bluuebunny/crossref_metadata_2025 huggingface dataset:
On the relationship between Indian Ocean sea surface temperature and Asian Summer Monsoon
Authors: Li Tim , Zhang Yongsheng , Chang C.‐P. , Wang Bin
Published: February 2004

Indian Ocean SST has been thought to play a weaker role in Indian summer monsoon rainfall than does the equatorial eastern Pacific SST. In this study we show that on the tropical biennial oscillation (TBO, 2–3 year) time scale the Indian monsoon rainfall has significant positive correlations with the Indian Ocean SST and moisture flux transport in the preceding winter and spring. The effect of this SST influence is quite different from the remote forcing of the Indian monsoon rainfall by the eastern Pacific SST, which is more dominant on the El Nino‐Southern Oscillation (ENSO, 3–7 year) time scale. We conclude that while the eastern Pacific SST and the Eurasian land temperature both may affect the monsoon on the ENSO time scale, they are not important on the TBO time scale. Our results support the tropical and local feedback theories of TBO that this most important component of the monsoon variation is largely influenced by the Indian Ocean SST and interactions within the tropical atmosphere‐ocean system (Chang and Li, Nichols).
Kinematics of the Mw=7.2, 12 November 1999, Düzce, Turkey Earthquake
Authors: Ayhan M. E. , Bürgmann R. , McClusky S. , Lenk O. , Aktug B. , Herece E. , Reilinger R. E.
Published: February 2004

The November 12, 1999 Düzce earthquake ruptured a ∼40‐km‐long fault segment of the North Anatolian fault system immediately to the east of the August 17, 1999 Izmit rupture. We use displacements of 32 sites derived from GPS measurements immediately before and after the Düzce earthquake to estimate the geometry and slip distribution of the coseismic rupture. The ∼51° northward dipping rupture plane, the rake of the slip vector (average 3.76±0.04 m right‐lateral, 0.76±0.04 m normal slip), and the slip distribution inferred from the GPS data are consistent with seismic observations and the distribution of surface offsets measured in the field. The geodetically determined moment magnitude is Mw=7.2. The Düzce earthquake had the highest slip‐to‐rupture‐length ratio of any historic earthquake along the North Anatolian fault. This is consistent with the Düzce earthquake being a part of a composite rupture with the preceding Izmit event.
Initial observations of mesospheric winds using IDI Radar measurements at the Bear Lake Observatory
Authors: Berkey F. T. , Fish C. S. , Jones G. O. L.
Published: February 2004

The adaptation of Imaging Doppler Interferometry (IDI) to the dynasonde deployed at the Bear Lake Observatory (41.9°N, 111.4°W) in northeastern Utah enables the routine measurement of mesospheric dynamics. Influenced by the direction of the prevailing wind, a clear seasonal variation is seen in the mesospheric echo numbers. The technique also provides a monitor for the amplitude of the main tidal modes as well as for studying planetary waves with periods of several days. The observations are found to be consistent with those from different instruments based at the same site thus confirming the IDI characterisation of the mesospheric wind field.
Traveling ionospheric disturbances observed in the OI 630‐nm nightglow images over Japan by using a Multipoint Imager Network during the FRONT Campaign
Authors: Kubota M. , Shiokawa K. , Ejiri M. K. , Otsuka Y. , Ogawa T. , Sakanoi T. , Fukunishi H. , Yamamoto M. , Fukao S. , Saito A.
Published: February 2004

Pilot observations using a network of five all‐sky imagers (ASIs) were conducted during the new moon period of May 19–22, 1998 as part of the F‐region Radio and Optical measurement of Nighttime TID (FRONT) campaign. The network observation enabled us to track propagation of medium‐scale traveling ionospheric disturbances (TIDs) in the OI 630‐nm nightglow over a distance of more than 2500 km. The TIDs were observed every night during the campaign period, but occurrence was limited from evening to midnight. They have horizontal wavelengths of 200–600 km, travel a horizontal distance of more than 1000 km, and last for more than three hours. In every case, the TIDs moved southwestward with a velocity of 83–137 m/s. Using dual‐site TID images, the altitude of the TID structures in the 630‐nm nightglow was calculated to be ∼260 km, which corresponds to the bottom side of the mid‐latitude ionospheric F layer.
The oceanic CO2 System and Carbon Budget in the Great Barrier Reef, Australia
Authors: Suzuki Atsushi , Kawahata Hodaka , Ayukai Tenshi , Goto Koichi
Published: February 2004

The Great Barrier Reef (GBR) is the largest reef system in the world. During winter (dry season), a relative increase of CO2 fugacity, together with a depletion in total alkalinity, was evident in the GBR lagoon water. This suggests the release of CO2 due to CaCO3 production in the lagoon. But, in detail, significant contribution from organic matter oxidation was also identified. Despite the dissolved carbon losses as carbonate, total dissolved inorganic carbon (DIC) concentration normalized at constant salinity was relatively uniform throughout the study area. This indicates the presence of external carbon input to the lagoon. The most likely source is river discharge, which carries sizeable amounts of dissolved and particulate organic carbon as well as DIC. The marine CO2 system of the GBR lagoon highlights the nature of tropical carbonate shelves as a strong alkalinity sink and a net oxidation site of land‐derived organic carbon.
Long‐term north‐south asymmetry in solar wind speed inferred from geomagnetic activity: A new type of century‐scale solar oscillation?
Authors: Mursula K. , Zieger B.
Published: February 2004

