bluuebunny/crossref_metadata_2025 huggingface dataset:
On the dissipation of magnetic fluctuations in the solar wind
Authors: Li Hui , Gary S. Peter , Stawicki Olaf
Published: February 2004

Magnetic fluctuations in the solar wind show an f−5/3 power‐law spectrum below the Doppler‐shifted proton cyclotron frequency but steepen to f−s with s ≥ 3 for higher frequencies. The origin of this steepening, however, remains unclear. The purpose of this study is to evaluate critically the often‐employed assumption that the steepening is caused by dissipation via kinetic wave damping. For both Alfvén and magnetosonic waves and for a broad range of propagation angles, we show that the wave damping rate usually increases very strongly with wavenumber k. Consequently, the wave energy transfer always becomes slower than the damping at sufficiently high k, resulting in a strong cutoff in the power spectra rather than a steepened power‐law. This result suggests that collisionless dissipation can not be the only physical basis for explaining the steepening. Furthermore, it casts serious doubts on the basic approach of treating magnetic fluctuations as an ensemble of linear waves.
Effect of electron resonant heating on the kinetic evolution and acceleration of the solar wind
Authors: Tam Sunny W. Y. , Chang Tom
Published: February 2004

We investigate the effects of electron cyclotron resonant heating on the kinetic evolution and acceleration of the fast solar wind. A previous study has shown that kinetic wave‐particle interactions due to ion resonant heating, may account for the bulk acceleration of the solar wind, the preferential heating of the helium ions over the protons, as well as the occasionally observed double‐peaked proton velocity distributions. The model followed the evolution of the particle distributions along an inhomogeneous field line under the effects of ion heating, Coulomb collisions, and an ambipolar electric field that was consistent with the distributions themselves. This study extends the model to take into account also the effect of electron cyclotron resonant heating. Our parametric study shows that the electron heating does not change the solar wind qualitative features described above. However, the wave‐particle interaction increases the ambipolar electric field, thereby enhancing the solar wind velocity.
Dual influence of Atlantic and Pacific SST anomalies on the North Atlantic/Europe winter climate
Authors: Cassou Christophe , Terray Laurent
Published: February 2004

Clustering analyses are used in both NCEP Reanalyses and model simulations to identify relationships between the low frequency variability of the zonal wind jet at 200hPa (U200) over the North Atlantic‐Europe domain and the geographical distribution of the Sea Surface Temperature (SST) anomalies. For winter months over the 1959‐1998 period, the U200 signature of the two phases of the North Atlantic Oscillation (NAO) is captured from NCEP in a cluster pair associated with the North Atlantic SST tripole. The classification also extracts a “La Niña” mode related to a strong ridge off Europe and reduced jet over the Azores. Model results confirm this dual oceanic association while exaggerating the ENSO influence. The role of the Atlantic SSTs is confirmed in model experiments where climatological SSTs are prescribed in the other basins. Tropical anomalies dominate the Atlantic SST signals and are linked to fluctuations of the jet consistently with the NAO phase.
Variations of ionospheric total electron content during the Chi‐Chi Earthquake
Authors: Liu J. Y. , Chen Y. I. , Chuo Y. J. , Tsai H. F.
Published: February 2004

On 20 September 1999 UT (21 September in local time, LT) a large earthquake Mw=7.7 struck central Taiwan near the small town of Chi‐Chi. The greatest plasma frequency in the ionosphere, foF2, observed by the Chung‐Li ionosonde (25.0°N, 121.2°E) reveals three clear precursors at 1, 3, and 4 days prior to the earthquake. This paper examines the ionospheric total electron content (TEC) observed by a network of the global positioning system (GPS) receivers in Taiwan area. It is found that variations in foF2 and overhead TEC recorded at Chung‐Li have a similar tendency. Combining the data of the network of 13 GPS receivers, time, and spatial variations of TEC prior to the Chi‐Chi earthquake are examined. Results show that the equatorial anomaly crest moves equatorward and its TEC value significantly decreases 1, 3, and 4 days before the earthquake. A comparison between the disturbed and reference (previous 15‐day median) days confirms that TEC decreases significantly around the epicenter in the afternoons of these days. Finally, possible mechanisms are proposed and discussed.
Shock surfing vs. shock drift acceleration
Authors: Lever Edward L. , Quest Kevin B. , Shapiro Vitali D.
Published: February 2004

We numerically investigate the pre‐injection mechanism by which pickup ions approaching quasi‐perpendicular shocks may be accelerated above the threshold velocity required to begin diffusive shock acceleration. We demonstrate that three distinct mechanisms contribute to the acceleration and that they operate on disjoint subsets of the pickup ion population. We quantitatively compare the efficiency of each mechanism as a function of shock Mach number, pickup ion mass and shock ramp width and show that shock surfing predominates below a critical ramp width.
Large electric potential perturbations in PMSE during DROPPS
Authors: Holzworth R. H. , Pfaff R. F. , Goldberg R. A. , Bounds S. R. , Schmidlin F. J. , Voss H. D. , Tuzzolino A. J. , Croskey C. L. , Mitchell J. D. , von Cossart G. , Singer W. , Hoppe U.‐P. , Murtagh D. , Witt G. , Gumbel J. , Friedrich M.
Published: February 2004

