bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficiency of conversion of kinetic energy to potential energy by a breaking internal gravity wave
Authors: Thompson Rory O. Rafi Y.
Published: February 2008

A simple model of turbulent mixing induced by a breaking internal gravity wave implies that one quarter of the kinetic energy lost goes into potential energy. The model is based on a critical Richardson number concept. The conceptual model and some numeric trials simulate the experiment of Thorpe (1973) quite well.
Barotropic response to cooling
Authors: Stommel Henry , Veronis George
Published: February 2008

Imposed horizontal density differences in a nonrotating fluid generate vertical circulation which has vanishing vertically integrated transports. When the system is rotating, geostrophic velocities can balance the density differences and the vertically integrated transports need not vanish locally. In a two‐layer fluid, finite amplitude disturbances lead to barotropic flows that have the same direction as the velocity in the layer that thickens as a result of the disturbance. Specific calculations are carried out for the geostrophic adjustment model in situations that approximate those in which 18° water is formed south of the Gulf Stream. The upper layer transport that results from sudden cooling (as simulated by density differences that are initially unbalanced geostrophically) is in the same direction as the Gulf Stream transport and comparable to it in magnitude. A lower level transport of the same magnitude flows in the opposite direction with a maximum value about an internal radius of deformation to the right of that of the upper layer. The barotropic transport is about 1/5 as large and flows downstream in the Gulf Stream and upstream to the right of the Gulf Stream.
Sulfate enrichment in marine aerosols owing to biogenic gaseous sulfur compounds
Authors: Bonsang Bernard , Nguyen Ba Cuong , Gaudry André , Lambert Gérard
Published: February 2008

The seawater SO4− ratio is 0.25. However, sulfate enrichments with respect to Na+ have been observed in marine aerosols by several authors. In the northern hemisphere, such an enrichment could be attributed to natural or to anthropogenic continental sources of sulfates. However, far from any continent, for example, in subantarctic areas, we have always observed SO4−/Na+ ratios greater than that of seawater and as large as 1. We have shown the existence in the oceanic atmosphere of a relationship between SO2 and primary productivity in seawater. The sulfate excess concentrations are found to be proportional to those of SO2. The sulfate enrichment could be consequently explained by the oxidation of marine SO2. This explanation is consistent with the distribution of SO4−/Na+ ratios on different size particles collected with a high volume cascade impactor. Highest values (>0.5) are always observed in the smallest particles (diameter <0.6 μm) the largest particles have a SO4−/Na+ ratio near 0.25. We conclude that sulfate marine aerosols are produced not only by the atmospheric injection of sea salt, but also by a gas‐to‐particle conversion process by oxidation of marine SO2. This last source has been estimated to be 84×106 tons of sulfate per year.
On the budget of sea salts and sulfur in the atmosphere
Authors: Petrenchuk O. P.
Published: February 2008

An approximate estimation of the intensities of the different aerosol sources and of the budget of sea salt is carried out. Chemical composition data of frontal precipitating cloud water, the results of the research of rainout and washout processes, and the annual global precipitation amount are used in this estimation. There is good agreement between the obtained results of the estimation of sea‐salt source intensity and data on river run off of chloride into ocean.
On the origin of tropospheric ozone
Authors: Liu S. C. , Kley D. , McFarland M. , Mahlman J. D. , Levy H.
Published: February 2008

The effects of NOx (NO + NO2) intrusion from the stratosphere on photochemical ozone production in the upper troposphere are investigated. Using the currently accepted reaction rate coefficients, we find that this upper tropospheric ozone source may be significantly larger than the direct injection of ozone from the stratosphere. Many features of the observed tropospheric temporal and spatial ozone distributions appear to be better explained by this upper tropospheric ozone source hypothesis than by either the classical ‘dynamical control’ or ‘photochemical control’ hypotheses. In addition, we find that NOx emissions from high flying subsonic aircraft in the northern hemisphere may cause an ozone increase in the troposphere. The calculated tropospheric ozone increase due to these NOx emissions is not inconsistent with the increases observed by the northern hemispheric ozonesonde stations.
Analysis of the August 1972 Solar Proton Event including chlorine chemistry
Authors: Solomon Susan , Crutzen Paul J.
Published: February 2008

Bombardment of the earth's atmosphere by charged particles produces odd nitrogen and odd hydrogen. These species take part in catalytic reactions which destroy atmospheric ozone. We present model studies of the effects of the August 1972 solar proton event on stratospheric ozone. Calculated ozone depletions following the event are in very good agreement with observations using presently accepted chemistry, especially between 30 and 45 km. The influence of chlorine chemistry on model simulations of this event is examined. The calculated decreases in ozone are expected to yield temperature decreases, since solar heating in this region strongly depends on ozone. Consequently, the temperature dependent reaction rate constants are affected, and we show that the inclusion of temperature feedback influences the calculations of the effects from about 42 to 55 km.
Surface ozone measurements in clean air
Authors: Oltmans Samuel J.
Published: February 2008

