bluuebunny/crossref_metadata_2025 huggingface dataset:
Observed OH and HO2 in the upper troposphere suggest a major source from convective injection of peroxides
Authors: Jaeglé L. , Jacob D. J. , Wennberg P. O. , Spivakovsky C. M. , Hanisco T. F. , Lanzendorf E. J. , Hintsa E. J. , Fahey D. W. , Keim E. R. , Proffitt M. H. , Atlas E. L. , Flocke F. , Schauffler S. , McElroy C. T. , Midwinter C. , Pfister L. , Wilson J. C.
Published: February 2004

ER‐2 aircraft observations of OH and HO2 concentrations in the upper troposphere during the NASA/STRAT campaign are interpreted using a photochemical model constrained by local observations of O3, H2O, NO, CO, hydrocarbons, albedo and overhead ozone column. We find that the reaction Q(¹D) + H2O is minor compared to acetone photolysis as a primary source of HOx (= OH + peroxy radicals) in the upper troposphere. Calculations using a diel steady state model agree with observed HOx concentrations in the lower stratosphere and, for some flights, in the upper troposphere. However, for other flights in the upper troposphere, the steady state model underestimates observations by a factor of 2 or more. These model underestimates are found to be related to a recent (< 1 week) convective origin of the air. By conducting time‐dependent model calculations along air trajectories determined for the STRAT flights, we show that convective injection of CH3OOH and H2O2 from the boundary layer to the upper troposphere could resolve the discrepancy. These injections of HOx reservoirs cause large HOx increases in the tropical upper troposphere for over a week downwind of the convective activity. We propose that this mechanism provides a major source of HOx in the upper troposphere. Simultaneous measurements of peroxides, formaldehyde and acetone along with OH and HO2 are needed to test our hypothesis.
Fluctuation in ozone column over Ahmedabad during the solar eclipse of 24 October 1995
Authors: Chakrabarty D. K. , Shah N. C. , Pandya K. V.
Published: February 2004

A solar eclipse occurred over Ahmedabad, India (23°N, 72°E) on 24 October 1995. We measured the vertical column abundance of ozone during this event using a Dobson spectrophotometer. We found that a sharp fall in the ozone column began from its normal value ∼15 minutes before the maximum obscuration (MO) of the sun, followed by a sharp rise ∼10 minutes after the MO. About 15 minutes after the MO, ozone column returned to normal values, but a wavelike fluctuation was still seen.
Ground‐based observations of ULF transients excited by strong lightning discharges producing elves and sprites
Authors: Fukunishi H. , Takahashi Y. , Sato M. , Shono A. , Fujito M. , Watanabe Y.
Published: February 2004

Optical and search coil magnetometer data obtained from the SPRITES'96 campaign carried out at Yucca Ridge Field Station, Colorado in July 1996 have presented clear evidence for the excitation of ULF transients with their dominant power at 1–2 Hz by strong lightning discharges producing elves and sprites. The most striking feature is that the ULF transients exhibit different wave forms in the case of sprites without preceding elves and the case of sprites with preceding elves. In the former case damped, quasi‐sinusoidal oscillations commence impulsively at the onset of sprites, while in the latter case quasi‐sinusoidal wavelets with a duration of ∼3 s are excited, and elves and sprites occur within each wavelet. It is likely that these ULF transients are due to the nonlinear excitation of the ionospheric Alfvén resonator by strong lightning discharge, as proposed by Sukhorukov and Stubbe [1997].
Vertical profile of the carbon isotopic ratio of stratospheric methane over Japan
Authors: Sugawara S. , Nakazawa T. , Shirakawa Y. , Kawamura K. , Aoki S. , Machida T. , Honda H.
Published: February 2004

Stratospheric air samples were collected over Japan on August 31, 1994 using a balloon‐borne cryogenic sampler and then analyzed for the CH4 concentration and δ13C in CH4. The δ13C value increased from about −47.5‰ at the tropopause to about −38.9‰ at 34.7 km, accompanied by a rapid decrease of the CH4 concentration with height. From the measured values of the CH4 concentration and δ13C, the apparent carbon isotopic fractionation factor was estimated to be 1.0131±0.0006. The contributions of the chemical CH4 reactions with OH, O(¹D) and Cl were also examined by using an one‐dimensional photochemical‐diffusion model. It is suggested from this examination that the reaction of CH4 with Cl is especially important for δ13C in the stratosphere.
Shuttle charging by fixed energy beam emissions
Authors: Burke W. J. , Raitt W. J. , Thompson D. C. , Machuzak J. S. , Gentile L. C. , Gilchrist B. E. , Huang C. Y. , Cooke D. L. , Hardy D. A. , Olson D. G. , Lebreton J.‐P. , Bonifazi C.
Published: February 2004

We present environmental responses observed by the Shuttle Potential and Return Electron Experiment during 13 prolonged electron beam emissions from the Fast Pulsed Electron Generator (FPEG) during the TSS 1R deployment. As the tether lengthened from 0.18 to 2.5 km, FPEG fired nine times at a nominal current of 100 mA at 1 keV. The motional potential induced across the system increased from 24 to 225 V. With a 15 Ω resistor connecting the tether to shuttle ground, current was higher and the degree of negative shuttle charging lower when FPEG was off than when it was on. While most FPEG firings left the shuttle uncharged, two created significant potentials: one to +70 V in a nighttime, equatorial plasma depletion and one to ‐60 V, with the tether ∼ 15 km.
Influence of sea ice on the thermohaline circulation in the Arctic‐North Atlantic Ocean
Authors: Mauritzen Cecilie , Häkkinen Sirpa
Published: February 2004

