bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison of theory and laboratory measurements of wave propagation and attenuation in grease ice
Authors: Newyear Karl , Martin Seelye
Published: February 2004

In an experimental study using a wave tank in a laboratory cold room we determine the dispersion relation and amplitude attenuation for surface waves propagating through different thicknesses of grease ice. We compare our results to two ice rheology models: the mass‐loading model, which predicts a wavelength decrease relative to open water, and an infinite depth viscous fluid model, which predicts an increasing wavelength as the wave Reynolds number decreases. For a thick grease ice layer in which the waves are strongly damped we observe that the wavelength increases by up to 30% over its open water value in the frequency range of 1.0 Hz<ƒ<1.6 Hz. This trend agrees with the viscous model, and the agreement improves as the ice thickness increases and at higher wave frequencies where conditions approach those of the infinite depth approximation. The Reynolds number decreases approximately exponentially with frequency and is in the range 1<R<10 for our experimental conditions. From the model the inferred viscosity of grease ice is at least 4 orders of magnitude larger than the open water value and increases with frequency, suggesting that grease ice is non‐Newtonian. For the observed parameter values our analysis shows that the mass‐loading model of grease ice is inapplicable while a one‐layer viscous model provides a better match to laboratory observations.
Global marine gravity field from the ERS‐1 and Geosat geodetic mission altimetry
Authors: Andersen Ole Baltazar , Knudsen Per
Published: February 2004

Satellite altimetry from the Geosat and the ERS‐I Geodetic Missions provide altimeter data with very dense spatial coverage. Therefore the gravity field may be recovered in great detail. As neighboring ground tracks are very closely distributed, cross‐track variations in the sea surface heights are extremely sensitive to sea surface variability. To avoid errors in the gravity field caused by such effects, sea surface variability needs to be carefully eliminated from the observations. Initially, a careful removal of gross errors and outliers was performed, and the tracks were fitted individually to a geoid model and crossover adjusted using bias and tilt. Subsequently, sea surface heights were gridded using local collocation in which residual ocean variability was considered. The conversion of the heights into gravity anomalies was carried out using the fast Fourier transform (FFT). In this process, filtering was done in the spectral domain to avoid the so‐called “orange skin” characteristics. Comparison with marine gravity was finally carried out in three different regions of the Earth to evaluate the accuracy of the global marine gravity field from ERS‐1 and Geosat.
Raman spectroscopic and statistical studies on natural clathrates from the Greenland Ice Core Project ice core, and neutron diffraction studies on synthetic nitrogen clathrates
Authors: Pauer Frank , Kipfstuhl Josef , Kuhs Werner F.
Published: February 2004

We present the results of Raman spectroscopic experiments on air clathrates in the GReenland Ice Core Project (GRIP) deep ice core, which differ markedly from previous measurements on the Dye 3 ice core. The N2/O2 ratio we observe is much closer to the atmospheric value. This has new implications for the interpretation of gas distributions in ice sheets. Raman spectroscopic scans to determine the N2/O2 ratios on different planes through a clathrate, in which the two axes of the scans are perpendicular to each other, give no indication of fractionation effects on the N2/O2 concentrations within a clathrate specimen. The frequency shift of the N2 and O2 peaks due to decomposition of a clathrate to an air bubble is shown qualitatively. From their peak integrals there is no indication of different retransformation rates to air bubbles between the oxygen and the nitrogen contents of clathrates. In air bubbles resulting from clathrate decomposition, the N2/O2 ratio shows similar values to those observed in clathrates and present atmospheric values. Statistical studies on the size, shape, and number concentration of clathrates are intended to give an estimate of the total amount of gas occluded in the clathrates. We present preliminary results obtained from 27 samples in a depth range between 1100 and 3000 m. The first neutron powder diffraction experiments reveal an overall degree of filling of 96.4% for a clathrate at a pressure of 449 bars and the existence of a type I phase at 1311 bars with an overall degree of filling of 107.5%.
Numerical simulations of the baroclinic dynamics of density‐driven coupled fronts and eddies on a sloping bottom
Authors: Swaters Gordon E.
Published: February 2004

Numerical simulations of the baroclinic dynamics of density‐driven coupled fronts and eddies are described. The simulations are based on a two‐layer intermediate length scale model which filters out barotropic instability and focuses on the subinertial baroclinic evolution of density‐driven flows within the context of allowing finite‐amplitude height variations in the lower layer. The baroclinic destabilization of a bottom‐trapped coupled front on a sloping bottom is described. In the overlying fluid the instability takes the form of amplifying topographic Rossby waves. In the coupled front the perturbations to the downslope incropping are preferentially amplified compared to those on the upslope incropping. The perturbations to the downslope incropping develop into downslope propagating plumes which eventually evolve into relatively coherent along‐slope propagating domes. We discuss the propagation characteristics of these domes. We also simulate the evolution of density‐driven eddies or domes. The first eddy simulation we describe is for an initial eddy configuration which satisfies a zero topographic Rossby wave condition in the upper layer. We show that these traveling solutions remain remarkably coherent over a period of about 40 eddy circulation times or about 250 days for typical continental slope values. For a sufficiently large initial eddy height, upper layer fluid parcels can be transported in the along‐slope direction by the baroclinic eddy. We also simulate the evolution of an initial eddy configuration which does not satisfy a zero topographic Rossby wave condition in the upper layer. A relatively intense cyclonic circulation develops in the overlying fluid over the traveling dome as does a topographic Rossby wave tail. However, even these solutions remain surprisingly coherent over many eddy circulation times.
Coastal wind field retrievals from ERS synthetic aperture radar images
Authors: Korsbakken Erik , Johannessen J. A. , Johannessen O. M.
Published: February 2004

