bluuebunny/crossref_metadata_2025 huggingface dataset:
Variability in the stratospheric background aerosol over Mauna Loa Observatory
Authors: Barnes J. E. , Hofmann D. J.
Published: February 2004

The stratospheric aerosol layer above Mauna Loa Observatory (MLO), Hawaii, has been at low background levels for the past 5 years. This is the first time that an extended non‐volcanic background aerosol period has been observed since modern measurements began in the early 1960s. Lidar backscatter at 532 nm shows a distinct maximum in winter and minimum in summer. The five annual cycles have included three easterly phases and two westerly phases of the quasibiennial oscillation (QBO). Differences in aerosol backscatter versus altitude profiles are seen for different QBO phases. There is also a switching of about 25% in the magnitude of the aerosol backscatter on a weekly time scale with varying particle size derived from multiwavelength data. Assumption of a tropical particle source at background suggests that the differing particle regimes are tropical and midlatitude.
Observations of highly nonlinear internal solitons generated by near‐inertial internal waves off the east coast of Korea
Authors: Kim Hyoung Rok , Ahn Saeyoung , Kim Kuh
Published: February 2004

Solitary internal wave packets were observed in May 1999, propagating toward the east coast of Korea with thermocline displacements up to twentysix meters downward from the initial depth of twenty meters. High nonlinearity of these waves is represented by the second‐order KdV model better than KdV equations. Regular occurrence of solitary internal wave packets with the period of about nineteen hours suggests the generation by near‐inertial internal waves, which has not been reported in the literature yet.
A tropospheric ozone maximum over the Middle East
Authors: Li Qinbin , Jacob Daniel J. , Logan Jennifer A. , Bey Isabelle , Yantosca Robert M. , Liu Hongyu , Martin Randall V. , Fiore Arlene M. , Field Brendan D. , Duncan Bryan N. , Thouret Valérie
Published: February 2004

The GEOS‐CHEM global 3‐D model of tropospheric chemistry predicts a summertime O3 maximum over the Middle East, with mean mixing ratios in the middle and upper troposphere in excess of 80 ppbv. This model feature is consistent with the few observations from commercial aircraft in the region. Its origin in the model reflects a complex interplay of dynamical and chemical factors, and of anthropogenic and natural influences. The anticyclonic circulation in the middle and upper troposphere over the Middle East funnels northern midlatitude pollution transported in the westerly subtropical jet as well as lightning outflow from the Indian monsoon and pollution from eastern Asia transported in an easterly tropical jet. Large‐scale subsidence over the region takes place with continued net production of O3 and little mid‐level outflow. Transport from the stratosphere does not contribute significantly to the O3 maximum. Sensitivity simulations with anthropogenic or lightning emissions shut off indicate decreases of 20–30% and 10–15% respectively in the tropospheric O3 column over the Middle East. More observations in this region are needed to confirm the presence of the O3 maximum.
Radiative cooling by stratospheric water vapor: Big differences in GCM results
Authors: Oinas V. , Lacis A. A. , Rind D. , Shindell D. T. , Hansen J. E.
Published: February 2004

The stratosphere has been cooling by about 2K/decade at 30–60 km over the past several decades and by lesser amounts toward the tropopause. Climate model calculations suggest that stratospheric water vapor is an important contributor to the observed stratospheric cooling, but there are large differences among recent GCM simulations for prescribed changes in stratospheric water vapor, which point to problems with the current GCM treatment of the absorption and emission by stratospheric water vapor. We show that the correlated k‐distribution treatment with sufficient resolution is capable of simulating accurately cooling by stratospheric water vapor. We obtain equilibrium cooling of about 0.3K that extends from 20 km to the top of the atmosphere, and adjusted radiative forcing of 0.12 Wm−2, for a stratospheric water vapor increase of 0.7 ppmv which has been estimated for the period 1979–1997.
The impact of ocean coupling on hurricanes during landfall
Authors: Shen Weixing , Ginis Isaac
Published: February 2004

The impact of ocean coupling on landfalling hurricanes is studied using a coupled hurricane‐ocean model with idealized atmospheric and oceanic conditions. We focus here on coastal sea surface temperature responses and their effects on hurricanes during landfall. We find that given the ocean thermal stratification, the hurricane‐induced sea surface cooling is nearly independent of the ocean depth as long as the ocean is considerably deeper than the mixed layer. After the storm center moves inland, the near‐surface processes around the storm core area are influenced by the sea surface cooling behind and on the right side of the storm track via reduction of near‐surface entropy advection into this area. The impact of ocean coupling is generally limited to the early times after landfall and nearly disappears after the hurricane center reaches about 200 km inland.
T‐waves excited by S‐waves and oscillated within the ocean above the Southeastern Taiwan Forearc
Authors: Lin Cheng‐Horng
Published: February 2004

The generation processes of T‐waves were investigated from seismograms produced by a local intermediate‐depth earthquake and recorded at one short‐period station in Taiwan. The first group of T‐phases arrived 44 seconds after the S‐phases, while the following 2 groups consistently had the same travel‐time difference of about 88 seconds each. Analyses of the ray paths and travel‐times of these phases show that the T‐waves were converted from the S‐waves and oscillated within the ocean above the forearc in the southeastern Taiwan area. Further comparisons of these results with those of previous studies suggest that the generation of T‐waves is probably dependent on the incidence angles of the seismic waves. The T‐waves were converted from S‐waves when the incidence angles of the seismic waves were near vertical, whereas they were generated from P‐waves when those angles were near horizontal.
Seasonal dependence of surface wind stress variability on SST and precipitation over the tropical Pacific
Authors: Yang Fanglin , Kumar Arun , Wang Wanqiu
Published: February 2004

