bluuebunny/crossref_metadata_2025 huggingface dataset:
Particulate matter and phytoplankton and bacterial biomass distributions in the Northeast Water Polynya during summer 1992
Authors: Smith Walker O. , Walsh Ian D. , Booth B. C. , Deming J. W.
Published: February 2004

The patterns of particulate matter distribution (chlorophyll, phytoplankton pigmentation, biogenic silica, particulate carbon, and nitrogen, bacterial and phytoplankton abundance, and optical particle concentration) in the Northeast Water Polynya off the northern coast of Greenland are described, and their relationships to environmental conditions (hydrography, nutrients, and ice cover) are analyzed. Particulate matter concentrations were substantial in the euphotic zone, with the largest fraction consisting of phytoplankton material. Most of this phytoplanktonic material was diatomaceous during the study period (late summer). Surface chlorophyll concentrations were inversely correlated with nitrate concentrations, which were often undetectable in the surface layer, suggesting that phytoplankton standing stocks were controlled by nitrogen availability. The particulate carbon to particulate nitrogen ratio was unusual, in that elevated (approximately nine by weight) mean values were observed near the surface and reduced values (near 6 by weight) occurred at the base of the euphotic zone. These elevated C/N ratios apparently resulted from adaptation to low nutrient conditions. Other elemental ratios (particulate carbon to chlorophyll, biogenic silica to particulate carbon) appear similar to other Arctic systems. Bacterial numbers were greatest in waters with intermediate ice concentrations but in all cases contributed a small fraction (approximately 3%) of organic carbon in the particulate pool. Though variable in spatial distribution, the polynya was a source of substantial quantities of particles; resolving the fate of this material requires further analysis of these data in conjunction with rate measurements and coupled physical‐biological models.
Simulations of the mesoscale circulation of the Greenland‐Iceland‐Norwegian Seas
Authors: Heburn George W. , Johnson Clifford D.
Published: February 2004

The Greenland, Iceland, and Norwegian Seas provide the only link between the North Atlantic and the Arctic Oceans. This is a very dynamic region, rich in mesoscale variability. A two‐layer, hydrodynamic version of the Navy layered ocean model is used to simulate the mesoscale frontal features and associated current systems. The model is wind‐driven using monthly mean wind stresses and inflow/outflow mass flux from the Arctic and North Atlantic Oceans. The current transports from the model results compare favorably with transport measurements from a number of observational experiments.
Higher‐order spectral analysis of nonlinear ocean surface gravity waves
Authors: Elgar Steve , Herbers T. H. C. , Chandran Vinod , Guza R. T.
Published: February 2004

Bispectral and trispectral analyses are used to detect secondary and tertiary wave components resulting from nonlinear interactions among large‐amplitude ocean surface gravity waves in 8‐ and 13‐m water depths. Bispectra of bottom‐pressure measurements indicate forced secondary waves at frequencies 2ƒp about twice the primary power spectral peak frequency ƒp. However, the interpretation of the bispectrum at sum frequencies of approximately 3ƒp is ambiguous because contributions of both secondary and tertiary forced waves may be significant. Trispectral analysis confirms the presence of tertiary waves with frequency approximately 3ƒp. In 8 m depth the tertiary bottom‐pressure field is dominated by interactions between three colinearly propagating wind‐wave components with frequencies close to ƒp. In 13 m depth these relatively short‐wavelength forced waves are strongly attenuated at the seafloor and the tertiary wave field is driven by interactions between the dominant waves at ƒp and obliquely propagating higher‐frequency wind waves. The phases of the higher‐order spectra are consistent with weakly nonlinear wave theory (Hasselmann, 1962).
The source of 90‐day oscillations at Wake Island
Authors: Mitchum Gary T.
Published: February 2004

Energetic 90‐day oscillations of sea level have been intermittently observed at Wake Island in the western tropical Pacific during the past 2 decades. The oscillations tend to occur about 1.5 years after El Niño‐Southern Oscillation events, to have amplitudes of 10–15 cm, and to persist for about 1 year. Sea surface heights from the Geosat altimeter are used to establish that these signals take the form of Rossby waves and have an energy source near the Big Island of Hawaii, which lies 40° of longitude to the east. Sea level and upper layer currents from an eddy‐resolving numerical model are examined and suggest that the energy source is eddies generated off the Big Island of Hawaii. These eddies appear to be associated with westward currents that intermittently impinge on the island. Several alternate hypotheses are also discussed and rejected.
An approximate Kaiman filter for ocean data assimilation: An example with an idealized Gulf Stream model
Authors: Fukumori Ichiro , Malanotte‐Rizzoli Paola
Published: February 2004

A practical method of data assimilation for use with large, nonlinear, ocean general circulation models is explored. A Kaiman filter based on approximations of the state error covariance matrix is presented, employing a reduction of the effective model dimension, the error's asymptotic steady state limit, and a time‐invariant linearization of the dynamic model for the error integration. The approximations lead to dramatic computational savings in applying estimation theory to large complex systems. We examine the utility of the approximate filter in assimilating different measurement types using a twin experiment of an idealized Gulf Stream. A nonlinear primitive equation model of an unstable east‐west jet is studied with a state dimension exceeding 170,000 elements. Assimilation of various pseudomeasurements are examined, including velocity, density, and volume transport at localized arrays and realistic distributions of satellite altimetry and acoustic tomography observations. Results are compared in terms of their effects on the accuracies of the estimation. The approximate filter is shown to outperform an empirical nudging scheme used in a previous study. The examples demonstrate that useful approximate estimation errors can be computed in a practical manner for general circulation models.
Energetics of a naturally occurring shear instability
Authors: Seim Harvey E. , Gregg Michael C.
Published: February 2004

