bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of convective outflow on water vapor mixing ratios in the tropical upper troposphere: An analysis based on UARS MLS measurements
Authors: McCormack J. P. , Fu R. , Read W. G.
Published: September 2002

The source of increased water vapor mixing ratios over the central and eastern tropical Pacific region during the 1992 El Niño event is examined using measurements of upper tropospheric water vapor provided by the Microwave Limb Sounder (MLS) on board the Upper Atmosphere Research Satellite. Horizontal winds on isentropic surfaces are combined with ISCCP cloud information to provide back‐trajectory calculations free of high clouds. These calculations show that the water vapor mixing ratio of an air parcel in the cloud‐free regions of the eastern Pacific decreases to approximately one‐half of its original value within the first 30 hours after encountering deep convection. This analysis also finds a larger number of air parcels encountering deep convection within 30 hours of observation, and therefore having higher mixing ratios, in March–April 1992 compared to March–April 1994. Hence, increased deep convection over the equatorial central and eastern Pacific in 1992 contributed to the moistening of the downstream tropical upper troposphere.
Shear velocities in Cascadia from seafloor compliance measurements
Authors: Willoughby E. C. , Edwards R. N.
Published: September 2002

Compliance is defined as the transfer function between the vertical displacement of the seafloor and the corresponding pressure expressed as a function of frequency. It is sensitive to the elastic parameters of the underlying sediments, particularly the shear modulus. We have measured normalized compliance from 0.001 to 0.049 Hz, using ocean surface gravity waves as a source, at sites in Cascadia near the Ocean Drilling Program (ODP) hole 889B. A differential pressure gauge, datalogger and self‐levelling gravimeter were lowered to the seafloor and each site was occupied for eight hours. The compliance estimates are reproducible and are consistent with other available data and simple models of sediment physical properties. Shear strength is increased from a normal profile in the uppermost few hundred meters, possibly an effect of the presence of a known hydrate layer, and is decreased between 1.2 and 2 km below the seafloor, suggesting the presence of a low velocity zone.
Seasonal variation of wind‐driven diurnal current cycling on the Texas‐Louisiana Continental Shelf
Authors: DiMarco Steven F. , Howard Matthew K. , Reid Robert O.
Published: September 2002

We describe observations of large amplitude wind‐driven current oscillations of 24‐hr period occurring in the near‐surface layer of waters of the Texas‐Louisiana continental shelf. The near‐surface anti‐cyclonic current amplitudes can reach 60 cm s−1 and represent the largest non‐storm induced high‐frequency currents on the shelf. These currents can persist for a week or more, as long as driving diurnal winds persist with uninterrupted phase. The latitude of the shelf and the diurnal period of the wind‐forcing combine to produce conditions for a near‐resonant response of the surface currents to the wind stress, such that, the resulting currents are almost an order of magnitude greater than those found from steady Ekman drift. The oscillations are phase‐locked to time of day suggesting a connection to the daily cycle of heating and cooling. The oscillations generally occur during the summer months when there is a shallow mixed layer, strong vertical stratification, maximum insolation, and infrequent frontal passages.
Quasi‐biennial winds in the far western equatorial Pacific phase‐Locking El Niño to the seasonal cycle
Authors: Clarke Allan J. , Shu Lianghua
Published: September 2002

At El Niño/Southern Oscillation (ENSO) frequencies, the ocean is mainly driven by zonal equatorial winds. Using zonal equatorial Pacific wind stress for the last 8 El Niños, we demonstrate that anomalous equatorial westerly winds typically begin to blow in the far western Pacific in about November prior to the El Niño year and then slowly move eastward, amplifying and reaching a maximum in the central Pacific in about the following October. The key phase‐locking in the far western Pacific winds that leads to calendar‐year phase‐locking in El Niño appears to be associated with quasi‐biennial (QB) variability in the zonal wind. Recent theory suggests that evaporation and the seasonal wind cycle in the far‐western equatorial Pacific are crucial to the generation of the QB variability. The biennial wind‐stress phase‐locking explains why there is a spring persistence barrier in often used ENSO indices.
Coronal magnetic field topology and source of fast solar wind
Authors: Guhathakurta M. , Sittler E. , Fisher R. , McComas D. , Thompson B.
Published: September 2002

We have developed a steady state, 2D semi‐empirical MHD model of the solar corona and the solar wind with many surprising results. This model for the first time shows, that the boundary between the fast and the slow solar wind as observed by Ulysses beyond 1 AU, is established in the low corona. The fastest wind observed by Ulysses (680–780 km/s) originates from the polar coronal holes at 70°–90° latitude at the Sun. Rapidly diverging magnetic field geometry accounts for the fast wind reaching down to a latitude of ±30° at the orbit of Earth. The gradual increase in the fast wind observed by Ulysses, with latitude, can be explained by an increasing field strength towards the poles, which causes Alfvén wave energy flux to increase towards the poles. Empirically, there is a direct relationship between this gradual increase in wind speed and the expansion factor, f, computed at r >20R⊙. This relationship is inverse if f is computed very close to the Sun.
A nonlinear model for auroral density cavities
Authors: Shukla Padma K. , Sakanaka Paulo H.
Published: September 2002

