bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations of phytoplankton and nutrients from a Lagrangian drifter off northern California
Authors: Abbott Mark R. , Brink Kenneth H. , Booth C. R. , Blasco Dolors , Codispoti L. A. , Niiler Pearn P. , Ramp Steven R.
Published: February 2008

A Lagrangian drifter was deployed in a cold filament off northern California as part of the Coastal Transition Zone program. The drifter was equipped with an optical package (consisting of a spectroradiometer, a fluorometer, and a beam transmissometer) suspended at 8.5‐m depth and a water sampler suspended at 16.3‐m depth. The drifter was recovered after 8 days. Optical, chemical, and biological properties changed considerably as the drifter moved offshore in the cold filament. Concentrations of phytoplankton chlorophyll increased rapidly in the first 2 days, in parallel with the disappearance of nitrate and nitrite. After this initial period, chlorophyll decreased gradually over the next 6 days with prominent diurnal fluctuations present in the last 3 days. Water transparency also showed similar long‐term as well as diurnal fluctuations. The phytoplankton community became increasingly dominated by large centric diatoms throughout the deployment. Although total cell volume was higher towards the middle of the deployment, this increase occurred without a parallel increase in chlorophyll. In addition, total particulate concentrations were highest nearshore. Although the drifter slippage was approximately 1 cm/s, the biological, chemical, and physical characteristics of the water were affected by both in situ changes and vertical motions of the water. These results are generally consistent with results from other up welling studies.
Sensitivity studies with a sea ice‐mixed layer‐pycnocline model in the Weddell Sea
Authors: Owens W. B. , Lemke P.
Published: February 2008

The sensitivity of a dynamic‐thermodynamic sea ice model coupled to a one‐dimensional mixed layer‐pycnocline model to variations of dynamic and thermodynamic model parameters is investigated. Furthermore, the modifications of the model results due to the inclusion of a prognostic snow cover and the implementation of simplified sea ice rheologies are investigated. In these comparisons special emphasis is placed upon the ice‐ocean boundary conditions (buoyancy fluxes) and the mixed layer properties.
Observations of nonlinear effects in directional spectra of shoaling gravity waves
Authors: Freilich M. H. , Guza R. T. , Elgar S. L.
Published: February 2008

The spatial evolution of a directionally spread wave field on a near‐planar natural beach is examined using data from longshore arrays of pressure sensors and wave staffs at 10.3 m and 4.1 m depth. High‐resolution frequency‐directional spectra from the deeper array are used to initialize a linear refraction model, and the resulting model predictions are compared with frequency‐directional measurements at the shallow array. Linear theory inaccurately predicts both the shapes of directional spectra in shallow water and the total variances in some frequency bands. The discrepancies are largest for frequencies associated with maxima in the bicoherence spectrum, suggesting the importance of nonlinear effects. Furthermore, the measured directional spectrum at energetic low frequencies (0.05–0.11 Hz) and the vector resonance conditions for triads of long waves can be used to predict accurately the directions of observed peaks in directional spectra at higher frequencies (0.12–0.21 Hz). Prominent features in the measured directional spectra at the shallow array are thus consistent with energy transfers resulting from near‐resonant triad interactions in the shoaling wave field.
Dynamical evaluation of the surface circulation using remote sensing of drifting ice floes
Authors: Larouche Pierre , Dubois Jean‐Marie M.
Published: February 2008

An analysis of ice drift from consecutive Landsat multispectral scanner images of the same area taken at 24‐h interval allowed the calculation of the surface circulation using a dynamical approach. Comparison between calculated and measured values shows that this method leads to a good approximation of the surface circulation in a region where ice floes are free drifting. On the other hand, the sole use of the floe drift over time to evaluate the currents leads to results that are far from the measured values. Tests made using various air and ice drag coefficients, and wind speeds and directions for different drift distances show that the error associated with these parameters is small. Although the values obtained using the numerical data involved considerably more effort and expense, the results were not significantly better than those found using photographic products. A good approximation of the surface circulation can thus be made using a simple digitization of the floe positions on photographic products. Application of the methodology to a set of four image pairs led to the recognition of two modes of circulation in southeastern Hudson Bay in spring 1985. This method can thus become a useful tool for rapid evaluations of surface currents in ice‐covered areas that can hardly be sampled otherwise.
Tropical data assimilation experiments with simulated data: The impact of the tropical ocean and global atmosphere thermal array for the ocean
Authors: Miller Robert N.
Published: February 2008

