bluuebunny/crossref_metadata_2025 huggingface dataset:
Control on dissolved iron concentrations in deep waters in the western North Pacific: Iron(III) hydroxide solubility
Authors: Kuma Kenshi , Isoda Yutaka , Nakabayashi Shigeto
Published: September 2003

The vertical profiles of nutrient, AOU (apparent oxygen utilization), and Fe(III) hydroxide solubility (Fe(III) solubility) in the western North Pacific commonly show that their concentrations increased with depth below the surface mixed layer and have strong gradients around the North Pacific Intermediate Water (NPIW) in a potential density (σθ) range of 26.7–27.0. They had the maximum values at a σθ range of 27.0–27.5, and then rapidly decreased with depth at higher σθ than 27.5. The similarity of their profiles versus σθ suggests that they are controlled by similar processes with an intrinsic timescale such as deep‐ocean circulation. The vertical profiles of dissolved Fe were also characterized by mid‐depth maxima and, subsequently, a slight decrease with depth, which is markedly similar to nutrient and Fe(III) solubility depth profiles. This implies that the major source of dissolved Fe in the deep ocean is release during the remineralization of biogenic organic matter. In the present study, we attempted to confirm that the dissolved Fe depth profiles are controlled by the sinking particulate organic matter (POM), the production of dissolved Fe from POM during carbon remineralization, the scavenging of dissolved Fe and the temporal fixed Fe(III) solubility depth profile. Using the production rate (α) of dissolved Fe (1/α = 5–10 years), the calculated depth profile of dissolved Fe is in remarkable agreement with the observed profile of dissolved Fe with mid‐depth maxima. Therefore we concluded that dissolved Fe concentrations in deep ocean waters are controlled primary by the Fe(III) solubility.
On the polarization of oscillatory currents in the Bay of Biscay
Authors: van Haren Hans
Published: September 2003

Rotary spectral properties were examined using ∼20 records of yearlong current observations in the Bay of Biscay. Here data are discussed from two representative records from 1000 m above the bottom at two sites, one above the continental slope and another above the abyssal plain. Nearly raw spectra revealed a strong prevalence for clockwise over anti‐clockwise circular motions at frequencies (σ) between ∼0.85f < σ < N (f and N denoting the local inertial and buoyancy frequencies, respectively). The observations showed rotary properties that were previously associated with free internal waves (for f < σ < N, N ≫ f), but only for motions in bands of ∼0.9 cpd width in frequency around inertial, tidal, and their nonlinear sum‐interaction frequencies. This width was larger than the enhanced kinetic energy bands of ∼0.15 cpd around inertial and tidal constituent frequencies. Nevertheless, it was suggested that both bands were associated with the same nonlinear interactions due to advection between subinertial and peak‐frequency motions that also resulted in internal wave intermittency.
Stratospheric ozone reaches new minima above McMurdo Station, Antarctica, between 1998 and 2001
Authors: Kröger Chris , Hervig Mark , Nardi Bruno , Oolman Larry , Deshler Terry , Wood Stephen , Nichol Sylvia
Published: September 2003

Ozonesonde measurements were performed annually in late winter and early spring from McMurdo Station, Antarctica, between 1998 and 2001, continuing a record starting in 1986. Mean column ozone during the same 47 day period in all four years are at least 11% below the average during the same period of the 1986–1997 record in the total column and at least 24% below the 1986–1997 record in the 12–20 km column. Average column ozone of 2000 and 2001 is also clearly below the minima observed between 1986 and 1997, with 2001 the lowest on record. These observations of lowest ozone are consistent with predictions and observations of peaking halogen abundance in the lower stratosphere around 2000 and a very slow decline thereafter. Such low ozone values are a combined consequence of stratospheric halogens and a continual and cold polar vortex. Man‐released halogens mainly affect the 12–20 km ozone column, while the ozone column above and below the 12–20 km column stays about constant. Several kilometer deep ozone‐depleted layers with mixing ratios below 0.1 ppmv appeared about 10 days earlier in 2001 than in 1998. Integrated ozonesonde measurements are compared to TOMS and Dobson spectrophotometer data with generally very good agreement. Measurement differences are largest when the vortex edge is close to McMurdo and decrease with increasing distance to the vortex edge region. The analysis of the vortex edge location at 400 K and 550 K shows that nearly all measurements were performed inside the polar vortex at 400 K, but extravortex air was sampled on occasion above 550 K. The earlier departure of the polar vortex edge above 550 K south of McMurdo led in 2000 to very high column ozone, both in the total column and in the 12–20 km column, which occasionally exceeds maximum observed values since 1986. Synchronous temperature measurements show correlations between high temperature, high ozone mixing ratio, and extravortex air.
Sources and budgets for CO and O3 in the northeastern Pacific during the spring of 2001: Results from the PHOBEA‐II Experiment
Authors: Jaeglé Lyatt , Jaffe Daniel A. , Price Heather U. , Weiss‐Penzias Peter , Palmer Paul I. , Evans Mathew J. , Jacob Daniel J. , Bey Isabelle
Published: September 2003

