bluuebunny/crossref_metadata_2025 huggingface dataset:
Intercomparison of spaceborne ocean color measurements between OCI and SeaWiFS
Authors: Ho Chung‐Ru , Lee Li‐Shang , Kuo Nan‐Jung , Li Hsien‐Wen , Chen Chun‐Te
Published: February 2004

Based on ten ocean color images that were obtained simultaneously by the Ocean Color Imager (OCI) and the Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS), an intercomparison study shows that the two data sets are highly correlated. The data from the two different sensors were processed with SeaWiFS atmospheric correction and bio‐optical algorithms to derive the chlorophyll‐a concentration (Chl‐a). The difference of total radiance received at the sensor of OCI and SeaWiFS is in the range of 3.8% at 510 nm to 21.5% at 865 nm. The difference of Chl‐a derived from OCI and SeaWiFS is about 12.4%. Correlation coefficients between OCI and SeaWiFS of total radiance and Chl‐a are higher than 0.91. The validity of the free data from OCI on‐board ROCSAT‐1, the first scientific experimental satellite of Taiwan, is established.
Role of non‐linear oceanic processes in the response to westerly wind events: New implications for the 1997 El Niño onset
Authors: Boulanger J.‐P. , Durand E. , Duvel J.‐P. , Menkes C. , Delecluse P. , Imbard M. , Lengaigne M. , Madec G. , Masson S.
Published: February 2004

In March 1997, a strong westerly wind event (WWE) occurred in the western equatorial Pacific prior to the 1997–1998 El Niño event. It produced downwelling Kelvin waves that interacted non linearly with the surface temperature, salinity and zonal current fronts located at the eastern edge of the warm‐fresh pool (EEWP). This non‐linear interaction locally increased zonal currents by a factor of three compared to a theoretical linear response, and advected the EEWP at an unexpected rate (∼ 1m/s) to which the ocean‐atmosphere coupled system may have been responding rapidly to trigger El Nino conditions.
Sea‐level change and true polar wander during the Late Cretaceous
Authors: Mound Jon E. , Mitrovica Jerry X. , Milne Glenn A.
Published: February 2004

We demonstrate that rapid changes in the Earth's rotation vector can drive relative sea‐level (RSL) variations in excess of 100 m in as little as 1 m.y. Stratigraphic constraints on sea‐level change can thus be used as an independent test of true polar wander (TPW) events proposed on the basis of paleomagnetic evidence. Recent estimates of Late Cretaceous TPW include a period of rapid motion, however a corresponding period of large and rapid sea‐level change is not consistently evident in our preliminary examination of the geological record. This suggests that the magnitude of Late Cretaceous TPW may have been overestimated, although a definitive conclusion requires a comprehensive study of high‐resolution Late Cretaceous sea‐level records. (Index Terms: 1239, 1527, 4556, 8159).
Scales of spatial variability for surface ocean pCO2 in the Gulf of Alaska and Bering Sea: Toward a sampling strategy
Authors: Murphy Paulette P. , Nojiri Yukihiro , Harrison D. E. , Larkin N. K.
Published: February 2004

Twenty‐four near‐exact repeat tracks (over a 48‐month period) of ocean surface pCO2 data from the North Pacific offer an uprecedented opportunity to examine the space scales of pCO2 in this region. Because previous basin scale studies of air‐sea carbon flux have shown that the field Of ΔpCO2 (air‐sea disequilibrium) largely controls the field of flux (and atmospheric pCO2 is relatively constant), knowing how to sample pCO2 in seawater is a crucial element of the design of a basin scale carbon flux observing system. Unbiased (within 3 µatm) along‐track means for ΔpCO2 can be obtained from measurements made every 40 km (∼ hourly for a ship traveling 20 knots). We find distinctly different characteristics of spatial variability in two open ocean regions, the Bering Sea and the Gulf of Alaska. The first zero crossing of the mean spatial autocorrelation function is 1.5° longitude in the Bering Sea and 3.5° in the Gulf of Alaska, when the cruise data are linearly detrended to remove the larger scale field. There is a strong seasonal variation in the zero crossing, with shorter scales in the summer. In near‐shore waters there is extreme variability, often with very small space scales and very large cruise‐to‐cruise differences. Neither the mean nor variability statistics from a single ship cruise data set appear likely to produce reliable information for designing an observing system.
Zonal—eddy coupling and a neutral mode theory for the Arctic Oscillation
Authors: Kimoto Masahide , Jin Fei‐Fei , Watanabe Masahiro , Yasutomi Natsuko
Published: February 2004

This study demonstrates that a dynamical mode that resembles the observed Arctic Oscillation (AO) pattern can be obtained as a least damped mode of a linear operator that expresses the dynamics of the zonally averaged flow interacting with stationary, zonally‐asymmetric waves. The spatial pattern of the leading singular mode of the operator bears much resemblance to the observed Arctic Oscillation both in terms of zonal and associated wave components. The mode has a damping time scale of more than a month, and is well separated from subsequent modes. Therefore, it is plausible that it survives on monthly and longer time scales. The simulated zonally asymmetric waves produce a meridional tilt due to advection by the AO‐like sheared zonal flow and positively feed back to the zonal flow through the momentum flux arising from the interplay with the climatological mean waves. The dominant contribution of this feedback is shown to come from the features in the North Atlantic sector, supporting the notion that the AO is a hemispheric extension of the more regional North Atlantic Oscillation.
Ozone and related gaseous pollutants in the boundary layer of eastern China: Overview of the recent measurements at a rural site
Authors: Wang T. , Cheung Vincent T. F. , Anson M. , Li Y. S.
Published: February 2004