A series of observing system simulation experiments (OSSE) is performed on a simulated data set which was designed to mimic the wind‐forced response of the tropical Pacific ocean. This data set was constructed by adding random perturbations to the FSU monthly mean pseudostress anomaly data. These perturbed pseudostress anomaly fields were used to drive a simple linear model whose output was sampled to form synthetic observations. The statistics of the perturbations are given by estimates of the errors in the pseudostress data calculated in an earlier study. OSSE are performed using simulated sea level height data from island tide gauge stations and from selected TOGA‐TAO (Tropical Ocean and Global Atmosphere Thermal Array for the Ocean) mooring sites. Data from the TOGA‐TAO moorings are assumed, in one experiment, to consist of sea level height data, identical to that from tide gauges. In a further experiment, mooring data consist of amplitudes of the first two vertical modes. Errors in the OSSE are seen to be comparable to errors obtained in comparison to real data where such comparisons are available. Assimilation of data at six island stations results in noticeable, but not dramatic improvement in the analysis, as was noted in an earlier study with actual observations. OSSE using simulated mooring data showed accuracy in the sea level height field comparable to that of the instruments across much of the basin. Inclusion of the separate baroclinic modes resulted in negligible improvement. Simulated fields of 20° isotherm depth anomaly were also produced. Results were similar to the sea level height results. As in the simulation of sea level height, inclusion of the separate baroclinic modes resulted in negligible improvement.
A dynamic and thermodynamic sea ice model for subpolar regions
Authors: Lu Qian‐Ming , Larsen Jesper , Tryde Per
Published: February 2008

A mesoscale dynamic thermodynamic sea ice model is presented. The model differs from the large scale sea ice model [Hibler, 1979; Parkinson and Washington, 1979] in both the dynamic and thermodynamic parts. In the dynamic calculation, a constitutive relation based on ice floe collision is used for the determination of the internal ice force in the Marginal Ice Zone (MIZ), while in the thermodynamic calculation, a three‐level approach for the ice thickness distribution is adopted instead of the common two‐level approach [Hibler, 1979]. The simulation results from the mesoscale sea ice model show that the three‐level approach is more sensitive to geophysical forcing than the two‐level approach. Thus it is demonstrated that the mesoscale sea ice model has the potential of a more accurate description of the dynamics and the thermodynamics than the previous models in the simulation of sea ice processes in subpolar regions. Giving the exact initial conditions and the atmospheric and oceanic forcings, this model can be used as a sea ice forecasting model in subpolar regions.
The vertical distribution of nutrients and oxygen 18 in the upper Arctic Ocean
Authors: Björk Göran
Published: February 2008

The observed vertical nutrient distribution including a maximum at about 100 m depth in the Arctic Ocean is investigated using a one‐dimensional time‐dependent circulation model together with a simple biological model. The circulation model includes a shelf‐forced circulation. This is thought to take place in a box from which the outflow is specified regarding temperature and volume flux at different salinities. It has earlier been shown that the circulation model is able to reproduce the observed mean salinity and temperature stratification in the Arctic Ocean. Before introducing nutrients in the model a test is performed using the conservative tracer δ18 (18O/16O ratio) as one extra state variable in order to verify the circulation model. It is shown that the field measurements can be simulated. The result is, however, rather sensitive to the tracer concentration in the Bering Strait inflow. The nutrients nitrate, phosphate, and silicate are then treated by coupling a simple biological model to the circulation model. The biological model describes some overall effects of production, sinking, and decomposition of organic matter. First a standard case of the biological model is presented. This is followed by some modified cases. It is shown that the observed nutrient distribution including the maximum can be generated. The available nutrient data from the Arctic Ocean are not sufficient to decide which among the cases is the most likely to occur. One case is, however, chosen as the best case. A nutrient budget and estimates of the magnitudes of the new production are presented for this case.
Linear instability of an anticyclonic vortex in a two‐layer ocean
Authors: Paldor Nathan , Nof Doron
Published: February 2008

The linear stability of a (zero potential vorticity) circular lens (i.e., warm‐core ring) is investigated for the case where the ocean surrounding the lens is of finite depth. The hydrostatic balance across the lens' interface couples the pressure variations inside the lens with those in the surrounding ocean which produces the instability. It is found that in contrast to lenses in an infinitely deep ocean which are always stable, lenses in a finite‐depth ocean are unstable. For a fixed lens thickness the growth rates (instability exponents) increase with decreasing total depth. For each azimuthal wave number there exists a total (ocean) depth cutoff value above which the lens is stable and below which the lens is unstable; this cutoff value increases with wave number. In most cases, instability would occur whenever the ocean‐lens depth ratio is less than 3 or 4, suggesting that actual rings in the ocean may become unstable as they approach the shore where the ocean depth is relatively small.
The Weddell‐Scotia confluence in midwinter
Authors: Muench Robin D. , Gunn John T. , Husby David M.
Published: February 2008

