bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparative study of scattering, intrinsic, and coda Q−1 for Hawaii, Long Valley, and central California between 1.5 and 15.0 Hz
Authors: Mayeda Kevin , Koyanagi Stuart , Hoshiba Mitsuyuki , Aki Keiiti , Zeng Yuehua
Published: February 2008

A new method recently developed by Hoshiba et al. (1991) was used to separate the effects of scattering Q−1 and intrinsic Q−1 from an analysis of the S wave and its coda in Hawaii, Long Valley, and central California. Unlike the method of Wu [1985], which involves integration of the entire S wave energy, the new method relies on the integration of the S wave energy for three successive time windows as a function of hypocentral distance. Using the fundamental separability of source, site, and path effects for coda waves, we normalized the energy in each window for many events recorded at many stations to a common site and source. We plotted the geometric spreading‐corrected normalized energy as a function of hypocentral distance. The data for all three time windows were then simultaneously fit to Monte Carlo simulations assuming isotropic body wave scattering in a medium of randomly and uniformly distributed scatterers and uniform intrinsic Q−1. In general, for frequencies less than or equal to 6.0 Hz, scattering Q−1 was greater than intrinsic Q−1, whereas above 6.0 Hz the opposite was true. Model fitting was quite good for frequencies greater than or equal to 6.0 Hz at all distances, despite the model's simplicity. The small range in energy values for any particular time window demonstrates that the site effect can be effectively stripped away using the coda method. Though the model fitting generally worked for 1.5 and 3.0 Hz, the model has difficulty in fitting the whole distance range simultaneously, especially at short distances. Despite the poor fit at low frequency, the results generally support that in all three regions the scattering Q−1 is strongly frequency dependent, decreasing proportional to frequency or faster, whereas intrinsic Q−1 is considerably less frequency dependent. This suggests that the scale length of heterogeneity responsible for scattering is at least comparable to the wavelength for the lowest frequencies studied, of the order of a few kilometers. The lithosphere studied in all three regions can be characterized as a random medium with velocity fluctuation characterized by exponential or Gaussian autocorrelation functions which predict scattering.

Q−1 decreasing proportional to frequency or faster. For all frequencies the observed coda Q−1 is intermediate between the total Q−1 and expected coda Q−1 in contrast with theoretical results for an idealized case of uniform distribution of scatterers and homogeneous absorption which predict that coda Q−1 should be close to the intrinsic Q−1. We will discuss possible causes for this discrepancy.
Low‐temperature and alternating field demagnetization of saturation remanence and thermoremanence in magnetite grains (0.037 μm to 5 mm)
Authors: Heider Franz , Dunlop David J. , Soffel Heinrich C.
Published: February 2008

Low‐temperature demagnetization (LTD), consisting of zero‐field cycling from room temperature to 77 K and back to room temperature, was performed on magnetites from different sources having grain sizes between 0.037 μm and 5 mm. The memory fractions, RI and RT of saturation isothermal remanent magnetization (IRMs) and 0.1 mT thermoremanent magnetization (TRM), respectively, have a strong intrinsic grain‐size dependence below ≈ 10 μm, but are almost size independent in the multidomain (MD) range above 10 μm. The size dependence of RI and RT in the MD range reported by Parry [1979, 1980] probably results from stress introduced during crushing to obtain finer size fractions. We demonstrate that the method of preparation of magnetites, irregularities in the crystals, and increase or decrease of the state of internal stress by quenching or annealing all have a direct effect on the amount of magnetic memory. Magnetic memories (the fractions of TRM and IRM5 surviving after LTD) are much more resistant against alternating‐field (AF) demagnetization than the original TRM and IRMs before LTD. Even large magnetite crystals (≫20 μm) reveal a hard, single‐domain‐like component of magnetization when the softer magnetization is removed by LTD. A comparison of AF demagnetization properties of IRMs and TRM in these MD magnetites shows that the Lowrie and Fuller [1971] test must be reinterpreted.
Acoustic tomography in the Straits of Florida
Authors: Chester David B. , Malanotte‐Rizzoli Paola , DeFerrari Harry
Published: February 2008

Variability of the Florida Current has been monitored via acoustic tomography. A reciprocal tomography experiment was conducted in the eastern half of the Florida Straits during mid‐October and November, 1983. A triangular array of transceivers, with leg separations of approximately 45 km, was deployed at 27°N. The presence of a surface mixed layer in the region allowed for the ducted propagation of acoustic energy in the surface layer. A deeper layer was sampled by an unresolved group of refracted, bottom‐reflected ray arrivals. Incorporating the complete set of arrivals, we are able to obtain depth‐dependent estimates of the temperature field, current velocity, and relative vorticity. The oceanography of the region has been shown to be dominated by the lateral shifting of the surface and subsurface core of the Florida Current. The influx of westward flowing water through the Northwest Providence Channel at 26°N also appears as a large‐scale signal in the eastern Florida Straits. Low‐frequency fluctuations of temperature, current velocity, and vorticity occur at periods ranging from several days to nearly 2 weeks, and are intimately related to meandering of the Florida Current system.
Global sea level rise
Authors: Douglas Bruce C.
Published: February 2008

