bluuebunny/crossref_metadata_2025 huggingface dataset:
Noctilucent clouds and wave dynamics: Observations at Sondrestrom, Greenland
Authors: Gerrard Andrew J. , Kane Timothy J. , Thayer Jeffrey P.
Published: February 2004

Rayleigh Lidar measurements of the arctic summer stratosphere and mesosphere have been conducted routinely since 1994 at the Sondrestrom atmospheric research facility near Kangerlussuaq, Greenland (67.0N, 50.9W). Between 1994 and 1996, seventeen separate events of noctilucent clouds (NLCs), as well as corresponding stratospheric wave structure, have been observed. We present in this study two main results: 1) the occurrence of persistent quasi‐monochromatic wave structure in the stratosphere having observed vertical wavelengths of 8 to 12 km and observed temporal periods of approximately 2–3 hours, and 2) evidence that the strength of such lower altitude waves may be associated with the overall strength of the observed NLC volume backscatter coefficient.
Ultrafine aerosol particles in aircraft plumes: Analysis of growth mechanisms
Authors: Kärcher B. , Yu F. , Schröder F. P. , Turco R. P.
Published: February 2004

An analysis of in situ measurements of ultrafine volatile aerosols in the plume near field of the DLR aircraft ATTAS using low (0.02 g/kg) and high (2.7g/kg) fuel sulfur contents (FSCs) is presented. The observed growth of nanoparticles (diameter 5–10 nm) is reproduced in detail by a microphysical simulation with chemi‐ion emissions of 2.6×1017/kg fuel. Volatile aerosol dynamics is controlled by sulfuric acid (H2SO4) for high FSC, consistent with a S to H2SO4 conversion of 1.8%. The very high conversion for low FSC (55%) prescribed in the model to match the observations contradicts direct in situ measurements of H2SO4 and suggests that species other than H2SO4, likely exhaust hydrocarbons, control particle growth in such cases.
A use of two‐channel radiances for an aerosol characterization from space
Authors: Nakajima Teruyuki , Higurashi Akiko
Published: February 2004

We report new satellite retrievals of an aerosol particle size index, Ångström exponent, along with aerosol optical thickness, obtained from a two channel algorithm for NOAA/AVHRR and ADEOS/OCTS satellite‐borne radiometers. The results show characteristic features of the global aerosol size index on global scale. Small aerosol particles were detected in fairly large‐scale areas around mid‐latitude industrial regions and tropical biomass burning regions, whereas large aerosol particles were detected over most of the ocean area and over subtropical arid areas.
Rainfall rate measurement with a polarimetric radar at an attenuated wavelength
Authors: Sauvageot Henri , Mesnard Frédéric , Illingworth Anthony J. , Goddard John W. F.
Published: February 2004

Among the many ways investigated for radar estimation of rainfall, polarimetric methods are the most promising. However most polarimetric algorithms are degraded by attenuation by precipitation and clouds and by calibration error. A new method was recently proposed in which the differential polarimetric attenuation is used to perform an accurate rain rate measurement. The method is independent of the radar calibration and of the attenuation by undetected clouds. This algorithm is also usable as a qualitative hail detector, as well as a detector of anomalous propagation. The goal of the paper is to describe the results of the first experimental implementation of this method using the 35 GHz RABELAIS radar, as attenuated radar, and the 3 GHz CAMRa radar as a reference. We show that the proposed algorithm is stable and enables us to retrieve the actual rain rate even from an observed signal attenuated by more than 30 dB. The results are insensitive to the value used for the power coefficient of the Z(R) relation.
A high‐latitude observation of sporadic sodium and sporadic E‐layer formation
Authors: Heinselman C. J. , Thayer J. P. , Watkins B. J.
Published: February 2004

High‐resolution radar and lidar measurements of sporadic sodium (Na) and sporadic E (E) layers were made at the Sondrestrom incoherent‐scatter radar facility on 11 December 1997. These measurements suggest a causal link between Es and Nas, supporting the proposed mechanism in which Na+ ions in the Es are neutralized to form the Nas. This Nas, by contrast, does not appear to have been formed by the presence of auroral precipitation or ionization, and, in fact, the sodium density is seen to decrease during an auroral event.
The impact of upper tropospheric humidity from microwave limb sounder on the midlatitude greenhouse effect
Authors: Hu Hua , Liu W. Timothy
Published: February 2004

This paper presents an analysis of upper tropospheric humidity, as measured by the Microwave Limb Sounder, and the impact of the humidity on the greenhouse effect in the midlatitudes. Enhanced upper tropospheric humidity and an enhanced greenhouse effect occur over the storm tracks in the North Pacific and North Atlantic. In these areas, strong baroclinic activity and the large number of deep convective clouds transport more water vapor to the upper troposphere, and hence increase greenhouse trapping. The greenhouse effect increases with upper tropospheric humidity in areas with a moist upper troposphere (such as areas over storm tracks), but it is not sensitive to changes in upper tropospheric humidity in regions with a dry upper troposphere, clearly demonstrating that there are different mechanisms controlling the geographical distribution of the greenhouse effect in the midlatitudes.
Jovian radio “bullseyes” observed by Ulysses
Authors: Kaiser M. L. , MacDowall R. J.
Published: February 2004

