bluuebunny/crossref_metadata_2025 huggingface dataset:
22 year solar modulation of Earth's northern hemisphere temperatures
Authors: Baranyi T. , Ludmány A. , Coffey H.
Published: February 2004

As reported earlier, solar particle events originating from the Sun's polar regions affect the Earth's troposphere in a way that is opposite to solar particle events from the Sun's equatorial regions. When the Sun's magnetic field reverses every 11 years, the tropospheric response also reverses. These results are based on European temperature data. The present extension (712 northern stations) to a more worldwide coverage shows that this complex behavior is reversed on the western side of the Earth's northern hemisphere. The border separating the two regimes (East vs. West) lies close to the meridian crossing the magnetic pole. These results imply that the physical mechanism linking the solar and tropospheric changes may be sensitive to the specific spatial conditions and magnetic polarity distributions.
Carbon isotopes in aquatic plants, Long Valley Caldera, California as records of past hydrothermal and magmatic activity
Authors: Reid John B. , Reynolds Jesse L. , Connolly Nathan T. , Getz Shari L. , Polissar Pratigya J. , Winship Lawrence J. , Hainsworth Laura J.
Published: February 2004

Hot and cold springs contribute “dead” (14C free) dissolved inorganic carbon (DIC) to the Owens River and Hot Creek. Headwaters aquatic plants have modern14C, but live plants downstream of the intracaldera springs are depleted in14C, (as low as 19% modern, with apparent ages up to 13.3 kyrs). In an abandoned meander of the upper Owens River, preserved streambed plants are buried by 600 year old Inyo Craters pumice. Apparent14C ages of these plants exceed true ages by ∼ 1100 years indicating that they also incorporated dead DIC as they grew. The preserved plants are downstream of Big Springs, whose elevated dead DIC may represent magmatic ‘CO2. The buried plants incorporated ∼10% dead carbon, although modern plants here have ∼50% dead carbon, suggesting that more magmatic CO2is now entering the upper Owens River than at the time of the Inyo Craters eruptions 600 years ago.
Scaling laws from geomagnetic time series
Authors: Vörös Z. , Kovács P. , Juhász Á. , Körmendi A. , Green A. W.
Published: February 2004

The notion of extended self‐similarity (ESS) is applied here for the X‐component time series of geomagnetic field fluctuations. Plotting nth order structure functions against the fourth order structure function we show that low‐frequency geomagnetic fluctuations up to the order n = 10 follow the same scaling laws as MHD fluctuations in solar wind, however, for higher frequencies (f > 1/5[h]) a clear departure from the expected universality is observed for n >6. ESS does not allow to make an unambiguous statement about the non triviality of scaling laws in ”geomagnetic“ turbulence. However, we suggest to use higher order moments as promising diagnostic tools for mapping the contributions of various remote magnetospheric sources to local observatory data.
On polarized frontal structures, type‐1 and quasi‐periodic echoes in midlatitude sporadic E
Authors: Tsunoda Roland T.
Published: February 2004

Sporadic‐E (ES) patches in the nighttime midlatitude ionosphere often appear to consist of quasi‐periodic (QP) frontal structures, i.e., strips of enhanced conductivity whose cross‐sectional dimensions are small compared to their length. Assuming that such ES patches are usually found at an ion‐convergent node in a wind‐shear profile, we show that the meridional neutral wind at that node would polarize these strips and produce an intense, electrojet‐like current accompanied by an electric field strength in excess of 10 mV/m. The validity of this model seems to be supported by its ability to account for several hitherto unexplained phenomena including type‐1 and QP radar echoes from nighttime ES patches, and the coupled appearance of altitude‐modulated isodensity contours in the F region when frontal structures are present in the E region. While much remains to be done to evaluate the importance of this process, this finding is exciting because it makes plausible the commonplace occurrence of what was previously referred to as anomalous energetics in the midlatitude ionosphere.
Influence of stream‐stream interaction on the winding angle of the IMF spiral
Authors: Bruno R. , Bavassano B.
Published: February 2004

The interplanetary magnetic field configuration on the ecliptic plane, within the inner heliosphere, has been compared to theoretical predictions based on the 1958 Parker's model. Taking into account that fast and slow wind have a different corotation radius, our analysis has shown that the overwinding of the spiral, which amounts to a few degrees as reported in the literature, can be largely reduced if we eliminate from the dataset those time intervals characterized by higher level of magnetic and plasma compression. Our results suggest that the presence of shocks and CME's alone is not a sufficient condition, as concluded by previous investigators, in order to justify the overwinding observed in the inner heliosphere. Plasma and magnetic field compressions, more generally speaking, have to be considered at the basis of this phenomenon.
Global warming and geothermal profiles: The surface rock‐temperature response in South Africa
Authors: Tyson P. D. , Mason S. J. , Jones M. Q. W. , Cooper G. R. J.
Published: February 2004