We present a summary of the latest measurements of ozone (O3) and primary air pollutants at a rural/agricultural site in the fast developing Yangtze Delta region of China. The results of this study show elevated levels of primary pollutants (CO, SO2 and NOx*), which are about 1–5 times of those typically found in rural areas of North America and Europe. O3 pollution events are frequently observed. CO and SO2 levels are particularly high, resulting from the unique energy‐use pattern in China. O3 shows strong positive correlation with NOx* and CO during periods of high photochemical activity. The O3‐NOx* slope is comparable to the result from rural North America, but the O3‐CO slope is substantially smaller for the Chinese site. With the anticipation of rapid changes of atmospheric composition in China, long‐term measurements of key air pollutants will be necessary for documenting their trends and for studying their environmental impacts.
Evaporative moisture sources during a sequence of floods in the Mediterranean region
Authors: Reale O. , Feudale L. , Turato B.
Published: February 2004

This study investigates, with the aid of a water vapor back‐trajectory technique, the large‐scale source of moisture for a series of floods that affected the north‐western and north‐central Mediterranean regions between 30 September and 8 October 1998. It is shown that three west‐ward moving hurricanes of the 1998 Atlantic season, even though decayed to extra‐tropical storms, carried noticeable amounts of moisture to the proximity of western Europe during the last days of September and the first days of October 1998. In spite of the fact that the weather systems that actually caused the floods were non‐tropical, results suggest that the additional contribution of these Atlantic hurricanes, in terms of moisture advection, was important. Therefore eastern Atlantic tropical systems, although rare, can have a severe hydrological impact on the Mediterranean region.
Constraints on magnetic fluctuation energies in the plasma sheet
Authors: Neagu Elena , Gary S. Peter , Borovsky Joseph E. , Baumjohann Wolfgang , Treumann Rudolf A.
Published: February 2004

Magnetic field and plasma observations from magnetotail passes of the AMPTE/IRM satellite are used to study the low‐frequency magnetic fluctuation energy density as a function of several local plasma parameters. Two statistical constraints on this quantity are found, one a function of proton pressure, one a function of proton flow speed, suggesting that ion‐driven electromagnetic instabilities may contribute to the observed fluctuations.
The importance of high horizontal resolution and accurate coastline geometry in modeling South China Sea Inflow
Authors: Metzger E. Joseph , Hurlburt Harley E.
Published: February 2004

As resolution is increased from 1/2° to 1/32° in Pacific Ocean simulations using the NRL Layered Ocean Model, marked changes are found in the Kuroshio's mean pathway as it intrudes into the South China Sea (SCS) via the Luzon Strait. With increased horizontal resolution comes a more accurate representation of the coastline geometry associated with the Batan/Babuyan Islands within the strait, and a reduction in the modeled westward intrusion of the Kuroshio into the SCS. The 1/16° model is extremely sensitive to two very small scale shoals (Calayan Bank and a shoal north of Calayan Island) that are resolvable at this grid spacing. The exclusion of these three model gridpoints significantly alters the mean Kuroshio pathway to resemble the pathway from the 1/8° model. In addition, excluding all islands within the Luzon Strait in the 1/16° model gives a deep intrusion mean pathway as found in the 1/2° model.
Oceanic and atmospheric anomalies of tropical instability waves
Authors: Polito Paulo S. , Ryan John P. , Liu W. Timothy , Chavez Francisco P.
Published: February 2004

Tropical instability waves (TIWs) are detected in remotely‐sensed sea surface height (SSH), temperature (SST), and wind records of the eastern equatorial Pacific. Analyses of TIW anomaly relationships reveal strong dynamical influence of TIWs within approximately 5° of the equator. The first influence is advective heat flux. The primary forcing of TIW SST anomalies is advection of the meridional temperature gradient by TIW currents. The second influence is modification of the wind stress and Ekman pumping fields by TIW surface ocean currents. By affecting surface stress and hence roughness, TIW currents in this low‐wind region introduce a significant bias in scatterometer vector wind measurement. This bias is evident in both NSCAT and QuikSCAT winds. The difference between wind measurements from TAO moorings and scatterometers is phase‐locked with TIW SST oscillations. These results have important implications for scatterometry and for understanding tropical dynamics, thermodynamics and biogeochemistry.
Troposphere‐stratosphere dynamic coupling under strong and weak polar vortex conditions
Authors: Perlwitz Judith , Graf Hans‐F.
Published: February 2004

The relationship between Northern Hemisphere (NH) tropospheric and stratospheric wave‐like anomalies of spherical zonal wave number (ZWN) 1 is studied by applying Canonical Correlation Analysis (CCA). A lag‐correlation technique is used with 10‐day lowpass filtered daily time series of 50‐ and 500‐hPa geopotential heights. Generally stratospheric circulation is determined by ultralong tropospheric planetary waves. During winter seasons characterized either by an anomalously strong or weak polar winter vortex different propagation characteristics for waves of ZWN 1 are observed. The non‐linear perspective of the results have implications for medium range weather forecast and climate sensitivity experiments.
Isotopic typology of the precipitation in the Western Mediterranean Region at three different time scales
Authors: Celle‐Jeanton Hélène , Travi Yves , Blavoux Bernard
Published: February 2004