A unique series of European Remote Sensing Satellite (ERS) 1 and 2 C band synthetic aperture radar (SAR) images was obtained off the southern coast of Norway during the Coast Watch'95 experiment in September 1995. In this paper we carry out a systematic analysis of the mesoscale coastal wind field conditions expressed in the SAR images. Four different categories of phenomena including windrows, fetch‐limited seas, wind fronts, and oceanographic fronts are examined and discussed. The quantitative retrievals of the wind field are based on examination of both the SAR image backscatter characteristics and the spectral properties. Results are compared and validated against coincident ship and buoy data, providing complementary and independent observations of the oceanographic and meteorological conditions.
Monsoons: Processes, predictability, and the prospects for prediction
Authors: Webster P. J. , Magaña V. O. , Palmer T. N. , Shukla J. , Tomas R. A. , Yanai M. , Yasunari T.
Published: February 2004

The Tropical Ocean‐Global Atmosphere (TOGA) program sought to determine the predictability of the coupled ocean‐atmosphere system. The World Climate Research Programme's (WCRP) Global Ocean‐Atmosphere‐Land System (GOALS) program seeks to explore predictability of the global climate system through investigation of the major planetary heat sources and sinks, and interactions between them. The Asian‐Australian monsoon system, which undergoes aperiodic and high amplitude variations on intraseasonal, annual, biennial and interannual timescales is a major focus of GOALS. Empirical seasonal forecasts of the monsoon have been made with moderate success for over 100 years. More recent modeling efforts have not been successful. Even simulation of the mean structure of the Asian monsoon has proven elusive and the observed ENSO‐monsoon relationships has been difficult to replicate. Divergence in simulation skill occurs between integrations by different models or between members of ensembles of the same model. This degree of spread is surprising given the relative success of empirical forecast techniques. Two possible explanations are presented: difficulty in modeling the monsoon regions and nonlinear error growth due to regional hydrodynamical instabilities. It is argued that the reconciliation of these explanations is imperative for prediction of the monsoon to be improved. To this end, a thorough description of observed monsoon variability and the physical processes that are thought to be important is presented. Prospects of improving prediction and some strategies that may help achieve improvement are discussed.
Water mass distribution and polar front structure in the western Barents Sea
Authors: Harris C. L. , Plueddemann A. J. , Gawarkiewicz G. G.
Published: February 2004

The water mass distribution in the western Barents Sea, the thermohaline structure of the western Barents Sea Polar Front, and the local formation of a dense water mass are described on the basis of an analysis of historical hydrographic data. This study concentrated on the frontal region between Bjørnøya and Hopen Island where Arctic water is found on the Spitsbergen Bank and Atlantic water in the Bear Island Trough and Hopen Trench. The distributions of Atlantic and Arctic waters in relation to topography were consistent with the hypothesis that the location of the polar front is fixed at about the 250 m isobath by the barotropic circulation of Atlantic water within the Bear Island Trough and Hopen Trench. In winter, vertical gradients of temperature and salinity were weak throughout the frontal region, consistent with a barotropic, topographically controlled front. In summer, vertical gradients remained weak below 100 m depth but increased in the upper layer as a result of the presence of fresh, warm surface water produced by melting ice. The topographic control of thermohaline properties at the surface was disrupted by the meltwater pool, and the meltwater contributed to water mass modification in the frontal region. The following seasonal cycle of water mass formation was hypothesized: Summer heating melts the sea ice on the Spitsbergen Bank and produces the surface meltwater pool. This meltwater not only increases vertical thermohaline gradients on the bank but also crosses the front and freshens the surface layer throughout the western Barents Sea. Subsequent winter cooling, which creates ice over the bank, also forms dense water in the Bear Island Trough and Hopen Trench by convective mixing of Atlantic water and the overlying meltwater.
Observations of swash under highly dissipative conditions
Authors: Ruessink B. G. , Kleinhans M. G. , van den Beukel P. G. L.
Published: February 2004

Video measurements of swash were made at the low‐sloping beach of the multiple bar system at Terschelling, Netherlands. The majority of the measurements were conducted under highly dissipative conditions with Iribarren numbers ξ0 (the ratio of beach slope to the square root of offshore wave steepness) less than 0.2. Infragravity (0.004–0.05 Hz) waves dominated the swash with an average ratio of infragravity and total swash height Rig/R of 0.85. Using linear regression we investigated the dependence of swash parameters on environmental conditions such as short‐wave height, period, and local beach slope. On average, Rig was about 30% of the offshore wave height H0; the slope in the linear H0 dependence of Rig amounted to only 0.18, considerably smaller than that observed on steeper beaches. The data set shows evidence for saturation of the higher infragravity frequencies for ξ0 less than, roughly, 0.27. In our opinion, this saturation caused the constant of proportionality in the linear relationship between Rig/H0 and ξ0 to be significantly larger than that observed under higher Iribarren number regimes. The saturated tails of the swash spectra had an approximate f−3 roll‐off (where f is frequency), whereas, in general, the nonsaturated parts were white. This lack of significant peaks casts doubt on the causality between infragravity waves and nearshore bars.
Precise orbit determination and gravity field improvement for the ERS satellites
Authors: Scharroo Remko , Visser Pieter
Published: February 2004

