bluuebunny/crossref_metadata_2025 huggingface dataset:
Cluster electric current density measurements within a magnetic flux rope in the plasma sheet
Authors: Slavin J. A. , Lepping R. P. , Gjerloev J. , Goldstein M. L. , Fairfield D. H. , Acuna M. H. , Balogh A. , Dunlop M. , Kivelson M. G. , Khurana K. , Fazakerley A. , Owen C. J. , Reme H. , Bosqued J. M.
Published: May 2003

On August 22, 2001 all 4 Cluster spacecraft nearly simultaneously penetrated a magnetic flux rope in the tail. The flux rope encounter took place in the central plasma sheet, βi ∼ 1–2, near the leading edge of a bursty bulk flow. The “time‐of‐flight” of the flux rope across the 4 spacecraft yielded Vx ∼ 700 km/s and a diameter of ∼1 Re. The speed at which the flux rope moved over the spacecraft is in close agreement with the Cluster plasma measurements. The magnetic field profiles measured at each spacecraft were first modeled separately using the Lepping‐Burlaga force‐free flux rope model. The results indicated that the center of the flux rope passed northward (above) s/c 3, but southward (below) of s/c 1, 2 and 4. The peak electric currents along the central axis of the flux rope predicted by these single‐s/c models were ∼15–19 nA/m2. The 4‐spacecraft Cluster magnetic field measurements provide a second means to determine the electric current density without any assumption regarding flux rope structure. The current profile determined using the curlometer technique was qualitatively similar to those determined by modeling the individual spacecraft magnetic field observations and yielded a peak current density of 17 nA/m2 near the central axis of the rope. However, the curlometer results also showed that the flux rope was not force‐free with the component of the current density perpendicular to the magnetic field exceeding the parallel component over the forward half of the rope, perhaps due to the pressure gradients generated by the collision of the BBF with the inner magnetosphere. Hence, while the single‐spacecraft models are very successful in fitting flux rope magnetic field and current variations, they do not provide a stringent test of the force‐free condition.
A comparison of hydroxyl rotational temperatures from Davis (69°S, 78°E) with sodium lidar temperatures from Syowa (69°S, 39°E)
Authors: Burns G. B. , Kawahara T. D. , French W. J. R. , Nomura A. , Klekociuk A. R.
Published: May 2003

We report the first substantive inter‐site comparison of high southern latitude mesopause region winter temperatures. Davis (69°S, 78°E) hydroxyl rotational nightly‐mean temperatures are significantly correlated with Syowa (69°S, 39°E) sodium lidar nightly‐mean temperatures at 87 km made in 2000 (correlation coefficient of 0.68) and 2001 (0.51) despite a site separation of ∼1500 km. The Davis winter average temperature in 2001, 203 K, differs from the Syowa value of 201 K only by the uncertainty in the measurement. A more substantial 7 K separates the year 2000 winter averages, Davis again being warmer. The temperature difference between the sites is attributed to either variations in the hydroxyl layer or short‐term cooling events in the mesopause region above Syowa that are not detected above Davis. Syowa winter temperatures at 87 km are ∼7 K cooler than for an equivalent latitude northern hemisphere site.
Effects of uncertainty in TRMM precipitation radar path integrated attenuation on interannual variations of tropical oceanic rainfall
Authors: Robertson Franklin R. , Fitzjarrald Dan E. , Kummerow Christian D.
Published: May 2003

Considerable uncertainty surrounds the issue of whether precipitation over the tropical oceans (30° N/S) systematically changes with interannual sea‐surface temperature (SST) anomalies that accompany El Nino (warm) and La Nina (cold) events. Time series of rainfall estimates from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) over the tropical oceans show marked differences with estimates from two TRMM Microwave Imager (TMI) passive microwave algorithms. We show that path‐integrated attenuation derived from the effects of precipitation on the radar return from the ocean surface exhibits interannual variability that agrees closely with the TMI time series. Our analysis of discrepancies between the PR rainfall and attenuation suggests that uncertainty in the assumed drop size distribution and associated attenuation/reflectivity/rainfall relationships inherent in single‐frequency radar methods is a serious issue for studies of interannual variability.
Advective‐diffusive mass flux and implications for stratosphere‐troposphere exchange
Authors: Hall Timothy M. , Holzer Mark
Published: May 2003

We show that the flux of mass crossing in one direction (the “gross” flux) through any specified surface S that divides anadvective‐diffusive flow in a closed domain is infinite. That is, the flux, (τ), through S of the fluid mass that spent at least time τ on one side of S diverges like τ−1/2 as τ → 0, in the continuum limit. The gross flux is completely dominated by fluid elements residing infinitesimally short times on one side of S before re‐crossing to the other side. This general result puts into context the widely varying estimates of gross mass flux across the midlatitude tropopause. Such estimates are dominated by the smallest resolved scales, leading us to conclude that gross mass flux is not a useful diagnostic of stratosphere‐troposphere exchange. The function (τ), however, provides important information on transport across the tropopause.
Molecular synthesis in hypervelocity impact plasmas on the primitive Earth and in interstellar clouds
Authors: Managadze George G. , Brinckerhoff William B. , Chumikov Alexander E.
Published: May 2003