Ground and airborne measurements of CO, ozone, and aerosols were obtained in the northeastern (NE) Pacific troposphere during 9 March–31 May 2001 as part of the PHOBEA‐II project (Photochemical Ozone Budget of the Eastern North Pacific Atmosphere). The GEOS‐CHEM global three‐dimensional model of tropospheric chemistry was used for flight planning, as well as for data analysis after the field mission to examine the origin of CO and ozone over the NE Pacific. The model successfully reproduces the observed CO levels, their temporal variability, and vertical gradients, strongly suggesting a good understanding of the sources, transport and chemistry of CO in the NE Pacific. For ozone the model underestimates mean surface observations by 8 ppbv, overestimates aircraft profiles by 5 ppbv, and does not reproduce the temporal variability of the observations. Possible explanations for model error in the ozone simulation are discussed. We find a pervasive influence of Asian and European anthropogenic sources on the levels of CO in the NE Pacific troposphere. In the 0–6 km column over our surface site, Asian and European emissions account for 33% (42 ppbv) and 15% (21 ppbv) of CO, respectively. Asian and European emissions are responsible for smaller fractions of the 0–6 km ozone column, 12% (5 ppbv) and 5% (2 ppbv), respectively. The full influence of Asian emissions (including secondary ozone production by export of its precursors) approaches 16% of ozone. The model successfully captures three intercontinental transport events observed during the PHOBEA‐II campaign: one at the surface and two in the free troposphere. While all three events were characterized by large CO enhancements (by 20–40 ppbv), only one case showed significant ozone enhancement (by 20 ppbv), induced by high‐latitude transport of Asian pollution mixed in with stratospheric ozone.
Improvements to a GPS radio occultation ray‐tracing model and their impacts on assimilation of bending angle
Authors: Liu H. , Zou X.
Published: September 2003

Several efforts are made to improve the accuracy and efficiency of a 2‐D GPS radio occultation forward ray‐tracing model. First, a large impact parameter offset existed in the forward model, caused by the inconsistency in the definition of the “occultation point” between the forward model and the GPS/MET data. The forward model is modified to be consistent with the GPS/MET data. Second, the errors in the simulation of the impact parameter and the bending angle due to the original starting point scheme of the ray integration are examined and a new starting point scheme is introduced to reduce the forward modeling errors. Third, to more accurately simulate the GPS/MET bending angle data, a derivation of the bending angle from a Doppler shift measurement under the application of Snell's law is incorporated into the ray‐tracing model. Fourth, a variable step size for the ray integration is proposed to the forward ray‐tracing model to reduce its computational cost. Assessment of the impacts of these modifications to the forward modeling of the bending angle and to the data assimilation of the bending angle is carried out with simulated bending angles and impact parameters derived from an accurate 3‐D ray‐tracing model. The 3‐D ray‐tracing model simulates a total of 133 occultation profiles with the actual satellite positions and velocities taken from the 133 GPS/MET occultations observed on 11 October 1995. The NCEP analysis at T126L28 resolution is used to represent the “true” refractivity field of the atmosphere. The bending angles and impact parameters in the 3‐D ray‐tracing model are derived following the same data processing procedure used in the GPS/MET experiment. All the input parameters (e.g., the tangent direction at the perigee point, etc.) required by the 2‐D ray‐tracing model are provided by the 3‐D ray‐tracing model. Numerical results with and without the above mentioned modifications to the 2‐D ray‐tracing model are examined and compared with the 3‐D ray‐tracing model results and the NCEP T126L28 analysis. It is shown that the modifications to the 2‐D ray‐tracing model significantly reduce the errors in the forward simulation of the bending angle and the impact parameter, and thus greatly improve the accuracy of the temperature, specific humidity, and surface pressure field analyses produced by GPS data assimilation, especially in middle and lower troposphere.
Continental runoff dynamics in the Community Climate System Model 2 (CCSM2) control simulation
Authors: Branstetter Marcia L. , Erickson David J.
Published: September 2003

We present an analysis of the river transport model (RTM) implementation in a fully coupled Earth system model, the Community Climate System Model, version 2 (CCSM2). The results of a 350‐year CCSM2 control simulation were compared to observational river flow data and previous simulations using the Community Climate Model, version 3 (CCM3). River discharge into the Arctic Ocean improved significantly over earlier CCM3 simulations. Significant interannual variability was evident in the control simulation, although at times it exceeded the observational variability. The CCSM2 river discharges to the ocean during the peak discharge month of June for the Amazon, Amur, Ob, St. Lawrence, and Ganges Rivers were found to be within 25% of observations. CCSM2 produced negative river discharges for the St. Lawrence, Parana, and Ob Rivers for some months of the year because of the methods CCSM2 used to calculate runoff resulting from lakes, wetlands, and glaciers. Precipitation and snow cover analyses explained some of the improvements of CCSM2 over CCM3 as well as lingering sources of inaccuracy in the river discharges. The lack of water impoundment in both CCSM2 and CCM3 was shown to be another source of discrepancy between model river discharge and observed streamgage data. We discuss the differences and similarities between CCSM2 river discharges and observations within the context of extant freshwater resource management, observational measurement techniques, and spatial and temporal scales.
Lightning activities on the Tibetan Plateau as observed by the lightning imaging sensor
Authors: Qie Xiushu , Toumi Ralf , Yuan Tie
Published: September 2003