The radial orbit error has long been the major error source in ERS‐1 altimetry, crippled by having only satellite laser ranging for precise tracking and relying on insufficiently accurate general‐purpose gravity field models. Altimeter crossovers are used very effectively as additional tracking data to laser ranging. The ERS Tandem Mission even provides the unique possibility to simultaneously determine orbits of two similar satellites flying the same orbit. Altimeter crossovers between the two satellites then link the two orbits into a common reference frame. Tailoring of the Joint Gravity Model 3 (JGM 3) is another step to reduce orbit errors. This technique is aimed at the reduction of the geographically anticorrelated orbit error (observed in the crossover height differences) through the adjustment of selected gravity field parameters. The resulting Delft Gravity Model (DGM)‐E04 has reduced this part of the orbit error by a factor of 2, performs even better with respect to the ESA‐provided orbits, and also outperforms the recent Earth Geopotential Model EGM96 in this respect. ERS‐1 and ERS‐2 orbits for the entire Tandem Mission are computed and studied in detail, and orbit errors due to the gravity field and nonconservative forces are identified. Analyses systematically show that the orbits computed with JGM 3 have a radial root‐mean‐square orbit accuracy of 7 cm, with DGM‐E04 5 cm.
The inertial chimney: The near‐inertial energy drainage from the ocean surface to the deep layer
Authors: Lee Dong‐Kyu , Niiler Pearn P.
Published: February 2004

A three‐dimensional primitive equation numerical model is used to study the behavior of near‐inertial waves generated by surface wind stress on an ƒ plane. The model is fixed depth with a rigid lid on the surface and is horizontally periodic. This study shows the behaviors of the wind‐generated near‐inertial waves for four different eddies: (1) a subtropical cold‐core eddy, (2) a subtropical warm‐core eddy, (3) a California subsurface warm‐core eddy, and (4) the Gulf Stream warm‐core ring. The mean secondary circulation generated by the wind‐eddy interaction has magnitude to comparable to that of the Ekman current, and its characteristics are determined by the relative angle between wind and current. The propagation characteristics of near‐inertial waves are quite different depending upon the sign of the relative vorticity. In a cyclonic eddy, near‐inertial wave propagation is outward from the core of the eddy. The propagation direction in an anticyclonic eddy is downward and toward the core. Vertically propagating waves inside the eddy are trapped above a critical layer and slowly dissipated by parameterized viscous effects. The model shows that anticyclones efficiently drain near‐inertial energy from the surface to the deep layer below the thermocline.
Sea ice motion from satellite passive microwave imagery assessed with ERS SAR and buoy motions
Authors: Kwok R. , Schweiger A. , Rothrock D. A. , Pang S. , Kottmeier C.
Published: February 2004

Observing the motion of sea ice from space is analogous to observing wind stress over the wet oceans; both provide surface forcing for modeling ocean dynamics. Ice motion also directly provides the advective component of the equations governing the mass balance of the sea ice cover. Thus its routine observation from space would be of great value to understanding ice and ocean behavior. To demonstrate the feasibility of creating a global multidecadal ice motion record from satellite passive microwave imagery and to quantitatively assess the errors in the estimated ice motions, we have tracked ice every 3 days in the Arctic Ocean and daily in the Fram Strait and Baffin Bay during the 8 winter months from October 1992 to May 1993 and daily in the Weddell Sea during the 8 winter months from March to October 1992. The method, which has been well used previously, involves finding the spatial offset that maximizes the cross correlation of the brightness temperature fields over 100‐km patches in two images separated in time by from 1 to 3 days. The resulting ice motions are compared with contemporaneous buoyand SAR‐derived ice motions. The uncertainties in the displacement vectors, between 5 and 12 km, are better than the spatial resolution of the data. Both 85‐GHz data with 12‐km spatial resolution and 37‐GHz data with 25‐km resolution are tracked. These trials with the 37‐GHz data are new and show quite surprisingly that the error is only about 1 km larger with these data than with the 12‐km 85‐GHz data. Errors are typically larger than average in areas of lower ice concentration; in the most dynamic regions, particularly near the ice edge in the Barents and Greenland Seas; and in zones of high shear. These passive microwave ice motions show a large increase in spatial detail over motion fields optimally interpolated from buoy and wind observations, especially where buoy data are virtually absent such as near coasts and in some passages between the Arctic Ocean and its peripheral seas. The feasibility of obtaining ice motion from the 37‐GHz data in addition to the 85‐GHz data should allow an important record of ice motion to be established for the duration of the scanning multichannel microwave radiometer (SMMR), special sensor microwave/imager (SSM/I), and future microwave sensors, that is, from 1978 into the next millenium.
Monitoring ice thickness in Fram Strait
Authors: Vinje Torgny , Nordlund Nina , Kvambekk Ånund
Published: February 2004

