bluuebunny/crossref_metadata_2025 huggingface dataset:
Mapping the northern portion of the Chelungpu fault, Taiwan by shallow reflection seismics
Authors: Wang Chien‐Ying , Li Chien‐Li , Yen Horng‐Yuan
Published: October 2002

The Chelungpu fault was activated by the 1999 Chi‐Chi earthquake (Mw = 7.6), Taiwan. This fault exhibited extraordinarily large surface ruptures (up to 9.8 m) as well as underground fault slippages (up to 12 m) during the earthquake. These large displacements were concentrated along the northern portion of the fault, 40 km north of the epicenter. To prepare data for the future drilling of deep wells in this area, many shallow seismic reflection surveys were conducted to investigate the sites. An approximate 3D structure of the fault surface can be deduced by this cost‐effective approach. Although the depth penetration may be limited (e.g., 3 km), the method still provides reliable information to study large ruptures, and to better plan future deep wells.
Effects of earth's spherical curvature and radial heterogeneity in dislocation studies—for a point dislocation
Authors: Sun Wenke , Okubo Shuhei
Published: October 2002

To the present, dislocation theories for a homogeneous half‐space are often used to calculate or interpret displacements and gravity changes caused by an earthquake or to inverse a seismic fault model. However, far‐field effects of spherical curvature and radial heterogeneity have to be considered. In this research, Okada [1985] and Sun et al. [1996] dislocation theories are used to calculate displacements caused by four independent dislocations in three earth models: a homogeneous half‐space, a homogeneous sphere, and a heterogeneous sphere. Effects of spherical curvature and radial heterogeneity are investigated through comparison of displacements. Results show that effects of both sphericity and stratification are very large. The stratified effect reaches a discrepancy of more than 25% everywhere on the surface of the earth, including the near field.
A sudden bottom‐water formation during the severe winter 2000–2001: The case of the East/Japan Sea
Authors: Kim Kyung‐Ryul , Kim Guebuem , Kim Kuh , Lobanov V. , Ponomarev V. , Salyuk A.
Published: October 2002

We observed a sudden initiation of bottom‐water formation in the East/Japan Sea associated with a severely cold winter in 2000–2001. An increase in dissolved oxygen concentration as well as decreases in temperature and nutrient concentrations for the bottom waters provides unequivocal evidence that cold, oxygen‐rich and nutrient‐poor surface waters were injected directly to the bottom. Since the conveyor‐belt in the East Sea has been undergoing dramatic change with a complete halt to bottom‐water formation since the mid‐1980s, this sudden episode of bottom‐water formation could easily be detected. Though the amount of bottom water formed was rather small, being only about 0.03% of the volume in the past time, the observation clearly demonstrates that the conveyor‐belt is directly connected to the weather system.
Non‐spherical aerosol retrieval method employing light scattering by spheroids
Authors: Dubovik O. , Holben B. N. , Lapyonok T. , Sinyuk A. , Mishchenko M. I. , Yang P. , Slutsker I.
Published: October 2002

Numerous studies indicate the need to account for particle non‐sphericity in modeling the optical properties of dustlike aerosols. The methods for simulating the scattering of light by various non‐spherical shapes have rapidly evolved over the last two decades. However, the majority of aerosol remote‐sensing retrievals still rely on the Mie theory because retrievals accounting for particle non‐sphericity are not as well defined methodologically and are demanding computationally. We propose a method for the retrieval of the optical properties of non‐spherical aerosol based on the model of a shape mixture of randomly oriented polydisperse spheroids. This method is applied to angular and spectral radiation measurements from the Aerosol Robotic Network (AERONET) in locations influenced by desert dust. Comparisons with Mie‐based retrievals show a significant improvement in dust‐particle phase functions, size distributions, and refractive indices.
Oxidative precipitation of groundwater‐derived ferrous iron in the subterranean estuary of a coastal bay
Authors: Charette Matthew A. , Sholkovitz Edward R.
Published: October 2002

Sediment cores from the intertidal zone of Waquoit Bay (Cape Cod, Massachusetts) yielded iron oxide‐coated sands in the subterranean estuary, which underlies the head of the bay. The oxides were dark red, yellow and orange colors and are formed by the oxidation of ferrous iron‐rich groundwater near the groundwater‐seawater interface. Within these iron oxide‐rich sediments, the concentration of the combined amorphous and crystalline forms of iron oxides ranged between 2500 and 4100 ppm of Fe. These concentrations were 4–6 times greater than the surface sands, and 10–15 times more Fe rich than sands collected from an off‐site location. The precipitation of iron oxides in subterranean estuaries could act as a geochemical barrier by retaining and accumulating certain dissolved chemical species carried to the coast by groundwater. Indeed, phosphorus concentrations in the iron oxide‐rich sands of Waquoit Bay were 5–7 times greater than the overlying surface sands.
Factors controlling the location of the Bow Shock at Mars
Authors: Vignes D. , Acuña M. H. , Connerney J. E. P. , Crider D. H. , Rème H. , Mazelle C.
Published: October 2002

