bluuebunny/crossref_metadata_2025 huggingface dataset:
Length of day and atmospheric angular momentum: A comparison for 1981–1983
Authors: Morgan Peter J. , King Robert W. , Shapiro Irwin I.
Published: April 2008

We combined measurements from laser ranging to the moon, laser ranging to the LAGEOS satellite, and very long baseline interferometric observations of extragalactic radio sources, to produce a series of universal time (UT1) and length‐of‐day (LOD) variations for 1981–1983. The UT1 series was obtained by convolving the ensemble of measurements from all three techniques, suitably weighted, with a Gaussian function whose full width at half‐maximum (FWHM) amplitude was 5 days; values of LOD at 3‐day intervals were obtained by differencing. These values of LOD have 80% of their one standard deviation (sigma) errors ranging from 0.03 to 0.06 ms. We compared our UT1‐derived series of LOD values with two series of LOD derived from variations in atmospheric angular momentum (AAM). One series was developed by Rosen and Salstein from wind analyses performed by the U.S. National Meteorological Center, the other by Barnes et al. from analyses performed at the European Centre for Medium Range Weather Forecasts (ECMWF). Our attempt to estimate the one‐sigma errors of both yielded bounds between 0.02 and 0.05 ms (80% limits). After removing a model for tidal effects from the UT1‐derived LOD series, we find that the major harmonic components of the UT1‐derived and the ECMWF AAM‐derived series agree within the root‐sum‐square uncertainties, except for amplitude differences (UT1‐AAM) of 0.05±0.03 ms, −0.02±0.01 ms, and 0.02±0.01 ms, for periods of 183 days, 122 days, and 27.5 days, respectively. The first two of these amplitude differences may be accounted for by some combination of high‐altitude winds, ocean currents, atmospheric pressure and groundwater effects, and errors in the LOD series. Half of the difference in the 27.5‐day component may be accounted for by errors in the tidal model, due to uncertainties in the effects of the oceans and the fluid core, as described by Yoder et al. The root‐mean‐weighted‐square (temporal) differences between UT1‐derived and AAM‐derived LOD series, after high‐pass filtering (Gaussian FWHM = 45 days), are 0.066 ms if the ECMWF series is used and 0.076 ms if the National Meteorological Center series is used. Including the effect of pressure, where available, in the AAM computations reduces by about 10% the short‐period differences between the observed (UT1) and inferred (AAM) changes in LOD. For the characteristic 30‐ to 70‐day fluctuations there is no significant evidence (±0.5 day) of a temporal lag between atmospheric excitation and the response of the solid earth. Interpretation of the differences in AAM‐derived and UT1‐derived LOD is limited by our lack of knowledge of the uncertainties in the AAM observations. To within these limits it appears that atmospheric and tidal contributions are sufficient to account for the observed variations in length of day for periods of 1 year or less. Thus there is no evidence for significant contributions from any other geophysical effects to such variations in length of day.
Asymptotic normal modes of a laterally heterogeneous Earth
Authors: Dahlen F. A. , Henson I. H.
Published: April 2008

In the geometrical optics limit on an aspherical earth, the 2l + 1 singlet eigenfunctions of an isolated multiplet nSl, or nTl with n ≪ l are associated with the stable closed orbits of propagating surface waves. The long‐term evolution of surface‐wave trajectories is in turn governed by the great circular average
of the local relative phase velocity perturbation ϵ = δωlocal/ω0 where ω0 is the degenerate multiplet eigenfrequency and δωlocal is the local eigenfrequency perturbation. Correct to first order in ϵ, the normal
to a surface wave orbital plane, averaged over an orbit, satisfies the fast gyroscope equation
, where Δ is the angular arc length along the orbit. This equation stipulates that
precesses around the contours of
at a rate proportional to the contour spacing. The only paths that remain closed in the presence of the perturbation ϵ are those corresponding to the critical or stationary points where
= 0. Stable closed paths correspond to local minima and maxima of
, while unstable paths correspond to saddle points. A singlet eigenfunction is composed of waves propagating around all the great circle paths belonging to a single precessing family, and the associated asymptotic eigenfrequency perturbation δω/ω0 is just the value of the particular contour of
around which the normal
is precessing. Since the contours are closed about the local minima and maxima of
, the singlet eigenfunctions are confined to the vicinity of the locally slow and fast great circle paths on the surface of the earth. Caustics that are the envelopes of the precessing trajectories separate regions of oscillatory behavior from regions of exponential decay. The quantization condition that selects the eigenfrequencies or eigencontours from the continuum of contours of
is derived from the requirement that the WKBJ singlet eigenfunctions be single valued and properly connected along the caustics. Correct to first order in ϵ the condition is that the length of either caustic be equal to
. Alternatively, if
is regarded as the orbital angular momentum of a precessing surface wave, the condition is that 〈Lz〉 = m where the
axis coincides with a local minimum or maximum of
and 〈Lz〉 is averaged over a full precession cycle. This latter form of the quantization condition emphasizes the gyroscopic analogy and obviously resembles the definition of angular momentum eigenstates in quantum mechanics. All but one of the 2l + 1 asymptotic eigenfrequencies on a nonrotating earth are doubly degenerate because of the even parity of
, but this degeneracy is removed by the earth's rotation, which splits each doublet by an additional amount Δω ≈ 2mβΩz, where β is the rotational splitting parameter and Ω2 is the
component of the angular velocity of rotation.
Surface deformation associated with the November 23, 1977, Caucete, Argentina, earthquake sequence
Authors: Kadinsky‐Cade Katharine , Reilinger Robert , Isacks Bryan
Published: April 2008

