bluuebunny/crossref_metadata_2025 huggingface dataset:
Average daytime F region disturbance neutral winds measured by UARS: Initial results
Authors: Fejer Bela G. , Emmert John T. , Shepherd Gordon G. , Solheim Brian H.
Published: February 2004

Thermospheric neutral winds play important roles on the dynamics of the upper atmosphere. We use extensive F region zonal and meridional wind data measured by the Wind Imaging Interferometer (WINDII) instrument on board the Upper Atmosphere Research Satellite (UARS) to study the mid‐and low‐latitude daytime average perturbation winds during magnetically disturbed periods. We have determined the perturbation winds by subtracting the quiet time wind values along the satellite orbits. Our data indicate large changes in the latitudinal profiles of both the zonal and meridional disturbance winds from morning to afternoon hours. The early morning zonal disturbance winds are eastward near the equator and at upper mid‐latitudes (above 50°), and westward at lower mid‐latitudes. The mid‐morning and afternoon zonal disturbance wind patterns show very small amplitudes at low latitudes and increasing westward winds at mid‐latitudes. These latitudinal profiles are in excellent agreement with the patterns derived from zonal wind measurements on board the DE‐2 satellite. The meridional daytime perturbation winds are equatorward and have magnitudes increasing linearly with latitude, with largest values in the early morning sector. The zonal and meridional disturbance winds show an approximately linear increase with the Kp index during geomagnetically active conditions.
The solar wind depletion (SWD) Event of 26 April 1999: Triggering of an Auroral “pseudobreakup” event
Authors: Zhou Xiaoyan , Tsurutani Bruce T. , Gonzalez Walter D.
Published: February 2004

The interplanetary solar wind depletion (SWD) event of 26 April 1999 and its magnetospheric consequences are examined. The SWD event is characterized by a solar wind density decrease from ∼3.0 to 0.7 cm−3 leading to a solar wind ram pressure decrease from ∼2.0 to 0.2 nPa. This SWD onset is followed by a dipolarization of nightside magnetospheric fields. At approximately the same time, an auroral pseudobreakup occurred in the near‐midnight auroral zone. A model is presented to explain the pseudobreakup as energy release by the tail magnetic field reconfiguration. The release of magnetic tension energy is estimated to have been ∼3.3 × 1019 ergs, while the auroral energy was approximately 30% of this value, ∼1.0 × 1019 ergs. This result may imply that the magnetic field collapse led to direct particle acceleration through parallel electric fields.
Sprites and possible mesospheric effects
Authors: Stenbaek‐Nielsen H. C. , Moudry D. R. , Wescott E. M. , Sentman D. D. , Sabbas F. T. Sâo
Published: February 2004

Images of sprites have been recorded at 1 ms resolution revealing several new sprite properties. Sprites appear to occur in a highly structured mesosphere, and we suggest that the cause of some of this structure is the sprite activity itself. Evidence is seen in events where a subsequent nearby sprite appears to re‐activate the volume of a previous sprite, in sprites where tendrils and branches develop away from the normally observed vertical direction, and in beads that lasts much longer that the parent sprite. Sprites can be large with horizontal widths of more than 40 km and can extend from the clouds up to the lower ionosphere thus affecting a large volume of the atmosphere. The total horizontal area of sprites during one storm over Nebraska was a significant fraction of the area covered by the associated thunderstorm raising the possibility of larger scale measurable mesospheric effects.
A kinetic isotope effect during ice formation by water freezing
Authors: Souchez R. , Jouzel J. , Lorrain R. , Sleewaegen S. , Stiévenard M. , Verbeke V.
Published: February 2004

A kinetic isotope effect is known to occur during ice formation from water vapour in a cloud ; it is due to the difference in molecular diffusivities in air of HDO and H218O molecules. A similar effect is likely during water freezing since diffusion coefficients of HDO and H218O are also different in liquid water. Their values are however less different from each other than those in air. Therefore, such a kinetic isotope effect during water freezing is less frequently observed in Nature. This paper describes a situation in Antarctica where this effect is conspicuous in icings (aufeis). In this type of ice indeed there is no relationship between δD (or δ18O) and deuterium excess whereas a clear inverse relationship between these parameters exists in ice formed by water freezing when equilibrium isotopic fractionation applies. This kinetic effect is potentially present in hail within clouds, in infiltration ice (formed during sea ice growth) and in some kinds of ground ice.
Uncertainties in thermohaline circulation response to greenhouse warming
Authors: Tziperman Eli
Published: February 2004

The uncertainty in the response of the thermohaline circulation to greenhouse forcing due to the use of flux adjustments in coupled ocean‐atmosphere models is evaluated. This is done by using a different yet physically justifiable flux adjustment procedure and examining its effect on the thermohaline response to greenhouse forcing in a three dimensional primitive equations coupled ocean atmosphere general circulation model. It is found that while the initial thermohaline circulation weakening is robust, its eventual recovery which is seen in some coupled model simulations may be more sensitive to the details of the flux adjustment procedure and may therefore be less certain.
Coeval changes in grain size and sedimentation rate of eolian loess, the Chinese Loess Plateau
Authors: Ding Z. L. , Yu Z. W. , Yang S. L. , Sun J. M. , Xiong S. F. , Liu T. S.
Published: February 2004