We report the observation of extremely rare semi‐bullseye or target‐like features in the dynamic spectra of Jupiter obtained in 1991–1994 by the Ulysses Unified Radio and Plasma wave instrument. The emissions lie in the 20–50 kHz band and consist of narrow band (∼1–2 kHz) semi‐concentric wisps on frequency‐time dynamic spectra. The individual wisps correspond to a 4π steradian radiated power in the range of tens of kilowatts to more than ten megawatts. The emissions show a tendency to occur in groups every 25–27 days with a spacing between some individual episodes of about 10.5 hours. The 25–27 day periodicity is strongly correlated with solar wind ram pressure at Jupiter. Speculation on the cause of these events includes constructive‐destructive interference or diffraction of a previously known radio source viewed through the Io plasma torus, or perhaps radio emission from Ganymede or from the magnetic flux tube threading through Ganymede.
Conjugacy of geomagnetic disturbances and the substorm current wedge
Authors: Feldstein Y. I. , Gromova L. I. , Levitin A. E. , Grafe A.
Published: February 2004

The conjugacy of geomagnetic phenomena at high latitudes in the northern and southern hemispheres is investigated using observations of the geomagnetic field variations. Similar the magnetic disturbances at the poleward edge of the auroral oval night sector were observed in both hemispheres. These results show that magnetic field lines at the periphery of the plasma sheet are closed and that processes leading to the appearance of magnetic disturbances are similar in conjugate regions. Modeling of geomagnetic field line structure has shown that field lines are closed up to a distance of several dozens of Earth radii during the existence of the tail current wedge. The region of closed field lines maps to the nightside ionosphere up to ∼ 80° geomagnetic latitude.
Mid‐ and low‐latitude prompt‐penetration ionospheric zonal plasma drifts
Authors: Fejer Bela G. , Scherliess Ludger
Published: February 2004

We have used ion drift observations from the DE‐2 satellite to determine the latitudinal variation and the temporal evolution of mid‐ and low‐latitude prompt penetration zonal plasma drifts driven by magnetospheric electric fields. Our results indicate that sudden increases in convection lead to predominantly westward perturbation drifts which decrease equartorwards and have largest amplitudes in the dusk‐midnight sector. The diurnal perturbation drift patterns shift to later local times with increasing storm time and decay to new quasi‐equilibrium values in about 2 hours, as the ring current readjusts to the new polar cap potential. The daily and latitudinal variations and temporal evolution of the DE‐2 prompt penetration drifts are generally in good agreement with predictions from the Rice Convection Model, although the experimental results show larger amplitudes and longer shielding time constants.
Source parameters of moderate‐sized earthquakes in the Tien Shan, central Asia from regional moment tensor inversion
Authors: Ghose Sujoy , Hamburger Michael W. , Ammon Charles J.
Published: February 2004

We estimate faulting geometry, depth, and seismic moment of 32 moderate‐sized earthquakes in the Tien Shan by matching observed and synthetic seismograms recorded at regional distances. The moment‐tensor compression axes are oriented in the direction 170°–350°, consistent with the orientation of India‐Eurasia convergence. This compression is manifested in reverse faulting on roughly east‐west trending fault planes. Faults within the mountain system have moderate‐to‐steep dips, but range‐bounding faults appear to dip more gently. Earthquake source depths are in the range 5–25 km, consistent with those determined from local earthquake studies. The distribution and mechanism of earthquakes in the Tien Shan suggests that a significant proportion of the active deformation in the Tien Shan is absorbed by shortening across intramontane basins. The absence of strike‐slip earthquake mechanisms associated with the Talas‐Ferghana Fault suggests that the fault is presently locked, with deformation accommodated on neighboring compressional structures.
Are north‐south aligned auroral structures an ionospheric manifestation of bursty bulk flows?
Authors: Henderson M. G. , Reeves G. D. , Murphree J. S.
Published: February 2004

Bursty Bulk Flow (BBF) events are an important means of plasma transport in the Earth's magnetotail during substorms. While several studies have been performed using in‐situ plasma and field data to determine the characteristics of BBFs, remarkably little attention has been paid to the question of whether or not these events also manifest themselves in the auroral ionosphere. In this paper, we present observations from the Viking UV imager, and the Los Alamos National Laboratory geosynchronous energetic particle detectors that strongly suggest that the north‐south aligned structures formed impulsively and repetitively during the expansion phase of substorms may be an ionospheric manifestation of BBFs.
Biological‐physical coupling in the Central Equatorial Pacific during the onset of the 1997–98 El Niño
Authors: Chavez Francisco P. , Strutton Peter G. , McPhaden Michael J.
Published: February 2004

Perturbations to phytoplankton biomass associated with the onset of the 1997–98 El Niño event are described and explained using physical and bio‐optical data from moorings in the central equatorial Pacific. The physical progression of El Niño onset is depicted, from reversal of the trade winds in the western equatorial Pacific, through eastward propagation of equatorially trapped Kelvin waves and advection of waters from the nutrient‐poor western equatorial warm pool. Fluctuations in chlorophyll and quantum yield of fluorescence are tightly coupled to thermocline variations.
Direct measurement of magnetic reversal polarity boundaries in a cross‐section of oceanic crust
Authors: Tivey Maurice A. , Johnson H. Paul , Fleutelot Corinne , Hussenoeder Stefan , Lawrence Roisin , Waters Cheryl , Wooding Beecher
Published: February 2004