Leveling data are combined with seismic observations from the November 23, 1977, Ms = 7.4 Caucete earthquake in western Argentina, in order to constrain models of crustal deformation in the Sierras Pampeanas tectonic province. The spatial pattern and amount of uplift ( ∼1 m) that accompanied this earthquake suggest 4 m of slip on a north‐south trending, west dipping fault with a dip of 35°, a downdip width of 24 km, and a length of 80 km. The top of the fault is 17 km below the surface. These fault parameters are generally consistent with the seismic focal mechanism and moment of the main shock, which occurred near the top of the fault. The fault length is derived from the distribution of local and relocated teleseismic aftershocks and from analysis of the main shock (a double event in which the two shocks occurred 21s apart and were separated by 65 km along the proposed fault plane strike). The fault width is determined from the locations of the larger hypocenters along the preferred fault plane. This fault is buried beneath the north‐south striking Sierra Pie de Palo, a Laramide style crystalline basement uplift in the western part of the Sierras Pampeanas province. The buried fault model is consistent with the lack of observed coseismic surface faulting and the broad, east‐west symmetric character of the overlying Sierra Pie de Palo. By combining the 1977 earthquake observations with topographic relief and with estimates of the age of deformation for the Sierras Pampeanas basement uplifts, we calculate a shortening rate of the order of 10 mm/yr for the past 5 m. y. for this Andean back arc province and estimate an average recurrence time of the order of 1000 years for earthquakes of this magnitude beneath the Sierra Pie de Palo.
Locations and spectral properties of earthquakes accompanying an eruption of Mount St. Helens
Authors: Fehler Michael
Published: April 2008

A joint hypocenter determination routine has been developed to accurately determine the locations of earthquakes occurring under Mount St. Helens. The method has a special application to Mount St. Helens, where most of the earthquakes are suspected to occur at shallow depth in a rather limited volume under the volcano. Differences in elevation among stations are allowed for in this routine. The location procedure determines, a best half‐space velocity and one station correction for each station simultaneously with earthquake hypocenters. Arrival time data from an array of portable digital seismic event recorders are supplemented with data from stations of the permanent University of Washington seismic network operating at the volcano. Earthquakes are found to occur along a line trending south‐east of the dome inside the crater. The shallowest events occur near the dome with hypocentral depth increasing with increasing distance from the dome. Station corrections can be interpreted to imply the existence of a high‐velocity body beneath the crater which extends at least between depths of .5 and 2.1 km beneath the crater floor. Spectra are calculated from earthquake waveforms recorded at three stations. The spectra show very little evidence for local site or path effects on frequency content of waveforms. Stress drops of earthquakes are calculated from measurements of corner frequency and low‐frequency spectral amplitude. Stress drops of earthquakes vary between .5 and 5 bars. There is no evidence for a limiting corner frequency for small earthquakes as has been found for earthquakes occurring in Mammoth Lakes, California. Data fit well a linear trend between log seismic moment and log source radius fit to data for earthquakes ranging in size from 1014 to 1027 dyn cm, suggesting that there is no limiting source radius observed for earthquakes in this range of size.
Borehole tilt measurements from Charlevoix, Québec
Authors: Peters John , Beaumont Christopher
Published: April 2008

An array of three borehole tiltmeters near Québec City in eastern Canada is designed to study the tidal and secular response of the crust in the Charlevoix seismic zone. The objectives of this study of the first year of data from two boreholes of the array are to investigate the spatial coherency of the tidal observations and determine whether there are time variations in the tidal amplitudes and phases and to describe the main features of the secular tilt signal. The tidal analysis was done using a modified version of the HYCON harmonic analysis program with which the time‐varying tidal amplitudes and phases were determined by the sequential analysis of overlapping 2‐monthly subsets of the data. The admittance observed for the major semidiurnal (M2) and diurnal (O1) constituents varies by up to 10 and 30%, respectively, and is strongly correlated between boreholes. Comparison with admittance variations determined from two nearby tide gauges indicates a strong correlation in the amplitude fluctuations, pointing to a predominantly marine loading source for the time‐varying tilt admittance. Differences of up to 20% in amplitude and 5° in phase were found between the mean M2 results determined from boreholes 1 and 2, located only 80 m apart, indicating small‐scale distortion of the local tilt field by lateral inhomogeneities. The secular tilt from both boreholes correlates strongly with transient and seasonal water table fluctuations, suggesting the dominant influence of pore pressure effects on the nontidal tilt. A preliminary estimate of the detectability of long‐term regional trends in tilt is 0.4 μrad/yr.
Southern hemisphere stratospheric aerosol measurements: 2. Time variations and the 1974–1975 aerosol events
Authors: Gras J. L. , Laby Jean E.
Published: April 2008

