bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterising the effect of large‐scale model resolution upon calculated OH production using MOZAIC data
Authors: Crowther R. A. , Law K. S. , Pyle J. A. , Bekki S. , Smit H. G. J.
Published: October 2002

The coarse spatial resolution of large‐scale models can be a significant source of error in calculating grid cell averaged rates of physical processes. We investigate here the influence of resolution in the case of chemical reactions. We use high resolution MOZAIC ozone and water vapour data to characterise the effects of unresolved structures on model‐calculated production of the hydroxyl radical (OH) in the upper troposphere/lower stratosphere region. The statistical analysis of MOZAIC data indicates that, on average, large‐scale models may overestimate OH production by 5% to 20% for resolutions ranging from ∼200 to ∼800 km respectively. This systematic bias is found to be most significant in the tropopause region.
ENSO‐like decadal variability and South African rainfall
Authors: Reason C.J.C. , Rouault M.
Published: October 2002

Decadal to multidecadal ‘ENSO‐like’ SST and circulation patterns in joint EOFs of global SST and MSLP, may be linked to South African rainfall variability. For eastern/northern South Africa (summer rainfall), the average of the 9–13 year and 18–39 year bandpass filtered EOFs tracks the rainfall well for 1903–1998. Higher (lower) pressure, warmer (cooler) SST in the Pacific and Indian Oceans and offshore (onshore) winds characterise the positive (negative) EOF signal and decreased (increased) rain. For southwestern South Africa (winter rainfall), the average of the 13–18 and 18–39 year filtered EOFs tracks the rainfall well from 1903–1982 with the 9–13 year EOF working better from 1983–1998. The suggested mechanism involves shifts in the upper level jet and in the strength of the subtropical high pressure belt and circumpolar trough.
Modeling magma‐drift interaction at the proposed high‐level radioactive waste repository at Yucca Mountain, Nevada, USA
Authors: Woods Andrew W. , Sparks Steve , Bokhove Onno , LeJeune Anne‐Marie , Connor Charles B. , Hill Brittain E.
Published: October 2002

We examine the possible ascent of alkali basalt magma containing 2 wt percent water through a dike and into a horizontal subsurface drift as part of a risk assessment for the proposed high‐level radioactive waste repository beneath Yucca Mountain, Nevada, USA. On intersection of the dike with the low pressure, horizontal drift, the ascending magma will be diverted into the drift. The fragmenting mixture expands down the drift to reach speeds of order 100–300 m/s. After this initial disruptive activity, parts of the repository can be filled with magma within a matter of hours until a pathway is found to allow the magma to vent. Magma flow through the drift network will cause intense heating of any waste canisters located along the pathway between the dike and the surface conduit. The assessments suggest a greater number of waste packages may be adversely affected than previously recognized.
Fractal analysis of drainage basins on Mars
Authors: Stepinski T. F. , Marinova M. M. , McGovern P. J. , Clifford S. M.
Published: October 2002

We used statistical properties of drainage networks on Mars as a measure of martian landscape morphology and an indicator of landscape evolution processes. We utilize the Mars Orbiter Laser Altimeter (MOLA) data to construct digital elevation maps (DEMs) of several, mostly ancient, martian terrains. Drainage basins and channel networks are computationally extracted from DEMs and their structures are analyzed and compared to drainage networks extracted from terrestrial and lunar DEMs. We show that martian networks are self‐affine statistical fractals with planar properties similar to terrestrial networks, but vertical properties similar to lunar networks. The uniformity of martian drainage density is between those for terrestrial and lunar landscapes. Our results are consistent with the roughening of ancient martian terrains by combination of rainfall‐fed erosion and impacts, although roughening by other fluvial processes cannot be excluded. The notion of sustained rainfall in recent Mars history is inconsistent with our findings.
On faulting in inhomogeneous media
Authors: Rybicki K. R. , Yamashita T.
Published: October 2002

Faulting of strike‐slip type in a vertically inhomogeneous medium is analyzed using antiplane models. It is shown that asperities boundaries where slip exhibits significant change may be associated with regions in which a rapid transition occurs from high to low rigidity and/or from high to low pore pressure. These boundaries are connected with stress concentrations within the ruptured regions where tectonic stress increases after faulting. Release of these stresses (aftershocks, interseismic earthquakes, aseismic faulting) and tectonic loading makes asperities boundaries a probable initiation site of a major earthquake during the following crustal deformation cycle. The present results also show that low rigidity layers should be deprived of driving stress during consecutive earthquake cycles, which explains the suppression of major earthquake ruptures and low level of seismicity that is generally observed in sediments.
The first Antarctic geomagnetic Reference Model (ARM)
Authors: De Santis Angelo , Torta J. Miquel , Gaya‐Piqué Luis R.
Published: October 2002

Spherical Cap Harmonic Analysis has been applied to obtain a reference model of geomagnetic secular change for Antarctica valid for the last forty years. In this paper, we use the latest available observatory data to update this model and to compare it with the 8th generation IGRF. In addition, the selected set of total field values used for the generation of the Oersted Initial Field Model have been employed together with observatory data to develop the first complete Antarctic Reference Model (ARM). This model improves the fit to the secular variation deduced from observatory data by about 60% relative to IGRF, and the fit to observatory and satellite field data by 8%. The model allows merging data sets taken at different altitudes and epochs in Antarctica, where significant temporal geomagnetic variations occur.
Pulsing of a focused mantle plume: Evidence from the distribution of foundation chain hotspot volcanism
Authors: O'Connor John M. , Stoffers Peter , Wijbrans Jan R.
Published: October 2002