Magnetic field measurements made by submersible define the cross‐sectional geometry of a magnetic polarity reversal boundary and the vertical variation of crustal magnetization in upper oceanic crust. Measured polarity boundaries show a systematic pattern of shallow dip towards the spreading axis within the upper extrusive lavas, and steeper dip in the lower extrusive lavas. This geometry is a consequence of the emplacement of extrusive lava at a midocean ridge. Reversal boundary geometry and magnetization estimates are used to calculate the magnetic contribution of the extrusive lava sequence to the overlying marine magnetic anomaly signal. From the forward modeling, the highly magnetized extrusive lavas contribute the majority (50–75%) of the observed sea surface magnetic anomaly, consistent with the extrusive crust forming the primary source layer for young marine magnetic anomalies.
Dispersive magnetosheath‐like ion injections in the evening sector on January 11, 1997
Authors: Sandahl I. , Koskinen H. E. J. , Mälkki A. M. , Pulkkinen T. I. , Budnik E. Yu. , Fedorov A. O. , Frank L. A. , Sigwarth J. B.
Published: February 2004

While the plasma cloud of the January 1997 CME event was passing the Earth, the Interball Auroral Probe (Interball‐2) crossed the duskside auroral oval toward a contracted polar cap. The PROMICS‐3 plasma instrument observed several consecutive dispersion ramps of magnetosheath‐like protons over a wide range of magnetic local times (16–21 MLT). The last dispersion ramps were observed at later local times than previously reported, likely caused by the extreme conditions during a period when the magnetosphere was immersed in the dense plasma cloud. The Polar/VIS images of the oval show a very contracted polar cap. During the first clear dispersion event energetic oxygen ions were detected. They were also observed by the the particle detectors of Polar which was in close conjugation with Interball‐2 right at this moment. We suggest that the dispersion ramps are signatures of ion injections formed by impulsive entry of magnetosheath ions through the dusk‐side flank into the magnetosphere during a period of strongly northward IMF and contracted polar cap.
On the relationship between coronal mass ejections and magnetic clouds
Authors: Gopalswamy N. , Hanaoka Y. , Kosugi T. , Lepping R. P. , Steinberg J. T. , Plunkett S. , Howard R. A. , Thompson B. J. , Gurman J. , Ho G. , Nitta N. , Hudson H. S.
Published: February 2004

We compare the substructures of the 1997 February 07 coronal mass ejection (CME) observed near the Sun with a corresponding event in the interplanetary medium to determine the origin of magnetic clouds (MCs). We find that the eruptive prominence core of the CME observed near the Sun may not directly become a magnetic cloud as suggested by some authors and that it might instead become the ”pressure pulse” following the magnetic cloud. We substantiate our conclusions using time of arrival, size and composition estimates of the CME‐MC substructures obtained from ground based, SOHO and WIND observations.
POLAR observations of coherent electric field structures
Authors: Franz Jason R. , Kintner Paul M. , Pickett Jolene S.
Published: February 2004

The POLAR plasma wave instrument often detects coherent electric field structures in the high altitude polar magnetosphere. The structures appear to be positively charged potentials which are found to move both up and down the ambient magnetic field. Typical estimated velocities and parallel scale sizes are the order of 1000 km/s and 100–1000 meters, respectively. We have observed the structures at radial distances of 2.02 to 8.5 Re and L shells of 6 − 12+, although the they are likely to occur over a broader range of space than suggested by this initial study. The structures are responsible for some of the the spectral features of broadband electrostatic noise, and are similar to recent GEOTAIL and FAST observations of solitary waves.
Field‐line resonances triggered by a northward IMF turning
Authors: Laakso H. , Fairfield D. H. , Russell C. T. , Clemmons J. H. , Singer H. J. , Giles B. L. , Lepping R. P. , Mozer F. S. , Pfaff R. F. , Tsuruda K. , Wygant J. R.
Published: February 2004

A sudden northward rotation of the IMF observed by IMP 8 near the bow shock at 21:22 UT on January 10, 1997, triggered surface waves and fast mode waves at the flanks of the duskside magnetosphere, as observed by GEOTAIL instruments. The power spectral density of these waves peaked in the frequency range where field‐line resonances were observed by the POLAR satellite in the region L = 6.6–10.2. The oscillation periods of the observed field‐line resonances were L‐dependent with two distinct peaks which may be explained by increased heavy ion content at those field lines. The ULF waves also caused enhanced low‐energy ion fluxes from the ionosphere.
Plasma populations in the magnetosphere during the passage of magnetic cloud on January 10–11, 1997: INTERBALL/tail probe observations
Authors: Yermolaev Yuri I. , Zastenker Georgy N. , Nozdrachev Mikhail N. , Skalsky Alexandre A. , Zelenyi Lev M.
Published: February 2004

