bluuebunny/crossref_metadata_2025 huggingface dataset:
The magnetosphere on May 11, 1999, the day the solar wind almost disappeared: I. Current systems
Authors: Le G. , Russell C. T. , Petrinec S. M.
Published: February 2004

We have examined magnetic field data from Polar MFE to study the magnetospheric current systems on May 11, 1999, when the solar wind density was well below 1 cm−3 and the IMF was generally weakly northward. We find that the magnetosphere was much more dipolar than usual but the ring current did not disappear. In the inner magnetosphere, the residual field, the observed magnetic field at Polar with the internal field removed, was dominated by the ring current contribution. The magnetic field data agreed well with the Tsyganenko 1996 model with a weak ring current but little magnetopause current. Weak field‐aligned currents were observed both in the northern and southern hemisphere on May 11, as expected for northward IMF. The cusp signature of a depressed magnetic field, normally seen by Polar when passing through the high altitude polar cusp, was not seen on May 11, indicating that the energy density of the plasma in the cusp was much smaller than usual, as would be expected if the solar wind source were of lower density.
Sources of heavy dust fall in Beijing, China on April 16, 1998
Authors: Sun Jimin , Liu Tungsheng , Lei Zhenfa
Published: February 2004

The dust storm of April 14–17, 1998 in China was mainly associated with the frontal systems and the Mongolia cyclonic depression, which caused heavy dust fall at Beijing on April 16. In nearly fifteen hours, approximately 38.3 g/m² of dust fell on Beijing. This dust storm was of strong intensity, long duration, and with a wide coverage; it not only affected southern Mongolia and the central and southeastern China, but also the North Pacific Ocean. The source areas of the dust storm were from the Gobi areas of southern Mongolia and the Gobi and desert areas of Inner Mongolia, China. This dust storm is a good example of long‐range transport and deposition of airborne materials, which provides a useful analogue for studying the dust sources and deposition in the geological record.
Enhancement of the warming trend in China
Authors: Wang Shaowu , Gong Daoyi
Published: February 2004

The 1998 temperature averaged for the globe is the highest on record. Annual mean temperature of China in 1998 is +1.38°C above the normal, which also labels 1998 the warmest year since 1880 for China. Additional ice core δ18O and tree ring evidence shows stronger upward trend (of 0.50°C/100 years) than ever estimated based on temperature observations in eastern coast region only during the last hundred years. Enhanced warming trend has occurred in most eastern Asia, the remarkable trend is making the middle‐high continent of eastern Asia one of the rapidest warming regions in world during the last 2 decades. And the warming time series in China indicates a sinusoidal variation over the past hundred years and is different than for the global average.
Swedish tree rings provide new evidence in support of a major, widespread environmental disruption in 1628 BC
Authors: Grudd Håkan , Briffa Keith R. , Gunnarson Björn E. , Linderholm Hans W.
Published: February 2004

Pine trees, recovered from a peat bog in south‐central Sweden, are used to develop a continuous, but “floating”, 200‐year tree‐ring chronology. By wiggle matching high‐precision 14C determinations against the radiocarbon calibration curve, the chronology is positioned at 1695–1496 BC with an uncertainty of ±65 years. One major event, denoted by four consecutive years with extremely narrow rings, indicative of highly unfavourable local tree‐growth conditions, occurred in the time window represented by the chronology. This growth depression is dated to 1637 BC (±65) and may be tentatively ascribed to the same phenomenon that caused frost damage in trees in California and a growth depression in European oak in 1628/27 BC, hence providing new evidence of a more northerly area of influence of this widespread phenomenon.
Future estimates of tropospheric ozone radiative forcing and methane turnover — The impact of climate change
Authors: Stevenson D. S. , Johnson C. E. , Collins W. J. , Derwent R. G. , Edwards J. M.
Published: February 2004

We present a range of estimates for future radiative forcings due to changes in tropospheric ozone (O3T). Ozone distributions were generated by the UKMO 3‐D chemistry‐transport model for 1990, 2030, 2060, and 2100, using four sets of boundary conditions. Anthropogenic emissions evolved following either the IPCC SRES “high” (A2) or “central” (B2) case. Each scenario was run with both a fixed (1990) climate, and with a changing climate, as generated by a coupled ocean‐atmosphere GCM, forced with IS92a emissions. Calculated global mean O3T radiative forcings for the A2 (B2) cases for 1990–2100 were +0.43 (+0.22) W m−2 when climate change was ignored; these fell to +0.27 (+0.09) W m−2 when climate change was included. Without climate change, CH4 lifetimes (τCH4) lengthened by 7–12% between 1990 and 2100; however, when climate change was included, τCH4 fell by 0–5%. Hence climate warming exerts a negative feedback on itself by enhancing O3T and CH4 destruction.
Westward traveling low‐frequency hemispheric waves in the atmosphere
Authors: B. E. Stepanov
Published: February 2004

The resonant response of a “shallow water” atmosphere is examined by applying forcing for each hemisphere separately. It is shown, that westward traveling waves tend to concentrate in hemispheres of their forcing for real damping and this tendency is greater for low‐frequency waves. These waves appear from the global Rossby modes and have resonant peaks only in one hemisphere. Since they are largely confined to one hemisphere and are thus qualitatively more similar to observations then are normal modes. The results were essentially unchanged when the basic experiments were repated many times, each with a different, randomly generated, forcing structure.
Shortwave direct radiative forcing of biomass burning aerosols estimated using VIRS and CERES data
Authors: Christopher Sundar A. , Chou Joyce , Zhang Jianglong , Li Xiang , Berendes Todd. A. , Welch Ronald M.
Published: February 2004