A fully prognostic coupled ocean‐ice model is used to study the sensitivity of the overturning cell of the Arctic‐North‐Atlantic system to sea ice forcing. The strength of the thermohaline cell will be shown to depend on the amount of sea ice transported from the Arctic to the Greenland Sea and further to the subpolar gyre. The model produces a 2–3 Sv increase of the meridional circulation cell at 25N (at the simulation year 15) corresponding to a decrease of 800 km³ in the sea ice export from the Arctic. Previous modeling studies suggest that interannual and decadal variability in sea ice export of this magnitude is realistic, implying that sea ice induced variability in the overturning cell can reach 5–6 Sv from peak to peak.
Aircraft‐borne measurements of peroxy radicals in the middle troposphere
Authors: Reiner Thomas , Hanke Markus , Arnold Frank
Published: February 2004

We have performed aircraft‐borne measurements of peroxy radicals in the free troposphere over southern Germany (48°N). The measurements were carried out on board a Dornier 228 research aircraft. At altitudes between 3.7 and 7.8 km measured peroxy radical concentrations were between 2 × 108 and 7×108 cm−3. Peroxy radicals were measured using amplifying chemical conversion of peroxy radicals to sulfuric acid via reactions with NO and SO2 and detection of sulfuric acid by ion molecule reaction‐mass spectrometry (IMR‐MS). The instrument was calibrated at the ground and thoroughly characterized by laboratory and in‐flight diagnostic measurements. The accuracy of the present aircraft‐borne measurements is estimated to be about ±45%. Regular background measurements have been performed during the flights to determine the extent of spurious radical or H2SO4 production, which may occur through ion source produced radicals or thermal decomposition of PAN or HNO4 in the sampling system.
TSS‐1R vertical electric fields: Long baseline measurements using an electrodynamic tether as a double probe
Authors: Williams S. D. , Gilchrist B. E. , Agüero V. M. , Indiresan R. S. , Thompson D. C. , Raitt W. J.
Published: February 2004

This paper presents measurements of vertical electric fields obtained using the Tethered Satellite System (TSS) as an electrodynamic double probe. During five hours of TSS‐1R deployment from the space shuttle Columbia in February 1996, observations of induced tether potential were gathered over a baseline from 2 to 20 km in the mid and low latitude F‐region ionosphere. The corresponding electric fields derived from the potential measurements are found to be consistent with previous satellite and ground‐based measurements for similar ionospheric conditions. The data are unique and demonstrate a new capability for measuring the vertical component of the ionospheric electric field. Comparison of the measured electric field at different tether deployment lengths for corresponding local times reveal that the vertical component of the ambient electric field exists on scales of at least 20 km.
On the Long‐Range transport of air pollutants from Europe to Africa
Authors: Kallos G. , Kotroni V. , Lagouvardos K. , Papadopoulos A.
Published: February 2004

The general climatic conditions and the physiographic characteristics of the area around the Mediterranean Sea, result in the formation of a flow pattern which is from North to South during all seasons and mainly during summer. This flow transports polluted air masses from southern Europe towards Africa. This transport is being investigated with the combined use of an atmospheric and a Lagrangian dispersion model. Air pollutants released from sources located in southern Europe were found in the entire tropospheric region over North Africa. The time scales for such a transport were found to be four to six days. This kind of transport can have several implications ranging from degradation of the air quality in North African cities to the water budget and regional climatic change.
Effect of ice cloud on GCM climate simulations
Authors: Ho Chang‐Hoi , Chou Ming‐Dah , Suarez Max , Lau Ka‐Ming
Published: February 2004

The effect of the interaction of SW (shortwave, solar) radiation with ice clouds on climate simulations is studied using the GEOS (Goddard Earth Observing System) climate GCM (general circulation model) coupled with an ocean mixed‐layer model. Due to much larger cloud particles, the single‐scattering co‐albedo of ice clouds is nearly ten times larger than that of water clouds, but the asymmetry factor is generally smaller. Offline calculations with a radiative transfer model show that inclusion of the ice cloud effect increases SW absorption in the upper troposphere and decreases the SW flux at the surface. For the earth‐atmosphere system, the change in the SW absorption is small due to compensation of the co‐albedo and asymmetry factor effects. The effect of ice clouds tends to increase the atmospheric stability by enhancing SW heating in the upper troposphere and reducing SW heating in the lower troposphere and at the surface. The GCM experiments demonstrate that the inclusion of ice clouds produces colder surface temperature, and leads to reduction in SW heating of the earth‐atmosphere system associated with changes in surface albedo and in cloud distribution. The enhanced atmospheric stability leads to decreased high cloud amount by a maximum of 80% and to increased middle cloud by a maximum of 60% over the tropics.
Radio emissions observed by Galileo near Io
Authors: Menietti J. D. , Gurnett D. A. , Kurth W. S. , Groene J. B. , Granroth L. J.
Published: February 2004