Using observations of an energetic shear instability (Seim and Gregg, 1994), we examine the energy budget of the mixing event by comparing microstructure measurements of the dissipation rates of turbulent kinetic energy ε and turbulent potential energy χpe with changes in fine‐scale velocity and density. Two sets of observations are used. The first set sampled the shear instability early in its evolution, when overturns occurred in strong stratification. The second set of observations found the same water vertically homogenized by turbulent mixing. In a frame of reference moving with the billows we solve a set of time‐dependent energy equations to estimate the buoyancy flux Jb, turbulent production P, and strength of nonlocal forcing in the mean kinetic and mean potential energy budgets. The turbulent energy equations are approximately steady when evaluated for several buoyancy periods, simplifying to local balances. We find Jb ≈ χpe/2 ≈ −5.5×10−7 W kg−1 and P ≈ ε − Jb ≈ 2.4×10−6 W kg−1 to within a factor of 2. The decrease in mean kinetic energy is approximately locally balanced by P, but unlike the kinetic energy, only 25% of the increase in mean potential energy is explained by Jb. This implies no net radiation of energy into the surrounding stratified fluid, but the large uncertainties in Jb and P make this result tenuous. We find the flux Richardson, Rƒ = Jb/P ≈ 0.22±0.1; that is, one quarter of the turbulent energy released by the instability goes toward increasing the mean potential energy of the water column. The billows generated an average momentum flux of 0.22 Pa for more than an hour, and peak values exceeded 1.5 Pa. The average value is comparable to maximum momentum flux values in boundary layers over ice and under ice.
On the performance of a mixed‐layer model based on the κ‐ε turbulence closure
Authors: Burchard Hans , Baumert Helmut
Published: February 2004

This paper investigates the interaction between stratification and turbulence by means of turbulence models. The standard and the advanced turbulent kinetic energy ‐ dissipation (κ‐ε) model are derived theoretically, including algebraic stress relations. It is shown that a certain empirical constant in the standard model turns out to be a complicated implicit function in the advanced model, namely, a function of the turbulent shear number, the turbulent buoyancy number, and a wall correction. For a better understanding and physical interpretation of the κ‐ε models, an analysis is carried out for a simplified case where diffusive fluxes are neglected. For this idealization it is shown that (1) the flux Richardson numberRfhas a certain lower boundRƒ−due to the establishment of convection, (2) a steady state flux Richardson numberRƒst(which is defined here for this purpose) labels the borderline between the tendency of turbulence to decrease or collapse (Rƒ>Rƒst) or to increase (Rƒ<Rƒst), and (3) the well‐known upper limit for turbulent shear flow,Rƒ+≈ 0.25, fits our theory. Using the standard model, the advanced model, a modified version of the level‐2 model of Mellor and Yamada and a modified version of Kochergin's model, the evolution of thermal stratification in the northern North Sea during the Fladen Ground Experiment (FLEX'76) is simulated numerically and compared with the measurements. In this specific application, the two κ‐ε models performed best.
System of numeric models for sand particle transport by wind
Authors: Li Long , Martz Lawrence W.
Published: February 2004

A system of experimental and mathematical models was developed from data on grain particle transport, collected from a series of experiments in a large‐scale wind tunnel, and from mathematical principles. The experimental model was derived from a FORTRAN program using the observed data. As a first attempt, it took into account the role played by the following factors in grain particle transport: the grain‐size distribution, the mean diameter of the particle size class, die mean diameter of the effective surface particles, the surface mobility, friction velocity, and threshold velocity. The comparison between the observed and the predicted results indicated that the experimental model was able to predict the transport rate of grain particles in different size classes over time with good reliability. The mathematical models used in conjunction with the experimental model could be employed to calculate the variation of the mean grain size, the grain‐size distribution, the approximate fluid threshold velocity, and the accumulated erosion of the particle surface over time. The experimental model should be applied with caution to natural conditions because of the assumption of a dry, loose, and large‐roughness‐free surface and aerodynamically dominant fluid. The mathematical models, except for fluid threshold velocity, were accurate, given a precise transport rate of grain particles in different size classes over time.
Examination of tracer transport in the NCAR CCM2 by comparison of CFCl3 simulations with ALE/GAGE observations
Authors: Hartley Dana E. , Williamson David L. , Rasch Philip J. , Prinn Ronald G.
Published: February 2004