When impact speeds exceed a critical range of ∼15–20 km s−1, the resulting plasma plume energizes very rapidly from a few eV, to as high as 30–50 eV when speeds reach 50–100 km s−1, and can be completely atomized and ionized. During post‐impact adiabatic dispersion, the degree of ionization drops. The remaining ion population is mostly atomic, sampling the elemental composition of the colliding bodies, but some molecular ions are also formed. We present here results of experiments in which the physical and chemical conditions in the plume of a hypervelocity micrometeorite impact well above 20 km s−1 were modeled with Q‐switched laser ablation. The formed molecular ions were analyzed with a time‐of‐flight (TOF) mass reflectron capable of distinguishing plasma‐synthesized from surface‐desorbed species. Singly‐ and multiply‐charged small organic molecules were identified as having formed in laser plasmas induced from inorganic carbonaceous substances. The results show the possibility of abiogenic synthesis of organic molecules in hypervelocity impacts of meteors on the primitive Earth during heavy bombardment and of dust particles in interstellar clouds.
The influence of the equatorial upper stratosphere on stratospheric sudden warmings
Authors: Gray Lesley J.
Published: May 2003

A stratosphere mesosphere model is used in a set of idealized experiments to investigate the sensitivity of the Northern Hemisphere winter stratospheric flow to the equatorial zonal winds in the upper and the lower stratosphere. Sensitivity is found to the lower stratospheric winds (below 40 km) only in the early part of the model integration as the model relaxes towards a perpetual winter state. On the other hand the model showed significant sensitivity to the upper stratospheric winds throughout the major part of the integration. This has possible implications for the influence of the quasi‐biennial oscillation (QBO) and solar cycle on the northern winter stratospheric flow. It suggests that the lower stratospheric QBO may influence the early winter, but later in the winter when the flow is highly non‐linear the greatest influence may come from variations in the semi‐annual oscillation (SAO) which dominates the equatorial winds in the upper stratosphere. Possible sources of variations in the SAO include both the influence of the QBO and of the 11‐year solar cycle.
Structuring of high latitude plasma patches with variable drive
Authors: Gondarenko N. A. , Guzdar P. N. , Sojka J. J. , David M.
Published: May 2003

Three‐dimensional nonlinear simulations of the structuring of high‐latitude patches with variable drive demonstrate the role of the gradient drift instability as the primary operative structuring mechanism. In this letter we show that by introducing a variable convective E × B drive obtained from the ionosphere module of a global MHD code simulation of a real substorm [Sojka et al., 1997], the nature of the structuring is strongly influenced by the drive. In fact, due to occasional reversal of the direction of the convection, the structuring from the gradient‐drift instability takes place on both edges of the patch. Using different ion‐neutral collisionality to account for the seasonal or solar cycle variability of the ionosphere, the four categories of structured patches identified by Kivanç and Heelis [1997] have been simulated.
Arctic Ocean variability derived from historical observations
Authors: Polyakov Igor , Walsh David , Dmitrenko Igor , Colony Roger L. , Timokhov Leonid A.
Published: May 2003

This study has been motivated by reports of extraordinary change in the Arctic Ocean observed in recent decades. Most of these observations are based on synoptic measurements, while evaluation of anomalies requires an understanding of the underlying long‐term variability. Historical climatologies give reference means, and while these datasets are a reliable source of the mean Atlantic Layer temperature, they significantly underestimate variability. Using historical data, we calculated statistical parameters for selected Arctic Ocean regions. They demonstrate a high level of Atlantic Layer temperature variability in the Nansen Basin and sea‐surface salinity fluctuations on the Siberian shelf and the Amundsen Basin. These estimates suggest strong limitations on our ability to define amplitudes of anomalies by comparing recent synoptic measurements with climatologies, especially for regions characterized by strong variability.
Eulerian mean surface velocity field derived by combining drifter and satellite altimeter data
Authors: Uchida Hiroshi , Imawaki Shiro
Published: May 2003

Combining surface drifter and satellite altimeter data,we estimate Eulerian mean sea‐surface velocity with a resolution of quarter degrees in both latitude and longitude. The Eulerian mean velocity is calculated by subtracting the altimeter‐derived velocity anomaly (i.e., deviation from the temporal mean) at the time when a drifter measured the surface velocity, from this drifter‐measured velocity. The method is applied to the surface flow of the North Pacific, using TOPEX/POSEIDON and ERS‐1/2 altimeter data, and WOCE‐TOGA surface drifter data obtained during October 1992 to January 2001. The estimated Eulerian mean velocities for the Kuroshio south of Japan and the Kuroshio Extension region tend to be smaller than simple averages of drifter‐derived velocities by 20 to 50 cm sec−1. The instantaneous velocities are obtained every ten days as sums of the Eulerian mean velocities and velocity anomalies. They agree well with in situ surface velocities measured by acoustic Doppler current profilers.
Geodetic strain in peninsular Italy between 1875 and 2001
Authors: Hunstad I. , Selvaggi G. , D'Agostino N. , England P. , Clarke P. , Pierozzi M.
Published: May 2003

We determine geodetic strain in peninsular Italy by the GPS reoccupation of the first order triangulation network of Italy installed from 1860. The uncertainties in the original measurements (about 3 ppm), and the time span between the two observations, imply that tectonic signals larger than about 0.03 ppm/yr are resolvable. Along the Apenninic belt, where the largest earthquakes are concentrated, the geodetic deformation has a clear and consistent strain pattern between adjacent regions, well above the uncertainties, and shows a pervasive NE‐SW extension. Along the Tyrrhenian and Adriatic coasts the geodetic signal is not homogeneous and is comparable with the uncertainty in the original measurements. Seismic deformation, calculated over the same time interval, agrees well with estimated extensional direction, but the magnitudes of geodetic and seismic strain differ suggesting that, in part of the Apennines, significant strain accumulation over the past 130 years may not have been released in earthquakes.
Rapid, large‐scale temperature changes in the polar mesosphere and their relationship to meridional flows
Authors: Espy P. J. , Hibbins R. E. , Jones G. O. L. , Riggin D. M. , Fritts D. C.
Published: May 2003