Using the rare case of a hotspot chain crossing a fossil microplate, we reveal fundamental mantle plume characteristics by comparing hotspot volcanism in a sequence of contrasting tectonic settings. Key new 40Ar/39Ar ages show that the Foundation mantle plume pulses hot masses from depth with an apparent periodicity of one Myr. Synchronous magmatism over large distances indicates that masses associated with individual pulses are focused initially into similarly sized zones under the Pacific plate. Since the plume, spreading on impact with the lithosphere, influences a very wide area, apparently unconnected hotspot volcanism can be produced simultaneously across wide swaths, often crosscutting seamount chains. Our model might explain in part much of the midplate volcanism scattered across the Pacific seafloor indicating the episodic addition of significantly greater masses of plume material into the upper mantle than suggested by the narrowness of major seamount chains.
Elasticity of (Mg,Fe)SiO3‐perovskite at high pressures
Authors: Kiefer B. , Stixrude L. , Wentzcovitch R. M.
Published: October 2002

We calculated the elasticity of (Mg,Fe)SiO3‐perovskite, using the plane‐wave pseudopotential method for a pressure range that encompasses the earth's lower mantle. Adding 25 mol% FeSiO3 to the Mg endmember decreases the shear modulus by 6% at zero pressure and by 8% at core mantle boundary pressures. The bulk modulus is less affected by iron, increasing by 2% at zero pressure and by 1% at the base of the mantle. For the isotropically averaged wave velocities we find that the compressional wave velocity decreases by 4% independent of pressure and the shear wave velocity decreases by 6% and 7% at zero pressure and at 136 GPa, repectively. For the relative variation of shear to compressional velocities at constant pressure due to variations in Fe‐content we find R = 1.6 at 136 GPa and for the relative variation of shear to bulk sound velocities we find ξ = 2.6 at 136 GPa.
A link between Fram Strait sea ice export and atmospheric planetary wave phase
Authors: Cavalieri Donald J.
Published: October 2002

A link is found between the variability of Fram Strait sea ice export and the phase of zonal wave 1 in SLP for the period 1958–1997. Previous studies have found that the link between ice export through Fram Strait and the NAO is inconsistent over time scales longer than the last two decades. Inconsistent and low correlations are also found between Fram Strait ice export and the AO index. The phase of zonal wave 1 explains 60%–70% of the simulated ice export variance after the removal of two anomalous phases in 1966 and 1967. Unlike the NAO and AO links, these high variances are consistent for both the first and second halves of the 40‐year period. This consistency is attributed to the sensitivity of wave‐1 phase to the presence of secondary low pressure systems in the Barents Sea that serve to drive Arctic sea ice southward through Fram Strait.
Decadal changes in global ocean chlorophyll
Authors: Gregg Watson W. , Conkright Margarita E.
Published: October 2002

The global ocean chlorophyll archive produced by the CZCS was revised using compatible algorithms with SeaWiFS. Both archives were then blended with in situ data to reduce residual errors. This methodology permitted a quantitative comparison of decadal changes in global ocean chlorophyll from the CZCS (1979–1986) and SeaWiFS (1997–2000) records. Global spatial distributions and seasonal variability of ocean chlorophyll were similar, but global means decreased over the two observational segments. Major changes were observed regionally: chlorophyll concentrations decreased in the northern high latitudes while chlorophyll in the low latitudes increased. Mid‐ocean gyres exhibited limited changes. The overall spatial and seasonal similarity of the two data records suggests that the changes are due to natural variability. These results provide evidence of how the Earth's climate may be changing and how ocean biota respond.
Kinetics of submicron oleic acid aerosols with ozone: A novel aerosol mass spectrometric technique
Authors: Morris J. W. , Davidovits P. , Jayne J. T. , Jimenez J. L. , Shi Q. , Kolb C. E. , Worsnop D. R. , Barney W. S. , Cass G.
Published: October 2002

The reaction kinetics of submicron oleic (9‐octadecanoic (Z)‐) acid aerosols with ozone was studied using a novel aerosol mass spectrometric technique. In the apparatus a flow of size‐selected aerosols is introduced into a flow reactor where the particles are exposed to a known density of ozone for a controlled period of time. The aerosol flow is then directed into an aerosol mass spectrometer for particle size and composition analyses. Data from these studies were used to: (a) quantitatively model the size‐dependent kinetics process, (b) determine the aerosol size change due to uptake of ozone, (c) assess reaction stoichiometry, and (d) obtain qualitative information about the volatility of the reaction products. The reactive uptake probability for ozone on oleic acid particles obtained from modeling is 1.6 (±0.2) × 10−3 with an upper limit for the reacto‐diffusive length of ∼10 nm. Atmospheric implications of the results are discussed.
Shell fluxes of solution‐resistant planktonic foraminifers as a proxy for mixed‐layer depth
Authors: Itou Masashi , Noriki Shinichiro
Published: October 2002