Comprehensive vector electric field detectors were flown during the DROPPS rocket experiment to study electrodynamic processes near the mesopause. This paper will discuss the first DROPPS rocket flight, which penetrated a strong polar mesosphere summer echo (PMSE) event that also included a weak noctilucent cloud (NLC) layer. During this flight, strong potential perturbations were observed which at first appeared to be caused by large geophysical electric fields. However, as shown here, the potential perturbations resulted from the rocket wake, and were not caused by an environmental electric field. This result strongly differs from other previous in‐situ experiments, which have reported large electric fields in PMSE regions.
Assessment of the effect of the Montreal Protocol on atmospheric ozone
Authors: Egorova Tatiana A. , Rozanov Eugene V. , Schlesinger Michael E. , Andronova Natalia G. , Malyshev Sergey L. , Karol Igor L. , Zubov Vladimir A.
Published: February 2004

Ozone depletion is a major global scientific and environmental problem. One of its causes is the anthropogenic increase of CFCs in the atmosphere, which results in the enhancement of the concentration of reactive chlorine in the stratosphere. To reduce the influence of anthropogenic ozone‐depleting substances, the Montreal Protocol was agreed by Governments in 1987, with several Amendments adopted later. What has been the result of the Montreal Protocol and its Amendments (MPA)? Here we present the first 3D‐model assessment of the effect of the MPA on atmospheric ozone which has been performed with the University of Illinois at Urbana‐Champaign (UIUC) Atmospheric Chemical Transport Model (ACTM). We find that the MPA has saved up to 2% of the present‐day total ozone in the Northern Hemisphere and about 5% in the Southern Hemisphere. Our calculations also show that CFCs do not play the major role in the observed recent total ozone variations.
The Pacific Plume as seen by S, ScS, and SKS
Authors: Bréger Ludovic , Romanowicz Barbara , Ng Christine
Published: February 2004

The forward modeling of S‐SKS and ScS‐S differential travel time residuals sensitive to structure beneath a localized region of the central Pacific suggests the presence of two anomalous domains: first a broad zone which becomes thinner as it extends into the mid‐mantle, where the S‐velocity is reduced by −2 to −4%, and which is deflected to the South‐East as it “rises” towards the surface; adjacent to it, a smaller domain, where the S‐velocity is about 4% higher. These strong velocity anomalies are likely the results of chemical heterogeneity that may involve subducted material, and partial melting. Strong heterogeneity appears to extend, at least locally, well above D', but the morphology of the anomalous domains is more reminiscent of localized rising or sinking currents rather than of a relatively uniform and thick geochemical reservoir.
The dominant mechanisms of variability in Atlantic Ocean Heat Transport in a Coupled Ocean‐Atmosphere GCM
Authors: Dong B.‐W. , Sutton R. T.
Published: February 2004

The variability of the Atlantic meridional ocean heat transport (OHT) has been diagnosed from a simulation of a coupled ocean‐atmosphere general circulation model (GCM), and the mechanisms responsible for this variability have been elucidated. Interannual variability is dominated by windstress‐driven Ekman fluctuations, which account for 50.3% of the OHT variance. By contrast, decadal and multidecadal variability in Atlantic OHT is dominated by a mixed thermohaline/gyre mode driven by variations in buoyancy fluxes and windstress curl. It accounts for 55.6% of low pass filtered OHT variance. The North Atlantic Oscillation (NAO) has a significant role in both the interannual mode and the low frequency mode, but it is not the only important driver. A notable feature of both modes is significant changes in the tropical atmosphere and ocean. We highlight a number of potential mechanisms involved in the tropical‐extratropical teleconnections.
Simulation of prognostic tsunamis on the Korean Coast
Authors: Choi Byung Ho , Hong Sung Jin , Pelinovsky Efim
Published: February 2004

Prognostic characteristics of potential tsunamis in the East (Japan) Sea are discussed. Zones of tsunami sources for potential danger are selected using the seismic gap theory. Numerical model based on linear long wave theory is used to simulate the tsunami propagation from 28 potential tsunamigenic earthquakes. As a result, the synthetic tsunami catalogue is obtained for each coastal point along the east Korean coast. Statistical analysis of data for tsunami wave height distribution can be described by the log‐normal curve. On the average, maximal value of tsunami wave height in each point does not exceed the mean value of computed wave heights by more than six times.
Plate convergence and long‐term crustal deformation in central Japan
Authors: Heki Kosuke , Miyazaki Shin'ichi
Published: February 2004

Surveys by continuous Global Positioning System in and around Japan revealed that the Amurian Plate collides with the North American Plate in central Japan by ∼2 cm/yr. Long‐term crustal deformation seems to be influenced mainly by this collision although subduction of oceanic plates governs short‐term elastic deformation over the arc. Here we study the long‐term deformation field by carefully removing the short‐term signals inferred from a‐priori plate convergence vectors and coupling strengths predicted by a thermal model. The obtained field shows that the change in velocities occurs along the longitude 135° ∼ 137°, and there exist a relatively rigid block and zones accommodating strains. Characteristic compressional deformation is found northwest of Izu due possibly to the collision of the Izu‐Bonin arc with Honshu. Plate convergence rate along the Nankai‐Suruga Trough is considerably smaller in eastern parts, due partly to the transition from the Amurian to the North American Plate of the landward side, and partly to the motion of the Izu Microplate relative to the Philippine Sea Plate. This accounts for longer recurrence intervals of interplate earthquakes in the Suruga Trough where the Tokai earthquake is anticipated to occur.
Electrical structure of PMSE and NLC regions during the DROPPS Program
Authors: Croskey Charles L. , Mitchell John D. , Friedrich Martin , Torkar Klaus M. , Hoppe Ulf‐Peter , Goldberg Richard A.
Published: February 2004

