bluuebunny/crossref_metadata_2025 huggingface dataset:
Elastic wave scattering by a random medium and the small‐scale inhomogeneities in the lithosphere
Authors: Wu R. S. , Aki K.
Published: April 2008

In this paper we use Born approximations to derive the mean square amplitudes of the scattered field for P‐P, P‐S, S‐P, and S‐S scattering by an elastic random medium characterized by perturbations of elastic constants and density. We also obtain the total scattered power or the scattering coefficient for the case of an incident P wave. We find that, in both the spatial scattering pattern and the frequency dependence of the scattering coefficient, there are some significant differences between scalar wave scattering and elastic wave scattering. These differences are most striking when the wavelength is comparable to the size of inhomogeneities, which is often encountered in the study of short‐period seismic body waves. Under certain conditions, the perturbations of the medium parameters can be decomposed into an impedance term and a velocity term. In the forward direction, scattered waves are primarily controlled by the velocity perturbations. For backscattering, scattered waves are generated mainly by impedance perturbations. We derive low‐ and high‐frequency asymptotic forms of the directional and total scattering coefficients. In the low‐frequency range, Rayleigh scattering with fourth‐power frequency dependence occurs. For the high‐frequency range the scattered power for common‐mode scattering has a second‐power frequency dependence, which is attributed to velocity perturbations. The scattered power of converted waves reaches a maximum, for the case of an exponential correlation function, in the high‐frequency range. We find that the scalar wave theory can be only approximately used for the forward scattering problem in the high‐frequency range, such as the phase and amplitude fluctuations in large seismic arrays. The case of coda wave excitation by local earthquakes, which is a backscattering or a large‐angle‐scattering problem, must be handled by the full elastic wave theory. A preliminary analysis of past observations using our theory suggests that the lithosphere may have multiple‐scale inhomogeneities. Besides the 10–20 km scale velocity inhomogeneities revealed by the forward scattering observations at LASA and NORSAR, the lithosphere in tectonically active regions may be rich in small‐scale (less than 1 km) inhomogeneities.
Geometry of silicic dikes beneath the Inyo Domes, California
Authors: Fink Jonathan H.
Published: April 2008

Structural geologic evidence in the vicinity of the Inyo Domes indicates that the youngest extrusive products were erupted from a silicic dike that divided into at least three segments which underwent up to 30° of clockwise rotation as they neared the surface. The geometry of ground cracks, explosion craters, and surface structures on the domes suggest that the dike may have propagated laterally from a source beneath Mammoth Mountain, with both the overall dike and the individual segments rising as they moved northward. Structural evidence and tephrochronology also imply that the actual vents may have migrated northward along individual dike segments as the activity evolved from explosive eruptions to the more quiet emplacement of lavas. Monitoring of changing patterns of ground cracks and faults may assist in predicting the sites and timing of future eruptions.
Root zone of the Late Proterozoic Salma Caldera, northeastern Arabian Shield, Kingdom of Saudi Arabia
Authors: Kellogg Karl S.
Published: April 2008

The eroded root of the late Proterozoic Salma caldera crops out in a striking, roughly elliptical feature, about 27 km long and 22 km wide, near the northeastern edge of the Arabian Shield. The caldera is genetically part of an elongate alkalic granitic massif (Jabal Salma) that extends 35 km from the caldera to the southwest. Comenditic ash flow tuff and lava(?) of the caldera fill, probably more than 1 km thick, are the oldest recognized rocks of the caldera complex. These rocks were erupted during caldera collapse associated with the rapid evacuation of the upper, mildly peralkalic part of a zoned magma reservoir. Within the caldera fill, a massive, lithic‐rich intracaldera rhyolite, probably a lava in excess of 1 km thick, is overlain by a layered ash flow sequence. Numerous megabreccia blocks, probably derived from the caldera wall, occur in the massive rhyolite. Open folds in the layered volcanic rocks may be due to high‐temperature slumping of the rocks toward the center of the caldera following collapse. Later peralkalic granite that intruded the caldera ring fracture zone occurs in an arcuate pattern outside the area of exposed caldera fill. After caldera collapse, metaluminous to peraluminous magma rose beneath the caldera at approximately 580 Ma and solidified as biotite alkali granite, rim syenogranite, and late, high‐level granophyre. Rare earth element abundances indicate that the layered rhyolite tuff, peralkalic granite, and granophyre are chemically more evolved than the biotite alkali granite and rim syenogranite. The granophyre intruded the caldera fill as a dome‐shaped body composed of numerous sheetlike masses. Granophyric texture resulted from rapid pressure release and quenching accompanying the intrusion of each sheet. Maximum penetration of the granophyre into overlying rocks occurred in the central region and along the west side of the caldera, where the caldera fill volcanic rocks have been removed by erosion. No apparent structural doming of the exposed volcanic rocks along the east side of the caldera took place; the layered ash flows commonly dip steeply toward the center of the caldera. Postemplacement deformation and metamorphism of the caldera are minimal. Small‐displacement strike‐slip faults cut the complex, which is tilted to the northeast by no more than about 2°.
Petrology of Mariana Trough and Lau Basin basalts
Authors: Hawkins J. W. , Melchior J. T.
Published: April 2008