Mesospheric temperatures derived from spectroscopic measurements of the hydroxyl (OH) nightglow have been observed from Rothera (67.6°S, 68.1°W) and Halley (75.6°S, 26.6°W) stations in Antarctica during the 2002 austral winter season. In addition to the normal seasonal changes, the temperatures at both sites, separated by 1658 km, showed several simultaneous shifts in temperature of between 10 and 20 K. These changes abruptly occurred in the space of 2–3 days and lasted for several days. These rapid variations in temperature were associated with large swings observed in the meridional component of the mesospheric wind measured by the Rothera MF radar. As there appeared to be no phase shift between the temperature variations at the two longitudinally separated stations indicating that planetary‐waves caused the changes, these large‐scale changes have been interpreted as variations in the inter‐hemispheric meridional jet, and a corresponding modulation of the mesospheric descent and adiabatic heating rates over the polar region.
Arctic Study on Tropospheric Aerosol and Radiation: Comparison of tropospheric aerosol extinction profiles measured by airborne photometer and SAGE II
Authors: Thomason Larry W. , Herber Andreas B. , Yamanouchi Takashi , Sato Kaoru
Published: May 2003

The Arctic Study on Tropospheric Aerosol and Radiation (ASTAR) is focused on understanding the climate effects of Arctic haze. As a part of this experiment, a tropospheric aerosol extinction profile was obtained by airborne sun photometer spatially and temporally close to a satellite‐based measurement. The results suggest that airborne photometry is a promising avenue for the validation of satellite‐derived aerosol extinction measurements in the middle and upper troposphere. The results also suggest that SAGE II measurements can be used to provide a regional context to more intensive but spatially limited aircraft and ground‐based data sets.
Disruptive earthquakes revealed by faulted archaeological relics in Samnium (Molise, southern Italy)
Authors: Galli P. , Galadini F.
Published: May 2003

Archaeoseismic and paleoseismic analyses carried out along the northern slope of the Matese massif (Samnium, southern Apennines) revealed cumulative offsets affecting the walls of the Hercules's sanctuary of Campochiaro (4th cent. BC‐5th cent. AD) and its foundation deposits. On the basis of the archaeological data, a first faulting event (unknown in historical sources and seismic catalogues) occurred during the 3rd cent. BC, followed by other displacements which are consistent with the catastrophic 1456 and 1805 earthquakes. The sanctuary is located close to one of the E‐W strands of the northern‐Matese fault system (NW‐SE trending), to which we relate the observed deformation. Our data suggest that the activity of this fault system is characterized by high slip‐rates (0.9 mm/yr) if compared to other known active faults in the Apennines, and irregular return time for earthquakes with M > 6.5.
Aircraft observations of the upper tropospheric fine particle aerosol in the Northern and Southern Hemispheres at midlatitudes
Authors: Minikin Andreas , Petzold Andreas , Ström Johan , Krejci Radovan , Seifert Marco , van Velthoven Peter , Schlager Hans , Schumann Ulrich
Published: May 2003

As part of the project INCA (Interhemispheric Differences in Cirrus Properties from Anthropogenic Emissions) two aircraft field campaigns have been performed to study aerosol and cirrus cloud properties of the upper troposphere (UT) in the midlatitudes of the southern hemisphere (SH) and the northern hemisphere (NH). This paper focuses on the measurements of UT number concentrations and tropospheric vertical profiles of volatile and refractory Aitken as well as total accumulation mode particles. The results are discussed with respect to interhemispheric differences. Aerosol number concentrations in the NH are more variable and typically a factor of 2–3 higher. The SH data considerably extend the few existing UT in situ aerosol measurements in the SH midlatitudes.
Deformation of Grímsvötn volcano, Iceland: 1998 eruption and subsequent inflation
Authors: Sturkell Erik , Einarsson Páll , Sigmundsson Freysteinn , Hreinsdóttir Sigrún , Geirsson Halldór
Published: May 2003

Grímsvötn is a subglacial volcano, under the Vatnajökull ice cap at the center of the Icelandic hotspot. This highly active volcano erupted in December 1998. GPS measurements at a single station on a nunatak at the caldera rim were made 7 times during 1992–2001. The measurements prior to the 1998 eruption reveal pre‐eruption inflation, but subsidence of more than 15 cm was measured during the eruption. Following the eruption, re‐inflation occurred initially, at a rate of 20 mm/month, then declined to 5 mm/month. Measurements were fitted to a Mogi model, assuming that the source was located under the center of the Grímsvötn caldera complex. Results indicate a source depth of at least 1.6‐km. The calculated amount of magma outflow during the eruption is comparable to field estimates of the erupted volume. Grímsvötn continues to inflate, but has not reached its 1998 pre‐eruption level.
Observation of dayside subauroral proton flashes with the IMAGE‐FUV imagers
Authors: Hubert B. , Gérard J. C. , Fuselier S. A. , Mende S. B.
Published: May 2003

