bluuebunny/crossref_metadata_2025 huggingface dataset:
The compatibility between aircraft and ground‐based air quality measurements
Authors: Van Valin Charles C. , Boatman Joe F. , Luria Menachem , Aneja Viney P. , Blake Donald R. , Rodgers Michael , Sigmon John T.
Published: February 2004

Trace gas concentrations and atmospheric state parameters were measured aboard the NOAA King Air research aircraft during flights on August 16, 1988, along the Appalachian Mountains from central Pennsylvania to northern Georgia. Stepwise profiles were flown over five surface sites where measurements of certain atmospheric parameters were being made. A stationary cold front lying across southern Virginia effectively divided the area into two weather regimes; to the north of the frontal zone the air was slightly cooler and much drier than that to the south. Considerable convective activity developed from early to midafternoon along and south of the front. The comparison between the aircraft and ground sites included measurements of the primary pollutants SO2 and several hydrocarbons, NOy, the secondary pollutants H2O2 and O3, and meteorological parameters. Continuity between the aircraft and surface meteorological and trace gas measurements was consistent at the northernmost site, which is situated in a relatively level valley. The agreement was poorer at the other four ground sites, which are located on or near mountaintops. Most of the meteorological and trace gas measurements, other than those made at Scotia, were found to differ by substantial margins, often by more than 10 times the resolution of the instruments. However, within a few hours after the flights, the surface measurements, particularly those of H2O2 and O3, achieved values comparable to those measured with the aircraft, thus suggesting that air sampled at the canopy level did not mix readily with the bulk of the boundary layer.
Aerosol effect on Umkehr ozone profiles using Stratospheric Aerosol and Gas Experiment II measurements
Authors: Newchurch M. J. , Cunnold D. M.
Published: February 2004

This study examines 1211 cases of coincident ozone profiles derived from 1164 Umkehrs and 928 Stratospheric Aerosol and Gas Experiment II (SAGE II) profiles within 1000 km and 12 hours between October 1984 and April 1989 to study the stratospheric‐aerosol effect on Umkehr ozone profiles. Because of the close correspondence of stratospheric aerosol optical depth at the SAGE II‐measured 0.525μm wavelength and the extrapolated 0.32 Umkehr wavelength determined in this study, we use the 0.525‐μm data to determine the aerosol effect on Umkehr profiles. At the 95% confidence level, we find the following errors to the Umkehr ozone amounts: in Umkehr layer 9 (−2.9±2.1), layer 8 (−2.3±1.1), layer 7 (0.1±1.1), layer 6 (2.2±1.0), layer 5 (−1.5±0.8), and layer 4 (−2.4±1.7) in percent ozone amount per 0.01 stratospheric aerosol optical depth. These results agree with previous theoretical and empirical studies within their respective error bounds in layers 9, 8, and 7. The results in layers 6, 5, and 4 differ significantly from those in previous works. Using only those eight stations with more than 47 coincidences results in mean aerosol effects that are not significantly different from the 14‐station results. Because SAGE II and Umkehr produce different ozone retrievals in layer 9 and because the intralayer correlation of SAGE II ozone and aerosol in layer 9 is nonzero, one must exercise some caution in attributing the entire SAGE Il‐Umkehr difference in this layer to an aerosol effect.
Global trends and annual releases of CCl3F and CCl2F2 estimated from ALE/GAGE and other measurements from July 1978 to June 1991
Authors: Cunnold D. M. , Fraser P. J. , Weiss R. F. , Prinn R. G. , Simmonds P. G. , Miller B. R. , Alyea F. N. , Crawford A. J.
Published: February 2004

Thirteen years of Atmospheric Lifetime Experiment/Global Atmospheric Gases Experiment CCl3F and CCl2F2 measurements at five remote, surface, globally distributed sites are analyzed. Comparisons are made against shipboard measurements by the Scripps Institution of Oceanography group and archived air samples collected at Cape Grim, Tasmania, since 1978. CCl3F in the lower troposphere was increasing at an average rate of 9.2 ppt/yr over the period July 1978 to June 1988. CCl2F2 was increasing at an average 17.3 ppt/yr in the lower troposphere over the same period. However, between July 1988 and June 1991 the increases of CCl3F and CCl2F2 in this region have averaged just 7.0 ppt/yr and 15.7 ppt/yr, respectively. The rate of increase has been decreasing 2.4 ppt/yr2 and 2.9 ppt/yr2 over this 3‐year period. Based on a recent scenario of the global releases of these compounds and using the new calibration scale SIO 1993, the equilibrium lifetimes are estimated to be and years for CCl3F and CCl2F2, respectively. Using these lifetime estimates and a two‐dimensional model, it is estimated that global releases of these two chlorofluorocarbons in 1990 were 249±28×106 kg for CCl3F and 366±30×106 kg for CCl2F2. It is also estimated that combined releases of these chlorofluorocarbons in 1990 were 21±5% less than those in 1986.
A particle grid air quality modeling approach: 1. The dispersion aspect
Authors: Chock David P. , Winkler Sandra L.
Published: February 2004