Surface ozone measurements at the four baseline U.S. geophysical monitoring for climatic change observatories provide a glimpse of tropospheric ozone behavior at locations generally isolated from local anthropogenic contamination. Variations on time scales from hours to years are considered. Observations in tropical and polar regions suggest weak coupling between tropospheric and stratospheric ozone in these regions. At subtropical and mid‐latitude stations, on the other hand, there appears to be stronger coupling between tropospheric and stratospheric ozone. A small diurnal variation in surface ozone at Samoa may indicate photochemical influence on the ozone budget there. Some of the year‐to‐year differences in surface ozone at the four stations indicate possible global influences on the tropospheric ozone budget. No significant long‐term trends are apparent in the data, however.
Observations of the velocity response to wind forcing in the upper ocean
Authors: Weller Robert A.
Published: February 2008

The response of the horizontal velocity field to forcing by the local wind was observed in the upper 150 m of the ocean by profiling with vector measuring current meters from the Research Platform Flip as it drifted off the coast of California in January 1977. In the mixed layer, approximately 50 m deep, motion at frequencies lower than 0.1 cph was coherent with the wind stress. Rotary cross spectral analysis showed that the shear in the surface layer was related to the local wind stress and that the structure of the response at low frequencies was similar to but did not agree completely with the predictions of simple linear, eddy viscosity models.
Stratospheric odd nitrogen: Nitric oxide measurements at 32°N in autumn
Authors: Ridley B. A. , Schiff H. I.
Published: February 2008

Nitric oxide was measured, by chemiluminescence, over the altitude range 14–40 km during three balloon flights from Palestine, Texas, in fall of 1977 and 1978. The three height profiles were quite similar, as were the height profiles of ozone and temperature. Our three profiles agree reasonably well with those generated by one‐dimensional models at the upper end of the altitude range of the measurements but are higher than the model profiles at the lower end of the altitude range. The integrated column densities from our measurements agree with those measured directly by long‐path infrared. The profiles obtained in these and other recent flights are higher than those we reported before using earlier versions of the instrument. Possible sampling errors in the earlier instruments are discussed. Caution is advised in attributing stratospheric variability to differences in NO profiles obtained by isolated measurements. The need for simultaneous measurements using more than one technique is stressed.
Monitoring winter sea ice dynamics in the Canadian Arctic with NOAA‐TIR images
Authors: Dey B.
Published: February 2008

The study revealed the unique features of winter sea ice dynamics in the Canadian Arctic during 1974–1978 winter seasons. The features included the presence of open water and thin ice in parts of Smith Sound, northern Baffin Bay, western Jones Sound, Foxe Basin, Lancaster Sound, and southeast Baffin Bay. In addition, persistency of leads and polynyas at Smith Sound, Melville Bay, northern Lancaster Sound, Jones Sound, Home Bay, eastern Beaufort Sea, and Amundsen Gulf was remarkable phenomenon. Further, active leads were found in Baffin Bay and Beaufort Sea throughout the winter season. Two ice dams at Smith Sound and Barrow Strait regulated the influx of ice into northern Baffin Bay. The influx of ice into northern Baffin Bay through Smith Sound, Jones Sound, and Lancaster Sound estimated to be 654 km3 per year, whereas the influx of ice from the Arctic Ocean and the Central Archipelago through Robeson Channel, Fram Sound, and Barrow Strait was about 201 km3 per year.
Elevation and velocity measurements of laboratory shoaling waves
Authors: Flick Reinhard E. , Guza Robert T. , Inman Douglas L.
Published: February 2008

Measurements of wave elevation and orbital velocity in the shoaling, breaking, and bore regime of single‐frequency laboratory waves show that third‐order Stokes theory, when energy flux is conserved, predicts the wave height change and harmonic growth in the regime where the Ursell number Ur = (H/ h)/(kh)2 is 0(1) or less. Shoreward of the Stokes region and up to the breakpoint, harmonic amplitudes are well described by the cnoidal theory. It is shown theoretically that a smooth transition regime exists between Stokes and cnoidal regions for waves which eventually break by plunging. The wave profile asymmetry about the vertical plane observed in near‐breaking waves and bores is due to slow changes of phase of the harmonics relative to the primary wave as the wave train shoals. By contrast, only asymmetry about the horizontal plane is possible in the Stokes and cnoidal wave theories, since these classical solutions allow no relative phase shifts between harmonics. Velocity measurements made with hot‐film anemometers show that ‘unorganized’ fluctuations at the bottom under breaking waves are of the order of half the rms amplitude of the wave‐induced ‘organized’ flow. The correlation between surface elevation and bottom velocity under breakers and bores suggests that turbulence contributes more strongly to the unorganized flow at the bottom under plunging than under spilling waves.
Reaction of the accumulation zone portions of glaciers to climatic change
Authors: Whillans I. M.
Published: February 2008