Shell fluxes of solution‐resistant planktonic foraminifera, G. scitula and N. dutertrei, collected by moored sediment traps, are examined as a possible tool to reconstruct the surface water convection in the past subtropical western North Pacific. Time‐series observation reveals that shell fluxes of these two species fluctuate in an opposite sense. When surface water is warmed and well stratified, N. dutertrei fluxes reach a maximum. In contrast, G. scitula increases in response to the deepening of the mixed‐layer. To amplify the response of shell fluxes to climatological variables, the shell flux ratio of G. scitula to N. dutertrei (FG.sci/N.dut) is introduced. The time series FG.sci/N.dut pattern is similar to that of the Monsoon Index (MOI) representing the strength of the East Asian Winter Monsoon. The FG.sci/N.dut is also well correlated with the mixed‐layer depth. These correlations allow reconstruction of the ancient MOI and MLD from the faunal ratio.
Pseudopaleosecular variation due to remanence anisotropy in a pyroclastic flow succession
Authors: Gattacceca Jerome , Rochette Pierre
Published: October 2002

In order to check the reliability of a paleosecular variation record in a sequence of pyroclastic rocks (Miocene, Sardinia), we measured various types of anisotropy: magnetic susceptibility (AMS), anhysteretic remanent magnetization (AARM) and thermoremanent magnetization (ATRM). The main magnetic carrier is pseudo‐single domain titanomagnetite. No general relation appears between the degrees of AMS and AARM, while the degrees of AARM and ATRM are almost identical. Measuring the AARM thus provides a fast and reliable method to correct paleomagnetic deviation in volcanic rocks. Once corrected for anisotropy deviation the apparent scatter of the paleomagnetic directions, mostly on inclination, is drastically reduced.
A new method in mineral magnetism for the separation of weak antiferromagnetic signal from a strong ferrimagnetic background
Authors: Liu Qingsong , Banerjee Subir K. , Jackson Michael J. , Zhu Rixiang , Pan Yongxin
Published: October 2002

This paper describes a new magnetic method for determining the contribution of weakly magnetic hematite against a strongly magnetic (e.g. magnetite) background. The method involves measurements of Mfr, a residual or “final” remanence after hysteretic demagnetization of saturated isothermal remanent magnetization. In terms of sensitivity and precision, our proposed method is superior to the currently popular approach known as the HIRM method. Compared to the latter, Mfr has no error amplification caused by subtraction of terms. The method utilizes the available software for hysteretic demagnetization function on an automated vibrating sample magnetometer (VSM). This, in turn, automatically decreases some of the disturbing effects of the strong magnetic background, e.g., magnetic viscosity, initially non‐zero offset of HIRM for partially oxidized magnetite, etc.
Strong interseismic coupling, fault afterslip, and viscoelastic flow before and after the Oct. 9, 1995 Colima‐Jalisco earthquake: Continuous GPS measurements from Colima, Mexico
Authors: Azúa Bertha Márquez , DeMets Charles , Masterlark Tim
Published: October 2002

Continuous GPS measurements from Colima, Mexico during 4/93–6/01, bracketing the Oct. 9, 1995 M = 8.0 Colima‐Jalisco earthquake, provide new constraints on Rivera plate subduction mechanics. Modeling of margin‐normal strain accumulation before the earthquake suggests the Rivera‐North America subduction interface was fully locked. Transient postseismic motion from 10/95–6/97 is well fit by a model that includes logarithmically‐decaying fault afterslip, elastic strain from shallow fault relocking, and possibly a minor viscoelastic response, but is fit poorly by models that assume a dominant Maxwell viscoelastic response of the lower crust and upper mantle, independent of the assumed viscosities. Landward, margin‐normal motion since mid‐1997 is parallel to but ∼75% slower than the pre‐seismic velocity. Afterslip alone fails to account for this slowdown. The viscoelastic response predicted by a FEM correctly resolves the remaining velocity difference within the uncertainties. Both processes thus offset elastic strain accumulating from the relocked subduction interface.
Degree‐one displacements on Mars
Authors: Van Hoolst T. , Dehant V. , de Viron O. , Defraigne P. , Barriot J.‐P.
Published: October 2002

An important characteristic of the Martian atmosphere is that a large proportion of its CO2 condensates during winter in the huge polar ice caps. This CO2 sublimation/condensation process is associated with large seasonal mass transport from the North pole to the South pole and vice versa. As the center of mass of the system—consisting of the planet and the CO2 layer—does not change due to this transport, the center of mass of the planet is displaced to satisfy the equilibrium. The effects of the planetary center of mass displacement on station positions are evaluated to be at the level of several centimeter in the direction along the rotation axis, and several millimeters in the perpendicular directions.
The atmospheric degradation of 1‐bromopropane (CH3CH2CH2Br): The photochemistry of bromoacetone
Authors: Burkholder James B. , Gilles Mary K. , Gierczak Tomasz , Ravishankara A. R.
Published: October 2002

The atmospheric degradation of 1‐bromopropane and its degradation products are examined with respect to their ability to deplete stratospheric ozone. It is shown that the OH initiated oxidation of 1‐bromopropane does not lead to long lived bromine containing species. Laboratory measurements of the UV absorption cross sections and photodissociation quantum yields of chloroacetone and bromoacetone are presented. The atmospheric photolysis lifetime of bromoacetone at mid‐latitudes is determined to be on the order of hours.
Trend analysis of upper stratospheric Umkehr ozone data for evidence of turnaround
Authors: Reinsel Gregory C.
Published: October 2002