Published values for the long‐term, global mean sea level rise determined from tide gauge records exhibit considerable scatter, from about 1 mm to 3 mm/yr. This disparity is not attributable to instrument error; long‐term trends computed at adjacent sites often agree to within a few tenths of a millimeter per year. Instead, the differing estimates of global sea level rise appear to be in large part due to authors' using data from gauges located at convergent tectonic plate boundaries, where changes of land elevation give fictitious sea level trends. In addition, virtually all gauges undergo subsidence or uplift due to postglacial rebound (PGR) from the last deglaciation at a rate comparable to or greater than the secular rise of sea level. Modeling PGR by the ICE‐3G model of Tushingham and Peltier (1991) and avoiding tide gauge records in areas of converging tectonic plates produces a highly consistent set of long sea level records. The value for mean sea level rise obtained from a global set of 21 such stations in nine oceanic regions with an average record length of 76 years during the period 1880–1980 is 1.8 mm/yr±0.1. This result provides confidence that carefully selected long tide gauge records measure the same underlying trend of sea level and that many old tide gauge records are of very high quality.
A synthetic geoid validation of Geosat mesoscale dynamic topography in the Gulf Stream region
Authors: Glenn Scott M. , Porter David L. , Robinson Allan R.
Published: February 2008

A validation study is carried out for the Geosat altimeter in the Gulf Stream meander and ring region. A synthetic geoid, containing the medium scales of interest for mesoscale research, is constructed by subtracting an independent estimate of the oceanographic mean dynamic topography from the altimetric sea surface. The oceanographic mean dynamic topography which is concurrent with the altimetric mean is derived from a year of real‐time nowcasts and forecasts (Gulfcast) based on assimilating a composite data set into a dynamical model. Using the synthetic geoid, absolute dynamic topography from Geosat and Gulfcast for a year and 4 months in 1988 and 1989 compare very well in signal shape and feature locations. Sixteen cases of comparison of dynamic heights derived from AXBTs along Geosat tracks in 1987 are made with Geosat absolute topography. The rms difference is less than 10 cm. Thus the comparison of these two independent data sets validates the altimeter and the synthetic geoid within the noise and error levels of the system.
Analysis of sulfur hexafluoride in seawater
Authors: Wanninkhof Rik , Ledwell James R. , Watson Andrew J.
Published: February 2008

Analysis procedures and instrumentation to measure low levels of sulfur hexafluoride in seawater are described. The minimum detectable level for a 500 mL sample is about 3×10−17 mol/L. Concentrations from 1.5 to 300×10−15 mol/L can be measured with approximately 2% precision. The procedure includes a concentration step employing a trap of Porapak‐Q© in a dry ice/2‐propanol bath. The system has been used for tracer experiments in Santa Monica Basin and Santa Cruz Basin, and will be improved for future tracer release experiments in the deep ocean.
Ocean wave spectral distortion in airborne synthetic aperture radar imagery during the Norwegian Continental Shelf Experiment of 1988
Authors: Rufenach Clifford L. , Shuchman Robert A. , Malinas Norman P. , Johannessen Johnny A.
Published: February 2008

C band radar images of ocean gravity waves off the Norwegian coast were processed into one‐dimensional azimuth spectra. These spectra were used to measure the azimuth spectral (width) cutoff on the basis of a least squares fit to a Gaussian spectral shape. The widths were calculated for a range of wave heights (2–5 m) and wind speeds (2–18 m/s) during 3 days in March, 1988. Velocity smearing (συ) estimates were extracted, independent of R/V and incidence angle, based on an imaging model and the measured azimuth cutoffs with συ values varying from 0.4 to 0.7 m/s. Quantitative velocity smearing estimates are important as input to models describing the distortion in wave imagery. We propose a first‐order model which neglects velocity bunching for ocean swell with peak wavelengths longer than about 250 m. This model is offered as a first estimate of when ocean wave swell will be detected by the C band SAR on board the ERS 1 spacecraft. The model predicts that this swell will be imaged under light winds of the order of 2–4 m/s. Higher wind speeds cause larger smearing, which may result in significant distortion of the imaged swell provided that the swell is traveling near the direction of the spacecraft ground track.
Evaluation of second‐order texture parameters for sea ice classification from radar images
Authors: Shokr Mohammed E.
Published: February 2008

