bluuebunny/crossref_metadata_2025 huggingface dataset:
Next generation of NOAA/NESDIS TMI, SSM/I, and AMSR‐E microwave land rainfall algorithms
Authors: McCollum Jeffrey R. , Ferraro Ralph R.
Published: May 2003

Revised versions of previous passive microwave land rainfall algorithms are developed for the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI), the Special Sensor Microwave/Imager (SSM/I), and the new Advanced Microwave Sounding Radiometer‐Earth Observing System (EOS) (AMSR‐E). The relationships between rainfall rate and 85 GHz brightness temperature are recalibrated with respect to previous algorithms using collocated TMI and TRMM Precipitation Radar (PR) data. Another new feature is a procedure to estimate the probability of convective rainfall, as convective/stratiform classification can reduce the ambiguity of possible rainfall rates for a given brightness temperature. These modifications essentially eliminate the global high bias found in studies [e.g., McCollum et al., 2000; Kummerow et al., 2001] of previous versions of the SSM/I and TMI algorithms. However, many regional and seasonal biases still exist, and these are identified. The applicability of the new features to the other microwave sensors is studied using SSM/I data, and a correction is developed to account for the differences in footprint resolution between the TMI and SSM/I. The AMSR‐E algorithm is the same as the TMI, as the footprint resolutions and frequencies of these instruments are very similar. The TMI algorithm will be used in the land portion of the official version 6 TMI instantaneous rainfall rate product, to be released in 2003, while the AMSR algorithm will be used in a similar manner for future AMSR‐E products.
Orographic influences on the multiscale statistical properties of precipitation
Authors: Nykanen Deborah K. , Harris Daniel
Published: May 2003

A case study consisting of three consecutive orographic thunderstorms that occurred on 27 June 1995 in the Blue Ridge Mountains of Virginia is examined from the perspective of relating the surrounding meteorological forcings and underlying orography to the multiscale structure of the rainfall fields. The statistical framework for this multiscale characterization is cascade based and offers a parsimonious parameterization, which can be used in future studies for the purposes of stochastically downscaling rainfall fields. Sequences of radar‐derived rainfall maps provide data with which to characterize the multiscale statistical structure and variability of the rainfall. In this case study, rainfall falling at higher topographic elevations was shown to be more intermittent and more organized than rainfall at lower elevations. This trend is contrary to previous studies analyzing the multiscale structure of orographic rainfall and is argued to be the direct result of differing meteorological factors for this type of storm such as the presence of warm rain processes and leeside orographic forcing.
Photo‐induced Hg(II) reduction in snow from the remote and temperate Experimental Lakes Area (Ontario, Canada)
Authors: Lalonde Janick D. , Amyot Marc , Doyon Marie‐Renée , Auclair Jean‐Christian
Published: May 2003

This paper reports a net snow‐to‐air Hg transfer from the remote and temperate Experimental Lakes area (Ontario, Canada). More than 40% loss of total Hg concentration was observed in surface snow within 24 hours of its deposition on the ground. Stratigraphic profiles of total Hg in various snowpacks demonstrated a systematic decrease in total Hg concentration with snow depth pointing to snow‐to‐air Hg transfer and not snow‐to‐ground transfer. These results confirm observations made in a suburban area (Sainte‐Foy, Quebec, Canada) receiving higher atmospheric deposition of Hg perhaps differently associated chemically. The occurrence of this phenomenon is therefore extended geographically to include snow from pristine regions. It is hypothesized that the loss of Hg is caused by a sunlight‐initiated Hg(II) reduction in snow and subsequent gas transfer of Hg0 to the atmosphere. Polychromatic action spectra demonstrated that Hg(II) reduction in snow was mostly mediated by UV‐B irradiation and not visible, or UV‐A wavelengths. In addition to Hg(II) reduction in snow, we observed Hg0 oxidation in snow samples spiked with Cl−. Hg0 oxidation could limit the potential for Hg loss from snowpacks from coastal polar or subpolar regions (where snow often contains high chloride levels) by competing with Hg(II) reduction and slowing the snow‐to‐air Hg transfer. However, in regions under minimal marine influences, watershed budgets of Hg should consider the possibility of Hg loss from snow with time of deposition on the ground. Also, snow core studies should consider historic sunlight irradiation if extrapolation from snow cores is desired to estimate past ambient Hg levels.
A semianalytical cloud retrieval algorithm using backscattered radiation in 0.4–2.4 μm spectral region
Authors: Kokhanovsky A. A. , Rozanov V. V. , Zege E. P. , Bovensmann H. , Burrows J. P.
Published: May 2003

