bluuebunny/crossref_metadata_2025 huggingface dataset:
Simultaneous observations of ocean surface winds and waves by Geosat radar altimeter and airborne synthetic aperture radar during the 1988 Norwegian Continental Shelf Experiment
Authors: Mognard Nelly M. , Johannessen Johnny A. , Livingstone Charles E. , Lyzenga David , Shuchman Robert , Russel Cathy
Published: February 2008

Quasi‐simultaneous measurements of the ocean surface by the Canada Centre for Remote Sensing (CCRS) Convair‐580 (CV‐580) synthetic aperture radar (SAR) were acquired on March 20, 1988, along an ascending pass of the Geosat radar altimeter as part of the prelaunch ERS‐1 Norwegian Continental Shelf Experiment (NORCSEX '88). Over a region where the SAR look direction is parallel to the wind vector, a relationship between the ocean scattering cross sections measured by the Geosat altimeter and the SAR is obtained. In the regions where the wind direction is changing, an estimate of the wind direction is derived from the differences measured between the altimeter and the SAR scattering cross sections. Wavelength and wave directions derived from the SAR wave spectra are in good agreement with the sea truth data obtained with the wave directional buoys and with the altimeter‐derived swell estimates. Significant wave height measured by the Geosat altimeter is compared with the buoy measurements and is used to assess the validity of the significant wave height deduced from the SAR.
Observations of short‐period ice floe accelerations during leg II of the Polarbjørn drift
Authors: Martin Seelye , Drucker Robert
Published: February 2008

During leg II of the Polarbjørn drift, we measured the orthogonal components of acceleration in the vertical and horizontal directions for the frequency interval 0.04–5 Hz, and the compass heading, at three sites adjacent to the ship. During days 310–329, the ice surrounding the ship underwent a transition from large floes with scales of 1–10 km, to small, broken floes with scales of 10–100 m. The deformation and fracture associated with this transition generated significant accelerations which were associated with ice shear, ridging, and ice floe collisions. For the shearing between two large floes, we observed stick‐slip accelerations with 0.4‐Hz frequencies and 3 mm s−2 amplitudes. For ridging, we observed two kinds of behavior, depending on floe size. For ridging of large kilometer‐scale floes, we observed 1‐Hz sinusoidal oscillations with 10 mm s−2 amplitudes, while for 100‐m‐scale floes, the spectra of the accelerations were white. When the field of 50‐ to 100‐m‐scale floes was divergent, ice collisions with amplitudes as large as 150 mm s−2 dominated; for two of the three sites these collisions excited the resonant bobbing and rocking frequency of the floe. Our observations ended on day 329, when the ice converged, the floes were apparently crushed, and the accelerometers ceased operation.
Critical frequencies at ocean boundaries
Authors: Clarke Allan J. , Shi Chuan
Published: February 2008

Past theoretical work has shown that for low‐frequency flow at a given ocean boundary location, a critical frequency ωc exists such that for ω > ωc unforced motion is trapped to the coast while for ω; < ωc energy leaves the coast. Alternatively, for motion of a given frequency ω on the boundary, there exists a critical latitude such that the motion is trapped to the coast poleward of that latitude but equatorward it is not. This theory is discussed physically for both meridional and nonmeridional boundaries. The simple formula for critical frequency along a nonmeridional boundary is used to document critical periods for the eastern and western Atlantic, Pacific, and Indian Ocean boundaries. The theory occasionally breaks down when boundary curvature is too large.
Subtidal Eulerian currents in the upper and lower East River tidal strait: Spring 1981
Authors: Filadelfo Ronald , Wilson Robert E. , Gomez‐Reyes Eugenio
Published: February 2008

Subtidal Eulerian currents determined from long‐term current moorings in the East River tidal strait connecting the lower Hudson River with Long Island Sound show a well‐defined two‐layer circulation pattern within the eastern (upper) part of the East River. Mean surface currents flow toward the sound, and current at depth flows toward the Hudson. Within the western part of the East River, residual currents are vertically sheared, but flow is directed toward the sound at all depths, with stronger flow near the surface. Mean current magnitudes are of the order of 5 cm s−1. Results from frequency domain regression show that in the western (lower) portion of the strait, current fluctuations at frequencies of 0.25 cycles per day and higher are associated primarily with a barotropic response to fluctuations in hydraulic head. At lower frequencies, currents exhibit a baroclinic response to fluctuations in the discharge of the Hudson River. Within the upper part of the strait, currents respond to along channel winds. Response to fluctuations in sea level head and Hudson River discharge is detectable but not as well defined as within the lower East River. These results can provide insight into the relative importance of different forcing functions in maintaining the residual flow through the strait. The difference in the response characteristics of the western and eastern segments of the strait could be related to differences in the intensity of tidal mixing along the strait and the degree of water column stratification.
Acoustic observation of oil slicks at sea
Authors: Belloul M. B. , Thorpe S. A.
Published: February 2008