The Galileo spacecraft observed spin modulation of radio wave emissions near Io in the frequency range from about 600 kHz to about 1.2 MHz. Assuming transverse EM radiation, we have used the modulation of the high‐frequency sweep‐frequency receiver signals of the electric dipole antenna over many spins to estimate the plane through the source. The emission has a range of frequencies close to the local upper hybrid frequency of the plasma near Io. We conclude that the emission may be associated with either the plasma torus or magnetic flux tubes in the wake of Io (the Alfvén current system). We postulate this emission may be associated with a free‐energy source such as density gradients, energetic plasma beams and/or an electron distribution with a temperature anisotropy. All of these free‐energy sources are observed or expected in the torus near Io. The observations are the first in the hectometric frequency range that have a source associated with Io or in the Io torus.
Sulfuric acid and soot particle formation in aircraft exhaust
Authors: Pueschel Rudolf F. , Verma Sunita , Ferry Guy V. , Howard Stephen D. , Vay Stephanie , Kinne Stefan A. , Goodman Jindra , Strawa Anthony W.
Published: February 2004

Size analyses of Ames wire impactor aircraft exhaust aerosol samples resulted in a continuous particle size distribution between 0.01 µm and 1.0 µm particle radius. The two orders of magnitude size range covered by the measurements correspond to 6–7 orders of magnitude particle concentration. The data determined a nucleation mode, composed of aircraft‐emitted sulfuric acid aerosol, that contributed between 62% and 85% to the total aerosol surface area and between 31% and 34% to its volume. Soot aerosol contributed 0.3% to the surface area and 0.07% to the volume of sulfuric acid aerosol. Emission indices were: EIH2SO4=0.09 g/kgFUEL and (0.2‐0.5) g/kgFUEL (for 75 ppmm and 675 ppmm fuel‐S, respectively), 1.7E‐4<EISOOT<1.3E‐3 g/kgFUEL, and EIN>0.01=1.7E14 and (7.7E14 and 5.2E15) particles/kgFUEL (for 75 and 675 ppmm fuel‐S, respectively). The sulfur (gas) to sulfuric acid (particle) conversion efficiency was between 10% and 37%.
Constraints on Q at long periods from Earth's rotation
Authors: Dickman S. R. , Nam Young S.
Published: February 2004

In this work we assess constant Q and frequency‐dependent Q models of mantle anelasticity. Our assessment uses the degree 2 Love numbers we had inferred previously from a comparison of observed and predicted changes in the length of day at monthly, fortnightly, and nine‐day lunar tidal periods. The comparison accounted for variable contributions to the tidal signals by dynamic oceans, and allowed for axial core‐mantle coupling that was either complete or absent. The Love number derived from an earlier analysis of the period of the Chandler wobble is also employed. We find that the similarity of the degree 2 Love number inferred at a nine‐day period to that at seismic frequencies, combined with the significant amount of relaxation at the Chandler period, together imply that Q models operating within the seismic band cannot extend all the way to long tidal periods. Our analysis of Q also allows us to refine estimates of the Love number at fortnightly and monthly periods.
North Pacific midlatitude cyclone characteristics and their effect upon winter precipitation during selected El Niño/Southern Oscillation events
Authors: Raphael M. N. , Cheung I. K.
Published: February 2004

North Pacific cyclone frequency, intensity and proximity to the receiving stations (track) in the two ENSO winters that contribute most strongly to the variability of precipitation are examined along with the regional scale circulation and sea surface temperatures (SSTs) prevailing during those winters. During winter 1982/83, the number of cyclones was not significantly different from average, but they were much more intense and moved closer to the receiving stations than average. In 1976/77 there were far fewer cyclones than average. In both winters, the effect of ENSO on precipitation was moderated by the cyclone characteristics and regional atmospheric circulation and SST patterns that prevailed.
Lateral mixing as a source of subtropical water vapor
Authors: Pierrehumbert R. T.
Published: February 2004

It is hypothesized that the subtropical tropospheric water vapor distribution results from the interplay of three factors: subsidence, which brings down dry air from aloft; lateral mixing, which brings in moistened air from the convective region at various rates; and drying by processing of air through the cold extratropics. A simplified Lagrangian model is formulated, and used to study how this process works during the CEPEX period (March, 1993). A key result is that the Northern subtropics should be viewed as a general background of dry air with mass mixing ratio of 10−4 or less on the 330K surface, interrupted by a few coherent moist plumes with mixing ratios on the order of 10−3.
Coastal wave generation in the Bohai Bay and propagation along the Chinese coast
Authors: Jacobs G. A. , Preller R. H. , Riedlinger S. K. , Teague W. J.
Published: February 2004

The Bohai Bay and Yellow Sea experience sea surface height (SSH) changes of 20 cm and larger during wintertime northerly and southerly wind bursts that have a time scale of a few days. These large SSH changes give rise to coastal shelf waves that subsequently propagate southward along the Chinese coast. Two models provide observations of these waves. The first one is a statistical model based on four years of TOPEX/POSEIDON (T/P) altimeter SSH observations and Navy Operational Global Atmospheric Prediction System (NOGAPS) wind stress fields. The second model is a numerical model forced by the wind stress. The numerical model provides an objective interpretation of the wind stress response based on dynamical equations. The statistical model is based on observations with a linear response to the wind forcing and thus complements the numerical model. The observed waves closely resemble gravest mode shelf waves derived by analytical solutions.
Dynamical length scales for turbulent magnetized flows
Authors: Politano Hélène , Pouquet Annick
Published: February 2004

