bluuebunny/crossref_metadata_2025 huggingface dataset:
The Sudbury Structure: A circular impact crater?
Authors: Morris W. A.
Published: November 2002

Petrological, geochemical, and structural evidence supports genesis of the Sudbury Structure by a meteorite impact. The Sudbury Igneous Complex (SIC) represents the ponded melt sheet. The primary morphology and size of the Sudbury Crater remains the subject of extensive discussion. A model is presented explaining the transformation of an originally circular crater to the current elliptical form. Processes involved in the geometrical transformation include; a) volume reduction through melt sheet crystallization, and repeated expulsion of melt into the surrounding footwall, b) translation and segmentation on multiple southeast dipping thrust surfaces, and c) relative displacement on steep north‐northwest trending faults. Paleomagnetic, geochemical and structural evidence supports the concept of periodic melt expulsions into the footwall. Seismic, potential field and paleomagnetic surveys provide evidence in support of multiple thrust surfaces. After over 9 km of subsequent erosion only a small volumetric portion of the original SIC remains, although complete vertical sections through the melt sheet have been preserved. None of the crater wall has been preserved. Thus the contacts between the SIC and the footwall on the North and South Ranges are interpreted as uplifted crater floor margins.
Seismological and mineralogical constraints on the inner core fabric
Authors: Garcia Raphaël
Published: November 2002

Under the assumption of lattice preferred orientation of iron hcp crystals, the seismic anisotropy of the inner core is related to single crystal elastic properties by a fabric model. This model is able to explain a new seismological constraint: the constant behaviour of the ratio k of two anisotropy coefficients, despite radial and lateral variations of the anisotropy level in the inner core. The relevance of the theoretical calculations of iron single crystal elastic properties at inner core conditions are tested by a comparison between seismic estimates and computed values of this ratio k. Taking into account the error bar of the seismic estimate, iron hcp structures presenting fast and slow c axis could fit the data equally well.
Taxon‐specific differences in C/P and N/P drawdown for phytoplankton in the Ross Sea, Antarctica
Authors: Arrigo Kevin R. , Dunbar Robert B. , Lizotte Michael P. , Robinson D. H.
Published: November 2002

Data from 11 cruises to the Ross Sea, Antarctica show that non‐Redfield N/P and C/P drawdown ratios for diatoms and Phaeocystis antarctica were a consistent feature of the phytoplankton communities between 1990 and 1998. Ratios of N/P drawdown for waters dominated by P. antarctica ranged from 17.2–19.5, consistently exceeding the Redfield ratio of 16. Similarly, the C/P drawdown ratio for P. antarctica‐dominated waters ranged from 120–154, 13–45% greater than the Redfield ratio of 106. Waters dominated by diatoms exhibited much lower ratios than Redfield for N/P (mean = 11.9) and C/P (mean = 76.2) drawdown. There was no seasonal trend to the drawdown ratios by either taxa. Sediment trap data exhibited C/P ratios for P. antarctica‐dominated samples that were twice that for diatoms, suggesting that the large taxonomic difference in C/P drawdown ratio is expressed as a difference in particulate C/P ratio which is subsequently exported to depth.
Initial balloon soundings of the electric field in winter nimbostratus clouds in the USA
Authors: Rust W. David , Trapp R. Jeffrey
Published: November 2002

Presented are the first known vertical profiles of electric field, E, in six winter nimbostratus clouds in the USA. No lightning was detected while the E profiles were collected. Deep convection was embedded in one of the clouds that had been a thunderstorm. The maximum magnitude of the vertical component of the electric field, Ez, in the profiles ranged from 1 to 12 kV m−1; the maximum horizontal component ranged from 0.2 to 28 kV m−1. The latter indicates that the charge in the cloud was not horizontally homogeneous. The Ez versus altitude profiles have 1–3 peaks inside the clouds. From the profiles, we inferred up to four charge regions stacked vertically. Peaks in Ez are found in regions of melting as evidenced by radar bright bands: Both polarities of charge are inferred in the bright bands. Three nimbostratus clouds without melting precipitation also were electrified.
Size and orientation of the fault plane for the 2001 Gujarat, India earthquake (Mw7.7) from aftershock observations: A high stress drop event
Authors: Negishi H. , Mori J. , Sato T. , Singh R. , Kumar S. , Hirata N.
Published: November 2002

We used a small array of portable seismographs to determine aftershock locations of the 2001 Gujarat earthquake. Our aftershock locations show a trend that dips toward the south at about 50° which is interpreted as the fault plane of the mainshock. The depth range of the aftershocks is from 10 to 35 km, which is somewhat deeper than other crustal earthquakes, and indicates that the faulting did not reach the surface. The area of the fault is about 40 × 40 km2, which is small for a Mw7.7 earthquake and results in a high static stress drop of 13 to 25 MPa. There are no mapped faults or obvious topographic features along the surface projection of this fault. These findings show that very large damaging earthquakes can occur without producing surface faulting, which is an important issue for earthquake hazard assessments in continental regions.
The impact of meteorology on the interannual growth rate of atmospheric methane
Authors: Warwick N. J. , Bekki S. , Law K. S. , Nisbet E. G. , Pyle J. A.
Published: November 2002