Using collocated data from the Visible Infrared Scanner (VIRS) and the Clouds and the Earth's Radiant Energy Budget Scanner (CERES) from the Tropical Rainfall Measuring (TRMM) satellite, observational estimates of the instantaneous Shortwave Aerosol Radiative Forcing (SWARF) of smoke aerosols at the top‐of‐atmosphere (TOA) are obtained for four days in May 1998 during a biomass‐burning episode in Central America. The detection of smoke aerosols is demonstrated using VIRS imagery. Assuming a single scattering albedo (ωo) of 0.86 (at 0.63 µm) that is representative of absorbing aerosols, smoke optical thickness (τ0.63) is retrieved over ocean areas. The average τ0.63 for these four days was 1.2 corresponding to a SWARF value of −68 Wm−2. The SWARF changes from −24 to −99 Wm−2 as τ0.63 changes from 0.2 to 2.2. Global observational estimates of biomass burning aerosol radiative forcing can be obtained by combining data sets from TRMM and Terra satellites.
Unexpected large uptake of O3 on sea salts and the observed Br2 formation
Authors: Mochida Michihiro , Hirokawa Jun , Akimoto Hajime
Published: February 2004

Uptake coefficients of O3 on various model compounds of sea salts at ambient temperature were measured using a Knudsen cell reactor coupled to a differentially pumped quadrupole mass spectrometer. Uptake of O3 was below the detection limit (<1×10−5) for pure alkali metal bromides, whereas reactive uptake with Br2 formation was observed on two types of synthetic sea salts (Aqua Ocean and Instant Ocean) and commercial natural sea salt. Measured uptake coefficients were 10−2–10−3, (1.4±1.1) × 10−3 and (9.7±4.6) × 10−4 for Aqua Ocean, Instant Ocean and natural sea salt, respectively. These uptake coefficients were about three orders of magnitude larger than that on bulk bromide solution estimated from known liquid phase reactions. The results imply that minor components enhance reactivity of O3 on synthetic and natural sea salts. This heterogeneous reaction is potentially an important Br source in the marine boundary layer on a global scale as well as in the polar troposphere.
Comparison of stratus cloud properties derived from coincident airborne visible and ground‐based infrared spectrometer measurements
Authors: Rathke Carsten , Armbruster Wolfgang , Fischer Jürgen , Becker Edo , Notholt Justus
Published: February 2004

Results of a remote sensing validation experiment are reported. Above cloud measurements of reflected solar radiation were made with a grating spectrometer, coincident below cloud measurements of emitted thermal radiation with a FTIR spectrometer. Two remote sensing algorithms based on radiative transfer simulations were employed to retrieve visible optical depths and effective droplet radii. The values derived from both measurements are consistent and indicative for the cloud vertical structure.
Mid‐latitude marine boundary‐layer ozone destruction at visible sunrise observed at Cape Grim, Tasmania, 41°S
Authors: Galbally Ian E. , Bentley Simon T. , Meyer C. P. (Mick)
Published: February 2004

An analysis is made of 13 years of observations of ozone concentrations in the remote marine boundary layer at Cape Grim, Tasmania 41°S. These data reveal a decrease in ozone concentration in the first few hours following sunrise at a rate of around 0.1 ppb h−1 in mid‐summer and in mid‐winter. This ozone destruction phenomenon causes an asymmetry in the daily ozone loss rate with enhanced destruction following sunrise, is statistically distinguishable from the O3‐HOx destruction cycle that peaks at mid‐day, and occurs at similar rates in mid‐summer and in mid‐winter. The cause of this sunrise ozone decrease is examined using the conservation equation for ozone. We speculate that ozone destruction at sunrise arises due to halogen chemistry. The absence of sunrise ozone decrease in models of marine boundary‐layer photochemistry means that the ozone destruction rate in the remote marine boundary layer is underestimated by perhaps a factor of two.
Dependency of VHF broad band lightning source mapping on Fourier spectra
Authors: Mardiana Redy , Kawasaki Zen‐Ichiro
Published: February 2004

In the VHF broad band interferometer, the Fourier transform is applied to analyze the whole frequency range of lightning radiation sources. The position of a radiation source can be determined by resolving the incident angle for each frequency component against at least three‐antenna sensors, and then by averaging the incident angles of all frequency components the angular position can be located. This arithmetic‐averaging method as proposed by previous authors has a disadvantage, especially for cloud‐to‐ground flashes, that is positions of lightning leader channels near ground level can not be mapped well. It is found that Fourier spectral amplitudes of broad band pulses decrease with increasing frequency, and frequency components having low spectral amplitudes give less contribution to the lightning mapping. To improve the mapping, a weighted‐averaging method is proposed. The method provides a way to minimize the influence of frequency components, which contribute less to the lightning mapping.
Spectral dispersion of cloud droplet size distributions and the parameterization of cloud droplet effective radius
Authors: Liu Yangang , Daum Peter H.
Published: February 2004