A significant and very similar annual variation in solar wind speed and in geomagnetic activity was recently found around all the four solar cycle minima covered by direct SW observations since mid‐1960's. We have shown that the phase of this annual variation reverses with the Sun's polarity reversal, depicting a new form of 22‐year periodicity. The annual variation results from a small north‐south asymmetry in SW speed distribution where the minimum speed region is shifted toward the northern magnetic hemisphere. Here we study the very long‐term evolution of the annual variation using early registrations of geomagnetic activity. We find a significant annual variation during the high‐activity solar cycles in mid‐19th century and since 1930's. Most interestingly, the SW speed asymmetry in mid‐19th century was opposite to the present asymmetry, i.e., the minimum speed region was then shifted toward the southern magnetic hemisphere. This change of asymmetry suggests for a possible new form of century‐scale oscillation in the north‐south asymmetry of the Sun. We explain the asymmetry in terms of a relic magnetic field dislocated slightly in the north‐south direction from the heliographic equator. The change in the asymmetry would result from the century‐scale north‐south oscillation of the location of the relic field across the ecliptic.
Nearly zero temperature trend in the polar summer mesosphere
Authors: Lübken Franz‐Josef
Published: February 2004

A series of in‐situ temperature measurements performed by falling spheres at high latitudes in the last ∼10 years is compared with historical temperature data collected by the rocket grenade technique in the mid 1960s. Concentrating on summer (here from mid May to mid August) and on altitudes between 50 and 85 km, where natural variability and instrumental uncertainties are small, the observed trend is very small, if present at all. Taking into account all data from 50 to 85 km the mean trend is −0.024 K/y with a statistical error of ±0.014 K/y, i.e., practically zero. The mean deviation of the grenade temperatures from the falling sphere data is 0.8±6.4 K and the differences are randomly distributed. We have also analyzed various subsets of the entire data set, e.g., in a restricted altitude range where lidars have shown large trends at mid latitudes, namely from 55 to 75 km. The main result remains unchanged: The deviation between ‘old’ and ‘new’ data is practically zero and the temperature trend in the high latitude summer mesosphere is certainly much smaller (if any at all) compared to that observed at mid latitudes.
First artificially induced modulation of PMSE using the EISCAT Heating Facility
Authors: Chilson Philip B. , Belova Evgenia , Rietveld Michael T. , Kirkwood Sheila , Hoppe Ulf‐Peter
Published: February 2004

A coordinated experiment involving ionospheric heating and VHF observations of polar mesosphere summer echoes (PMSE) has recently been conducted at the EISCAT facility near Tromsø, Norway. We have demonstrated for the first time that ionospheric heating can influence VHF radar returns associated with PMSE. Artificially elevating the electron temperatures within the PMSE layer has been shown to reduce the echo power. Based on this and other results from the experiment, it is suggested that the observed reduction in PMSE power is related to an enhancement of the electron diffusivity through the heating.
Small‐world networks in geophysics
Authors: Yang Xin‐She
Published: February 2004

Many geophysical processes can be modelled as interconnected networks. The small‐world network model has recently attracted much attention in physics and applied sciences. In this paper, we modify and apply the small‐world network theory to model geophysical processes such as diffusion and transport in disordered porous rocks. We develop an analytical approach as well as numerical simulations to characterize the properties of small‐world networks in geophysics using system saturation time and fractal dimensions.
Arctic decadal and interdecadal variability
Authors: Polyakov Igor V. , Johnson Mark A.
Published: February 2004

Atmospheric and oceanic variability in the Arctic shows the existence of several oscillatory modes. The decadal‐scale mode associated with the Arctic Oscillation (AO) and a low‐frequency oscillation (LFO) with an approximate time scale of 60–80 years, dominate. Both modes were positive in the 1990s, signifying a prolonged phase of anomalously low atmospheric sea level pressure and above normal surface air temperature in the central Arctic. Consistent with an enhanced cyclonic component, the arctic anticyclone was weakened and vorticity of winds became positive. The rapid reduction of arctic ice thickness in the 1990s may be one manifestation of the intense atmosphere and ice cyclonic circulation regime due to the synchronous actions of the AO and LFO. Our results suggest that the decadal AO and multidecadal LFO drive large amplitude natural variability in the Arctic making detection of possible long‐term trends induced by greenhouse gas warming most difficult.
Ørsted Initial Field Model
Authors: Olsen N. , Holme R. , Hulot G. , Sabaka T. , Neubert T. , Tøffner‐Clausen L. , Primdahl F. , Jørgensen J. , Léger J.‐M. , Barraclough D. , Bloxham J. , Cain J. , Constable C. , Golovkov V. , Jackson A. , Kotzé P. , Langlais B. , Macmillan S. , Mandea M. , Merayo J. , Newitt L. , Purucker M. , Risbo T. , Stampe M. , Thomson A. , Voorhies C.
Published: February 2004

Magnetic measurements taken by the Ørsted satellite during geomagnetic quiet conditions around January 1, 2000 have been used to derive a spherical harmonic model of the Earth's magnetic field for epoch 2000.0. The maximum degree and order of the model is 19 for internal, and 2 for external, source fields; however, coefficients above degree 14 may not be robust. Such a detailed model exists for only one previous epoch, 1980. Achieved rms misfit is <2 nT for the scalar intensity and <3 nT for one of the vector components perpendicular to the magnetic field. For scientific purposes related to the Ørsted mission, this model supercedes IGRF 2000.
Internally and externally forced climate variability: A dynamical systems approach using the central England temperature record
Authors: van der Schrier Gerard , Versteegh Gerard J. M.
Published: February 2004