During the first year of the Mars Global Surveyor (MGS) mission, 553 shock crossings have been identified from a total of 363 orbits. The shape of the shock has been determined by examining the MGS spacecraft Magnetometer/Electron Reflectometer (MAG/ER) data. The location of the shock was found highly variable. The present study shows that the high crustal magnetic sources, found in the southern hemisphere, do not seem responsible for the Bow Shock (BS) variability. The present study shows that contrary to many expectations there is no obvious strong one to one correlation between the location of the highest crustal sources and the variability of the shock position. On the other hand, the shock appears farthest from Mars in the hemisphere of locally upward interplanetary electric field consistent with the idea that mass loading play a role in controlling the BS location, which confirms previous results.
Observation of a large amplitude wave and inversion layer leading to convective instability in the mesopause region over Fort Collins, CO (41°N, 105°W)
Authors: Williams Bifford P. , White M. A. , Krueger D. A. , She C. Y.
Published: October 2002

Sodium resonance lidar observations on the night of Nov 3, 1997 UT recorded a temperature inversion with 80 K amplitude moving downward from 90 to 83 km with the maximum temperatures exceeding 280 K. These are the highest temperatures and largest inversion layer observed in 10 years over Fort Collins, Colorado. The inversion can be decomposed into a 50 K peak‐to‐peak amplitude oscillation with an apparent 8‐hr period and 25 km vertical wavelength plus a residual 30 K inversion layer. The temperature gradient above this maximum is near‐adiabatic from 88–100 km for 4 hours with multiple super‐adiabatic layers several km in depth. Streamlines derived from the sodium mixing ratio and the potential temperature both indicate a 10 km upward movement in the adiabatic region. Presumably, a large‐amplitude upward‐propagating wave saturated when it reached the inversion layer just below the mesopause and broke, leading to convective instabilities with large vertical and temporal scales.
Implications of the recent fluctuations in the growth rate of tropospheric methane
Authors: Simpson Isobel J. , Chen Tai‐Yih , Blake Donald R. , Rowland F. Sherwood
Published: October 2002

Global measurements show that the mixing ratio of tropospheric methane (CH4) increased by 1.1% (19.5 ± 1.7 ppbv) over the five‐year period 1996–2000, with striking fluctuations in its annual growth rate. Whereas the global CH4 growth rate reached 15.9 ± 0.7 ppbv yr−1 in 1998, the growth rate was −2.1 ± 0.8 ppbv yr−1 in 2000. This is the first time in our 23‐year global monitoring program that we have measured a negative annual CH4 growth rate. The CH4 growth rate fluctuates in an unpredictable fashion, and we reemphasize that global CH4 concentrations cannot be extrapolated into the future based on past trends. As a result, we suggest that the slowing of the CH4 growth rate during much of the 1980s and 1990s cannot be used to imply that CH4 will no longer be of concern in greenhouse gas studies during this century.
A quantitative theory for terrestrial foreshock radio emissions
Authors: Kuncic Z. , Cairns I. H. , Knock S. , Robinson P. A.
Published: October 2002

We present the first quantitative theoretical results for the spatial distribution and flux levels of fundamental (fp) and second harmonic (2fp) plasma radiation generated in Earth's foreshock by beam‐driven Langmuir waves. The theory predicts that both the fp and 2fp source regions typically extend over several hundred Earth radii (RE) along the tangent magnetic field line. In the direction perpendicular to the magnetic tangent, however, the source regions are more localized, with the peak emission confined to ≲10RE for 2fp radiation and ≲1RE for fp radiation. The flux levels predicted by our model are in close agreement with the levels measured in situ by various spacecraft, with typical values ∼10−14W m−2 for 2fp radiation. The fp flux densities are typically 2–3 orders of magnitude lower.
Kinetics of HO2 + HO2 → H2O2 + O2: Implications for Stratospheric H2O2
Authors: Christensen L. E. , Okumura M. , Sander S. P. , Salawitch R. J. , Toon G. C. , Sen B. , Blavier J.‐F. , Jucks K. W.
Published: October 2002

The reaction HO2 + HO2 → H2O2 + O2(1) has been studied at 100 Torr and 222 K to 295 K. Experiments employing photolysis of Cl2/CH3OH/O2/N2 and F2/H2/O2/N2 gas mixtures to produce HO2 confirmed that methanol enhanced the observed reaction rate. At 100 Torr, zero methanol, k1 = (8.8 ± 0.9) 10−13 × exp[(210 ± 26)/T] cm3 molecule−1 s−1 (2σ uncertainties), which agrees with current recommendations at 295 K but is nearly 2 times slower at 231 K. The general expression for k1, which includes the dependence on bath gas density, is k1 = (1.5 ± 0.2) × 10−12 × exp[(19 ± 31)/T] + 1.7 × 10−33 × [M] × exp[1000/T], where the second term is taken from the JPL00‐3 recommendation. The revised rate largely accounts for a discrepancy between modeled and measured [H2O2] in the lower to middle stratosphere.
Crustal structure and upper mantle stratigraphy of the Arabian shield
Authors: Kumar M. Ravi , Ramesh D. S. , Saul Joachim , Sarkar Dipankar , Kind Rainer
Published: October 2002

Analysis of receiver functions from an eight‐station network on the Saudi Arabian shield indicates that the Moho depths vary between 35–38 km. The crust appears to be rather felsic in nature as evidenced by Poisson's ratios of 0.25–0.27. A prominent negative phase following the Moho conversion is suggestive of a zone of velocity inversion. Indication of mantle stratification is observed beneath the coastal region of Arabia, by way of an additional upper mantle discontinuity at about 240 km. The conversions from the 410 and 660‐km discontinuities are significantly delayed, suggesting a slow and hot upper mantle.
Network allometry
Authors: Maritan A. , Rigon R. , Banavar J. R. , Rinaldo A.
Published: October 2002

