bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction of the Gulf Stream and Deep Western Boundary Current where they cross
Authors: Pickart Robert S.
Published: February 2004

The long‐timescale variability of the Deep Western Boundary Current (DWBC) where it crosses under the Gulf Stream is analyzed using a 3‐year array of bottom current meters and inverted echo sounders. The relationship of this variability to fluctuations in the upper layer Gulf Stream is specifically addressed. At periods shorter than a year the DWBC variability shows no relationship to the local Gulf Stream, 100‐day fluctuations show a pulsing of the DWBC transport, whereas longer‐period fluctuations are indicative of a meandering‐type variability. By contrast, on timescales greater than a year, variations in the orientation and transport of the DWBC are directly related to such fluctuations in the local Gulf Stream. The coupling reveals that the DWBC is forced by changes in the Gulf Stream rather than causing such variations, which is in contrast to earlier modeling results.
On the generation of the Northeast Water Polynya
Authors: Schneider Wolfgang , Budéus Gereon
Published: February 2004

In spring and summer of 1993 a multidisciplinary survey of the Northeast Water (NEW) Polynya, located on the continental shelf northeast of Greenland, was undertaken by R/V Polarstern. Hydrographic and remotely sensed data from this expedition are analyzed with respect to the generation and the seasonal development of the NEW. Its formation is concluded to result from the combined effect of a fast ice barrier, extending perpendicular from the coast and bridging a trough system, and a northward flowing coastal current. The fast ice barrier protects the region downstream of it from ice import while current driven ice export continues. The temporal development and spatial distribution of hydrographie parameters in the NEW is primarily controlled by its generation mechanism. Continental and sea ice melt induce vertical stability in certain parts of the polynya, giving rise to enhanced primary production there.
Hierarchy and sea ice mechanics: A case study from the Beaufort Sea
Authors: Overland James E. , Walter Bernard A. , Curtin Thomas B. , Turet Philip
Published: February 2004

Hierarchy implies that the study of sea ice can be divided into analysis of subsets of processes based on scale and their interaction with adjacent scales. We apply these concepts to regional sea ice dynamics. The apparent self‐similar property of ice floes seen in aircraft or satellite images argues for an aggregate nature of sea ice, that viscouslike regional behavior arises from discrete floe interactions. However, for some regions and some times, characteristic behavior, where lead patterns seen in basin‐wide advanced very high resolution radiometer images appear to be related to coastal orientation hundreds of kilometers away, suggests that small regional scale processes O(10 km) and discontinuities in the velocity or stress state along boundaries can affect the larger‐scale sea ice distribution and dynamics O(500 km). Thus sea ice displays both aggregate type behavior and discontinuous type behavior based on the history of forcing and shape of the enclosing basin. The appropriate matching of atmospheric processes to sea ice processes in air‐ice interaction is through the sea ice deformation field rather than the response of ice velocity to the local wind. This is because atmospheric forcing and sea ice deformation have matching energetic scales at several hundred kilometers and timescales of days. An example of northerly winds during the April 1992 Arctic Leads Experiment period suggests discontinuous type behavior upwind of the Alaska coast followed by a general opening behavior with easterly winds. There appear to be natural scale divisions between climate scale sea ice processes of O(100–300 km) which resolve aggregate behavior, regional scale O(10–50 km) which is necessary to resolve observed shearing behavior, and the floe scale O(1 km). Because the climate scale is two levels removed from the floe scale, care must be exercised in using ice properties from the floe scale in climate scale models; ice strength is an example of such a scale dependent parameter.
Atmospheric convective plumes emanating from leads: 2. Microphysical and radiative processes
Authors: Pinto James O. , Curry Judith A.
Published: February 2004

