bluuebunny/crossref_metadata_2025 huggingface dataset:
Dual‐site imaging observations of small‐scale wave structures through OH and OI nightglow emissions
Authors: Ejiri M. K. , Shiokawa K. , Ogawa T. , Kubota M. , Nakamura T. , Tsuda T.
Published: October 2002

Four all‐sky CCD imagers have been simultaneously operated at Shigaraki (34.9°N, 136.1°E) and Murou (34.6°N, 136.0°E), Japan from January to March 1998 to obtain OH and OI (557.7 nm) nightglow images. We determined height of observed small‐scale wave structures (horizontal wavelengths of ∼7–9 km) by a triangulation technique. For an event of January 26, the structures seen in both nightglow images are estimated to have existed at around 91 km, suggesting that the structures occur at altitudes where these emission layers overlap. For another event of January 30, the structures with a height of 82 km were observed only in the OH images. These results indicate that the height extent of the small‐scale wave structures is fairly small, suggesting that such structures are instability features rather than gravity waves. Even if we assume that the structures are gravity waves, their vertical wavelengths estimated by using the dispersion relation are very small.
Slip distribution of the Mw 5.9, 1999 Athens earthquake inverted from regional seismological data
Authors: Baumont David , Courboulex Francoise , Scotti Oona , Melis Nicos S. , Stavrakakis George
Published: October 2002

We studied the kinematic rupture process of the moderate magnitude (Mw 5.9), 1999 Athens earthquake using broadband seismic recordings at regional distances. The Apparent Source Time Functions (ASTF), obtained by retrieving the wave propagation and site effects from the seismic recordings using an empirical Green's function method, indicate a rather complex rupture with a source directivity primarily pointing towards Athens. To further characterize the faulting, we inverted the ASTFs for the kinematic history of the rupture using a damped‐least square inversion scheme with inequality constraints. The rupture extent is delimited by a 10 km along‐strike ×20 km along‐dip zone. The mean slip amplitude on the observed rupture area is equal to 25 cm. The slip concentrates in two elongated zones with amplitudes reaching locally 60 cm. The total rupture lasted between 5 and 6 s.
Ozone budget in the upper stratosphere: Model studies using the reprocessed LIMS and the HALOE datasets
Authors: Natarajan Murali , Remsberg Ellis E. , Gordley Larry L.
Published: October 2002

Recently reprocessed LIMS dataset has been used with a contemporary photochemical model to study the balance between photochemical production and destruction of ozone in the upper stratosphere. Model results corresponding to January 1979 indicate that the ozone deficit is less than 15% in the pressure range of 5 to 0.5 mb between 50°S and 50°N latitude. The imbalance at 40 km is much smaller than reported by the earliest studies with the archived LIMS data. The same model, when initialized with HALOE (version 19) data for January, 1996, shows similar results with peak ozone deficits being less than 10%. For both cases, the model shows a near balance in the ozone budget above 1 mb, contrary to recent studies based on balloon‐borne measurements. The magnitude of the ozone imbalance seen in this study is within the uncertainties of the data and model.
Potential predictability of seasonal precipitation over the United States from canonical ensemble correlation predictions
Authors: Lau K.‐M. , Kim Kyu‐Myong , Shen Samuel S. P.
Published: October 2002

Potential predictability of seasonal precipitation over the US is explored using a new canonical ensemble correlation (CEC) prediction model, which optimally utilizes intrinsic sea surface temperature (SST) variability in major ocean basins. Results show that CEC yields a remarkable (10–20%) increase in baseline prediction skills for seasonal precipitation over the US for all seasons, compared to traditional statistical predictions using global SST. While the tropical Pacific, i.e., El Niño, contributes to the largest share of potential predictability in the southern tier States during boreal winter, the North Pacific and the North Atlantic are responsible for enhanced predictability in the northern Great Plains, Midwest and the southwest US during boreal summer. Overall, CEC significantly reduces the spring‐summer predictability barrier over the conterminous US, thereby raising the skill bar for seasonal precipitation predictions.
Three‐dimensional energetic ion sounding of the magnetopause using Cluster/RAPID
Authors: Oksavik K. , Fritz T. A. , Zong Q.‐G. , Søraas F. , Wilken B.
Published: October 2002

We present new results using energetic particles to remotely sound the high‐latitude magnetopause in three‐dimensions. Less than two gyro radii from an absorbing boundary a trapped particle distribution appears non‐gyrotropic, as particles start to cross the boundary. Knowing the magnetic field and the particle mass and energy, it is possible to derive the direction and distance to the magnetopause just by examining the azimuthal distribution of locally mirroring particles. Combining observations from at least three spacecraft gives a three‐dimensional picture of the magnetopause surface. We have performed this analysis for a high‐latitude boundary crossing on January 14, 2001. The very first results give a consistent overall picture of how the magnetopause boundary is coming towards, just passing, and then retreating away from the spacecraft. This clearly illustrates that the magnetopause ion sounding technique can be used to remotely study the three‐dimensional orientation and location of the magnetopause surface.
Consequences of a saturated convection electric field on the ring current
Authors: Liemohn M. W. , Kozyra J. U. , Hairston M. R. , Weimer D. R. , Lu G. , Ridley A. J. , Zurbuchen T. H. , Skoug R. M.
Published: October 2002