To determine the temporal‐spatial relationship between strength of the winds transporting the Chinese loess and aridity conditions of the loess source area, six loess sections located respectively in the northern, middle, and southern Loess Plateau were studied. Grain size distributions were analyzed on loess‐paleosol samples that are closely spaced in the sections. Time scales were established by tuning each of the grain size records to theoretical changes in the Earth‧s orbital parameters. Results obtained show that during the last two glacial cycles, particle size of the loess co‐varies with apparent sedimentation rates, suggesting that variations in winter monsoon intensity and the aridity of the loess source area are tightly coupled. This proximal relationship is in striking contrast with the observation of distal eolian clays in North Pacific sediments. We propose that this phenomenon may result from the proximity of the Loess Plateau to the source area and from the significant control of the winter monsoon on the expansion‐retreat changes of the deserts in the northern and northwestern China.
Emission of carbon dioxide from a Tropical Estuarine System, Goa, India
Authors: Sarma V. V. S. S. , Kumar M. Dileep , Manerikar M.
Published: February 2004

Carbon dioxide species were studied in Mandovi‐Zuari system, a tropical estuarine complex influenced by strong monsoonal run‐off, with implications to build up and air‐water exchange of CO2. Total carbon dioxide (TCO2) behaved conservatively during the estuarine mixing. Partial pressure of carbon dioxide (pCO2), evaluated from TCO2 and pH couple, and carbonic acid dissociation constants, exhibited supersaturation with respect to atmospheric CO2 round the year. The pCO2 attained maximal levels over 2000 µatm in waters of early estuarine mixing. Average pCO2 in estuarine system were 1045 and 1153 µatm (three times to that in atmosphere) in non‐ southwest (SW) and SW monsoon seasons, respectively. An experimental study revealed that soil‐water interaction could be an important controller of pCO2 abundance in these estuarine waters. The calculated water‐to‐air average fluxes were 67 and 11 mmol m−2 d−1, respectively, in SW monsoon due to higher wind speeds and non‐SW monsoons. This study strongly suggests that pH regulation by soil‐water interaction is important, besides biological processes, in river and estuarine systems.
Land use changes and northern hemisphere cooling
Authors: Govindasamy B. , Duffy P. B. , Caldeira K.
Published: February 2004

Recent reconstructions of Northern Hemisphere mean temperatures over the past millennium show a long‐term cooling of about 0.25K between 1000 and 1900 AD, prior to the 20th century's warming. In this paper, we present the results of equilibrium climate model simulations that indicate that the land‐use change occurring over this period may largely explain this observed cooling, although other factors also could have played a significant role. The simulated annual mean cooling due to land‐use change is 0.25K globally and 0.37 K for the Northern Hemisphere, suggesting that the cooling of the prior centuries could have been largely the result of anthropogenic interference in the climate system.
An apparent atmospheric teleconnection between snow cover and the North American Monsoon
Authors: Ellis Andrew W. , Hawkins Timothy W.
Published: February 2004

Snow cover has been shown to reduce lower‐atmospheric temperatures thereby modifying atmospheric circulation patterns over time scales of days to months. Over the past three decades an inverse relationship between Eurasian winter snow cover extent and subsequent summer rainfall across India has been studied. Very little research has addressed the potential relationship between North American snow cover and the North American monsoon. The work presented here identifies an apparent inverse relationship between July and August snow cover across western North America and August precipitation across a portion of the southwestern U.S. that is susceptible to an annual monsoon circulation. Results suggest that during a summer season characterized by low snow cover across western North America, the typical subtropical ridge across the southern U.S. intensifies. The product appears to be an atmosphere that is conducive to advection of low‐level moisture northward across areas of the southwestern U.S.
The influence of deformation bands upon fluid flow using profile permeametry and positron emission tomography
Authors: Ogilvie S. R. , Orribo J. M. , Glover P. W. J.
Published: February 2004

Cataclastic deformation bands are significant discontinuities in sandstone reservoirs since they have dramatically reduced porosity and permeability relative to their host rock, despite their mm‐scale displacements. Consequently, these discontinuities often have a large impact upon the flow of fluids at both micro and macro‐scales. The effect of this impact in highly porous sandstone has been analyzed using a range of novel and conventional techniques, including pressure decay profile permeametry (PDPK) and positron emission tomography (PET). There are greater reductions in PDPK permeability in deformation bands relative to their host rock compared to conventional nitrogen permeametry measurements. This apparent discrepancy is the outcome of the higher spatial resolution of PDPK technique in measurements of much smaller rock volumes. There are greater porosity reductions using image analysis than conventional core techniques. These changes are reflected in a significant increase in irreducible water saturations (Swi) in deformation bands indicating much reduced fluid storage capacities. PET was used to monitor fluid flow as a function of pore volume of a sandstone plug containing deformation bands, demonstrating the direct effect of deformation bands as a potential barrier to fluid flow. The results of this study provide a detailed characterization of deformation bands at high resolution, which can be included in advanced reservoir simulation models.
Shock‐induced transition of NaAlSi3O8 feldspar into a hollandite structure in a L6 chondrite
Authors: Tomioka Naotaka , Mori Hiroshi , Fujino Kiyoshi
Published: February 2004