We derive two symmetric global scaling laws for third‐order structure functions of magnetized fluids under the assumptions of full isotropy, homogeneity and incompressibility. The compatibility with previous laws involving both structure and correlation functions of only the longitudinal components of the fields is demonstrated. These new laws provide a better set of functions with which one can determine intermittency scaling of MHD turbulence, as in the Solar Wind.
Radar measurements of the electromagnetic energy rates associated with the Dynamic Ionospheric Load/Generator
Authors: Thayer Jeffrey P.
Published: February 2004

High resolution incoherent‐scatter radar measurements from Sondrestrom, Greenland, are used to evaluate the energy characteristics of the dynamic load/generator throughout the high‐latitude E region. The measurements provide a unique view of E‐region electrodynamics and show for the first time the E‐region processes that dictate ionospheric load/generator behavior. Also, the energy rate associated with the, often assumed, passive ionospheric load is shown for two extended periods of observations to be an overestimate of the actual energy transfer rate, typically by more than a factor of 1.5 for these data. The distribution and partitioning of the energy transfer rate into Joule heating and mechanical energy rates is also evaluated throughout the E region with both showing an altitude‐dependent influence on the energy rates associated with the net load. These estimated quantities provide significant insight into understanding the contributing factors involved in the net transfer of electromagnetic energy between the ionosphere and magnetosphere.
Contrail formation and impacts on aerosol properties in aircraft plumes: Effects of fuel sulfur content
Authors: Yu Fangqun , Turco Richard P.
Published: February 2004

The formation and evolution of fine particles and ice contrails in an aircraft exhaust plume containing varying amounts of fuel sulfur have been simulated using an advanced aerosol microphysics model. The “core” sulfate and soot particles are tracked during the contrail formation and dissipation phases. When ion electrostatic effects are incorporated into the microphysics, sulfuric acid vapor emitted by high‐sulfur‐content fuels generates water‐soluble particles that are large enough to be activated into contrails, improving the agreement between simulations and measurements. Our results also suggest that ice crystals formed in contrails efficiently scavenge vapors and particles, creating a sulfate aerosol accumulation mode that may contribute to cloud CCN/IN. The size distributions of aerosols produced both in the presence and absence of contrails agree reasonable well with the two characteristic types observed in the plumes of commercial aircraft.
Cloud condensation nuclei measurements in the high troposphere and in jet aircraft exhaust
Authors: Hudson James G. , Xie Youghong
Published: February 2004

Extensive measurements of cloud condensation nuclei (CCN) spectra (1 to 0.02% supersaturation; S) at altitudes up to 12 km are presented. These were similar to many marine boundary layer measurements when normalized to standard sea level pressure. Extremely low CCN concentrations (<10 cm−3) were sometimes found in association with very high CN (condensation nuclei) concentrations (>3000 cm−3). This was suggestive of cloud scavenging of CCN and production of small particles. Measurements in the exhaust of a B‐757 jet aircraft showed very high CCN/CN ratios and enhancements of CCN concentrations for all S. This suggests a greater impact of jet aircraft on clouds and climate than previous measurements.
A fully coupled GCM simulation of the climate of the mid‐Holocene
Authors: Hewitt Chris D. , Mitchell John F. B.
Published: February 2004

The response of a fully coupled ocean‐atmosphere model to mid‐Holocene insolation forcing is compared with results from an atmospheric model with prescribed present day sea surface temperatures and mid‐Holocene insolation. The ocean response increases the amplitude of the seasonal temperature response over land, and increases its lag behind the solar forcing. The tropical oceans in the coupled model are coldest, relative to the control, in May at 6ka leading to a relative reduction in evaporation, precipitation and ascending motion over the ocean, and relative ascent and increased precipitation over equatorial Africa. By September, the tropical oceans are warmer than in the fixed SST experiment which leads to increased moisture flux from the oceans into the southeast monsoon, and a larger increase in monsoon precipitation than in the fixed SST experiment. In addition, the enhanced warming of the northern hemisphere SSTs relative to the southern subtropics leads to a northward shift of the Intertropical Convergence Zone. As a result, increased wetness of the tropical land surface in the mid Holocene experiments is more pronounced and extends further northwards when the sea surface temperatures are allowed to respond. The coupled model results are more in accord with lake level data, especially over North Africa.
CIRRIS‐1A measurements of stratospheric carbon tetrachloride (CCl4) and carbon tetrafluoride (CF4)
Authors: Zhou D. K. , Bingham G. E. , Anderson G. P. , Nadile R. M.
Published: February 2004

Stratospheric infrared spectral measurements were made by the Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS‐1A) during the Space Transportation System 39 mission (28 April to 6 May 1991). The moderate‐resolution (1.0 cm−1) spectra from the CIRRIS‐1A measurements reveal infrared emissions from the stratospheric gases of carbon tetrachloride (CCl4) and carbon tetrafluoride (CF4). Volume‐mixing ratios of these gases were retrieved using FASCOD3 with the HITRAN96 database as a forward model. These volume‐mixing ratios are compared with other measurements.
Meteor luminosity at 160 km altitude from TV observations for bright Leonid meteors
Authors: Fujiwara Yasunori , Ueda Masayoshi , Shiba Yasuo , Sugimoto Masatoshi , Kinoshita Masao , Shimoda Chikara , Nakamura Takuji
Published: February 2004