Environmental isotopes (18O, ²H) have been measured, between March 1997 and March 1999, at 10 stations located in the Mediterranean seaside countries (2 in Spain, 1 in Tunisia, 7 in France). Data collected on monthly, event and fractionated basis allow to understand the modifications of the isotopic content of precipitation due to meteorological phenomena. A monthly monitoring shows that the Western Mediterranean has a unique isotopic characteristic that is between Atlantic and Eastern Mediterranean. A daily survey highlights the impact of the origins and trajectories of air masses on the amount and the oxygen‐18 content of rainfalls: enriched and higher amount Mediterranean precipitation, depleted and lower amount Atlantic precipitation. At last, fractionated sampling of heavy precipitation allows to establish a typology of the variations of the isotopic composition during a rain event.
Dependence of multiple climate states on ocean mixing parameters
Authors: Schmittner Andreas , Weaver Andrew J.
Published: February 2004

Multiple equilibria of the climate system, inferred from paleo reconstructions, have also been observed in both ocean‐only and coupled ocean‐atmosphere general circulation models. These multiple states are thought to be associated with different modes of operation of the meridional overturning circulation in the North Atlantic. It has recently been suggested that the stability of these states depends on the amount of vertical mixing in ocean models. Here we investigate the dependence of the hysteresis behaviour of the thermohaline circulation to sub‐gridscale mixing processes in the ocean. Using a simplified coupled ocean‐atmosphere model we find that both vertical and horizontal diffusivities have considerable influence on the stability of the different circulation modes. They also change the transition points from one circulation pattern to another. Larger vertical diffusivities lead to higher values of additional precipitation into the North Atlantic being necessary to stop the formation of deep water. However, for slightly increased evaporation, the state without deep water formation becomes increasingly unstable for stronger vertical diffusion. Larger values of horizontal mixing lead to a narrowing of the phase space for which two equilibria are stable. These results suggest that it is currently not possible, given the large uncertainty in ocean mixing, to quantitatively determine possible thresholds for the transition of the North Atlantic thermohaline circulation between on and off modes. This presents a policy predicament as it makes it extremely difficult to assign a probability for the future occurence of such nonlinear climate transition.
Using analysis increments to estimate atmospheric heating rates following volcanic eruptions
Authors: Andersen Uffe J. , Kaas Eigil , Alpert Pinhas
Published: February 2004

By using the analysis increments of the temperatures from atmospheric re‐analyses it is possible to roughly estimate the stratospheric radiative heating rates from volcanic eruption. The method is applied to the 30 hPa temperature from the 15 years of the ECMWF‐reanalysis. After the influence from the Quasi Biennial Oscillation is subtracted maximum values of the zonal mean radiative heating rates related to El Chichón and Pinatubo volcanic eruptions are estimated to 0.30 K/day and 0.25 K/day, respectively. The estimated heating rates are not solely due to aerosol heating but includes the effects of ozone reduction and geostrophic adjustment as well.
The annual cycle of iron and the biological response in central California coastal waters
Authors: Johnson Kenneth S. , Chavez Francisco P. , Elrod Virginia A. , Fitzwater Steve E. , Pennington J. Timothy , Buck Kurt R. , Walz Peter M.
Published: February 2004

Iron has been measured for 16 months with ∼21 day resolution at three stations in the upwelling ecosystem of central California, providing the first detailed assessment of the annual iron cycle in the coastal zone. A large pulse of iron occurs during the first spring upwelling event of the year. Iron concentrations then decay up to 100‐fold over several months, although upwelling continues. Excess surface nitrate and low iron are the result during the summer and fall at the two stations furthest offshore (20 and 45 km), while nitrate is depleted and iron high nearshore (5 km). Phytoplankton biomass, primary production and community structure appear to be controlled by iron concentrations in offshore waters during this period.
Measurement of LAGEOS‐2 rotation by satellite laser ranging observations
Authors: Bianco G. , Chersich M. , Devoti R. , Luceri V. , Selden M.
Published: February 2004

The unprecedented single shot precision of the new‐born Matera Laser Ranging Observatory (MLRO), that can reach a scattering down to a few millimeters on LAGEOS orbit, discloses new chances in studying the high frequency dynamics. In this work we present the very first LAGEOS‐2 observations in terms of range residuals and discuss the cause of the high frequencies noticed since the testing phase of the MLRO system. There are sufficient theoretical and experimental evidences to interpret those signals as rotational signatures of the spinning satellite and the first quantitative results we obtained indicates a rotation period of 23.5 s on May 31, 2000.
Uplift of Tainan Tableland (SW Taiwan) revealed by SAR Interferometry
Authors: Fruneau B. , Pathier E. , Raymond D. , Deffontaines B. , Lee C. T. , Wang H. T. , Angelier J. , Rudant J. P. , Chang C. P.
Published: February 2004

Interferometric processing of five SAR‐ERS images reveals uplift of the Tainan Tableland (SW of Taiwan) during the period 1996–1998. The maximum measured ground motion for these two years is 2.8 cm along the radar line of sight towards the satellite, indicating for the displacement vector a vertical component of 3.2 cm, and a horizontal component of 1.6 cm towards the WSW considering additional information from GPS data. The reconstructed displacement field is consistent with the geological interpretation of the Tainan Tableland as an actively growing anticline connected to the Taiwan fold‐and‐thrust belt. This implies that the deformation front is located farther west than usually assumed in the Tainan area. The large Tainan city is thus located in an active deformation zone. Seismic hazard assessment is however difficult because the mechanisms and kinematics are not known in detail.
New information on the deep lunar interior from an inversion of lunar free oscillation periods
Authors: Khan A. , Mosegaard K.
Published: February 2004