A balloon‐borne photoelectric counter and jet impactor have been used to examine the southern hemisphere stratospheric aerosol from late 1974 to mid‐1976. Changes in particle morphology and loading observed in this period are consistent with a new source of aerosol in 1974. In the 10‐ to 16‐km altitude range the loading of particles with r > 0.15 μm increased by slightly greater than a factor of 2 from September 1974 to July 1976, while the loading of particles with 0.028 μ m < r < 0.15 μm decreased by approximately a factor of 2. The increased loading of particles with r > 0.15 μm in the 1975 southern winter was only about one‐fifth that observed at northern mid‐latitudes in the preceding northern winter.
Irradiance and beam transmittance measurements off the West Coast of the Americas
Authors: Spinrad Richard W. , Zaneveld J. Ronald V. , Pak Hasong
Published: April 2008

Measurements of total irradiance versus depth and beam transmission versus depth were made at stations near shore along the west coast of the North and South American continents. The water types at each station were optically classified according to the system of Jerlov (1976), thus providing additional information for the description of the distribution of the world's ocean water types. In addition, the parameter k/c, where k is the irradiance attenuation coefficient and c is the beam attenuation coefficient, has been shown to be a useful parameter for determining the relative particle concentrations of ocean water.
Deep currents in the Yucatan Strait
Authors: Hansen Donald V. , Molinari Robert L.
Published: April 2008

Current meter and hydrographic data were collected in the Yucatan Channel during a month in the autumn of 1970. Currents 15 m above the bottom are characterized by diurnal modulation and oscillations of 4‐ to 5‐day periods. The observed tidal currents are in phase with their counterpart in the Straits of Florida but of insufficient amplitude for consistency with the amplitude of diurnal tide observed in the Gulf of Mexico. The average current observed over the month was 3.9 cm/s toward SSW. Geostrophic current circulation and dissolved oxygen observations indicate a generally southward flow below about 1000‐m depth and at all depths in the eastern side of the channel during the latter part of the observation.
Direct evidence of solar flare modification of stratospheric electric fields
Authors: Holzworth R. H. , Mozer F. S.
Published: April 2008

Direct evidence of solar flare modification of stratospheric electric fields is presented through comparison of atmospheric electric field variations with fluxes of solar protons that bombarded the atmosphere during the August 1972 solar flares. Observed order of magnitude variations of the vertical electric field at 30‐km altitude in anticorrelation with the intensity of solar protons are quantitatively interpreted in terms of atmospheric conductivity variations produced by solar proton ionization of the air. Other geophysical data are presented which indicate the state of the magnetosphere during this epoch and which further indicate a phenomenological coupling between atmospheric and extraterrestrial events.
Fair weather electric charge transfer by convection in an unstable planetary boundary layer
Authors: Willett John C.
Published: April 2008

A second‐order‐closure approach is used to model the behavior of the turbulent convection current in an unstable planetary boundary layer over horizontally uniform terrain. The model identifies the surface fluxes of heat and momentum and the height of the inversion capping the layer as the primary meteorological parameters determining the strength of this current. Results indicate that convection of charge supplied by the electrode effect can have a significant impact on the local atmospheric electric circuit. A sample calculation for a very unstable layer shows that convection currents act as a local generator capable of reducing the total downward current density by as much as 44%.
Distribution of solar cycle signal in surface air temperature over North America
Authors: Currie Robert G.
Published: April 2008

Further analysis strengthens the conclusion of Currie (1974) that a solar cycle signal in surface air temperature does exist in North America. New findings are as follows: Geographically the distribution displays a highly coherent pattern. From a total 100 records the signal is detected or marginally detected at 55 locations. The northeast quadrant of the continent bounded by latitude 35°N and a trend line drawn northwest from (35°N, 105°W) parallel to the eastern edge of the Rocky Mountains contains 54 records and the signal is evidenced at 51 of these stations. The respective mean and standard deviation of amplitude and period are 0.29±0.15°C and 10.7±0.4 yrs. A significant portion of the variance is due to a latitude gradient of 0.20±0.05°C/103 km. The temperature records also show some evidence for a small 0.06°C signal at the 18.6 yr lunar‐nodal period. By increasing the bandwidth an order of magnitude, the findings buttress recent work on historical observations (Eddy, 1977) and climate modeling (Schneider and Mass, 1975) which indicate a coherent relation between events on the sun as reflected in solar activity and excursions in earth climate on time scale of order 102 yr.
Sensitivity of the predicted CO‐OH‐CH4 perturbation to tropospheric NOx concentrations
Authors: Hameed Sultan , Pinto Joseph P. , Stewart Richard W.
Published: April 2008