A particle grid air quality modeling approach that can incorporate chemistry is proposed as an alternative to the conventional partial differential equation (PDE) grid air quality modeling approach. In this approach, each particle is tagged with different species masses and particles in the same grid participate in chemical reactions. The approach is flexible and removes the advection and point source problems encountered in the PDE approach. For a typical grid size of 5 km × 5 km × 50 m used in the lowest layer of an urban air quality model, use of 2000–3000 particles of unequal masses per grid cell will yield a highly accurate grid‐averaged instantaneous concentration field that undergoes eddy diffusion for a period of about 1 day. Use of an hourly averaged concentration reduces the demand of particle per cell to about 500. Increasing the grid size also reduces the demand on the number of particles per cell. For the choice of our Lagrangian integral time scales, the time step must be small (10 s) for vertical dispersion simulation but can be large (200 s) for horizontal dispersion simulation. To reduce computation time, a time‐splitting scheme is, proposed to simulate the horizontal and vertical dispersion simulations in an alternating sequence. The present study also shows that the oft‐used second‐order‐accurate finite difference scheme for solving the diffusion equation tends to overpredict the peak of a sharply peaked concentration.
Heterogeneous reactions in sulfuric acid aerosols: A framework for model calculations
Authors: Hanson David R. , Ravishankara A. R. , Solomon Susan
Published: February 2004

A framework for applying rates of heterogeneous chemical reactions measured in the laboratory to small sulfuric acid aerosols found in the stratosphere is presented. The procedure for calculating the applicable reactive uptake coefficients using laboratory‐measured parameters is developed, the necessary laboratory‐measured quantities are discussed, and a set of equations for use in models are presented. This approach is demonstrated to be essential for obtaining uptake coefficients for the HOCl + HCl and ClONO2 + HCl reactions applicable to the stratosphere. In these cases the laboratory‐measured uptake coefficients have to be substantially corrected for the small size of the atmospheric aerosol droplets. The measured uptake coefficients for N2O5 + H2O and ClONO2 + H2O as well as those for other heterogeneous reactions are discussed in the context of this model. Finally, the derived uptake coefficients were incorporated in a two‐dimensional dynamical and photochemical model thus for the first time the HCl reactions in sulfuric acid have been included. Substantial direct chlorine activation and consequent ozone destruction is shown to occur due to heterogeneous reactions involving HCl for volcanically perturbed aerosol conditions at high latitudes. Smaller but significant chlorine activation also is predicted for background aerosol loadings at extreme high latitudes, suggesting chlorine activation can occur on background sulfuric acid aerosol in these regions. The coupling between homogeneous and heterogeneous chemistry is shown to lead to important changes in the concentrations of various reactive species. The basic physical and chemical quantities needed to better constrain the model input parameters are identified.
Atmosphere‐biosphere exchange flux of carbon dioxide in a tallgrass prairie modeled with satellite spectral data
Authors: Gao W.
Published: February 2004

The estimation of the rate of net CO2 uptake of vegetated land surfaces is essential for studies of global carbon cycle. The present paper demonstrates the use of spectral reflectance data from satellite remote sensing to model net CO2 flux (NCF) of a tallgrass canopy at the Konza prairie, Kansas. A bidirectional reflectance canopy model was used to estimate seasonal changes in canopy leaf area index (LAI) from surface reflectances remotely sensed by SPOT 1 and Landsat 5 satellites. The radiation model was also coupled with leaf conductance‐photosynthesis models to scale up stomatal conductance and NCF from individual leaves to canopy level according to radiation distribution inside the canopy. The satellite‐data‐driven model was able to closely simulate the seasonal change in LAI as well as the short‐term variation of canopy LAI caused by the dry period during late July and early August in the area. Modeled canopy stomatal conductance (gc) and NCF agree with measurements within 0.16 cm s−1 and 0.28 mg m−2 s−1, respectively, during the growth season from late May to late August. In October both measured and modeled NCF turned to small negative values as canopy photosynthesis diminished and predicted LAI approached zero. In addition to data scatter, some of the differences between modeled and measured gc and NCF may be attributed to uncertainties in seasonal changes of plant physiological status that were not detected by satellite data; some of the differences were caused by inadequate description of the dependence of nighttime CO2 flux of soil respiration on near‐surface turbulent mixing.
Aircraft observations of aerosols in the free marine troposphere over the North Pacific Ocean: Particle chemistry in relation to air mass origin
Authors: Yamato Masahiko , Tanaka Hiroshi
Published: February 2004