A one‐dimensional, second‐order turbulence model with bulk cloud microphysics and detailed radiative transfer is used to simulate the evolution of a thermal internal boundary layer (TIBL) which develops above a wide, open lead. A mixed‐phase cloud, originally based at the surface, is produced within the TIBL. The cloud initially fills the entire TIBL but is later elevated above the surface with its top coincident with the top of the TIBL. Model‐derived cloud ice and cloud liquid water mixing ratios exceed 0.06 g kg−1 directly above the open lead, with a secondary maximum near the top of the TIBL. In addition, precipitating ice particles or snow fills the TIBL with a maximum snow mixing ratio of about 0.05 g kg−1. Radiative flux divergence results in strong cooling at cloud top (which contributes to the local maxima in cloud water mixing ratio at this level) and warming near the surface. The lead‐induced cloud increases the downwelling long‐wave irradiance received at the surface by up to 70 W m−2 (reducing the surface radiative cooling by over 40%) during the baseline case. This value is quite sensitive to the assumed particle size and cloud particle concentration. The vertical structure and composition of the lead‐induced cloud is shown to strongly depend on the rate of snow production and the cloud water partitioning.
Instability of density fronts in layer and continuously stratified models
Authors: Fukamachi Yasushi , McCreary Julian P. , Proehl Jeffrey A.
Published: February 2004

The instability of density fronts is investigated as a possible generation mechanism for the small‐scale, wavelike patterns that are commonly observed along up welling fronts and filaments. Unstable‐wave solutions are obtained in two linearized models: a 1½‐layer model, and a continuously stratified model confined to the surface region of the ocean. In both systems the thickness of the upper region is held constant for the background state, the front being specified by allowing the temperature field T within the region to vary zonally. The background state in the layer model consists of vertically oriented isotherms associated with a depth‐independent current, whereas in the continuously stratified model it consists of steeply tilted isotherms and a vertically sheared current. Solutions are found both when the background velocity field V is zonally uniform and when it is zonally sheared. When V is weak and zonally uniform, approximate solutions are derived analytically for both models that are valid for low‐frequency, low‐wavenumber waves. These solutions demonstrate that the unstable waves in the two systems are dynamically related, both being representations of ageostrophic baroclinic instability. Numerical solutions corroborate the analytic results and extend their range of validity. Energetics analyses confirm that the energy source for the waves is the background potential energy associated with the zonally varying T field. When V is a zonally sheared jet, the models still exhibit a band of instability, which is identifiable with ageostrophic baroclinic instability. The most unstable wave in this band has a short wavelength, a frequency near ƒ/2, and a rapid growth rate consistent with observed features. The layer model also has a band of larger‐scale waves that is a mixed, baroclinic‐barotropic instability; however, for a typical frontal structure this band is weaker than the baroclinic band.
Observations of currents and water properties in the Amazon Frontal Zone
Authors: Geyer W. Rockwell , Kineke Gail C.
Published: February 2004

Measurements of currents and water properties were obtained at various locations in the frontal zone of the Amazon River outflow plume during four cruises in 1989–1991 as part of A Multidisciplinary Amazon Shelf Sediment Study. A salinity front resembling a salt wedge is found approximately 150 km seaward of the river mouth. It continues northwestward more than 400 km along the shelf between the 10‐ and 20‐m isobaths. Tidal currents, which are oriented principally in the cross‐shelf direction, reach 200 cm s−1 during spring tides and drop to less than 80 cm s−1 during neaps in the vicinity of the river mouth. The nontidal flow is strongly sheared, with near‐surface speeds of up to 100 cm s−1 and weak near‐bottom velocities. The direction of the near‐surface flow is generally northwestward except near the river mouth, where river discharge leads to a significant offshore component of flow. The strong velocity shears are stabilized by strong stratification by salinity and by highly concentrated suspended sediment (or fluid mud) near the seabed. Variations in stratification and frontal position are due principally to spring‐neap variations in tidal mixing and seasonal variations in runoff.
A tidal model for eastern Juan de Fuca Strait and the southern Strait of Georgia
Authors: Foreman M. G. G. , Walters R. A. , Henry R. F. , Keller C. P. , Dolling A. G.
Published: February 2004

A three‐dimensional, barotropic, finite element model is used to calculate the tidal flows in eastern Juan de Fuca Strait and the southern Strait of Georgia. The harmonics of eight constituents are computed and compared with those from previous finite difference models and those from historical tide gauge and current meter observations. Root‐mean‐square differences between observed and calculated sea level amplitudes are within 2.0 cm for all constituents, and the phases are within 4.0° for all constituents except K2. Horizontal currents from the model are found to reproduce the observed vertical variations in shear except in regions where stratification effects and internal tides exist. In particular, the model representation of currents at six stations in the Canadian Tide and Current Tables (volume 5) is accurate. The pattern of tidal residual currents has much more detail than previous, coarser resolution models, and numerous eddies are predicted. Computed energy flux fields reveal that over a 29‐day period only 38% of the tidal power entering Juan de Fuca Strait is transmitted into the southern Strait of Georgia, and of the 39% entering Haro Strait, 36% is dissipated within the strait itself.
Accuracy of satellite altimeter elevations over the Greenland Ice Sheet
Authors: Ekholm Simon , Forsberg René , Brozena John M.
Published: February 2004