Southern hemisphere and South African regional air temperature anomalies for the period 1860–1996 are compared to borehole‐derived surface rock‐temperature anomalies to assess the extent to which surface rock temperatures reflect possible global warming in South Africa. The warming of the southern hemisphere since the mid‐nineteenth century is evident in the regional air temperatures for South Africa. Following a temperature increase to a maximum in the 1920s, the climate cooled until strong warming recommenced in the mid 1970s. Highest temperatures have been experienced in the 1990s. Borehole‐derived surface rock temperatures followed a similar pattern, but with a lag of a few decades in the case of the 1920s maximum. The overall warming trend is clearly evident in the rock temperatures. Despite uncertainties in the different data sets, an encouraging degree of agreement exists between the increase in rock temperatures during the twentieth century, the corresponding regional South African air temperature increase and the southern hemisphere counterpart.
Variability of the equatorial oscillations induced by gravity wave filtering
Authors: Mayr H. G. , Mengel J. G. , Reddy C. A. , Chan K. L. , Porter H. S.
Published: February 2004

Large variations are observed in the Semi‐Annual Oscillation (SAO) and Quasi‐Biennial Oscillation (QBO) near the equator that are not well understood. We had shown earlier that small scale gravity waves (GW) can generate these oscillations. Here we demonstrate that GW filtering can also produce the variability. Our model incorporates Hines' Doppler Spread Parameterization (DSP) for GW. In the present version, we employ a larger GW flux and a more realistic description of Newtonian cooling. This model produces a QBO with amplitudes close to 15 m/s at 25 km and periods around 33 months. At higher altitudes, the model produces a SAO with amplitudes varying between 5 and 30 m/s. We interpret these variations in terms of GW filtering by the QBO that produces beat periods between 4 and 8.5 years. To provide better understanding, we present also a case in which the QBO period is virtually locked at 18 months. The SAO amplitude then varies with a regular pattern having a period of 18 months, and the Annual Oscillation (AO) amplitude varies with a period of 36 months. For QBO's with periods of 18 (or 30) months, the phase relationship with the seasonal cycle of solar forcing would tend to synchronize and stabilize the oscillations.
Searching for a regional fingerprint of aerosol radiative forcing in the southeastern US
Authors: Saxena V. K. , Yu Shaocai
Published: February 2004

Although aerosols have long been considered to exert a cooling influence on the regional climate due to direct and indirect radiative forcing, persuasive evidence of the response to this forcing has been lacking. Here, we analyze the regional patterns of climate change in the Southeast US during the period 1949–94 to search for a fingerprint of aerosol radiative forcing. The results show that direct and indirect radiative forcing of both natural (such as Pinatubo volcanic aerosols) and anthropogenic aerosols (such as those transported from the polluted regions of US) may be responsible for the regional cooling trend in the Southeast during the past 46 years. Lack of availability of long term measurements precludes a rigorous cause‐and‐effect analysis. Circumstantial evidence presented here amply justifies immediate establishment of a network of measurements of aerosol optical depth and cloud reflectivity in the southeastern US.
Lidar observations of gravity wave activity and Arctic stratospheric vortex core warming
Authors: Duck Thomas J. , Whiteway James A. , Carswell Allan I.
Published: February 2004

Measurements of stratospheric thermal structure and gravity wave activity have been obtained with a Rayleigh lidar in the Canadian High Arctic at Eureka (80°N, 86°W) during five recent winters. The observations reveal that an annual late December warming of the upper stratosphere occurred in the polar vortex core and was sustained through the winter. Increased gravity wave activity was detected in the vortex jet during the warming. That these two phenomena developed in parallel suggests they are related. It is proposed that increased gravity wave momentum deposition above the jet maximum forced flow into the vortex core where it descended and warmed adiabatically.
Seasonal variation of tropospheric methyl bromide concentrations: Constraints on anthropogenic input
Authors: Wingenter Oliver W. , Wang Charles J.‐L. , Blake Donald R. , Rowland F. Sherwood
Published: February 2004

Although removal of tropospheric methyl bromide (CH3Br) is dominated by the reaction with the seasonally varying hydroxyl (HO) radical concentration, the anticipated corresponding seasonal dependence of CH3Br, as found for other gases with major HO sinks, has been sought previously without success [WMO, 1995]. Our observations of northern hemispheric boundary layer CH3Br concentrations do reveal substantial seasonal changes. The high latitude CH3Br North/South interhemispheric concentration ratio (IHR) varies from a maximum of 1.35±0.04 (1σ) in March–April to 1.10±0.04 in September, with an equal area and seasonally (EAS) weighted average IHR of 1.21±0.03. These observations suggest northern hemispheric emissions are about 15 kilotons/year less than when an IHR of 1.3 is considered [WMO, 1995]. The observed seasonality also partially explains the differences in the IHR reported by several research groups [WMO, 1995] and places needed constraints on the magnitude and seasonality of sources and sinks of CH3Br.
Remote analysis of cleft ion acceleration using thermal plasma measurements from Interball Auroral Probe
Authors: Dubouloz N. , Delcourt D. , Malingre M. , Berthelier J.‐J. , Chugunin D.
Published: February 2004