This study is devoted to the development of a semianalytical algorithm for the determination of the optical thickness, the liquid water path, and the effective size of droplets from spectral measurements of the intensity of light reflected from water clouds with large optical thickness. The probability of photon absorption by droplets in the visible and near‐infrared spectral regions is low. This allows us to simplify and modify well‐known asymptotic equations of the radiative transfer theory, taking into account the fact that the single scattering albedo is close to one. Modified asymptotic equations are used to develop the inverse algorithm. We also avoid the use of the Mie theory, applying parametrizations and geometrical optics results with account for wave corrections. The main advantage of the method proposed lays in the fact that the equations derived not only provide a valuable alternative to the numerical radiative transfer solution but also are much more simple than equations of a conventional asymptotic theory. This simplicity allows both the simplification of the cloud retrieval algorithm and, even more important, the insight into various factors involved in a retrieval scheme.
Characteristics of biomass burning emission sources, transport, and chemical speciation in enhanced springtime tropospheric ozone profile over Hong Kong
Authors: Chan C. Y. , Chan L. Y. , Harris J. M. , Oltmans S. J. , Blake D. R. , Qin Y. , Zheng Y. G. , Zheng X. D.
Published: May 2003

Tropospheric ozone (O3) enhancements have been continuously observed over Hong Kong. We studied the O3 enhancement events and assessed their relation to the springtime O3 maximum in the lower troposphere over Hong Kong using a 6‐year (1993 to 1999) ozonesonde data set. We identified the source regions of biomass burning emission, and established the chemical and transport characteristics of O3‐rich air masses in the enhanced O3 profiles using satellite imagery, air trajectory and trace gas data measured on board the DC‐8 aircraft during the PEM‐West‐B experiment. We identified a total of 39 O3 enhancement events, among which 35 events (90%) occurred from late February to May and 30 events (77%) had O3 enhancement within the 2.0–6.0 km altitude. The excess O3 in the O3‐rich layers adds an additional 12% of O3 into the tropospheric O3 column and results in an overall springtime O3 maximum in the lower troposphere. Forward trajectory analysis suggests that the O3‐rich air masses over Hong Kong can reach central Pacific and the western coast of North America within 10 days. Back air trajectories show that the O3‐rich air masses in the enhanced profiles pass over the Southeast (SE) Asia subcontinent, where active biomass burning occurs in the O3 enhancement period. We identified the Indo‐Burma region containing Burma, Laos and northern Thailand, and the Indian‐Nepal region containing northern India and Nepal as the two most active regions of biomass burning emissions in the SE Asia subcontinent. Ozone and trace gas measurement on board the DC‐8 aircraft revealed that O3‐rich air masses are found over many parts of the tropical SE Asia and subtropical western Pacific regions and they have similar chemical characteristics. The accompanying trace gas measurements suggest that the O3‐rich air masses are rich in biomass burning tracer, CH3Cl, but not the general urban emission tracers. We thus believe that the springtime O3 enhancement over Hong Kong is as a result of transport of photochemical O3 produced from biomass burning emissions from the upwind SE Asian continent. The large‐scale enhancements of O3 in tropical SE Asia and the subtropical western Pacific rim that result from SE Asian biomass burning activities such as presented here thus are of atmospheric importance and deserve further research efforts.
Aerosol time‐of‐flight mass spectrometry during the Atlanta Supersite Experiment: 1. Measurements
Authors: Liu Don‐Yuan , Wenzel Ryan J. , Prather Kimberly A.
Published: May 2003

In August 1999 an intensive field campaign was conducted in Atlanta, Georgia, focusing on the characterization of urban particulate matter. During the study an aerosol time‐of‐flight mass spectrometer (ATOFMS) was used to measure continuously the aerodynamic size and chemical composition of individual particles in the fine fraction (0.2–2.5 μm) of the atmospheric aerosol. The inorganic and organic components of the particles were analyzed using laser desorption ionization time‐of‐flight mass spectrometry, generating positive and/or negative ion mass spectra. Here an overview of the ATOFMS results is presented with respect to the major species detected, including sodium, carbon (EC, OC, EC/OC), dust (Li, Na, Al, K, Ca, Fe), sulfate, nitrate, and ammonium. As described, many of the dust particle types have similar composition to those observed in ATOFMS coal source characterization studies. The ion signals, size distributions, and temporal evolution (30–60 min resolution) of the different particle types are described. The complexity of the Atlanta aerosol is shown here on an individual particle basis, demonstrating how single particle data obtained with ATOFMS can be used to gain unique insights into the mixing state of urban aerosols. The second paper in this two part series focuses on the scaling procedures used for converting the unscaled ATOFMS data presented in this paper into atmospherically representative number concentrations [Wenzel et al., 2002].
Aerosol time‐of‐flight mass spectrometry during the Atlanta Supersite Experiment: 2. Scaling procedures
Authors: Wenzel Ryan J. , Liu Don‐Yuan , Edgerton Eric S. , Prather Kimberly A.
Published: May 2003

