bluuebunny/crossref_metadata_2025 huggingface dataset:
Two adjacent forested catchments: Dramatically different NO3− export
Authors: Schiff S. L. , Devito K. J. , Elgood R. J. , McCrindle P. M. , Spoelstra J. , Dillon P.
Published: December 2002

Two adjacent catchments with similar temperate forest cover and podzolic soils have annual nitrate (NO3−) export that differs by a factor of 10. Monthly rates of mineralization and nitrification measured by the buried bag technique, soil C/N ratios, and the contribution of microbial NO3− to total NO3− in the groundwater as determined by analysis of δ18O in NO3− are also similar. In both catchments, maximum NO3− export occurs during spring melt, but in the catchment with higher export, NO3− concentrations in the stream begin to increase in the fall period. Groundwater NO3− concentrations measured in wells are very different in the two catchments with high groundwater NO3− in the catchment exhibiting high NO3− export. Following spring melt, steeper slopes in the high NO3− catchment promote faster drainage, and the water table declines rapidly while high NO3− concentrations are maintained in groundwaters. Deeper water tables will preserve high NO3− in water infiltrating below the rooting zone and organic‐rich upper soil horizons. In the low NO3− catchment, slower drainage on shallower slopes lead to an increase in soil saturation, and the NO3− disappears from the water before the water table declines. Analyses of δ15N in NO3− during NO3− loss do not show evidence of denitrification, although denitrification proceeding to completion in isolated pockets followed by mixing with higher NO3− groundwaters would yield the same result. Alternatively, active uptake of NO3− by vegetation following spring melt will also deplete the groundwater NO3− in the shallow soil depths without isotopic fractionation. The low NO3− catchment also has lower NO3− in shallow soil waters during spring melt. Shallower slopes promote near‐surface flow paths in organic‐rich soil horizons which may facilitate denitrification during spring melt. Although the catchment with low NO3− export has a large wetland near the catchment outlet, the NO3− attenuating capacity of this wetland is largely unused except in the late fall because growing season groundwater concentrations of NO3− are undetectable and the wetland is frozen during snowmelt. In the high NO3− catchment, organic‐rich soils and vegetation in the riparian zone cannot completely attenuate high NO3− in discharging groundwaters. In our study, factors controlling NO3− in groundwater such as slope, stratigraphy, and hydraulic conductivity can play a larger role than riparian zones in controlling differences in annual NO3− export observed between catchments.
Eigenpatterns in southern California seismicity
Authors: Tiampo K. F. , Rundle J. B. , McGinnis S. , Gross S. J. , Klein W.
Published: December 2002

Earthquakes in seismically active regions of the world are known to be associated with a variety of spatial and temporal patterns. Examples include precursory quiescence or activation, seismic clustering, and Mogi donuts. Although the characteristics of these patterns can be qualitatively described, a systematic quantitative analysis has proved elusive. In this paper we employ a new method, developed using numerical simulations, that allows a systematic quantification of the spatial and temporal characteristics of the patterns in historic seismicity in southern California. This method decomposes a set of boolean activity functions, representing historic seismicity, into their orthonormal eigenvalues and eigenfunctions. Here we show the results of this analysis which strongly support the hypothesis that seismic activity is highly correlated across many space scales and timescales within large volumes of the Earth's crust.
Dynamic triggering of earthquakes: The nonlinear slip‐dependent friction case
Authors: Voisin C.
Published: December 2002

The problem of earthquake triggering by dynamic stress waves is studied. A finite fault of length L embedded in an elastic space is considered. The prescribed nonlinear slip‐dependent friction law is characterized by a nonconstant weakening rate α. The fault is perturbed by a sinusoidal stress wave of wavelength λ and amplitude a. As a general result, it is shown that for a given fault and a given friction law, low frequencies are more likely to trigger the rupture than high frequencies. In addition, the occurrence of triggering depends on the balance between intrinsic fault mechanics and the loading parameters. Two behaviors are possible depending on the friction law: some faults exhibit a threshold in frequency to be triggered, while other faults exhibit a threshold in amplitude. These two qualitative behaviors may be explained by considering the nondimensional weakening rate β = α × L/2 and β0 the universal constant of stability computed by Dascalu et al. [2000]. The faults that present a threshold in frequency are intrinsically unstable: their initial nondimensional weakening rate β(0) exceeds β0. On the contrary, the faults that present a threshold in amplitude are intrinsically stable, i.e., initially β(0) < β0. Because of the nonlinearity of the friction law, there is a characteristic slip uc for which β(uc) ≥ β0. For a sufficiently large amplitude the fault may then experience a stability/instability transition. These results are independent of the shape of the perturbation and also hold for a static stress increase.
Importance of the eastern Indian Ocean for the abyssal Pacific
Authors: Nakano H. , Suginohara N.
Published: December 2002