Aircraft measurements of atmospheric aerosol particles were performed in the free troposphere up to 5.0 km altitude over the North Pacific Ocean in August 1983 and 1984. Particles were analyzed for a single‐particle base with the regent thin‐film technique in conjunction with a transmission electron microscope. The calcium thin‐film method was used for the specific determination of the molecular form of sulfate particles. Nitrate and sulfate in particles was identified by the nitron and barium chloride thin‐film method, respectively. Ammonium was examined by the thin‐film method of sodium tetraphenyl boron. Collected aerosols were related to the origin of air parcels. Sulfuric acid particles in submicron size range formed by the photochemical oxidation of sulfur‐bearing gases and subsequent gas‐to‐particle conversion are the basic aerosols in the unpolluted free marine troposphere. They contain a small amount of NH4+ and more acidic than NH4HSO4. The chemical composition of the predominant aerosol changed drastically according to the origin of air parcels. Sulfuric acid aerosols were predominant in the air parcels originating from the midlatitude maritime atmosphere. On the other hand, for air parcels that have passed over the continent within several days, sulfate aerosols neutralized fully by ammonia are predominant. The extension of the continental air mass supplies ammoniated sulfate aerosols to remote marine atmosphere about 1200 km from land. Mineral dust particles are transported from Asian continent over the northwestern Pacific Ocean via the free troposphere. Nitrate was heterogeneously formed on the mineral dust particles and they were present in the air parcels passed over mainland of Japan, whereas few nitrate particles were found in the midlatitude marine atmosphere. Ammoniated sulfate particles, nitrate‐containing particles, and mineral dust particles are the tracers of the continental air mass.
Analysis of the interannual heat flux response in an atmospheric general circulation model in the tropical Pacific
Authors: Kleeman Richard , McAvaney Bryant J. , Balgovind Ramesh C.
Published: February 2004

A 10‐year run of the Bureau of Meteorology Research Centre atmospheric General Circulation Model is analyzed in the tropical Pacific to determine its heat flux response to El Niño/Southern Oscillation sea surface temperature anomalies. It is determined that the expected negative feedback occurs with approximately the right magnitude. Such a feedback occurs primarily as a result of changes in the latent heat flux. In addition to this local feedback in the eastern Pacific a response of the opposite sign occurs in the Indonesian region. Again this is caused mainly by evaporation changes. These changes are caused by changes in the scalar wind speed not associated with circulation changes implying that changes in the variance of the wind are important. Radiative changes were found to be, in general, less important and are associated with changes in low‐level clouds.
Climate sensitivity and tropical moisture distribution
Authors: Sinha Ashok , Allen Myles R.
Published: February 2004

The possibility that a drying of the tropical upper troposphere might accompany tropospheric warming, substantially reducing the climate's sensitivity to a change in radiative forcing, has been subject to extensive debate. A simple one‐dimensional model of tropical convection and humidity originally proposed by Lindzen (1990a) and Sun (1990) is used to explore mechanisms for “cumulus‐induced drying,” and a narrowband radiation model to investigate its radiative implications. Low‐level moistening, which accompanies warming in all cases, significantly offsets the radiative effects of any upper‐level drying, making the net effect on radiative forcing critically sensitive to undetermined parameters in the model. When the model is tuned to reproduce mean relative humidities from Pacific radiosonde data, no substantial drying is observed to accompany a 1 K tropospheric warming. However, the clear‐sky moisture feedback is in all cases substantially less than that suggested by a scheme in which relative humidity is held constant, illustrating the importance of upper tropospheric relative humidity for climate sensitivity. Finally, the feasibility of placing constraints on critical parameters through satellite observations of interannual variability of the tropical clear‐sky radiation field is investigated.
Analysis of hydroxyl earthlimb airglow emissions: Kinetic model for state‐to‐state dynamics of OH (υ,N)
Authors: Dodd James A. , Lipson Steven J. , Lowell John R. , Armstrong Peter S. , Blumberg William A. M. , Nadile Richard M. , Adler‐Golden Steven M. , Marinelli William J. , Holtzclaw Karl W. , Green B. David
Published: February 2004

Detailed spectroscopic analysis of hydroxyl fundamental vibration‐rotation and pure rotation emission lines has yielded OH(υ,N) absolute column densities for nighttime earthlimb spectra in the 20 to 110‐km tangent height region. High‐resolution spectra were obtained in the Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS 1A) experiment. Rotationally thermalized populations in υ = 1–9 have been derived from the fundamental bands between 2000 and 4000 cm−1. Highly rotationally excited populations with N ≤ 33 ( ≤ 2.3 eV rotational energy) have been inferred from the pure rotation spectra between 400 and 1000 cm−1. These emissions originate in the airglow region near 85–90 km altitude. Spectral fits of the pure rotation lines imply equal populations in the spinrotation states F1 and F2 but a ratio Π(A′):Π(A″) = 1.8±0.3 for the Λ‐doublet populations. A forward predicting, first‐principles kinetic model has been developed for the resultant OH(υ,N) limb column densities. The kinetic model incorporates a necessary and sufficient number of processes known to generate and quench OH(υ,N) in the mesopause region and includes recently calculated vibration‐rotation Einstein coefficients for the high‐N levels. The model reproduces both the thermal and the highly rotationally excited OH(υ,N) column densities. The tangent height dependence of the rotationally excited OH(υ,N) column densities is consistent with two possible formation mechanisms: (1) transfer of vibrational to rotational energy induced by collisions with O atoms or (2) direct chemical production via H + O3 → OH(υ,N) + O2.
Coherent variations of monthly mean total ozone and lower stratospheric temperature
Authors: Randel William J. , Cobb Janel B.
Published: February 2004