We have obtained crucial information on the deep lunar interior through a Monte Carlo inversion of a number of fundamental lunar spheroidal free oscillations. The results indicate a homogeneous upper mantle with a velocity and density of 3.75±1.1 km/s and 3.3±0.5 g/cm³. A transition between the upper and middle mantle in the range 520‐580 km depth also seems to be implied. Middle mantle velocities and densities are 5.4±1.2 km/s and 3.5±0.2 g/cm³. Moreover, a velocity decrease is seen in the lower mantle (1150–1450 km depth) consistent with earlier inferences of partial melt in this region. The density seems to increase gradually from 1250 km depth to the center of the moon, where it reaches values indicative of an FeS or silicate composition.
Decadal variations in the tropical South Atlantic and linkages to the Pacific
Authors: Mo Kingtse C. , Hakkinen Sirpa
Published: February 2004

Linkages between the sea surface temperature anomalies (SSTAs) in the southern tropical Atlantic (STA) and in the Pacific on decadal time scales were examined. Seven to eight years before warming in the STA, an ENSO‐like decadal SSTA pattern with positive anomalies in the Tropics and negative anomalies in the subtropics appears in the Pacific. In the Atlantic, negative anomalies are located in the North Atlantic, while the corresponding sea level pressure anomaly (SLPA) composite resembles a North Atlantic Oscillation (NAO) pattern. After the establishment of the NAO, a pattern with the band structure of alternating positive and negative anomalies with warming in the STA appears 6 years later in the Atlantic. In the Pacific, warm SSTAs shift from the date line to the eastern Pacific three to four years later after the ENSO ‐like pattern appears. Soon after, a wave train extends from the Pacific to the tip of Argentina and negative anomalies appear in the South Atlantic. Warming starts in the STA. While SSTAs in the Pacific and the Atlantic may not vary as a single mode, two oceans interact when SSTAs in the Pacific are strong enough to generate downstream responses. These anomalies in turn contribute to the variations of SSTAs over the STA.
Distribution of marine ice beneath the Amery Ice Shelf
Authors: Fricker Helen Amanda , Popov Sergey , Allison Ian , Young Neal
Published: February 2004

We present a map of the marine ice accreted to the base of the Amery Ice Shelf (AIS), East Antarctica. This map is obtained by converting a Digital Elevation Model (DEM) of the AIS generated from satellite radar altimeter data to an ice thickness map, assuming hydrostatic equilibrium, and subtracting from that a second ice thickness map, derived from airborne radio‐echo sounding (RES) measurements. The RES signal does not penetrate the marine ice, so the measurement is only to the meteoric‐marine ice boundary, and therefore the difference between the two maps is the marine ice thickness. The marine ice is up to 190 m thick and accounts for about 9% of the shelf volume. It is concentrated in the northwest of the shelf, a result of the clockwise ocean circulation in the cavity below.
Dynamics of monsoon‐induced biennial variability in ENSO
Authors: Kim K.‐M. , Lau K.‐M.
Published: February 2004

The mechanism of the quasi‐biennial tendency in ENSO‐monsoon coupled system is investigated using an intermediate coupled model. The monsoon wind forcing is prescribed as a function of SST anomalies based on the relationship between zonal wind anomalies over the western Pacific to sea level change in the equatorial eastern Pacific. The key mechanism of quasi‐biennial tendency in El Niño evolution is found to be in the strong coupling of ENSO to monsoon wind forcing over the western Pacific. Strong boreal summer monsoon wind forcing, which lags the maximum SST anomaly in the equatorial eastern Pacific approximately 6 months, tends to generate Kelvin waves of the opposite sign to anomalies in the eastern Pacific and initiates the turnabout in the eastern Pacific. Boreal winter monsoon forcing, which has zero lag with maximum SST in the equatorial eastern Pacific, tends to damp the ENSO oscillations.
Observations of OIO in the remote marine boundary layer
Authors: Allan B. J. , Plane J. M. C. , McFiggans G.
Published: February 2004

We report observations of iodine dioxide (OIO) in the remote marine boundary layer. The measurements were made at the remote site of Cape Grim in Tasmania, using the technique of differential optical absorption spectroscopy (DOAS), in the 540–570 nm spectral region. Employing a cross‐section of 6.8 × 10−17 cm² at 548.6 nm, the concentration of OIO was found to vary from below the detection limit of the instrument (≈ 0.5 parts per trillion (ppt)) to a maximum of almost 3 ppt after sunset. During the day the upper limit to the atmospheric turnover time of OIO was found to be 20 min., when removal by gas‐phase reaction and/or photolysis appears to dominate. At night the much longer turnover time of ≈ 1–4 hours can be explained by uptake on aerosol.
The microscopic origin of thermal cracking in rocks: An investigation by simultaneous time‐of‐flight neutron diffraction and acoustic emission monitoring
Authors: Meredith Philip G. , Knight Kevin S. , Boon Stephen A. , Wood Ian G.
Published: February 2004

We demonstrate that neutron diffraction measurements make it possible to quantity elastic strains within the interior of solid samples, and thus have great potential for addressing a wide range of problems connected with the characterization of the mechanical properties of geological materials. We use the time‐of‐flight neutron diffraction technique, in combination with acoustic emission monitoring, to study the evolution of thermal strain within the interior of samples of a pure quartzite during slow heating, and the onset of the associated thermal cracking. Thermal cracking commences around 180°C when the thermal strain deficit along the a‐axes of quartz grains induces a thermal stress that is close to the bulk tensile strength of the rock.
Observation of anomalous elastic behavior in rock at low temperatures
Authors: Ulrich T. J. , Darling T. W.
Published: February 2004