Time series of ice thickness in Fram Strait are evaluated together with ice drift for estimation of the ice flux from the Arctic Ocean. Ice draft was measured from moored sonars every 4 min, suggesting a nominal sampling interval of 30 m. On the basis of these data the annual cycle of many statistics can be resolved. The modal ice thickness shows a maximum of 3.15 m in May and a minimum in September of 2.43 m, indicating an annual variation range of 0.72 m. This compares with model results, comprehensive drillings, and most of the submarine observations during the last 2–3 decades, indicating no significant long‐term ice thickness change. This is also concurrent with the lack of significant temperature changes in the Arctic Ocean during the same period. The mean ice thickness in the central core of the ice stream shows an annual amplitude of 1 m with a minimum in September of 2.25 m and a maximum in April‐May of 3.25 m. The mean thickness of ice only (open water excluded) is 3.27 m and compares with 3.29 m which is the mean thickness of ice only from 17 submarine tracks in the Arctic Ocean 1960–1982. The mean annual ice export, which is equal to the mean annual net production of ice in the Arctic Ocean, is ∼2850 km3 yr−1 for the period 1990–1996. This efflux shows significant variations from year to year with a minimum in 1990–1991 of ∼2050 km yr−1 and a maximum in 1994–1995 of ∼4700 km3 yr−1. This significant variation of nearly 130% is mainly caused by an increased atmospheric forcing and to a lesser degree by an increase in the annual mean ice thickness of ∼20% over the same period.
Forecasting regional sea surface temperatures in the tropical Pacific by neural network models, with wind stress and sea level pressure as predictors
Authors: Tangang Fredolin T. , Hsieh William W. , Tang Benyang
Published: February 2004

We constructed two types of neural network models for forecasting the sea surface temperature anomaly (SSTA) over several standard equatorial Pacific regions (Niño 3, 3.4, 3.5, 4, P2, P4, and P5). The first type used the sea level pressure (SLP) as predictors, while the second one used the wind stress. By ensemble averaging over 20 forecasts with random initial weights, the resulting forecasts were much less noisy than those in our earlier models. The models performed best in the western‐central equatorial regions and less well in the eastern boundary regions. At longer leads of 9–12 months, the cross‐validated skills (1952–1993) for the models using the tropical Pacific SLP as predictors were statistically higher than those using the wind stress. Overall, the models using the tropical SLP showed usable cross‐validated skills up to 12‐month lead. The true out‐of‐sample forecast performances during the 1982–1993 period for the Niño 3.5 SSTA at lead times of 9, 12, and 15 months attained correlation skills of 0.78, 0.80, and 0.75, respectively.
Rain‐formed barrier layer of the western equatorial Pacific warm pool: A case study
Authors: You Yuzhu
Published: February 2004

During the intensive observation period of the Tropical Ocean ‐ Global Atmosphere / Coupled Ocean ‐ Atmosphere Response Experiment, a rain‐formed barrier layer was observed in a R/V Franklin survey. Currents measured with an acoustic Doppler current profiler were mainly southward. Winds were predominantly westerly with an average speed of 15 knots (7.5 m s−1), but they occasionally reached 25–30 knots (12.5–15 m s−1), during strong tropical storms that yielded 20–80 mm of rain. Wind mixing was active during the survey. The isothermal layer deepened from 25 to 70 m in 5 days. Sea surface water diluted by rainfall penetrated deep under wind forcing through turbulent mixing and entrainment. The diluted water was strongly stratified in salinity with a vertical salinity change of 0.1–0.15 practical salinity units, but it had a temperature change (∼0.1°C) close to that of the isothermal layer. As a result, the halocline was shallower than the thermocline and a 10‐m‐thick barrier layer existed between the two. A barrier ‐ layer is defined as the vertical distance difference between a halocline and a thermocline, in which there is very little temperature change but a large salinity change. Thus the observations suggest that tropical rainfall has a greater impact on salinity than temperature. The descending low‐salinity water is slightly warmer during daytime and slightly colder during nighttime, reflecting a link with the diurnal cycle of solar radiation. I propose a mechanism for the formation of a rain‐induced barrier layer. When the temperature in the descending dilution water has been mixed to the same level as the environmental temperature, the salinity is mixed more slowly, so that a salinity difference exists between the dilution water and environmental water. Thus more time is required to reduce this rain‐induced salinity difference compared to the temperature, which is the cause of the barrier layer. A one‐dimensional, time‐dependent, rain‐fonned, barrier layer model is thus developed through integration of a set of one‐dimensional equations of temperature, salinity, and turbulent mechanical energy. The model shows that a rain‐formed barrier ‐ layer is sensitive to many atmospheric inputs, such as evaporation minus precipitation, surface heat flux and wind forcing at the sea surface. The model proves that with both a small amount of warming but strong freshening and a small amount of cooling but strong freshening, a rain‐formed barrier layer can be produced.
Application of the adjoint of the WAM model to inverse wave modeling
Authors: Hersbach H.
Published: February 2004