The crust of actively opening back arc basins has close chemical and mineralogic similarities to normal mid‐ocean ridge basalts (N‐MORB) but some subtle, but distinctive, differences exist. These are largely due to differences in volatiles, Fe oxidation ratio, abundances of large ion lithophile elements (LIL), and some high field strength (HFS) elements. Isotope data for Sr, Pb, Nd, He, and O are variable but broadly are MORB‐like. We present data contrasting Mariana Trough (MTB) and Lau Basin basalts (LBB) showing how they differ in certain trace element and isotopic signatures and compare both to N‐MORB. Relative to N‐MORB and LBB, the MTB are enriched in alkalis, alkaline earths, light rare earth elements (REE), H2O, and Fe'''/Fe'', even for “primitive” samples, while having MORB‐type He (3/4 = 7.8 to 8.4 × RA), Sr (87/86 mean = 0.70293) and Nd (ε = +10.2). The Lau Basin is zoned with a central area having N‐MORB characteristics for H2O, LIL, REE, Nd (ε = +8.1 to 9.0), and O but a depletion in HFS elements. Sr is more radiogenic (mean 87/86 = 0.70347) and 3He/4He (3/4 = 7.2 to 11.0 × RA) is high relative to N‐MORB. The Lau Basin has a zone, bordering the adjacent island arcs, which is like MTB. In both back arc basins, relatively primitive (unfractionated) basalts with Mg/100(Mg + Fe″) > 62 are found which resemble postulated primitive N‐MORB. Calculated parental magmas (obtained by adding xenocrystic olivine) plot near or on 3 and 4 phase boundaries at 1–1.5 GPa for the OL‐DI‐SI system. Low P fractional crystallization and magma mixing explain most of the observed rock types. Possible explanations for differences between MTB and LBB include differences in the extent of previous melting episodes of their mantle sources and effects of source metasomatism through dehydration and partial melting of subducted lithosphere. The long and complex history of Mariana Trough mantle sources led to a metasomatized mantle which gives rise to the distinctive MTB. In contrast, the Lau Basin is dominated by basalts derived from a source depleted in volatiles, LIL, and HFS elements. A previous melting history is implied. Mixing with a mantle component enriched in 87Sr and 3He may be due to mantle counterflow driven by the subduction process.
The evolution of impact basins: Cooling, subsidence, and thermal stress
Authors: Bratt Steven R. , Solomon Sean C. , Head James W.
Published: April 2008

Potentially important contributors to the topography and tectonics of multi‐ring impact basins are the thermal contraction and thermal stress that accompany the loss of heat emplaced during basin formation. Heat converted from impact kinetic energy and contributed from the uplift of isotherms during cavity collapse are important components in the energy budget of a newly‐formed basin. That the subsequent cooling may have been an important factor in the tectonic evolution of the Orientale basin is suggested by the deep central depression and by a surrounding region of extensive fissuring. To test these concepts, we develop models for the anomalous temperature distribution immediately following basin formation, and we calculate the resulting elastic displacement and stress fields that then would accompany cooling of the basin region. All models predict subsidence of the basin floor and a near‐surface stress field consistent with fissuring. In addition, the rates of cooling and of accumulation of thermal stress are in agreement with the inferred timing of fissure formation in Orientale. The sensitivity of the predicted displacements and stresses to the initial temperature field allows us to place bounds on the quantity and distribution of impact heat emplaced during basin formation. In order to be consistent with the observed topography and the distribution of fissures in the Orientale basin, the buried heat deposited during the basin‐forming event was between 1032 and 1033 erg. It is likely that most of this heat was concentrated within a distance of 100–200 km from the point of impact.
Neogene tectonic rotation of the Santa Ynez Range, Western Transverse Ranges, California, Suggested by paleomagnetic investigation of the Monterey Formation
Authors: Hornafius J. Scott
Published: April 2008

A paleomagnetic investigation was conducted on dolomite beds in the middle and upper Miocene Monterey Formation in order to determine the timing and amount of post‐early Miocene tectonic rotation experienced by the Santa Ynez Range (part of the western Transverse Ranges province of California). Five stratigraphic sections of the Monterey Formation exposed along the coastline west of Santa Barbara were extensively sampled. The sections were correlated using tuff beds, and ages were assigned to each dolomite bed on the basis of magnetostratigraphy and diatom biostratigraphy. The dolomite beds possess stable primary remanent magnetic directions which pass fold tests and reversal tests, and show a consistent decrease in magnetic declination with decreasing age. Rocks 14.8 to 15.8 m.y. old have a mean magnetic declination of 92±7°, whereas rocks 8 to 11 m.y. old have a mean magnetic declination of 36±7°. The consistent upsection decrease in magnetic declination within these stratigraphic sections is attributed to a rapid 56±10° clockwise rotation of the entire Santa Ynez Range between 15.2±0.1 and 10±1 m.y. B.P. The mean magnetic declination of 36±7° in rocks 8 to 11 m.y. old is probably due to continued clockwise rotation of the Santa Ynez Range during the Plio‐Pleistocene. An early Miocene palinspastic reconstruction is proposed in which the area of the presently east‐west trending Santa Ynez Range is restored to an initially north‐south orientation.
Resistivity models of the Bell Creek Granite, Michigan determined by the magnetotelluric method
Authors: Young Charles T. , Rogers James C.
Published: April 2008