The response of the accumulation regions of glaciers to changes in accumulation rate and in surface temperature is calculated by considering perturbations to the ice flow. The analysis is limited to glaciers in which flow is dominated by internal shear and not by bottom sliding and for which flowlines are geographically parallel. In general, glaciers begin to alter thickness immediately after a change in accumulation rate, but the effect of a change in surface temperature is delayed by the time for this temperature change to penetrate to depth in the glacier. A warming leads to glacial thinning. The amount and timing of the response is very different for different glaciers. Characteristic times are on the order of tens of years for mountain glaciers and tens of thousands of years for the east antarctic ice sheet. As an example, the theory is applied to the ice sheet near Byrd Station, Antarctica. For hypothetical changes in surface accumulation rate and temperature, rates and amounts of thickness change are calculated, and it is found that the measured thinning is probably too fast to have been caused by climatic variation alone. The effects of hypothetical climatic variations on the depth‐age and depth‐temperature relationships through the ice sheet are also calculated. It is hoped that the theory will prove valuable in the interpretation of future drill hole results.
A climate model with cryodynamics and geodynamics
Authors: Ghil Michael , Le Treut Hervé
Published: February 2008

We present a highly simplified, zero‐dimensional model of the climatic system. The model attempts to incorporate mechanisms important on the time scale of glaciation cycles, namely, 104–105 years. In particular, the radiation balance of the ocean‐atmosphere, the plastic flow of continental ice sheets, and the viscous flow of the upper mantle are taken into account. The stress is on the interaction between the cryosphere (ice sheets) and the asthenosphere (upper mantle), which had not been taken into account in previous energy‐balance or ice‐sheet models of climate (Weertman, 1976; Källén et al., 1979). The model exhibits free, self‐sustained oscillations of an amplitude and period comparable to those found in the paleoclimatic record of glaciations, viz., O(10 deg K) and O(104 years), respectively. Such oscillations had already been found in the simpler model of Källén et al. (1978, 1979). The fact that nonlinear, self‐sustained oscillations also obtain for the present, slightly more complex model is interesting: it offers mild support to the idea that unforced oscillations can actually exist in the real climatic system itself. These oscillations are characterized by a quarter‐phase lag between ice extent and global temperature. Given that the climatic system is a nonlinear oscillator with a period of O(104 years), it is expected that astronomical forcing at 19,000, 23,000 and 41,000 years will lead to subharmonic oscillations with a period close to 100,000 years, the dominant period of glaciation cycles. Such effects have already been noticed in the work of Birchfield and Weertman (1978) with an even simpler model, including only glacial dynamics. The careful study of the interplay between internal mechanisms and external forcing with comparable time scales represents an interesting challenge to the theory of ice ages. The results of such theoretical studies can also provide guidance for observational work. In particular, periodicities of O(104 years) in the climate record and phase lags between ice volume and temperature appear to be supported by the most recent paleogeochemical investigations (Ruddiman and Mclntyre, 1981).
Preliminary analysis of experiments on the climatic effects of increased CO2 with an atmospheric general circulation model and a climatological ocean
Authors: Gates W. L. , Cook K. H. , Schlesinger M. E.
Published: February 2008

Preliminary results from numerical experiments designed to show the seasonal and geographical distribution of the climatic changes resulting from increased atmospheric CO2 concentration are presented. These simulations were made for both doubled and quadrupled CO2 levels with an improved version of the two‐level OSU atmospheric GCM. In these experiments and in a control run with normal CO2, the solar radiation incident at the top of the model atmosphere and the sea‐surface temperature and sea ice were given prescribed seasonal climatological variations. In January the globally averaged tropospheric temperature is increased with respect to the control mean by 0.30°C (0.48°C) for doubled (quadrupled) CO2, which may be compared with an interannual January temperature variability of 0.15°C in the control (as measured by the root‐mean‐square of January monthly averages in a 3‐year control integration). In July, the globally averaged tropospheric temperature rises by 0.33°C (0.60°C) for doubled (quadrupled) CO2, with an average warming over land surfaces of 0.71°C (1.04°C); these values may be compared with a root‐mean‐square interannual July temperature variability of only 0.03°C in the control. These results are clearly due to the model's differing thermal response over ocean and continent in the summer and winter seasons. In comparison with the results from models using a swamp ocean (which absorbs no heat), the present experiments with a climatological ocean represent the opposite limiting case in which the ocean is an infinite reservoir of heat. Although the present model gives a small but significant overall warming without poleward amplification, and does not indicate a significant change of the atmosphere's general circulation or hydrological cycle, these results are due to the unrealistic suppression of water vapor‐ and albedo‐temperature feedbacks.
Infragravity energy in the surf zone
Authors: Holman R. A.
Published: February 2008