The latest version of the National Center for Atmospheric Research community climate model (CCM2) contains a semi‐Lagrangian tracer transport scheme for the purpose of advecting water vapor and for including chemistry in the climate model. One way to diagnose the CCM2 transport is to simulate CFCl3 in the CCM2 since it has a well‐known industry‐based source distribution and a photochemical sink and to compare the model results to Atmospheric Lifetime Experiment/Global Atmospheric Gases Experiment observations around the globe. In this paper we focus on this comparison and discuss the synoptic scale issues of tracer transport where appropriate. We compare the model and observations on both 12‐hour and monthly timescales. The higher‐frequency events allow us to diagnose the synoptic scale transport in the CCM2 associated with the observational sites and to determine uncertainties in our high‐resolution source distribution. We find that the CCM2 does simulate many of the key features such as pollution events and some seasonal transports, but there are still some dynamical features of tracer transport such as the storm track dynamics and cross‐equatorial flow that merit further study in both the model and the real atmosphere.
Thundercloud electric field modeling for the ionosphere‐Earth region: 1. Dependence on cloud charge distribution
Authors: Velinov Peter I. Y. , Tonev Peter T.
Published: February 2004

The transmission of DC electric fields by thunderclouds with charge distributions is investigated analytically for the region between the ionosphere and the Earth surface. In such a way the hitherto existing presentations of thunderclouds by electric charge centers (monopole presentation) are generalized to much more adequate three‐dimensional model charge regions. A modified ellipsoidal Gaussian profile for the charge distribution of the electrified cloud is accepted. The electrical conductivities are approximated by piecewise exponential functions of altitude. An assumption is made that the geomagnetic field lines in the lower and middle atmosphere are straight and vertical. Analytical solutions to Maxwell equations for the electric potential U and field E are obtained. The effect of the spatial distribution of the charge on E is investigated. The variations of the electric fields at the ionospheric and surface levels, which are caused by different charge distributions, horizontal sizes, and heights of the electrified clouds, are analyzed.
High‐resolution absorption cross sections of chlorine nitrate in the ν2 band region around 1292 cm−1 at stratospheric temperatures
Authors: Orphal Johannes , Morillon‐Chapey Mireille , Guelachvili Guy
Published: February 2004

The infrared absorption spectrum of ClONO2 has been recorded between 500 and 1600 cm−1 at temperatures between 188 K and 222 K and resolutions of up to 0.004 cm−1. The infrared absorption cross sections were determined for the entire ν2 band between 1260 and 1320 cm−1. The cross sections (with 0.025 cm−1 resolution) for the central Q branch absorption maximum at 1292.68 cm−1 are (in 10−18 cm2 molecule−1) 3.12±0.06 at 201 K, 3.45±0.15 at 211 K, and 3.31±0.06 at 222 K. The influence of resolution on the cross section of the Q branch maximum is small only for resolutions between 0.025 and 0.100 cm−1. In the P and R branches, the cross sections change considerably with increasing resolution. The new absorption cross sections are important for the determination of stratospheric ClONO2 concentrations from atmospheric infrared absorption spectra and for modeling atmospheric transmission in the spectral region around 1292 cm−1.
Transport distance of ammonia and ammonium in Northern Europe: 1. Model description
Authors: Hov Øystein , Hjøllo Bjørn Aage , Eliassen Anton
Published: February 2004

A Lagrangian model for the emission, transport, transformation, and deposition of NH3 and species derived from NH3 emissions is described. This model also involves SO2 and NOx, since the chemistries of NH3, NOx, and SO2 are interlinked. The model is evaluated by comparing it with measurements of sulfur and nitrogen compounds in air and precipitation during an intensive 3‐month period in August–October 1985 at six Scandinavian European Monitoring and Evaluation Programme sites. The concentrations of NO2 are underestimated at all sites except one, and they almost follow the curve for a 1:2 ratio when they are compared to the measured values. This is a consistent feature which is not strongly linked to meteorological variability or emission changes but rather is caused by the chemical formulation of the model and its physical assumptions. For nitrate aerosol there is a systematic overestimation in the model, while for the sum of ammonia and ammonium aerosol the observed average concentration is twice the calculated one, with particularly large discrepancies where there are local ammonia sources. The average of all observations of SO2 is matched by the calculations, but the regression line has a wrong slope and a nonzero intercept. For sulfate aerosol the calculations give concentrations which are about 50% of the measured values, while for nitrate, ammonium, and sulfate in precipitation, the correlations between observations and calculated values are lower than those for the airborne species. This difference arises in part from the differences between precipitation in the model and as measured at the sites.
Statistics on artificially triggered lightning
Authors: Depasse P.
Published: February 2004

The Faculté Polytechnique of Mons has participated in the last three programs of artificially triggered lightning in Saint‐Privat d'Allier, France (1986, 1990, and 1991). Measurements of the vertical part of the electric field E and electric field derivative (dE/dt) only 50 m from the discharge were made in 1990 and 1991. Our data, combined with those of the Centre National d'Etudes des Télécommunications, the Centre d'Etudes Nucléaires de Grenoble, and the Ecole Centrale de Lyon, lead us to a statistical study of the electrical parameters obtained from artificially triggered discharges in Saint‐Privat d'Allier. We define the statistical distributions of these electrical parameter populations and establish some relations between them. We compare artificially triggered lightning with natural lightning and conclude that the triggered lightning strokes are very similar to the subsequent strokes of natural lightning. We also compare the Saint‐Privat d'Allier triggered lightning with the Kennedy Space Center (Florida) triggered lightning. The Kennedy Space Center is at sea level and has a high ground conductivity, while Saint‐Privat d'Allier is a mountainous country with strong resistivity. Main results are, for the current, 50% of triggered strokes are higher than 12.1 kA in Florida (statistics of 305 strokes) and 9.8 kA in Saint‐Privat d'Allier (54 strokes); for dl/dt, 50% of triggered strokes have a dl/dt higher than 91.4 kA/μs in Florida (134 strokes) and 36.8 kA/μs in Saint‐Privat d'Allier (47 strokes); 5% of the strokes have a dI/dt higher than 297.7 kA/μs in Florida. The best relation (best correlation coefficient) between dI/dt (kA/μs) and I (kA) is dI/dt = 2.6 I1.34 in Florida (134 strokes) and dI/dt = 2.0 I1.28 in Saint‐Privat d'Allier (47 strokes).
Transport of exhaust products in the near trail of a jet engine under atmospheric conditions
Authors: Kärcher B.
Published: February 2004