A detailed description of an intense flash of auroral emissions that occurs equatorward of the dayside auroral oval observed with the IMAGE‐FUV imagers is presented. The comparison of simultaneous snapshots of this subauroral flash obtained with the three FUV cameras indicates that proton precipitation is dominant. This transient proton aurora is triggered by the sudden increase of a solar wind dynamic pressure pulse. It occurs on closed field lines mapping to the equatorial plane at distances as small as ∼4 RE. A second similar event is presented, and several other cases are mentioned. These shock induced transcient emissions develop with a time scale of a few minutes (typically ∼5 min), and have a relaxation time on the order of ∼10 minutes.
Kink mode oscillation of the current sheet
Authors: Volwerk M. , Glassmeier K.‐H. , Runov A. , Baumjohann W. , Nakamura R. , Zhang T. L. , Klecker B. , Balogh A. , Rème H.
Published: May 2003

Oscillations of the current sheet observed by the Cluster spacecraft are investigated, using the special ability of Cluster to separate between spatial and temporal variations. We find that before substorm onset, a thin current sheet moves with a velocity of 10 km/s mainly in the vertical direction; after substorm onset the current sheet thickens and moves with greater velocity, ∼25 km/s. Oscillations of the current sheet observed before and after substorm onset can well be interpreted and modeled as a driven magnetoacoustic, with different values for the (Harris) current sheet half thickness and the current sheet velocity before and after substorm onset. The damping rate of the wave can be shown to be related to the thickening rate of the current sheet.
Effect of near‐IR photolysis of HO2NO2 on stratospheric chemistry
Authors: Evans J. T. , Chipperfield M. P. , Oelhaf H. , Stowasser M. , Wetzel G.
Published: May 2003

We use a 3D model to assess the impact of the recently reported near‐IR (NIR) photolysis of HO2NO2 on global stratospheric chemistry. Including this process in the model leads to a significant reduction in HO2NO2 for all latitudes and seasons. The effect is larger at high latitudes with the maximum reduction (>95% near 20 km) in winter. While the basic model strongly overestimates the MIPAS balloon observations of HO2NO2 at mid‐high latitudes, this discrepancy is largely removed by including the NIR photolysis. In high latitude winter below 25 km the model still overestimates HO2NO2 but this may be due to remaining uncertainties in HO2NO2 formation/loss rates and modelled NO2. The NIR photolysis increases model HOx (OH + HO2). At high latitudes around 18 km HOx increases by over 30% all‐year‐round, with much larger enhancements (>70%) near the terminator. However, there is a corresponding NOx (NO + NO2) decrease of ∼10% in high latitude summer. Consequently, at this altitude O3 decreases by only 1–2%.
Controls of dust emissions by vegetation and topographic depressions: An evaluation using dust storm frequency data
Authors: Engelstaedter S. , Kohfeld K. E. , Tegen I. , Harrison S. P.
Published: May 2003

The degree to which dust emissions are controlled by vegetation cover and geomorphic setting (specifically closed topographic depressions) was investigated using dust storm frequency (DSF) data based on visibility measurements from >2400 meteorological stations worldwide. Comparisons with distributions of vegetation types suggest that DSF is highest in desert/bare ground (median: 60–80 d/yr) and shrubland (median: 20–30 d/yr) regions, and comparatively low in grassland regions (median: 2–4 d/yr). Average DSF is inversely correlated with leaf area index (an index of vegetation density) and net primary productivity. In non‐forested regions, DSF increases as the fraction of closed topographic depressions increases, likely due to the accumulation of fine sediments in these areas. These findings support the importance of incorporating vegetation and geomorphic setting as explicit controls on emissions in global dust cycle models.
Modeling the barotropic response of the global ocean to atmospheric wind and pressure forcing ‐ comparisons with observations
Authors: Carrère Loren , Lyard Florent
Published: May 2003

A global simulation of the ocean response to atmospheric wind and pressure forcing has been run during the Topex/Poseidon (T/P) period (1992–2002), using a new hydrodynamic finite element (FE) model, MOG2D‐G. Model outputs are compared to in situ observations with tide gauge data (TG) and bottom pressure gauge data (BPR), and also with T/P altimetric cross over points (noted CO). Intercomparisons were performed over the 1993–1999 period. The model correction reduces the sea level variance by more than 50% at TG locations, and by more than 15% at T/P CO, when compared to the classical inverse barometer correction (IB). The model impact differs between high and low latitudes: in the very energetic high latitudes areas, MOG2D‐G is efficient in reducing the variance, while at low latitudes, the results are similar to the IB static response. In shallow water, the model shows an oceanic response very different from the IB response. In conclusion, MOG2D‐G models the high frequency (HF) atmospheric forced variability of the global ocean with unprecedented accuracy.
Seismotectonics of the Amenthes Rupes thrust fault population, Mars
Authors: Schultz Richard A.
Published: May 2003