Aerosol time‐of‐flight mass spectrometry (ATOFMS) was used for characterizing the aerodynamic size and chemical composition of individual particles during the Atlanta Supersite Experiment in 1999. During certain time periods, increased numbers of particles scattered light but did not produce mass spectra. Upon comparison of the size‐resolved unscaled particle counts from an aerosol time‐of‐flight mass spectrometer with those from a laser particle counter, the presence of a chemical bias became apparent in the single particle mass spectral measurements. Upon further analysis, it was determined that these events occurred during time periods of elevated ammonium and sulfate mass concentrations measured with semicontinuous particulate analysis instruments. The missed particle type occurred mostly in the smallest size range (0.35–0.54 μm) and correlated well with optical scattering measurements. As described herein, a scaling procedure is developed that allows one to account for the ATOFMS chemical bias. This procedure is tested by comparing the scaled ATOFMS data with multiple measurements from other techniques made during the 1999 Atlanta Supersite study. This is the second paper in a two‐part series focusing on ATOFMS data collected during the Atlanta Supersite experiment in 1999 [Prather et al., 2002].
A numerical study of the effect of gravity‐wave propagation on minor species distributions in the mesopause region
Authors: Xu Jiyao , Smith A. K. , Ma Ruiping
Published: May 2003

A photochemical‐dynamical gravity‐wave model is developed in this paper and is applied to the impact of a nonbreaking propagating gravity wave on chemical species distributions in the mesopause region. The model is time‐dependent, two‐dimensional, nonlinear, and nonhydrostatic; it includes diabatic processes produced by photochemistry and the effects of the gravity wave on atmospheric chemical species. The model simulates the changes to the distributions of oxygen and hydrogen compounds instantaneously in the presence of the wave and also determines the residual effect on composition after the wave packet has passed through the region. The results indicate that a gravity wave propagating through the mesopause region influences the mean distributions of chemical species even if the wave does not break. The relative perturbations are larger during night than during daytime. The chemical density perturbations persist for several hours after the dynamical wave has propagated out of the region.
Tropical–extratropical connection in interannual variation of the tropopause: Comparison between NCEP/NCAR reanalysis and an atmospheric general circulation model simulation
Authors: Wong Sun , Wang Wei‐Chyung
Published: May 2003

Interannual variation of the tropopause is investigated by applying principal component analysis (PCA) to the zonal mean and eddy tropopause temperatures obtained from the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis. For the zonal mean tropopause temperatures, we find that the first PC represents the out‐of‐phase coherent variations between the tropics and the Northern Hemispheric (NH) polar region during NH late winter to early spring and the second PC represents the variations between the tropics and the Southern Hemispheric (SH) polar region during SH spring. The same analysis is applied to the zonal mean tropopause simulated in SUNYA Community Climate Model version 3 (CCM3), and the tropopause variations associated with the two PCs are reproduced, with about 74% of the NCEP/NCAR tropopause variability for the first PC and about 44% of the variability for the second PC. The model thermal budget indicates that the first PC is associated with the variation of dynamical heating in the NH polar region and the second PC is associated with the variation of O3 anomalies in the SH polar region. To investigate how the tropopause variation is modulated by the quasi‐biennial oscillation (QBO), which is not simulated in the model, singular value decomposition (SVD) is applied to the NCEP/NCAR tropopause temperatures and zonal winds. The QBO accounts for about 16% of the zonal wind variability associated with the first PC and about 36% of the zonal wind variability associated with the second PC. For the eddy tropopause temperatures, the interannual variation associated with the El Niño–Southern Oscillation (ENSO) is evident. In the extratropics over the Pacific North American (PNA) sector, the anomalies are out of phase with the dumbbell‐shaped anomalies located in the tropical eastern Pacific and are related to the anomalies in horizontal heat advection caused by the response of extratropical stationary waves. The model can simulate the ENSO‐related tropopause variability close to the corresponding NCEP/NCAR's variability, although the model anomalies in the tropical western Pacific are too small.
Estimation of runoff rates, mass balance, and elevation changes on the Greenland ice sheet from passive microwave observations
Authors: Mote Thomas L.
Published: May 2003

Annual melt duration from Special Sensor Microwave/Imager satellite data is used in a simple surface mass balance (SMB) model to estimate runoff rates, mass balance, and surface elevation changes for the Greenland ice sheet. Estimates are made using a variable accumulation rate that is based on precipitation from a dynamic climate model using European Centre for Medium‐Range Weather Forecasts analysis data. The overall SMB is positive for the 1988–1999 period, but it is near the estimate of calving rates. Two years, 1995 and 1998, show a negative SMB. There is some evidence that years with higher runoff are associated with lower accumulation and that years with higher than average runoff in southern Greenland are associated with lower than average runoff in the north. Variations in accumulation rates dominate SMB variability in east and southeast Greenland, while runoff rates dominate in west Greenland. SMB is also used to estimate elevation changes resulting from trends in SMB during the 1988–1999 and 1993–1999 time periods, which in general agree with laser altimeter finding of thinning below 2000 m above sea level and near equilibrium above that elevation.
Modeling δ18O in precipitation over the tropical Americas: 1. Interannual variability and climatic controls
Authors: Vuille M. , Bradley R. S. , Werner M. , Healy R. , Keimig F.
Published: May 2003