Measurements indicate that ambient NOx(NO + NO2) concentrations vary over at least an order of magnitude in the troposphere. Thus it is of interest to study atmospheric chemistry with NOx concentrations covering this range. In this paper we present steady state calculations which show that as NOx concentrations are increased from very low values, the hydroxyl radical concentration [OH] increases at first and then decreases. This change of behavior occurs at [NO2] ∼ 0.23 ppb in our model. Also, the response of the atmosphere to increased CO fluxes undergoes a qualitative change as a function of [NOx]. At low levels of [NOx], an increase in CO fluxes into the atmosphere depletes [OH] and increases [CH4] and [H2], as reported in the literature. However, at high values of [NOx], increased CO fluxes give rise to an increase in [OH] and, consequently, a decrease in [CH4] and [H2].
An assessment of the possible future climatic impact of carbon dioxide increases based on a coupled one‐dimensional atmospheric‐oceanic model
Authors: Hunt B. G. , Wells N. C.
Published: April 2008

A radiative‐convective equilibrium model of the atmosphere has been coupled with a mixed layer model of the ocean to investigate the response of this one‐dimensional system to increasing carbon dioxide amounts in the atmosphere. For global mean conditions a surface temperature rise of about 2°K was obtained for a doubling of the carbon dioxide amount, in reasonable agreement with the commonly accepted results of Manabe and Wetherald. This temperature rise was essentially invariant with season and indicates that including a shallow (300 m) ocean slab in this problem does not basically alter previous assessments. While the mixed layer depth of the ocean was only very slightly changed by the temperature increase, which extended throughout the depth of the mixed layer, the impact of this increase on the overall behavior of the ocean warrants further study. A calculation was also made of the temporal variation of the sea surface temperature for three possible carbon dioxide growth rates starting from an initial carbon dioxide content of 300 ppm. This indicated that the thermal inertia of the slab ocean provides a time lag of 8 years in the sea surface temperature response compared to a land situation. This is not considered to be of great significance as regards the likely future climatic impact of carbon dioxide increase.
Property distributions along the σθ = 26.8 isopycnal in the Atlantic Ocean
Authors: Broecker Wallace S. , Östlund H. Göte
Published: April 2008

The Atlantic Geosecs data for main oceanic thermocline provide a basis for reexamining the conventional views with regard to the origin and movement of these waters. Our analysis of these data suggests the following: (1) More attention must be given the dynamics associated with the fronts at 15°N and 15°S. The study of these important features has been sorely neglected. (2) The possibility that waters in the equatorial thermocline are generated by vertical mixing rather than by lateral ventilation must be seriously considered. (3) The tritium results in hand clearly demonstrate the potential of repeated surveys of this transient tracer in refining our knowledge of thermocline dynamics. (4) The tritium results are not, however, likely to resolve the question of the relative importance of vertical and horizontal mixing. This can only be done through the direct addition of tracers to the interior of the thermocline.
Temperature fine structure near the Sea‐ice margin of the Chukchi Sea
Authors: Paquette Robert G. , Bourke Robert H.
Published: April 2008

Temperature fine structure with peak‐to‐peak fluctuations often exceeding 2°C is prevalent throughout the marginal sea‐ice zone of the shallow Chukchi Sea in midsummer. It is normally found within 20–35 km outside of the ice and seldom farther than 5–10 km inside the ice margin. It has also been infrequently found more than 100 km south of the ice. Temperature and salinity fronts of all degrees of sharpness occur in the same general area, but the two types need not be coincident. Considerable variability in time and length scales of fine structure elements has been noted with persistences ranging from 2 hours or less to more than 20 hours and length scales ranging from 600 m to more than 20 km. While much of this variability is intrinsic, part can be accounted for by the inability to sample in the direction of flow and the relative motion between the sampling platform and fine structure element. Fine structure lenses are considerably longer parallel to the ice edge with similarity in temperature structure noted over distances of 80 and 100 km.
Long‐term observations of bottom current and bottom sediment movement on the mid‐Atlantic continental shelf
Authors: Butman Bradford , Noble Marlene , Folger David W.
Published: April 2008

Long‐term in situ observations made at three locations on the mid‐Atlantic continental shelf during 1975–1976 clearly show intermittent movement of bottom sediment caused by currents, waves, and other forcing mechanisms. In winter, storm‐associated bottom currents greater than 30 cm s−1 resuspended and transported sediments. Net water particle excursions during storms were about 20–30 km longshelf and 5–10 km cross‐shelf. Wave‐induced bottom currents also resuspended sediments during periods of low mean flow. Sediment motion was observed in summer, although bottom conditions were generally tranquil. Significant changes in suspended matter concentration were observed that were only partially related to bottom currents. These changes may have been caused by biological activity or advection. Bottom currents on the mid‐Atlantic region of the continental shelf were characterized by a coherent, primarily cross‐shelf tidal flow of 5–10 cm s−1 and a low‐frequency longshelf component of 5–20 cm s−1. The longshelf current was coherent over length scales of 100 km at tidal frequencies and for motions with periods greater than 50 hours. For these longer periods the longshelf flow was coherent with wind stress, which implies that winds were a major driving force of the longshelf current. The cross‐shelf current was not coherent at stations separated by 100 km except at tidal frequencies. Packets of high‐frequency internal waves were observed during stratified conditions in summer with bottom currents as large as 20 cm s−1.
Low‐frequency current fluctuations in Lake Ontario, winter 1972–1973 (IFYGL)
Authors: Marmorino George O.
Published: April 2008

