bluuebunny/crossref_metadata_2025 huggingface dataset:
Stratospheric CFCl3, CF2Cl2, and N2O height profile measurements at several latitudes
Authors: Goldan P. D. , Kuster W. C. , Albritton D. L. , Schmeltekopf A. L.
Published: February 2008

The mixing ratios of CFCl3, CF2Cl2, and N2O have been measured as a function of altitude from 6 to 37 km above sea level by using a balloon‐borne grab‐sampling system. The 24 flights were made during the period July 1976 to March 1979 from Wyoming, Panama, Brazil, and Antarctica. These data are reported here both numerically and graphically, the latter being examined for latitudinal and temporal trends. A mean tropopause height for each location and date was used as the reference for the height profiles. The resulting set of CF2Cl2 and N2O profiles show a discernible dependence on latitude; the lapse rate of these mixing ratios is greater for the mid‐latitudes when compared to the equatorial latitudes. The upper tropospheric portion of the CFCl3 and CF2Cl2 data show annual increases of 10.4±3.9 and 10.7±1.9%/yr, respectively, in the northern hemisphere for the middle of the measurement period (end of 1977). Furthermore, the limited number of southern hemispheric data for these constituents are about 8% lower than the northern hemispheric values but have a comparable annual increase. The corresponding N2O data show no interhemispheric differences and the possibility of only a slight increase (less than 2%/yr).
Time scales in wind‐driven lake circulations
Authors: Mohammed‐Zaki Mamdouh A.
Published: February 2008

The effect of turbulent friction on transient three‐dimensional wind‐driven circulation in large lakes is studied. Horizontal friction is neglected, and vertical friction is modeled by a constant eddy viscosity. The linearized Ekman equations are used in a constant depth lake model which is assumed deep (of small Ekman number). High‐frequency transients due to acoustic, internal, and surface gravity wave modes are eliminated through assumptions of incompressibility, homogeneity, and rigid lid surface, respectively. The initial value problem arising from a suddenly imposed wind stress on an initially quiescent lake is analytically solved, and significant time scales are identified. It is found that the manner in which transient currents adjust to temporal variations in wind stress depends not only on a lake's physical parameters but also on the wind stress spatial pattern. While the inertial period is always significant, the spin‐up time is significant only when the wind stress has a nonzero curl.
Lightning return stroke models
Authors: Lin Y. T. , Uman M. A. , Standler R. B.
Published: February 2008

We test the two most commonly used lightning return stroke models, Bruce‐Golde and transmission line, against subsequent stroke electric and magnetic field wave forms measured simultaneously at near and distant stations and show that these models are inadequate to describe the experimental data. We then propose a new return stroke model that is physically plausible and that yields good approximations to the measured two‐station fields. Using the new model, we derive return stroke charge and current statistics for about 100 subsequent strokes.
The asymptotic distribution of the maximum of N wave crest heights for any value of the spectral width parameter
Authors: Walden A. T. , Prescott P.
Published: February 2008

The probability distribution of the largest value attained by a stationary random variable over a period of time, containing many oscillations, is shown to converge to a type 1 extreme value distribution for any value of the spectral width parameter. This result is derived by using recently presented methods of Galambos [1978] from the general form of the probability that any wave crest exceeds a specified crest height as given by Rice [1944, 1945] and further analyzed by Cartwright and Longuet‐Higgins [1956]. A consequence of this generalized derivation is that several asymptotic properties of kth extremes from such distributions, previously obtained by Cartwright [1958], using Rayleigh approximations, may be verified directly. These results illustrate the way in which the spectral width parameter affects the longterm behavior of the system.
The geographical distribution of the solar semidiurnal surface pressure oscillation
Authors: Hamilton Kevin
Published: February 2008

New observations of the solar semidiurnal surface pressure oscillation (S2(P)) at 35 stations throughout the world are presented. These observations are used to supplement those in the literature to produce a large compilation of S2(P) data (403 stations). The geographical distribution of S2(P) is then examined by fitting a series of Hough functions to the station data.
A preliminary radar observation of long‐period waves in the tropical mesosphere over Jicamarca
Authors: Fukao Shoichiro , Sato Toru , Hirota Isamu , Kato Susumu
Published: February 2008

Zonal wind velocity in the tropical upper mesosphere was observed on 3 contiguous days in November 1977 by the VHF radar at Jicamarca, Peru (12.0°S, 76.9°W). A day‐to‐day recurring wind pattern was not always evident in the height range observed, but rather long‐period oscillations with a period longer than 1 day seemed to coexist with tidal winds. The present observation suggests a possibility that the VHF radar technique is applicable to the study on large‐scale waves on a time scale of the order of days.
Measuring rms wave height and the scalar ocean wave spectrum with HF skywave radar
Authors: Maresca Joseph W. , Georges T. M.
Published: February 2008