The dependence of interannual variability of surface zonal and meridional wind stresses (τx and τy) on sea‐surface temperature (SST) and precipitation over the tropical Pacific is examined using observed data. A strong seasonality in the dependence is found. In January, the largest SST and precipitation anomalies are located in the central to eastern and central tropical Pacific respectively. τx anomalies in the southern central tropical Pacific and τy anomalies in the northern tropical Pacific are highly correlated to both the SST and precipitation anomalies. In contrast, during July the largest SST and precipitation anomalies are located at the eastern and western tropical Pacific respectively. East of the dateline, τx anomalies present little dependence on the SST anomalies. West of the dateline, τx anomalies depend strongly on the precipitation anomalies that are not linked to the leading modes of SST.
An investigation of South Pole HOx chemistry: Comparison of model results with ISCAT observations
Authors: Chen G. , Davis D. , Crawford J. , Nowak J. B. , Eisele F. , Mauldin R. L. , Tanner D. , Buhr M. , Shetter R. , Lefer B. , Arimoto R. , Hogan A. , Blake D.
Published: February 2004

Unexpected high levels of OH and NO were recorded at the South Pole (SP) Atmospheric Research Observatory during the 1998–99 ISCAT field study. Model simulations suggest a major photochemical linkage between observed OH and NO. A detailed comparison of the observations with model predictions revealed good agreement for OH at NO levels between 120 and 380 pptv. However, the model tended to overestimate OH for NO levels <120 pptv, while it underestimated OH at levels >380 pptv. The reasons for these deviations appear not to involve NO directly but rather HOx radical scavenging for the low NO conditions and additional HOx sources for the high NO conditions. Because of the elevated levels of NO and highly activated HOx photochemistry, the SP was found to be a strong net source of surface ozone. It is quite likely that the strong oxidizing environment found at the South Pole extends over the entire polar plateau.
HF radio wave attenuation due to a meteoric layer in the atmosphere of Mars
Authors: Witasse O. , Nouvel J.‐F. , Lebreton J.‐P. , Kofman W.
Published: February 2004

In the atmosphere of Mars, the effect of an ionospheric layer of meteoric origin on an HF radio wave propagation is investigated. We consider the putative magnesium ion layer which results from the ablation of sporadic meteors from a work recently published. To account for day‐night variability, two electron profiles are considered in an altitude range around 80 km. First we argue that there may be some observational evidence of this magnesium layer in early Mars observations that were not noticed before. Then we study the effect of this ionospheric layer on the attenuation of HF waves. For a propagation path through the ionosphere as envisaged for HF subsurface sounding on future Mars missions, the one‐way attenuation may range from up to 360 dB's at 1.8 MHz and up to 18 dB's at 9 MHz.
Proton temperature anisotropy constraint in the solar wind: ACE observations
Authors: Gary S. Peter , Skoug Ruth M. , Steinberg John T. , Smith Charles W.
Published: February 2004

The electromagnetic proton cyclotron anisotropy instability may arise in collisionless plasmas in which the proton velocity distribution is approximately bi‐Maxwellian with T⟂p/T∥p > 1, where ⟂ and ∥ denote directions relative to the background magnetic field Bo. Theory and simulations predict that enhanced field fluctuations from this instability impose a constraint on proton temperature anisotropies of the form

where
, and the fitting parameters Sp ≲ 1 and αp ≃ 0.4. Plasma and magnetic field observations from the ACE spacecraft reported here show for the first time that this constraint is statistically satisfied in the high speed solar wind near 1 AU, and magnetic power spectra provide evidence that this instability is the source of the constraint.
Varieties of shallow temperature maximum waters in the Western Canadian Basin of the Arctic Ocean
Authors: Shimada Koji , Carmack Eddy C. , Hatakeyama Kiyoshi , Takizawa Takatoshi
Published: February 2004

The properties and spreading pathways of shallow temperature maximum waters (STMs) in the western Canadian Basin are investigated using CTD and mooring data obtained in 1997–98 as part of the SHEBA (Surface Heat Budget of the Arctic Ocean) drift experiment and available historical data. Three distinct varieties of STM are recognized on the basis of salinity range: (1) Surface Mixed Layer Water (SMLW) with S < 30 psu; (2) Eastern Chukchi Summer Water (ECSW) with 31 < S < 32 psu; and (3) Western Chukchi Summer Water (WCSW) with S > 32 psu. These STMs carry sufficient heat within the upper layers of the ocean to significantly affect the rates of ice cover and decay. For example, during the winter of 1997–98 anomalously warm STM (> 0°C) originating from ECSW was observed to spread northwards along the Northwind Ridge and Chukchi Plateau, where the maximum reduction of the ice covers was subsequently observed in late summer, 1998 [Maslanik et al., 1999]. Regional climate variability and ice cover in the western Canadian Basin are thus affected not only by anomalous atmospheric circulation patterns, but also by the circulation of upper ocean water masses.
Deliquescence of ammonium sulfate particles at sub‐eutectic temperatures
Authors: Braban C. F. , Abbatt J. P. D. , Cziczo D. J.
Published: February 2004