Space‐time patterns of correlation between total ozone and lower stratospheric temperature are documented, based on 14 years (1979–1992) of global monthly mean observations. Data are obtained from the total ozone mapping spectrometer (TOMS) and microwave sounding unit (MSU) channel 4, the latter being a weighted mean temperature of the 150‐ to 50‐mbar layer. These data are analyzed (separately) for linear trend, solar cycle, quasi‐biennial oscillation (QBO), and El Niño‐Southern Oscillation (ENSO) variations via linear regression: significant signals are identified for each term, and the corresponding structures in ozone and temperature are found to be highly coherent. The temperature trends derived here show significant cooling of the lower stratosphere over Northern Hemisphere (NH) midlatitudes in winter‐spring and over Antartica in Southern Hemisphere (SH) spring; the overall space‐time patterns are similar to those determined for ozone trends. Interestingly, temperatures do not decrease over SH midlatitudes during midwinter, in spite of large ozone losses. These data furthermore show globally coherent ozone and temperature perturbations associated with both QBO and ENSO variations; a new result here shows large total ozone anomalies in middle‐to‐high latitudes of both hemispheres associated with ENSO events. Residuals from the ozone and temperature time series (defined as the deseasonalized total minus the regression fits) show strong positive correlation in middle‐to‐high latitudes but weak correlations in the tropics. Time periods following the volcanic eruptions of El Chichon and Pinatubo are clearly identified from the coupled signatures of decreased ozone and increased temperature, opposite to the positive ozone‐temperature correlations observed at other times. The ratios of ozone to temperature anomalies derived here show quantitative signatures indicating that either radiative (trend, solar, and QBO) or dynamical (ENSO and residuals) processes are responsible for the strong ozone‐temperature correlations.
An estimate of the flux of stratospheric reactive nitrogen and ozone into the troposphere
Authors: Murphy D. M. , Fahey D. W.
Published: February 2004

The globally averaged net downward annual fluxes of reactive nitrogen (NOy) and O3 from the stratosphere are estimated using observed correlations of N2O with NOy and O3. The linearity of the observed correlations in the lower stratosphere allows the downward fluxes of NOy and O3 to be related to the upward flux of N2O. The upward flux N2O can be calculated from a mass balance and stratospheric photochemistry. In this way, the complicated photochemistry and transport of NOy and O3 can be bounded by a much simpler calculation involving N2O. The estimated NOy net flux of 0.45 Tg (N) yr−1 (range 0.23–0.73) is slightly less than previous estimates, but within the range of uncertainty. Precipitation of NOy from the Antarctic winter stratosphere may be a significant fraction of the annual global flux out of the lower stratosphere. The global budget for stratospheric NOy shows that an N2O lifetime greater than 160 years is inconsistent with extensive mass flow through the Antarctic winter vortex. The estimated O3 flux of 3.5×1010 molecules cm−2 s−1 (range 1.5–6.8) agrees well with previous estimates using completely independent techniques.
(H2)2 mole‐fraction altitude profile in the atmosphere of Jupiter: A computational study
Authors: Slanina Zdenēk , Kim Sang J. , Fox Kenneth
Published: February 2004

The mole fraction x2 of (H2)2 in equilibrium mixture with H2 under the atmospheric conditions of Jupiter is evaluated from the dimerization equilibrium constant calculated by quantum‐chemical treatments and also from the Lennard‐Jones potential. The treatments are of an ab initio type with the second and fourth order Møller‐Plesset perturbation techniques and a basis set superposition error evaluation. The computed dimerization equilibrium constant is combined with observed height profiles of temperature and pressure. In six treatments considered it is found that the mole fraction decreases with increasing height. Various approximations suggest the dimeric mole fraction at the Jupiter 1 atm pressure level between 0.04 and 1.06%.
Jovian S emission: Model of radiation source
Authors: Ryabov Boris P.
Published: February 2004

A physical model of the radiation source and an excitation mechanism have been suggested for the S component in Jupiter's sporadic radio emission. The model provides a unique explanation for most of the interrelated phenomena observed, allowing a consistent interpretation of the emission cone structure, behavior of the integrated radio spectrum, occurrence probability of S bursts, location and size of the radiation source, and fine structure of the dynamic spectra. The mechanism responsible for the S bursts is also discussed in connection with the L type emission. Relations are traced between parameters of the radio emission and geometry of the Io flux tube. Fluctuations in the current amplitude through the tube are estimated, along with the refractive index value and mass density of the plasma near the radiation source.
Auroral Lyman α and H2 bands from the giant planets: 1. Excitation by proton precipitation in the Jovian atmosphere
Authors: Rego Daniel , Prangé Renée , Gérard Jean‐Claude
Published: February 2004

This paper is part of a work aimed at modeling the ratio of the observed Jovian auroral intensity at H Lyman α and in the H2 Lyman and Werner bands and interpreting them as diagnostic of the incident magnetospheric particle species and energy. The work is planned in three steps: (1) modeling of the volume excitation rate, (2) modeling of the radiative transfer at Lyman α, (3) application to existing observational data and new data obtained from the Hubble Space Telescope. The present paper deals with the first step. Models of the volume excitation rate have previously been developed for low energy electrons and oxygen ions. However, the energy range of the study has to be extended towards higher energy in view of recent results on the penetration depth of the primary particles. Protons have not been modeled so far. We have used an existing electron code of degradation of energy [Gérard and Singh, 1982] which has been improved, updated and adapted to the case of precipitating protons. The issues of nonequilibrium beam H/H+ fractions and of getting reliable cross sections over a wide energy range have been considered with particular care. The altitude distribution of the volume excitation rate is compared for electrons and protons, for various initial energies in the range 10–50 keV and 50 keV to 1 MeV, respectively.
Thermal history of lodranites Yamato 74357 and MAC88177 as inferred from the chemical zoning of pyroxene and olivine
Authors: Miyamoto M. , Takeda H.
Published: February 2004