The INTERBALL/Tail Probe observations of several unusual features of the plasma populations in the Earth's magnetosphere during the passage of the magnetic cloud on January 6–11, 1997 are presented. Interaction of high‐pressure pulses on leading and trailing edges of the cloud with the magnetosphere resulted in its strong compression and large‐scale motions of the geomagnetic tail. Several important consequences of this interaction were: (1) observations of the magnetopause position 6RE nearer to the Earth than on average; (2) a huge increase in the magnetosheath plasma density and temperature; and (3) oscillation of magnetospheric tail structures past the satellite. These observations are discussed and compared with several models.
Heavy precipitation processes in a warmer climate
Authors: Frei Christoph , Schär Christoph , Lüthi Daniel , Davies Huw C.
Published: February 2004

Climate simulations have suggested that a greenhouse‐gas induced global warming would also lead to a moistening of the atmosphere and an intensification of the mean hydrological cycle. Here we study possible attendant effects upon the frequency of heavy precipitation events. For this purpose simulations with a regional climate model are conducted, driven by observed and modified lateral boundary conditions and sea‐surface temperature distributions. The modifications correspond to a uniform 2K temperature increase and an attendant 15% increase of the specific humidity (unchanged relative humidity). This strategy allows to isolate the effects of an increased atmospheric moisture content from changes in the atmospheric circulation. The numerical experiments, carried out over Europe and for the fall season, indicate a substantial shift towards more frequent events of strong precipitation. The magnitude of the response increases with the intensity of the event and reaches several 10s of percent for events exceeding 30 mm per day. These results appear to apply to all precipitation events dominated by sea‐to‐land moisture transport.
Solar excursion phases during the last 14 solar cycles
Authors: Mursula K. , Zieger B.
Published: February 2004

The strong half solar rotation (about 13–14 days) periodicity in solar wind, IMF and geomagnetic activity was recently shown to arise from intervals during which the heliospheric current sheet is flat and tilted. These intervals denote the excursion phases of the solar dipole. In this letter we locate the solar excursion phases for the last 14 solar cycles using long‐term observations of geomagnetic activity. This allows us to study the evolution of the solar corona for more than 150 years, i.e. far longer than with any other continuous data set. In the last eight cycles, largest excursions were found in mid‐ to late declining phase of the solar cycle, in agreement with the present view on coronal development during the solar cycle. However, in most of the earlier cycles 9–14, excursions were less frequent and occurred close to sunspot maximum. This suggests that the solar corona was exceptionally stable during the early low‐activity cycles, having open coronal holes until close to sunspot maximum. Furthermore, we find that there is a connection between new sunspot activity and the solar dipole tilt.
Effects of ice particle shape and orientation on polarized microwave radiation for off‐nadir problems
Authors: Czekala Harald
Published: February 2004

The effect of ice crystal shape and orientation from high altitude clouds (9 to 10 km height) on the angular distribution and state of polarization of microwave radiation emerging from the earth's atmosphere is investigated. The potential effects of nonspherical shapes are studied at 200 GHz and for two different shapes: Oblate and prolate spheroids with a preferred orientation of the axis of symmetry and an aspect ratio of 5.0 and 0.2, respectively. The results show strong effects of shape and orientation on both the total intensity and polarization state. Propagation directions close to the horizontal are of special interest to troposphere/lower stratosphere microwave limb‐sounding investigations. Although the presented calculations do not consider realistic ice clouds with hexagonal particles and the limb sounding geometry is not explicitly taken into account, the results obtained for large off‐nadir angles lead to the conclusion that particle shapes, especially in case of particles with preferred axis of orientation, have a significant effect on intensity (up to 15 K) and polarization difference (up to 30 K).
Effects of topography on the interpretation of the deformation field of prominent volcanoes—Application to Etna
Authors: Cayol Valérie , Cornet François H.
Published: February 2004

We have investigated the effects of topography on the surface‐deformation field of volcanoes. Our study provides limits to the use of classical half‐space models. Considering axisymmetrical volcanoes, we show that interpreting ground‐surface displacements with half‐space models can lead to erroneous estimations of the shape of the deformation source. When the average slope of the flanks of a volcano exceeds 20°, tilting in the summit area is reversed to that expected for a flat surface. Thus, neglecting topography may lead to misinterpreting an inflation of the source as a deflation. Comparisons of Mogi's model with a three‐dimensional model shows that ignoring topography may lead to an overestimate of the source‐volume change by as much as 50% for a slope of 30°. This comparison also shows that the depths calculated by using Mogi's solution for prominent volcanoes should be considered as depths from the summit of the edifices. Finally, we illustrate these topographic effects by analyzing the deformation field measured by radar interferometry at Mount Etna during its 1991–1993 eruption. A three‐dimensional modeling calculation shows that the flattening of the deflation field near the volcano's summit is probably a topographic effect.
A simple avalanche model as an analogue for magnetospheric activity
Authors: Chapman S. C. , Watkins N. W. , Dendy R. O. , Helander P. , Rowlands G.
Published: February 2004

