bluuebunny/crossref_metadata_2025 huggingface dataset:
A method to relate initial elastic stress to fault population strains
Authors: Schultz Richard A.
Published: June 2003

A relationship between the cumulative elastic driving stress (or far‐field elastic differential stress) and the inelastic strain of a fault population can be defined from the displacement‐length scaling relations of the population. Two solutions are presented: one in which the elastic parameters remain constant, and the other that assumes a progressive reduction in modulus with increasing fracture spatial density. The method is illustrated by using fault populations from Mars. Cumulative differential stresses of 37 MPa and 87 MPa (computed here for 1 km depth) are implied to have produced the strains observed at Amenthes Rupes (widely spaced thrust faults) and Tempe Terra (closely spaced normal faults), respectively.
Shock front nonstationarity of supercritical perpendicular shocks
Authors: Hada Tohru , Oonishi Makiko , Lembège Bertrand , Savoini Philippe
Published: June 2003

The shock front nonstationarity of perpendicular shocks in super‐critical regime is analyzed by examining the coupling between “incoming” and “reflected” ion populations. For a given set of parameters including the upstream Mach number (MA) and the fraction α of reflected to incoming ions, a self‐consistent, time‐stationary solution of the coupling between ion streams and the electromagnetic field is sought for. If such a solution is found, the shock is stationary; otherwise, the shock is nonstationary, leading to a self‐reforming shock front often observed in full particle simulations of quasi‐perpendicular shocks. A parametric study of this numerical model allows us to define a critical αcrit between stationary and nonstationary regimes. The shock can be nonstationary even for relatively low MA(2–5). For a moderate MA(5–10), the critical value αcrit is about 15 to 20%. For very high MA (>10), αcrit saturates around 20%. Moreover, present full simulations show that self‐reformation of the shock front occurs for relatively low βi and disappears for high βi, where βi is the ratio of upstream ion plasma to magnetic field pressures. Results issued from the present theoretical model are found to be in good agreement with full particle simulations for low βi case; this agreement holds as long as the motion of reflected ions is coherent enough (narrow ion ring) to be described by a single population in the model. The present model reveals to be “at variance” with full particle simulations results for the high βi case. Present results are also compared with previous hybrid simulations.
Global distribution of coronal mass outputs and its relation to solar magnetic field structures
Authors: Wei Fengsi , Feng Xueshang , Cai Hongchang , Zhou Qingjun
Published: June 2003

The basic characteristics of the coronal mass output near the Sun are analyzed with the statistic and numerical methods by using observational data from K corona brightness, interplanetary scintillation, and photospheric magnetic field during the descending phases (1983) and the minimum (1984) of solar activity. The methods used here are based on the global distribution of the solar magnetic field on the source surface (at 2.5 solar radii (RS)). Our main results are the following: (1) There are certain regular persistent patterns in the global distributions of coronal mass outputs fluxFm(density ρ × speedV), which shows that the highestFmin 1983 and 1984 display more regularly double peaks and single‐peak wave‐like patterns on the source surface (2.5RS), respectively. The highest and the lowestFmare associated with the coronal current sheet and the polar corona regions, respectively, and the other regions are associated with a moderateFm. (2) The speed dependence ofFmis different for various magnetic structures. The dependence is nearly constant in the polar coronal region and monotonically rises in the current sheet regions both for the descending (1983) and the ascending (1976) phases. (3) The different frequency number distributions ofFmalso correspond to different magnetic field structures, with average valuesm,p= 8.3 × 1011particles/cm2(s) for the polar coronal region andm,c= 17.7 × 1011particles/cm2(s) for the coronal current sheet. (4) As a theoretical test, a preliminary numerical study of the global distribution near 2.5RSfor the Carrington rotation 1742 in 1983 has been made by solving a self‐consistent MHD system based on the observations of K coronal brightness and the photospheric magnetic fields. The numerical results indicate that the global distributions of the coronal mass outputs on the source surface could be used to understand/predict the change of the interplanetary conditions.
Magnetopause erosion: A global view from MHD simulation
Authors: Wiltberger M. , Lopez R. E. , Lyon J. G.
Published: June 2003

In this paper we use a global magnetohydrodynamic simulation of the magnetosphere to examine the behavior of the magnetopause position when the interplanetary magnetic field suddenly changes from northward to southward. The inward motion of the magnetopause under the influence of a southward IMF is generally referred to as magnetopause “erosion.” Physical models to explain erosion have been proposed, notably the “onion” peeling model, a model based on the effects of fringe fields from the Region 1 Birkeland currents and the nightside cross‐tail current. The simulation shows behavior consistent with aspects of these models, but it also shows behavior that is most consistent with the major driver of erosion being the growth of the nightside cross‐tail current. In particular, the simulation exhibits a marked delay between the arrival of the southward IMF at the magnetopause and the inward motion of the magnetopause. We attribute this delay to the delay in the growth of the nightside current system in response to the southward turning of the IMF.
Internal structure of magnetic clouds: Plasma and composition
Authors: Lynch B. J. , Zurbuchen T. H. , Fisk L. A. , Antiochos S. K.
Published: June 2003