Results from kinetic simulations of hot ion transport in the inner magnetosphere are used to show that the ring current energy content must have a nonlinear (asymptotic) coupling relationship to extreme solar wind conditions due to saturation of the near‐Earth convection electric field Ey, conv(defined as a function of cross polar cap potential ΔΦPC). This study examines the Bastille Day magnetic storm (July 14–17, 2000), where the z‐component of the interplanetary magnetic field reached −58 nT and the solar wind speed exceeded 1100 km s−1. A large discrepancy in the modeled ΔΦPCconfirms a nonlinear response of the high‐latitude potential during this event. It is found that this nonlinearity of Ey, convis necessary to obtain reasonable agreement between the simulation results and the observed geoeffectiveness (Dst) of the storm.
Data assimilation of stratospheric ozone using a high‐resolution transport model
Authors: Fierli Federico , Hauchecorne Alain , Bekki Slimane , Théodore Bertrand , Fanton d'Andon Odile
Published: October 2002

We describe a method for assimilating sequentially tracer measurements in isentropic chemistry‐transport models (CTMs) of the stratosphere. The parametrisation of the forecast error covariance and its evolution is largely based on simplifications described in Menard and Chang [2000] and Khattatov et al. [2000]. The model used here is a high resolution isentropic advection model which is driven by ECMWF (European Center for Medium range Weather Forcast) meteorological analyses. The assimilation on isentropic surfaces allow us to exploit the well‐established correlation between tracer mixing ratio and potential vorticity in the formulation of the forecast error covariance. Multiple 20‐day sequential assimilations of MLS (Microwave Limb Sounder onboard UARS satellite) ozone data during an ozone depletion event are performed. χ2 (chi‐square) and OmF (observation minus forecast) statistics are used to optimise the assimilation system by adjusting parameters of the error covariance. The quality of the analysis is found to be significantly improved when the strong correlation between ozone and potential vorticity is taken into account.
A “broad‐shelf effect” upon postglacial relative sea level history
Authors: Peltier W. R. , Drummond Rosemarie
Published: October 2002

Recently published analyses of postglacial relative sea level (RSL) histories from coastal locations which are proximate to broad continental shelves that were significantly exposed land at Last Glacial Maximum, have demonstrated that the Holocene RSL variations at such sites are not adequately explained unless particular care is taken to treat the influence of shelf inundation. This is herein shown to require a local adjustment to the water load based upon a mass conservation constraint. Previously revealed misfits of theory to data from such regions therefore do not signify a requirement for lateral heterogeneity in model viscoelastic structure. The quality of the revision to the theory required to account for this “broad shelf effect” is illustrated through analysis of RSL histories from the east coast of the South American continent and from Northwestern Europe.
Impact of including dissolved organic matter in a global ocean box model on simulated distributions and fluxes of carbon and nitrogen
Authors: Popova Ekaterina E. , Anderson Thomas R.
Published: October 2002

Two ecosystem models, one with dissolved organic matter and the other without, were run to equilibrium in a global ocean box model. Predicted distributions of nitrate and dissolved inorganic carbon were similar between the two runs. Export fluxes to the deep ocean were dominated by sinking particles in both instances, and so showed little sensitivity to the choice of whether or not an explicit representation of DOM is chosen. Significant differences did however occur in predicted primary production and f‐ratio, giving rise to alkalinity changes (up to 22 mmol m−3) which could be important when calculating pCO2 and atmospheric exchange of CO2 in studies addressing the global carbon cycle.
Multifractal properties of evolving convective systems over tropical South America
Authors: Carvalho Leila M. V. , Lavallée Daniel , Jones Charles
Published: October 2002

This paper examines variations in multifractal properties of evolving mesoscale convective systems over tropical South America using infrared satellite images and a tracking technique. It is shown that multifractal coefficients have diurnal variation and seem to be modulated by intraseasonal low‐level circulations. This remote sensing approach has potential application to infer convective‐scale processes occurring in individual mesoscale systems.
Tidal stress/strain and acoustic emission activity at the Underground Research Laboratory, Canada
Authors: Iwata Takaki
Published: October 2002

We study the correlation between the phase of the moon and the occurrences of acoustic emissions (AEs) monitored at the Underground Research Laboratory in Canada. On 9 December 1997, a significant increase of AEs began and this activity decayed with time day by day. During the period of the decay, we observed that the activity often increased. Most of these increases corresponded with moments of new or full moon. We investigate whether the increase of AEs is correlated with the moments of new or full moon using a statistical method. We consider two models concerned with the daily occurrence rate of AEs. In the first model, the existence of the correlation is not assumed. In the second model, the existence is assumed. Using AIC (Akaike Information Criterion), it is shown that the second model is a significantly better fit to the observed time series of AEs.
Two modes of bottom water in the Australian‐Antarctic Basin
Authors: Whitworth T.
Published: October 2002

Recent data from the deep Australian‐Antarctic Basin show that waters colder than about −0.4°C are fresher by as much as 0.02 than data collected prior to 1994. It is possible that the freshening represents a fundamental change in the sources of bottom water for the basin, but it is more likely that the fresh mode recurs periodically and is underrepresented in the historical database. The freshening may be caused by a change in fresh bottom water input from the Antarctic coast between 120°E – 160°E or by a reduction in the outflow of saline Ross Sea Bottom Water.
Tropospheric response to stratospheric perturbations in a relatively simple general circulation model
Authors: Polvani Lorenzo M. , Kushner Paul J.
Published: October 2002