An analysis is presented of the low‐frequency (ω ≲ 0.6 cycles per day) current fluctuations in Lake Ontario, using measurements made at 15 and 75 m during the 1972–1973 winter. The data, collected as part of the International Field Year for the Great Lakes (IFYGL), were obtained at nine stations: one near midlake and the other eight spaced around the lake, about 50 km apart and 12 km from shore. Let U denote the alongshore velocity (positive leaving the shore to the right) and V the cross‐shore velocity (positive offshore). It is found that (1) the standard deviation of V is approximately constant; (2) the standard deviation of U, which is about 2.4 times greater than that of V, may be depth independent and is less at the southern shore stations than at the shallower northern stations where the flow appears to be directly wind driven; (3) the velocity fluctuations are roughly aligned with the local orientation of the coastline; (4) the U fluctuations show much better mutual correlation than the V fluctuations, having an alongshore coherence length of about 250 km (nearly half the basin perimeter); (5) the U signal shows high coherence for periods of about 10–25 and 4–5 days; and (6) the computation of lagged correlations shows the U fluctuations to propagate in a counterclockwise sense from the northern shore at a rate of about 42 km d−1 (0.5 m s−1), which implies a period of about 13 days for a complete circuit around the lake. These results provide additional evidence for the existence of topographic Rossby waves (shelf waves) in Lake Ontario, the calculated period being consistent with results of previous studies which used data from the summer and fall of 1972.
Lake surface fluctuations and the mass flow through the narrows of Lake Winnipeg
Authors: Kenney Bernard C.
Published: April 2008

Lake Winnipeg is a large (23,000 km2), shallow (12 m), homogeneous lake composed of two well defined basins separated by a central area of irregular geometry that includes the Narrows. Lake current was measured at 3 depths from two moorings in the Narrows and was compared with water level records from 7 gauges around the lake throughout the ice free season (May 15–October 15, 1976). The dominant lake response was a forced response produced by natural fluctuations in the wind with periods of 50–100 hours. Large amplitude water level and current fluctuations were produced by low wind speeds due to resonance caused by wind periodicity near the 39 hour natural cobasin oscillation of the lake. Although damping is subcritical, allowing for a resonant response, Lake Winnipeg is heavily damped compared to deep lakes. The cobasin oscillation is so low in frequency that a classical wind setup is unlikely to occur. Free oscillations were of secondary importance to the large scale dynamics of the lake. Several whole lake modes higher than the first were identified from the current and water level records but the amplitudes of these modes were very small compared to the free response of the Great Lakes. There was also a detectable response in the records at several natural frequencies of the individual basins and at the M2 tide.
Levels of ammonium, sulfate, chloride, calcium, and sodium in snow and ice from Southern Greenland
Authors: Busenberg Eurybiades , Langway Chester C.
Published: April 2008

Chemical analysis of surface snows and dated ice core samples from Dye 3, Greenland, suggests that the ammonium cation is a major constituent in all samples and that the annual ammonium levels present in the south Greenland samples have varied from 3.3 to 26.3 μg/kg between the seventeenth century and the present time. The annual range of 1974–1975 surface samples was between 3.8 and 8.8 μg/kg, while the mean was 5.7±1.8 μg/kg. The recent large‐scale uses of fixed nitrogen fertilizers and industrial pollution have apparently not affected the levels of ammonia reaching southern Greenland. The sodium and chloride present are predominantly derived from ocean spray, while more than 90% of the calcium is of continental origin. The levels of these three elements have not apparently been affected by human activity since the industrial revolution. Sulfate levels have increased dramatically since the industrial revolution, suggesting that sulfate of anthropogenic origin is the most important source of sulfate in modern snows from southern Greenland. The amount of the sulfuric acid neutralized by the ammonium cations was approximately 100% in the seventeenth and eighteenth centuries, dropping to approximately 20% in the 1974–1975 samples. These figures imply that there has been an increase in the acidity of precipitation in southern Greenland since the end of the eighteenth century.
Considerations of the enrichment, sources, and flux of arsenic in the troposphere
Authors: Walsh P. R. , Duce R. A. , Fasching J. L.
Published: April 2008

The tropospheric burden of arsenic has been estimated from representative global surface concentrations and an estimated small particle tropospheric scale height of 3.9 km to be ∼8×108 g As. Total atmospheric arsenic emissions from both natural and anthropogenic sources have been estimated to be 31×109 g As/yr. On a global basis the major source of atmospheric arsenic appears to be from anthropogenic volatilization processes, and the major natural sources of arsenic appear to be volcanoes and the terrestrial biosphere. Total atmospheric arsenic removal is estimated to be 30–50×109 g As/yr. The global tropospheric residence time of arsenic appears to be about 9 days.
Combined wave and current interaction with a rough bottom
Authors: Grant William D. , Madsen Ole Secher
Published: April 2008