In this paper the adjoint to the full WAM model, a third‐generation ocean wave model, is presented. This adjoint, ADWAM, was constructed from the WAM source code level by using an automatic adjoint code generator. As a first application, ADWAM has been used for inverse modeling with the object to get a better insight into the numerical values of several model parameters in the WAM source terms. Two adjoint runs were performed. For the first, both deep water fetch data, which were compiled by Kahma and Calkoen, and shallow water fetch data, which were obtained from Lake George by Young and Verhagen, were considered simultaneously. The second adjoint run was performed for a storm which occurred in the North Sea in February 1993. Both adjoint runs lead to a consistent trend: a reduction in the integral strengths of both the wind input and the whitecapping source terms with respect to the best estimate so far. In this best estimate, the whitecapping dissipation is proportional to the square of the wave steepness. Both runs in addition suggested that this dependency should be increased to a cubic one. It was found that the improved model performance was not only limited to the optimization windows but consistent for other intervals that were not optimized.
Deteriorating air or improving measurements? On interpreting concatenate time series
Authors: White Warren H.
Published: February 2004

Measurements reported byEldred and Cahill[1994] provide an extended record of fine‐particle sulfur concentrations at Shenandoah National Park. Begun in 1982, the measurements were upgraded in 1986 to improve time resolution and again in 1988 to improve sensitivity and particle size discrimination. Standard hypothesis rejection tests indicate a statistically significant upward trend in measured concentrations from 1982 to 1992. However, similar tests also indicate statistically significant differences between measurements made by the different methods, even when the apparent trend is accounted for. Does the trend in measured concentrations reflect increasing atmospheric concentrations, or is it an artifact of evolving measurement methods? This paper frames the question in rudimentary Bayesian terms and shows that one's interpretation of the trend is sensitive to one's prior confidence in the measurements.
Nitrogen partitioning in the middle stratosphere as observed by the Upper Atmosphere Research Satellite
Authors: Morris Gary A. , Considine D. B. , Dessler A. E. , Kawa S. R. , Kumer J. , Mergenthaler J. , Roche A. , Russell J. M.
Published: February 2004

This paper presents an analysis of odd nitrogen partitioning determined from instruments aboard the Upper Atmosphere Research Satellite (UARS). The UARS data set provides the first global maps and the best temporal coverage to date of NOx/NOy. Our analysis spans latitudes from 60°S to 60°N and altitudes between 22 and 35 km for three separate, month‐long periods between August 1992 and March 1993. These periods are characterized by substantial stratospheric aerosol loading as a result of the eruption of Mount Pinatubo in June 1991. Active odd nitrogen (NOx) is estimated from sunset measurements of NO and NO2 made by the halogen occultation experiment (HALOE). Total odd nitrogen (NOy) is the sum of NOx and correlated nighttime measurements of ClONO2 and HNO3 made by the cryogenic limb array étalon spectrometer (CLAES). Typical values of UARS NOx/NO3, during our study periods are 0.85 at 1000 K (35 km), 0.60 at 800 K (31 km), 0.25 at 650 K (26 km), and 0.10 at 550 K (22 km). Significant latitudinal gradients in nitrogen partitioning are observed in the winter hemisphere at altitudes below 1000 K, with the highest values of NOx/NOy found at midlatitudes. Comparison of the UARS NOx/NOy with predictions from a constrained version of the Goddard two‐dimensional fixed circulation model of stratospheric photochemistry demonstrates generally good agreement at the altitudes and latitudes studied. The model estimates have a slightly low bias that diminishes as the aerosol loading decreases between August 1992 and March 1993. At lower altitudes under high aerosol loading, the model does not predict the winter hemispheric, subtropical gradients of NOx/NOy seen in the UARS data. This discrepancy may be due to the lack of similar gradients in the ozone and surface area density fields which constrain the model.
Electromagnetohydrodynamic nature of tropical cyclones, hurricanes, and tornadoes
Authors: Krasilnikov Evgeny Y.
Published: February 2004

The problem of genesis and intensification of tropical cyclones, hurricanes, and tornadoes is highly important in meteorology and to date has not been solved. At the same time, practically all researches made concerning these phenomena fail to take into account that the origin and intensification of tropical cyclones, hurricanes, and tornadoes take place under conditions of an abnormally strong electric field which together with electromagnetohydrodynamic interaction occupies a key position in the intensification process. The detailed description of the electromagnetohydrodynamic model explaining the processes of energy conversion in tropical cyclones, hurricanes, and tornadoes is presented.
Systematic long‐term comparison of spectral UV measurements and UVSPEC modeling results
Authors: Mayer B. , Seckmeyer G. , Kylling A.
Published: February 2004