The sensitivity of the tropospheric extratropical circulation to thermal perturbations of the polar stratosphere is examined in a dry primitive equation general circulation model with zonally symmetric forcing and boundary conditions. For sufficiently strong cooling of the polar winter stratosphere, the winter‐hemisphere tropospheric jet shifts polewards and strengthens markedly at the surface; this is accompanied by a drop in surface pressure at high latitudes in the same hemisphere. In addition, this extratropical tropospheric response is found to be very similar to the model's leading pattern of internal variability. These results are tested for robustness at several horizontal and vertical resolutions, and the same tropospheric response is observed at all but the lowest resolution tested. The behavior of this relatively simple model is broadly consistent with recent observational and modeling studies of trends in extratropical atmospheric variability.
Heterogeneous nucleation of ice in (NH4)2SO4‐H2O particles with mineral dust immersions
Authors: Zuberi Bilal , Bertram Allan K. , Cassa Christopher A. , Molina Luisa T. , Molina Mario J.
Published: October 2002

Using optical microscopy, we investigated the heterogeneous nucleation of ice in aqueous (NH4)2SO4‐H2O particles containing two types of mineral dusts, kaolinite and montmorillonite. The efficacy of montmorillonite and kaolinite to nucleate ice in (NH4)2SO4‐H2O particles is similar. The difference in freezing temperatures, compared to the homogeneous freezing temperatures, is found to vary from 8–20 K and it is larger for particles with concentrations greater than 27 wt %. Our freezing data shows that for temperatures ranging from 239 K to 198 K, ice super‐saturations between 1.35 and 1.51 are required for ice to heterogeneously nucleate in NH4SO4‐H2O particles containing mineral dust immersions. Based on our results, we conclude mineral dust is an efficient nuclei for ice in NH4SO4‐H2O aerosols and as a result, it can initiate the formation of upper tropospheric ice clouds at warmer temperatures and lower super‐saturations in comparison to homogeneous freezing.
HF radar observations of Pc5 ULF pulsations driven by the solar wind
Authors: Stephenson J. A. E. , Walker A. D. M.
Published: October 2002

We present HF radar observations of Pc5 field line resonances in the post‐midnight Antarctic ionosphere on April 28/29 1997. Simultaneous oscillations were seen in the solar wind parameters observed by WIND. The spectra of both sets of data show peaks near 1.3 mHz, 1.9 mHz, 2.7 mHz and 3.3 mHz. The data were bandpass filtered and a complex demodulation technique applied to calculate the instantaneous energy flux in the solar wind in each band and hence the power incident on the front of the magnetosphere 70 minutes later. The magnitude of the instantaneous power deposited in the ionosphere at each frequency through Joule heating followed this closely and was an order of magnitude smaller. We conclude that, at least on this occasion, the field line resonances could have been directly driven by the solar wind oscillations.
Sediment fluidization events in a lake caused by large monthly rainfalls
Authors: Colomer Jordi , Serra Teresa , Soler Marianna , Casamitjana Xavier
Published: October 2002

In the last fourteen years (1986–1999), fluidizations of confined bed–sediments due to underground springs in basin BII of lake Banyoles (Spain) have been detected. As a result of periods of high precipitation, sediment confined at the bottom of karstic basins migrates from 45 m depth to approximately 25 m depth. Fluidization processes are associated to monthly rainfall 1.5 to 4.5 times larger than the long‐term mean (1970–1999). As a result of a fluidization event, the water column of the lake maintains the particle volume concentrations of suspended sediment (pVC) as high as 44 μl/l, which is ∼8–29 times larger than the usual values of pVC.
Polarization analyses of broadband seismic data recorded on Stromboli Volcano (Italy) from 1996 to 1999
Authors: Falsaperla Susanna , Wassermann Joachim , Scherbaum Frank
Published: October 2002

We analyze broadband seismic data recorded at a single station deployed on Stromboli island from 1996 to 1999 in order to determine basic parameters of the seismic wavefield and study their relationship with volcanic activity. In addition to a characterization in the frequency domain, we apply polarization analysis and study long‐term variations of these parameters possibly reflecting also changes in source properties. Our analysis is twofold. First, we focus on a meaningful reduction of the data to selected parameters, i.e., azimuth and incidence angle, which can be correlated with volcanic activity. Secondly, we investigate if there is maintenance of the correlations over long time spans. We observe statistically significant long‐term changes (from several months to year) in the wavefield parameters considered. We interpret such changes as possibly being caused by the enhanced strength of a deep source, potentially by supply of fluids from a low part of the magma feeder between the end of 1997 and the first months of 1998.
Wet winters, dry summers? Three centuries of precipitation data from Paris
Authors: Slonosky Victoria C.
Published: October 2002

Precipitation measurements taken at the Paris Observatory from the 1680s to the 1750s are presented; these values are blended with modern data until 2001. The most striking change in the precipitation patterns over the past 300 years is the change in seasonal distribution; in the late 17th and 18th centuries, summer precipitation accounted for 60% of the yearly total, changing to a uniform seasonal distribution in the 20th century. Winter precipitation has increased by 24 mm/century, while summer precipitation increased by 4 mm/century. The winter of 2000/2001 was the wettest of the past three centuries; the year 2000 recorded the largest amount of precipitation since observations began.
Possibly inverted‐polarity electrical structures in thunderstorms during STEPS
Authors: Rust W. David , MacGorman Donald R.
Published: October 2002