The Bell Creek Granite in northern Michigan is indicated on magnetotelluric soundings as a region of extremely high apparent resistivities (over 10,000 ohm m). The tippers point toward the center of the granite. Sixty‐five magnetotelluric soundings over the granite have been used to find a regional model. Soundings in the frequency range 1 to 384 Hz indicate a three‐layer regional model. The highly resistive middle layer of the regional model is interpreted as the root of the Bell Creek Granite. The thickness of the resistive layer has been fit to a two‐dimensional polynomial, which indicates that the thickness of the granite ranges from 12.5 to 17.5 km, increasing to the southeast.
Rift Structure of the Northern Mississippi Embayment from the analysis of gravity and magnetic data
Authors: Hildenbrand Thomas G.
Published: April 2008

Gravity and magnetic data have been simultaneously inverted to derive a crustal model of the northern Mississippi Embayment which is compatible with geologic and seismic refraction data. The results indicate that this region is a site of a late Precambrian‐early Paleozoic rift system. An anomalously dense layer is present at the base of the crust and thickens beneath a broad northeast trending graben that formed during the initial phases of rifting. The thickest part of anomalous crust occurs beneath the region of greatest seismic activity, which lies within the geographic limits of the graben. It is suggested from this correlation that strain accumulates within the anomalous crust layer, which acts as an inhomogeneity in a relatively homogeneous lithosphere. Based on the results of this study and previous geophysical studies, the complex tectonic evolution of the upper Mississippi Embayment since late Precambrian time is rift formation possibly along a pre‐existing shear zone, graben development in Cambrian time, reactivations in Permian and Cretaceous time, and subsequent formation of the present Mississippi Embayment and fault zones with large influences from rift structures.
Deformation in the Long Valley Caldera, California, 1983–1984
Authors: Estrem J. E. , Lisowski M. , Savage J. C.
Published: April 2008

Measurements of deformation in and around the Long Valley caldera in the interval July 1983 to August 1984 indicate that deformation is proceeding at a roughly uniform rate and that the net deformation for the year is about the same as for the preceding year. The 1983–1984 deformation of the 40‐line trilateration network can be approximated as the effect of the expansion (0.022 km3) of a spherical magma chamber located 10 km beneath the resurgent dome plus right‐lateral slip (50 mm) on the uppermost 2 km of the 8.5‐km‐long 1983 rupture surface in the south moat of the caldera. This same model furnishes an approximate fit to the tilting observed at six 1‐km aperture bench mark arrays within the caldera, although the quantitative fit lies somewhat outside the estimated observational error. The model, though obviously too simple to furnish a detailed fit to the complex process of magma chamber reinflation, does furnish a reasonable overall picture of the deformation.
Earthquake deformation cycle in the Andean Back Arc, western Argentina
Authors: Reilinger Robert , Kadinsky‐Cade Katharine
Published: April 2008

Repeated leveling surveys conducted in 1938, 1967, 1975–1976, 1978–1979, 1980, and 1981 provide information on preseismic, coseismic, and postseismic movements associated with the Ms ∼ 7.4 1977 Caucete, Argentina, earthquake sequence. The spatial pattern and amount of uplift (∼1 m) that accompanied the earthquake suggest 4 m of slip on a north‐south trending, west dipping fault, buried 17 km below the surface, with a dip of 35°, a downdip width of 24 km, and a length of 80 km. These fault parameters are generally consistent with the seismic focal mechanism, the moment of the double main shock, and the distribution of aftershocks. Vertical movements during the first preseismic period (1938–1967), while an order of magnitude smaller, have a spatial pattern similar to the observed coseismic movements. The second period of preseismic deformation (1967–1976) is characterized by movements opposite those which accompanied the earthquake (∼2±1 cm of relative subsidence). During the first postseismic interval (1978–1980), deformation continued in the same sense as the coseismic movements (an additional 10±1 cm of relative uplift). Subsequent postseismic movements (1980–1981) were opposite in sense to the coseismic deformation (∼12±1 cm of relative subsidence). We suggest that the preseismic movements for the 1938–1967 time period result from reverse slip (∼50 cm) on a downdip section of the 1977 earthquake fault. This slip may have been induced by a Ms ∼ 7.5 earthquake that occurred near San Juan in 1944 or may represent coseismic slip for a M ∼ 6.5 earthquake that occurred in 1941. Deformation during the second preseismic period (1967–1976) is interpreted as being due to steady strain accumulation on the fault (∼9 mm yr−1). The initial postseismic movements (1978–1980) are roughly consistent with afterslip on the 1977 earthquake fault (∼40 cm) in the same sense as the coseismic slip. The second phase of postseismic deformation may represent the period of rapid postseismic recovery (i.e., strain accumulation) observed previously in interplate areas. There is some evidence that strain accumulation following the earthquake began on the updip section of the fault. This process of strain accumulation may be responsible for the fact that the 1977 main shock initiated at the updip end of the coseismic fault. Assuming that the time predictable model of earthquake occurrence is applicable to this area, we estimate that the next earthquake on the 1977 earthquake fault will occur in 200–600 years.
Comparison of 2.8‐ and 21‐cm microwave radiometer observations over soils with emission model calculations
Authors: Burke W. J. , Schmugge T. , Paris J. F.
Published: April 2008