By using concepts from dynamical systems theory, we demonstrate a technique which has the potential to distinguish explicitly between internally forced and externally forced climate variability. This technique is applied to the instrumental Central England Temperature (CET) record, where variability related to changes in the (external) solar activity and variability due to (internal) climate dynamics are separated. Based on the CET record and the sunspot record, we reconstruct a map relating successive summer temperature maxima given the number of sunspots. For low values of the sunspot number, the equilibrium behaviour of this map shows chaotic motion, indicating dominant internal climate dynamics, for high values of the sunspot number this is not the case. The robustness of the reconstruction is tested using surrogate data.
Width and structure of mesoscale optical auroral arcs
Authors: Knudsen D. J. , Donovan E. F. , Cogger L. L. , Jackel B. , Shaw W. D.
Published: February 2004

Arc widths were calculated for 3126 stable auroral arcs observed by an all‐sky camera located in Gillam, Manitoba. The camera is filtered to accept 5577‐Å emissions and has a single‐pixel spatial resolution of 1.7 km at zenith. The measured mean width of stable mesoscale arcs located within ±5° of magnetic zenith is 18 km with a standard deviation of 9 km. The width distribution exhibits a steep cutoff below 8 km; when combined with studies of small‐scale auroral structure this cutoff suggests a gap in the occurrence of arcs with widths of order 1 km. This feature of the arc width spectrum argues against the notion of a turbulent cascade of energy from larger to small scales. Residuals from the Gaussian fits are only about 3% of the arc amplitude on average, indicating little sub‐structure within arcs at scales down to the measurement resolution.
Synoptic sections of the Denmark Strait Overflow
Authors: Girton James B. , Sanford Thomas B. , Käse Rolf H.
Published: February 2004

We report on a rapid high‐resolution survey of the Denmark Strait overflow (DSO) as it crosses the sill, the first such program to incorporate full‐water‐column velocity profiles in addition to conventional hydrographic measurements. Seven transects with expendable profilers over the course of one week are used to estimate volume transport as a function of density. Our observations reveal the presence of a strongly barotropic flow associated with the nearly‐vertical front dividing the Arctic and Atlantic waters. The seven‐section mean transport of water denser than σθ=27.8 is 2.7±0.6Sv, while the mean transport of water colder than 2.0°C is 3.8±0.8 Sv. Although this is larger than the 2.9 Sv of θ < 2°C water measured by a 1973 current meter array, we find that a sampling of our sections equivalent to the extent of that array also measures 2.9Sv of cold water. Both the structure and magnitude of the measured flow are reproduced well by a high‐resolution numerical model of buoyancy‐driven exchange with realistic topography.
The 1998 Bovec‐Krn Mountain (Slovenia) Earthquake Sequence
Authors: Bajc J. , Aoudia A. , Saraò A. , Suhadolc P.
Published: February 2004

We study the 1998 Bovec‐Krn mountain (Slovenia) earthquake sequence by combining hypocenters relocation, strong motion inversion, digital elevation modelling and field geology. The main shock (Ms=5.7), a 12 km right lateral strike‐slip event on the Dinaric fault system, occurred on a sub‐vertical fault plane. The rupture, confined between 3 and 9 km depth, with no evidence of surface faulting, propagated bilaterally within two structural barriers. The northwestern barrier is at the junction between Dinaric and Alpine structures where there is a sharp change in the geometry of faulting. The southeastern barrier is within the Dinaric system and its surface expression corresponds to the Tolminka‐spring perched basin, a 1 km restraining step‐over. At this site, the Bovec‐Krn earthquake‐fault overlaps with a 30 km strike‐slip fault segment that is free of aftershocks and could be undergoing an increase of stress. This fault system represents the northern branch of the Idrija right‐lateral fault.
Why is mean sea level along the Indian Coast higher in the Bay of Bengal than in the Arabian Sea?
Authors: Shankar D. , Shetye S. R.
Published: February 2004

Levelling observations conducted during the Great Trigonometrical Survey of India (1858–1909) and subsequent observations showed that mean sea level along the coast of India is higher in the Bay of Bengal than in the Arabian Sea, the difference in sea level between Vishakhapatnam and Mumbai (Bombay) being about 30 cm. Using simulations with a 1½‐layer reduced‐gravity model, we attribute this to the mean, large‐scale wind‐forced circulation (∼60%) and the alongshore gradient in salinity (∼40%). The former (latter) is a consequence of the distribution of wind stress (rainfall) because of the monsoon.
Remote infrared detection of the cessation of volcanic eruptions
Authors: Aries S. E. , Harris A. J. L. , Rothery D. A.
Published: February 2004

When an effusive eruption ends lava surfaces initially cool rapidly so that within minutes temperatures across the hottest zones have dropped by 600°C. This means that eruption cessation is simple to detect using satellite infrared data, where a sudden, irrecoverable decline in thermal radiance, occurring over a period of hours, is characteristic of termination. AVHRR data acquired during and after 5 eruptions at Krafla (Iceland) illustrate this. In all cases the 3.9 µm spectral radiance in the first image following the known time of eruption cessation is markedly reduced compared to that recorded during the eruption, and subsequently remains at persistently low levels.
An Alpine ice‐core record of anthropogenic HF and HCl emissions
Authors: Eichler Anja , Schwikowski Margit , Gäggeler Heinz W.
Published: February 2004