Lightning flash activities on the Tibetan Plateau are investigated using observations from the lightning imaging sensor. About 95% of the flashes are found to occur during May to September with a single peak in the summer from June to August. There is substantial lightning activity in May on the plateau, especially on the southern and eastern plateau. The diurnal variation of the lightning activity shows a prominent peak from 1500 to 1700 LT for most of the plateau with earlier activity on the eastern and southern plateau and a delay on the western, northern, and central plateau. Few lightning flashes are observed between 0000 and 1000 LT. The highest flash density is found in the grassland central plateau with a value of 4.5 flashes km−2 yr−1, while the minimum is found in the semiarid western plateau with a value of 1.5 flashes km−2 yr−1. The optical radiance of flashes fits a lognormal distribution. More energetic flashes are found on the mountainous eastern and northern plateau, and weaker flashes are found on the wet southern and semiarid western plateau. A nonlinear relationship between lightning activity and monthly averaged convective available potential energy (CAPE) is found. The flash number per CAPE on the Tibetan Plateau is much larger than it is for other regions with prominent lightning activity (but low altitude).
Carbon monoxide, regional‐scale transport, and biomass burning in tropical continental Southeast Asia: Observations in rural Thailand
Authors: Pochanart Pakpong , Akimoto Hajime , Kajii Yoshizumi , Sukasem Phaka
Published: September 2003

Surface CO variations from continuous measurements during 1997–2000 at a tropical site in rural Thailand are reported for the first time. The CO seasonal cycle at Srinakarin (14°22′N, 99°07′E, 296 m above sea level) shows a maximum during the late dry season (February–March) and a minimum during the midwet season (June–August) with a larger amplitude than other remote sites in the Northern Hemisphere. The 4‐year annual average, averaged monthly minimum, and averaged monthly maximum of CO mixing ratios are 260, 97, and 560 ppbv, respectively. The long‐range transport of air masses driven by the Asian monsoon and biomass burning activity in continental Southeast Asia are found to be the main factors controlling CO variation in Thailand. Trajectory analysis indicates that during the wet season when the southwest monsoon from the Indian Ocean prevails, relatively low CO mixing ratios of 101 ± 32 ppbv on average are observed. Meanwhile, an average of 306 ± 83 ppbv of CO is observed when the site is influenced by regionally polluted continental air transported by the northeast monsoon from East Asia during the early dry season. Air mass transport, however, cannot explain high CO mixing ratios during the late dry season. Analysis of fire hot spots from the Along Track Scanning Radiometer (ATSR) satellite data indicates that the seasonal cycle of biomass burning in continental Southeast Asia is regular and is at a maximum in March, coincident with the CO maximum. The good correlation between CO and the number of ATSR hot spots provides evidence that this high CO during the late dry season is due to biomass burning in continental Southeast Asia. In addition, we found possible influences from the 1997 Indonesian fires and the 1998 Siberian Fires on the CO variations at Srinakarin.
NMHCs and halocarbons in Asian continental outflow during the Transport and Chemical Evolution over the Pacific (TRACE‐P) Field Campaign: Comparison With PEM‐West B
Authors: Blake Nicola J. , Blake Donald R. , Simpson Isobel J. , Meinardi Simone , Swanson Aaron L. , Lopez Jimena P. , Katzenstein Aaron S. , Barletta Barbara , Shirai Tomoko , Atlas Elliot , Sachse Glen , Avery Melody , Vay Stephanie , Fuelberg Henry E. , Kiley Christopher M. , Kita Kazuyuki , Rowland F. Sherwood
Published: September 2003

We present an overview of the spatial distributions of nonmethane hydrocarbons (NMHCs) and halocarbons observed over the western north Pacific as part of the NASA GTE Transport and Chemical Evolution over the Pacific (TRACE‐P) airborne field campaign (February–April 2001). The TRACE‐P data are compared with earlier measurements from the Pacific Rim during the Pacific Exploratory Mission‐West B (PEM‐West B), which took place in February–March 1994, and with emission inventory data for 2000. Despite the limited spatial and temporal data coverage inherent to airborne sampling, mean levels of the longer‐lived NMHCs (including ethane, ethyne, and benzene) were remarkably similar to our results during the PEM‐West B campaign. By comparison, mixing ratios of the fire extinguisher Halon‐1211 (CF2ClBr) increased by about 50% in the period between 1994 and 2001. Southern China (south of 35°N), and particularly the Shanghai region, appears to have been a substantial source of Halon‐1211 during TRACE‐P. Our previous analysis of the PEM‐West B data employed methyl chloroform (CH3CCl3) as a useful industrial tracer. However, regulations have reduced its emissions to the extent that its mixing ratio during TRACE‐P was only one‐third of that measured in 1994. Methyl chloroform mixing ratio “hot spots,” indicating regions downwind of continuing emissions, included outflow from the vicinity of Shanghai, China, but particularly high emission ratios relative to CO were observed close to Japan and Korea. Tetrachloroethene (C2Cl4) levels have also decreased significantly, especially north of 25°N, but this gas still remains a useful indicator of northern industrial emissions. Methyl bromide (CH3Br) levels were systematically 1–2 pptv lower from 1994 to 2001, in accord with recent reports. However, air masses that had been advected over Japan and/or South Korean port cities typically exhibited elevated levels of CH3Br. As a consequence, emissions of CH3Br from Japan and Korea calculated employing CH3Br/CO ratios and scaled to CO emission inventory estimates, were almost as large as for all of south China (south of 35°N). Total east Asian emissions of CH3Br and CH3Cl were estimated to be roughly 4.7 Gg/yr and 167 Gg/yr, respectively, in 2001.
Role and character of seasonal peat soil deformation on the hydrology of undisturbed and cutover peatlands
Authors: Price Jonathan S.
Published: September 2003