Recent upper stratospheric (∼35–45 km) Umkehr ozone data from three high‐quality stations have been examined, with residual and change‐in‐trend analyses performed. These data show a consistent feature of mildly positive tendency in values for the recent several years. Trend analyses of these data yield significant positive change‐in‐trend estimates of about 0.75% per year since 1996 relative to negative trends of about −0.55% per year existing prior to 1996, leading to a (nonsignificant) estimate of about 0.2% per year positive trend for the recent 5‐year period since the 1996 change‐in‐trend date.
Assessment of “storage correction” required for in situ 14CO production in air sample cylinders
Authors: Lowe D. C. , Levchenko V. A. , Moss R. C. , Allan W. , Brailsford G. W. , Smith A. M
Published: October 2002

We draw attention to an effect that has the potential to compromise measurements of atmospheric 14CO by the in situ production of 14C in air sample cylinders. We present first experimental determinations of the size of this effect using measurements made on cylinders containing an air sample and a CO/nitrogen calibration gas stored in laboratories in New Zealand from a few months to 11 years. These data are collated with measurements made on air samples stored at Scott Base, Antarctica to determine a mean in situ production rate for 14CO of 4.7 ± 0.5 molecules cm−3 yr−1 (STP) at sea level and in the latitude range 40–90° (geomagnetic) in a single floor laboratory. This rate is significant compared to observed annual cycles in 14CO (typically 5–10 14CO molecules cm−3) caused by OH variations and clearly has to be corrected for when 14CO data are used to determine atmospheric OH distributions.
Coupled seismoacoustic modes on the seafloor
Authors: Butler Rhett , Lomnitz Cinna
Published: October 2002

Wave‐to‐wave coupling arises when an acoustic pulse selects a Rayleigh mode of the same speed and both travel together swapping energy across an interface [Ewing et al., 1957]. A distinctive signal is observed at the Hawaii‐2 Observatory for purely oceanic paths from earthquakes on the Blanco and Mendocino Fracture Zones, off the coast of North America. The signal appears to be a composite of undispersed higher Rayleigh modes propagating along the ocean floor both in the sediments and in the water. The new coupled modes are identified by their frequency composition and their phase and group velocities. Seismoacoustic coupling at the seafloor is conditioned on (a) the presence of a low‐velocity interface at the ocean floor, and (b) the wavelength of the Rayleigh component being shorter than the depth of the water layer.
The effect of the July 14, 2000 “Bastille Day” solar flare event on >70 MeV galactic cosmic rays observed at V1 and V2 in the distant heliosphere
Authors: Webber W. R. , McDonald F. B. , Lockwood J. A. , Heikkila B.
Published: October 2002

Decreases in the >70 MeV rates of galactic cosmic rays are observed in the outer heliosphere in 2001 at V2 (63 AU) and V1 (80 AU) coincident with the arrival of the interaction region from the Bastille Day event in 2000 at the Earth. These decreases began ∼180 days after the event at the Sun at V2 and ∼245 days at V1 corresponding to average propagation speeds of 605 and 567 km/s respectively. The intensity decrease was 13.1% at V2 and 9.3% at V1. The intensity of these galactic cosmic rays recovered very slowly at V2 and V1 this recovery continuing for ∼150–120 days or more after the transient passed these spacecraft. The intensity time profiles show no obvious effects at the time when the interaction region might be expected to encounter the termination shock and suggest that the modulation associated with interaction region continued well beyond the location of the termination shock, into the heliosheath and perhaps to the heliopause.
Evidence for persistent 7000‐ and 3500‐year geomagnetic oscillations
Authors: Southon John
Published: October 2002

A 14,500‐year record of atmospheric 14C contains evidence for 7000‐ and 3500‐ year oscillations. Since the Holocene archaeomagnetic record also contains features consistent with a 7000‐year cycle, a likely explanation is that the 14C data are recording modulation of cosmogenic isotope production due to variations in geomagnetic shielding. A longer‐term 36Cl record contains evidence for similar periodicities, suggesting that these geomagnetic variations may have been present for tens of millennia.
High‐resolution numerical simulation of a polar low
Authors: Yanase W. , Niino H. , Saito K.
Published: October 2002

The first high‐resolution simulation of an observed polar low using a non‐hydrostatic mesoscale numerical model with 2‐km horizontal resolution is reported. The case studied is a remarkable polar low that developed over the Japan Sea on 21 January 1997. The simulation successfully reproduced the observed features of the polar low such as its horizontal scale, movement, spiral bands, a cloud‐free eye, and cloud streets associated with the cold air outbreak. Detailed three‐dimensional structures of the simulated polar low, which are difficult to observe by in situ measurement, have been clarified and its development mechanism is discussed.
Sounding of the topside ionosphere/plasmasphere based on GPS measurements from CHAMP: Initial results
Authors: Heise S. , Jakowski N. , Wehrenpfennig A. , Reigber Ch. , Lühr H.
Published: October 2002

Beside the GPS radio occultation measurements of the troposphere and ionosphere, the CHAMP satellite tracks presently up to 8 GPS satellites simultaneously for navigation. The received dual frequency GPS signals provide valuable information on the ionization state of the topside ionosphere and plasmasphere. This paper briefly describes a new developed model assisted technique to improve the three dimensional electron density estimation above the CHAMP orbit from these GPS measurements. Application of this assimilation algorithm provides a 2‐D electron density slice of the ionosphere/plasmasphere system within the CHAMP orbit plane from the CHAMP altitude up to GPS orbit heights. We estimate the accuracy of the GPS TEC calibration and perform a first validation by comparing the retrieved electron density of the ionosphere/plasmasphere slice at CHAMP altitude to simultaneous electron density measurements of the Langmuir Probe onboard CHAMP.
Power‐law residence time distribution in the hyporheic zone of a 2nd‐order mountain stream
Authors: Haggerty Roy , Wondzell Steven M. , Johnson Matthew A.
Published: October 2002