The southern central Scotia Sea, site of the Weddell‐Scotia Confluence where outflowing Weddell Sea waters converge with the eastward flowing waters of the Scotia Sea, was sampled during June‐August (austral winter) 1988 with respect to temperature and salinity. Both drogued and ice‐mounted drifters, tracked by Argos, were deployed in the region and yielded Lagrangian drift tracks of ice and water motion. The data substantiate past accounts of the region, based upon summer field research, as dominated by eastward flow upon which a complex array of mesoscale features is superimposed. Weddell‐Scotia Confluence Water, documented by past summer work in the region and characterized by decreased static stability, was not detected, and the Scotia Front was not well defined. The region was one of intense mixing activity and primarily anticyclonic mesoscale features. Two such features, one an eddy and the other either an eddy or a meander in the Scotia Front, dominated the mesoscale field. With warm cores and containing Polar Front Water, they may have been advected eastward from Drake Passage or may have formed as detached eddies from a sharp northward bend in the Polar Front which typically lies just west of the study region. Several smaller eddies, primarily anticyclonic and some having warm cores, were also detected. There was no evidence of the deep convective mixing which has been hypothesized, on the basis of past summer data, to occur in winter, and vigorous vertical mixing was limited to a 100‐m‐thick upper mixed layer. Vertical stability in the upper layers was enhanced by low‐salinity water derived from melting ice. Temperature‐salinity analyses show that winter water in the study region can be derived through isopycnal mixing between waters from the Scotia Sea and waters from the northwestern Weddell Sea. This is in apparent contrast with summer conditions, wherein conditioning of water either through vertical mixing or via lateral mixing on continental margins has been invoked to arrive at the water mass characteristics which typify the Weddell‐Scotia Confluence.
Settling speeds of floes in fresh water and seawater
Authors: Burban Pierre‐Yves , Xu Yao‐Jun , McNeil Joe , Lick Wilbert
Published: February 2008

The settling speeds of floes of fine‐grained, natural sediments approximately 10–200 μm in diameter have been measured in both fresh water and seawater. These floes were formed at fluid shears of 100, 200, and 400 s−1 and at sediment concentrations of 10, 100, and 400 mg/L, values typical of conditions in the near‐shore areas of lakes and oceans, especially during storm conditions. It is demonstrated that the settling speed of a floe is a strong function of fluid shear and sediment concentration as well as of the diameter of the floe, but it is a weak function of salinity. For the same diameter and salinity, floes produced at the lower fluid shears and sediment concentrations have lower settling speeds than do floes produced at higher fluid shears and sediment concentrations. If the conditions of fluid shear and sediment concentration under which the floes were produced are unknown or ignored, it is shown that the settling speed of a floe is a weak function of diameter and salinity.
On parameterization of sea spray
Authors: Wu Jin
Published: February 2008

Sea spray in the atmospheric layer near the sea surface was measured by several investigators (Monahan, 1968; Preobrazhenskii, 1973; Wu et al., 1984; de Leeuw, 1986). Their data, obtained at various elevations under different wind velocities, are shown to be generally complementary and are herewith analyzed toward deducing a general description of sea spray. Size spectra are shown to follow an exponential distribution for small droplets and a power law distribution for large droplets. The droplet concentration increases exponentially with the wind velocity, and the production rate of droplets decreases as their size increases. Both numerical and volumetric concentrations of droplets increase with the wind velocity, following a power law; its exponent is greater for volumetric than for numerical concentrations. The droplet has a maximum average size above the sea surface, falling in the range of 15–20 μm. Both numerical and volumetric concentrations decrease exponentially toward higher elevations; the length scale characterizing the decrease of volumetric concentrations is about one half that characterizing numerical concentrations.
On the importance of time varying eddy viscosity in generating higher tidal harmonics
Authors: Davies A. M.
Published: February 2008

By using a spectral/modal expansion in the vertical, a method is developed for determining tidal current profiles subject to either a slip or no‐slip bottom boundary condition. An arbitrary vertical profile of eddy viscosity can be used in the calculation, the magnitude of which can be related to the flow field. The nature of the modal solution is such that the high shear bottom boundary layer can be accurately resolved using a few modes (of order five), compared with the order of 45 grid boxes on a logarithmic transformation which would be required in a finite difference approach. Calculations show the importance of a time‐varying eddy viscosity in generating higher harmonics when a no‐slip condition is applied at the seabed. By relating the current one meter above the bed to the bed stress, a value of friction coefficient C100 in reasonable agreement with observations was obtained from these no slip calculations. However the value of friction coefficient was strongly dependent upon the height above the bed, at which the current was calculated, with friction coefficient increasing rapidly in the near‐bed region. Current profiles on the continental shelf determined using the modal method developed in the paper were in good agreement with observations, with computed profiles in the Celtic Sea giving the observed midwater maximum.
Physical and biological oceanographic interaction in the spring bloom at the Bering Sea marginal ice edge zone
Authors: Niebauer H. J. , Alexander Vera , Henrichs Susan
Published: February 2008

At the edge of the melting sea ice pack in the Bering Sea in spring, physical, biological, and chemical oceanographic processes combine to generate a short‐lived, intense phytoplankton bloom that is associated with the retreating ice edge. The bloom begins a week or so before the first of May triggered by insolation and by the low‐salinity meltwater stratification in the presence of high nitrate concentrations (∼ > 25 μM). Meltwater (salinity) stratification delineates ice edge blooms from open water blooms where temperature gradients generate the stratification. Five cross‐ice sections of temperature, salinity, σt, chlorophyll, and nitrate are presented as a time series from April 27 to May 5 illustrating the bloom. Evidence of two separate but concurrent blooms in the ice edge zone are presented. In addition, meteorological and oceanographic conditions were observed that should have been conducive to ice edge up welling. While significant ice and water movement occurred, upwelling was not observed. Finally, the Bering Sea ice edge spring bloom is compared with other ice edge systems in both hemispheres, showing that initial Bering Sea nitrate concentrations are among the highest observed but quickly become limiting owing to the rapid build up of phytoplankton populations. This primary production is not coupled to the pelagic Zooplankton because Zooplankton are largely absent on account of the cold temperatures. Observed maximum chlorophyll concentrations in the bloom are several times greater than those observed in other systems.
Measurements of stratospheric NO2 from the Solar Mesosphere Explorer satellite: 1. An overview of the results
Authors: Mount George H. , Rusch David W. , Noxon John F. , Zawodny Joseph M. , Barth Charles A.
Published: February 2008

