bluuebunny/crossref_metadata_2025 huggingface dataset:
optical properties of PSC Ia‐enhanced at UV and visible wavelengths: Model and observations
Authors: Reichardt J. , Tsias A. , Behrendt A.
Published: September 2002

Model calculations suggest that PSC‐Ia optical properties measured by lidar at ultraviolet and visible wavelengths are strongly correlated; particle depolarization ratios and backscatter coefficients are 17% smaller and 41% larger at a wavelength of 532 nm than at 355 nm, respectively. The model relations are used to compute 532‐nm particle backscatter and depolarization ratios from 355‐nm lidar data of a PSC Ia‐enhanced, i.e., a PSC of type Ia with unusually high backscatter ratios, measured with a UV Raman lidar over Esrange, Sweden (67.9° N, 21.1° E), on 20 Jan 1997. The calculated optical properties agree well with lidar observations at 532 nm of this PSC type.
Verification of the consistency of POLDER Aerosol Index over land with ATSR‐2/ERS‐2 fire product
Authors: Goloub Philippe , Arino Olivier
Published: September 2002

The remote sensing of aerosol over land remains a difficult task. Global distribution of polarizing aerosols (urban, industrial, smoke particles) are obtained, over land, from POLDER/ADEOS‐1 visible and near‐infrared measurements. In the paper, we study the correlation between POLDER aerosol index retrieved over land from polarimetric measurements and fire products derived from ATSR‐2/ERS‐2 3.7 µm channel. At global scale, fire patterns and aerosol index distributions agree well. A selection of 9 continental sites distributed in Africa, America and Asia have been studied. Monthly variations of aerosol index as well as fire occurence are presented. A good correlation is observed, in tradional biomass burning regions, between aerosol index monthly average and fire count. These results clearly demonstrate POLDER capability to monitor biomass burning aerosol and also suggests polarizing aerosol presence in countries such as India or China.
Flow rates and duration within Kasei Valles, Mars: Implications for the formation of a Martian Ocean
Authors: Williams Rebecca M. , Phillips Roger J. , Malin Michael C.
Published: September 2002

Calculated maximum discharges for the largest outflow channel system on Mars, Kasei Valles, based on elevation data from the Mars Orbiter Laser Altimeter (MOLA), are 2 to 4 orders of magnitude lower (8 × 104 – 2 × 107 m³ s−1) than estimated previously. Mars Orbiter Camera (MOC) images show morphological evidence consistent with these relatively modest flow rates. Topographic profiles of the outflow channels reveal previously unrecognized narrow, inner channels. Development of a sapping channel network between flow events suggests the system was active over a significant period of time and likely involved several separate flood events. The longer formation history and lower discharge rates may require a long fill time (>25 years) and a warmer climate to form a martian ocean.
Scales of response of the convective boundary layer to land‐surface heterogeneity
Authors: Baidya Roy Somnath , Avissar Roni
Published: September 2002

The convective boundary layer (CBL) over domains with meso‐γ‐scale (2–20 km) heterogeneity is characterized by preferentially located, organized rolls of characteristic size equivalent to the length‐scale of the heterogeneity. Additionally, random turbulent thermals also develop when the length‐scale of the heterogeneity exceeds 5–10 km. This is due to a complex interaction between the horizontal pressure gradient generated by the heterogeneity and the buoyancy forcing. Consequently, the corresponding wavelet spectrum exhibits two peaks — one representing the turbulent thermals at a characteristic scale of about 1.5 times the CBL height and another denoting the organized eddies at a scale similar to that of the heterogeneity. This implies that subgrid‐scale parameterizations in models with grid size larger than 5–10 km, which account only for random turbulence, are inadequate for heterogeneous domains. Also, this study may provide a more objective classification of scales of atmospheric processes.
The North American Monsoon System in the Hadley Centre Coupled Ocean‐Atmosphere GCM
Authors: Arritt Raymond W. , Goering Dustin C. , Anderson Christopher J.
Published: September 2002

The North American monsoon system (NAMS) as represented in the second‐generation Hadley Centre coupled ocean‐atmosphere model is examined using high‐time‐resolution (six‐hourly) records of model output. A current‐climate simulation gives a realistic depiction of the NAMS, with date of onset and precipitation trends agreeing with observations. The model reproduces the observed negative relationship between precipitation over the southwestern U.S. and that over the central U.S. Changes in tropospheric circulation and moisture after onset are consistent with observed changes although mid‐level moistening is less than is observed. An enhanced greenhouse‐gas simulation gives higher precipitation and stronger tropospheric dynamical and moisture changes after onset.
Predictable winter climate in the North Atlantic sector during the 1997–1999 ENSO cycle
Authors: Dong B. ‐W. , Sutton R. T. , Jewson S. P. , O'Neill A. , Slingo J. M.
Published: September 2002