Estimates of rms wave height and the scalar ocean wave frequency spectrum were made by inverting high‐frequency (HF) skywave radar‐measured sea‐echo Doppler spectra. Whereas low‐power surface‐wave radars can make these measurements out to approximately 100 km from the radar, coverage out to 3000 km can be obtained with skywave radars that illuminate the sea via a single ionospheric reflection. To demonstrate this capability, we used the Wide Aperture Research Faculty (WARF) HF skywave radar to measure Pacific Ocean sea backscatter near NOAA data buoy EB 20 during the passage of an at mospheric cold front. The height of the wind‐generated waves measured at the buoy doubled within a 6‐h period. Two new analysis techniques were used to derive rms wave height and the scalar ocean wave frequency spectrum from radar echoes. Estimates of rms wave height were made east and west of the front by using a power‐law relation that was derived from theoretical simulations of the sea‐echo Doppler spectrum for a wide range of wave conditions. Two of the rms wave height estimates were compared with the estimates made at EB 20 at two different times and are in agreement to within 7 and 17%, respectively. Scalar wave spectrum and rms wave height estimates were made by matching a theoretical Doppler spectrum derived in terms of a five‐parameter model of the wind‐wave spectrum to the measured Doppler spectrum. The radar and buoy estimates of the rms wave height agree within 7%. Agreement between the WARF‐derived and buoy‐derived rms wave height and wave spectra is within the combined experimental error of the buoy and the radar measurements.
A spectral model of the atmospheric general circulation of Mars: A numerical experiment including the effects of the suspended dust and the topography
Authors: Moriyama Shigeru , Iwashima Tatsuya
Published: February 2008

A numerical experiment of the Martian atmospheric general circulation was performed by using a spectral three‐level linear‐balance model. We examined effects of topography and of radiative scattering of dust suspended in the Martian atmosphere upon the general circulation. Computations were made for a period corresponding to the equinoctial season for the southern hemisphere. Our results indicate that in the stage of development of a dust storm, topography, when it exists in the dusty field, would have a very important role for intensifying winds and suspending dust particles blown up from the surfaces in such a specified region as the Hellas region and that thermally forced transient waves produced by radiative effect of dust are superposed on the quasistationary disturbances induced by the topography. As a result, large coupled oscillations appear in the atmosphere, especially in the temperature fields, having the predominant components of wave number 1 and 2 which would correlate with diurnal and semidiurnal wave components, respectively.
On the energy density and forms of ball lightning
Authors: Barry J. D.
Published: February 2008

The range of values for the energy density of ball lightning has been determined from the observational reports detailed enough to allow evaluation and from experimental measurements made during the laboratory production of a ball lightning‐like phenomenon. Ball lightning is shown to be a phenomenon of relatively low energy density below the plasma limit within the range of 2×10−3 J cm−3 to 2×102 J cm−3 with a median value of the order of 1 J cm−3. Further analysis indicates ball lightning to be a single form phenomenon in contrast to previous assumptions.
A numerical study of the effects of heat diffusion through the base of the mixed layer
Authors: Posmentier Eric S.
Published: February 2008

A simple numerical model is used to investigate the warming of the mixed layer during the early summer. The structure consists of two layers separated by a thermocline, across which there is both downward diffusion of heat and upward entrainment of the lower layer by the warmer upper layer. Assuming that the diffusion rate in the thermocline varies with Richardson number (Ri) according to Munk and Anderson's (1948) formulation, it follows that the heat flux through the thermocline is small for either very small or very large gradients of temperature (i.e., density). The heat flux is maximum at a tempeature gradient corresponding to a ‘limiting Richardson number’ Ri* = 0.6. This maximum value of heat flux is proportional to the vertical velocity shear squared. Model results for a shallow area show that, for low surface heat fluxes throughout the early summer, weak warming occurs uniformly at all depths in proportion to the heat flux. For high surface heat fluxes, much stronger warming occurs, but it is confined to the surface layer. As a consequence the early summer warming of the cold bottom water actually will be decreased if the surface heat flux is increased beyond the maximum heat flux in the thermocline. If a 6‐day period of strong surface heating were to occur in the early spring, the model would predict that the resulting strong thermocline would persist for the remainder of the summer, allowing only 27% of the entire spring surface heat flux to penetrate to the lower layer. If the 6‐day period of strong surface heating were postponed until the end of the early summer, 52% more heat would be able to penetrate the thermocline during the entire spring. It is concluded that conditions favorable for the formation of a cold pool can prevail if the early summer surface heating is stronger or if a brief strong heating event occurs soon after the spring surface heating begins.
Dedication: John W. Wright, 1929–1978
Authors: Wright John W.
Published: February 2008

The death of John W. Wright in an automobile accident on November 20, 1978, came as a great shock to all who knew him. His family and friends lost a stimulating, compassionate human being whose many‐faceted personality they greatly admired. The scientific community working on remote sensing of the air‐water interface lost one of its pioneers and leaders. To dedicate this issue of the Journal of Geophysical Research to Dr. Wright seems a fitting tribute to his many scientific achievements.
Bimodal distribution of atmospherics associated with tornadic events
Authors: Johnson R. L.
Published: February 2008