The results of an open sea experiment devised to investigate the feasibility of detecting and monitoring oil slicks by sonar through their effect on the acoustic backscatter signal are presented. The analysis, carried out over an angular range 10° to 70° from the horizontal, reveals a reduction in backscatter from the slick. The reduction in the mean backscatter <σ> shows an angular dependence which reaches a maximum in the range 45° to 65°. A gradual decrease of <σ> as wind speed decreased and as the slick developed was also observed. Comparison of the acoustic data with Ku band radar reflection from an oil covered surface under similar wind speed conditions shows that differential radar backscatter from oil slicks may exceed that of sonar by a factor 5.
Diurnal cycles of current, temperature, and turbulent dissipation in a model of the equatorial upper ocean
Authors: Schudlich Rebecca R. , Price James F.
Published: February 2008

We have used a simple, one‐dimensional model to simulate the diurnal cycle of the equatorial upper ocean. The model is initialized with the stratification and shear of the Equatorial Undercurrent (EUC) and is driven with heating and wind stress. A surface mixed layer is determined by bulk stability requirements, and a transition layer below the mixed layer is simulated by requiring that the gradient Richardson number be no less than ¼. A principal result is that the nighttime phase of the diurnal cycle is strongly affected by the EUC, resulting in deep mixing and large dissipation at night consistent with observations of the equatorial upper ocean during the 1984 Tropic Heat experiment. The day time (heating) phase of the simulated diurnal cycle is very similar to that seen at mid‐latitudes. Solar heating produces a stably stratified surface layer roughly 10 m thick within which there is little, O(3 × 10−8 W kg−1), turbulent dissipation. For the typical range of conditions at the equator, diurnal warming of the sea surface is 0.2°–0.5°C, and the diurnal variation of surface current (diurnal jet) is 0.1–0.2 m s−1, consistent with observations. The nighttime (cooling) phase of the simulated diurnal cycle is quite different from that seen at mid‐latitudes. As cooling removes the warm, stable surface layer, the wind stress can work directly against the shear of the EUC. This produces a transition layer that can reach to 80 m depth, or nearly to the core of the EUC. Within this layer the turbulent dissipation is quite large, O(2 × 10−7 W kg−1). Thus the simulated dissipation has a diurnal range of more than a factor of 5, as observed in Tropic Heat, though the diumal cycle of stratification and current are fairly modest.
Observations of a cyclonic ring‐Gulf Stream coalescence event over the Blake Plateau
Authors: McClean‐Padman Julie , Atkinson Larry P.
Published: February 2008

Hydrographic data collected in September 1980 over the Blake Plateau were analyzed using a combination of empirical search and inverse techniques. Five sections, extending from the continental shelf break eastward across the Blake Plateau, were positioned at approximately 1° intervals between 28° and 32°N. The empirical search procedure was applied to four closed regions (boxes), constructed from adjacent sections, where each region was assumed to consist of two conservative layers. Five geostrophic velocity sections were obtained using the average optimum reference level for the four boxes. The inverse technique provided barotropic correction velocities that caused all layers to conserve mass. The sections and the resulting transport streamline fields revealed the presence of a cyclonic feature whose meridional and zonal extent was about 200 km in both directions. This feature was shown to be a coalescing Gulf Stream ring in a late stage of decay. Water mass analyses, current meter data, and earlier studies were used to support this hypothesis. The cyclonic advection of Gulf Stream water around the ring formed a meander in the eastern Gulf Stream wall. Topography appeared to be affecting this flow, suggesting that other rings entering the region would be similarly influenced. Evidence of recurring rings at or near this location and hence, meanders of the eastern Gulf Stream wall, was found in hydrographic data collected by NOAA over a 12‐month period from 1965 to 1966. These data suggested that two such events, lasting about 4 weeks each, occurred during this period. The frequency of these events was in agreement with earlier findings, while the duration of these events was supported by current meter observations.
In situ measurements of surface tension, wave damping, and wind properties modified by natural films
Authors: Wei Yi , Wu Jin
Published: February 2008

A fully instrumented catamaran was used to carry out in situ measurements of physical and dynamical properties of slick and clean sea surfaces. The surface tension and wave‐damping rate were found to vary across the slick. The latter is further associated with the Marangoni effect. In addition to wave suppression, the augmentation of wind speed and the reduction of wind stress by slicks were recorded. The formation of slick bands was also observed. Finally, surface films influence air‐sea transfers and other interfacial processes were discussed.
A correction for Saharan dust effects on satellite sea surface temperature measurements
Authors: May Douglas A. , Stowe Larry L. , Hawkins Jeffrey D. , McClain E. Paul
Published: February 2008

Sea surface temperature (SST) retrievals obtained from NOAA advanced very high resolution radiometer (AVHRR) data can determine SST within 0.7°C on a global basis. However, retrievals have been severely limited in the presence of tropospheric aerosol particles because no adequate aerosol correction algorithm exists. High tropospheric aerosol concentrations in the atmosphere significantly increase infrared signal attenuation and prevent the retrieval of accurate satellite SSTs. This paper presents tropospheric aerosol correction algorithms derived from NOAA AVHRR SST and optical depth measurements and from drifting buoy in situ SSTs. We show that the correction algorithms perform better than the current global algorithm in an atmosphere that contains high Saharan dust concentrations and generate statistical accuracy comparable to satellite SST performance globally. These corrections would significantly increase the quantity and quality of satellite retrievals under such atmospheric conditions, and the observations would greatly benefit both global climate research and maritime operations conducted in such regions.
Changes in ice cover thickness and lake level of Lake Hoare, Antarctica: Implications for local climatic change
Authors: Wharton Robert A. , McKay Christopher P. , Clow Gary D. , Andersen Dale T. , Simmons George M. , Love F. Gordon
Published: February 2008