The winters of 1997/98 and 1998/99 were marked by strikingly different weather conditions over the North Atlantic ocean and adjacent continents. We use a state‐of‐the‐art atmospheric general circulation model forced with observed sea surface temperatures (SSTs) to investigate the hypothesis that the anomalous conditions in the North Atlantic sector during the winters of 97/98 and 98/99 were related to the ENSO cycle and were therefore potentially predictable. We demonstrate that the major circulation anomalies observed in the North Atlantic sector are reproducible in both winters. We show further that these circulation anomalies were forced primarily by ENSO‐related SST anomalies in the Pacific Ocean, but that SST anomalies in the Atlantic Ocean also had an influence. Our results are encouraging for the prospects of useful seasonal predictions for wintertime in the North Atlantic sector.
A slow thrust slip event following the two 1996 Hyuganada Earthquakes beneath the Bungo Channel, southwest Japan
Authors: Hirose Hitoshi , Hirahara Kazuro , Kimata Fumiaki , Fujii Naoyuki , Miyazaki Shin'ichi
Published: September 2002

We report a “slow thrust slip event” that occurred beneath the Bungo Channel region, southwestern Japan. On Oct. and Dec., 1996, two Hyuganada earthquakes (both Mw = 6.7), followed by afterslips, occurred. In addition, a crustal movement characterized by an extremely slow rise was observed around the Bungo Channel, about 200 km north from the epicenters, and continued for about 300 days long. Assuming a slow slip on the plate boundary, we estimate its duration and surface displacements from GPS time series data by curve‐fitting, and then, determine the fault slip distribution. We found that a slow slip without any earthquakes continued for nearly one year and released the seismic moment comparable to that of the Hyuganada earthquakes. Occurrence of the slow thrust slip event suggests that this kind of event may be a characteristic mode of stress release at a transition region of interplate coupling.
Importance of salinity measurements in the heat storage estimation from TOPEX/POSEIDON
Authors: Sato Olga T. , Polito Paulo S. , Liu W. Timothy
Published: September 2002

Sea surface height anomalies from satellite altimeter data are used to estimate heat storage. Since variability in sea surface height is mostly due to expansion and contraction of the water column it can be correlated with variations in the heat and salt content. Therefore, estimation of heat storage from altimeter data, when compared to in situ estimates, requires corrections for the haline effect. Three sites with a nearly continuous time series of temperature and salinity profiles simultaneous with TOPEX/POSEIDON data are studied: HOT, CalCOFI and Hydrostation “S”. Haline corrections based on in situ and climatological salinity measurements are contrasted. For the studied regions, the haline corrections based on climatology provide equivalent or worse results than not applying a correction at all. The use of in situ salinity estimates decreased the differences between the heat storage estimates (up to 17 × 107 J m−2) and significantly improved their correlation (up to 0.18).
Absorption cross‐section measurements of water vapour and oxygen at 185 nm. Implications for the calibration of field instruments to measure OH, HO2 and RO2 radicals
Authors: Creasey David J. , Heard Dwayne E. , Lee James D.
Published: September 2002

Absorption cross sections for oxygen and water vapour were measured using a low‐pressure mercury lamp optically filtered to isolate the emission close to 184.9 nm. The cross‐sections were determined for conditions typically used in the calibration of OH, HO2 and RO2 field instruments that employ photolysis of water vapour as a radical source, and O2 absorption as the actinometer for lamp flux. For water vapour, an absorption cross‐section of 7.22 (± 0.22) × 10−20 cm² molecule−1 was determined at 25°C, in excellent agreement with recent studies, but ∼30% higher than the recommended value. The absorption cross‐section for O2 was found to vary with the O2 column and the choice and operating current of the lamp, reinforcing the requirement that practitioners of OH, HO2 and RO2 field measurements who calibrate by this method should measure effective O2 cross‐sections at frequent intervals under their particular field conditions.
The effect of clouds and surface albedo on UV irradiances at a high latitude site
Authors: Kylling A. , Dahlback A. , Mayer B.
Published: September 2002

At high latitudes the Earth's surface is covered by snow large parts of the year. In spring the snow cover significantly increases UV radiation for cloudless as well as cloudy situations. In Tromsø (69.65° N, 18.95° E), Norway, independent measurements have been made of the effective regional spectral surface albedo, the total ozone column, the effective cloud optical depth, and the surface UV irradiance. These measurements are used together with model simulations to study the effect of snow and clouds on surface erythemal radiation doses. Snow on the surface increases the monthly erythemal doses by more than 20%. Relative to cloudless sky, the clouds reduce the monthly erythemal doses by 20–40%. During snow free conditions monthly doses derived from Earth Probe/Total Ozone Mapping Spectrometer (EP‐TOMS) total ozone and cloud reflectivity agree with the measurements within the experimental uncertainties. In presence of snow, however, the EP‐TOMS derived data are too low by 30–40% due to snow covered surfaces being misinterpreted as clouds.
An El‐Nino Prediction System using an intermediate ocean and a statistical atmosphere
Authors: Kang In‐Sik , Kug Jong‐Seong
Published: September 2002

An El‐Nino prediction model is developed based on an intermediate ocean model similar to the Cane and Zebiak (CZ) and a statistical atmosphere model. The present ocean model differs from CZ in the parameterization of sub‐surface temperature and the basic state. The predictability skill of the present model is better than that of CZ. The better performance is particularly distinctive for early stage of the prediction everywhere in the domain and in the central Pacific for all period of prediction. It is suggested that the better performance for the early stage is due to the use of SST anomalies in the initialization, and the better performance in the central Pacific results from a better representation of subsurface temperature in the present model.
Evaluating ozone depletion from very short‐lived halocarbons
Authors: Olsen Seth C. , Hannegan Bryan J. , Zhu Xin , Prather Michael J.
Published: September 2002