Directionally resolved records of sferic burst counts were acquired from thunderstorms during April–June 1977. Three tornadoes were reported, two being confirmed as hook echoes on National Weather Service radar. The sferic burst rates, plotted as a function of 2 min intervals, showed a 4–6 min period of relative inactivity followed by an abrupt enhancement of the burst rate. Numerous investigators have reported an enhancement of sferic activity associated with tornadic storms; however, these results do not indicate a lull in sferics immediately prior to the enhancement. The bimodal distribution of sferic activity has not been observed within nontornadic storms by this laboratory.
Behavior of VLF atmospherics around morning hours on the coast of the Bay of Bengal
Authors: Sarkar S. K. , Bhattacharya A. B.
Published: February 2008

Simultaneous observations of VLF atmospherics at 10, 20, and 30 kHz recorded in a low‐latitude tropical station, Calcutta, on the coast of the Bay of Bengal, exhibit a ‘stepped‐fall’ on the level of atmospherics activity around morning hours. As many as three steps have been observed in some of the cases. The phenomenon has been analyzed in relation to its occurrence, duration, starting time, and magnitude. The seasonal variations and frequency dependence also have been examined. Results reveal that both duration and magnitude of the main step are greater than those for the second and third steps. In general, there are seasonal characteristics. The probable explanation of the phenomenon has been made in terms of the distribution of effective noise sources at such times, mainly at the sea thunderstorms around the observing site.
Global distribution of sulfur compounds in the troposphere estimated in a height/latitude transport model
Authors: Rodhe Henning , Isaksen Ivar
Published: February 2008

A global two‐dimensional time‐dependent model has been used to estimate the tropospheric distributions of sulfur compounds resulting from natural emissions of H2S or DMS and from man‐made emissions of SO2. Comparisons of observations of H2S, DMS, SO2, and SO4− in remote areas with the model estimates indicate that the global flux of H2S and DMS, taken together, amounts to at most a few tens of Tg S yr−1. The present man‐made emissions Of SO2 (about 80 Tg S yr−1) can account for a dominant part of the SO2 and SO4− observed in the lower troposphere of the northern hemisphere. On the other hand, neither natural emissions of H2S and DMS at the surface nor man‐made emissions of SO2 seem to be able to explain the relatively high values of SO2 observed in the middle and upper troposphere in both hemispheres. Our calculations indicate that a relatively long‐lived precursor must be involved as a source for this SO2. The amount of SO2 produced by the oxidation of CS2 and OCS does not seem sufficiently high. Average residence times in the atmosphere for H2S, SO2, and SO4− have been estimated to about 1, 1.5, and 5 days, respectively. If only higher portions of the troposphere are considered, the residence times increase considerably.
Specific nonmethane hydrocarbons and their relationship to ozone in an eastern urban area, Manhattan
Authors: Altwicker Elmar R. , Whitby Robert A. , Lioy Paul J.
Published: February 2008

Specific hydrocarbons emitted from mobile and stationary sources enter into the formation of secondary pollutants, such as ozone and aerosols. The extent to which specific hydrocarbons perform this role is due to their differences in reactivities. Detailed knowledge of the hydrocarbon composition of the atmosphere as a function of time and altitude therefore is desirable. Measurements were carried out at ground level and simultaneously at elevated sites which were frequently above the inversion. Together with continuous information on ozone, two to four ambient air samples were collected per site per day for individual species hydrocarbon analysis by gas chromatography. The resultant data base is examined here in terms of the four major hydrocarbon classes (paraffins, olefins, aromatics, and acetylene) with respect to absolute concentrations, characteristic ratios, decay rates, and ozone/hydrocarbon relationships. With occasional notable exceptions all hydrocarbon species were present in lower concentrations at the elevated sites (40–50%) characteristic ratios to acetylene reflected changes in automobile exhaust composition and stationary source contributions. Decreases in hydrocarbon/acetylene ratios were used to estimate ambient hydroxyl radical concentrations. The percent contributions of olefins was lower in 1975/1978 than in 1969. Although hydrocarbon concentrations appear to have declined between 1975 and 1978, ozone concentrations during the study periods were higher in 1978.
Bubble populations and spectra in near‐surface ocean: Summary and review of field measurements
Authors: Wu Jin
Published: February 2008

Previous measurements of small bubbles in the near‐surface ocean are summarized and are reviewed to obtain variations of bubble populations and size distributions with depth and wind velocity, to explore mechanisms of bubble production, and to suggest further studies.
Intra‐annual variation in large‐scale moisture fields
Authors: Peixoto José P. , Salstein David A. , Rosen Richard D.
Published: February 2008

To identify better the annual cycle in the northern hemisphere fields of integrated water vapor and its flux, we have separated 5 years of upper‐air rawinsonde station data into four composite seasonal quarters. Maps and zonal means of the fields attest to the intensity of the summer‐winter contrast, increasing and sharpening prior estimates of this difference based on semester definitions of these seasons. Interestingly, results for the transition seasons of spring and of autumn are not identical but rather tend to resemble their antecedents, reflecting in part the importance of the ocean's thermal inertia. Our study should prove useful as a basis for comparison with results expected during the next decade from analyses of the Global Weather Experiment.
Self‐similarity in stress‐driven entrainment experiments
Authors: Kundu Pijush K.
Published: February 2008