In full and partial vertical profiles of the electric field in thunderstorms during the Severe Thunderstorm Electrification and Precipitation Study in 2000, we find evidence for inverted‐polarity electrical structures in the convective region of thunderstorms. The evidence consists of polarities opposite from normal (1) in the peaks in the profile of the vertical component of the electric field, Ez, and (2) in the vertical sequence of inferred charges. In storms that possibly are inverted in polarity, the lowest peak in Ez inside the cloud is negative, followed by a positive peak farther up. Near storm top, the uppermost peak is negative, and the uppermost inferred charge is positive. The sounding data do not conclusively prove that inverted‐polarity thunderstorms exist, but they support it. If additional data corroborate that such storms do exist, it will require modification of at least some aspects of our conceptual models of storm electrification.
Reduced effectiveness of terrestrial carbon sequestration due to an antagonistic response of ocean productivity
Authors: Ridgwell Andy J. , Maslin Mark A. , Watson Andrew J.
Published: October 2002

Biological productivity in a number of ocean regions appears to be at least partly limited by the availability of iron. Any reduction in the present‐day aeolian iron supply to the open ocean is therefore likely to result in further limitation of productivity. The stabilization of soils for the purpose of carbon sequestration could give rise to such an effect. With the aid of a global carbon cycle model, we show that the effectiveness of carbon removal from the atmosphere by sequestration on land will be diminished as a result of a reduction of up to 9% in the rate of anthropogenic CO2 uptake by the ocean. This interconnectedness, both within the `natural' system and in relation to human activities, highlights the importance of analyzing global change within an integrated ‘Earth system’ framework.
A deep convective chimney in the winter greenland sea
Authors: Wadhams P. , Holfort J. , Hansen E. , Wilkinson J. P.
Published: October 2002

During two cruises to the Greenland Sea in winter 2001 a narrow convective chimney extending from the surface to a depth exceeding 2400 meters was discovered and mapped in detail. The feature was observed to be stable over a period of a month and its centre moved only 700 m in that time; its diameter was only 10 km. At a time when deep convection is thought to have ceased in the Greenland Sea the existence of this feature is a challenge to our understanding of the causes and impacts of open ocean winter convection.
Observed reductions of total solar irradiance by biomass‐burning aerosols in the Brazilian Amazon and Zambian Savanna
Authors: Schafer J. S. , Eck T. F. , Holben B. N. , Artaxo P. , Yamasoe M. A. , Procopio A. S.
Published: October 2002

Several aerosol and solar flux monitoring sites were established in Brazil for the Large Scale Biosphere‐Atmosphere Experiment in Amazônia project. CIMEL sunphotometers and collocated pyranometers were employed at two southern Amazonian sites in order to quantify instantaneous reductions of total irradiance due to high aerosol optical thickness (AOT) smoke events (relative to values modeled for background aerosol conditions). Results from the Brazilian sites are presented for 1999 and for comparison, a similar analysis is discussed for data from three south‐central African sites during the burning season of 2000. The relative reductions in total irradiance at the surface resulting from biomass burning aerosol are observed to be substantial at all sites, ranging from 16% for an aerosol optical thickness (500 nm) of 1.0 for the Brazilian sites to an average rate of 22% for the African sites. For a solar zenith interval (25–35°), these rates equate to reductions of roughly 145 W/m2 and 210 W/m2 respectively, for an AOT = 1.0. Instantaneous reductions of 337 W/m2 were observed for the heaviest smoke conditions (AOT: ∼3.0) in Brazil.
Continental heat gain in the global climate system
Authors: Beltrami Hugo , Smerdon Jason E. , Pollack Henry N. , Huang Shaopeng
Published: October 2002

Recent estimates have shown the heat gained by the ocean, atmosphere, and cryosphere as 18.2 · 1022 J, 6.6 · 1021 J, and 8.1 · 1021 J, respectively over the past half‐century. However, the heat gain of the lithosphere via a heat flux across the solid surface of the continents (29% of the Earth's surface) has not been addressed. Here we calculate that component of Earth's changing energy budget, using ground‐surface temperature reconstructions for the continents. In the last half‐century there was an average flux of 39.1 mW m−2 across the land surface into the subsurface, leading to 9.1 · 1021 J absorbed by the ground. The heat inputs during the last half‐century into all the major components of the climate system — atmosphere, ocean, cryosphere, lithosphere‐reinforce the conclusion that the warming during the interval has been global.
Production mechanism and global budget of N2O inferred from its isotopomers in the western North Pacific
Authors: Toyoda Sakae , Yoshida Naohiro , Miwa Tatsuya , Matsui Yohei , Yamagishi Hiroaki , Tsunogai Urumu , Nojiri Yukihiro , Tsurushima Nobuo
Published: October 2002

We measured the intramolecular distribution of 15N as well as conventional nitrogen and oxygen isotope ratios in oceanic nitrous oxide (N2O) in the western North Pacific for the first time. In contrast to a nearly homogeneous vertical distribution of a bulk nitrogen isotope ratio, a wide variation in site preference for intramolecular 15N distribution was found, suggesting the subsurface and deep source mixing and the production mechanism in the ocean. The oceanic composition of N2O isotopomers quantitatively outlines the ocean as the most significant source after the terrestrial one.
Shallow seismic imaging of folds above the Puente Hills blind‐thrust fault, Los Angeles, California
Authors: Pratt Thomas L. , Shaw John H. , Dolan James F. , Christofferson Shari A. , Williams Robert A. , Odum Jack K. , Plesch Andreas
Published: October 2002