The role of the eastern Indian Ocean in controlling the abyssal circulation in the Pacific is examined using a 1° × 1° world ocean model. Thanks to the improvement of bottom topography and the incorporation of a bottom boundary layer model, the bottom water formation off the Adélie Coast is produced. This bottom water is not only the source of the abyssal water in the eastern Indian but also has a great influence on the whole abyssal Pacific. The lower part of Circumpolar Deep Water (CDW), which enters the abyssal Pacific passing through south of New Zealand, changes its property through mixing with this bottom water flowing underneath CDW in the Australian‐Antarctic Basin and the South Australia Basin. The tracer experiments show that the water ventilated off the Adélie Coast occupies about 20% of the abyssal Pacific, whereas North Atlantic Deep Water (NADW) occupies about 50%, the Weddell Sea bottom water about 20%, and the Ross Sea bottom water about 10%. The flux of the ventilated water estimated by the tracer experiments is 17.1 Sv for NADW, 6.3 Sv from the Weddell Sea, 6.2 Sv from off the Adélie Coast, and 3.5 Sv from Ross Sea in this model. The total flux of 33.1 Sv is not far from the estimate from observations, though it may overestimate by 1–4 Sv. This does not directly indicate that the real world ocean should have the large amount of the bottom water sources in the Pacific‐Indian sector. However, the model offers a picture of the water properties consistent with the observation.
Improved Limb Atmospheric Spectrometer (ILAS) data retrieval algorithm for Version 5.20 gas profile products
Authors: Yokota T. , Nakajima H. , Sugita T. , Tsubaki H. , Itou Y. , Kaji M. , Suzuki M. , Kanzawa H. , Park J. H. , Sasano Y.
Published: December 2002

The Improved Limb Atmospheric Spectrometer (ILAS), a sensor for stratospheric ozone layer observation using a solar occultation technique, was mounted on the Advanced Earth Observing Satellite (ADEOS), which was put into a Sun‐synchronous polar orbit in August 1996. Operational measurements were recorded over high‐latitude regions from November 1996 to June 1997. This paper describes the data processing algorithm of Version 5.20 used to retrieve vertical profiles of gases such as ozone, nitric acid, nitrogen dioxide, nitrous oxide, methane, and water vapor from the infrared spectral measurements of ILAS. To simultaneously derive mixing ratios of individual gas species as a function of altitude, the nonlinear least squares method was utilized for spectral fitting, and the onion peeling method was applied to perform vertical profiling. This paper also discusses in detail estimation of errors (internal and external errors) associated with the derived gas profiles and compares the errors with repeatability. The internal error estimated from residuals in spectral fitting was generally larger than the repeatability, which suggests either that some unknown factors have not been incorporated into the forward model for simulating observed transmittance data or that some parameters in the model are inaccurate. The external error was almost comparable in magnitude to the repeatability. Numerical simulations were carried out to investigate performance of the nongaseous correction technique. The results showed that the background level of sulfuric acid aerosols has little effect on the retrieved profiles, while polar stratospheric clouds (PSCs) with extinction coefficients of the order of 10−3 km−1 at a wavelength of 780 nm have nonnegligible effects on the profiles of some gas species. Despite the problems that require further investigations, it is shown that the ILAS Version 5.20 algorithm generates scientifically useful products.
A study of impacts of tropospheric synoptic processes on the genesis and evolution of extreme total ozone anomalies over southern South America
Authors: Canziani Pablo O. , Compagnucci Rosa H. , Bischoff Susana A. , Legnani Walter E.
Published: December 2002

During the austral autumn of 1997, a sequence of record low ozone events with anomalous behavior occurred at subtropical latitudes to midlatitudes over southern South America, also known as the South Cone (Chile, Argentina, Uruguay, and Southern Brazil). The extreme low ozone events took place in May and early June 1997, i.e., at a time of the year when according to the climatological studies for Northern Hemisphere ozone miniholes, the most significant events would not be expected (if such studies could be simply extrapolated to the Southern Hemisphere). The first and most prominent ozone minihole, with a quasi‐stationary evolution, reached values near 200 DU, i.e., a negative anomaly near 90 DU, close to 40°S. Simultaneously, extreme weather conditions were observed over the South Cone: three significant blocking events took place separated by short intervals. Both the behavior of the ozone layer over the region and the evolution of the blocking events were analyzed. As expected, the evolution of the total ozone column is shown to be linked to these perturbed weather conditions. Despite the apparently similar nature of the blocking events and of the ozone decrease during each of these events, the present study shows that the response of the UT/LS region is different in each case. The respective roles of the vertical displacement of the tropopause and the horizontal advection/divergence of ozone is discussed for the two most important events, showing how these two mechanisms combine in different ways to yield very low total ozone values. The vertical displacement of the tropopause, coupled to the size of the tropopause pressure gradient, appears to be the most efficient mechanism to modify the total ozone column amounts.
Large‐scale chemical evolution of the Arctic vortex during the 1999/2000 winter: HALOE/POAM III Lagrangian photochemical modeling for the SAGE III—Ozone Loss and Validation Experiment (SOLVE) campaign
Authors: Pierce R. B. , Al‐Saadi J. , Fairlie T. D. , Natarajan M. , Harvey V. L. , Grose W. L. , Russell J. M. , Bevilacqua R. , Eckermann S. D. , Fahey D. , Popp P. , Richard E. , Stimpfle R. , Toon G. C. , Webster C. R. , Elkins J.
Published: December 2002

