bluuebunny/crossref_metadata_2025 huggingface dataset:
Aircraft active and passive microwave validation of sea ice concentration from the Defense Meteorological Satellite Program special sensor microwave imager
Authors: Cavalieri D. J. , Crawford J. P. , Drinkwater M. R. , Eppler D. T. , Farmer L. D. , Jentz R. R. , Wackerman C. C.
Published: February 2008

During March 1988 a series of coordinated special sensor microwave imager (SSM/I) underflights were carried out with NASA and Navy aircraft over portions of the Bering, Beaufort, and Chukchi seas as part of the NASA Defense Meteorological Satellite Program SSM/I Sea Ice Validation Program. The two Navy research aircraft, a Naval Research Laboratory P‐3 with the NOARL Ka band radiometric mapping system operating at 33.6 GHz and a Naval Air Development Center (NADC) P‐3 with the NADC‐Environmental Research Institute of Michigan (ERIM) C band synthetic aperture radar (SAR), provided wide‐swath, high‐resolution microwave imagery for direct comparison with sea ice concentrations calculated from SSM/I radiances using the NASA sea ice algorithm. Coincident measurements made with the Jet Propulsion Laboratory (JPL) C band SAR and the Goddard Space Flight Center (GSFC) aircraft multifrequency microwave radiometers (AMMR) on the NASA DC‐8 airborne laboratory provided additional verification of the algorithm. NASA DC‐8 AMMR data from Bering Sea ice edge crossings were used to verify that the ice edge location, defined as the position of the initial ice bands encountered by the aircraft, corresponds to an SSM/I ice concentration of 15%. Direct comparison of SSM/I and aircraft ice concentrations for regions having at least 80% aircraft coverage reveals that the SSM/I total ice concentration is lower on average by 2.4%±2.4%. For multiyear ice, NASA and Navy flights across the Beaufort and Chukchi seas show that the SSM/I algorithm correctly maps the large‐scale distribution of multiyear ice: the zone of first‐year ice off the Alaskan coast, the large areas of mixed first‐year and multiyear ice, and the region of predominantly multiyear ice north of the Canadian archipelago. Quantitative comparisons show that the SSM/I algorithm overestimates multiyear ice concentration by 12%±11% on average in the Chukchi and Beaufort seas. Excluding data for a day which gave anomalously large positive biases, the multiyear ice concentration difference reduces to 5%±4%, also indicating a positive SSM/I bias. Anomalously low SSM/I concentrations were found in the coastal zone north of Ellesmere Island. Differences between multiyear ice concentrations estimated from the JPL C band SAR imagery and from the GSFC AMMR radiances using an SSM/I type algorithm show that the AMMR concentrations are smaller on average by 6%±14%. Sea ice conditions are described, and possible causes of the observed differences are discussed.
A comparison between polytopic vector analysis and empirical orthogonal function analysis for analyzing quasi‐geostrophic potential vorticity
Authors: Evans J. C. , Ehrlich R. , Krantz D. , Full W.
Published: February 2008

Output from highly resolved, long‐duration ocean models, and measurements taken by satellites and other modern observational tools, present critical problems in storage and assessment. While empirical orthogonal function analysis (EOFA) can be used for data compression, the data are often difficult to assess in compressed form. A relatively new procedure, polytopic vector analysis, has compression capabilities equal to those of EOFA but improves assessment of the data in the compressed form. The two procedures are illustrated by analysis of upper layer quasi‐geostrophic potential vorticity from a simple two‐layer ocean circulation model.
Shear stress and bed roughness estimates for combined wave and current flows over a rippled bed
Authors: Drake David E. , Cacchione David A. , Grant William D.
Published: February 2008

High‐quality bottom boundary layer measurements and bottom photographs were obtained over a sand substrate during a 10‐day deployment of the GEOPROBE tripod at an inner shelf (35‐m water depth) location off northern California. The seafloor surrounding the tripod was composed of well‐sorted medium‐grained (mean diameter, 0.25 mm) sand which was formed into symmetrical wave ripples with heights of 3–4 cm and wavelengths of 22–30 cm. Mean velocity profiles in the region from 23 cm to 102 cm above the rippled bed were highly logarithmic (R > 0.95) approximately 30% of the time. Nineteen profiles exhibiting R > 0.997 were analyzed to obtain the shear velocity (U*c) and roughness length (Z0c) for the mean current. The near‐bottom flow field was composed of quasi‐steady currents (up to 12 cm s−1 at z = 102 cm) and wave‐induced, oscillatory currents (up to 14 cm s−1). The data‐derived estimates of U*c and Z0c were 0.3–0.93 cm s−1 and 0.82–1.5 cm, respectively. The mean shear estimates are 50–100% larger than those predicted using a drag coefficient (CD) of 3 × 10−3 that is typical for rough boundaries, and the roughness lengths are up to an order of magnitude larger than the maximum expected values based on the observed wave‐rippled bottom. These results indicate the importance of the combined flow turbulent interaction in producing a large apparent Z0c. However, comparison of the shear and roughness estimates derived from the velocity profile analysis to predictions made by the combined flow model of Grant and Madsen (1979) show that direct application of the wave‐ripple roughness equation of Grant and Madsen (1982) yields large overestimates of z0c and U*c. Selecting the physical roughness length kb(=30z0) that produced the best agreement with the data resulted in z0 values ranging from 0.03 to 0.43 cm. Moreover, a direct correlation exists between these physical roughness estimates and the angle (θcr) formed by the mean current and the trend of the wave ripple crests. A simple linear relationship between kb and θcr is suggested by our limited data set.
Reconciling aggregation theory with observed vertical fluxes following phytoplankton blooms
Authors: Hill Paul S.
Published: February 2008