The visible light spectrometer on board the Solar Mesosphere Explorer spacecraft measures stratospheric NO2 in the 20–40 km altitude region and provides accurate daytime NO2 density profiles with nearly complete latitudinal coverage over an extended period of time. The instrument and data analysis are discussed in detail, and NO2 results for winter/spring 1982 are presented and compared to current theoretical models. Agreement with other measurements is good, and comparison with NOx models indicates that although the overall agreement is acceptable, improvements in the models are required before good agreement is reached at all latitudes. The data indicate that NO2 has a strong memory of the physical conditions present in the stratosphere over a time period of several days.
Meteorological associations with aerosol composition in the boundary layer
Authors: Guest Peter S. , Mach William H. , Winchester John W.
Published: February 2008

The associations of meteorological parameters with aerosol elemental concentrations in the boundary layer have been studied with measurements obtained at the Boulder Atmospheric Observatory from November 29 to December 6, 1979. Air motions were documented by measurements at the tower up to 300 meters and by regional weather data. Aerosols were sampled at 4, 9, 23, and 49 meters by particle size selective cascade impactors and by time sequence filter samplers and were analyzed by proton induced X ray emission (PIXE). Principal sources of fine particle (<1 μ m aerodynamic diameter) components were automotive emissions for Pb and Br and tall stack emissions and atmospheric conversion of pollution gases to sulfate for S. In coarse particles the major earth crustal elements Al, Si, K, Ca, and Fe were soil derived. Pb and Br concentrations and the ratio Br/Pb generally decreased with height. Also, these concentrations varied with ventilation and vertical mixing and were greatest during southerly air flow from Denver. S concentrations did not generally vary with height, ventilation, vertical mixing, or wind direction, suggesting long‐range transport, although 10‐fold temporal variations were observed. Crustal element concentrations generally decreased with height but depended in part on sampler position on the tower structure, indicating microscale shielding effects of coarse particles which were not observed for fine particle elements. Temporal variations of all elements were associated with major meteorological changes, including a cold front passage and a chinook wind.
Photodissociation of molecular oxygen in the terrestrial atmosphere: Simplified numerical relations for the spectral range of the Schumann‐Runge bands
Authors: Nicolet Marcel
Published: February 2008

A numerical method is presented for modeling the photodissociation of molecular oxygen in the spectral range 175–200 nm of the Schumann‐Runge bands (19–0) to (2–0) in the terrestrial atmosphere. It is possible to obtain realistic photodissociation rates that are in good agreement with detailed and complete calculations by using the following simple formulae: In the thermosphere, JSRB = 1.1 × 10−7 exp [−1.97 × 10−10N0.522] s−1 for N ≤1×1019 O2 molecules cm−2 with a precision better than ±10%, and in the mesosphere, JSRB = 1.45 × 108N−0.83s−1 for N≥15×1019 O2 molecules cm−2 with a precision better than ±15%. The lower boundary conditions can be introduced near the stratopause level with the same precision at 50 km and 45 km as a result of the ozone absorption effect. The upper limit for the formula corresponds to N(O2) = 1022cm−2 with a precision of ±15%. If the solar activity action is characterized by increases of 20%, 15%, 10%, and 5% for the four groups of bands (19–0) to (15–0), (14–0) to (10–0), (9–0) to (6–0), and (5–0) to (2–0), respectively, the photodissociation frequency increases by a factor of 1.15 in the thermosphere and 1.11±0.04 in the mesosphere. The accuracy of the formulae depends on the experimental accuracy of the solar irradiance between 175 and 200 nm and on the parameters (oscillator strengths and line widths) of each Schumann‐Runge band.
A numerical test of connections between the stratospheric sudden warming and the quasi‐biennial oscillation
Authors: Bridger Alison F. C.
Published: February 2008

A numerical model of the stratospheric sudden warming is used to test the observationally based suggestion that the warming is sensitive to the phase of the quasi‐biennial oscillation in the equatorial lower‐stratospheric zonal wind field. Some tests show essentially no sensitivity, while in others small differences are noted between integrations representing the east and west phases of the oscillation. The nature of such differences as we find appears to support observational results. The numerical results neither contradict nor strongly support the observations, but may suggest that over the entire winter period differences may be sufficient in a cumulative sense to give the appearance of a sensitivity in the warming.
Sulfur dioxide content of Mount St. Helens' ash
Authors: Weschler Charles J.
Published: February 2008