With the advent of airborne and spaceborne synthetic aperture radar (SAR) systems, sea ice classification from SAR images has become an important research subject. Since gray tone alone has proven to be of limited capability in differentiating ice types, texture has naturally become an attractive avenue to explore. Accordingly, performance of texture quantification parameters as related to their ability to discriminate ice types has to be examined. SAR image appearance depends on radar parameters involved in the image construction procedures from the doppler history record. Therefore the feasibility of using universal texture/ice type relationships that hold for all combinations of radar parameters also has to be investigated. To that end, imagery data from three different SAR systems were used in this study. Five conventional texture parameters, derived from the gray level co‐occurrence matrix (GLCM), were examined. Two of them were modified to ensure their invariant character under linear gray tone transformations. Results indicated that all parameters were highly correlated. The parameters did not, in general, vary with the computational variables used in generating co‐occurrence matrices. Ice types can be identified uniquely by the mean value of any texture parameter. The relatively high variability of texture parameters, however, confuses ice discrimination, particularly of smoother ice types. Ice classification was conducted using a per‐pixel maximum likelihood supervised scheme. When texture was combined with gray tone, the overall average classification accuracy was improved. Texture was successful in improving the classification accuracy of multiyear ice but was less promising in discriminating first‐season ice types. The best two GLCM texture parameters, according to the computed overall average classification accuracies, were the inverse difference moment and the entropy. A brief description of GLCM texture parameters as related to ice's physical characteristics is presented.
A numerical, three‐layered, stationary salt wedge model
Authors: Sorgard Eirik
Published: February 2008

A numerical, three‐layered, stationary salt wedge model is presented. It contains the effects of wind stress, interfacial stress, bed and wall stress, breadth variations, and mixing between the upper fresh layer and the homogeneous saline bottom layer. Because of the mixing an intermediate mixing layer develops which increases in thickness along the estuary toward the sea. The solutions obtained are compared with observations reported by Sorgard et al. (1990). Good agreement is obtained, both with regard to the thickness and position of the pycnocline, and with the velocities in each layer. The model was tested with different values for the bed and wall drag coefficient. To obtain a best fit with the observations, the modeled interfacial stress had to be decreased when the bed and wall drag coefficient was increased. The modifications to the dynamics due to the presence of the mixing layer are analyzed by comparing with the two‐layer model of Schijf and Schonfeld (1953). It turns out that the modeled interfacial stress has to be decreased because of the changed pressure field introduced by the mixing layer.
Examination of full‐wave solutions and “exact numerical results” for one‐dimensional slightly rough surfaces
Authors: Bahar Ezekiel
Published: February 2008

In this paper, the principal elements of the full‐wave solution and its direct analytical links to the physical‐optics and small‐perturbation solutions are reviewed succinctly. Thus a two‐step analytical procedure that transforms Rice's “first‐order” small‐perturbation solution into the physical‐optics solution is prescribed. Questions of convergence raised by Rice himself are also addressed since the small‐perturbation solution (when applied to random rough surfaces) diverges as the slope parameter becomes smaller and smaller. Furthermore, it is shown that the “exact numerical results” based on the moments method do not include the diffraction term, while the corresponding full‐wave results, used for comparison do include the diffraction term. No true comparisons can be made between the full‐wave solution and the small‐perturbation solution unless the excitations assumed in both cases are the same and unless the diffraction term is not added to the full‐wave solution for the diffusely scattered field.
The Coastal Transition Zone program
Authors: Brink K. H. , Cowles T. J.
Published: February 2008

Filaments are cold surface features often found in eastern boundary current regions. A typical filament originates near the shelf and extends as a narrow (100 km or less) tongue extending hundreds of kilometers offshore. These features represent the main focus of the the Coastal Transition Zone program, which took place in 1987 and 1988 off the northern coast of California. The historical background for the program is discussed, as well as the questions that motivated it. The general approach of the program is described, followed by an overview of the initial findings, representing a summary of our current understanding of these features and their relation with eastern boundary current dynamics.
Nitrate utilization by plankton in the equatorial Pacific March 1988 along 150°W
Authors: Eppley R. W. , Renger E. H.
Published: February 2008

Rates of nitrate utilization were measured in March 1988, from 6°N to 8°S on longitude 150°W in the Pacific Ocean. Surface waters in the equatorial upwelling contained about 5‐μM nitrate. Samples of seawater incubated on deck, as in primary production experiments, lost about 150‐nM nitrate during the day and an equal amount at night at the equator. These rates exceeded by several fold the rates of nitrate incorporation into particulate matter. The carbon equivalent of the 24‐hour nitrate consumption also exceeded the rate of 14C primary production. The large nitrate consumption is not readily explained in terms of phytoplankton physiology but may serve to fuel speculation on the possible production of dissolved organic nitrogen and on the role of bacteria in processing nitrate in the equatorial Pacific upwelling region.
The lower atmosphere over the Gulf of California
Authors: Badan‐Dangon Antoine , Dorman Clive E. , Merrifield Mark A. , Winant Clinton D.
Published: February 2008