Two atmospheric trajectories have been determined by simultaneous observations with image intensifier‐fitted TV cameras and conventional photographic cameras for two bright Leonid meteors (fireballs) in 1995 and 1996. Beginning heights recorded by the photographic method are lower than about 130 km, but those observed by the TV systems are closer to 160 km. The primary reason for this difference is the sensitivity of the observing systems. However, the difference in the sensitive wavelengths (up to 900 nm for the TV systems) could be another factor contributing to the large difference between the two methods. This suggests that the beginning heights of high speed bright meteors such as Leonid meteors are much higher than previously thought.
The role of heterogeneous freezing nucleation in upper tropospheric clouds: Inferences from SUCCESS
Authors: DeMott Paul J. , Rogers David C. , Kreidenweis Sonia M. , Chen Yalei , Twohy Cynthia H. , Baumgardner Darrel , Heymsfield Andrew J. , Chan K. Roland
Published: February 2004

A temperature spectrum of heterogeneous freezing nuclei concentrations in continental air in the upper troposphere was determined based on airborne measurements. Numerical model simulations incorporating ice formation by heterogeneous and homogeneous freezing of deliquesced soluble aerosol particles were performed to investigate the effect of the heterogeneous process on the microphysics of upper tropospheric clouds. Heterogeneous freezing nuclei were predicted to cause lower maximum concentrations of ice particles formed in clouds. These nuclei also initiate the first ice formation and act to broaden ice crystal size distributions in upper tropospheric clouds. Observations of ice formation in an orographic wave cloud supported these predictions.
Two years of continuous measurements of tidal and nontidal variations of gravity in Boulder, Colorado
Authors: van Dam Tonie M. , Francis Olivier
Published: February 2004

We report here on the results of an analysis of 2 years of data from NOAA's superconducting gravimeter located at the Table Mountain Gravity Observatory in Boulder, Colorado. Observed tidal parameters, corrected for ocean loading effects, are compared with theoretical tidal parameters predicted for a non‐hydrostatic inelastic Earth model and demonstrate excellent agreement. Tidal residuals, corrected for polar motion and a linear instrument drift are highly correlated with gravity changes measured by two absolute gravimeters over the same time period. The admittance to local pressure is found to be −0.356 µGal/mbar. However, this admittance factor is found to be seasonally and frequency dependent. Correlations between rainfall events and gravity changes are observed. Attempts to model these gravity changes as exponential functions of time were unsuccessful.
Self‐organization during reactive fluid flow in a porous medium
Authors: Renard F. , Gratier J.‐P. , Ortoleva P. , Brosse E. , Bazin B.
Published: February 2004

When a reactive fluid circulates inside a porous medium it can dissolve some minerals if equilibrium is not reached and modiy the porosity and permeability. The positive feedback between fluid transport and mineral dissolution lead to complex reaction front morphologies such as fingers. Our study is carried out with two objectives: 1) to evaluate experimentally these processes at a decimeter scale, 2) to compare the experiment to a numerical model of water‐rock interaction. The experiment consists of a two‐dimensional porous medium that allows for the dissolution of halite under an imposed fluid flow. The numerical code used solves the equations of reaction and transport in a porous medium. Both experiment and numerical simulation indicate the development of an instability whose propagation rate depends on the rate of water injection raised to a 2/3 power.
A lattice‐gas and lattice Boltzmann study of mixing at continuous fracture Junctions: Importance of boundary conditions
Authors: Stockman Harlan W. , Li Chunhong , Wilson John L.
Published: February 2004

The lattice‐gas automata and lattice Boltzmann (BGK) methods were used to estimate the mixing of fluid streams at a continuous fracture junction, for Peclet number (Pe) from 0 to 1547. Agreement with experimental results is good, particularly at Pe ≤ 25. At low Pe, a large fracture length/width is needed to obtain accurate mixing ratios (Mr). For a 90° intersection of two fractures with equal widths and flow rates, Mr approaches 0.5 (complete mixing) at Pe ≈ 1. At the highest Pe studied, Mr=0.022, in contrast with the streamline routing prediction Mr=0.
HALOE observations of the Arctic Vortex during the 1997 spring: Horizontal structure in the lower stratosphere
Authors: Pierce R. Bradley , Fairlie T. Duncan , Remsberg Ellis E. , Russell James M. , Grose William L.
Published: February 2004

In late March, 1997, HALOE observed very low ozone (less than 1 ppmv at 48OK), low HCl, generally high NOx, and normal levels of H2O within the Arctic vortex. Trajectory mapping techniques show that the lower stratospheric Arctic vortex was locally chemically perturbed during this period. Regions of low HCl and low NOx mixing ratios found within the Arctic vortex indicate that partitioning within the odd chlorine family had been shifted from reservoir species to active species. Low O3 mixing ratios within these regions strongly suggest that chlorine‐catalyzed photochemical destruction of O3 had recently taken place. Regions of low HCl and higher NOx mixing ratios are also observed within the Arctic vortex. Correlations of O3, H2O, NOx and HCl with HF are used to quantify the changes in these constituents during March and early April, 1997. Temporal changes in the correlation of HCl and NOx with HF indicate increases in these species. No trend in the correlations of H2O or O3 with HF was found in the lower stratosphere.
Upper limits to the outflow of ions at Mars: Implications for atmospheric evolution
Authors: Fox J. L.
Published: February 2004