High‐resolution seismic reflection profiles image discrete folds in the shallow subsurface (<600 m) above two segments of the Puente Hills blind‐thrust fault system, Los Angeles basin, California. The profiles demonstrate late Quaternary activity at the fault tip, precisely locate the axial surfaces of folds within the upper 100 m, and constrain the geometry and kinematics of recent folding. The Santa Fe Springs segment of the Puente Hills fault zone shows an upward‐narrowing kink band with an active anticlinal axial surface, consistent with fault‐bend folding above an active thrust ramp. The Coyote Hills segment shows an active synclinal axial surface that coincides with the base of a 9‐m‐high scarp, consistent with tip‐line folding or the presence of a backthrust. The seismic profiles pinpoint targets for future geologic work to constrain slip rates and ages of past events on this important fault system.
Role of Indian Ocean warming in the development of Philippine Sea anticyclone during ENSO
Authors: Watanabe Masahiro , Jin Fei‐fei
Published: October 2002

The anomalous, low‐level anticyclone near the Philippines and suppressed convection over the western Pacific associated with the mature warm phase of El Niño–Southern Oscillation (ENSO) have been suggested as important elements in the interaction between ENSO and the East Asian monsoon. We examined the causes of these anomalies in the circulation and convection using a newly developed, linear baroclinic model that includes interactive moist processes of the cumulus convection and surface heat fluxes. A conventional version of the linear model forced by prescribed heating indicates that the diabatic cooling due to suppressed convection over the maritime continent generates the Philippine Sea anticyclone. From a series of the moist linear model experiments, we found that the modest warming of the Indian Ocean, in addition to the strong warming in the central–eastern Pacific and weak cooling in the western Pacific, is significant to suppress the convection over the maritime continent. Observed data also show a coincidence of the development between the Philippine Sea anticyclone, Indian Ocean warming, and the ascending motion over the Indian Ocean, supporting the model results. The above results indicate that the atmosphere‐ocean system in the Indian Ocean may be one of important factors to improve predictability of the East Asian climate during ENSO.
Biogenic opal indicating less productive northwestern North Pacific during the glacial ages
Authors: Narita Hisashi , Sato Masayasu , Tsunogai Shizuo , Murayama Masafumi , Ikehara Minoru , Nakatsuka Takeshi , Wakatsuchi Masaaki , Harada Naomi , Ujiié Yukika
Published: October 2002

Biogenic opal and ice‐rafted detritus (IRD) data from sediments in the Okhotsk Sea and the neighboring North Pacific revealed the remarkable reduction in opal production and southward advancement of sea‐ice covered area during the last glacial maximum, resulting also southward shift of high biological productive area in the northwestern North Pacific. It implies that the substantial reduction in outflux of CO2 to the atmosphere in northwestern North Pacific and the pronounced increase in CO2 sequestering in temperate North Pacific. This could be an additional CO2 reduction mechanism of atmospheric CO2 in the last glacial period.
Viscosity change and structural transition of Molten Fe at 5 GPa
Authors: Terasaki Hidenori , Kato Takumi , Urakawa S. , Funakoshi K. , Sato K. , Suzuki A. , Okada T.
Published: October 2002

The in situ viscosity measurements of the pure molten Fe under high pressures were made by falling sphere X‐ray radiography method. Viscosity coefficients at about 2000 K were 15–24 mPa s at 2.7–5.0 GPa, and 4–9 mPa s at 5.0–7.0 GPa. Drastic decrease was found at around 5 GPa, at which stable solid phase below the melting temperatures change from delta (bcc) to gamma (fcc) phases. The observation indicates the possibility that the structural change in the molten Fe occurs in a narrow pressure interval (1 GPa) at the similar condition with the phase transformation in the solid.
Electrical structure across the Indus Tsangpo suture and Shyok suture zones in NW Himalaya using magnetotelluric studies
Authors: Gokarn S. G. , Gupta Gautam , Rao C. K. , Selvaraj C.
Published: October 2002

Magnetotelluric studies in the NW Himalayan region have shown anomalously high conductance of about 20,000 siemens in the crust beneath the Indus Tsangpo suture (ITS) and the adjoining Tso‐Morari dome in the depth range of 1–20 km. High heat flow and high attenuation of the seismic waves in the Himalayan crust, together with the observed high conductance indicate presence of wide spread partial melt generated from the subducted Indian crust. The Ladakh batholith appears as a resistive block to the north of ITS. A moderately conductive zone demarcates the Ladakh batholith from Karakoram batholith to the north. The similarity in the resistive structure with the results reported from the Tibetan region by Wei et al. [2001] about 1500 km to the east is rather significant, indicative of a two dimensional nature of the Himalayan collision belt, at least to the first order.
Sub‐catchment melt and long‐term stability of ice stream D, West Antarctica
Authors: Parizek Byron R. , Alley Richard B. , Anandakrishnan Sridhar , Conway Howard
Published: October 2002

The apparent long‐term persistence and short‐term variability of the Siple Coast ice streams of West Antarctica are tied to regional thermal conditions and local basal lubrication. Numerical simulations indicate that the flux of latent heat in a throughgoing hydrologic system fed by melt beneath thick inland ice maintains the lubrication of fast‐moving modern and ice‐age ice streams despite their tendency to freeze to the bed, and would allow additional thinning and grounding‐line retreat.
Low altitude quasi‐periodic radar echoes observed by the Gadanki VHF radar
Authors: Pan C. J. , Rao P. B.
Published: October 2002