The electrical structure of NLC/PMSE regions was investigated by different rocket‐borne in situ probe techniques as part of the DROPPS program. Gerdien condenser measurements of very small mobility values suggest concentrations of positively charged aerosols/dust comparable to the density of more mobile positive ions at PMSE/NLC altitudes. Relative electron density values and associated large‐ and small‐scale vertical structure measured by DC Langmuir probes revealed very deep (by a factor of 50) biteouts in PMSE/NLC regions. These biteouts were seen during strong and weak NLC conditions when PMSEs were either present or absent.
Trends in upper‐tropospheric humidity
Authors: Bates John J. , Jackson Darren L.
Published: February 2004

Water vapor is the most radiatively active greenhouse gas, and the process of water‐vapor feedback may significantly amplify global warming induced by anthropogenic greenhouse gasses. Satellite radiance observations from the past 20 years, which are sensitive to the water vapor and temperature of the upper troposphere, provide the first global observations of trends in upper‐tropospheric humidity. These decadal trends are strongly positive in the deep tropics, negative in the Southern Hemisphere subtropics and midlatitudes, and of mixed sign in the Northern Hemisphere subtropics and midlatitudes. The trends are shown to be consistent with atmospheric circulation changes observed in the past 20 years, including a tendency toward more El Niño‐Southern Oscillation warm events and changes in transient eddy activity in the subtropics.
Hydroacoustic detection of submarine landslides on Kilauea Volcano
Authors: Caplan‐Auerbach Jacqueline , Fox Christopher G. , Duennebier Frederick K.
Published: February 2004

Landslides produced at the site where lava flows into the ocean at Kilauea volcano have been detected hydroacoustically. Up to 10 landslides per day were detected by a hydrophone on the Hawaii Undersea Geo‐Observatory (HUGO), located 50 km south of the entry site. The largest of these landslides, partly subaerial events known as bench collapses, were detected by a network of hydrophones in the eastern Pacific, 5000–7000 km away from the source. The landslides display a characteristic spectral signature easily recognizable among other signals such as earthquake T‐phases and anthropogenic noises. The fact that signals are detected at great distances suggests that hydroacoustic detection of landslides could be a powerful tool in tsunami monitoring and modeling efforts.
The Mg II index: A proxy for solar EUV
Authors: Viereck Rodney , Puga Lawrence , McMullin Donald , Judge Darrell , Weber Mark , Tobiska W. Kent
Published: February 2004

This paper shows that the Mg II core‐to‐wing ratio is a better proxy for Solar Extreme Ultraviolet (EUV) radiation, between 25 and 35 nm than is the F10.7 index. The He II 30.4 nm solar emission, by itself, is an important source of energy for the upper atmosphere. We will compare the NOAA Mg II Index and the F10.7 Index to the He II 30.4 data taken with the CELIAS/Solar EUV Monitor (SEM) on the Solar and Helospheric Observatory (SOHO).
Coexisting shear‐ and compressional‐wave seismic velocity discontinuities beneath the central Pacific
Authors: Russell Sara A. , Reasoner Colin , Lay Thorne , Revenaugh Justin
Published: February 2004

Stacking of broadband shear waves (S) and short‐period compressional waves (P) provides compelling evidence for the existence of a localized discontinuous increase in both S and P wave velocity 230 km above the core‐mantle boundary (CMB) beneath the central Pacific. Modelling indicates a 1.7% increase in S velocity (VS) and a 0.75% increase in P velocity (VP). Similar features have been detected intermittently on a global basis, but seldom with S and P structure being resolved in the same location. Previous evidence for anisotropy near the CMB beneath the central Pacific suggests that the discontinuity may be related to anisotropic fabrics induced by flow in the thermal boundary layer above the core.
Recent northern hemisphere snow extent: A comparison of data derived from visible and microwave satellite sensors
Authors: Armstrong R. L. , Brodzik M. J.
Published: February 2004

During the past four decades much important information on Northern Hemisphere snow extent has been provided by the NOAA weekly snow extent charts derived from visible‐band satellite imagery. Passive microwave satellite remote sensing can enhance snow measurements based on visible data alone because of the ability to penetrate clouds, provide data during darkness and the potential to provide an index of snow depth or water equivalent. We compare the fluctuation of Northern Hemisphere snow cover over the past twenty years using these two satellite remote sensing techniques. Results show comparable inter‐annual variability with similar long‐term hemispheric‐scale trends indicating decreases in snow extent of approximately 0.2 percent per year. The passive microwave snow algorithm applied in this study indicates less snow‐covered area than the visible data during fall and early winter when the snow is shallow. New algorithms designed to reduce this apparent error are being developed and tested.
Source and path of magma for volcanoes in the subduction zone of northeastern Japan
Authors: Wyss M. , Hasegawa A. , Nakajima J.
Published: February 2004

The assumption that the source of magma for volcanoes in subduction zones is located in the mantle immediately above the top of the subducting slab, at approximately 100 km depth and straight beneath the volcanoes is incorrect in northeastern Japan. The combination of evidence from velocity tomography in the mantle wedge above the slab and mapping of earthquake size distribution within it strongly points to a source of fluids at the top of the slab at 140 to 150 km depth, from where material rises along an inclined path to the volcanoes.
Photolysis frequency measurements at the South Pole during ISCAT‐98
Authors: Lefer B. L. , Hall S. R. , Cinquini L. , Shetter R. E.
Published: February 2004