A rapid heating (980°C)‐gas chromatographic‐mass spectrometric technique was developed to measure the SO2 produced from Mt. St. Helens' ash collected after the May 18, 1980, eruption. The average values of evolved SO2 for ash samples from Moses Lake, Missoula, and Helena are 215, 800, and 1250 ppm, respectively. The results suggest that the SO2 is associated primarily with new magmatic material. Experiments indicate that the SO2 is not due to sulfate species scavenged from the eruption plume or to sulfur gases adsorbed on the ash. Other possible sources include reduction of sulfate salts within the ash, bubbles of SO2 trapped within the ash, or sulfur blebs contained in the ash. Approximately as much SO2 or SO2 precursors are associated with the ash as Mount St. Helens injected into the stratosphere.
The isotopic composition of atmospheric water vapor and the concurrent meteorological conditions
Authors: White James W. C. , Gedzelman Stanley David
Published: February 2008

A high positive correlation is found between the isotopic composition of atmospheric water vapor and both the specific and relative humidities at Palisades, New York, during the growing season. This relationship is explained in terms of the meteorological setting. In general, the lowest δD values occur when cool, dry Canadian air that is stable aloft moves southeastward, while much higher values occur in hot, more humid air that is unstable aloft. The highest δD values approach the local groundwater value and occur when the surface air is stably stratified.
New in‐flight calibration adjustment of the NIMBUS 6 and 7 Earth Radiation Budget wide field of view radiometers
Authors: Kyle H. Lee , House Frederick B. , Ardanuy Philip E. , Jacobowitz Herbert , Maschhoff Robert H. , Hickey John R.
Published: February 2008

The in‐flight space environment of the NIMBUS 6 and 7 earth radiation budget instrument differs in many important ways from the steady state preflight laboratory calibration environment. Because of this, the first 20 months of NIMBUS 7 wide field of view (WFOV) channels had their calibration adjusted through a comparison with the in‐flight calibrated longwave scanner data. The adjustments were most important for the reflected solar radiation channel 13. The scanner failed on June 22, 1980, leading to the requirement for new algorithms to process the remainder of the WFOV data set. On the basis of detailed studies of the sensor characteristics, in‐flight calibration adjustments of the WFOV channels are developed which account for the major thermal, chemical, and radiative dynamics of the orbital environment. These adjustments correct for (1) long‐term changes in the rsponse of the sensors; (2) thermal transients due to the instrument's on‐off duty cycle, and (3) absorption of longwave radiation by the filter domes. In addition, these studies have led to improved in‐flight calibration adjustments for channel 12, the broadband total irradiance sensor. The rational behind the new algorithm is described, and differences between the new and old algorithms are discussed.
Satellite and correlative measurements of stratospheric ozone: Comparison of measurements made by SAGE, ECC balloons, chemiluminescent, and optical rocketsondes
Authors: McCormick M. P. , Swissler T. J. , Hilsenrath E. , Krueger A. J. , Osborn M. T.
Published: February 2008

The validity of ozone profile data from the satellite sensor SAGE was tested in a series of correlative experiments conducted at five fixed sites between 6°S and 65°N during 1979–1980. The intercomparisons included data taken with electrochemical ozone (ECC) balloonsondes and chemiluminescent and optical rocketsondes. The average mean difference for 17 separate comparisons between the SAGE and ECC balloonsonde observations over the altitudes 18–28 km was 9.3% with a standard deviation of 2.8%. Excluding comparisons separated by greater than 500 km reduces the average mean difference to 8.9% and the standard deviation to 2.1%. The average mean difference between SAGE and three optical rocketsonde observations over the altitudes 25–50 km was 11% and between SAGE and two chemiluminescent rocketsondes over the altitudes 20–60 km it was 13.5%. Considering the differences in vertical resolution, experimental errors, and ozone time and space gradients, the agreement between SAGE‐derived ozone profiles and these correlative measurements is considered very good. In addition, isopleths of ozone mixing ratio versus latitude and altitude are in good agreement with previously published results.
Monthly distributions of precipitable water from the NIMBUS 7 SMMR data
Authors: Chang H. D. , Hwang P. H. , Wilheit T. T. , Chang A. T. C. , Staelin D. H. , Rosenkranz P. W.
Published: February 2008

The first year of data from the NIMBUS 7 Scanning Multichannel Microwave Radiometer (SMMR), covering the period December 1978 through November 1979, was used to study the monthly mean distributions of precipitable water over the global oceans. The water vapor algorithm is based on a multiple regression technique, utilizing three of the higher frequency channels on SMMR. The results obtained are in good agreement with other independent studies. They reveal features associated with other independent studies. They reveal features associated with the general circulation of the atmosphere and the ocean currents. Samples of monthly and annual distributions of precipitable water over oceans are presented, and their characteristics are discussed.
Collection and coalescence efficiencies for accretion
Authors: Beard Kenneth V. , Ochs Harry T.
Published: February 2008