A comprehensive analysis of magnetic clouds observed by the Advanced Composition Explorer (ACE) spacecraft from February 1998 to July 2001 is presented. The magnetic field data from the MAG instrument is fit with the cylindrically symmetric, linear force‐free model and the fit parameter distributions are examined. This magnetic field model enables us to map plasma data from the SWEPAM and SWICS instruments to a position within the model cylinder. A superposed epoch analysis of all our magnetic cloud events is used to construct diameter cuts through an “average” cloud profile in any desired plasma, elemental composition, or charge state quantity. These diameter cuts are found to have nontrivial structure and there appears to be significant composition and structural differences between clouds of different speeds. The slow magnetic clouds (〈Vrad〉 < 500 km/s) have an almost constant proton density profile whereas the fast magnetic cloud (〈Vrad〉 ≥ 500 km/s) profile is depleted throughout with symmetric dips and a local maximum at the cloud center. The fast magnetic clouds have a slightly higher Nα/Np ratio than the slow clouds. Both the fast and slow events have enhanced oxygen and iron charge states compared to the slow solar wind. The fast events have a slightly increased O7+/O6+ average profile and a much stronger Fe≥16+/Fetotal profile than the slow events. We briefly discuss the implications for physical conditions at the Sun, the role these coronal mass ejections (CMEs) may play in transporting magnetic flux, and the application of our structure results to the current flux rope CME modeling effort.
Source regions and storm effectiveness of frontside full halo coronal mass ejections
Authors: Zhao X. P. , Webb D. F.
Published: June 2003

Full halo coronal mass ejections (CMEs) erupting from the side of the Sun facing Earth, i.e., frontside full halo CMEs, are considered to be a likely cause of major, transient geomagnetic storms. However, this hypothesis has not been tested over a full solar cycle. We compare all frontside full halo CMEs observed during the first half of solar cycle 23, from 1996 to the end of 2000, with moderate or larger storms at Earth. We show that the association of frontside full halo CMEs with such storms tends to decrease from 1997 to 2000, though this decreasing trend is not monotonic. We examine the locations of the frontside full halo CMEs from 1996 to 2000 with respect to two kinds of coronal closed field regions: bipolar closed field regions between opposite‐polarity open field regions and unipolar closed field regions between like‐polarity open field regions. We find that even during solar maximum when the occurrence frequency of the two kinds of regions is nearly the same, the central positions of the frontside full halo CMEs are mostly located under the bipolar coronal streamer belt, suggesting that most full halo CMEs originate in the bipolar coronal helmet streamers that are sandwiched between coronal holes having opposite magnetic polarity. Because the inclination of the heliospheric current sheet increases toward solar maximum, the fraction of CMEs emitted into the ecliptic decreases, and the inclination of associated flux ropes increases. These effects help to explain the solar cycle effect on the storm effectiveness of frontside full halo CMEs.
Instability of inertial Alfvén waves in transverse sheared flow
Authors: Wu K. , Seyler C. E.
Published: June 2003

We study the stability of dispersive Alfvénic structures with transverse scales near the electron inertial length c/ωpe. As demonstrated by Seyler and Wu [2001], inertial Alfvén waves can be driven unstable by the parallel current sheets associated with the Alfvénic structures. In this paper we extend that study by including the effect of the transverse sheared flow due to the E × B drift. We show that the sheared flow decreases the growth rate of the instability, but the instability still exists even in the presence of the shear. In addition, we show that the sheared flow itself can drive the plasma unstable. Owing to a resonance between the sheared flow velocity and the phase velocity of the Alfvén wave, energy can be transferred from the sheared flow to the wave, driving the plasma unstable. We present an extensive analytical study of the linear stability. The result of this paper shows how inertial Alfvén waves can be generated in the auroral region and may explain the origin of broadband extremely low frequency (BBELF) waves associated with Alfvénic structures.
The dynamical heliosphere
Authors: Zank G. P. , Müller H.‐R.
Published: June 2003

The solar cycle induces substantial changes in the solar wind, which can have an important effect on the structure of the global heliosphere. In the ecliptic the ram pressure can vary from one cycle to the other, being greater during periods of minimum activity. We investigate the response of the heliosphere to a temporally varying solar wind. Since neutral hydrogen is a key component in determining the large‐scale structure of the heliosphere, we employ a multifluid model in which the charge‐exchange interaction between neutral hydrogen and protons is included self‐consistently. The variability of the termination shock location is described and the response of the hydrogen wall to the temporal solar wind is discussed. Both two‐shock and one‐shock models are considered. The propagation of global shock waves analogous to those driven by global merged interactions (GMIR) is considered too for both one‐ and two‐shock models. The global response of the heliosphere to a single GMIR disturbance can last for nearly a solar cycle (∼9.5 years). As a result of both a variable solar cycle ram pressure and the presence of disturbances of global extent, such as GMIRs, the large‐scale heliosphere is most likely highly time‐dependent and dynamical.
Computing magnetospheric force equilibria
Authors: Lemon Colby , Toffoletto Frank , Hesse Michael , Birn Joachim
Published: June 2003