We measured the hyporheic residence time distribution in a 2nd‐order mountain stream at the H. J. Andrews Experimental Forest, Oregon, and found it to be a power‐law over at least 1.5 orders of magnitude in time (1.5 hr to 3.5 d). The residence time distribution has a very long tail which scales as t−1.28, and is poorly characterized by an exponential model. Because of the small power‐law exponent, efforts to characterize the mean hyporheic residence time (ts) in this system result in estimates that are scale invariant, increasing with the characteristic advection time within the stream channel (tad). The distribution implies the hyporheic zone has a very large range of exchange timescales, with significant quantities of water and solutes stored over time‐scales very much longer than tad. The hyporheic zone in such streams may contribute to short‐time fractal scaling in time series of solute concentrations observed in small‐watershed studies.
Sun photometer and lidar measurements of the plume from the Hawaii Kilauea Volcano Pu'u O'o vent: Aerosol flux and SO2 lifetime
Authors: Porter John N. , Horton Keith A. , Mouginis‐Mark Peter J. , Lienert Barry , Sharma Shiv K. , Lau Eric , Sutton A. Jeff , Elias Tamar , Oppenheimer Clive
Published: October 2002

Aerosol optical depths and lidar measurements were obtained under the plume of Hawaii Kilauea Volcano on August 17, 2001, ∼9 km downwind from the erupting Pu'u O'o vent. Measured aerosol optical depths (at 500 nm) were between 0.2–0.4. Aerosol size distributions inverted from the spectral sun photometer measurements suggest the volcanic aerosol is present in the accumulation mode (0.1–0.5 micron diameter), which is consistent with past in situ optical counter measurements. The aerosol dry mass flux rate was calculated to be 53 Mg d−1. The estimated SO2 emission rate during the aerosol measurements was ∼1450 Mg d−1. Assuming the sulfur emissions at Pu'u O'o vent are mainly SO2 (not aerosol), this corresponds to a SO2 half‐life of 6.0 hours in the atmosphere.
Observable signatures of a convectively generated wave field over the tropics using Indian MST radar at Gadanki (13.5°N, 79.2°E)
Authors: Dhaka S. K. , Choudhary R. K. , Malik S. , Shibagaki Y. , Yamanaka M. D. , Fukao S.
Published: October 2002

An experiment was conducted in the month of June 2000 to study the atmospheric dynamical behavior in the troposphere and lower stratosphere in the presence of a cloudy and moist background environment due to the onset of the summer monsoon over Indian peninsula. The cardinal objective was to observe the gravity wave signatures in the convective environment. We successfully monitored the development, maximizing and weakening of convective phenomena within a time span of 3–4 hours on 21–22 June 2000. The vertical wind in the troposphere during this period was found about 6–8 m/s. Variations of the radar returned signal power for the vertical beam with height and time show the continuous growth of high turbulence in the ambient air, ascending as high as the tropopause. The satellite cloud images exhibited the temporal growth and movement of cloud clusters over the region of the radar site during this period.
Loki, Io: A periodic volcano
Authors: Rathbun J. A. , Spencer J. R. , Davies A. G. , Howell R. R. , Wilson L.
Published: October 2002

Loki is the most powerful volcano in the Solar System. It has been observed to be in continuous though variable activity since 1979. Synthesis of more than a decade of groundbased data suggests that Loki eruptions are cyclic, with a 540 day period. Application of a simple lava cooling model to temperatures in Loki Patera, and eruption start and end times, implies that brightenings are due to a resurfacing wave propagating across the patera. The data are most consistent with lava lake overturn, but resurfacing by lava flows cannot be ruled out. A porosity gradient in the lake crust could cause lava lake overturn to occur periodically on the timescale observed.
The Landau damping of magnetospherically reflected whistlers within the plasmasphere
Authors: Bell T. F. , Inan U. S. , Bortnik J. , Scudder J. D.
Published: October 2002

Evidence for significant energetic electron precipitation by magnetospherically reflected (MR) whistlers has recently been found in SAMPEX energetic electron data [Blake et al., 2001], implying that these waves undergo many reflections before being attenuated through Landau damping. We quantify the Landau damping of MR whistlers, using recent energetic electron data from the HYDRA instrument on POLAR and show that the MR wave components can endure for as long as ∼20 seconds and undergo as many as 17 reflections before experiencing a 6 dB power loss due to Landau damping. Our results suggest that MR whistler wave energy may thus significantly enhance the total amount of energetic electron precipitation induced by each individual lightning discharge.
Forcing of the quasi‐biennial oscillation from a broad spectrum of atmospheric waves
Authors: Giorgetta Marco A. , Manzini Elisa , Roeckner Erich
Published: October 2002