To better understand atmospheric aerosol phase transitions under free tropospheric conditions, the behavior of ammonium sulfate (AS) particles mounted on a silicon substrate has been investigated between 229 and 295 K. Experiments were performed in a chamber where water partial pressure and particulate infrared spectra were monitored as the temperature was lowered. Deliquescence experiments at temperatures above the eutectic (254 K) are not new, however results defining deliquescence relative humidity (DRH) at temperatures below the eutectic have been lacking. At sub‐eutectic temperatures the system is supersaturated with respect to ice, therefore both deliquescence and ice formation were possible. Within experimental error, deliquescence was observed at the thermodynamically predicted value both above and below the eutectic. The lack of a significant kinetic barrier to deliquescence implies that AS particles could form supercooled solution droplets at high relative humidities, and function as ice nuclei if these droplets homogeneously freeze.
The effects of geophysical fluids on motions of the Global Positioning System satellites
Authors: Johnson Thomas J. , Kammeyer Peter , Ray Jim
Published: February 2004

For over a decade, laser ranging satellites have been used to study variations in the low‐order terms of the Earth's gravitational potential. The primary non‐tidal source of these variations is redistribution of the mass contained in the Earth's atmosphere, oceans, and continental hydrology. This paper presents an independent detection of these variations using five years of Global Positioning System (GPS) satellite orbits from the International GPS Service. This detection is based on comparisons of observed Earth‐referenced positions for the GPS satellites with orbit planes predicted in Earth‐centered inertial coordinates. The difference between a GPS UT1‐like quantity (UTGPS) and UTC represents the net nodal drift of the GPS constellation and contains both changes in the difference UT1‐UTC and effects from even zonal variations in the Earth's gravitational field. Our results indicate that J2 variations at sub‐monthly to annual time scales predicted by the National Center for Environmental Prediction's atmosphere model are, in fact, significantly correlated with variations estimated from UTGPS‐UT1. In addition, ocean and continental hydrology models suggest that these geophysical fluids make non‐negligible contributions at seasonal and other specific time scales.
Seasonal and intraseasonal thermocline variability in the central south China Sea
Authors: Liu Qinyu , Jia Yinglai , Liu Penghui , Wang Qi , Chu Peter C.
Published: February 2004

Seasonal and intraseasonal variability of thermocline and relative surface height in the central South China Sea (SCS) are investigated using time series data of temperature from three buoys and sea surface height anomaly data from TOPEX/POSEIDON and ERS‐1/ERS‐2 satellites (T/P‐ERS) from Feb, 1998 through Mar. 1999. We found that the thermocline becomes deeper and thinner in winter, owing to a great loss of the heat on the sea surface. This feature is more evident in the northern than the southern part of the central SCS. The intraseasonal variation of the thermocline is mainly controlled by the geostrophic vorticity and is out‐of‐phase with sea surface height (SSH). Furthermore, we find a double‐thermocline phenomenon occurs in the SCS: In spring, owing to maximum net downward heat flux at the surface, with the new thermocline appearing above 80 m and the old thermocline keeping under 80 m deep.
On the formation of streaks on wind‐driven water surfaces
Authors: Tsai Wu‐ting
Published: February 2004

Evidence derived from numerical experiments is presented to show that, contrary to the prevalent notion, the generation of elongated wind‐induced streaks on water surfaces with spacing of centimeters is not necessarily attributed to interactions between surface waves and the shear current. Although the water surface is artificially designated as a flat boundary in the numerical simulations here, high‐speed streaks appear on the surface arising from an underlying shear current. Floating Lagrangian tracers cluster along the streaks and, in accordance with field and laboratory observations, undergo dislocation and amalgamation.
Effect of water on the spinel‐postspinel transformation in Mg2SiO4
Authors: Higo Yuji , Inoue Toru , Irifune Tetsuo , Yurimoto Hisayoshi
Published: February 2004

The phase boundary between ringwoodite and perovskite plus periclase in Mg2SiO4 was determined at 1600 °C under hydrous conditions with 1∼3 wt% H2O. We found that the boundary moved to high‐pressure side by ∼0.2 GPa in these hydrous conditions compared with that in anhydrous condition. The SIMS measurements confirmed that the ringwoodite in hydrous condition contained a significant amount (∼1 wt%) of water, whereas the perovskite accepted only very little (∼0.05 wt%) water in its crystal structure. The discrepancy between the pressure of 660 km seismic discontinuity and that of the postspinel transformation reported in a recent in situ x‐ray study is not explained by the effect of water on the transformation.
Wavelet transform: A tool for the interpretation of upper mantle converted phases at high frequency
Authors: Castillo Julie , Mocquet Antoine , Saracco Ginette
Published: February 2004

P to S converted receiver functions recorded at VBB FDSN California stations are studied in the frequency range of 0.1 to 1 Hz. Microseismic noise is maximum in this frequency range, but signal processing by the wavelet transform enables us: (1) to enhance seismic phases associated with seismic velocity gradients and discontinuities at the base of the upper mantle, (2) to extract accurate arrival times, and (3) to obtain an accurate insight into the frequency content. In the case of California, one seismic discontinuity and two zones of high gradients in the depth range of 625 to 720km are recurrently observed for two different data sets.
Discovery of a water vapor layer in the Arctic summer mesosphere: Implications for polar mesospheric clouds
Authors: Summers Michael E. , Conway R. R. , Englert C. R. , Siskind D. E. , Stevens M. H. , Russell J. M. , Gordley L. L. , McHugh M. J.
Published: February 2004