The transport of exhaust effluents and the possibility of water ice contrail formation are investigated under the specific fluid dynamical conditions in the near exhaust trail of a subsonic jet aircraft at cruise altitude. By means of a computational model describing the two‐dimensional turbulent mixing of a single jet of hot exhaust gas with the atmosphere, representative results are discussed on the temperature and saturation ratio evolutions of air parcels in the jet flow field as well as on radial distributions of exhaust effluents undergoing chemical reactions behind the nozzle exit with prescribed, typical net reaction rates. The results underline the importance of a simultaneous treatment of spatially resolved jet expansion together with microphysical and chemical processes, because this coupling leads to distinct concentration patterns for various classes of chemical reactants and is essential for the detailed prediction of contrails.
Global precipitation estimations using Defense Meteorological Satellite Program F10 and F11 special sensor microwave imager data
Authors: Weng Fuzhong , Ferraro Ralph R. , Grody Norman C.
Published: February 2004

F10 and F11 satellites from the Defense Meteorological Satellite Program currently observe the earth‐atmosphere system four times a day, at 0530, 1030, 1730, and 2230 local solar time. This study uses the special sensor microwave imager data from both satellites to retrieve precipitation over land and ocean and presents some preliminary results of the spatial and temporal variations of rainfall during a month. Diurnal variations of precipitation over the globe are analyzed for August 1993 using measurements from both satellites. Over most oceans, precipitation displays the well‐known morning maximum. However, over land, precipitation is highly variable for the study period. Error analyses indicate that over ocean the monthly precipitation estimates from the F11 satellite alone may result in 20–25% errors due to insufficient temporal sampling. This error increases over some land regions to as much as 50–70%. This study also analyses the difference between the monthly rainfall estimates using a sample‐averaging method and that using a lognormal probability density function. It is found that an overall difference over the globe is small with less than 5%.
Kinetics of reactions of ground state nitrogen atoms (4S3/2) with NO and NO2
Authors: Wennberg Paul O. , Anderson James G. , Weisenstein Debra K.
Published: February 2004

The discharge flow technique has been used with resonance fluorescence detection of N atoms to study the fast radical‐radical reaction of ground state nitrogen atoms (4S3/2) with NO and NO2. The rate constants obtained are (in units of cm3 molecule−1 s−1) k1 = (2.2±0.2) × 10−11exp[(160±50)/T] in the temperature range 213 K ≤ T ≤ 369 K for N + NO → N2 + O and k2 = (5.8±0.5) × 10−12 exp [(220±50)/T] in the temperature range 223 K ≤ T ≤ 366 K for N + NO2 → N2O + O. The reported error limits are at the 95% confidence level. The reaction kinetics are consistent with other radical‐radical reactions, essentially no enthalpic barrier is observed. Substitution of the measured rate of R1 for the value recommended hi the latest Jet Propulsion Laboratory compendium [DeMore et al., 1992] results in a small change in the concentration of ozone predicted in a two‐dimensional photochemical model. Modeled ozone concentrations are higher (approximately 1%) in the high‐latitude upper stratosphere as a result of a 3–10% reduction in the calculated concentrations of NOy.
An assessment of satellite temperature distributions used to derive the net diabatic transport for zonally averaged models of the middle atmosphere
Authors: Remsberg Ellis E. , Bhatt Praful P. , Miles Thomas
Published: February 2004

Determinations of the zonally averaged and diabatically derived residual mean circulation (RMC) are particularly sensitive to the assumed zonal mean temperature distribution used as input. Several different middle atmosphere satellite temperature distributions have been employed in models and are compared here: a 4‐year (late 1978 to early 1982) National Meteorological Center (NMC) climatology, the Barnett and Corney (or BC) climatology, and the 7 months of Nimbus 7 limb infrared monitor of the stratosphere (LIMS) temperatures. All three climatologies are generally accurate below the 10 hPa level, but there are systematic differences between them of up to ±5 K in the upper stratosphere and lower mesosphere. The NMC/LIMS differences are evaluated using time series of rocketsonde and reconstructed satellite temperatures at station locations. Much of those biases can be explained by the differing vertical resolutions for the satellite‐derived temperatures; the time series of reconstructed LIMS profiles have higher resolution and are more accurate. Because the LIMS temperatures are limited to just two full seasons, one cannot obtain monthly RMCs from them for an annual model calculation. Two alternate monthly climatologies are examined briefly: the 4‐year Nimbus 7 stratospheric and mesospheric sounder (SAMS) temperatures and for the mesosphere the distribution from the Solar Mesosphere Explorer (SME), both of which are limb viewers of medium vertical resolution. There are also differences of the order of ±5 K for those data sets. It is concluded that a major source of error in the determination of diabatic RMCs is a persistent pattern of temperature bias whose characteristics vary according to the vertical resolution of each individual climatology.
Interannual variability over the eastern North Atlantic Ocean: Chemical and meteorological evidence for tropical influence on regional‐scale transport in the extratropics
Authors: Doddridge Bruce G. , Dirmeyer Paul A. , Merrill John T. , Oltmans Samuel J. , Dickerson Russell R.
Published: February 2004

