bluuebunny/crossref_metadata_2025 huggingface dataset:
Bottom pressure correlations in the South Atlantic
Authors: Hughes C. W. , Smithson M. J.
Published: February 2004

Bottom pressure in the Fine Resolution Antarctic Model (FRAM) shows regions where fluctuations are dominated by small‐scale internal variability of the currents, and are not directly related to the wind. There are often very sharp boundaries between these regions and regions of large scale coherence. Bearing this in mind, the measured coherence of BPR measurements near Tristan da Cunha island in the South Atlantic is taken as evidence that mesoscale variability associated with the Antarctic Circumpolar Current (ACC) reaches further north in the model than in reality. There are many possible reasons for this, but the significant result is that the BPR measurements can provide useful information about the dynamical regime of the deep ocean, which can not be discovered by surface measurements.
The hydrogen budget of the stratosphere inferred from ATMOS measurements of H2O and CH4
Authors: Abbas M. M. , Gunson M. R. , Newchurch M. J. , Michelsen H. A. , Salawitch R. J. , Allen M. , Abrams M. C. , Chang A. Y. , Goldman A. , Irion F. W. , Moyer E. J. , Nagaraju R. , Rinsland C. P. , Stiller G. P. , Zander R.
Published: February 2004

The total hydrogen budget of the stratosphere and lower mesosphere has been examined using vertical mixing ratio profiles of H2O and CH4 measured by the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment from four space shuttle missions. The oxidation of CH4 and H2 is investigated by evaluating the quantity H (=H2O + 2 CH4) entering the stratosphere, and examining its conservation with altitude in the upper atmosphere. Data from all four ATMOS missions indicate H to be nearly conserved in the lower stratosphere and to exhibit a broad maximum in the 35‐ to 65‐km range. The observations provide evidence of a secondary source of H2O from H2 oxidation at altitudes from 35 to 55 km, and net production of H2 at altitudes above ∼55 km. ATMOS measurements of H2O and CH4 permit the first evaluation of a sickle‐shaped vertical profile of H2 that is qualitatively consistent with profiles calculated using two‐dimensional models.
Control of terrestrial low frequency bursts by solar wind speed
Authors: Desch M. D. , Kaiser M. L. , Farrell W. M.
Published: February 2004

Using WIND spacecraft data from the WAVES, SWE, and MFI experiments for the period from January through July, 1995, we show that the occurrence of the terrestrial low frequency (LF) radio bursts is controlled primarily by the solar wind speed. A possible secondary factor in determining the occurrence of the bursts is the direction of the IMF in the x‐y plane, with the ‘toward’ direction (By< 0) favored. The correlation with bulk speed suggests, on a gross scale, a viscous‐like coupling mechanism between the solar wind and the magnetosphere. In terms of the nature of the solar wind correlation, terrestrial LF bursts strongly resemble the Earth's AKR and Jovian quasi‐periodic bursts.
On blue jet dynamics
Authors: Sukhorukov A. I. , Mishin E. V. , Stubbe P. , Rycroft M. J.
Published: February 2004

A model is proposed for blue jets [Sentman and Wescott, 1995; Wescott et al., 1995a], which explains their dynamics, in particular the jet vertical velocity of about 100 km/s, the terminal altitudes of about 40–50 km, and the competitive occurrence of blue jets and the recently discovered blue starters [Wescott et al., 1995b]. A blue jet is considered to be formed by an attachment‐controlled ionizing wave, which moves upward via an electron avalanche in the wavefront due to the mainly vertical, downward directed quasi‐electrostatic field, caused by the extraordinarily large (>100 C) charge transfer in a high‐altitude intracloud discharge or in a positive cloud‐to‐ground discharge with a long continuing current.
Solar cycle variation of the dominant frequencies of Pc3 geomagnetic pulsations at L = 1.6
Authors: Vellante M. , Villante U. , De Lauretis M. , Barchi G.
Published: February 2004

The variation of the spectral characteristics of daytime Pc3 geomagnetic pulsations recorded at L'Aquila (Italy, L ∼ 1.6) during one solar cycle (1985–1994) is investigated on a yearly time scale. We find in the frequency domain two peaks in the event distribution for the H component during years of minimum solar activity and a single peak during years of maximum solar activity. These features can be interpreted in terms of the solar cycle variation of the predicted dominant frequency of the main driving source (upstream waves) as well as of the local fundamental field line eigenfrequency. The dominant frequency for the D component also changes according to the expected solar cycle variation of the dominant source frequency. The solar cycle variation of the estimated fundamental field line eigenfrequency is consistent with a general increase of the plasmasphere density along the local field line by a factor of ∼2 from minimum to maximum solar activity which is in agreement with theoretical models.
Satellite measurements of hydroxyl in the mesosphere
Authors: Conway Robert R. , Stevens Michael H. , Cardon Joel G. , Zasadil Scott E. , Brown Charles M. , Morrill Jeff S. , Mount George H.
Published: February 2004