We report the discovery of a layer of enhanced water vapor in the Arctic summer mesosphere that was made utilizing two new techniques for remotely determining water vapor abundances. The first utilizes Middle Atmosphere High Resolution Spectrograph Investigation (MAHRSI) OH measurements as a proxy for water vapor. The second is a reanalysis of Halogen Occultation Experiment (HALOE) water vapor data with a technique to simultaneously determine polar mesospheric cloud (PMC) ice particle extinction along with the water vapor abundance. These results reveal a narrow layer of enhanced water vapor centered between 82–84 km altitude and coincident with PMCs, that exhibits water vapor mixing ratios of 10–15 ppmv. This indicates that a higher degree of supersaturation is present in the PMC region, and that PMCs are thus more efficient at sequestering total water (both ice particles and vapor) within the layer, than previously believed.
Northern hemisphere atmospheric effects due to the July 2000 Solar Proton Event
Authors: Jackman Charles H. , McPeters Richard D. , Labow Gordon J. , Fleming Eric L. , Praderas Cid J. , Russell James M.
Published: February 2004

The third largest solar proton event in the past thirty years took place during July 14–16, 2000, and had a significant impact on the earth's atmosphere. These energetic protons produced both HOx (H, OH, HO2) and NOx (N, NO, NO2) constituents in the mesosphere and upper stratosphere at polar latitudes (> 60° geomagnetic) of both hemispheres. The temporal evolution of increases in NO and NO2 during the event at northern polar latitudes were measured by the UARS HALOE instrument. Increases in mesospheric NOx of over 50 ppbv were found in the HALOE measurements. Measurements from the UARS HALOE and NOAA 14 SBUV/2 instruments indicate short‐term (∼day) middle mesospheric ozone decreases of over 70% caused by short‐lived HOx during the event with a longer‐term (several days) upper stratospheric ozone depletion of up to 9% caused by longer‐lived NOx. We believe this is the first time that the three constituents NO, NO2, and ozone were all measured simultaneously during a proton event. The observations constitute a dramatic confirmation of the impact of a large particle event in the control of ozone in the polar middle atmosphere and offer the opportunity to test theories of constituent changes driven by particle precipitation.
Mesosphere‐troposphere coupling due to sprites
Authors: Pasko Victor P. , Inan Umran S. , Bell Timothy F.
Published: February 2004

Results from a new three‐dimensional fractal model of sprites as well as recent experimental data on thundercloud charge moment changes associated with sprites indicate that ionized regions in sprites can sometimes reach thundercloud tops, creating favorable conditions for establishing a highly conducting link between the Earth's surface and the lower ionosphere.
A magnetotelluric study in the southern Chilean Andes
Authors: Brasse Heinrich , Soyer Wolfgang
Published: February 2004

Long‐period magnetotelluric investigations were carried out along two transects traversing the Southern Chilean Andes from the Pacific Ocean until the Argentinian border near latitude 39°S to study the mid‐ and deep‐crustal distribution of electrical conductivity. Dimensionality analysis showed that the MT data may be regarded as 2‐D with the exception of areas in the Longitudinal Valley and the region east of the volcanic chain; a subsequent multi‐site decomposition of magnetotelluric impedances yielded approx. N‐S regional strike directions for most parts of the two profiles. First 2‐D inversion revealed a zone of moderately high conductivities (approx. 0.1 S/m) in the deep crust below the active volcanic arc, extending eastwards to the Argentinian border. Inversion results of both profiles are very similar, except of a good mid‐crustal conductor in the Longitudinal Valley, which only appears in the north and may image a fault zone running obliquely to the main South Andean structures.
Slip distribution and tectonic implication of the 1999 Chi‐Chi, Taiwan, Earthquake
Authors: Ji Chen , Helmberger Donald V. , Alex Song Teh‐Ru , Ma Kuo‐Fong , Wald David J.
Published: February 2004

We report on the fault complexity of the large (Mw = 7.6) Chi‐Chi earthquake obtained by inverting densely and well‐distributed static measurements consisting of 119 GPS and 23 doubly integrated strong motion records. We show that the slip of the Chi‐Chi earthquake was concentrated on the surface of a ”wedge shaped” block. The inferred geometric complexity explains the difference between the strike of the fault plane determined by long period seismic data and surface break observations. When combined with other geophysical and geological observations, the result provides a unique snapshot of tectonic deformation taking place in the form of very large (>10m) displacements of a massive wedge‐shaped crustal block which may relate to the changeover from over‐thrusting to subducting motion between the Philippine Sea and the Eurasian plates.
Factors influencing 7Be accumulation on rock varnish
Authors: Moore Willard S. , Liu Tanzhuo , Broecker Wallace S. , Finkel Robert C. , Wright Allen
Published: February 2004

Rocks coated with desert varnish were translocated from Scottsdale, Arizona, and Panamint Valley, California, to a fenced‐in plot near Biosphere 2 where they were allowed to accumulate a new crop of the 53 day half life, cosmic ray‐produced 7Be. Those exposed to precipitation accumulated several times more of this isotope than those shielded from precipitation. No significant difference in 7Be accumulation was observed between a set which was UV irradiated (in an attempt to kill resident bacteria) and a set which received no UV irradiation. This experiment suggests that 62 ± 10 percent of the beryllium accumulated on the varnish was supplied by precipitation and 38 ± 10 percent by some combination of dew, dust, and aerosols. If bacteria are, as has been proposed, responsible for varnish growth, then either our UV irradiation was inadequate to squelch their activity or the 7Be we measured had not yet been built into the varnish.
A no‐net‐rotation model of present‐day surface motions
Authors: Kreemer Corné , Holt William E.
Published: February 2004