Thrust faults within the Amenthes Rupes population in eastern Mars accommodated contractional strains of ∼0.06% with total cumulative moment (energy) release of ∼2 × 1024MJ during Late Noachian time. “Small” faults, that scale three‐dimensionally, accommodate only 12–17% of the strain and 6–9% of the moment release, indicating that inventories of Martian faults need not be complete down to the smallest lengths for meaningful estimates of strain and moment to be obtained. Frictional stability relations for Martian lithosphere suggest that most (83%) of the largest fault, Amenthes Rupes, was seismogenic during displacement accumulation, with smaller faults being progressively less seismogenic as shallower depths are penetrated with decreasing fault lengths. Given plausible displacement rates from terrestrial intraplate thrust faults of ∼1–0.01 mm yr−1, the Amenthes fault population may have taken as little as 1.5 m.y. to grow into its present configuration, corresponding to slow homogeneous strain rates of 10−17s−1, or less, that are comparable to those of terrestrial plate interiors.
New constraints on the motion of the Fairweather fault, Alaska, from GPS observations
Authors: Fletcher Hilary J. , Freymueller Jeffrey T.
Published: May 2003

GPS velocities from sites near to the Fairweather fault in southern Alaska are combined with line length data from geodetic surveys by the U. S. Geological Survey (USGS) to estimate the slip rate and locking depth of the Fairweather fault using dislocation theory. We perform a weighted least‐squares inversion of the geodetic data and obtain a best‐fitting slip rate of 45.6 ± 2.0 mm/yr and locking depth of 9.0 ± 0.8 km. The slip rate we estimate is one of the highest observed across any strike slip fault. We also include the Dalton Creek segment of the Denali fault in our model and estimate a slip rate of 3.8 ± 1.4 mm/yr for this section of the fault. This is substantially lower than the rate observed for the Denali fault segment to the northwest, which ruptured in the November 3, 2002 MW 7.9 Denali fault earthquake.
The 2002 ocean color anomaly in the Florida Bight: A cause of local coral reef decline?
Authors: Hu Chuanmin , Hackett Keith E. , Callahan Michael K. , Andréfouët Serge , Wheaton Jennifer L. , Porter James W. , Muller‐Karger Frank E.
Published: May 2003

The status of coral reef communities has been monitored annually since 1996 at two sites north of Key West, Florida, [Smith Shoal (24.72°N, 81.92°W) and Content Keys (24.82°N, 81.49°W)]. Percent cover of selected benthic community categories and stony (hermatypic) coral species number at these sites were relatively stable from 1996 to 2001, but decreased by >70% and >40%, respectively, from 2001 to 2002. Clionid sponges ranged from 12–16 colonies in 2001, but none were observed in 2002. Satellite ocean color imagery showed the transit of water with abnormally low water‐leaving radiance values between March and May 2002 over these sites. Field observations showed that this “black” water contained the red tide organism Karenia brevis and high diatom concentrations. The observations from satellite ocean color data suggested that the decline in the benthic communities was related to the passage of the water patch over the reef sites.
Effect of tracer buoyancy on tracer experiments conducted in fractured crystalline bedrock
Authors: Becker Matthew W.
Published: May 2003

Tracer buoyancy has been shown to influence breakthrough from two‐well tracer experiments conducted in porous media. Two‐well tracer experiments are presented from fractured crystalline bedrock, in which the specific gravity of the tracer injectate varied from 1.0002 to 1.0133. Under the forced hydraulic conditions imposed, no difference in breakthrough was noted for the three experiments. These results show that even relatively dense tracer injectate solutions may have an insignificant effect on breakthrough when imposed gradients are sufficiently large.
The thermal history of leaky chronometers above their closure temperature
Authors: Albarède Francis
Published: May 2003

A theory is presented which describes the simultaneous radiogenic ingrowth and loss of a radiogenic isotope by volume diffusion in crystals cooling slowly above their closure temperatures. When the diffusion parameters of a given radiogenic isotope in the host mineral are known, the age deficit resulting from the open system behavior can be simply related to the cooling rate. An application to the apparent147Sm‐143Nd ages of pyrope garnets in Archean eclogite xenoliths attests to the slow cooling rate of the subcontinental lithosphere.
A moving‐boundary box model (MBBM) for oceans in change: An application to the East/Japan Sea
Authors: Kang Dong‐Jin , Park Sunyoung , Kim Young‐Gyu , Kim Kuh , Kim Kyung‐Ryul
Published: May 2003

The East/Japan Sea has undergone dramatic changes during the last 50–60 years as the result of a shift in its ventilation system from bottom water formation to intermediate water formation. A moving‐boundary box model (MBBM) was developed to quantify these changes. The model consists of three boxes for deep waters representing Central, Deep, and Bottom Waters, respectively, and two boundaries in between, which are moving according to the volume changes of these water masses. The model calibrated with CFC‐11 and tritium distribution shows the bottom water formation of ∼0.02 Sv in magnitude in the past slowed down and came to a complete halt in mid‐1980s and late‐1990s. Furthermore, this model predicts the Bottom Water will disappear completely in 2040 as Central Water penetrates deeper. Considering the recent observations that many oceans are in change, a MBBM could be a valuable tool to investigate the nature of such changes.
Implementing cellular automata models for earthquakes on parallel computers
Authors: Castellaro S. , Mulargia F.
Published: May 2003

Cellular automata models require simulations on both large grids, to avoid border effects, and on a large number of realizations, to study the system properties under stationarity. Implementing the cellular automata codes on parallel computers would appear as an ideal solution. Unfortunately, the cellular automata models which are appropriate for earthquakes can only be partially parallelized because they have an intrinsically sequential component. Under extensive modeling using MPI on CRAY T3 and Origin 8300 supercomputers we show that a substantial speed‐up can nevertheless be achieved by coarsening the system and making a few mild assumptions on the logical flow of the interactions among macro‐cells.
Extratropical control of tropical climate, the atmospheric bridge and oceanic tunnel
Authors: Liu Zhengyu , Yang Haijun
Published: May 2003