The global distribution of hydroxyl (OH) in the middle atmosphere was recently measured by the Middle Atmosphere High Resolution Spectrograph Investigation (MAHRSI) on a satellite deployed and retrieved by the space shuttle. During 75 orbits, MAHRSI acquired 1800 daytime limb scans of the OH ultraviolet solar resonance fluorescence intensity. Each limb scan extends over the altitude region from 30 to 90 km and across 10° of latitude between 53°S and 63°N. OH number densities were retrieved using a Twomey regularization scheme constrained by the smoothness of the retrieved profile. Results provide a detailed description of the diurnal variation of mesospheric OH. Midmorning OH densities had a well defined peak of about 6 ×106 cm³ near 70 km, a broad minimum centered near 64 km, and rose to about 1 × 107 cm³ at 50 km. This profile is in substantial disagreement with photochemical model predictions [Summers et al., this issue]. The observations are compared with the two previous measurements.
Transformation of hematite to maghemite as observed by changes in magnetic parameters: Effects of mechanical activation?
Authors: Petrovský Eduard , Kropáček Vladimír , Dekkers Mark J. , deBoer Cor , Hoffmann Viktor , Ambatiello Alex
Published: February 2004

A natural hematite of hydrothermal origin shows evidence of time‐dependent behavior related to the sample preparation procedure (involving significant crushing and milling). A strongly magnetic phase with a Curie temperature (∼630°C) corresponding to that of maghemite is present after storage for one‐and‐a‐half‐years, while being absent in the original sample material. The magnetic properties of the hematite‐maghemite in relation to mechanical treatment are compared and possible mechanisms of the hematite transformation are discussed. The hematite‐maghemite transformation is suggested to have resulted primarily from recrystallization induced by shear stress resulting from crushing and milling.
The dimethyl sulfide reaction with atomic chlorine and its implications for the budget of methyl chloride
Authors: Langer Sarka , McGovney Brian T. , Finlayson‐Pitts Barbara J. , Moore Robert M.
Published: February 2004

DMS is produced in large quantities by natural oceanic processes. Its chemistry and emissions have been postulated to play a role in the radiative balance of the atmosphere. While its reactions with OH and NO3 radicals are well known, the reaction with chlorine atoms in the marine boundary layer has also been suggested recently. If this produces CH3Cl, it would contribute to the global budget of this naturally occuring halocarbon. Experiments were carried out to measure the yield of CH3Cl in the Cl+DMS reaction. CH3Cl was indeed formed in this reaction in laboratory experiments at 1 atm. and 298 K, with a small yield of (1.34±0.07) × 10−3. This yield is sufficiently small that the contribution to the global CH3Cl budget is estimated to be ≤2% and it is unlikely to be responsible for the anomalously high CH3Cl concentrations measured recently over the Labrador Sea.
Radon transport into dwellings: Considering groundwater as a source
Authors: Oostrom M. , Lenhard R. J.
Published: February 2004

A mathematical model is used to investigate whether radon degassing from groundwater may contribute to indoor radon levels. Specifically, the transport of radon in the soil‐gas phase from the groundwater‐soil gas interface to under‐pressurized dwellings is modelled. The question whether radon in groundwater may contribute to indoor radon levels arises from observed high radon concentrations in groundwater, and recent findings that advection in the gas phase may be an important transport mechanism for radon into slightly under‐pressurized dwellings. Most previous radon transport investigations did not consider groundwater as a potential source for contributing to indoor radon. The mathematical model includes a method to directly calculate indoor radon concentrations and an equivalent continuum approach to represent cracks in concrete foundations. The results of the simulations indicate that radon, which partitions from groundwater to the soil gas, may be advectively transported by the gas phase to slightly underpressurized dwellings in relatively permeable soils such that indoor radon concentrations may exceed 148 Bq/m³, which is the action limit imposed by EPA.
Impact of heterogeneous BrONO2 hydrolysis on ozone trends and transient ozone loss during volcanic periods
Authors: Randeniya L. K. , Vohralik P. F. , Plumb I. C. , Ryan K. R. , Baughcum S. L.
Published: February 2004

The hydrolysis of BrONO2 on sulphate aerosols has been included in a 2‐D model calculation of ozone changes over the period 1980–1995. Inclusion of this reaction has only a marginal impact on the calculated ozone trends between 1980 and 1990. The effect of the reaction on an atmosphere which has been heavily perturbed by sulphate aerosols for the period June 1991–1995 has been examined by using the idealised WMO 1995 scenario. The results show that the addition of this reaction has a major impact on the calculated transient ozone loss under enhanced aerosol conditions and approximately doubles the calculated ozone loss between 60°S and 60°N in 1992 (when maximum loss of ozone occurs). In contrast to the effects of the hydrolysis of N2O5, the effects of the hydrolysis of BrONO2 are most marked at high latitudes in summer.
Earthquake prediction evaluation standards applied to the VAN Method
Authors: Jackson David D.
Published: February 2004

Earthquake prediction research must meet certain standards before it can be suitably evaluated for potential application in decision making. For methods that result in a binary (on or off) alarm condition, requirements include (1) a quantitative description of observables that trigger an alarm, (2) a quantitative description, including ranges of time, location, and magnitude, of the predicted earthquakes, (3) documented evidence of all previous alarms, (4) a complete list of predicted earthquakes, (5) a complete list of unpredicted earthquakes. The VAN technique [Varotsos and Lazaridou, 1991; Varotsos et al., 1996] has not yet been stated as a testable hypothesis. It fails criteria (1) and (2) so it is not ready to be evaluated properly. Although telegrams were transmitted in advance of claimed successes, these telegrams did not fully specify the predicted events, and all of the published statistical evaluations involve many subjective ex post facto decisions. Lacking a statistically demonstrated relationship to earthquakes, a candidate prediction technique should satisfy several plausibility criteria, including: (1) a reasonable relationship between the location of the candidate precursor and that of the predicted earthquake, (2) some demonstration that the candidate precursory observations are related to stress, strain, or other quantities related to earthquakes, and (3) the existence of co‐seismic as well as pre‐seismic variations of the candidate precursor. The VAN technique meets none of these criteria.
Near‐infrared spectral measurements of liquid water absorption by clouds
Authors: Evans W. F. J. , Puckrin E.
Published: February 2004