The power law dependence of the power spectrum of auroral indices, and in‐situ magnetic field observations in the earth's geotail, may be evidence that the coupled solar wind‐magnetospheric system exhibits scale free self organised criticality and can to some extent be described by avalanche models. In contrast, the intensity of, and time interval between, substorms both have well defined probability distributions with characteristic scales. We present results from a simple cellular automaton that models avalanches in a one dimensional “sandpile”; here we examine the simplest case of constant inflow. This model generates a probability distribution of energy discharges due to internal reorganization that is a power law implying SOC, whereas systemwide discharges (flow of “sand” out of the system) form a distinct group which do not exhibit SOC. The energy dissipated in a systemwide discharge follows a probability distribution with a well defined mean, as does the time interval between one systemwide discharge and the next. Internal and external avalanches can therefore in principle be identified with distinct processes in the dynamic geotail. If so, the avalanche model places restrictions on the class of physical process that may be invoked to explain the observed geomagnetic dynamics.
Pre‐sunrise mesospheric echoes and turbulent wind structure observed with the MU radar
Authors: Muraoka Yoshikazu , Fukao Shoichiro , Sugiyama Takuya
Published: February 2004

Summer mesospheric observations using the MU radar at Shigaraki, Japan show that radar echoes could be detected before sunrise under some circumstances. The pre‐sunrise radar echoes observed at heights above 80 km are weak but clearly occur in a layer. Strong radar echoes observed after sunrise at similar heights show an unusual broadening of the spectral width in the echo power. This indicates the presence of strong atmospheric turbulence. In addition, frequency spectra for the vertical wind fluctuations show an enhancement of the spectral power density in a wide range of periods shorter than the local Brunt‐Väisälä one. This is consistent with the occurrence of strong turbulence layer in the upper mesosphere though not immediately identified with the turbulence activity. Thus the presence of strong turbulence layer might yield us a possibility of detecting radar echoes before sunrise.
Inversion of GPS occultation measurements using Fresnel diffraction theory
Authors: Mortensen Mette D. , Høeg Per
Published: February 2004

Occultation data from the GPS/MET experiment are inverted to temperature profiles of the neutral atmosphere of the Earth using the Fresnel inversion technique. The technique is not limited in resolution by diffraction effects thus a good vertical resolution is achieved. In the derivation a thin screen approximation is used. The influence of this approximation on the results is discussed. The results obtained using the Fresnel inversion is compared to results obtained using the traditional geometrical optics inversion approach and to numerical weather prediction data.
The detection of the hydroxyl nightglow layer in the mesosphere by ISAMS/UARS
Authors: Zaragoza G. , López‐Puertas M. , López‐Valverde M. Á. , Taylor F. W.
Published: February 2004

Measurements of night‐time radiance near 4.6 µm by the ISAMS instrument on board the UARS satellite exhibit an enhancement in the upper mesosphere. We show in this work that this increase around 85 km tangent height is due to the OH(9–8) and OH(8–7) Meinel bands. The ISAMS database therefore contains valuable information on the variability over a seasonal cycle of the OH high vibrational populations from which the chemical heating of the upper mesosphere can be derived.
Spectral measurements of HCl in the plume of the Antarctic Volcano Mount Erebus
Authors: Keys J. G. , Wood S. W. , Jones N. B. , Murcray F. J.
Published: February 2004

A favourable combination of circumstances on 7 September 1996 allowed tracking of the sun through the plume of the active Antarctic volcano, Mount Erebus (77.5°S, 167.2°E, height 3794m). Fourier transform spectrometer (FTS) measurements were therefore possible from the Arrival Heights laboratory (77.8°S, 166.7°E), located approximately 30km south of the volcano. FTS scans were made with the interferometer looking upwind and downwind of the summit, resulting in spectra of HCl which showed large column enhancements of the gas when the sun was viewed through the volcanic plume. Pressure broadened spectra confirm that this enhancement was due to an additional tropospheric component in the column. Assumptions have been made of the plume dimensions and velocity, and a daily downwind flux of HCl derived. This is compared with the daily average flux emitted at the volcanic crater source during periods of passive outgassing, as derived from measurements using other techniques. The result suggests that for this quiescent type of emission from the volcano there is no evidence of rapid tropospheric scavenging of HCl, as might be expected for more explosive events and a less dry atmosphere.
First‐principles determination of elastic properties of CaSiO3 perovskite at lower mantle pressures
Authors: Karki Bijaya B. , Crain Jason
Published: February 2004

We investigate the equation of state and elasticity of cubic CaSiO3 perovskite up to 140 GPa using the plane wave pseudopotential method within the local density approximation. The calculated equation of state parameters of the cubic phase are in excellent agreement with those from recent quasi‐hydrostatic compression data and from all‐electron linearized augmented plane wave calculations. We determine the elastic constant tensor of the mineral from the calculated stress‐strain relations. The bulk modulus of CaSiO3 perovskite is similar to that of MgSiO3 perovskite, however, its shear modulus is much higher at pressures corresponding to the lower mantle. This suggests that CaSiO3 perovskite can no longer be considered as an invisible component in modelling the composition of the lower mantle, and even small amounts of the mineral may affect significantly the seismic properties, particularly shear wave velocity, of the generally accepted Mg‐rich silicate perovskite dominated composition of this region. Moreover, CaSiO3 perovskite exhibits strong anisotropy (about 30% shear‐wave polarization anisotropy) at pressures corresponding to the transition zone and the top of the lower mantle.
Comparison of mixing properties in convection with the Particle‐Line Method
Authors: Ten Arkady A. , Podladchikov Yuri Yu. , Yuen David A. , Larsen Tine B. , Malevsky Andrei V.
Published: February 2004