The impact of interannual changes in meteorology on the local and global growth rates of atmospheric methane is assessed in a nineteen year simulation using a tropospheric chemical transport model forced by ECMWF meteorological analyses from 1980 to 1998. A very simple CH4 chemistry scheme has been implemented, using prescribed OH fields. There are no interannual variations in modeled methane emissions or in the OH fields, so any changes in the modeled growth rate arise from changes in meteorology. The methane simulation shows significant interannual variability at both local and global scales. The local scale variability is comparable in magnitude to the interannual variability found in surface observations and shows some clear correlation with observed changes in growth rates. This suggests that, even over interannual timescales, meteorology could be important in driving the interannual fluctuations of atmospheric methane at the surface.
Coral oxygen isotope evidence for recent groundwater fluxes to the Australian Great Barrier Reef
Authors: Gagan Michael K. , Ayliffe Linda K. , Opdyke Bradley N. , Hopley David , Scott‐Gagan Heather , Cowley Joan
Published: November 2002

High‐resolution measurements of Sr/Ca and 18O/16O in mid‐Holocene and modern Porites corals were used to derive a history of freshwater fluxes to the Australian Great Barrier Reef (GBR). Interannual variations in dry‐season seawater 18O/16O evident in the coral record for the late 20th century, but not 6200 years ago, correlate with variations in groundwater recharge of coastal aquifers. The results suggest that a delay in groundwater recharge following the post‐glacial sea‐level rise, and recent deforestation for agriculture, may have lead to higher land‐sea hydraulic gradients and greater groundwater discharge to the GBR today. Oxygen‐isotope mass balance calculations show that ∼3% in‐mixing of CO2‐enriched groundwater could raise the partial pressure of CO2 in coastal seawater by ∼90 μatm following strong summer monsoons. Consequently, modern nearshore corals in the GBR may now be subjected to lower aragonite saturation states, which could reduce coral calcification and contribute to recent reef degradation.
Reduced methane emissions from large‐scale changes in water management of China's rice paddies during 1980–2000
Authors: Li Changsheng , Qiu Jianjun , Frolking Steve , Xiao Xiangming , Salas William , Moore Berrien , Boles Steve , Huang Yao , Sass Ronald
Published: November 2002

Decreased methane emissions from paddy rice may have contributed to the decline in the rate of increase of global atmospheric methane (CH4) concentration over the last 20 years. In China, midseason paddy drainage, which reduces growing season CH4 fluxes, was first implemented in the early 1980s, and has gradually replaced continuous flooding in much of the paddy area. We constructed a regional prediction for China's rice paddy methane emissions using the DNDC biogeochemical model. Results of continuous flooding and midseason drainage simulations for all paddy fields in China were combined with regional scenarios for the timing of the transition from continuous flooding to predominantly mid‐season drainage to generate estimates of total methane flux for 1980–2000. CH4 emissions from China's paddy fields were reduced over that period by ∼5 Tg CH4 yr−1.
Reply to “Comment on lsquo;A new estimate for Present‐day Cocos‐Caribbean plate motion: Implications for slip along the Central American volcanic arc’” by Marco Guzmãn‐Speziale and Juan Martín Gómez
Authors: DeMets Charles
Published: November 2002

I thank Guzman‐Speziale and Gomez (GSG02) for their comments on DeMets (2001) (DM2001). GSG02 do not challenge the fundamental observation reported by DM2001, namely, that earthquake slip directions along the Middle America trench between western Guatemala and Costa Rica are rotated ∼10° clockwise relative to the Cocos‐Caribbean convergence direction. However, they dispute the interpretation that this oblique convergence causes dextral shear across the Central American forearc in this region [White, 1991; DeMets, 2001]. Below, I address their reservations.
Lusaka, Zambia, during SAFARI‐2000: Convergence of local and imported ozone pollution
Authors: Thompson Anne M. , Witte Jacquelyn C. , Freiman M. Tal , Phahlane N. Agnes , Coetzee Gert J. R.
Published: November 2002

In August and September, throughout south central Africa, seasonal clearing of dry vegetation and other fire‐related activities lead to intense smoke haze and ozone formation. The first ozone soundings in the heart of the southern African burning region were taken at Lusaka, Zambia (15.5S, 28E) in early September 2000. Maximum surface ozone was over 90 ppbv and column tropospheric ozone exceeded 50 DU. These values are higher than concurrent measurements over Nairobi (1S, 38E) and Irene (25S, 28E, near Pretoria). At least 30% of Lusaka surface ozone appears to be from local sources. A layer at 800–500 hPa has ozone >120 ppbv and originates from trans‐boundary recirculation. Starting out over Zambia, Angola, and Namibia, ozone‐rich air travels east to the Indian Ocean, before heading back toward Mozambique, Zimbabwe and Zambia. Thus, Lusaka collects local and imported pollution, consistent with its location within the southern African gyre.
Anomalous chlorofluorocarbons in the Southern California Borderland Basins
Authors: Min Dong‐Ha , Bullister John L. , Weiss Ray F.
Published: November 2002