Automated meteorological observations at coastal and island stations, instrumented aircraft flights, and coastal soundings were made between July 1983 and June 1985 to define the variations of the lower atmosphere over the northern half of the Gulf of California during the two important climatic seasons, the mid‐latitude winter and the subtropical summer. A marine layer is well defined over water during both seasons but dissipates within a few kilometers inland. The winter large‐scale pressure field is dominated by the Great Basin high over the southwestern United States. Modulated by upper level synoptic activity, it causes 3 to 6 days events of northwesterly winds (8–12 m s−1) directed along the gulf's axis, which are coherent over basin scales, and bring cool, dry desert air over the gulf. The vertical scale of these winds is 700–1000 m over land on the western side of the gulf, close to the height of the Baja California mountains, but only 100–400 m over water, defined by the wintertime inversion. Cross‐gulf winds, related to topographic effects during upper level trough passages over Baja California, are particularly intense in the northwestern portion of the gulf. The winter marine layer is defined by a 1° to 4.5°C temperature inversion and a dew point temperature of 6°–11°C (a moisture content of 6–8 g kg−1); weak subsidence reduces dew point values to −4°C above the inversion. Winter winds above the marine layer are coherent (0.8) across the width of the gulf. The summer large‐scale pressure field is dominated by a thermal low over the southwestern United States, and drives weak (2–5 m s−1) southeasterly winds, also directed primarily along the gulf, which are less spatially uniform than winter winds. Air temperature and moisture content are rather constant, and topographic effects are absent. The summer marine layer is on the order of 200–300 m thick, with dew point temperatures of 26°–28°C (21–24 g kg−1), and capped by a weak temperature inversion (1°–2°C) over water. Aloft, the dew point temperature is 17°–21°C, and winds are weak and uncorrelated across the width of the Gulf. During June and early July 1984, four week‐long pulses of southeasterly winds (10 m s−1) support the existence, reported previously, of moisture surges from the gulf into the Sonoran desert. A dynamical analysis of subdiurnal motions shows that the cross‐gulf momentum balance is geostrophic, the along‐gulf balance is ageostrophic, with the along‐gulf pressure gradient opposed by friction at the surface. These results are consistent with a scale analysis of the equations of motion in the marine layer over the Gulf of California.
Simulation of an interferometric synthetic aperture radar imagery of an ocean system consisting of a current and a monochromatic wave
Authors: Shemer Lev , Kit Eliezer
Published: February 2008

A model which simulates azimuthal imaging of a monochromatic ocean wave and current by an interferometric synthetic aperture radar (INSAR) is developed. The model allows one to obtain simulation of a regular synthetic aperture radar (SAR) as a particular case. The effects of velocity bunching and scanning distortion, as well as the dependence of the output on wave propagation direction, are considered. SAR and INSAR imaging of a monochromatic wave is compared both qualitatively and quantitatively for a wide range of governing parameters. Analytical expressions for both SAR and INSAR outputs were obtained for small values of the velocity‐bunching parameter. The accuracy of these analytical approximations was checked numerically.
Multifrequency polarimetric synthetic aperture radar observations of sea ice
Authors: Drinkwater Mark R. , Kwok R. , Winebrenner D. P. , Rignot E.
Published: February 2008

The first known fully polarimetric airborne synthetic aperture radar (SAR) data set of sea ice is introduced. Images were acquired in the Beaufort, Bering and Chukchi seas in March 1988, during a campaign for validation of Defense Meteorological Satellite Program Special Sensor Microwave Imager radiometer ice products. Statistics of the magnitude, phase and polarization of complex backscattered signals recorded by the Jet Propulsion Laboratory three‐frequency SAR are examined in detail for various scenes with different ice characteristics. The full Stokes matrix information generated from C, L, and P band data characterize the scattering behavior of different ice types. Polarization ratios and phase differences between linear copolarized returns are used for discrimination between particular image features and mechanisms are suggested for the observed polarimetric characteristics. Results indicate that combinations of frequency and polarization enhance current capability to distinguish ice of different properties using single frequency, fixed polarization micro‐wave radar. A specific example is the polarimetric identification of new ice formation which may not be easily distinguished in ERS‐1 5.3GHz, VV polarization SAR data. Such findings are consistent with theoretical model simulations of scattering characteristics of sea ice. Overall, these preliminary results demonstrate that radar polarimetry will likely add a new dimension to our current capability for extracting geophysically important ice variables using radar remote sensing methods.
We still say iron deficiency limits phytoplankton growth in the subarctic Pacific
Authors: Martin John H. , Fitzwater Steve E. , Gordon R. Michael
Published: February 2008

The failure of Banse (1990) to use a reasonable initial particulate organic nitrogen (PON) value resulted in erroneously high, and physiologically impossible, estimates of phytoplankton growth rates. To correct this situation, we used an initial PON value of 1 μmol PON L−1 for both experimentals and controls; rates similar to those expected under prevailing light and temperature conditions were obtained. This reinterpretation of our data again demonstrates the dramatic effects that are observed when small quantities of iron are made available to the phytoplankton inhabiting offshore subarctic Pacific waters.
Variability of the wind stress curl over the North Pacific: Implications for the oceanic response
Authors: Chave Alan D. , Luther Douglas S. , Filloux Jean H.
Published: February 2008