Spectrally resolved actinic flux measurements from 280 to 420 nm were made on the roof of the South Pole Atmospheric Research Observatory during December 1998. Photolysis frequencies of O3→O2 + O(¹D) and NO2→ NO + O(³P) were calculated from the measured actinic flux spectra and established absorption cross‐section and quantum yield data. The average values of jNO2 and jO(¹D) were observed to be 1.1 × 10−2 ± 1.3 × 10−3 s−1 and 9.0 × 10−6 ± 1.4 × 10−6 s−1, respectively. The variability of jNO2 was due to decreases in direct UV‐A radiation during overcast conditions, while the larger variability observed for jO(¹D) was primarily the result of changes in the overhead ozone column. Modeled photolysis frequencies were obtained using the NCAR TUV radiation model. The downwelling modeled and measured photolysis frequencies agree well during clear sky conditions. As a consequence of the high albedo and 24 hours of sunlight at this time of the year, the daily averaged jNO2 measured at the South Pole was three times higher than predicted for a tropical location.
Tropical Atlantic air‐sea interaction and its influence on the NAO
Authors: Okumura Yuko , Xie Shang‐Ping , Numaguti Atusi , Tanimoto Youichi
Published: February 2004

An atmospheric general circulation model (AGCM) is forced with a prescribed SST dipole anomaly in the tropical Atlantic to investigate the cause of cross‐equatorial SST gradient (CESG) variability and its teleconnection to the extratropics. The model response bears a striking resemblance to observations in both the tropics and extratropics. The tropical response is robust and can act to reinforce the prescribed SST anomalies through wind‐induced evaporation. A new feedback mechanism involving low‐level stratiform clouds in the subtropics is also identified in the model and observations. The tropical SST dipole forces a barotropic teleconnection into the extratropics that projects onto the North Atlantic Oscillation (NAO). It further induces the extratropical portion of the North Atlantic SST tripole when the AGCM is coupled with an ocean mixed layer model. CESG variability thus appears to be the centerpiece of a pan‐Atlantic climate pattern observed to extend from the South Atlantic to Greenland.
On the relations among CFC derived water mass ages
Authors: Sonnerup Rolf E.
Published: February 2004

In waters formed before ∼1975, Chlorofluorocarbon (CFC) −12 ventilation ages are usually older than CFC‐11 ages, which are in turn older than CFC ratio ages. A simple model shows that these discrepancies result from the effects of mixing on CFC ages, which are biased due to the nonlinear increases in atmospheric CFCs before 1975. CFC‐11 ages are biased younger than CFC‐12 ages because CFC‐11's relative increase rate in the atmosphere was higher. In the model results, ideal ages are consistently older than CFC ages in waters ventilated prior to ∼1975. The differences between CFC ages and ideal ages are reflected in the discrepancies among CFC‐11, CFC‐12, and CFC ratio ages, however, and increase with increasing importance of diffusive versus advective tracer transport. Thus it may prove possible to estimate the magnitude of CFC age mixing biases based on differences measured between CFC‐11, CFC‐12, and CFC ratio ages.
Indirect long‐term global radiative cooling from NOx Emissions
Authors: Wild Oliver , Prather Michael J. , Akimoto Hajime
Published: February 2004

Anthropogenic emissions of short‐lived, chemically reactive gases, such as NOx and CO, are known to influence climate by altering the chemistry of the global troposphere and thereby the abundance of the greenhouse gases O3, CH4 and the HFCs. This study uses the characteristics of the natural modes of the tropospheric chemical system to decompose the greenhouse effect of NOx and CO emissions into (i) short‐lived modes involving predominantly tropospheric O3 and (ii) the long‐lived mode involving a global coupled CH4‐CO‐O3 perturbation. Combining these two classes of greenhouse perturbations—large, short‐lived, regional O3 increases and smaller, long‐lived, global decreases in CH4 and O3—we find that most types of anthropogenic NOx emissions lead to a negative radiative forcing and an overall cooling of the earth.
Emission cross section of O I (135.6 nm) at 100 eV resulting from electron‐impact dissociative excitation of O2
Authors: Noren C. , Kanik I. , Ajello J. M. , McCartney P. , Makarov O. P. , McClintock W. E. , Drake V. A.
Published: February 2004

In this Letter, we report for the first time, the ratio of the O I (135.6 nm)/O I (130.4 nm) absolute emission cross sections from electron‐impact dissociative excitation of O2 at 100 eV using facilities located at the University of Colorado, Laboratory for Atmospheric and Space Physics (LASP). The O I (135.6 nm) emission glow produced in the laboratory from the long‐lived transition O I g³P ← 5S° was measured in a large collision chamber (1m diameter) with a long focal length (50 cm) electrostatic electron gun. The ratio of the absolute emission cross sections of the O I (135.6 nm) and O I (130.4 nm) features resulting from electron‐impact dissociative excitation of O2 at 100 eV was found to be 2.3±0.6. From this ratio, the absolute emission cross section for the O I (135.6 nm) feature at 100 eV electron‐impact energy was determined to be (6.4±2.2)×10−18 cm². The O I (135.6 nm) cross section reported here can be used to better understand the recent Hubble Space Telescope observations of the O I (130.4 nm) and O I (135.6 nm) emission intensities from Ganymede [Feldman et al., 2000] and Europa [Hall et al., 1995].
The eastern end of the Pyrenees: Seismic features at the transition to the NW Mediterranean
Authors: Gallart J. , Díaz J. , Nercessian A. , Mauffret A. , Reis T. Dos
Published: February 2004