A new approach is needed for calculating the ozone depletion potential (ODP) of short‐lived gases with mean lifetimes less than 100 days. Clearly, the ozone loss from such gases depends strongly on the location and season of emissions. It is proposed that delivery to the tropical tropopause is a surrogate for the amount of halogen entering the stratosphere. Thus 3‐D global models, with accurate simulation of tropospheric chemistry and transport, can calculate the ODP specific to tropical sources (high) and high‐latitude sources (low). The ODP of CH2BrCH2CH3 from this analysis ranges from 0.0002 to 0.06 depending on the location and season of emissions.
Effect of ENSO and the MJO on western North Pacific tropical cyclones
Authors: Sobel Adam H. , Maloney Eric D.
Published: September 2002

Prior work has suggested that Rossby wave accumulation in the lower troposphere may be an important mechanism for the development of synoptic‐scale disturbances in the western north Pacific in northern summer. This work examines the intraseasonal and interannual variability of wave accumulation by computing the barotropic wave activity flux divergence at 850 hPa for different phases of the Madden‐Julian oscillation (MJO) and El Niño/southern oscillation (ENSO). Indirectly, and without ruling out other influences, the results suggest a physical mechanism behind previously identified relationships between tropical cyclogenesis statistics and these two modes of variability (MJO and ENSO).
4‐Chlorocrotonaldehyde as a unique chlorine‐containing compound from the reaction of atomic chlorine with 1,3‐butadiene in air at room temperature
Authors: Wang Weihong , Finlayson‐Pitts Barbara J.
Published: September 2002

Chlorine atoms may play an important role in the tropospheric chemistry of coastal areas and the Arctic at polar sunrise. However, the sources of chlorine are not well established and measuring its precursors in a specific manner is difficult. A potential approach to probe Cl production in the troposphere is to identify and measure chlorine‐containing products unique to the reactions of Cl with organics in air, e.g. 1,3‐butadiene, which is emitted from motor vehicles. We present here product studies of the reaction of Cl with 1,3‐butadiene in the presence and absence of NO in 1 atm air at room temperature using FTIR, API‐MS and GC‐MS. 4‐Chlorocrotonaldehyde (CCA) is identified as a unique chlorine‐containing product from this reaction, with a yield of (28 ± 8)% (2σ) independent of the presence of NO. CCA may therefore be useful in field studies as a marker for Cl chemistry in urban coastal areas.
Low mantle heat flow at the edge of the North American Continent, Voisey Bay, Labrador
Authors: Mareschal J. C. , Poirier A. , Rolandone F. , Bienfait G. , Gariépy C. , Lapointe R. , Jaupart C.
Published: September 2002

Heat flow measurements in 4 deep drillholes near Voisey Bay, Labrador, have yielded the lowest value ever reported in the Canadian Shield, 22 mW m−2. This very reliable estimate is also one of the lowest continental heat flow values world wide. It requires the crust to be very poor in radioelements in this part of the Archean Nain Province. It also strongly supports the view that mantle heat flow is low (<15 mW m−2) throughout the Canadian Shield, with no trend of increasing mantle heat flow near the edges of the continent. It also raises questions about the controlling mechanism for rifting and the opening of the Labrador Sea at 100 Ma.
Seismological evidence for the existence of serpentinized wedge mantle
Authors: Kamiya Shin'ichiro , Kobayashi Yoji
Published: September 2002

Serpentinized peridotite is detected seismologically by mapping Poisson's ratio beneath the Kanto district, central Japan, because serpentinite has a higher Poisson's ratio than other rocks in the crust and upper mantle. We determine three‐dimensional P and S wave velocity models using travel time tomography and then construct a three‐dimensional map of Poisson';s ratio. The models show low velocity anomalies near the upper boundary of the slab in a depth range from 20 to 70 km. In the low velocity region, there is an area with Poisson's ratio greater than 0.3 at depths of 20–45 km, which we attribute to serpentinized peridotite. The rest of the low velocity region is interpreted as descending oceanic crust with a Poisson's ratio of about 0.25. The high Poisson's ratio area is associated with low seismicity and weak interplate coupling, which is consistent with the ductility of serpentinite.
Ecosystem dynamics and the Sahel Drought
Authors: Wang Guiling , Eltahir Elfatih A. B.
Published: September 2002

The Sahel region in West Africa has been experiencing a persistent drought throughout the last three decades. Here, we present a new perspective on the underlying physical mechanism behind this phenomenon. We use a coupled biosphere‐atmosphere model including explicit representation of ecosystem dynamics to demonstrate that, regardless of the nature of the initial forcing, the natural response of the local grass ecosystem to the dry conditions of the late 1960s played a critical role in maintaining the drought through the following decades. The onset of the drought has been marked by a forced shift from a self‐sustaining wet climate equilibrium to a similarly self‐sustaining but dry climate equilibrium.
Chemiion concentration measurements in jet engine exhaust at the ground: Implications for ion chemistry and aerosol formation in the wake of a jet aircraft
Authors: Arnold F. , Kiendler A. , Wiedemer V. , Aberle S. , Stilp T. , Busen R.
Published: September 2002