An airborne experiment was conducted under NASA auspices to test the feasibility of detecting soil moisture by microwave remote sensing techniques over agricultural fields near Phoenix, Arizona at midday of April 5, 1974 and at dawn of the following day. Extensive ground data were obtained from 96 bare, sixteen hectare fields. Observations made using a scanning (2.8 cm) and a nonscanning (21 cm) radiometer were compared with the predictions of a radiative transfer emission model. It is shown that (1 )the emitted intensity at both wavelengths correlates best with the near surface moisture, (2) surface roughness is found to more strongly affect the degree of polarization than the emitted intensity, (3) the slope of the intensity‐moisture curves decreases in going from day to dawn, and (4) increased near surface moisture at dawn is characterized by increased polarization of emissions. The results of the experiment indicate that microwave techniques can be used to observe the history of the near surface moisture. The subsurface history must be inferred from soil physics models which use microwave results as boundary conditions.
Laboratory observations of turbulent penetrative‐convection planforms
Authors: Willis G. E. , Deardorff J. W.
Published: April 2008

A laboratory model of the convective planetary boundary layer has been used to observe planforms near the surface and the top of the mixed layer. Near the surface the dominant convection pattern consists of irregular open cells with average horizontal dimension of 1.2h, where h is the height of the mixed layer. Smaller‐scale dendritic convergence lines appear near the edges of the open cells and are swept horizontally toward the most energetic plumes. These are often located where several open cell convergence lines intersect. Sometimes a plume is observed to be in a state of rotation, giving the appearance of a dust devil. Viewed in planform near the top of the mixed layer, or in side view, the plumes appear as penetrating, spreading domes of mixed layer fluid. Together, the plumes and their domes constitute closed cells which coexist with the open cells and have about the same horizontal dimension of 1.2h. In planview the closed cells usually appear to be randomly distributed. Over about 4% of the available area, however, the closed cells form the periphery of a large open cell ring with average diameter 3.3h, corresponding to the large rings observed by Hardy and Ottersten [1969] using radar.
An instrument system for long‐term sediment transport studies on the continental shelf
Authors: Butman Bradford , Folger David W.
Published: April 2008

A bottom‐mounted instrument system has been designed and built to monitor processes of bottom sediment movement on the continental shelf. The system measures bottom current speed and direction, pressure, temperature, and light transmission and photographs the bottom. The system can be deployed for periods of 2–6 months to monitor intermitent processes of sediment movement such as storms and to assess seasonal variability. Deployments of the system on the U.S. east coast continental shelf show sediment resuspension and changes in bottom microtopography due to surface waves, tidal currents, and storms.
On the equilibrium linear basin response to fluctuating winds and mesoscale motions in the Ocean
Authors: Harrison D. E.
Published: April 2008

The linear equilibrium theory of the response of a homogenous fluid in a flat bottom basin on the β‐plane to oscillatory wind forcing has in the past been used to examine the possible relevance of wind forcing to the existence of mesoscale motions in the ocean. It is here shown that the predicted response to forcing at frequencies appropriate to these motions is unsatisfactorily sensitive to the poorly known value assumed to characterize the model dissipative process. Modest changes in this value lead to order one changes in the character of the forced response. It does not appear appropriate at this time to assess the importance of the direct wind forcing process in the generation of mesoscale motions using this model.
Long‐range transport of trace elements
Authors: Husain Liaquat , Samson Perry J.
Published: April 2008

Concentrations of 13 trace elements and total suspended particulates were measured for 24 consecutive days in July 1975 at Whiteface Mountain, a remote site in the Adirondack Mountains of New York. High episodic concentrations were observed during a five‐day period, July 16 through 20. Air trajectory calculations showed that stagnant air masses originating southwest of Whiteface Mountain were the primary sources of these high concentrations. During July 1976 the sampling network was extended to four stations separated by hundreds of kilometers in New York State plus a site in New Jersey. Air trajectory calculations for July 19 and 20, when peak concentrations of particulates and trace metals were observed at all five stations, strongly suggest that the particulates and trace metals were transported from sources southwest of New York State.
Response of atmospheric surface layer turbulence to a partial solar eclipse
Authors: Antonia R. A. , Chambers A. J. , Phong‐Anant D. , Rajagopalan S. , Sreenivasan K. R.
Published: April 2008

Measurements of velocity and temperature fluctuations were made over a period including a solar eclipse of 80% totality to determine the response of surface layer to the change in ground heat flux. The response of the rms velocity fluctuation lags behind that of the rms temperature fluctuation by about 20 min. Although the velocity spectrum exhibits a good inertial subrange for the whole period of observation, the inertial subrange in the temperature spectrum disappears shortly after the start of the eclipse. It is found that during the eclipse the surface layer turbulence approximately follows a continuum of equilibrium states in response to stability changes brought about by the change in surface heat flux.
Lightning location and lower‐ionospheric height determination from two‐station magnetic field measurements
Authors: McDonald T. B. , Uman M. A. , Tiller J. A. , Beasley W. H.
Published: April 2008