A nonlinear model for the short‐scale auroral density cavity (SSADC) is presented. Specifically, it is shown that the SSADC is associated with nonlinear short wavelength (in comparison with the collisionless electron skin depth) dispersive convective cells (DCCs) whose frequencies are much smaller than the ion gyrofrequency. In a stationary frame, the relevant equations governing the dynamics of the nonlinear DCCs are put in the form of an energy integral with an effective potential. The latter is analyzed to demonstrate the existence of density cavities (or holes). Larger amplitude cavities are necessarily quasi‐stationary. The present theoretical model is capable of describing the salient features of SSADCs that are seen in data from the Freja satellite.
Unambiguous evidence of HF pump‐enhanced airglow at auroral latitudes
Authors: Brändström B. U. E. , Leyser T. B. , Steen Å , Rietveld M. T. , Gustavsson B. , Aso T. , Ejiri M.
Published: September 2002

Simultaneous observations by up to three low‐light imaging stations belonging to the Auroral Large Imaging System (ALIS) have provided the first strong evidence of high‐frequency (HF) pump‐enhanced airglow at auroral latitudes. The airglow was enhanced by an ordinary mode 4.04 MHz electromagnetic wave with an effective radiated power (ERP) of about 210 MW that was transmitted from the EISCAT‐Heating facility near Tromsø, Norway. While often observed at low or mid‐latitudes, and despite numerous earlier experiments, no unambiguous observations of pump‐enhanced airglow have been reported at auroral latitudes. On February 16, 1999, the first successful results were obtained, and this paper concentrates on discussing optical data from this event. Triangulated estimations of the altitude and position of the enhanced airglow are also presented. Auroral‐latitude observations of HF pump‐enhanced airglow are important in order to better understand the underlying excitation mechanisms.
Experiments on anomalous electron currents to a positive probe in a magnetized plasma stream
Authors: Gunell H. , Larsson M. , Brenning N.
Published: September 2002

The first laboratory experiments are reported of anomalously high currents drawn by an electron collecting probe in a magnetized plasma stream. The currents exceed the theoretical values by Parker and Murphy [Parker and Murphy, 1967] by more than a factor of three. Measurements of the potential pattern around the probe indicate that the enhanced currents are possible because electrons E × B‐drift into a local field‐aligned current channel.
The ionospheric oxygen Green airglow: Electron temperature dependence and aeronomical implications
Authors: Peverall Robert , Rosén Stefan , Larsson Mats , Peterson James R. , Bobbenkamp Rolf , Guberman Steven L. , Danared Håkan , af Ugglas Magnus , Al‐ Khalili Ahmed , Maurellis Ahilleas N. , van der Zande Wim J.
Published: September 2002

The laboratory measurement of processes involved in terrestrial airglows is essential in developing diagnostic tools of the dynamics and photochemistry of the upper atmosphere. Dissociative electron recombination of O2+ in the ionospheric F‐region is expected to produce both O(¹D) and O(¹S) which are the sources of the 630.0 nm red airglow and the 557.7 nm green airglow lines, respectively. We present both theoretical and experimental evidence, the latter from a heavy ion storage ring technique, that the O(¹S) quantum yield from O2+(υ = 0) is a strong function of the electron temperature due to a molecular resonance phenomenon. At present the O2+(υ = 0) theoretical and laboratory recombination data cannot explain rocket observations of the ionospheric green and red airglows [Takahashi et al. 1990; Sobral et al. 1992].
Toroidal ion distributions observed at high altitudes equatorward of the cusp
Authors: Huddleston M. M. , Pollock C. J. , Wüest M. P. , Pickett J. S. , Moore T. E. , Peterson W. K.
Published: September 2002

We examine events where the TIDE and TIMAS ion instruments on board the Polar spacecraft have observed transversely accelerated ions (TAI) at altitudes greater than 20,000 km. We report both H+ and O+ populations that have been heated perpendicular to the local B field but that also have a sharp low‐energy cutoff to the distribution occurring at 20–100 eV. Analysis of an event on 21 April 1996 indicates that the formation of ion toroids may be related to solitary structures or low frequency wave pulses observed during the event. We address some of the implications of using time (as opposed to frequency) domain techniques to analyze wave/particle energization events.
Jovian X‐ray emission from solar X‐ray scattering
Authors: Maurellis Ahilleas N. , Cravens Thomas E. , Gladstone G. Randall , Waite J. Hunter , Acton Loren W.
Published: September 2002

Soft x‐ray emissions with brightnesses of about 0.01–0.2 Rayleighs have been observed from both the equatorial and auroral regions of Jupiter. It has been proposed that the equatorial emission, like the auroral emission, may be largely due to precipitation of energetic heavy ions into the atmosphere [Waite et al., 1997]. In this paper we model two alternative mechanisms for low‐latitude x‐ray emission: (1) elastic scattering of solar x‐rays by atmospheric neutrals, (2) fluorescent scattering of carbon K‐shell x‐rays from methane molecules located below the jovian homopause. Our modeled brightnesses agree, up to a factor of two, with the bulk of low‐latitude ROSAT measurements. This suggests that solar photon scattering (approximately 90% elastic scattering) may act in conjunction with energetic heavy ion precipitation to generate jovian equatorial x‐ray emission.
Long‐term rise in geomagnetic activity – A close connection between quiet days and storms
Authors: Vennerstroem Susanne
Published: September 2002