We describe a method to compute three‐dimensional force equilibria in the Earth's magnetosphere. The method is embodied in a code called the MagnetoFriction code which solves a set of ideal magnetohydrodynamic (MHD) equations that are modified to include a frictional dissipation term in the momentum equation. The friction takes the form of a force which is directed against the fluid motion and is therefore an energy sink. This allows the system to settle into a minimum energy equilibrium. A nonuniform cartesian grid is used along with initial conditions supplied by empirical magnetic field and pressure models. These initial conditions do not, in general, satisfy the force balance condition , and the code must iterate until approximate force balance is achieved. Pressure and magnetic field solutions are presented for several different configurations of the magnetosphere.
A petrologic anomaly accompanying outboard earthquakes beneath Fiji‐Tonga: Corresponding evidence from broadband P and S waveforms
Authors: Brudzinski Michael R. , Chen Wang‐Ping
Published: June 2003

Using high‐resolution, triplicate body waveforms, we investigate strong lateral variations in P and SH wave speeds (VP and VS) beneath the Tonga subduction zone where cold lithosphere is subducting rapidly at 200 mm yr−1. Under these conditions, the lack of prominent anomalies of high VP and VS in the lower mantle implies that a large amount of recently subducted material remains above the lower mantle. This inference is also evident from a subhorizontal swath of outboard earthquakes in the transition zone that is up to 1000 km away from the Wadati‐Benioff zone. Beneath the back arc, we find a sharp, east‐west trending demarcation north of which outboard earthquakes occur and VP and VS abruptly drop by ∼3%. Thus the effect of cold temperature to raise VP and VS, as indicated by the presence of outboard earthquakes, must be counteracted by petrologic variations. We interpret that outboard earthquakes occur where impounding of subducted metastable olivine or volatiles reduces seismic wave speeds and triggers deep earthquakes. Considering the density of these candidates and the strong effect of partial melt on VS, volatiles in the form of hydrous phases or melt induced by dehydration are not consistent with observed reductions in VP and VS. Meanwhile, metastable olivine remains a viable candidate. As a cold slab passes below the 410‐km discontinuity, olivine becomes metastable and makes the tip of the slab buoyant. Such a mechanism could explain why the leading end of a fast subducting slab may be successively sequestered in the transition zone.
Magmatic feeding system and crustal magma accumulation beneath Vulcano Island (Italy): Evidence from CO2 fluid inclusions in quartz xenoliths
Authors: Zanon Vittorio , Frezzotti Maria‐Luce , Peccerillo Angelo
Published: June 2003

Pure CO2 fluid inclusions are observed in quartz xenoliths from four lava flows in the Island of Vulcano, corresponding to distinct activity stages during the last 120 kyr. Xenoliths, which consist of aggregates of quartz grains, are present in lavas of contrasting composition ranging from basaltic‐andesites to rhyolites. Two main generations of CO2 inclusions are observed: early (type I) inclusions were trapped prior to the ascent of the host xenoliths, while type II inclusions were trapped during the ascent into the host magma. Fluid inclusions show a bimodal distribution of homogenisation temperatures, corresponding to two distinct density intervals: 0.89–0.52 g/cm3(type I) and 0.42–0.13 g/cm3(type II). Type I inclusions indicate pressures of 0.56–0.33 GPa (21–13 km), relating to the levels of xenolith entrapment in the host lavas. Type II fluid inclusions show considerably lower pressures ranging from 0.14 to 0.03 GPa (5.5–3 km). Present data suggest ponding of mantle‐derived magmas in at least two distinct reservoirs, located at lower crustal depths and at shallow levels, respectively. Combined fluid inclusion and petrological data suggest that the deep reservoirs were the sites of extensive fractional crystallization, mixing with source‐derived magmas, and various degrees of crustal assimilation. Evolutionary processes also occurred inside shallow magma chambers, in which deep magma mixed with residing melts and rested for short periods of time before being erupted to the surface.
Topographic evolution and morphology of surfaces evolving in response to coupled fluvial and hillslope sediment transport
Authors: Simpson Guy , Schlunegger Fritz
Published: June 2003

This paper quantifies how the ratio of sediment transport on hillslopes to sediment transport in channels influences surface and channel network morphologies and the dynamics of topographic evolution. This problem is investigated by development and investigation of a simple deterministic model incorporating mass balance of sediment and runoff coupled with a law combining dispersive and concentrative sediment transport processes. Our analysis includes the identification of a new nondimensional parameter De that is a function of rainfall, system size, rock type, and hydraulic regime and that is a measure of the relative importance of fluvial and hillslope sediment transport. We show that De has an important influence on the surface morphology (e.g., total exposed surface area and interface width which reflects surface roughness and relief), channel network form (e.g., channel sinuosity), channel spacing, and timescale of surface evolution. Surface and channel network morphologies are also strongly influenced by the overall surface slope relative to the magnitude of initial topographic roughness. Topographic evolution occurs in distinct phases of relief growth and decay, the transition between which is controlled by a saturation phenomenon related to the growth of spatial correlations. The scaling behavior of simulated topography with respect to both time and space is obtained and is shown to be independent of De. Roughness exponents are found to be independent of De but dependent on the magnitude of initial roughness. Interface width is shown to grow and decay as a logarithm of time.
Radiatively driven convection in an ice‐covered lake investigated by using temperature microstructure technique
Authors: Jonas Tobias , Terzhevik Arkady Y. , Mironov Dmitrii V. , Wüest Alfred
Published: June 2003