Spectral measurements of the solar flux in the near‐infrared region using an FTIR spectrometer have yielded important information concerning the absorption of solar radiation by clouds. A comparison of the spectra of solar fluxes for clear and overcast sky conditions measured from the ground for a northern mid‐latitude location demonstrates that about 118 W/m² of the solar radiation is absorbed preferentially by clouds in the 3,000–10,000 cm¹ region. The cloud radiative forcing ratio was estimated to be 1.24. Climate model calculations generally predict that clouds mainly scatter solar radiation while absorbing on average about 4% of the extraterrestrial insolation. The interaction of solar radiation with clouds may be dominated by the absorption of liquid water rather than by scattering, particularly if a sufficient number of liquid water droplets reside in the upper reaches of a cloud. This may contribute, in part, to the anomalous cloud absorption effect.
Measurements of O3, H2O and ClO in the Middle Atmosphere Using the Millimeter‐Wave Atmospheric Sounder (MAS)
Authors: Hartmann G. K. , Bevilacqua R. M. , Schwartz P. R. , Kämpfer N. , Künzi K. F. , Aellig C. P. , Berg A. , Boogaerts W. , Connor B. J. , Croskey C. L. , Daehler M. , Degenhardt W. , Dicken H. D. , Goldizen D. , Kriebel D. , Langen J. , Loidl A. , Olivero J. J. , Pauls T. A. , Puliafito S. E. , Richards M. L. , Rudian C. , Tsou J. J. , Waltman W. B. , Umlauft G. , Zwick R.
Published: February 2004

The Millimeter‐Wave Atmospheric Sounder (MAS) is a shuttle‐based limb‐sounding instrument designed for global spectroscopic studies of O3, and constituents important in O3 photochemistry, in the middle atmosphere. It is part of the NASA's Atmospheric Laboratory for Applications and Science (ATLAS) spacelab shuttle mission. This paper presents an overview of the instrument, operation, and data analysis. In addition, as an example of the results, we present zonal average retrievals for O3, H2O and ClO obtained in ATLAS 1. The MAS O3 and H2O measurements are shown to agree well with simultaneous observations made with the UARS MLS instrument.
In situ observations of NOy, O3, and the NOy/O3 ratio in the lower stratosphere
Authors: Fahey D. W. , Donnelly S. G. , Keim E. R. , Gao R. S. , Wamsley R. C. , Del Negro L. A. , Woodbridge E. L. , Proffitt M. H. , Rosenlof K. H. , Ko M. K. W. , Weisenstein D. K. , Scott C. J. , Nevison C. , Solomon S. , Chan K. R.
Published: February 2004

Extensive in situ measurements of reactive nitrogen (NOy) and ozone (O3) were made in the lower stratosphere over a broad latitude range (60°N–70°S) during two different seasons (March and October) in 1994. Both NOy and O3 mixing ratios show a strong latitude dependence, with values increasing toward the poles. The NOy/O3 ratio reveals a high‐gradient region near the tropics that is not well‐represented in standard 2‐D photochemical transport models. Improving the representation by changing the horizontal eddy‐diffusion coefficients near the tropics has important implications for the predicted impacts of aircraft emissions on stratospheric O3.
Statistical evaluation of the VAN Method using the historic earthquake catalog in Greece
Authors: Aceves Richard L. , Park Stephen K. , Strauss David J.
Published: February 2004

A statistical test of the VAN method compares its prediction rate (number of successful predictions divided by the total number of predictions issued) between 1987 and 1989 to that from randomly sampling the earthquake catalog. Unlike previous tests, this one samples distributions derived from the historic spatial and magnitude distribution between 1960 and 1985. The VAN method yields a prediction rate of 67.9% at a time delay of 22 days, which is achievable in less than 0.06% (P‐value ≤ 0.06%) of the realizations in randomly sampling the full NEIC catalog (37.2% mean prediction rate). VAN's prediction rate drops to 66.7% with aftershocks removed from the catalog and prediction list, which is still significant at a p‐value of less than 0.1%. With an alternate aftershock model, the prediction rate drops to 48.0%. This latter value is significant only for P‐values less than 7.96%. We conclude from these tests that the VAN method is formally significant at a time lag of 22 days.
Source spectra and site‐response estimates using the Coda of Lg waves in western Europe
Authors: Chevrot S. , Cansi Y.
Published: February 2004

Source spectra are investigated by using regional events recorded by the LDG French short‐period seismic network. Empirical relations describing the Lg coda envelope allow us to separate source, site and propagation effects. 28 events recorded by 14 stations of the LDG network are selected for this study. Source spectra and site‐response are determined in the frequency‐band of 1–16 Hz. A Lg‐coda magnitude can be defined from these source spectra. Magnitudes obtained by this technique are strongly correlated to local magnitudes given by the LDG bulletin but the standard deviation is reduced by a factor 3. Other parameters such as siteresponse, corner‐frequency and coda Q are determined very accurately.
Hygrosonde‐A direct measurement of water vapor in the stratosphere and mesosphere
Authors: Khaplanov M. , Gumbel J. , Wilhelm N. , Witt G.
Published: February 2004