Geomagnetic quiet days and magnetic storms are naturally believed to be due to very different solar wind conditions. In this study we however demonstrate that the long‐term variation of geomagnetic quiet and disturbed days are surprisingly similar. By the use of daily averages of the geomagnetic index aa we examine the activity level of the most quiet and most disturbed days separately through 130 years from 1868 to 1998. We find that the linear correlation between the average level of activity at the 5 most quiet days pr year and the yearly average is 0.8. For the 5 most disturbed days it is 0.7. The results indicate that the long‐term increase is due to an increase in the background solar wind parameters, rather than in the number of solar wind disturbances.
Magnetopause transects from two spacecraft: A comparison
Authors: Hu Qiang , Sonnerup Bengt U. Ö.
Published: September 2002

We recover two‐dimensional, magnetohydrostatic structures from measured data for a pair of partial magnetopause crossings by the spacecraft AMPTE/IRM and UKS, when they were separated by only about 40 km. After inter‐calibration of the two data sets, magnetopause transects are produced for UKS and IRM separately. They are similar in terms of overall features, indicating robustness of the reconstruction technique. The event was caused by inward‐outward magnetopause motion, as well as by tangential motion of magnetopause structures, first in one, and then in the opposite direction. Implications of observed island structures and intervening magnetic X points for transport across the magnetopause are discussed.
Ulysses observations of the magnetic field structure within CIRs
Authors: Clack D. , Forsyth R. J. , Dunlop M. W.
Published: September 2002

Ulysses encountered two separate sequences of corotating interaction regions (CIRs) in 1992–3 and 1996–7 when the spacecraft was in the southern and northern solar hemispheres, respectively. We have examined magnetometer data from one event observed in each hemisphere. Using two separate analytical methods we provide evidence for the magnetic field vectors within these CIRs being strongly confined to a series of near‐parallel planes. The distribution of the field within the interaction region is characteristic of that observed in planar magnetic structures. This planar order is evident over both small (3‐hour) and large (whole event) scales. The CIRs display opposed north‐south tilts that are consistent with previous authors' analysis of solar wind plasma data. These results are in direct agreement with the tilted dipole model of three‐dimensional corotating stream interactions.
Characteristics of energy transfer of Pi 2 magnetic pulsations: Latitudinal dependence
Authors: Uozumi T. , Yumoto K. , Kawano H. , Yoshikawa A. , Olson J. V. , Solovyev S. I. , Vershinin E. F.
Published: September 2002

To investigate the generation and propagation mechanisms of Pi 2 magnetic pulsations, we have analyzed magnetic field data from the 210° magnetic meridian (MM) stations. We used 50 Pi 2 events that were simultaneously observed at seven stations along the 210° MM during January 1995, and focused our analysis on associated magnetic energy, ((ΔH)²+(ΔD)²)/µ0. The times when the amplitude of the magnetic energy attained the maximum (Tmax) were compared among these stations. We found that Tmax has a latitudinal dependence, especially at higher latitudes, which has not been previously reported. At Kotel'nyy (L=8.50) on the poleward side of the auroral region, Tmax occurred an average of 21 seconds earlier than Tmax at Guam (L=1.01), and often as much as one minute earlier. The existence of latitudinal variation has implications for interpretation of issues related to timing of substorm onset; it is necessary to consider the global features of Pi 2 events in the study of auroral and magnetospheric substorms.
A two hundred years record of atmospheric cadmium, copper and zinc concentrations in high altitude snow and ice from the French‐Italian Alps
Authors: Van de Velde Katja , Boutron Claude F. , Ferrari Christophe P. , Moreau Ann‐Laure , Delmas Robert J. , Barbante Carlo , Bellomi Tania , Capodaglio Gabriele , Cescon Paolo
Published: September 2002

Cd, Cu and Zn have been measured using ultraclean procedures in snow and ice deposited at a high altitude location in the French/Italian Alps during the past two centuries. These data provide the first time series of changes in the occurrence of heavy metals in ice and snow from temperate regions since the Industrial Revolution. Concentrations are constant until the end of the nineteenth century. Then they increase by 10, 15 and 30 fold for Cu, Cd and Zn, respectively till the 1970s. During the following two decades Cd and Zn concentrations then decrease whilst Cu continues to increase. These temporal changes are compared with changes in emissions in Western Europe.
Planetary‐scale tropopause folds in the southern subtropics
Authors: Baray J. ‐L. , Daniel V. , Ancellet G. , Legras B.
Published: September 2002

Daily measurements of tropospheric ozone at La Reunion Island (55 E, 21 S) in July 1998 show that ozone layers are quasi‐permanent in the troposphere between 6 and 10 km with values reaching 80 to 100 ppbv. Meridional cross sections of potential vorticity reveal that these layers are related to tropopause folds beneath the subtropical jet. Folding is persistent and extends over a considerable longitude range from mid‐Atlantic to mid‐Pacific. We suggest that this structure is due to the convergent flow associated to the descent branch of the Hadley circulation during austral winter.
Direct measurement of the production rate of 14C near Earth's surface
Authors: Mak J. E. , Brenninkmeijer C. A. M. , Southon J. R.
Published: September 2002