Relations have been developed for the entrainment of a turbulent layer into a stratified medium under the action of a surface stress. A constant gradient Richardson number J is assumed at the interface, and the solutions are assumed to be self‐similar. It has been shown that the requirements of similarity are that the scales of the (mean and turbulent) velocity and temperature should all be powers of time t. The cases of linear and two‐layer density distributions have been given special attention, and a constant of proportionality in each case is determined by comparison with numerical solutions. The results are identical to those obtained by Pollard et al.‐type slab models if Rv ≃ 2J, where Rv = buoyancy/(mean velocity)2. The nondimensional entrainment rate for the two‐layer case is nearly twice that for linear stratification, as observed. The density gradient in the two‐layer case is proportional to t−2, which explains the observed gradual disappearance of the density step. Numerical solutions show that the self‐similarity assumption is quite good with two layers and is approximately valid with linear stratification if 100 < tN < 500. For tN > 500, nonlinear mechanisms create a sharp interface with linear stratification. Thus whereas a two‐layer experiment destroys the initial sharp interface, an experiment with initially linear stratification creates a sharp interface.
Two major dust storms, one Mars year apart: Comparison from Viking data
Authors: Ryan J. A. , Sharman R. D.
Published: February 2008

The Viking Mars Landers have been on the Mars surface for over two Mars years. During the first year two major, probably global, dust storms occurred. The first was unusually early compared to most previous Earth‐based observations. A major storm occurred during the second year, almost precisely one year after the first storm of the first year. Meteorological data show roughly similar atmospheric behavior for the two early storms. Of particular note is the increase in amplitude of pressure oscillations (probably of baroclinic origin) and concurrent increases in wind speed during the build‐up phase of all three storms. The generation of these waves appears to be a natural consequence of seasonal effects not associated with the dust storms. It is suggested that ‘baroclinic’ waves, should they exist in the southern hemisphere during the time of dust storm generation, could be an important factor in growth and development of the dust storms.
Subtidal Water level variations in Lake Pontchartrain, Louisiana
Authors: Chuang Wen‐Ssn , Swenson Erick M.
Published: February 2008

Lake Pontchartrain, Louisiana, has two major tidal passes connecting it to the Mississippi Sound and thence to the Gulf of Mexico. The subtidal variability in this system and its relation to wind forcing over a 7‐month period were examined. The coherence of water level fluctuations in the lake and passes with those of the sound was high at all time scales, and the water level in all data sets responded to the east‐west wind at time scales shorter than 15 days. Since the local coastline is approximately in the east‐west direction, the results suggest a coupled coastal ocean‐lake response. A linear friction model was developed, and it accounted for most of the observed features.
Observation of spectrally resolved infrared chemiluminescence from vibrationally excited O3(v3)
Authors: Rawlins W. T. , Caledonia G. E. , Kennealy J. P.
Published: February 2008

Infrared emission from the v3 band of ozone near 9.6 μm has been observed in the COCHISE cryogenic chemical reactor/spectrometer. Vibrationally excited O3, formed principally by recombination of O2 with discharge‐produced oxygen atoms at 1 torr and 80–120 K, is expanded into a low‐pressure (∼3 mtorr) environment where its infrared radiation is observed without interference from infrared background effects. The observed spectral distributions are interpreted by using a least squares/spectral synthesis method, in which the vibrational state populations and spectroscopic parameters are adjusted in computed spectra so as to provide the best fits to the observed spectra. The (001) → (000) transition is responsible for most of the observed intensity; however, (Δυ3 = 1) emission from higher vibrational levels is also seen, extending to ∼11 μm (υ3′ ∼ 6). Although the observed spectral distributions are affected by collisional deactivation occurring in the discharge region, the apparent degree of vibrational excitation observed in these experiments should have considerable bearing on investigations of infrared radiation in the upper atmosphere.
Dynamics and geometry of wave‐generated ripples
Authors: Nielsen Peter
Published: February 2008

Semi‐empirical formulae for the size and shape of sand ripples are derived from an analysis of the water and sediment motion over a rippled bed in oscillatory flow. Simple physical arguments show that ripple steepness should be a function of the nondimensional shear stress θ′ and the angle of repose of the bed material. All available data seem to support this. The mechanisms that determine the ripple length are very complex, and at least four nondimensional parameters are important. However, for practical purposes the ripple length is well determined by the mobility number ψ. ψ is essentially the ratio of the water velocity amplitude to the sediment settling velocity. Both ripple length and ripple height are shown to depend mainly on ψ, when only quartz sand and natural wave periods are considered. The derived formulae apply well to the full range of flow conditions, where ripples occur. Natural ripples obey essentially the same rules as laboratory ripples; however, they are generally shorter and flatter owing to the irregularity of natural waves.
Evidence for equatorial trapped waves at the Galápagos Islands
Authors: Ripa P. , Hayes S. P.
Published: February 2008