The coalescence efficiency for accretion was assumed to be governed by a collisional Weber number. This concept was used with the aid of theoretical collision efficiences to organize collection efficiency data from several sources into a unified set. The resulting collection efficiencies show a maximum of 71% for a collector drop of 115 μm and a cloud droplet of 12‐μm radius. Accretion calculations were made for a monodisperse cloud to illustrate the effects of cloud droplet sizes and collection efficiencies on drop growth. The time average collection efficiency for growth from 50 to 500 μm by accretion of 30‐μm droplets is reduced by 50% when compared to the time average collision efficiency. A maximum of 65% in the time average collection efficiency occurs for accretion of 10‐μm droplets. The contribution to accretion by cloud droplets smaller than 5 μm appears to be negligible.
Microwave radiances from precipitating clouds containing aspherical ice, combined phase, and liquid hydrometeors
Authors: Wu Rongzhang , Weinman J. A.
Published: February 2008

Microwave radiances have been computed as a function of rainfall rates from precipitating clouds containing ice, combined phase, and water hydrometeors. The ice at the top of the precipitating cloud depresses the brightness temperatures by reflecting radiances that emerge from the liquid hydrometeors at lower altitudes. Because the density of ice hydrometeors is related to the rainfall rate at the surface, the brightness temperatures are sensitive to large rainfall rates. The solution of the transfer equation considers the vertically inhomogeneous structure of the precipitation as well as the polarized emissivity of the underlying surface. The altitudes from which radiances derive their energy are presented for several rainfall profiles and frequencies. It is shown that the lower‐frequency radiances are sensitive to liquid precipitation at low altitudes while the higher‐frequency radiances are more sensitive to the ice hydrometeors at the cloud tops. The extinction coefficients of aspherical hydrometeors are presented as a function of rainfall rates. Measurements at 37.0‐GHz microwave radiances from Nimbus 7 suggest that the vertically polarized radiances are 12±2°K warmer than the horizontally polarized radiances at high rainfall rates. This difference diminishes at lower frequencies. The present model reveals that such effects can be traced to aspherical ice hydrometeors in the upper regions of precipitating clouds.
The variability of stratospheric and mesospheric NO2 in the polar winter night observed by LIMS
Authors: Russell James M. , Solomon Susan , Gordley Larry L. , Remsberg Ellis E. , Callis Linwood B.
Published: February 2008

The LIMS experiment sounded the upper atmosphere from late October 1978 to late May 1979 and provided vertical profiles of atmospheric temperature, O3, H2O, HNO3, and NO2. The data were collected over the latitude range from 64°S to 84°N, both night and day. We have used the technique of radiance averaging before retrieval to measure the altitude distribution of NO2 over the altitude range from the lower stratosphere into the mesosphere. Observations in the polar winter night region north‐ward of about 70°N reveal NO2 levels near 175 ppbv at about 70 km, and they show a significant longitudinal variability (factor of 4 to 7). A definite temporal trend exists, showing a buildup of mesospheric and stratospheric NO2 during the polar night and a subsequent slowing of the increase or decline after sunlight returns, depending on altitude. These results provide further insight regarding the importance of NO2 conversion to N2O5 in the polar night, and they suggest that downward transport in the mesosphere can be quite localized. The data represent the first experimental evidence that the thermosphere is an NOx source for the mesosphere and stratosphere.
Atlas of stratospheric submillimeter lines: 1. The 7–20 cm−1 interval
Authors: Baldecchi Maria Grazia , Carli Bruno , Mencaraglia Francesco , Bonetti Alberto , Carlotti Massimo
Published: February 2008

The stratospheric emission in the submillimeter spectral region has been measured from 38.2 km altitude with a resolution of 0.0033 cm−1. In most cases this resolution makes possible the separation of contributions caused by the individual rotational transitions. An atlas of the observed features is given as a guide to both the measurements of minor stratospheric constituents concentration and the evaluation of stratospheric transparency for the measurement of nontelluric sources.
Concurrent measurements of ozone dry deposition using eddy correlation and profile flux methods
Authors: Droppo James G.
Published: February 2008

Simultaneous surface layer ozone flux measurements by eddy flux and profile methods are reported with supporting micrometeorological data. The results show a close correspondence between the eddy diffusivities of ozone and sensible heat rather than momentum eddy diffusivity. Ozone deposition velocities are computed both from the eddy flux and profile fluxes of ozone. As with eddy diffusivities, these results clearly show the sensible heat analogy giving the better fit with the eddy flux values. These sets of deposition velocities also have a consistent temporal variation, with peak values of up to 1 cm/s at midday changing to less than 0.1 cm/s in the evening.
The solar spectral irradiance between 150 and 200 nm
Authors: Mentall J. E. , Guenther B. , Williams D.
Published: February 2008

Three rocket measurements of the solar spectral irradiance have been obtained for the wavelength region 150–200 nm. These flights occurred on November 16, 1978; May 22, 1980; and October 16, 1981. Evidence was found for a variation in the solar irradiance with the solar cycle but smaller than that reported by Mount and Rottman (1981). There is good agreement between the October 16, 1981, flight and the last two flights of Mount and Rottman (1983a, b, 1985).
Behavior of trace NOX species in the nighttime urban atmosphere
Authors: Killus J. P. , Whitten G. Z.
Published: February 2008