We have measured qualitative elastic properties of basalt and Berea sandstone from room temperature down to 4 K using Resonant Ultrasound Spectroscopy (RUS). A simple elastic solid should show a monotonic increase in the elastic constants as temperature decreases. The basalt samples show this gross behavior while the sandstone shows a very unexpected anomalous regime between 40 K and 200 K where the elastic constants decrease with decreasing temperature. Both rocks show temperature‐dependent structure in both the modulus and internal friction, and also significant hysteresis, indicating history and rate‐dependent properties. This data provides insight into the time and energy scales of dynamical effects observed in sandstones. The low temperature range (4K–300K) is of interest due to the renewed interest in Mars and Lunar rocks.
Penetration depth of interferometric synthetic‐aperture radar signals in snow and ice
Authors: Rignot Eric , Echelmeyer Keith , Krabill William
Published: February 2004

Digital elevation models of glaciated terrain produced by the NASA/Jet Propulsion Laboratory (JPL) airborne interferometric synthetic‐aperture radar (InSAR) instrument in Greenland and Alaska at the C‐ (5.6 cm wavelength) and L‐band (24‐cm) frequencies were compared with surface elevation measured from airborne laser altimetry to estimate the phase center of the interferometric depth, or penetration depth, δp. On cold polar firn at Greenland summit, δp = 9±2m at C‐ and 14±4m at L‐band. On the exposed ice surface of Jakobshavn Isbrae, west Greenland, δp = 1±2 m at C‐ and 3±3 m at L‐band except on smooth, marginal ice where δp=15±5 m. On colder marginal ice of northeast Greenland, δp reaches 60 to 120 m at L‐band. On the temperate ice of Brady Glacier, Alaska, δp is 4±2 m at C‐and 12±6 m at L‐band, with little dependence on snow/ice conditions. The implications of the results on the scientific use of InSAR data over snow/ice terrain is discussed.
Subsidence and isostasy along a sheared margin—Cauvery Basin, Eastern Continental Margin of India
Authors: Chand Shyam , Subrahmanyam C.
Published: February 2004

We have applied a process‐oriented method to a seismo‐geological section across Cauvery Basin, a sedimentary basin along the southern part of the Eastern Continental Margin of India (ECMI) to examine the isostatic mechanism operating beneath the margin. The evolution of the ECMI appears to be within a shear‐rift tectonic setting, mainly driven by the difference in the relative motions of India and East Antarctica and the subsequent direction of spreading and the Cauvery Basin seems to have formed in this pull‐apart tectonic setting. Shearing along the southern ECMI is modeled with gravity anomalies and the resultant crustal configuration, through various models of isostasy. Backstripping analysis suggests a very low Te of 3 km beneath the basin. The shelf edge gravity anomaly reflects a strong contrast across a wrench fault parallel to the coast inferred from gravity forward modeling, denoting coast‐parallel transform motion in the initial stages of continental separation prior to rotation and spreading.
Low energy neutral atoms in the magnetosphere
Authors: Moore T. E. , Collier M. R. , Burch J. L. , Chornay D. J. , Fuselier S. A. , Ghielmetti A. G. , Giles B. L. , Hamilton D. C. , Herrero F. A. , Keller J. W. , Ogilvie K. W. , Peko B. L. , Quinn J. M. , Stephen T. M. , Wilson G. R. , Wurz P.
Published: February 2004

We report observations of low energy neutral atoms (LENA) from the solar wind and the ionosphere, obtained by the LENA Imager on the IMAGE spacecraft. The LENA Imager detects and images LENAs arriving at the spacecraft from within a 90° field of view (8° × 8° pixels), swept through 360° every two minutes by spacecraft spin. Neutral atoms arriving at the sensor are converted to negative ions by a conversion surface. The resulting negative ions are separated in energy (3 bins, 10–250 eV) and arrival direction (±45°). They are then accelerated, detected, and time‐of‐flight mass analyzed. The solar wind and the ionosphere both emit measurable neutral atom fluxes, the latter responding rapidly to to variations of the former.
Stratospheric water vapor increases over the past half‐century
Authors: Rosenlof K. H. , Oltmans S. J. , Kley D. , Russell J. M. , Chiou E.‐W. , Chu W. P. , Johnson D. G. , Kelly K. K. , Michelsen H. A. , Nedoluha G. E. , Remsberg E. E. , Toon G. C. , McCormick M. P.
Published: February 2004

Ten data sets covering the period 1954–2000 are analyzed to show a 1%/yr increase in stratospheric water vapor. The trend has persisted for at least 45 years, hence is unlikely the result of a single event, but rather indicative of long‐term climate change. A long‐term change in the transport of water vapor into the stratosphere is the most probable cause.
An edge detection technique to estimate melt duration, season and melt extent on the Greenland Ice Sheet using Passive Microwave Data
Authors: Joshi Maneesha , Merry Carolyn J. , Jezek Kenneth C. , Bolzan John F.
Published: February 2004

The melt extent, duration and melt season on the Greenland ice sheet were estimated using an edge detection technique on passive microwave data from the SSM/I and SMMR instruments (18/19V GHz channel) for the period 1979 to 1997. The annual brightness temperature (Tb) time series at a pixel location that experiences summer melt has a steep rise and drop in Tb with the onset and end of melt, respectively. A derivative‐of‐Gaussian edge detector is used to detect edges corresponding to the onset and end of melt. The time lapsed between the first upward and last downward edge on the annual Tb time series gives an estimate of the melt season and the time lapsed between successive upward and downward edges gives the duration of melt. While the maximum melt extent increased by 18%, the total duration of melt increased by 3.7% and the total melt season decreased by 3.8% during the period 1979–1997.
Estimating source parameters of the earthquake swarm in the Hida Mountains Region, central Japan, using near‐field waveforms
Authors: Sato Kazuhiko , Mori James
Published: February 2004