We use two atmospheric general circulation models (AGCMs), the ECHAM‐4 and the GISS II models, to analyze the interannual variability of δ18O in precipitation over the tropical Americas. Several different simulations with isotopic tracers forced with observed global sea surface temperatures (SST) between 1950 and 1998 reveal the influence of varying temperature, precipitation amount, and moisture source contributions on the predicted δ18O distribution. Observational evidence from climatic (NCEP‐NCAR) and sparse stable isotope (IAEA‐GNIP) data is used to evaluate model performance. The models capture the essential features of surface climate over the tropical Americas in terms of both their spatial and temporal characteristics. Using a low‐resolution model (GISS II), adjusted to provide a more realistic Andean topography, or a higher‐resolution model (ECHAM‐4 T106) leads to an improved δ18O distribution over the tropical Americas with an altitude effect comparable to observations. Water vapor transport and gradual rainout and increasingly depleted composition of water vapor along its trajectory are correctly simulated in both models, although the ECHAM model appears to underestimate the continentality effect over the Amazon basin. A significant dependence of δ18O on the precipitation amount is apparent in both models, in accordance with observations, while the influence of temperature seems to be less significant in most regions and is accurately reproduced by the ECHAM model only. Over most regions, however, the δ18O signal in precipitation is influenced by a combination of factors, such as precipitation amount, temperature, moisture source variability, and atmospheric circulation changes. Over parts of the tropical Americas, the δ18O signal is therefore also significantly correlated with ENSO because ENSO is an integrator of many factors affecting the δ18O composition of precipitation.
Atmospheric and environmental effects of the 1783–1784 Laki eruption: A review and reassessment
Authors: Thordarson Thorvaldur , Self Stephen
Published: May 2003

The 1783–1784 Laki flood lava eruption in Iceland emitted ∼122 megatons (Mt) SO2into the atmosphere and maintained a sulfuric aerosol veil that hung over the Northern Hemisphere for >5 months. The eruption columns extended to 9–13 km and released ∼95 Mt SO2into the upper troposphere/lower stratosphere (i.e., the polar jet stream), enforcing a net eastward dispersion of the plumes which reacted with atmospheric moisture to produce ∼200 Mt of H2SO4aerosols. Away from source, the Laki aerosols were delivered to the surface by subsiding air masses within anticyclones. We show that ∼175 Mt of H2SO4aerosols were removed as acid precipitation and caused the extreme volcanic pollution (i.e., dry fog) that effected Europe and other regions in 1783. The remaining ∼25 Mt stayed aloft at tropopause level for >1 year. The summer of 1783 was characterized by extreme and unusual weather, including an unusually hot July in western Europe, most likely caused by perseverance of southerly air currents. The following winter was one of the most severe winters on record in Europe and North America. In these regions, the annual mean surface cooling that followed the Laki eruption was about −1.3°C and lasted for 2–3 years. We propose that the upper troposphere/lower stratosphere aerosols from Laki disrupted the thermal balance of the Arctic regions for two summers and were the main mechanism for the associated climate perturbations. Eruptions of Laki magnitude have occurred in the recent past in Iceland and will occur again. If such an eruption were to occur today, one of the most likely immediate consequences would be disruption to air traffic over large portions of the Northern Hemisphere.
Topographically induced north‐south asymmetry of the meridional circulation in the Martian atmosphere
Authors: Takahashi Yoshiyuki O. , Fujiwara Hitoshi , Fukunishi Hiroshi , Odaka Masatsugu , Hayashi Yoshi‐Yuki , Watanabe Shigeto
Published: May 2003

A Martian atmospheric general circulation model is developed to investigate the effect of topographic elevation in the meridional circulation of the Martian atmosphere. It is confirmed that, even at equinoxes, the meridional circulation below ∼20 km altitude has an asymmetric pattern with respect to the equator. Sensitivity experiments reveal that the topographic elevation difference between the northern and southern hemispheres is the most dominant factor for producing such an asymmetric circulation. Contributions from variations of surface thermal inertia and surface albedo are weak compared with that of surface elevation. Thermal budget analyses show that the mean meridional circulation below ∼20 km altitude is driven by convective heating whose magnitude is controlled by the potential temperature of the surface mixed layer. Since the Martian atmosphere is optically and thermally thin, the potential temperature of the surface mixed layer is directly influenced by the geometric height of the surface. The elevated southern hemisphere induces the upward motion of the Martian Hadley circulation to be located in the southern hemisphere even at equinoxes when the surface temperature distribution is symmetric with respect to the equator. At southern summer solstice, when the potential temperature of the southern surface mixed layer is highest, the convective activity there becomes most active, and thus the Martian Hadley circulation becomes most intensive. This seasonal intensification of the convective activity and the Hadley circulation may account for the frequent occurrence of dust loading in the summer southern hemisphere.
Patterns of export production in the eastern equatorial Pacific over the past 130,000 years
Authors: Loubere Paul , Fariduddin Mohammad , Murray Richard W.
Published: May 2003