Three trace NOX species—HONO, N03. and N2O5—may play important roles in urban smog formation. Alternative mechanisms for these species have recently been proposed. This report presents a brief analysis of simulation results indicating that the traditional chemistry for these species can still explain the results of some recent observational studies.
Stratospheric H2O and HNO3 profiles derived from solar occultation measurements
Authors: Fischer H. , Fergg F. , Rabus D. , Burkert P.
Published: February 2008

Compact two‐channel radiometers for solar occultation experiments have been constructed in order to measure stratospheric trace gases. The instruments can be used as filter‐ or correlation‐type radiometers, depending on the trace gas under investigation. Within the LIMS correlative measurement program, balloon flights were performed with a payload of up to four of these two‐channel radiometers. From the filter‐type measurements, profiles of the trace gases H2O and HNO3 are inferred for the height region between the tropopause and the balloon float level. The data evaluation also includes a comprehensive analysis of the error sources and their effect on the accuracy of the trace gas profiles. The derived H2O and HNO3 profiles are assessed against the observations of other authors and are discussed in the light of the trace gas distributions calculated from photochemical models.
Sea ice: Multiyear cycles and white ice
Authors: Ledley Tamara Shapiro
Published: February 2008

An interesting feature of previous sea ice modeling studies [Semtner, 1976; Washington et al., 1976] was the multiyear cycles in sea ice thickness despite repeating year to year forcing. It is shown here that a number of factors combine to produce these cycles. The most important of these is the insulating properties of the snow layer; however, the timing of the refreezing of new ice at the end of an ice free summer season, and the vertical ocean flux play a role in determining the length and character of these cycles. It is also shown that the inclusion of the formation of white ice in the model greatly reduces its ability to produce multiyear cycles.
Polarization catastrophe theory of cloud electricity‐speculation on a new mechanism for thunderstorm electrification
Authors: Handel Peter H.
Published: February 2008

During the last two decades, ice has been recognized as a hindered ferroelectric, i.e., a substance that is supposed to be ferroelectric at 0°K, but turns out to have the protonic disorder frozen in, and to persist in a me tas table finite‐entropy state down to arbitrarily low temperatures. Small, heterogeneously nucleated aggregates of water and ice may therefore be saturation ‐ polarized and may keep most of their polarization while they grow, perhaps up to sizes of the order of 1 μ for water and more than 10 μ for ice crystallites. This upper size limit is likely to increase with the growth rate. More important, if the criterion Nν2 > 2.5 1021cm−3 is satisfied, a polarization catastrophe occurs, rendering the cloud ferroelectric. Here N is the concentration of aggregates, ν the number of H2O molecules in each. The direction of the spontaneous polarization is usually determined by the fair‐weather field vector, leading to negative polarization charges on top of the cloud and positive on the lower end of the polarization catastrophe region. Masking charges of opposite sign accumulate in these regions during the formation of the cloud, compensating most of the polarization charges. When the aggregates grow too large, they lose their dipole moment, i.e., when the cloud dissipates, the polarization catastrophe disappears, and the masking charges generate lightning if the process of dissipation is fast.
Characteristics of atmospheric ions in contrasting environments
Authors: Wilkening Marvin
Published: February 2008

Properties of atmospheric small ions are studied in different environments including a valley in a semiarid region of the southwestern United States, a nearby mountain top, and a cave where the radon concentration and the absolute humidity are quite high and the condensation nuclei concentration is low. Owing to a high ion pair production rate from the radon and low condensation nuclei content, the electrical conductivity and the small ion densities in the cave air exceed those of the free atmosphere by 2 and 3 orders of magnitude, respectively. The relatively high water vapor and carbon dioxide levels coupled with a low aerosol concentration in the cave appear to favor the growth of ion complexes having lower mobilities than ordinary atmospheric small ions. Atmospheric electrical parameters on the mountain differ by small amounts in comparison with the valley. Atmospheric variables at the mountain site hinge largely on the summer thunderstorm season that set it off from the semiarid setting of the valley location.
Large‐scale charge separation in thunderclouds
Authors: Williams Earle R.
Published: February 2008

Currently available evidence for the mechanisms thought to be responsible for large‐scale charge separation in thunderclouds is reviewed. The evidence suggests that electrically charged precipitation particles are basic to the electrification process but that convective motions are essential in accounting for the electrical energy of active thunderstorms. The relative contributions of air and particle motions remain largely unquantified, and the physical origins of thundercloud electrification have yet to be established.
Electrical discharge propagation in and around space charge clouds
Authors: Williams Earle R. , Cooke Chathan M. , Wright Kenneth A.
Published: February 2008