The subinertial frequency‐wavenumber structure and spatial coherence of wind stress curl, and their spatial and temporal variability, are described with the emphasis on characteristics which affect the ocean's response to the wind stress curl forcing function. Wind stress curl over the North Pacific between 25° and 60°N was computed for 3 years (1985–1988) from the Fleet Numerical Oceanography Center wind product. The range from winter peak to summer trough for the mean and variance are typically a factor of 3–4 and ≈10 respectively, with superimposed interannual changes of up to a factor of 2. Power spectra vary seasonally and interannually in an essentially frequency‐independent manner that is consistent with the curl variance. However, the spectrum over the period band 5–100 days often fails a statistical test for whiteness at the 95% level. Zonal and meridional wavenumber spectra were estimated for 13 sites distributed around the central‐eastern North Pacific using the maximum likelihood method. Directional trends with frequency are comparable to those from earlier studies if 3‐year‐long data segments are analyzed, with approximate wavenumber symmetry except for the zonal term at mid‐latitudes for periods shorter than 10 days, where eastward propagation is dominant. However, spectra for shorter data sections sometimes display eastward and westward excursions which are only weakly similar over distances of ≈1000 km and essentially dissimilar over longer separations. The spatial correlation structure of wind stress curl is shown typically to have a main lobe of ≈1000 km and multiple intercorrelation lobes separated by ≥ 2000 km. The strength and location of the intercorrelation peaks vary slowly with time. These results suggest that curl behavior is more complex than was previously believed, that the use of long‐term averages of or simple parameterizations for the frequency‐wavenumber spectrum of wind stress curl in model studies may be unrealistic, and that more attention to actual curl characteristics at the time oceanic measurements are collected will be required to reconcile models with observations.
Energy density directional spectra of a nearshore wave field measured by interferometric synthetic aperture radar
Authors: Marom M. , Shemer L. , Thornton E. B.
Published: February 2008

The nearshore wave field within Monterey Bay, California, is studied using remote sensing imaging by an interferometric synthetic aperture radar (INSAR) and simultaneous ground‐based measurements. It is shown that INSAR imagery of the ocean surface offers some advantages over conventional synthetic aperture radar. Because of the direct imaging mechanism of INSAR, quantitative information about the complicated wave field can be obtained. The INSAR‐derived directional energy density spectra and the corresponding ground‐based spectra compare well.
Interannual variability in phytoplankton blooms observed in the northwestern Arabian Sea during the southwest monsoon
Authors: Brock John C. , McClain Charles R.
Published: February 2008

Interannual changes in the strength and seasonal evolution of the 1979 through 1982 surface level southwest monsoon winds have been related to variations in the summer phytoplankton bloom of the northwestern Arabian Sea by synthesis of satellite ocean color remote sensing with analysis of in situ hydrographic and meteorological data sets. The 1979–1981 southwest monsoon phytoplankton blooms in the northwest Arabian Sea peaked during August‐September, extended from the Omani coast to about 65°E, and appeared to lag the development of open‐sea upwelling by at least 1 month. In all 3 years the bloom was driven by spatially distinct upward nutrient fluxes to the euphotic zone forced by the physical processes of coastal upwelling and offshore Ekman pumping. Coastal upwelling was evident from May through September, yielded the most extreme concentrations of phytoplankton biomass, and along the Omani coast was limited in its impact on upper ocean biological variability to the continental shelf. Ekman pumping stimulated the development of a broad open‐ocean component of the southwest monsoon phytoplankton bloom oceanward of the Omani shelf. Phytoplankton biomass on the Omani continental shelf was increased during both the early and late phases of the 1980 southwest monsoon due to stronger coastal upwelling under the most intense southwesterly winds of the four summers investigated. Diminished coastal upwelling during the early phase of the weak 1982 southwest monsoon resulted in a coastal bloom that reached a mean phytoplankton pigment concentration that was 28% of that seen in 1980. The lack of a strong regional northwestern Arabian Sea bloom in late summer 1982 is attributed to the development of persistent, shallow temperature stratification that rendered Ekman pumping less effective in driving upward nutrient fluxes.
On the use of lognormal statistics to simulate one‐ and two‐dimensional under‐ice draft profiles
Authors: Hughes B. A.
Published: February 2008

The probability density function of one‐dimensional measurements of ice draft is shown to be fitted accurately by a set of lognormal distributions. A technique is also described for generating synthetic ice draft data by interspersing filtered random number sequences drawn from the fitted lognormal distributions. The sequences are interspersed by random selection to produce one‐ and two‐dimensional model ice draft profiles. The filter characteristics can be chosen so that one‐dimensional spectra of the model profiles agree well with measurements. For features with horizontal length scales greater than ∼10 m, realizations of ice draft data are in good visual agreement with measured profiles.
On the remote forcing of the circulation in the Bay of Bengal
Authors: Yu Lisan , O'Brien James J. , Yang Jiayan
Published: February 2008

We present the hypothesis that the remote forcing is one of the mechanisms that determine the semiannual reversal of the upper ocean circulation in the Bay of Bengal. A simple reduced‐gravity oceanic model is used to explain the hypothesis. Three numerical experiments have been performed to compare the oceanic responses to a remote forcing, a local forcing and a combined forcing. It is found that the long Rossby waves excited by the remotely forced Kelvin waves contribute substantially to the variability of the local circulation. This research indicates that equatorial Kelvin waves are one of the major factors determining the circulation in the eastern equatorial Indian Ocean.
Growth of wind waves with fetch observed by the Geosat altimeter in the Japan Sea under winter monsoon
Authors: Ebuchi Naoto , Kawamura Hiroshi , Toba Yoshiaki
Published: February 2008

