confirmed by a Kp‐dependent model plasmapause position. We show that the cross‐phase response from stations separated by < 0.5 L is inhibited when the plasmapause is overhead. We are thus able to track the motion of the plasmapause polewards during the day by plotting the time development of the cross‐phase spectra as a function of latitude. In addition we observe anomalous frequency values obtained from more widely separated station pairs (> 1 L) spanning the plasmapause leading us to conclude that caution must be exercised when interpreting the cross‐phase response from pairs of stations at mid‐latitudes.
Physical and acoustic measurements on cohesionless sediments from the northwest Florida Sand Sheet
Authors: Brandes Horst G. , Silva Armand J. , Sadd Martin H.
Published: February 2004

The effects of grain size and density on compressional wave speed and attenuation are investigated for a clastic silica sand from a seabed study site south of Panama City, Florida, using an automated core logging device that allows for highly accurate, non‐destructive, fine‐scale measurements to be taken on unopened core sections. Measurements were conducted on relatively undisturbed cores obtained using a large‐diameter gravity corer, as well as on reconstituted sections containing sediment segregated into narrow grain size ranges. Findings indicate that whereas density is the primary physical sediment attribute controlling speed, attenuation at 500 kHz is primarily a function of grain size and grain structure. Sandy sediments, particularly those with narrow sorting, are susceptible to liquefaction, which can reduce attenuation dramatically.
The response of an ENSO Model to climate noise, weather noise and intraseasonal forcing
Authors: Roulston Mark S. , Neelin J. David
Published: February 2004

The response of an intermediate coupled model of the tropical Pacific to different forms of stochastic wind forcing is studied. An estimate of observed Pacific wind variance that is unrelated to Pacific sea surface temperature (SST) has a red spectrum, inconsistent with standard definitions of “weather noise”. The reddening is likely due to SST outside the basin; we propose a definition of “climate noise” for such reddened variance. Effects are compared for (i) red climate noise; (ii) the corresponding white weather noise estimate; (iii) intraseasonal and interannual components of the white noise (to test frequency response); and (iv) a noise product with extra power in the 30–60 day range. Power is not effectively channeled from subannual frequencies to the frequencies associated with ENSO in this model. This suggests that ENSO impacts of the Madden‐Julian oscillation are largely restricted to the low‐frequency tail rather than the 30–60 day spectral peak. Interannual climate noise originating outside the tropical Pacific appears important.
Cirrus horizontal inhomogeneity and OLR bias
Authors: Fu Qiang , Carlin B. , Mace G.
Published: February 2004

The outgoing longwave radiation (OLR) bias due to the neglect of cloud horizontal inhomogeneities has been examined in this study. It is argued that this OLR bias is most significant for semi‐transparent cirrus clouds that are located in the cold upper troposphere. Using two cirrus cases observed from cloud radar, it is found that the OLR biases due to the plane‐parallel homogeneous assumption are ∼14 W m−2. These biases are largely caused by the horizontal variation of cloud optical depth. It is also shown that in general the OLR biases are strongly dependent on the cloud height and mean and standard deviation of cloud optical depth. We have demonstrated that the gamma‐weighted radiative transfer scheme, which is efficient for GCM applications, can be used to account for the effect of cloud horizontal inhomogeneity on the infrared fluxes.
Breaking of small‐scale gravity wave and transition to turbulence observed in OH airglow
Authors: Yamada Y. , Fukunishi H. , Nakamura T. , Tsuda T.
Published: February 2004

We report on observations of small‐scale gravity wave breaking into turbulence around the mesopause height using an OH airglow CCD camera and a meteor radar performed on December 23, 1995 in Japan. The small‐scale gravity wave propagated against the background wind with a horizontal wavelength of ∼27 km, an apparent horizontal phase velocity of ∼7 ms−1, and an intrinsic period of ∼5.6 minutes. Wave breaking event began with an appearance of smaller‐scale structures, which were aligned parallel to the phase fronts of the breaking wave and advanced into more random, turbulence‐like features. The instability structures were present in the OH images for about 40 minutes.
Simulated Response of the Atmosphere‐Ocean System to deforestation in the Indonesian Archipelago
Authors: Delire Christine , Behling Pat , Coe Michael T. , Foley Jonathan A. , Jacob Robert , Kutzbach John , Liu Zhengyu , Vavrus Steve
Published: February 2004

