bluuebunny/crossref_metadata_2025 huggingface dataset:
Saharan dust transport to the Caribbean during PRIDE: 1. Influence of dust sources and removal mechanisms on the timing and magnitude of downwind aerosol optical depth events from simulations of in situ and remote sensing observations
Authors: Colarco P. R. , Toon O. B. , Holben B. N.
Published: July 2003

Dust emissions, transport, and deposition are simulated for the Puerto Rico Dust Experiment (June–July, 2000) with a three‐dimensional aerosol transport model driven by assimilated meteorology. Sensitivity to the dust source formulation is tested by comparing simulations run with two different source modules to TOMS and AERONET measurements. Central and east African dust sources are more accurately simulated with the Ginoux et al. [2001] source model than with the Marticorena and Bergametti [1995] source model. The timing of high aerosol optical depth (AOD) dust events at Puerto Rico is largely independent of the timing of dust emissions, implying a persistent reservoir of suspended dust particles exists over Africa and that the timing of downwind dust events is more strongly coupled to transport dynamics than to the dust source model chosen. The downwind AOD and particle size distribution are accurately simulated using the dust particle size distribution produced by the Ginoux et al. [2001] source model or by fitting the Marticorena and Bergametti [1995] dust emissions to the d'Almeida [1987] background desert aerosol particle size distribution. The dust distribution determined by fitting the Marticorena and Bergametti [1995] emissions to the Schulz et al. [1998] initial particle size distribution produces aerosol optical depths that are consistently too high. Large dust particles observed far downwind of source areas may be partially explained if they are treated as flat disks rather than spheres in the particle fall velocity calculation. With the Ginoux et al. [2001] source model we estimate African and Arabian dust emissions during July 2000 to be 214 Tg for particles smaller than 10 μm radius. Nineteen percent of the emitted mass is transported west of Africa and over the North Atlantic. Twenty percent of the dust leaving Africa passes west of Puerto Rico.
Seasonal variability and trends of volatile organic compounds in the lower polar troposphere
Authors: Gautrois M. , Brauers T. , Koppmann R. , Rohrer F. , Stein O. , Rudolph J.
Published: July 2003

Measurements of the atmospheric mixing ratios of 10 nonmethane hydrocarbons (NMHC) and four halocarbons (methyl chloride, dichloromethane, trichloroethene, and tetrachloroethene) were conducted between January 1989 and July 1996 at Alert (Canadian Arctic, 82°27′N, 62°31′W). About 270 canister samples were analyzed covering the 7‐year period with an average frequency of about one sample every 9 days. The mixing ratios of these volatile organic compounds (VOC) exhibit considerable variability, which can partly be described by systematic seasonal dependencies. The highest mixing ratios were always observed during winter. During spring, the mixing ratios decrease for some compounds to values near the detection limit. The amplitudes of the seasonal variability, the time of the occurrence of the maxima, and the relative steepness of the temporal gradients show a systematic dependence on OH reactivity. The steepest relative decrease is less than 1% d−1 for methyl chloride, increasing to about 4% d−1 for highly reactive VOC. Similarly, the highest relative increase rates vary between 0.5% d−1 for VOC with low reactivity to 4% d−1 for reactive VOC. With the exception of ethyne, toluene, and methyl chloride the concentrations of all measured VOC decrease during the studied period, although this decrease is not always statistically significant. In general, the largest changes were found for the most reactive VOC, although the seemingly random overall variability observed for these compounds results in substantial uncertainties. For the less reactive VOC (ethane, benzene, and propane) the average relative annual decrease rate is in the range of a few percent per year. Dichloromethane and tetrachloroethene showed a decrease of 4 and 14% yr−1, respectively. The average decrease rate for the other alkanes is in the range of some 10% yr−1, indicating a substantial change of emission rates during this period. A likely explanation is a reduction in VOC emissions in the area of the former Soviet Union, most likely Siberia, as a consequence of the recent major economic changes in this region. The measurements were compared with the results of chemical transport models' simulations using the Emission Database for Global Atmospheric Research NMHC emission inventory. Although the model captures most of the main features of the shapes of the seasonal cycles of the NMHC, the results clearly show that model estimates are consistently too low compared to the observations. Most likely this is the consequence of an underestimate of the NMHC emission rates in the emission inventory.
Upper tropospheric ozone derived from the cloud slicing technique: Implications for large‐scale convection
Authors: Ziemke J. R. , Chandra S. , Bhartia P. K.
Published: July 2003