The wind speeds and the significant wave heights derived from the Geosat altimeter are validated by comparing with the data obtained at Japanese ocean data buoy stations. A systematic error is found in the altimeter wind speeds at high winds. An experimental equation is derived in order to correct this error for the present study. By using the corrected wind speeds and the wave heights, growth of wind waves with fetch in the Japan Sea under winter monsoon is investigated. The altimeter‐derived nondimensional significant wave height and nondimensional fetch show good agreement with the empirical fetch graph formulas. Fetch variation of the wind speeds is also discussed in relation to the evolution of the turbulent boundary layer over wind waves by using the altimeter data.
Precipitable water and surface humidity over global oceans from special sensor microwave imager and European Center for Medium Range Weather Forecasts
Authors: Liu W. Timothy , Tang Wenqing , Wentz Frank J.
Published: February 2008

The two most promising methods of estimating precipitable water W over global oceans rely on spaceborne microwave radiometers and atmospheric general circulation models. Global fields of W from the special sensor microwave imager (SSMI) were compared with those from the European Center for Medium Range Weather Forecasts (ECMWF) model. They agree over most ocean areas; both data sets capture the two annual cycles examined and the interannual anomalies during an El Niño‐Southern Oscillation episode. However, they show significant differences in the dry air masses over the eastern tropical‐subtropical oceans, particularly in the southern hemisphere. In these regions, comparisons with radiosonde data indicate that overestimation by the ECMWF model accounts for a large part of the differences. As a check on the W differences, surface level specific humidity Q derived from W, using a statistical relation, were compared with Q from the ECMWF model. The differences in Q were found to be consistent with the differences in W, and indirectly validating the Q‐ W relation. In both W and Q, SSMI was able to discern clearly the equatorial extension of the tongues of dry air in the eastern tropical ocean, while both ECMWF and climatological fields have reduced spatial gradients and weaker intensity. One of the reasons for the ECMWF moisture overestimation is suggested to the poor resolution of Tiros‐N operational vertical sounder data which were assimilated into the ECMWF model.
Response of the National Center for Atmospheric Research community climate model to improvements in the representation of clouds
Authors: Slingo A. , Slingo J. M.
Published: February 2008

A new parameterization for the shortwave radiative properties of water clouds and the European Centre for Medium‐range Weather Forecasts (ECMWF) cloud prediction scheme have both been included in the National Center for Atmospheric Research (NCAR) community climate model. The techniques employed to treat the contribution by water vapor absorption to the cloud radiative properties, the overlaps between cloud layers, and the spectral dependence of the properties are described, and comparisons are made with a more detailed radiation code. Only minor adjustments were necessary to implement the cloud prediction scheme. Results from a suite of integrations are used to examine the effect on model simulations. There are improvements in the model's temperature structure and in the radiation budget and cloud radiative forcing when compared with results from the Earth Radiation Budget Experiment. It is shown that the changes in the cloud distribution over the subtropical oceans induce changes not only in the surface radiative fluxes but also in the surface turbulent fluxes, through modifications to the boundary layer stability. The turbulent fluxes change in such a way as to maintain the cloud. While the cloud distributions in these areas appear realistic, it is argued that important physical processes are ignored by the model and that a more comprehensive formulation of the cloudy boundary layer is required.
Mesospheric effects of solar ultraviolet variations: Further analysis of SME IR ozone and Nimbus 7 SAMS temperature data
Authors: Hood L. L. , Huang Z. , Bougher S. W.
Published: February 2008

An analysis is presented of 3.8 years of Solar Mesosphere Explorer (SME) IR ozone data and 4.3 years of Nimbus 7 stratosphere and mesosphere sounder temperature data for the purpose of estimating and characterizing the zonal mean response of the mesosphere to solar ultraviolet variations occurring on the solar rotation time scale. In agreement with an earlier study by Keating et al. (1987) the maximum low‐latitude ozone and temperature response amplitudes occur at essentially the same level (∼0.06 mbar; approximately 68 km altitude). The ozone response is negative and occurs at nearly zero lag, while the peak temperature response is positive and occurs at a lag of 3 to 5 days. The derived ozone response sensitivities and phase lags in the lower mesosphere merge smoothly with those previously determined for the upper stratosphere using independent satellite data sets. Some evidence for a weak negative ozone response near 75 km at high winter latitudes is also obtained. Temperature perturbations at low latitudes that correlate with solar ultraviolet flux variations are connected in phase with those occurring at higher latitudes in the winter hemisphere, suggesting the existence of a dynamical component of the mesospheric response. The coexistence of positive temperature and negative ozone response maxima at the same level (∼68 km) indicates strong coupling between photochemical and thermal components of the response. The negative ozone response can potentially be explained by a combination of temperature feedback from the observed temperature response and increased Lyman a dissociation of water vapor (followed by HOχ destruction of ozone). The positive temperature response cannot be due to ozone radiative heating since the ozone perturbation is negative. However, other heating terms, including those due to exothermic chemical reactions, are known to contribute to the mesospheric heat budget. In particular, HOχ chemical heating (mainly from H + O3 → OH + O2) will increase with ozone destruction and may therefore be a likely candidate mechanism.
Particle size distributions in polar mesospheric clouds derived from Solar Mesosphere Explorer measurements
Authors: Rusch D. W. , Thomas G. E. , Jensen E. J.
Published: February 2008