For the evaluation of radiative transfer models and for investigations on the influence of parameters like aerosols or clouds on ground level UV irradiance, a combination of spectral measurements and model calculations is required. We show an efficient method for such a combination and present a systematic comparison of the freely available UVSPEC radiative transfer model package with two years of spectrally resolved measurements made at Garmisch‐Partenkirchen, Germany (47.48°N, 11.07°E, 730 m above sea level) for cloudless sky and low albedo. More than 1200 spectra have been used for the comparison, covering a wide range of ozone and aerosol conditions. Applying the PSEUDO‐SPHERICAL model type, a discrete ordinate model with correction for the sphericity of the Earth, the systematic differences between measurement and model were found to range between −11 and +2% for wavelengths between 295 and 400 nm and solar zenith angles up to 80°. The small observed statistical differences of 2–3% can mostly be explained by the random error of the measurement system. Only two input parameters, total ozone column and aerosol optical depth, the latter parameterized by the Angstrom formula, are required to reach this level of agreement. It was further found that knowledge of the aerosol optical depth is essential for obtaining such a good agreement. The evaluated UVSPEC model package, together with the presented interface SDMODEL, provides an efficient tool for the investigation of the processes that control surface UV irradiance.
Long‐range transport of North African dust to the eastern United States
Authors: Perry Kevin D. , Cahill Thomas A. , Eldred Robert A. , Dutcher Dabrina D. , Gill Thomas E.
Published: February 2004

The long‐range transport of North African dust to the Middle East, Europe, South America, and the Caribbean has been well documented during the past 25 years. With the advent of routine collection and analysis of fine aerosols at national parks, monuments, and wilderness areas in the continental United States, these North African dust incursions can now be tracked, characterized, and quantified across much of the eastern half of the United States. Identification of the North African source of these dust episodes is confirmed by mass distribution measurements, a characteristic Al/Ca ratio, isentropic backward air mass trajectories, and sequential plots of the spatial distribution of the dust plumes. North African dust incursions into the continental United States persist for ∼10 days and occurred, on average, 3 times per year from 1992 to 1995. Fine soil mass usually exceeds 10 μg m−3 during these dust episodes and dominates local fine soil dust by an order of magnitude or more, even in the so‐called “dust bowl” states of the central United States. Size‐resolved measurements of elemental composition taken during July 1995 indicate that the mass mean diameter of the transported North African dust is <1 μm. The high mass scattering efficiency and abundant particle surface area associated with these submicron soil aerosols could have important consequences for both the radiative balance of the region and the chemistry of the local aerosols during summer when the long‐range transport of North African dust to the United States is most common.
An early‐autumn polar low formation over the Norwegian Sea
Authors: Nielsen N. W.
Published: February 2004

Around October 15, 1993, an unusual polar low formation took place over the Norwegian Sea. The evolution is studied by means of the HIRLAM forecasting model at the Danish Meteorological Institute, satellite imagery and observations. The investigation, to some extent based on generalized forms of the equations for omega and geopotential tendency, reveals that the disturbance forms initially by baroclinic instability along a frontal zone within a maritime polar air mass and in close proximity of an intense extratropical cyclone. During its growth to a polar low, air‐sea interaction seems to work in conjunction with the baroclinic process. A parallel forecast with the latent heat set to zero shows that heating of the atmosphere, associated with precipitation, is necessary for the polar low formation.
Improvement of the tetrachloromercurate absorption technique for measuring low atmospheric SO2 mixing ratios
Authors: Jaeschke W. , Beltz N. , Haunold W. , Krischke U.
Published: February 2004

During the Gas‐Phase Sulfur Intercomparison Experiment (GASIE) in 1994 an analytical system for measuring sulfur dioxide mixing ratios at low parts per trillion (pptv) levels was employed. It is based on the absorption of SO2 on a tetrachloromercurate(II)‐impregnated filter. The subsequent analysis uses a chemiluminescence reaction by treating the resulting disulfitomercurate(II) complex with an acidic cerium sulfate solution. An improved sampling device has been introduced that increases the maximum sampling volume from 200 L to 500 L. It is also possible to determine the blank value accurately for each sample. The absorption efficiency of the sampling system is 98.7±6.4% at a nominal flow rate of 10 L/min. The calculated (3σ) detection limit is 3±1 pptv SO2. The sample solution is stable for up to 30 days, which allows the samples to be safely stored or shipped before analysis. This permits the use of a sensitive, compact, and reliable sampling system in the field with subsequent analysis under optimal conditions in the laboratory. A continuous flow chemiluminescence (CFCL) analyzer for on‐line measurements is also presented. The system is based on the same chemical principles as the described filter technique.
Energy and water transport in climates simulated by a general circulation model that includes dynamic sea ice
Authors: Watterson I. G. , O'Farrell S. P. , Dix M. R.
Published: February 2004