Field measurements of onshore and longshore velocities in the surf zone have been obtained on Martinique Beach, Nova Scotia, for the purpose of investigating the dynamics of the infragravity band (0.003–0.03 Hz) of the spectra. A total of 35 data runs were obtained during a 1‐week period. Of particular interest is the response of the infragravity energy to the changing incident waves, which increased considerably in size during the latter half of the week due to an approaching hurricane. It is shown theoretically, using equilibrium arguments, that the infragravity amplitude should vary approximately linearly with incident wave amplitude. This is supported from the field data if significant wave height is used as a measure of incident amplitude. The incident band of spectra observed by instruments in the surf zone is limited by breaking. Thus the infragravity band appears to dominate these spectra during storms. The analysis is carried out in terms of a spectral transformation, the spectrum which would be observed at an offshore instrument if the shoreline amplitude spectrum were white with unit spectral energy density. For onshore velocity the transformation predicts the observed spectral structure in the infragravity band, showing that the structure did not represent any true frequency selection. The match of theory and data also implies that the onshore motions are free waves, forced near resonance. The longshore spectra are red and show no structure which would be associated with free waves. This is consistent with the theoretical prediction that many edge wave modes, including high modes, would be forced given the broad directional spread of the storm waves. It is noted that further field experiments would be simpler on the Pacific coast where the typical, narrow‐band, incident swell should force only a few, low, edge wave modes, a more accommodating situation to observe and analyze.
Verification studies of Seasat‐A satellite scatterometer (SASS) measurements
Authors: Halberstam Isidore
Published: February 2008

Comparisons are made between the Seasat‐A satellite scatterometer (SASS) data and surface truth gathered from the Gulf of Alaska Seasat Experiment (GOASEX) and the Joint Air‐Sea Interaction (JASIN) program. One comparison attempts to evaluate the performance of SASS irrespective of the algorithms employed to convert SASS data to geophysical parameters. This is accomplished by separating the backscatter measurements into small bins of incidence and azimuth angles and polarity and regressing against wind speed measurements. The algorithms themselves are tested by comparing their predicted slopes and y intercepts with those derived from the regressions. The algorithms are further tested by comparing each SASS backscatter measurement with the backscatter derived from the algorithms, given wind velocity from the observations. Results of the comparisons show that SASS becomes insensitive to winds at high incidence angles for horizontal polarizations. For other angles, fairly high correlations exist between backscatter and wind speeds. The algorithms are shown to function well at midranges of incidence angle and backscattering coefficient. Failure to predict accurately at the extremes may be attributed to saturation of the sensor at these values. Another study shows that averaging the backscatter from two orthogonal beams produces a result which is essentially independent of wind direction and correlates well with the observed wind speed. Results also fail to favor any particular parameterization of the ‘surface wind.’
Tropospheric chemistry: A global perspective
Authors: Logan Jennifer A. , Prather Michael J. , Wofsy Steven C. , McElroy Michael B.
Published: February 2008

A model for the photochemistry of the global troposphere constrained by observed concentrations of H2O, O3, CO, CH4, NO, NO2, and HNO3is presented. Data for NO and NO2are insufficient to define the global distribution of these gases but are nonetheless useful in limiting several of the more uncertain parameters of the model. Concentrations of OH, HO2, H2O2, NO, NO2, NO3, N2O5, HNO2, HO2NO2, CH3O2, CH3OOH, CH2O, and CH3CCl3are calculated as functions of altitude, latitude, and season. Results imply that the source for nitrogen oxides in the remote troposphere is geographically dispersed and surprisingly small, less than 107tons N yr−1. Global sources for CO and CH4are 1.5 × 109tons C yr−1and 4.5 × 108tons C yr−1, respectively. Carbon monoxide is derived from combustion of fossil fuel (15%) and oxidation of atmospheric CH4(25%), with the balance from burning of vegetation and oxidation of biospheric hydrocarbons. Production of CO in the northern hemisphere exceeds that in the southern hemisphere by about a factor of 2. Industrial and agricultural activities provide approximately half the global source of CO. Oxidation of CO and CH4provides sources of tropospheric O3similar in magnitude to loss by in situ photochemistry. Observations of CH3CCl3could offer an important check of the tropospheric model and results shown here suggest that computed concentrations of OH should be reliable within a factor of 2. A more definitive test requires better definition of release rates for CH3CCl3and improved measurements for its distribution in the atmosphere.
Background NOx mixing ratios in air masses over the North Atlantic Ocean
Authors: Helas Günter , Warneck Peter
Published: February 2008

A chemiluminescence analyzer was used to measure NOx mixing ratios at the west coast of Ireland. Two measurement modes allowed the determination of NO and NOx = NO + NO2. In a third mode using a molybdenum converter, higher signals were observed than was in the second mode indicating that nitrogen compounds other than NO + NO2 are registered. They are denoted ‘excess NOx.’ The average NO2 mixing ratio for a 3 week period was 101±87 pptv. In pure marine air masses identified by means of trajectory calculations, the NO2 mixing ratios were lower and exhibited in addition a diurnal variation with nighttime values of 37±6 pptv and average values of 87±47 pptv. Possible origins of the diurnal variation are discussed. For such conditions, the NO mixing ratio generally was immeasurably small, certainly less than 10 pptv. The excess NOx is also higher during the day compared with nighttime values of about 70 pptv. Further studies are required to identify the compounds involved.
The 2‐day wave in the middle atmosphere: Observations and theory
Authors: Salby Murry L.
Published: February 2008