During the past two decades, unexpectedly high concentrations of chlorofluorocarbons (CFCs) have been observed in the bottom waters of the Southern California Borderland Basins (SCBB), with relatively constant spatial distribution patterns. In contrast to offshore waters in this region, CFC concentrations below the oxygen minimum layer (OML) in the deep SCBB increase with depth. The uniformity of the bottom‐enhanced CFC signals and the near‐zero levels of tritium suggest that this feature is likely maintained by release of CFCs from sediments and vertical mixing, and not by dumped CFC‐bearing materials or an intrusion of recently ventilated waters. We hypothesize that CFC scavenging processes, either on particulate organic matter or hydrocarbon residues from the adjacent natural seeps, occur in these high‐productivity near‐surface coastal waters. The subsequent release of CFCs at the bottom boundary layer during the degradation of particulate material may cause the anomalous CFC distributions in the SCBB.
Along‐strike variability in the seismogenic zone below Nicoya Peninsula, Costa Rica
Authors: Newman A. V. , Schwartz S. Y. , Gonzalez V. , DeShon H. R. , Protti J. M. , Dorman L. M.
Published: November 2002

At the subduction zone in northwestern Costa Rica, the seismogenic zone lies directly beneath the Nicoya Peninsula, allowing for near source seismic studies of earthquake activity. We located 650 earthquakes along the seismogenic plate interface using a dense seismic network in the vicinity of the Nicoya Peninsula. Using these data we constrained the updip limit of the seismogenic zone there and found a transition in depth, 10 km in the south to 20 km in the north, that occurs where the subducting oceanic crust changes from warmer Cocos‐Nazca Spreading center (CNS) origin to colder East Pacific Rise (EPR) origin. We argue that the temperature of the incoming oceanic crust controls the seismogenic updip limit beneath Nicoya, Costa Rica; subducting colder oceanic crust deepens the seismogenic updip limit.
Statistical distribution of the storm‐time proton ring current: POLAR measurements
Authors: Ebihara Y. , Ejiri M. , Nilsson H. , Sandahl I. , Milillo A. , Grande M. , Fennell J. F. , Roeder J. L.
Published: November 2002

Equatorial proton energy densities in the ring current region have been statistically investigated by compiling data acquired with the POLAR/MICS instrument (1–200 keV) in terms of the storm phases and Dst levels. The energy density is found to increase with decreasing Dst and to exhibit strong local time dependence during the storm main phase. In particular, the energy density at noon is interestingly shown to decrease during the main phase and increase during the recovery phase. A numerical simulation, which traces drift trajectories of the plasma sheet protons in the Volland‐Stern type convection electric field, gives a reasonable result in comparison with the statistically obtained distribution. Those results support the scenario that the prime source of the higher energy density of the ring current protons is the plasma sheet protons whose drift motion is governed by the large‐scale convection electric field most likely driven by the solar wind and IMF.
Cluster observations of the exterior cusp and its surrounding boundaries under northward IMF
Authors: Lavraud B. , Dunlop M. W. , Phan T. D. , Rème H. , Bosqued J.‐M. , Dandouras I. , Sauvaud J.‐A. , Lundin R. , Taylor M. G. G. T. , Cargill P. J. , Mazelle C. , Escoubet C. P. , Carlson C. W. , McFadden J. P. , Parks G. K. , Moebius E. , Kistler L. M. , Bavassano‐Cattaneo M.‐B. , Korth A. , Klecker B. , Balogh A.
Published: November 2002

We have studied in detail multi‐spacecraft observations of the exterior cusp on 04 February 2001, during a steady northward Interplanetary Magnetic Field (IMF) interval. At a radial distance of 11 Re, Cluster encountered a well‐bounded region where the magnetic field exhibited very low diamagnetic values and the ions displayed high levels of isotropisation. We refer to this region as the Stagnant Exterior Cusp (SEC). Its equatorward edge is magnetopause like, whereas on the poleward side of the SEC, high‐speed plasma jets were observed consistent with a reconnection site poleward of the cusp. The SEC/magnetosheath boundary is characterized by abrupt changes in the magnetic field and plasma parameters that satisfy the Walén test, and by an S‐shaped magnetic hodogram. The latter may suggest the presence of an intermediate/slow transition.
Spatial and temporal variability of Antarctic ice sheet microwave brightness temperatures
Authors: Schneider David P. , Steig Eric J.
Published: November 2002

Annual and interannual variability of 21 years of passive microwave brightness temperatures on the Antarctic ice sheet is documented through principal component analysis. The leading modes show that brightness temperatures are dominantly forced by the annual temperature cycle, with surface melting signals explaining about 5% of the total variance of the data. Analysis of the data with the annual cycle and melting signals removed results in two significant interannual modes. The first is consistent with the Antarctic Oscillation and its influence on Antarctic surface temperatures, while the second reflects regional scale variability that appears to be linked to sea‐ice anomalies and the El Niño‐Southern Oscillation. The expression of these characteristic patterns of Southern Hemisphere climate variability on the Antarctic continent provides a framework for interpreting modern climate records, as well as a basis for reconstructing past climate variability with ice cores.
Observations of equatorial spread‐F from Haleakala, Hawaii
Authors: Kelley Michael C. , Makela Jonathan J. , Ledvina Brent M. , Kintner Paul M.
Published: November 2002