We analyze energy and water transport in present, doubled CO2, and tripled CO2 climates simulated by the Mark 2 CSIRO nine‐level general circulation model with a mixed layer ocean. The model differs from the Mark 1 version by the inclusion of dynamic sea ice, a semi‐Lagrangian water vapor transport, and an enhanced land‐surface scheme, and it includes prescribed ocean heat transport. We describe a 30‐year climatology of the 1×CO2 simulation, emphasizing the sea ice and the mean meridional energy and water transport. The ice depths, concentrations, and velocities are moderately realistic in both hemispheres. Poleward energy transport is inferred (calculated indirectly from vertical energy fluxes) for both the atmosphere and ocean, although the oceanic flux is much weaker than observational estimates for the southern hemisphere. Atmospheric water transport is also poleward outside the tropics and compares well with observations. Energy transport within the ice layer has been evaluated by both direct and indirect methods. As it is largely due to the latent heat of ice formation, it is closely proportional to the water transport by ice. The meridional transports by ice of both energy and water are relatively important at high latitudes. The divergence of the ice energy transport corresponds to a significant component of the surface energy budget, reaching ±10 W m−2 or more at some polar locations. The equilibrated doubled CO2 global mean surface warming of the Mark 2 mixed layer model is 4.3°C. The reduction from the Mark 1 result (4.8°C) follows largely from a 40% reduction of the warming over high‐latitude oceans. This is attributed to the presence of dynamically induced leads in the ice cover. The equilibrated warming for 3 × CO2 is 6.8°C. The model atmosphere transports less heat poleward in the doubled CO2 climate, largely as a response to increased solar radiation absorbed at high latitudes. This behavior contrasts with the change at CO2 doubling in a transient simulation by the Mark 2 model coupled to a full ocean model, in which heat is taken up in the midlatitudes, particularly by the Southern Ocean, and supplied by a net top‐of‐atmosphere radiative imbalance distributed over all latitudes (global mean, 1.8 W m−2). The atmospheric water transport is enhanced by 10–20% in the warmer climates at most latitudes.
The long‐wavelength photochemistry of carbon disulfide
Authors: Colman Jonah J. , Trogler William C.
Published: February 2004

The photochemistry of carbon disulfide was examined over a concentration range that pertains to tropospheric conditions. At low mixing ratios (67.79, 282.4, and 485.4 parts per billion by volume (ppbv)) in air, photochemical oxidation is very slow and carbonyl sulfide (OCS) product was not observed. Upper limits were established for the quantum yield based on a practical OCS quantification limit of 10 ppbv (ΦOCS<0.0022, 0.00079, and 0.00045, respectively). Solar photolysis at a mixing ratio of 282.4 ppbv gave ΦOCS<0.00065. At mixing ratios between 13 and 223.6 parts per million by volume (ppmv), ΦOCS increases linearly with PCS2 from 0.001 to 0.01. The ΦCS2, ΦOCS, and ΦCO measured did not depend significantly on the light intensity employed, which argues against the involvement of two‐photon processes. At high PCS2 (above 3 torr) ΦCS2, ΦOCS, and ΦCO were independent Of PCS2. This behavior resembles that observed for photopolymerization of CS2 in the absence of oxygen. Carbon monoxide, observed at mixing ratios as low as 72.0 ppmv, forms by photodegradation of (CS2)x polymer that has previously photoincorporated oxygen. Photopolymerization under a nitrogen atmosphere was also first‐order in CS2 with quantum yields of 0.0027, 0.0036, and 0.0063 at 74.83, 145.1, and 297.2 ppmv, respectively. Both photopolymerization and photooxidation appear to cease below about 1 ppmv. This is the behavior expected from a bimolecular reaction involving a long‐lived excited state (CS2*′) that is necessary for particle growth. Regardless of the mechanism of photooxidation, the observed quantum yields are too small to compete with hydroxyl‐initiated oxidation of CS2 at tropospheric mixing ratios.
A parameterization of mixdown time for atmospheric chemicals
Authors: Thuburn John , Tan David G. H.
Published: February 2004

The finite spatial resolution of grid‐based numerical chemical transport models can lead to overestimation of chemical reaction rates that are in reality limited by the rate of mixing. A parameterization has been developed to compensate for this effect. It estimates the time taken to mix chemical features down from the model grid scale to the physical scale at which they really react, then builds an appropriate time lag into the chemistry by reducing the rate constant. The parameterization is shown to work in idealized tests, where it allows low‐resolution parameterized experiments to mimic the results of higher‐resolution unparameterized experiments in terms of the total reaction product. The parameterization is applied in a single‐layer chemical transport model of the winter stratosphere to the deactivation of ClOx. by reaction with NOx. It is found to have a large effect on the deactivation of ClOx. The resulting impact on the rate of catalytic destruction of O3 by ClOx is estimated to be significant.
Ozone diurnal variations observed by UARS and their model simulation
Authors: Huang Frank T. , Reber Carl A. , Austin John
Published: February 2004

Several years of ozone measurements from the Microwave Limb Sounder onboard the Upper Atmosphere Research Satellite are analyzed using a two‐dimensional Fourier series in day of year and time of day. Because of limited temporal coverage near local noon, only the diurnal and semidiurnal components are included. Data are investigated in detail at 28°N in the middle stratosphere to lower mesosphere, where the data are considered most reliable. The observations show that ozone is a maximum in the afternoon at 3 mbar and a minimum in the afternoon at 1 mbar and above with a narrow transition zone of reduced diurnal variation in between. This strong dependency on altitude in the transition from a maximum in the afternoon to a minimum in the afternoon, coupled with the small percentage changes in ozone, imposes strict requirements on the data and on the analysis of the data. Comparisons are made with results from a photochemical box model run at 11 levels between 0.46 mbar and 21.5 mbar for 28°N at spring equinox and near the solstices. This is the first time that a data analysis and model comparison of this kind has been made, leading to the identification of relatively small diurnal variations, especially in the transition zone. In the middle stratosphere the model results are in poor agreement with the observations because of the influence of stratospheric dynamics which are neglected in the model runs. In the upper stratosphere the model shows the expected underprediction of absolute ozone amounts, although the percentage change from the midnight value is in excellent agreement with the observations and in particular correctly simulates the diurnal variation in the transition zone between 3 and 1 mbar. Model sensitivity studies are performed to determine the effects of major reaction rate changes and simplified tidal effects.
Observation of an ultraslow large‐scale wave near the tropical tropopause
Authors: Hamilton Kevin
Published: February 2004