Natural NaAlSi3O8 hollandite was found in the Tenham chondrite. It occurs as aggregates of extremely fine grains of several tens of nanometers. The hollandite phase seems to have formed from host feldspar in a solid‐state reaction during the shock event. It is very sensitive to electron beam irradiation and easily becomes amorphous, similar to MgSiO3 perovskite contained in the same chondrite. The existence of crystalline silicate perovskite and hollandite in Tenham indicates that the peak pressure and the post‐shock temperature were much lower than previously believed.
Estimating lateral structure in the Earth's outer core
Authors: Piersanti Antonio , Boschi Lapo , Dziewonski Adam M.
Published: February 2004

Lateral density structure could exist in the Earth's fluid outer core, owing to the gravitational perturbations induced by the asphericity of the mantle. We take a realistic tomographic image of lateral heterogeneities in the topography of the core—mantle boundary (CMB), as an upper bound for the amplitude of lateral structure in the surface of constant gravitational potential, at the same average depth. With this boundary condition, we apply the theory of Wahr and de Vries [1989], to estimate quantitatively the corresponding lateral density anomalies in the outer core structure; we find that their value, relative to PREM, must be everywhere smaller than ∼0.1%. The resulting, theoretical maps of the outer core are dominated by long‐wavelength structure, with a pattern closely resembling that of the assumed CMB topography; they do not correlate with any of the existing tomographic images of the core.
Near‐surface imaging using coincident seismic and GPR data
Authors: Baker G. S. , Steeples D. W. , Schmeissner C. , Pavlovic M. , Plumb R.
Published: February 2004

In many near‐surface applications, detailed subsurface characterization is important. Characterization often is obtained using ground‐penetrating radar (GPR) or shallow seismic‐reflection (SSR) imaging methods, depending upon depth of interest and surficial geology. Each method responds to different physical properties; thus, each may produce different images of the same near‐surface volume. By incorporating the two methods, we generated a cross‐section of the subsurface at an alluvial test site and identified the depths of three interfaces accurately to ±5 cm. We present here experimental results and examples of SSR and GPR images obtained along the same traverse, showing coincident and noncoincident reflections from multiple interfaces within 3 m of the surface.
Global maps of Rayleigh wave attenuation for periods between 40 and 150 seconds
Authors: Billien Magali , Lévêque Jean‐Jacques , Trampert Jeannot
Published: February 2004

Studies of seismic attenuation must account for the large amplitude deviations caused by elastic focusing of energy. In a new approach, we jointly invert phase and amplitude measurements of 19,000 minor arc Rayleigh waves between periods of 40 and 150 seconds. The simultaneous inversion ensures that attenuation and phase velocity are mutually consistent because the phase and focusing term of amplitude are modelled using a common elastic model. At the shortest periods the maps show a good correlation between attenuation and phase velocity, suggesting a common cause in the uppermost mantle, most probably thermal in origin. This correlation is lost at longer periods. The main signal beyond periods of 100 seconds is a strongly attenuating circum Pacific zone and a pronounced ring of high attenuation around Africa. This feature seems reliable in our attenuation maps but not correlated to an equivalent structure in phase velocity. We thus favour scattering of wave energy on large size structures as a possible cause.
Trace of the recent deep water formation in the Japan Sea Deduced from historical 137Cs data
Authors: Miyao Takashi , Hirose Katsumi , Aoyama Michio , Igarashi Yasuhito
Published: February 2004

Historical 137Cs data obtained in the Japan Sea were statistically analyzed. 137Cs concentrations in the upper 200 m layer decreased almost monotonously after 1970's, while those in the deeper layers below 1500 m depth sharply increased during the period of 1985–1995, accompanied with the increase of the 137Cs inventory. It follows that considerable amount of 137Cs‐rich surface water was conveyed into the deep layers after 1985, suggesting that the deep water formation occurred. The spatial distribution of 137Cs in the deep layers in 1990's indicates that the recent deep water formation occurred in the northwestern area of the Japan Sea, around Peter the Great Bay.
Detection of vortices and saddle points in SST data
Authors: Yang Q. , Parvin B. , Mariano A.
Published: February 2004

We extend the Horn‐Schunck model of flow field computation to incorporate incompressibility for tracking fluid motion. This is expressed as a weak form of zero‐divergence constraint in the variational problem and implemented with a multigrid approach for efficient computation. The resulting feature displacement velocity field provides the basis for higher level abstraction and representation of the data for data mining. A robust and efficient algorithm, based on the Jordan curve index, for detecting vortices and saddle points in feature displacement fields derived from sequences of satellite‐derived SST fields is presented.
Tonga slab deformation: The influence of a lower mantle upwelling on a slab in a young subduction zone
Authors: Gurnis Michael , Ritsema Jeroen , Van Heijst Hendrick‐Jan , Zhong Shijie
Published: February 2004

There are fundamental geographic variations in the deformation of slabs in the transition zone. The seismic energy release and morphology of the Tonga slab show that it is deforming faster and has accumulated more deformation than any other slab. We show that Tonga overlies the edge of the large‐scale Pacific superplume. There is no substantial aseismic penetration into the lower mantle beneath Tonga, consistent with initiation of subduction during the Eocene. Other major subduction systems overlay seismically fast structures. For long‐lived subduction systems, the lower mantle tends to pull down on slabs while in Tonga the lower mantle pushes upward, partially accounting for the intense deformation. The perturbation to the state of slab stress due to large‐scale mantle flow is 10 to 40 MPa — nearly as large as that expected from slab pull.
Long‐term trend of tropopause over New Delhi and Thiruvananthapuram
Authors: Chakrabarty D. K. , Shah N. C. , Pandya K. V. , Peshin S. K.
Published: February 2004