A recurrent, global‐scale, 2‐day oscillation, in the middle atmosphere is well documented in a variety of data sources: meteor wind, partial reflection, satellite, and rocketsonde. The observed period is almost invariably near 2.1 days, and the zonal structure has been established as a westward propagating, wave number 3 mode. Observations also indicate that the meridional wind component maximizes near the equator and dominates the wind field at low latitudes. These features suggest the disturbance's identification with the wave number 3 Rossby‐gravity normal mode of a windless, isothermal atmosphere. Such modes are found to exist largely independent of the mean fields. The eigenperiods are only modestly altered by mean wind variations on the lowest three scale heights, and the influence on the mode structure is local. The vertical growth of amplitude is enhanced in regions of weak westerly wind relative to the wave and equatorward temperature gradient, while the vertical growth rate is retarded and amplitudes may even decay in regions of strong westerlies or poleward temperature gradient. In realistic mean fields, the third Rossby‐gravity mode has magnified responses very near 2.25 days in both equinox and solstice conditions. The horizontal structure remains largely intact in the lowest levels. However, considerable asymmetry is introduced in the solstice upper stratosphere and mesosphere by the magnified vertical growth of amplitude in the summer hemisphere. The latter results from the moderate easterlies and equatorward temperature gradient characteristic of the region. As for the simple eigenstructure, the meridional wind component in this region maximizes near the equator and dominates the wind field up to mid‐latitudes.
A negative feedback mechanism for the long‐term stabilization of Earth's surface temperature
Authors: Walker James C. G. , Hays P. B. , Kasting J. F.
Published: February 2008

We suggest that the partial pressure of carbon dioxide in the atmosphere is buffered, over geological time scales, by a negative feedback mechanism in which the rate of weathering of silicate minerals (followed by deposition of carbonate minerals) depends on surface temperature, and surface temperature, in turn, depends on carbon dioxide partial pressure through the greenhouse effect. Although the quantitative details of this mechanism are speculative, it appears able partially to stabilize earth's surface temperature against the steady increase of solar luminosity believed to have occurred since the origin of the solar system.
Determination of vertical profiles of aerosol size spectra from aircraft radiative flux measurements: 1. Retrieval of spherical particle size distributions
Authors: Kondratyev K. Ya. , Welch R. M. , Cox S. K. , Grishechkin V. S. , Ivanov V. A. , Prokofyev M. A. , Zhvalev V. F. , Vasilyev O. B.
Published: February 2008

During the GATE observational program, aircraft radiative flux measurements were taken at several altitudes in the Saharan dust. On the basis of these flux measurements at 28 wavelengths in the 0.4–0.9 μm wavelength region, the corresponding vertical particle size spectra have been inferred. These particle size distributions, calculated by using spherical Mie theory, have been represented by quadramodal combinations of gamma functions. The calculated quadramodal size distributions were characterized by mode radii at 0.1, 0.2, 1.0, and 2.0 μm, with a relatively narrow spread of particle sizes centered about each mode radius. The number density of the smallest particle mode was found to increase with increasing height, while that of the largest particle mode decreased with increasing height. Comparison of deduced particle sizes of a ‘dusty’ day (September 4) and a ‘clear’ day (August 13) showed that the dusty day was characterized far more by the presence of large particles than by an increase in small particle concentration. Heating rates as large as 0.4°C/hour μm were found for September 4, 1974.
Numerical simulation of the annual cycle of climate during the ice ages
Authors: Adem Julian
Published: February 2008

By using a hemispheric thermodynamic grid model, the annual cycle of climate for 18,000 years ago is simulated. It is shown that the difference between the position of the snow‐ice boundary of 18,000 years ago and the one of today was much larger in summer than in winter and that the annual cycle of the snow‐ice boundary for today has more variability than that for 18,000 years ago. Owing to the temperature snow‐ice feedback, the zonally averaged ground and midtropospheric temperature anomalies (with respect to today normals) are negative and their absolute values are larger in summer than for the other seasons of the year and increase from lower to higher latitudes. In lower latitudes, in some regions of Asia and Africa, the spring and early summer temperatures were higher during the ice age climate because the insolation was about 20 W m−2higher than it is today, and the lower latitudes are much more sensitive to insolation than the higher latitudes are, where the temperature snow‐ice feedback is the main mechanism which produced a dominant decrease of temperature. Comparison of the computed surface temperature values with the ‘Observed’ values shows generally good agreement. The computed average ground temperature anomaly for the northern hemisphere for July is equal to −4.7°C, in good agreement with the values −4.8°C obtained by Gates.
Mixed‐layer simulation of buoy observations taken during Hurricane Eloise
Authors: Martin Paul J.
Published: February 2008

A one‐dimensional mixed‐layer model is used to simulate observations made by a NOAA buoy in the Gulf of Mexico during Hurricane Eloise. The model‐predicted SST, mixed‐layer depth, and inertial current agree favorably with the observations. In addition, model experiments demonstrate the importance of the veering of the wind vector during the passage of the eye to the amplitude of the inertial current generated by the wind and the extent of vertical mixing.
Two‐dimensional surf beat: Long wave generation by a time‐varying breakpoint
Authors: Symonds Graham , Huntley David A. , Bowen Anthony J.
Published: February 2008