The deep crustal features at the transition from the Pyrenean range to the NW Mediterranean basin have been investigated by onshore/offshore recording of LIgurian SArdinian (LISA) seismic profiles. The predominance in this area of the Neogene extensional tectonics over the Paleogene compressional one is revealed from the present‐day deep structure sampled by the new wide‐angle data. The existence of a crustal root beneath the Pyrenean Axial Zone and the outstanding differences in Moho depths between the Iberian and European domains, well established from previous seismic studies on central and western Pyrenees, are not observed anymore at the easternmost part of the range. This area is marked by a continued crustal thinning seawards (the Moho rises about 10 km along distances of 60 km) that affects already the mainland. Further evidences on lateral variations and topography of the crust‐mantle boundary are indicative of the extent of the different tectonic episodes.
Ozone loss episodes in the free Antarctic troposphere, suggesting a possible climate feedback
Authors: Roscoe H. K. , Kreher K. , Friess U.
Published: February 2004

Sudden loss of tropospheric ozone well above the boundary layer was observed on three occasions at two coastal sites in Antarctica in spring 1995. Back trajectories show that the air sampled the boundary layer near the northern edge of the sea ice (1000 km from the coast) between 3 and 5 days previously. Enhanced BrO observed over sea ice in spring suggests that such ozone loss is common offshore, hence it may cause a small climate effect whose sign would create positive feedback, if sea ice reduced during warming.
Unexpected high levels of NO observed at South Pole
Authors: Davis D. , Nowak J. B. , Chen G. , Buhr M. , Arimoto R. , Hogan A. , Eisele F. , Mauldin L. , Tanner D. , Shetter R. , Lefer B. , McMurry P.
Published: February 2004

Reported here are the first Austral summer measurements of NO at South Pole (SP). They are unique in that the levels are one to two orders of magnitude higher (i.e., median, 225 pptv) than measured at other polar sites. The available evidence suggests that these elevated levels are the result of photodenitrification of the snowpack, in conjunction with a very thin atmospheric mixing depth. Important chemical consequences included finding the atmospheric oxidizing power at SP to be an order of magnitude higher than expected.
Crustal structure beneath southern Africa and its implications for the formation and evolution of the Kaapvaal and Zimbabwe cratons
Authors: Nguuri T. K. , Gore J. , James D. E. , Webb S. J. , Wright C. , Zengeni T. G. , Gwavava O. , Snoke J. A. ,   Kaapvaal Seismic Group
Published: February 2004

The formation of Archean crust appears to involve processes unique to early earth history. Initial results from receiver function analysis of crustal structure beneath 81 broadband stations deployed across southern Africa reveal significant differences in the nature of the crust and the crust‐mantle boundary between Archean and post‐Archean geologic terranes. With the notable exception of the collisional Limpopo belt, where the crust is thick and the Moho complex, the crust beneath undisturbed Archean craton is typically thin (∼35–40 km), unlayered, and characterized by a strong velocity contrast across a relatively sharp Moho. This crustal structure contrasts markedly with that beneath post‐Archean terranes and beneath Archean regions affected by large‐scale Proterozoic events (the Bushveld complex and the Okwa/Magondi belts), where the crust tends to be relatively thick (∼45–50 km) and the Moho is complex.
First detection of absolute gravity change caused by earthquake
Authors: Tanaka Yoshiyuki , Okubo Shuhei , Machida Morito , Kimura Isao , Kosuge Toshihiro
Published: February 2004

Unequivocal coseismic gravity change was detected for the first time by absolute gravimetry. The measurements were done just one day before and only 7 days after a M6.1 earthquake (M6.1). The absolute gravity change was −6 microgal, significantly larger than the observational error of about 1 microgal. Of particular interest is that the observed spatial gravity variations agree remarkably well with those expected from an elastic dislocation model constructed on displacement data alone. The result strongly encourages us to perform a simultaneous inversion of both gravity and displacements to have better insight of earthquakes.
Isothermal remanent magnetization of Greenland ice: Preliminary results
Authors: Lanci Luca , Kent Dennis V. , Biscaye Pierre E. , Bory Aloys
Published: February 2004

The magnetic mineral content of wind‐transported dust should reflect atmospheric transport dynamics and conditions in its source areas, and could thus be used as an environmental proxy. To test the feasibility of determining the magnetic mineral content in polar ice, isothermal remanent magnetization (IRM) was measured on a small suite of Greenland ice samples of Holocene (interglacial) and Last Glacial Maximum (LGM) age. Although the extremely low dust concentrations limit weak field (susceptibility) measurements, all samples contained an easily measurable concentration of magnetic minerals that can be estimated using IRM intensity provided that special precautions are used. IRM experiments at liquid nitrogen temperatures indicate ice magnetic properties which are consistent with that expected from varying concentrations of magnetite or maghemite. Interestingly, the Holocene ice samples tend to have higher magnetic concentrations, despite having much lower total polar dust contents, than the few LGM ice samples tested thus far.
Sensitivity of ozone production rate to ozone precursors
Authors: Kleinman Lawrence I. , Daum Peter H. , Lee Yin‐Nan , Nunnermacker Linda J. , Springston Stephen R. , Weinstein‐Lloyd Judith , Rudolph Jochen
Published: February 2004

The photochemical equations describing O3 formation in the lower troposphere contain 2 major sink terms for free radicals; combination reactions and reactions with NOx. Knowing the fraction of radicals removed by reactions with NOx, termed LN/Q, allows one to predict the sensitivity of O3 production to NO and VOCs. We derive an analytic formula that gives LN/Q in terms of readily measured O3 precursors and test this formula using constrained steady state calculations based on field observations gathered in Phoenix, Arizona. The formula quantifies well‐known results regarding the effects of dilution, oxidation, and the production of oxidants on the transition from VOC to NOx sensitive behavior as an air parcel is advected away from an urban source.
Coupled land/atmosphere interactions in the West African Monsoon
Authors: Grodsky Semyon A. , Carton James A.
Published: February 2004