Convection in an ice‐covered lake, driven by the absorption of solar radiation, is investigated by means of temperature microstructure technique. This type of convection typically occurs in spring, when melting snow on the ice cover enables solar radiation to penetrate into the water body. The diurnal dynamics of the stratification system of five distinct layers is analyzed by means of consecutive CTD profiles and with the aid of a one‐dimensional model. The model solves the transfer equation of heat and salinity and includes convective procedures to react on density instabilities. This study is focused on the turbulent kinetic energy (TKE) balance. The stratification analysis reveals the importance of several processes for the TKE balance, namely: (1) the entrainment into the top layer from the convective layer below, (2) the inflow of water from melted ice, and (3) the volumetric solar heating. Enabled by the analysis of the temperature microstructure profiles, two TKE budgets are presented. The temporally averaged budget reveals a vertical distribution of generation and dissipation rate similar to the case of cooling‐induced convection in a surface boundary layer. But contrary to this reference regime, a transition layer was found in the upper convective layer, where both rates drop back to zero toward the layer above. The second TKE budget is spatially averaged over the convective layer but resolves the diurnal dynamics. The generation rate and dissipation rate feature similar diurnal dynamics, where the dissipation lags on average by 1.5 hours. The temporal change rate of TKE was found to be on the same order of magnitude as the generation rate and the dissipation rate, while the export rate of TKE out of the convective layer was found to be less significant.
Dissipation in the Baltic proper during winter stratification
Authors: Lass Hans Ulrich , Prandke Hartmut , Liljebladh Bengt
Published: June 2003

Profiles of dissipation rates and stratification between 10 and 120 m depth were measured with a loosely tethered profiler over a 9‐day winter period in the Gotland Basin of the Baltic Sea. Supplementary measurements of current profiles were made with moored ADCPs. Temporal and spatial patterns of the stratification were observed by means of towed CTD. Shallow freshwater lenses in the surface mixed layer, mesoscale eddies, inertial oscillations, and inertial waves as part of the internal wave spectrum provided the marine physical environment for the small‐scale turbulence. Two well‐separated turbulence regimes were detected. The turbulence in the surface mixed layer was well correlated with the wind. The majority of the energy flux from the wind to the turbulent kinetic energy was dissipated within the surface mixed layer. A minor part of this flux was consumed by changes of the potential energy of the fresh water lenses. The penetration depth Hpen of the wind‐driven turbulence into the weakly stratified surface mixed layer depended on the local wind speed (W10) as Hpen = cW103/2 Active erosion of the Baltic halocline by wind‐driven turbulence is expected for wind speeds greater than 14 m/s. The turbulence in the strongly stratified interior of the water column was quite independent of the meteorological forcing at the sea surface. The integrated production of turbulent kinetic energy exceeded the energy loss of inertial oscillations in the surface layer suggesting additional energy sources which might have been provided by inertial wave radiation during geostrophic adjustment of coastal jets and mesoscale eddies. The averaged dissipation rate profile in the stratified part of the water column, best fitted by ε ∝ EN, was different from the scaling of the dissipation in the thermocline of the ocean [Henyey et al., 1986]. The diapycnical mixing coefficient (Kv) was best fit by Kv = a0/N according to Stigebrandt [1987] with a0 ≈ 0.87 × 10−7 m2/s2. The diapycnal diffusivity estimated from the dissipation rate was lower than those estimated by the bulk method.
Phytoplankton response to intrusions of slope water on the West Florida Shelf: Models and observations
Authors: Walsh John J. , Weisberg Robert H. , Dieterle Dwight A. , He Ruoying , Darrow Brian P. , Jolliff Jason K. , Lester Kristen M. , Vargo Gabriel A. , Kirkpatrick Gary J. , Fanning Kent A. , Sutton Tracey T. , Jochens Ann E. , Biggs Douglas C. , Nababan Bisman , Hu Chuanmin , Muller‐Karger Frank E.
Published: June 2003