Sediment trap data show that rapidly sinking pulses of phytodetritus form after phytoplankton blooms, even when bloom intensity is low. A numerical model of physical aggregation and sedimentation in the surface ocean was used to gauge whether predicted aggregation rates were high enough to generate postbloom sediment pulses. Initial models behaved inaccurately without a full range of particle sizes, abundant nonphytoplankton particles, and explicit hydrodynamic retardation of particle contact. Provision for background particles while tracking phytoplankton required implementation of a novel bookkeeping scheme. To address the degree of retardation for contact between particles, an expression for contact efficiency for collision by turbulent shear was developed. The most realistic way to produce model results that mimicked field data was to include background particles, to invoke particle stickiness in the range 0.1–1.0, and to make modest upward adjustments to contact efficiencies calculated for impermeable spheres. For all but the highest background particle concentrations, the magnitude of a postbloom sediment pulse scaled nonlinearly with vertically integrated cell number in the surface layer of our two layer model. The existence of a nonlinear relationship between pulse size and bloom intensity makes initial cell number per unit of area in the surface layer, and not productivity, the proximate determinant of carbon export flux. This result emphasizes the need for caution when applying established scalings between export flux and productivity. Further, it provides a mechanistic explanation both for tight pelagic‐benthic coupling under waters prone to intense blooms and for interannual variability in export flux in polar regions.
Variation of the stable isotopes of water with altitude in the Saint Elias Mountains of Canada
Authors: Holdsworth G. , Fogarasi S. , Krouse H. R.
Published: February 2008

The stable isotopes of water, measured in melt samples taken from snow pits and cores at locations between 1750‐ and 5930‐m altitude on Mount Logan (5951 m) and between 2900 and 4900 m on Mount Steele (5079 m), in the Saint Elias Mountains, Yukon, show a distinctive altitudinal distribution. Several δ18O and δD versus altitude profiles indicate the general persistence of a nearly iso‐δ step, or staircase structure, separating a lower region of altitude dependent isotopic fractionation between 1750 and 3350 m from another apparent fractionation sequence appearing above about 5300 m. Both of these sequences, but especially the lower one, indicate orderly processes. On the one hand, postdepositional changes to isotope ratios in snow at different altitudes may cause distortions to an otherwise nearly monotonic isotope fractionation sequence, but the main anomaly appears to be far too large to be explained in this way. On the other hand, an explanation linked to processes occurring in the lower and midtroposphere is based on established meteorological principles as well as on upper air data. This hypothesis is proposed as the primary one to explain the gross features of the observed isotope profiles. It is compatible with the concept of secondary‐source moisture arriving via the upper troposphere, and it does not exclude the effects of postdepositional stratigraphic and stable isotope ratio changes. Over interannual time scales, any vertical modulation of the observed isotope‐altitude structure, from, for example, changes in wind regime, would give rise to an additional signal in any ice core δ time series. These findings identify a potential difficulty in the interpretation of stable isotope records obtained from high mountain ice core sites. It is possible that the results may have application to atmospheric circulation modeling, where the effects of extreme topography are being studied.
Terpenes emitted from agricultural species found in California's Central Valley
Authors: Arey Janet , Winer Arthur M. , Atkinson Roger , Aschmann Sara M. , Long William D. , Morrison C. Lynn , Olszyk David M.
Published: February 2008

More than a dozen monoterpenes have been identified as emissions from agricultural and natural plant species occupying large acreages in the Central Valley of California, including as dominant emissions camphene, 2‐carene, Δ3‐carene, limonene, myrcene, trans‐ocimene, β‐phellandrene, α‐pinene, β‐pinene, sabinene, γ‐terpinene, and terpinolene. Isoprene was not a significant emission from any of the crop species examined but was emitted by a Valley Oak. In addition to the monoterpenes, sesquiterpenes were emitted from approximately one third of the species investigated, in some cases at higher levels than the monoterpene emissions from the same plant. The possible contributions of these biogenic emissions to the ozone exceedances in the Central Valley should be considered in planning future emission control strategies.
Infrared spectroscopic measurements of the vertical column abundance of sulfur hexafluoride, SF6, from the ground
Authors: Zander R. , Rinsland C. P. , Demoulin P.
Published: February 2008