From June 28 to November 23, 1979, sea level fluctuations at three locations on the western side of the Galápagos Islands were measured with shallow bottom‐moored pressure and temperature gauges. Gauges were deployed at 1°24′N, 0°, and 1°S. The sea level variations were dominated by a highly coherent low frequency fluctuation with a period of the order of 100 days. In addition, high‐frequency spectral peaks were observed with periods of 5.3 and 2.8 days. Temperature fluctuations also showed the dominant low‐frequency change and the high‐frequency spectral peaks; however, the temperature fluctuations were less coherent because of the thermal front in this region. Empirical orthogonal functions of the pressure gauge data showed that most (95%) of the low‐pass filtered data could be explained by the first mode. This mode had a meridional shape consistent with a first baroclinic mode equatorial Kelvin wave. The second mode accounted for about 3.6% of the variance with periods from 15 to 5 days. Its shape was consistent with a first baroclinic mode mixed Rossby‐gravity wave. The higher frequency peaks occur at frequencies where equatorial trapped inertial‐gravity waves have zero zonal group velocity.
Surface currents in the Caribbean Sea as deduced from Lagrangian observations
Authors: Molinari Robert L. , Spillane Michael , Brooks Irving , Atwood Donald , Duckett Carol
Published: February 2008

The results of a satellite tracked drifting buoy experiment conducted in the Caribbean Sea from October 1975 through June 1976 are presented. The buoy trajectories suggest that the Aves Rise, Beata Ridge, and Nicaraguan Rise are regions where considerable mesoscale variability occurs in the surface flow. The variability is in the form of current deflections; small diameter eddies ranging in size from 20 to 100 km; large amplitude meanders, with amplitudes greater than 150 km; and large diameter eddies, with diameters greater than 200 km which form on and near these rises and ridges. In the central Caribbean, where the topographic relief is not as dramatic, the flow is predominantly zonal. Intensifications in the surface flow occur off the coast of Colombia, south of the Nicaraguan Rise, and south of the Yucatan Strait.
Large‐scale synoptic thermal fronts in the mid‐latitude North Pacific from 1976–1978
Authors: Levine E. R. , White W. B.
Published: February 2008

Temperature data obtained from June 1976 to May 1978 in the TRANSPAC ships‐of‐opportunity XBT program have been used to examine the large‐scale evolution of synoptic thermal fronts from 165°E to 135°W, from 30° to 50°N in the mid‐latitude North Pacific on a 2° latitude by 5° longitude grid. These results were referenced to a climatology computed from all XBT data collected in the region from 1968–1974. The primary indicator of frontal strength and position was the zonal continuity of the modulus of horizontal temperature gradient in the upper 300 m. Over the 2‐year period, the Subarctic Front was observed as a quasi‐zonal coherent feature, ranging in latitude between 38° and 46°N, strongest at the sea surface, decreasing in strength toward the east. This front was found to have had two realizations, a northern one dominant in winter‐spring between 42° and 46°N and a southern one dominant in summer‐fall between 38° and 42°N. Generally, these frontal realizations were vertically coherent with depth. The transition from the southern front to the northern front occurred in either November or December of both years, while the transition from the northern to the southern front took place in either March or April. In winter‐spring, there existed considerable overlap of the existence of these two fronts; however, in summer‐fall, the northern front was not observed. The northern front had a tendency to be displaced southward 2°–4° through the winter‐spring period, while the southern front had no consistent tendency over the 2 years. At depth, the strength of these fronts shows no significant variability over the 2‐year period, and the two fronts are comparable in strength. Two other thermal fronts were observed intermittently, i.e., the Subtropical Front in the eastern part of the region between 30° and 36°N and the Kuroshio Extension Front in the western part of the region along approximately 36°N. These fronts were observed to form transient links or filaments with both realizations of the Subarctic Front.
On critical roughness Reynolds numbers of the atmospheric surface layer
Authors: Wu Jin
Published: February 2008

Detailed features of drag coefficient (C10) varying with wind velocity (U10) are used to determine critical values of roughness Reynolds number (Re). Boundary‐layer regimes of the atmospheric surface layer are identified as aerodynamically smooth, Re<0.5 (U10<3 m s−1); transition, 0.5<Re<2 (3 m s−1<U10<7 m s−1); and aerodynamically rough Re>2 (U10>7 m s−1). Features of C10 varying with Re and determination of critical values of Re are also substantiated.
The distribution of carbon monoxide and ozone in the free troposphere
Authors: Seiler Wolfgang , Fishman Jack
Published: February 2008

The two‐dimensional distributions of CO and O3 in the free troposphere during July and August, 1974, are discussed. The data confirm the previous findings that both of these gases are considerably more abundant in the northern hemisphere, but the degree of the asymmetry is somewhat different from what had been reported previously, especially for CO. When examined with respect to other available data sets, the conclusion is drawn that a pronounced seasonal cycle exists for CO in both hemispheres which may be driven by the likely seasonal cycle of the OH radical. The data also indicate that CO concentrations exhibit significant variability with height in the northern hemisphere, whereas southern hemispheric concentrations are quite constant with altitude except in cases where interhemispheric exchange of air may be occurring. A discussion on the vertical and horizontal transport processes inferred from the CO and O3 measurements is presented. The possible interdependence of the photochemical cycles of these two trace gases is also discussed.
Stratospheric chemical and thermal response to long‐term variability in solar UV irradiance
Authors: Brasseur G. , Simon P. C.
Published: February 2008