The electron trapping characteristic of a solid dielectric material (polymethylmethacrylate) is exploited to study electrical discharge propagation in laboratory‐scale space charge clouds. Similarities with the static and dynamic behaviors of thundercloud electricity are identified, and a combination of theoretical and empirical scaling relationships enables a rough translation of parameters from laboratory scale to thundercloud scale. Applications of the laboratory technique to specific thunderstorm situations reinforce the value of discharge structure studies in exposing the very important space charge configuration that gives rise to lightning.
The initial streamer of intracloud lightning flashes
Authors: Liu Xin‐Sheng , Krehbiel Paul R.
Published: February 2008

The initial development of four vertical intracloud lightning flashes has been studied using time‐resolved measurements of the electric field change from 7–8 ground locations at Kennedy Space Center, Florida. The initial field changes of the flashes were analyzed with a unidirectional piecewise‐linear streamer model in an attempt to determine the direction and sign of the initial charge transfer. The results indicate that the discharges were initiated by an upward propagating negative streamer, rather than by a downward propagating positive streamer. The initial streamer appeared to progress upward at speeds between 1 and 3×105 m/s for durations of 10–30 ms and deposited 1 to 4 Coulombs per kilometer of extent. These results disagree with those of earlier studies which used the shape of the overall electric field change to infer the sense of the streamer, and which gave relatively low values for progression speeds (104 m/s). The results agree with observations of VHF radiation source locations by Proctor in South Africa.
Progress in stratospheric hydroxyl measurement by balloon‐borne LIDAR
Authors: Heaps William S. , McGee Thomas J.
Published: February 2008

Knowledge of the concentration of hydroxyl radical is crucial to understanding the chemistry of the stratosphere. Hydroxyl participates in several catalytic cycles which destroy ozone and strongly influences the cycles of chlorine and nitrogen oxides by its reactions which form or destroy reservoirs for chlorine and odd‐nitrogen compounds. We have measured the concentration of hydroxyl radical between the altitudes of 32.5 and 38.5 km using the technique of laser‐induced fluorescence. Our results ranging from 4 to 9×106 cm−3 (with an accuracy of ±50%) are about 2–3 times lower than predicted by current one‐dimensional models, although the uncertainties in our determination and in the models are sufficiently large to explain the differences. A number of potential improvements to the instrument are discussed.
Speed and current for lightning stepped leaders near ground as determined from electric field records
Authors: Thomson E. M. , Uman M. A. , Beasley W. H.
Published: February 2008

The speed and current during the final stages of the lightning stepped leader were determined from features of the electric field waveform. The average speed of the leader tip was found below the height where dE/dt was zero for close lightning. This height was in the range 0.6–2.0 km for flashes at the distances considered here, 3.6–5.7 km. For 10 stepped leaders observed near Tampa, Florida, the mean final one‐dimensional speed was 4.4×105 m/s, the standard deviation was 3.8×105 m/s, and the range was 1.0–14×105 m/s. These speeds are consistent with other stepped leader speeds reported in the literature that were found using optical techniques. The current was estimated when the leader was near ground from dE/dt during the last hundred microseconds before the return stroke. For 62 stepped leaders observed at distances of 3.6–14 km, the mean final leader current was 1.3 kA, the standard deviation was 1.0 kA, the geometric mean was 1.0 kA, and the range was 110 A to 5.0 kA. Errors resulting from uncertainties in distance, charge center height, calibration, ground channel inclination, and channel branching were found to be about 40–50% rms for both speed and current.
Improvements to the algorithm for computing CO2 transmissivities and cooling rates
Authors: Schwarzkopf M. Daniel , Fels Stephen B.
Published: February 2008

A new interpolation algorithm is derived for obtaining CO2 15‐μm transmissivities at any pressure from tables of transmission functions at standard pressures. The new method is a revision of the Fels‐Schwarzkopf (1981) technique. Improvements to the standard transmissivity tables are also discussed. An extension of these methods to calculate transmissivities at CO2 concentrations other than those used for the tables is described.
5‐cm radar echoes and their microphysical significance in Florida cumuli
Authors: López R. E. , Reinking R. F. , Hallett J. , Rosenfeld D.
Published: February 2008

Aircraft microphysical and 5‐cm radar data from the second Florida Area Cumulus Experiment (FACE‐2) have been interrelated to study the development of precipitation in Florida cumuli. Both sets of data demonstrate the importance of the generation of large drops not only at temperatures warmer than freezing but also at altitudes where drops become supercooled. The radar data and, to a limited extent, the microphysical data support the suggestion that a considerable number of Florida cumuli reach very substantial supercoolings, to −10°C or −20°C for example, before producing drops large enough to generate a first echo. The existence of high updraft speeds, as detected by both the aircraft platform and the radar, implies short transit times of the droplets upward through the clouds and adds credibility to these observations. The radar data further indicate that if a cloud can grow above the −10°C level before generating an echo, then it will probably grow to much greater final altitudes than one that generates a first echo at temperature levels warmer than freezing. This may result from updrafts that rise free of the load of precipitation‐size drops in transit to the higher altitudes and then are enhanced owing to the release of latent heat of fusion derived from the larger amounts of supercooled liquid water transported to the higher altitudes, where a high rate of heat input from accelerated freezing is relatively more effective in maintaining convection.