Ice‐core records of an Alpine glacier from the southern Swiss Alps were used to reconstruct sources of inorganic F and Cl− in precipitation. Our results suggest that sea salt transported together with mineral dust mainly from the Saharan area is the predominant source of Cl− in the southern Alps. However, on the average 16% of the Cl− and most of the F deposition in the period 1937–94 could be related to HCl and HF emissions from anthropogenic sources. The record of non‐sea‐salt Cl− was found to represent the historical development of HCl emissions mainly from waste incineration in the Swiss Plateau, whereas the F deposition record reflects HF emissions from the aluminum industry in the Swiss Rhone valley. Thus, our data indicate a strong impact of emissions of short lived atmospheric species such as HCl and HF on local and regional precipitation chemistry.
Waves close to the crossover frequency in the Jovian middle magnetosphere
Authors: Petkaki Panagiota , Dougherty Michele K.
Published: February 2004

The presence of heavy ions in a plasma introduces additional characteristic frequencies one of which is a crossover frequency between each adjacent pair of gyrofrequencies of the ions present. The crossover frequency is controlled by the fractional ion charge densities. The phase speed of the L and R wave modes have the same phase velocity at this frequency. For oblique propagation waves become linearly polarized at the crossover frequency. They reverse their natural polarization from left to right (or vice versa) as the wave frequency transverses the crossover frequency. Here we present polarization analysis of a portion of the Ulysses magnetometer observations in the middle Jovian magnetosphere during the inbound pass and close to a plasma sheet approach. The analysis show transverse waves with frequency between the gyrofrequencies of SO+ and S+. We observe polarization reversal at this frequency, which could be an indication of wave observations at the crossover frequency. On this assumption these observations can then be used to derive heavy ion composition of the resident plasma.
Improving GPS surveying with modeled ionospheric corrections
Authors: Rocken Christian , Johnson James M. , Braun John J. , Kawawa Hiroshi , Hatanaka Yuki , Imakiire Tetsuro
Published: February 2004

We model the ionospheric delay of Global Positioning System (GPS) signals with high precision and use it to correct single frequency (L1) GPS baseline estimations. We find that baselines up to 30 km in length are more precisely determined using corrected L1 data than using dual frequency data. The high resolution ionospheric modeling technique (called HiRIM in this paper) is demonstrated with 195 days of data from a 25‐site GPS network at ∼1 km spacing in central Japan. The network was designed for high vertical precision tectonic studies. We compute ionospheric corrections using data from a surrounding grid of nine GPS sites spaced ∼50 km. Based on the observations from the surrounding grid, epoch and satellite specific ionospheric delays are interpolated to correct L1 observations from the internal sites. HiRIM has potential post‐processing and real‐time applications in navigation, surveying, and GPS meteorology.
Stress estimations from fault geometries applied to sand‐box accretionary wedges
Authors: Koyi Hemin A. , Schott Bertram
Published: February 2004

Analysis of stress distribution along imbricate surfaces within a sand‐box model of an accretionary wedge is used to calculate the condition for slip along an active frontal fault and the basal dećollement. The same theory is applied for finding the stress limit that allows formation of a new fault in front of the sand wedge. When this stress limit is reached, the sole thrust propagates rapidly forward along the basal dećollement and a new fault is created. Comparison between theory and experiment shows that stresses would be underestimated, if compaction of the shortened layer is not accounted for in the calculations.
Interplay of variable thermal conductivity and expansivity on the thermal structure of oceanic lithosphere
Authors: Honda S. , Yuen D. A.
Published: February 2004

The sensitivity of pressure‐ and temperature‐dependent thermal conductivity (k: W/m/K) and the thermal expansivity (α:1/K) on the thermal structure of the oceanic plate is investigated parametrically by comparing the ocean floor depth and heat flux calculated by one‐dimensional conduction model with those of GDH1, a theoretical thermal model of the oceanic lithosphere. We find that an optimum fit is obtained, when the value of thermal expansivity is ∼ 3 × 10−5, while those associated with the thermal conductivity have many possibilities. The estimates, which give an equally good fit to the GDH1 model, of the plate thickness D (km) and the temperature at the base of the plate Tm (°C) may be given by Tm ∼ 1450‐(k0−4.5) × 100‐(α−3.0 × 10−5) × 105×100, D ∼ 90 + (k0−4.5) × 20 ‐ (α−3.0 × 10−5) × 105 × 20 where k0 (W/m/K) is the lattice thermal conductivity at the ocean floor. A similar relation is obtained for constant thermal conductivity.
Small subsidence of the 660‐km discontinuity beneath Japan probed by ScS reverberations
Authors: Kato Mamoru , Misawa Mika , Kawakatsu Hitoshi
Published: February 2004

We investigate layering structure in the mantle beneath Japan using ScS reverberation waveforms of two recent large deep events in the northwest Pacific. We estimate regional variation of the elastic and anelastic structure of the mantle as well as properties of the major velocity discontinuities by modeling broadband seismograms recorded at two dense networks, J‐Array and FREESIA. The 660‐km discontinuity is the deepest in the region where the stagnant subducting slab in the transition zone is tomographically imaged, but the subsidence is of ∼10 km, much smaller than previous estimates with SS precursors. No significant elevation is detected for the 410‐km discontinuity.
Warming asymmetry in climate change simulations
Authors: Flato G. M. , Boer G. J.
Published: February 2004