Previous hypotheses had suggested that upwelled intrusions of nutrient‐rich Gulf of Mexico slope water onto the West Florida Shelf (WFS) led to formation of red tides ofKarenia brevis. However, coupled biophysical models of (1) wind‐ and buoyancy‐driven circulation, (2) three phytoplankton groups (diatoms,K. brevis, and microflagellates), (3) these slope water supplies of nitrate and silicate, and (4) selective grazing stress by copepods and protozoans found that diatoms won in one 1998 case of no light limitation by colored dissolved organic matter (CDOM). The diatoms lost toK. brevisduring another CDOM case of the models. In the real world, field data confirmed that diatoms were indeed the dominant phytoplankton after massive upwelling in 1998, when only a small red tide ofK. breviswas observed. Over a 7‐month period of the CDOM‐free scenario the simulated total primary production of the phytoplankton community was ∼1.8 g C m−2d−1along the 40‐m isobath of the northern WFS, with the largest accumulation of biomass on the Florida Middle Ground (FMG). Despite such photosynthesis, these models of the WFS yielded a net source of CO2to the atmosphere during spring and summer and suggested a small sink in the fall. With diatom losses of 90% of their daily carbon fixation to herbivores the simulation supported earlier impressions of a short, diatom‐based food web on the FMG, where organic carbon content of the surficial sediments is tenfold those of the surrounding seabeds. Farther south, the simulated near‐bottom pools of ammonium were highest in summer, when silicon regeneration was minimal, leading to temporary Si limitation of the diatoms. Termination of these upwelled pulses of production by diatoms and nonsiliceous microflagellates mainly resulted from nitrate exhaustion in the model, however, mimicking most del15PON observations in the field. Yet, the CDOM‐free case of the models failed to replicate the observed small red tide in December 1998, tagged with the del15N signature of nitrogen fixation. A large red tide ofK. brevisdid form in the CDOM‐rich case, when estuarine supplies of CDOM favored the growth of the shade‐adapted, ungrazed dinoflagellates. The usual formation of large harmful algal blooms of >1 ug chl L−1(105cells L−1) in the southern part of the WFS, between Tampa Bay and Charlotte Harbor, must instead depend upon local aeolian and estuarine supplies of nutrients and CDOM sun screen, not those from the shelf break. In the absence of slope water supplies, local upwelling instead focuses nitrate‐poor innocula of co‐occurringK. brevisand nitrogen fixers at coastal fronts for both aggregation and transfer of nutrients between these phytoplankton groups.
Local and deep‐ocean forcing contributions to anomalous water properties on the West Florida Shelf
Authors: Weisberg Robert H. , He Ruoying
Published: June 2003

Material property distributions on continental shelves result from the mixing and modifications of estuarine and deep‐ocean source waters. How this occurs depends on the momentum and buoyancy that are input either locally on the shelf or from the deep‐ocean at the shelf break. We address this question of local versus deep‐ocean forcing for the West Florida Shelf (WFS) using in situ data and a numerical circulation model. The spring and summer seasons of 1998 and 1999 show distinctively different water properties on the shelf and at the shelf break. We account for these differences by a combination of local forcing, independent of the adjacent Gulf of Mexico Loop Current, and interactions of the Loop Current with the shelf. The primary role of the deep ocean is to set the height of material isopleths along the shelf slope. Whether or not these material isopleths broach the shelf break is then a consequence of local, shelf‐wide wind and buoyancy forcing. The subsequent along‐ and across‐shelf distributions are accomplished through a combination of local and deep‐ocean effects, with the bottom Ekman layer being the major conduit for the across‐shelf transport of ecologically important materials.
Evidence for an eastward flow along the Central and South American Caribbean Coast
Authors: Andrade Carlos Alberto , Barton Eric Desmond , Mooers Christopher N. K.
Published: June 2003

Hydrographic transects suggest an eastward flow with a subsurface core along the entire southern boundary of the Caribbean Sea. The transport of the coastal limb of the Panama‐Colombia Gyre (PCG), known as the Panama‐Colombia Countercurrent, decreases toward the east (from ∼6 Sv off Panama), as water is lost into the recirculation of the PCG. Off Panama, the flow is strongest at the surface, but, off Colombia, it is strongest at around 100 m. A portion of the counterflow (∼1 Sv) continues eastward along the Colombian coast as far as the Guajira region (12°N, 72°W), where it submerges to become an undercurrent beneath the coastal upwelling center there. The eastward flow also occurs in the Venezuela Basin, beneath the coastal upwelling region off Cariaco Basin and exits the Caribbean through the Grenada Channel at around 200 m depth. Numerical simulations suggest that this flow, counter to the Caribbean Current, is a semi‐continuous feature along the entire southern boundary of the Caribbean, and that it is associated with offshore cyclonic eddies. It probably constitutes part of the Sverdrup circulation of the Tropical North Atlantic cyclonic cell.
Characterization of sources for southern African aerosols through fatty acid and trajectory analyses
Authors: Billmark Kaycie A. , Swap Robert J. , Macko Stephen A.
Published: June 2003

Biogeochemical cycles in southern Africa are affected by emissions from extensive biomass burning. Emitted trace gases and aerosols frequently accumulate and recirculate in the well‐defined synoptic pattern that persists for long time periods over southern Africa. The role of organic aerosols during atmospheric transport and the influence of neighboring air masses on biogeochemical dynamics in this nutrient‐limited region are insufficiently studied. The Southern African Regional Science Initiative (SAFARI 2000) was conducted in part to investigate the impacts of this large‐scale transport and deposition of increasingly anthropogenic emissions on southern African biogeochemical cycling. This study explores the understanding of regional atmospheric transport through the identification of chemical biomarkers to describe aerosols collected during the SAFARI 2000 dry season research campaign. Total suspended particulate aerosol samples were collected diurnally for a period of two weeks in Mongu, Zambia. Mongu is bordered by the Zambezi River on the west and the Miombo woodland savanna in all other directions. It also lies on the northern extent of the Kalahari Desert. This region is characterized by high biomass burning emissions of river floodplain grasses and woodland savanna during the dry season. Fatty acids were extracted from the collected aerosols and analyzed using gas chromatography. The resultant fatty acid compositions were examined for temporal patterns and trends. Furthermore, these results were compared to both synoptic meteorological patterns over the region, as well as to modeled air parcel trajectories, to gain insight into changes in aerosol composition resulting from changes in atmospheric transports from regions of different vegetation. The results of these analyses confirm that abundances of fatty acids are dependent on local and synoptic meteorology and can thus be used as an additional geochemical tracer to better describe aerosol sources and transport processes within the region.
On the relationship between the interannual and decadal SST variability in the North Pacific and tropical Pacific Ocean
Authors: Yeh Sang‐Wook , Kirtman Ben P.
Published: June 2003