Rainfall in subSaharan West Africa is concentrated in a rainy season beginning in summer whose arrival is of critical importance for local economies. Here we use new surface wind observations made available by the QuickSCAT satellite and rainfall estimates from the Tropical Rainfall Measuring Mission to provide the first documentation of a biweekly oscillation in rainfall and wind that precedes the onset of the rainy season. This oscillation in rainfall occurs in conjunction with monsoonal wind patterns and is particularly noticeable in the zonal wind field. It is also associated with a cooling of surface temperature and a reduction in zonal surface pressure gradient. Together the phasing of these variables implies a feedback cycle acting between the monsoonal winds and their clouds, soil moisture, and surface temperature.
Magnification of atmospheric mercury deposition to polar regions in springtime: The link to tropospheric ozone depletion chemistry
Authors: Lu Julia Y. , Schroeder William H. , Barrie Len A. , Steffen Alexandra , Welch Harold E. , Martin Kathleen , Lockhart Lyle , Hunt Robert V. , Boila Gail , Richter Andreas
Published: February 2004

Mercury—in the chemical/physical forms present in the biosphere—is a persistent, toxic, bioaccumulative pollutant that is dispersed throughout the environment on a global scale, mainly via the atmosphere. It is among the “heavy metals” for which the natural biogeochemical cycle has been perturbed by a wide range of human activities, including fossil‐fuel combustion and waste incineration. Results of our recent measurements of gaseous elemental mercury (GEM), as well as total particulate‐phase mercury (TPM) concentrations in Arctic air, ‘total Hg’ concentrations in Arctic snow, and tropospheric BrO concentrations from an earth‐orbiting‐satellite platform are presented and discussed. Findings of our research, and the conclusions derived therefrom, are important for environmental protection as well as the health and well‐being of aboriginal people in Arctic circumpolar nations.
Multiple wavelength optical observations of a long‐lived meteor trail
Authors: Clemesha B. R. , de Medeiros A. F. , Gobbi D. , Takahashi H. , Batista P. P. , Taylor M. J.
Published: February 2004

A long‐lived meteor trail has been observed at wavelengths of 572.5 nm, 557.7 nm, 630.0 nm, 865.5 nm and in the near infrared band from 715 to 930 nm. The trail was detected at all these wavelengths, with the possible exception of 865.5 nm, where its identification was marginal. It was seen longest (17 minutes) through the wide band NIR 715‐930 nm filter. The fact that the trail was only marginally visible in the 865.5 nm (0–1) band of molecular oxygen, and was strongest in the wide‐band NIR image, raises serious doubts about an earlier suggestion that the infrared light from long‐lived meteor trails corresponds to emissions from molecular oxygen excited by the Chapman mechanism.
Ocean currents evident in satellite wind data
Authors: Kelly Kathryn A. , Dickinson Suzanne , McPhaden Michael J. , Johnson Gregory C.
Published: February 2004

Satellite‐mounted radar scatterometers designed to quantify surface winds over the ocean actually measure the relative motion between the air and the ocean surface. Estimates of the wind stress from conventional surface wind measurements are usually derived neglecting ocean currents. However, when the relative motion is used, the differences in the estimated stress can be as large as 50% near the equator and may even reverse sign during an El Niño. This assertion is supported by the strong relationship between the surface currents measured by the Tropical Atmosphere‐Ocean (TAO) array in the Pacific Ocean and the differences between the winds estimated from scatterometer data and those measured by TAO anemometers. The fact that the scatterometer measures relative motion, and not wind alone, makes scatterometer‐derived stress a more accurate representation of the boundary condition needed for both atmospheric and oceanic models than stress fields derived neglecting ocean currents.
Composition of energetic neutral atoms during a storm main phase
Authors: Lui A. T. Y. , McEntire R. W. , Nosé M. , Williams D. J.
Published: February 2004

The first composition observation of energetic neutral atom (ENA) emissions during the main phase of a geomagnetic storm is reported here. The measurements were made by the Energetic Particles and Ion Composition (EPIC) instrument on the Geotail on October 22, 1999 when the ring current was strengthening. For this geomagnetic storm, while the Dst index was monotonically decreasing during the main phase, ENA fluxes showed two major enhancements with distinctly different temporal profiles. For the first enhancement, the increases in ENA fluxes were rapid and the subsequent evolution was species dependent. Both the integral ENA (E > ∼ 12 keV) and neutral hydrogen (E > 67 keV) fluxes remained relatively unchanged after the increase while the neutral oxygen (E > 203 keV) fluxes decreased rapidly. For the second enhancement, the increases in ENA fluxes of all species were rather gradual and the subsequent decrease in the neutral oxygen flux was also slow. The slow decrease may be related to the continual AE enhancement during that time. For total energies above 200 keV, the intensity of ENA oxygen was the highest, followed by hydrogen, and then by helium. This ordering of ENA intensity for these species is similar to the previous ENA composition results obtained for the recovery phase of another geomagnetic storm.
JNO2 at high solar zenith angles in the lower stratosphere
Authors: Gao R. S. , Del Negro L. A. , Swartz W. H. , Salawitch R. J. , Lloyd S. A. , Proffitt M. H. , Fahey D. W. , Donnelly S. G. , Neuman J. A. , Stimpfle R. M. , Bui T. P.
Published: February 2004