We derive a new allometric scaling law for loopless networks, which we confirm with studies on rivers, exact network results and computer simulations. We provide evidence suggesting that ensemble averaging of the allometric property (where individual realizations are different networks) leads to results in excellent accord with the known limit scaling of efficient and compact networks with remarkably little scatter. Our results complement recent work suggesting that network‐related allometric scaling in living organisms is regulated by metabolic supply‐demand balance, because we show that scaling features are robust to geometrical fluctuations of network properties.
IMF‐driven overshielding electric field and the origin of the plasmaspheric shoulder of May 24, 2000
Authors: Goldstein J. , Spiro R. W. , Reiff P. H. , Wolf R. A. , Sandel B. R. , Freeman J. W. , Lambour R. L.
Published: October 2002

Between the hours of 6–10 UT on May 24, 2000, the IMAGE extreme ultraviolet (EUV) instrument observed a shoulder‐shaped bulge in the morning sector plasmapause [Burch et al., 2001a, 2001b]. Simulation results of the data‐driven Magnetospheric Specification Model (MSM) have reproduced the formation (during 4:00–5:15 UT) and subsequent evolution of the shoulder. In the model, the shoulder is created by a dusk‐to‐dawn overshielding electric field, triggered by two sudden, strong northward (Nwd) turnings of the IMF. Overshielding causes antisunward flow of pre‐dawn plasma, producing an asymmetric bulge that rotates eastward.
Iron Boltzmann lidar temperature and density observations from Arecibo ‐ An initial comparison with other techniques
Authors: Raizada Shikha , Tepley Craig A.
Published: October 2002

We introduce the first measurements of upper atmospheric temperature made from the Arecibo Observatory using the iron Boltzmann lidar technique. We use a single laser transmitter that can flip between two emissions every other pulse, which is suitable to observe the two iron transitions within the same region of space. Comparisons are made with airglow measurements and the MSIS‐90 model to estimate temperature, and with incoherent scatter radar observations to associate the structure of electron concentration with enhancements observed in the concentration of neutral iron. We find good agreement between lidar and airglow derived temperatures near the mesopause, while the model tends to underestimate the thermal depth of the mesopause at Arecibo compared with observations. In addition, simultaneous temperatures measured via lidar and airglow may help to clarify the heights where the airglow emissions occur.
Distribution of Io's volcanoes: Possible influence on spin axis
Authors: Stoddard Paul R. , Jurdy Donna M.
Published: October 2002

We examine the potential effect of volcano distribution on the orientation of Io's spin axis. Volcanoes dominate Io's surface and the massive outpourings documented in short intervals could cause instability in Io's rotation and a corresponding reorientation of its spin axis. Currently, the volcanoes and mountains exhibit a complementary distribution, with the maximum principal axis for the set of 351 volcanoes close to the position of the rotation axis. In addition, a delicate balance results from the near equivalence of the magnitudes of the maximum and intermediate eigenvalues. Assuming an otherwise homogeneous body, a changing mass distribution on its surface could control the location of the spin axis. In our models, changing the location of as few as three volcanoes is sufficient to cause dramatic shifts of the principal axis positions, and hence the spin axis orientation. This result, although somewhat diminished, still prevails even when a strong influence of Io's tidal bulge is included in the model.
Large NAT particle formation by mother clouds: Analysis of SOLVE/THESEO‐2000 observations
Authors: Fueglistaler S. , Luo B. P. , Buss S. , Wernli H. , Voigt C. , Müller M. , Neuber R. , Hostetler C. A. , Poole L. R. , Flentje H. , Fahey D. W. , Northway M. J. , Peter Th.
Published: October 2002

During the SOLVE/THESEO‐2000 Arctic stratospheric campaign in the winter 1999/2000 widespread occurrences of very large HNO3‐containing particles, probably composed of nitric acid trihydrate (NAT), were observed in situ by instruments on board the ER‐2 stratospheric research aircraft. These large NAT particles were found with low number densities (n ≈ 10−4 cm−3) in vast regions, in air generally supersaturated with respect to NAT. Within the same campaign other instruments have performed airborne and ground‐based measurements of polar stratospheric clouds (PSCs), often showing the existence of type 1a and type 1a‐enh clouds. Such PSCs often occur on the mesoscale with particle number densities n ≳ 10−2cm−3 and are also most likely composed of NAT. We use forward trajectories for the path of NAT particles, which are advected by winds based on ECMWF analyses and sediment due to gravity, to show that high number density NAT PSCs (mother clouds) could give rise to low number density NAT particle populations several days downstream.
Interannual variations of the diurnal tide in the mesosphere induced by a zonal‐mean wind oscillation in the tropics
Authors: McLandress Charles
Published: October 2002

An interannual variation of the propagating diurnal tide in the mesosphere is simulated using a middle atmosphere general circulation model (GCM) and interpreted using a linear mechanistic tidal model. The GCM results show that the semiannual amplitude variation of the tide, which is characterized by strong tides near equinox and weak tides near solstice, exhibits a strong interannual variation in the presence of a long‐period mean wind oscillation in the tropics. Changes in the latitudinal gradients of the mean winds in the subtropical mesosphere are shown to be primarily responsible for this behavior. It is suggested that this shear mechanism may explain the possible link between the quasi‐biennial oscillation in the zonal‐mean zonal winds in the stratosphere and the amplitude of the diurnal tide in the lower thermosphere that is seen in observations.
Climate reconstruction using ‘Pseudoproxies’
Authors: Mann Michael E. , Rutherford Scott
Published: October 2002