A coupled ocean‐atmosphere model study shows that the extratropical impact on tropical climate is as strong as the tropical impact on extratropical climate. A 2°C SST warming in the global extratropics increases equatorial ocean temperature by ∼1°C in the surface and subsurface. The surface temperature change is caused by the atmospheric bridge of the Hadley circulation (70%) and the oceanic tunnel of thermocline subduction (30%), while the subsurface temperature change is forced predominantly through the oceanic tunnel. Furthermore, the dominant influence on the equator comes from the southern hemisphere atmosphere and ocean.
Evidence for the nucleation of polar stratospheric clouds inside liquid particles
Authors: Irie Hitoshi , Kondo Yutaka
Published: May 2003

The Improved Limb Atmospheric Spectrometer on board the Advanced Earth Observing Satellite first detected the onset of denitrification at 19 and 20 km in the 1996/1997 Arctic winter stratosphere. Box model calculations along back trajectories were used to estimate the degree of denitrification caused by the formation of nitric acid trihydrate (NAT) particles inside liquid aerosols. The loss of reactive nitrogen calculated assuming conversion of nitric acid dihydrate to NAT and direct NAT formation explains well the observed loss, demonstrating that such NAT particle formation mechanisms play a critical role in Arctic denitrification.
A transport model study of the breakup of the Antarctic ozone hole in November 2000
Authors: Grainger Simon , Karoly David J.
Published: May 2003

A 3‐D off‐line transport model is used to examine the breakup of the Antarctic ozone hole in late November and early December 2000. The use of a transport model enables an analysis of the vortex breakup that is not possible from the use of ozonesonde observations alone. By initializing ozone mixing ratio on 1 September 2000, and using parameterized ozone production and loss rates, the evolution of the Antarctic ozone hole is simulated. The model simulation shows that during late November and early December 2000, the Antarctic ozone hole splits into two sections, with low‐ozone air subsequently transported over New Zealand and south‐eastern Australia. Modeled ozone values agree well with ozonesonde profiles, confirming the role of horizontal transport in the dilution of mid‐latitude ozone.
Cross‐shelf passage of coastal water transport at the South Atlantic Bight observed with MODIS Ocean Color/SST
Authors: Li Chunyan , Nelson James R. , Koziana James V.
Published: May 2003

Images of cross‐shelf fronts of ocean color parameters and Sea Surface Temperature (SST) of the South Atlantic Bight (SAB) area are presented and analyzed. The ocean color parameters (K‐490 and suspended solid concentration) and SST clearly indicate a penetrating front originating from the coastal water within the inner shelf. The front is triangular shaped with its broad base on the coast and its sharp end penetrating into the outer shelf and merging into the Gulf Stream, depicting a passage of coastal water transport across the shelf. This passage changes in position and orientation (from southwest‐northeast to west‐east). The horizontal Ekman number was estimated to be outside the limit of baroclinic instability, suggesting that the process is deterministic. Thus, the water transport passage may play a significant role in a non‐diffusive transport process of heat and land‐derived biogeochemical materials.
Three‐dimensional structure of magnetic reconnection in a laboratory plasma
Authors: Cothran C. D. , Landreman M. , Brown M. R. , Matthaeus W. H.
Published: May 2003

The local three‐dimensional structure of magnetic reconnection has been measured for the first time in a magnetohydrodynamic (MHD) laboratory plasma at the Swarthmore Spheromak Experiment. An array of 600 magnetic probes which resolve ion inertial length and MHD time scale dynamics on a single shot basis measured the magnetic structure of partial spheromak merging events. Counter‐helicity spheromaks merge rapidly, and reconnection activity clearly self‐generates a local component of B which breaks the standard 2D symmetry at the ion inertial scale. Consistent with prior results, no reconnection is observed for co‐helicity merging.
Current sheet flapping motion and structure observed by Cluster
Authors: Sergeev V. , Runov A. , Baumjohann W. , Nakamura R. , Zhang T. L. , Volwerk M. , Balogh A. , Rème H. , Sauvaud J. A. , André M. , Klecker B.
Published: May 2003

Fast vertical flapping oscillations of the plasma sheet have been observed by Cluster on September 26, 2001. The flapping motion had vertical speeds exceeding 100 km/s, an amplitude in excess of 1 RE and a quasiperiod of ∼3 min. The current sheet was mostly tilted in the Y‐Z plane (with the tilt sometimes exceeding 45°). The waves had the properties of a kink mode and propagated toward the dusk flank. The flapping allowed to probe the vertical structure of the plasma sheet. Three different methods gave consistent evidence of a bifurcated structure of the cross‐tail current with about half of all current concentrated in two sheets (each ∼500–1000 km thick). The current density peaks at ∣Bx∣ ∼ 0.5 BL, with a pronounced current density minimum and a plasma density plateau between these peaks.
A new technique for short‐term forecast of auroral activity
Authors: Lui A. T. Y. , Lai W. W. , Liou K. , Meng C. I.
Published: May 2003