Total positive chemiion concentrations n in jet engine exhaust at the ground were measured using an electrostatic probe. Data were obtained for two different engines (RR M45H and JT9D‐7) for one power setting (half thrust), two fuel sulfur contents (2 and 66 ppmm), and four distances d (1.39, 2.19, 4.19, and 18.6 m) behind the engines. The corresponding plume ages tp ranged from about 12 to 170 ms. As tp increases n decreases steeply from 1.6×108 cm−3 at tp = 12 ms to 3×106 cm−3 at tp = 170 ms. We conclude that this decrease mostly reflects ion removal by ion‐ion recombination with a mean rate coefficient of about 7.5×10−7 cm³/s. Our experimental findings have interesting implications for the chemical evolution and potential roles of chemiions in jet engine exhaust plumes. These implications are briefly addressed.
Pore scale study of flow in porous media: Scale dependency, REV, and statistical REV
Authors: Zhang Dongxiao , Zhang Raoyang , Chen Shiyi , Soll Wendy E.
Published: September 2002

Flow in porous media is studied at the pore‐scale with lattice Boltzmann simulations on pore geometries reconstructed from computed microtomographic images. Pore scale results are analyzed to give quantities such as permeability, porosity and specific surface area at various scales and at various locations. With this, some fundamental issues such as scale dependency and medium variability can be assessed quantitatively. More specifically, the existence and size of the well known concept, representative elementary volume (REV), can be quantified. It is found that the size of an REV varies spatially and depends on the quantity being represented. For heterogeneous media, a better measure may be the so called “statistical REV”, which has weaker requirements than does the deterministic REV.
Quantitative analysis and scaling of sheared granitic magmas
Authors: Koenders M. A. , Petford Nick
Published: September 2002

We present a quantitative treatment of the macroscopic behaviour of a sheared granitic magma using Biot's theory [Biot, 1941] and a shear‐dilatancy sensitive material model for the solids. The calculations are relevant to a magma in the solidosity range 0.55–0.7. The resulting excess pore pressure distribution is a function of the position and the time. Results are presented in graphical form. A scaling emerges that enables the results to be presented in non‐dimensional form. A sensitivity study is carried out of the parameters describing the rheology of the solid matrix (including permeability features). The model enables the estimate of pressure and flow rates, thus opening a way of understanding the features in the granite crystal mush that are caused by upflowing magma. At high strain rates (10−10S−1) flow rates due to shear far exceed melt movement due to buoyancy effects.
Direct observations of skin‐bulk SST variability
Authors: Murray M. J. , Allen M. R. , Merchant C. J. , Harris A. R. , Donlon C. J.
Published: September 2002

Skin sea‐surface temperatures from the first Along Track Scanning Radiometer (ATSR) are compared with coincident bulk temperatures from the Tropical Atmosphere Ocean (TAO) moored buoy array in the equatorial Pacific Ocean. The response of the skin‐bulk sea‐surface temperature difference (ΔT) to variations in wind speed and surface heat flux is examined. The use of remotely‐sensed skin temperatures for this purpose is enabled by ATSR's unique design which permits the independent retrieval of ocean skin temperature to an accuracy of 0.3 K. For the four‐year period considered (August 1991–August 1995), almost 6000 coincident skin and bulk sea surface temperature (SST) measurements were available; at night, the mean value of ΔT is −0.20±0.46K, with a daytime mean value of +0.05 ± 0.51 K. ΔT is found to depend on both net heat flux and local wind speed as predicted by the Saunders [1967] model and other formulations, and an estimate of the Saunders λ parameter is obtained.
Measurements of iodine monoxide (IO) above Spitsbergen
Authors: Wittrock F. , Müller R. , Richter A. , Bovensmann H. , Burrows J. P.
Published: September 2002

Zenith sky measurements of scattered light have been made at Ny‐Ålesund, Spitsbergen (79°N, 12°E) since the beginning of 1995. A differential optical absorption spectroscopy (DOAS) algorithm has been used to retrieve differential slant column densities (DSCD) of IO for the observations from 1995–1998. IO was detected every year for several days within each month. Model simulations result in an estimated stratospheric IO mixing ratio in the range from 0.65 to 0.80 (±0.2) pptv in polar spring 1997. In addition, indications for the presence of tropospheric IO have been found in late spring and summer of each year.
Ultrafine aerosol formation via ion‐mediated nucleation
Authors: Yu Fangqun , Turco Richard P.
Published: September 2002

The role of background ionization in the generation and evolution of ultrafine atmospheric particles is developed through modeling and data analysis. It is found that charged molecular clusters condensing around natural air ions can grow significantly faster than corresponding neutral clusters, and thus preferentially achieve stable, observable sizes. Detailed microphysical simulations of this process seem to explain recent measurements of ultrafine particle behavior, as well as the diurnal variation seen in tropospheric mobility spectra. The proposed ion‐mediated nucleation mechanism leads to the production of new particles under conditions that are unfavorable for binary homogeneous nucleation, and provides a consistent explanation for a variety of tropospheric observations.
Intercomparison of NO2 photolysis frequency measurements by actinic flux spectroradiometry and chemical actinometry during JCOM97
Authors: Kraus Alexander , Rohrer Franz , Hofzumahaus Andreas
Published: September 2002