A theoretical analysis of the chemical response of the stratosphere to possible long‐term variability of solar ultraviolet irradiance has been performed, taking into account the thermal feedback effect on the reaction rates. Numerical values of ultraviolet and visible irradiation fluxes used in this work are given for aeronomic modeling purposes and a possible variability related to the 11‐year solar cycle is suggested on the basis of recent and reliable observations of solar ultraviolet irradiance. This variability has been introduced in a stratospheric two‐dimensional model which simulates the zonally averaged distribution of the chemical species related to the oxygen, hydrogen, nitrogen and chlorine families. The results lead to a total ozone variation of the order of 3% from the minimum to the maximum solar activity, with a maximum of about 10% in the upper stratosphere. At these heights, the calculated temperature change is close to 2–4 degrees. The N2O concentration appears to be one of the most sensitive to long‐term solar variability and a monitoring of this constituent would be useful to give information on the solar variability in the ultraviolet.
Measurements of CF2Cl2, CFCl3, and N2O in the lower stratosphere between 2° S and 73° N latitude
Authors: Vedder J. F. , Inn E. C. Y. , Tyson B. J. , Boitnott C. A. , O'hara D.
Published: February 2008

Mixing ratios are presented for CF2Cl2, CFCl3, and N2O in the lower stratosphere. They are derived from measurements made on samples collected by a high‐altitude aircraft during a survey in the northern hemisphere in the summer of 1977. The vertical distributions of the mixing ratios of these species show a decrease with increasing altitude and a marked decrease at a given altitude with increasing latitude from 2°S to 73°N latitude. These results agree with our measurements at similar latitudes in the fall of 1976 and with results of other experiments. The experimental apparatus and procedures are described in greater detail than in previous papers.
Aerosol formation, transformation, and effects in Denver's emissions plume
Authors: Van Valin C. C. , Pueschel R. F. , Wellman D. L.
Published: February 2008

Aerosols and trace gases over the Denver metropolitan area and in one case to 175 km downwind were measured with an instrumented aircraft. Typical background concentrations measured above the polluted layer were light scattering coefficient (bscat), 0.2 × 10−4 m−1;; total particle (CN) concentration, 1–5 × 103 cm−3;; O3, 30 parts per billion (ppb); SO2, <5 ppb; NO, <5 ppb; NO2, 5 ppb. Below the inversion and near the city center (main emissions source) typical measured values were as follows: bscat, 0.5–1.5 × 10−4 m−1; CN, 105 cm−3, O3, 10 ppb; SO2, 30–50 ppb; NO, 50–100 ppb; NO2, 50–100 ppb. As the plume aged, the CN concentration was found to decrease to one third or one fourth of the initial value, but bscat increased, in one instance to >4 × 10−4 m−1, with increases in particle population in the accumulation mode. At the same time the NO2 concentration was only about one tenth of the value predicted by the O3 and NO concentrations and solar irradiance; removal of NO2 by dissolution in liquid water is indicated. For refractive indices assumed to be realistic for dry urban aerosols, the absorption‐to‐backscatter ratio decreased with increasing age of the cloud. Therefore, freshly formed emission plumes had the potential to warm the atmosphere under sunlight, but after 10 hours or more the plume had much less warming potential; cooling probably occurred over most surfaces.
Wind measurement techniques available for the middle atmosphere program
Authors: Gage K. S. , VanZandt T. E.
Published: February 2008

The study of atmospheric dynamics in the Middle Atmosphere Program (MAP) will depend strongly on both the quality and quantity of wind measurements taken during the program. This paper presents a survey of the status of the many techniques which can be utilized to measure wind in the middle atmosphere. Most wind observations in the stratosphere and mesosphere have been made in situ by using balloons and rockets. These observations have been supplemented for many years by observations from ground‐based remote systems such as the meteor radar. In addition, geostrophic winds can be inferred from satellite radiance measurements. In recent years, several radar techniques have been developed that could add significantly to the data base of wind observations for MAP. These include the incoherent scatter radar method, the spaced antenna drift method, and the MST radar technique. The real problem for MAP is to obtain adequate wind data in the 30–80 km range. For this altitude range a variety of rocket techniques are used routinely (about once a week) at stations of the world‐wide Meteorological Rocket Network (MRN). While recent developments in radar measurements of the middle atmosphere raise the possibility of continuous remote wind measurement by using the MST radar and the spaced antenna drift method at a few locations, a truly global set of wind observations must await the development of new satellite techniques that will not be available for another 5–10 years.
A zonally averaged chemical‐dynamical model of the lower thermosphere
Authors: Kasting J. F. , Roble R. G.
Published: February 2008

A zonally averaged numerical model of the thermosphere is used to examine the coupling between neutral composition, including N2, O2, and O, temperature, and winds at solstice for solar minimum conditions. The meridional circulation forced by solar heating results in a summer‐to‐winter flow, with a winter enhancement in atomic oxygen density that is a factor of about 1.8 greater than the summer hemisphere at 160 km. The O2 and N2 densities are found to be higher in the summer hemisphere by factors of 2–3 at altitudes near 100 km. The O2 and N2 variations are associated with a latitudinal gradient in total number density, which is required to achieve pressure balance in the presence of large zonal jets. Latitudinal profiles of OI (5577 Å) green line emission intensity are calculated by using both Chapman and Barth mechanisms. Composition of the lower thermosphere is shown to be strongly influenced by circulation patterns initiated in the stratosphere and lower mesosphere, below the lower boundary used in the model.
High‐level temperatures and winds over tropics and Indian summer monsoon
Authors: Mukherjee B. K. , Reddy R. S. , Murty Bh. V. Ramana
Published: February 2008