A two‐dimensional parametrization of a surf zone with a time‐dependent breakpoint due to groupiness in the incident wave field is developed. The breakpoint is defined in terms of a mean position X plus a modulation Δa. Free wave solutions are obtained on a plane beach at the group frequency and its harmonics. Shoreward of the breakpoint, standing waves are found, while seaward an outgoing progressive wave exists. The amplitude of the standing wave is relatively insensitive to the incident wave field. The amplitude of the outgoing wave depends on X, the group frequency σ, and the beach slope tan β. For certain values of X = (σ2X/g tan β) the amplitude of the outgoing wave goes to zero. It appears that any ‘resonant’ response of the standing wave shoreward of the breakpoint is suppressed by seaward radiation of energy by the outgoing wave.
The dependence of space charge spectra on Aitken nucleus concentrations
Authors: Anderson Robert V.
Published: February 2008

The theoretical behavior of atmospheric space charge in a field of turbulent mixing is reviewed, and the possible usefulness of space charge as a tracer of the turbulent process is introduced. It is shown that power spectra of space charge recordings could serve to identify whether the charge is primarily on large or small particles, and previous data are found to be insufficient to verify the validity of this prediction. An instrumental ensemble is described with which to record space charge fluctuations at temporary sites. A series of measurements is described in which the only significant background variation over a 24‐hour period is in the Aitken nucleus density, and this variation exhibits a cyclic pattern attributable to morning rush hour activity. The spectral decay slopes of the corresponding space charge recordings are seen to vary inversely with the Aitken density in excellent agreement with the theoretical prediction.
A time series analysis of Umkehr data from Arosa
Authors: Penner J. E. , Golen L. P. , Mensing R. W.
Published: February 2008

A time‐series autoregressive‐moving average model is fit to Umkehr data from Arosa for the time period March 1961 through December 1977. The ozone data in Umkehr levels 7, 8, and 9 are examined for trend commencing in January 1970. The summed data in levels 7, 8, and 9 are also examined. No significant trend is found at the 5% significance level. Models are then refit for the entire sample period, and detection thresholds are estimated for time periods after December 1977. The change in O3 due to trend over the next 10 years would need to be as large as 3.5, 10.4, and 23.3% in levels 7, 8, and 9, respectively, for tests based on these models to conclude there was a significant nonzero trend in the future. The trend in the summed data would need to be 5.3%. Thus we find that the data in Umkehr level 7 provide the smallest detection threshold for future detection of trend in upper level O3. The detection thresholds found here are compared to detectability limits from total O3 data.
Measurements of storm‐generated bottom stresses on the continental shelf
Authors: Cacchione David A. , Drake David E.
Published: February 2008

Large values of bottom friction velocity, u*, and roughness length, z0, determined from burst‐averaged speed data taken on the continental shelf in outer Norton Sound, Alaska, with the GEOPROBE tripod during a storm in September 1977 are correlated with extremely large values of near‐bottom concentration of total suspended particulate matter (TSM). Combined wind‐driven and tidal currents exceeding 30 cm/s at 1 m above the bottom and intense oscillatory bottom currents with maxima above 45 cm/s were associated with the largest measured values of TSM at 2 m above the sea floor. The values of u* and z0 obtained from the ‘law of the wall’ velocity‐depth relationship are diminished substantially throughout the storm period (average reduction of 44%) when the turbulence reducing effects of the vertical concentration gradient of TSM are considered. The form of the latter correction was adapted from Smith and McLean (1977a). Values of the mean u* computed from the theory of Grant and Madsen (1979), which predicts an enhanced shear stress due to nonlinear wave‐current interactions, compare favorably with the u* values determined from the measured velocity profiles. The measured values of z0, however, are considerably larger than any of the estimates based on (1) the actual scales of the physical roughness elements; (2) the apparent roughness of Grant and Madsen (1979); or (3) the thickness of the bed‐load layer as formulated by Smith and McLean (1977a).
Coastal fresh water discharge in the northeast Pacific
Authors: Royer Thomas C.
Published: February 2008

Very high annual rates of precipitation in the coastal mountains that border the northeast Pacific Ocean produce large fresh water discharges (23000 m3 s−1). This discharge has been ignored previously since it does not enter the ocean in the form of large rivers, but, instead, the water enters by way of numerous small rivers and streams. Thus, it acts as a line source instead of a point source. This coastal discharge contributes at least 40% of the fresh water that enters the northeast Pacific from the atmosphere. The discharge is comparable to the mean annual discharge of the Mississippi River system. The fresh water creates a cross‐shelf density gradient that drives an alongshore baroclinic jet. The width of this jet is less than 25 km with speeds in excess of 100 cm s−1. It extends along the coast from southeast Alaska to at least Kodiak Island. Apparently, the flow is maintained as a narrow current adjacent to the coast by wind stress that causes downwelling conditions here throughout most of the year.
Meteorological and oceanographic factors affecting sea ice in cook inlet
Authors: Poole F. W. , Hufford G. L.
Published: February 2008