Spatial resolution in mixing processes is an acute problem. We propose a line method, akin to the contour dynamics technique, which is an extension of the particle method but with the particles redistributed on the line with time. We have used up to 105 particles per line and ten lines to investigate the dynamical and structural properties of mixing for both Newtonian and non‐Newtonian temperature‐dependent viscosity convection in 2D geometry. The spatial structures and the time history of the lines formed in Newtonian convection are different from those produced in non‐Newtonian convection, which has the tendency for producing long‐living horizontal structures. Efficient mixing in the upper mantle would be inhibited by non‐Newtonian rheology.
EURD observations of EUV nightime airglow lines
Authors: López‐Moreno José J. , Morales Carmen , Gómez José F. , Trapero Joaquín , Bowyer Stuart , Edelstein Jerry , Lampton Michael , Korpela Eric J.
Published: February 2004

The extreme ultraviolet (EUV) airglow has yet to be studied extensively due to observational difficulties in this range of the spectrum. EURD is an instrument designed to study diffuse EUV radiation flown on the Spanish MINISAT‐01 satellite. In this paper we present observations of the terrestrial night airglow as observed from EURD in the range of 400 to 1060 Å. The high sensitivity and high resolution of the instrument, compared with previous observations, and the long integration times provided by MINISAT‐01 permits the identification for the first time of the complete Lyman series of atomic hydrogen resolving up to Lyman ϵ. It has also been possible to identify a feature at 537 Å as helium Lyman β line and the detection of other lines of the blended Lyman series of helium at 515 and 522 Å.
The impact of sea level data assimilation on the Lamont Model Prediction of the 1997/98 El Niño
Authors: Chen Dake , Cane Mark A. , Zebiak Stephen E. , Kaplan Alexey
Published: February 2004

Assimilating the sea level data from tropical Pacific tide gauges greatly improved the Lamont model prediction of the 1997/98 El Niño while retaining its overall performance during the past few decades. The implication is that the Lamont forecast system is limited by the observational data used for initialization probably probably as much as by its simplified model physics. The sea level measurements in the vicinity of the equator are extremely effective in correcting the model ocean state and preconditioning it for ENSO prediction.
Upper ocean heat and freshwater advection in the western Pacific Ocean
Authors: Morris Michele Y. , Roemmich Dean H. , Meyers Gary , Weisberg Robert
Published: February 2004

Mean net surface heating of the Pacific Ocean shows areas of high heat gain in the eastern tropics and heat loss in the western midlatitudes. For steady state conditions, westward and poleward transport of heat is implied. Mean geostrophic and Ekman fluxes of heat and freshwater through the sides of a western tropical Pacific box bounded by World Ocean Circulation Experiment (WOCE) high‐resolution expendable bathythermograph (XBT) transects are presented. Water mass properties of currents transporting heat and freshwater through the enclosed region are seen to be modified in transit. Net transport convergences within the volume of water extending to 800 m in the vertical show a shallow ocean circulation cell (σθ<26) with relatively dense subtropical gyre water entering the volume and lighter water leaving in western boundary currents, eastward flowing tropical currents, Ekman flow, and outflow to the Indian ocean. Surface buoyancy fluxes are dominated by freshwater rather than heat fluxes. Freshwater gain through the surface allows warm, salty water to enter in the same density range as cool, fresh water leaving the volume. For steady state conditions the XBT‐derived oceanic heat convergence of 0±0.3 PW implies negligible heat loss to the atmosphere. Traditional surface heat flux climatologies predict too much heat gain. Part of the discrepancy may be due to anomolous meteorological conditions during the XBT experiment (1987–1995). Oceanic freshwater divergence of 0.70±0.08 Sv falls in the range of climatological predictions from surface freshwater gain.
Improved remote sensing of sea surface skin temperature using a physical retrieval method
Authors: Nalli Nicholas R. , Smith William L.
Published: February 2004

A new physically based method for retrieving sea surface skin temperature (SST) from satellite measurements of upwelling infrared radiance is developed. The method accounts for atmospheric interference by utilizing multispectral window information to explicitly solve the radiative transfer equation. Two essential elements are required for this SST retrieval: (1) a priori specification of sea surface emissivity and reflectivity spectra and (2) atmospheric transmittances that accurately portray the relative spectral dependence of molecular absorption. The algorithm can be directly applied to any multispectral instrument (e.g., the NOAA advanced very high resolution radiometer and/or the ERS‐1 along track scanning radiometer), as well as high resolution spectrometers such as the University of Wisconsin high‐resolution interferometer sounder (HIS). Error analyses have shown that SST can theoretically be retrieved to within 0.22 K RMS using high spectral resolution data (or approximately 0.51 K RMS using broadband split‐window data) provided that the a priori surface emissivity spectrum does not deviate by more than 0.005 from the true surface emissivity. High spectral resolution has distinct advantages in reducing the effects of atmospheric absorption and instrumental noise errors, as well as providing better guess atmospheric profiles for the transmittance calculations. Application of the method to HIS radiance data acquired from high‐altitude aircraft during the 1993 Convection and Moisture Experiment and 1995 Ocean Temperature Interferometric Survey suggests the possibility of physical retrieval of SST from future satellite remote sensing systems (e.g., the EOS advanced infrared sounder) with accuracies limited primarily by detector performance.
Observations of sea surface mean square slope under light wind during the Tropical Ocean‐Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment
Authors: Walsh E. J. , Hagan D. E. , Rogers D. P. , Weller R. A. , Fairall C. W. , Friehe C. A. , Burns S. P. , Khelif D. , Vandemark D. C. , Swift R. N. , Scott J. F.
Published: February 2004