The LaRC Lagrangian Chemical Transport Model (LaRC LCTM) is used to simulate the kinematic and chemical evolution of an ensemble of trajectories initialized from Halogen Occultation Experiment (HALOE) and Polar Ozone and Aerosol Measurement (POAM) III atmospheric soundings over the SAGE III—Ozone Loss and Validation Experiment (SOLVE) campaign period. Initial mixing ratios of species which are not measured by HALOE or POAM III are specified using sunrise and sunset constituent CH4 and constituent PV regressions obtained from the LaRC IMPACT model, a global three dimensional general circulation and photochemical model. Ensemble averaging of the trajectory chemical characteristics provides a vortex‐average perspective of the photochemical state of the Arctic vortex. The vortex‐averaged evolution of ozone, chlorine, nitrogen species, and ozone photochemical loss rates is presented. Enhanced chlorine catalyzed ozone loss begins in mid‐January above 500 K, and the altitude of the peak loss gradually descends during the rest of the simulation. Peak vortex averaged loss rates of over 60 ppbv/day occur in early March at 450 K. Vortex averaged loss rates decline after mid‐March. The accumulated photochemical ozone loss during the period from 1 December 1999 to 30 March 2000 peaks at 450 K with net losses of near 2.2 ppmv. The predicted distributions of CH4, O3, denitrification, and chlorine activation are compared to the distributions obtained from in situ measurements to evaluate the accuracy of the simulations. The comparisons show best agreement when diffusive tendencies are included in the model calculations, highlighting the importance of this process in the Arctic vortex. Sensitivity tests examining the large‐scale influence of orographically generated gravity‐wave temperature anomalies are also presented. Results from this sensitivity study show that mountain‐wave temperature perturbations contribute an additional 2–8% O3 loss during the 1999/2000 winter.
Boreal forest fires in Siberia in 1998: Estimation of area burned and emissions of pollutants by advanced very high resolution radiometer satellite data
Authors: Kajii Yoshizumi , Kato Shungo , Streets David G. , Tsai Nancy Y. , Shvidenko Anatoly , Nilsson Sten , McCallum Ian , Minko Nickolay P. , Abushenko Nickolay , Altyntsev Dmitry , Khodzer Tamara V.
Published: December 2002

The NOAA 12 advanced very high resolution radiometer detected extensive forest fires in boreal Siberia and northern Mongolia during April through October 1998, a year of extremely dry weather, in particular, in the Russian Far East. Analysis of the satellite data has been carried out to estimate the area burned and gaseous emissions to the atmosphere from the point of view of ozone precursors. The fires started in western and eastern Siberia and moved eastward during the summer, until they were concentrated in the Russian Far East, near Sakhalin Island, in the period of July to October. Satellite observations for the fire season and detailed characteristics of terrestrial vegetation in the form of multilayer geographic information systems were used along with published emission factors from similar fires to calculate the gaseous emissions. The total area burned is estimated to be 1.1 × 107ha with 350 Tg of biomass consumed and 176 Tg of carbon released into the atmosphere. The carbon released into the atmosphere is calculated to contribute 516 Tg of CO2, 50 Tg of CO, 1.6 Tg of CH4, 1.1 Tg of NMHC, and 9.5 Tg of C particles as smoke. In addition, we estimate that 1.8 Tg of NOx(as NO2) were released.
Migrating and nonmigrating diurnal tides in the middle and upper atmosphere excited by tropospheric latent heat release
Authors: Hagan M. E. , Forbes J. M.
Published: December 2002

The global‐scale wave model (GSWM) is used to investigate mesospheric and lower thermospheric migrating and nonmigrating diurnal tidal components that propagate upward from the troposphere, where they are excited by latent heat release associated with deep tropical convection. Our diurnal tidal forcing parameterization is derived from a 7‐year database of global cloud imagery. The GSWM migrating response is sufficiently large to modulate the dominant radiatively excited migrating diurnal tide in the middle and upper atmosphere during every month of the year. Five additional nonmigrating diurnal components, the eastward propagating zonal wave numbers 2 and 3, the westward propagating zonal wave number 2, and the standing oscillations, also introduce significant longitudinal variability of the diurnal tide in these regions. The comparative importance of the nonmigrating components evolves from month to month and varies with tidal field. Our GSWM investigation suggests that other dynamical models must account for the tropospheric latent heat source in order to make realistic predictions of the diurnal tide in the middle and upper atmosphere.
Drag coefficient and plant form response to wind speed in three plant species: Burning Bush (Euonymus alatus), Colorado Blue Spruce (Picea pungens glauca.), and Fountain Grass (Pennisetum setaceum)
Authors: Gillies J. A. , Nickling W. G. , King J.
Published: December 2002