This study evaluates the spatial distributions and seasonal cycles in upper tropospheric ozone (pressure range 200–500 hPa) from low to high latitudes (60°S to 60°N) derived from the satellite retrieval method called “cloud slicing.” The cloud slicing method determines ozone profile information in the troposphere by combining colocated measurements of cloud top pressure and above‐cloud column ozone. Measurements of Nimbus 7 Total Ozone Mapping Spectrometer (TOMS) above‐cloud column ozone and Nimbus 7 Temperature Humidity Infrared Radiometer (THIR) cloud top pressure during 1979–1984 were merged to derive upper tropospheric ozone. Because of large footprint measurements from TOMS (∼100 km diameter on average), upper tropospheric ozone derived from cloud slicing coincides with large‐scale convection events. These events are not necessarily representative of average atmospheric conditions in regions near and poleward of the tropospheric wind jets (around ±30° latitude), especially in winter and spring seasons when dynamical wave activity in the troposphere and lower stratosphere is most intense. The cloud slicing method with Nimbus 7 geometry in any case provides a unique opportunity to investigate the behavior of upper tropospheric ozone under condition of intense broad‐scale convection. In the tropics the measured upper tropospheric ozone shows year‐round enhancement in the Atlantic region and evidence of a possible semiannual variability. Outside the tropics, upper tropospheric ozone from cloud slicing shows greatest abundance in winter and spring seasons in both hemispheres with largest variance and largest amounts in the northern hemisphere. This seasonal cycle behavior under conditions of intense convection is different from general ozonesonde climatology which shows instead upper tropospheric ozone maximizing around early to middle summer months. The seasonal cycles and spatial characteristics in upper tropospheric ozone from cloud slicing are similar to lower stratospheric ozone. It is suggested that the large‐scale convection events with cloud slicing coincide with an occurrence of stratosphere‐troposphere exchange (STE).
Characterization of African dust transported to Puerto Rico by individual particle and size segregated bulk analysis
Authors: Reid Elizabeth A. , Reid Jeffrey S. , Meier Michael M. , Dunlap Michael R. , Cliff Steven S. , Broumas Aaron , Perry Kevin , Maring Hal
Published: July 2003

As part of the Puerto Rico Dust Experiment (PRIDE), airborne and surface dust particle samples from Africa were collected and subjected to bulk elemental and single‐particle analysis. Airborne samples were collected on polycarbonate filters at various altitudes and underwent single‐particle scanning electron microscopy with energy dispersive analysis with X‐rays (EDAX) to derive elemental ratios of key soil elements. Particle chemistry was related to size and morphological characteristics. At the principle surface site, particles were collected on a Davis Rotating Drum (DRUM) cascade impactor strips in eight stages from 0.1 to 12 μm at 4 hour time resolution. These samples were subjected to X‐ray florescence (XRF) to determine bulk elemental composition from Al through Zn. The elemental data showed good correlation between the DRUM and the aircraft samples. Cluster analysis of single‐particle data resulted in 63 statistically significant clusters. Several clusters can be easily related to their parent mineralogical species. However, as dust particles are to a large extent aggregates, most clusters are based on a continuum of varied mineralogical species and cannot be easily categorized. With 60,500 total particles counted from the airborne filters, a statistically significant number of large particles could be analyzed. Estimated mean surface area modal diameter is ∼5 μm, with an average aspect ratio of 1.9. An apparent change in source region is seen in the morphological data and non alumino‐silicate minerals but is not seen in the aluminum to silicon ratio. We suspect homogenization during long‐range transport.
Stretching rates and equivalent length near the tropopause
Authors: Scott R. K. , Shuckburgh E. F. , Cammas J.‐P. , Legras B.
Published: July 2003

Diagnostics of mixing in the upper troposphere/lower stratosphere region reveal interesting seasonal and interannual variability and illustrate how the subtropical tropopause can be identified with a region of minimum mixing, a partial barrier to the transport of air between the troposphere and stratosphere. Both the strength and the location of this barrier show substantial seasonal variability, with a stronger barrier and weaker mixing observed during winter. The interannual variability of the mixing intensity near the tropopause on the 350 K isentropic surface suggests a correlation with the phase of the El Niño‐Southern Oscillation, with weaker mixing occurring during strong El Niño years. The diagnostics are based on the analyses and reanalyses from the European Centre for Medium‐Range Weather Forecasts over the 21 year period 1979–2000 and include the exponential stretching rates of material contours and Nakamura's [1996] modified Lagrangian mean effective diffusivity/equivalent length. As well as providing information about the spatial and temporal distribution of mixing intensity, the diagnostics also indicate sensitivity to changes in the analyses/reanalyses data sets. In particular, a stronger seasonal cycle and greater interannual variability is found in the more recent (1994–2000) analyses than in the earlier (1979–1993) reanalyses.
Water vapor retrievals using Moderate Resolution Imaging Spectroradiometer (MODIS) near‐infrared channels
Authors: Gao Bo‐Cai , Kaufman Yoram J.
Published: July 2003

At present, two Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on board the NASA Terra and Aqua Spacecraft platforms are operational for global remote sensing of the land, ocean, and atmosphere. In this paper, we describe an algorithm for water vapor derivations using several MODIS near‐IR channels. The derivations are made over areas that have reflective surfaces in the near‐IR, such as clear land areas, clouds, and oceanic areas with Sun glint. The algorithm relies on observations of water vapor attenuation of near‐IR solar radiation reflected by surfaces and clouds. Techniques employing ratios of water vapor absorbing channels centered near 0.905, 0.936, and 0.940 μm with atmospheric window channels at 0.865 and 1.24 μm are used. The ratios partially remove the effects of variation of surface reflectance with wavelengths and result in the atmospheric water vapor transmittances. The column water vapor amounts are derived from the transmittances based on theoretical calculations and using lookup table procedures. Typical errors in the derived water vapor values are in the range between 5% and 10%. The daily “pixel‐based” near‐IR water vapor product, which is a standard MODIS level 2 data product, at the 1‐km spatial resolution of the MODIS instrument, and the daily, 8‐day, and monthly near‐IR water vapor products, which are standard MODIS level 3 products, at a 1° by 1° latitude‐longitude grid globally are now routinely produced at a NASA computing facility. We present samples of water vapor images and comparisons to ground‐based measurements by microwave radiometers.
An evaluation of trends in middle atmospheric water vapor as measured by HALOE, WVMS, and POAM
Authors: Nedoluha Gerald E. , Bevilacqua Richard M. , Gomez R. Michael , Hicks Brian C. , Russell James M. , Connor Brian J.
Published: July 2003