This paper describes the nature and magnitude of peat soil volume changes and its relation to seasonal changes in water table at an undisturbed bog peatland and on two cutover sections of the same peatland and its effect on hydraulic conductivity. In the latter two sites, operations had ceased 2 and 7 years prior to this study, respectively. The water table dropped to a maximum depth of 40, 50, and 68 cm, respectively, at the undisturbed, 2‐year, and 7‐year abandoned sites and a resulted in subsidence of 0.96, 3.84, and 2.65 cm m−1, respectively. At the undisturbed site, surface elevation changes did not always correspond to water table changes, but peat underwent a period of swelling even as the water table fell, probably due to the accumulation of methane in soil pores. At all sites most volume change occurred in the upper 50 cm layer, with maximum strain of 5, 15, and 5% at the undisturbed, 2‐year, and 7‐year abandoned sites, respectively, and was strongly related to water table decline. A model of peat deformation in the zone of saturation (100 cm depth), based on changes in saturated soil moisture (6%), grossly overestimated strain (1%) in the saturated zone, and again methane accumulation was the suspected cause of the soil moisture decrease. Peat compression (and perhaps methane accumulation) caused hydraulic conductivity to decrease over two orders of magnitude at 75, 125, and 170 cm depth. The decrease in hydraulic conductivity as a peatland dries may be an important self‐preservation mechanism (i.e., against further water loss).
On the use of block‐effective macrodispersion for numerical simulations of transport in heterogeneous formations
Authors: Rubin Yoram , Bellin Alberto , Lawrence Alison E.
Published: September 2003

The fundamental question we consider in this paper is how to allow flexibility in numerical grid design without discounting the dispersive action of the unmodeled variability. In doing that, we wish to preserve the interplay between all relevant length scales: those relevant to the spatial variability as well as those created by design. In this study we extend and test the concept of block‐scale macrodispersion introduced by Rubin et al. [1999] for modeling unresolved hydraulic property variations at scales smaller than the numerical grid blocks. We present closed‐form analytical results for the block‐scale macrodispersion and test them numerically. Closed‐form analytical results are presented for the large‐time aymptotic limits, and it is shown that these limits are attained very fast. The conditions of applicability are investigated, and we show that ergodicity with regard to block‐scale heterogeneity is attained surprisingly fast.
Sediment pulses in mountain rivers: 1. Experiments
Authors: Cui Yantao , Parker Gary , Lisle Thomas E. , Gott Julie , Hansler‐Ball Maria E. , Pizzuto James E. , Allmendinger Nicholas E. , Reed Jane M.
Published: September 2003

Sediment often enters rivers in discrete pulses associated with landslides and debris flows. This is particularly so in the case of mountain streams. The topographic disturbance created on the bed of a stream by a single pulse must be gradually eliminated if the river is to maintain its morphological integrity. Two mechanisms for elimination have been identified: translation and dispersion. According to the first of these, the topographic high translates downstream. According to the second of these, it gradually diffuses away. In any given river both mechanisms may operate. This paper is devoted to a description of three controlled experiments on sediment pulses designed to model conditions in mountain streams. Each of the experiments began from the same mobile‐bed equilibrium with a set rate and grain size distribution of sediment feed. In one experiment the median size of the pulse material was nearly identical to that of the feed sediment. In the other two the pulse material differed in grain size distribution from the feed sediment, being coarser in one case and finer in the other case. In all cases the mode of pulse deformation was found to be predominantly dispersive, a result that constitutes the main conclusion of this paper. The pulses resulted in a notable but transient elevation of sediment transport rate immediately downstream. When the pulse was coarser than the ambient sediment, the bed downstream remained armored, and a migrating delta formed in the backwater upstream. When the pulse was finer than the ambient sediment, translation was observed in addition to dispersion. The presence of the finer material notably elevated the transport of ambient coarse material on the bed downstream. In part 2 [Cui et al., 2003], the experimental results are used to test a numerical model.
Sediment pulses in mountain rivers: 2. Comparison between experiments and numerical predictions
Authors: Cui Yantao , Parker Gary , Pizzuto James , Lisle Thomas E.
Published: September 2003

Mountain rivers in particular are prone to sediment input in the form of pulses rather than a more continuous supply. These pulses often enter in the form of landslides from adjacent hillslopes or debris flows from steeper tributaries. The activities of humans such as timber harvesting, road building, and urban development can increase the frequency of sediment pulses. The question as to how mountain rivers accommodate pulses of sediment thus becomes of practical as well as academic significance. In part 1 [Cui et al., 2003], the results of three laboratory experiments on sediment pulses are reported. It was found there that the pulses were eliminated from the flume predominantly by dispersion of the topographic high. Significant translation was observed only when the pulse material was substantially finer than the ambient load in the river. Here the laboratory data are used to test a numerical model originally devised for predicting the evolution of sediment pulses in field‐scale gravel bed streams. The model successfully reproduces the predominantly dispersive deformation of the experimental pulses. Rates of dispersion are generally underestimated, largely because bed load transport rates are underestimated by the transport equation used in the model. The model reproduces the experimental data best when the pulse is significantly coarser than the ambient sediment. In this case, the model successfully predicts the formation and downstream progradation of a delta that formed in the backwater zone of the pulse in run 3. The performance of the model is less successful when the pulse is composed primarily of sand. This is likely because the bed load equation used in the study is specifically designed for gravel. When the model is adapted to conditions characteristic of large, sand bed rivers with low Froude numbers, it predicts substantial translation of pulses as well as dispersion.
Plume‐transform interactions at ultra‐slow spreading ridges: Implications for the Southwest Indian Ridge
Authors: Georgen Jennifer E. , Lin Jian
Published: September 2003