The relationship between meteorological and oceanographic parameters to the onset of ice formation and winter severity in Cook Inlet is investigated using data from 1969 to 1980. Air temperature, in the form of adjusted frost degree‐days, is the parameter most highly correlated with onset of significant ice (r = 0.960) in the upper inlet. From this relationship, a curve is developed to provide a simple operational method for predicting ice formation. In the lower inlet, a more complex relationship exists between heat flux from the Gulf of Alaska waters, river runoff, and air temperature to the onset of ice. The heat exchange between Gulf of Alaska and Cook Inlet waters is of primary importance to onset of ice. Attempts at correlating winter severity to the meteorological and oceanographic parameters show that the southern extent of the ice in the lower inlet is due to climatic differences affecting the rate of inflow and temperature of the Gulf of Alaska coastal water into Cook Inlet and modification by the local wind‐driven drift of ice.
Stratospheric measurements of collision‐induced absorption by molecular oxygen
Authors: Rinsland C. P. , Smith M. A. H. , Seals R. K. , Goldman A. , Murcray F. J. , Murcray D. G. , Larsen J. C. , Rarig P. L.
Published: February 2008

Collision‐induced absorption by the fundamental vibration‐rotation band of O2 has been studied in high‐resolution (0.02 cm−1) stratospheric solar absorption spectra. The data were recorded during sunset with the University of Denver balloon‐borne interferometer from a float altitude of 33 km. The O2 continuum has been identified in the 1400–1700 cm−1 region in spectra obtained at tangent altitudes below 22 km. Measurements of transmittances in narrow intervals nearly free of atmospheric line absorption are in good agreement with values calculated with the O2 absorption coefficients as compiled by Timofeyev and Tonkov (1978). Absorption by other atmospheric species (primarily from wings of strong H2O lines) contributes only a small fraction of the total absorption at the measured frequencies. The measurements indicate an upper limit of 20% for the uncertainty of the available O2 absorption coefficients at lower stratospheric temperatures (≈220 K).
The SEASAT altimeter data and its accuracy assessment
Authors: Tapley Byron D. , Born George H. , Parke Michael E.
Published: February 2008

The SEASAT satellite, launched on June 27, 1978, carried a radar altimeter designed to measure the altitude of the satellite above the ocean surface, the surface wave height, and the ocean‐surface backscatter coefficient from which wind speed can be inferred. Postlaunch engineering assessment indicated that the SEASAT altimeter met the performance specification for 10‐cm precision (noise) in the altitude measurements. However, to determine the accuracy of this measurement as well as the accuracy of the wave height and wind speed measurements a significant calibration, validation, and model development effort was required. This summary describes the instrument, atmospheric, and geophysical effects which influence the radar altimeter measurement accuracies and the attendant correction models adopted for the altimeter geophysical data record. Also summarized are the activities of the SEASAT Altimeter/Precision Orbit Determination Experiment Team directed towards the validation and improvement of these models, as well as the investigations required to assess the accuracy of the altimeter measurement and the computed satellite altitude ephemeris. Finally, an accuracy assessment is made for the various altimeter measurement corrections which are included on the altimeter geophysical data record.
Wind direction alias removal studies of SEASAT scatterometer‐derived wind fields
Authors: Wurtele M. G. , Woiceshyn P. M. , Peteherych S. , Borowski M. , Appleby W. S.
Published: February 2008

Owing to the antenna configuration, and the biharmonic nature of the anisotropic return of the probing radar, the SEASAT scatterometer wind reports consist of as many as four wind directions at each point of observation. A systematic methodology is proposed for selection of the true direction from among these, in the absence of any in situ observations. The techniques employed are those familiar to meteorological analysts. They were subjected to rigorous testing for the JASIN workshop, with two teams performing independent analyses. The agreement of the two analyses was striking. Comparison with wind directions from the JASIN data set, and those estimated from the analyzed pressure field, show agreement largely within the SEASAT specifications. It is concluded that the methodology employed is suitable for SEASAT scatterometer data users.
The free radical chemistry of cloud droplets and its impact upon the composition of rain
Authors: Chameides W. L. , Davis D. D.
Published: February 2008

Calculations are presented that simulate the free radical chemistries of the gas phase and aqueous phase within a warm cloud during midday. It is demonstrated that in the presence of midday solar fluxes the heterogeneous scavenging of OH and HO2 from the gas phase by cloud droplets can represent a major source of free radicals to cloud water, provided the accommodation or sticking coefficient for these species impinging upon water droplets is ≥10−4. The aqueous‐phase HO2 radicals are found to be converted to H2O2 by aqueous‐phase chemical reactions at a rate that suggests that this mechanism could produce a significant fraction of the H2O2 found in cloud droplets. The rapid oxidation of sulfur species dissolved in cloudwater by this free‐radical‐produced H2O2 as well as by aqueous‐phase OH radicals could conceivably have a significant impact upon the chemical composition of rain.
Antarctic sea ice concentrations inferred from Nimbus 5 ESMR and Landsat imagery
Authors: Comiso J. C. , Zwally H. J.
Published: February 2008