A significant portion of the Earth's surface consists of zones of diffuse deformation. The interior regions of these diffuse zones of deformation move at distinctly different velocities from that of adjacent plates, and, because of their complexities, have been ignored in previous no‐net‐rotation (NNR) models. We have calculated a new NNR model from a continuous velocity field that incorporates both rigid plate motion and velocity gradients within plate boundary zones. When compared with earlier NNR models we find significantly different angular velocities for many plates. Differences between the NNR model presented here and earlier NNR models can be attributed to the effect of including velocity gradients in diffuse plate boundary zones as well as to the actual differences between geodetically derived surface motions and geologic estimates.
Coupled electrodynamics in the nighttime midlatitude ionosphere
Authors: Tsunoda Roland T. , Cosgrove Russell B.
Published: February 2004

We describe a new, self‐consistent scenario in which sporadic‐E doublets, height bands of upward‐displaced F‐layer profiles, F‐region plasma depletions, and radar backscatter plumes, are all manifestations of a coupled electrodynamical response by the nighttime midlatitude ionosphere to the presence of a traveling ionospheric disturbance (TID). We show that the response consists of (1) formation of image plasma structure in the E region, (2) initiation of a Hall‐current‐driven polarization process by the E‐region plasma structure, and (3) mapping of the polarization electric field to the F region, where it strengthens the electrical properties of the TID that initiated the E‐region processes. This scenario provides ready answers for several, hitherto puzzling, questions and a basis for new directions on this research topic.
Spectral features of stimulated electromagnetic emission, measured in the 4.3–9.5 MHz pump wave frequency range
Authors: Frolov V. L. , Sergeev E. N. , Ermakova E. N. , Komrakov G. P. , Stubbe P.
Published: February 2004

Steady state spectral features of stimulated electromagnetic emissions (SEEs) for their major emission components (DM, NC, BC, BUM, and BUS) are studied in a wide pump wave frequency range, from 4.3 to 9.5 MHz, i.e., from slightly above the 3rd to slightly above the 7th gyroharmonic frequency. Based on these systematic experimental data, new peculiarities in the behaviour of the SEE intensity and of the spectral properties, in relation to the gyroharmonic mode number, have been found. The experimental results, discussed in the paper, were collected during the years 1996–2000 at the Sura heating facility in Russia by modification of the ionospheric F region, using ordinary mode HF pump waves.
Measurements of raindrop breakup by using UHF wind profilers
Authors: Kobayashi Takahisa , Adachi Ahoro
Published: February 2004

A UHF wind profiler was used to measure a very interesting vertical profile of the raindrop size spectra in a convective rain which went over the profiler at Tsukuba, Japan. It can measure both the fall velocity of raindrops and the ambient air‐motion including the mean velocity and the turbulence, which enables to derive an accurate drop size distribution from the Doppler spectra. The measured Doppler spectra had significant altitude variations. It further was found that a considerable high number of giant raindrops larger than 6 mm in diameter appeared at an altitude of 3.25 km. These giant raindrops, however, almost disappeared at altitudes below 2.75 km, while an increase in the number of smaller raindrops of less than 1.5 mm in diameter was observed. These variations are interpreted to be due to breakup.
Response of the equatorial ionosphere in the South Atlantic Region to the Great Magnetic Storm of July 15, 2000
Authors: Basu S. , Basu Su , Groves K. M. , Yeh H.‐C. , Su S.‐Y. , Rich F. J. , Sultan P. J. , Keskinen M. J.
Published: February 2004

The effects of the great magnetic storm of July 15, 2000 on the equatorial ionosphere have been studied by ground‐based and satellite in‐situ measurements. A large westward plasma drift in the evening equatorial ionosphere was observed as a result of the ionospheric disturbance dynamo. In that environment, the IMF Bz turned southward and presumably caused penetration of E‐fields to low latitudes. This E‐field initiated the onset of 250 MHz and L‐band scintillations at Ascension Island (15°W) and precipitous TEC decrease at Fortaleza, Brazil (38°W), bounding the narrow longitude region in the South Atlantic. These impulsive ionospheric effects were extremely well correlated with abrupt decreases of SYM‐H (1‐min resolution Dst). The DMSP in‐situ measurements showed the presence of severe ion density bite‐outs extending over 30° latitude in the South Atlantic Magnetic Anomaly region. The ROCSAT‐1 satellite measured upward and large southward ion drifts in the same sector.
Recurrent flare/CME events from an emerging flux region
Authors: Nitta Nariaki V. , Hudson Hugh S.
Published: February 2004