We report results from 10 years of ice thickness measurements at perennially ice‐covered Lake Hoare in southern Victoria Land, Antarctica. The ice cover of this lake had been thinning steadily at a rate exceeding 20 cm yr−1 during the last decade but seems to have recently stabilized at a thickness of 3.3 m. Data concerning lake level and degree‐days above freezing are presented to show the relationship between peak summer temperatures and the volume of glacier‐derived meltwater entering Lake Hoare each summer. From these latter data we infer that peak summer temperatures have been above 0°C for a progressively longer period of time each year since 1972. We also consider possible explanations for the thinning of the lake ice. The thickness of the ice cover is determined by the balance between freezing during the winter and ablation that occurs all year but maximizes in summer. We suggest that the term most likely responsible for the change in the ice cover thickness at Lake Hoare is the extent of summer melting, consistent with the rising lake levels.
Sea ice thickness distribution in the Greenland Sea and Eurasian Basin, May 1987
Authors: Wadhams Peter
Published: February 2008

Upward sonar data from a 3400‐km track in the Greenland Sea and the Eurasian Basin of the Arctic Ocean, obtained by a British submarine in May 1987, have been statistically analyzed. Mean ice thicknesses in the Greenland Sea show significant melting with downstream distance, at an average rate of 0.38 m per degree of latitude, equivalent to about 2140 km3 yr−1 of freshwater input between 80°N and 75°N. In the region north of Fram Strait, between 82°N and 80°N, there is remarkable consistency between mean ice drafts in 1987 and in three previous cruises (1976, 1979, 1985), while between Greenland and the North Pole there was a significant thinning in 1987 relative to 1976. In Fram Strait the mean ice draft shows evidence of thinning within the region of influence of a semipermanent eddy. Ice draft distributions show that the probability density function of deformed ice follows a negative exponential distribution and that the change of shape of the distribution with downstream distance in the Greenland Sea is due to preferential melting of thicker ice. Pressure ridge draft distributions also fit a negative exponential, while their spacings fit a lognormal distribution. Lead width distribution follows a power law with an exponent of −1.45 for narrow leads and −2.50 for wider leads, if leads are defined as having a 1‐m maximum draft ( −1.67 and −2.76 for a 0.5‐m maximum draft). Lead spacings follow a negative exponential distribution for moderate spacings (400–1500 m) but with an excess of lead pairs at small and very large spacings.
The sensitivity of regional ozone modeling to biogenic hydrocarbons
Authors: Roselle Shawn J. , Pierce Thomas E. , Schere Kenneth L.
Published: February 2008

The sensitivity of regional ozone concentrations to biogenic hydrocarbons in the northeastern United States has been examined using an Eulerian grid photochemical model having a horizontal resolution of 18 km. A 6‐day period during which observed ozone concentrations exceeded 200 ppb was simulated. Detailed estimates of biogenic nonmethane hydrocarbon (NMHC) emissions were included in the model simulations. Overall, biogenic emissions were of the same order of magnitude as anthropogenic emissions. Approximately 33% of the biogenic inventory was in the form of isoprene, with the remainder of the NMHC in the form of monoterpenes and unidentified NMHC. Three model sensitivity runs were analyzed in which biogenic emissions, and then anthropogenic hydrocarbon emissions, were selectively removed from the emissions data set. Episode maximum predicted ozone concentrations were compared for each simulation, and a detailed chemical analysis was performed on two trajectories within the modeling domain. The analysis showed that the relative impact of biogenic compared to anthropogenic hydrocarbons on ozone generation varied spatially over the model domain. The biogenic influence on ozone was greatest in western and southern sections of the domain, particularly in the Ohio Valley, while the anthropogenic influence was greatest in the urbanized Northeast Corridor and industrial Great Lakes area.
A test of odd‐oxygen photochemistry using Spacelab 3 Atmospheric Trace Molecule Spectroscopy observations
Authors: Allen Mark , Delitsky Mona L.
Published: February 2008

The ozone profile calculated using a one‐dimensional time‐dependent photochemical model, with recommended absorption cross sections and reaction rate constants, is systematically less than Spacelab 3 (May 1985) Atmospheric Trace Molecule Spectroscopy (ATMOS) observations at sunset (χ = 90°), 30°N latitude, throughout the upper stratosphere and mesosphere. Model results are ∼9% smaller than the nominal ATMOS O3 value at 40 km and 50% less at 76 km. Given the uncertainties associated with the ATMOS profile, the model “deficit” may be as large as 15% at 36 km, increasing to ∼70% at 76 km. A similar model O3 deficit exists at sunrise, 47°S latitude, in the stratosphere: nominal differences of ≤25%, increasing to ≤45% when the ATMOS uncertainties are considered. Model results closely approximate ATMOS observations in both the upper stratosphere and mesosphere upon enhancing odd‐oxygen production by increasing the O2 Schumann‐Runge band and Herzberg continuum cross section values used in the calculations.
The effect of the global background on a synoptic‐scale simulation of tracer concentration
Authors: Brost Richard A. , Heimann Martin
Published: February 2008