Observations of sea surface mean square slope (mss) were made with a scanning radar altimeter (SRA) from a low‐flying research aircraft on a light‐wind day during the Tropical Ocean‐Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment. Wind speed (measured at 60‐ to 90‐m height and extrapolated to the 10‐m level) and mss were found to be positively correlated, with correlation coefficients in some cases as high as those obtained for wind speed measurements on adjacent aircraft flying wingtip to wingtip with a 100‐m lateral separation of their fuselages. The SRA measurements suggest a much larger azimuthal asymmetry in mss at 36 GHz than was observed in the seminal Cox and Munk optical experiment; the SRA measurements showed a crosswind‐to‐upwind ratio as low as of 0.26 at 1.8 m s−1 compared to the typical value of 0.8 for Cox and Munk. For higher wind speed the mss becomes more isotropic. The data suggest that waves generated by a wind speed less than 2 m s−1 are restricted to the downwind direction. The crosswind‐to‐upwind ratio would probably have been even lower had it not been for an isotropic background mss caused by an assortment of swell.
On the importance of the choice of wind stress forcing to the modeling of the Mediterranean Sea circulation
Authors: Myers Paul G. , Haines Keith , Josey Simon
Published: February 2004

A 1/4° degree ocean general circulation model is used to examine the role that four different wind stress climatologies play on the circulation of the Mediterranean. The wind stress climatologies examined are those derived from numerical weather prediction models (National Meteorological Center (NMC) and European Centre for Medium‐Range Weather Forecasts (ECMWF)) and one based on observations (Southampton Oceanography Centre (SOC)). Significant differences exist between the wind climatologies over the Mediterranean and in the response of an ocean general circulation model forced by the different climatologies. Excessive coastal upwelling/downwelling is found to be associated with the extreme zonal nature of one of the climatologies. Surface circulation differences include the position and penetration of the Mid‐Mediterranean Jet into the Levantine, the Ionian, and the Tyrrhenian circulations. Significant differences exist in the pathways for dispersal of Levantine Intermediate Water. Under the SOC forcing, there is a reduction in Eastern Mediterranean Deep Water formation in the Southern Adriatic, compensated by the production of intermediate or deep water in the Aegean. The ECMWF climatology is found to be associated with much more cyclonic doming in the Gulf of Lions, leading to better formation of Western Mediterranean Deep Water.
Cyclic loading and creep response of aligned first‐year sea ice
Authors: Cole D. M. , Johnson R. A. , Durell G. D.
Published: February 2004

Characteristics such as brine and gas porosity and crystallographic features can have a profound impact on the mechanical properties of first‐year sea ice. These characteristics vary spatially and temporally, and it is important in the development of constitutive models to address their variability in physically meaningful terms. A program of laboratory experiments on field cores of first‐year sea ice has been conducted to aid in the development of such models. A thorough assessment of the bulk physical properties and microstructural characteristics of the ice has been carried out in conjunction with a detailed set of cyclic loading and creep experiments. Methodology was developed to calculate an orientation factor that determines the average shear stress resolved on the basal planes, given the background normal stress. Examination of the constitutive behavior using laboratory cyclic loading and constant load creep experiments revealed that the elastic, anelastic (time‐dependent recoverable), and viscous strains varied systematically with the orientation factor. The observations also indicate significant brine porosity effects on the elastic, anelastic, and viscous components of strain. A recently developed constitutive model was expanded to include a frequency‐ and orientation‐dependent viscous straining term, and the model predictions agreed well with the experimental observation.
Surface heat flux variability over the northern California shelf
Authors: Beardsley Robert C. , Dever Edward P. , Lentz Steven J. , Dean Jerome P.
Published: February 2004

Surface heat flux components are estimated at a midshelf site over the northern California shelf using moored measurements from the 1981–1982 Coastal Ocean Dynamics Experiment (CODE) and the 1988–1989 Shelf Mixed Layer Experiment (SMILE). Time series of estimated fluxes extend from early winter through summer upwelling conditions, allowing examination of seasonal variations as well as synoptic events. On a seasonal timescale, the surface heat flux is strongly influenced net surface heat flux are the annual variation in incident shortwave solar radiation (insolation) and the atmospheric spring transition. Between mid‐November 1988 and late February 1989, insolation is weak and the mean daily averaged heat flux is nearly zero (absolute value less than 10 W m−2), with a standard deviation of ∼50 W m−2. Beginning in March, insolation increases markedly, and typical daily‐averaged heat fluxes increase to greater than 100 W m−2 by the spring transition in April or May. In June and July, the average heat flux is near 200 W m−2, with a standard deviation of ∼90 W m−2. In winter, the daily‐averaged heat flux varies on periods of several days. Net heat flux losses can range up to 130 W m−2. These losses are not identified with any one type of event. For example, comparable heat flux losses can occur for very low relative humidities (RHs), moderate winds, and clear skies, and for high RHs, high winds, and cloudy skies. In summer, surface heat flux variability is strongly influenced by upwelling and relaxation events. Upwelling is characterized by clear skies and high equatorward winds, while relaxation is characterized by the presence of clouds and low or northward winds. These conditions lead to opposing changes in insolation and in longwave radiative cooling and latent heat flux. Variability in insolation dominates, and the daily‐averaged heat flux into the ocean is greatest during upwelling events (up to 350 W m−2 or more) and least during relaxation events (sometimes less than 100 W m−2).
Quasi‐periodicity and global symmetries in interdecadal upper ocean temperature variability
Authors: White Warren B. , Cayan Daniel R.
Published: February 2004