We test the performance of proxy‐based climate field reconstruction methods using sets of synthetic proxy climate indicators. ‘Pseudoproxies’ are constructed through the degradation of instrumental surface temperature data by additive noise with variable statistical properties. Experiments are performed using pseudoproxy networks of varying spatial and seasonal representation and with varying noise attributes. Implications for sampling strategies for improved paleoclimate reconstructions are discussed.
Solar cycle modulation of the North Atlantic Oscillation: Implication in the spatial structure of the NAO
Authors: Kodera Kunihiko
Published: October 2002

The spatial extent of the North Atlantic Oscillation (NAO) is investigated. The results suggest that the spatial structure of the NAO differs significantly according to the phase of the solar cycle. During the solar maximum phases, the NAO has a hemispherical structure extending into the stratosphere, which is similar to the Arctic Oscillation (AO) except for the Pacific sector. However, during the minimum phase, the NAO is confined to the eastern Atlantic sector in the troposphere. Whether or not the NAO is modulated by the solar cycle, these results may shed new light on the controversy of the physical reality of the two modes of variability, the NAO and the AO.
Ocean response to wind sheltering in the Southern California Bight
Authors: Caldeira R. M. A. , Marchesiello P.
Published: October 2002

A particularly warm surface oceanic wake persisted during the period 6–16 June 1999 in the south‐eastern part of Santa Catalina Island in the Southern California Bight. From satellite images, regional atmospheric model results and hydrographic measurements around Catalina Island, a strong correlation appears between observed sea surface temperature, wind‐stress and surface stratification. It is suggested that the warm island wake was probably due to lower turbulent mixing rates associated with wind sheltering effect. We argue that the sheltering effect may also account for a portion of the relatively warm sea surface temperature characteristic of the whole Bight, opposing previous arguments that temperature evolution of the surface ocean in this region is primarily driven by lateral advective fluxes.
Biophysical effects of a decadal shift in summer wind direction over the Laurentian Great Lakes
Authors: Waples James T. , Klump J. Val
Published: October 2002

Analysis of summer surface wind fields over the Laurentian Great Lakes from 1980 to 1999 show a statistically significant shift in wind direction beginning around 1990. Directional changes in the average wind field over the Great Lakes basin are consistent with a southward migration of the dominant summer storm track. In Green Bay (NW Lake Michigan), we show that the new wind field has most likely resulted in a decrease in water mass exchange with Lake Michigan leading to a decrease in bottom water hypoxia, warmer bottom water temperatures and an increase in benthic microbial metabolism.
Real time GPS data processing for regional atmospheric delay derivation
Authors: Jarlemark Per O. J. , Johansson Jan M. , Stoew Borys , Elgered Gunnar
Published: October 2002

We have developed a GPS data processing software and demonstrate that by using receivers in an area of approximately 800 × 400 km we can produce estimates of the atmospheric zenith total delay (ZTD) with a latency of a few seconds. It is based on a Kalman filter which simultaneously estimates clock offsets and satellite coordinates. The ZTD quality is typically 15 mm in terms of rms difference to post‐processed ZTD time series. This level of uncertainty is useful in many navigation applications and if an additional reduction in the uncertainty can be obtained the usefulness for short term weather forecasting could be significant.
Evidence for a peculiar style of ground deformation inferred at Vesuvius volcano
Authors: Lanari R. , De Natale G. , Berardino P. , Sansosti E. , Ricciardi G. P. , Borgstrom S. , Capuano P. , Pingue F. , Troise C.
Published: October 2002

We present results obtained via an innovative spaceborne SAR interferometry algorithm showing that the Somma‐Vesuvius volcanic complex, despite of its quiescent stage, is subject to a particular deformation process. This is characterized by a rather continuous subsidence, revealed by ERS satellite data and levelling surveys, between 1992 and 2000. These deformations are mainly localized in two zones involving the Vesuvius cone and a narrow annular area that, although not fully continuously, extends around the base of the Somma edifice. We propose an interpretation of subsidence at both sites involving joint effects of gravitational sliding and extensional tectonic stress occurring at the contact between different lithological units. Some simple elastic models show how such localized subsidence can be generated. These results shed new light on the Vesuvius dynamics and, more generally, on the link between gravitational effects of volcano loading and seismic‐deformative processes, which is a subject of intense scientific debate.
A whirling ecosystem in the equatorial Atlantic
Authors: Menkes Christophe E. , Kennan Sean C. , Flament Pierre , Dandonneau Yves , Masson Sébastien , Biessy Benjamin , Marchal Emile , Eldin Gérard , Grelet Jacques , Montel Yves , Morlière Alain , Lebourges‐Dhaussy Anne , Moulin Cyril , Champalbert Gisèle , Herbland Alain
Published: October 2002