The climatic effects of large‐scale deforestation in the Indonesian Archipelago are investigated using a fully coupled atmosphere‐ocean model— the Fast Ocean Atmosphere Model (FOAM). Extremely rapid rates of deforestation across the Archipelago motivate this study. We compare two simulations (one with fixed ocean temperatures, another where the ocean responds to changing atmospheric conditions), to investigate the potential for oceanic feedbacks on deforestation‐induced climate change. With fixed sea surface temperatures, evaporation decreases over land but increases over the surrounding oceans where the wind speeds increase. Regional deep convection is enhanced and precipitation increases over the islands. With an interactive ocean the initial decrease in evaporation over the deforested land reduces convergence and increases the easterlies in the Bay of Bengal. More intense equatorial upwelling cools the surface temperatures over that region and reduces ocean evaporation. Regional convection is less intense and precipitation drops by 9% over deforested land.
Particle‐in‐cell simulations of the lunar wake with high phase space resolution
Authors: Birch Paul C. , Chapman Sandra C.
Published: February 2004

The evolution of the lunar wake in simplified geometry can be simulated via a 1½D electromagnetic particle‐in‐cell code. By using a sufficient number of particles per cell, we are able, for the first time, to resolve the full phase space dynamics of both electrons and ions. This simulation begins immediately downstream of the moon, before the solar wind has infilled the wake region, then evolves in the solar wind rest frame. The electrons immediately begin to move into the void but are trapped by two potential wells, thus generating vortices in phase space on both sides of the wake, between which counter‐streaming electron beams interact. Ion beams are generated after the lighter electrons have moved into the void, creating a two‐stream distribution which mixes in phase space due to the potentials created by the electron two‐stream instability. Other structures are also evident. The simulations are consistent with both WIND observations and the results of earlier electrostatic simulations which focus only on the ion dynamics.
Sea level change from Topex‐Poseidon altimetry for 1993–1999 and possible warming of the southern oceans
Authors: Cabanes C. , Cazenave A. , Le Provost C.
Published: February 2004

In this study we investigate the contribution of individual oceanic regions to the global mean sea level change (mean trend and interannual variations) observed by the satellite Topex‐Poseidon from 1993 through 1999. This allows us to analyse sea level change in regions not primary influenced by short‐term climate fluctuations, in particular the 1997–1998 ENSO event. We report that the sea level in the southern oceans (here defined as the region between 60°S and 30°S) has been rising between January 1993 and December 1999 at a rate of 1.0±0.1 mm/yr and 1.7±0.1 mm/yr between December 1994 and April 1999. This rise is positively correlated with an increase of sea surface temperature and thus could reflect a warming of the southern oceans waters.
Will aerosol measurements from Terra and Aqua Polar Orbiting satellites represent the daily aerosol abundance and properties?
Authors: Kaufman Yoram J. , Holben Brent N. , Tanré Didier , Slutsker Ilya , Smirnov Alexander , Eck Thomas F.
Published: February 2004

The Terra and Aqua missions will help quantify aerosol radiative forcing of climate by providing innovative measurements of the aerosol daily spatial distribution and identifying dust, smoke and regional pollution. However, these measurements are acquired at specific times of the day. To what extent can such measurements represent the daily average aerosol forcing of climate? We answer this question using 7 years of data from the Aerosol Robotic Network (AERONET) of 50–70 global ground‐based instruments. AERONET measures the aerosol spectral optical thickness and the total precipitable water vapor every 15 minutes throughout the day. With a data set of 1/2 million measurements, AERONET demonstrates that Terra and Aqua aerosol measurements can represent the annual average value within 2% error. This excellent Terra representation of the daily average optical thickness is independent of the particle size or range of the optical thickness. This finding should facilitate ingest of satellite aerosol measurements in models that calculate radiative forcing and predict climate change.
Rupture history of September 30, 1999 intraplate earthquake of Oaxaca, Mexico (MW=7.5) from inversion of strong‐motion data
Authors: Hernandez B. , Shapiro N. M. , Singh S. K. , Pacheco J. F. , Cotton F. , Campillo M. , Iglesias A. , Cruz V. , Gómez J. M. , Alcántara L.
Published: February 2004