Since the 1920s it has been known that the equatorial ionosphere can become highly disturbed in the post‐sunset period. We have placed a new array of instruments on top of the Haleakala Volcano in Hawaii to study these disturbances from midlatitudes. Two airglow imagers provide two‐dimensional snapshots of the development of these disturbances during the night, while two GPS receivers can quantify their severity. Here we report on the spectacular February 16–17, 2002 disturbance, which reached an altitude of 1500 km over the magnetic equator and mapped magnetically to latitudes well north of Hawaii. The signals from every Global Positioning System satellite in the field of view from Maui were severely disturbed whenever the corresponding look direction passed through one of the turbulent features. We also present an example from March 19, 2002 in which the spread‐F activity is not as severe to demonstrate that the instrumentation still provides valuable information.
Role of Asian and African orography in Indian summer monsoon
Authors: Chakraborty A. , Nanjundiah R. S. , Srinivasan J.
Published: November 2002

Role of Asian and African orography in the Indian summer monsoon has been investigated using a general circulation model. Orography of Asian region west of 80°E appears to have more impact on the Indian summer monsoon rainfall than the orography to the east of 80°E. It has been found that removal of the African orography increases the seasonal precipitation over the Indian sub‐continent by 28%, whereas removal of orography over the entire globe reduces it by 25%. Moreover, there was a substantial delay in all‐India monsoon onset in the experiment in which mountains were removed globally, mainly due to the intrusion of midlatitude dry air west of 80°E. The increase in precipitation in which orography over Africa was removed was due to the positive feedback between the wind over the East African coast/Arabian Sea and precipitation over Bay of Bengal, with the latter leading the former by about 2 days.
First comparison of tropospheric NO2 column densities retrieved from GOME measurements and in situ aircraft profile measurements
Authors: Heland Jörg , Schlager Hans , Richter Andreas , Burrows John P.
Published: November 2002

For the first time tropospheric NO2 columns from GOME were compared to tropospheric columns derived from in situ measurements with the DLR research aircraft Falcon on a clear day above Austria. Under these conditions the agreement between the two methods is very good. The in situ measurements yield a tropospheric NO2 column of (4.2 ± 1.7)·1015 molec./cm2, whereas the GOME data result in columns of (3.5 ± 0.9)·1015 molec./cm2 and (4.1 ± 1.0)·1015 molec./cm2 for near‐real‐time and dedicated analyses, respectively. The most important uncertainty of the aircraft measurements is caused by the lack of data in the lower boundary layer. The GOME uncertainties in this particular case are dominated by the assumptions made for the airmass factor calculation. This work is the first independent validation of tropospheric NO2 columns from satellite instrumentation. Further validation at other seasons, and regions, including a more comprehensive sampling of the boundary layer is needed.
Shallow geometry and displacements on the San Andreas Fault near Point Arena based on trenching and 3‐D georadar surveying
Authors: Gross Ralf , Green Alan , Holliger Klaus , Horstmeyer Heinrich , Baldwin John
Published: November 2002

To characterize buried portions of the San Andreas Fault (SAF) near its northern extremity in California, three trenches were excavated perpendicular to it and a 3‐D georadar data set was acquired. Similar sequences of unconsolidated fluvial sediments, Franciscan serpentinite and active fault zones were observed in the three trenches. Fault traces in the trenches were initially assumed to be part of a single SAF strand. However, the georadar data demonstrated the existence of two SAF strands, one of which was exposed in the central and southern trenches and the other in the northern trench. Offset of a linear‐trending georadar feature (possibly a fluvial paleochannel) suggests that 4.5–5.5 m of horizontal displacement occurred across the eastern SAF strand, either during the 1906 San Francisco earthquake or earlier. Georadar reflections from flat‐lying and trough‐shaped sedimentary boundaries are vertically offset by 0.2–0.3 m along both fault strands.
Configurational entropy of critical earthquake populations
Authors: Goltz C. , Böse M.
Published: November 2002

We present an approach to describe the evolution of distributed seismicity by configurational entropy. We demonstrate the detection of phase transitions in the sense of a critical point phenomenon in a 2D site‐percolation model and in temporal and spatial vicinity to the 1992, M7.3 Landers earthquake in Southern California. Our findings support the assumption of intermittent criticality in the Earth's crust. We also address the potential usefulness of the method for earthquake catalogue declustering.
A chemical kinetic model for reactive transformations of aerosol particles
Authors: Worsnop D. R. , Morris J. W. , Shi Q. , Davidovits P. , Kolb C. E.
Published: November 2002

A simple formalism is presented to model chemical interactions between aerosols and reactive trace gases over a wide range of conditions. The model takes into account gas phase diffusion, mass accommodation, bulk phase chemical reactions, surface reactions and particle phase reactant diffusion from the aerosol interior toward the surface. While previous models have focused on the heterogeneous uptake of trace gases by atmospheric droplets and particles, this model focuses on the reactive transformation of condensed phase species. In limiting cases, the model leads to simple analytical expressions for the condensed phase species depletion as a function of aerosol/gas interaction time.
Analysis of the 23 June 2001 Mw = 8.4 Peru underthrusting earthquake and its aftershocks
Authors: Bilek S. L. , Ruff L. J.
Published: November 2002

On 23 June 2001, a Mw = 8.4 underthrusting earthquake occurred in the southern Peru subduction zone, followed by several large aftershocks, including 26 June (Mw = 6.7) and 7 July (Mw = 7.5). Broadband analyses of seismic data for the largest of these earthquakes show southeastward rupture of 180 km along the portion of the subduction zone previously ruptured in 1868 (Mw 8.8–9). Moment release distributions determined are consistent with aftershock location patterns. Earthquake rupture mode varies along southern Peru, from larger multi‐segment rupture in 1868 to several smaller segment ruptures in 2001, similar to rupture variation observed in northern Peru and other subduction zones. Based on models of subduction zone segment interaction, the 2001 earthquake sequence may suggest a shorter recurrence time for future earthquakes along this portion of the Peru‐Chile subduction zone.
The importance of spatial variability in the generation of secondary gravity waves from local body forces
Authors: Vadas Sharon L. , Fritts David C.
Published: November 2002