The equatorial Pacific and Atlantic oceans exhibit remarkable meridional undulations in temperature and chlorophyll fronts visible from space over thousands of kilometers and often referred to as tropical instability waves. Here, we present new observations of an ecosystem ranging through three trophic levels: phytoplankton, zooplankton and small pelagic fish whirling within a tropical vortex of the Atlantic ocean and associated with such undulations. Cold, nutrient and biologically rich equatorial waters are advected northward and downward to form sharp fronts visible in all tracers and trophic levels. The equatorward recirculation experiences upwelling at depth, with the pycnocline and ecosystem progressively moving toward the surface to reconnect with the equatorial water mass. The observations thus indicate that it is a fully three‐dimensional circulation that dominates the distribution of physical and biological tracers in the presence of tropical instabilities and maintains the cusp‐like shapes of temperature and chlorophyll observed from space.
Validation of reanalysis upper‐level winds in the Arctic with independent rawinsonde data
Authors: Francis Jennifer A.
Published: October 2002

Reanalysis products from meteorological forecast centers perform well in areas where conventional data are dense, but the realism of their fields in data‐sparse regions, such as the Arctic Ocean, is less certain. Upper‐level winds from two reanalysis data sets, the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) and the ECMWF (European Center for Medium Range Weather Forecasting) Reanalyses are evaluated in this study. Rawinsonde data from two Arctic field programs that were not assimilated by the models are compared to reanalysis wind products for five layers between 1000 and 300 hPa. Both reanalysis products exhibit large biases and are significantly too westerly and too northerly. Total wind speeds are too strong by 25 to 65% relative to rawinsonde values. Root‐mean‐square errors in u‐ and v‐component winds are substantially larger than the mean values. Possible sources and ramifications of these discrepancies are discussed.
Evidence for a ‘Medieval Warm Period’ in a 1,100 year tree‐ring reconstruction of past austral summer temperatures in New Zealand
Authors: Cook Edward R. , Palmer Jonathan G. , D'Arrigo Rosanne D.
Published: October 2002

The occurrence of the Medieval Warm Period (MWP) in the Southern Hemisphere is uncertain because of the paucity of well‐dated, high‐resolution paleo‐temperature records covering the past 1,000 years. We describe a new tree‐ring reconstruction of Austral summer temperatures from the South Island of New Zealand, covering the past 1,100 years. This record is the longest yet produced for New Zealand and shows clear evidence for persistent above‐average temperatures within the interval commonly assigned to the MWP. Comparisons with selected temperature proxies from the Northern and Southern Hemispheres confirm that the MWP was highly variable in time and space. Regardless, the New Zealand temperature reconstruction supports the global occurrence of the MWP.
Multiple auroral brightenings and associated Pi 2 pulsations
Authors: Shiokawa K. , Yumoto K. , Olson J. V.
Published: October 2002

All‐sky auroral data at Kotzebue (KOT, 64.4° MLAT), Alaska, and magnetic field data from both high‐ and low‐latitude stations are used to demonstrate the relation between multiple auroral brightenings and Pi 2 magnetic pulsations during an isolated substorm. At least five Pi 2 wave packets are identified in the magnetic field data around the end of the growth phase. Auroral luminosity variations do not show oscillations in the Pi 2 frequency range, though each Pi 2 wave packet has good correspondence with each small‐scale auroral brightening and poleward motion. This fact may contradict the idea of high‐latitude Pi 2 generation by oscillations of substorm field‐aligned currents. We discuss possible reasons of this discrepancy from localization of the Pi 2 current system and low‐energy electrons as the current carrier.
Antarctic circumpolar wave impact on marine biology: A natural laboratory for climate change study
Authors: Le Quéré Corinne , Bopp Laurent , Tegen Ina
Published: October 2002

We use the observed variations in ocean surface chlorophyll, temperature and height caused by the Antarctic Circumpolar Wave (ACW) as a natural laboratory to determine how marine biology responds to changes in ocean stratification in the Southern Ocean. Interannual variations of surface chlorophyll (±5%) observed by SeaWiFS satellite during 1997–2001 vary in phase over the entire Southern Ocean in spite of large east‐west dipoles in ocean dynamics. We suggest that this behavior is due to the regional predominance of light versus nutrient limitation over the most productive regions of the Southern Ocean.
Tasman leakage: A new route in the global ocean conveyor belt
Authors: Speich Sabrina , Blanke Bruno , de Vries Pedro , Drijfhout Sybren , Döös Kristofer , Ganachaud Alexandre , Marsh Robert
Published: October 2002

The existence of a new route that draws relatively cold waters from the Pacific Ocean to the North Atlantic via the Tasman outflow is presented. The new route materialises with comparable magnitude and characteristics in three independent numerical realisations of the global ocean circulation. Its realism is supported by hydrographic data interpolated via an inverse model. The “Tasman leakage” constitutes a sizeable component of the upper branch of the global conveyor belt and represents an extension to the prevailing views that hitherto emphasised the routes via the Drake Passage and the Indonesian Throughflow [Gordon, 1986].
Finite size scaling in the solar wind magnetic field energy density as seen by WIND
Authors: Hnat B. , Chapman S. C. , Rowlands G. , Watkins N. W. , Farrell W. M.
Published: October 2002