We compare middle atmospheric water vapor measurements from the HALogen Occultation Experiment (HALOE), Water Vapor Mm‐wave Spectrometer (WVMS), and Polar Ozone and Aerosol Measurements (POAM) instruments. Coincident WVMS and HALOE data are compared at the Network for the Detection of Stratospheric Change (NDSC) sites at Mauna Loa, Hawaii (19.5N, 204.4E), from 1996–2002 and at Lauder, New Zealand (45.0S, 169.7E), from 1994–2002. We find that, at most altitudes, there is no significant instrumental drift between the HALOE measurements and the measurements obtained from the two WVMS instruments over these time periods. We also find that at altitudes below ∼60 km, where the solar cycle effects are unimportant, there were no significant trends in either the HALOE or WVMS data sets over the periods of intercomparison. This is in marked contrast to the early 1990s where large trends (2%/year) were obtained from both HALOE and WVMS measurements. Similarly, we compare the HALOE data with the high‐latitude 1998–2002 POAM data set at equivalent latitudes from 45N–55N. Again, the trends are small, and the instrumental trend differences are at most only slightly >1σ. We also look at the HALOE water vapor and H2O + 2CH4 data globally and find that, after a large increase from 1991–1995, there is almost no trend below ∼60 km from 1996–2002. The water vapor trend over the entire HALOE measurement period (1991–2002) is <1%/year. The unusual stratospheric dynamics at the beginning of the 1990s caused large changes in upper stratospheric and lower mesospheric water vapor that were unrelated to the amount of water vapor entering the stratosphere, hence in this region the less dynamically sensitive quantity H2O + 2CH4 probably provides a better measure of water vapor entering the stratosphere during this period. The trend in H2O + 2CH4 over the 1991–2002 HALOE measurements period is ∼0.5%/year.
Early plate tectonics versus single‐plate tectonics on Mars: Evidence from magnetic field history and crust evolution
Authors: Breuer D. , Spohn T.
Published: July 2003

The consequences of an early epoch of plate tectonics on Mars followed by single‐plate tectonics with stagnant lid mantle convection on both crust production and magnetic field generation have been studied with parameterized mantle convection models. Thermal history models with parameterized mantle convection, not being dynamo models, can provide necessary, but not sufficient, conditions for dynamo action. It is difficult to find early plate tectonics models that can reasonably explain crust formation, as is required by geological and geophysical observations, and allow an early magnetic field that is widely accepted as the cause for the observed magnetic anomalies. Dating of crust provinces and topography and gravity data suggest a crust production rate monotonically declining through the Noachian and Hesperian and a present‐day crust thickness of more than 50 km. Plate tectonics cools the mantle and core efficiently, and the core may easily generate an early magnetic field. Given a sufficiently weak mantle rheology, plate tectonics can explain a field even if the core is not initially superheated with respect to the mantle. Because the crust production rate is proportional to temperature, however, an early efficient cooling will frustrate later crust production and therefore cannot explain, for example, the absence of prominent magnetic anomalies in the northern crustal province and the northern volcanic plains in the Early Hesperian. Voluminous crust formation following plate tectonics is possible if plate tectonics heat transfer is inefficient but then the crust growth rate has a late peak (about 2 Ga b.p.), which is not observed. These models also require a substantial initial superheating of the core to allow a dynamo. If one accepts the initial superheating, then, as we will show, a simple thermal evolution model with monotonic cooling of the planet due to stagnant lid mantle convection underneath a single plate throughout the evolution can better reconcile early crust formation and magnetic field generation.
Variations in flow and transport in thick desert vadose zones in response to paleoclimatic forcing (0–90 kyr): Field measurements, modeling, and uncertainties
Authors: Scanlon Bridget R. , Keese Kelley , Reedy Robert C. , Simunek Jirka , Andraski Brian J.
Published: July 2003