We estimated source durations for larger events in a strong swarm that occurred from August 7, 1998 in the Hida mountains region, central Japan. We used broadband seismograms recorded at the Kamitakara observatory at distances of about 30 km. The events had seismic moments from 1014 to 1017 Nm. To determine the source durations, we systematically searched for the half duration of source time functions which minimized the difference between synthetic waveforms and observed data. In the data we could clearly see the near‐field contributions to the waveforms, suggesting that the durations were longer than expected for typical events, considering their size and the distance to the station. We estimated the source durations (half duration of source time functions), source dimensions, and stress drops to study the source parameters of these event. Source dimensions are determined from these source durations under the assumption of circular faults and seismic moments are estimated from maximum amplitudes. These results show that source durations are longer and source dimensions are larger compared to most earthquakes with the same seismic moments.
Lidar observations of polar mesospheric clouds at South Pole: Seasonal variations
Authors: Chu Xinzhao , Gardner Chester S. , Papen George
Published: February 2004

Polar mesospheric clouds (PMCs) were observed above the geographic South Pole by an Fe Boltzmann temperature lidar from 11 Dec 99 to 24 Feb 00. During this 76‐day period 297 h of observations were made on 33 different days and PMCs were detected 66.5% of the time. The mean PMC peak backscatter ratio, peak volume backscatter coefficient, total backscatter coefficient, layer centroid altitude, and layer rms width are 50.59±2.33, 2.70±0.12 × 10−9 m−1sr−1, 3.61±0.22 × 10−6 sr−1, 85.49±0.09 km, and 0.71±0.03 km, respectively. The PMCs are highest near summer solstice when upwelling over the pole is strongest. The altitudes are 2–4 km higher than that typically observed elsewhere, including the North Pole. After solstice the mean altitudes decreases by about 64 m/day as the upwelling weakens.
Lidar observations of polar mesospheric clouds at South Pole: Diurnal variations
Authors: Chu Xinzhao , Gardner Chester S. , Papen George
Published: February 2004

Polar mesospheric clouds (PMCs) were observed by a ground‐based Fe Boltzmann temperature lidar for 65 h on 17–19 and 24–26 January 2000 above the geographic South Pole. The mean PMC backscatter ratio, volume backscatter coefficient, total backscatter coefficient, layer centroid altitude, and layer rms width are 53.5, 2.9 × l0−9 m−1sr−1, 4.3 × 10−6 sr−1, 85.37 km, and 0.78 km, respectively. Strong semidiurnal and diurnal oscillations were observed in the PMC backscatter ratio, volume backscatter coefficient, total backscatter coefficient, and centroid altitude. The oscillations are all maximum around 0630 and 1900 UT. The variations appear to be linked to vertical advection of the PMC scattering layers by a persistent oscillation in the vertical wind velocity. Scattering is strongest when the PMCs are highest which suggests that the colder temperatures at higher altitudes near the mesopause facilitate the formation of larger PMC particles.
Ionospheric reflection of small‐scale Alfvén waves
Authors: Lessard M. R. , Knudsen D. J.
Published: February 2004

The transfer of energy from the magnetosphere to the ionosphere occurs through complex mechanisms that often involve shear Alfvén waves, implying that the interaction of these waves with the ionosphere is fundamental to our understanding of the coupling process. Indeed, a variety of problems that involve magnetosphere‐ionosphere coupling assume that the ionosphere acts as a perfectly reflecting boundary, although we know that this is not the case in general. In this work, we calculate the reflection coefficient of shear Alfvén waves incident on the ionosphere under three different ionospheric profiles. Our results indicate that 1) under all profiles considered, reflection of shear Alfvén waves with perpendicular lengths of ∼ 1 km or less is negligible and 2) under a profile that might be typical of a nightside ionosphere, reflection of shear Alfvén waves is significant only for waves with frequencies below ∼0.4 Hz and λx above ∼2km; reflection of waves with λx less than ∼2 km is poor.
Observation and simulation of direct and reflected GPS signals in Radio Occultation Experiments
Authors: Beyerle Georg , Hocke Klemens
Published: February 2004

GPS/MET radio occultation observations are analyzed with the radio holographic method. Using the Multiple Signal Classification algorithm power spectra of 2038 radio holograms observed between 2 February and 16 February 1997 are calculated. In about 28% of the analyzed L1‐band spectra secondary frequency components are found at power levels of about 10–20 dB below the main component. These secondary components are interpreted as signatures of GPS signals reflected at Earth's surface. Results from geometrical ray tracing simulations support our interpretation.
On the relationship of cosmic ray flux and precipitation
Authors: Kniveton Dominic R. , Todd Martin C.
Published: February 2004