Data from the visible and ultraviolet spectrometers on the Solar Mesosphere Explorer are used to derive the color ratios of the reflectance at 265, 296, and 393 nm of light scattered from polar mesospheric cloud particles. This analysis extends the spectral coverage into the visible region of the spectrum. The data reduction technique compared the cloud brightness to the brightness scattered from the background atmosphere at the same wavelength. The ratios determined in this way are independent of systematic errors in instrument radiometric calibration. The data are analyzed using theoretical determinations of the color ratios from the Mie theory of small particle scattering, assuming a lognormal distribution for the particle size dispersion. By “size” we mean the average radius of the sphere having the same ice volume. The present results confirm earlier findings that the effective sizes of polar mesospheric cloud particles are less than 70 nm. Still, there exists a small number of measurements which result in particle sizes of the order of 80 nm. Even for these large particle sizes the required vertical column content of water vapor does not exceed limits imposed by the available atmospheric water vapor concentrations.
Analysis of 5‐year aerosol data from the Stratospheric Aerosol and Gas Experiment II
Authors: Brogniez C. , Lenoble J.
Published: February 2008

The Stratospheric Aerosol and Gas Experiment (SAGE) II measured aerosol extinction coefficients at 1.02 μm averaged over a 10° latitude band and over short periods of nearly 5 days are used for latitudinal and seasonal studies. The most evident feature of the time series is the exponential decrease confirming the decay of El Chichon influence; in some latitude bands and at several height levels, small seasonal variations are superimposed. For latitudinal variations, extinction minima at 25°/35° in both hemispheres appear clearly. Using aerosol extinctions at 0.525, 0.453, and 0.385 μm together with the 1.02‐μm data permits one to deduce one parameter of the size distribution, the particle effective radius. Seasonal variations of the deduced aerosol radius are not so obvious compared to the extinction data, but latitudinal variations of the radius do exhibit the same behavior as the extinction data, with minima at 25°/35°. This study also shows that SAGE II aerosol data can be used to detect volcanic eruption from extinction variations such as the Nevado del Ruiz and to determine the size of the injected particles.
Altitude distributions of stratospheric constituents from ground‐based measurements at twilight
Authors: McKenzie R. L. , Johnston P. V. , McElroy C. T. , Kerr J. B. , Solomon S.
Published: February 2008

A technique for extracting height profiles from ground‐based column measurements at twilight is introduced. Its sensitivities to chemical processes, initialization, and air mass factors are investigated. The method is applied to observations made at Lauder, New Zealand, in 1987. The technique provides information on the vertical structure of atmospheric absorbers such as ozone or NO2 from the surface to about 50 km and is particularly valuable for identifying the influence of pollution on such measurements. When tropospheric pollution is low, it yields profiles in reasonable agreement with model predictions and with satellite measurements.
Ice core evidence for an explosive tropical volcanic eruption 6 years preceding Tambora
Authors: Dai Jihong , Mosley‐Thompson Ellen , Thompson Lonnie G.
Published: February 2008

High‐resolution analyses of ice cores from Antarctica and Greenland reveal an explosive volcanic eruption in the tropics in A.D. 1809 which is not reflected in the historical record. A comparison in the same ice cores of the sulfate flux from the A.D. 1809 eruption to that from the Tambora eruption (A.D. 1815) indicates a near‐equatorial location and a magnitude roughly half that of Tambora. Thus this event should be considered comparable to other eruptions producing large volumes of sulfur‐rich gases such as Coseguina, Krakatau, Agung, and El Chichón. The increase in the atmospheric concentration of sulfuric acid may have contributed to the northern hemisphere cooling observed in the early nineteenth century and may account partially for the decline in surface temperatures which preceded the eruption of Tambora in A.D. 1815.
Different methods of modeling the variability in the monthly mean concentrations of atmospheric CO2 at Mauna Loa
Authors: Martín F. , Díaz A.
Published: February 2008