To address the relationship between the North Pacific and tropical SST anomalies on decadal and interannual timescales, we analyzed observed SST during the period 1950–2000. The SST variability in the North Pacific has two fairly well separated timescales: (1) decadal and (2) interannual, and each has a markedly different relationship with tropical variability. Both the decadal and interannual variability in the North Pacific is connected to the evolution of tropical SST variability with different lead‐lag relationships. The decadal SST variability in the North Pacific is found to lead tropical decadal variability by approximately 5 ∼ 7 years; however, the interannual SST variability is in the North Pacific in equilibrium with the tropical interannual variability. It is also shown that the spatial structure of the decadal variability in the North Pacific is significantly different from the interannual variability.
Distribution and modes of occurrence of lunar anorthosite
Authors: Hawke B. R. , Peterson C. A. , Blewett D. T. , Bussey D. B. J. , Lucey P. G. , Taylor G. J. , Spudis P. D.
Published: June 2003

We have utilized telescopic near‐infrared spectra and multispectral images of the Moon provided by the Galileo and Clementine missions to determine the distribution and modes of occurrence of pure anorthosite. Anorthosites have now been identified in all portions of the nearside, including the site of the putative Procellarum basin. Anorthosite is associated with the rings of Orientale, Grimaldi, Humorum, Nectaris, Nubium, Mutus‐Vlaq, and Balmer basins. Major portions of the inner rings of Grimaldi, Humorum, Crisium, Orientale, and Nectaris are composed of pure anorthosite. The large spatial extent of these anorthosites appears to rule out an origin in the upper portions of discrete differentiated Mg‐suite plutons. In every instance, the anorthosites were exposed from beneath a shallower near‐surface layer of more pyroxene‐rich material. More mafic material also occurs beneath the pure anorthosite unit. Large expanses of the northern farside exhibit very low FeO values. This region contains abundant anorthosite and stands in stark contrast to the mafic composition exhibited by the interior of the South Pole‐Aitken basin (SPA). The distribution of compositional units on large portions of the lunar farside as well as the southern portion of the lunar nearside appears to be largely attributable to the SPA impact event. The distribution and modes of occurrence of anorthosites clearly indicate that a thick, global layer of anorthosite is present at various depths beneath most portions of the lunar surface. This anorthosite layer dominated the upper portion of the primordial crust and was produced by plagioclase flotation in the global magma ocean.
Highland contamination in lunar mare soils: Improved mapping with multiple end‐member spectral mixture analysis (MESMA)
Authors: Li Lin , Mustard John F.
Published: June 2003

Multiple end‐member spectral mixture analysis (MESMA) was applied to the Clementine UVVIS global 1 km multispectral data set, and the resulting highland material fraction image was used to investigate highland contamination of mare surfaces by impact cratering. MESMA decomposes each pixel with the number of end‐members fewer than the number of the spectral bands of Clementine UVVIS data. This allows the use of variable end‐member combinations to accommodate global spectral variance. A 13‐end‐member set of lunar soil components that spans the lunar spectral diversity was selected from the UVVIS data and included 1 mature and 4 fresh highland soils, 4 mature and 2 fresh mare soils, and 2 soils of dark mantling materials. This set was applied to the lunar data through MESMA, and an aggregated global highland abundance was derived. Comparison of the highland fraction results from MESMA and traditional spectral mixture analysis (SMA) demonstrated that MESMA better accommodates the compositional variation of mare soils, resulting in a greater accuracy in the measurement of highland. With the derived products, we investigated highland contamination in Mare Nectaris, Mare Fecunditatis, and Mare Crisium. These mare surfaces are proximal to the large craters Theophilus, Taruntius, Langrenus, and Proclus and provided an opportunity to investigate highland contamination by large impacts. The analyses indicated that Theophilus impact resulted in highland contamination of 20–80% on most of Mare Nectaris, while Taruntius and Langrenus impacts caused 5–40% contamination of Mare Fecunditatis. The trend of minimal highland abundance in Mare Fecunditatis correlates poorly with basalt thickness, suggesting an efficient lateral mixing due to the large craters Taruntius and Langrenus. Additionally, Proclus, combining with other craters, was responsible for highland contamination in most of the Mare Crisium surface, and some basalt classification in this mare reflects highland contamination of the spectral properties. MESMA significantly reduces uncertainty in calculating global composition variations due to mixing, and these analyses demonstrate that large impacts played a dominant role in delivering highland materials onto three mare surfaces.
Thrust faults along the dichotomy boundary in the eastern hemisphere of Mars
Authors: Watters Thomas R.
Published: June 2003