Parameterization of effective radius (re) as proportional to the cube root of the ratio of cloud liquid water content (L) to droplet concentration (N), i.e., re = α(L/N)⅓, is becoming widely accepted. The principal distinction between different parameterization schemes lies in the specification of the prefactor α. This work focuses on the dependence of α on the spectral dispersion of the cloud droplet size distribution. Relationships by Pontikis and Hicks [1992] and by Liu and Hallet [1997] that account for the dependence of α on the spectral dispersion are compared to each other and to cloud microphysical data collected during two recent field studies. The expression of Liu and Hallet describes the spectral dependence of α (or re) more accurately than the Pontikis and Hicks relation over the observed range of spectral dispersions. The comparison shows that the different treatments of α as a function of spectral dispersion alone can result in substantial differences in re estimated from different parameterization schemes, suggesting that accurately representing re in climate models requires predicting α in addition to L and N.
On the widespread winter fog in northeastern Pakistan and India
Authors: Hameed Sultan , Mirza M. Ishaq , Ghauri B. M. , Siddiqui Z. R. , Javed Rubina , Khan A. R. , Rattigan O. V. , Qureshi Sumizah , Husain Liaquat
Published: February 2004

During the last two winters widespread fog frequently occurred in northeastern India and Pakistan, in a region extending over 1500 km. A particularly severe fog episode lasted from mid‐December, 1998 to early January, 1999. The fog caused extensive economic damage and disruptions in transport. We determined concentrations of SO42−, NO3−, and selected trace elements at Lahore, Pakistan during and after the fog event by collecting aerosols on Whatman 41 filters every 12 h. SO42− concentrations of up to 100 µg/m³ were observed during fog. The SO42−/Se ratios and trace element data suggest a distant source of SO42− aerosols, hundreds of kms away. Lahore was downwind of coal‐burning in India during the fog. The high concentrations of SO42− observed suggest a more extensive investigation of the chemistry and transport processes in this region is necessary to delineate emission sources and develop control strategies as there are serious likely effects on human health and economy in a region populated by hundreds of millions of people, and on global climate change through direct and indirect forcing.
Variability of total ozone at Arosa, Switzerland, since 1931 related to atmospheric circulation indices
Authors: Brönnimann S. , Luterbacher J. , Schmutz C. , Wanner H. , Staehelin J.
Published: February 2004

Atmospheric circulation determines to a considerable extent the variability of lower stratospheric ozone and can modulate its long‐term trends in Europe and the North Atlantic Region. Due to dynamical stratosphere‐troposphere coupling, important features of the variability of the surface pressure field are reflected in the long‐term total ozone record from Arosa, Switzerland. Significant (p<0.01) correlations between total ozone and different atmospheric circulation indices (NAOI, AOI, EU1, EU2) are found in all months except for April, June, July, and November for the period 1931 to 1997. An analysis of geopotential heights for the period 1958 to 1997 shows that these circulation anomaly patterns have upper tropospheric features over the North Atlantic‐European sector that are consistent with a dynamical influence on total ozone.
Broadband and narrowband RF interferometers for lightning observations
Authors: Kawasaki Zen , Mardiana Redy , Ushio Tomoo
Published: February 2004

Two‐dimensional locations of VHF/UHF radiation sources emitted by lightning discharges are measured by both conventional narrowband and recently developed broadband interferometers during a field campaign in Darwin, Australia. Lightning channel images are recorded by an all sky video camera simultaneously. Observation results are compared with each other to confirm the function of the broadband interferometer. The conclusion of comparisons is that these observations show excellent agreement from the aspects of accuracy in azimuth and elevation. The potential capability of the broadband interferometer is evaluated. Advantages and disadvantages of both interferometers are discussed by introducing 2D mapping for additional flashes. It is shown that the broadband interferometer can locate multiple radiation sources, which propagate simultaneously through branching, in time and space.
Perturbation in atmospheric charged species after the eruption of Mount Pinatubo
Authors: Beig Gufran
Published: February 2004

This paper presents the results of coupled neutral‐ion photochemical model to demonstrate that gas‐phase sulfur chemistry played a vital role in perturbations of the stratospheric ion composition following the Pinatubo eruption. Model calculations indicate that immediately after the eruption, the large amount of SO2 injected directly into the tropical stratosphere produced additional sulfuric acid vapor which increased the abundance of heavy negative ion family (called HSO4− ‐ core) by several orders of magnitude over the ambient. After 2 to 3 months, most of the sulfuric acid vapor gets condensed and converted to HSO4 / H2O droplets (aerosols) and the density of ultrafine charged aerosol (which are driven by aerosol) also increases several folds (∼1500%) in the tropics for 20–30 km. The perturbation in ionic species was evident even after one year of eruption (which attains a global coverage) but it finally settled down to its background level after about 2 years.
Plate motions predictions based on the constraint of toroidal‐poloidal equipartition
Authors: Spada Giorgio , Alfonsi Laura
Published: February 2004

Using a kinematic approach, we study the evolution of a system of plates whose Euler poles and shapes are dictated by the requirement of toroidal‐poloidal equipartition. Though no attempt is made to model the dynamical aspects of the problem and the time‐scales involved, the simulations performed lead to configurations of plates which share with the currently observed one an excess of drift energy with respect to spin energy. The existence of fastly spinning plates seems to be in contradiction with the constraint of toroidal‐poloidal equipartition. Their fate is to quickly disappear to prevent an excess of toroidal energy in the tectonic plates system.
Strain accumulation along the Cascadia Subduction Zone
Authors: Murray Mark H. , Lisowski Michael
Published: February 2004