Three dimensional distributions of low energy (0–80 eV) ions have been obtained in the high‐latitude dayside sector between 10,000 and 20,000 km by the Hyperboloid experiment onboard Interball‐Auroral Probe. H+, He+ and O+ ions exhibit a latitude‐energy dispersion characteristic of the cleft fountain. Test particle simulations are used to investigate the properties of the outflowing ion source region. Regardless of ion mass, it is shown that the bulk of the outflowing population originates from a narrow (< 2°) latitudinal interval inside the dayside cleft. Ion acceleration in the direction perpendicular to the magnetic field is shown to occur at all altitudes at least up to 10,000 km, that is, higher than previously reported in cleft fountain studies. The simulations clearly display a gradual decrease of the heating efficiency with increasing altitude and suggest a weaker gradient for O+ than for H+. Parallel acceleration at low altitudes also appears to contribute to the net ion energization within the cleft.
Estimates of fault dimensions for small earthquakes using stopping phases
Authors: Imanishi Kazutoshi , Takeo Minoru
Published: February 2004

We propose a new method to estimate the fault dimensions of small earthquakes based on stopping phases without assuming a rupture velocity. We detected two high‐frequency stopping phases being the Hilbert transforms of each other for several earthquakes at two local stations, during an earthquake swarm at the eastern offshore of Ito in the Izu peninsula, Japan, which started on March 2, 1997. If we assume the geometry of fault to be circular, we can determine relative locations of nearest and farthest edges of the circular fault employing the difference of arrival times between these two stopping phases. Applying this method to several small earthquakes in the swarm, we succeeded in estimating the fault dimensions of these earthquakes. We also could determine the fault plane from two nodal planes by comparing the fault radii obtained at individual station.
The error in conventionally reported 13C/12C ratios of atmospheric CO due to the presence of mass independent oxygen isotope enrichment
Authors: Röckmann Thomas , Brenninkmeijer Carl A. M.
Published: February 2004

An inherent disadvantage of stable isotope mass spectrometry on CO2 is that 13C‐ and 17O‐substituted CO2 are not resolved. Therefore, CO2‐based mass spectrometry relies on the widely applicable assumption of mass dependent fractionation in the oxygen isotopes, rendering the measurement of 17O superfluous. For atmospheric CO, however, recently published determinations of its oxygen isotopic composition reveal the presence of significant deviation from mass dependent fractionation. For instance, the observed 17O excess of tropospheric CO at high northern latitudes shows a prominent seasonal cycle peaking at 7.5‰ in late summer. This implies that the CO2 based determination of the 13C content of CO introduces a systematical error that needs to be corrected for, and a correction formula is derived. Based on the available Δ17O data and the now identified sources of mass independent fractionation in CO, the extent of this correction for CO isotope analysis in clean tropospheric air is estimated.
Apparent pressure derived from ADEOS‐POLDER observations in the oxygen A‐band over ocean
Authors: Vanbauce C. , Buriez J. C. , Parol F. , Bonnel B. , Sèze G. , Couvert P.
Published: February 2004

The POLDER radiometer was on board the ADEOS satellite from August 1996 to June 1997. This instrument measures radiances in eight narrow spectral bands of the visible and near infrared spectrum. Two of them are centered on the O2 A‐band in order to infer cloud pressure. By assuming the atmosphere behaves as a pure absorbing medium overlying a perfect reflector, an ”apparent” pressure Papp is derived from POLDER data. For validation purposes, Papp is first compared to the sea‐surface pressure Ps for clear‐sky conditions; Papp is found to be close to Ps (within ∼30 hPa) for measurements in the sunglint region. For overcast conditions, Papp differs from the cloud‐top pressure mainly because of multiple scattering inside the cloud. When Papp is compared to the cloud pressure determined from brightness temperature measurements, large differences are observed (typically 180 hPa).
Toward the theory of homogeneous nucleation and its parameterization for cloud models
Authors: Khvorostyanov Vitaly , Sassen Kenneth
Published: February 2004

Following the classical approach in homogeneous nucleation theory, a general but simple expression for the homogeneous freezing rate is derived with account for solution and curvature effects, and applied to the examples of ammonium sulfate and sulfuric acid solutions. After showing that this method compares well with other approaches, a parameterization suitable for use in various cloud models is discussed.
IUE's detection of tenuous SO2 frost on Ganymede and its rapid time variability
Authors: Domingue Deborah L. , Lane Arthur L. , Beyer Ross A.
Published: February 2004

International Ultraviolet Explorer (IUE) observations of Ganymded demonstrate decade length or less temporal variations at a few discreet trailing side longitude regions. The temporal changes are seen in comparisons of IUE spectra from 1984–1986 with new IUE observations from 1996. Variations are observed on the trailing side associated with the new detection of SO2 frost. A distinctive SO2 frost spectral signature at 0.32 µm is detected in the 1984–1986 spectra of trailing side regions from 225° to 285° which are absent in corresponding 1996 measurements.
Plasma sheet beyond the distant neutral line
Authors: Nishida A. , Mukai T. , Yamamoto T. , Kokubun S.
Published: February 2004

We have studied the properties of the plasma sheet in the distant magnetotail during a 12‐h interval when the GEOTAIL satellite stayed rather continually in the plasma sheet. When magnetic reconnection was operative at the distant neutral line the tailward flow speed in the distant plasma sheet is given by the sum of the Alfven speed and the tailward flow speed in the tail lobe. Appreciable twist of the tail should be incorporated in order to properly estimate the magnetic flux that traverses the distant neutral sheet to the south. The magnetic field beyond the distant neutral line is characterized by active and persistent oscillations whose power spectrum has a kink around 0.01 Hz. These oscillations roughly satisfy the Walén relation and could be due to incidence of the interplanetary Alfven waves along the IMF‐type field lines that fill the plasma sheet beyond the distant neutral line.
The effect of channel spacing during magma migration on trace element and isotopic ratios
Authors: Kenyon Patricia M.
Published: February 2004