A detailed analysis of the time series of the monthly average atmospheric CO2 concentrations from March 1958 to December 1985 has been carried out. Seasonal decomposition of the CO2 time series has been done in order to obtain estimations of the trend, seasonal, and irregular components. The seasonal variation includes a cycle of 6‐month period superimposed to the strong annual cycle. These two harmonic explain more than 95% of the seasonal variation of the CO2 concentration. Three different models for the atmospheric CO2 concentrations have been analyzed: univariate stochastic model, curve fitting and a model with exogenous variables. A quadratic function and a four‐harmonic Fourier series with the amplitude increasing in time have been fitted to the CO2 trend and seasonal component, respectively. Global monthly fossil fuel combustion data and the smoothed sea surface temperature off the Peruvian coast have been used as exogenous variables explaining the CO2 trend for the third model. Smoothed sea surface temperature cross‐correlated significantly with the anomalies of the time derivative of the CO2 trend at lags of 12 and 13 months. The results of the third model seem to confirm that changes in the upwelling and the CO2 outgassing from the eastern tropical Pacific Ocean are responsible of changes in the CO2 growth rate observed at Mauna Loa. It is estimated that the CO trend has risen about 0.5 ppm per El Niño event. The model with exogenous variables offered the closest fit to the measured data and seems to be the best model in forecasting the monthly average atmospheric CO2 concentration during the years 1986–1989.
A comparison of surface and airborne trace gas measurements at a rural Pennsylvania site
Authors: Van Valin Charles C. , Luria Menachem , Ray John D. , Boatman Joe F.
Published: February 2008

A comparison of trace gas concentrations between a ground sampling site and an instrumented aircraft was performed at the Scotia field site in central Pennsylvania. The comparison included four research flights in August 1988. The ground site was operated by the National Oceanic and Atmospheric Administration (NOAA) Aeronomy Laboratory, and the NOAA King Air instrumented aircraft was operated by the NOAA Air Resources Laboratory. The study demonstrates continuity in the values of the state parameters (wind speed and direction, temperature, and dew point) from the surface to the aircraft observations at the times of the four flights. Considered within the context of the differing time‐space scales, continuity was also demonstrated in the trace gas measurements. The aircraft and surface measurements of the trace gas concentrations were in better agreement when the aircraft measurements demonstrated uniform concentrations over the length of the flight path. The mean O3 and H2O2 values of the lowest‐altitude aircraft readings were usually greater than those measured at the surface, thus indicating higher‐altitude sources and removal processes at lower altitudes. The aircraft‐measured values for SO2, NOy, and hydrocarbons were usually lower than those measured at the surface, as expected for primary pollutants emitted near ground level. Closer agreement was obtained in the comparisons of secondary (O3, H2O2) than of primary (SO2, NOy, hydrocarbons) pollutants.
An improved filter pack technique for airborne measurement of low concentrations of SO2
Authors: Ferek Ronald J. , Hegg Dean A. , Herring John A. , Hobbs Peter V.
Published: February 2008

Recent improvements to the carbonate‐impregnated filter technique for measuring low‐level SO2concentrations have resulted in dramatically improved performance. The improvements are (1) a better cleaning procedure for the paper filter substrates, resulting in approximately 60% reduction of their sulfate blank, (2) the use of an ion‐exchange resin to remove the carbonate matrix from the sample extract, resulting in a 100% increase in the signal‐to‐noise ratio, (3) the use of high‐purity glycerol in the filter impregnate, resulting in approximately 10% further reduction of blanks, and (4) improved Chromatographic and standardization procedures for more accurate quantification of sample peaks. Combined, these improvements allow measurements to be made of SO2 concentrations in marine background air with a 2σ uncertainty of ±6 parts per trillion by volume (pptv) and, based on this, a 3σ detection limit of 9 pptv for air volumes of 4 m3 (which can be collected in 15 min aboard our research aircraft). Measurements in polluted air show better than 95% collection efficiency, even at concentrations as high as 100 ppbv. Vertical profiles of SO2 measured during three research flights off the Washington coast (one in clean marine air) showed concentrations ranging from 15 to 86 pptv in the mixed layer and from 40 to 93 pptv in the free troposphere.
Ground‐based lidar studies of ozone exchanges between the stratosphere and the troposphere
Authors: Ancellet G. , Pelon J. , Beekmann M. , Papayannis A. , Megie G.
Published: February 2008

Ground‐based lidar measurements of ozone were conducted at the Observatoire de Haute Provence (OHP) (44°N, 6°E, 700 m above sea level (asl)) to study ozone exchanges between the stratosphere and the troposphere. Three case studies are presented, corresponding to intensive lidar measurements obtained during two or three consecutive days within the range 5–11 km. Whenever it was possible, additional data such as backward/forward air mass trajectories, synoptic weather maps, and total ozone mapping spectrometer (TOMS) maps were also used to obtain a better understanding of the ozone increases and to infer the impact of stratospheric air mass at tropospheric level. For the three cases, elevated ozone content in the upper troposphere (>80 ppb at 6 km) corresponded to the passage of a frontal system above the OHP. An upper limit of 2.1033 ozone molecules transferred within the frontal zone of a well‐developed low is derived for a 2‐ to 3‐day event. This number multiplied by the average number of lows gives a coarse estimate of the contribution to the annual stratospheric ozone outflow in the northern hemisphere (1.5×1036 molecules yr−1). It is smaller than the total outflow (3.5–6.1036 molecules yr−1) inferred from previous studies using radioactivity deposition or general circulation model, which includes the additional impact of cutoff lows.