We use an Eulerian, three‐dimensional tracer model driven by European Center for Medium Range Weather Forecasting winds to study the effect of the global background on synoptic‐scale tracer concentration. Inside the global domain we put a synoptic‐scale domain that includes North America, the North Atlantic Ocean, as well as parts of the eastern North Pacific Ocean, Africa, and Europe; and inside the synoptic‐scale domain we have a regional subdomain over North America. We determine the percentage PI of concentration inside the regional subdomain that came from outside the synoptic‐scale domain for species whose only source is at continental surfaces and whose only loss is a spatially and temporally independent first‐order decay with an exponential decay time r. In the annual average, PI ≈ 0% at the surface and increases with height: at z = 11.8 km, PI is 3% for τ = 1 day, 50% for τ = 5.5 days, and 60% for τ = 30 days. Month‐to‐month changes in convection over land and in horizontal transport produce a seasonal cycle in PI with a summer minimum and winter maximum, and the amplitude of this seasonal cycle in PI decreases as τ increases. The most interesting species have τS near 5.5 days, because species with τ ≫ 5.5 days have less of a seasonal cycle in PI and have less variation with height of PI in the free troposphere than for a species with τ ≈ 5.5 days, while species with τ ≪ 5.5 days have such small PIs as to be uninteresting. To help us interpret these Eulerian model results, we use simple Lagrangian models to derive three main conclusions. First, the apparent travel time from other source regions, particularly Asia, to North America decreases a factor of 2 as τ decreases from 30 days to 1 day, which means that more of the 1‐day lifetime species arrives than one would expect based on the amount of the longer‐lived species that arrives. Second, in the regional subdomain, PI usually increases as τ increases, but sufficiently remote from the sources in the subdomain, PI may decrease as τ increases. Third, although the concentration imported to the middle and upper troposphere generally increases as the vertical mass flux by clouds increases, PI can be insensitive to changes in the cloud mass flux, as long as the cloud mass flux changes similarly both inside and outside the synoptic‐scale domain.
Air mass origins and troposphere‐to‐stratosphere exchange associated with mid‐latitude cyclogenesis and tropopause folding inferred from 7Be measurements
Authors: Kritz Mark A. , Rosner Stefan W. , Danielsen Edwin F. , Selkirk Henry B.
Published: February 2008

The 1984 extratropical mission of NASA's Stratosphere‐Troposphere Exchange Project (STEP) studied cross‐jet transports in regions of cyclogenesis and tropopause folding. Correlations of 7Be, ozone, water vapor, and potential vorticity measured on a NASA U‐2 research aircraft flying in high shear regions above the jet core are indicative of mixing between the cyclonic and the anticyclonic sides of the jet and are consistent with the hypothesis that small‐scale entrainments of upper tropospheric air into the lower stratosphere during cyclogenesis are important in maintaining the vertical gradients of 7Be, ozone, water vapor and other trace constituents in the lower few kilometers of the mid‐latitude stratosphere. Correlations between 7Be and ozone suggest a lower tropical stratospheric origin for the ozone‐poor lamina observed above the jet core.
Horizontal wind fluctuations in the stratosphere during large‐scale cyclogenesis
Authors: Chan K. R. , Scott S. G. , Bowen S. W. , Gaines S. E. , Danielsen E. F. , Pfister L.
Published: February 2008

The meteorological measurement system (MMS) on the U‐2 aircraft measured pressure, temperature, and the horizontal wind during a cyclogenesis event over western United States on April 20, 1984. The aircraft flew above the jet core and traversed in a vertical plane normal to the jet stream axis at four altitudes, making measurements on both the cyclonic and anticyclonic sides of the jet. Horizontal wind data were processed by digital filters to permit analyses of large‐scale gradients and of small‐scale fluctuations. The mean horizontal wind in the stratosphere decreases monotonically with altitude. Superimposed on the mean stratospheric wind is a perturbation wind vector, which is an elliptically polarized wave with an amplitude of 4 to 10 m s−1 and a vertical wavelength of 2 to 3 km. The perturbation wind vector rotates anticyclonically (clockwise) with altitude and produces alternating advection in the plane of the aircraft flight path. This differential advection folds surfaces of constant tracer mixing ratio and contributes to the observed tracer laminar structures and inferred cross‐jet transport.
Simulations in site error estimation for direction finders
Authors: López Raúl E. , Passi Ranjit M.
Published: February 2008

The performance of an algorithm for the recovery of site‐specific errors of direction finder (DF) networks is tested under controlled simulated conditions. The simulations show that the algorithm has some inherent shortcomings for the recovery of site errors from the measured azimuth data. These limitations are fundamental to the problem of site error estimation using azimuth information. Several ways for resolving or ameliorating these basic complications are tested by means of simulations. From these it appears that for the effective implementation of the site error determination algorithm, one should design the networks with at least four DFs, improve the alignment of the antennas, and increase the gain of the DFs as much as it is compatible with other operational requirements. The use of a nonzero initial estimate of the site errors when working with data from networks of four or more DFs also improves the accuracy of the site error recovery. Even for networks of three DFs, reasonable site error corrections could be obtained if the antennas could be well aligned.
Diurnal and seasonal variations of stratomesospheric ozone: Analysis of ground‐based microwave measurements in Bordeaux, France
Authors: Ricaud P. , Brillet J. , De La Noe J. , Parisot J. P.
Published: February 2008