Radiosonde observations taken during the past 32 years at New Delhi (28°N, 77°E) and 26 years at Thiruvananthapuram (8°N, 76°E) have been analyzed to examine the long‐term trend of tropopause height (TPH) and tropopause temperature (TPT) at these two stations. It appears that TPH is increasing and TPT is decreasing over the years. The trend of change is not same throughout the period of study. Considering the whole period of data we find that the increase of TPH is in the range of +0.57 to +1.13%/decade and the decrease of TPT is in the range range of −0.53 to −0.94%/decade. Qualitatively this is explainable with the decreasing trend of ozone in the stratosphere.
Episodic melt transport at mid‐ocean ridges inferred from magnetotelluric sounding
Authors: Heinson Graham , Constable Steven , White Antony
Published: February 2004

Oceanic crust is generated at mid‐ocean ridges by decompression melting of upwelling mantle at depths of between 50 and 120 km. Geodynamic and geochemical models of upwelling, melt extraction, and melt emplacement into crustal magma reservoirs present a variety of possible migration geometries, most of which assume steady‐state or near steady‐state processes. Here we present results from marine magnetotelluric (MT) measurements, carried out as part of the RAMESSES experiment on the slow spreading Reykjanes Ridge, which support a model of melt extraction and migration that is episodic, rather than steady‐state.
Two‐dimensional reconstruction of the surface ground motions of an earthquake: The September 21, 1999, Chi‐Chi, Taiwan earthquake
Authors: Huang Bor‐Shouh
Published: February 2004

The observed time history and spatial dependence of the surface ground motions of the September 21, 1999, Chi‐Chi, Taiwan earthquake over the entire island are presented. For the first time, this report presents an analysis of time‐dependent spatial ground motions at both near‐source and local distances using strong motion records. The two‐dimensional ground motions of the Chi‐Chi earthquake were reconstructed from more than 400 free‐field strong motion records after being corrected for absolute times. The reconstructed seismic wavefields can be considered as a new type of observed data, named “3‐D seismograms” here. Results of this study offer some insight into the study of earthquake source and wave propagation based on 3‐D numerical modelling and greatly compliment our ability to distinguish wave generations due to sources and/or structures.
On possible impact of the Indian Summer Monsoon on the ENSO
Authors: Goswami B. N. , Jayavelu V.
Published: February 2004

The Indian summer monsoon (ISM) could influence the El Niño and Southern Oscillation (ENSO) only if it could induce significant surface wind anomalies in the active regions of central and eastern equatorial Pacific. Using 50‐year NCEP reanalysis, it is shown that observed surface winds in the central and eastern Pacific associated ‘purely’ with ISM and unrelated to ENSO are very weak (∼0.5m.s−1). Strong surface winds in the central and eastern Pacific following a ‘strong’ or ‘weak’ ISM, noted in some earlier composite analyses, are related not to ISM but to the concurrent sea surface temperature (SST) forcing associated with the ENSO. A long run of an atmospheric general circulation model (AGCM) without inter‐annual SST forcing also show that a ‘pure’ ISM induces only very weak surface winds in the equatorial central and eastern Pacific. Thus, we conclude that the ISM by itself is unlikely to influence the ENSO in a significant way.
Direct current measurements at Kruzenshterna Strait in summer
Authors: Katsumata Katsurou , Yasuda Ichiro , Kawasaki Yasuhiro
Published: February 2004

Flow measurements at Kruzenshterna Strait, one of the two major gaps connecting the Sea of Okhotsk and the North Pacific were performed with a Lowered Acoustic Doppler Current Profiler in summer of 1999. Nearly one‐day time series at 2 stations were obtained by eleven consecutive casts, each being started every 2 and a half hours. The tidal components are estimated by least square fittings. The flow consists of a two layer exchange flow and the tide of the comparable magnitude. A volume transport of the upper layer is estimated to be 1.6 Sv (1 Sv = 106 m³/s) from the Okhotsk Sea to the North Pacific, while that of the lower layer is 1.3 Sv in the opposite direction. Hydrographic and oxygen data support the existence of the residual exchange flow.
Near‐field modeling of the July 17, 1998 tsunami in Papua New Guinea
Authors: Heinrich Philippe , Piatanesi Alessio , Okal Emile , Hébert Hélène
Published: February 2004

Modest earthquakes may trigger large submarine landslides, responsible for disastrous tsunami waves, as demonstrated by the Papua New Guinea event of July 17, 1998. The relatively small earthquake was followed by unexpectedly high waves, up to 15 m, wiping out 3 villages and killing more than 2200 people. Numerical simulations show that seismic dislocation sources are not energetic enough to reproduce the observed tsunami along the coast. Tsunami generation by a submarine landslide has been simulated by a finite‐difference model, assimilating the landslide to a flow of granular material. Long‐wave approximation is adopted for both water waves and the slide. Numerical results show that observed inundation heights are well reproduced for a volume of 4 km³ located 20 km offshore, sliding downslope with a Coulomb‐type friction.
Comparison of total ozone overburden from handheld photometers with the Wallops Island Dobson Spectrophotometer
Authors: Holdren Dawn H. , Olsen Robert O. , Schmidlin Francis J.
Published: February 2004