Observed boreal fall season (September–November) 1991 surface CO data from Mace Head, Ireland, are characterized by particularly high mixing ratios, as evidenced by high means, medians, and maxima for those months, relative to the same dato for boreal fall 1992. Air parcels characterized by elevated CO during fall 1991 are attributed to European sources on the basis of isentropic back trajectory analysis. A histogram of the 1991 data shows a bimodal distribution representing two discrete source regions, North Atlantic and European, while the 1992 data show only one mode, representing primarily zonal westerly flow over the North Atlantic Ocean. A similar distinction exists in O3 data between the two years. Considerable interannual variability has important implications for observationalists and modelers alike; an inherent uncertainty is introduced by basing any determination of trend from only a few years of data. An isentropic flow climatology for Mace Head illustrates significant differences in the regional‐scale flow patterns to Mace Head between the 1991 and the 1992 fall seasons. These differences have been examined in terms of general dynamical principles and tropical/extratropical coupling. There is evidence of the existence of Rossby wave links with the tropical upper troposphere over South America and the central Pacific Ocean which are responsible for the climatic forcing giving rise to the observed interannual variation in large‐scale flow patterns and influencing the chemical character of air parcels reaching Mace Head. Using CO as a tracer for short‐lived continental anthropogenic O3 precursors and calculating ΔO3/ΔCO for air parcel trajectories following anticyclonic paths over western Europe during the late summer and fall season of 1991, we estimate O3 production over western Europe at about 66 (40–96) billion moles of O3 per summer (∼3 Tg O3 per summer), based on 1985 CO emission inventory dam (37 Tg CO yr−1 for western Europe).
Quasi‐biennial oscillation and tropical waves in total ozone
Authors: Ziemke J. R. , Stanford J. L.
Published: February 2004

Westward and eastward propagating tropical waves in total ozone are investigated in 13 years (1979–1991) of version 6 total column ozone data from the Nimbus 7 total ozone mapping spectrometer (TOMS) satellite instrument. A clear synchronization between the stratospheric quasi‐biennial oscillation (QBO) zonal winds and the fast (periods < 15 days) propagating waves in tropical TOMS data is detailed. Largest total ozone wave amplitudes (∼3–6 Dobson units) occur when their phase propagation direction is primarily opposite the Singapore QBO lower‐stratospheric winds. This effect is most apparent in meridionally symmetric components. Examination of specific episodes, including cross‐spectral calculations with Singapore rawinsonde wind data (10–70 hPa), reveals signatures of tropically confined eastward propagating Kelvin waves of zonal wavenumbers 1–2 during the descending eastward QBO phase, consistent with acceleration of that QBO phase by Kelvin waves. The TOMS results are also consistent with possible forcing of the westward QBO wind phase by episodes of both meridionally symmetric and asymmetric westward waves (W' events in the text). However, in contrast to the case of eastward (Kelvin) waves the strongest westward events (W events in the text) appear to be filtered by, rather than forcing, the westward phase of the stratospheric QBO wind. These dominant westward episodes are interpreted as meridionally symmetric westward global normal modes and tropically confined equatorial‐Rossby waves 2–6. The events exhibit phase and group speeds characteristic of wave dynamics rather than simple wind advection. These results underscore the utility of the long time series and excellent horizontal coverage of TOMS data for dynamical investigations in the relatively observation‐poor tropical stratosphere.
System for locating the sources of wideband dE/dt from lightning
Authors: Thomson E. M. , Medelius P. J. , Davis S.
Published: February 2004

A system has been developed to measure wideband electric field derivatives (dE/dt) at five ground stations in a 15 km × 15 km network at Kennedy Space Center. Individual station responses are normalized using digital filters. Pulse‐timing resolution is improved to much less than the 50‐ns sample interval by interpolation using packing in the frequency domain. A time tag for each pulse is defined as the mean of the times of the rising‐edge half peak, peak, and falling‐edge half peak. The standard deviation in these times defines the timing error and is shown to be a function of noise and bandwidth rather than digitization rate. Each of the four unknowns for a pulse source location (x,y,z) and time of occurrence (t) is found from the five time‐tag measurements using different weightings for all five combinations of the four‐station hyperbolic equations. Weighting factors and errors in x,y,z and t are estimated using error propagation techniques.
Daily surface wind variations over the equatorial Pacific Ocean
Authors: Deser Clara
Published: February 2004