The chemical zoning profiles of pyroxene and olivine in the Yamato (Y) 74357 and Mac Alpine Hills (MAC) 88177 acapulcoite‐lodranite primitive achondrites were measured by using an electron probe microanalyzer in order to study their cooling histories. The reverse zoning of Fe and Mg, and MnO enrichment were observed within a few tens of micrometers from the rim of orthopyroxene in Y74357; this is probably related to reduction. The CaO of orthopyroxene in Y74357 and MAC88177 decreases gradually toward the rim, as do the Cr2O3, Al2O3, TiO2, and Na2O in orthopyroxene and augite. These results suggest that interstitial melt was present and was then extracted at a late stage in the formation of these meteorites. In addition to these observations, the absence of Fe‐Mg reverse zoning and MnO enrichment at the rim of MAC88177 orthopyroxene implies that the reduction process of Y74357 took place after partial melting. A calculated cooling rate of 2–3°C/yr gives the best fit for the observed Fe‐Mg and CaO profiles of orthopyroxene, and CaO of olivine in Y74357, suggesting that the zonings were formed during the same event that probably caused the reduction. Thermal model calculations show that the maximum attainable temperature in the parent body was about 1000°C, if the decay of 26Al is the heat source and if the 26Al/27Al ratio is 5×10−6, identical to that used for the ordinary chondrite parent body. Partial melt was probably produced at this temperature; this is an important part of the history of some primitive achondrites.
Scaling craters in carbonates: Electron paramagnetic resonance analysis of shock damage
Authors: Polanskey Carol A. , Ahrens Thomas J.
Published: February 2004

Carbonate samples from the 8.9‐Mt nuclear (near‐surface explosion) crater, OAK, and a terrestrial impact crater, Meteor Crater, were analyzed for shock damage using electron paramagnetic resonance (EPR). Samples from below the OAK apparent crater floor were obtained from six boreholes, as well as ejecta recovered from the crater floor. The degree of shock damage in the carbonate material was assessed by comparing the sample spectra to spectra of Solenhofen and Kaibab limestone, which had been shocked to known pressures. Analysis of the OAK Crater borehole samples has identified a thin zone of allocthonous highly shocked (10–13 GPa) carbonate material underneath the apparent crater floor. This ∼5‐ to 15‐m‐thick zone occurs at a maximum depth of ∼125 m below current seafloor at the borehole, sited at the initial position of the OAK explosive, and decreases in depth towards the apparent crater edge. Because this zone of allocthonous shocked rock delineates deformed rock below, and a breccia of mobilized sand and collapse debris above, it appears to outline the transient crater. The transient crater volume inferred in this way is found to be 3.2±0.2×106 m3, which is in good agreement with a volume of 5.3×106 m3 inferred from gravity scaling of laboratory experiments [Schmidt et al., 1986]. A layer of highly shocked material is also found near the surface outside the crater. The latter material could represent a fallout ejecta layer. The ejecta boulders recovered from the present crater floor experienced a range of shock pressures from ∼0 to 15 GPa with the more heavily shocked samples all occurring between radii of 360 and ∼600 m. Moreover, the fossil content, lithology, and Sr isotopic composition all demonstrate that the initial position of the bulk of the heavily shocked rock ejecta sampled was originally near surface rock at initial depths in the 32 to 45‐m depth (below sea level) range. The EPR technique is also sensitive to prehistoric shock damage. This is demonstrated by our study of shocked Kaibab limestone from the 49,000‐year‐old Meteor (Barringer) Crater Arizona. We found shock damage present in the β member of the Kaibab Formation exposed in the crater walls corresponding to peak shock stress in the 0.3‐ to 0.6 GPa range. Carbonate ejecta recovered from within the crater experienced shock pressures of up to 0.6 GPa. Assuming shock damage levels of 0.3 to 0.6 GPa for the lightly shocked carbonate on the walls of the Meteor crater, combined with the shock pressure versus distance model of Moss [1988] and Lamb et al. [1991], Meteor Crater impact energies of 2.4 to 8.9 Mt are obtained. This approximately agrees with energies of 3.3 to 7.1 Mt calculated from the crater scaling of Schmidt and Housen [1987].
Potential reconciliation of Devils Hole and deep‐sea pleistocene chronologies
Authors: Crowley Thomas J.
Published: February 2004