Escape of ions is potentially important for the evolution of volatiles on Mars, but the mechanisms and rates of ion escape processes are not fully understood. Instruments on the Russian Phobos 2 orbiter have, however, measured fluxes of heavy ions apparently of ionospheric origin in the optical shadow of Mars. These ions are assumed to arise from escape processes induced by the interaction of the solar wind with the ionosphere. We determine here upper limits to the ion loss rates by imposing upward flux boundary conditions on models of the low and high solar activity Mars ionosphere. The maximum fluxes obtained for high solar activity are about a factor of 4 larger than the fluxes derived from the Phobos ASPERA measurements, and the major ion is predicted to be O2+ rather than O+. If ions are scavenged at or near their maximum rates, the resulting escape fluxes are significant when compared to other non‐thermal escape mechanisms for heavy atoms.
On Doppler‐spreading models of internal waves
Authors: Broutman Dave , Macaskill C. , McIntyre Michael E. , Rottman James W.
Published: February 2004

Present Doppler‐spreading models for short internal waves in the atmosphere and the ocean either neglect the time dependence of the background long‐wave shear entirely, or ignore time‐dependent effects in their parameterization of dissipation. We use ray and numerical simulations to examine the Doppler spreading of a short internal‐wave packet by an inertia‐wave packet. The results are enough to show that time dependence in the long‐wave shear can make a significant difference to short‐wave behavior, and will need to be taken into account in future modelling efforts.
The missing dimension in Magsat and POGO anomaly studies
Authors: Purucker Michael E. , Sabaka Terence J. , Langel Robert A. , Olsen Nils
Published: February 2004

The development of a comprehensive model of the near‐Earth magnetic field in terms of sources in the core, ionosphere, and magnetosphere has allowed the isolation of heretofore unknown north‐south trending anomalies of lithospheric origin. Previously, along‐track filtering of satellite magnetic field data had been necessary in order to remove unmodeled magnetospheric and ionospheric magnetic fields. These fields change between adjacent passes by tens of nanoTeslas and have wavelengths which overlap the crustal spectrum. An example from Australia illustrates the additional information that can be extracted from the Magsat data set when this ‘missing dimension‧ is included. A north‐south trending low covers most of eastern Australia, in agreement with the aeromagnetic map of Australia. This feature is seen in both the dawn and dusk subsets collected from Magsat. The center of this low is roughly coincident with the Eromanga Basin but extends for almost 2000 km in a N‐S direction. The low corresponds to a region of almost featureless magnetic field on the aeromagnetic map. It is also consistent with an elevated geotherm previously proposed from studies of xenoliths in southeastern Australia. Filtering the new map in a north‐south direction reproduces the previous best estimate of the Australian satellite anomaly field. We expect that this comprehensive model will provide a new window into the magnetic field of the earth's lithosphere. The model continues to be enhanced.
Direct observation of OH production from the ozonolysis of olefins
Authors: Donahue Neil M. , Kroll Jesse H. , Anderson James G. , Demerjian Kenneth L.
Published: February 2004

Ozone olefin reactions may be a significant source of OH in the urban atmosphere, but current evidence for OH production is indirect and contested. We report the first direct observation of OH radicals from the reaction of ozone with a series of olefins (ethene, isoprene, trans‐2‐butene and 2,3 dimethyl‐2‐butene) in 4–6 torr of nitrogen. Using LIF to directly observe the steady‐state of OH produced by the initial ozone‐olefin reaction and subsequently destroyed by the OH‐olefin reaction, we are able to establish OH yields broadly consistent with indirect values. The identification of the OH is unequivocal, and there is no indication that it is produced by a secondary process. To support these observations, we present a complete ab‐initio potential energy surface for the O3‐ethene reaction, extending from the reactants to available products.
Accurate azimuth estimates from a large aperture hydrophone array using T‐phase waveforms
Authors: Hanson Jeffrey A. , Given Holly K.
Published: February 2004

A simple method is described whereby station‐to‐source azimuths are estimated by fitting a plane wave to envelope functions of T‐phases observed on a 5‐element hydrophone array around Ascension Island, South Atlantic Ocean. When applied to a data set of 55 earthquakes of known location ranging between 2 and 45 degrees distance from Ascension Island, estimated azimuths have a standard deviation of 3.3 degrees from reference azimuths when 3 or more hydrophone elements are used. The standard deviation decreases to 1.8 degrees if T‐phase data from all 5 hydrophone elements are used. We also investigate variations in predicted errors for different array geometries and arrival azimuths. This simple method is amenable to automation and can easily be incorporated into a global monitoring system.
The upper ocean heat balance in the western equatorial Pacific warm pool during September–December 1992
Authors: Cronin Meghan F. , McPhaden Michael J.
Published: February 2004

The upper ocean heat budget in the western equatorial Pacific warm pool is analyzed for a 3‐month period from mid‐September through mid‐December 1992 using data from the Tropical Atmosphere Ocean (TAO) array enhanced for the Coupled Ocean Atmosphere Response Experiment. Surface heat and moisture fluxes were measured from a centrally located TAO current meter mooring at 0°, 156°E. Lateral heat advection was estimated using temperature data from moorings within 150–250 km of 0°, 156°E. Mixing was estimated as the residual of the heat balance and compared to estimates of mixing based on the Niiler‐Kraus parameterization of entrainment mixing. The analysis shows that for the diurnal cycle and for daily to weekly timescale variations like those associated with westerly wind bursts, the sea surface temperature (SST) variability is to a large extent controlled by shortwave radiation and latent heat flux. However, three‐dimensional processes can also be important. For example, in early October 1992, the SST at 0°, 156°E increased by nearly 1°C in 7 days due predominately to westward heat advection. Also, the dynamical response to a moderately strong wind burst in late October 1992 included a deepening of the pycnocline, which affected the rate of entrainment cooling, and a reversal of the surface current, which affected the zonal heat advection. The importance of three‐dimensional processes (particularly heat advection) in the warm‐pool heat balance during this 3‐month study period is confirmed by comparing the observed temperature variability with that simulated by a one‐dimensional mixed layer model.
Indonesian throughflow in a coupled general circulation model
Authors: Schneider Niklas , Barnett Tim P.
Published: February 2004