Daily surface wind variations over the equatorial eastern Pacific Ocean during summer 1992 are documented, using hourly observations from the tropical atmosphere ocean moored buoy array. Diurnal and semidiurnal variations are apparent in the zonal wind component, with peak‐to‐peak amplitudes of a few tenths of a meter per second. The phase of the semidiurnal cycle in zonal wind is approximately uniform across the equatorial eastern Pacific Ocean, with westerly wind maxima at ∼0300 and 1500 LT. The diurnal cycle dominates the daily march of meridional wind. The range of the diurnal meridional wind variations is ∼0.6–0.8 ms−1 at most locations: more than twice as large as the daily zonal wind changes. The low‐level flow is southward across the equator at night (relative to the daily mean), regardless of whether the mean winds are southerly or northerly. The diurnal meridional wind variations along the equator may be related to the diurnal cycle of deep convection in the Intertropical Convergence Zone (ITCZ) to the north. In particular, surface wind divergence along the equator (which is dominated by the meridional component) exhibits a pronounced diurnal cycle, with the strongest divergence in the early morning when deep convection in the ITCZ is at a maximum. The average daily range of the equatorial surface wind divergence is 1.5×10−6 s−1, or ∼30% of the daily mean. The semidiurnal zonal wind variations are dynamically consistent with the well‐known semidiurnal cycle in surface pressure, which is thought to be a manifestation of the atmospheric thermal tide.
Electrochemical concentration cell ozonesonde performance evaluation during STOIC 1989
Authors: Komhyr W. D. , Barnes R. A. , Brothers G. B. , Lathrop J. A. , Opperman D. P.
Published: February 2004

Electrochemical concentration cell (ECC) ozonesondes flown by NOAA and NASA Wallops Flight Facility (WFF) personnel during the Stratospheric Ozone Intercomparison Campaign (STOIC) conducted at the Jet Propulsion Laboratory's Table Mountain Facility, Wrightwood, California, July 21 to August 1, 1989, exhibited highly similar ozone measurement precisions and accuracies even though considerably different methods were used by the two research groups in preparing the instruments for use and in calibrating the instruments. The Table Mountain data as well as data obtained in the past showed the precisions to range from about ±3 to ±12% in the troposphere, remain relatively constant at ±3% in the stratosphere to 10 mbar, then decrease to about ±10% at 4‐mbar pressure altitude. Corresponding ozone measurement accuracies for individual ozonesonde soundings were estimated to be about ±6% near the ground, decrease to −7 to 17% in the high troposphere where ozone concentrations are low, increase to about ±5% in the low stratosphere and remain so to an altitude of about 10 mbar (∼32 km), then decrease to −14 to 6% at 4 mbar (∼38 km) where ozone concentrations are again low. Stratospheric ozone measurements were also made during STOIC with ground‐based lidars and a microwave radiometer that will be used for ozone measurements in the future at sites of the Network for the Detection of Stratospheric Change (NDSC). The ECC ozonesonde observations provided useful comparison data for evaluating the performance of the lidar and microwave instruments.
Fast yet accurate net flux calculation for realistic atmospheres with variable aerosol loadings
Authors: Trautmann T. , Box M. A.
Published: February 2004

Using a perturbation approach computational results have been obtained for the net radiative flux at selected wavelengths in realistic aerosol atmospheres. A simple interpolation scheme is presented that employs three base model computations and allows one to obtain quasi‐exact flux results from precomputed perturbation data in a highly efficient manner. It is shown how the adjoint transfer equation can be employed to probe the atmosphere for certain radiative effects, i.e., in the present case for the net radiative flux as a function of height. Results for three different aerosol profiles were obtained and compared with exact calculations. Contour plots showing the relative error of the net flux underline that, over a wide range of aerosol perturbations (compare 0.1 ≲ τc≲ 0.4 for continental‐type aerosols) and for all solar zenith angles, perturbation theory produces relative errors below ±0.25%. Compared to commonly used two‐stream approximations, the perturbation approach not only offers the possibility to obtain the required model parameters off‐line, that is, in a precomputed manner, but also enables one to study radiative effects for thin and moderately thick optical media in the sense of a functional sensitivity approach. Thus it can clearly be concluded that the methodological approach as presented in this study is superior to the commonly employed two‐stream approximations for radiative transfer computations and in the future may be exploited to overcome the shortcomings of flux models.
Calibration and postlaunch performance of the Meteor 3/TOMS instrument
Authors: Jaross G. , Krueger A. , Cebula R. P. , Seftor C. , Hartmann U. , Haring R. , Burchfield D.
Published: February 2004

Prelaunch and postlaunch calibration results for the Meteor 3/TOMS instrument are presented here. The instrument, launched aboard a Russian spacecraft in 1991, is the second in a series of total ozone mapping spectrometer (TOMS) instruments designed to provide daily global mapping of ozone overburden. Ozone amounts are retrieved from measurements of Earth albedo in the 312‐ to 380‐nm range. The accuracy of albedo measurements is primarily tied to knowledge of the reflective properties of diffusers used in the calibrations and to the instrument's wavelength selection. These and other important prelaunch calibrations are presented. Their estimated accuracies are within the bounds necessary to determine column ozone to better than 1%. However, postlaunch validation results indicate some prelaunch calibration uncertainties may be larger than originally estimated. Instrument calibrations have been maintained postlaunch to within a corresponding 1% error in retrieved ozone. Onboard calibrations, including wavelength monitoring and a three‐diffuser solar measurement system, are described and specific results are presented. Other issues, such as the effects of orbital precession on calibration and recent chopper wheel malfunctions, are also discussed.
Lidar measurements of stratospheric temperature during STOIC
Authors: Ferrare R. A. , McGee T. J. , Whiteman D. , Burris J. , Owens M. , Butler J. , Barnes R. A. , Schmidlin F. , Komhyr W. , Wang P. H. , McCormick M. P. , Miller A. J.
Published: February 2004