The standard model of Pleistocene climate fluctuations being driven by orbital insolation changes has been challenged by results from a high‐precision, radiometrically dated deposit from Devils Hole, Nevada. Although the Devils Hole record agrees with a previously derived ice volume record for most of the last 500,000 years, clear indication of warming prior to the orbitally dated onset of the last interglacial forms the prime basis for this conclusion. I suggest that “early warming” at Devils Hole needs to be understood in light of the prior very extensive glaciation at 150,000 B.P. Marine records in both the North Pacific and North Atlantic, from the same latitude as Devils Hole, indicate that the subpolar fronts during the penultimate glaciation (150,000 years ago) were 5° father south than during the last glaciation. Continental glaciation may also have been more extensive at this time. The first phase of ice retreat ∼ 145,000 years ago is associated with a northward shift of these fronts, which results in full‐interglacial sea surface temperatures in the North Atlantic. The early warming at Devils Hole may reflect the northward movement of the ice margins and associated fronts. If so, both the Devils Hole and deep‐sea chronologies may be correct, with differences between 130,000 and 150,000 years ago reflecting a regionally varying response to climate shifts associated with a very extensive glaciation.
The Arctic Sea Ice‐Climate System: Observations and modeling
Authors: Barry R. G. , Serreze M. C. , Maslanik J. A. , Preller R. H.
Published: February 2004

Significant advances are being made in our understanding of the Arctic sea ice‐climate system. The mean circulation of the Arctic sea ice cover is now well defined through analysis of data from drifting stations and buoys. Analysis of nearly 20 years of daily satellite data from optical, infrared, and passive microwave sensors has documented the regional variability in monthly ice extent, concentration, and surface albedo. Advances in modeling include better treatments of sea ice dynamics and thermodynamics, improved atmosphere‐ice‐ocean coupling, and the development of high resolution regional models. Diagnostic studies of monthly and interannual sea ice variability have benefited from better sea ice data and geostrophic wind analyses that incorporate drifting buoy data. Some evidence exists for a small retreat of Arctic sea ice over the last 2 decades, but there are large decadal fluctuations in regional ice extent. Antiphase relationships between ice anomalies in different sectors can be related to changes in atmospheric circulation. Evidence suggests that episodes of significant salinity reduction in the North Atlantic, associated with extensive sea ice in the Greenland Sea, may be a manifestation of a decadal oscillation in the Arctic climate system. Aspects of the Arctic system in need of further attention include the surface energy budget and its variability, particularly with respect to the roles of cloud cover and surface types in summer. Sea ice thickness distribution data remain meager, and there are many unknowns regarding the circulation and hydrologic cycle of the Arctic Ocean and its links to the world ocean. Planned measurements from a new generation of satellites, supported by field programs, will provide much needed data to address these issues.
Calculations of riometer absorption associated with F region plasma structures based on Sondre Stromfjord incoherent scatter radar observations
Authors: Wang Z. , Rosenberg T. J. , Stauning P. , Basu S. , Crowley G.
Published: February 2004

On several occasions significant riometer absorption has been measured at South Pole station in association with F region plasma patches formed in the cusp and propagating into the polar cap. The analysis of these events has used imaging riometer, photometer, and ionosonde data from South Pole as well as simultaneous observations of the patches by the Halley HF coherent scatter radar. However, detailed information about the F region structures such as plasma densities and temperatures, which is required to quantitatively study the response of riometer absorption, is unavailable from the instrumentation in Antarctica. Because both incoherent scatter radar and imaging riometer data are available from Sondre Stromfjord, it is possible to study such phenomena from that location. We have analyzed an event that occurred on September 14, 1991, when the radar and local ionosonde observed an F region plasma patch moving poleward on the dayside. Calculated values of the zenithal riometer absorption, arising from electron‐ion collisions in the F region, were of the same order as the measured absorption when the patch was overhead. After the patch had passed, however, the measured zenithal absorption significantly exceeded the calculated contribution from the F region. We attribute this to the later presence of absorption in lower altitude regions of the ionosphere, which is confirmed by the ionosonde measurements of increased ƒmin.
Collaborative experiments by Akebono satellite, Tromsø ionospheric heater, and European incoherent scatter radar
Authors: Kimura I. , Stubbe P. , Rietveld M. T. , Barr R. , Ishida K. , Kasahara Y. , Yagitani S. , Nagano I.
Published: February 2004

Joint experiments using the Akebono satellite and the ionospheric heating facility and European incoherent scatter radar near Tromsø were carried out in November 1990 and February 1991. In these experiments, Tromsø HF transmissions were amplitude modulated at frequencies of 2.5 and 4.0 kHz. Signals radiated from the polar electrojet (PEJ) antenna in the heated ionosphere at these VLF frequencies were detected for five passes out of seven passes of the semipolar orbiting Akebono satellite. A ground‐based observation of the VLF radiation from the PEJ was made in the November campaign at Lycksele in Sweden, 554 km south of the heating facility. Measurements of electron density profiles and dc electric fields in the ionosphere were carried out by the EISCAT incoherent scatter radar [Folkestad et al., 1983] located in the vicinity of the ionospheric heater. The results of the experiments are compared with those obtained by ray tracing and full‐wave analyses.
Chaotic behavior of ionospheric scintillation: Modeling and observations
Authors: Wernik A. W. , Yeh K. C.
Published: February 2004

The chaotic, but nondeterministic, structure of the ionosphere and radio wave amplitude and phase scintillation measured on the ground have been simulated using the phase screen model with the power law spectrum of random Gaussian phase fluctuations. Comparison of the information dimension calculated for phase fluctuations on a screen with that for amplitude scintillation at the receiver shows that the original chaotic structure in the ionosphere is completely masked by the propagation effects. Hence the ionospheric turbulence attractor (if it exists) cannot be reconstructed from amplitude scintillation data. On the other hand, measured phase scintillation data adequately reproduce the assumed chaotic structure in the ionosphere. Results of the attractor reconstruction for amplitude scintillation observed at high latitudes show an excellent agreement with our simulation.
Effects of field line mapping on the gradient‐drift instability in the coupled E and F region high‐latitude ionosphere
Authors: Chaturvedi P. K. , Keskinen M. J. , Ossakow S. L. , Fedder J. A.
Published: February 2004