An analytical theory is presented to describe the combined motion of waves and currents in the vicinity of a rough bottom and the associated boundary shear stress. Characteristic shear velocities are defined for the respective wave and current boundary layer regions by using a combined wave‐current friction factor, and turbulent closure is accomplished by employing a time invariant turbulent eddy viscosity model which increases linearly with height above the seabed. The resulting linearized governing equations are solved for the wave and current kinematics both inside and outside the wave boundary layer region. For the current velocity profile above the wave boundary layer, the concept of an apparent bottom roughness is introduced, which depends on the physical bottom roughness as well as the wave characteristics. The net result is that the current above the wave boundary layer feels a larger resistance due to the presence of the wave. The wave‐current friction factor and the apparent roughness are found as a function of the velocity of the current relative to the wave orbital velocity, the relative bottom roughness, and the angle between the currents and the waves. In the limiting case of a pure wave motion the predictions of the velocity profile and wave friction factor from the theory have been shown to give good agreement with experimental results. The reasonable nature of the concept of the apparent bottom roughness is demonstrated by comparison with field observations of very large bottom roughnesses by previous investigators. The implications of the behavior predicted by the model on sediment transport and shelf circulation models are discussed.
Mapping of sea ice and measurement of its drift using aircraft synthetic aperture radar images
Authors: Leberl F. , Bryan M. L. , Elachi C. , Farr T. , Campbell W.
Published: April 2008

Side‐looking radar images of Arctic sea ice were obtained as part of the Arctic Ice Dynamics Joint Experiment. Repetitive coverages of a test site in the Arctic were used to measure sea ice drift, employing single images and blocks of overlapping radar image strips; the images were used in conjunction with data from the aircraft inertial navigation and altimeter. Also, independently measured, accurate positions of a number of ground control points were available. Initial tests of the method were carried out with repeated coverages of a land area on the Alaska coast (Prudhoe). Absolute accuracies achieved were essentially limited by the accuracy of the inertial navigation data. Errors of drift measurements were found to be about ±2.5 km. Relative accuracy is higher; its limits are set by the radar image geometry and the definition of identical features in sequential images. The drift of adjacent ice features with respect to one another could be determined with errors of less than ±0.2 km.
A seasonal zonal energy balance climate model with an interactive lower layer
Authors: Thompson Starley L. , Schneider Stephen H.
Published: April 2008

The mean annual energy balance climate model of Gal‐Chen and Schneider (1976) is expanded to a more general model which includes an interactive lower layer. The two‐layer model is used to simulate the seasonal cycle through the use of seasonally varying insolation. Rather than greatly modifying the zonal model parameterizations, we choose to determine the extent to which the use of the present parameterizations in a completely zonally averaged model can reasonably simulate the seasonal cycle of surface air temperature and meridional heat transport. It is found that the model‐derived cycle of surface air temperature lags the observations by 1–2 months, but the amplitude of the seasonal cycle can be well simulated by using reasonable annual mean values of the seasonally effective zonal thermal inertia. The seasonal variations in the meridional transport of energy by the atmosphere agree qualitatively in mid‐latitudes with the data of Oort (1971), but they suffer from large errors in the tropics. Seasonal simulation indicates that the diffusive atmospheric energy transport parameterization based on annual data is inappropriate in this region. Comparisons of annual and seasonal models show that there is little difference in temperature sensitivity for solar constant changes. Unlike previous low‐resolution climate models the seasonally effective thermal inertia is also allowed to vary with time to simulate the seasonal variation of the oceanic mixed layer depth. This modification requires the addition of a second lower vertical layer in the model, the temperature of which is predicted explicitly. Such seasonal thermal inertia variations have little effect on the model's equilibrium response to solar constant changes. Experiments employing step function and exponential solar constant increases show the time‐dependent response of global surface temperature to lag the solar constant perturbation by from a few years to a few decades, depending on the assumptions of seasonal thermal inertia variation and lower layer thickness. The uncertainty in the range of global temperature lag time implies that modeling the time‐dependent temperature response to a CO2 perturbation will require refined treatment of the coupling between upper and lower oceanic heat reservoirs. The most important general conclusion from these experiments is that realistic values of seasonally effective thermal inertia (i.e., primarily the oceanic mixed layer depth) are needed for the realistic simulation of the seasonal cycle of temperature. Use of realistic seasonal thermal inertia implies that climate sensitivity experiments with seasonal models (including global circulation models) will require decades of model simulation time to approach a reasonable climatic equilibrium.
Stratospheric temperatures during solar cycle 20
Authors: Quiroz Roderick S.
Published: April 2008