The accuracy of Geosat satellite altimetry over the Greenland ice sheet is evaluated by comparing the measured heights to radar elevations from the airborne Greenland Aerogeophysics Project. At the center of the ice sheet where the ice surface is nearly level, surface comparisons show a fit at the 1 to 3 m level as expected, but even at moderately sloping ice regions (0.3°–0.6°), satellite altimetry mean errors in the range of 10 to 35 m are observed. These errors are found for slope‐corrected and waveform‐retracked data, so most previous accuracy estimates of current satellite altimetry ice sheet elevations in regions of sloping or undulating ice appear to be too optimistic.
Climatology of tropospheric ozone in southern Europe and its relation to potential vorticity
Authors: Beekmann M. , Ancellet G. , Mégie G.
Published: February 2004

A climatology of the vertical ozone distribution in the troposphere is obtained by balloon‐borne Brewer‐Mast sondes at the Observatoire de Haute Provence (OHP), southern France (44°N, 6°E, 700 m above sea level), during the period 1984 to 1990. The tropospheric ozone seasonal variation is characterized by a large maximum in spring and summer. A comparison to other ozone sounding stations gives evidence for a meridional ozone gradient in the middle and upper troposphere in Western Europe, with larger ozone values at Uccle (51°N, 4°E) and Jülich (50°N, 6°E) than at the OHP (44°N, 6°E.). A statistical analysis of ozone concentrations together with potential vorticity, a tracer of stratospheric air masses, shows a partial but significant correlation between both variables (r = 0.40, significance > 99.9%), implying a noticeable impact of stratosphere‐troposphere exchange on the ozone variability. Concerning the spring/summer maximum of tropospheric ozone, it is shown to be caused both by ozone transfer from the stratosphere and by in situ photochemical ozone production. A climatology of the ozone/potential vorticity ratio is established for the OHP and its altitude and seasonal dependence is given. Finally, it is shown that the interannual variability of potential vorticity can cause dynamically induced trends of the ozone concentrations, which have to be taken into account to determine accurately the relative part due to human activity.
Mechanisms for the release of halogens from sea‐salt particles by free radical reactions
Authors: Mozurkewich Michael
Published: February 2004

A possible source of gas phase bromine in the Arctic winter and early spring is the sea‐salt aerosol. In this paper, chemical mechanisms for the release of photochemically active bromine from sea‐salt are examined. The first of these is oxidation of bromide to elemental bromine by peroxymonosulfuric acid (Caro's acid) produced by the free radical chain oxidation of S(IV). The chain reaction could be initiated in the dark by NO2 or, following polar sunrise, by the reaction of ozone with Superoxide. Although the yield of Caro's acid at 298 K is small, the yield may increase at the low temperatures encountered in the Arctic. This could result in the conversion of a large fraction of the initial sea‐salt alkalinity to Caro's acid. Caro's acid is known to oxidize bromide to Br2. Since this mechanism requires low temperatures and high SO2 concentrations, it is only effective during the winter and early spring and should not oxidize significant amounts of halides in the global marine boundary layer. A second possible mechanism is the free radical oxidation of aqueous bromide to bromine by OH and HO2. This may be effective at moderate pH and may contribute to Br cycling on a global scale. The evaluation of both mechanisms is highly uncertain because of incomplete physical‐chemical data. In addition to these primary release mechanisms, there are possible autocatalytic cycles for the release of bromine from sea‐salt. These involve the gas phase production of either BrO or HOBr and the return of these species to the sea‐salt particles where they initiate additional oxidation of bromide. The efficiency of these cycles should depend critically on the relative amounts of HOBr and HBr produced by the gas phase chemistry. These mechanisms do not appear to be effective as sources of photochemically active Cl.
Tracer redistribution by clouds in West Africa: Numerical modeling for dry and wet seasons
Authors: Renard M. , Chaumerliac N. , Cautenet S. , Nickerson E. C.
Published: February 2004