Environmental 14C is well known for its application in carbon dating organic material, as well as its use as a geochemical tracer in the oceans and atmosphere. More recently, 14C in the form of atmospheric 14CO has been used to estimate the concentration of hydroxyl radical, which is the primary oxidant of the atmosphere. This latter application is dependent upon accurate knowledge of the cosmogenic production rate, which has been calculated, but not directly measured. We have measured the atmospheric production rate of 14C near the earth's surface on a 300‐meter research tower in Colorado, at the South Pole, at Scott Base, Antarctica, and near Mount Cook, New Zealand. The observed production rate near the surface was 50% of the production rate calculated by an earlier study. We also find that the ‘ground effect’, which causes an increase in the thermal neutron flux resulting in an enhancement of the production rate of 14C, is significantly smaller than calculated in earlier studies.
ILAS observations of chemical ozone loss in the Arctic vortex during early spring 1997
Authors: Sasano Y. , Terao Y. , Tanaka H. L. , Yasunari T. , Kanzawa H. , Nakajima H. , Yokota T. , Nakane H. , Hayashida S. , Saitoh N.
Published: September 2002

Chemical ozone loss rates were estimated for the Arctic stratospheric vortex by using ozone profile data (Version 3.10) obtained with the Improved Limb Atmospheric Spectrometer (ILAS) for the spring of 1997. The analysis method is similar to the Match technique, in which an air parcel that the ILAS sounded twice at different locations and at different times was searched from the ILAS data set, and an ozone change rate was calculated from the two profiles. A statistical analysis indicates that the maximum ozone loss rate was found on the 450 K potential temperature surface in February, amounting to 84 ppbv/day. The integrated ozone loss for two months from February to March 1997 showed its maximum of 1.5±0.1 ppmv at the surface that followed the diabatic descent of the air parcels and reached the 425 K level on March 31. This is about 50% of the initial (February 1) ozone concentration. The present study demonstrated that data from a solar occultation sensor with a moderate altitude resolution can be used for the Match analysis.
Chemical forecasts used for measurement flight planning during POLINAT 2
Authors: Flatøy Frode , Hov Øystein , Schlager Hans
Published: September 2002

A three dimensional regional chemistry transport model driven by data from a weather prediction model was applied to deliver chemistry forecasts suitable for scientific flight planning purposes throughout the POLINAT 2 measurement campaign from September to October 1997. The forecasts gave an overview of the expected distributions of ozone and its precursors in possible flight regions, including a separation of the influence of the aircraft NOx source on upper tropospheric NOx and ozone concentration, from lightning, surface and stratospheric sources. The usefulness was documented several times during the campaign, in particular for the investigation of corridor effects due to North Atlantic air traffic emissions.
Match observations in the Arctic winter 1996/97: High stratospheric ozone loss rates correlate with low temperatures deep inside the polar vortex
Authors: Schulz A. , Rex M. , Steger J. , Harris N. R. P. , Braathen G. O. , Reimer E. , Alfier R. , Beck A. , Alpers M. , Cisneros J. , Claude H. , De Backer H. , Dier H. , Dorokhov V. , Fast H. , Godin S. , Hansen G. , Kanzawa H. , Kois B. , Kondo Y. , Kosmidis E. , Kyrö E. , Litynska Z. , Molyneux M. J. , Murphy G. , Nakane H. , Parrondo C. , Ravegnani F. , Varotsos C. , Vialle C. , Viatte P. , Yushkov V. , Zerefos C. , von der Gathen P.
Published: September 2002

With the Match technique, which is based on the coordinated release of ozonesondes, chemical ozone loss rates in the Arctic stratospheric vortex in early 1997 have been quantified in a vertical region between 400 K and 550 K. Ozone destruction was observed from mid February to mid March in most of these levels, with maximum loss rates between 25 and 45ppbv/day. The vortex averaged loss rates and the accumulated vertically integrated ozone loss have been smaller than in the previous two winters, indicating that the record low ozone columns observed in spring 1997 were partly caused by dynamical effects. The observed ozone loss is inhomogeneous through the vortex with the highest loss rates located in the vortex centre, coinciding with the lowest temperatures. Here the loss rates per sunlit hour reached 6 ppbv/h, while the corresponding vortex averaged rates did not exceed 3.9 ppbv/h.
Measurements of chlorine partitioning in the winter Arctic stratosphere
Authors: Stachnik Robert A. , Salawitch Ross , Engel Andreas , Schmidt Ulrich
Published: September 2002

Measurements of the concentration profiles of key stratospheric reactive, reservoir and source gases, ClO, O3, HCl, N2O and CCl2F2, were made during two balloon flights in the Arctic on 27 January and 08 March 1995 that were part of the Second European Stratospheric Arctic and Mid‐latitude Experiment (SESAME). On 27 January, low abundances of HCl (∼250 ppt at 50 hPa) were measured in air parcels that had been at temperatures below the type I PSC existence threshold accompanied by high concentrations of ClO (1.6 ppb at 50 hPa). Calculations using the currently recommended photochemical data yield a ratio of [ClO]+2[Cl2O2]+[HCl] to [Cly] near unity in these air parcels. The 08 March flight sampled warm stratospheric conditions outside the vortex with normal mid‐latitude ClO (<100ppt at 50 hPa) and HCl abundances comprising about half of the available chlorine at 50 hPa.
Theoretically correct decimation of GPS data
Authors: Sleewaegen J. M.
Published: September 2002

As the spectrum of GPS applications continuously widens, it becomes usual to collect GPS data at a high rate and to decimate them to slower rates depending on the applications. It is shown in this paper that the decimation process is not as trivial as it sounds. Some important rules are presented that have to be observed for the decimation to be theoretically correct. Two decimation algorithms are proposed. The first one follows these rules, but it is shown that it gives rather poor results in terms of measurement noise (yielding a noise reduction by a factor of 2 for a decimation from 1 to 30 seconds). The second one is not perfectly “correct”, but is more successful in reducing the noise (achieving a reduction by a factor of 5.5 for a 1–30 decimation), and it proves to be adequate for all practical purposes.
Sunrise ozone destruction found in the sub‐tropical marine boundary layer
Authors: Nagao Ippei , Matsumoto Kiyoshi , Tanaka Hiroshi
Published: September 2002