An understanding of unsaturated flow and potential recharge in interdrainage semiarid and arid regions is critical for quantification of water resources and contaminant transport. We evaluated system response to paleoclimatic forcing using water potential and Cl profiles and modeling of nonisothermal liquid and vapor flow and Cl transport at semiarid (High Plains, Texas) and arid (Chihuahuan Desert, Texas; Amargosa Desert, Nevada) sites. Infiltration in response to current climatic forcing is restricted to the shallow (∼0.3–3 m) subsurface. Subsurface Cl accumulations correspond to time periods of 9–90 kyr. Bulge‐shaped Cl profiles generally represent accumulation during the Holocene (9–16 kyr). Lower Cl concentrations at depth reflect higher water fluxes (0.04–8.4 mm/yr) during the Pleistocene and earlier times. Low water potentials and upward gradients indicate current drying conditions. Nonisothermal liquid and vapor flow simulations indicate that upward flow for at least 1–2 kyr in the High Plains and for 12–16 kyr at the Chihuahuan and Amargosa desert sites is required to reproduce measured upward water potential gradients and that recharge is negligible (<0.1 mm/yr) in these interdrainage areas.
Comparison of estimators of linear time trend in Weibull‐distributed low flows
Authors: Clarke Robin T.
Published: July 2003

For low‐flow data sequences that can plausibly be assumed to have a Weibull distribution, possibly with time trend superimposed, both estimation of a linear trend parameter and tests for its statistical significance are more efficient where information about the underlying Weibull distribution is incorporated into estimation and testing procedures. Both maximum likelihood and linear‐regression estimates of linear trend are unbiased in sample sizes commonly found in hydrological practice (from 30 to 50 years). In samples of this relatively limited size, maximum likelihood (ML) estimates of a linear trend parameter have smaller variance than the linear regression (LR) estimate, except when the Weibull parameter k is near to one, when the distribution reduces to an exponential form. For the larger sample size used in simulation, N = 50, empirical tests based on the distribution of the ML and LR estimates showed that those based on maximum likelihood were always more powerful. However, a critical assumption in the paper is that annual low flows are independently distributed, and this may not always be justified.
Local scouring at grade‐control structures in alluvial mountain rivers
Authors: Lenzi M. A. , Marion A. , Comiti F.
Published: July 2003

Scour holes below 73 grade‐control structures (check dams and bed sills) in six mountain rivers located in the eastern Italian Alps have been surveyed. The most likely formative water discharge is used to evaluate jet thickness at each structure, which along with drop height, appears to determine scour hole dimensions, as shown by the consistent trends observed for nondimensional plots of both maximum scour depth and length versus the respective drop ratio. Sediment differences regarding size and lithology apparently play a minor role in determining scour hole dimension. Measured maximum scour depths are well predicted by a semiempirical equation developed through laboratory results, showing an average relative error of 0.13. Scour hole geometry is described by several ratios that are thought to represent approximately invariant characteristics. A new energy‐based normalization for scour hole dimensions is proposed as the most suited to evaluate the role of jet geometry and aeration upon scouring efficiency. It is noteworthy that the ratio between the maximum scour depth and the total energy available at a drop tends toward an asymptotic value around unity for increasing drop heights.
Dispersal of the Suwannee River plume over the West Florida shelf: Simulation and observation of the optical and biochemical consequences of a flushing event
Authors: Jolliff Jason K. , Walsh John J. , He Ruoying , Weisberg Robert , Stovall‐Leonard Antoya , Coble Paula G. , Conmy Robyn , Heil Cynthia , Nababan Bisman , Zhang Haiying , Hu Chuanmin , Muller‐Karger Frank E.
Published: July 2003

We have combined a circulation model with one of colored dissolved organic matter (CDOM) photolysis to describe the fate of terrestrial CDOM on the West Florida shelf (WFS). Our results for summer 1998 suggest that a near shore plume of CDOM became entrained in a coastal jet extending south from the Suwannee River (Big Bend) region of the WFS towards the Florida Keys—a feature also evident in satellite ocean color imagery. The coupled models suggest that photochemical losses of CDOM were significant, but provided only a minimal nitrogen source for phytoplankton growth on the WFS.
Patterns of tropospheric response to solar variability
Authors: Gleisner Hans , Thejll Peter
Published: July 2003

Despite numerous reports of apparent climate responses to the 11‐year solar cycle, the Sun's role for weather and climate has remained a matter of controversy. One important reason is the difficulty of reliably attributing the observed atmospheric effects to solar variability, rather than to other forcing factors or intrinsic variability. Here we show that consistent patterns of statistically significant solar signals emerge in all major observables throughout the low‐ and mid‐latitude troposphere, when El Niño and volcanic signals are removed from meteorological data. Solar forcing is strongest in the tropics and at mid‐latitudes, and the heating and moistening of the troposphere during solar maximum is accompanied by a modulation of the large‐scale tropospheric circulation systems. These findings have implications for the question of where and how the Sun exerts its influences in the climate system.
A model of the bifurcated current sheet
Authors: Sitnov M. I. , Guzdar P. N. , Swisdak M.
Published: July 2003

Recent Geotail and Cluster observations revealed that thin current sheets in the near‐Earth tail may have a bifurcated structure. In some cases the electrons are found to dominate the current. We present a generalization of the Harris current sheet equilibrium, which reproduces these features. The model ion distribution contains an additional element, viz. the quasi‐adiabatic invariant of the ion motion across the sheet, and assumes ion temperature anisotropy outside the sheet. Bifurcated current sheets appear in the case of small ion anisotropy with T⟂i > T∥i (pancake distributions). In the opposite case (cigar distributions) the model describes a single‐peaked ion‐dominated current sheet embedded in a thicker Harris sheet, which is more relevant to the outflow region of the collisionless reconnection pattern in the deHoffman‐Teller frame.
Impact of the wintertime North Atlantic Oscillation (NAO) on the summertime atmospheric circulation
Authors: Ogi Masayo , Tachibana Yoshihiro , Yamazaki Koji
Published: July 2003