An analytical, mathematical model is discussed for the transport of trace element and isotopic ratios during magma migration, when no major dissolution or precipitation of minerals occurs, but diffusive exchange of atoms between magma and solid is important. This model is then used to elucidate the effect of channel spacing on the transport of trace element and isotopic ratios during the migration of basaltic magma. It is found that, when total reequilibration occurs, as it will in migration through closely spaced channels on grain boundaries, isotopic ratios are transmitted to the surface unchanged but trace element ratios may vary wildly. When channels are far enough apart so that only partial reequilibration occurs, variations in both isotopic and trace element ratios are reduced or eliminated during magma migration. Finally, when channels are sufficiently distant so that negligible reequilibration occurs, both trace element and isotopic ratios are transmitted to the surface unchanged.
Seasonal global water mass budget and mean sea level variations
Authors: Chen J. L. , Wilson C. R. , Chambers D. P. , Nerem R. S. , Tapley B. D.
Published: February 2004

Analysis of TOPEX/Poseidon satellite altimeter data indicates that the global mean sea level variation has a clear seasonal signal with an amplitude of about 2 to 3 mm, along with a long term drift. This seasonal variation is associated with mass redistribution within the global hydrological cycle plus steric thermal contributions. We investigate seasonal variations of water vapor in the atmosphere and water storage on land using both assimilated atmospheric models and climatological data, and to estimate the corresponding global mean sea level changes. The predicted seasonal global mean sea level changes are then compared with the seasonal variabilities observed by TOPEX/Poseidon altimetry data, after the latter are corrected for the steric effect using a simplified thermal model derived from the NOAA World Ocean Atlas 1994. The good agreement in both amplitude and phase indicates that the T/P altimeter may provide key information for the global water mass budget by placing observational constraints on the mass budget variations predicted by global atmospheric and hydrological models.
A parameterization for the activity of H+ in aqueous sulfuric acid solutions
Authors: Michelsen H. A.
Published: February 2004

Recent studies have suggested that the rates of reactions that occur on and in sulfuric acid solutions depend strongly on the activities of H2O and H+. To simplify the application of formulations for calculating rates of these reactions and thus facilitate their use in photochemical models of the atmosphere, this letter presents a parameterization for the activity of H+ based on the results of a comprehensive, but computationally intensive, thermodynamic model. The parameterization deviates from values given by the full thermodynamic model by <2% for temperatures between 186 and 326 K and sulfuric acid concentrations between 10 and 80 weight percent.
Trans‐ionospheric pulse pairs (TIPPs): Their occurrence rates and diurnal variation
Authors: Zuelsdorf R. S. , Strangeway R. J. , Russell C. T. , Franz R.
Published: February 2004

Trans‐Ionospheric Pulse Pairs (TIPPs) have been detected by the Blackbeard instrument aboard the ALEXIS spacecraft in the VHF band between 28 and 166 MHz with dispersion indicating a subionospheric source. Using a database that runs from 2 November 1993 to 19 November 1996, the rate and diurnal variation of TIPP detection are calculated for central Africa, Indonesia, and North America. The rate of TIPP detection by Blackbeard in the frequency band from 28–95 MHz is 0.02 and 0.04 TIPPs per second for central Africa and Indonesia respectively. For North America the data were acquired in a narrow band from 28–37.9 MHz and the TIPP detection rate is 0.007 events per second. The diurnal variation of TIPPs resembles the diurnal variation of CG lightning during daylight hours. However the TIPP production remains strong through midnight and into the morning hours, whereas CG flash production tends to decrease more sharply after peaking around 4 PM local time. Thus the diurnal variation suggests that TIPPs are not produced in CG flashes, a conclusion consistent with their correlation with intracloud pulses.
Land surface feedbacks and palaeomonsoons in northern Africa
Authors: Broström A. , Coe M. , Harrison S. P. , Gallimore R. , Kutzbach J. E. , Foley J. , Prentice I. C. , Behling P.
Published: February 2004

We ran a sequence of climate model experiments for 6000 years ago, with land‐surface conditions based on a realistic map of palaeovegetation, lakes and wetlands, to quantify the effects of land‐surface feedbacks in the Saharan region. Vegetation‐induced albedo and moisture flux changes produced year‐round warming, forced the monsoon to 17°–25°N two months earlier, and shifted the precipitation belt ≈300 km northwards compared to the effects of orbital forcing alone. The addition of lakes and wetlands produced localised changes in evaporation and precipitation, but caused no further extension of the monsoon belt. Diagnostic analyses with biome and continental hydrology models showed that the combined land‐surface feedbacks, although substantial, could neither maintain grassland as far north as observed (≈26°N) nor maintain Lake “MegaChad” (330,000 km²).
LASCO observations of an Earth‐directed coronal mass ejection on May 12, 1997
Authors: Plunkett S. P. , Thompson B. J. , Howard R. A. , Michels D. J. , St. Cyr O. C. , Tappin S. J. , Schwenn R. , Lamy P. L.
Published: February 2004