The Indonesian throughflow is analyzed in an extended simulation with a coupled ocean‐atmosphere model. The model, developed by the Max‐Planck‐Institut für Meteorologie, Hamburg, Germany, combines an atmospheric general circulation model at T42 resolution (2.8° latitude by 2.8° longitude) and a primitive equation ocean model with zonal resolution of 2.8° and a meridional resolution of 0.5° in the tropics and is coupled without flux correction equatorward of a latitude of 60°. The onset and strength of the monsoon in the Indonesian waters agree well with climatology, and many aspects of the observed temperature fields in the eastern Indian Ocean and Timor Seas are found in simulation. Differences between simulation and observations of temperature occur in mean and seasonal cycles in the far western Pacific. The annual cycles of sea level along the coast of Sumatra and Java are simulated satisfactorily. The simulated throughflow transports on average 13.8 Sv (106m3S−1) from the Pacific to the Indian Ocean. The vertically averaged (barotropic) component of the throughflow has a seasonal range of 13.1 Sv and is weakest in February and strongest in July. In contrast, deviations from the vertical average of the throughflow (baroclinic) are strongest in March and September. The average and seasonal cycle of the barotropic component of the throughflow are forced by winds over the Pacific and along the western coasts of Australia and South America, as described by the island rule. For closed Torres Strait, the contribution of the average bottom pressure torque is small, and friction closes the vorticity balance. For annual timescales, baroclinic flows affect the throughflow transport through the bottom pressure torque. The annual cycle of the baroclinic component of the throughflow is forced predominantly by winds over the Indonesian Seas. The throughflow exports 0.9 PW of heat from the Pacific into the Indian Ocean and is an important heat sink for the western Pacific. The throughflow is a major heat source for the Indian Ocean and is associated with reversal of the divergence of the meridional transport of heat south of 10°S that is balanced by heat fluxes from the ocean to the atmosphere.
The carbon dioxide system in the Atlantic Ocean
Authors: Lee Kitack , Millero Frank J. , Wanninkhof Rik
Published: February 2004

During the National Oceanic and Atmospheric Administration's Ocean Atmosphere Carbon Exchange Study expedition in the eastern North Atlantic in summer 1993, measurements of four CO2 parameters, along with hydrographic properties, were made: fugacity Of CO2, ƒCO2 (measured at 20°C and in situ);pH (measured at 20°C); total inorganic carbon, TCO2; and total alkalinity, TA. The major objective of this cruise was to establish a benchmark against which future measurements of the transient invasion of CO2 can be made. The large‐scale distributions of surface water CO2 parameters were related to temperature and salinity in this region. The subsurface TA and TCO2 measurements were fitted to multiple linear functions of salinity, in situ temperature, apparent oxygen utilization, and silicate. The measurements of the inorganic carbon system were also used to examine the internal consistency of the carbonate system in this area. The measurements were internally consistent to ±1.3% in ƒCO2, ±0.006 in pH, ±3 μmol kg−1 in TCO2, and ±3 μmol kg−1 in TA if proper carbonic acid dissociation constants are used for different input combinations. The thermodynamic constants of Goyet and Poisson [1989], Roy et al. [1993], Millero [1995], and Lee and Millero [1995] were most consistent with the measurements of pH (at 20°C), TCO2, and TA. However, if ƒCO2 (at 20°C) is used in thermodynamic calculations, the constants of Mehrbach et al. [1973] gave the best representation of measurements. The constants of Lee and Millero [1995] were also reasonable agreement with these measurements.
Textures and fabrics in the GRIP ice core
Authors: Thorsteinsson Thorsteinn , Kipfstuhl Josef , Miller Heinz
Published: February 2004

A comprehensive study of textures and fabrics has been carried out on the Greenland Ice Core Project (GRIP) ice core. Crystal sizes and c axis orientations have been measured on thin sections with conventional techniques, yielding new information on the growth, rotation and recrystallization of ice crystals in the Greenland Ice Sheet. Normal grain growth is found to persist to a depth of 700 m in the core, where the onset of polygonization due to increasing strain prevents a further increase in grain size in the Holocene ice. Smaller crystals are observed in the Wisconsin ice, larger crystals are found in the Eemian ice, and the crystal size is found to vary with climatic parameters in these periods. This dependence, which probably results from variable impurity content in the ice, persists to a depth of 2930 m. Coarse‐grained ice, probably resulting from rapid growth of crystals at comparatively high temperatures, is found in the lowest 100 m of the core. The data on c axis orientations reveal a steady evolution of the fabric from random near the surface to a strong single maximum in the lower part of the ice sheet. A significant strengthening is not observed at the Holocene‐Wisconsin transition. The fabric development indicates that vertical compression at the ice divide is the main mode of deformation down to a depth of 2850 m. The evolution toward a single maximum fabric hardens the ice against vertical compression but softens it against simple shear. Evidence of simple shear deformation is clearly observed between 2850 m and 2950 m depth. Stretched fabrics in coarse‐grained ice in the lowest 100 m could be due to tensional stresses; this ice is unlikely to be undergoing any significant horizontal deformation at the present time.
Upper ocean thermohaline fields near 2°S, 156°E, during the Tropical Ocean‐Global Atmosphere‐Coupled Ocean‐Atmosphere Response Experiment, November 1992 to February 1993
Authors: Huyer Adriana , Kosro P. Michael , Lukas Roger , Hacker Peter
Published: February 2004