Measurements of stratospheric temperature and density were acquired by the NASA/GSFC lidar during the Stratospheric Ozone Intercomparison Campaign (STOIC) experiment at the Jet Propulsion Laboratory Table Mountain Facility (TMF) (34.4°N, 117.7°W) in July and August 1989. Lidar temperatures, obtained on 21 nights preceding and during this experiment, are compared with temperatures derived by radiosondes, datasondes, Stratospheric Aerosol and Gas Experiment (SAGE II) satellite experiment, and National Meteorological Center (NMC) analyses. Radiosondes were flown from the TMF site as well as from San Nicholas Island (33.2°N, 119.5°W) located about 225 km southwest of TMF. Datasondes were deployed from Super‐Loki rockets also launched at San Nicholas Island. SAGE II satellite temperature measurements were made within 1000 km of the Table Mountain site. NMC temperature analyses derived from the NOAA satellite measurements were interpolated to coincide in space and time with the lidar measurements. The lidar temperatures, which were derived for altitudes between 30 and 65 km, were within 2–3 K of the temperatures measured by the other sensors in the altitude range 30–45 km. Between 30 and 35 km, lidar temperatures were about 2 K cooler than those obtained from the datasondes and the NMC analyses but were about 1–2 K warmer than those obtained from the radiosonde. These differences may be due to the time difference between the measurements as well as possible nonnegligible aerosol scattering near 30 km. Near and above the stratopause the temperature differences increased to 3–8 K. Lidar temperature profiles also show small‐scale variations possibly caused by wave activity.
Evaluation of the effects of Mount Pinatubo aerosol on differential absorption lidar measurements of stratospheric ozone
Authors: Steinbrecht W. , Carswell A. I.
Published: February 2004

Substantially increased aerosol backscattering and extinction after a major volcanic eruption can lead to errors in differential absorption lidar (DIAL) measurements of stratospheric ozone. Mie calculations, performed for the wavelengths 308 and 353 nm and based on size distributions measured over Laramie, Wyoming (41°), were used to assess size and temporal evolution of these errors. In many situations, neglecting the different aerosol backscattering at the absorption and reference wavelengths can lead to relative errors in the ozone concentration larger than 100% for the 308‐, 353‐nm pair. The error due to neglecting the differential aerosol extinction, however, will rarely exceed 2%. A correction for this differential extinction should only be attempted when high concentrations (>100 cm−3) of small aerosol particles with radii below 0.1 μm are present, e.g., shortly after an eruption. A correction for the differential backscatter can be made by using additional lidar measurements at a second reference wavelength or by having general size distribution information on the aerosol. Possible corrections were tested and will usually reduce the error in the ozone concentration considerably. For the 308‐, 353‐nm pair, both Mie calculations and a comparison with ozone profiles from electrochemical cell sondes show, however, that even after the correction the uncertainty in the ozone concentration within some regions of the strongly enhanced Mt. Pinatubo aerosol layer can still be substantial, of the order of 10–50%. Wavelength separation smaller than 40 nm or use of wavelengths shorter than 300 nm will reduce the error. The best solution seems to be the addition of Raman channels. It avoids the large error due to the differential backscatter term.
Comparison of cloud fields from atmospheric general circulation model, in situ and satellite measurements
Authors: Haskins Robert D. , Barnett Tim P. , Tyree Mary Meyer , Roeckner Erich
Published: February 2004

This paper focuses on the comparison of cloud amounts derived from an atmospheric general circulation model (AGCM), Satellite‐observed clouds, and Ground‐based cloud observations. This is distinctly different from Earth Radiation Budget Experiment (ERBE)‐type comparisons because it does not mix potential errors in the cloud amount with those in the radiation code embedded in the model. Long term cloud climatologies were used to compare global cloud amounts and regional seasonal cycles. The results obtained were surprising in many respects. The AGCM successfully reproduced the signatures of the warm pool and North Pacific seasonal cycle cloudiness but failed in the low stratus region off the coast of South America, a known problem for AGCMs. The data sets also reproduced the anomaly signature associated with El Niño in the warm pool region, but the model amounts were lower. Global results had a similar success rate, with the model generally producing lower total cloud amounts compared to the satellite and in situ measurements. Also, an attempt was made to compare cloud vertical distributions between the data sets. Because of the inherent differences in the measuring processes among the three data sets, the cloud height may need to be validated using the corresponding radiation fields. Unfortunately there were also some large discrepancies between the two observed cloud data sets. We conclude that the character of the observed cloud data sets, while tremendously improved over the last decade, must be substantially enhanced before they will be useful in validating AGCMs by any but the crudest levels of comparison.
On the derivation of tropospheric column ozone from radiances measured by the total ozone mapping spectrometer
Authors: Hudson Robert D. , Kim Jae‐Hwan , Thompson Anne M.
Published: February 2004