Coronal mass ejections (CMEs) that occur near the center of the solar disk are most likely to impact Earth. Detection of such events as ‘halos’ in white‐light coronagraphs has been somewhat controversial in recent years. We present observations from the LASCO coronagraphs on SOHO that provide convincing evidence of the detection of an Earth‐directed CME on May 12, 1997. The event began at about 04:35 UT and propagated outwards from the Sun with a projected speed of around 250 km s−1. Using some reasonable assumptions about the geometry of the CME, we estimate the true speed to be around 600 km s−1. The onset of the event in LASCO is coincident (to within measurement uncertainties) with an eruptive event detected in extreme ultraviolet observations of the solar disk by the SOHO EIT. This is the first reported observation of a halo CME at projected distances greater than 10 R⊙, with a clearly identifiable solar origin. We discuss the possibility that at least some of the enhanced brightness observed by LASCO may be due to a compressional wave propagating in the corona.
Modulation of magnetospheric EMIC waves by Pc 3 pulsations of upstream origin
Authors: Rasinkangas R. , Mursula K.
Published: February 2004

We recently [Mursula et al., 1997] studied a series of bursts of electromagnetic ion cyclotron (EMIC) waves observed by the Viking satellite and on ground, and showed that these bursts can not be explained by the bouncing wave packet model. Here we show that the burst structure is due to simultaneous Pc 3 waves of upstream origin.
Self‐organized criticality in a landslide model
Authors: Hergarten Stefan , Neugebauer Horst J.
Published: February 2004

From landslide mapping it is known that the frequency of landslide occurence as a function of their magnitude can be described by a power law in many regions. In order to investigate the magnitude distribution of landslides from a theoretical point of view, we present a physically based landslide model combining aspects of slope stability and mass movement. If the long term driving processes (fluvial or tectonic) are integrated, the model shows self‐organized criticality (SOC). The results coincide with results obtained from landslide mapping, so that our model suggests that landsliding may be seen as a SOC process. In contrast to other models showing SOC that are mostly based on cellular automata, our model is based on partial differential equations. The results show that SOC is not a fashion of cellular automata, but can also occur in differential equation models.
SOHO/EIT observations of an Earth‐directed coronal mass ejection on May 12, 1997
Authors: Thompson B. J. , Plunkett S. P. , Gurman J. B. , Newmark J. S. , St. Cyr O. C. , Michels D. J.
Published: February 2004

An earth‐directed coronal mass ejection (CME) was observed on May 12, 1997 by the SOHO Extreme ultraviolet Imaging Telescope (EIT). The CME, originating north of the central solar meridian, was later observed by the Large Angle Spectrometric Coronagraph (LASCO) as a “halo” CME: a bright expanding ring centered about the occulting disk. Beginning at about 04:35 UT, EIT recorded several CME signatures, including dimming regions close to the eruption, post‐eruption arcade formation, and a bright wavefront propagating quasi‐radially from the source region. Each of these phenomena appear to be associated with the same eruption, and the onset time of these features corresponds with the estimated onset time observed in LASCO. We discuss the correspondence of these features as observed by EIT with the structure of the CME in the LASCO data.
Heavy precipitation on the alpine southside: An upper‐level precursor
Authors: Massacand Alexia C. , Wernli Heini , Davies Huw C.
Published: February 2004

Analyses of four separate autumnal events of very heavy precipitation on the southern slopes of the European Alps indicate that each was accompanied by a strikingly similar anomaly at upper‐tropospheric levels. It took the form of a narrow (∼500km), deep (∼4km) and elongated (∼2000 km) streamer of intruded stratospheric air [sic. high potential vorticity air] extending north‐south from the British Isles to the western Mediterranean. In each case the streamer translated comparatively slowly eastward, and the storm event ensued as its forward flank approached the Alpine ridge. Empirical indicators and theoretical considerations support the thesis that the streamer is an ubiquitous, dynamically significant, and distinctive precursor of storms on the Alpine southside.
POLAR magnetic field observations at apogee during the January 1997 magnetic cloud event
Authors: Fenrich F. R. , Luhmann J. G. , Le G. , Russell C. T.
Published: February 2004

Magnetic field measurements from the POLAR satellite are presented for three dusk to dawn apogee passes during the January 1997 magnetic cloud event. The variability in the residual fields from one orbit to the next are investigated in terms of the changing solar wind and magnetospheric current systems. The observed fields are compared to the Tsyganenko 96 (T96_01) model which allows dynamic solar wind and Dst inputs. The model fields are found to generally agree with the observed fields with the greatest discrepancy occurring during periods of large dynamic pressure. An investigation of the contributions to the T96_01 model by the various solar wind and Dst inputs provides insight into the solar wind control of the high altitude magnetosphere above the polar cap. It is found that the ring current is responsible for the largest proportion of the observed magnetic field residuals while the interplanetary magnetic field and solar wind dynamic pressure control a smaller proportion primarily producing the shorter time scale variations in the observed fields.
The influence of thermodynamic formulation on simulations of subduction zone geometry and history
Authors: Ita Joel , King Scott D.
Published: February 2004