A first intercomparison of JNO2 measurements by actinic flux spectroradiometry (SR) and chemical actinometry (CA) was performed in summer 1997 in Jülich, Germany. During this experiment (JCOM97) a large set of data was collected with a time resolution of ∼ 1 min, showing a high linear correlation (R = 0.998) in JNO2. Linear regression indicates a good absolute agreement with the CA being 6% higher than SR if the quantum yield recommended by NASA/JPL (1997) and recently published data of the NO2 absorption spectrum (σNO2) is used for the evaluation of the SR‐data. The influence of using previously published σNO2 data is discussed. Overall the comparison suggests that JNO2 can be measured by either CA or SR with an accuracy of better than 10%.
Coseismic spring flow changes associated with the 1995 Kobe Earthquake
Authors: Sato Tsutomu , Sakai Ryutaro , Furuya Kazuo , Kodama Toshio
Published: September 2002

Flow rate in many springs increased rapidly after the 1995 Kobe earthquake, which is likely caused by permeability enhancement. The flow rates at nine springs on Awaji Island near Kobe from 1995 to 1998 reveals that the enhancement of flow rate gradually decreased exponentially within two years. The enhanced hydraulic diffusivity of the aquifer is estimated at from 130 to 2,300 cm²/s by using a very simple diffusional model. About seven‐fold increase in spring flow rate and permeability due to the earthquake is inferred from the analysis.
Definition of Antarctic Oscillation index
Authors: Gong Daoyi , Wang Shaowu
Published: September 2002

Following Walker's work about his famous three oscillations published during the 1920–30s, many papers were written about atmospheric oscillations. A fourth atmospheric oscillation in the middle and high southern latitudes was found, and named the Antarctic Oscillation (AO). AO refers to a large scale alternation of atmospheric mass between the mid‐latitudes and high latitudes surface pressure. In order to understand the spatial structure of sea level pressure variation in detail, empirical orthogonal function analysis is applied. An objective index of the Antarctic Oscillation Index (AOI) is defined as the difference of zonal mean sea level pressure between 40°S and 65°S. The AOI has the potential for clarifying climate regimes in the southern hemisphere, similar to how the NAO and the NPO has been used in the northern hemisphere.
The relationship between tropical CO2 fluxes and the El Niño‐Southern Oscillation
Authors: Rayner Peter J. , Law Rachel M. , Dargaville Roger
Published: September 2002

This paper summarizes some features of the interannual variability of tropical CO2 sources during 1980–95. Sources are derived from inversion of atmospheric concentration and isotopic data using three different techniques and two different transport models. We show that the tropical source is significantly correlated with the SOI. Composite CO2 sources for ENSO events show an initial negative anomaly followed by a positive anomaly. We tentatively attribute the negative anomaly to the ocean and the positive anomaly to a terrestrial response.
The influence of the IMF By component on the location of pulsed flows in the dayside ionosphere observed by an HF radar
Authors: Provan G. , Yeoman T. K. , Cowley S. W. H.
Published: September 2002

A study has been performed on the effect of the By and Bz components of the Interplanetary Magnetic Field (IMF), as measured by the WIND satellite, on the occurrence of pulsed ionospheric flows as observed by the CUTLASS Finland radar. These flows have been suggested as being created at the ionospheric footprint of newly reconnected field lines. The statistical location of the pulsed flows is strongly dependent on the IMF By component, moving to the pre‐noon sector during intervals of positive By and into the post‐noon sector for intervals of negative By. These results directly confirm previous predictions, demonstrating that during intervals of flux transfer at the magnetopause, pulsed ionospheric convective flows are initiated. In the northern hemisphere these flows are shifted about noon in the opposite sense to the IMF By component, consistent with the average ionospheric convection pattern.
Sequential atmospheric profiles near a fixed location derived from GPS‐LEO occultation measurements
Authors: Yan Haojian , Huang Dong , Huang Cheng
Published: September 2002

We discuss a method to obtain daily sequential atmospheric profiles near a fixed Earth location by the optimal selection of a satellite in a Low Earth Orbit (LEO). The simulations have shown the possibility to design a LEO that can control the drift of sounding locations to be less than 100 km for periods of 60–200 days. An optimal LEO satellite selection may have practical applications for regional weather prediction and climate analysis.
Secular gravitational instability of a compressible viscoelastic sphere
Authors: Hanyk Ladislav , Matyska Ctirad , Yuen David A.
Published: September 2002

For a self‐gravitating viscoelastic compressible sphere we have shown that unstable modes can exist by means of the linear viscoelastic theory by both initial‐value and normal‐mode approaches. For a uniform sphere we have derived analytical expressions for the roots of the secular determinant based on the asymptotic expansion of the spherical Bessel functions. From the two expressions, both the destabilizing nature of gravitational forces and the stabilizing influences of increasing elastic strength are revealed. Fastest growth times on the order of ten thousand years are developed for the longest wavelength. In contrast, a self‐gravitating incompressible viscoelastic model is found to be stable. This result of linear approximation suggests that a more general approach, e.g., non‐Maxwellian rheology or a non‐linear finite‐amplitude theory, should be considered in global geodynamics.
Temperature and pressure dependent kinetics of the gas‐phase reaction of the hydroxyl radical with nitrogen dioxide
Authors: Dransfield Timothy J. , Perkins Katherine K. , Donahue Neil M. , Anderson James G. , Sprengnether Michele M. , Demerjian Kenneth L.
Published: September 2002