Using the NCEP/NCAR reanalysis dataset and other observations, we show that the summer high‐latitude climate in the Northern Hemisphere is influenced by the NAO of the previous winter. We find this influence in the summertime surface air temperature, the geopotential height, the sea surface temperature (SST), sea‐ice/continental snow cover extent fields as well as in the zonal mean geopotential height and zonal wind fields. This summertime NAO signal is annular but its meridional scale is much smaller than the winter annular mode. Distinct summer anomalies are located at the nodal latitudes of the winter anomalies. We suggest that the sea‐ice, SST and snow cover anomalies provide the memory allowing the winter NAO to affect the summer climate.
Exploring links between physical and probabilistic models of volcanic eruptions: The Soufrière Hills Volcano, Montserrat
Authors: Connor C. B. , Sparks R. S. J. , Mason R. M. , Bonadonna C. , Young S. R.
Published: July 2003

Probabilistic methods play an increasingly important role in volcanic hazards forecasts. Here we show that a probability distribution characterized by competing processes provides an excellent statistical fit (>99% confidence) to repose intervals between 75 vulcanian explosions of Soufrière Hills Volcano, Montserrat in September–October, 1997. The excellent fit is explained by a physical model in which there are competing processes operating in the upper volcano conduit on different time scales: pressurization due to rheological stiffening and gas exsolution, and depressurization due to development of permeability and gas escape. Our experience with the Soufrière Hills Volcano eruption sequence suggests that volcanic eruption forecasts are improved by accounting for these different conduit processes explicitly in a single probability model.
First evidence for the detection of natural surface films by the QuikSCAT scatterometer
Authors: Lin I.‐I. , Alpers Werner , Liu W. Timothy
Published: July 2003

For the first time it is demonstrated that with the QuikSCAT scatterometer it is possible to detect natural surface films resulting from enhanced biological activity in the ocean. It is shown for two regions in the Norwegian and Baltic Sea that areas of strongly reduced Normalized Radar Cross Section (NRCS) are associated with areas of enhanced chlorophyll‐a concentration as evidenced by quasi‐simultaneously acquired SeaWiFS data. This result has two implications. Firstly, it opens up the possibility to map globally natural surface film coverage using QuikSCAT data. Secondly, it demonstrates that in ocean areas with high biological activity the presence of natural surface films can give rise to significant errors in wind vector retrieval when using the current QuikSCAT wind retrieval algorithm.
Dispersion analysis of ULF waves in the foreshock using cluster data and the wave telescope technique
Authors: Narita Y. , Glassmeier K.‐H. , Schäfer S. , Motschmann U. , Sauer K. , Dandouras I. , Fornaçon K.‐H. , Georgescu E. , Rème H.
Published: July 2003

Cluster provides us with a unique possibility to study ULF waves. We analyze ULF wave activity in the near‐Earth upstream solar wind. Using Cluster as a wave telescope we investigate in detail wave propagation directions and wave numbers for various frequencies, obtaining, for the first time, three dimensional dispersion relations experimentally. After Doppler shift correction, we find that the dispersion relations are not linear and the waves are propagating in the sunward direction in the plasma rest frame. Comparison of the experimentally derived dispersion relation with that one for a beam plasma system shows good agreement. We suggest that the ULF waves in the foreshock are generated by a proton population backstreaming from the shock.
Effect of secondary minerals on electrokinetic phenomena during water‐rock interaction
Authors: Guichet Xavier , Zuddas Pierpaolo
Published: July 2003

The main geophysical application of spontaneous potentials (SP) anomalies, i.e., electrical signal generated by hydroelectric coupling, is the mapping of hydrothermal zones. Laboratory studies of hydroelectric coupling as a function of temperature are scarce, because of experimental difficulties. Up today experiments carried out by Ishido and Mizutani [1981] with quartz‐Al‐K‐NO3 system for temperatures ranging from 20°C to 80°C are not well understood. In this work, we show that Ishido and Mizutani [1981]'s solutions are oversaturated with aluminium, and that the precipitation of Al(OH)3s is expected. Triple Layer Model (TLM) calculations for a gibbsite‐KNO3 system can account for Ishido and Mizutani [1981]'s measurements. These results highlight that (1) the precipitation of a secondary mineral can hide the electrical properties of the primary rock; (2) the geochemical fluid surveys should be taken into account to grasp the interfacial processes (precipitation/dissolution), and to interpret the SP measurements in the field.
Clathrate formation and the fate of noble and biologically useful gases in Lake Vostok, Antarctica
Authors: McKay C. P. , Hand K. P. , Doran P. T. , Andersen D. T. , Priscu J. C.
Published: July 2003