Near‐source strong motions are inverted to estimate the rupture history of intraslab, normal‐faulting September 30, 1999, Oaxaca, Mexico earthquake. Two focal mechanisms (Harvard and NEIC CMT solutions) are tested for the source geometry. The inversion with the NE dipping fault plane of the Harvard solution best matches the data (strike=295°, dip=50°, rake=−82°). We estimated the slip distribution on the fault and the associated rupture front propagation, as well as the rise time. The inversion results show that the rupture mainly propagated from ESE to WNW and slightly downdip, with an average rupture velocity of about 3 km/s. The rise time ranges between 1 and 2 s. The slip distribution on the fault is mainly concentrated in two interconnected patches with a maximum slip of 2.5 m located about 20 km and 40 km WNW of the hypocenter. Most of the slip is released at an average depth of 45 km. A smaller area with a maximum slip of 1.5 m is also observed close to the hypocenter. The total co‐seismic moment released is equal to 1.8 × 1020 Nm.
A regional study of shear wave splitting above the Cascadia Subduction Zone: Margin‐parallel crustal stress
Authors: Currie Claire A. , Cassidy John F. , Hyndman Roy D.
Published: February 2004

Recordings of local earthquakes from 16 three‐component broadband seismic stations in southwestern British Columbia, Washington, and northern Oregon are used to study regional variations of shear wave anisotropy in the North American plate above the subducting Juan de Fuca plate. There is evidence for shear wave splitting at all sites, with good agreement of fast polarization directions and travel time delays at adjacent stations. Most stations exhibit fast directions parallel to the strike of the margin, with anisotropy of 1–2%. These fast polarization directions are consistent with earthquake focal mechanisms and borehole stress studies, indicating that the observed anisotropy is likely due to crustal stresses (i.e., extensive dilatancy anisotropy theory). The margin‐parallel stresses may be due to oblique subduction of the Juan de Fuca plate. However, at the station closest to the coast (OZB), the fast direction shows a more margin‐normal orientation that may be associated with the proximity of the locked portion of the underlying subduction thrust fault.
Tsunamis within the Eastern Santa Barbara Channel
Authors: Borrero Jose C. , Dolan James F. , Synolakis Costas Emmanuel
Published: February 2004

Several locally generated tsunamis have been reported in Southern California during the past 200 years, yet the hazard from locally generated tsunamis has received considerably little attention. We consider here tsunamis generated by coseismic displacements on the Channel Islands Thrust (CIT) system, as well as waves generated by slope failures along the walls of the Santa Barbara Channel. We find that purely tectonic sources could generate regional tsunamis with ≈ 2mrunup, whereas combinations of tectonic sources and submarine mass movements could generate local runup as large as ≈ 15m.
A possible mechanism for in situ forcing of planetary waves in the summer extratropical mesosphere
Authors: Osprey Scott M. , Lawrence Bryan N.
Published: February 2004

An examination of zonal asymmetries in meridional momentum flux reaching the mesosphere is made using the Hines Doppler spread parameterization of gravity waves. As expected a general correspondence is seen between wave one wind in the stratosphere and wave one signals in gravity wave momentum flux leaving the stratosphere. However, a significant difference is the presence of wave one features in the gravity‐wave momentum flux at 56 km and ∼70°N during mid‐summer which contrast with minimal signals in stratospheric wave one wind. The prominence of this feature is accounted for by a significant wave one Brunt‐Väisälä feature at the tropopause amplifying a wave one signal in momentum flux which can then propagate to great heights. Such a feature could result in mesospheric planetary waves which are coupled to the tropopause forcing without intervening planetary wave signals in the stratosphere.
Effect of small‐scale atmospheric inhomogeneity on positioning accuracy with GPS
Authors: Bock Olivier , Tarniewicz Jérôme , Thom Christian , Pelon Jacques
Published: February 2004

Global Positioning System (GPS) measurements through a field of km‐size atmospheric boundary layer (ABL) inhomogeneities with a 10‐ppm index of refraction excess have been simulated and inverted. Biases of up to 1–2 cm in height, 1–5 mm in horizontal, and ∼5 mm in zenith tropospheric delay (ZTD) are found, in either static or dynamic atmospheres, using 24‐h solutions and estimating ZTD parameters. For 1‐h sessions the scatter can increase by a factor of up to 5. These biases are attributed to the inadequacy of standard mapping functions. The use of numerical weather prediction (NWP) models and additional sounding techniques is discussed as a means of improving mapping functions. Raman lidars are thought to offer the highest potential for this purpose and for external calibration of both hydrostatic and wet path delay.