We report on six recurrent ‘halo' coronal mass ejections (CMEs) that occurred (in November 2000) during a 60‐hour period in clear association with major flares in an active region on the solar disk. The region was undergoing dynamic restructuring due to flux emergence. The flares were not long‐decay events (LDEs) in terms of soft X‐ray light curves and morphologies, although, in the impulsive phase, they produced ejections in soft X‐rays that are characteristic of CMEs. We do not detect global changes in EUV and X‐ray full‐disk images prior to these flares. We suggest that emerging magnetic flux in the core of an active region may be responsible for the occurrence of such repeated flare/CME events.
Magnetotelluric imaging of fluids in intraplate earthquake zones, NE Japan Back Arc
Authors: Ogawa Yasuo , Mishina Masaaki , Goto Tadanori , Satoh Hideyuki , Oshiman Naoto , Kasaya Takafumi , Takahashi Yukie , Nishitani Tadashi , Sakanaka Shin'ya , Uyeshima Makoto , Takahashi Yuji , Honkura Yoshimori , Matsushima Masaki
Published: February 2004

Intraplate earthquake zones in the back arc of NE Japan were imaged by wide‐band magnetotelluric (MT) soundings. The 90km long MT profile of 34 stations extends over the two topographic features, the Dewa Hills and the Ou Backbone Range, which were uplifted by thrust faults. MT data show two‐dimensionality and strong TE/TM anisotropic responses at the periods around 100 s. After tensor decompositions with regional strike of N12°E, two‐dimensional inversion was carried out where static shift was also a model parameter. The final model is characterized by conductive blocks in the mid‐crust to account for the anisotropic responses. Correlation of the conductors to the seismic scatterers and to the low velocity anomalies suggests that the conductors represent fluids. High seismicity clustering near the rims of conductors suggests that the intraplate seismicity results either from the migration of the fluids to less permeable crust or from local stress concentration near the structural boundary.
Strong seismic scatterers near the core‐mantle boundary west of Mexico
Authors: Niu Fenglin , Wen Lianxing
Published: February 2004

PKP phases observed in Japan show strong precursors with clear onsets for earthquakes that occurred in south America. The onset times of the PKP precursors can all be explained by existence of seismic scatterers in the lowermost 100 km of the mantle west of Mexico, within an area of 200 km × 300 km. Forward modeling of PKP precursor amplitudes indicates that a P‐wave velocity variation of at least 6% is required to explain the large amplitudes of the observed PKP precursors, suggesting that the core‐mantle boundary region beneath west of Mexico is a highly anomalous region characterized by strong seismic scatterers.
Solute dispersion in rock fractures by Non‐Darcian Flow
Authors: Yeo In Wook , Ge Shemin
Published: February 2004

This study aims at investigating the relationship between the ratio of dispersion coefficient to molecular diffusion coefficient (DL/Dm) and Peclet number (Pe) for a multi‐solute system in non‐Darcian flow regimes. Existing understanding on solute dispersion is primarily derived from Darcian flow regime with one solute. We find that solute dispersion in rock fractures can be characterized by the mechanism of both macrodispersion and Taylor dispersion, in non‐Darcian flow domains. For the Darcian flow regime, different solutes lead to the same DL/Dm‐Pe relationship. However, as the flow becomes non‐Darcian, solute with a higher molecular diffusion coefficient result in higher DL/Dm at the same Pe than that with a lower diffusion coefficient.
Lack of correlation between paleoprecipitation and magnetic susceptibility of Chinese Loess/Paleosol Sequences
Authors: Guo B. , Zhu R. X. , Roberts Andrew P. , Florindo Fabio
Published: February 2004

We have conducted a detailed mineral magnetic study of loess unit 8 (L8) and paleosol unit 8 (S8) from three localities (Jingbian, Yichuan, and Duanjiapo) along a N‐S transect in the Chinese loess plateau. As expected, the low‐field magnetic susceptibility (χ) has higher values in S8 and lower values in L8. Similarly, superparamagnetic particle concentrations increase in S8 with increasingly humid climates along the N‐S transect, which suggests that pedogenic magnetic enhancement is related to climate. However, in S8 at Duanjiapo, χ is so low that there is no correlation between χ and the degree of pedogenesis in this loess‐paleosol cycle. It therefore appears that χ is not consistently the most suitable indicator of paleoclimate in Chinese loess‐paleosol sequences. Our results indicate that there are complexities in the mineral magnetic response to pedogenesis, which could invalidate interpretation of the χ record of Chinese loess‐paleosol sequences in terms of paleoprecipitation.
Multiple spacecraft flux rope modeling of the Bastille Day magnetic cloud
Authors: Mulligan T. , Russell C. T. , Anderson B. J. , Acuna M. H.
Published: February 2004

The Bastille Day magnetic cloud in July 2000 occurred with NEAR in conjunction with the Earth at a radial distance of 1.76 AU and 1.9° from the Earth‐Sun line. Propagation time from ACE at 0.99 AU to NEAR indicates the cloud did not decelerate significantly between the Earth and 1.76 AU. Using a non‐force‐free, kinematic flux rope model we find the rope contained 130 TWb of magnetic flux, was oriented with clock and cone angles of 50° and 83°, and had a radius of 0.25 AU at ACE. At NEAR its radius had expanded to 0.43 AU. Simultaneous modeling of ACE and NEAR data indicate the axial and poloidal magnetic fields vary as R−1.4 and R−1.2 where R is heliocentric distance. Magnetosheath thicknesses of 0.14 AU and 0.23 AU indicate the rope cross section is elongated normal to the cloud axis and the radial direction.
In‐situ measurement of atmospheric NO3 and N2O5 via cavity ring‐down spectroscopy
Authors: Brown Steven S. , Stark Harald , Ciciora Steven J. , Ravishankara A. R.
Published: February 2004