Atmospheric ozone spectra recorded since September 1985 with a millimeter‐wavelength radiotelescope located at Bordeaux Observatory are used to determine ozone profiles. These concentrations are retrieved using the Backus‐Gilbert inversion method. The experimental difficulties due to the so‐called baseline effect, calibration errors, and fluctuations in the temperature profile are discussed and their influence on the ozone density evaluated. Three heights are optimally selected at 33, 42, and 55 km. The main source of measurement error is the baseline effect. As this affects strongly the ozone density retrieved at 33 km, results are given only for two layers: 42±4.5 km and 55±8 km. Diurnal variations can be estimated in the 42±4.5 km layer during three periods, September 1985, September 1989, and October 1989 with the daytime decrease about 5%–10%. In the 55±8 km layer the variations for these three periods can reach 30%. For both layers the measured variation is greater than that predicted by models because the resolving power of the measurement spreads over higher layers where the variation is actually larger. At 42±4.5 km, seasonal variations in ozone concentration exhibit a semiannual oscillation with summer maxima and pronounced winter peaks. At 55±8 km the daytime and nighttime seasonal variations in ozone concentration exhibit a semiannual oscillation with large summer maxima and small winter peaks.
Surface cooling due to forest fire smoke
Authors: Robock Alan
Published: February 2008

In four different cases of extensive forest fire smoke the surface temperature effects were determined under the smoke cloud. In all cases, daytime cooling and no nighttime effects were found. The locations of smoke clouds from extensive forest fires in western Canada in 1981 and 1982, in northern China and Siberia in 1987, and in Yellowstone National Park in northwestern Wyoming in 1988 were determined from satellite imagery. As these smoke clouds passed over the midwestern United States for the Canadian and Yellow‐stone fires and over Alaska for the Chinese/Siberian fires, surface air temperature effects were determined by comparing actual surface air temperatures with those forecast by model output statistics (MOS) of the United States National Weather Service. MOS error fields corresponding to the smoke cloud locations showed day‐time cooling of 1.5° to 7°C under the smoke but no nighttime effects. These results correspond to theoretical estimates of the effects of smoke, and they serve as observational confirmation of a portion of the nuclear winter theory. This also implies that smoke from biomass burning can have a daytime cooling effect of a few degrees over seasonal time scales. In order to properly simulate the present climate with a numerical climate model in regions of regular burning it may be necessary to include this smoke effect.
Oceanic consumption of CH3CCl3: Implications for tropospheric OH
Authors: Butler James H. , Elkins James W. , Thompson Thayne M. , Hall Brad D. , Swanson Thomas H. , Koropalov Valentin
Published: February 2008

Strong and extensive negative saturation anomalies for CH3CCl3 were observed in the mid‐Pacific Ocean during the spring of 1990. Anomalies were largest at the equator, where upwelling and biological activity were greatest, but present virtually everywhere in our sampling range of 15°S to 20°N. The mean saturation anomaly for all of our data, corrected for physical effects, was −11.0%, implying that the ocean is a significant sink for CH3CCl3. The loss rate to maintain this anomaly is supported roughly by known hydrolysis rates, but contributions from other processes cannot be ruled out at this time. If hydrolysis and mixing are the only processes removing CH3CCl3 from seawater, then about 6% of atmospheric CH3CCl3 is removed by consumption in the oceans. Our data show that losses to the ocean most probably would range from 5 to 11% of the CH3CCl3 removed from the atmosphere. This range translates to a partial residence time of 59–128 years for atmospheric CH3CCl3 relative to oceanic consumption. Although these data indicate that the ocean is not an overwhelmingly large sink, its neglect does represent a systematic error in the calculation of tropospheric OH concentration from CH3CCl3 production, growth, and distribution in the atmosphere.
Size and critical supersaturation for condensation of jet engine exhaust particles
Authors: Pitchford Marc , Hudson James G. , Hallett John
Published: February 2008

In situ measurements of jet engine exhaust from a Sabreliner were made by instruments on board the NCAR Electra during a brief period of coordinated flying. Particle size distribution and critical supersaturation spectra were monitored before, during, and after the encounter with the jet exhaust plume by a condensation nucleus counter, an active scattering aerosol spectrometer probe (ASASP), and a cloud condensation nuclei (CCN) spectrometer. The relationships between particle size and corresponding critical supersaturation in the background air and within the jet exhaust plume are developed. Results indicate that background particles are much more active as CCN than exhaust particles of the same size, of which less than 1:100 are active at 0.8% supersaturation. An estimate of the engine sooting efficiency lies between 3×10−5 and 10−6.
Anomalous temperature and zonal wind in the tropical upper stratosphere, 1982/1983
Authors: Dunkerton Timothy J. , Delisi Donald P.
Published: February 2008