A new mechanism of ozone loss is found in the sub‐tropical marine boundary layer over the north Pacific. This ozone destruction occurs just after sunrise (hereafter Sunrise Ozone Destruction, SOD) and is commonly found throughout the year. SOD is a predominant ozone loss mechanism in winter, which takes place after sunrise in a few hours with 1∼2 ppbv of ozone depletion for 40∼50 ppbv of background ozone, while, in summer, SOD is weaker than in winter with small ozone depletion for 10∼20 ppbv of background ozone. In summer, daytime ozone destruction (hereafter, DOD) associated with UV photolysis and subsequent HOx reaction is more active. Since DOD is not active in early morning, SOD should be a new ozone loss mechanism. After demonstrating the observational findings, halogen chemistry associated with sea‐salt aerosols is described as a possible mechanism.
Motion of the South Bismarck Plate, Papua New Guinea
Authors: Tregoning Paul , Jackson Russell J. , McQueen Herbert , Lambeck Kurt , Stevens Colleen , Little Rodney P. , Curley Robert , Rosa Robert
Published: September 2002

The absolute motion of the South Bismarck Plate was first estimated by Tregoning et al. [1998] from three site velocities estimated from Global Positioning System (GPS) observations. We report an improved estimate of the Euler vector for this plate using site velocities derived from new GPS data which include the velocity of a site located ∼25 km from the pole of rotation. The GPS velocities of Madang, Witu, Jacquinot Bay and Finschafen can be modelled to within ∼3 mm/yr using a single pole of rotation located at 6.75°S, 147.98°E with a clockwise rotation rate of 8.11°/My. The known tectonic features and available geophysical data surrounding the South Bismarck Plate can also be explained by a rotation of the South Bismarck Plate about this pole.
Anomalous scaling of mesoscale tropospheric humidity fluctuations
Authors: Cho John Y. N. , Newell Reginald E. , Sachse Glen W.
Published: September 2002

Water vapor fluctuations are measured and analyzed at an unprecedented 10‐m resolution throughout the troposphere. Computation of structure functions shows that specific humidity variations observed by research aircraft over the Pacific Ocean exhibit anomalous scaling from about 50 m to 100 km in horizontal range. The scaling laws show different characteristics for the marine boundary layer, the tropical free troposphere, and the extratropical free troposphere. More specifically, boundary‐layer humidity fluctuations are less smooth and more stationary than those in the free troposphere, while the extratropical free tropospheric variations are less intermittent than those in the other two regions. The anomalous scaling results argue against passive advection by a spatially smooth flow (chaotic advection) at these scales.
Electric‐field changes of lightning observed in thunderstorms
Authors: Beasley William H. , Eack Kenneth B. , Morris Heidi E. , Rust W. David , MacGorman Donald R.
Published: September 2002

During the Summer and Fall of 1998 we launched five balloon‐borne instruments into thunderstorms to observe changes in the vertical component of electric field caused by lightning. Four of these were for measurement of field change only. The fifth was part of a larger package that included a gamma radiation detector and a GPS receiver on board. We have processed electric‐field‐change data from two of these flights. We discuss examples of field changes observed at altitude and compare them with data from the National Lightning Detection Network (NLDN) for cloud‐to‐ground lightning flashes that were coincident in time. Limits on time resolution and timing accuracy prevent unambiguous identification of the lightning processes that caused the field changes. It appears that they may have been caused by charge movements relatively near the instruments as compared with the ground‐strike location of coincident flashes.
The excitation of the Na airglow from Coqui Dos rocket and ground‐based observations
Authors: Hecht J. H. , Collins S. , Kruschwitz C. , Kelley M. C. , Roble R. G. , Walterscheid R. L.
Published: September 2002

On February 20 1998 two rockets were launched from Puerto Rico as part of the Coqui Dos campaign. Data from on‐board photometers and ground‐based data from a Na lidar and an airglow imager allowed an estimate to be made, using both the TIME‐GCM and MSIS models, of the branching coefficient α for the Na airglow emission. Assuming the hydrogen density is within the range predicted by the two models the data are consistent with α being less than 0.05. This value is well below a recent theoretical estimate of 0.67 and also below the nominally accepted value of 0.1 derived from previous aeronomic data.
Comparison of SAGE‐II and HIRS co‐located cloud height measurements
Authors: Wylie Donald P. , Wang Pi‐Huan
Published: September 2002