Lightning locations in two maritime nocturnal thunderstorms, one occurring over the Atlantic Ocean, the other over the Gulf of Mexico, were determined using wide band magnetic direction finding from Gainesville and Kennedy Space Center, Florida. Within experimental error, all lightning was found to occur within National Weather Service radar reflectivity patterns. From the lightning locations and measured arrival times of first and second sky waves at Kennedy Space Center, ionospheric reflecting heights for both sky waves were determined. Lightning distance and ionospheric height were also computed using the single‐station technique recently described by Kinzer [1974]. Kinzer's technique is shown to be very inaccurate for one of the two storms studied because effective reflecting heights for first and second sky waves were different. During a 15‐min interval, the Atlantic storm produced an average of about 6 flashes per minute, an average of about 3 strokes per flash, and a mean initial electric field peak, normalized to 100 km, of 5.4 V/m for first strokes and 3.6 V/m for subsequent strokes. During a 45‐min interval the Gulf storm produced an average of about 5 flashes per minute, an average of about 4 strokes per flash, and a mean initial peak field, normalized to 100 km, of 10.2 V/m and 5.5 V/m for first and subsequent strokes, respectively.
The history of air forming various marine fogs off Nova Scotia in August 1975
Authors: Bressan David J. , Larson Reginald E.
Published: April 2008

Radon, chemical, and condensation nuclei measurements were used to characterize air in which marine fogs formed off the coast of Nova Scotia in August 1975. Tracing of air mass trajectories from weather maps showed that either continental or maritime air could reside at the fog sites, with some fog events bridging the boundary between these two types of air. Radon and chemical data were used to assess the relative continental contributions to the foggy air parcels as well as to define boundaries between parcels. Chemical results also showed that the fog waters contained varying levels of continental and marine components, probably derived from the original aerosol content of the air. Meteorological limitations on air mass histories supported evidence for K enrichment in the sea‐surface‐derived aerosol component. Similarly, evidence of SO4= being enriched in those aerosols, as well as being added to the fog water from continental sources, was found. A device for acquisition of fog water samples and the measurement of their ionic conductivities in real time is described. It enabled monitoring changes in the salt load of the air within fogs and thereby marked air mass transitions in some of them. Besides magnitudes, the rates of change of the monitored variables appear to be practical real‐time indicators.
Oxygen levels in the prebiological atmosphere
Authors: Kasting J. F. , Liu S. C. , Donahue T. M.
Published: April 2008

A photochemical model of the early terrestrial atmosphere is used to find oxygen profiles as a function of the hydrogen and carbon monoxide outgassing rates from volcanoes and the rate of oxidation of the earth's crust. Steady state solutions for the amount of O2 in the atmosphere are possible only when the combined loss rate from all three processes can balance the production of oxygen from photodissociation of H2O, followed by escape of hydrogen to space. If limiting flux controls the escape rate, then the production rate of oxygen atoms depends linearly upon the water vapor mixing ratio at the tropopause. Evidence is presented which indicates that the hydrogen outgassing alone was sufficient to overwhelm the production of oxygen, leading to ground level O2 mixing ratios of the order of 10−12 times the present atmospheric level (PAL) or below. The O2 mixing ratio increases rapidly with altitude up to a peak of 10−5 PAL at 60 km owing to the presence of CO2. Present‐day concentrations of N2, CO2, and H2O are assumed in the calculation. The effect of possible temperature variations upon the H2O content is discussed.
Studies of different energy strategies in terms of their effects on the atmospheric CO2 concentration
Authors: Niehaus F. , Williams J.
Published: April 2008

Energy options for the medium‐ to long‐term future have to be studied in terms of demand, resources, technologies, strategies, and constraints. A joint effort of the International Atomic Energy Agency (IAEA) and the International Institute for Applied Systems Analysis (IIASA) is directed toward assessing risks inherent in the deployment of any energy system. A combination of three energy supply technologies is available to satisfy projected requirements. These are nuclear, solar, and (to a limited extent) fossil fuel energy conversion systems.
Ozone in the upper troposphere from gasp measurements
Authors: Nastrom G. D.
Published: April 2008

Several aspects of tropospheric ozone variations are examined by using ozone measurements made from commercial airliners (Gasp data). The east‐west variations of ozone have a predominant wavelength near 2400 km, by visual inspection of the autocorrelation function, while temperature and wind have predominant wavelengths near 3300 km. The different wavelengths may be due to a sampling bias. Distance‐lagged correlation functions of ozone with temperature and wind show a definite periodicity with wavelengths near 2400 km. The low correlation of ozone with meridional wind speed at lag zero makes it necessary to have many pairs of data to estimate even the sign of the meridional ozone flux with confidence. Tropical tropospheric ozone values above 100 parts per billion by volume (ppbv) appear to be associated with meridional transport from middle latitudes, and in some cases, relatively large tropical ozone values are coincident with clouds. A diurnal variation with amplitude near 2.0 ppbv is found with phase (time of maximum value) near 0800 LT at 32°–64°N but with phase near 1700 LT at 16°–32°N.
Atmospheric negative ion hydration derived from laboratory results and comparison to rocket‐borne measurements in the lower ionosphere
Authors: Keesee Robert G. , Lee Naisin , Castleman A. W.
Published: April 2008