This paper evaluates whether there is empirical evidence to support the hypothesis that solar variability is linked to the Earth's climate through the modulation of atmospheric precipitation processes. Using global data from 1979–1999, we find evidence of a statistically strong relationship between cosmic ray flux (CRF), precipitation (P) and precipitation efficiency (PE) over ocean surfaces at mid to high latitudes. Both P and PE are shown to vary by 7–9% during the solar cycle of the 1980s over the latitude band 45–90°S. Alternative explanations of the variation in these atmospheric parameters by changes in tropospheric aerosol content and ENSO show poorer statistical relationships with P and PE. Variations in P and PE potentially caused by changes in CRF have implications for the understanding of cloud and water vapour feedbacks.
Sea surface temperatures in the subarctic northeast Pacific reflect millennial‐scale climate oscillations during the last 16 kyrs
Authors: Kienast Stephanie S. , McKay Jennifer L.
Published: February 2004

Changes of sea surface temperature (SST) in the subarctic NE Pacific over the last 16,000 calendar years before present (16 kyr BP) have been inferred from the study of C37 alkenone unsaturation in a sediment core from the western Canadian continental slope. Between 16.0 and 11.0 kyr, three distinct cold phases (6–7°C) interrupt two warmer periods (9–10°C). Within the 2σ range of the radiocarbon based time control, the observed SST oscillations correspond to the Oldest Dryas, the Bølling, the Older Dryas, the Allerød, and the Younger Dryas periods in the GISP2 δ18O record. These results represent the first high resolution marine paleo‐temperature estimates off the northern west coast of North America and imply that the climate of this region may be very strongly coupled to that of the North Atlantic. Given the fast rates of SST change (1°C/40–80 yr), such coupling must be controlled by atmospheric transmission of the climate signal.
Oscillations of Bay of Bengal sea surface temperature during the 1998 Summer Monsoon
Authors: Sengupta Debasis , Ravichandran M.
Published: February 2004

New measurements from moored buoys in the Bay of Bengal, along with satellite cloud data, reveal strong monsoon intraseasonal oscillations (ISO) during the summer of 1998. The active phase of the monsoon is marked by high surface wind and deep atmospheric convection. The buoy data show that sea surface temperature (SST) in the Bay of Bengal warm pool rises and falls with periods of weeks. These intraseasonal oscillations of SST are not adequately captured in a satellite derived weekly SST analysis. They are a direct response to ISO of net surface heat flux into the ocean, which is negative in the active phase of the monsoon and positive in the quiescent phase. Fresh water from rivers and rain appears to control northern Bay of Bengal SST in late summer by allowing sunlight to escape below a shallow mixed layer.
Detection of deep overflows with satellite altimetry
Authors: Høyer Jacob L. , Quadfasel Detlef
Published: February 2004

In‐situ observations downstream of the sills in the Faroe Bank Channel and Denmark Strait show large temperature and current variability of the overflows with time‐scales of a few days. These fluctuations are associated with meso‐scale eddies and have an impact on sea surface height. This is confirmed by observations from the TOPEX/POSEIDON and ERS 1+2 satellites that show substantial enhancement of eddy kinetic energy and sea level variability immediately down‐stream of the sills.
Tropospheric response to stratospheric ozone loss
Authors: Kindem Ina T. , Christiansen Bo
Published: February 2004

The response to realistic total column ozone trends on the troposphere and the stratosphere as simulated by the ARPEGE General Circulation Model (GCM) has been investigated. In both hemispheres, the lower stratosphere cooled and the polar vortex strengthened significantly during spring/early summer. The cooling trend was weaker than the observed trend in the Northern Hemisphere (NH), but stronger than the observed trend in the Southern Hemisphere (SH). In the troposphere, the changes in geopotential height resembled the positive phase of the Arctic Oscillation (AO) in the NH in March and the positive phase of the Antarctic Oscillation (AAO) in the SH during summer (December–February).
The influence of subseasonal wind variability on tropical instability waves in the Pacific
Authors: Benestad R. E. , Sutton R. T. , Allen M. R. , Anderson D. L. T.
Published: February 2004

Tropical Instability Waves are a prominent feature in analyses of tropical Pacific sea surface temperature and sea level height variability, and may play a significant role in the heat, salt and momentum budgets of the equatorial oceans. Here we show that they may be strongly influenced by forcing from the atmosphere. In experiments with an ocean GCM we find that a phase shift in the subseasonal wind forcing gives rise to a corresponding phase shift in the TIWs, indicating a systematic influence of the high frequency wind forcing.
Complex flow patterns through Hydrate Ridge and their impact on seep biota
Authors: Tryon Michael D. , Brown Kevin M.
Published: February 2004

Our recent measurements of long‐term fluid flux rates and output fluid chemistry at seep sites on Hydrate Ridge, Cascadia, suggest that the mechanisms driving fluid flow in gas hydrate bearing forearc settings may be significantly more complex than previously thought. Temporal changes in the polarity and magnitude of flow and in seep fluid chemistry were observed. The nature of flow appears to generate a strong response in the chemosynthetic seep community ecology. We document here: 1) the frequency and range of temporal variability in flow rates, 2) the relatively rapid changes in outflow composition, 3) strong outflow of seawater‐like fluids, 4) the association of Calyptogena (sp) clams with oscillatory and inflow settings, and 5) microbial mat communities associated with strong advection of altered fluids. These results suggest that a reappraisal may be required of the nature of the hydrologic system and its effect on related processes such as benthic seep community ecology and biogeochemical cycles.
Far‐ultraviolet observations of the neutral comae of comet Hale‐Bopp (C/1995 01) near perihelion
Authors: Brittnacher M. , Kang J. , Parks G. , Elsen R. , Germany G. , Spann J. , Fox N. , Puetter R. C. , Yahil A.
Published: February 2004