We explore a potentially important variable in controlling ridge‐hot spot interaction, the effect of transform offsets in limiting along‐axis flow of plume material. We focus on the Southwest Indian Ridge (SWIR), where the “transform damming” effect is likely to be pronounced because of both long offset lengths and large contrasts in lithospheric thickness across the transform faults due to the ultra‐slow spreading rate. We investigate the degree to which transform faults affect axial asthenospheric flow by performing a series of three‐dimensional (3‐D) numerical experiments with simplified channel‐flow geometry and extrapolating their results to the SWIR. 3‐D mantle viscosity structure for a ridge‐transform‐ridge system is determined based on temperature‐ and pressure‐dependent viscosity laws. We consider six transform lengths, spanning 0 to 250 km in increments of 50 km. We then calculate the 3‐D viscous flow in response to an along‐axis pressure gradient corresponding to a ridge‐centered hot spot. Modeling results predict that transform faults affect along‐axis asthenospheric flow in two important ways. First, transforms reduce along‐axis flux. The longer the transform offset, the greater the reduction in across‐transform flux relative to the zero‐offset case. Second, transforms deflect shallow asthenospheric along‐axis flow. The predicted transform damming effect is most pronounced for a viscosity structure that is strictly pressure‐ and temperature‐dependent. Flux reduction effects could be less significant for viscosity laws that additionally consider dehydration, melting, and change in deformation mechanism. This model predicts that the waist width of an on‐axis plume is dependent not only on such previously explored factors as buoyancy and spreading rate, but also on the geometry of ridge segmentation. Along the SWIR, axial flow driven by the Marion plume is likely curtailed by the long‐offset Andrew Bain and Discovery II fracture zones, severely limiting its lateral extent.
Melting, dehydration, and the dynamics of off‐axis plume‐ridge interaction
Authors: Hall Paul S. , Kincaid Chris
Published: September 2003

We present results from a series of two‐dimensional numerical experiments in which a thermally buoyant, off‐axis mantle plume interacts with a nearby ridge axis. These experiments incorporate melting and a number of related dynamical feedbacks, including energy loss to latent heating and Fe depletion buoyancy as well as viscosity increases due to dehydration during melting. Results indicate that dehydration, which acts to increase the viscosity of the residual mantle during melting, profoundly impacts the morphology of flow between plume and ridge axis. As upwelling plume material begins to melt, it becomes significantly more viscous and readily accretes to the overlying lithosphere. This creates a viscous plug that grows downward from the base of the lithosphere directly above the plume conduit. Plume material traveling to the ridge axis is then deflected horizontally at subsolidus depths by this plug, allowing pristine, unmelted plume material to reach the ridge axis. Experiments without dehydration show that the loss of thermal energy to latent heating during melting marginally decreases the flow of plume material along the base of the lithosphere to the ridge axis. Alternatively, extraction of Fe from the solid during melting slightly increases plume flow to the ridge. These results also demonstrate that the flow of plume material to the ridge axis is sensitive to the slope of the base of the rheological lithosphere, consistent with previous studies of off‐axis plume ridge interaction.
Transition to solar minimum at high solar latitudes: Energetic particles from corotating interaction regions
Authors: Hofer M. Y. , Marsden R. G. , Sanderson T. R. , Tranquille C. , Forsyth R. J.
Published: September 2003

One of the key questions to be addressed during the solar maximum phase of the Ulysses mission has been the nature of the ubiquitous energetic particle populations observed at all helio‐latitudes from equator to poles. During the current, post‐maximum phase of its mission, Ulysses has encountered the return to more stable solar wind, high speed stream structure, leading to the formation of stream and/or corotating interaction regions, in addition to the coronal mass ejection associated transients. The analysis reported here presents the identification of the first CIR after the recent solar maximum recorded by Ulysses COSPIN/LET at high helio‐latitudes based on energetic particle composition data recorded in the ∼5–30 MeV/n range. The recurrent compression region appears during 3–6 solar rotations in 2002 and is observed from ≈52°N to ≈37°N heliographic latitude at heliocentric distances from ≈3.1 AU to ≈3.8 AU.
Steady‐state event‐excluded proton spectra at solar minimum at all heliolatitudes
Authors: Patterson J. D. , Armstrong T. P.
Published: September 2003