Whole‐plant drag coefficients (Cd) for three plant species: Burning Bush (Euonymus alatus), Colorado Blue Spruce (Picea pungens glauca.), and Fountain Grass (Pennisetum setaceum) in five different porosity configurations were developed from force versus wind speed data collected with a force balance in a recirculating wind tunnel. The average Cd for the Burning Bush, Colorado Spruce, and Fountain Grass in their untrimmed forms were 0.42 (±0.03), 0.39 (±0.04), and 0.34 (±0.06), respectively. Drag curves (Cd versus flow Reynolds number (Re) function) for the Burning Bush and Colorado Spruce were found to exhibit, for the lower porosity configurations, a rise to a maximum around flow Reynolds numbers (Re = ρuhh/ν) of 2 × 105. Fountain Grass Cd was shown to be dependent upon Re to values >5 × 105. The Burning Bush and Colorado Spruce plants reduced their drag, upon reaching their maxima, by decreasing their frontal area and increasing their porosity. Maximum Cd for these plants occurred at optical porosities of ∼0.20. The Fountain Grass reduced drag at high Re by decreasing frontal area and porosity. The mechanism of drag reduction in Fountain Grass was continual reconfiguration to a more aerodynamic form as evidenced by continual reduction of Cd with Re.
Tritiated water vapor in the stratosphere: Vertical profiles and residence time
Authors: Ehhalt D. H. , Rohrer F. , Schauffler S. , Pollock W.
Published: December 2002

The historic and partly unpublished measurements of the tritium content in stratospheric water vapor made at the National Center for Atmospheric Research between 1975 and 1983 are reanalyzed. The resulting vertical profiles of the T content, mainly at 32°N latitude, show little variation with altitude above 20 km but a strong decay with time. This decay is a consequence of the large T injections into the stratosphere by the atmospheric tests of high‐yield thermonuclear devices prior to 1963 and seems to proceed with a single e‐fold time of 5.12 years. Correcting for the radioactive decay of HTO within the stratosphere and for a temporal increase in stratospheric H2O, we obtain a decay time for stratospheric HTO of 7.7 ± 2.0 years. This decay time, which is solely due to the transport of HTO into the troposphere, is much longer than the age of stratospheric air at these altitudes or the accepted values for stratospheric residence times. The differences are discussed and resolved by interpreting the HTO decay time as the Eigentime of the longest‐lived mode of the stratospheric transport equations. This Eigentime should provide a useful constraint in modeling stratospheric transport.
In situ measurements of background aerosol and subvisible cirrus in the tropical tropopause region
Authors: Thomas Andreas , Borrmann Stephan , Kiemle Christoph , Cairo Francesco , Volk Michael , Beuermann Jürgen , Lepuchov Boris , Santacesaria Vincenzo , Matthey Renaud , Rudakov Vladimir , Yushkov Vladimir , MacKenzie A. Robert , Stefanutti Leopoldo
Published: December 2002

In situ aerosol measurements were performed in the Indian Ocean Intertropical Convergence Zone (ITCZ) region during the Airborne Polar Experiment‐Third European Stratospheric Experiment on Ozone (APE‐THESEO) field campaign based in Mahé, Seychelles between 24 February and 6 March 1999. These are measurements of particle size distributions with a laser optical particle counter of the Forward Scattering Spectrometer Probe (FSSP)‐300 type operated on the Russian M‐55 high‐altitude research aircraft Geophysica in the tropical upper troposphere and lower stratosphere up to altitudes of 21 km. On 24 and 27 February 1999, ultrathin layers of cirrus clouds were penetrated by Geophysica directly beneath the tropical tropopause at 17 km pressure altitude and temperatures below 190 K. These layers also were concurrently observed by the Ozone Lidar Experiment (OLEX) lidar operating on the lower‐flying German DLR Falcon research aircraft. The encountered ultrathin subvisual cloud layers can be characterized as (1) horizontally extending over several hundred kilometers, (2) persisting for at least 3 hours (but most likely much longer), and (3) having geometrical thicknesses of 100–400 m. These cloud layers belong to the geometrically and optically thinnest ever observed. In situ particle size distributions covering diameters between 0.4 and 23 μm obtained from these layers are juxtaposed with those obtained inside cloud veils around cumulonimbus (Cb) anvils and also with background aerosol measurements in the vicinity of the clouds. A significant number of particles with size diameters around 10 μm were detected inside these ultrathin subvisible cloud layers. The cloud particle size distribution closely resembles a background aerosol onto which a modal peak between 2 and 17 μm is superimposed. Measurements of particles with sizes above 23 μm could not be obtained since no suitable instrument was available on Geophysica. During the flight of 6 March 1999, upper tropospheric and lower stratospheric background aerosol was measured in the latitude band between 4°S and 19°S latitude. The resulting particle number densities along the 56th meridian exhibit very little latitudinal variation. The concentrations for particles with sizes above 0.5 μm encountered under these background conditions varied between 0.1 and 0.3 particles/cm3 of air in altitudes between 17 and 21 km.
Seasonal variations of medium‐scale gravity wave parameters in the lower thermosphere obtained from spectral airglow temperature imager observations at Shigaraki, Japan
Authors: Gavrilov Nikolai M. , Shiokawa Kazuo , Ogawa Tadahiko
Published: December 2002