Recent laboratory results on the hydration of CO3− and HCO3− are extrapolated to atmospheric conditions to determine the extent of hydration of these ions in the stratosphere and lower ionosphere. Comparison with rocket‐borne measurements in the lower ionosphere is made. It is concluded that in the normal nighttime lower ionosphere, monohydrates or dihydrates of the atmospheric negative ions CO3−, HCO3−, and NO3− should be prevalent; however, the extent of hydration is sensitive to atmospheric temperature.
Laboratory simulation of the gyre in the Alboran Sea
Authors: Whitehead John A. , Miller A. R.
Published: April 2008

A laboratory experiment is described which appears to exhibit flows which are similar to the flow‐counterflow in the Strait of Gibraltar and, for certain values of the parameters involved, to the gyre and front in the western Alboran Sea. The experiment is transient in nature and is made with two connecting basins on a rotating turntable. A sliding door is fitted into the channel connecting the two basins. Each basin is filled with water, the door is closed, and salt is added to one side so that the two waters have different densities. After the waters have spun up to rest in the rotating frame, the door is opened. A flow, driven by the density imbalance, is observed shortly thereafter, the lighter fluid rising up over the heavier fluid and pushing into the basin containing the heavy fluid. Likewise the heavy fluid pushes into the basin containing lighter fluid. For very rapid rotation these flows are violently unstable. For less rapid counterclockwise rotation both currents stay confined to a narrow jet which clings to the right‐hand wall of the basins which they are entering. At some lower rate of rotation the jet cannot hold to a sufficiently curved wall, and the jet separates from the wall—a gyre is observed between the jet and the wall. The gyre and the jet initially are both a Rossby radius in size, but gradually the gyre grows larger. Growth of the gyre seems to result from an accumulation of fluid from the jet as it returns to the wall. Scaling arguments and estimates of buoyancy, Coriolis, and wind forces are advanced in support of the concept that this laboratory‐produced gyre and the gyre in the Alboran Sea share the same dynamics.
The transient response of the North Atlantic: Some model studies
Authors: Anderson David L. T. , Bryan Kirk , Gill A. E. , Pacanowski R. C.
Published: April 2008

Four numerical experiments have been designed to clarify the role of stratification and topography on the transient response of the ocean to a change in wind forcing. The geometry and topography appropriate to the North Atlantic between the equator and 50°N are used to make the study more appropriate to a real ocean. In all four experiments, zonally symmetric wind stresses are ‘switched on’ at the upper surface of a resting model ocean. Two short experiments, 1 and 2, with a duration of 100 days, are first discussed. These are for a homogeneous ocean with and without topography. The response in the flat‐bottomed case can be described either in terms of planetary waves or basin modes, but when topography is present, no obvious wave propagation was identified. Higher‐frequency basin modes are detectable, but their amplitude is much lower than that in the flat‐bottomed case. They are damped out on a time scale of ∼50 days. Two longer experiments, 3 and 4, are then analyzed. These are the analogs of 1 and 2, but stratification was included. The introduction of stratification for the ocean with topography leads to a new, longer time scale, not just for the baroclinic modes, but also for the barotropic. Despite the presence of topography, modal analysis was found useful in analyzing the results. Propagation effects are analyzed, both on the moderately fast time scale of internal Kelvin waves and on the slow time scale of internal planetary waves. Kelvin waves are apparent along the equator, the northern boundary, and on the eastern coast in the Gulf of Guinea from the equator to 20°N. They are not clearly visible anywhere on the west coast. Planetary waves can be detected in the interior both in the presence and absence of topography. When topography is present without stratification, the transport of the Gulf Stream is reduced from 30 to 14 million tons per second. This is a well‐known result. With stratification there is no significant difference in transport between the case with or without topography.
Turbulent flow in a depth‐limited boundary layer
Authors: Nowell Arthur R. M. , Church Michael
Published: April 2008

Turbulent flow was investigated at a constant flow Reynolds number in a depth‐limited boundary layer. Relative roughness was 0.12. Roughness density (ratio of plan area of elements to total bed area) was varied to cover the range of flow types described by Morris [1955]. The effect of roughness density on velocity profile shape factors, energy dissipation, and streamwise kinetic energy confirmed the existence of three types of roughness density‐flow interaction, namely, ‘skimming,’ ‘wake interaction,’ and ‘isolated roughness’ flows. The velocity profiles and kinetic energy measures identified three layers in the vertical profile: an outer layer (y/D > 0.35), a wake layer (0.35 > y/D > 0.10), and an inner region (y/D < 0.10). The wake layer is produced by strong turbulent action accompanying vortex shedding at intermediate roughness densities. Spectral measurements and calculations of the turbulent macroscale indicated that the spectral shape is affected by the free surface but that below y/D = 0.5 a parametric model using the turbulent Reynolds number in the spectral energy equation adequately describes the spectral shape for all roughness densities. Implications of these results are discussed for the study of shallow, natural flows with high relative roughness.
The effect of a tropical sea surface temperature anomaly in a Coupled Ocean‐Atmosphere Model
Authors: Wells N. C.
Published: April 2008