We report the application of cavity ring‐down spectroscopy (CaRDS), a high‐sensitivity absorption technique, to the in‐situ detection of both NO3 and N2O5 in ambient air. The detection limit for NO3, measuring absorption in its strong, 662‐nm band, is 0.3 pptv at STP (50 s integration time). Heating the air flow through the inlet thermally dissociates N2O5 to yield NO3, whose detection gives the ambient concentration of N2O5. The instrument was successfully field tested in March–April, 2001 at a site in the tropospheric boundary layer in Boulder, Colorado. This study is the first fast‐response (5s‐1 min), in‐situ detection of NO3. It is also the first in‐situ detection of N2O5 and the first observation of this species in the troposphere. Both NO3 and N2O5 showed considerable temporal variability, highlighting the need for a fast‐response instrument.
Non‐stationary entrainment and tunneling eruptions: A dynamic link between eruption processes and magma mixing
Authors: Bergantz George W. , Breidenthal Robert E.
Published: February 2004

The products of many intermediate arc volcanoes and batholiths manifest compositional complexity with mafic and mixed material occurring early and through‐out a period of eruption and pluton assembly. We present a vesiculation model suggesting that the progressive and repeated vesiculation of volatile‐rich magmas yields a super‐linear buoyancy acceleration. This style of non‐stationary entrainment provides a mechanism for compositional reversal, the intimate co‐occurrence of mixed and un‐mixed magmas, and rapid, chaotic crystal and melt dispersal. Under some circumstances, entrainment can cease entirely, producing eruptions with compositional tunneling where nearly unmixed mafic, or newly intruded silicic magma, exits first.
Preliminary analysis of an expanded corona database for Venus
Authors: Stofan Ellen R. , Smrekar Suzanne E. , Tapper Simon W. , Guest John E. , Grindrod Peter M.
Published: February 2004

We have conducted an extensive survey of the Magellan data to reassess the population of coronae. We identify a new type of coronae, here referred to as ‘Type 2 coronae’, having the same basic morphology as previously identified coronae (Type 1), but lacking a significant (>50%) annulus of closely spaced fractures. 106 Type 2 coronae are included in the new database giving a total of 515 coronae on Venus. The characteristics of the expanded population of Type 1 coronae are similar to those of the previously described population, but the Type 2 coronae are smaller, tend to have relatively flat interiors surrounded by a topographic rim, and are more likely to be found isolated from other features. Our observations, in particular the morphology and setting of the Type 2 coronae, may provide supporting evidence for the existence of a depleted mantle layer under the venusian plains.
Baseline maritime aerosol: Methodology to Derive the optical thickness and scattering properties
Authors: Kaufman Yoram J. , Smirnov Alexander , Holben Brent N. , Dubovik Oleg
Published: February 2004

Satellite measurements of the global distribution of aerosol and their effect on climate should be viewed in respect to a baseline aerosol. In this concept, concentration of fine mode aerosol particles is elevated above the baseline by man‐made activities (smoke or urban pollution), while dust or sea‐spray elevates the coarse mode. Using 1–3 years of measurements in 10 stations of the Aerosol Robotic network (AERONET) we develop a methodology and derive the optical thickness and properties of this baseline aerosol for the Pacific and Atlantic Oceans. Defined as the median for periods of stable optical thickness (standard deviation <0.02) during 2–6 days, the median baseline aerosol optical thickness over the Pacific Ocean is 0.052 at 500 nm with Ångström exponent of 0.77, and 0.071 and 1.1 respectively, over the Atlantic Ocean.
Earth's eccentricity cycles and Indian Summer Monsoon variability over the past 2 million years: Evidence from deep‐sea benthic foraminifer
Authors: Gupta Anil K. , Dhingra Hitesh , Mélice Jean‐Luc , Anderson David M.
Published: February 2004

Spectral analysis of a Uvigerina proboscidea time series from DSDP Site 214 using the Lomb‐Scargle method for unevenly sampled data, exhibits two dominant power peaks at 412 and 94 kyrs over the last 2 million years, which correspond to the Earth's eccentricity cycles. The results indicate that the SW monsoon varied at about 100 kyr and 400 kyr periodicities within Earth's eccentricity domain (Milankovitch range) over the past 2 million years. Wavelet transform analysis reveals the non‐stationary nature of monsoon upwelling over this interval. The amplitude of the 400 kyr cycle in the U. proboscidea time series began to increase at ∼900 kyrs as has also been observed in few recent studies. We do not see a strong relation between eccentricity highs and intense summer monsoons over the studied interval.
Evidence for on‐going inflation of the Socorro Magma Body, New Mexico, from interferometric synthetic aperture radar imaging
Authors: Fialko Yuri , Simons Mark
Published: February 2004

Interferometric synthetic aperture radar (InSAR) imaging of the central Rio Grande rift (New Mexico, USA) during 1992–1999 reveals a crustal uplift of several centimeters that spatially coincides with the seismologically determined outline of the Socorro magma body, one of the largest currently active magma intrusions in the Earth's continental crust. Modeling of interferograms shows that the observed deformation may be due to elastic opening of a sill‐like intrusion at a rate of a few millimeters per year. Despite an apparent constancy of the geodetically determined uplift rate, thermodynamic arguments suggest that it is unlikely that the Socorro magma body has formed via steady state elastic inflation.
Co‐generation of hydrogen sulfide and methane in marine carbonate sediments
Authors: Mitterer Richard M. , Malone Mitchell J. , Goodfriend Glenn A. , Swart Peter K. , Wortmann Ulrich G. , Logan Graham A. , Feary David A. , Hine Albert C.
Published: February 2004