We combine triangulation, trilateration, and GPS observations to determine horizontal strain rates along the Cascadia subduction zone from Cape Mendocino to the Strait of Juan de Fuca. Shear‐strain rates are significantly greater than zero (95% confidence) in all forearc regions (26–167 nanoradians/yr), and are not significant in the arc and backarc regions. The deformation is primarily uniaxial contraction nearly parallel to Juan de Fuca‐North America plate convergence (N55°–80°E). The strain rates are consistent with an elastic dislocation model for interseismic slip with a shallow 100‐km wide locked zone and a deeper 75‐km transition zone along the entire megathrust, except along the central Oregon coast where relatively lower strain rates are consistent with 30–40 km wide locked and transition zones.
Ice cloud inhomogeneity: Quantifying bias in emissivity from radar observations
Authors: Pomroy Hannah R. , Illingworth Anthony J.
Published: February 2004

In numerical models the infra‐red emissivity of ice clouds is generally computed from the optical depth. The convex relationship between these two quantities implies that if ice clouds are inhomogeneous, emissivities calculated from a grid‐box mean optical depth will be biased high. An analogous effect in stratocumulus albedo and liquid water path is compensated for by multiplying liquid water by 0.7 to calculate albedo. However it is unclear that a similar correction is valid for all cloud types. In this paper profiles of radar reflectivity in mid‐latitude winter ice clouds are analysed to derive the variability of optical depth and quantify any biases introduced into emissivities calculated from grid‐box mean optical depths. The bias is small for grid‐lengths of 10km, but the average optical depth should be multiplied by a correction factor of 0.44 for calculating emissivities in a 300km box.
Remote sensing of total precipitable water vapor in the near‐IR over ocean glint
Authors: Kleidman Richard G. , Kaufman Yoram J. , Gao Bo‐Cai , Remer Lorraine A. , Brackett Vincent G. , Ferrare Richard A. , Browell Edward V. , Ismail Syed
Published: February 2004

A method for remote sensing of total precipitable water vapor using water vapor absorption band at 0.94 µm was previously developed for continental regions. Here we apply a similar technique for ocean areas over the glint region. The glint, or oceanic specular reflection, has a high value of surface reflectance and thus, can work as well as or better than applications over land regions. The method is applied for glint regions measured by the Moderate Resolution Imaging Spectro‐radiometer (MODIS) simulator, an imager flown on the NASA ER‐2 research aircraft and simulating the expected measurements from the MODIS instrument on board the Earth Observing System (EOS)‐Terra satellite. The measurements are made for the Atlantic coast of the United States during the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX). The remote sensing technique is compared with measurements of water vapor column by the Lidar Atmospheric Sensing Experiment (LASE) Differential Infrared Absorption Lidar (DIAL) lidar system also on board the ER‐2. Water vapor was derived with an error of ±5 mm PW (precipitable water vapor). Most of the errors are associated with the limitations of an experiment that was not originally designed for this purpose. Much better performance is expected from the actual MODIS instrument.
Modeling of lightning generated electric field transitional processes
Authors: Smirnova E. I. , Mareev E. A. , Chugunov Yu. V.
Published: February 2004

A new quasi‐electrostatic model of high altitude electric field generation due to the lightning‐induced change of a thundercloud electric structure is presented. The key point of the model is the assumption that a highly conducting channel arises due to a cloud‐to‐ground (CG) discharge, which brings the ground potential to a region near the cloud bottom in some tens of milliseconds after the discharge initiation. Substantial increase in the electric field strength above the thundercloud at this moment is found. A horizontal extension of the lightning channel is taken into account in the framework of the bidirectional model of the channel propagation. This geometry provides a substantially bigger electric field perturbation than the simplest geometry of the vertical lightning channel does.
First observations of long‐lived meteor trains with resonance lidar and other optical instruments
Authors: Kelley M. C. , Gardner C. , Drummond J. , Armstrong T. , Liu A. , Chu X. , Papen G. , Kruschwitz C. , Loughmiller P. , Grime B. , Engelman J.
Published: February 2004

In November 1998 the earth passed through a maximum in the cometary material responsible for the yearly Leonids meteor shower. The meteor storm event produced numerous examples of long‐lived chemiluminescent trails—visible to the naked eye—over New Mexico, where a major observation campaign was centered. One trail was detected for over an hour with a CCD camera employing a narrow sodium filter, and many others were observed for over ten minutes each. For the first time, sodium densities in such trails were measured while also being imaged in sodium light. We have verified one source of long‐lived light emissions—a sodium‐catalyzed reaction involving ozone—but it is far too weak to explain the visibility of such trails. In addition, we present a new explanation for the cylindrical shell appearance long reported for chemiluminescent trails and show that ozone depletion by chemical processes is a possible explanation for this phenomenon.
Emissions of methyl chloroform (CH3CCl3) from biomass burning and the tropospheric methyl chloroform budget
Authors: Rudolph J. , von Czapiewski K. , Koppmann R.
Published: February 2004