A method of statistical analysis is used to study parameters of the medium‐scale internal gravity waves (IGWs) from the data of the spectral airglow temperature imager (SATI) observations of the OH and O2 nightglow emissions at Shigaraki, Japan (35°N, 136°E) during April 1998 to May 2001. Average relative magnitudes of spectral components of airglow variations are 1.8–2.4% for the emission rates and 0.5–1% for the rotational temperature in different seasons. Distributions of periods, horizontal wavelengths, and phase speeds have the main maxima at 0.5–2 hours, 100–500 km, and 50–150 m/s, respectively. In winter, the distributions of propagation azimuths are broad with a dominance in the northwest sector and in the southern half of the sky for OH and in the northwest and southeast sectors for O2. In spring and summer, IGWs propagate mainly to the northern half of the sky with larger occurrence in the northeast sector for OH emission. Seasonal variations of the average and median IGW magnitudes do not exceed 20–30% and are not stable. In winter, IGWs have maximum occurrence with larger magnitudes, horizontal wavelengths, and phase speeds, particularly at azimuths of 90–210 deg. These results are compared with previous studies.
Seasonal cycles of ozone and oxidized nitrogen species in northeast Asia 1. Impact of regional climatology and photochemistry observed during RISOTTO 1999–2000
Authors: Tanimoto Hiroshi , Furutani Hiroshi , Kato Shungo , Matsumoto Jun , Makide Yoshihiro , Akimoto Hajime
Published: December 2002

Measurements of oxidized nitrogen species, including peroxyacetyl nitrate (PAN), nitrogen oxides (NOx), nitric acid (HNO3), and nonmethane hydrocarbons (NMHCs), were made along with ozone (O3) and carbon monoxide (CO) at Rishiri Island, a remote island in northern Japan, as part of the Rishiri Island Study of Oxidants and Transport for Tropospheric Ozone (RISOTTO). Full seasonal observations of O3, CO, NMHCs, and PAN, together with data sets of NOx, and HNO3 for 6 months reveal short‐term and seasonal characteristics of chemistry of the air masses in northeast Asia. Temporal variations of O3, PAN, and HNO3 typically show day‐to‐day variations in winter and diurnal variations in summer, dominated by long‐range transport and local photochemistry, respectively. Seasonal variations of O3 and PAN show a spring maximum and a summer minimum, which are consistent with previous field observations made in Europe and North America. Air mass segregation based on back trajectory calculation suggests that PAN, which is photochemically produced in continental source regions, is most effectively transported to remote sites in spring owing to low temperatures in this season, while HNO3 is not effectively transported due to its high deposition velocity. It is concluded that transport of polluted air masses from continental source regions considerably enhances the April maximum in O3 and PAN observed at remote sites in northeast Asia. Back trajectory analysis also indicates that the seasonal cycles of PAN in the Eurasian continental background air masses are maximum in spring, minimum in summer, and show a secondary maximum in fall in contrast to NOx and HNO3 which have a summer maximum and a winter minimum.
Simulation of the Martian dust aerosol at low wind speeds
Authors: Merrison J. P. , Bertelsen P. , Frandsen C. , Gunnlaugsson P. , Knudsen J. M. , Lunt S. , Madsen M. B. , Mossin L. A. , Nielsen J. , Nørnberg P. , Rasmussen K. R. , Uggerhøj E.
Published: December 2002

Performing realistic simulations is crucial for developing, testing, and subsequently analyzing results of experiments sent to the surface of Mars. A wind tunnel has been constructed, in which the atmospheric conditions of pressure and wind speed are controlled to match those observed by the Pathfinder mission to Mars. Injection into the wind tunnel of an analogue dust from Salten Skov in Denmark allows simulation of the Martian aerosol. Here experiments can be tested in preparation for a planned mission to the planet (Mars Exploration Rovers to be launched in 2003). Observations of adhesion and cohesion effects have been made in the wind tunnel, which are relevant to particle transport and of significance for validating the performance of specific experiments on Mars. Preliminary studies have been made, at Mars atmospheric pressure, of dust capture on magnet arrays similar to those flown on the Mars Pathfinder mission.
Cenozoic deformation of the Tarim plate and the implications for mountain building in the Tibetan Plateau and the Tian Shan
Authors: Yang Youqing , Liu Mian
Published: December 2002

The Tarim basin in NW China developed as a complex foreland basin in the Cenozoic in association with mountain building in the Tibetan Plateau to the south and the Tian Shan orogen to the north. We reconstructed the Cenozoic deformation history of the Tarim basement by backstripping the sedimentary rocks. Two‐dimensional and three‐dimensional finite element models are then used to simulate the flexural deformation of the Tarim basement in response to the sedimentary loads and additional tectonic loads associated with overthrusting of the surrounding mountain belts. The results suggest that uplift of both the western Kunlun Shan and the Tian Shan orogens started during or before Oligocene. Since the Miocene, mountain building accelerated in the western Kunlun Shan but showed segmented development in the Tian Shan. The results also indicate reduced tectonic load along the Altyn Tagh fault since late Miocene, consistent with geological and geophysical evidence of the fault cutting the entire lithosphere and migrating southward during its cause of the Cenozoic evolution.
Self‐organizing linear output map (SOLO): An artificial neural network suitable for hydrologic modeling and analysis
Authors: Hsu Kuo‐lin , Gupta Hoshin V. , Gao Xiaogang , Sorooshian Soroosh , Imam Bisher
Published: December 2002