We hypothesized earlier that the zonal mean body force required to close the mesospheric jets is sporadic in time, and is composed of a large number of spatially and temporally localized body forces. To explore the effects of such localization, we randomly generate a series of localized, 3D body forces in the mesosphere which create a mean acceleration of ∼100 m s−1 day−1 over this forcing volume. Secondary waves are also generated, and because they have large vertical scales, phase speeds, and vertical group velocities, they may induce important variabilities in the lower thermosphere where they dissipate. We find that the secondary waves from spatially smoothed body forces have much smaller momentum fluxes, frequencies, and vertical group velocities. Thus, global models having coarse resolution may be missing a significant source of sporadic wave drag and its effect throughout the middle atmosphere and lower thermosphere.
Scatterometer winds explain damped Rossby waves
Authors: Kelly Kathryn A. , Thompson Lu Anne
Published: November 2002

Westward propagating waves in the North Pacific Ocean from 10–16°N are overwhelmed by a zonally coherent response at the annual period, as observed in sea surface height (SSH) anomalies from the TOPEX/POSEIDON altimeter. SSH from a simple model of wind‐forced Rossby waves and from seasonal heating are compared with observed SSH to understand the processes responsible for the observed signal. The seasonal heating cycle is out‐of‐phase and too weak to explain the SSH. The oceanic response to wind stress curl forcing more closely resembles the observations, but the response to NCEP Reanalysis winds does not show a strong annual cycle. Wind stress curl from the QuikSCAT/SeaWinds scatterometer has a strong and zonally coherent annual cycle that produces a corresonding strong annual signal in SSH. The model forced by scatterometer winds demonstrates that the response to Ekman pumping is the source of the strong annual cycle in the SSH.
A rapidly declining perennial sea ice cover in the Arctic
Authors: Comiso Josefino C.
Published: November 2002

The perennial sea ice cover in the Arctic is shown to be declining at −9% per decade using satellite data from 1978 to 2000. A sustained decline at this rate would mean the disappearance of the multiyear ice cover during this century and drastic changes in the Arctic climate system. An apparent increase in the fraction of second year ice in the 1990s is also inferred suggesting an overall thinning of the ice cover. Surface ice temperatures derived from satellite data are negatively correlated with perennial ice area and are shown to be increasing at the rate of 1.2 K per decade. The latter implies longer melt periods and therefore decreasing ice volume in the more recent years.
Control of Pa/Th ratio by particulate chemical composition in the ocean
Authors: Guo Laodong , Chen Min , Gueguen Celine
Published: November 2002

Controlled laboratory experiments were carried out using pure sorbents to examine the interactions of 234Th (or 233Pa) with particle surfaces and whether there is a fractionation between 234Th and 233Pa by particulate chemical composition. Our results show that the adsorption of 233Pa and 234Th on particle surfaces is highly selective and compound specific, resulting in a fractionation of 233Pa/234Th ratio, especially on SiO2 (Kd ratio, Kd‐233Pa/Kd‐234Th, = 10) and CaCO3 (Kd ratio, Kd‐233Pa/Kd‐234Th, = 0.01) surfaces. These new results agree well with previously published field observations that showed an increase of 231Pa/230Th ratio (or Kd of 231Pa) with increasing opal abundance and decreasing carbonate content in oceanic particles. In addition, they highlight the complications of using 231Pa/230Th ratio as a proxy and have implications for both oceanography and trace element geochemistry although more studies are needed to further examine the influence of natural organic matter on the fractionation of Th/Pa ratios.
Velocities of sprite tendrils
Authors: Moudry D. R. , Stenbaek‐Nielsen H. C. , Sentman D. D. , Wescott E. M.
Published: November 2002

The University of Alaska deployed a high speed (1000 fps) camera at the Wyoming Infrared Observatory to observe sprites over Midwest U.S. thunderstorms as part of the 1999 NASA Sprites Balloon Campaign. Here we report on the velocity of development of downward spatial structures known as tendrils in several sprite events recorded during a large thunderstorm over eastern Nebraska the night of 18 August 1999. Downward tendril development occurred at velocities that varied by more than two orders of magnitude, ranging from ∼105 to ≥3 × 107 m/s. The tendrils progressed through multiple velocity regimes, typically in the order fast‐slow or slow‐fast‐slow. Examples are presented of multiple sets of temporally distinct tendrils that develop from the same sprite event and tendrils that have a horizontal component of expansion.
Vapor clouds generated by laser ablation and hypervelocity impact
Authors: Kadono T. , Sugita S. , Mitani N. K. , Fuyuki M. , Ohno S. , Sekine Y. , Matsui T.
Published: November 2002