Sulfate reduction and methanogenesis are considered to be mutually exclusive microbial reactions in marine sediments. Typically, methane does not appear in significant concentrations in sediment pore waters until almost all dissolved sulfate has been reduced to sulfide. An exception to this commonly accepted pattern occurs in an approximately 500‐meter thick sequence of Quaternary carbonates on the continental margin of the Great Australian Bight. An unusual combination of geochemical and sedimentological conditions leads to extensive simultaneous sulfate reduction and methane production throughout the 500‐m interval. A probable explanation for the co‐production of these reduced gases in this deeper biosphere is the presence of noncompetitive substrates for the two types of microbiota.
Temperature and pore pressure effects on the shear strength of granite in the Brittle‐Plastic Transition Regime
Authors: Odedra Anita , Ohnaka Mitiyasu , Mochizuki Hiromine , Sammonds Peter
Published: February 2004

Currently published lithospheric strength profiles lack constraints from experimental data for shear failure of typical crustal materials in the brittle‐plastic transition regime in wet environments. Conventional triaxial shear fracture experiments were conducted to determine temperature and pore pressure effects on shear fracture strength of wet and dry Tsukuba granite. Experimental conditions were 70MPa < Pc < 480MPa, 10MPa < Pp < 300MPa, 25°C < T < 480°C, at a constant strain rate of 10−5s−1. An empirical relation is proposed which can predict the shear strength of Tsukuba granite, within the range of experimental conditions. Mechanical pore pressure effects are incorporated in the effective stress law. Chemical effects are enhanced at temperatures above 300°C. Below 300deg;C wet and dry granite strengths are temperature insensitive and wholly within the brittle regime. Above 400°C, semi‐brittle effects and ductility are observed.
Atlantic thermohaline circulation and its response to increasing CO2 in a coupled atmosphere‐ocean model
Authors: Sun Shan , Bleck Rainer
Published: February 2004

We discuss aspects of the Atlantic thermohaline circulation (THC) and its response to increased greenhouse gas concentration, using a coupled atmosphere‐ocean general circulation model (AOGCM) whose oceanic component is a new hybrid‐isopycnal model. Two 200‐year model integrations are carried out—a control run assuming fixed atmospheric composition and a perturbation run assuming gradual doubling of CO2. We employ no flux corrections at the air‐sea interface, nor do we spin up the ocean prior to coupling. The surface conditions in the control run stabilize after several decades. When doubling CO2 at the rate of 1% per year, the model responds with a 2°C increase in global mean surface air temperature (SAT) after 200 years and a virtually unchanged Atlantic meridional overturning circulation. The latter is maintained by a salinity increase that counteracts the effect of global warming on the surface buoyancy.
3‐D surface deformation of the 2000 Usu Eruption measured by matching of SAR images
Authors: Tobita Mikio , Murakami Makoto , Nakagawa Hiroyuki , Yarai Hiroshi , Fujiwara Satoshi , Rosen Paul A.
Published: February 2004

A subpixel level offset estimation technique was applied to SAR (Synthetic Aperture Radar) images of Usu volcano, Japan. Using RADARSAT SAR amplitude images acquired from ascending and descending orbits, we generated a map of three‐dimensional displacement vectors showing ground deformation associated with criptdome formation in April, 2000. Moreover, displacement velocities and volume changes were estimated. From April 3–29, inflation was observed with vertical and horizontal displacements each exceeding 20m. During the period of major activity from April 3–5, uplift and N‐S spreading velocities reached 3.3m/day and 2.7m/day, respectively, while volume change was + 3.4 × 106 m³/day. Although this technique is less precise than other methods and is not very sensitive to local deformations, it provides several key advantages including (1) personnel are not required to enter hazardous areas, (2) it provides wide spatial coverage, and (3) it does not depend on coherence, making it more widely applicable than InSAR.
Chlorine deposition on dust particles in marine atmosphere
Authors: Zhang Daizhou , Iwasaka Yasunobu
Published: February 2004

A scanning electron microscope and an energy dispersive X‐ray spectrometer were applied to analyze the particles collected during dust‐storm events at southwestern Japan in spring 2000. Particle morphology and elemental composition were investigated and the weight ratios of different elements in individual particles were obtained. The results indicated that, besides the coagulation of sea‐salt and dust particles, chlorine could deposit onto dust particles through the absorption of chlorine‐containing gases when the particles passed through the marine atmosphere between China and Japan. The quantitative estimation revealed that the chlorine deposition on many particles was not negligible compared to sulfur deposition, suggesting that dust particles could remarkably modify the chlorine chemistry in marine atmosphere and possibly vise versa.
Annual persistence in observed and modelled UK precipitation
Authors: Tomsett Ashley C. , Toumi Ralf
Published: February 2004

This paper examines the correlation structure of inter‐decadal precipitation variability across the UK by using a scaling analysis technique. The level of persistence displayed by the observations between different types of precipitation is remarkably constant. Comparison with synthetic long‐memory time series suggests that the behaviour of the observed precipitation is consistent with a scaling process. The Hadley Centre HadCM2 model captures some of the observed behaviour, but underestimates the degree of persistence in all precipitation intensities. The scaling analysis method is a useful diagnostic to test for climate model variability.