The authors from the earlier investigations of the M‐100 Soviet rocketsonde temperature and wind data for the tropical station Thumba (8.5°N, 76.9°E) identified occurrence of high‐level warmings during both the winter and the summer monsoon seasons. There was good agreement between the occurrence of high‐level warmings and the monsoon activity in the Indian region. The study further indicated a possible relationship between the stratospheric quasi‐biennial structure and the monsoon rainfall. To test the validity of the above results for tropics, the rocketsonde temperature and wind data for Ascension Island (8.0°S, 14.4°W) and Kwajalein (8.7°N, 167.7°E) for four winter seasons (December to February of 1970–1971, 1971–1972, 1974–1975, and 1975–1976) and four summer monsoon seasons (May to September of 1971, 1972, 1975, and 1976) were studied. The above periods are the same as those of the earlier study for Thumba. Out of the above years, 1972 and 1975 were the years of contrasting monsoon activity. The results of Ascension Island and Kwajalein agreed with those of Thumba.
Wave‐current interaction effects on water velocity and surface wave spectra
Authors: Lambrakos K. F.
Published: February 2008

Measurements of tidal and wave water velocities which were made in shallow water near the seafloor in the Strait of Juan de Fuca indicate strong tidal current influence on waves. This effect is reflected in the variation of the velocity frequency spectrum with the direction and magnitude of the tidal current. The area under the spectrum decreases when the current propagates in the direction of the waves, and it increases when the current propagates against the waves. These spectral area variations increase with the current magnitude. The observations are generally consistent with predictions of a spectral model derived from the energy balance principle.
Mid‐level intrusions at the continental shelf edge
Authors: Welch Christopher S.
Published: February 2008

Observations across the continental shelf offshore from New Jersey in late summer 1976 show an intrusion of saline water at the mid level of the water column across the shelf edge front, which appears in density only as an offshore thickening of the pycnocline. This internal density field produces horizontal pressure gradient forces within the pycnocline in the onshore direction. These forces, in the linearized equation of motion with a constant eddy viscosity, drive a circulation which resembles a double Ekman spiral for internal pressure vertical distributions which are thin with respect to the Ekman depth. For thick pressure distributions, the circulation is geostrophic. The resulting flow pattern has no net crossshelf transport. For the continental shelf edge in the example, a northward geostrophic mid‐level jet is predicted by the theory. Ekman depth, and thus the vertical coefficient of eddy viscosity, can be determined from hydrographic data describing an intrusion.
Sea ice displacement from Seasat synthetic aperture radar
Authors: Hall R. T. , Rothrock D. A.
Published: February 2008

Images obtained by a synthetic aperture radar on SEASAT have been used to measure sea ice displacements over a three day interval in October 1978. The position of a natural ice feature was measured on 5 October and again on October 8; the difference in these two positions is a displacement. The displacement of many features was measured. The tracked features lie roughly along a line and are quite dense—about 2 km apart—over a distance of 865 km. The displacements are about 20 km. Displacement errors grow with distance from shore becoming as large as 3 km. The graph of displacement versus distance has occasional discontinuities of several kilometers. Displacement discontinuities are accurate to ±0.07 km along track and 3% of their magnitude across track.
Radar observations of lightning
Authors: Proctor D. E.
Published: February 2008

Radar echoes from lightning were observed at wavelengths of 5.5, 50, and 111 cm. The 50‐cm and the 111‐cm radars produced strong echoes from every flash that we saw passing through the beams of the radars. Echoes were particularly strong on the radar with the longest pulse. Echoes received on radars that transmitted pulses 200 ns long consisted of short components. Some flashes reflected only one echo, but usually there were many more, and as many as 30 separate components of echoes have been counted. No echoes were detected by the 3‐cm radar set, presumably because its pulse repetition rate was too low. A very small number of flashes produced detectable echoes at 5.5 cm, although many flashes were seen passing through the beam of the radar. These echoes behaved in either of two ways. Occasionally we saw strong echoes that appeared singly and moved rapidly in range, and we ascribed these to the tips of underdense channels. Stationary echoes that extended in range to become multiple echoes similar to those we observed at VHF were seen at 5.5 cm also, and we supposed that they were reflected by many channel segments that happened to be overdense at 5.5 GHz. This paper supplies data relating to the mean values and to the dispersion of radar cross‐sectional areas of lightning channels viewed by VHF radar.
Direct measurements of the atmospheric electrical potential, using tethered balloons
Authors: Willett J. C. , Rust W. David
Published: February 2008

The progress toward a direct measurement of ionospheric potential is summarized. The measurement technique is described, and the results and their implications are discussed. The maximum altitude and potential attained to date are 5.3 km msl and 195 kV, operating from a 3.2 km msl mountain ridge.
An ocean transport model for the North Atlantic
Authors: Sarmiento J. L. , Bryan K.
Published: February 2008