Productivity at six core locations in the eastern equatorial Pacific (EEP) was reconstructed with a benthic foraminiferal transfer function. The core records show strong regionality, especially where affected by Peru margin upwelling of deeper Equatorial Undercurrent Water (EUC) (originally coming from the subantarctic). This “Peru margin” record differs from that seen along the equator where divergence leads to shallow upwelling, and it is generally inverse to that seen in cores outside the areas of equatorial upwelling. Principal components analysis shows that the main productivity pattern correlates well to the global oxygen isotope record and has lowest values during isotope stages 2 and 4. In addition to this, equatorial cores show a higher frequency pattern of variation which becomes much more pronounced during MIS 3 and 2. The reconstructions based on benthic foraminifera were tested against those from nonaccumulation rate based inorganic chemical proxies of export production. These were found to correlate well in the region influenced by Peru upwelling, and also to share common features for sites along the equator. All the nonaccumulation rate based paleotracers are consistent with one another and differ from accumulation rate derived proxies. The differences between the two classes of paleotracers may result from uncertainties in calculating actual biogenic fluxes since 230Th‐normalized results conform more to those we obtained. Analysis of planktonic carbon isotope values for the EEP, and their comparison to the record of the Pacific subantarctic, indicates that the subantarctic contribution to the EUC was reduced during MIS 3 and 2.
Saw‐tooth pattern of North Atlantic current speed during Dansgaard‐Oeschger cycles revealed by the magnetic grain size of Reykjanes Ridge sediments at 59°N
Authors: Snowball Ian , Moros Matthias
Published: May 2003

Detailed mineral (rock) magnetic measurements, including high‐resolution magnetic hysteresis loops, were carried out on three sediment cores recovered from the Reykjanes Ridge in the North Atlantic. Supported by physical grain‐size analyses, titanomagnetite grain‐size variations form a proxy of the speed of near‐bottom currents and reveal a cyclic “saw‐tooth” pattern between Dansgaard‐Oeschger cycles 8 and 5. The magnetic grain‐size data suggest that these Dansgaard‐Oeschger cycles were characterized by gradual intensification of the near‐bottom current speed, while other paleoceanographic proxies indicate escalating iceberg discharge and declining sea surface temperatures. These observations are contrary to the frequently assumed and strictly applied positive relationship between high‐latitude warmth and North Atlantic Deep Water formation. Within the confines of temporal control, however, it would appear that peaks in iceberg discharge and slow near‐bottom current speeds were synchronous. The magnetic hysteresis data also demonstrate that magnetic concentration parameters, such as magnetic susceptibility, do not necessarily provide direct evidence of paleocirculation.
Gravity wave dynamics and effects in the middle atmosphere
Authors: Fritts David C. , Alexander M. Joan
Published: May 2003

Atmospheric gravity waves have been a subject of intense research activity in recent years because of their myriad effects and their major contributions to atmospheric circulation, structure, and variability. Apart from occasionally strong lower‐atmospheric effects, the major wave influences occur in the middle atmosphere, between ∼ 10 and 110 km altitudes because of decreasing density and increasing wave amplitudes with altitude. Theoretical, numerical, and observational studies have advanced our understanding of gravity waves on many fronts since the review by Fritts [1984a]; the present review will focus on these more recent contributions. Progress includes a better appreciation of gravity wave sources and characteristics, the evolution of the gravity wave spectrum with altitude and with variations of wind and stability, the character and implications of observed climatologies, and the wave interaction and instability processes that constrain wave amplitudes and spectral shape. Recent studies have also expanded dramatically our understanding of gravity wave influences on the large‐scale circulation and the thermal and constituent structures of the middle atmosphere. These advances have led to a number of parameterizations of gravity wave effects which are enabling ever more realistic descriptions of gravity wave forcing in large‐scale models. There remain, nevertheless, a number of areas in which further progress is needed in refining our understanding of and our ability to describe and predict gravity wave influences in the middle atmosphere. Our view of these unknowns and needs is also offered.
A comprehensive approach to monitoring volcano deformation as a window on the eruption cycle
Authors: Dzurisin Daniel
Published: May 2003

Since the 1980 eruption of Mount St. Helens, volcanologists have made considerable progress toward predicting eruptions on the basis of precursors that typically start a few days to several months in advance. Although accurate eruption prediction is by no means routine, it may now be possible in some cases to extend the effective warning period by anticipating the onset of short‐term precursors. Three promising indicators of deep magmatic processes are (1) deep, long‐period earthquakes and tremor that indicate the ascent of magma through the crust, (2) magmatic CO2emission rate as a proxy for magma supply rate, and (3) relatively broad, generally aseismic surface uplift caused by magmatic intrusions. In the latter case it is essential to sample the deformation field thoroughly in both time and space to adequately constrain source models. Until recently, this has been nearly impossible because high‐precision sensors could not be deployed in sufficient numbers, nor could extensive geodetic surveys be conducted often enough. Advances in instrumentation, interferometric synthetic aperture radar (InSAR), and telecommunications are helping to overcome these limitations. As a result, comprehensive geodetic monitoring of selected volcanoes is now feasible. A combination of InSAR, large‐aperture GPS surveys, microgravity surveys, and dense arrays of continuous GPS stations, strain meters, and tiltmeters can reveal both spatial and temporal patterns of ground deformation throughout the eruption cycle. Improved geodetic monitoring of many of the world's volcanoes would be a major stride toward better understanding of magmatic processes and longer‐term eruption forecasts.
A novel concept for finding proper orthogonal wavelets effectively to solve a large object scattering problem
Authors: Chen Chih‐Ming , Tarng Jenn‐Hwan , Huang Jiunn‐Ming
Published: May 2003