A rocket‐borne optical hygrometer for night time in situ measurements of the middle atmospheric water content was successfully launched from Esrange, Sweden, in December 1994. Utilizing the OH photofragment fluorescence technique, the instrument takes measurements in an undisturbed volume outside the rocket shock front. A profile of water vapor was obtained between 17 and 70 km. The stratospheric mixing ratio increases from 3.5 ppmv near 20 km to around 6 ppmv above 45 km, while the mesospheric profile shows a strongly stratified structure. The results are discussed in terms of horizontal transport and compared to recently published model results on the redistribution of water vapor in the winter polar mesosphere.
Simple permeability model for natural granular media
Authors: Knackstedt Mark A. , Duplessis J. Prieur
Published: February 2004

A previously published pore scale model provides a simple analytic expression relating the permeability of a natural granular media to its porosity. This model is quantitatively accurate at high to intermediate porosities. It is based on two independent parameters, porosity and average grain size. At low porosities, however, the model is unable to capture the experimentally observed trends. Percolation provides a natural description of the pore closure evident in sedimentary media at low porosities. The use of percolation concepts provides the necessary input to predict the permeability in the porosity range where pore blocking occurs. Thus a simple analytic model, utilizing an experimental value for the percolation threshhold, is derived for the permeability of sandstones and calcite aggregates over the full range of porosity.
UNAM Scientific Drilling Program of Chicxulub Impact Structure‐Evidence for a 300 kilometer crater diameter
Authors: Urrutia‐Fucugauchi J. , Marin L. , Trejo‐Garcia A.
Published: February 2004

As part of the UNAM drilling program at the Chicxulub structure, two 700 m deep continuously cored boreholes were completed between April and July, 1995. The Peto UNAM‐6 and Tekax UNAM‐7 drilling sites are ∼150 km and 125 km, respectively, SSE of Chicxulub Puerto, near the crater's center. Core samples from both sites show a sequence of post‐crater carbonates on top of a thick impact breccia pile covering the disturbed Mesozoic platform rocks. At UNAM‐7, two impact breccia units were encountered: (1) an upper breccia, mean magnetic susceptibility is high (∼55 × 10−6 SI units), indicating a large component of silicate basement has been incorporated into this breccia, and (2) an evaporite‐rich, low susceptibility impact breccia similar in character to the evaporite‐rich breccias observed at the PEMEX drill sites further out. The upper breccia was encountered at ∼226 m below the surface and is ∼125 m thick; the lower breccia is immediately subjacent and is >240 m thick. This two‐breccia sequence is typical of the suevite‐Bunte breccia sequence found within other well preserved impact craters. The suevitic upper unit is not present at UNAM‐6. Instead, a >240 m thick evaporite‐rich breccia unit, similar to the lower breccia at UNAM‐7, was encountered at a depth of ∼280 m. The absence of an upper breccia equivalent at UNAM‐6 suggests some portion of the breccia sequence has been removed by erosion. This is consistent with interpretations that place the high‐standing crater rim at 130–150 km from the center. Consequently, the stratigraphic observations and magnetic susceptibiity records on the upper and lower breccias (depth and thickness) support a ∼300 km diameter crater model.
The Atmospheric Trace Molecule Spectroscopy (ATMOS) Experiment: Deployment on the ATLAS space shuttle missions
Authors: Gunson M. R. , Abbas M. M. , Abrams M. C. , Allen M. , Brown L. R. , Brown T. L. , Chang A. Y. , Goldman A. , Irion F. W. , Lowes L. L. , Mahieu E. , Manney G. L. , Michelsen H. A. , Newchurch M. J. , Rinsland C. P. , Salawitch R. J. , Stiller G. P. , Toon G. C. , Yung Y. L. , Zander R.
Published: February 2004

The ATMOS Fourier transform spectrometer was flown for a fourth time on the Space Shuttle as part of the ATLAS‐3 instrument payload in November 1994. More than 190 sunrise and sunset occultation events provided measurements of more than 30 atmospheric trace gases at latitudes 3–49°N and 65–72°S, including observations both inside and outside the Antarctic polar vortex. The instrument configuration, data retrieval methodology, and mission background are described to place in context analyses of ATMOS data presented in this issue.
High‐resolution stratospheric dynamics measurements with the NASA/JPL Goldstone Solar System Radar
Authors: Cho John Y. N. , Jurgens Raymond F. , Slade Martin A.
Published: February 2004

We have used, for the first time that we are aware of, the NASA/JPL Goldstone planetary radar to study the Earth's atmosphere. With its high bandwidth and power, we were able to achieve a height resolution of 20 m, which is significantly better than the usual 150‐m resolution for stratospheric radars. Here we discuss the observation of a very thin scattering layer that persisted over several hours at the same height just above the tropopause. We question the assumption of turbulent radar scatter based on the available evidence, and also investigate the two‐minute oscillation observed in the vertical velocity.
Signal enhancement using pattern recognition techniques with application to near vertical crustal seismic reflection experiments
Authors: Roy Baishali , Mereu R. F.
Published: February 2004