The reaction of OH with NO2 is pivotal in both stratospheric and tropospheric chemistry; in each case it is the dominant homogeneous mechanism for conversion of NOx to NOy. The rate constant is a strong function of pressure and temperature, and key portions of the pressure‐temperature domain are poorly or ambiguously covered by the available data. These include conditions typical of the tropospheric boundary layer and of the lower stratosphere. At surface conditions differences of 60% exist both in the literature data and between the major recommendations, while at lower stratospheric conditions there are few available data. Our High Pressure Flow kinetics system is ideally suited to studying this reaction, as we are able to scan both temperature and pressure while maintaining wall‐less conditions, eliminating the possible complications of heterogeneous chemistry. Here we report a temperature‐ and pressure‐dependent study (220–300 K, 50–150 torr) of this reaction; the measured rate constants are in excellent agreement with previously published values down to 240 K, but lie 10–20% lower than the historical data available below that temperature. An analysis of all available data motivates a large (∼ 20%) downward revision in the recommended rate constant below room temperature.
The influence of the diurnal tide on the O(¹S) and OH emission rates observed by WINDII on UARS
Authors: Zhang Shengpan P. , Shepherd Gordon G.
Published: September 2002

WINDII data provide the first comprehensive observations of emission rates and winds from both the O(¹S) and OH night airglows for the same time periods. The latitudinal distributions of the two nightglows are found to have a phase relationship which is dependent on season and local time. The O(¹S) emission rate has an almost permanent equatorial “trough”, but the OH emission rate has an equatorial maximum (until 4 hours local time) at equinox, and a “trough” after midnight at solstice. WINDII meridional winds show that the descending phase progression of the diurnal tide (upward propagation of tide) is correlated with the emission rate patterns of the two airglows.
Methane in the northern Atlantic controlled by microbial oxidation and atmospheric history
Authors: Rehder Gregor , Keir Robin S. , Suess Erwin , Rhein Monika
Published: September 2002

During May ‐ August, 1997, the distributions of dissolved methane and CCl3F (CFC11) were measured in the Atlantic between 50° and 60°N. In surface waters throughout the region, methane was observed to be close to equilibrium with the atmospheric mixing ratio, implying that surface ocean methane is tracking its atmospheric history in regions of North Atlantic Deep Water formation. Despite the different atmospheric history and ocean chemistry of CH4 and CFC11, their spatial distribution patterns in the water column are remarkably similar. One‐dimensional distributions have been simulated with an advection‐diffusion model forced by the atmospheric histories. The results suggest that the similar patterns result from the increasing input of CH4 and CFC11 to newly formed deep waters over time, combined with the effect of horizontal mixing and the oxidation of methane on a 50 year time scale.
Estimating present‐day postglacial rebound and horizontal movements in Fennoscandia By Repeated GPS Campaigns in 1993 and 1997
Authors: Pan Ming , Sjöberg Lars E.
Published: September 2002

A well‐known geophysical phenomenon, the postglacial rebound in Fennoscandia, is investigated by data from the Baltic Sea Level Project GPS Campaigns in 1993 and 1997. Preliminary results indicate that the estimated uplift rates vary from 1 mm yr−1 to 11 mm yr−1 with standard errors of the order of 1–3 mm yr−1, which is partly consistent with traditional terrestrial data. In addition, there is a horizontal component of plate motion of 21±1 mm yr−1 towards northeast. After subtracting the average velocity, differential horizontal velocities suggest that there is a right‐hand strike slip fault with a relative velocity of about 1.5±0.5 mm yr−1 along a N‐S direction in the middle of the Baltic Sea, which agrees with some geologists' belief of N‐S trending 1.9–1.8 Ga old strike‐slip megashears in the Baltic shield.
Heliospheric magnetic field polarity inversions at high heliographic latitudes
Authors: Balogh A. , Forsyth R. J. , Lucek E. A. , Horbury T. S. , Smith E. J.
Published: September 2002

The heliospheric magnetic field over the poles of the sun has been examined to identify intervals when the polarity of the magnetic field deviates significantly from the calculated Parker spiral, using Ulysses observations in 1994 and 1995, near solar minimum. Intervals with deviation > 90° have been identified, corresponding to magnetic field vectors pointing in the hemisphere opposite to that of the dominant polarity in the high speed solar wind originating in the polar coronal holes. The number of inversion periods decreases as the averaging period is increased from 1 to 12 hours. Their distribution was found to vary in time over the northern solar pole, where the average direction also deviated from the Parker direction. The propagation direction of waves during polarity inversions show that these are caused by large‐scale folds in the magnetic field, rather than by opposite polarity magnetic flux tubes originating near the sun.
The Central Andean Altiplano‐Puna magma body
Authors: Chmielowski Josef , Zandt George , Haberland Christian
Published: September 2002

Receiver function analysis of 14 teleseismic events recorded by 6 temporary PASSCAL broadband stations within the Altiplano‐Puna volcanic complex (APVC) shows a consistent ∼2 s negative‐polarity P‐to‐S conversion for all stations for all available azimuths. Forward modeling of the largest amplitudes suggests that this conversion is produced by the top of a very low velocity zone at a depth of ∼19 km, with a Vs <0.5 km/s and a thickness of 750–810 m. We interpret the characteristics of the low‐velocity zone (low Vs, areal extent, and flatness) to be consistent with a sill‐like magma body. On the basis of additional data from the German ANCORP experiment, the Altiplano‐Puna magma body appears to underlie much of the APVC, and it may therefore be the largest known active continental crustal magma body.
A volcanism dependent model for the extinction profile of stratospheric aerosols in the UV‐visible range
Authors: Fussen D. , Bingen C.
Published: September 2002