The circulation of the stratosphere, and its influence on the trace constituent distribution, is an important component of the climate system, which must be included in simulations of global climate change. However, the ability to simulate a dominant stratospheric phenomenon, the Quasi‐Biennial Oscillation (QBO) in equatorial zonal wind, is an outstanding challenge in climate modeling. Although confined to the tropics, the QBO affects the circulation and the interannual variability of the entire stratosphere, parts of the mesosphere and possibly also of the troposphere. Here we show that the QBO is successfully simulated in a general circulation model (GCM) of the newest generation. Key factors are a sufficient spatial resolution, a realistic simulation of tropical convection, and the consideration of the effects of gravity waves. From this simulation it is inferred that a broad spectrum of atmospheric waves is necessary to generate the QBO in the model.
Rheologic inferences from high water marks of debris flows
Authors: Glaze L. S. , Baloga S. M. , Barnouin‐Jha O. S.
Published: October 2002

High water marks left by water rich debris flows can be used to constrain the rheologic character of the flow. A simplified time‐dependent model based on the conservation of flow volume is used to illustrate the approach. An example from Madison County, Virginia is shown.
A new field‐aligned current index AF and its relation to the storm‐time ring current and energetic neutral atom (ENA) emissions
Authors: Sun W. , Akasofu S.‐I.
Published: October 2002

It is shown that a newly devised field‐aligned current index AF is well correlated with the Dst index, the correlation coefficient being 0.93. The AF index is based on the fact that geomagnetic Y (or D) component variations in the middle and low latitudes are mainly caused by field‐aligned currents. It is also demonstrated that energetic neutral atom (ENA) emissions measured by the Geotail satellite are well correlated with the AF index.
Deep‐water renewal in Lake Issyk‐Kul
Authors: Vollmer Martin K. , Weiss Ray F. , Schlosser Peter , Williams Robert T.
Published: October 2002

The deep‐water renewal rates of Lake Issyk‐Kul are studied using the time‐dependent anthropogenically produced tracers sulfur hexafluoride (SF6), chlorofluorocarbons (CFCs) and tritium‐helium‐3. SF6 and the CFCs are used to calibrate a mixing model from which the vertical age distribution is calculated and found to be comparable to the SF6 apparent ages. Based on this model, the mean age of the water below 100 m depth is 6.1 yrs. The mean oxygen consumption rate for the same depth range is 6.4 μmol kg−1 yr−1 and the mean remineralization rates for nitrate, phosphate and silicate are 0.53, 0.003 and 0.67 μmol kg−1 yr−1, respectively.
Evidence for a thick mantle transition zone beneath the Philippine Sea from multiple‐ScS waves recorded by JISNET
Authors: Ohtaki Toshiki , Suetsugu Daisuke , Kanjo Kenji , Purwana Ibnu
Published: October 2002

We deployed the JISNET broadband seismic network in west and central Indonesia. Using data from JISNET and other broadband stations, we estimate the thickness of the mantle transition zone beneath East and Southeast Asia and the Philippine Sea using the ScS reverberation method. The thickness is about 240 km beneath East and Southeast Asia, 280–290 km beneath the western edge of the Philippine Sea, 260–280 km beneath the central part of the Philippine Sea, and 260 km beneath the Izu‐Bonin Arc. These results imply that the temperature is about 300 K lower than the global average beneath the western edge of Philippine Sea, 200 K lower beneath the mid part of the Philippine Sea, 130 K lower beneath the Izu‐Bonin arc, and almost equal to the average beneath East and Southeast Asia.
A systematic search for mantle discontinuities using SS‐precursors
Authors: Deuss Arwen , Woodhouse John H.
Published: October 2002

We perform a systematic search for reflectors in the upper and lower mantle using SS‐precursors. The largest number of robust reflections comes from a depth of 220 km, which we associate with the Lehmann discontinuity. This discontinuity is observed below both continental and oceanic areas, though the largest amplitudes appear beneath the continents. There is also evidence for weak discontinuities at approximately 260 and 310 km depth. The regions where we find the Lehmann discontinuity, in a global search, correspond to regions where local studies have found reflectors at similar depth. There are suggestions of lower mantle reflectors, in particular in the Indonesian subduction zone area where other studies have found similar reflections.
First observations of intense GPS L1 amplitude scintillations at midlatitude
Authors: Ledvina B. M. , Makela J. J. , Kintner P. M.
Published: October 2002

First observations of intense GPS L1 amplitude scintillation activity in the midlatitude ionosphere at latitudes corresponding to the northeastern United States have been made. Moderate to severe, these scintillations result from space weather effects due to a disturbed ionosphere. Moderate to severe scintillations can degrade or even disrupt communication and navigation systems relying upon transionospheric radio wave propagation. A modified GPS receiver was used to record GPS satellite signal strength at Cornell University (53.2° magnetic latitude) during a magnetospheric disturbance on September 25–26, 2001 from 0000–0400 UTC. This disturbance (Kp = 6, minimum Dst = −110 nT) prompted the ionospheric trough to move equatorward over the northeastern U.S. and produced large plasma densities and gradients attributed to storm‐time effects. This disturbance resulted in intense L‐band amplitude scintillations (≥20 dB, S4 ≈ 0.8) which are highly uncharacteristic at this magnetic latitude. Concurrent measurements of TEC showed steep density gradients (∼30 TEC/deg) and evidence of irregularity structuring.
Combination of Kalman filter and an empirical method for the correction of near‐surface temperature forecasts: Application over Greece
Authors: Anadranistakis Manolis , Lagouvardos Kostas , Kotroni Vassiliki , Skouras K.
Published: October 2002