The linear theory of the gradient drift instability in the E and F region ionosphere, including intraionospheric coupling effects, is developed. It is found that when intraionospheric coupling effects are included the instability onset criteria are modified depending on the ratio of the integrated conductivities in the region of the instability onset to the neighboring altitude regions. New results are found for the growth rates of the gradient‐drift instability in (1) the F region with inhomogeneous E region coupling and (2) the E region with inhomogeneous F region coupling. The instability growth rate in the F region case is modified as a function of and , where ∑PO and ∑HO are the equilibrium integrated Pedersen and Hall conductivities respectively, and superscripts E and F refer to the ionospheric regions. For P ≫ 1 and Q ≫ 1, modes in the F region are modified significantly by the E region coupling effects, whereas in the opposite limit, the usual results for the local stability analysis of the F region gradient drift mode are recovered, especially at small wavelengths. For the E region gradient drift modes, F region coupling effects have an important influence on the instability for Q ≪ 1, especially at longer wavelengths, while for Q ≫ 1, the instability characteristics are relatively unaffected by the coupling effects. In addition to the well‐known reductions to the growth rate proportional to the conductivity ratio of the two regions, we find that the contributions from the inhomogeneous E region ( F region) may be destabilizing under certain conditions and may well overshadow the reductions in the growth rate for the instability in the F region (E region). This effect is found especially important for the F region gradient‐drift instability. Among the consequences of the coupling on the local instability process, it is found that the unstable modes may show a rotation of the wave vector with respect to the E×B drift, and the growth rate for the instability has a peak as a function of the wavelength. The results are discussed in light of observations of long‐wavelength irregularities in the E and F regions.
Coordinated convection measurements in the vicinity of auroral cavities
Authors: Doe R. A. , Mendillo M. , Vickrey J. F. , Ruohoniemi J. M. , Greenwald R. A.
Published: February 2004

Meridional radar scans of electron density from the Sondrestrom incoherent scatter radar (Greenland, 66.99°N, 50.95°W) have been used to identify latitudinally narrow, field‐aligned depletions of the auroral F region ionosphere. Observations of these so‐called “auroral cavities” have been reported in earlier case studies in close proximity to E layer arcs at the poleward edge of the nightside oval (Doe et al. 1993). These radar data indicated that the cavities and arcs remained as collocated pairs for periods as long as an hour, while coordinated imaging and satellite measurements indicated that the pairs were extended in magnetic local time. These observations suggested at least two causal mechanisms: (1) cavity formation by the convective distortion of an existing density depletion, or (2) cavity formation by vertical evacuation from a downward field‐aligned current. New results from a model developed to examine the convection mechanism suggest that a distorted polar cap density depletion will elongate parallel to the local convection streamline when observed in the morning sector (far from the location of divergent flow lines or the Harang discontinuity). In order to establish evidence for these two mechanisms and further refine the physical properties of auroral cavities, a joint imaging/radar experiment was carried out in February 1991, at the Sondrestrom and Goose Bay (Labrador, 54.4°N, 60.4°W) radars with an emphasis on multispectral imaging, horizontal convection and off‐meridional density measurements. When compared to coincident all‐sky images, the convection data indicate significant cross‐arc flow during cavity formation sequences on 6 and 10 February, 1991, questioning the applicability of mechanism (1). A third example on February 8, 1991, shows the alignment of a cavity/arc pair with the local streamline at the edge of an E region auroral arc. This last example illustrates the difficulty in establishing the relative dominance of either mechanism for a particular event. The continued association of cavities with auroral precipitation and failure to detect elongated cavities or those oriented along the local convection streamline lead to the conclusion that cavities are probably created by localized field‐aligned currents.
A time domain numerical model of a warm plasma
Authors: Young Jeffrey L. , Brueckner Frank P.
Published: February 2004

A new numerical model is proposed herein that predicts the space‐time profile of an electromagnetic wave in an anisotropic warm plasma. The model is based upon a second‐order spatial and temporal discretization of the coupled equations of Maxwell and Euler. In order to comply with the basic nature of the curl, divergence, and gradient operators, an uncollocated nodal scheme is used to approximate the electric field, magnetic field, velocity, and pressure throughout the computational domain. The theory is postulated in a three‐dimensional domain but is verified in two dimensions. A magnetic line source is used to excite the medium, and the numerical data are tested against closed‐form solutions. As demonstrated herein, the agreement is shown to be excellent.
Boundary condition transfer method for the solution of electromagnetic scattering by rotationally symmetric penetrable bodies
Authors: Tosun Haluk
Published: February 2004