The unresolved ν3 band Q branch of sulfur hexafluoride, SF6, at 947.9 cm−1 has been identified and quantitatively analyzed in series of high‐quality infrared solar spectra recorded at the International Scientific Station of the Jungfraujoch, Switzerland, and at the National Solar Observatory facility on Kitt Peak in Arizona. Series of monthly mean total vertical column abundances of SF6 above both stations, deduced from that feature with line‐by‐line nonlinear least squares fitting methods, are reported over the time intervals from June 1986 to June 1990 for the Jungfraujoch and from March 1981 to June 1990 for Kitt Peak. Assuming an exponential growth model for fitting these series of measurements, it is found that the vertical column abundances have increased at mean rates of 6.9±2.8 %/yr above the Jungfraujoch (calculated columns of 2.99×1013 molecules/cm2 in June 1986 and 3.94×1013 molecules/cm2 in June 1990) and 6.6±7.2 %/yr above Kitt Peak (calculated columns equal to 2.97×1013 molecules/cm2 in June 1981 and 5.38×1013 molecules/cm2 in June 1990), the uncertainties corresponding to 2 sigma confidence levels. These results are further discussed within the context of variability and compared with previously published measurements.
A model evaluation of noninductive graupel‐ice charging in the early electrification of a mountain thunderstorm
Authors: Ziegler Conrad L. , MacGorman Donald R. , Dye James E. , Ray Peter S.
Published: February 2008

The role of noninductive graupel‐ice charge separation in the early electrification of the July 31, 1984, New Mexico mountain thunderstorm is assessed with a three‐dimensional kinematic cloud model along with multiple Doppler radar and in situ measurements. Observations of the early electrification rate and the electric field distribution are consistent with modeled values that result when the noninductive mechanism works under the influence of convective motions and precipitation growth. An increase in ice particle concentrations and sizes, arising from vigorous precipitation growth, accelerates graupel‐ice collision rates and hence the noninductive charging rate. Growing graupel particles experience increasing fall speed as they rise toward the top of the updraft. The resulting vertical flux convergence of graupel containing charge from previous noninductive collisions is a significant factor in the growth of the main negative charge density. This implies that a combination of air motion, precipitation interaction, and sedimentation contributes to the rapid intensification of storm electric fields. The linear electrification phase, which begins with the cessation of convective growth, is caused by a roughly constant noninductive charging rate and by the separation of negatively charged graupel and positively charged smaller ice particles by differential sedimentation, downdrafts, and horizontal advection in vertically sheared flow. When the sign reversal temperature for noninductive charging is assumed to be −10°C, the model results are characterized by a main negative charge in middle levels and provide the best overall agreement with the in situ field measurements in the July 31 storm. For a sign reversal temperature of −21°C the model results are characterized by a main positive charge center in middle levels, and the electric field polarity is opposite to the polarity measured at low and middle levels of the storm. The model and observational data, combined with findings of some laboratory studies, support the hypothesis that the actual reversal temperature in the July 31 storm is around −10°C. When the model includes the inductive graupel‐droplet charging mechanism in addition to the noninductive mechanism, the effect of inductive charging is secondary to that of noninductive charging. The net effect of adding induction is dissipative. For example, the maximum field strength at the location of the aircraft measurements is slightly less than in the case where the noninductive mechanism acts alone. Weak charge screening layers were found to develop on the boundary of the modeled cloud.
A continuous 770‐year record of volcanic activity from east Antarctica
Authors: Moore John C. , Narita Hideki , Maeno Norikazu
Published: February 2008

A 100‐m ice core from site G 15 (accumulation rate 0.1 m water yr−1, mean annual temperature −38°C) on the Mizuho plateau, Dronning Maud Land, East Antarctica, has been analysed using the dielectric profiling (DEP) technique. The capacitance and conductance of the core were measured at ac frequencies (20 Hz‐300 kHz). The high‐frequency conductivity profile shows variations that are primarily related to the strong acids derived from volcanic activity. The Tambora (1815) eruption can be identified with the aid of an approximate chronology based on the firn densification rate, other historic eruptions can then be recognised. Beyond about 300‐years historical observations are very few, however if a constant overall accumulation rate is assumed, a well‐known eruption of 1259 A.D. can be found near the bottom of the core. Other peaks in the conductivity profile can then be assigned dates accurate to within a few years. Using the conductivity profile it is possible to estimate the relative acid deposition fluxes produced by the main eruptions with reasonable accuracy. The estimated acid deposisition fluxes realtive to the Tambora (1815) eruption, of Agung (1963) is 27%, Krakatoa (1883), 25%, the signal of 1601, 28%, and that of 1259, 53%.
Dimethyl sulfide and cloud condensation nucleus correlations in the northeast Pacific Ocean
Authors: Hegg Dean A. , Ferek Ronald J. , Hobbs Peter V. , Radke Lawrence F.
Published: February 2008