In response to the need of improved daily operational weather forecasts, a method has been developed and applied for the correction of operationally forecasted near surface temperatures in Greece. Four distinct corrections are applied. The first two are based on Kalman theory making two different assumptions on the dependence of the forecast to the observed temperature. The third correction is based on an empirical method while the fourth provides a corrected temperature combining the corrected temperatures from the previous three methods, with dynamic weights assigned to each of them. The analysis showed that the combined method gives always the best results. Large mean absolute errors of temperature forecasts as high as 6.2°C are suppressed down to 1.5°C after correction, showing that a large part of the forecast error has a systematic character which can be corrected by the method described in this paper.
Intra‐decadal variability in the Ekman heat flux from scatterometer winds
Authors: Sato O. T. , Polito P. S. , Timothy Liu W.
Published: October 2002

We examine evidences of low frequency variability in the Ekman heat flux due to changes in the global temperature and wind patterns. The 10‐year long time series of high resolution surface wind vectors was provided by the European Remote Sensing Satellites 1 and 2. A linear regression of the zonally averaged Ekman heat flux shows a latitudinal trend for the period between 1992 and 1997. This trend indicates a decrease in the poleward Ekman heat flux of warmer waters from the tropics and a slight decrease in the equatorward flux in the high latitudes. This intra‐decadal trend ended after the 1998 El Niño event. These variations are mostly due to changes in the wind stress field. The decrease in the poleward Ekman heat flux may have far reaching consequences involving the global heat balance.
Prediction of a CO22+ layer in the atmosphere of Mars
Authors: Witasse O. , Dutuit O. , Lilensten J. , Thissen R. , Zabka J. , Alcaraz C. , Blelly P.‐L. , Bougher S. W. , Engel S. , Andersen L. H. , Seiersen K.
Published: October 2002

The calculation of the dication CO22+ density in the atmosphere of Mars is performed for the first time. The metastable lifetime of these species reaches 4 seconds. The density of a layer centered around 155–160 km altitude can reach from 3 to and 5 106 m−3. The ions are produced by CO2 photoionization and photoelectron impact on CO2. They are lost by dissociative recombination with the thermal electrons and chemical reaction with CO2. This work is based upon relevant chemical reaction coefficient rates that have been measured in laboratory very recently. We suggest that this ion layer can be detectable by a mass spectrometer onboard the orbiter of the CNES PREMIER 07 mission. This work opens a series of promising studies on double ionization processes in the Mars ionosphere, such as their implications for the production of energetic electrons or fast fragmentation ion products which could participate in atmospheric escape.
On the boundary flow off Brazil at 5–10°S and its connection to the interior tropical Atlantic
Authors: Schott Friedrich A. , Brandt Peter , Hamann Meike , Fischer Jürgen , Stramma Lothar
Published: October 2002

Within the context of the German CLIVAR program, an observational program in the western tropical Atlantic with shipboard sections, profiling floats and a moored array aims at studying the role of the shallow thermohaline subtropical cell (STC) in tropical‐subtropical interactions and the cold water transports underneath. From 6 repeated shipboard profiling sections off Brazil near 5°S a northward warm water transport above 1100 m of 25.0 ± 4.4 Sv is determined, of which 13.4 ± 2.7 Sv occur in the thermocline layer supplying the Equatorial Undercurrent. Trajectories of 15 profiling floats released near the western boundary are presented that drift at shallow levels (200 m and 400 m) and delineate the different STC branches. For the southward flow of North Atlantic Deep Water (NADW) a section‐mean transport of −31.7 ± 9.2 Sv was determined at 5°S. However, different from the steady NADW flow observed earlier along the topography north of the equator, the NADW currents at 5–10°S are much more variable with long periods of northward counterflow along the topography.
Sea ice concentration estimates from satellite passive microwave radiometry and openings from SAR ice motion
Authors: Kwok Ron
Published: October 2002

Openings in the Arctic Ocean ice cover from small‐scale sea ice motion fields are compared with open water fractions retrieved from satellite passive microwave observations. We find very little agreement between the results. Passive microwave retrieval algorithms seem to be insensitive to small areas of open‐water in winter leads. Variability in the passive microwave retrievals is mostly due to anomalous and persistent regions of lower ice concentration where no openings are found. Between January and April of 1998, openings cover ∼0.3 ± 0.1% of the total area within the perennial ice zone. This is smaller, in one instance ten times, than the open water fraction from the passive microwave retrievals. Previous bounds of open water coverage of the ice cover imposed on climate simulations based on uncertainties in passive microwave retrievals (±4 − 7%) are too high and the over‐estimated open water fraction on model results should be re‐examined.
Dynamics of seasonal and interannual variability of the Peru‐Chile Undercurrent
Authors: Pizarro Oscar , Shaffer Gary , Dewitte Boris , Ramos Marcel
Published: October 2002

Coastal sea level, current, satellite altimeter data and an equatorial Kelvin wave model are used to study the dynamics of seasonal and interannual fluctuations of the Peru‐Chile Undercurrent. Satellite altimetry shows that low frequency, sea level anomalies near 30°S propagate offshore as expected from Rossby wave theory. Those anomalies are related to disturbances of equatorial origin observed near the coast of South America. With a wind‐forced equatorial Kelvin wave model and simple Rossby wave dynamics we show that much of the sea level anomalies, and more than 50% of the observed undercurrent variability near 30°S, at seasonal and interannual periods can be explained by long Rossby waves forced by the equatorial Kelvin waves. The amplitude of the equatorial Kelvin wave can be used to estimate the amplitude of the Rossby wave near the South American coast, and thus, to monitor low frequency changes in the Peru‐Chile Undercurrent.
Shortwave Aerosol Radiative Forcing from MODIS and CERES observations over the oceans
Authors: Christopher Sundar A. , Zhang Jianglong
Published: October 2002