The vertical transport by clouds of an inert tracer and its redistribution by complex West African circulations are examined using a two‐dimensional mesoscale meteorological model with explicit microphysics. The model reproduces the tropical distribution of clouds and precipitation along a meridional cross section over West Africa, corresponding to the position of the Intertropical Convergence Zone (ITCZ) during the dry and rainy seasons. The resulting redistribution of the inert tracer is therefore closely related to the northward migration of the ITCZ between January and July. The occurrence of biomass burning during the dry season is shown to be an important source of tracer enrichment at upper levels in the atmosphere.
Error analysis for the ground‐based microwave ozone measurements during STOIC
Authors: Connor Brian J. , Parrish Alan , Tsou Jung‐Jung , McCormick M. Patrick
Published: February 2004

We present a formal error analysis and characterization of the microwave measurements made during the Stratospheric Ozone Intercomparison Campaign (STOIC). The most important error sources are found to be determination of the tropospheric opacity, the pressure‐broadening coefficient of the observed line, and systematic variations in instrument response as a function of frequency (“baseline”). Net precision is 4–6% between 55 and 0.2 mbar, while accuracy is 6–10%. Resolution is 8–10 km below 3 mbar and increases to 17 km at 0.2 mbar. We show the “blind” microwave measurements from STOIC and make limited comparisons to other measurements. We use the averaging kernels of the microwave measurement to eliminate resolution and a priori effects from a comparison to SAGE II. The STOIC results and comparisons are broadly consistent with the formal analysis.
A long‐term comparison of middle atmosphere winds measured at Saskatoon (52°N, 107°W) by a medium‐frequency radar and a Fabry–Perot interferometer
Authors: Phillips A. , Manson A. H. , Meek C. E. , Llewellyn E. J.
Published: February 2004

Since late 1988, a medium‐frequency radar (MFR) and an imaging Fabry‐Perot interferometer (FPI) have been operating continuously at Saskatoon, measuring winds and waves in the upper mesosphere and lower thermosphere. When weather and auroral conditions permit, the FPI measures Doppler winds from the atomic oxygen OI 557.7‐nm airglow layer centered at an altitude of about 97 km. This study is similar to earlier comparisons between the MFR/FPI systems except that it draws on 4 years of simultaneous observations. Because the MFR and FPI are somewhat mutually exclusive in their data acquisition rate, real‐time comparisons of winds are often poor. However, with the much larger FPI data set now available, rather better long‐term comparisons between the two systems can be made. Once again, strong similarities in the MF radar and FPI Doppler wind fields are observed, although there are some differences. These differences and the causes are discussed.
Satellite analysis of the severe 1987 forest fires in northern China and southeastern Siberia
Authors: Cahoon Donald R. , Stocks Brian J. , Levine Joel S. , Cofer Wesley R. , Pierson Joseph M.
Published: February 2004

Meteorological conditions, extremely conducive to fire development and spread in the spring of 1987, resulted in forest fires burning over extremely large areas in the boreal forest zone in northeastern China and the southeastern region of Siberia. The great China fire, one of the largest and most destructive forest fires in recent history, occurred during this period in the Heilongjiang Province of China. Satellite imagery is used to examine the development and areal distribution of 1987 forest fires in this region. Overall trace gas emissions to the atmosphere from these fires are determined using a satellite‐derived estimate of area burned in combination with fuel consumption figures and carbon emission ratios for boreal forest fires.
Sensitivity of a GCM climate simulation to differences in continental versus maritime cloud drop size
Authors: Kiehl J. T.
Published: February 2004

Extensive observations indicate a distinct difference between maritime and continental effective drop size, re, for warm clouds. The latest version of the NCAR Community Climate Model (CCM2) is used to explore the sensitivity of differentiating between continental and maritime re on the simulated climate. The results of this study indicate that the smaller drop size over continents leads to a reduction of surface‐absorbed solar radiation from 20 to 60 W m−2. This reduction in surface solar flux leads to a cooling of the continents by up to −3.5 K. The reduction in surface solar flux and temperature also leads to a reduction in latent heat flux and precipitation over land. In the January simulation, there is a significant shift in tropical precipitation associated with the Australian monsoon. This shift leads to a response in the extra tropical geopotential height field over the western United States. All of these changes reduce biases in the current version of CCM2.
Dry deposition of ammonia and ammonium aerosols over heathland
Authors: Duyzer Jan
Published: February 2004