We present a climatological model of the extinction coefficient of stratospheric aerosols in the UV‐visible range based on SAGE II data. The model is a function of wavelength, latitude, relative altitude with respect to the tropopause and depends on the volcanism level. The vertical structure describes the tropopause region, the Junge layer and the high altitude domain. The model is shown to predict realistic extinction profiles with an reasonable accuracy.
Richtmyer‐Meshkov Instability and the Dynamics of the Magnetosphere
Authors: Wu C. C. , Roberts P. H.
Published: September 2002

When a shock wave encounters a fluid discontinuity, the interface may become unstable and form bubbles and spikes. We consider this Richtmyer‐Meshkov instability in magnetohydrodynamics through a set of numerical calculations for the magnetopause and the magnetotail configurations. We suggest that the instability may be a mechanism for generating transient events in the magnetosphere.
Extratropical subduction and decadal modulation of El Niño
Authors: Weaver Andrew J.
Published: September 2002

An extension of the Battisti/Hirst delayed oscillator model is developed in an attempt to understand the potential effects of extratropical subduction on El Niño. In particular, a meridional delay term is included to parameterise the effects of extratropical subduction on eastern equatorial Pacific pycnocline anomalies. The magnitude of the eastern equatorial pycnocline displacement, and the time delay for its response to an extratropical sea surface temperature anomaly, are inferred from both ocean and coupled atmosphere‐ocean GCM experiments. The inclusion of the delayed subduction term causes El Niño to modulate on decadal‐interdecadal timescales, consistent with observations and the expectations of Gu and Philander.
MHD simulations of the response of high‐latitude potential patterns and polar cap Boundaries to sudden southward turnings of the interplanetary magnetic field
Authors: Lopez R. E. , Wiltberger M. , Lyon J. G. , Goodrich C. C. , Papadopoulos K.
Published: September 2002

3‐D MHD simulations were used to investigate the behavior of the high‐latitude convection and the polar cap variations during two events characterized by sudden southward IMF turnings. In agreement with recent observations the simulation results indicate that the convection pattern across the entire polar cap begins to change a few minutes after the arrival of the southward IMF. In contrast, the onset of the equatorward motion of the open closed field‐line boundary depends on the local time, with equatorward motion of the midnight boundary delayed by about 20 minutes relative to the the onset of the boundary motion at noon. We interpret this delay as the time required to convect newly merged flux from the dayside to the nightside. We belive that these two different responses can reconcile apparent contradictions in studies of ionospheric reconfigurations in response to changes in the IMF.
Some doubts concerning a link between cosmic ray fluxes and global cloudiness
Authors: Kernthaler Simon C. , Toumi Ralf , Haigh Joanna D.
Published: September 2002

Svensmark and Friis‐Christensen (1997, henceforth SFC) showed a strong correlation between cosmic ray flux and ISCCP total cloudiness between 1984 and 1990. They concluded that ionisation by cosmic rays, more prevalent at times of lower solar activity, might explain apparent correlations between solar activity and climate through changes in cloud radiative forcing. We have extended SFC's approach with a study of the different cloud types, restricting our analysis to the period 1985 to 1988 during which the ISCCP calibration is believed to be stable. We find no clear relationship between individual cloud types and cosmic ray flux. Inclusion of data at high latitudes decreases the amplitude of the apparent correlation although ionisation by cosmic rays is greatest at high latitudes. Thin high cloud shows an increase throughout the period such that the combined effect of the changes in cloud types suggests an almost monotonic increase in cloud radiative forcing between 1985 and 1988 which is not related to cosmic ray activity.
Monsoon changes for 6000 years ago: Results of 18 simulations from the Paleoclimate Modeling Intercomparison Project (PMIP)
Authors: Joussaume S. , Taylor K. E. , Braconnot P. , Mitchell J. F. B. , Kutzbach J. E. , Harrison S. P. , Prentice I. C. , Broccoli A. J. , Abe‐Ouchi A. , Bartlein P. J. , Bonfils C. , Dong B. , Guiot J. , Herterich K. , Hewitt C. D. , Jolly D. , Kim J. W. , Kislov A. , Kitoh A. , Loutre M. F. , Masson V. , McAvaney B. , McFarlane N. , de Noblet N. , Peltier W. R. , Peterschmitt J. Y. , Pollard D. , Rind D. , Royer J. F. , Schlesinger M. E. , Syktus J. , Thompson S. , Valdes P. , Vettoretti G. , Webb R. S. , Wyputta U.
Published: September 2002

Amplification of the northern hemisphere seasonal cycle of insolation during the mid‐Holocene causes a northward shift of the main regions of monsoon precipitation over Africa and India in all 18 simulations conducted for the Paleoclimate Modeling Intercomparison Project (PMIP). Differences among simulations are related to differences in model formulation. Despite qualitative agreement with paleoecological estimates of biome shifts, the magnitude of the monsoon increases over northern Africa are underestimated by all the models.
Measuring ground displacements from SAR amplitude images: Application to the Landers Earthquake
Authors: Michel Rémi , Avouac Jean‐Philippe , Taboury Jean
Published: September 2002