We present spectra of a steady foreground population of particles in the inner heliosphere observed by the Heliosphere Instrument for Spectra, Composition, and Anisotopy at Low Energies (HISCALE) on board the Ulysses spacecraft. The observed spectra come from the full range of heliolatitudes visited by Ulysses, −80 to +80 degrees, during Ulysses' first full orbit of the Sun during solar minimum. New corrections for background were applied resulting in a more sensitive and higher energy resolution data set that we used here to analyze quiet‐time (event‐excluded) spectra. We found a persistent foreground population of energetic protons that permeate the inner heliosphere. These protons have complex energy spectra suggesting multiple acceleration sources, and these particles move predominently in non‐radial directions. These findings support the idea that the inner heliosphere acts as a reservoir for energetic protons.
Properties of high‐latitude CME‐driven disturbances during Ulysses second northern polar passage
Authors: Reisenfeld D. B. , Gosling J. T. , Forsyth R. J. , Riley P. , St. Cyr O. C.
Published: September 2003

Ulysses observed five coronal mass ejections (CMEs) and their associated disturbances while the spacecraft was immersed in the polar coronal hole (CH) flow above 70° N in late 2001. Of these CMEs, two were very fast (>850 km s−1) driving strong shocks in the wind ahead, and two others were over‐expanding. The two fast CMEs were observed leaving the Sun by LASCO/SOHO, and were observed in the ecliptic by Genesis and ACE. These were large events, spanning at least from the northern heliospheric pole to the ecliptic. One‐dimensional hydrodynamic simulations indicate that these could be described as overpressured CMEs launched from the Sun at speeds initially faster than ambient, but then decelerating to the ambient solar wind speed as they propagated outward. The two over‐expanding CMEs mark their first occurrence since Ulysses’ first orbit when such CMEs were only observed in polar CH flow.
Solar magnetic field reversal as seen at Ulysses
Authors: Jones Geraint H. , Balogh André , Smith Edward J.
Published: September 2003

The rapid motion of the Ulysses spacecraft from high southern to high northern latitudes in 2000–2001 provided an excellent opportunity to make inferences regarding the solar magnetic dipole's behaviour around solar maximum. A simple dipole model is fitted to Ulysses measurements of the polarity of the heliospheric magnetic field mapped back to the solar wind source surface. Although higher order components of the field are ignored, the gradual reversal in orientation of the dipole field component can be followed during solar maximum, with the dipole axis crossing the solar equator during early 2000–early 2001. The dipole appears to exhibit a rotation at a slower rate than the Carrington frame of reference, similar to previous measurements made around solar maximum in the solar equatorial regions.
VLF wave activity in the solar wind and the photoelectron effect in electric field measurements: Ulysses observations
Authors: Lin Naiguo , Kellogg Paul J. , MacDowall R. J. , McComas D. J. , Balogh A.
Published: September 2003

We present observations of very low frequency (VLF) waves (0.2 to 448 Hz) made by Ulysses during the solar maximum and compare the observations with those obtained when the solar activity was approaching a minimum. The occurrences and properties of the waves are found to be similar during the solar maximum and solar minimum periods for slow and intermediate speed solar wind. The maximum intensities of the electromagnetic waves for the two solar cycle periods are comparable. These similarities suggest that the plasma conditions for the waves' excitation are similar for the slow and intermediate solar wind in both solar maximum and minimum phases. It is also found that the electric field noise detected in the low band channels, which are measuring less than 10 Hz signals, is contaminated by the spin modulation of the electric field caused by the photoelectron cloud around the spacecraft, especially when the ambient plasma density is low. This effect enhances with increasing solar aspect angle.
Magnetic clouds with east/west orientated axes observed by Ulysses during solar cycle 23
Authors: Rees A. , Forsyth R. J.
Published: September 2003

The second Ulysses orbit of the Sun has provided a unique opportunity for the study of the interplanetary manifestation of coronal mass ejections (ICMEs) over a wide range of heliographic latitudes. The Ulysses dataset between July 1995 and mid April 2003 has been surveyed for magnetic clouds (MCs), a subset of ICMEs. As a result of the rising solar activity during this time, ICMEs were observed over a wide range of heliographic latitudes. By fitting a constant α, force‐free flux rope model to each event we determine whether the local axis orientation of the MCs are directed in an eastward or a westward sense. We show that during this period in solar cycle 23, those MCs whose hemispheric origin is clear display a trend, with MCs in the southern hemisphere having predominantly westward directed local axes and those in the northern hemisphere having eastward directed local axes.
Evolution of the galactic cosmic ray electron to proton ratio: Ulysses COSPIN/KET observations
Authors: Heber B. , Clem J. M. , Müller‐Mellin R. , Kunow H. , Ferreira S. E. S. , Potgieter M. S.
Published: September 2003

The Ulysses orbit provides a unique opportunity to study the propagation of cosmic rays in a wide range of heliographic latitudes and during different solar activity and polarity in the inner heliosphere. Around July 2000 the solar magnetic field reversed its global polarity. In late 2000, the electron to proton ratio at the rigidities of 1.2 GV and 2.5 GV, measured by the Kiel Electron Telescope aboard Ulysses, was roughly the same as in the previous solar maximum. During 2001 the ratio profile began to flatten, however after late 2001 the ratio began to increase again, leading to the conclusion that drifts are becoming increasingly important again. Comparing the Ulysses observations with the IMP and ICE measurements in the 1980s reveals a similar time profile. If solar cycle 23 would evolve similar to solar cycle 21 then the electron intensity will increase more quickly than the helium and proton intensities in 2003/2004.
Shear wave splitting in a young continent‐continent collision: An example from Eastern Turkey
Authors: Sandvol Eric , Turkelli Niyazi , Zor Ekrem , Gok Rengin , Bekler Tolga , Gurbuz Cemil , Seber Dogan , Barazangi Muawia
Published: September 2003