We introduce varying approximations to the thermodynamic properties of a convecting system similar to Earth's mantle. A realistic geometry, rheology and faults are included to insure that the variations we see are robust in a dynamic, self‐buffering environment. We find two levels of response in the system. First, some approximations lead to very different patterns of flow in the simulations. Second, other sets of approximations lead to similar patterns of flow, but the time history of the flow varies significantly with the formulation used. Last, we note that only minor changes to an existing code would be needed to integrate a complex thermodynamic model.
A possible change in cloud radiative forcing due to aircraft exhaust
Authors: Wyser K. , Ström J.
Published: February 2004

Aircraft exhaust may reduce the crystal size in natural cirrus. This work investigates the change in cloud radiative forcing from such a size reduction by assuming a constant ice water content. A 1‐dim model with radiative properties that depend on the mean crystal size is used to compute the radiative transfer for an atmospheric column. The results show that the negative shortwave cloud forcing is enhanced with smaller crystals as they mainly increase the reflectivity of clouds. The change in the longwave cloud forcing is always positive although its magnitude depends strongly on the ice water path. The weighted sum of SW and LW cloud forcings depends on the mean crystal size, surface albedo and ice water content. It appears that there is a range of diameters between 15 and 25 µm where the response to a reduction in crystal size is fairly insensitive. Below and above this range the change is negative or positive, respectively. In regions of dense airtraffic the magnitude of the change in cloud forcing could be on the order of 0.3 W m−2 under the assumption of a 20% decrease of the mean crystal size from about 30 µm to 24 µm. Aircraft exhaust thus has the potential to affect the climate but the results should be taken with caution as they are based on parameterized optical properties for cirrus clouds.
On the effect of cloud inhomogeneity an area averaged radiative properties of contrails
Authors: Schulz Jörg
Published: February 2004

Certainly cloud inhomogeneity is not only important for cumulus or stratocumulus clouds on which the focus of most of the current studies is. To show that the impact of contrail cirrus microphysical inhomogeneity on cloud albedo can be deduced, fields of ice water content, effective radius, number density, and size distribution of ice particles generated by large eddy simulations (LESs) have been used within two‐dimensional radiative transfer schemes to elucidate the effect of cloud inhomogeneity on area average radiative properties of contrails at evolution stages in the late dispersion regime. The results obtained indicate that differences in shortwave cloud albedo between homogeneous and inhomogeneous conditions remain small for fresh contrails but can become important if contrails would attain larger optical depths. In that case larger differences were obtained at which the albedo for horizontal homogeneous conditions is always larger than the corresponding value for inhomogeneous conditions.
Minimizing methyl bromide emissions from soil fumigation
Authors: Yates S. R. , Wang D. , Gan J. , Ernst F. F. , Jury W. A.
Published: February 2004

There is great controversy concerning the need to phase out methyl bromide (MeBr) to protect stratospheric ozone. Unlike chlorinated hydrocarbons, MeBr occurs naturally in the atmosphere making it difficult to differentiate the threat to stratospheric ozone depletion from anthropogenic use of MeBr compared to natural sources. New technology has been developed which could nearly eliminate MeBr emissions from soil fumigation, bringing into question the need for a phase out. A field experiment demonstrated that virtually impermeable films (VIF) reduced MeBr emissions to near‐zero levels. When compared to soil fumigation using conventional high‐density polyethylene film (HDPE), the total global MeBr emission could be reduced from 32 Gg/yr to less than 1 Gg/yr, if VIF were required. In addition, reduced application rates are possible since using VIF reduces wasteful leakage and increases pest‐control efficiency. With such low emission rates, and considering the large uncertainty in global estimates of MeBr, it seems that the phase‐out of MeBr as a soil fumigant is unjustified.
A comparison of thermospheric [O] derived at EISCAT with [O] predicted by MSIS
Authors: Schoendorf J. , Oliver W. L.
Published: February 2004

In recent years aeronomic considerations of the value of the O+−O collision cross‐section (QO+−O) in the ionospheric F‐region have resulted in many values of a multiplicative adjustment factor (F) to the standard value of QO+−O which had been in use from the mid sixties to the late eighties. QO+−O and oxygen concentration ([O]) appear as a product in aeronomic calculations, so F can also be considered a multiplicative factor for the oxygen. [O] derived at EISCAT for data from 1984 to 1997 is compared to oxygen predicted by MSIS and values of F are calculated as a function of solar cycle and year. There is a solar cycle variation, with F varying from .65 at solar minimum to 1.18 at solar maximum. For solar fluxes between 100 and 160 solar flux units F at EISCAT is in good agreement with a value of F calculated for MSIS. No long term trend in the relationship between EISCAT [O] and MSIS [O] was found.
The Pioneer 6 Faraday rotation transients‐On the interpretation of coronal Faraday rotation data
Authors: Pätzold M. , Bird M. K.
Published: February 2004

The interpretation that the Pioneer 6 Faraday rotation transient events were caused by streamer stalks of angular width 2° entering and leaving the radio ray path [Woo, 1997] is rejected on the basis that: (a) the magnetic field reversal in the streamer stalk produces a measurement signature inconsistent with the observations, (b) the observed magnitude of the events can only be achieved with unrealistically large values of product electron density times magnetic field, and (c) the short duration of the events cannot be reproduced by solar rotation. The most probable explanation for these events is still a series of coronal mass ejections.
Implications of enhanced mesospheric water vapor observed by HALOE
Authors: Siskind David E. , Summers Michael E.
Published: February 2004