A regression analysis on measurements of cloud condensation nucleus (CCN) and dimethyl sulfide (DMS) concentrations in the boundary layer over the northeastern Pacific Ocean shows these two parameters to be highly correlated. This complements and supports coherent seasonal trend data on DMS and CCN concentrations obtained at Cape Grim, Tasmania. The correlation between CCN and DMS at both northern and southern hemispheric remote marine sites, provides empirical support for the DMS‐cloud‐climate hypothesis. A possible nonlinear relationship between DMS and size‐segregated CCN concentrations is suggested by the data.
The NASA spring 1984 Stratosphere‐Troposphere Exchange experiment: Science objectives and operations
Authors: Russell P. B. , Danielsen E. F. , Craig R. A. , Selkirk H. B.
Published: February 2008

We present an overview of the first experiment of the Stratosphere‐Troposphere Exchange Project (STEP), conducted in spring 1984 over the southwestern United States. The objective was to identify modes of transport during large‐scale cyclogenesis, both (1) within the stratosphere, from the anticyclonic to the cyclonic side of the jet, and (2) from the troposphere to the stratosphere. The primary platform was the NASA U‐2 high‐altitude research aircraft, supported by the regular twice‐daily radiosonde network. Measurements included temperature, pressure, horizontal wind, ozone, cosmogenic radionuclides, water vapor, and condensation nuclei. U‐2 flights were made on 4 days. On 3 days the flight path was in a vertical plane orthogonal to the jet stream flow, extending from the anticyclonic side of the jet, across it, and into the cyclonic vortex. The other flight was directed at processes associated with the upper level cirrus outflow from a tropical vortex. Aircraft direction was performed using analysis of NMC prognostications, commercial diagnostics and predictions, radiosonde data, and satellite infrared imagery. The cross‐jet flight most intensively analyzed (April 20–21, 1984) was coordinated with simultaneous flights in the troposphere and lower stratosphere made by the NASA CV‐990 and Electra as a part of the Global Tropospheric Experiment. This paper briefly reviews the U‐2 instrument payload, shows the flight paths of April 20–21 and May 6 in relation to the respective meteorological situations, and reviews the procedures used to predict large‐scale cyclogenesis and associated tropopause folding and to direct the aircraft. The following papers report the measurement data and interpret the results in terms of reversible and irreversible cross‐jet transport mechanisms.
The Ozone and Aerosol Fine Structure experiment: Observing the fine structure of ozone and aerosol distribution in the atmosphere from the Salyut 7 Orbiter: 3. Experimental results
Authors: Elansky N. F. , Grechko G. M. , Plotkin M. E. , Postylyakov O. V.
Published: February 2008

An investigation of the fine structure of the ozone and aerosol distribution in the atmosphere through photography of the rising and setting Sun in four wavelengths and of the Earth's twilight limb was performed from the Soviet orbital station Salyut 7 in September 1985. Using a renewed mathematical algorithm, vertical distributions of ozone and aerosol and their layered structure over separate regions were derived from photographs. Subsequent validation of the data obtained has confirmed that the data were retrieved with sufficient accuracy. Analysis of the images obtained reveals typical features of the fine structure of aerosol distribution in the troposphere and stratosphere. The aerosol layered structure was observed in the northern and southern hemispheres at the heights 0–18 km and 0–36 km, respectively. In both hemispheres the aerosol fine structure possesses equal altitudinal periodicity of 2.4–2.6 km.
Airborne measurements of particle and gas emissions from the 1990 volcanic eruptions of Mount Redoubt
Authors: Hobbs Peter V. , Radke Lawrence F. , Lyons Jamie H. , Ferek Ronald J. , Coffman Derek J. , Casadevall Thomas J.
Published: February 2008

Airborne in situ and remote sensing (lidar and correlation spectrometer) measurements are described for the volcanic emissions from Mount Redoubt, Alaska, in January and June 1990. The lidar provided excellent real‐time information on the distribution of the volcanic effluents. In postanalysis the lidar observations were used to determine cross‐sectional areas of the plumes of emissions which, together with the airborne in situ measurements, were used to derive the fluxes of particles and gases from the volcano. For the intraeruptive emissions the ranges of the derived fluxes were for water vapor, ∼160–9440 kg s−1; for CO2, ∼30–1710 kg s−1; for SO2, ∼1–140 kg s−1; for particles (<48 μm diameter), ∼1–6 kg s−1; for SO4=, <0.1–2 kg s−1; for HCl, <0.01–2 kg s−1; and for NOx, <0.1–2 kg s−1;. Independent measurements of SO2 from a correlation spectrometer during the period of active dome growth between late March and early June 1990 gave fluxes from 12 to 75 kg s−1;. The particles in the intraeruptive emissions consisted primarily of silicate rock and mineral fragments devoid of any sulfuric acid coating. Very little of the SO2 (∼0.1%) was oxidized to sulfate in the cold, dark conditions of the Arctic atmosphere. During a large eruption of Mount Redoubt on January 8, 1990, the particle (<48 μm diameter) emission flux averaged ∼104 kg s−1. During posteruptive emissions on June 11, 1990, the fluxes of both particles and gases were either close to or less than our lower detection limits (except for water vapor, which had a flux of ∼6×103 kg s−1).
On the ozone minimum over the equatorial Pacific Ocean
Authors: Piotrowicz Stephen R. , Bezdek Hugo F. , Harvey George R. , Springer‐young Margie , Hanson Kirby J.
Published: February 2008