A quantitative comparison is made of Antarctic sea ice concentration derived from the Nimbus 5 electrically scanning microwave radiometer (ESMR) and from the Landsat 1 and Landsat 2 MSS‐7 near‐infrared band images. The set of images includes regions near the ice edge and near the continental boundary during late winter or spring. The ice‐covered areas in the southern ocean exhibit microwave brightness temperature predominantly characteristic of first‐year sea ice with emissivity of 0.92. The percentage ice cover is derived from the microwave data, using an algorithm that uses this emissivity and interpolated climatological physical temperatures and that is not dependent on spatial resolution. Classification of ice floes and open water in cloud‐free Landsat images provides an alternative determination of large‐scale ice concentrations, but the limitations of this method are shown. In various areas, especially near the ice edge, Landsat data are limited in their ability to resolve individual ice floes. A classification procedure for Landsat data based on a threshold radiance level for water overestimates the ice concentration because this method tends to classify mixtures of open water and unresolved ice floes as fully ice covered. A proportional classification based on observed reflectance gives better agreement with the ESMR ice concentration values because it does not require that each open water area be resolved in the Landsat imagery. The derived ice concentrations from the ESMR and Landsat data, using the proportional classification method, agree to ±15%, with the largest uncertainties occurring in regions of low concentration.
Positive cloud‐to‐ground lightning in summer thunderstorms
Authors: Fuquay Donald M.
Published: February 2008

This paper describes cloud‐to‐ground lightning that lowers positive charge to earth over mountainous terrain in the northern Rocky Mountain region. A sample of 14 visually confirmed ground flashes provided criteria for identifying positive ground flashes by using only measured electric fields. According to these criteria, 75 positive ground flashes occurred within the 2830 km2 sampling area during three consecutive summer seasons. About 3% of all ground flashes lowered positive charge. The area density of positive ground flashes is about 0.01/km2 per summer season compared to an area density of negative ground flashes of 0.3/km2 per summer season.

Positive ground flashes occurred within the sampling area on 16 of 48 thunderstorm days. Daily occurrences ranged from 1 to 11. When lightning could be associated with individual thunderstorms, the positive flashes usually occurred in sequence during the final 30 min of the storm. The 75 positive flashes are very similar. Each has a single R stroke followed by a continuing current interval. The continuing current duration distribution is approximately log normal, with range 5 to 160 ms and mean of about 60 ms. The prestroke intervals, the total period of field change preceding the first R stroke, are similarly distributed over the range 65 to 210 ms with mean of about 130 ms. Leader field change durations, the latter portion of the prestroke interval, range from 40 to 70 ms with mean of about 50 ms.

The positive ground flashes occurred over mountainous and forested terrain free of man‐made structures. Available data indicate that the positive ground flashes for this region may, in most instances, be initiated by positive downward leaders following a horizontally elongated out‐of‐cloud path to ground.
A simple model of subsurface mesoscale eddies
Authors: Ikeda Motoyoshi
Published: February 2008

Motion in and around small mesoscale eddies is studied. The model is composed of an upper layer, a motionless and infinitely deep lower layer, and the water mass that intrudes between the two layers. This water mass is deformed from a cylinder to a lenslike shape during intrusion. Assuming that potential vorticity (with a relative vorticity of zero before the intrusion) is conserved during the process of intrusion, rotation in and above the radially symmetric intruding mass is determined for a steady state established after intrusion. The rotation is anticyclonic in and above the intruding mass and is fastest at the rim of the mass. In the asymptotic case of the small intruding mass, the azimuthal velocity in the mass exceeds the velocity in the water above the mass. The velocity above the mass tends to be comparable to the velocity in the mass as the mass radius approaches the deformation radius.
Acoustic backscattering from the basin and margins of the Arctic Ocean
Authors: Dyer I. , Baggeroer A. B. , Zittel J. D. , Williams R. J.
Published: February 2008

Sound waves created by high‐energy explosives were used to measure reverberation and backscattering in the Arctic Ocean. From an ice camp in the Beaufort Sea, signals were backscattered from the continental margin and other major features of the basin. An acoustic array was used to analyze the signals in azimuth. Based on these data we constructed charts of normalized backscatter level, which can be compared with known topography of the Arctic Ocean. Resolution of this remote sensing technique for our experimental conditions (analysis frequency, 9 Hz; averaging time, 20 s; array size, 600×600 m) is about 8° in azimuth, 15 km in radial extent, and 1 km in depth. We obtained interpretable signals out to 2700 km. For 1000 km or less, the backscatter charts provide continuous coverage of the margins and major submerged features. Strong returns from about 73.2°N, 139.0°W indicate one or more prominent features that many contemporary topographic charts do not show, but which we believe to be real. Other strong returns are evident from the Northwind Escarpment and from the continental slopes of Alaska and the Canadian Archipelago. Via a backscatter model, we estimate the roughness product (rms height times correlation radius) of these features to be about 4500 m2 on average.