Aerosol from the eruption of El Chichón (April 1982, 17°N) warmed the tropical lower stratosphere in 1982. Temperature data from the Nimbus 7 stratospheric and mesospheric sounder (SAMS) indicate that in mid‐1982, cooling occurred in the upper and middle tropical stratosphere, starting shortly after the eruption. Radiative (IR) cooling above the aerosol cloud was a predicted, but unverified, response to El Chichón. In this paper an attempt was made to determine whether the cooling could be attributed to El Chichón Rocketsonde data from Kwajalein gave additional evidence of cooling and revealed that zonal winds in the upper and middle stratosphere were anomalous in 1982 and also in 1983. Where comparison can be made, rocketsonde observations were consistent with balance winds derived from SAMS. Upper level cooling was linked to anomalous easterlies near the equator and therefore could not be interpreted as a radiative (nondynamical) response to El Chichón. The structure of an expected two‐dimensional dynamical response to aerosol heating is examined with a numerical model and compared to the data. This response is partly consistent with observations but is inadequate to explain the magnitude of cooling and associated easterlies in the tropical upper stratosphere in mid‐1982. It is suggested that internal sources of atmospheric variability (e.g., extratropical forcing and quasi‐biennial oscillation) contributed to equatorial cooling observed in 1982.
Electric fields and current densities under small Florida thunderstorms
Authors: Deaver Lance E. , Krider E. Philip
Published: February 2008

The surface electric field E and Maxwell current density JM have been measured simultaneously under and near small Florida thunderstorms. These records show that the amplitude of JM is of the order of 1 nA/m2 or less in the absence of precipitation and that there are regular time variations in JM during the intervals between lightning discharges that tend to have the same shapes after different discharges in different storms. Negative cloud‐to‐ground (CG) lightning produces an abrupt negative change in E and a corresponding negative (or bipolar) transient in JM that is followed by a positive overshoot. Under a storm, this overshoot peaks about 1 nA/m2 above background and then decays in a quasi‐exponential or linear fashion until the next discharge occurs. Nearby cloud discharges produce a lightning transient and then either a small change in JM or a negative change that subsequently relaxes back to the predischarge level in 5 to 20 s. CG flashes at a range of about 20 km produce a fast transient in JM and then a positive overshoot that subsequently relaxes back to the predischarge level in 5 to 20 s. Distant cloud discharges produce overshoots and subsequent decays that are very similar to CG flashes but of opposite (i.e., negative) polarity. We believe that the major causes of the aforementioned time variations in JM between lightning discharges are currents that flow in the finitely conducting atmosphere in response to the field changes rather than rapid time variations in the strength of the cloud current sources. The displacement current densities that are computed from the E records dominate JM except when there is precipitation, when E is large and steady, or when E is unusually noisy.
Detectability of Martian carbonates from orbit using thermal neutrons
Authors: Feldman W. C. , Jakosky B. M.
Published: February 2008

Numerical simulations of Martian neutron leakage flux spectra are made in order to explore the detectability of magnesium and calcium carbonate deposits using neutron spectroscopic techniques from orbit. The primary signature of such deposits is found to be an enhanced thermal amplitude. Although this enhancement is weakened by (1) partial burial beneath an aeolian regolith blanket, (2) admixture with regolith on a microscopic (centimeter) or macroscopic (tens of centimeters) scale, and (3) reduction in the areal size of the deposit, near‐surface stratigraphies of carbonates hypothesized by some authors as possible on Mars are still detectable by simple neutron sensors from orbit. However, the large variations in the magnitude of the thermal neutron enhancements caused by different carbonate deposit configurations found in this study require a combined gamma ray and neutron analysis for their unique specification.
Compressible convection in a viscous Venusian mantle
Authors: Leitch A. M. , Yuen D. A.
Published: February 2008

Finite element simulations of axisymmetric spherical shell compressible convection were carried out to investigate the effect of various surface boundary conditions in a Venusian mantle. We employed a thermal expansivity α which decreased with depth, a uniform viscosity an order of magnitude greater than the Earth's, and zero and chondritic quantities of internal heating. As long as hot plumes from the core‐mantle boundary were strong, the convection pattern was typical of that for variable α flow; that is, it was characterized by steady upflowing regions, unsteady collections of downflowtng plumes, and large aspect ratio cells. Increases in the internal heating or the temperature T0 at the lop of the convecting layer weakened the hot plumes and therefore decreased the width of the cells. A rigid surface increased the internal temperature and also decreased the widih of convection cells. Extensive regions of subadiabaticity were found in the mantle. We compare our results with those for fully three‐dimensional convection under similar conditions (Schubert et al., 1990).
Electron impact excitation and dissociation of N2 via the b1Πu state
Authors: Ratliff J. M. , James G. K. , Trajmar S. , Ajello J. M. , Shemansky D. E.
Published: February 2008

Electron impact excitation of the b1Πu state in N2 plays a prominent role in the dissociation of the molecule and thus in the production of atomic nitrogen in planetary atmospheres. Electron impact excitation cross sections combined with electron‐impact‐induced fluorescence measurements can yield the corresponding dissociation cross sections. Serious discrepancies exist among excitation cross sections reported in the literature. To clarify the situation, we measured these cross sections at two impact energies using electron energy loss spectroscopy. The new results are in agreement with recent values deduced from optical measurements and fall midway between previous results which are too high or low by factors of 2.
A laboratory facility for mid‐UV absorption spectroscopy of molecular compounds for planetary atmospheres
Authors: Bruston Paul , Raulin François , Poncet Henri
Published: February 2008