Laser ablation experiments are carried out using a high intensity laser (∼1010 W/cm2) and basalt targets. Using a high‐speed camera and a spectrometer, the radius and the temperature of the silicate vapor clouds generated by laser ablation are observed as a function of time. Then a numerical simulation of vapor expansion is carried out, and the thermodynamic state of the silicate vapor is determined so as to reproduce the experimental results. The result of the analysis indicates that the impact velocity which would generate a vapor cloud with this thermodynamic state is ∼120 km/s for collisions between two basaltic bodies.
Coherent sea level response to the Antarctic Oscillation
Authors: Aoki Shigeru
Published: November 2002

Large‐scale sea level variations around Antarctica were studied and their relationship with atmospheric variations was investigated. Tide gauge data at five coastal stations were used. Coherent sea level variations were clearly detected for all stations on intraseasonal time scales. The coherent variations had significant negative correlations with an index of the atmospheric annular mode variation (Antarctic Oscillation). Coherence was significant for periods from 10 to 100 days with negligible time lag. The negative correlation is consistent with the mechanism that a high (low) westerly anomaly leads to a stronger (weaker) northward Ekman drift and causes divergence (convergence) around Antarctica.
Motion of the dipolarization front during a flow burst event observed by Cluster
Authors: Nakamura R. , Baumjohann W. , Klecker B. , Bogdanova Y. , Balogh A. , Rème H. , Bosqued J. M. , Dandouras I. , Sauvaud J. A. , Glassmeier K.‐H. , Kistler L. , Mouikis C. , Zhang T. L. , Eichelberger H. , Runov A.
Published: November 2002

In this paper we study a flow burst event which took place during enhanced geomagnetic activity on July 22, 2001, when Cluster was located in the postmidnight magnetotail. The flow burst was associated with a clear dipolarization ahead of the high‐speed part of the predominantly Earthward directed flow. Based on the analysis of the four spacecraft data, we found that a ∼2000 km thick dipolarization front moves Earthward and dawnward with a speed of ∼77 km/s. The plasma before this front is deflected, consistent with the plasma ahead of a localized plasma bubble centered at midnight side being pushed aside by the moving obstacle. The main body of the high‐speed flow is directed mainly parallel to the dipolarization front. These observations indicate that the evolution of the dipolarization front across the tail is directly coupled with the fast flow.
Absorbing mediterranean aerosols lead to a large reduction in the solar radiation at the surface
Authors: Markowicz Krzysztof M. , Flatau Piotr J. , Ramana M. V. , Crutzen P. J. , Ramanathan V.
Published: November 2002

We present direct radiometric observations of aerosol radiative forcing taken during the MINOS experiment (2001) at Finokalia Sampling Station located on North‐Eastern shores of Crete, Greece. The mean value of aerosol optical thickness was 0.21 at 500 nm. Aerosols, mostly of anthropogenic origin, lead to a diurnal average reduction of 17.9 W m−2 in the surface solar radiation, an increase of 11.3 W m−2 in the atmospheric solar absorption, and an increase of 6.6 W m−2 in the reflected solar radiation at the top‐of‐the atmosphere. Thus, the present data gives observational proof for the large role of absorbing aerosols in the Mediterranean. The negative surface forcing and large positive atmospheric forcing values observed for the Mediterranean aerosols is nearly identical to the highly absorbing south Asian haze observed over the Arabian Sea.
A new convection state at substorm onset: Results from an MHD study
Authors: Ashour‐Abdalla M. , El‐Alaoui M. , Coroniti F. V. , Walker R. J. , Peroomian V.
Published: November 2002

A global simulation of a December 22, 1996 substorm revealed a previously unknown state of magnetospheric convection. Earthward flow from a tail neutral line reversed direction in the inner magnetosphere and formed a large‐scale vortical nightside convection pattern. The dawnside vortex formed a flux rope just prior to the substorm onset, but this was not the cause of the substorm breakup. The vortex structure of the dusk‐side flow created strong field‐aligned currents directed away from the Earth that connected to the region of maximum auroral luminosity in the ionosphere. These currents are probably related to the westward traveling surge. The flow reversal and formation of the tail vortices may be a result of the simulation's earthward convection being limited by the high near‐Earth plasma pressure and/or by line‐tying caused by the high ionospheric conductance.
High frequency gravity waves observed in OH airglow at Starfire Optical Range, NM: Seasonal variations in momentum flux
Authors: Tang Jing , Liu Alan Z. , Swenson Gary R.
Published: November 2002

Airglow imager and Na wind/temperature lidar measurements at Starfire Optical Range, New Mexico (35°N, 107°W) are used to estimate the seasonal variation of the vertical fluxes of horizontal momentum carried by high frequency Atmospheric Gravity Waves (AGWs). The cross‐correlation coefficients between the vertical and horizontal wind perturbations were calculated from the OH airglow imager data collected during 32 nights in 1998, 1999 and 2000. The RMS wind velocities were deduced from the lidar measurements. The combined information was used to estimate the upper limit of the momentum flux. The meridional component of the vertical flux of horizontal momentum was observed to be towards the summer pole. The zonal component had westward preference in winter and weak preference in summer. The unanticipated large meridional component may act to regulate the summer to winter circulation in the mesosphere.
Tropical links of the Arctic Oscillation
Authors: Lin Hai , Derome Jacques , Greatbatch Richard J. , Andrew Peterson K. , Lu Jian
Published: November 2002