Since 1977, several ship and aircraft expeditions to the equatorial Pacific have reported extremely low (≤10 ppbv) or undetectable levels of ozone within the marine boundary layer. Of necessity, field programs from mobile platforms are limited in both their temporal and spatial coverage. However, a 10‐year record of observations at the geophysical monitoring for climatic change site in American Samoa suggests that low ozone mixing ratios are a common occurrence and may reflect a spatially variable but permanent region of low ozone in the equatorial Pacific. The spatial and temporal limits of this feature as well as some aspects of the intensity of the minimum appear to be maintained by the large‐scale atmospheric circulations of the equatorial Pacific. Perturbations in the large‐scale circulations as well as episodic events are reflected in observations of O3 in the equatorial Pacific. Variations in the large‐scale, zonal circulation patterns (i.e., Walker circulation) of the equatorial Pacific appear to have a major influence on the spatial distribution of O3 across the equatorial Pacific. The relative importance of variations in large‐scale, meridional circulation patterns on the distribution of O3 in the tropical Pacific is uncertain; however, they may be important at latitudes somewhat removed from the equator such as at American Samoa.
Seasonal dependence of boundary layer peroxide concentration: The low and high NOx regimes
Authors: Kleinman Lawrence I.
Published: February 2008

Concentrations of H2O2, organic peroxides, and other photochemically generated species were calculated using a zero‐dimensional box model. The range of emission rates considered centered on values that are representative of conditions in a moderately polluted region such as the eastern United States. Solar intensity, temperature, humidity, and mixing layer height were varied to simulate changing conditions over a yearly cycle. Predicted concentrations of H2O2 have a pronounced seasonal dependence similar to that observed. Evidence is presented that the seasonal behavior of peroxide concentration is due to a transition between two qualitatively different photochemical states of the atmosphere. These states are called the low and high NOx regimes according to whether radical production is greater or less than the NOx emission rate. In the low NOx regime, more radicals are formed than can be accommodated by reaction with NOx, and the “excess” radicals are removed by bimolecular radical‐radical reactions leading in large part to peroxides. In this regime, peroxide formation is nearly proportional to the difference between radical source strength and the NOx emission rate and peroxide concentration scales with the factors affecting radical source strength (e.g., water vapor and photolysis rate constants). Radical production in the high NOx regime is insufficient to react with and remove all NOx. Consequences include the suppression of peroxide formation, a reduction in the oxidizing capacity of the atmosphere, and high concentrations of primary pollutants.
The temperature dependence of collision‐induced absorption by oxygen near 6 μm
Authors: Orlando John J. , Tyndall Geoffrey S. , Nickerson Karen E. , Calvert Jack G.
Published: February 2008

Coefficients for oxygen absorption in the infrared induced by collisions with O2 and N2 are reported over the range 1400–1800 cm−1 and 225–356 K. These coefficients are used to calculate the absorption for O2 in air as a function of temperature and wavenumber, and comparisons are made with previous determinations. In addition, structured absorption features superimposed on the broad collision‐induced absorption band, which were observed at all temperatures studied, are interpreted in terms of the presence of (O2)2 and O2‐N2 van der Waals molecules.
Adaptive filtering and maximum entropy spectra with application to changes in atmospheric angular momentum
Authors: Penland Cecile , Ghil Michael , Weickmann Klaus M.
Published: February 2008

The spectral resolution and statistical significance of a harmonic analysis obtained by low‐order maximum entropy methods (MEM) can be improved by subjecting the data to an adaptive filter. This adaptive filter consists of projecting the data onto the leading temporal empirical orthogonal functions obtained from singular spectrum analysis (SSA). The combined SSA‐MEM method is applied both to a synthetic time series and a time series of atmospheric angular momentum (AAM) data. The procedure is very effective when the background noise is white and less so when the background noise is red. The latter case obtains in the AAM data. Nevertheless, we detect reliable evidence for intraseasonal and interannual oscillations in AAM. The interannual periods include a quasi‐biennial one and a low‐frequency one, of 5 years, both related to the El Niño/Southern Oscillation. In the intraseasonal band, separate oscillations of about 48.5 and 51 days are ascertained.
Use of a three‐dimensional cloud‐chemistry model to study the transatlantic transport of soluble sulfur species
Authors: Luecken D. J. , Berkowitz C. M. , Easter R. C.
Published: February 2008