Most near‐vertical crustal seismic reflection experiments are conducted over regions where in the past the crust has undergone some form of tectonic deformation. The deep structures differ from the near surface sedimentary structures in that they are generally not layered. Seismic energy after travelling through long ray paths in such media arrives at slightly different times at the receivers and hence tends to be poorly aligned along its respective theoretical travel time curves. Conventional seismic processing routines which attempt to increase the signal to noise ratio (S/N) by some stacking technique can in many cases actually destroy the poorly aligned signals such that the resultant subsurface images are not very satisfactory. Our study focuses on a signal enhancement technique based on a pattern recognition approach which is applied in the prestack processing stream in an effort to increase the S/N ratio. The discrimination between signal and noise is based on attributes such as the frequency, amplitude, waveshape, and lateral continuity of the signal. The method was first tested on synthetic data, and then applied to real data acquired over the Canadian shield. Signal enhancement using a pattern recognition approach as outlined in this paper dramatically improved the subsurface images over those obtained by more conventional stacking methods.
On PP‐P differential travel time measurements
Authors: Paulssen Hanneke , Stutzmann Eléonore
Published: February 2004

This study investigates the stability of PP‐P travel time measurements using a waveform crosscorrelation method on both broadband and long‐period data. This study finds correspondence between 50% of the PP‐P travel times read from broadband and long‐period data, but also finds 50% of the measurements differ more than 1.0 second. The inconsistent measurements are demonstrated to be due to two causes. (1) Diffraction near the core‐mantle boundary causes dispersion of the P phase which yields an underestimate of the PP‐P travel time determined from long‐period data. This effect is identified at epicentral distances as small as 88°and may amount to several seconds. (2) Interference of the PP phase with secondary arrivals causes distortion of the PP waveform and produces a non‐systematic measurement error. This effect are most clearly seen on broadband seismograms and may even hamper an unambiguous broadband PP‐P travel time measurement. Although strong high‐frequency effects associated with interference are filtered out on the long‐period data, the long‐period PP‐waveform may still be contaminated. We conclude that the accuracy of PP‐P travel time measurements is on the order of l s for both broadband and long‐period seismograms.
Water vapor and temperature lapse rate feedbacks in the mid‐latitude seasonal cycle
Authors: Hu Haijun
Published: February 2004

The ongoing scientific debate regarding the role of water vapor feedback in climate change centers on the effects of water vapor vertical distribution and variation with climate change. The temperature lapse rate is another vertically dependent variable; its combination and interaction with water vapor feedback have an even greater potential for influencing the climate. Here we examine the vertical dependence of the feedbacks, as presently observed in the mid‐latitude seasonal cycle, by means of a radiative‐convective model with climatological lapse rates. It is found that both the water vapor and lapse rate feedbacks are positive, amplifying the seasonal surface temperature cycle by approximately 23% and 15%, respectively, and have considerable thermal coupling. The feedback contributions from the various vertical levels are essentially additive. These vertical contributions are characterized by a bimodal water vapor feedback, with upper and lower troposphere maxima, and by a predominant lapse rate feedback from the lower troposphere. Although a small negative water vapor feedback contribution is found at 150 mb, its significance is overshadowed by the strong positive feedbacks at all other levels, especially in the lower troposphere. The implications for climate change are discussed.
Measurement of chlorine nitrate in the stratosphere using the ν4 and ν5 bands
Authors: Johnson D. G. , Orphal J. , Toon G. C. , Chance K. V. , Traub W. A. , Jucks K. W. , Guelachvili G. , Morillon‐Chapey M.
Published: February 2004

We present laboratory measurements of the absorption cross sections of the ν5 band (540–580 cm−1) of chlorine nitrate made under stratospheric conditions of temperature and pressure. We use the measured cross sections and observed mid‐infrared stratospheric emission spectra to retrieve mid‐latitude vertical mixing ratio profiles for both day and night in the altitude range 20–34 km, and compare the results with a sunset profile obtained simultaneously from solar absorption measurements of the ν4 Q branch at 780 cm−1. The profiles obtained using these two methods are shown to be in excellent agreement, validating retrievals using the ν4 band. We also find good agreement in this altitude range between the observed day/night ratio and the results of a 1‐D photochemical model
Longitudinal gradients of the distribution of anomalous cosmic rays in the outer heliosphere
Authors: Fichtner Horst , de Bruijn Han , Sreenivasan S. Ranga
Published: February 2004

Recent results, both from observation and theory, suggest that the termination shock of the solar wind is not spherical. First, observations made with the Ulysses spacecraft have confirmed that the solar wind momentum flux increases with latitude, implying an elongation of the shock above the sun's poles. Second, results of modeling the global structure of the heliosphere indicate that a so‐called upwind‐downwind asymmetry of the shock is probable. In view of these findings as well as the observed upwind‐downwind asymmetry in pick‐up ion fluxes, one might suspect the existence of longitudinal gradients in the distributions of anomalous cosmic rays, which are supposedly identical with the pick‐up ions accelerated at the termination shock. We demonstrate that such longitudinal gradients should indeed be expected in the outer heliosphere and estimate their magnitude using a three‐dimensional modulation model.
predicting the initial IMF Bz polarity's change at 1 AU caused by shocks that precede coronal mass ejections
Authors: Wu Chin‐Chun , Dryer Murray
Published: February 2004