Artificial neural networks (ANNs) can be useful in the prediction of hydrologic variables, such as streamflow, particularly when the underlying processes have complex nonlinear interrelationships. However, conventional ANN structures suffer from network training issues that significantly limit their widespread application. This paper presents a multivariate ANN procedure entitled self‐organizing linear output map (SOLO), whose structure has been designed for rapid, precise, and inexpensive estimation of network structure/parameters and system outputs. More important, SOLO provides features that facilitate insight into the underlying processes, thereby extending its usefulness beyond forecast applications as a tool for scientific investigations. These characteristics are demonstrated using a classic rainfall‐runoff forecasting problem. Various aspects of model performance are evaluated in comparison with other commonly used modeling approaches, including multilayer feedforward ANNs, linear time series modeling, and conceptual rainfall‐runoff modeling.
Deep arid system hydrodynamics 2. Application to paleohydrologic reconstruction using vadose zone profiles from the northern Mojave Desert
Authors: Walvoord Michelle A. , Phillips Fred M. , Tyler Scott W. , Hartsough Peter C.
Published: December 2002

Site‐specific numerical modeling of four sites in two arid alluvial basins within the Nevada Test Site employs a conceptual model of deep arid system hydrodynamics that includes vapor transport, the role of xeric vegetation, and long‐term surface boundary transients. Surface boundary sequences, spanning 110 kyr, that best reproduce measured chloride concentration and matric potential profiles from four deep (230–460 m) boreholes concur with independent paleohydrologic and paleoecological records from the region. Simulations constrain a pluvial period associated with infiltration of 2–5 mm yr−1 at 14–13 ka and denote a shift linked to the establishment of desert vegetation at 13–9.5 ka. Retrodicted moisture flux histories inferred from modeling results differ significantly from those determined using the conventional chloride mass balance approach that assumes only downward advection. The modeling approach developed here represents a significant advance in the use of deep vadose zone profile data from arid regions to recover detailed paleohydrologic and current hydrologic information.
Statistical estimation of streamflow depletion from irrigation wells
Authors: Burt Oscar R. , Baker Maurice , Helmers Glenn A.
Published: December 2002

A multiple regression model was applied to annual time series data (1936–1998) in an attempt to quantify the influence of irrigation wells on annual streamflows of Frenchman Creek in Southwestern Nebraska where intensive well development has taken place since 1950. A strong statistical relationship was found between the logarithm of streamflow and number of wells, current and lagged annual precipitation, and two variables that are the geometric mean of precipitation and number of wells in the current year and the year before last. Estimated mean streamflow from the statistical model in 1998 is approximately one third of that in 1950. A simpler model without the interaction terms between number of wells and precipitation was estimated for the Republican River near its final entry into Kansas from Nebraska, and an even greater decline in mean annual streamflow was found. The present mean is approximately one quarter of the 1950 level.
El Niño–Southern oscillation and the climate, ecosystems and rivers of Amazonia
Authors: Foley Jonathan A. , Botta Aurélie , Coe Michael T. , Costa Marcos Heil
Published: December 2002

The El Niño–Southern Oscillation (ENSO) phenomenon is one of the dominant drivers of environmental variability in the tropics. In this study, we examine the connections between ENSO and the climate, ecosystem carbon balance, surface water balance, and river hydrology of the Amazon and Tocantins river basins in South America. First we examine the climatic variability associated with ENSO. We analyze long‐term historical climate records to document the “average” climatic signature of the El Niño and La Niña phases of the ENSO cycle. Generally speaking, the “average El Niño” is drier and warmer than normal in Amazonia, while the “average La Niña” is wetter and cooler. While temperature changes are mostly uniform through the whole year and are spatially homogeneous, precipitation changes are stronger during the wet season (January‐February‐March) and are concentrated in the northern and southeastern portions of the basin. Next we use a land surface/ecosystem model (IBIS), coupled to a hydrological routing algorithm (HYDRA), to examine how ENSO affects land surface water and carbon fluxes, as well as changes in river discharge and flooding. The model results suggest several responses to ENSO: (1) During the average El Niño, there is an anomalous source of CO2 from terrestrial ecosystems, mainly due to a decreased net primary production (NPP) in the north of the basin. There is also a decrease in river discharge along many of the rivers in the basin, which causes a decrease in flooded area along the main stem of the Amazon. (2) During the average La Niña, there is an anomalous sink of CO2 into terrestrial ecosystems, largely due to an increase in NPP in the northern portion of the basin. In addition, there is a large increase in river discharge in the Amazon basin, especially from the northern and western tributaries. There is a corresponding increase in flooded area, largely in the northern rivers. These results illustrate that changes in water and carbon balance associated with ENSO have complex, spatially heterogeneous features across the basin. This underscores the need for comprehensive analyses, using long‐term observational data and model simulations, of regional environmental systems and their response to climatic variability.
Substorm onset location and the equatorward boundary of the proton auroral oval
Authors: Jayachandran P. T. , MacDougall J. W. , Moorcroft D. R. , St‐Maurice J.‐P. , Liou K. , Newell P. T.
Published: December 2002

An examination of the substorm onset location inferred from Polar UVI and the location of the equatorward boundary of the proton auroral oval inferred from ground based SuperDARN radars is presented. A study of 96 individual substorm events reveals that the substorms can be initiated either near the equatorward boundary of the proton auroral oval or far poleward of the equatorward boundary of the proton auroral oval depending on the preceding interplanetary conditions. When the Interplanetary Magnetic Field (IMF) is predominantly southward prior to the substorm onset, the onset location is near the equatorward boundary of the proton auoral oval; when the IMF is predominantly northward prior to the onset; the onset location is far poleward of the equatorward boundary of the proton auroral oval. The latitudinal separation (ΔΛ) between the onset location and the equatorward boundary of the proton auroral oval shows a linear dependence on the IMF.
Direct estimation of sea state impacts on radar altimeter sea level measurements
Authors: Vandemark D. , Tran N. , Beckley B. D. , Chapron B. , Gaspar P.
Published: December 2002