A tropical sea surface temperature (SST) anomaly is imposed as an initial condition in a coupled mixed layer ocean‐atmosphere model of the Southern Hemisphere, which is integrated for 80 days. The atmospheric response to the anomaly is shown to be similar to that occurring in an atmospheric model with a fixed SST anomaly, reflecting the persistent nature of tropical SST anomalies. However, in the equatorial region of the coupled model, the anomalous zonal wind circulation produced by the SST anomaly results in enhanced wind mixing, surface heat loss and upwelling on the eastern edge of the anomaly, and reduced wind mixing and surface heat loss on the western edge of the anomaly. This causes an increased SST on the western edge and a decreased SST on the eastern edge, which lead to a westward movement of the anomaly of 20° longitude in 80 days. At extratropical latitudes the changes in the circulation of the atmosphere as a result of the initial anomaly are shown to produce new SST anomalies of up to 2°C. Correlations between the atmospheric forcing and the SST anomalies reveal that wind mixing is a major cause of the anomalies, while the correlation with surface heat flux is small.
Solar modulation of the supply current for atmospheric electricity?
Authors: Willett J. C.
Published: April 2008

Motivated by a recent paper by Markson (1978), a simple model is developed to estimate the effect of a solar particle absorption event on the current supplied by thunderstorms to the global circuit of atmospheric electricity. It is concluded that the fractional increase in this supply current due to such an event may be substantially smaller than that suggested by Markson and may be independent of the height of the storm tops. An explanation is offered for the disagreement.
Carbon dioxide in the urban atmosphere: Dependencies and trends
Authors: McRae J. E. , Graedel T. E.
Published: April 2008

Carbon dioxide data from three urban sites in New Jersey covering periods of up to 9 years have been analyzed by a variety of statistical techniques. Hourly average concentration maxima as high as 585 ppm are seen, as are minima as low as 285 ppm. The diurnal patterns appear to be influenced strongly by local mixing and turbulence conditions and seldom show the ‘rush hour’ peaks often found in urban carbon monoxide data. Seasonal analysis demonstrates that maxima in monthly medians of daily mean CO2 concentration occur in winter and that minima occur in summer. Such a pattern suggests a strong contribution from stationary combustion sources to urban CO2 levels, at least in the winter months. The winter‐summer difference in the monthly median of daily mean CO2 is of the order of 30 ppm, a much larger difference than is found in the rural setting. The long‐term trend of the baseline CO2 concentration in these urban data is not monotonic but shows a time‐integrated increase of ∼0.6 ppm/yr, consistent with the range and pattern of concentration gradients observed at global background sites.
Atmospheric transmission from the Smithsonian Astrophysical Observatory Pyrheliometric measurements from 1923 to 1957
Authors: Hoyt Douglas V.
Published: April 2008

Using the pyrheliometric measurements of the Smithsonian Astrophysical Observatory (APO), the relative atmospheric transmission is calculated at four locations during the period 1923–1957. Decreases in atmospheric transmission caused by three major volcanic eruptions are evident in the Mt. Montezuma, Chile, records. For those volcanic eruptions in the tropics the transmission also decreases at Table Mountain, California. Each volcanic eruption is widely separated from the others in time and easily distinguishable in the radiation records. Both stations appear to suffer from local anthropogenic aerosol pollution near the ends of their records. It is concluded that the post 1940 cooling is not likely to be caused by increased volcanic activity. The annual cycle in atmospheric transmission is caused by variations in total precipitable water, so the climatology of total precipitable water is also investigated. Although an annual cycle in total precipitable water and aerosol loading is clearly evident, no long‐term trend in water vapor occurs at the APO sites. The large temporal and spatial variability of water vapor causes adjacent years to differ.
Instantaneous global nitrous oxide photochemical rates
Authors: Johnston H. S. , Serang O. , Podolske J.
Published: April 2008

In recent years, vertical profiles of nitrous oxide have been measured by balloon up to midstratosphere at several latitudes between 63°N and 73°S, including one profile in the tropical zone at 9°N. Two rocket flights measured nitrous oxide mixing ratios at 44 and 49 km. From these experimental data plus a large amount of interpolation and extrapolation, we have estimated a global distribution of nitrous oxide up to the altitude of 50 km. With standard global distributions of oxygen and ozone we carried out instantaneous, three‐dimensional, global photochemical calculations, using recently measured temperature‐dependent cross sections for nitrous oxide. The altitude of maximum photolysis rate Of N2O is about 30 km at all latitudes, and the rate of photolysis is a maximum in tropical latitudes. The altitude of maximum rate of formation of nitric oxide is latitude dependent, about 26 km at the equator, about 23 km over temperate zones, and 20 km at the summer pole. The global rate of N2O destruction is 6.2×1027 molecules s−1, and the global rate of formation of NO from N2O is 1.4×1027 molecules s−1. The global N2O inventory divided by the stratospheric loss rate gives a residence time of about 175 years with respect to this loss process. From the global average N2O profile a vertical eddy diffusion profile was derived, and this profile agrees very closely with that of Stewart and Hoffert (1975).
The physical structure and life history of cyclonic Gulf Stream Ring Allen
Authors: Richardson P. L. , Maillard C. , Stanford T. B.
Published: April 2008