An analysis is made of very high resolution radiosonde data taken at seven western Pacific island stations during TOGA‐COARE (Tropical Ocean‐Global Atmosphere and Coupled Ocean‐Atmosphere Response Experiment). Evidence is found for a wave near the tropopause with periods ∼30–40 days and with very slow (∼3 m s−1) eastward propagation. This oscillation appears quite coherent across the region considered (a 37° longitude spread). The oscillation has a short vertical wavelength (∼3 km) and is strongly attenuated above the tropopause and thus would be very hard to observe in either satellite data or conventional meteorological analyses.
An inertial wave‐driven stratospheric horizontal electric field: New evidence
Authors: Hu Hua , Holzworth Robert H.
Published: February 2004

We report our recent measurements of horizontal electric fields from multiple stratospheric balloon platforms during the Extended Life Balloon‐Borne Observatories (ELBBO) experiment. The ELBBO project involved launches of five superpressure balloons into the stratosphere from Dunedin, New Zealand, during November and December 1992. Most of the balloons floated at a constant altitude of 26 km for over 3 months, covered a wide range of latitudes from the south pole to 281°S, and circled around the southern hemisphere several times. The electric field measurements from the ELBBO experiment have confirmed the earlier discovery of a new source of stratospheric horizontal electric fields [Holzworth, 1989], with wider latitude coverages than the original finding. This newly found horizontal electric field has an average magnitude of 10 to 20 mV/m at night and 100 to 150 mV/m in the daytime. Its field vector has a unique characteristic of counterclockwise rotation in the southern hemisphere, with the rotation period near the atmospheric inertial wave period. The horizontal scale size of this new‐source E field was found to be near 500 km, of the order of the horizontal wavelength of the inertial wave in the stratosphere. This new‐source E field is a steady background feature of the stratosphere, with local disturbance from underlying thunderstorms or other sources. At high latitude, a dawn‐to‐dusk electric field mapped down from the magnetosphere was observed at the local midnight, with a larger amplitude than that of the new‐source E field. One of the implications of the new‐source E field is that the neutral dynamic processes are strongly coupled into the electrodynamic processes in the stratosphere, making this region electrically active and not passive as previously thought by many.
Variability of the Tropical Ocean‐Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment rain rate observations
Authors: Polyak Ilya , North Gerald R. , Kucera Paul A. , Smith Neil R.
Published: February 2004

This paper presents the description of the Tropical Ocean‐Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment (TOGA COARE) rain rate database and its different spatial and temporal variability characteristics. Accuracy and reliability of this database are evaluated with the position of the appropriateness of its use for the practical (ground truth, beam filling error for the Tropical Rainfall Measuring Mission) and theoretical (spectral estimation) problems. The following is shown in this paper: the concentration of a significant power in the origin of the frequency axis in the temporal spectra; the existence of a diurnal cycle (which has a range of variation of about 1.43 to 2.03 mm/h); the distinction between the north‐south and east‐west transport of rain, reflected in the two‐dimensional spectrum and correlation function of the spatial field, and character of its anisotropy; the scales of the differences between the corresponding estimates of the TOGA and Global Atmospheric Research Program (GARP) Atlantic Tropical Experiment (GATE) data. The documentation of the TOGA COARE database is given. Methodology and software (in IDL and Fortran languages) for management of the TOGA COARE database system and for estimating of different variability statistics were developed. The results obtained can be used for choosing any subset appropriate for the particular rain analysis study, for rain modeling, for comparison with corresponding estimates of other sources of data (satellite or simulated by physical models), and for solving some other scientific and engineering problems connected with rain measurements and modeling.
Daily variations in TOMS total ozone data
Authors: Allen D. R. , Reck R. A.
Published: February 2004

The spatial and seasonal distributions of daily fluctuations in total ozone from 60°N to 60°S are analyzed by using 14.5 years of total ozone mapping spectrometer (TOMS) data on a 5° latitude by 15° longitude grid. Root mean square day to day differences maximize near 30 Dobson units (DU) in the midlatitudes of both hemispheres from late fall to early spring. The contributions of these fluctuations due to planetary‐ and medium‐scale waves are analyzed using sinusoidal zonal wave filtering. Daily midlatitude variations from planetary‐scale waves are smaller than those from medium‐scale waves and mainly occur from late fall to early spring, while strong medium‐scale variations persist throughout fall, winter, and spring. An exception is the southern hemisphere high latitudes, where contortions and breakup of the polar vortex cause large daily variations on planetary scales during September and October. Tropical total ozone fluctuations due to planetary‐scale waves are slightly larger than those due to medium‐scale waves in all seasons. A climatological table of monthly RMS day to day total ozone changes is provided as a reference.