A novel concept of “visible energy” is proposed, and its magnitude is shown to be valuable information for determining whether the chosen orthogonal wavelet is proper in solving a large object scattering problem. With the properly chosen wavelets for the targeting problem the (transformed) wavelet‐domain impedance matrix can be sparsified effectively for solving electromagnetic integral problems. Visible energy is defined as the energy of all dilations of a single mother wavelet for an arbitrary translation in the spectral domain over the entire “visible region.” It is found that for large matrix sizes, using wavelets with smaller visible energy will lead to a greater sparsification of the matrix. Numerical examples considering various scatterers with different shapes such as a circular cylinder, an L‐shaped scatterer, and a duct show the validity of our findings.
Efficient integral equation formulation of diffraction at the edge of a truncated dielectric structure based on PO solutions: Application to the case of arbitrarily polarized line sources
Authors: Volski Vladimir A. , Vandenbosch Guy A. E.
Published: May 2003

The radiation patterns of electric and magnetic line sources placed near the truncation of a semi‐infinite grounded dielectric layer structure have been investigated. Two polarizations (parallel and normal to the edge) have been considered for both sources. In order to perform the analysis a new formulation is proposed for the aperture integral equations derived from the principle of equivalence. The novelty of this formulation is that it involves only the fringe components of the magnetic current. The total magnetic current flowing on the aperture is expressed in terms of the physical optics (PO) current and the fringe current. Although the PO current is not known analytically, we can calculate the field excited by this current using the relationship between the surface magnetic PO current on the aperture and the electric polarization PO current in the grounded dielectric slab. The latter PO current is approximated analytically by the expansion wave concept. This step opens a simple and effective way to calculate the right part of the integral equations and as a consequence the radiation pattern of the line sources. For comparison reasons the problem is solved also by using the method of Physical Optics and the Uniform Theory of Diffraction.
Radio tomographic imaging as an aid to modeling of ionospheric electron density
Authors: Dabas R. S. , Kersley L.
Published: May 2003

Models of the ionosphere, used in applications for the prediction or correction of propagation effects on practical radio systems, are often inadequate in their representation of the structure and development of large‐scale features in the electron density. Over northern Europe, characterization of the main trough presents particular problems for such empirical or parameterized models and hence for radio propagation forecasting and ionospheric mapping. Results are presented from a study aimed at investigating the possible role of radio tomographic imaging in adapting models to yield a better representation of the ionosphere over Europe. It is shown that use of radio tomography gives better agreement with actual ionosonde data than can be obtained from any of the models used alone. It is suggested that the technique may have a possible role in the mapping of ionospheric conditions in near‐real time for future systems applications.
Transmission of waves near the lower oblique resonance using dipoles in the ionosphere
Authors: Chugunov Y. V. , Mareev E. A. , Fiala V. , James H. G.
Published: May 2003

The observations in the OEDIPUS‐C experiment of bistatic propagation along the lower oblique resonance cone between a separated transmitter and receiver in the ionosphere are explained through detailed calculations of the radiated field of the V‐dipole antenna used in the experiment and by a novel theory of the receiving antenna under resonance conditions. Unexpectedly high values of 25 kHz signal observed at the resonance and its structure agree well with calculations of the transmission between the exciter and receiver, when antenna layout and dispersive properties of the plasma at resonance are taken into account.
Determining riometer quiet day curves 2. Derivation of filter cutoff frequencies
Authors: Drevin G. R. , Stoker P. H.
Published: May 2003

A method for the determination of riometer quiet day curves which is based on the filtering of a discrete two‐dimensional function or matrix has been proposed. The two dimensions of the matrix are siderial time and day number, with each row of the matrix representing one siderial day. The filtering is done in the Fourier domain using a low‐pass filter. With a low‐pass filter the low frequency Fourier coefficients are retained, while the high frequency Fourier coefficients are discarded. The highest Fourier coefficient that is retained is the cutoff frequency of the filter. In this paper the filter cutoff frequencies are derived directly from the antenna reception pattern as well as from the data itself. A number of methods can be used to infer a cutoff frequency from the data; however, only a number of entropy based methods are investigated in this paper.
Characterization of frequency effect in SuperDARN spectral width distributions
Authors: Vallières X. , Villain J.‐P. , André R.
Published: May 2003

This study investigates the frequency dependence of spectral width distributions observed by the SuperDARN HF radars. The evolution of spectral width values with range is shown to be dependent on the operating radar frequency. First, this evolution is clearly pointed out using a multifrequency scanning mode. This study is then generalized and this effect is shown to affect the whole SuperDARN spectral width data set. Several studies are performed in order to determine the dependence of this effect upon season, beam orientation and mean radar orientation.
Multiplicative regularization for contrast profile inversion
Authors: van den Berg Peter M. , Abubakar Aria , Fokkema Jacob T.
Published: May 2003