There are important geomagnetic implications whenever the interplanetary magnetic field (IMF) turns northward or southward. This paper addresses only the initial turning when the solar events' shock signals first reach 1 AU. A three‐dimensional (3D), time‐dependent, MHD model [Han et al., 1988] of disturbances' propagation through the solar wind and interplanetary magnetic field (IMF) has been used by Wu (1993) to develop a “recipe” for the initial north‐ or south‐turning of the IMF's polarity. Its temporal behavior thereafter is not addressed in this paper. Four independent data sets have been used [Wu et al., 1996a, b, c] in a study currently underway to test this idea. A fifth data set [Gosling et al., 1990] is used in this paper to examine, via this idea, the initial Bz polarity's change at 1 AU caused by shocks associated with interplanetary/coronal mass ejection events and large geomagnetic storms during the period of August 1978 to October 1982. Twenty‐five events from this fifth data set are studied; the prediction model is in agreement with twenty‐one of them. Our results suggest that the initial IMF Bz polarity's change at 1 AU may be associated with a simple relationship between the location of the solar disturbance, the relative position of the heliospheric current sheet, and the initial toward or away polarity of the IMF at Earth.
The N2 pressure broadening coefficient of the J = 1 ← 0 transition of ¹H35Cl measured by tunable far infrared (TuFIR) spectroscopy
Authors: Bryant C. H. , Davies P. B. , Sears T. J.
Published: February 2004

A tunable far infrared (TuFIR) laser sideband spectrometer has been used to determine the N2 pressure broadening coefficient of the lowest rotational transition of ¹H35Cl between 0 and 1.8 Torr at room temperature (298 K). The parameters defining a Voigt lineshape were fitted to the J = 1 ← 0 transition using a Levenberg‐Marquardt non‐linear least squares fitting routine. The average N2 broadening coefficient of the three components was determined to be 4.10(10)/(MHz/Torr), 0.104(2)/(cm−1/atm).
In‐situ observations of an Antarctic polar stratospheric cloud: Similarities with Arctic observations
Authors: Dye J. E. , Baumgardner D. , Gandrud B. W. , Drdla K. , Barr K. , Fahey D. W. , Delnegro L. A. , Tabazadeh A. , Jonsson H. H. , Wilson J. C. , Loewenstein M. , Podolske J. R. , Chan K. R.
Published: February 2004

Measured particle volumes in a type I polar stratospheric cloud near the Antarctic polar vortex during ASHOE/MAESA show that the onset of the cloud occurred near 193 K, 3 degrees colder than nitric acid trihydrate (NAT) saturation. The onset temperature, the smooth increase of volume with decreasing temperature, the inverse correlation of particle volume and enhanced NOy (HNO3 in the particles) with temperature, and comparisons of observations with an equilibrium model of ternary droplet growth all support the notion that much of this type I PSC was ternary solution droplets. This provides confirmation of previous findings in the northern hemisphere. However, the ternary model does not fit the observations in all regions. This may be due to the presence of some solid phase growth in agreement with impactor observations.
Unexpectedly low ozone concentration in midlatitude tropospheric ice clouds: A case study
Authors: Reichardt J. , Ansmann A. , Serwazi M. , Weitkamp C. , Michaelis W.
Published: February 2004

Raman lidar measurements of ozone, water vapor, and cirrus optical properties over northern Germany (53.4°N, 10.4deg;E) in autumn 1995 are presented. In contrast to smooth ozone profiles with values of 50 to 100 ppbv in a cloud‐free and dry upper troposphere, pronounced minima in the ozone distribution with values close to zero were found several times in the presence of ice cloud layers.
SOLCON Solar Constant Observations from the ATLAS Missions
Authors: Crommelynck Dominique , Fichot Alain , Domingo Vicente , Lee Robert
Published: February 2004

The solar constant observations obtained by the SOLCON/ATLAS experiment during the three successive missions are presented based on the Space Absolute Radiometric Reference (SARR) defined during the ATLAS‐2 mission. The objectives of SOLCON, namely to obtain accurate measurements of the solar constant and to compare them with the observations obtained from free flyers in the hope of establishing a baseline and strategy for monitoring the solar constant at climate scale, have been achieved successfully with the three ATLAS missions. The long range objective of insuring the solar constant data continuity will, however, require that an alternative approach than that of the ATLAS program be found to fly and retrieve SOLCON.
Impact of dynamical and stochastic processes on the predictability of ENSO
Authors: Flügel Moritz , Chang Ping
Published: February 2004

Large ensembles of prediction experiments were conducted using a coupled ocean‐atmosphere model consisting of a reduced gravity ocean and a simple atmospheric feedback model. By varying the coupling strength we maneuver the system through a wide range of dynamical regimes, i.e., stable, unstable and chaotic regimes, in the presence of various stochastic forcing. The analysis of the time evolution of the ensembles suggests that the stochastic forcing has a considerably larger impact on ENSO predictions on short lead times up to about nine months than the nonlinear dynamics. However, at longer lead times the effect of chaotic dynamics is reflected in the time evolution of the ensembles.
Evaporation studies of model polar stratospheric cloud films
Authors: Middlebrook Ann M. , Tolbert Margaret A. , Drdla Katja
Published: February 2004