In situ measurements of NO, NO2, O3, HO2, ClO, pressure, and temperature have been made at high solar zenith angles (SZA, 70°–93°) in the lower stratosphere. These measurements are used to derive the photolysis rate of NO2, JNO2, using a time‐dependent method. The resultant JNO2 values and the results of a multiple‐scattering actinic flux model show a linear relationship throughout the SZA range. The difference of the two sets of JNO2 values of about 11% suggests that the model scattering calculation is very accurate at high SZA conditions near sunrise and sunset.
Direct measurement of winds on Titan
Authors: Kostiuk Theodor , Fast Kelly E. , Livengood Timothy A. , Hewagama Tilak , Goldstein Jeffrey J. , Espenak Fred , Buhl David
Published: February 2004

We report the first direct measurement of wind velocity in the atmosphere of Titan, one of only two examples in our solar system of a slowly‐rotating body with a dense atmosphere and a prime target of the Cassini mission. Zonal wind velocity was determined from Doppler shift of ethane lines emitted from Titan's stratosphere (∼0.1–7 mbar) measured by infrared heterodyne spectroscopy near 12 µm (λ/Δ λ ≥ 106). Prograde zonal circulation, in the direction of global rotation, is established with 94% statistical confidence. Results provide information regarding Titan meteorology constraining dynamical theories for slowly‐rotating bodies, provide otherwise unobtainable data to optimize the Cassini Huygens Probe investigations, and demonstrate the capability for remotely measuring winds on a small, distant object.
The loss of NO2, HNO3, NO3/N2O5, and HO2/HOONO2 on soot aerosol: A chamber and modeling study
Authors: Saathoff H. , Naumann K.‐H. , Riemer N. , Kamm S. , Möhler O. , Schurath U. , Vogel H. , Vogel B.
Published: February 2004

The heterogeneous loss of NO2, HNO3, NO3/N2O5, and HO2/HO2NO2 on soot aerosol was investigated in a large aerosol chamber for interaction times of up to several days. By fitting a detailed model to the measured time profiles of the trace gas concentrations in the presence / absence of soot aerosol, the following reaction probabilities have been deduced at 294 K and < 10 ppm H2O (in parentheses: at 50% r.h.):γ(NO2) ≤ 4× 10−8; γ(HNO3→NO2) ≤ 3× 10−7; γ(NO3) ≤ 3 × 10−4 (≤10−3); γ(N2O5, hydrolysis)=(4±2) ×10−5 ((2±1 ) × 10−4); γ(N2O5, reduction)=(4±2) × 10−6; γ(HO2≤ 10−2; γ(HO2NO2) ≤ 10−5. These results were adopted in a series of box model calculations for four‐day summer smog episodes, probing a wide range of NO emission rates. The 2nd day ozone maxima were reduced up to 10% in the presence of 20 µg m−3 soot aerosol, mainly due to the heterogeneous loss of HO2.
First lidar observations of middle atmosphere temperatures, Fe densities, and polar mesospheric clouds over the north and south poles
Authors: Gardner Chester S. , Papen George C. , Chu Xinzhao , Pan Weilin
Published: February 2004

An Fe Boltzmann temperature lidar was used to obtain the first measurements of middle atmosphere temperatures, Fe densities, and polar mesospheric clouds (PMCs) over the North and South Poles during the 1999–2000 summer seasons. The measured temperature structure of the mesopause and lower thermosphere regions in mid‐summer at both Poles is consistent with the MSIS90 model. The density profiles of the normal Fe layer between 80–100 km at summer solstice are similar at both the North and South Poles with maximum densities of about 2000 cm−3. Sporadic Fe (Fes) layers were observed at both Poles with peak densities at 106 km altitude. The maximum densities of the Fes layers were 232 × 10³ cm−3 at North Pole and 6.52 × 10³ cm−3 at South Pole. PMCs were detected above both Poles. The altitudes of PMCs over the South Pole were consistently 2–3 km higher than those observed over the North Pole.
Recent sea level change in the Mediterranean Sea revealed by Topex/Poseidon satellite altimetry
Authors: Cazenave A. , Cabanes C. , Dominh K. , Mangiarotti S.
Published: February 2004

Using altimetry data of the Topex/Poseidon satellite available since early 1993, we show that the eastern Mediterranean sea level has been continuously rising during 1993–1999, at a rate up to 20 mm/yr southeast of Crete. Sea level rise is also observed in the Algerian‐Provencal basin as well as in the Tyrrhenian and Adriatic seas. The north Ionian sea, on the other hand, shows an opposite trend, i.e., a sea level drop during the past seven years. Sea surface temperature trends are strongly correlated to sea level trends, indicating that at least part of the observed sea level change has a thermal origin. The recent Mediterranean sea level rise observed by Topex/Poseidon may be related to the warming trends reported from hydrographic cruises in the intermediate and deep waters of the eastern basin since the early 1990s, and of the western basin since the 1960s.
Does the urban CO2 dome of Phoenix, Arizona contribute to its heat island?
Authors: Balling Robert C. , Cerveny Randall S. , Idso Craig D.
Published: February 2004

Phoenix, Arizona has both a strong urban heat island and a large near‐surface atmospheric CO2 “dome” during periods of atmospheric stability. In this investigation, we use a detailed one‐dimensional infrared radiation simulation model to determine the thermal impact of the elevated CO2 levels in the urban environment. We find that the increased CO2 concentrations below the inversion layer contribute only slightly to the observed heat island, which suggests that other factors, such as absorption of solar energy by urban surface materials and lower soil moisture levels, are largely responsible for the observed increase in urban temperatures.
Short and long term deformation patterns in the Aegean‐Anatolian Systems: Insights from space geodetic data (GPS)
Authors: Mantovani Enzo , Viti Marcello , Cenni Nicola , Albarello Dario , Babbucci Daniele
Published: February 2004