Zonal and meridional Seasoar sections centered at 1°50′S, 156°06′E were repeated >30 times in three 20‐day periods between November 13, 1992, and February 15, 1993. Both sections were 130 km long, and sampling depth was 0–280 m, with a vertical resolution of ∼2 dbar (2×104 Pa) and a horizontal resolution of ∼3 km. The observed fields are complex and variable and are summarized graphically in several forms. Characteristics of the near‐surface layer varied with the local winds which were variable and weak (<6 m s−1) during the first 20‐day period, strong and westerly (>10 m s−1) during much of the second, and moderate and westerly (4–10 m s−1) during most of the third. Near‐surface temperatures were warmest (up to 30°C) during the first period and coldest (often <29°C) during the second. Thermal stratification in the near‐surface layer was strong under weak winds and weak under strong and moderate winds. Except during and after heavy rainfall, salinity stratification in the near‐surface layer was generally weak. Surface salinity generally decreased toward the north. The depth of the surface isopycnal layer was often but not always limited by salinity stratification; the surface isohaline layer was shallower than the top of the thermocline throughout. Strong lateral temperature and salinity gradients occurred on a few occasions. Increased wind stress was associated with lateral homogenization as well as vertical mixing. Structure and water properties of the thermocline also varied between cruises and within each cruise. The upper thermocline was shallowest in late January after prolonged easterly winds. Isotherms in the upper and midthermocline (20°–25°C) sloped generally upward to the north, while those in the lower thermocline (12°–14°C) sloped down to envelop the core of the Equatorial Undercurrent, which shoaled (from 225 to 160 m) and warmed (from 15°to 20°C) between the first and last survey periods. Mesoscale and fine‐scale water mass features were usually recognizable in sections less than a few days apart and migrated eastward at about 0.3 m s−1. There is a remarkably high degree of nonstationarity in these thermohaline fields from the Warm Pool of the western Pacific Ocean.
Air mass trajectories to Summit, Greenland: A 44‐year climatology and some episodic events
Authors: Kahl Jonathan D. W. , Martinez Dewayne A. , Kuhns Hampden , Davidson Clifford I. , Jaffrezo Jean‐Luc , Harris Joyce M.
Published: February 2004

The seasonal variation in atmospheric transport patterns to Summit, Greenland, is examined using a 44‐year record of daily, 10‐day, isobaric back trajectories at the 500‐hPa level. Over 24,000 modeled trajectories are aggregated into distinct patterns using cluster analysis. Ten‐day trajectories reaching Summit are longest during winter, with 67% extending upwind (westward) as far back as Asia or Europe. Trajectories are shortest during summer, with 46% having 10‐day origins over North America. During all seasons a small percentage (3–7%) of trajectories originate in west Asia/Europe and follow a meridional path over the Arctic Ocean before approaching Summit from the northwest. Trajectories at the 700‐hPa level tend to be shorter than at 500 hPa, with many of the 700‐hPa trajectories from North America tracking over the North Atlantic and approaching Summit from the south. The long‐range transport climatology for Summit is similar to a year‐round climatology prepared for Dye 3, located 900 km to the south [Davidson et al., 1993b]. An analysis of several aerosol species measured at Summit during summer 1994 reveals examples of the usefulness and also the limitations of using long‐range air trajectories to interpret chemical data.
Subtidal circulation on the Scotian Shelf: Assessing the hindcast skill of a linear, barotropic model
Authors: Thompson Keith R. , Sheng Jinyu
Published: February 2004

Currents measured during the winter of 1985–1986 by four moorings on the inner Scotian Shelf are used to assess the hindcast skill of a three‐dimensional circulation model forced by local wind stress and coastal sea level. The model is linear and barotropic. The integration scheme is based on the modification of the Galerkin spectral method proposed recently by Sheng and Thompson [1993]. The skill of the model is measured by the variance of the hindcast errors divided by the variance of the observations (henceforth γ2). The model is most effective within 30 km of shore (0.51≤γ2≤0.66). At the mooring in the Nova Scotia Current, a surface intensified southwestward jet with its center approximately 50 km from shore, the model fails to capture the bulk of the variance at current meters within 70 m of the surface (0.81≤γ2≤0.87). The skill of the model is lowest at the mooring 65 km from shore (0.92≤γ2≤0.94). To put these measures of skill into perspective, the currents are hindcast using a linear statistical model with the same inputs as the circulation model. The statistical model is optimal in the sense no other linear model with these inputs can achieve a lower hindcast error variance. For half of the current meters within 30 km of shore and two in the Nova Scotia Current the skill of the circulation model is not significantly lower than that of the statistical model. The largest discrepancies in the skill of the two models are found at the offshore mooring. We show that the suboptimal performance of the circulation model is due in part to the assumption of a spatially uniform wind field. We speculate that another contributing factor is the assumed form of the sea level profile along the open boundary that is upstream in the sense of coastal trapped wave propagation. Finally, the statistical model is used to estimate the increase in skill of the circulation model that may result from the assimilation of hydrographic data and additional coastal sea levels.