The dry deposition velocities of ammonia (NH3) and particulate ammonium were determined using the micrometeorological gradient method. About 130 measurements of 1 hour duration were conducted in the Netherlands from 1984 to 1987 in different seasons, mainly over heather/purple moor grass vegetation. The results show that NH3 is deposited more rapidly than other trace gases, such as ozone, sulfur dioxide or nitrogen dioxide. An average deposition velocity of 1.9 cm/s was observed during the measurements (most of them carried out during the daytime) over all heather locations. The average flux of NH3 during these periods was equivalent to 16 kg NH3/ha/yr. The canopy resistance for NH3 varied between close to zero and 150 s/m, which is low relative to the stomatal resistance to water vapor. The effect of several variables on the canopy resistance was investigated, but only that of surface wetness and air temperature was established clearly. The results indicate that wet vegetation acts as an almost perfect sink for NH3. The low canopy resistance observed and the lack of any diurnal variation suggest that uptake at the leaf surface is relevant. No clear‐cut difference between the various locations was found. The observed variation in the measured deposition velocities could be explained to some 60% with a surface layer resistance model on the basis of fluctuations in meteorological variables, surface wetness, and air temperature. To obtain an estimate of the long‐term average deposition velocity of NH3, we used a surface‐layer model to account for the effect of nighttime meteorology. Measurements and calculations indicate an annual average 24‐hour deposition velocity to heathland of 1.4 cm/s. For particulate ammonium, only one in 10 measurements leads to flux values significantly higher than the detection limit of the method, owing to the low deposition velocity of particulate NH4+. The average flux measured is equivalent to 3.8 kg NH4+/ha/yr. The annual average 24‐hour dry deposition velocity for particulate NH4+ is 0.17 cm/s. Under the circumstances encountered in the Netherlands, only about 20% of NHx dry deposition was by way of dry deposition of particulate NH4+. For a typical site in the Netherlands the dry deposition was about 50% of the estimated input by wet deposition.
Effect of changes in radiatively active species upon the lower stratospheric temperatures
Authors: Ramaswamy V. , Bowen M. M.
Published: February 2004

A one‐dimensional radiative‐convective model is employed to investigate the thermal effects in the lower stratosphere due to changes in the concentrations of radiatively active species. In particular, we consider the comparative influences due to species that exert surface‐troposphere radiative forcings of opposite signs. Two examples of such competing surface‐troposphere forcings are (1) increases in the well‐mixed greenhouse gases versus increases in tropospheric aerosols and (2) stratospheric ozone loss versus increase in tropospheric ozone. The radiative equilibrium of the lower stratosphere is perturbed both by the local changes in the concentrations of radiatively active species and by the changes in species' concentrations occurring in the troposphere and the middle/upper stratosphere. Perturbations in the concentrations of each of the species, as considered above, leads to a temperature decrease in the lower stratosphere. Relative to the well‐mixed greenhouse gases only case, simultaneous increases in these gases and tropospheric aerosols cause a reduction of the net surface‐troposphere radiative forcing, thereby diminishing the surface warming. However, since tropospheric aerosols contribute to a cooling of the lower stratosphere, the temperature decrease there is enhanced above that due to trace gases alone, with the aerosol‐induced effects scaling approximately linearly with their optical depth. A complete offset of the greenhouse gas surface‐troposphere forcing by tropospheric aerosols, while resulting in a null change in the surface temperature, would double the cooling of the lower stratosphere. Increases in tropospheric ozone would enhance the lower stratospheric cooling over and above that caused by the stratospheric ozone depletion. This is in contrast to the cooling and warming effects exerted upon the surface‐troposphere system by the stratospheric and the tropospheric ozone changes, respectively. Tropospheric ozone increases of 20% or more can yield a lower stratospheric cooling that is a significant fraction of the effects due to the observed stratospheric ozone loss. Both the surface effects and the enhancement of the lower stratospheric cooling scale approximately linearly with tropospheric ozone increases.
Reflection of solar radiation by the Antarctic snow surface at ultraviolet, visible, and near‐infrared wavelengths
Authors: Grenfell Thomas C. , Warren Stephen G. , Mullen Peter C.
Published: February 2004