Mars Orbiter Laser Altimetry (MOLA) data have been used to characterize lobate scarps along the dichotomy boundary in the eastern hemisphere of Mars. These structures are the surface expression of thrust faulting of the southern highlands. Displacement on the thrust faults is generally less than 1 km except in the case of the Amenthes Rupes thrust fault, where the maximum displacement is on the order of 3 km. The ratio of maximum displacement to fault length γ of the population of thrust faults is ∼6.2 × 10−3 (n = 26), consistent with previous estimates for Martian thrust faults based on photoclinometrically derived topography, and other planetary thrust fault populations. Thrust faulting is roughly coincident with Late Noachian to Early Hesperian fracturing and normal faulting along the dichotomy boundary. This suggests that the formation of the present‐day dichotomy boundary involved compressional and extensional deformation. The long‐wavelength topography suggests that the dichotomy boundary in the eastern hemisphere may have been formed by flexure of the southern highlands lithosphere. Lithospheric flexure alone cannot account for the thrust faulting of the highlands along the dichotomy boundary. A combination of stresses due to bending, erosion, and global contraction may have formed the lobate scarp thrust faults.
Interactions between impact‐induced vapor clouds and the ambient atmosphere: 1. Spectroscopic observations using diatomic molecular emission
Authors: Sugita Seiji , Schultz Peter H.
Published: June 2003

The importance of interactions between impact‐induced vapor clouds and an ambient atmosphere has been widely recognized, and theoretical approaches have provided significant insights. Few experiments, however, have been done to observe directly the energy partitioning during the interactions between impact vapor clouds and the ambient atmosphere. The present study attempts to understand the difference between actual and theoretical model impact vapor clouds produced under an atmosphere. A series of hypervelocity impact experiments was conducted using a spectroscopic measurement method. Plastic (polycarbonate) impactors allowed simulating vaporization phenomena associated with natural impactors (e.g., silicates and metals) at high impact velocities into water. Water as the target material served to suppress the effect of fine‐grained fragments from the target. Emission spectra of the leading part of downrange‐moving impact vapor clouds were captured with high‐speed spectrometers as a function of time for various ambient pressures. The emission spectra exhibit strong molecular bands from carbon compounds as well as blackbody continuum radiation. In order to estimate the temperature of the radiation source, we carried out a spectral‐form inversion analysis based on diatomic emission theory. Obtained molecular radiation temperatures range from 4500 K to 5500 K with relatively high accuracy (∼2%) and place a number of well‐defined constraints for the radiation source. A simple theoretical model that is often assumed for an impact‐induced vapor cloud, however, does not readily satisfy the constraints. This strongly suggests that real impact‐induced vapor clouds may be more complex than previously thought.
Interactions between impact‐induced vapor clouds and the ambient atmosphere: 2. Theoretical modeling
Authors: Sugita Seiji , Schultz Peter H.
Published: June 2003

Interaction between impact‐induced vapor clouds and the ambient atmosphere may play an important role in planetary evolution. In the companion study, Sugita and Schultz [2003] conducted a series of impact experiments detailing observation of this interaction process. The laboratory experiments using diatomic molecular spectroscopy provide several well‐defined observational constraints on this process. In this study, we examine five different physical models for the interaction process against these observational constraints. Calculation results reveal that the observed high‐temperature radiation could not come from either the impact‐induced vapor or the shock front between impact vapor and the ambient atmosphere. Rather, the radiation is attributed to ablation vapor from the surface of small, high‐speed fragments of the projectile entrained in the impact vapor cloud. Calculations with a simple ablation model indicate that the observed small ambient‐pressure dependence of the initial radiation temperature requires a very large heat of vaporization. The estimated heat of vaporization is comparable to dissociation energy for formation of carbon radicals from the polymer of projectile fragments. The small dependence of radiation temperature on atmospheric composition strongly suggests that the majority of radiation comes from extremely small impact fragments whose size is comparable to the mean free path of ambient atmosphere (i.e., free‐molecular flow regime). These results have a wide range of potential implications for planetary science, including augmentation of impact vapor/melt production in a thick atmosphere; production of metastable chemical compounds in ablation vapor around high‐speed impact fragments; and intense downrange radiation from an oblique impact.
Direct and inverse scattering problems for inhomogeneous impedance cylinders of arbitrary shape
Authors: Akduman Ibrahim , Kress Rainer
Published: June 2003

The direct and inverse scattering problems related to objects having inhomogeneous impedance boundaries are addressed by considering cylindrical bodies. In the solution of the direct scattering problem, the scattered field is first expressed in terms of a combined single‐ and double‐layer potential through Green's formula and the boundary condition. By using the jump relations on the boundary of the object, the scattering problem is reduced to a boundary integral equation that can be solved via a Nyström method. The aim of the inverse impedance problem is to reconstruct the inhomogeneous surface impedance of the body from the measured far field data. Here representing the scattered field as a single‐layer potential leads to an ill‐posed integral equation of the first kind for the density that requires stabilization for its numerical solution; for example, by Tikhonov regularization. With the aid of the jump relations the single‐layer potential enables the evaluation of the total field and its derivative on the boundary of the scatterer. Consequently, from the boundary condition the surface impedance can be reconstructed either by direct evaluation or by a minimum norm solution in the least squares sense. The numerical results show that our methods yields good resolution both for the direct and the inverse problem.
Measurement of tropospheric/stratospheric transmission at 10–35 GHz for H2O retrieval in low Earth orbiting satellite links
Authors: Eriksson Patrick , Jiménez Carlos , Murtagh Donal , Elgered Gunnar , Kuhn Thomas , Bühler Stefan
Published: June 2003