ERS SAR amplitude images are utilized to map ground displacements from a sub‐pixel correlation method. It yields a ground two‐dimensional displacement field with independent measurements about every 128m in azimuth and 250m in range. The accuracy depends on the characteristics of the images. For the Landers test case, the 1‐σ uncertainty is 0.8m in range and 0.4m in azimuth. We show that this measurement provides a map of major surface fault ruptures accurate to better than 1km and information on coseismic deformation comparable to the 92 GPS measurements available. Although less accurate, this technique is more robust than SAR interferometry and provides complementary information since interferograms are only sensitive to the displacement in range.
Interplate coupling along the Nankai Trough off southwest Japan derived from GPS measurements
Authors: Ozawa Taku , Tabei Takao , Miyazaki Shin‐ichi
Published: September 2002

We investigate interplate coupling between the Philippine Sea and the Eurasian plates at the Nankai Trough off southwest Japan during the interseismic period. Plate coupling is modeled by imaginary backward normal slip superposed on the steady‐state subduction. We divide the plate interface into several segments, and estimate coupling on each segment from GPS horizontal velocity data. Estimated coupling is in general agreement with the rate of steady‐state subduction predicted from a plate motion model. This implies that current coupling at the Nankai Trough is so strong that much of the relative plate motion is taken up by shortening of the leading edge of the overriding plate. It seems that stronger interseismic coupling is realized on the segment where larger coseismic dislocation occurred, and vice versa. Time fluctuation of plate coupling from 1995 to 1996 is found on a small segment.
Generation of plumes under a localized high viscosity lid in 3‐D spherical shell convection
Authors: Yoshida Masaki , Iwase Yasuyuki , Honda Satoru
Published: September 2002

We conduct numerical simulations of incompressible infinite Prandtl number convection in a spherical shell with a single localized high viscosity lid (HVL) on the top surface to understand the possible effects of the continental lithosphere on plume generation. The temperature under the HVL increases rapidly after the emplacement of the HVL on constant viscosity convection with internal and bottom heatings. Later, upwellings at the bottom merge into a large scale flow and a large plume emerges under the HVL. This time‐scale depends on the existence of phase changes. In our model, whose Rayleigh number is 106, the large plume is formed on a time‐scale of 1 Gyr. A simple scaling suggests that this time‐scale may be reduced by a several times, if the Rayleigh number is around 107. Despite the complicated 3‐D thermal structure, it is dominated by an l = 1 pattern controlled by the position of the HVL.
Evidence for planetary wave effects on midlatitude backscatter and sporadic E layer occurrence
Authors: Voiculescu Mirela , Haldoupis Christos , Schlegel Kristian
Published: September 2002

In this paper a large database of midlatitude E region coherent backscatter, obtained with a 50 MHz Doppler system, is used to investigate the long‐term variability in echo occurrence. The backscatter is found to be dominated by pronounced quasi‐periodic variations with periods in the range from about 2 to 9 days that persist for time intervals from about 10 to maybe more than 20 days and have no relation to geomagnetic activity. The most commonly observed periods appear in two preferential bands, that is, the 2 to 3 day and the 4 to 6 day band. Using concurrent ionosonde data we find the variations in backscatter to be exactly in‐phase with similar periodicities in the occurrence of relatively strong sporadic E layers. The present findings support the possibility that planetary waves are responsible for the observed long‐term periodicities which indicates also a close relation between planetary waves and the well known, but not well understood, seasonal Es dependence. We suggest, the planetary wave option constitutes a new component into the research of midlatitude sporadic E layer formation and occurrence that needs to be considered and closely investigated.
The distribution of olivine in the Crater Aristarchus inferred from Clementine NIR data
Authors: Le Mouélic Stéphane , Langevin Yves , Erard Stéphane
Published: September 2002

Clementine imaged the Moon entirely at eleven wavelengths. This paper presents new results obtained on the crater Aristarchus using a heuristic method for the calibration of the near infrared (NIR) data set. We computed band ratios and we extracted spectra using a telescopic spectrum as reference. A new ∼4×10 km olivine rich area has been identified on the southeastern rim of the crater, in addition to a smaller olivine rich area previously reported. The olivine to pyroxene ratio exceeds 6 in this new zone. This demonstrates the uniqueness of the Clementine NIR data set in discriminating olivine from pyroxene on the lunar surface, with implications for magmatic processes in the lunar mantle and crust.
Measurements of erythemal irradiance near Davis Station, Antarctica: Effect of inhomogeneous surface albedo
Authors: Smolskaia Irina , Nunez Manuel , Michael Kelvin
Published: September 2002

To examine effects of inhomogeneous surface albedo on UV irradiance, measurements were taken near Davis Station (68.58°S, 77.97°E), East Antarctica during November/December 1997. Data were collected in transects perpendicular to an ice/water boundary, while one instrument continuously measured at the ice edge. Irradiances along transects were normalised by coincident measurements at the ice edge. Systematic differences in downwelling irradiance near the ice edge were observed over the highly reflective surface and open water. For cloudless conditions, the relative change in irradiance reached limiting values of about +5% from the ice edge to a point 2.5 km over snow‐covered ice, and about −5% from the ice edge to a point 2.5 km over water. In overcast conditions, higher relative changes were observed (about +30% from the ice edge to a point 2.5 km over ice on 17 November 1997) with no sign of a constant relative change being reached.