Available laboratory UV spectroscopic data do not usually fulfill all the conditions which are required for reducing observational data of planetary atmospheres: absolute wavelength calibration, wide wavelength range including the mid‐UV, spectral resolution, absolute determination of the absorption coefficients, data at various temperatures. Faced with this fact in our research program on the structure and composition of Titan atmosphere, we have developed a suitable laboratory facility. We describe this experimental facility: it gives absolute absorption coefficients at 0.1 Å resolution in the range 185–350 nm with sample temperatures adjustable between −50°C and +50°C. The future program to be implemented with this facility includes studies on nitriles and polyacetylenes.
High‐resolution, low‐temperature photoabsorption cross sections of C2H2, PH3, AsH3, and GeH4, with application to Saturn's atmosphere
Authors: Chen Fengzhong , Judge D. L. , Robert Wu C. Y. , Caldwell J. , White H. Peter , Wagener R.
Published: February 2008

Using synchrotron radiation as a continuum background light source, the VUV absorption cross sections of (1) C2H2 and PH3 have been obtained under physical conditions approximating the stratosphere of Saturn and (2) AsH3 and GeH4 have been obtained under room temperature conditions. We have combined these new laboratory measurements with International Ultraviolet Explorer observations of the albedo of Saturn, for which improved data reduction techniques have been used, to produce new models for that atmosphere. When the effects of C2H2 absorption are accounted for, additional absorption by other molecules is required. The best fitting model also includes absorption by H2O, CH4, C2H6, PH3, and GeH4. The abundance of H2O is reduced by a factor of 2 as a direct consequence of the new low‐temperature cross section data of C2H2. The model abundance distributions of PH3 and GeH4 on Saturn decrease with increasing altitude, suggesting a possible consequence of UV photolysis.
Irradiation effects in a comet's outer layers
Authors: Johnson R. E.
Published: February 2008

Laboratory data and cosmic ray doses are used to understand the irradiation‐induced formation and destruction of organics in the outer layers (mantle) of a comet in the Oort cloud and for determining the fate of volatiles in the mantle. This is used to estimate the change in the orthowater/parawater ratio with depth in the outer layers of a new comet and the average thickness of the refractory part of the mantle of a new comet. Because comets will have large‐scale irregularities, regions of the mantle will be unstable, leading to enhanced activity on a new comet and producing “permanently” active regions.
Radio wave dissipation in turbulent auroral plasma during the precipitation of energetic electrons
Authors: Mishin E. V. , Lukjanova L. N. , Makarenko S. F. , Atamanjuk B. M.
Published: February 2008

The results of the theoretical analysis of anomalous (collisionless) radio wave absorption in the turbulent auroral ionosphere during the intrusion of energetic electrons (i.e., in aurorae) are presented. The implications of the plasma turbulent layer (PTL) theory are used. It is shown that the dissipation of radio waves with frequencies much higher than the plasma frequency is caused by the nonlinear (combined) scattering in turbulent plasma of the PTL. In the auroral electrojet layer the principal dissipative process for the radio waves with frequencies close to the plasma frequency is O‐Z transformation on the field‐aligned, small‐scale density fluctuations. The typical dissipation decrements are estimated.
Middle atmosphere response to the 27‐day solar rotation as observed by lidar
Authors: Keckhut P. , Chanin M. L.
Published: February 2008

The response of the middle atmosphere temperature to short term solar UV radiation related to the 27‐day period of the sun has been studied by Rayleigh Lidar at mid‐latitude in the height range 30–90 km. Among the 9 sequences, each of 3 to 4 months duration, which corresponds to clear solar signature, two types of behavior have been found: either the temperature response is positively correlated with the solar UV flux in the whole height range, or the response reverses abruptly from positive to negative within the height interval 40–60 km. It is important to notice that this second type of behavior is observed as well in summer or in winter, i.e. even in the absence of planetary wave activity, but has only been seen during the Westward phase of the QBO.

If such a change of the temperature is confirmed to be solar induced, this response to change in the UV flux is clearly different from the one we observed for the 11‐year solar cycle. Therefore the 27‐day signature of atmospheric structure should not be used as a proxy for the 11‐year variation.
Precipitation of fast ion beams from the plasma sheet boundary layer
Authors: Ashour‐Abdalla M. , Zelenyi L. M. , Bosqued J. M. , Kovrazhkin R. A.
Published: February 2008

This paper presents a model of precipitated fluxes from the PSBL and CPS. Simulation results and data from Aureol‐3 spacecraft indicate the presence of velocity dispersed precipitated ion structures (VDIS) at the poleward edge of the auroral oval. These structures are associated with fast ion beams in the PSBL region of the Earth's magnetotail, confirming previous experimental results. The simulations also reveal possible substructuring of the VDIS. The bulk of the PSBL population which is not precipitated is very effectively thermalized and quasi‐isotropized after multiple interactions with the magnetotail current layer. After each reflection cycle some part of the distribution is precipitated and forms multiple ‘echoes’ of VDIS. The CPS distributions occurring as a result of scattering, convection, multiple reflections and Fermi acceleration appear isotropic in the simulation model. This paper portrays the important role of the VDIS auroral region medium for complicated and energetically significant processes occurring in different regions of the distant magnetotail.
A source mechanism producing HF‐induced plasma lines (HFPLS) with up‐shifted frequencies
Authors: Kuo S. P. , Lee M. C.
Published: February 2008