Recently reprocessed water vapor data from the Halogen Occultation Experiment (HALOE) on the UARS satellite show significant deviations from the expected constant value of 2*CH4 + H2O. An unusual enhancement in the H2O is seen from 65–70 km which exceeds the stratospheric the value of 2*CH4 + H2O by 0.6–0.8 ppmv. This is inconsistent with the conventional view of transport of H2O and CH4 up from the lower stratosphere and photodissociation in the mesosphere and suggests the presence of another source of H2O. We re‐evaluate the hypothesis that there is an extraterrestrial source of water deposited at mesospheric altitudes. The HALOE data above 60 km provide stringent new constraints on the magnitude and altitude of such a source, but cannot rule out the possibility of a small contribution in the middle mesosphere.
Deep conductivity structure in Abitibi, Canada, using long dipole magnetotelluric measurements
Authors: Tournerie Benoit , Chouteau Michel
Published: February 2004

Magnetotelluric data recorded in the period range 10²–2.104s using 100 km telluric dipoles in western Quebec, Canada, yield impedance estimates free from galvanic distortion and static shift. Analysis of the apparent resistivity, phase and magnetic transfer function data favors a regional 1D anisotropic model for the subsurface resistivity structure in the Abitibi Subprovince; lower resistivity direction of the anisotropy is EW, parallel to the main fault system. Joint 1D inversion of both principal impedances indicates a conductivity anisotropy in the upper and middle crust and in the upper mantle. It might originate for all depths from the same tectonic mechanism, mainly a NS shortening followed by an EW dextral shearing in the Archean.
Total electron content changes in the ionosphere during the January 10, 1997 disturbance
Authors: Musman Steven , Mader Gerry , Dutton C. Everett
Published: February 2004

We have used the CORS network of GPS receivers to record ionospheric TEC changes in the continental United States caused by the well observed geomagnetic disturbance of January 10, 1997. This event produced numerous worldwide consequences. Although the initial arrival of this disturbance was before sunrise in the U.S. the TEC levels were most significantly altered later during the daylight hours. We display temporal and spatial changes through time series at selected sites and maps of the entire network. The usual sequence of diurnal changes was not greatly altered, but most of the TEC values were increased by about a factor of one and a half to two. Stations in the northeast and upper north central were exceptions and showed a small decrease in TEC. We interpret the TEC changes as consequences of changes in neutral chemical composition resulting from storm heating.
Heterogeneous crustal structure across a seismic block boundary along the Nankai Trough
Authors: Mochizuki Kimihiro , Fujie Gou , Sato Toshinori , Kasahara Junzo , Hino Ryota , Shinohara Masanao , Suyehiro Kiyoshi
Published: February 2004

The Nankai trough, which runs along the western Japanese islands, is widely known for its systematic activity of large earthquakes with the Magnitudes greater than 7. According to the fault‐plane studies of these earthquakes, a major seismic block boundary is supposed to run off the Kii Peninsula almost perpendicular to the trough axis. A seismic experiment was conducted across this boundary region in order to determine seismic crustal structure. P‐wave travel time analyses were applied to the data from the OBSs deployed along the trough axis, including travel time nonlinear inversion. The result shows an abrupt change in thickness of the subducting Philippine Sea Plate's crust at the expected location of the seismic block boundary. The crust is thicker in the east by about two kilometers, and the interface between the overriding and subducting plates runs shallower in the east. These structural features may affect the mode of earthquake occurrence.
GOME observations of tropospheric BrO in northern hemispheric spring and summer 1997
Authors: Richter Andreas , Wittrock Folkard , Eisinger Michael , Burrows John P.
Published: February 2004

Measurements from the Global Ozone Monitoring Experiment GOME have been analysed for tropospheric BrO in the northern hemispheric spring and summer 1997. Tropospheric excess columns have been determined by subtracting measurements from a longitude range which is assumed to represent background conditions. From February until the end of May enhanced tropospheric BrO columns are observed over the Hudson Bay area and parts of the Canadian Arctic. This large and persistent event has not been reported before and can only be explained by a large local source of bromine. In addition, from March to May other smaller and shorter tropospheric BrO events are detectable along the coast lines of the Arctic Sea and over the polar ice. They correspond to the ground‐based observations of enhanced tropospheric BrO reported from several stations in the high Arctic.
A low‐velocity lamella in D″
Authors: Thomas Carsten , Weber Michael , Agnon Amotz , Hofstetter Abraham
Published: February 2004

We investigate local variations of the P‐wave velocity structure in the lower‐most mantle ( D″) beneath Western Siberia. Data of earthquakes in the Kurile Island region recorded at short‐period stations of the Israel Seismic Network show a high‐amplitude phase (PdP) after P which cannot be explained by standard Earth models. We present evidence that this phase is a reflection from a low‐velocity lamella in D″. The best, locally valid, 1‐D model consists of a low‐velocity lamella 282km (±20km) above the core‐mantle boundary with a thickness of 8km (±3km). The very high amplitudes of PdP cannot be reproduced by a 1‐ D model. The PdP observation reported here is a regional feature. The area north of it does not show a P‐velocity anomaly, whereas further north positive jumps in P‐ and S‐velocity have been documented. Our observation once more demonstrates the complexity of D″.
A three‐year lagged correlation between the North Atlantic Oscillation and winter conditions over the North Pacific and North America
Authors: Lin Hai , Derome Jacques
Published: February 2004