Three‐dimensional solutions are obtained for the circulation of the North Atlantic using a robust diagnostic model. In contrast to previous diagnostic models the robust diagnostic model incorporates the conservation of the large‐scale fields of heat and salinity as well as momentum. An approximate fit to observed fields of temperature and salinity is obtained by a closure condition. The method is robust in the sense that it does not have the extreme sensitivity to the density input fields of the classical diagnostic method. Equilibrium solutions are obtained by numerical integration of the time‐dependent equations. Error estimates for the velocity field can be obtained indirectly from the numerical solutions. Temperature observations used as input have an effective resolution of 3°×3° of latitude and longitude and a sampling error of ± 0.15°C. The equivalent vertically integrated velocity error is estimated to be ±0.5–1.0 cm/s depending on bottom topography. The suitability of the model for geochemical work is judged by comparison with heat and salinity balance estimates. Best results are obtained for the case in which the model has a minimum observational constraint below the surface.
Bars, bumps, and holes: Models for the generation of complex beach topography
Authors: Holman R. A. , Bowen A. J.
Published: February 2008

In shallow water, any two waves of the same frequency are shown to produce complex patterns of drift velocity above the sea bed. If the longshore components λ1, λ2of the wave numbers of the two waves are different, these steady flow patterns exhibit a longshore periodicity of wave number (λ1‐ λ2) irrespective of whether the waves propagate in the same direction (say λ1, λ2positive) or in opposite directions (λ2negative). The interaction of two edge wave modes is examined in detail. The drift velocities are calculated and a simple sediment transport model is used to predict the beach topography that would be in equilibrium with these flow patterns. As expected, crescentic sand bars are produced by the special case of standing edge waves (λ1= −λ2). Intriguingly, for all other cases a combination of complex transverse bars plus meandering or straight offshore bars result, patterns that are surprisingly reminiscent of many published descriptions of complex, rhythmic topography. The extension of the model to three or more waves produces topography that appears to be very irregular. Although the pattern should repeat over sufficiently long distances along the beach, even with only three waves these distances may be very large compared to the scale of the bars.
The role of tilt in double diffusive interleaving
Authors: Posmentier Eric S. , Hibbard Charles B.
Published: February 2008

The growth rate of double‐diffusive interleaving has been evaluated using Stern's (1967) model, which assumes vertical T/S gradients in the salt‐fingering domain and compensating horizontal T/S gradients. The interleaving may take place along planes tilted with respect to the horizontal. For a given vertical scale, various cross‐gradient and along‐gradient tilts result in a variety of modes including two different growing modes, a decaying mode, and growing or damped vertically propagating modes. The relative importance of the processes causing momentum, salinity, and temperature changes is discussed for each mode. A quartic equation is obtained for the tilt at which the growth rate is maximum. Near‐maximum growth rates occur at widely differing along‐gradient tilts of either sign, but the cross‐gradient tilt is critical to the growth rate. The three kinds of derivatives of S, T, and density (Eulerian, Lagrangian, and synoptic along‐core) are found to have different signs and phases, confounding attempts to confirm double diffusion by fine‐scale observations. T‐S diagrams in intrusion‐affected regions can assume a variety of shapes. For a salinity perturbation amplitude S, the effective coefficients of horizontal diffusion can exceed S2·106 cm2/s for salt and heat, which is large enough to account for a significant part of the large‐scale, nonadvective fluxes in the ocean. The vertical coefficients are greater than S2·103 cm2/s (S2·102 for density) and negative! The resulting strong positive feedback between large‐scale gradients and medium‐scale intrusions has widespread implications for the generation and maintenance of water mass properties.
A note on the generation of capillary waves by steep gravity waves: The effect of wind growth
Authors: Valenzuela G. R.
Published: February 2008

Longuet‐Higgins' (1963) theory for the generation of capillaries by a steep gravity wave is generalized to the case of wind. Wind growth enhances the steepness of the crest‐generated capillaries, and their maximum steepness now occurs further away from the crest. Implications to remote sensing are discussed.
Estimation of atmospheric sea salt dry deposition: Wind speed and particle size dependence
Authors: McDonald R. L. , Unni C. K. , Duce R. A.
Published: February 2008

Cascade impactor and bulk filter samples of atmospheric sea salt were collected at wind speeds from 3.4 to 10 m/s at coastal tower sites in the Florida Keys and Enewetak Atoll as part of the SEAREX (Sea Air Exchange) Program. Simultaneous dry deposition measurements were made to polyethylene plates. The samples were analyzed for Na as an indicator of sea salt. If the observed atmospheric sea salt particle mass distributions are corrected for the reduced collection efficiency of large particles, the observed dry deposition rates agree well with rates estimated from atmospheric sea salt particle concentrations and theoretical particle deposition velocities derived from gravitational settling velocities or from the equations of Slinn and Slinn (1980, 1981) for deposition to smooth, solid surfaces as well as natural water surfaces. The results emphasize the fact that even though large particles may represent only a small fraction of the total mass of sea salt over the ocean, they can dominate the dry deposition rates of the sea salt aerosol.