To investigate evaporation of polar stratospheric clouds (PSCs), mixed nitric‐acid/ice films with varying HNO3 content were heated at 0.3 K min−1 in vacuum and monitored with transmission Fourier transform infrared (FTIR) spectiroscopy. The ability for HNO3 inclusions to hinder ice evaporation was found to depend on the concentration of HNO3. Specifically, films with initial compositions of ∼80:1 and ∼150:1 H2O:HNO3 evaporated ∼8 K and ∼3 K higher than pure ice, respectively. In addition, the surface coverage of nitric acid trihydrate (NAT) appears to control the overall evaporation rate. In the atmosphere, NAT may form on the surface of an ice PSC by direct HNO3 adsorption or by evaporation of a PSC with HNO3 in the bulk.
Evidence for orographic wave heating in the equatorial thermosphere at solar maximum
Authors: Meriwether J. W. , Mirick J. L. , Biondi M. A. , Herrero F. A. , Fesen C. O.
Published: February 2004

Fabry Perot interferometer observations of equatorial 630 nm airglow thermospheric winds and temperatures were made at Arequipa, Peru (16.5 S, 71.5 W) during the solar maximum years of 1989 and 1990. Examination of the thermospheric winds measured from Doppler shifts of the 630 nm airglow emission in the two directions east and west of Arequipa shows that the zonal wind is often significantly weaker over the Andes (east) than over the Pacific (west) in winter. Between 19 LT and 24 LT, the typical reductions in speed found were ∼40 to 70 m/s. In the same time period the temperature results show elevated values of ∼200‐500 K for the three directions (north, east, and zenith) over mountainous terrain compared with those of the two directions (west and south) over Water. This effect fades near equinoctial periods. Examination of the standard deviation of the temperature observations for the five directions showed an increase in this value above the measurement error by a factor of three for the direction toward the Andes (East) but not for the direction over water (South); this elevation is consistent with wave activity as a source of the heating. Viscous dissipation of waves propagating into the thermosphere region from below is suggested as an explanation for the localized regions of heating.
Observed influence of clouds on ultraviolet‐B radiation
Authors: Schafer J. S. , Saxena V. K. , Wenny B. N. , Barnard W. , De Luisi J. J.
Published: February 2004

A Brewer Spectrophotometer was utilized to make ground‐based measurements of solar ultraviolet (UVB) radiation received at Black Mountain, NC (35.66°N) in order to quantify the reduction of UV‐B due to cloud cover. Observations were made over the interval February–July 1995 with continuous coverage except for a three‐week period in May. A wide‐angle lens video camera at the site was used for the assessment of cloud conditions at the time of each scan. Integrated UV‐B (290–320 nm) values were evaluated and a regression through the values for clear conditions was produced for the range of zenith angles from 25°–70°. This regression effectively represents an average effect of the ambient aerosols and attenuating gases and was used to normalize the UV‐B values measured under different cloud cover amounts, providing an estimate of the reduction in irradiance due to a given cloud amount as a function of solar zenith angle. For a solar zenith angle of 50°, average UV‐B transmission was observed to be 30% for overcast skies, 61% for 8–9 tenths cloud cover, 74% for 6–7 tenths cover, and 79% for the scans during 4‐5 tenths cover. A number of fractional cloud cover cases were observed where cloud reflections resulted in measured surface irradiances exceeding the expected clear sky values by as much as 11 percent.
An explanation of the kilometer scale wave in the equatorial electrojet
Authors: Duhau Silvia , de Mendoza Diego Hurtado
Published: February 2004

Density irregularities in the equatorial electrojet are dominated by kilometer scale waves. In this report we combine a few simple ideas about strong turbulence and non‐local effects due to the vertical structure of the equatorial E‐region. This leads to a preference for kilometer scale waves. We include the vertical current conservation effect, the eddy turnover, and the growth velocity. We determine the saturation of density perturbation driven by the gradient drift instability. This heuristic theory predicts phenomena consistent with sounding rocket and coherent radar observations. It also gives same general clues about the interaction between the ambient and the turbulent scale flows.
Core‐log‐seismic integration as a framework for determining the basin‐wide significance of regional reflectors in the eastern equatorial Pacific
Authors: Bloomer Stephen F. , Mayer Larry A.
Published: February 2004

ODP Leg 138 in the eastern equatorial Pacific (EEP) provided a unique opportunity to understand the paleoceanographic significance of seismic reflectors in this climatically sensitive region. Carefully offset multiple cores were spliced into a complete stratigraphic section for the upper 250 m at each site and accurate, astronomically tuned time scales were generated from these composites. Well log data provided a means to correct composite depths to true depths as well as density and velocity data for the generation of synthetic seismograms. These synthetic seismograms were used to determine the paleoceanographic significance of regionally traceable reflectors by linking variations in the core record to the seismic record. The EEP reflectors are due to changes in carbonate content, primarily due to variations in surface productivity, as indicated by the presence of mats of the upwelling diatom Thalassiothrix longissima. The EEP composite GRAPE records were successfully used as a tuning target for GRAPE records in the central equatorial Pacific (CEP), as a means to determine the basin‐wide extent of EEP reflectors, and as a guide to the further interpretation of the CEP seismic record. It was found that EEP reflectors R3‐t, R5, R6, R8‐b, and Site 844 reflectors R10, R12‐b and R13, correspond to reflectors in the CEP. However, some of the CEP reflectors, which were postulated to be due to periods of enhanced dissolution, also correspond to diatom mats, and hence the origin of these reflectors must be reconsidered.
Sound velocities of olivine and beta polymorphs of Mg2SiO4 at Earth's transition zone pressures
Authors: Li Baosheng , Gwanmesia Gabriel D. , Liebermann Robert C.
Published: February 2004