Climate change simulations made with coupled global climate models typically show a marked hemispheric asymmetry with more warming in the northern high latitudes than in the south. This asymmetry is ascribed to heat uptake by the ocean at high southern latitudes. A recent version of the CCCma climate model exhibits a much more symmetric warming, compared to an earlier version, and agrees somewhat better with observed 20th century trends. This is associated with an improved parameterization of ocean mixing which results in a decrease in heat penetration into the Southern Ocean, in accord with earlier ocean‐only and simple coupled model investigations. The global average warming and the net penetration of heat into the global ocean (and hence its thermal expansion) are essentially unchanged. Observed trends in sea‐ice extent over the past two decades exhibit hemispheric asymmetry with a statistically significant decrease in northern but not in southern ice cover. Both model versions are consistent with these observations implying that observed ice extent is not yet an indicator of asymmetry in future global warming. Taken together, these results suggest that southern hemisphere climate warming at a rate comparable to that in the northern hemisphere should be considered a realistic possiblity.
Secondary bubble production from breaking waves: The bubble burst mechanism
Authors: Leifer Ira , de Leeuw Gerrit , Cohen L. H.
Published: February 2004

Bubble mediated processes such as gas transfer and bubble‐burst aerosol production have long been of geophysical interest. In contrast, the bubble generation by bubble bursting remains unquantified. Based on a series of laboratory experiments, evidence for bubble production by bursting bubbles is presented as well as the bubble distribution produced by this mechanism for salt and fresh water.
The midlatitude warming during 1998–2000
Authors: Hoerling Martin P. , Whitaker Jeffrey S. , Kumar Arun , Wang Wanqui
Published: February 2004

Large scale tropospheric warming of the Northern and Southern Hemisphere extratropics occurred during the period January 1998–January 2000. The anomalies were remarkable for their amplitude, their persistence, their zonal symmetry with warming occurring at all longitudes between 30–50 degrees latitude, and their axial symmetry with respect to the equator. The origin of the anomalies are investigated using atmospheric general circulation models forced by the global sea surface temperatures (SSTs) of this period. Two ensembles, based on different models, reproduce the key observed features indicating that the unusual climate state was forced by the global SSTs. However, the atmospheric states were unrelated to the strong and protracted La Niña of the east equatorial Pacific Ocean during this time. We speculate on the role of the Indo‐Pacific warm pool, which itself experienced unprecedented warming in 1998 and 1999.
Mud Volcanoes revealed and sampled on the Western Moroccan Continental Margin
Authors: Gardner Joan M.
Published: February 2004

We surveyed and sampled two active and 3 inactive mud volcanoes on the Atlantic continental margin of Morocco. The active mud volcanoes (named Yuma and Ginsburg) are each about 4 km in diameter, rise between 150–250 meters above the seafloor and are the first active methane‐related mud volcanoes to be identified in this region. The inactive volcanoes range in diameter from 1–3 km, with relief between 50 and 80 meters. Gravity cores from the crest of the active mud volcanoes yielded methane hydrates and mud breccia deposits. Chemosynthetic communities of Pogonophora worms and the bivalve Solemya were found on the surface of the active mud volcanoes. Sediment cores from the inactive volcanoes contained hemipelagic sediments, rich in foraminifera and ahermatypic coral debris, overlying mud breccia
Stratospheric CH3CN from the UARS Microwave Limb Sounder
Authors: Livesey Nathaniel J. , Waters Joe W. , Khosravi Rashid , Brasseur Guy P. , Tyndall Geoffrey S. , Read William G.
Published: February 2004

CH3CN in the stratosphere has been measured by the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite (UARS), providing the first global CH3CN dataset. The MLS observations are in broad agreement with past high and midlatitude observations of CH3CN, although concentrations are a little larger than previously observed. In the tropics, where CH3CN has not up to now been measured, a persistent ‘peak’ in the profiles is seen around 22 hPa, which may be evidence of a tropical stratospheric CH3CN source. Comparisons are made with the NCAR SOCRATES model, including runs having an artificial tropical stratospheric CH3CN source.
Quantifying the complexity in mapping energy inputs and hydrologic state variables into land‐surface fluxes
Authors: Katul Gabriel G. , Lai Chun‐Ta , Albertson John D. , Vidakovic Brani , Schäfer Karina V. R. , Hsieh Cheng‐I , Oren Ram
Published: February 2004

This study explores the complexity (or disorder) in mapping energy (Rn) forcing to land surface fluxes of sensible heat (Hs), water vapor (LE), and carbon dioxide (or net ecosystem exchange, NEE) for different soil water states (θ). Specifically, we ask, does the vegetation act to increase or dissipate statistical entropy injected from Rn? We address this question using novel scalar complexity measures applied to a long‐term time series record of Rn, θ, Hs, LE, and NEE collected over a uniform pine forest. This analysis is the first to demonstrate that vegetation dissipates scalar flux entropy injected through Rn. We also find that the entropy or disorder in scalar fluxes increases with increasing Rn and that the complexity in mapping Rn to scalar fluxes is reduced with increasing θ.
Viscoelastic folding: Maxwell versus Kelvin Rheology
Authors: Schmalholz S. M. , Podladchikov Y. Y.
Published: February 2004