We have determined the shear wave splitting fast polarization direction and delay time using data from the ETSE broadband experiment (Eastern Turkey Seismic Experiment), a deployment of 29 broadband seismic stations across the collision zone of the Arabian, Eurasian, and Anatolian plates. Our results show that the fast polarization directions are relatively uniform and they exhibit primarily NE–SW orientations. No abrupt changes in anisotropy directions are observed across the main tectonic units in the region: the Bitlis Suture (BS) and the North and Eastern Anatolian Fault zones. The fast polarization directions are determined to be sub‐parallel to the Anatolian, Arabian, and Eurasian absolute plate velocities, except for those stations in the northeastern corner of the Anatolian Plateau. Observed delay times range from 0.7 to 2.0 seconds with an average value of 1.0 second; the largest values are within the northern Anatolian Plateau which is underlain by an exceptionally low velocity zone in the uppermost mantle. We interpret shear wave splitting as the vector difference of the Eurasian lithosphere and northeastern or southwestern directed flow of the asthenospheric mantle. Comparisons of the polarization anisotropy with measurements of Pn azimuthal anisotropy suggest vertical anisotropic layering except in those areas which are underlain by partially molten uppermost mantle.
Tomographic Pn velocity and anisotropy structure beneath the Anatolian plateau (eastern Turkey) and the surrounding regions
Authors: Al‐Lazki Ali I. , Seber Dogan , Sandvol Eric , Turkelli Niyazi , Mohamad Randa , Barazangi Muawia
Published: September 2003

We use Pn phase travel time residuals to invert for mantle lid velocity and anisotropy beneath northern Arabia‐eastern Anatolia continent‐continent collision zone. The primary phase data were obtained from the temporary 29‐station broadband PASSCAL array of the Eastern Turkey Seismic Experiment. These data were supplemented by phase data from available stations of the Turkish National Seismic Network, the Syrian National Seismic Network, the Iranian Long Period Array, and other stations around the southern Caspian Sea. In addition, we used carefully selected catalog data from the International Seismological Centre and the National Earthquake Information Center bulletins. Our results show that low (<8 km/s) to very low (<7.8 km/s) Pn velocity zones underlie the Anatolian plateau, the Caucasus, and northwestern Iran. Such low velocities are used to infer the presence of partially molten to absent mantle lid beneath these regions. In contrast, we observed a high Pn velocity zone beneath northern Arabia directly south of the Bitlis‐Zagros suture indicating the presence of a stable Arabian mantle lid. This sharp velocity contrast across the suture zone suggests that Arabia is not underthrusting beneath the Anatolian plateau and that the surface suture extends down to the uppermost mantle. Pn anisotropy orientations within a single plate (e.g. Anatolia plate) show a higher degree of lateral variation compared to Pn velocity. Areas of coherent Pn anisotropy orientations are observed to continue across major fault zones such as the EAF zone.
Acoustic measurements of pore‐scale displacements
Authors: DiCarlo David A. , Cidoncha Jose I. G. , Hickey Craig
Published: September 2003

We describe how experimentally measurable acoustic and hydroacoustic events occur when one fluid displaces another within a porous medium. We show that the events are directly related to discrete fluid bursts (“Haines jumps”) that occur at the pore scale. We find that the events show power law statistics with respect to magnitude for drainage (air invading) but not for imbibition (water invading). These observations agree with simple conceptual arguments on how the displacements take place. The results show that acoustic and hydroacoustic measurements can be an excellent technique for observing Haines jumps in‐situ.
A less dusty future?
Authors: Mahowald Natalie M. , Luo Chao
Published: September 2003

Atmospheric desert dust is potentially highly sensitive to changes in climate, carbon dioxide and human land use. In this study we use 6 different scenarios of the processes responsible for changes in source areas and explore changes in desert dust loading in pre‐industrial and future climates, although all the scenario results are likely to be sensitive to the climate model simulations used for this study. Simulations suggest that future dust may be 20 to 60% lower than current dust loadings. The anthropogenic portion of the current dust loading may be as large as 60%, or humans may have caused a 24% decrease in desert dust, depending on the relative importance of land use, carbon dioxide and human induced climate change. These results suggest there may be a high sensitivity of ‘natural aerosols’ to human intervention, which has enormous implications for climate and biogeochemistry in the future.
Deep dissolved iron profiles in the eastern North Atlantic in relation to water masses
Authors: Laës A. , Blain S. , Laan P. , Achterberg E. P. , Sarthou G. , de Baar H. J. W.
Published: September 2003

Concentrations of dissolved iron (DFe, 0.2μm) were determined at two stations in the Biscay Abyssal Plain (North East Atlantic) in March 2002. DFe concentrations in the surface layer (0.23–0.34 nM) were typical of winter conditions in this area. At 1000 m, DFe concentrations increased to 0.62–0.86 nM. This feature is consistent with the production of DFe by remineralization of the biogenic material. However, at this depth, Mediterranean Outflow Water (MOW) could be an additional source of DFe. Below 2500 m, DFe concentrations were constant (0.75 ± 0.04 nM). An interesting feature of the profiles was the intermediate maximum of DFe (1.19–1.12 nM) around 2000 m, associated with the Labrador Sea Water (LSW). We suggest that the iron enrichment of LSW occurred when this water mass reached the continental margin, likely in the vicinity of the Goban plateau. Vertical distributions were highly dependent on water masses encountered.
The role of hydrologically‐driven ice fracture in drainage system evolution on an Arctic glacier
Authors: Boon Sarah , Sharp Martin
Published: September 2003