This paper describes the development and application of a three‐dimensional, global‐scale Eulerian model with an explicit description of cloud and chemical processes. The current configuration of the model calculates clear air and aqueous chemistry, cloud and rainwater scavenging and deposition, and long‐range transport using meteorological data from a global circulation model. As an example of the model capabilities, results of simulations of the transport of sulfur from North America and Europe across the North Atlantic Ocean during 30‐day periods in January and July are presented. The model predicted that sulfur associated with North American and European anthropogenic sources contributed about equally to atmospheric sulfur deposition in remote areas of the North Atlantic. Oceanic sources of DMS were predicted to contribute to sulfur deposition over some areas of the North Atlantic Ocean.
Spectroscopic measurement of HO2, H2O2, and OH in the stratosphere
Authors: Park J. H. , Carli B.
Published: February 2008

Stratospheric concentrations of HO2, H2O2 and OH have been retrieved simultaneously from the far infrared emission spectra obtained with a balloon‐borne Fourier transform spectrometer in June 1983 at 32°N latitude. Retrieved concentrations of HO2 and H2O2 are reported in this paper, along with vertical distributions of OH which were reported in an earlier paper for the afternoon, sunset, and nighttime periods for altitudes from 26 to 38 km. HO2 distributions are obtained with uncertainties that are about the same as OH for the same vertical range and for the afternoon and sunset periods. H2O2 concentration is obtained at an altitude of 30 km for the period that covers afternoon and sunset hours. The retrieved concentrations of these HOx species agree well with other individually measured results and the steady state photochemical predictions. The ratio HO2/OH at around 32 km seems to increase from the afternoon period to the sunset period.
Comparison of the signal strength of positive and negative cloud‐to‐ground lightning flashes in northeastern Colorado
Authors: López Raúl E. , Maier Michael W. , Holle Ronald L.
Published: February 2008

The frequency distribution of the peak signal strength associated with the first detected return stroke of positive and negative cloud‐to‐ground flashes was studied using lightning data from northeastern Colorado. These data were obtained during 1985 with a network of medium‐high gain direction finders (DFs) having a nominal range of 300 km. The median normalized signal strength of positive flashes was almost 2 times that of the negatives for flashes within 300 km of the DFs (170 versus 96 Lightning Location and Protection, Inc. (LLP), units). These DFs have an inherent detection threshold bias that tends to discriminate against weak signals. This bias increases with range and affects the detection of positive and negative flashes in different ways because of the differing character of their distributions. Positive flashes appear to have a large percentage (12 times larger than that of negative flashes) of signals clustered around very weak values (below 30 units) that are lost to the Colorado detection system of medium‐high gain very quickly with increasing range (most of these are undetected by 125 km). The resulting median for positive signals thus could appear to be much larger than the median for negative signals, which are more clustered around intermediate values (80 units). When only flashes very close (20–60 km) to the DFs are considered, however, the two distributions have almost identical medians (70 units). The large percentage of weak positive signals (below 30 units) detected close to the DFs (about 10 times larger than that of negative signals) has not been previously explored. It has been suggested that they come from intracloud discharges and are improperly classified as coming from CG flashes. The evidence in hand, however, points to their being real positive, albeit weak, cloud‐to‐ground flashes. Whether or not they are real positive ground flashes, it is important to be aware of their presence in data from magnetic DF networks. Even if the weak positive signals are eliminated by considering only distant flashes (beyond about 125 km), the frequency distributions of positive and negative signal strengths are very different, the positives lacking the large percentage of intermediate signals (around 80 units) of the negatives but having a somewhat larger relative frequency of large and very large signals (beyond 130 units).
Sub‐ice topography and meteorite finds near the Allan Hills and the Near Western Ice Field, Victoria Land, Antarctica
Authors: Delisle G. , Sievers J.
Published: February 2008

We have investigated the glaciological causes of large meteorite concentrations on blue ice fields west and southwest of the Allan Hills in Antarctica. A sub‐ice topography map for the area was prepared from data of a radio echo sounding survey. The map reveals a mesa‐type paleosurface. It was formed prior to and modified by glacial processes during the initial stage of glaciation of Antarctica. Ice flow toward Mawson Glacier north of the Allan Hills is largely confined to a N‐S trending depression between the Allan Hills Ice Field and the Near Western Ice Field. Blue ice at the margins of the ice stream flows over the mesas on both sides of this depression. Meteorites entrained in blue ice are uncovered by sublimation and ablation. We present arguments showing that currently almost all of the blue ice flowing into the Allan Hills Ice Field is sublimated, leaving meteorites on the ice surface. We present evidence that windblown meteorites are trapped by snow bridges across crevasses, resulting in a near‐surface meteorite concentration near the ice ridges of the Allan Hills Ice Field. Nevertheless, most meteorites are exposed for only a short period of time to the atmosphere before they are blown by the wind across the ice toward the western foot of the Allan Hills, from where they are slowly carried northward to Mawson Glacier and the Ross Sea.
Mantle downwelling and crustal convergence: A model for Ishtar Terra, Venus
Authors: Kiefer Walter S. , Hager Bradford H.
Published: February 2008