A new and significant correlation is found between the amplitude of mean‐winter atmospheric anomalies over the North Atlantic Ocean and those over the North Pacific Ocean and western North America three winters later. It is as strong as the previously known and much discussed correlation between the ocean temperature in the eastern tropical Pacific (El Niño region) and the North Pacific winter atmospheric anomalies. No physical explanation is given at this time for this correlation. A statistical prediction model for mean‐winter conditions is constructed based on the above new and previously known correlations. The prediction model is tested on 36 winters of the past. The model predictions are shown to be of remarkable quality over the North Pacific and western North America.
Effects of removing concentric positioning on postglacial vertical displacement in the presence of lateral variation in lithospheric thickness
Authors: Ni Zhihong , Wu Patrick
Published: February 2004

In order to understand the effects of non‐concentric positioning on postglacial rebound in the presence of lateral lithospheric thickness variations, vertical displacements are calculated for disc‐like loads placed on non‐axisymmetric earth models. Results show that removal of concentric positioning do not produce significant effects that can be resolved by relative sealevel data, and the edge of the ice load remains most sensitive to the effects of lateral heterogeneities. This implies that earlier results of axisymmetric models can be extended to fully 3D laterally heterogeneous models.
Multiwavelength lidar aerosol measurements made at Eureka (80°N, 86°W) during early 1995
Authors: Donovan D. P. , Carswell A. I. , Shibata T. , Bird J. C. , Duck T. J. , Itabe T. , Nagai T. , Pal S. R. , Uchino O. , Whiteway J. A.
Published: February 2004

Principal Component Analysis (PCA) aerosol retrievals have been applied to multiwavelength lidar measurements made in early 1995 in the Canadian Arctic. The lidar data have been inverted to provide estimates of stratospheric aerosol volume, surface area, effective radius, and sulfate mass mixing ratio. Above the vortex lower boundary the aerosol parameters were relatively constant but changed notably in the sub‐vortex region throughout the winter.
Dynamic instability of stratified shear flow in the upper equatorial Pacific
Authors: Sun Chaojiao , Smyth William D. , Moum James N.
Published: February 2004

The role of stratified shear instability in maintaining the deep cycle of turbulence immediately below the equatorial mixed layer is examined by means of linear stability analysis. The Taylor‐Goldstein equation is solved numerically, using observed currents and stratification from the Tropical Instability Wave Experiment (TIWE). Multiple unstable modes are found, each associated with a local minimum of the gradient Richardson number. Wave radiation due to the unstable modes fluxes momentum downward through the Equatorial Undercurrent. The frequency, wavelength and propagation direction of the unstable modes are consistent with those estimated from observations of internal waves made during TIWE. These results, in combination with the previous observation that the internal waves are closely associated with deep cycle turbulence, lead us to conclude that shear instability is a dominant factor in the generation of the deep cycle.
Variability of pCO2 on diel to seasonal timescales in the Sargasso Sea near Bermuda
Authors: Bates Nicholas R. , Takahashi Taro , Chipman David W. , Knap Anthony H.
Published: February 2004

Continuous underway measurements of atmospheric and surface seawater pCO2 were collected on numerous cruises in the Sargasso Sea (32°N, 64°W) near Bermuda from June 1994 to November 1995. We observed that seawater pCO2 was highly variable on different timescales, ranging from diel to seasonal. On diel timescales, pCO2 changes of 5–25 μatm occurred in response to diurnal warming and cooling associated with solar heat fluxes. Over longer timescales, pCO2 was influenced by atmospheric forcing and tropical cyclones. For example, a surface cooling of 3°C and decrease in pCO2 of 45–50 μatm occurred after Hurricane Felix passed near Bermuda in August 1995. The decrease in pCO2 was significant considering the annual change was 90–100 μatm. Over all timescales, temperature was the dominant control on pCO2 variability. We found that surf ace pCO2 conditions were accurately predicted from temperatures with small errors (4–9 μatm) if seasonal pCO2‐temperature relationships were established. In future synthesis of regional pCO2 data it should be feasible to use surface temperature, remotely sensed from space, as a tool for extrapolation over wider spatial scales in the North Atlantic subtropical gyre. Net annual fluxes of CO2 for 1994 and 1995 (−0.25 to −0.6 mol CO2 m−2 yr−1) were directed from atmosphere to ocean and were similar to values reported for 1989–1993 by Bates et al. [1996b]. We found that short‐term variability of pCO2 (diel warming and cooling or atmospheric forcing), frequency of sampling (every 3–4 days or monthly), or use of temperature‐derived pCO2 did not affect estimates of net yearly CO2 fluxes by more than 10–20%. However, strong winds associated with hurricanes decreased the net annual flux of CO2 into the ocean by 19–28% in 1995. The major sources of error for air‐sea gas exchange was uncertainty associated with gas transfer‐wind speed relationships and differences in the types of wind speed data used (daily averaged versus climatological). Such uncertainties make it difficult to quantify the contribution of gas exchange to the carbon cycle and the balance of carbon import and export terms in the upper ocean of the Sargasso Sea.