Statistical properties of the interplanetary magnetic field fluctuations can provide an important insight into the solar wind turbulent cascade. Recently, analysis of the Probability Density Functions (PDF) of the velocity and magnetic field fluctuations has shown that these exhibit non‐Gaussian properties on small time scales while large scale features appear to be uncorrelated. Here we apply the finite size scaling technique to explore the scaling of the magnetic field energy density fluctuations as seen by WIND. We find a single scaling sufficient to collapse the curves over the entire investigated range. The rescaled PDF follow a non Gaussian distribution with asymptotic behavior well described by the Gamma distribution arising from a finite range Lévy walk. Such mono scaling suggests that a Fokker‐Planck approach can be applied to study the PDF dynamics. These results strongly suggest the existence of a common, nonlinear process on the time scale up to 26 hours.
Towards 3‐D fabric in the continental lithosphere and asthenosphere: The Tien Shan
Authors: Vinnik Lev , Peregoudov Dmitry , Makeyeva Larissa , Oreshin Serge , Roecker Steve
Published: October 2002

As shown by previous observations of shear wave splitting of the SKS phase, the fast direction of azimuthal anisotropy beneath the Tien Shan tends to be aligned with the strike of the belt. This direction implies that the anisotropy is related to the current orogenesis. Now we describe an attempt to constrain the distribution of the anisotropy with depth by combining observations of SKS and P receiver functions. The data are inverted for the parameters of anisotropy with the aid of a genetic algorithm. The results of the joint inversion suggest that the actual distribution of anisotropy with depth can be more complicated than usually thought. The deformed mantle layer can be a few hundred kilometres thick. In the most reliable models fast direction of anisotropy in the shallow mantle is significantly different from that inferred from the observations of SKS. At some stations the data require anisotropy in the crust.
A model study of ocean circulation beneath Filchner‐Ronne Ice Shelf, Antarctica: Implications for bottom water formation
Authors: Jenkins Adrian , Holland David M.
Published: October 2002

An isopycnic coordinate ocean circulation model has been applied to the southern Weddell Sea, including the cavity beneath Filchner‐Ronne Ice Shelf, with the aim of investigating the buoyancy‐forced circulation on the continental shelf. Buoyancy forcing is associated with both the annual growth and decay of sea ice and the interaction between ice shelf and ocean. In the model a generally anti‐cyclonic circulation develops beneath the ice shelf, so that new shelf waters entering the cavity in the west emerge colder and fresher in the east. The outflow contributes to a dense current that spills off the continental shelf and descends the slope. Oceanographic observations from the region are consistent with this picture and highlight the overflow as a major source of Weddell Sea Bottom Water.
Impact of non‐LTE processes on middle atmospheric water vapor retrievals from simulated measurements of 6.8 μm Earth limb emission
Authors: Mertens Christopher J. , Mlynczak Martin G. , Lopez‐Puertas Manuel , Remsberg Ellis E.
Published: October 2002

We present an efficient and accurate algorithm for the retrieval of water vapor (H2O) volume mixing ratio (vmr) in the middle atmosphere from satellite measurements of 6.8 μm Earth limb emission, which rigorously includes non‐local thermodynamic equilibrium (non‐LTE) processes. A number of retrieval studies have been conducted with this algorithm leading to three major conclusions about the retrieval of H2O in the middle atmosphere: (1) satellite measurements of 6.3 μm limb emission must be made to high altitudes (85–90 km), where the few optically thick H2O absorption lines become optically thin, in order to prevent large errors in retrieved stratospheric and mesospheric H2O vmr; (2) the impact of non‐LTE on nighttime H2O retrievals is greater than previously thought; (3) the enhancements in the daytime H2O channel radiances of the NIMBUS 7 LIMS experiment may be entirely due to non‐LTE emission from the H2O 6.3 μm bands.
Is low Rayleigh number convection possible in the Earth's core?
Authors: Busse F. H.
Published: October 2002

A simple model based on the rotating cylindrical annulus configuration is presented which demonstrates that two different sources of buoyancy one of which is characterized by a very low diffusivity can interact such that the latter balances the non‐geostrophic part of the Coriolis force. It is suggested that the concentration of light elements in the Earth's core could play this role thereby facilitating immensely convection driven by thermal buoyancy.
Global structure of asteroid 433 Eros
Authors: Thomas P. C. , Prockter L. , Robinson M. , Joseph J. , Veverka J.
Published: October 2002

Models of asteroid formation and evolution suggest a variety of internal structures, ranging from gravitationally bound accumulations of debris to fully rigid monolithic bodies. The NEAR Shoemaker spacecraft has provided detailed imaging and gravity data relevant to the characteristics of structural features and global mass properties. A long ridge, coplanar with a degraded trough/ridge system, and an approximately parallel surface facet suggest exploitation of a nearly global fabric by both compressive and extensional failure at significantly different times.
The relationship between the SOI and extended tropical precipitation in simulations of future climate change
Authors: Doherty Ruth , Hulme Mike
Published: October 2002

The Southern Oscillation Index (SOI), its relationship with precipitation, and how greenhouse gas‐induced changes in climate may modify these relationships has been examined in 12 coupled atmosphere‐ocean Global Climate Model (GCM) experiments. The model SOI series predominantly show a tendency towards more positive (La Niña‐like) SOI values as climate warms, but opposing trends with regard to changes in its interannual variability. EOF analyses of the dominant mode of precipitation reveals that most models display the main observed features of tropical precipitation related to ENSO. Only modest changes in the modelled EOF1 coefficient fields between the simulated periods 1900–1949 and 2050–2099 are found. The model EOF1 amplitude series, in general, correlate highly with the model SOI series for the historic 1900–1949 period. For the future 2050–2099 period, however, this correlation decreases in a number of the simulations, due either to a shift in the centres of ENSO action or to an overall weaker SOI signal.
Comment on “Return stroke transmission line model for stroke speed near and equal that of light’ by R. Thottappillil, J. Schoene, and M. A. Uman
Authors: Kordi B. , Moini R. , Rakov V. A.
Published: October 2002