A nonlinear scattering process has been analyzed as a source mechanism producing the frequency up‐shifted HF‐enhanced plasma lines (HFPLs) observed in the Arecibo ionospheric heating experiments. Parallelly propagating Langmuir waves generated by the parametric decay instability of the HF pump near the reflection height scatter off the background lower hybrid density fluctuations to produce the up‐going and down‐going Langmuir waves with frequencies greater than the pump frequency by several tens of KHz. The frequency up‐shifted nature of excited Langmuir waves stems from the fact that the natural frequencies of the obliquely propagating Langmuir waves are higher than those of the parallelly propagating Langmuir waves at the same altitude. A physical picture is thus offered to explain how Langmuir waves with frequencies greater than the HF heater wave frequency can be produced in the heating experiments and be detected by incoherent radars as frequency up‐shifted HFPLs. Since the considered scattering process occurs in a region near the reflection height, it explains why the frequency up‐shifted HFPLs should originate from the altitude near the reflection height as observed. Moreover, the theory also shows that the amount of frequency up‐shift is inversely proportional to the frequency of the HF heater and increases linearly with the electron temperature. The quantitative analysis of the theory shows a good agreement with the experimental results.
Near real‐time merging of Gloria and Hydrosweep pseudo‐sidescan images
Authors: Searle R. C.
Published: February 2008

A method has been developed for merging GLORIA and Hydrosweep data into single combined sidescan‐type images, by adding a shaded relief representation of the seafloor topography to the near‐nadir part of the GLORIA image, which is usually poorly insonified. Several examples are presented, taken from a variety of seafloor terrains.
Characterizing surface roughness from pressure‐joint closure using an inversion procedure
Authors: Zhao Xiaomin , Toksöz M. N.
Published: February 2008

An inversion procedure is formulated based on the modification of the theory proposed by Brown and Scholz (1985) and has been successfully tested with synthetic and laboratory data. The inversion finds average height
, standard deviation σ, and average aperture. These three parameters characterize the surface roughness and aperture of a fracture. The inversion results agree with the profile measurements quite well.
Correlated optical and ULF magnetic observations of the winter cusp – Boundary layer system
Authors: McHarg Matthew G. , Olson John V.
Published: February 2008

We have found a consistent correlation between ground based ultra low frequency (ULF) magnetic and optical measurements of the dayside cusp/boundary layer system which, we believe, may allow ground based identification of the boundary layers and central cusp. We have based our analysis on data taken at Longyearbyen Svalbard, Norway. Under normal magnetic conditions, as the station rotates beneath the auroral zone each day it passes under the ionospheric projection of the cusp‐boundary layer system, near magnetic noon at approximately 0830 UT. During the passage of the cusp‐boundary layer system a distinctive sequence of magnetic spectral features is observed. The boundary layer passage is characterized by a sharp increase in the power spectral density of broad band, unpolarized noise, combined with a polarized low frequency (1–3 mHz) signal. This is followed by a period of greatly reduced power spectral density of the unpolarized noise. A narrow band polarized signal in the 3–5 mHz band persists throughout this quiet period which is observed to be predominantly left hand polarized before local magnetic noon. This narrow band feature also appears to rise in frequency as the cusp passes overhead, and then falls again after noon. Optical observations are strongly correlated with the magnetic data. We believe the observed features have their source in the ionospheric footprint of the boundary layers and central cusp. The polarized signals may arise from Alfven waves spawned at the magnetopause which propagate down the magnetic field lines that map to the boundary layers. As the cusp may move with changing geomagnetic activity, observations of the features noted here may not be seen on every day. The statistical question of how often, and under what conditions, these features appear is an ongoing research topic. We plan to address this statistical question in a future manuscript.
Simultaneous stratospheric aerosol and ozone lidar measurements after the Pinatubo volcanic eruption
Authors: D'Altorio Alfonso , Masci Fabrizio , Visconti Guido , Rizi Vincenzo , Boschi Enzo
Published: February 2008

Preliminary results of simultaneous ozone and aerosol lidar measurements taken in the period July‐early October 1991 are presented. The main problem for retrieving the ozone profile is the correction of the on and off DIAL signals. The backscattering ratio obtained by the off signal is used for this purpose and ozone profiles are validated against ozonesonde data. A number of cases are presented including a few occasions of layers with large backscattering ratio. For these events the differences between ECC sonde and DIAL range between 5% to 20% and indicate that the method adopted for correction needs improvements especially for very thin layers. Sensitivity tests show that the retrieved ozone may change by roughly 10% depending on the choice of the aerosol optical parameters. Absolute difference between ECC and DIAL could not be completely explained in terms of the uncertainty in those parameters. The data obtained may still be used to prove the effects of heterogeneous chemistry on ozone destruction rate. Given the uncertainties introduced by the aerosol correction large amount of data need to be accumulated.