Recent studies find interannual (i.e., 3 to 7 year), decadal (i.e., 9 to 13 year), and interdecadal (i.e., 18 to 23 year) periodicities, and a trend dominating global sea surface temperature (SST) and sea level pressure (SLP) variability over the past hundred years, with the interdecadal signal dominating sub‐El Niño‐Southern Oscillation (ENSO) frequencies. We isolate interdecadal frequencies in SST and SLP records by band passing with a window admitting 15 to 30 year periods. From 1900 to 1989, the rms of interdecadal‐filtered SST and SLP anomalies is largest in the extratropics and eastern boundaries. First‐mode empirical orthogonal functions (EOFs) explain about half the interdecadal variance in both variables, with the tropical warm phase peaking near 1900, 1920, 1940, 1960, and 1980. From 1955 to 1994, EOF spatial patterns of interdecadal SST, SLP, and 400m temperature (T400) anomalies reveals global reflection symmetries about the equator and global translation symmetries between ocean basins, with tropical and eastern ocean SSTs warmer (cooler) than normal, covarying with stronger (weaker) extratropical westerly winds, cooler (warmer) SSTs in western‐central subarctic and subantarctic frontal zones (SAFZs), stronger (weaker) subtropic and subarctic gyre circulations in North Pacific and North Atlantic Oceans, and warmer (cooler) basin and global average SSTs of 0.1°C or so. Evolution of interdecadal variability from the tropical warm phase to the tropical cool phase is propagative, also characterized by reflection and translation symmetries. During the tropical warm phase, cool SST anomalies along western‐central SAFZs are advected slowly eastward to the eastern boundaries and subsequently advected poleward and equatorward by the mean gyre circulation, the latter conducting extratropical SST anomalies into the tropics. A delayed action oscillation model is constructed that yields the quasiperiodicity of interdecadal variability in a manner consistent with these global symmetries in both pattern and evolution.
A 5‐year satellite climatology of winter sea ice leads in the western Arctic
Authors: Miles Martin W. , Barry Roger G.
Published: February 2004

The distribution of openings (leads and polynyas) in polar sea ice is not well known. This study estimates the large‐scale distribution and variability of leads in the Arctic of the western hemisphere in winter, using a 5‐year record of Defense Meteorological Satellite Program thermal‐ and visible‐band imagery. The occurrence (density) and orientation of leads are derived from gridded maps made at 10‐day intervals. Their mean value and interannual, seasonal, and monthly variabilities are estimated. Lead densities are observed to be highest in early winter, decreasing 20% from November through April. The highest densities are observed in the central Canada Basin, and the lowest are in the East Siberian Sea. There is limited interannual variability in the positions of maximum and minimum densities. Preferred lead orientations are identified as generally north‐south in the Beaufort Sea sector and east‐west in the East Siberian Sea sector, with transitional orientations in the intermediate area. The mean distributions of lead density and orientation are observed to be associated with large‐scale mean fields of ice divergence and shear, respectively.
Observations of melt ponds on Arctic sea ice
Authors: Fetterer Florence , Untersteiner Norbert
Published: February 2004

In an introductory section we review the physical processes influencing the formation and evolution of melt ponds on sea ice during the Arctic summer. As melt progresses, the changing properties of the surface interact strongly with the surface heat balance. The small interannual variability of the seasonal ice extent suggests an interannual variability of the surface heat balance of ±1 W m−2 or less. The interannual variance of atmospheric forcing represented by the transport of moist static energy into the Arctic is an order of magnitude greater. This appears to contradict the notion of a highly sensitive sea ice cover and emphasizes the need to generate albedo as an important internal variable in interactive models. Observations of melt ponds are needed in order to derive improved relationships between surface albedo and parameters such as the amount of snow, the onset and termination of melting, the ice thickness distribution, and ice deformation. Here classified (National Technical Means) imagery is used to measure melt pond coverage as it evolves over a summer on ice surrounding a drifting buoy. Local variability of pond cover is greatest at the beginning of the melt season, that is, pond coverage from 5% to 50% depending on ice type, as previously found by Russian investigators. An important distinction is found in the temporal change of pond cover: it decreases with time on thick ice, and it increases with time on thin ice (eventually leading to the disappearance of thin ice at the end of summer). An attempt to relate pond coverage to ice concentrations derived from passive microwave data proved unsuccessful.