An age‐old challenge in space research is the search for an accurate prediction algorithm of auroral disturbances in the complex space environment system. Based on six months of observations from the Ultraviolet Imager on the Polar satellite, we have conducted a statistical study of four attributes of over 9000 auroral activity sites. These attributes are area, power, and their rates of change. The results provide us with a new technique to forecast auroral activity by setting up criteria on these activity attributes. The derived criteria for predicting 1 TJ total auroral energy dissipation at an activity site give a probability of correct high dissipation prediction of 0.85, a probability of correct low dissipation prediction of 0.95, a true skill score of 0.80, and an averaged advance warning time of 42 min. Similar prediction statistics are found for 0.1 and 10 TJ energy dissipation predictions. The prediction statistics indicate a high degree of forecast accuracy for this new technique.
Initial cloud images with the NRL high power 94 GHz WARLOC radar
Authors: Manheimer W. M. , Fliflet A. W. , St. Germain K. , Linde G. J. , Cheung W. J. , Gregers‐Hansen V. , Danly B. G. , Ngo M. T.
Published: May 2003

The Naval Research Laboratory has recently developed a high power 94 GHz radar with scanning capability, WARLOC. One application has been to image clouds. New capabilities of WARLOC include imaging with greatly improved sensitivity and detail, the ability to detect much lower cloud returns, the capability of using chirped pulses with pulse compression for high range resolution, the rapid generation of high resolution three dimensional images, and the possibility of producing extremely fine scale images with stretch processing. WARLOC is now set up on the western shore of Chesapeake Bay. This letter presents some of the first cloud images obtained.
On the response of Southern Ocean water‐masses to atmospheric meridional moisture advection
Authors: Saenko Oleg A. , England Matthew H.
Published: May 2003

We investigate the role of atmospheric moisture advection in determining Southern Ocean water‐mass properties in a coupled climate model. Two sensitivity experiments are presented in which the winds advecting moisture are either reduced or enhanced south of 45°S. It is shown that a variation in meridional winds in the Southern Ocean can generate large anomalies of subsurface potential temperature (T) and salinity (S). A reduction (increase) in southward atmospheric moisture advection tends to be balanced by a corresponding reduction (increase) in northward freshwater transport in Antarctic Intermediate Water. The response of both T and S is larger in the case of reduced southward moisture advection, as this corresponds to an overall reduction of Southern Ocean stratification. The interior ocean T–S response is not always density‐compensating, particularly in the Indian and Pacific Oceans. This is unlike zonal wind variations which have a tendency to change T–S in a density‐conserving manner. Our study suggests that variability in meridional winds over the Southern Ocean can alter local water‐mass formation rates significantly.
Configuration of subducting Philippine Sea plate and crustal structure in the central Japan region
Authors: Iidaka T. , Iwasaki T. , Takeda T. , Moriya T. , Kumakawa I. , Kurashimo E. , Kawamura T. , Yamazaki F. , Koike K. , Aoki G.
Published: May 2003

A seismic experiment with 6 explosive sources and 391 seismic stations was conducted in August 2001 in the central Japan region. A large lateral variation of the thickness of sedimentary layer was observed. P‐wave velocity values below the sedimentary layer obtained were 5.3 km/s ∼ 5.8 km/s. P‐wave velocity values at the lower part of upper crust and lower crust are estimated to be 6.0 km/s ∼ 6.4 km/s and 6.6 km/s ∼ 6.8 km/s, respectively. Two clear later phases were observed at the record section of shot‐J5. The phases are interpreted to be reflected waves at the boundaries with depths of about 10–20 km and 20–35 km. The dip angle of the deep boundary is about 26°. The shallower reflector is interpreted to be a lithological boundary. The deeper reflector is the upper boundary of subducting Philippine Sea plate. The configuration of the subducting Philippine Sea slab was revealed.
Aerosol spectral optical depths over the Bay of Bengal: Role of transport
Authors: Moorthy K. Krishna , Babu S. Suresh , Satheesh S. K.
Published: May 2003

Recent experiments have shown the potential role of air masses in transporting aerosols to locations far away from source regions. Despite the importance of the Bay of Bengal to Indian climate and monsoon, no serious aerosol observations are available for this region. Extensive aerosol optical depth estimates, made for the first time from an island location, Port Blair (11.63°N; 92.71°E) in the Bay of Bengal, during the Indian winter of 2002, are used to examine the impact of air trajectories in modifying the optical depths and their spectral dependences. The results are examined for their distinctiveness with respect to the origin as well as transport. It is seen that the trajectories arriving from the regions east of the station (South China, Thailand, Laos, Cambodia, Vietnam, Burma) are richer in aerosol abundance, more in the sub micron size range, than those arriving from the west, across the Indian landmass.
Radar echoes from lightning and their microphysical environment
Authors: Atlas David , Williams Christopher R.
Published: May 2003

A UHF Profiler radar has detected lightning echoes which occurred preferentially in a “balance layer”, the stratum of mean zero Doppler velocity with rising small ice particles and falling graupel and hail, thus providing the conditions for collisional charging and lightning. The results support prior findings of the role of the balance layer in lightning generation. The 32.8 cm Profiler radar is particularly well suited for these observations because the lightning echoes are not masked by the precipitation echoes, thus allowing simultaneous measurement of the microphysical and kinematic properties.
Observations of the 5‐day planetary wave in PMC measurements from the Student Nitric Oxide Explorer Satellite
Authors: Merkel A. W. , Thomas G. E. , Palo S. E. , Bailey S. M.
Published: May 2003