A primitive equation dry atmospheric model is used to investigate the response of the Arctic Oscillation (AO) to diabatic forcing. Integrations are made for 51 winter seasons (DJF) from 1948/49 to 1998/99. For each winter the model uses a time‐averaged forcing that is calculated empirically from the NCEP/NCAR reanalyses. The ensemble mean of the simulations reproduces much of the observed AO interannual variability. Two additional sets of experiments are conducted. In one case the interannually varying forcing is prescribed only in the tropics, while in another it is prescribed only in the extratropics. These simulations indicate that a significant part of the interannual variability of the wintertime AO, as well as its trend, is linked to forcing from the tropics, and that extratropical forcing has no role to play, independent of the tropical forcing, in reconstructing the observed AO variability.
Modelling photochemical NOX production and nitrate loss in the upper snowpack of Antarctica
Authors: Wolff Eric W. , Jones Anna E. , Martin Timothy J. , Grenfell Thomas C.
Published: November 2002

Experimental observations have shown photochemical production in the upper layers of firn. We use a modeling approach for Antarctica in summer, calculating the actinic flux in snowpack, and estimating NOX production from nitrate photolysis. Assuming nitrate photolysis is about as efficient for ice as for aqueous solution, and that all nitrate in the ice is available for photolysis, we find good agreement with measured fluxes of NOX from the snow surface at Neumayer Station, Antarctica. We estimate fluxes for other sites, and confirm that they could significantly affect boundary layer chemistry, especially where an atmospheric surface temperature inversion is present. We find that there is considerably more NOX production in the upper snowpack than in the entire tropospheric column above it. Photolysis explains a proportion of the nitrate loss observed from snow at some sites, but other processes (sorption/desorption) are necessary to explain the magnitude and depth profiles observed.
Walking traverse and scanning DOAS measurements of volcanic gas emission rates
Authors: McGonigle A. J. S. , Oppenheimer C. , Galle B. , Mather T. A. , Pyle D. M.
Published: November 2002

We report here the first measurements of volcanic SO2 fluxes obtained on foot, using a miniature ultraviolet spectrometer. Our measurements, based on differential optical absorption spectroscopy (DOAS), were performed ≈1 km from the summit of Masaya volcano (Nicaragua) in December 2001, and yielded a mean SO2 emission rate of 4 kg s−1, comparable with a set of contemporaneous measurements obtained by road vehicle traverses (average 6 kg s−1). SO2 flux estimates (average 4 kg s−1) were also obtained from a fixed position by scanning the plume. This range of fluxes confirms an apparent decrease in gas output from the volcano since 2000. The portability and ease of use of the spectrometer offer considerable scope for routine measurements of SO2 emissions from volcanoes, especially where road access or opportunities for airborne campaigns are limited. These approaches can be readily extended to monitor other sources and gases.
The outer source of pickup ions and anomalous cosmic rays
Authors: Schwadron N. A. , Combi M. , Huebner W. , McComas D. J.
Published: November 2002

The traditionally accepted source of Anomalous Cosmic Rays (ACRs) is neutral atoms penetrating the heliosphere from the local interstellar cloud (LIC). The ACR composition should be depleted in easily ionized atoms such as C, Si, and Fe. However, significant fluxes of these ions are observed in ACRs and their source has not been previously identified. We show that there is an “outer source” of pickup ions, and hence ACRs, caused by sputtered atoms (subsequently ionized and picked up by the solar wind) from small grains generated via collisions of objects in the Edgeworth‐Kuiper Belt. The outer source accounts for the abundance and composition of the additional population of ACRs. The discovery that ACRs are generated from material in the Edgeworth‐Kuiper Belt provides an exciting new tool for understanding the mass distribution and composition of the Edgeworth‐Kuiper Belt, and for probing the plasma‐dust interactions in stellar environments.
Impact of updates to the HITRAN spectroscopic database on the modeling of clear‐sky infrared radiances
Authors: Newman Stuart M. , Taylor Jonathan P.
Published: November 2002

Recent versions of the HITRAN spectroscopic database are evaluated to assess the impact of the latest revisions to line parameters on the ability to model clear‐sky radiances. Observations made using the Met Office C‐130 aircraft with an infrared interferometer are compared with line‐by‐line radiative transfer simulations incorporating the HITRAN 96 and HITRAN 2000 databases. Substantial reductions in the differences between observed and calculated spectra are found when including the latest database in the model, largely due to refinements in water vapor parameters. Although the use of HITRAN 2000 is broadly successful in reproducing the observed spectra, a number of discrepancies remain in some spectral regions which may indicate further room for improvement in the database.
An important constraint on tropical cloud ‐ climate feedback
Authors: Hartmann Dennis L. , Larson Kristin
Published: November 2002

Tropical convective anvil clouds detrain preferentially near 200 hPa. It is argued here that this occurs because clear‐sky radiative cooling decreases rapidly near 200 hPa. This rapid decline of clear‐sky longwave cooling occurs because radiative emission from water vapor becomes inefficient above 200 hPa. The emission from water vapor becomes less important than the emission from CO2 because the saturation vapor pressure is so very low at the temperatures above 200 hPa. This suggests that the temperature at the detrainment level, and consequently the emission temperature of tropical anvil clouds, will remain constant during climate change. This constraint has very important implications for the potential role of tropical convective clouds in climate feedback, since it means that the emission temperatures of tropical anvil clouds and upper tropospheric water vapor are essentially independent of the surface temperature, so long as the tropopause is colder than the temperature where emission from water vapor becomes relatively small.
Detecting anthropogenic influence with a multi‐model ensemble
Authors: Gillett N. P. , Zwiers F. W. , Weaver A. J. , Hegerl G. C. , Allen M. R. , Stott P. A.
Published: November 2002