Active microwave limb sounding is a possible technique for measuring water vapor in the upper troposphere and lower stratosphere, and here a first assessment of the retrieval capabilities of transmission measurements in the range 10–35 GHz is presented. The proposed observing system consists of a constellation of low Earth orbiters measuring atmospheric transmission at the frequencies 10.3, 17.2, and 22.6 GHz. The use of these relatively long wavelengths guarantees a minimal, for being a remote sensing technique, influence from scattering. The original objective of the measurements was to derive water vapor profiles, but the potential to retrieve the liquid water content of clouds was also identified during the study. Retrieval errors due to thermal noise, gain instability, and spectroscopic uncertainties were considered. With the assumed instrument characteristics a measurement precision for water vapor in the upper troposphere of 5–10% is obtained, with capability to observe through ice clouds and clouds with a low water content.
A perturbation model of radiometric manifestations of oceanic currents
Authors: Godin Oleg A. , Irisov Vladimir G.
Published: June 2003

Extracting quantitative oceanographic information from microwave images of the ocean surface requires a physical understanding and an efficient mathematical model of surface wave interaction with currents. In this paper, we consider “weak” currents (with velocities up to a few tens of centimeters per second) and discuss a perturbation approach that leads to numerically efficient models of surface roughness modulation by the current fields with arbitrary dependence on horizontal coordinates and time. With the wave‐atmosphere interaction being described within the relaxation approximation, closed‐form analytic expressions are obtained for surface roughness modulation. The hydrodynamic theory is combined with an electromagnetic model based on the small‐slope approximation to simulate microwave emission from the ocean surface. Analysis of the theoretical results demonstrates that the physics of surface wave interaction with time‐dependent currents, which are inhomogeneous in two spatial dimensions, is more rich and complex than is suggested by the one‐dimensional models considered theoretically in the past. Of particular interest for remote sensing is the finding that realistic two‐dimensionally inhomogeneous currents, unlike their one‐dimensional models, can produce perturbations in microwave brightness temperature that extend well beyond the current field itself. Our model suggests that microwave brightness temperature measurements should be a sensitive tool of observing and quantitatively evaluating surface currents in the ocean.
Effect of superrefraction on inversions of radio occultation signals in the lower troposphere
Authors: Sokolovskiy Sergey
Published: June 2003

Radio occultation remote sensing of the Earth's atmosphere by use of GPS encounters problems in the moist lower troposphere (planetary boundary layer). The negative errors in retrieved refractivity (bias) may not be explained by the horizontal inhomogeneity in refractivity. In part, these errors can be attributed to the use of signal tracking algorithms inappropriate for the complicated structure of radio occultation signals propagated through the moist troposphere. However, another fraction of the negative bias in retrieved refractivity can be related to the superrefraction. In this study we introduce the problem and give an estimate of the negative refractivity errors in the moist planetary boundary layer, which in some cases can be as large as ∼10%. We show that the magnitude of these errors significantly varies over oceanic areas. We validate the canonical transform method by use of the radio occultation signals simulated for complicated refractivity structures, including multiple superrefraction layers and small‐scale irregularities. We find that this method does not introduce errors additional to those existing in geometric optics. Also, we discuss and estimate an additional error source when inverting occultation signals by radioholographic methods: insufficient extension of the acquired signal, which can contribute to about 1% error of the retrieved refractivity.
Equatorial Atmosphere Radar (EAR): System description and first results
Authors: Fukao Shoichiro , Hashiguchi Hiroyuki , Yamamoto Mamoru , Tsuda Toshitaka , Nakamura Takuji , Yamamoto Masayuki K. , Sato Toru , Hagio Masahiro , Yabugaki Yoshiyuki
Published: June 2003

A VHF Doppler radar with an active phased‐array antenna system, called the Equatorial Atmosphere Radar (EAR), was established recently at the equator near Bukittinggi, West Sumatra, Indonesia (0.20°S, 100.32°E, 865 m above sea level). The EAR is a large monostatic radar which operates at 47.0 MHz with peak output power of 100 kW. The EAR uses a circular antenna array, approximately 110 m in diameter, which consists of 560 three‐element Yagi antennas. Each antenna is driven by a solid‐state transmitter‐receiver module. This system configuration allows the antenna beam to be steered electronically up to 5,000 times per second. The scientific objective of the EAR is to advance knowledge of dynamical and electrodynamical coupling processes in the equatorial atmosphere from the near‐surface region to the upper atmosphere. The equatorial atmosphere over Indonesia is considered to play an important role in global change of the Earth's atmosphere. This paper presents the system description of the EAR, including observational results of the equatorial atmosphere made for the first time with altitude resolution of 75–150 m.