The only known sources of atmospheric methyl chloroform are industrial production and biomass burning. With the phase‐out of industrial methyl chloroform production the atmospheric burden of methyl chloroform is rapidly declining. Consequently the potential importance of nonindustrial sources is increasing. Up to now only one experimental investigation of methyl chloroform emissions from biomass burning has been published. Here laboratory studies of methyl chloroform emission from wood burning are presented. The emission ratios relative to carbon dioxide and carbon monoxide are 12.7 ± 2.6 × 10−8and 15.6 ± 3.3 × 10−7, respectively. Although based on a limited number of measurements, they strongly suggest that methyl chloroform emissions from biomass burning are at the lower end of previous estimates. The impact of these emissions on the chemistry of the atmosphere will be marginal. However, reliable knowledge of the biomass burning source strength will be essential for a detailed analysis of the trend of atmospheric methyl chloroform concentrations.
Rupture dimensions of the 1998 Antarctic Earthquake from low‐frequency waves
Authors: McGuire Jeffrey J. , Zhao Li , Jordan Thomas H.
Published: February 2004

We inverted frequency dependent phase and amplitude measurements from 1st orbit Rayleigh waves at global stations for the 1st and 2nd degree polynomial moments of the stress‐glut rate tensor. The higher moments of the slip‐rate distribution determine the fault plane and approximate rupture dimensions. The results show strong rupture propagation to the west with an average velocity of the instantaneous centroid of 3.6±.1 km/s. The rupture had a characteristic length of 178±46 km in the east‐west direction and a characteristic duration of 48±2 s. The results are consistent with unilateral rupture on the east‐west fault plane of the focal mechanism and rule out significant rupture on the north‐south nodal plane.
What caused the March 25, 1998 Antarctic Plate earthquake?: Inferences from regional stress and strain rate fields
Authors: Kreemer Corné , Holt William E.
Published: February 2004

We investigate possible driving forces behind the occurrence of the 1998 Antarctic plate earthquake. We determine first a regional strain rate field associated with the accommodation of relative plate motion, and second, a vertically averaged minimum deviatoric stress field associated with lithospheric gravitational potential energy differences and deglaciation of the Antarctic ice cap. We find that the mechanism of this event is inconsistent with strain orientations inferred from kinematic modeling of a diffuse zone of deformation within the triple junction region. Stress perturbations associated with deglaciation cannot be ruled out as a triggering mechanism for this event.
Deployment of a broadband seismic network in west Antarctica
Authors: Anandakrishnan S. , Voigt D. E. , Burkett P. G. , Long B. , Henry R.
Published: February 2004

A network of six broadband seismic stations was deployed in West Antarctica in November, 1998. A new data recording instrument and power system was developed to operate the stations year round using solar energy in the summer and wind energy in the winter. The data logging technology, designed to record geophysical parameters (broadband seismic and geodetic GPS—Global Positioning System), is also appropriate for other remote Antarctic and Arctic data recording applications with similar data band‐widths. The seismicity of Antarctica is hypothesized to be low, but that could be an artifact of the poor distribution and small number of seismic stations on the continent. One goal of the experiment is to record data in the West Antarctic (the region most likely to exhibit seismic activity) for sufficient lengths of time in order to address this hypothesis fully. In addition, the data are useful for determining crust and mantle structure and properties. The network has been active for about half the time since installation, which is sufficient to draw statistically significant conclusions on regional seismicity. The experiment will continue for the next two years, with system modifications that should improve the performance of the network.
On the spatio‐temporal distribution of acoustic emissions in two granitic rocks under triaxial compression: The role of pre‐existing cracks
Authors: Lei X. ‐L. , Kusunose K. , Nishizawa O. , Cho A. , Satoh T.
Published: February 2004

We used a new rapid data acquisition system to examine the role of pre‐existing crack density in determining the mechanical properties of crystalline rock. Two similar coarse‐grained samples, Tsukuba granite (TG) and granitic porphyry (GP), were used in triaxial compression tests. The main difference between the two rocks is that TG contains main large pre‐existing cracks, whereas GP is almost crack‐free. In our tests, the two rocks showed significantly different behaviors. In GP, before the fault nucleation, AE activity was low and showed increasing b‐values with increasing stress. But in TG, a large number of AEs were observed and showed short‐term b‐value anomalies ‐ mutual fluctuations on a decreasing background. The short‐term fluctuations of b‐values are closely correlated with those of the spatio‐temporal clustering of AE locations. Our results demonstrate: 1) pre‐existing cracks are the most dominant factor of all heterogeneities that govern the fault nucleation process in laboratory rock samples; 2) failure predictability is dependent on the pre‐existing crack density.
Climate and ozone response to increased stratospheric water vapor
Authors: Shindell Drew T.
Published: February 2004

Stratospheric water vapor abundance affects ozone, surface climate, and stratospheric temperatures. From 30–50 km altitude, temperatures show global decreases of 3–6 K over recent decades. These may be a proxy for water vapor increases, as the GISS climate model reproduces these trends only when stratospheric water vapor is allowed to increase. Observations suggest that stratospheric water vapor is indeed increasing, though measurements are extremely limited in either spatial coverage or duration. Model results suggest that the observed changes may be part of a global, long‐term trend. Furthermore, the required water vapor change cannot be accounted for by increased stratospheric production, suggesting that climate change may be altering tropospheric input. The calculated water vapor increase contributes an additional ≈ 24% (≈ 0.2 W/m²) to the global warming from well‐mixed greenhouse gases over the past two decades. Observed ozone depletion is also better reproduced when destruction due to increased water vapor is included. If the trend continues, it could increase future global warming and impede stratospheric ozone recovery.
Source rupture process of the Kocaeli, Turkey, earthquake of August 17, 1999, obtained by joint inversion of near‐field data and teleseismic data
Authors: Yagi Yuji , Kikuchi Masayuki
Published: February 2004