A novel differential formulation of electromagnetic scattering by rotationally symmetric penetrable bodies is presented. The formulation is essentially based on the representation of vector fields in terms of spherical vector wave functions. In regions where we have physical inhomogenity the representation is in terms of position‐dependent expansion coefficients. The differential equation system for these variable coefficients is deduced from the relevant wave equation. This system is numerically solved as an initial value problem, and the unknown constant expansion coefficients are found with a matrix inversion. The method was tested and validated on a number of problems, whose exact solutions are available, and the results obtained for scatterers for which no exact solutions are present were succesfully compared with the ones obtained by other methods.
Geodynamic models of fault‐controlled extension
Authors: Boutilier R.R. , Keen C.E.
Published: February 2004

Results from geodynamic models for lithospheric extension that includes one or two large‐scale upper crustal faults are presented. The study does not address the origin of these faults, but the consequences if they exist. Model components include a solid mechanical lithosphere composed of thermoelastic‐plastic material with viscous creep that is subject to extension, buoyant supporting forces and sedimentary loads, and a coincident, but thicker, thermal lithosphere that includes the effect of sediment blanketing and radiogenic heating. We have chosen for comparison purposes a “standard” reference model which minimizes creep in the crust; consequently, our results depend strongly on plastic deformation. Our models show that large faults can control the position and growth history of the mantle instabilities that can lead to rupture. We observe that these instabilities have secondary, “normal mode”‐like character. Models with two faults show that the normal mode behavior can interact and create an enhancement to the necking process, provided the faults are an ideal distance apart. We compare models with two rates of extension, 1.2 cm yr−1 (“fast”) and 0.038 cm yr−1 (“slow”), which show remarkably little difference. We compare our reference model with models using “wet” and “dry” rheologies and observe that flow in the crust can attenuate the propagation effect created by the faults.
Covariance of structural and stratigraphic trends: Evidence for anticlockwise rotation within the Walker Lane belt Death Valley region, California and Nevada
Authors: Snow J. Kent , Prave Anthony R.
Published: February 2004

Large‐magnitude relative rotations of range‐scale structural blocks are inferred to be products of crustal extension in the Death Valley region, in California and Nevada. Reconstructions of the extended terrain restore pre‐Tertiary contractile structures with currently diverse trends into a relatively simple, north‐northeast trending thrust belt. We interpret trends of major contractile structures throughout the Death Valley region as characteristically discordant to, and thus geometrically independent from, stratigraphic trends. We compare trends of pre‐Tertiary contractile structures with paleoflow orientations in Lower Cambrian strata throughout the extended terrain. Significant differences between mean paleoflow orientations are consistent in magnitude and sense with differences observed in the structural trends. Available evidence does not support interpretation of paleoflow data from apparently rotated areas as representing an original paleogeography distinct from that of adjacent areas. Facies variations are present within the contractile structures. We interpret the strong covariance throughout the study area between structural and paleoflow trends of diverse orientations as evidence for vertical axis rotations. Combined rotation estimates from these data indicate clockwise rotations of 85° ± 12° for Bare Mountain and 73° ± 24° for the Striped Hills but anticlockwise rotations of 30° ± 35° and 87° ± 29°, respectively, for the northern and southern Grapevine Mountains. Such large rotations of opposite sense may be related to north‐south shortening accommodated by conjugate strike‐slip faults during large‐magnitude extension in the Death Valley region but are difficult to explain as products of regional dextral shear within the southern Walker Lane belt.
Eruption of alkali basalts during crustal shortening in southern California
Authors: Glazner Allen F. , Bartley John M.
Published: February 2004

The common occurrence of alkali basalts in continental rifts has led to the widespread assumption that late Cenozoic alkali basalts of the western United States indicate an extensional tectonic regime. However, field relations of late Cenozoic alkali basalt flows and cinder cones in the Mojave Desert area, including flows that bear mantle xenoliths, indicate that many were erupted in contractional or transpressional tectonic settings. These observations call into question models of extensional magmatism in which lithospheric extension facilitates transport of magmas to the surface and suggest that an association of alkali basalts and coarse clastic sedimentary rocks need not indicate rifting.
A physical explanation for an observed area‐slope‐elevation relationship for catchments with declining relief
Authors: Willgoose Garry
Published: February 2004

A general relationship between the contributing area, slope, and mean elevation of catchments with relief declining after a tectonic uplift event is presented. This relationship is based on the continuity equation for runoff and erosion processes in the catchment. The key hypothesis underlying this relationship is that as a catchment declines, the nondimensionalized catchment approaches a constant form. This hypothesis is verified for computer simulated catchments. The area‐slope‐elevation relationship covers several cases: catchments declining toward a peneplain; catchments declining from a high slope dynamic equilibrium (resulting from a high rate of tectonic uplift) to a low slope one (resulting from a lower rate of tectonic uplift); and catchments declining from an elevated initial condition, as, for example, in the decline of a mine spoil heap. A previously published relationship between slope and area for catchments in dynamic equilibrium and based on runoff and erosion physics is shown to be a special case of this general relationship. The new area‐slope‐elevation relationship is compared with data from simulated catchments and a field catchment. It is thus shown that for declining catchments the area‐slope‐elevation relationship is a good predictor of catchment form for catchments with declining relief. It is argued that the slope‐area‐elevation relationship is sufficient, with the planiform drainage pattern, to completely define the elevation properties of the catchment such as, for instance, the hypsometric curve.