Total ozone column measurements are compared between the Dobson spectrophotometer located at Wallops Flight Facility, Wallops Island, VA, and two Microtops II photometers. The purpose of these comparisons is to determine whether the Microtops II ozone measurements are comparable to those obtained with the Dobson spectrophotometer. Results have shown that the handheld photometer can provide measurements within about 2% of the Dobson's. A comparison between the two Microtops showed approximately a 3% difference in the derived ozone overburdens. Better results with the two Microtops were obtained using the 305.5‐nm and the 312.5‐nm filters only.
The effect of global climate change on the regions of tropical convection in CSM1
Authors: Dutton Jan F. , Poulsen Chris J. , Evans Jenni L.
Published: February 2004

The impact of enhanced carbon dioxide concentrations on deep tropical convection (DTC) is explored using the National Center for Atmospheric Research (NCAR) Climate System Model (CSM1) model. A 134‐year simulation in which CO2 concentrations increase 1 % year−1 is analyzed. With approximately present‐day CO2 concentrations (367 ppmv) the CSM1 simulation captures the observed relationship between outgoing longwave radiation (OLR) and sea‐surface temperature (SST) in the tropics. The temperature threshold for deep convection in the model is approximately 24.75°C. As CO2 concentrations increase, the simulated threshold temperature for tropical convection progressively increases to ∼25.55° C and 26.55°C at 2×CO2 (year 80) and 3.4×CO2 (year 133). The fully coupled climate model response to increased CO2 concentrations implies that the expansion of the 26°C isotherm, the present‐day observed threshold, will not yield an expansion of the regions of DTC.
Near‐global survey of cloud column susceptibilities using ISCCP data
Authors: Han Qingyuan , Rossow William B. , Chou Joyce , Welch Ronald M.
Published: February 2004

A new parameter, cloud column susceptibility, is introduced to study the aerosol indirect effect, which describes the aerosol indirect effect more directly without assuming how cloud droplet size will respond to changes of droplet number concentration. Between the two approaches that used to retrieve cloud column susceptibilities, the one that makes no assumption of constant liquid water content leads to smaller, even negative cloud column susceptibilities. This finding is consistent with results of model studies and observations from the 1998–1999 Indian Ocean Experiment (INDOEX) that suggest that cloud liquid water content may be reduced during aerosol‐cloud interactions. The results of this survey suggest that using constant liquid water content in models may lead to significant overestimation of the aerosol indirect effect.
Climatological characteristics of cloud distribution and planetary boundary layer structure in Jakarta, Indonesia revealed by lidar observation
Authors: Sugimoto Nobuo , Matsui Ichiro , Shimizu Atsushi , Pinandito Mego , Sugondo Santoso
Published: February 2004

For two years we observed the vertical distribution of clouds and aerosols in Jakarta, Indonesia, with ground‐based Mie scattering lidars. A histogram of the cloud base height shows a notable maximum at an altitude of approximately 5 km, especially in the wet season. The planetary boundary layer height we inferred from the upper boundary of the aerosol layer was approximately 1.5–2 km in the wet season and 2–3 km in the dry season.
The effects of buffer and temperature feedback on the oceanic uptake of CO2
Authors: Yi Chuixiang , Gong Peng , Xu Ming , Qi Ye
Published: February 2004

The feedback between climate and carbon cycle systems is critical to the prediction of future CO2 concentration in the atmosphere and the capacity of the oceans to take up CO2 from the atmosphere. We calculated the magnitudes of the potential feedback between the increase of atmospheric CO2 concentration, the carbonate chemistry of the oceans (via a buffer factor), and the global temperature. We find that the magnitude of the buffer feedback depends strongly on the level of the dissolved inorganic carbon (DIC) in the oceans and increases rapidly with the increase of the atmospheric CO2 concentration. The buffer feedback would result in an increase of 95 ppm in the atmospheric CO2 concentration and a decrease of 236 GtC absorbed by the oceans from the atmosphere between year 2000 and 2100 under the Intergovernmental Panel on Climate Change (IPCC) scenario IS92e. By coupling our buffer feedback model with a global energy balance model, we find that global mean temperature increased 0.65°C from 1860 to 1990, which agreed well with the recorded value of 0.61°C. However, the ocean carbonate chemistry is quite insensitive to global temperature.
Local environmental conditions related to seasonal tropical cyclone activity in the northeast Pacific Basin
Authors: Collins J. M. , Mason I. M.
Published: February 2004

Tropical cyclone formation in the NE Pacific Ocean is poorly understood. We show that by dividing the NE Pacific Ocean into two regions, east and west of 116°W, our understanding is enhanced in terms of which climatological factors are involved. We show that for the period 1972–1997, in our western region, significant relationships exist between several environmental parameters and tropical cyclone numbers on a seasonal timescale, and there is also a significant increasing trend with time. Important parameters common to all tropical cyclone indices examined include relative humidity, sea surface temperature, pressure vertical velocity and precipitable water. The potential for predictability of tropical cyclones in this region is noted.
Is the Adriatic returning to dominate the production of Eastern Mediterranean Deep Water?
Authors: Klein Birgit , Roether Wolfgang , Civitarese Giuseppe , Gacic Miroslav , Manca Beniamino B. , d'Alcala Maurizio Ribera
Published: February 2004