The rupture process of the 1999 Turkey earthquake is examined using both near‐field strong motion data and teleseismic body wave data. The derived source parameters are as follows: (strike, dip, slip) = (268°, 86°, 180°), nearly pure strike‐slip; the seismic moment, Mo = 1.7 × 1020 Nm (Mw = 7.4); the source duration = 20 sec; the fault length = 70 km; the fault width = 15 km. The rupture process is characterized by an asymmetric bilateral rupture propagation and smooth slip. It consists of two major fault segments, a rupture propagating to the west and a second rupture propagating to the east. The maximum dislocation and the maximum dislocation velocity are 6.3 m and 2.7 m/s, respectively, both found at the former segment. The average dislocation is about 4 m. The extent of the coseismic rupture suggests that a considerable part of the anticipated seismic gap remains unruptured.
Near real‐time radar interferometry of the Mw 7.1 Hector Mine Earthquake
Authors: Sandwell David T. , Sichoix Lydie , Agnew Duncan , Bock Yehuda , Minster Jean‐Bernard
Published: February 2004

The Hector Mine Earthquake (Mw 7.1, 16 October 1999) ruptured 45 km of previously mapped and unmapped faults in the Mojave Desert. The ERS‐2 satellite imaged the Mojave Desert on 15 September and again on 20 October, just 4 days after the earthquake. Using a newly‐developed ground station we acquired both passes and were able to form an interferogram within 20 hours of the second overflight. Estimates of slip along the main rupture are 1–2 meters greater than slip derived from geological mapping. The gradient of the interferometric phase reveals an interesting pattern of triggered slip on adjacent faults as well as a 30 mm deep sink hole along Interstate 40.
The effect of stabilising atmospheric carbon dioxide concentrations on global and regional climate change
Authors: Mitchell J. F. B. , Johns T. C. , Ingram W. J. , Lowe J. A.
Published: February 2004

The effect on climate of stabilising atmospheric carbon dioxide concentrations at 550ppm and 750ppm is investigated using a coupled ocean‐atmosphere model and compared with the response to a baseline case (1% per year increase in carbon dioxide concentrations beyond 1990). Changes in other well‐mixed greenhouse gases are not considered (although these are expected to increase in the future), so in practical terms the simulated changes in climate correspond to lower levels of carbon dioxide stabilisation. The global‐mean warming between 1990 and 2100 is reduced by 40% and 55% respectively, in close agreement with estimates using energy balance models. Sea‐level rise up to 2100 is also reduced, but in the longer stabilisation runs, unlike temperature, sea‐level continues to rise throughout the simulations with little reduction of the rate of rise. The patterns of temperature and precipitation change are largely unchanged except that the southern hemisphere warms relative to the northern hemisphere. Changes over five subcontinental regions are considered in more detail. All of the regions, for all of the simulations, show a statistically significant warming by 2100. The reduction in annual‐mean warming resulting from stabilisation is also significant by 2100. The seasonal changes in precipitation are significant by 2100 in the baseline simulation but the significance of differences in precipitation between the baseline and stabilisation simulations depends on location and season.
Seasonal variations of HCN over northern Japan measured by ground‐based infrared solar spectroscopy
Authors: Zhao Y. , Kondo Y. , Murcray F. J. , Liu X. , Koike M. , Irie H. , Strong K. , Suzuki K. , Sera M. , Ikegami Y.
Published: February 2004

Ground‐based infrared solar spectra were recorded at Rikubetsu (43.5°N) and Moshiri (44.4°N) in Japan using Fourier transform infrared (FTIR) spectrometers from 1995 to 1997. Total column amounts and tropospheric mixing ratios of HCN were derived from these spectra in the 3287.05–3287.40 cm−1 micro‐window using a nonlinear least squares spectral fitting method. The HCN values at these two locations showed significant seasonal variations. The HCN total column reached a maximum value of 6.57±0.84×1015 molecules cm−2 in summer (June–August) and a minimum value of 3.97±0.30×1015 molecules cm−2 in winter (December–February). The maximum and minimum tropospheric HCN mixing ratios were 333±44 (summer) and 195±16 (winter) parts per trillion by volume (pptv), respectively. These seasonal variations suggest that the lifetime of HCN is shorter than one year. The enhancement of HCN above its seasonal mean (ΔHCN) was correlated with the enhancement of CO ( ΔCO). A constant ΔHCN/ΔCO ratio suggests biomass burning as a source of HCN.
New particle formation in the continental boundary layer: Meteorological and gas phase parameter influence
Authors: Birmili Wolfram , Wiedensohler Alfred
Published: February 2004