A new sea state bias modeling approach is presented that makes use of altimeter‐derived marine geoid estimates. This method contrasts with previous models that require differencing between repeat altimeter passes for SSB isolation, along with complex bivariate inversion, to derive a relation between wind speed, wave height and SSB. Here one directly bin‐averages sea height residuals over the wind and wave correlatives. Comparison with the most current nonparametric repeat‐pass model shows close agreement and provides a first validation of this simpler and more direct technique. Success is attributed mainly to extensive space and time averaging. Ease in implementation and benefits in working with absolute levels provide much appeal. Further advantages and potential limitations, centered on the need to effectively randomize large sea level anomaly components to expose the bias, are also discussed.
Northwestward decline of magnetic susceptibility for the red clay deposit in the Chinese Loess Plateau
Authors: Xiong S. F. , Jiang W. Y. , Yang S. L. , Ding Z. L. , Liu T. S.
Published: December 2002

The loess‐paleosol‐red clay sequence in the Chinese Loess Plateau has attracted attention for its potential in recording late Cenozoic climatic changes over northern China, although the details of the climatic implications of the proxies (for example, magnetic susceptibility) and the reconstructed summer monsoon changes remain unclear. Here we report on a new section from Baishui, in Gansu province and compare it with the Lingtai and Jingchuan sections. By correlating the magnetic susceptibility from these sections, we show that there is a clear systematic decrease of the magnetic susceptibility in the red clay deposits from the southeast (Lingtai section) to the northwest (Baishui section). This result suggests that the climatic parameters (probably precipitation) had a decreasing northwestward gradient during the red clay deposition. This climatic pattern is similar to the present condition, implying that the influence of the East Asian summer monsoon on the Chinese Loess Plateau has persisted from at least 6 Ma.
The spectral radiative signature of wind‐blown mineral dust: Implications for remote sensing in the thermal IR region
Authors: Sokolik Irina N.
Published: December 2002

This study investigates how the loading and composition of atmospheric dust affect IR radiances observed by satellite narrowband and high‐resolution sensors. To compute monochromatic radiances accounting for multiple scattering and absorption by aerosols and atmospheric gases, we employed a new radiative transfer code which combines the line‐by‐line algorithm and discrete ordinate technique. New dust optical models required for such computations were developed for the representative mineral mixtures. We demonstrate that dust decreases the brightness temperature observed by satellite sensors depending mainly on the dust burden and composition, though the sensitivity to the composition differs between the satellite sensors. We found that mineral dust has a unique radiative signature (termed here a “negative slope”) which separates the effect of dust from that of clouds and gases. We conclude that dust must be accounted for in atmospheric correction algorithms if the retrievals of the sea surface temperature and atmospheric gaseous species from the thermal IR radiances are to be of high accuracy.
Principal filter analysis for luminescence excitation‐emission data
Authors: Brunsdon Chris , Baker Andy
Published: December 2002

A new method (termed Principal Filter Analysis (PFA)) for analysing large time series of luminescence excitation‐emission matrices (EEMs) is proposed, based on the idea of identifying ‘filters’ that detect time periods where interesting variations in the EEMs occur. A mathematical exposition of the technique is supplied, followed by a discusion of how it may be implemented in practice. The method is applied to EEMs taken from a stalagmite in Crag Cave, W. Ireland resulting in three distinct time periods of luminescence properties being identified.
3‐D refractivity field from GPS double difference tomography
Authors: Troller M. , Bürki B. , Cocard M. , Geiger A. , Kahle H.‐G.
Published: December 2002

GPS meteorology can be successfully used to model the tropospheric refraction effect on radiowave signals. We describe an approach to estimate and model the spatial distribution of the tropospheric water vapor. We refine the tomographic software package AWATOS which is based on the assimilation of GPS double difference observations. The observations are allocated to a voxel model, which is defined according to the distribution of the GPS stations. Performing a least‐squares adjustment, the refractivity of each voxel is determined. Tests of the software are performed, based on simulated and real data. The latter were obtained during a dedicated field campaign on the Big Island of Hawaii. The tomographic profiles are compared with radiosonde data. The results obtained for continuous atmospheric conditions fit well, whereas larger differences occur in discontinuous atmospheric weather conditions. Overall, an accuracy of 5–20 ppm (refractivity units) has been achieved.
North America plate is driven westward by lower mantle flow
Authors: Liu Zhen , Bird Peter
Published: December 2002