Sound velocities of olivine (α) and beta (β) polymorphs of Mg2SiO4 are measured to P > 12 GPa at room temperature on polycrystalline samples in a multi‐anvil apparatus using ultrasonic interferometry. The new velocity data for olivine are lower by 1% for P waves and 2% for S wave at transition zone pressures than extrapolations of low pressure (<1 GPa) data. However, the elastic bulk (KS) and shear (G) moduli for the polycrystalline olivine exhibit good agreement to 10 GPa with recent Brillouin scattering and ultrasonic data for single crystals. The velocity data for the polycrystalline beta phase at 12 GPa agree within 1% with Eulerian finite strain extrapolations of previous data by Gwanmesia et al. (1990b) for similar specimens. The pressure derivatives of the elastic moduli calculated by linear fittings to KS and G vs. pressure yield K0′ = 4.4 and G0′ = 1.3 for the olivine and K0′ = 4.2 and G0′ = 1.5 for the beta phases. The isothermal velocity contrast at room temperature between these two phases, (Vβ‐Vαrpar;/Vα decreases systematically with increasing pressure, reaching 8.0% for P wave and 11.3% for S wave at pressures equivalent to 410 km depth.
Determination of Fe‐Mg partitioning between perovskite and magnesiowüstite
Authors: Katsura Tomoo , Ito Eiji
Published: February 2004

The partition coefficient of Fe and Mg between perovskite and magnesiowüstite KMg‐FePv‐Mw has been measured by adopting a B2O3 catalyst technique. The present experimental results demonstrate that KMg‐FePv‐Mwis a factor of two closer to unity than that obtained in previous studies. KMg‐FePv‐Mw increases from 0.16 to 0.35 with increasing Mg# of magnesiowüstite from 50 to 86. On the basis of these results, the compositions of enstatite and magnesiowüstite included in diamond imply that the temperature at the top of the lower mantle is 1870–2040 K. The Mg# (100Mg/(Mg+Fe)) of perovskite and magnesiowüstite at the top of the lower mantle are 93 and 82–83, respectively, for a pyrolitic mantle model. The upper bound of the lower mantle temperature estimated in this study do not allow a larger fraction of perovskite than the pyrolitic mantle.
Implications of the large carbon kinetic isotope effect in the reaction CH4 + Cl for the 13C/12C ratio of stratospheric CH4
Authors: Bergamaschi P. , Brühl C. , Brenninkmeijer C. A. M. , Saueressig G. , Crowley J. N. , Grooß J. U. , Fischer H. , Crutzen P. J.
Published: February 2004

Recent investigations of the carbon kinetic isotope effect (KIE) of the reaction CH4 + Cl yielded KIECl = 1.066±0.002 at 297 K (increasing to 1.075±0.005 at 223 K) [Saueressig et al., 1995]. In order to assess the effect of the exceptionally large KIEcl on δ13C of stratospheric CH4 we applied a two‐dimensional, time dependent chemical transport model. The model results demonstrate the strong influence of the CH4 + Cl reaction on δ13CH4 in particular in the middle and upper stratosphere, where this reaction contributes several tens of percent to the total CH4 sink. The Cl sink helps to explain the relatively large overall isotope fractionation of 1.010–1.012 observed in the lower stratosphere [Brenninkmeijer et al., 1995; Brenninkmeijer et al., 1996], even though the model results predict a smaller effect than observed.
Subdaily Earth rotation determined from GPS
Authors: Grejner‐Brzezinska Dorota A. , Goad Clyde C.
Published: February 2004

A UT1‐TAI series was determined with triple‐differenced GPS data for January 15–28, 1995. A priori UT1‐TAI values at 30‐minute intervals were taken from the IERS Bulletin B prediction and constrained to 6.5 × 10−3 s; increments to the initial UT1‐TAI were estimated. The tidal correction according to IERS Standards, and the atmospheric effects were removed. The remaining signal was smoothed with a Vondrak smoother and compared with UT1 tidal model empirically determined from VLBI [Herring and Dong, 1994]. In a second test, normalized length of day variations and the pole coordinates, with once‐per‐day resolution (at 12 h UT), were estimated. Bulletin B a priori values were introduced only at the beginning of a four‐week period. Since UT1‐TAI is related to lod variations in the following way: δ(lod)/lod = −d(UT1‐TAI)/dt, [Lambeck, 1980, p. 63], the variation in UT1‐TAI can be obtained by integrating normalized variation in lod. The a priori standard deviation for δ(lod)/lod was 6.5 × 10−3 s/day.
A fast velocity anomaly to the west of the Australian‐Antarctic discordance
Authors: Kuo Ban‐Yuan , Chen Chau‐Huei , Zhang Yu‐Shen
Published: February 2004

To examine the hypothesis that the Australian‐Antarctic Discordance overlays an anomalously cold upper mantle, we have measured Rayleigh wave group velocities along paths between the Southeast Indian Ridge and the Australian station NWAO. The group velocity peaks for events in the vicinity of 117°E, rather than for those within the discordance zone between 120 and 127°E. This variation is resolved at least for periods of 35–45 s. To model the cause, assumed velocity anomalies with simple geometry were tested using the surface wave Gaussian beam method in a forward sense. The preferred model consists of an elongated structure centered 300–500 km west of the discordance and stretching northward for at least 1000 km. The position of the anomalous structure is consistent with recent global tomographic models in this region.