New particle formation in the polluted continental boundary layer was studied, based on 1.5‐year observations of the particle size distribution, meteorological and gas phase parameters. Events of new particle formation involving significant ultrafine particle number concentrations (>104 cm−3 in the size range 3–11 nm) were observed on 20% of all days, pointing out that a frequent particle production from gaseous precursors can occur despite the relatively high pre‐existing particle surface area in the area of investigation. The maximum in the observed particle size distributions was mostly above 3 nm, suggesting the actual particle nucleation to take place upwind of the measurement site. A particle growth analysis yielded 2.3±1.4 h as an upper limit of the time for the particles to grow from the critical cluster size till the observation of the peak in ultrafine number concentration. On 80% of the significant events of new particle formation (though not on all), SO2 concentrations increased considerably (by an average factor of 7), most likely by entrainment from aloft. Particle surface area was, on average, higher on event days compared to non‐event days, indicating only a weak competition between condensation onto the pre‐existing particle surface area and the new particle formation process. The highest statistical correlation was found between the events of new particle formation and solar radiation, indicating a high degree of meteorological control.
Rossby waves detected in global ocean colour data
Authors: Cipollini Paolo , Cromwell David , Challenor Peter G. , Raffaglio Stefano
Published: February 2004

We demonstrate for the first time the detectability of mid‐latitude Rossby waves in global ocean colour data from the Japanese Ocean Colour and Temperature Scanner (OCTS) and U.S. Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) radiometers. By producing longitude‐time plots of the merged OCTS and SeaWiFS datasets we observe at some latitudes westward propagating signals. Their signature is much weaker than the annual phytoplankton cycle, but can be highlighted by filtering the plots. The main propagating speed is estimated with the Radon Transform and increases equatorward, as expected for Rossby waves. A comparison with both speeds derived from altimeter data and the zonal mean of the speed predicted by a recent theory of Rossby wave propagation shows a broad agreement. We conclude that Rossby waves are sometimes observable in the ocean colour field and thus have some effects on biology, and we suggest two simple hypotheses for the underlying interaction mechanism.
Evidence of low Q below Popocatépetl Volcano, and its implication to seismic hazard in Mexico City
Authors: Shapiro N. M. , Singh S. K. , Iglesias‐Mendoza A. , Cruz‐Atienza V. M. , Pacheco J. F.
Published: February 2004

Seismograms recorded in Mexico City reveal that the amplitudes of seismic waves whose wavepaths pass below Popocatépetl, presently an volcano, before reaching the city are diminished by a factor of about one‐third at frequencies greater than 1 Hz as compared to those which do not cross the volcano. The high attenuation of seismic waves below the volcano may be attributed to the presence of magma and partial melting of rocks. Q of shear waves below the volcano is roughly estimated as 60. A consequence of the large attenuation of high‐frequency seismic waves is a decrease in the seismic hazard to low‐rise buildings in Mexico City from intraplate earthquakes whose wavepaths cross the volcano.
Fractionation of 14N15N16O and 15N14N16O during photolysis at 213 nm
Authors: Zhang Hui , Wennberg Paul O. , Wu Vincent H. , Blake Geoffrey A.
Published: February 2004

Motivated by Yung and Miller's [1997] suggestion that N2O is isotopically fractionated during UV photolysis in the stratosphere, we have studied the photolysis rates of the 14N15N16O and 15N14N16O structural isotopomers. In this study, we follow the concentrations of these compounds with FTIR spectroscopy during photolysis at 213 nm. When fitted to a Rayleigh fractionation model, the observations yield single‐stage enrichment factors of ϵ(14N15N16O / 14N14N16O) = −73 ± 5 per mil and ϵ(15N14N16O / 14N14N16O) = −41 ± 10 per mil. As predicted by Yung and Miller [1997], the photolysis rate of 15N14N16O is faster than 14N15N16O at this wavelength. The magnitude of the observed fractionation, however, is significantly larger than predicted.
Prototype autonomous earthquake locator for regional networks
Authors: Pinsky V.
Published: February 2004

A fully autonomous source location algorithm, which identifies the local earthquake P and S phases by finding the network seismogram envelope maxima Pmax and Smax, is designed. These picks are approximated to theoretical travel times of the wavefield intensity by varying epicenter and origin time, thus providing initial estimates for source coordinates, origin time and phase onsets. Then the onsets are improved by detection of the time‐series discrepancy points with the subsequent fitting to the theoretical first arrival times for the final source location. Fitting is performed using a grid‐search robust optimization procedure based on the bell‐like factor functions. Application of the algorithm to 61 local earthquakes recorded by the Israel Seismic Network shows location accuracy of 3 km for epicenter and ±7 km for depth. For the four blasts from a quarry near the Dead Sea with known coordinates and ignition time the automatic locator provided accuracy of 0.3–1.7 km and even outperformed the analyst solutions.
Application of ionospheric tomography to real‐time GPS carrier‐phase ambiguities Resolution, at scales of 400–1000 km and with high geomagnetic activity
Authors: Hernández‐Pajares M. , Juan J. M. , Sanz J. , Colombo O. L.
Published: February 2004