Averaging results from multiple models has previously been found to improve estimates of the climatology and seasonal predictions of atmospheric variables. Here we describe how a multi‐model mean of the simulated response to greenhouse gas and sulphate aerosol changes may be used to detect anthropogenic influence on surface temperature. The scaling factor on a combined greenhouse gas and sulphate aerosol response pattern is estimated using a five model ensemble, and is found to be similar to that estimated using individual models, with similar uncertainties. When applied to the simultaneous detection of separate greenhouse gas and sulphate aerosol responses, the multi‐model method indicates a closer consistency between the observations and simulated responses, with reduced uncertainties. This improvement is at least in part due to the larger ensemble sizes and increased length of control integration available when data from multiple models are combined.
Degree‐1 Earth deformation from very long baseline interferometry measurements
Authors: Lavallée D. , Blewitt G.
Published: November 2002

The presence of degree‐1 deformations in very long baseline interferometry (VLBI) measurements is detected for the first time. We compare VLBI measurements with the deformation field predicted using a GPS‐determined load moment. Degree‐1 series in the center of figure frame have root mean square values up to 3 and 1.5 mm in the up and horizontal components respectively. The predicted baseline series are compared with VLBI baseline series where there are >50 matching points. For the period 1996–2001, 14 baselines out of 35 are significantly correlated (5% significance level). For the period 1985–2001, a sinusoidal fit to the GPS load‐moment series predicts baseline series at all VLBI epochs, 49 out of 110 baselines are significantly correlated (5% significance level). Comparison between annual signals estimated from the VLBI and predicted baseline series shows that degree‐1 deformation most likely dominates the annual phase of the VLBI series.
Ribbon spacing in Venusian tessera: Implications for layer thickness and thermal state
Authors: Ghent Rebecca R. , Tibuleac Ileana M.
Published: November 2002

We report on measurements of characteristic extensional wavelength represented by ribbons in Venusian tessera terrain. Fourier power spectra for ribbons in 35 areas from 9 geographic regions show dominant wavelengths of 2 to 6 km. We used these values to estimate mechanical layer thickness during ribbon formation at 0.6 to 2.9 km. Because ribbons accommodate extension of a single strong layer overlying a ductile substrate, we conclude that the base of this mechanical layer corresponded to the local brittle‐ductile transition (BDT) during ribbon formation. Maintaining a BDT at <3 km depth for a significant length of time requires a locally hot environment, as over a plume impinging on thin lithosphere. These results indicate that locally hot conditions prevailed at widely distinct locations in the past.
The block‐like behavior of Anatolia envisaged in the modeled and geodetic strain rates
Authors: Jiménez‐Munt Ivone , Sabadini Roberto
Published: November 2002

The geodetic velocity and strain rate patterns in Anatolia constrain the rheology of the lithosphere, once compared with thin shell finite element tectonic model predictions. Geodetic and modeled deformation favors a hard lithospheric rheology, responsible for the high East‐West horizontal velocities in the center of Anatolia, between 39°–41°N, in proximity of the North Anatolian Fault. The block like behavior of Anatolia, due to the hard lithospheric rheology, is responsible for the low geodetic and modeled strain rates in the center of the peninsula. The low strain rate is well correlated with the region of low release of seismic energy between 33°–36°E and 38°–40°N. The high seismic and geodetic strain rate region in the far west part of the NAF is also well reproduced by the modeling.
Banderas Rift Zone: A plausible NW limit of the Jalisco Block
Authors: Alvarez Román
Published: November 2002

Echo soundings recently made in Bahía de Banderas show that this region is a graben with steeply dipping walls and several basins; it is the offshore continuation of the Valle de Banderas graben, and of a branching rift (Río Ameca rift) originating in the Tepic‐Zacoalco rift zone. The general trend of the three structures is ENE with some NE trending offsets, and they have a total length of 150 km; this Banderas Rift Zone is proposed as the NW limit of the Jalisco block. The existence of this limit suggests that there is another platelet, or block, between the Jalisco block and a portion of the Rivera plate, probably bounded by the Tres Marías escarpment, the Jalisco block and the North America plate.
Compressional MHD wave transport in the magnetosphere 1. Reflection and transmission across the plasmapause
Authors: Lee Dong‐Hun , Hudson Mary K. , Kim Kihong , Lysak Robert L. , Song Yan
Published: November 2002

Magnetohydrodynamic (MHD) wave properties in inhomogeneous plasmas such as the magnetosphere are complicated by existence of local cutoff, coupling, and dissipation. We study the transport of MHD waves when compressional waves are assumed to propagate into the plasmasphere from the outer magnetosphere. By assuming a region of the Alfven speed crest, which approximates the plasmapause region, we investigate how the initial compressional MHD wave energy is reflected, absorbed, and delivered across the plasmapause. Our results present the exact reflection, transmission, and absorption coefficients without any theoretical approximations for given frequencies and wave numbers. It is found that relatively strong absorption of compressional waves occurs where the frequency ranges from the local resonant condition to the cutoff condition at the maximum of the Alfven speed crest. We compare and discuss the behavior of compressional waves in our results with previous observations.