The Ultraviolet Imager on the Polar spacecraft observed the neutral oxygen and carbon comae of Comet Hale‐Bopp (C/1995 01) at far‐ultraviolet wavelengths near perihelion on March 31 and April 2, 1997. The OI (1304) coma was circularly symmetric with a diameter of about 5 million km. The coma was smaller in the longer wavelength (1400–1600 Å and 1600–1800 Å) bands, which is probably due to fluorescence of neutral carbon at 1561 Å and 1657 Å. The production rate for O calculated from the observed OI (1304) flux was (9.8±2.5) × 1030. Using this value the estimated production rate for OH was (8.9±2.5) × 1030 and for H2O was (1.0±0.3) × 1031.
Ice nucleation in NH4HSO4, NH4NO3, and H2SO4 aqueous particles: Implications for cirrus cloud formation
Authors: Cziczo D. J. , Abbatt J. P. D.
Published: February 2004

The temperature at which ice nucleation occurs in aqueous NH4HSO4, NH4NO3, and H2SO4 particles has been studied as a function of solute concentration. The onset of freezing was determined using FTIR extinction spectroscopy coupled to a low‐temperature flow tube system. The greatest supercooling with respect to equilibrium freezing was observed for H2SO4/H2O. Considerably less supercooling was observed for NH4NO3/H2O, and less yet for the NH4HSO4/H2O system. All three aerosol types exhibit a lower freezing temperature, as a function of solute concentration, than (NH4)2SO4 particles previously studied by this approach. These results suggest that air masses containing ammoniated sulfate particles will promote cirrus cloud formation at higher temperatures and lower relative humidities than will those containing pure H2SO4 particles.
Temporal variability in the strength of proxy‐climate correlations
Authors: Aykroyd R. G. , Lucy D. , Pollard A. M. , Carter A. H. C. , Robertson I.
Published: February 2004

The strength of the correlation between annually resolved tree‐ring carbon isotope indices and climate was explored using a moving window technique. Significant variations in the correlation with fixed‐date monthly temperature were observed using a 15‐year moving window. To investigate the influence of phenological changes upon this relationship, a 20‐day moving window was applied to daily temperature data to define the period of optimal tree response. For oaks growing in east England, the strongest association began 87 days after initial bud burst, which corresponds to the opening of the second flush of leaves. These results demonstrate that daily climatic data may be used to calibrate proxy‐climate relationships.
Physical mechanisms behind biogeochemical glacial‐interglacial CO2 variations
Authors: Gildor Hezi , Tziperman Eli
Published: February 2004

The atmospheric concentration of CO2 has undergone significant and fairly regular changes on a time scale of 100 kyr during the at least last four glacial‐interglacial cycles. Here we present a novel coupled physical‐biogeochemical mechanism for these variations. Previous studies had to arbitrarily specify the behavior of the physical climate system in order to invoke a biogeochemical mechanism for the glacial CO2 changes, be it an arbitrarily specified change in the vertical ocean mixing [Toggweiler, 1999], or arbitrarily specified sea ice cover changes [Stephens and Keeling, 2000]. Instead, we present here a new, self‐consistent, qualitative physical mechanism for both the vertical mixing and sea ice cover changes. In this mechanism, the cooling of North Atlantic Deep Water due to northern hemisphere glaciation is transported southward by the thermohaline circulation, and cools the deep water upwelling in the Southern Ocean. This, in turn, affects the Southern Ocean stratification, reduces the rate of vertical mixing of the surface water with the deep water and increases the sea ice cover. We also explain the continuous time evolution between glacial and interglacial states rather than treat them as two steady states, and are able to model explicitly for the first time the amplification of the glacial‐interglacial variability of the physical climate system by the ocean biogeochemistry.
A coupled model study of the Last Glacial Maximum: Was part of the North Atlantic relatively warm?
Authors: Hewitt Chris D. , Broccoli Anthony J. , Mitchell John F. B. , Stouffer Ronald J.
Published: February 2004

A coupled ocean‐atmosphere general circulation model is used to simulate the climates of today and the last glacial maximum (LGM). The model, which does not require artificial flux adjustments, produces a pattern of cooling at the LGM that is broadly consistent with the findings from simpler models and palaeoclimatic data. However, changes to the ocean circulation produce anomalously warm LGM surface conditions over parts of the North Atlantic, seemingly at odds with palaeoceanographic data. The thermohaline circulation is intensified for several centuries, as is the northward heat transport in the Atlantic equatorward of 55°N, but this may be a transient result. Mechanisms that lead to this response are discussed.
Tectospheric structure beneath southern Africa
Authors: James D. E. , Fouch M. J. , VanDecar J. C. , van der Lee S. ,   Kaapvaal Seismic Group
Published: February 2004

P‐wave and S‐wave delay times from the broadband data of the southern Africa seismic experiment have been inverted to obtain three‐dimensional images of velocity perturbations in the mantle beneath southern Africa. High velocity mantle roots appear to extend to depths of at least 250 km, and locally to depths of 300 km beneath the Kaapvaal and Zimbabwe cratons. Thick roots are confined to the Archean cratons, with no evidence for similar structures beneath the adjacent Proterozoic mobile belts. The Kaapvaal craton was modified ca. 2.05 Ga by the Bushveld magmatic event, which affected a broad swath of cratonic mantle beneath and to the west of the exposed Bushveld Complex. The mantle beneath the extended Bushveld province is characterized by seismic velocities lower than those observed in regions of undisturbed cratonic mantle. The mantle beneath the Limpopo Belt, an Archean collisional zone sandwiched between the Kaapvaal and Zimbabwe cratons, exhibits a cratonic signature.