We report here on the low altitude quasi‐periodic (LQP) radar echoes from low latitude sporadic E layer (Es) observed by the Gadanki (13.5°N, 79.2°E; geomagnetic latitude 6.3°N) VHF radar. The LQP echoes occurred both during daytime and nighttime and are confined to a slowly descending layer with a thickness of about 2–4 km in the height range of 90–100 km. The periods are found to range from tens of seconds to less than about 3 minutes. The Doppler velocities vary over a range of −20 to +20 m/s during daytime and 0 to 10 m/s during nighttime and are known to be sensitive to the layer height, being dominated by the effect of zonal electric field above and meridional neutral wind below a height of ∼97 km for the type 2 irregularities [Krishna Murthy et al., 1998]. The spectral widths are found to be of the order of 50 to 75 m/s during daytime and 30 to 60 m/s during nighttime. The LQP echoes reported here are similar to that observed recently over midlatitudes [Rao et al., 2000; Urbina et al., 2000], but distinctly different from the widely reported quasi‐periodic (QP) echoes occurring at higher altitudes (>100 km). The observations are discussed briefly in terms of the potential source mechanisms.
Multi‐decadal decrease of net community production in western subarctic North Pacific
Authors: Ono T. , Tadokoro K. , Midorikawa T. , Nishioka J. , Saino T.
Published: October 2002

Temporal variation of phosphate concentration in the mixed layer of western subarctic North Pacific from 1968 to 1998 was investigated with quasi‐monthly resolution. February and July phosphate time series showed a linear decreasing trend of −0.008 ± 0.003 and −0.019 ± 0.005 μmol/l/y, respectively, while no multi‐decadal trend was observed in April/May phosphate time series. With this result, net biological phosphate consumption between February and April linearly decreased at the rate of −0.43 ± 0.11 mmolP/m2/y, while that between May and July increased at the rate of +0.16 ± 0.05 mmolP/m2/y. Net biological phosphate consumption from February through August was linearly diminished at the rate of −0.40 ± 0.07 mmolP/m2/y, corresponding to a −0.51 ± 0.09 gC/m2/y decrease of net community production under assumption of the constant C/P ratio of 106. Chl.a inventory in the April mixed layer also showed a decreasing trend of −2.35 ± 1.22 mg/m2/y, which correlated with the observed net production decrease between February and April.
Distribution of Dynamic and Static Stress Changes during 2000 Tottori (Japan) Earthquake: Brief Interpretation of the Earthquake Sequences; Foreshocks, Mainshock and Aftershocks
Authors: Dalguer L. A. , Irikura K. , Zhang W , Riera J. D.
Published: October 2002

The dynamic and static stress changes during the 2000 Tottori earthquake have been recovered from the results of waveform inversion. We use the DEM to solve the elastodynamic equation specifying the slip along the fault obtained by a kinematic fault model. The resulting shear stress distribution suggests an explanation of the foreshock and aftershock distributions. We conclude that the fault zone heterogeneity is strong and most of the foreshocks and aftershocks were located in the zone of negative stress drop and mainly in the area surrounding the asperity. This suggests that the asperity behaved as a barrier during the foreshocks and after the main shock the stress in the area surrounding the asperity increased and triggered most of the aftershocks. The foreshock distribution was confined to a finite localized zone in the central part of the fault, suggesting that this zone was bordered by barriers.
Potential effects of global warming on the Sacramento/San Joaquin watershed and the San Francisco estuary
Authors: Knowles Noah , Cayan Daniel R.
Published: October 2002

California's primary hydrologic system, the San Francisco estuary and its upstream watershed, is vulnerable to the regional hydrologic consequences of projected global climate change. Projected temperature anomalies from a global climate model are used to drive a combined model of watershed hydrology and estuarine dynamics. By 2090, a projected temperature increase of 2.1°C results in a loss of about half of the average April snowpack storage, with greatest losses in the northern headwaters. Consequently, spring runoff is reduced by 5.6 km3 (∼20% of historical annual runoff), with associated increases in winter flood peaks. The smaller spring flows yield spring/summer salinity increases of up to 9 psu, with larger increases in wet years.
Methane emission from the mud volcanoes of Sicily (Italy)
Authors: Etiope G. , Caracausi A. , Favara R. , Italiano F. , Baciu C.
Published: October 2002

Mud volcanoes represent the largest expression of natural methane release into the atmosphere; however, the gas flux has never been investigated in detail. Methane output from vents and diffuse soil degassing is herewith reported for the first time. Measurements were carried out at 5 mud volcano fields around Sicily (Italy). Each mud volcano is characterized by tens of vents and bubbling pools. In the quiescent phase, methane emission from single vents ranges between 0.01 and 6.8 kg/day. Diffuse soil leakage around the vents is in the order of 102–104mg m−2d−1. An exceptional flux of 106mg m−2d−1was recorded close to an everlasting fire. Soil CH4flux is positive even at large distances from the mud volcano fields suggesting a diffuse microseepage over wider areas. A total of at least 400 tons CH4per year can be estimated over the area investigated alone (∼1.5 km2).
On the nature of internal wave spectra near a continental slope
Authors: van Haren Hans , Maas Leo , van Aken Hendrik
Published: October 2002