Folding of a viscoelastic layer embedded in a viscous matrix is studied analytically using two viscoelastic rheological models: The Maxwell and the Kelvin model. The layer deformation behaviour approximates the viscous or elastic limits depending on the single parameter, R, which is proportional to the viscosity contrast and the ratio of layer‐parallel stress to shear modulus. A layer with Maxwell rheology approximates this limit that generates the fastest amplification whereas a layer with Kelvin rheology approximates the slowest limit. For R < 1 the viscous limit is fastest whereas for R > 1 the elastic limit is fastest. The Kelvin rheology is suitable to describe the effective flexural response of a lithospheric plate consisting of an elastic layer overlying a viscous layer, since the Kelvin rheology yields an identical bending moment. A critical elastic layer thickness, R² H/3 (H=lithospheric thickness), is derived at which the deformation behaviour of the lithospheric plate changes from quasi‐viscous to quasi‐elastic.
Storm time plasma irregularities in the pre‐dawn hours observed by the low‐latitude ROCSAT‐1 satellite at 600 km altitude
Authors: Yeh H. C. , Su S. Y. , Heelis R. A.
Published: February 2004

Large scale ion density depletions were detected in the nighttime sector by ROCSAT‐1 for over 10 hours during the 22 October 1999 geomagnetic storm. Prominent depletion structures (bubbles) that are characterized by large‐amplitude density decrease (N/No ≤ 1%) with rapid horizontal ion drift (600 ∼ 800 m/s) are found to cluster in the 03:00 ∼ 04:30 local time sector and at magnetic latitudes 14° ∼ 20° S when the storm was in its early recovery phase. These presunrise bubbles are positively correlated to the enhanced eastward electric fields of greater than 1 ∼ 2 mV/m, which were in response to the storm‐time disturbances resulting from the in‐phase contributions of the prompt penetration magnetospheric and the long lasting ionospheric disturbance dynamo electric fields. Further analyses of the field‐aligned and cross‐field ion drifts within the depletions reveal that bubble plasma were driven by the eastward polarization electric fields to move upward, but these upward velocities were compensated by large downward field‐aligned diffusive motions. These features confirm that the disturbance electric fields produced during a great magnetic storm can significantly affect the occurrence timing and spatial extent of severe plasma irregularities in low‐latitude ionosphere. The spatial dimensions of the pre‐sunrise irregularities may exceed the large region observed by the 35° inclined circular orbiting ROCSAT‐1.
A synthesis of regional climate change simulations—A Scandinavian perspective
Authors: Christensen J. H. , Räisänen J. , Iversen T. , Bjøge D. , Christensen O. B. , Rummukainen M.
Published: February 2004

Four downscaling experiments of regional climate change for the Nordic countries have been conducted with three different regional climate models (RCMs). A short synthesis of the outcome of the suite of experiments is presented as an ensemble, reflecting the different driving atmosphere‐ocean general circulation model (AOGCM) conditions, RCM model resolution and domain size, and choice of emission scenarios. This allows the sources of uncertainties in the projections to be assessed. At the same time analysis of the climate change signal for temperature and precipitation over the period 1990–2050 reveals strong similarities. In particular, all experiments in the suite simulate changes in the precipitation distribution towards a higher frequency of heavy precipitation.
ENSO prediction using an ENSO trigger and a proxy for Western Equatorial Pacific Warm Pool Movement
Authors: Clarke Allan J. , Van Gorder Stephen
Published: February 2004

The zonal windstress anomaly in the far‐western equatorial Pacific (130–160°E) is a precursor to El Niño and La Niña episodes. A linear combination of this windstress with the El Niño index NINO3.4 can be used to predict ENSO successfully. Cross‐verified prediction results for NINO3.4 compare favorably with those of leading ENSO prediction models. The model is improved slightly if the time trend in sea surface temperature (SST) near the eastern edge of the western Pacific warm pool is included in the linear combination. Physically this trend is related to zonal equatorial ocean flow which advects the warm pool. The trend therefore aids prediction since it is a precursor to warm pool position and hence ENSO variability.
Interaction of rising and sinking mantle plumes
Authors: Schaeffer Nathanaël , Manga Michael
Published: February 2004

The frequency of plume formation in fully‐developed thermal convection is determined experimentally. Because the fluid has a temperature‐dependent viscosity, the cold and hot thermal boundary layers have different thicknesses and viscosities. As a result, plumes are released from these layers with different frequencies. There also appears to be a direct temporal interaction between the cold and hot boundary layers. In particular, whereas there is a single frequency for cold plume formation, hot plumes form with multiple frequencies, one of which is similar to the frequency of cold plumes. The measurements thus suggest that cold sinking “plumes” may induce hot rising plumes.
Impact of rotational Raman scattering in the O2A band
Authors: Sioris Christopher E. , Evans Wayne F. J.
Published: February 2004

Radiative transfer calculations with scattering and absorption by aerosols and molecules are used to estimate the magnitude of the Ring effect in the O2A band. Rotational Raman scattering significantly alters the A band line depths and shapes for a satellite nadir‐viewing case at high solar zenith angles in the absence of thick clouds. In the limb view, at low spectral resolution, the only impact of rotational Raman scattering is that it significantly reduces the radiance in the shoulder of the R branch. The latter effect is also observed for zenith viewing geometry from the ground.
Topographic core‐mantle coupling in geodynamo modeling
Authors: Kuang Weijia , Chao Benjamin Fong
Published: February 2004