Lake Vostok is a large lake located 4 km beneath the East Antarctic Ice Sheet that should be supersaturated with dissolved gases in equilibrium with clathrate present in the water column. Here we show that if the age of the lake is such that the lake water mass has been cycled over 30 times then the total dissolved gas equilibrates at about 2.5 liters (STP) of gas per kg of water; high enough to have important implications for drilling into this deep subglacial lake. Different air gases are preferentially incorporated into the clathrate and thus the molar ratios in the water column will reflect the presence of clathrate and indicate a more precise age of the lake. Preferential incorporation of CO2 into the clathrate would result in the clathrate sinking if the carbon input is 1% of the air input and the lake water is fresh water. The redox state of the lake is set by the high oxygen concentration which is 50 times more than air‐equilibrated water and may be a severe biological stress.
The importance of the third dimension in granular shear
Authors: Hazzard James F. , Mair Karen
Published: July 2003

We present new numerical results showing the importance of the third dimension in simulations of granular shear. Our 3‐D numerical models of gouge layers under shear exhibit friction levels notably higher than 2‐D models and values that approach those of recent laboratory experiments on spherical beads. Fluctuations in friction are directly related to grain reorganization normal to shear. In 3‐D, these fluctuations are reduced due to significant particle motion in the third dimension, leading to a steady frictional sliding curve. Since these fluctuations are small compared with 2‐D models, our 3‐D simulation offers potential to investigate small amplitude but extremely important second order rate and state friction effects that fundamentally control the strength and stability of fault zones.
A role of eddies in formation and transport of North Pacific Subtropical Mode Water
Authors: Uehara Hiroki , Suga Toshio , Hanawa Kimio , Shikama Nobuyuki
Published: July 2003

Hydrographic data acquired during 2001 by Argo profiling floats deployed in the Kuroshio recirculation region are used to verify the inference that mesoscale eddies prevailing in the recirculation region play an important role in the formation and transport of North Pacific Subtropical Mode Water (NPSTMW). That is, the deeper winter mixed layer is formed preferentially where the thermocline is deeper in association with anticyclonic eddies. In the succeeding seasons, mesoscale eddies retain NPSTMW during their southwestward movement from the NPSTMW formation region, so that anticylonic eddies contribute substantially to the NPSTMW transportation. The spatial distributions of the mixed layer depth in winter and the NPSTMW thickness in the succeeding seasons, based on the float data, suggest that they are affected by mesoscale eddies. The float data also provide the statistical relations of these quantities against the thermocline depth, which are consistent with our inference.
Timing of Recent Accelerations of Pine Island Glacier, Antarctica
Authors: Joughin Ian , Rignot Eric , Rosanova Christine E. , Lucchitta Baerbel K. , Bohlander Jennifer
Published: July 2003

We have used Interferometric Synthetic Aperture Radar (InSAR) data and sequential Landsat imagery to identify and temporally constrain two acceleration events on Pine Island Glacier (PIG). These two events are separated by a period of at least seven years (1987–1994). The change in discharge between two flux gates indicates that the majority of the increase in discharge associated with the second acceleration originates well inland (>80 km) from the grounding line. An analysis indicates that changes in driving stress consistent with observed thinning rates are sufficient in magnitude to explain much of the acceleration.
Correction to “Kelvin‐Helmholtz instability around the tropical tropopause observed with the Equatorial Atmosphere Radar”
Authors: Yamamoto Masayuki K. , Fujiwara Masatomo , Horinouchi Takeshi , Hashiguchi Hiroyuki , Fukao Shoichiro
Published: July 2003

In the paper “Kelvin‐Helmholtz instability around the tropical tropopause observed with the Equatorial Atmosphere Radar” by Masayuki K. Yamamoto, Masatomo Fujiwara, Takeshi Horinouchi, Hiroyuki Hashiguchi, and Shoichiro Fukao (Geophys. Res. Lett., 30(9), 1476, doi:10.1029/2002GL016685, 2003), several corrections to the proof were omitted from the final published article. The corrected text appears below.
Long‐term flow forecasts based on climate and hydrologic modeling: Uruguay River basin
Authors: Tucci Carlos Eduardo Morelli , Clarke Robin Thomas , Collischonn Walter , da Silva Dias Pedro Leite , de Oliveira Gilvan Sampaio
Published: July 2003

This paper describes a procedure for predicting seasonal flow in the Rio Uruguay drainage basin (area 75,000 km2, lying in Brazilian territory), using sequences of future daily rainfall given by the global climate model (GCM) of the Brazilian agency for climate prediction (Centro de Previsão de Tempo e Clima, or CPTEC). Sequences of future daily rainfall given by this model were used as input to a rainfall‐runoff model appropriate for large drainage basins. Forecasts of flow in the Rio Uruguay were made for the period 1995–2001 of the full record, which began in 1940. Analysis showed that GCM forecasts underestimated rainfall over almost all the basin, particularly in winter, although interannual variability in regional rainfall was reproduced relatively well. A statistical procedure was used to correct for the underestimation of rainfall. When the corrected rainfall sequences were transformed to flow by the hydrologic model, forecasts of flow in the Rio Uruguay basin were better than forecasts based on historic mean or median flows by 37% for monthly flows and by 54% for 3‐monthly flows.
Measuring mechanical properties of the vastus lateralis tendon‐aponeurosis complex in vivo by ultrasound imaging
Authors: Bojsen‐Møller J. , Hansen P. , Aagaard P. , Kjær M. , Magnusson S. P.
Published: July 2003