Observations from Ellesmere Island suggest that the connection between surface and subglacial drainage on a predominantly cold glacier is made abruptly by hydrologically‐driven propagation of fractures from the surface to the bed. Where ice is 150 m thick, water ponded to a depth of 6.9 m within a supraglacial stream system before establishing a permanent bed connection. Multiple premonitory drainage events preceded the final drainage of ponded water, implying that fracturing is necessary, but insufficient, to establish a permanent link between surface and subglacial drainage. Refreezing of water that penetrates the first fractures to form may reseal the connection, while flow resistance within the subglacial system may delay the onset of continuous through‐flow. A large volume of ponded water is required to enlarge fractures sufficiently by melting to maintain continuous drainage, while feedbacks between subglacial hydrology and ice dynamics may assist in maintaining the connection and initiating subglacial outflow.
Influence of the solar wind dynamic pressure on the decay and injection of the ring current
Authors: Wang C. B. , Chao J. K. , Lin C.‐H.
Published: September 2003

The influence of the solar wind dynamic pressure on the decay and injection of the ring current is investigated empirically, on the basis of the solar wind and the geomagnetic index Dst of the OMNI database, for the period from January 1964 to July 2001. We found that when the position of the ring current is closer to the Earth for a higher solar wind dynamic pressure, the decay time of the ring current decreases. The decay time, in hours, varies as follows, τ = 8.70 exp(6.66/(6.04 + P)), for northward interplanetary magnetic fields (IMF), where P is the solar wind dynamic pressure in nanopascals. It is also found, by minimizing the root mean square errors of the hourly Dst difference between the calculated values and the measured ones, that the ring current injection rate is proportional to the solar wind dynamic pressure, with a power index equal to 0.2 during southward IMF. This implies that the ring current injection increases when the magnetosphere is more compressed by high solar wind dynamic pressure. On the basis of our new results we demonstrate that the predictions of Dst using O'Brien and McPherron's [2000a] model are improved, especially for intense geomagnetic storms when the influence of the solar wind dynamic pressure on the decay and injection of ring current is taken into consideration.
Improvement of ionospheric electron density estimation with GPSMET occultations using Abel inversion and VTEC information
Authors: Garcia‐Fernandez M. , Hernandez‐Pajares M. , Juan M. , Sanz J.
Published: September 2003

As it is known, the Abel transform has been proven to be a useful tool that offers the possibility to obtain vertical description of ionospheric electron density (among other neutral atmosphere parameters) through inversion of Global Positioning System (GPS) observations gathered by Low Earth Orbiters (LEO). This work is focused on extending the application of this technique to GPSMET data considering Vertical Total Electron Content. With this information, the horizontal variability of the electron concentration is accounted for. This approach shows how this information improves the results obtained in electron densities with respect to the traditional approach of Abel inversion that assumes spherical symmetry. Moreover, the ability of this inversion algorithm to obtain true‐height profiles of electron density is contrasted with common procedures to obtain these profiles, especially the hmF2 parameter.
Global response of the plasmasphere to a geomagnetic disturbance
Authors: Spasojević M. , Goldstein J. , Carpenter D. L. , Inan U. S. , Sandel B. R. , Moldwin M. B. , Reinisch B. W.
Published: September 2003

Global images of the plasmasphere obtained by the Extreme Ultraviolet (EUV) imager on the IMAGE satellite are used to study the evolving structure of the plasmasphere during two geomagnetic disturbances. By tracking the location of the plasmapause as a function of L shell and magnetic local time, quantitative measurements of radial and azimuthal motions of the boundary are made for intervals ≥7 hours in duration with a time resolution of 10 min. The two cases presented are 26–27 June 2001, a relatively weak but isolated geomagnetic disturbance, and 9–10 June 2001, a moderate event with a multistaged onset and recurring substorm activity after the main disturbance. In both cases the onset of the disturbance, correlated with a southward turning of the IMF, is characterized by inward motion or erosion of the plasmapause and a smoothing of any existing azimuthal variations across the nightside. Over a period of many hours, a plasmaspheric plume forms in the afternoon sector as a result of sunward flows from dusk and corotational flows across the dayside. Azimuthal variations in the plasmapause radius tend to form in the local time sector from dawn to the western edge of the plume, including mesoscale (≤0.5 in L and ≤2 hours in local time) crenulations and larger‐scale shoulder features, while the nightside boundary remains featureless. In the 26–27 June 2001 case, the magnetosphere entered a period of deep quiet after the main disturbance, and the plasmaspheric plume began to corotate with the main plasmasphere from the afternoon sector across the nightside. In contrast, the plume in the 9–10 June 2001 event became wrapped around the main plasmasphere and a second plume formed in the afternoon sector, perhaps due to continued substorm activity. In situ density data for these events show highly irregular density structure within the plumes as measured at geosynchronous orbit, whereas a measurement by IMAGE RPI suggests that there may be less structure near the base of the plume closer to the main plasmasphere.