The sense of shear traction which the deeper mantle exerts on the North America plate is controversial. To test this, we compute laterally‐varying thin‐shell models. Fault elements are used to outline the plate, so the velocity of North America is not fixed. The basal boundary condition is set in one of three ways: (a) for resistive drag, we assume that the lower mantle is static with respect to Africa; (b) we test models with no basal traction; (c) for active drag, we assume that the lower mantle moves as a rigid plate but 10% faster than North America. Each model is scored by comparison with sea‐floor spreading rates, geodetic velocities, stress directions, and NUVEL‐1A. Only models with active drag are successful. While these results do not determine the exact azimuth or pattern of basal drag on the North America plate, they establish the modal sense as active.
Modeling study of long‐range transport of Asian dust and anthropogenic aerosols from East Asia
Authors: Takemura Toshihiko , Uno Itsushi , Nakajima Teruyuki , Higurashi Akiko , Sano Itaru
Published: December 2002

A three‐dimensional aerosol transport‐radiation model, SPRINTARS, successfully simulates the long‐range transport of the large‐scale Asian dust storms from East Asia to North America which crossed the North Pacific Ocean during the springtime of 2001 and 2002. It is found from the calculated dust optical thickness that 10 to 20% of the Asian dust around Japan reached North America. The simulation also reveals the importance of the contribution of anthropogenic aerosols, which are carbonaceous and sulfate aerosols emitted from the industrialized areas in East Asia, to air turbidity during the dust storms. The contribution of the anthropogenic aerosol to the total optical thickness is simulated to be of a comparable order to that of the Asian dust, which is consistent with the observed values of the particle size index from the satellite and ground‐based sun/sky photometry.
Alfvénic turbulence in high‐latitude solar wind: Radial versus latitudinal variations
Authors: Bavassano B. , Pietropaolo E. , Bruno R.
Published: December 2002

Plasma and magnetic field measurements by Ulysses during its first out‐of‐ecliptic orbit have allowed extensive investigations on the behavior of Alfvénic turbulence in high‐latitude solar wind from 1 to 5 AU. Most analyses have shown that the turbulence evolution in high‐latitude wind is radial, rather than latitudinal, in nature. However, a recent study, based on magnetic field fluctuations, has suggested that latitudinal effects might play a nonnegligible role. Here we further examine this possibility by using Elsässer's variables, quantities that directly are related to the Alfvénic content of solar wind fluctuations. Our conclusion, supported by a comparison between polar and ecliptic observations, is that latitude does not appear to have an appreciable influence on the turbulence evolution in high‐latitude solar wind.
Simultaneous measurement of duskside subauroral irregularities from the CUTLASS Finland radar and EISCAT UHF system
Authors: Hosokawa K. , Sugino M. , Lester M. , Sato N. , Yukimatu A. S. , Iyemori T.
Published: December 2002

Dusk scatter event (DUSE) (first reported by Ruohoniemi et al. [1988]) is one of the most reproducible features among the SuperDARN radar backscatter within the subauroral ionosphere. Hosokawa et al. [2001] analyzed the scattering occurrence percentage of the Northern Hemisphere SuperDARN radars in a statistical fashion and pointed out that the region where the DUSE appears has a close relationship with the duskside end of the midlatitude trough in longitudinal direction. They proposed a model explaining the generation of the DUSE which employs a Sunward density gradient at the duskside edge of the trough and an ambient poleward electric field. In order to confirm the model proposed by Hosokawa et al. [2001], we have investigated two DUSE events which had been observed by the CUTLASS Finland radar and the EISCAT UHF system simultaneously. Consequently, when the CUTLASS Finland radar observed the DUSE, a Sunward directed density gradient was observed by the EISCAT in the vicinity of the DUSE. After the passage of the DUSE the EISCAT observed an ion temperature enhancement which suggested that the EISCAT entered the trough through its duskside edge. These observational facts suggest that the geometry of the parameters around the DUSE is quite consistent with the model proposed by Hosokawa et al. [2001]. In addition, the EISCAT observed an enhancement of the poleward electric field around the DUSE, and a signature of the substorm was identified by the ground magnetometer on the nightside. We suggest generation mechanisms of the trough responsible for the DUSE during substorm conditions in terms of the role of the enhanced subauroral electric field and discuss a relationship between the DUSE and the other substorm‐related phenomena.
Penetration electric fields at the nightside dip equator associated with the main impulse of the storm sudden commencement of 8 July 1991
Authors: Sastri J. Hanumath
Published: December 2002

The geomagnetic storm sudden commencement (ssc) of 8 July 1991 was reported [Wilson et al., 2001] to be characterized by a reduction (enhancement) of X component at midlatitudes in the noon (midnight) sector in the 1‐hour period after its start at 1636 UT. This distinctive feature is seen even after accounting for the effects of the Chapman‐Ferraro current by subtracting the step‐like increase of X/H component at low‐latitude stations on the same magnetic meridian from the midlatitude data. We present evidence to show that over the same 1‐hour period after the start of the ssc on 8 July 1991 an eastward electric field disturbance (peak value ≈1.2 mV/m) grew up and decayed at the premidnight dip equator. The eastward electric field evidenced at the nightside dip equator is interpreted as the signature of the penetration of the dawn‐to‐dusk electric field associated with an enhancement of region 1 field‐aligned currents (FACs) driven by the solar wind. The negative disturbance in the H/X component at midlatitudes in the noon sector is explained as the magnetic effect of FACs that carry the large‐scale electric fields from the magnetosphere to the polar ionosphere as well as the disturbance of polar origin‐type 2 ionospheric currents excited by the large‐scale electric field.