The Student Nitric Oxide Explorer (SNOE) satellite has been observing Polar Mesospheric Clouds (PMCs) since 1998 and has successfully measured seven PMC seasons. In the summer seasons, the Ultraviolet Spectrometer (UVS) limb measurements include detections of PMCs between 80 – 90 km. SNOE observations of PMCs have a significant advantage over other PMC measurements in that it can observe them globally each day. Because SNOE orbits the earth 15 times a day, daily global images of PMC brightness may be produced. Variations in the PMC brightness with a 5‐day period are observed from the measurements. The 5‐day wave is observed in both the northern and southern hemisphere polar summers at high latitudes. This is the first direct global scale wave analysis performed on PMC measurements and indicates the effects of dynamics on PMC formation.
A comparison of Northern and Southern Hemisphere cross‐tropopause ozone flux
Authors: Olsen Mark A. , Douglass Anne R. , Schoeberl Mark R.
Published: May 2003

The downward flux of ozone across the midlatitude (30°–60°) tropopause is calculated using changes in potential vorticity (PV) and a statistical relationship between the PV changes and ozone flux. This approach separates dynamical aspects of transport from the seasonal cycle of ozone in the lowermost stratosphere. The Northern Hemisphere (NH) ozone flux is larger (∼24%) than that calculated in the Southern Hemisphere (SH) during the year 2000. The midlatitude SH total horizontal area of exchange is equal to or slightly greater than the area of exchange in the NH throughout an annual cycle. The mean changes in potential vorticity of parcels near the tropopause are also similar or slightly greater in the SH, suggesting that NH and SH downward air mass transport to the troposphere are comparable. These results show that the greater NH midlatitude ozone flux is mostly due to the amount of ozone available for exchange rather than dynamical differences near the tropopause level at these latitudes.
Biogeochemical signatures of nitrogen fixation in the eastern North Atlantic
Authors: Mahaffey Claire , Williams Richard G. , Wolff George A. , Mahowald Natalie , Anderson William , Woodward Malcolm
Published: May 2003

Stable nitrogen isotopic determination of particulate organic matter over the eastern North Atlantic in spring 2000 reveal a region of low natural abundance of 15N relative to 14N between 26°N and 32°N along 20°W. This light isotopic signal, together with phytopigment data and persistently elevated nitrate to phosphate ratios in the upper thermocline, suggest that nitrogen fixation provides a local dominant supply of nitrogen to phytoplankton over part of the eastern North Atlantic. These independent biogeochemical proxies are coincident with a region of enhanced atmospheric dust deposition, as suggested by an atmospheric transport model. Hence, the atmospheric dust events may spatially and temporally constrain the distribution of N2 fixers.
Low latitude ice cores record Pacific sea surface temperatures
Authors: Bradley R. S. , Vuille M. , Hardy D. , Thompson L. G.
Published: May 2003

Oxygen isotope variations in ice cores from Bolivia and Peru are highly correlated with sea surface temperatures (SSTs) across the equatorial Pacific Ocean, which are closely linked to ENSO variability. Circulation anomalies associated with this variability control moisture flux from the equatorial and tropical Atlantic Ocean and Amazon Basin to the ice core sites. Below average SSTs lead to higher accumulation rates and isotopically lighter snow; such conditions are also associated with lower atmospheric freezing levels. During warm events, opposite conditions prevail. Oxygen isotope variations in an ice core from the Himalayas also reflect SST variations in the equatorial Pacific Ocean, pointing to the prospect of reconstructing low latitude circulation anomalies from a network of ice cores in selected locations.
Nature and hydrological relevance of the Shalbatana complex underground cavernous system
Authors: Rodriguez Jose Alexis Palmero , Sasaki Sho , Miyamoto Hideaki
Published: May 2003

The geomorphology of the North East trending long fractured depression between the Ganges Chasma and the Shalbatana Vallis headwater source region is examined and interpreted to be the result of collapse of part of an extensive underground cavernous system. We propose that this cavernous system undermines at least a valley, which extends from the vicinities of the Ganges Chasma and terminates in the Shalbatana Vallis headwater source region and the Aromatum Chaos. We believe that the origin of this cavernous system was related to the formation and interconnection of discrete cavernous bodies and propose a hypothesis, which involves the interaction of permafrost and intrusive magmatism to explain their formation. The Shalbatana Vallis headwater source is interpreted as produced by a Noachian impact crater and surface collapse over part of the underground cavernous system. Finally, we propose that the water sources, which were involved in the excavation of the Shalbatana and Ravis outflow channels might have included water segregated from the permafrost through interaction of intrusive magmatism and permafrost, water drained from a paleolake in the Ganges Chasma and water released from the catastrophic evacuation of confined aquifers.
Dynamical aspects of climate sensitivity
Authors: Boer George J. , Yu Bin
Published: May 2003

Dynamical aspects of climate feedback/sensitivity are investigated in climate change simulations with a common atmospheric general circulation model coupled to a full ocean model, which responds both dynamically and thermo‐dynamically, and to a mixed‐layer ocean component which responds only thermodynamically. Temperature responses differ with a warmer tropics and an El Niño‐like pattern in the full ocean case but not in the mixed‐layer case. There is also more warming in Arctic and less in Antarctic regions. The geographical patterns of radiative feedback also differ with positive feedback in the tropical Pacific in the full ocean case contrasting with negative feedback in the mixed‐layer case. Positive feedback in the tropical Pacific directly supports an El Niño‐like response to positive (and a La Niña‐like response to negative) radiative forcing. Radiative feedback depends implicitly on dynamical quantities and differences are a consequence of missing oceanic transport pathways in the mixed‐layer ocean.