Summertime rocketsonde temperature data for 1965–1977 at seven sites, 8°S‐64°N, were adjusted to reduce previously uncorrected instrumental errors. The data were then carefully processed to yield yearly average temperature departures from the average temperatures for 1965–1977. At two levels, 35 and 50 km, the yearly departures as well as 3‐year moving averages (with 1‐2‐1 weighting) were compared to the mean annual sunspot number, both for individual stations and for the combined station data. The smoothed temperature departures for the combined data show a correlation of +0.89 with sunspot numbers at both altitudes but with greater temperature range (4.5°C) at 35 km. Except for two special circumstances, correlations at individual stations (smoothed data) range from +0.72 to +0.94; the corresponding amount of temperature change from near‐solar maximum (1969) to near‐solar minimum (1975) varies among the stations from −3°C to −6°C. The observed temperature variations during solar cycle 20 are well within recent model calculations that are based on observed fluctuations in solar ultraviolet radiation.
Concentration and size distribution of particulate trace elements in the south polar atmosphere
Authors: Maenhaut Willy , Zoller William H. , Duce Robert A. , Hoffman Gerald L.
Published: April 2008

Samples of atmospheric particulate material were collected at the South Pole between December 1974 and February 1975. The filter samples were analyzed by neutron activation analysis and atomic absorption. The concentrations of 36 trace elements were determined and compared to previous results of antarctic research. The source of many of the elements can be identified as either the weathering of crustal material or oceanic sea salt. These sources account for approximately 10% of the particulate mass measured. Volatile elements not strongly associated with either of these two sources are Zn, Cu, In, W, Sb, Pb, Au, As, Ag, Cd, Se, Br, and I, which account for up to 3% of the particulate mass measured. The mass of the antarctic aerosol is dominated (∼80–90%) by sulfate, which is believed to be transported to the interior of the continent through the upper troposphere or through the lower stratosphere. Although the sources of the volatile elements are unknown, they are more closely correlated with the sulfate aerosols than with either a crustal or oceanic source.
An analysis of the charge structure of lightning discharges to ground
Authors: Krehbiel Paul R. , Brook Marx , McCrory Roy A.
Published: April 2008

Sources of charge for the individual strokes of four multiple‐stroke flashes to ground have been determined, using measurements of the electrostatic field change obtained at eight locations on the ground beneath the storm. The resulting charge locations have been compared to 3‐cm radar measurements of precipitation structure in the storm. The field changes of individual strokes were found to be reasonably consistent with the lowering to ground of a localized or spherically symmetric charge in the cloud. The centers of charge for successive strokes of each flash developed over large horizontal distances within the cloud, up to 8 km, at more or less constant elevation between the −9° and −17°C environmental (clear air) temperature levels. Comparison with the radar measurements has shown that the discharges developed through the full horizontal extent of the precipitating region of the storm and appeared to be bounded within this extent. In one instance where cellular structure of the storm was apparent, the strokes selectively discharged regions where the precipitation echo was the strongest. Vertical extent of the stroke charge locations was small in comparison with the vertical extent of the storm. The field changes in the intervals between strokes have been found to exhibit many of the features which Malan and Schonland used to infer that ground flashes discharge a nearly vertical column of charge in the cloud. This and other evidence is used to show that their observations, which were made at a single station, could instead have been of horizontally developing discharges. The interstroke field changes have been analyzed using a point dipole model and found to correspond to predominantly horizontal charge motion that was closely associated with the ground stroke sources for the flashes. The interstroke activity served effectively to transport negative charge in the direction of earlier stroke volumes and often persisted in the vicinity of an earlier stroke volume, while subsequent strokes discharged more distant regions of the cloud. Long‐duration field changes that sometimes preceded the first stroke of a flash have been analyzed and found to correspond to a series of vertical and horizontal breakdown events within the cloud, prior to development of a leader to ground. These events were associated in part with the negative charge region that became the source of the first stroke and effectively transported negative charge away from the first stroke charge volume and from the charge volumes of subsequent strokes. Several continuing current discharges were found also to progress horizontally within the cloud and sustained currents in the range of 580 A to less than 50 A. The continuing current field changes were consistently better fitted by the monopole charge model than the field changes of discrete strokes within the same flash.
Interferometric directions of lightning sources at 34 MHz
Authors: Warwick James W. , Hayenga Craig O. , Brosnahan John W.
Published: April 2008

We present a new technique for measuring the VHF radio centroid of nearby lightning flashes at 5‐μs intervals. Its ability to provide continuous positions during long (
100 μs) emissions is, we believe, new and reveals new information about the discharge process. The new technique solves many of the data‐handling problems in old techniques. We have built and demonstrated this technique in one angular coordinate of the lightning flash. We present data from five flashes showing complex positional and motional patterns. The breakdown phase consists of many impulses. The average speed from impulse to impulse lies in the range of 10–100 km s−1. During individual impulses, speeds measure from one to several tens of thousands of kilometers per second. At times of strong VLF bursts there is usually a similar VHF burst. Its speed is like the speeds of individual impulses. We identify VLF‐associated VHF burst sources with the main electrical current flow in lightning flashes. We identify the motion from one impulse to another in the breakdown phase as being caused by avalanching electrons accelerating along paths soon to become the discharge paths within thunderclouds. The high speeds in impulses represent the gross current flow in breakdown channels not yet large enough to create large VLF emissions or flashes.
Current‐induced sediment movement in the deep Florida Straits: Critical parameters
Authors: Wimbush Mark , Lesht Barry
Published: April 2008