Amongst the most energetic motions in the deep ocean are internal waves supported by stable vertical stratification in density. Previously, these waves were considered freely propagating as described by a smooth continuum internal wave band (IWB) frequency spectrum. We studied details of the IWB using yearlong current observations from the Bay of Biscay. Instead of observing continuum IWB spectra near a continental slope, we show that (at least) the first half‐decade of the IWB is dominated by motions at localized frequencies determined by strong non‐linear interactions between waves at the fundamental semidiurnal tidal and atmospherically induced inertial frequencies.
Oxygen isotope composition of stratospheric carbon dioxide
Authors: Lämmerzahl Peter , Röckmann Thomas , Brenninkmeijer Carl A. M. , Krankowsky Dieter , Mauersberger Konrad
Published: October 2002

Heavy oxygen isotope enrichment in stratospheric CO2 has been identified in the past as a direct result of the large O3 isotope anomaly though no simultaneous measurements are known. Results from 8 stratospheric balloon flights at two latitudes are reported that provide now a complete oxygen isotope analysis of both gases. An unambiguous, very tight correlation between enrichments of 17O and 18O in CO2 has been found. The large ratio δ17O/δ18O of 1.71 ± 0.03 shows a faster transfer of 17O than of 18O into CO2 and establishes a standard throughout the lower and middle stratosphere between midlatitudes and high northern latitudes. Ozone isotope transfer can now be treated in models with reliable atmospheric data.
Impact of global warming on permafrost conditions in a coupled GCM
Authors: Stendel M. , Christensen J. H.
Published: October 2002

A climate change scenario experiment conducted with the state‐of‐the‐art coupled atmosphere‐ocean general circulation model ECHAM4/OPYC3 is analysed with the objective to quantify changes in present‐day Arctic permafrost conditions. An efficient procedure is adopted which overcomes the many problems associated with an explicit treatment of soil freezing and thawing processes. The zero degree soil temperatures as well as induced permafrost index characteristics simulated by the model for present day conditions match well the observed permafrost zonation. For a future scenario of greenhouse gas emissions (SRES A2 issued by IPCC), we estimate the amounts that the permafrost zones moves poleward and how the thickness of the active layer deepens in response to the global warming by the end of the 21st century. The simulation indicates a 30–40% increase in active‐layer thickness for most of the permafrost area in the Northern Hemisphere, with largest relative increases concentrated in the northernmost locations.
The influence of ENSO on air‐sea interaction in the Atlantic
Authors: Alexander Michael , Scott James
Published: October 2002

Observations and model experiments are used to investigate the influence of El Niño/the Southern Oscillation (ENSO) on air‐sea interaction in the north Atlantic, Gulf of Mexico and Caribbean Sea. In one experiment, observed sea surface temperatures (SSTs) in the tropical Pacific are specified as boundary conditions in an atmospheric general circulation model (AGCM), while SSTs over the remainder of the global oceans are simulated by a mixed layer model. The observed warming in the tropical North Atlantic and cooling in the Gulf of Mexico in the winter/spring after ENSO peaks is well simulated by the model. Prior to the basin wide warming, latent heat fluxes generate negative SST anomalies in the Caribbean during August–October. Ocean‐atmosphere coupling outside of the tropical Pacific significantly enhances the warm season atmospheric response to ENSO in the Caribbean region.
Phase diagram of iron, revised‐core temperatures
Authors: Ahrens Thomas J. , Holland Kathleen G. , Chen George Q.
Published: October 2002

Shock‐wave experiments on iron preheated to 1573 K from 14 to 73 GPa, yield sound velocities of the γ‐ and liquid‐phases. Melting is observed in the highest pressure (∼71 ± 2 GPa) experiments at calculated shock temperatures of 2775 ± 160 K. This single crossing of the γ‐liquid boundary agrees with the γ‐iron melting line of Boehler [1993], Saxena et al. [1993], and Jephcoat and Besedin [1997]. This γ‐iron melting curve is ∼300°C lower than that of Shen et al. [1998] at 80 GPa. In agreement with Brown [2001] the discrepancy between the diamond cell melting data and the iron shock temperatures require the occurrence of yet another sub‐solidus phase along the principal Hugoniot at ∼200 GPa. This would reconcile the static and dynamic data for iron's melting curve. Upward pressure and temperature extrapolation of the γ‐iron melting curve to 330 GPa yields 5300 ± 400 K for the inner core‐outer core boundary temperature.
Testing paleogeographic controls on a Neoproterozoic snowball Earth
Authors: Poulsen Christopher J. , Jacob Robert L. , Pierrehumbert Raymond T. , Huynh Tran T.
Published: October 2002

The distribution of continents during the Neoproterozoic has been hypothesized to play an important role in the initiation of an ice‐covered Earth. In this study, the influence of paleogeography on the Neoproterozoic climate is evaluated using a fully coupled ocean‐atmosphere general circulation model (FOAM). Three simulations were completed with different continental distributions. Each simulation included a reduced solar luminosity (93% of present‐day) and low atmospheric CO2 (140 ppmv). Model results indicate that a low‐latitude concentration of continents leads to lower tropical temperatures, through reduced receipt of shortwave radiation and a smaller tropical greenhouse effect, but does not significantly affect high‐latitude temperatures or sea‐ice extent. In contrast, the presence of snow‐covered, mid‐ and high‐latitude continents increases the sensible heat transport over the ocean, giving rise to sea‐surface cooling, deep‐water formation, and an advanced sea‐ice margin. Nonetheless, an ice‐covered Earth is not simulated in these experiments.
Lidar observations of sporadic Na layers over Wuhan (30.5°N, 114.4°E)
Authors: Yi Fan , Zhang Shaodong , Zeng Haijian , He Yujin , Yue Xianchang , Liu Jingbo , Lv Hongfang , Xiong Donghui
Published: October 2002