Since the Aegean took over the deep water production of the Eastern Mediterranean at the end of the 1980s, the proficiency of the Adriatic as a formation site has been under question. The salt supply in the intermediate water enabling the Adriatic to produce dense water was diminished because of a salinity decrease by upwelling mid‐depth waters. Tracer data indeed indicate that the deep layer in the Adriatic has not been ventilated for most of the 1990s. The data presented also show that the dilution of the intermediate water reached a peak in 1995, after which more ventilated and saline waters were added. The recent increase of salt supply to the Adriatic by an extremely saline intermediate water mass supplied from the Aegean, establishes the preconditioning required to resume dense water production in the Adriatic.
Calculated upper stratospheric effects of solar UV flux and NOY variations during the 11‐year solar cycle
Authors: Callis Linwood B. , Natarajan Murali , Lambeth James D.
Published: February 2004

Model derived sensitivities of O3 near 40 km to solar UV flux changes (11‐year and 27‐day) fall within the range 0.36–0.55 with S11y ≈ S27d. These sensitivities derived from observations have been reported to be 0.91 and 0.39–0.46, respectively. This discrepancy appears to be due to long‐term (2–10 years) fluctuations in stratospheric NO2 in the 1980s. Such fluctuations, if not taken into account in the analysis of the data, could lead to high values of the sensitivity for the 11‐year activity cycle but not for the 27‐day solar rotation period. Simulations accounting for such effects suggest a consistency between theoretical values of S11y and those derived from data if NO2 effects are included. The appropriate values are approximately 0.48, a value similar to published model calculations and results from the analysis of data from the 27‐day solar rotation period. Verification of this suggestion awaits an NO2 data base of sufficient quality and length to permit solar‐cycle trend calculations to be made.
Effect of pollution from Central American fires on cloud‐to‐ground lightning in May 1998
Authors: Murray Natalie D. , Orville Richard E. , Huffines Gary R.
Published: February 2004

In the spring of 1998, numerous fires from seasonal biomass burning in Central America, mainly in Mexico and Guatemala, produced aerosol particles that were advected into the central plains of the United States. The effects of the fires continued from approximately April 9 through June 11. The most intense smoke concentration was on May 8 as seen from a NASA Shuttle mission. Characteristics of cloud‐to‐ground (CG) lightning flashes recorded by the National Lightning Detection Network were examined for May 1998 by subtracting the lightning characteristics for May 1995–1997, and 1999. This produces “difference value” maps with approximately 100 km resolution for polarity, peak currents, and multiplicity. Several significant differences are revealed. The percentage of positive flashes increased by a factor of two. Median first stroke peak currents have been calculated for both positive and negative flashes. For negative flashes, the median peak current decreased during the fire period. For positive flashes, the median peak current increased by over 20 kA in Texas, Oklahoma, Kansas, Arkansas and Nebraska. Mean multiplicity values, or the number of strokes per flash, were calculated. Positive flash multiplicity did not change. Mean multiplicity values for negative flashes, however, changed dramatically. For a region including Texas, Oklahoma, Kansas, and Louisiana multiplicity values for negative flashes decreased from 2.8 to 1.0–1.4 strokes per flash. The data analyzed were a corrected set from which we had deleted positive flashes with peak currents less than 10 kA, thus removing most of the intracloud contamination. Further studies may reveal the relation between the effect of pollution and aerosol size on the characteristics of CG flashes.
Estimation of rupture propagation direction and strong motion generation area from azimuth and distance dependence of source amplitude spectra
Authors: Miyake Hiroe , Iwata Tomotaka , Irikura Kojiro
Published: February 2004

Strong motion generation areas which reproduce ground motions in 0.2 to 10Hz were estimated using the empirical Green's function method. This strong motion generation area was somewhat smaller than the total rupture area, and coincident with the area of asperities derived from heterogeneous slip distributions estimated by waveform inversions using lower frequencies (<1Hz). We confirmed that the azimuth and distance dependence of observed source amplitude spectra in the near‐source area, i.e. rupture directivity effects, were controlled by rupture propagation style and size of the strong motion generation area. We found that the source displacement spectra at stations in forward rupture propagation directions had higher corner frequencies and steeper high‐frequency decays, compared with stations in sideways directions. Stations in backward directions had opposite tendencies. Different relationships between size and average corner frequencies of the strong motion generation area were proposed for unilateral and bilateral ruptures with radial propagation.
Evidence for the offshore transport of terrestrial organic matter due to the rise of sea level: The case of the East China Sea Continental Shelf
Authors: Oguri Kazumasa , Matsumoto Eiji , Saito Yoshiki , Honda Makio C. , Harada Naomi , Kusakabe Masashi
Published: February 2004

Accelerator mass spectrometry (AMS) 14C dating and analyses of the stable isotope ratio of organic carbon (δ13Corg) were carried out on two piston cores obtained from the continental slope and the Okinawa Trough in the East China Sea (ECS). These cores covered the last ca. 15 14C kyr BP (17 to 18 cal kyr BP). Mass and organic carbon (org. C) accumulation rates decreased gradually after the last deglaciation period. On the other hand, δ13Corg showed distinct depletion from ca. 14 to 12 14C kyr BP (17.5 to 13.2 cal kyr BP). The depletion relates to the large supply of terrestrial org. C from the ECS shelf triggered by the sea's intrusion onto the shelf area because of the rise in sea level.
Long‐term retention of impact crater topography on Ganymede
Authors: Dombard Andrew J. , McKinnon William B.
Published: February 2004