The mechanical properties of the human vastus lateralis (VL) tendon‐aponeurosis complex were investigated in eight male subjects. Knee extensor force, knee joint angle, and corresponding longitudinal VL aponeurosis displacement were monitored synchronously during graded (10‐s) maximal isometric knee extension contractions. Displacement observed during isometric conditions may be regarded as an expression of deformation in the tissues distal to the measurement site. Furthermore, aponeurosis displacement was measured during passive knee extension (90–75°°), and used to correct displacement values obtained during active contraction for joint angular motion. The passive trial yielded a highly linear relationship between aponeurosis displacement and joint angular motion
(r2 = 0.998 ± 0.002) with a mean correction factor of 0.41 ± 0.10 mm/degree. Maximal knee extensor force was 5834 ± 1341 N with a corresponding VL aponeurosis displacement of 12.7 ± 2.5 mm, while correcting for joint angular motion reduced maximal displacement ∼9% (to 11.6 ± 2.5 mm, P < 0.005) (data presented as means ± SD). Two separate graded contraction trials were performed, and no between‐trial differences were observed in either maximal force or maximal displacement. Between trial coefficient of determination and CV for maximal force and maximal displacement were r2 = 0.97, CV = 2.9% and r2 = 0.92, CV = 4.6%, respectively, indicating intra‐day reproducibility of measurements. These data demonstrate that when applying the newly established ultrasound‐based method of investigating quadriceps connective tissue mechanical properties, maximal isometric contraction is inevitably associated with some joint angular motion that significantly influences the calculations.
Tendon properties in relation to muscular activity and physical training
Authors: Magnusson S. P. , Hansen P. , Kjær M.
Published: July 2003

Movement is caused by force transmission from contracting muscles to bone via tendon. The collagen structure of tendon is organized in a very hierarchical manner. The collagen fibril is considered the basic force‐transmitting unit of tendon, and it is embedded in a hydrophilic extracellular matrix of proteoglycans, glycoproteins and glycosaminoglycans. It has recently been shown in human peritendinous tissue is more metabolically active in response to activity than previously thought, although it remains to be established, if the level of activity influences affects fibril diameter and/or total tendon cross‐sectional area. Moreover, it cannot be unequivocally concluded that tendon adaptation to physical activity is one of a quantitative and/or qualitative nature. The currently available information is almost exclusively obtained from animal data, however, techniques such as microdialysis for tendon metabolism and ultrasound combined with MRI for tendon mechanical properties has already provided information on human tendon behavior, and is likely to further add to our understanding of how tendon adapt to physical activity. This review will address the structure and function of tendon, and the current knowledge of how tendons respond to activity with respect to biomechanical properties.
The effect of dance training on joint mobility, muscle flexibility, speed and agility in young cross‐country skiers – a prospective controlled intervention study
Authors: Alricsson M. , Harms‐Ringdahl K. , Eriksson K. , Werner S.
Published: July 2003

We evaluated a short‐term (3 months) and a long‐term (8 months) effect of dance training on joint mobility and muscle flexibility of the spine, hip and ankle and on speed and agility in young cross‐country skiers. Twenty elite cross‐country skiers – aged 12–15 years – participated in the study. Five males and five females received dance training (intervention group) and five males and five females did not dance (reference group). Joint mobility and muscle flexibility of the spine, hip and ankle joints were measured using a goniometer, a kyphometer, a measuring tape and a ruler. Two sports‐related functional tests – the slalom‐test and the hurdle‐test – were also performed. These measurements/tests were performed before the start of the dancing period and after 3 and 8 months. The subjects from the intervention group increased their speed with 0.3 s after 3 (P = 0.05) and 8 months (P = 0.02), respectively, when measured with the slalom‐test. They also improved their speed and agility according to the hurdle‐test after 3 months with 0.8 s (P = 0.000) and 8 months with 0.6 s (P = 0.01). Furthermore, they increased flexion–extension of the thoracic spine with 7.5° after 3 months (P = 0.05) and with 9°° after 8 months (P = 0.03) and lateral flexion of the spine with 0.04 m (P = 0.005) and 0.03 m (P = 0.02) after 3 and 8 months, respectively. The reference group was impaired or unchanged in the studied parameters after both 3 and 8 months. We conclude that dance training has a positive effect on speed and agility and on joint mobility and muscle flexibility in flexion–extension and lateral flexion of the spine in young cross‐country skiers.
Secular trends in acute myocardial infarction in relation to physical activity in the general Danish population
Authors: Sjøl A. , Thomsen K. K. , Schroll M. , Andersen L. B.
Published: July 2003

Secular trends in AMI rates were analyzed in relation to physical activity levels. The population attributable risk of physical inactivity was calculated.

Participants were randomly selected subjects from a suburb of Copenhagen, Denmark, screened during the years 1964–1991. Occupational physical activity and in leisure time were assessed 1964, 1974, 1976, 1982, 1987 and 1991 by self‐administered questionnaire along with smoking habits and alcohol consumption. Blood pressure, weight, height and serum lipids were measured according to WHO‐standards.