Based on lidar measurements between March and September 2001, the characteristics of sporadic Na layers (Nas layers) over Wuhan (30.5°N, 114.4°E) are presented. Nas layers were observed on 29 occasions from 275 h observational data. They tended to show a seasonal variation with a maximum occurrence rate in July. The maximum Na density was 24080 cm−3 which was comparable with those observed at low and high latitudes. Different from the observations at all other sites over the world, most Nas layers over Wuhan tended to occur around the peak altitudes of the normal Na layers (∼92 km). However, a Nas layer was observed at 112.9 km altitude. The formation of the Nas layers over Wuhan generally needed a longer time than those at low and high latitudes. The formation processes usually consisted of consecutive density enhancement bursts. The Nas layers often exhibited broader layer widths than those at low and high latitudes.
Geochemical indicators of possible ongoing volcanic unrest at Nisyros Island (Greece)
Authors: Chiodini Giovanni , Brombach Tatjana , Caliro Stefano , Cardellini Carlo , Marini Luigi , Dietrich Volker
Published: October 2002

Significant changes occurred in the chemistry of gases discharged from Nisyros fumaroles in the years, 1997–2001, following a strong seismic crisis. Increasing H2S/CO2 ratios and decreasing CH4/CO2 ratios are attributed to an increased contribution of magmatic fluids to the hydrothermal system. Some fumaroles showed concurrent increases in H2 and CO contents implying increases in temperature and pressure in the upper parts of the hydrothermal system. These changes reinforce the possibility of an increased hazard of hydrothermal eruptions at present with respect to the '90's. Moreover, both the present events and the historical hydrothermal eruptions may represent precursory signals of a new period of volcanic unrest at Nisyros.
A glaciation indirect aerosol effect caused by soot aerosols
Authors: Lohmann U.
Published: October 2002

Anthropogenic aerosols can influence the climate indirectly by changing the optical properties and precipitation formation of water clouds. An indirect effect that has not been considered involves the subset of anthropogenic aerosols that act as ice nuclei and thereby determines the lifetime of ice and mixed‐phase clouds. If, in addition to mineral dust, a fraction of the hydrophilic soot aerosol particles is assumed to act as contact ice nuclei as evident from recent laboratory studies, then increases in aerosol concentration from pre‐industrial times to present‐day pose a new indirect effect, a “glaciation indirect effect”, on clouds. Here increases in contact ice nuclei in the present‐day climate result in more frequent glaciation of clouds and increase the amount of precipitation via the ice phase. This effect can at least partly offset the solar indirect aerosol effect on water clouds.
Magnetospheric control of the energy input into the thermosphere
Authors: Barth C. A. , Baker D. N. , Mankoff K. D. , Bailey S. M.
Published: October 2002

A thermospheric photochemical model has been used in conjunction with satellite observations of nitric oxide to determine the flux of precipitating electrons into the thermosphere in the northern auroral region. Satellite measurements have shown that electron precipitation occurs predominantly between 1800 and 2400 hours magnetic local time. This time dependence has been incorporated into the thermospheric model calculation of nitric oxide density. Polar displays of the results of the model calculations show that the electrons deposit their energy between geomagnetic latitudes 60°–70°N. The longitudinal distribution is asymmetric with more energy being deposited at western geomagnetic longitudes and less at eastern longitudes. A calculation for equinox conditions shows that energy input as a function of longitude is 50% greater at 90°W than at 90°E. Therefore, the tilted, offset magnetic dipole field of the Earth seems to be controlling the precipitation of electrons in the northern auroral region.
Winter surface pressure anomalies over Eurasia and Indian summer monsoon
Authors: Rajeevan M.
Published: October 2002

In this study, the spatial relationships between the monthly mean sea level pressure (MSLP) anomalies and Indian summer monsoon rainfall (ISMR) have been examined using the gridded MSLP data (GMSLP2) for 46 years (1949–1994). Winter MSLP anomalies over NW Europe (south Europe) are negatively (positively) correlated with ISMR. During the strong (deficient) monsoon years, there is enhanced (weakened) poleward pressure gradient over Eurasia. The Europe pressure gradient index, which is an indicator of the winter poleward pressure gradient, is significantly and positively correlated with ISMR. This relationship also suggests a link between the North Atlantic Oscillation and ISMR on inter‐annual time scale. The winter pressure gradient over Eurasia has physical linkage with Indian summer monsoon rainfall, through winter snow cover anomalies and springtime mid latitude activities like upper tropospheric blocking highs and stationary wave anomalies.
GPS radio occultation measurements of the ionosphere from CHAMP: Early results
Authors: Jakowski N. , Wehrenpfennig A. , Heise S. , Reigber Ch. , Lühr H. , Grunwaldt L. , Meehan T. K.
Published: October 2002

The paper deals with initial analyzes of radio occultation measurements of the ionosphere carried out on board the CHAMP satellite since 11 April 2001. The accuracy of the operationally retrieved electron density profiles has been estimated by comparing with independent measurements. The derived ionospheric key parameters such as f0F2 and hmF2 agree with a standard deviation of 18 and 13%, respectively. It is shown that the CHAMP data products can essentially contribute to the establishment of operational data sets of the global electron density distribution for developing and improving global ionospheric models and to provide operational space weather information.