The influence of the ionosphere can be one of the main obstacles to GPS carrier phase ambiguity resolution in real‐time, particularly over long baselines. This is important to all users of GPS requiring sub‐decimeter positioning, perhaps in real time, especially with high geomagnetic activity or close to the Solar Maximum. Therefore, it is desirable to have a precise estimation of the ionospheric delay in real‐time, to correct the data. In this paper we asses a real‐time tomographic model of the ionosphere created using dual‐frequency phase data simultaneously collected with the receivers of a network of stations in the USA and Canada, with separations of 400–1000 km, during a period of high geomagnetic activity (Kp=6). When the tomographic ionospheric correction is included, the resolution on‐the‐fly (OTF) of the widelane double‐differenced ambiguities at the reference stations is nearly 100% successful for satellite elevations above 20 degrees, while the resolution of the L1, L2 ambiguities at the rover is typically more than 80% successful.
Seismic remote sensing for the earthquake source process and near‐source strong shaking: A case study of the October 16, 1999 Hector Mine earthquake
Authors: Dreger Douglas , Kaverina Anastasia
Published: February 2004

A new methodology to automatically determine the earthquake source process and near‐source strong ground motions using regional and local distance data was used to study the October 16, 1999 Hector Mine earthquake (MW7.1). Broadband displacement data were inverted for the seismic moment tensor and to resolve the fault plane ambiguity independent of aftershock location and surface faulting information. The identified NNW striking fault plane was used to invert for the distribution of fault slip over a planar surface. The slip model was used to predict near‐fault peak ground velocity, which was found to agree well with the TriNet ShakeMap, and also with near‐fault observations that were not available at the time of the initial analysis. Our method if automated is capable of providing near‐source strong ground motion information within 30 minutes of the earthquake origin time even in cases where there are few near‐fault recording instruments.
Snow megadune fields on the East Antarctic Plateau: Extreme atmosphere‐ice interaction
Authors: Fahnestock Mark A. , Scambos Ted A. , Shuman Christopher A. , Arthern Robert J. , Winebrenner Dale P. , Kwok Ron
Published: February 2004

Large dune fields occupy more than 500,000 km² of the East Antarctic Plateau. The “megadunes”, or long‐wavelength surface ripples, have amplitudes of only a few meters, wavelengths of a few kilometers, and parallel crests which can extend one hundred kilometers. They occur in areas characterized by low accumulation, extensively recrystallized snow, and strong scattering of the microwave part of the spectrum. Dune crests are oriented perpendicular to the regional katabatic wind direction. Snow megadunes are unlikely to be formed by simple wind transport of snow particles.
Electromagnetic induction effects by the solar quiet magnetic field at satellite altitude
Authors: Tarits Pascal , Grammatica Naphsica
Published: February 2004

We show that magnetic fields induced by a near‐earth ionospheric source can produce, at a satellite altitude of 400 km, an induced magnetic anomaly field with an amplitude of 2–3 nT at dawn and dusk local times and 3–4 nT at noon local time. Our results are based on an earth model which has an upper 4 km thick shell with a laterally varying electrical conductivity representing the distribution of continents and oceans. The upper shell overlies a one‐dimensional mantle with a radially varying electrical conductivity. In some regions, the induced anomaly field does not change sign between dawn and dusk and appears static when sampled by a satellite such as MAGSAT. This induced anomaly field could explain some of the weak oceanic static anomalies observed in satellite global magnetic anomaly maps.
Impact of gas‐phase HNO3 and NH3 on microphysical processes in atmospheric clouds
Authors: Hegg Dean A.
Published: February 2004

Model calculations are presented for the impact of trace gas absorption on aerosol activation and precipitation formation in clouds. In contrast to previous studies, acidic aerosols are examined. The results suggest a significant impact, primarily associated with NH3.
Evidence for a time‐varying pattern of Greenhouse warming in the Pacific Ocean
Authors: Cai Wenju , Whetton Peter H.
Published: February 2004

The observed warming trend in recent decades has had an El Niño‐like character, but the cause of this pattern has been a contentious issue. Here we report results from the CSIRO climate model forced by historical and projected future increases in greenhouse‐gas concentrations. These show a warming pattern that initially has the largest warming in the extratropics with a weak La Niña‐like pattern in the tropics, but is eventually (after the 1960s) El Niño‐like. This behaviour is present in each of an ensemble of three simulations. The switch in warming pattern is driven by the extratropical warmed water that subducts and penetrates through the subtropics and into the tropics, where it upwells and initiates the change. This result strengthens the argument, in terms of a physical mechanism, that the recent observed El Niño‐like warming trend may be at least in part greenhouse‐induced.
Dry/wet alternation and global monsoon
Authors: Qian Weihong
Published: February 2004

This paper deals with dry/wet alternation and related globe‐scale monsoon. The data sets used are the Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP), the National Meteorological Center global wind analysis and the Upper‐Tropospheric Water Vapor (UTWV) band Brightness Temperature (BT) observed by NOAA polar orbiting satellites for 1980–1995. The BT and wind at 850hPa level are compared with the CMAP. Results show that the BT can indicate the convective precipitation in both tropical and subtropical regions. The summer monsoon in subtropics is defined as the expansions of three deep convective areas or three wet centers at the equatorial region. The major distributions of dry/wet alternation are determined according to the threshold of BT less than 244K. In the global mid‐low latitudes, there are six major seasonal dry/wet alternative regions with the dry/wet period lasting more than one month. The largest one is located over the subtropical North Africa‐Asia‐northwest Pacific. Other five alternative regions appear in the subtropical South Africa, Indonesia‐Australia, southwest Pacific, Mexico‐Caribbean Sea and subtropical South America. In Asia, the largest dry/wet alternative region covers all India, Indochina Peninsula, South China and southern Japan. These wet/dry alternative regions are the reflection of the seasonal advance of summer monsoon.