The Ishtar Terra region contains the highest topography known on Venus, over 10 km above mean planetary radius, as well as abundant tectonic features, many of apparently compressional origin. These characteristics suggest that Ishtar is a crustal convergence zone overlying downwelling mantle. In order to explore quantitatively the implications of this hypothesis for Ishtar's origin, we present models of viscous crustal flow driven by gradients in topography. Assuming a free‐slip surface boundary condition, we find that if the crustal convergence hypothesis is correct, then the crustal thickness in the plains surrounding Ishtar can be no more than about 25 km thick. This upper bound assumes a cold (10 K km−1) geotherm and the stiffest available diabase flow law. If the geothermal gradient is larger or the rheology is weaker, the crust must be even thinner for net crustal convergence to be possible. This upper bound is in good agreement with several independent estimates of crustal thickness of 15–30 km in the plains of Venus based on modeling of the spacing of tectonic features and of impact crater relaxation. If the surface layer of Venus provides a no‐slip boundary, then our models allow the crustal thickness in the plains to be up to 50 km, but the likely existence of faults that cut through the crust makes a no‐slip surface layer unlikely. Our upper bound on crustal thickness is much less than that derived from an Airy isostasy model of Ishtar's gravity anomaly. Much of the observed gravity anomaly must be due to density anomalies in the mantle beneath Ishtar. Although we treat Ishtar as a crustal convergence zone, our crustal flow model shows that under some circumstances near‐surface material may actually flow away from Ishtar, providing a possible explanation for grabenlike structures in Fortuna Tessera.
The thermal gradient of Callisto constrained by Asgard Basin: Rheological and chemical implications
Authors: Allemand Pascal , Thomas Pierre G.
Published: February 2008

Using the width of concentric grabens formed during the relaxation of the Asgard basin on Callisto, in combination with rheological flow laws of ice and laws concerning the variations in strain rate around a relaxing crater, the surface thermal gradient of Callisto at −4 b.y. is estimated to be near 0.5°K km−1. It is assumed that the graben width depends on the depth of the brittle/ductile transition zone. Around the Asgard basin, the depth of this brittle/ductile transition zone varies from 23 km (at 200 km from the crater rim) to 4 km (at 800 km from the crater rim). It is assumed that the thermal characteristics were constant over the extended zone and that the difference in the depth of the brittle/ductile transition zone is only due to differences in the strain rate around the basin during the relaxation of the initial cavity. Calculations show that Newtonian flow law for ice gives a strain rate of external relaxation at the crater rim of about 10−14 s−1, while a power law gives a strain rate of about 10−6 s−1, assuming a surface temperature between 100 and 150°K. The order of magnitude of the calculated thermal gradient is independent of the chosen flow law. This calculated gradient is, however, one order of magnitude lower than those calculated theoretically with a chondritic abundance of radioactive elements in the silicate part of Callisto.
Pacific CaCO3 Preservation and δ18O Since 4 Ma: Paleoceanic and Paleoclimatic Implications
Authors: Farrell John W. , Prell Warren L.
Published: February 2008

The Pliocene‐Pleistocene history of CaCO3 preservation in the central equatorial Pacific is reconstructed from a suite of deep‐sea cores and is compared to fluctuations in global ice volume inferred from δ18O records. The results are highlighted by: (1) a strong covariation between CaCO3 preservation and ice volume over 104 to 106 year time scales; (2) a long‐term increase in ice volume and CaCO3 preservation since 3.9 Ma demonstrated by a deepening of the lysocline and the carbonate critical depth; (3) a dramatic shift to greater CaCO3 preservation at 2.9 Ma; (4) distinctive ice‐volume growth and CaCO3 preservation events at 2.4 Ma, which are associated with the significant intensification of northern hemisphere glaciation; (5) a mid‐Pleistocene transition to 100‐kyr cyclicity in both CaCO3 preservation and ice volume; and (6) a 600‐kyr Brunhes dissolution cycle superimposed on the late Pleistocene glacial/interglacial 100‐kyr cycles. CaCO3 preservation primarily reflects the carbonate chemistry of abyssal waters and is controlled by long‐term (106 year) and short‐term (104 to 105 year) biogeochemical cycling and by distinct paleoclimatic events. We attribute the long‐term increase in CaCO3 preservation primarily to a fractionation of CaCO3 deposition from continental shelf to ocean basin, and secondarily to a gradual rise in the riverine and glaciofluvial flux of Ca++. On shorter time scales, the fluctuations in CaCO3 preservation slightly lag ice volume fluctuations and are attributed to climatically induced changes in the circulation and chemistry of Pacific deep water.
Using 230Th in Marine Sediments to Reconstruct the Late Quaternary History of Sea Level
Authors: Slowey Niall C. , Curry William B.
Published: February 2008