Previous analyses into viscous relaxation of impact craters on Ganymede have predicted short characteristic relaxation times (of the order of 100 Myr or less for larger craters), in disagreement with the apparent great ages of Ganymede's terrains. By applying improved understanding of rheologic parameters and initial crater shapes to a viscoelastic model, we calculate upper limit (zero heat flow) relaxation times in excess of the age of the solar system, eliminating this discrepancy. These very long relaxation times are not due to elastic effects, but are simply due to the effective viscosity of water ice at the appropriate temperatures and stresses.
Laboratory studies of sources of HONO in polluted urban atmospheres
Authors: Saliba Najat A. , Mochida Michihiro , Finlayson‐Pitts Barbara. J.
Published: February 2004

Laboratory studies reported here and in previous work show that the reaction of NO(g) with surface adsorbed HNO3 may be a significant source of HONO in polluted urban atmospheres. If these laboratory studies can be extrapolated to ambient conditions, this heterogeneous reaction may generate HONO to about the same extent as the hydrolysis of NO2 on surfaces, which is greater than the heterogeneous reaction of NO, NO2 and water. It may also be involved in generating HONO in snowpacks, and important in reconciling the discrepancy between measured and modeled HNO3/NOx ratios in the troposphere.
Ring laser detection of rotations from teleseismic waves
Authors: Pancha A. , Webb T. H. , Stedman G. E. , McLeod D. P. , Schreiber K. U.
Published: February 2004

Horizontal and vertical rotational components of teleseismic surface and body waves are detected by large ring laser gyroscopes. This is illustrated with records from magnitudes 7.0 and 7.3 events at distances of 31 deg. and 42.6 deg. respectively. Phase comparisons with synchronous linear seismometer records confirm the gyroscopic coupling.
Understanding uncertainties in the response of ENSO to greenhouse warming
Authors: Collins Matthew
Published: February 2004

The response of ENSO to increases in greenhouse gases is found to be markedly different in climate change simulations using two different versions of the Hadley Centre Coupled Models (HadCM2 and HadCM3). Using HadCM2, Collins [2000] found an increase in the amplitude, an increase in the frequency, and a shift in the phase of ENSO at 4×CO2. In HadCM3 it is shown that there are no significant changes in ENSO statistics at 4×CO2. Differences in the two models ENSO response are traced to differences in the response of the mean meridional gradients of temperature either side of the equator. These differences in the mean pattern of climate change are brought about by subtle changes in the physical parametrisation schemes, rather than the main differences between HadCM2 and HadCM3 which are enhanced horizontal ocean resolution and the removal of flux adjustments. Thus the response of ENSO variability to increasing greenhouse gases can depend in an unexpected and quite non‐linear way to subtle changes in the models representation of sub grid‐scale processes.
Methodology for use of isotopic climate forcings in ice sheet models
Authors: Cuffey K. M.
Published: February 2004

In ice sheet models, an internally consistent calculation of climatic temperature forcing from ice‐core isotopic records (δ) requires that corrections be made for an ice core site's elevation changes. Such corrections can be important for two reasons. First, elevation change at an ice divide can be large compared to elevation change at the migrating ice margin, resulting in erroneous estimates of marginal melt rate. Second, the δ of precipitation at an ice divide responds less to regional climatic temperature changes than to local temperature changes of the same magnitude that are caused by elevation changes. Significant elevation‐change corrections may also be necessary for inferring the relationships used to calculate climatic temperature from δ. A simple methodology incorporating both of these elevational effects is presented here. Further, I recommend that the δ to temperature conversion relations used in ice sheet models should derive from independently reconstructed temperature and δ time‐series rather than from spatial correlations, and justify this recommendation based on current understanding of the atmospheric isotopic distillation system.
Seismic imaging of the 1999 Izmit (Turkey) Rupture inferred from the near‐fault recordings
Authors: Bouchon Michel , Toksöz Nafi , Karabulut Hayrullah , Bouin Marie‐Paule , Dietrich Michel , Aktar Mustafa , Edie Margaret
Published: February 2004

We use near‐fault accelerograms to infer the space‐time history of rupture on the fault during the Izmit earthquake. The records show that the ground displacement and velocity near the fault were surprisingly simple. Rupture propagated toward the west at a velocity of about 3 km/s, and toward the east at a remarkably high average velocity of 4.7 km/s over a distance of about 45 km before decelerating to about 3.1 km/s on the eastern segment. Slip on the fault is particularly large down to a depth of 20 km on the central portion of the fault where it reaches about 7 m. Slip is large also below 10 km on the eastern fault segment, and this may have contributed to the loading of shear stress on the Düzce fault. On the western fault segment, large slip seems confined to shallow depths.
Eddy‐correlation measurement of hydrothermal gases
Authors: Werner C. , Wyngaard J. C. , Brantley S. L.
Published: February 2004