Electric fields on the ground 500 m, 5 km, and 50 km from the lightning channel base computed using the transmission line (TL) and antenna theory (AT) return‐stroke models for a typical subsequent stroke current at the channel base and a return‐stroke speed equal to the speed of light (v = c) are compared. The AT model gives a total electric field peak that is about 10% lower than the field peak predicted by the TL model. Optical measurements of the return‐stroke speed within the bottom 100 m of the lightning channel are reviewed and found to be not supporting the assumption of v = c.
Interpretation of cirrus cloud polarization measurements from radiative transfer theory
Authors: Liou K. N. , Takano Y.
Published: October 2002

A theoretical framework has been developed for the computation of polarized radiative transfer involving ice crystal clouds to interpret the polarization pattern observed from space. Based on the limited available observations in near infrared window wavelengths, we demonstrate that the reflected linear or full polarization from sunlight can be employed to discriminate between spherical water droplets (water clouds) and nonspherical ice crystals (ice clouds) in the direction of rainbow angles, about 140° from the sun. In the case of ice clouds, we show that information regarding the ice crystal shape and orientation can be inferred from reflected polarization patterns based on a comprehensive theoretical interpretation.
Precise measurement of changes in ice‐shelf thickness by phase‐sensitive radar to determine basal melt rates
Authors: Corr H. F. J. , Jenkins A. , Nicholls K. W. , Doake C. S. M.
Published: October 2002

We describe a novel technique for measuring the basal melt rate at a point on an ice shelf. The method uses a phase‐sensitive radar to observe the change in thickness of the ice column between an upper reference horizon and the ice shelf base. The observed thickness change is a combination of basal melting, horizontal ice divergence and firn compaction. The latter two components are determined independently by the repeat survey of surface markers and from estimates of surface accumulation rate and density at the depth of the reference horizon. The technique has been applied at a site on George VI Ice Shelf, Antarctica, where a melt rate of 2.78 ± 0.08 m yr−1 was observed over a twelve‐day period. Our technique is applicable to almost any ice shelf or floating glacier tongue, and its high precision over short time intervals will permit the measurement of seasonal variations in melt rate.
Detecting climate change at a regional scale: the case of France
Authors: Spagnoli B. , Planton S. , Déqué M. , Mestre O. , Moisselin J.‐M.
Published: October 2002

An optimal detection method, already used for global climate change detection, is applied to regional anthropogenic climate change detection, in the particular case of France. This case was chosen for the availability of high quality, statistically homogenized near‐surface temperature observations on one hand, and high‐resolution climate simulations over this region on the other hand. The detection is conducted on centered patterns, in order to only focus on pattern similarities between observations and model predictions. Detection is successful for 30‐year trends of summer minimal daily temperatures at a 90% confidence level, while it failed on summer maximal daily and winter temperatures. This partial success is very encouraging as it shows for the first time the detection of a climate change signal at the regional scale which resembles the one computed by a regional climate model.
Can current climate model forcings explain the spatial and temporal signatures of decadal OLR variations?
Authors: Allan Richard P. , Slingo A.
Published: October 2002

Top of atmosphere broadband radiative fluxes derived from satellite measurements exhibit surprisingly large decadal variability in the tropics which appears to be related to changes in cloudiness. Climate models fail to reproduce these changes, even when all of the currently known climate forcing agents are prescribed. The interannual variability and spatial signal of the observed changes are analysed and compared to various configurations of the Hadley Centre climate model. Applying EOF analysis to the spatial patterns of the variability shows that these are dominated by El Niño in both the satellite data and the model. However, the second EOF reveals the pattern due to the observed decadal‐scale variation in outgoing longwave radiation (OLR), but this is not captured by the climate model. This suggests that either the model lacks some internal physical process or some additional external forcing that is responsible for the observed changes in OLR.
Power‐laws and snow avalanches
Authors: Birkeland K. W. , Landry C. C.
Published: October 2002

This paper presents evidence of frequency‐size power‐laws in several groups of snow avalanche paths. Other natural hazards, such as earthquakes and forest fires, exhibit similar power‐law relationships. In addition, an analysis of the response of one group of snow avalanche paths to storms through time demonstrates a power‐law between the response of the system and the binned frequency of those responses. Our results, as well as our experience with these complex, non‐linear systems, are consistent with self‐organized criticality. The practical implication of this work is that the frequency‐size relationship for small and medium sized avalanches may be useful for quantifying the risk of large snow avalanches within a group of avalanche paths.
The influence of interior mantle temperature on the structure of plumes: Heads for Venus, Tails for the Earth
Authors: Jellinek A. Mark , Lenardic Adrian , Manga Michael
Published: October 2002