We propose a method to determine past sea levels based on the record of 230Th accumulating in seafloor sediments. The decay of uranium in seawater produces this nuclide, which then adsorbs rapidly onto particles settling to the seafloor. Since the concentration of uranium is similar at all depths in the water column, the flux of 230Th to the seafloor at any location is proportional to water column height. Consequently, changes in sea level must cause changes in these fluxes. At shallow depths (<1000 m), fluctuations of sea level cause changes in the expected 230Th flux that are large enough to produce measurable changes in the 230Th content of the sediment. We have developed two approaches to determine past sea levels from the content of 230Th in sediments: (1) in a single core, the ratio of the past and present fluxes of 230Th to a site on the seafloor is a measure of the ratio of the past and present depths of the site below sea level and (2) in two or more cores from a region where the vertical input of sediment is similar at all depths in the water column, the concentrations of 230Th in synchronous sediment samples are linearly related to depth and indicate past sea level as the depth where the concentrations extrapolate to zero. The latter approach requires fewer assumptions and allows sea level to be estimated at discrete points in time. The methodology, assumptions, advantages and disadvantages of the first approach is illustrated using preliminary data from a core recovered from the margin of Little Bahama Bank.
Environmental information from ice cores
Authors: Delmas Robert J.
Published: February 2008

Human activities have a serious impact on climate and on the natural composition of the atmosphere. Information recorded in polar ice cores over the last several hundred millennia is invaluable to studies aimed at understanding the preindustrial environmental system and anticipating the future evolution of the atmosphere. An excellent understanding of the mechanisms of the ice record formation as well as a good assessment of the present polar atmospheric composition (trace gases, aerosol) is a prerequisite to interpreting correctly the past variations of the measured parameters. This paper explains what and how atmospheric parameters are recorded. Ambient air samples are encapsulated and stored in the ice bubbled by relatively simple processes. The isotopic composition of the H2O (ice) lattice is a reliable paleothermometer. The interpretation of the chemical composition of deposited snow in terms of past atmospheric composition of deposited snow in terms of past atmospheric composition (trace gases, aerosol) is more intricate and necessitates detailed discussions. The data obtained from deep ice cores provide precise information on the ice age environmental conditions: when polar temperatures were some 10°C lower than now, atmospheric CO2 and CH4 contents were factors of 2 and 4 lower, respectively, than present conditions. At this time, sea salt and overall crustal dust depositions were significantly higher. The biogeochemical cycles of S and N were also disturbed according to modifications in source intensity and transport of gaseous precursors.
Ion cyclotron emissions observed by the satellite Akebono in the vicinity of the magnetic equator
Authors: Kasahara Yoshiya , Sawada Akira , Yamamoto Masayuki , Kimura Iwane , Kokubun Susumu , Hayashi Kanji
Published: February 2008

In our wave observations by a wave measuring instrument named ELF on board the Akebono satellite, interesting ELF emissions in the frequency ranges above the cyclotron frequencies of He+ and/or O+ ions have been detected. This paper is to propose that these emissions are due to electromagnetic ion cyclotron waves, which might have been generated by the ion cyclotron resonant instability due to a temperature anisotropy of hot H+ ions, trapped along the magnetic field lines around the geomagnetic equatorial plane. In order to confirm the characteristics of these ELF emissions, statistical characteristics, refractive index, and wave normal direction of the emissions are first estimated. The propagation characteristics of these ELF emissions are examined by ray tracing for ion cyclotron waves in the magnetosphere using both cold and hot plasma models.
Optimal analysis of incoherent scatter radar data
Authors: Holt J. M. , Rhoda D. A. , Tetenbaum D. , van Eyken A. P.
Published: February 2008

A lag‐profile data collection mode has recently become operational at Millstone Hill. A new data analysis technique has been developed in which one or more matrices of ion‐line lagged products are analyzed simultaneously, along with any available a priori information on ionospheric and system parameters such as ionosonde and plasma‐line estimates of f0F2. The analysis yields spline function estimates of height‐varying ionospheric parameter profiles. The effect of the full two‐dimensional (range‐lag) radar ambiguity function is included in this analysis. Millstone Hill single‐pulse lag profile data are presented and analyzed and the new technique is shown to produce ionospheric parameter profile estimates with significantly better height resolution than would be possible if the lag profile matrix were first divided into ACFs by application of a summation rule.
A recursive T‐matrix algorithm for strips and patches
Authors: Gürel L. , Chew W. C.
Published: February 2008

A recursive T‐matrix algorithm (RTMA) is formulated to extend its applicability to infinitely thin and conducting scatterers. Canonical geometries consisting of strips or patches are considered. These geometries have direct application in finite‐size frequency selective surfaces (FSSs). The formulation of this T‐matrix algorithm starts from the method of moments (MOM). Thus, the connection between the MOM and the T‐matrix algorithm is established. Three‐dimensional patch problems are formulated analogously to the two‐dimensional strip problems so that the need to use the vector addition theorem for the patch problems is eliminated and a unified formulation results. The T‐matrix for a single strip or patch is also derived using MOM ideas. Computation of the current distributions on the conducting scatterers is also achieved. Results displaying the radar cross section (RCS) of and the current distribution on a sample FSS geometry are presented.