The CO2 Slicing analysis of HIRS satellite data for cloud heights at the University of Wisconsin (Wylie and Menzel, 1999) is known to report cloud heights that are below the upper boundary (i.e., the geometric top) of the clouds for semi‐transparent cirrus. The reason for the discrepancy between the geometric cloud top and the cloud height derived from the CO2 Slicing analysis is well understood from radiative transfer calculations. It occurs because the CO2 Slicing analysis uses satellite measurements of infrared absorption and emission in clouds. For clouds semi‐transparent to terrestrial radiation, absorption and emission occur throughout the cloud so that the CO2 Slicing analysis reports a height indicative of where the absorption and emission occurred inside the cloud. However, some applications need data on the geometric cloud top and need to know the bias of the CO2 Slicing analysis from the geometric top. To statistically evaluate this bias, cloud height data derived from the CO2 Slicing analysis were compared to a more sensitive measurement of the geometric cloud top from the SAGE‐II satellite sensor. This study employed 71 clouds where both the HIRS and SAGE‐II sensors made height measurements at nearly the same time. The comparison found that the Wisconsin CO2 Slicing analysis underestimated the geometric cloud top by an average of 1.6 km. This bias increased slightly to 2.0 km for upper troposphere clouds. This is close to the previous studies of the CO2 Slicing analysis.
Densities and surface tensions of H2SO4/HNO3/H2O solutions
Authors: Martin Emmanuel , George Christian , Mirabel Philippe
Published: September 2002

The density and surface tension of the H2SO4/HNO3/H2O ternary system have been measured as a function of temperature from 245 to 298 K. The acid compositions range from 0 to 65 wt % for sulfuric acid and 0 to 45 % for nitric acid. The densities and surface tensions for the ternary system, combined with the data for the two binary mixtures water/nitric acid and water/sulfuric acid have been expressed as polynomials of the nitric acid and sulfuric acid weight % for the temperatures of 253 and 293 K. Since the densities and surface tensions vary linearly with temperature, data at temperatures other than 253 and 293 K can easily been obtained by interpolation.
Melting and seismic structure beneath the Northeast Japan Arc
Authors: Iwamori Hikaru , Zhao Dapeng
Published: September 2002

Transportation of H2O associated with subduction of the Pacific plate beneath the northeast Japan arc is modeled to predict distribution of aqueous solution and melt, and the consequent P‐wave velocity structure. The observed velocity structure coincides well with the model for equilibrium transport of H2O: most of H2O subducted is brought down to 150–200 km depth along the slab, then the aqueous fluid generated ascends to initiate melting, which explains the low velocity regions (∼6% reduction) observed beneath the backarc, rather than beneath the volcanic front. If equilibrium transport of H2O occurs, initiation of melting beneath the backarc with deep subduction of H2O is likely to be the case also for other subduction zones with slabs older than several tens of m.y., cold enough to stabilize serpentine to a great depth.
Global variation in the 2.7 µm NO overtone limb‐emission from the lower thermosphere
Authors: Sharma R. D. , Wheeler N. B. , Wise J. O. , Dothe H. , Duff J. W.
Published: September 2002

The overtone vibration‐rotation band (Δv=−2) limb‐emission from NO around 2.7 µm observed by the Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS‐1A) at 120 km tangent altitude is shown to arise from the nascent molecule produced by the reactions of N(4S) and N(²D) atoms with O2. Measurement of the 2.7 µm emission from NO therefore permits modeling of the local rate of production of NO, a quantity important in odd nitrogen chemistry in the thermosphere. The 2.7 µm limb‐radiance in the nonauroral region is observed, above the instrument noise level, only during the day and shows about a factor of 2 variation indicating a similar variation in the rate of production of NO. In the aurorally dosed region however the observations lead to about an order of magnitude variation in this rate.
Formation of subtropical westerly jet core in an idealized GCM without mountains
Authors: Inatsu Masaru , Mukougawa Hitoshi , Xie Shang‐Ping
Published: September 2002

In boreal winter, subtropical westerlies in the upper troposphere reach maxima in speed over the eastern edges of the Asian and North American continents. The zonal variations in the westerlies are generally attributed to large‐scale orography and thermal forcing, but the latter mechanism remains largely unsubstantiated. Here we conduct general circulation model (GCM) experiments without orography to identify the most important thermal forcing for generating zonal asymmetries in subtropical westerlies. By changing sea surface temperature (SST) distribution in the GCM, we find that the tropical SST distribution plays a decisive role in producing a subtropical jet core to the north of the tropical warm water pool, while the effects of extratropical continent‐ocean heating contrast on upper‐level zonal wind speed distribution are secondary. The results from Aqua Planet runs further support this conclusion.
ENSO's impact on the annual cycle: The view from Galápagos
Authors: Hartten Leslie M. , Gage Kenneth S.
Published: September 2002

UHF profiler observations of lower tropospheric winds at San Cristóbal in Ecuador's Galápagos Islands commenced in October 1994. The available data give a detailed picture of the lower troposphere‧s annual cycle over this portion of the East Pacific cold tongue. The profiler tracks the low‐level southerly wind maximum from its weakest state in austral summer, when it may briefly rise above 1 km, to its strongest state mid‐year, when it is often found below 400 m. The profiler operated during much of the 1997–98 El Niño and gives us an unprecedented look at dramatic changes in the flow over the cold tongue during a warm event. The seasonal deepening of the low‐level flow was enhanced as the ITCZ moved into the Southern Hemisphere for a few months and the lower tropospheric winds became northerly.
New geophysical constraints on the deep structure of the Pyrenees
Authors: Ledo Juanjo , Ayala Conxi , Pous Jaume , Queralt Pilar , Marcuello Alex , Muñoz Josep A.
Published: September 2002