To form mantle plumes with large heads and narrow trailing conduits requires large (>102) viscosity variations within the hot thermal boundary layer at the plume source. However, new and published data from laboratory experiments show that if a layer of fluid with a temperature‐dependent viscosity is heated from below and cooled from above, convection occurs beneath a stagnant lid, and the interior fluid temperature remains close to that of the hot boundary. Consequently, the viscosity reduction across the hot thermal boundary layer is always <10 and upwellings take the form of discrete plume heads (thermals). Subduction of the stagnant layer (equivalent to recycling lithospheric plates on the Earth) will cool the interior of the mantle, thus increasing the viscosity ratio. Hence, the existence of Earth‐like mantle plumes may be a consequence of plate tectonics. An absence of plate tectonics on Venus may lead to upwellings composed of thermals, the surface expression of which are coronae, as well as a smaller core heat flux than on Earth.
Characteristic small‐earthquake sequence off Sanriku, northeastern Honshu, Japan
Authors: Matsuzawa Toru , Igarashi Toshihiro , Hasegawa Akira
Published: October 2002

We found eight similar earthquakes of M4.8 regularly occurring from 1957 to 1995 on the plate boundary off Sanriku, northeastern Japan. The mean recurrence interval of the events is 5.35 years and its standard deviation is only 0.53 years. These events have the same focal mechanisms of low‐angle thrust fault type and their source sizes are estimated to be around 1 km. The slip of each event is comparable to the cumulative amount of relative plate motion in the inter‐seismic period. Thus, these events are probably caused by repeating slip at a small but strong asperity surrounded by creeping zone on the plate boundary. The next event was expected to occur by the end of November 2001 with 99% probability and actually M4.7 event occurred on November 13, 2001.
Evidence for component merging near the subsolar magnetopause: Geotail observations
Authors: Kim K.‐H. , Lin N. , Cattell C. A. , Song Y. , Lee D.‐H.
Published: October 2002

On January 29, 1996, the Geotail satellite skimmed inside the magnetopause from the morningside to the subsolar region and observed multiple magnetopause crossings near the subsolar region (∼1100–1200 local time). Geotail observed accelerated northward (southward) flows accompanied by duskward (dawnward) flows at the magnetopause and/or in the boundary layer near the subsolar region. Such accelerated flows are qualitatively and quantitatively consistent with the theoretical predictions for reconnection. These events were observed when the interplanetary magnetic field (IMF) was steady and was directed southward (Bz < 0)/dawnward (By < 0). The amplitude of the IMF By was larger than that of the IMF Bz. The accelerated flow reversals near the subsolar region may be interpreted by the motion (i.e., slightly moving up and down) of the reconnection line, which tilts from the north‐dawn quadrant to the south‐dusk quadrant and passes through the subsolar point, with respect to the satellite. We suggest that our observations can be taken as evidence for the component merging model.
Steady magnetospheric convection: Statistical signatures in the solar wind and AE
Authors: O'Brien T. P. , Thompson S. M. , McPherron R. L.
Published: October 2002

We identify steady magnetospheric convection (SMC) whenever AE ≥ 200 nT and AL does not decrease by more than 25 nT in one minute. We demonstrate that the distribution of durations of SMCs has a larger tail than would be expected by assuming that long intervals of SMC are chance conjunctions of shorter SMCs. This implies that the magnetosphere can resist substorm onset and remain in a steady convective state. We also examine the distribution of interplanetary parameters during the long SMCs to determine what conditions are associated with SMCs. We document that solar wind velocity below 450 km s−1 and magnetic field Bz ∼ −3 nT are the hallmarks of the SMC intervals identified by our criteria. We note that the variability of Bz is only somewhat smaller during SMC intervals than during other times. We conclude by demonstrating that the appropriate solar wind conditions alone are not sufficient for producing an SMC.
Estimates of heat flow in the deep mantle based on the power requirements for the geodynamo
Authors: Buffett Bruce A.
Published: October 2002

Regeneration of the magnetic field by convection in the core places demands on heat flow into the base of the mantle. If the heat flow is too low, thermal convection is shut off and the rate of generation of compositional buoyancy by the solidification of the core becomes too low to sustain the geodynamo. Conversely, a large heat flow causes rapid growth of the inner core, so that convection prior to the appearance of the inner core must be sustained by thermal buoyancy alone. The attendant requirements on primordial heat become more severe as the age of the inner core decreases. We show that estimates of the present‐day heat flow satisfy the power requirements for the geodynamo. However, the resulting thermal history is incompatible with estimates of mantle temperatures prior to 3 Ga. This discrepancy can be resolved by accumulating radioactive isotopes in D″ or adding heat sources to the core.
Flux transfer events in global numerical simulations of the magnetosphere
Authors: Fedder J. A. , Slinker S. P. , Lyon J. G. , Russell C. T.
Published: October 2002

A magnetohydrodynamic numerical simulation model is used to study nonsteady features of magnetic reconnection between southward interplanetary magnetic field (IMF) and the geomagnetic field. The magnetic field near the dayside magnetopause intermittently shows the bipolar normal magnetic field and field‐aligned flow features that are similar to the observed flux transfer events. The results show that the magnetic signature extends outward into the magnetosheath and inward into the magnetosphere. The magnetic features are not steady, and they evolve as they propagate along the magnetopause. Magnetic field lines are traced from the magnetopause in order to show the connectivity of the field from the ionosphere to the solar wind. The results shown are consistent with Russell and Elphic's [1978] interpretation of the magnetic signals as evidence of nonsteady reconnection between the IMF and the geomagnetic field. Finally, we suggest a merging mechanism along the dayside magnetic null‐null line that naturally leads to the observed magnetic structure.