In the first application of eddy correlation in a hydrothermal region, we measured turbulent fluxes ranging between −17 and 13,500 g CO2 m−2 d−1 in Yellowstone National Park (YNP). These turbulent fluxes are similar in magnitude to chamber measurements of diffuse fluxes in the region. Negative turbulent fluxes due to vegetative uptake were measured in non‐thermal regions. The flux footprint was used to compare turbulent with surface fluxes within the source area of EC measurements, and turbulent fluxes were consistent within error to the spatial extrapolation of chamber measurements. EC is more representative than chamber techniques, providing a viable alternative to measuring gas emissions in volcanic and hydrothermal terrain.
Characteristics of coda envelope for Slant‐Stacked Seismogram
Authors: Matsumoto Satoshi , Obara Kazusige , Hasegawa Akira
Published: February 2004

We discuss the single scattering model by using seismic array data. By analyzing observed seismic array records, we found that coda energy level for slant‐stacked record is smaller than that for single station record as expected from the single scattering model. The energy level of slant‐stacked waveform is dependent on stacking direction. The energy level variation for different slant‐stacking directions suggests that horizontally aligned scatterers predominate over vertical ones. The present analysis is probably useful to detect scattering anisotropy.
Interdecadal climate variability and regime‐scale shifts in Pacific North America
Authors: Gedalof Ze‧ev , Smith Dan J.
Published: February 2004

A transect of climate sensitive tree ring‐width chronologies from coastal western North America provides a useful proxy index of North Pacific ocean‐atmosphere variability since 1600 AD. Here we use this high‐resolution record to identify intervals of an enhanced interdecadal climate signal in the North Pacific, and to assess the timing and magnitude of abrupt shifts in this system. In the context of this record, the step‐like climate shift that occurred in 1976–1977 is not a unique event, with similar events having occurred frequently during the past 400 years. Furthermore, most of the pre‐instrumental portion of this record is characterized by pronounced interdecadal variability, while the secular portion is more strongly interannual in nature. If the 1976–1977 event marks a return to this mode of variability there may be significant consequences for natural resources management in the North Pacific Sector.
The effect of Amazonian deforestation on the northern hemisphere circulation and climate
Authors: Gedney Nicola , Valdes Paul J.
Published: February 2004

Concern about tropical deforestation has often focused on local climate or ecological change. Less research has been carried out on its possible effects on the global climate, although possible mechanisms for such an occurrence have been proposed. Here we use a general circulation model (GCM) to show that complete Amazonian deforestation can result in changes in the climate far afield from the region of deforestation. In particular, the model predicts statistically significant changes to winter rainfall over the NE Atlantic, extending towards western Europe. These are associated with large‐scale circulation changes in middle and high latitudes. Simulation of these circulation changes with a simple model confirms the physical mechanism responsible (planetary wave propagation) implying that the result is robust and relatively independent of the GCM used.
UARS MLS observations of gravity waves associated with the Arctic Winter Stratospheric Vortex
Authors: Jiang Jonathan H. , Wu Dong L.
Published: February 2004

Passive satellite microwave limb radiances were used to study interactions between gravity waves and stratospheric winds in mid‐ to high latitude winter. We found that the radiance variances depend significantly on the instrument line‐of‐sight (LOS) and the background wind. The radiance variances are outstanding at two viewing angles where the LOS is about 30° or 90° from the wind vector. Waves propagating in preferred directions likely cause the two optimal angles observed. The variances at the 90° angle, located inside the polar vortex, seem produced by the gravity waves propagating nearly parallel to the wind direction. The variances at the 30° angle, located near the edge of the vortex, are likely associated with perturbations propagating almost perpendicularly to the wind direction. The variance of both modes increases with the background wind speed, but saturation is observed for the waves inside the vortex as wind speed exceeds about 60m/s. Interestingly, we also found that the temperature co‐located with the variance inside the vortex is warmer by 20K at background wind speeds >60m/s, which might be correlated with the wave breaking in the vortex.
Atmospheric correction of ocean color imagery through thick layers of Saharan dust
Authors: Moulin C. , Gordon H. R. , Chomko R. M. , Banzon V. F. , Evans R. H.
Published: February 2004

Airborne plumes of desert dust from North Africa are observable all year on satellite images over the Tropical Atlantic. In addition to its radiative impact, it has been suggested that this mineral dust has a substantial influence on the marine productivity. This effect is however difficult to gauge because present atmospheric correction algorithms for ocean color sensors are not capable of handling absorbing mineral dust. We apply a new approach to atmospheric correction in which the atmosphere is removed and the case 1 water properties are derived simultaneously. Analysis of SeaWiFS images acquired off Western Africa during a dust storm demonstrates the efficacy of this approach in terms of increased coverage and more reliable pigment retrievals.
A comparison of signals of regional aerosol‐induced forcing in eastern China and the southeastern United States
Authors: Yu Shaocai , Saxena V. K. , Zhao Zongci
Published: February 2004

This paper compares the temperature change patterns and the signals of regional aerosol‐induced forcing in eastern China and the southeastern US during the latter half of the twentieth century. Both regions show decreasing trends in the mean maximum temperature over recent decades and the cooling effect of Pinatubo volcanic aerosols. In contrast to the southeastern US, we found a slight overall warming trend in eastern China. Our analysis suggests that in addition to greenhouse warming effect, observed high concentrations of absorbing aerosols over eastern China during winter and spring might be one of the major reasons for the observed warming trend.