A 2D modeling of geoid/quasigeoid data across the Pyrenees is consistent with electromagnetic images of the Pyrenean lithospheric structure, showing a subducted Iberian lower crust. Using new magnetotelluric data acquired through the orogen, a 3D electrical conductivity model of the Pyrenean lithospheric structure is obtained. The most outstanding feature is the presence of a high conductivity zone at lower crustal depths along the orogen in the contact zone between the Iberian and European plates. The integration of various geophysical parameters suggests that the simplest and most reasonable mechanism to explain the observed data is partial melting of the subducted Iberian lower crust.
An inter‐hemisphere comparison of the persistent stratospheric polar vortex
Authors: Zhou Shuntai , Gelman Melvyn E. , Miller Alvin J. , McCormack John P.
Published: September 2002

Based on 19 years (1979–1998) of NCEP/NCAR reanalyses data and potential vorticity (PV) area diagnostics, we found that in the southern hemisphere (SH) the polar vortex has lasted about two weeks longer in the 1990s than in the early 1980s and the northern hemisphere (NH) polar vortex has lasted four weeks longer. The SH vortex persisted within the layer (12–22 km) with almost complete ozone loss, but did not persist at higher altitudes where ozone was not depleted. However, the NH vortex persisted in a broader vertical range not limited to the ozone‐depletion layer. We show that wave activity has weakened in recent years in the NH, but not in the SH. The springtime Antarctic ozone hole seems to be the main cause for the SH polar vortex persistence, while the cause for the NH vortex persistence involves changes in polar ozone as well as changes in dynamics.
On the effect of small‐scale oceanic variability on topography‐generated currents
Authors: Álvarez A. , Hernández‐García E. , Tintoré J.
Published: September 2002

Small‐scale oceanic motions, in combination with bottom topography, induce mean large‐scale along‐isobaths flows. The direction of these mean flows is usually found to be anticyclonic (cyclonic) over bumps (depressions). Here we employ a quasigeostrophic model to show that the current direction of these topographically induced large‐scale flows can be reversed by the small‐scale variability. This result addresses the existence of a new bulk effect from the small‐scale activity that could have strong consequences on the circulation of the world's ocean.
Ancient Martian nitrogen
Authors: Marti K. , Mathew K. J.
Published: September 2002

The isotopic signatures and elemental ratios of nitrogen, argon and xenon determined in shock‐melted glass in shergottite meteorites were found to closely resemble the Viking spacecraft data for the present Martian atmosphere. Searches for early signatures, before the Martian atmosphere was subjected to fractionation mechanisms, can be carried out on Martian meteorite ALH84001 and show that nitrogen signatures are incompatible with those of the present atmosphere. We report here the identification of two ancient, a distinctly light and an only slightly evolved, nitrogen isotopic signatures (δ15N = −30‰ and +4‰, respectively), as well as a correlation with the isotope ratio 129Xe/132Xe. Since this ratio evolved rapidly during the early history, due to the short (16 million year) half‐life of the extinct precursor 129I, it serves as a useful time marker.
Borehole electrokinetic responses in fracture dominated hydraulically conductive zones
Authors: Worthington M. H. , Hunt Craig W.
Published: September 2002

Electrokinetic borehole logging experiments conducted in fracture dominated Devonian metasediments and Carboniferous limestone boreholes containing dissolution discontinuities, indicate a strong relative amplitude correlation between a downhole electrokinetic response and previously obtained hydrogeological data for the respective boreholes. Voltages in the range 0.2–1.5 volt were recorded per MPa of gauge pressure induced in the borehole fluid. A relationship between fracture aperture and the frequency content of the electrical data has also been observed.
Observed albedo decrease related to the spring snow retreat
Authors: Kuang Zhiming , Yung Yuk L.
Published: September 2002

We study the impact of the spring snow retreat on albedo from 1979 to 1991 using the ultraviolet (UV) reflectivity measured by the Total Ozone Mapping Spectrometer (TOMS). Over the Northern Hemisphere (NH) snowy land area that was snow covered at least once during this period, we find a 1.5% decrease over the 13 years in the springtime UV reflectivity, related to a 5 × 106km² decrease in the satellite derived spring snow cover. About half of the reflectance decrease occurred over regions where snow cover and reflectance correlate at a 99% significance level. The 1.5% UV reflectivity decrease corresponds to a 1% decrease in the visible albedo over the snowy region, and a ∼2 Wm−2 increase in the shortwave heating when averaged over the entire NH land. Based on observed interannual reflectivity changes over the entire NH snowy land area, our study provides a direct constraint on the shortwave forcing of the spring NH snow retreat.
Absorption of solar energy in cloudless and cloudy atmospheres over Germany and in GCMs
Authors: Wild Martin
Published: September 2002

Clear‐sky and all‐sky shortwave atmospheric absorption in several General Circulation Models (GCM) is assessed using observational data from selected sites in Germany. Estimates of shortwave absorption in the atmosphere are obtained by combining surface clear‐sky and all‐sky climatologies derived from the ground observations with collocated top of atmosphere (TOA) clear‐sky and all‐sky fluxes from the Earth Radiation Budget Experiment (ERBE). It is shown that the atmospheric absorption in the cloud‐free atmosphere is on average 12 Wm−2 too low in the GCMs. GCMs which include state‐of‐the‐art radiation schemes and aerosol effects may be able to eliminate a large part of this clear‐sky bias. The model‐calculated absorption in the cloudy (all‐sky) atmosphere is generally not significantly enhanced compared to the cloud‐free atmosphere. This is in line with the observational estimates which are similar under all‐sky and clear‐sky conditions, indicating that the presence of clouds does not substantially alter the absorption of solar radiation within the atmospheric column. The observations therefore do not support recent arguments that clouds in GCMs absorb insufficient solar radiation.
Physical properties of the Indian aerosol plume derived from six‐wavelength lidar Observations on 25 March 1999 of the Indian Ocean Experiment
Authors: Müller Detlef , Wagner Frank , Althausen Dietrich , Wandinger Ulla , Ansmann Albert
Published: September 2002