Mortality data were obtained from death certificates, from hospital records or autopsies. Acute myocardial infarctions (AMI) 1964–1994 were included. 13.925 men and women aged 30, 40, 50 and 60 years, were drawn as random samples from a background population of 300.000 inhabitants. A cohort born in 1914 was examined in 1964 and 1974, a cohort born in 1936, was examined in 1976 and 1987; Monica (Monitoring trends and determinants in cardiovascular diseases) I cohort were examined in 1982 and 1987; MONICA II in 1986, and MONICA III in 1991.

Mean physical activity level at leisure adjusted for age and sex increased over time (P < 0001). 25% of the men were sedentary, and more women reported a sedentary lifestyle than men. The overall trend was from 1964 to 1992 a decline in physical activity at work (P < 0001) in both gender and all age groups.

The difference in AMI incidence rates between leisure time physical activity (LTPA) levels increased over time. No change was found in AMI rates comparing sedentary in different time periods. A remarkable decrease over time in the AMI incidence rate was found in physically active during leisure time. Population attributable risk (PAR) exceeded 40% in both genders in the late 1980s.

In conclusion the difference in AMI rates between LTPA subgroups has increased over time. The low AMI rates observed among the most physically active reveal a substantial potential for the prevention of AMI through physical activity. A population attributable risk of more than 40% for physical inactivity suggests a potential for primary prevention through increased physical activity.
The effect of exercise regimens on reflex response time of the vasti muscles in patients with anterior knee pain: a prospective randomized intervention study
Authors: Witvrouw E. , Cambier D. , Danneels L. , Bellemans J. , Werner S. , Almqvist F. , Verdonk R.
Published: July 2003

The purpose of this prospective randomized intervention study was to evaluate the effect of two exercise protocols on reflex response time of vastus medialis obliquus (VMO), vastus lateralis (VL), in patients with anterior knee pain. Sixty patients were randomized into a 5‐week treatment program, which consisted of only open kinetic chain tonification exercises (group I) (n = 30), or only closed kinetic chain tonification exercises (group II) (n = 30). Assessment of an aspect of neuromotor control was obtained by measuring the reflex response times of VMO and VL at the time of initial clinical examination, at the end of the exercise period (five weeks), and three months after the completion of the exercise period. At these evaluation occasions, the intensity and the number of times that the patients experienced anterior knee pain during daily life was recorded on a Visual Analog Scale (VAS). No alterations in reflex response times of VMO and VL were observed in either group. Changes of anterior knee pain over time were statistically significant in both groups. Only small and not statistically supported differences in anterior knee pain were found between the two groups. These results suggest that the reflex response times of the two vasti muscles can not be altered after a five week open or closed kinetic chain exercise program. In contrast, knee pain decreased significantly in both groups.
Hamstring injury occurrence in elite soccer players after preseason strength training with eccentric overload
Authors: Askling C. , Karlsson J. , Thorstensson A.
Published: July 2003

The primary purpose of this study was to evaluate whether a preseason strength training programme for the hamstring muscle group – emphasising eccentric overloading – could affect the occurrence and severity of hamstring injuries during the subsequent competition season in elite male soccer players. Thirty players from two of the best premier‐league division teams in Sweden were divided into two groups; one group received additional specific hamstring training, whereas the other did not. The extra training was performed 1–2 times a week for 10 weeks by using a special device aiming at specific eccentric overloading of the hamstrings. Isokinetic hamstring strength and maximal running speed were measured in both groups before and after the training period and all hamstring injuries were registered during the total observational period of 10 months. The results showed that the occurrence of hamstring strain injuries was clearly lower in the training group (3/15) than in the control group (10/15). In addition, there were significant increases in strength and speed in the training group. However, there were no obvious coupling between performance parameters and injury occurrence. These results indicate that addition of specific preseason strength training for the hamstrings – including eccentric overloading – would be beneficial for elite soccer players, both from an injury prevention and from performance enhancement point of view.
The effect of advice by health care professionals on increasing physical activity of older people
Authors: Hirvensalo M. , Heikkinen E. , Lintunen T. , Rantanen T.
Published: July 2003

The aim of this study was to investigate whether advice by health care professionals is associated with increased exercise activity in older people. As part of the Evergreen follow‐up study, self‐report data on exercise related advice were collected in 1996 and physical activity in 1988 and 1996 among 611 non‐institutional people initially aged 65–84 years. Logistic regression analyses were used to study the association of recollection of having received exercise counseling with increased activity. Of all the subjects, 92% reported having been in contact with health care professionals during the follow‐up period, and 58% of them recalled having been advised to exercise. Those men and women who recalled having received advice, started to participate in supervised exercise classes 5–6 times more often than those who did not recall being advised. The odds ratio (95% confidence interval) in men was 6.27 (1.19–32.9), and in women 5.27 (1.97–14.1). For calisthenics at home, the corresponding figure was 12.5 (3.52–44.4) in men. We concluded that initiating new physical activities in old age is strongly connected to encouragement to exercise by health care professionals. Health care professionals should be supported to promote exercise among older patients.