In this paper we discuss a new type of regularization technique for the nonlinear inverse scattering problem, namely the multiplicative technique. The main advantage is that we do not have to determine the regularization parameter before the inversion process is started. We consider different norms of the total variation as regularization factor. Specifically, we investigate a weighted L2‐norm, and by using an appropriate updating scheme we show that this multiplicative regularization factor does not increase the nonlinearity of the inversion problem. Numerical examples using synthetic and experimental data demonstrate the robustness of the presented method.
A thorough look at the nonuniqueness of the electromagnetic scattering integral equation solutions as compared to the scalar acoustic ones
Authors: Langenberg Karl J.
Published: May 2003

It is well‐known that solutions of electromagnetic scattering integral equations of the first or second kind (EFIE and MFIE) for perfectly electric or perfectly magnetic conducting scatterers are nonunique for those frequencies which correspond to interior Maxwell resonances of the scatterer; hence, the null spaces of the respective interior problem operators are under concern. In principle, all mathematical facts and proofs regarding this problem and cited in this paper are available from the book by Colton and Kress [1983], yet, these authors mainly concentrate on single and double layer potentials for the scalar acoustic (Dirichlet and Neumann) as well as the magnetic dipole layer ansatz for the perfectly electric conducting (Maxwell) problem and treat the Huygens‐type representation, which is more common in the electrical engineering community, not in the same detail. This might be the reason that part of the electrical engineering literature suffers from some confusion regarding the proper null spaces and their physical relevance, in particular, if the electromagnetic problem is considered in 2‐D, where it reduces to scalar TM/TE‐problems. The present contribution comments on these issues emphasizing that the null spaces of 2‐D electromagnetics are the nonphysical null spaces originating from the Huygens‐type representation of scalar acoustics.
Mobile multimedia antenna systems for station wagons and the achievable diversity effectiveness obtained by analysis of virtual test drives
Authors: Hopf J. F. , Lindenmeier H. K. , Reiter L. M.
Published: May 2003

For modern cars, antennas are required for AM reception, FM and TV diversity reception, weatherband reception (USA), terrestrial digital radio, remote control functions, keyless entry, mobile phone for all worldwide used systems, GPS, and in the future, satellite broadcast radio services. Those services cover the frequency range from 150 kHz up to 2.4 GHz. Such kind of a multiantenna system developed for station wagons is presented in this paper. The obtainable FM and TV diversity effectiveness is discussed for several types of antenna arrangements in detail. This value is the number of fictitious completely decorrelated antenna signals and is obtained by virtual test drives. The characteristic of the respective antennas under test is introduced in the software as antenna pattern, measured or calculated with respect to amplitude and phase. During the computer analysis the car with the antennas is driven virtually through a Rayleigh field scenario with desired and undesired signals.
A Green's tensor approach to the modeling of nanostructure replication and characterization
Authors: Paulus Michael , Martin Olivier J. F.
Published: May 2003

We use the Green's tensor technique to study the optical processes taking place in configurations typically used for the replication and characterization of nanostructures. For the replication process we investigate light‐coupling masks for optical contact lithography and for the characterization process the mode scattered by a defect or a short grating in a planar waveguide. Both configurations consist of structures embedded in a stratified background composed of a stack of material layers with different permittivities. We perform calculations for two‐dimensional and three‐dimensional structures and compare their optical behavior. Our results show that the additional material interfaces in three‐dimensional systems can lead to significantly different field distributions and must be taken into account for a complete understanding of the electromagnetic properties of the systems.
Shock structure for electromagnetic waves in bianisotropic, nonlinear materials
Authors: Sjöberg Daniel
Published: May 2003

Shock waves are discontinuous solutions to quasi‐linear partial differential equations and can be studied through a singular perturbation known as the vanishing viscosity technique. The vanishing viscosity method is a means of smoothing the shock, which we use to study the case of electromagnetic waves in bianisotropic materials. We derive the conditions arising from this smoothing procedure for a traveling wave, and the waves are classified as fast, slow, or intermediate shock waves.
Time domain theory of open waveguide resonators: Canonical problems and a generalized matrix technique
Authors: Sirenko Yuriy K. , Yashina Nataliya P.
Published: May 2003

In this paper, we consider new solutions and algorithms for initial boundary‐value problems in the electromagnetic theory of open waveguide resonators. The approaches are based on a description of the scattering properties of such resonators in terms of the transform operators for an evolutionary basis of the non‐stationary signal, that have the same significance in the course of analyses in time domain as generalized scattering matrixes in frequency domain. All suggested approaches imply using mathematically correct computational procedures at the key stages of forming the solution, in particular, the analytical regularization method—the semi‐inversion method.
A quasi‐Newton reconstruction algorithm for a complex microwave imaging scanner environment
Authors: Franchois A. , Tijhuis A. G.
Published: May 2003