We have developed a new algorithm to retrieve tropospheric column ozone on a daily basis directly from the measured total ozone mapping spectrometer (TOMS) albedos at a spatial resolution of about 50 km. This new algorithm is applied to the retrieval of tropospheric ozone over the region bounded by 20°W and 60°E longitude and 20°S and 0°S latitude during the 1989 biomass burning season when tropospheric ozone approaches 20% of total ozone. We find that for the conditions of high tropospheric ozone during biomass burning, the archived TOMS data underestimates total ozone over cloud free regions and overestimates ozone over the marine stratocumulus cloud off the west coast of Africa. This error can be as high as 15 Dobson units. Thus previous methods which derive tropospheric ozone from the TOMS archived ozone data are subject to error. Details of the algorithm and an analysis of the expected error are presented.
Relativistic electron fluxes in May 1992 and their effect on the middle atmosphere
Authors: Gaines E. E. , Chenette D. L. , Imhof W. L. , Jackman C. H. , Winningham J. D.
Published: February 2004

Enhancements in the fluxes of relativistic electrons trapped within the Earth's magnetosphere have been measured by the high‐energy particle spectrometer, part of the particle environment monitor on the upper atmosphere research satellite (UARS). The largest increase in the electron fluxes with energies greater than 1 MeV observed on UARS from October 1991 through July 1994 was in early May 1992. The fluxes of trapped electrons in the drift loss cone and locally precipitating electrons showed differing buildup and decay rates as a function of invariant latitude. Increases of more than 2 orders of magnitude were observed in drift loss cone fluxes at magnetic latitudes of 40°–66° and in precipitating fluxes from 48° to 66°. The energy flux contained in the most intense local precipitation observed was ∼0.1 erg cm−2 s−1, entering the atmosphere and creating up to 1000 ion pairs cm−3 s−1 at 55‐km altitude. The daily averaged energy flux from directly precipitating electrons with energies >1 MeV deposited >1020 erg d−1 worldwide into the atmosphere for the period May 12–21, 1992, producing >1031 odd nitrogen molecules below 60‐km altitude.
Low‐wavenumber spectral characteristics of velocity and temperature in the atmospheric surface layer
Authors: Katul Gabriel G. , Chu Chia R. , Parlange Marc B. , Albertson John D. , Ortenburger Teresa A.
Published: February 2004

The structure of atmospheric surface layer turbulence at low wavenumbers was analyzed using 56 Hz triaxial velocity and temperature measurements above a uniform dry lake bed. A key feature of this experiment was the small roughness length of the surface that resulted in a small roughness Reynolds number. Under near‐neutral atmospheric stability conditions, a −1 power law was observed in both measured velocity and temperature spectra which is consistent with previously proposed dimensional analysis for rough and smooth turbulent boundary layer flows. The wavenumber at which the −1 power law terminates and the −5/3 power law commences was derived as a function of the Kolmogorov and von Karman constants. Good agreement between the predicted and the measured transition wavenumber from −1 to −5/3 was noted for fully rough‐flow conditions. However, this was not the case for other roughness conditions. The similarity theory constants for the neutral case were determined and they compared favorably with other laboratory and field studies. For unstable atmospheric conditions, directional dimensional analysis was used to predict the slopes of the power spectra of temperature and velocity. It was demonstrated that for moderately unstable conditions, the temperature and vertical velocity power spectra exhibited a −1 power law, but the longitudinal velocity exhibited a −2 power law. The agreement between predicted and measured power laws was within experimental errors. Some differences between the constants determined from this experiment and other experiments are also discussed.
Estimates of total organic and inorganic chlorine in the lower stratosphere from in situ and flask measurements during AASE II
Authors: Woodbridge E. L. , Elkins J. W. , Fahey D. W. , Heidt L. E. , Solomon S. , Baring T. J. , Gilpin T. M. , Pollock W. H. , Schauffler S. M. , Atlas E. L. , Loewenstein M. , Podolske J. R. , Webster C. R. , May R. D. , Gilligan J. M. , Montzka S. A. , Boering K. A. , Salawitch R. J.
Published: February 2004

Aircraft sampling has provided extensive in situ and flask measurements of organic chlorine species in the lower stratosphere. The recent Airborne Arctic Stratospheric Expedition II (AASE II) included two independent measurements of organic chlorine species using whole air sample and real‐time techniques. From the whole air sample measurements we derive directly the burden of total organic chlorine (CCly) in the lower stratosphere. From the more limited real‐time measurements we estimate the CCly burden using mixing ratios and growth rates of the principal CCly species in the troposphere in conjunction with results from a two‐dimensional photochemical model. Since stratospheric chlorine is tropospheric in origin and tropospheric mixing ratios are increasing, it is necessary to establish the average age of a stratospheric air parcel to assess its total chlorine (ClTotal) abundance. Total inorganic chlorine (Cly) in the parcel is then estimated by the simple difference, Cly = ClTotal ‐ CCly. The consistency of the results from these two quite different techniques suggests that we can determine the CCly and Cly in the lower stratosphere with confidence. Such estimates of organic and inorganic chlorine are crucial in evaluating the photochemistry controlling chlorine partitioning and hence ozone loss processes in the lower stratosphere.