A 3‐dimensional, fully nonlinear numerical geodynamo model is used to study the core‐mantle coupling arising from a non‐hydrostatic pressure field acting on an aspherical core‐mantle boundary (CMB) based on a seismological model. The simulation results demonstrate that the topographic coupling torque is close to being proportional to the square of the amplitude of the CMB topography. We conclude that the contribution of the topographic coupling to the total torque that is responsible for the axial angular momentum transfer on decadal timescales (for the decadal length‐of‐day variation) is significant only if the amplitude of the CMB topography is considerably larger than 3km inferred from seismological evidence.
Surface heat flux histories from geothermal data: Inferences from inversion
Authors: Beltrami Hugo
Published: February 2004

Past changes in the Earth's surface energy balance propagate into the subsurface and appear as perturbations of the subsurface thermal regime. A singular value decomposition inversion (SVD) scheme has been used to reconstruct surface heat flux histories (SHFH) from the heat flux anomalies detected in the subsurface. Synthetic data tests yield results in agreement with analytical expressions. Inversion of a temperature log from central Canada is used to illustrate this procedure. Results show that reconstruction of SHFH is possible with existing data. Application of this method to the existing geothermal data base should permit a quantification of the energy balance at the Earth's surface for the past few centuries.
A seasonal variation in the convection response to IMF orientation
Authors: Milan Stephen E. , Baddeley Lisa J. , Lester Mark , Sato Natsuo
Published: February 2004

We investigate the response of dayside convection, measured by the CUTLASS Finland HF radar, to differing orientations of the interplanetary magnetic field (IMF), determined by the ACE spacecraft, for solstice and equinox periods during 1998, 1999, and 2000. Our results indicate that the influence of the By component of the IMF on the convection flow differs from season to season, suggesting an interhemispheric asymmetry in convection excitation; the influence of By is greatest near summer solstice and in the pre‐noon sector. The influence of IMF Bz remains the same throughout the year.
High concentrations of reactive biogenic VOCs at a high altitude site in late autumn
Authors: Karl T. , Fall R. , Crutzen P. J. , Jordan A. , Lindinger W.
Published: February 2004

Volatile organic compounds (VOCs) at the Sonnblick Observatory, Austria (3106 m a.s.l.) were measured in autumn 1999 using proton‐transfer‐reaction mass spectrometry (PTR‐MS). Anthropogenic VOCs at this remote site, such as benzene and toluene (50 pptv to 2 ppbv), were primarily traced to air from urban areas. In mid‐November, following a hard freeze in the central Alps, a different pattern of VOCs developed similar to that seen with C5 and C6 leaf wound compounds (0.5 to 5 ppbv range). The common origins of these compounds are proposed to be freeze‐damaged leaves, inferred from laboratory investigations that identified hexenals, hexanal, methylbutanals, pentenol and pentenone formation in such leaves. We suggest that deciduous forests can release large amounts of reactive VOCs during the autumn, and that these releases may be important for regional tropospheric chemistry.
The mechanism of solution of aluminum oxide in MgSiO3 perovskite
Authors: Stebbins Jonathan F. , Kroeker Scott , Andrault Denis
Published: February 2004

We report 27Al and 29Si Nuclear Magnetic Resonance (NMR) spectra, collected at magnetic fields of 14.1 and 18.8 Tesla on samples as small as 1 mg, for Al‐bearing MgSiO3 perovskite synthesized at 26–28 GPa. For Al, we find a 1∶1 ratio of two types of sites: a symmetrical, octahedral site and a low symmetry, distorted site that is most likely to be Al in modifications of normally eight‐coordinated Mg sites. A charge coupled substitution of 2 Al for one Si and one Mg cation is strongly supported as the predominant mechanism in this pressure range.
Transition between stable states in the dynamics of soil development
Authors: D'Odorico Paolo , Porporato Amilcare , Ridolfi Luca
Published: February 2004

The dynamics of soil development and erosion is studied through a stochastic soil mass balance in which the soil production by bedrock weathering is expressed as a state‐dependent deterministic function, while the erosion by landslides is modeled as a marked Poisson process. For a range of values of the parameters the dynamics is bistable and the noise drives the transitions from a state to another through a potential barrier. The rates of such a transition are analytically estimated and their dependence on the system parameters is briefly discussed.
A Spectro‐Photometric Model of Mars in the near‐infrared
Authors: Erard Stéphane
Published: February 2004

The present model provides estimates of the spectral radiance of Mars in the 0.4–5.7 µm domain. The model is based on several composite surface spectra that correspond to the main types of materials observed. Photometric effects are simulated with both a Minnaert model and a phase function derived from ISM spectra. Aerosols scattering is taken into account for small opacities (single scattering). Thermal emission is accounted for through an emissivity model previously used to derive reflectance from IRS data. Emission and scattering by molecules are also included. Temperature and pressure are allowed to vary with season, local time, and latitude; regional effects, including surface elevation, are averaged out in this version. Results are validated by comparisons with various data sets. One of the main discrepancies with observations is related to atmospheric absorptions deeper than observed, which is probably due to coupling between absorption and scattering.
Seasonal variations in elemental carbon aerosol, carbon monoxide and sulfur dioxide: Implications for sources
Authors: Antony Chen L.‐W. , Doddridge Bruce G. , Dickerson Russell R. , Chow Judith C. , Mueller Peter K. , Quinn John , Butler William A.
Published: February 2004