An iterative complex permittivity reconstruction technique for two‐dimensional near‐field imaging is presented. A particular feature of the algorithm is that it takes into account the complicated environment of a circular 434 MHz microwave imaging scanner, which was developed to conduct biomedical imaging experiments. This is accomplished in a computationally efficient way by means of an embedding technique. The reconstruction technique is further based on a quasi‐Newton optimization scheme with approximate line search, in which the Hessian matrix is iteratively updated with the Broyden–Fletcher–Goldfarb–Shanno (BFGS) formula. This way, second derivative information is exploited to a large extent. The technique is illustrated with complex permittivity reconstructions of homogeneous and inhomogeneous lossy dielectric cylinders of moderate and high contrast from simulated data.
INDEPTH III seismic data: From surface observations to deep crustal processes in Tibet
Authors: Haines Seth S. , Klemperer Simon L. , Brown Larry , Jingru Guo , Mechie James , Meissner Rolf , Ross Andrew , Wenjin Zhao
Published: May 2003

During the summer of 1998, active‐source seismic data were collected along a transect running 400 km NNW‐SSE across the central Tibetan Plateau as the third phase of project INDEPTH (International Deep Profiling of Tibet and the Himalaya). The transect extends northward from the central Lhasa block, across the Jurassic Bangong‐Nujiang Suture (BNS) at 89.5°E, to the central Qiangtang block. A seismic velocity model for the transect to ∼25 km depth produced by inversion of P wave first arrivals on ∼3000 traces shows (1) a ∼50‐km‐wide region of low velocity (at least 5% less than surrounding velocities) extending to the base of the model at the BNS; (2) sedimentary cover for the southern Qiangtang block that is ∼3.5 km thick; (3) a distinct interface between sedimentary cover and Qiangtang basement or underplated Jurassic melange in the central Qiangtang block; and (4) evidence that the Bangoin granite extends to a depth of at least 15 km. The BNS has little geophysical signature, and appears unrelated to the ∼5 km northward shallowing of the Moho which is associated with the BNS in central Tibet. Geophysical data along the main INDEPTH III transect show little evidence for widespread crustal fluids, in contrast to the seismic “bright spots” found in southern Tibet and to magnetotelluric evidence of fluid accumulations in eastern Tibet. A comparison between the global average and Tibetan velocity‐depth functions offers constraints for models of plateau uplift and crustal thickening. Taken together with the weak geophysical signature of the BNS, these velocity‐depth functions suggest that convergence has been accommodated largely through pure‐shear thickening accompanied by removal of lower crustal material by lateral escape, likely via ductile flow. Although we cannot resolve the details, we believe lateral lower crustal flow has overprinted or destroyed evidence in the deep crust for the earlier assembly of Tibet as a series of accreted terranes.
The ultimate arc: Differential displacement, oroclinal bending, and vertical axis rotation in the External Betic‐Rif arc
Authors: Platt J. P. , Allerton S. , Kirker A. , Mandeville C. , Mayfield A. , Platzman E. S. , Rimi A.
Published: May 2003

The External Betic‐Rif arc, which lies between the converging African and Iberian plates, is one of the tightest orogenic arcs on Earth. It is a thin‐skinned fold and thrust belt formed in Miocene time around the periphery of the Alborán Domain, an older contractional orogen that underwent extensional collapse coevally with the formation of the thrust belt. Restoration of four sections across the thrust belt, together with kinematic and paleomagnetic analysis, allows a reconstruction of the prethrusting geometry of the Alborán Domain, and the identification of the following processes that contributed to the formation of the arc: (1) The Alborán Domain moved some 250 km westward relative to Iberia and Africa during the Miocene. This initiated the two limbs of the arc on its NW and SW margins, closing to the WSW in the region of Cherafat in northern Morocco. The overall convergence direction on the Iberian side of the arc was between 310° and 295°, and on the African side it was between 235° and 215°. The difference in convergence direction between the two sectors was primarily a result of the relative motion between Africa and Iberia. (2) Extensional collapse of the Alborán Domain during the Miocene modified the geometry of the western end of the arc: the Internal Rif rotated anticlockwise to form the present north trending sector of the arc, and additional components of displacement produced by extension were transferred into the external thrust belt along a series of strike‐slip faults and shear zones. These allowed the limbs of the arc to rotate and extend, tightening the arc, and creating variations in the amounts and directions of shortening around the arc. The Betic sector of the arc rotated clockwise by 25° during this process, and the southern Rif rotated anticlockwise by ∼55°. (3) Oblique convergence on the two limbs of the arc, dextral in the Betics and sinistral in the southern Rif, resulted in strongly noncoaxial deformation. This had three related effects: (1) large rotations of individual thrust sheets resulted from the oblique propagation of thrusts away from the thrust front, followed by pinning and rotation as the thrust sheets peeled off, (2) continued oblique convergence resulted in distributed shear, particularly in the rear of the thrust wedge, causing rotation of stacks of thrust sheets on the scale of a few tens of kilometers, and (3) distributed shear in the orogen resulted in the rotation of folds as they amplified, the hinges migrating through the rock body, and rotating at a slower rate than the rock. These rotations were substantially larger than the bulk rotations of the limbs of the arc, and they strongly modified the orientations of folds, thrust traces, and the structural indicators of fault slip directions.