Using spatially and temporally collocated data sets from the Clouds and Earth's Radiant Energy System (CERES) and Moderate‐Resolution Imaging Spectroradiometer (MODIS) instruments on the Terra satellite, a new strategy is presented for studying the Shortwave Aerosol Radiative Forcing (SWARF) over the global oceans. Using collocated data, for September 2000, the global averaged optical thickness (τ0.55) for cloud‐free CERES pixels is 0.07 with a SWARF of −6 Wm−2. The τ0.55 and SWARF values derived from two independent instruments are in excellent agreement with the following relationship: SWARF = 0.35 −105.34τ0.55 +61.47τ0.552 (0 ≤ τ0.55 ≤ 0.7) Wm−2. The synergistic use of the MODIS and CERES data sets can be used to provide independent estimates of SWARF, and can be used as a validation tool for studies that attempt to model the role of aerosols on climate.
On the role of inter‐basin surface salinity contrasts in global ocean circulation
Authors: Seidov D. , Haupt B. J.
Published: October 2002

The role of sea surface salinity (SSS) contrasts in maintaining vigorous global ocean thermohaline circulation (TOC) is revisited. Relative importance of different generalizations of sea surface conditions in climate studies is explored. Ocean‐wide inter‐basin SSS contrasts serve as the major controlling element in global TOC. These contrasts are shown to be at least as important as high‐latitudinal freshwater impacts. It is also shown that intra‐basin longitudinal distribution of sea surface salinity, as well as intra‐ and inter‐basin longitudinal distribution of sea surface temperature, is not crucial to conveyor functionality if only inter‐basin contrasts in sea surface salinity are retained. This is especially important for paleoclimate and future climate simulations.
Teleconnections of soil moisture and rainfall during the 1993 midwest summer flood
Authors: Pal Jeremy S. , Eltahir Elfatih A. B.
Published: October 2002

Here, we investigate the role of spring soil moisture distribution during the 1993 summer flood in North America. A series of idealized numerical experiments are performed using a regional climate model with different soil moisture conditions. It is concluded that the abnormally dry conditions in the Southwest may be partially responsible for the meridional location of the intense flooding in the Upper Midwest. Furthermore, the abnormally wet soil moisture conditions in the Midwest are likely to be partially responsible for the flood's persistence and large magnitude, but not for its spatial location. These impacts are initiated via processes involving the local energy and water budgets and then propagated to the surrounding regions through the large scale dynamics. Depending on the location, soil moisture anomalies over relatively small regions can significantly alter rainfall both locally and in surrounding regions.
Air–sea flux of anthropogenic carbon dioxide in the North Atlantic
Authors: Anderson Leif G. , Olsen Are
Published: October 2002

A conceptual advective model is employed to evaluate the mechanism of oceanic uptake of anthropogenic CO2 in the North Atlantic, and its sensitivity to climate change. Given initial carbon system parameters, and climatological wind speed, sea surface temperatures, sea surface salinities, and mixed layer depths, the air–sea exchange of CO2 in a water parcel flowing from low to high latitudes is calculated using an iterative procedure. The calculations are carried out under present and preindustrial atmospheric conditions, with the difference assigned to be air–sea flux of anthropogenic CO2. The result reveals a flux of anthropogenic CO2 into the surface water at latitudes south of ∼50 oN and a flux out of the surface water at higher latitudes. The quantitative air–sea flux of anthropogenic CO2 is very sensitive to several factors, important ones being the flow speed and thickness of the north flowing surface water. This suggests a strong feedback on anthropogenic CO2 uptake in the North Atlantic if climate change affects the strength of the oceanic circulation.
Analysis of adjustments to the United States Historical Climatology Network (USHCN) temperature database
Authors: Balling Robert C. , Idso Craig D.
Published: October 2002

The United States Historical Climatology Network (USHCN) temperature database is commonly used in regional climate analyses. However, the raw temperature records in the USHCN are adjusted substantially to account for a variety of potential contaminants to the dataset. We compare the USHCN data with several surface and upper‐air datasets and show that the effects of the various USHCN adjustments produce a significantly more positive, and likely spurious, trend in the USHCN data.
Coherency detection of multiscale abrupt changes in historic Nile flood levels
Authors: Jiang Jianmin , Mendelssohn Roy , Schwing Franklin , Fraedrich Klaus
Published: October 2002

A scanning algorithm based on the classical Student t‐test is extended to detecting the presence and coherency of multiscale abrupt changes in two time series. It functions similarly to the Haar wavelet transform, but also provides thresholds of the statistical significance for testing change‐points. The algorithm is applied to the historic series (AD 622–1469) of the maximum and minimum flood levels of the Nile River using the “Table‐Look‐Up Test” for correction of dependence in the series. The results reveal several abrupt changes, and separate wet/dry episodes on 30–160 year time‐scales. Most of the episodes coincide with historic records of catastrophe in Egypt. Some changes correspond to changes in China and Europe, and to reconstructions of fish stocks off the west coast of North America, indicating that they are driven and linked by global teleconnection processes.