As part of Maryland Aerosol Research and CHaracterization (MARCH‐Atlantic) study, measurements of 24‐hr average elemental carbon (EC) aerosol concentration were made at Fort Meade, Maryland, USA, a suburban site within the Baltimore‐Washington corridor during July 1999, October 1999, January 2000, April 2000 and July 2000. Carbon monoxide (CO) and sulfur dioxide (SO2) were also measured nearly continuously over the period. Tight correlation between EC and CO in every month suggests common or proximate sources, likely traffic emissions. The EC versus CO slope varies in different seasons and generally increases with ambient temperature. The temperature dependence of EC/CO ratios suggests that EC source strength peaks in summer. By using the well established emission inventory for CO, and EC/CO ratio found in this study, EC emission over North America is estimated at 0.31±0.12 Tg yr−1, on the low end but in reasonable agreement with prior inventories based on emission factors and fuel consumption.
Simultaneous measurements of temperature in the upper mesosphere with an Ebert‐Fastie Spectrometer and a VHF meteor radar on Svalbard (78°N, 16°E)
Authors: Nielsen Kristian Pagh , Röttger Jürgen , Sigernes Fred
Published: February 2004

From the 14th of November to the 21st of November 1999 measurements of the upper mesospheric temperatures were performed on Svalbard (78°N, 16°E). Both the SOUSY Svalbard Radar and a one meter focal length Ebert‐Fastie spectrometer were used, the first instrument measured the decay and phase changes of meteor echoes, and the latter measured the OH(6–2) rotational spectrum. These allowed us to deduce themperature estimates at 80–90 km altitude. Due to the differences in the height of the measurements the temperatures were compared on the background of the temperature profile according to the COSPAR International Reference Atmosphere and reasonable agreement was found.
Anomalous peak in Antarctic sea‐ice area, Winter 1998, coincident with ENSO
Authors: Hanna Edward
Published: February 2004

The results of an updated satellite analysis of hemispheric and regional Antarctic sea‐ice cover are presented based on October 1987–September 1999 Special Sensor Microwave/Imager (SSM/I) data. These show an ongoing slight but significant hemispheric increase of 3.7(±0.3)% in extent and 6.6(±1.5)% in area. In the two principal sectors, Weddell Sea ice extent (area) decreased by 3.4(±1.0) (3.9(±4.6)) % and Ross Sea ice extent (area) increased by 10.9(±1.0) (18.3(±4.6)) %. Hemispheric, Ross Sea and Western Pacific Ocean ice peaks in September 1998 were anomalously high, and may have been related to atmospheric and oceanic anomalies in the Pacific Ocean and beyond associated with that year's exceptionally strong ENSO. Preliminary comparison of Antarctic sea‐ice‐concentration data with European Centre for Medium‐Range Weather Forecasts (ECMWF) operational analyses fields suggests that the unusually extensive sea ice in winter 1998 was concomitant with an equatorward shift of the circumpolar westerly surface winds over the southern Pacific Ocean.
Hemispheric comparison of PMC altitudes
Authors: Carbary J. F. , Morrison D. , Romick G. J.
Published: February 2004

A middle ultraviolet imager observed the vertical structure of polar mesospheric clouds (PMCs) in the northern and southern polar regions during the austral summer of 1997–1998 and the arctic summer of 1999. During 23 transpolar passes, the imager obtained over 15,000 images at latitudes poleward of 55°. The accuracy and stability of the satellite platform and the large database permit the first statistical investigation of the small scale (∼1 km) altitude structure of PMCs on a transpolar scale. During a satellite pass over either polar region, PMCs clustered at different altitudes between 80 and 85 km. Southern clouds had a mean altitude of 83.2±1.4 km above the Earth ellipsoid, while northern clouds had a mean altitude of 82.6d±1.3 km, so southern and northern clouds had the same altitudes to within statistical variations. The mean PMC altitude was 82.7±1.3 km for both hemispheres. In neither hemisphere did cloud altitudes exhibit systematic variation with latitude.
Lithospheric mantle evolution of the Kaapvaal Craton: A Re‐Os isotope study of peridotite xenoliths from Lesotho kimberlites
Authors: Irvine Gordon J. , Pearson D. Graham , Carlson Richard W.
Published: February 2004

Understanding the generation and evolution of cratonic lithospheric keels requires detailed knowledge of their age, timescale of formation, and the relationship between the crust and mantle part of the lithosphere. Re‐Os isotope analyses of peridotite xenoliths from Lesotho kimberlites indicate that large portions of the lithospheric keel beneath the SE Kaapvaal craton were stabilized during the late Archean. This process and subsequent additions of new lithospheric mantle coincide with events recorded by lower crustal xenolith studies from this region.
Mesospheric clouds and the neutral atmosphere during the 1999 DROPPS/MIDAS Campaign
Authors: Schmidlin F. J. , Schauer Allison G.
Published: February 2004

Inflatable passive falling spheres launched in conjunction with the DROPPS/MIDAS campaign during July 1999 are used to infer thermal advection and its relationship to Polar Mesospheric Summer Echoes (PMSE) and Noctilucent Cloud (NLC) events. Hodograph analysis, although not new, is used at mesospheric altitudes where non‐hydrostatic conditions may possibly inhibit useful results. Nonetheless, the concept of applying thermal advection to PMSE and NLC events is tried here with a possibility of interpreting neutral atmosphere measurements and their relationship with the electrodynamic environment. Although the material presented represents only results from the DROPPS/MIDAS campaign, it shows changes in the temperature structure within a few hours at the time of the PMSE event that indicate thermal advection may be connected to temperature changes of a few degrees. The warm advection between 80 and 86 km may be significantly related to the height of the PMSE, i.e., 85 km.