A major pollution outbreak from the Indian subcontinent was observed with a six‐wavelength aerosol lidar at Hulule island (4.1°N, 73.3° E) on 25 March 1999 during the Indian Ocean Experiment. From the observed backscatter and extinction data, vertical profiles of physical particle properties were determined. Effective radii between 0.14 and 0.22 µm, complex refractive indices of about 1.65 in real part and between 0.03i and 0.08i in imaginary part, and single‐scattering albedos between 0.79 and 0.86 at 532 nm suggest anthropogenic activities and biomass burning as source of the particles. First estimates from radiative‐transfer calculations show a cooling of −6.4 W/m² at the top of the atmosphere and −70 W/m² at ground level.
A Box Model for the paleoceanography of the Black Sea
Authors: Karaca M. , Wirth A. , Ghil M.
Published: September 2002

The evolution of the Black Sea's salinity after the opening of the Bosporus about 7500 years ago is investigated using a simple two‐box model. The model consists of watermass and salt conservation equations, and allows for changes in halocline depth. The paleoceanographic box model is forced by present‐day Mediterranean inflow and outflow, and atmospheric forcings. Analytic solutions for the evolution of the box volumes are given. Model salinities reach 90% of their the present‐day values in both boxes about 2,500 years after the opening of the Bosporus. The evolution of the salinities is shown to be almost independent of the evolution of the box volumes, and the results are compared with the existing paleoceanographic proxy records.
Two‐year (1996/1997) ozone DIAL measurement over Dumont d'Urville (Antarctica)
Authors: Santacesaria Vincenzo , Stefanutti Leopoldo , Morandi Marco , Guzzi Donatella , MacKenzie A. Robert
Published: September 2002

Two years of ozone measurements (1996, 1997), sorted according to the analysed potential vorticity over Dumont d'Urville (66 °S), are presented. Subsidence in the vortex was observed by tracing the descent of the ozone maximum. Chemical depletion was also observed. In springtime, the ozone mixing ratio was reduced by a factor 10 on isentropes between about 400 K and 475 K. Using the observations of descent and depletion, it is shown that, at the latitude of Dumont d'Urville, chemical depletion starts close to mid‐winter. Depletion starts earlier at higher altitudes (above 450 K) than at lower altitudes (below 450 K). The earlier presence of Polar Stratospheric Clouds (PSCs) at higher altitudes than at lower altitudes is a likely reason. The mid‐winter maximum in Antarctic total ozone columns [Roscoe et al., 1997] is then due to the integrated effect of these phase‐shifted maxima on the various isentropic surfaces.
Decadal‐scale variability in long‐range atmospheric transport to the Summit of the Greenland Ice Sheet
Authors: Kahl Jonathan D. W. , Galbraith Jennifer A. , Martinez Dewayne A.
Published: September 2002

Ice cores extracted from the Summit of the Greenland Ice Sheet date to >110 kyr b.p. and reveal fluctuations in chemical and physical characteristics on time scales ranging from days to millenia. Long‐range atmospheric transport patterns contribute substantially to variability in both airborne and snow‐deposited chemical species, and are thus one of the most important considerations in assessing climate variability preserved in polar ice cores. Here we present new evidence of decadal‐scale climate variability through an analysis of 44 years of modeled, 10‐day air trajectories arriving daily at Summit, Greenland. Trajectory residence times over specific upwind regions reveal interannual oscillations with periods of 4–14 years, and are correlated with three climate teleconnection indices. Our results suggest that the observed link between upstream source regions and the phases of large‐scale climate oscillations may be exploited to further understand paleoclimatic oscillations.
Stratified shear turbulence: Evolution and statistics
Authors: Werne Joseph , Fritts David C.
Published: September 2002

The highest‐resolution 3D direct numerical simulations to date of Kelvin‐Helmholtz instability are reported. The ensuing turbulence spans a broad range of spatial scales and exhibits Kolmogorov spectra in horizontal planes. Non‐Gaussian statistics are observed, with highly intermittent entrainment zones at the edges of the resulting shear layer. Profiles of the local gradient‐Richardson number are presented and shown to remain less than 1/4 throughout the entire evolution of the turbulence.
Type I PSC‐particle properties: Measurements at ALOMAR 1995 to 1997
Authors: Mehrtens Hela , von Zahn Ulf , Fierli Federico , Nardi Bruno , Deshler Terry
Published: September 2002

Polar stratospheric clouds (PSC) were observed above Andenes, Norway (69°N, 16°E) with the ALOMAR Rayleigh/Mie/Raman‐Lidar during three winters and with an optical particle counter on two occasions. Multiwave‐lengths measurements allow the derivation of the parameters of a monomodal particle size distribution and the derivation of volume densitiespaper if the refractive index is known. The particle counter results are used to determine the best refractive index value. The relation of volume density to temperature is compared to thermodynamic models. This confirms that the PSCs observed consist mainly of a ternary solution with low water content. PSC Type I a and I b can be distinguished by backscatter ratio, color ratio and cooling rate.