Geodetic measurements (GPS) in the eastern Mediterranean suggest higher rates of motion, of about 10 mm/yr, in the Aegean ‐ Western Anatolian zone with respect to those in the central‐eastern Anatolia. In this work we explore the plausibility of the hypothesis that the observed kinematics may be significantly influenced by post ‐ seismic relaxation processes induced by the seismic activation of the North Anatolian Fault since 1939. The major implications of this hypothesis are tentatively quantified by a simplified model, constituted by an elastic lithosphere (100 km thick) coupled with a viscous asthenosphere (250 km thick with a viscosity of 1019 Pa s). The predicted perturbation of the displacement and stress fields is consistent with geodetic velocities and could also account for the major features of seismic activity in the period considered.
Summer season land cover—Convective cloud associations for the midwest U.S. “Corn Belt”
Authors: Carleton Andrew M. , Adegoke Jimmy , Allard Jason , Arnold David L. , Travis David J.
Published: February 2004

Human‐induced land cover modifications impact the planetary boundary layer's (PBL) thermal and moisture regimes on mesoscales. We investigate the association of croplands, forest, and the crop‐forest “boundary” (CFB) with convective‐cloud development (timing, amount) for three target areas (TAs) in the U.S. Midwest “Corn Belt”, during the summer seasons (JJA) 1991–98. For each land cover, hourly satellite‐retrieved albedo and cloud‐top temperature values are composited for three classes of mid‐tropospheric synoptic circulation. On days with the strongest anticyclonicity, there are no consistent differences in convection related to land cover type: cloud development is regionalized and tied primarily to synoptic conditions. However, on days having weaker anticyclonicity the CFB is the dominant site of free convection, suggesting that Non‐Classical Mesoscale Circulations (NCMCs) between cropped and adjacent forest areas may operate when reduced subsidence in the mid‐troposphere does not effectively cap the PBL. Index terms: Land/atmosphere interactions (3322), Mesoscale meteorology (3329), Climate dynamics (1620), Anthropogenic effects (1803).
First medium energy neutral atom (MENA) Images of Earth's magnetosphere during substorm and storm‐time
Authors: Pollock C. J. , Asamura K. , Balkey M. M. , Burch J. L. , Funsten H. O. , Grande M. , Gruntman M. , Henderson M. , Jahn J.‐M. , Lampton M. , Liemohn M. W. , McComas D. J. , Mukai T. , Ritzau S. , Schattenburg M. L. , Scime E. , Skoug R. , Valek P. , Wüest M.
Published: February 2004

Initial ENA images obtained with the MENA imager on the IMAGE observatory show that ENAs emanating from Earth’s magnetosphere at least crudely track both Dst and Kp. Images obtained during the storm of August 12, 2000, clearly show strong ring current asymmetry during storm main phase and early recovery phase, and a high degree of symmetry during the late recovery phase. Thus, these images establish the existence of both partial and complete ring currents during the same storm. Further, they suggest that ring current loss through the day side magnetopause dominates other loss processes during storm main phase and early recovery phase.
Chemistry of hydrothermal fluids at the TAG Active Mound, MAR 26°N, in 1998
Authors: Chiba H. , Masuda H. , Lee S.‐Y. , Fujioka K.
Published: February 2004

Black smoker and clear fluids were sampled at the TAG active mound (26°08′N, 44°50′W) in August 1998. The major ion chemistry of the black smoker fluid appears to be stable over 12 years, indicating that the physico‐chemical condition of the deep reaction zone have not changed significantly within this period. The black smoker fluid chemistry is the same independent of the place of the venting on the mound, suggesting that the black smoker fluid is supplied from the single source. Two medium temperature clear fluid samples (256° and 219°C) are depleted in Ca2+, Fe2+, and H2S compared to the black smoker fluid due to the precipitation of anhydrite and iron sulfide caused by mixing with entrained seawater. These clear fluids are formed by the same mechanism as the white smoker and diffuse fluids.
Two major volcanic cooling episodes derived from global marine air temperature, AD 1807–1827
Authors: Chenoweth Michael
Published: February 2004

A new data set of global marine air temperature data for the years 1807–1827 is used to show the impact of volcanic eruptions in ∼ 1809 (unlocated) and 1815 (Tambora, Indonesia). Both eruptions produced cooling exceeding that after Krakatoa, Indonesia (1883) and Pinatubo, Philippines (1991). The ∼1809 eruption is dated to March‐June 1808 based on a sudden cooling in Malaysian temperature data and maximum cooling of marine air temperature in 1809. Two large‐scale calibrated proxy temperature records, one from tree‐ring‐density data, the other using multi‐proxy sources are compared to the marine air temperature data. Correlation is highest with maximum latewood density data and lowest with the multi‐proxy data.
The northern auroral region as observed in nitric oxide
Authors: Barth C. A. , Baker D. N. , Mankoff K. D. , Bailey S. M.
Published: February 2004

The distribution of thermospheric nitric oxide in the northern polar region has been measured from the Student Nitric Oxide Explorer (SNOE). A polar image of a one‐year average at 106 km shows the maximum density lies between 60° and 70° N geomagnetic latitude. The density around this auroral oval varies as a function of longitude with the larger densities occurring at western geomagnetic longitudes. A polar image of a second year of observations demonstrates the same latitudinal‐longitudinal density distribution indicating that the asymmetry is a persistent property of the auroral region. For a period of high geomagnetic activity, the nitric oxide observations indicate that the flux of precipitating electrons at 90° W geomagnetic longitude was 75% larger than the flux at 90° E geomagnetic longitude. We suggest that this asymmetry is caused by the longitudinal variation in the magnetic field strength around the auroral oval.