A time‐lapse movie of the seabed at 710 m in the Florida Straits shows an irregular sequence of sediment ripple migration and suspension events, occupying 17% of the 43‐day duration of the record. Sediment in the region is a moderately sorted carbonate medium sand. Simultaneous current meter records at various positions in and above the benthic boundary layer are compared in various ways with the movie record to develop reliable predictive criteria for sediment motions in situ. With initiation and termination of sediment ripple migration predicted to occur when mean current at 3‐m elevation is 24 and 22 cm/s, respectively, 96% of the record is correctly predicted.
Observations of a ‘notch’ in the stratospheric ozone layer
Authors: Evans W. F. J. , Asbridge I. A. , Mateer C. L.
Published: April 2008

A persistent minimum was observed in the ozone partial pressure profile at 38 mb over Yorkton, Saskatchewan (51°N, 102°W), on each of 27 ozonesonde flights between August 7 and 31, 1976. This notch in the profile has an average vertical extent of 3 km and an average decrease in the partial pressure or mixing ratio of 35% below the adjacent maxima. The persistence and spatial extent of this phenomenon were investigated. An ozone‐aerosol flight at Laramie, Wyoming (41°N, 106°W), on August 6 also showed a minimum in both the ozone and aerosol profiles. It is demonstrated that this is a frequent phenomenon of the stratosphere which occurs at mid‐latitudes in late summer. The phenomenon occurs within a broader layer of very light winds situated between the westerlies below and easterlies above. From the evidence available it is not possible to choose between differential quasi‐horizontal advection and a photochemical sink as the mechanism responsible for producing the layer.
Radionuclides in the south pole atmosphere
Authors: Maenhaut W. , Zoller W. H. , Coles D. G.
Published: April 2008

Surface air concentrations of 222Rn, 210Pb, 7Be, and fission products at the geographic south pole have been determined during the 1973–1974 and 1974–1975 austral summer seasons. The 222Rn concentration was generally very low (0.3–0.4 pCi per standard cubic meter). However, on some days, very high radon levels, indicative of ‘radonic storms,’ were observed. The concentrations of fission products, from new nuclear tests in 1974, increased as a function of time. This indicated that the stratospheric reservoir of nuclear debris was still drastically changing some 3–4 months after the nuclear detonations. The 7Be and fission product concentrations from old debris origin showed a good correlation with the concentrations of some atmospheric trace elements, such as S and Br. This and other facts suggested a stratospheric origin for those trace elements. There were also several indications which pointed to a substantial stratospheric source of 210Pb during the austral summer season. The size distribution data for the various fission products differed from the 7Be size distribution data, possibly as a result of the different age of the 7Be‐bearing aerosols or mode of transport to the antarctic continent.
Time‐dependent calculations of the vertical distribution of 222Rn and its decay products in the atmosphere
Authors: Beck Harold L. , Gogolak Carl V.
Published: April 2008

A model has been developed to simulate the one‐dimensional time‐dependent vertical diffusion of 222Rn and its decay products in the atmosphere. Computed activities and activity ratios as a function of height above the ground are in excellent agreement with experimental data. The simulations indicate that near the air‐ground interface a quasi steady state is reached within a few hours after establishment of a particular atmospheric mixing regime. Radioactive equilibrium between radon and its short‐lived daughters is approached at all heights except for very close to the ground during weak mixing conditions.
Effect of the Earth's atmosphere on contrast for zenith observation
Authors: Kaufman Yoram J.
Published: April 2008

The reduction of contrast due to atmospheric extinction is calculated for zenith observation. The procedure of calculation is based on a simplified solution of the radiative transfer equation. The simplified solution is obtained by an approximation method similar to the two‐stream approximation used for flux calculation. The resulting approximate intensities are shown to agree fairly well with those obtained by numerically solving the transfer equation. It is shown that the simplified solution can be used to interpolate between numerical results.
Forced secondary circulations in hurricanes
Authors: Willoughby H. E.
Published: April 2008

In this study, application of Eliassen's (1951) forced secondary circulation model to the hurricane vortex is reexamined. It is shown by scale analysis that the symmetric tangential flow is in hydrostatic and gradient balance if the asymmetric part of the tangential flow and the radial and vertical symmetric motions are appreciably smaller than the symmetric tangential flow. When surface friction and cumulus transports of heat and momentum are included, the forced symmetric radial and vertical motions may be diagnosed. The approximations on which this system of balanced equations is based are valid everywhere in the hurricane vortex except in the upper tropospheric outflow layer. In the absence of Fickian diffusion of momentum and heat, both deep inflow in the outer vortex and subsidence within the eye are forced by radial gradients of convective heating. If corresponding gradients of cooling arise in the upper troposphere by mechanisms such as detrainment from overshooting cumuli, descent may be induced in the lower stratosphere above and around the eye. Convective momentum transports act to weaken the thermally induced secondary flow somewhat. If the vertical resolution of the finite difference mesh is too coarse to resolve the detrainment layer properly, the model may diagnose an unrealistic secondary flow with ascent throughout the eye. In the absence of all cumulus processes, the frictionally converged air no longer rises to the tropopause but rather flows outward in a shallow layer in the lower troposphere.