A cyclonic Gulf Stream ring, Allen, was followed over its life from September 1976 to April 1977 in the region north of Bermuda. Conductivity, temperature, and depth; expendable bathythermograph; and velocity profile measurements were made in Allen, and over the last 5 months of its life, satellite buoys were used to track continuously its movement. The measurements indicate that in December 1976 Allen split into two rings, a large one, Allen, and a small one, Arthur. Arthur moved rapidly eastward and coalesced with the Gulf Stream near the New England seamounts. Allen moved in a large clockwise loop; at the end of February 1977 it became attached to the Gulf Stream and reformed into a modified ring, smaller in size and faster in rotation. At the end of April 1977 the modified ring coalesced with the Gulf Stream and disappeared as it was advected downstream in the stream. The principal results of this study are that (1) the New England Seamount chain was a major influence in the genesis of Allen and on the trajectories of nearby rings; (2) while a free eddy, months after its formation, Allen evolved into a bi modal or peanut‐shaped structure; (3) the bimodal structure ultimately bifurcated, spawning a new isolated eddy, denoted as Arthur, and a modified remnant, Allen; (4) the velocity field of Allen involved the whole water column, with bottom velocities of 10–15 cm s−1; (5) the barotropic velocity at the center of Allen (6 cm s−1 to NNW) was about equal to its translation velocity (4 cm s−1 to NW); (6) especially energetic inertial motions were seen at the center of Allen, and these may play a role in enhancing the stirring of water properties; (7) Allen survived several close encounters or entrainments with the Gulf Stream, proving that such encounters can be nonfatal to a ring; (8) the encounters appear to result in injections (exchanges) of water (momentum, heat, etc.) into the rings at an estimate rate of 106 m3 s−1 per ring; and (9) the behavior of Allen and Arthur was in contrast to the results of some other studies which have shown that rings generally drift slowly and passively southwestward.
Atmospheric removal processes for high molecular weight organochlorines
Authors: Bidleman Terry F. , Christensen Eric J.
Published: April 2008

Factors influencing the atmospheric removal of polychlorinated biphenyls (PCB) and the chlorinated insecticides p,p′,‐DDT, chlordane, and toxaphene were investigated in the city of Columbia, South Carolina, and at the North Inlet estuary on the South Carolina coast. Dry deposition velocities (Vd) for individual organochlorines (OC) varied by 1–2 orders of magnitude from day to day, and in Columbia log Vd was correlated with average wind velocity. Higher Vd were observed for the less volatile OC, reflecting a greater degree of attachment to aerosols. Average Vd (cm/s) in Columbia were: Aroclor 1016 = ≤0.04, Aroclor 1254 = 0.43, chlordane = 0.068, and p,p′‐DDT = 1.3. The trend in Vd paralleled the percentages of these OC retained by a glass fiber filter during high volume air sampling. Vd for Aroclor 1254 and p,p′‐DDT at North Inlet were about 3–4 times lower than those in Columbia. Toxaphene was the most prevalent OC in precipitation at North Inlet, with concentrations exceeding 100 ng/1 during the late summer and early fall. Average washout ratios at North Inlet were: Aroclor 1254 = 94, p,p′‐DDT = 87, chlordane = 8.4, and toxaphene = 246. Dry and wet removal rates for Aroclor 1254 and p,p′‐DDT were more similar than might be expected from the large difference (more than 2 orders of magnitude) in their reported vapor pressures, although the vapor pressure for Aroclor 1254 is not accurately known. The similarity of PCB and p,p′‐DDT removal rates suggests an explanation for the fact that PCB and p,p′‐DDT ratios in seawater are about the same as those in the ocean atmosphere.
Drop size distribution measurements in convective storms with a vertically pointing 35‐GHz Doppler radar
Authors: Pasqualucci F.
Published: April 2008

Measurements at vertical incidence in convective storms with a 35‐GHz pseudonoise coded high‐resolution radar at Johannesburg, South Africa, are discussed. The radar is bistatic and has the capability to measure targets at very short ranges (≈ 19 m). This capability is used to derive an accurate experimental mean velocity‐reflectivity (
‐Z) relationship in convective storm systems. It is shown that at an altitude of 19 m the standard deviation of the data points from the mean
‐Z relationship is about 0.25 m s−1, indicating that the contribution of the vertical air velocity at the low altitude of 19 m is less than about ±0.5 m s−1 (95% confidence limit). The experimental
‐Z relationship is then used to derive drop size distributions from the measured Doppler spectra in convective rainfall with high time resolution (10 s). Some of the measured drop size distributions are discussed and related to specific kinematic features of the storm under study. For example, drop size distributions measured in a severe squall line show a large abundance of smaller drops (< 1.5 mm in diameter) in regions of wind shear near the edges of the main downdraft core. A possible explanation of this large concentration of smaller drops is sorting of the hydrometeors caused by shear in the horizontal wind that is generated by the divergence of the downdraft at the ground. These observations show the usefulness of this radar measurement technique to detect features of drop size distributions in convective systems and relate them to storm structure and kinematics.