The variation of snow albedo with wavelength across the solar spectrum from 0.3 μm in the ultraviolet (UV) to 2.5 μm in the near infrared (IR) was measured at Amundsen‐Scott South Pole Station during the Antarctic summers of 1985–1986 and 1990–1991. Similar results were obtained at Vostok Station in summer 1990–1991. The albedo has a uniformly high value of 0.96–0.98 across the UV and visible spectrum, nearly independent of snow grain size and solar zenith angle, and this value probably applies throughout the interior of Antarctica. The albedo in the near IR is lower, dropping below 0.15 in the strong absorption bands at 1.5 and 2.0 μm; and it is quite sensitive to grain size and somewhat sensitive to zenith angle. Near‐IR albedos were slightly lower at Vostok than at South Pole, but day‐to‐day variations in the measured grain size due to precipitation, drifting, and metamorphism were found to cause temporal variations in near‐IR albedo larger than those due to any systematic geographical change from South Pole to Vostok. The spectrally averaged albedos ranged from 0.80 to 0.85 for both overcast and clear skies, in agreement with measurements by others at South Pole and elsewhere in Antarctica. Using a two‐layer radiative transfer model, the albedo can be explained over the full wavelength range. Tests were made to correct for systematic errors in determining spectral albedo. Under clear skies at about 3000‐m elevation the diffuse fraction of downward irradiance varied from 0.4 in the near UV to less than 0.01 in the near IR; knowledge of this fraction is required to correct the measured irradiance for the instrument's deviation from a perfect cosine‐response. Furthermore, the deviation from cosine response is itself a function of wavelength. Under clear skies a significant error in apparent albedo can result if the instrument's cosine collector is not parallel to the surface; e.g., if the instrument is leveled parallel to the horizon, but the local snow surface is not horizontal. The soot content of the snow upwind of South Pole Station was only 0.3 ng/g. It was somewhat greater at Vostok Station but was still too small to affect the albedo at any wavelength. Bidirectional reflectance at 0.9‐μm wavelength, measured from a 23‐m tower at the end of summer after the sastrugi (snow dunes) had diminished, showed a pattern remarkably similar to the spectrally averaged pattern obtained from the Nimbus 7 satellite.
Radiatively driven dynamics of the plume from 1991 Kuwait oil fires
Authors: Herring John A. , Hobbs Peter V.
Published: February 2004

Optical properties of the aerosol from the 1991 Kuwait oil fires are calculated using measured aerosol size distributions and a spectral refractive index based on the measured chemical composition of the particulate matter. At a wavelength of 538 nm the calculated light‐scattering coefficient agrees well with measurements, but the calculated single‐scattering albedo is systematically higher by about 18% than the measured value. Radiative transfer calculations indicate maximum net daytime heating rates of 94 and 56 K d−1 for smoke 1 and 3 hours downwind of the fires, respectively. In the upper regions of the plume, where the calculated heating rates decrease with height, a radiauve‐convective mixed layer developed. There was no significant temperature inversion at the top of this layer, which allowed rapid entrainment of air into the top of the plume, causing it to thicken at an observed rate of ∼0.1 m s−1. In addition, radiative heating of the plume as a whole caused it to lift as a unit at a measured rate of ∼0.1 m s−1 during the first few hours of plume evolution. A theory, based on mixed layer modeling and a scale analysis of the equations of motion, is presented that successfully reproduces the two rates of vertical transport. This model of the dynamics of a radiatively heated plume can be used to predict the evolution and lofting of large composite smoke plumes, such as those from forest fires; it also has implications for the transport, lifetime, and climatic importance of smoke generated on continental scales.
Numerical simulation of global variations of temperature, ozone, and trace species in the stratosphere
Authors: Smith Anne K.
Published: February 2004

A three‐dimensional dynamical chemical model of the middle atmosphere is used to examine the global response to planetary waves in the middle and high latitudes of the northern hemisphere. The model indicates that larger wave activity in the lower stratosphere at 60°N is correlated with decreasing zonal mean temperatures throughout the tropical and summer hemisphere stratosphere as a result of an induced global‐scale circulation. The tendency of mean ozone is positively correlated with the temperature tendency in the lower stratosphere and negatively correlated in the upper stratosphere. In the upper stratosphere, the anticorrelation of mean ozone and temperature is due primarily to the temperature dependence of many of the reaction rates. The quantitative agreement of the model results with available observations is better when the dependence of the ozone‐temperature relation on the mean ozone amount is removed (by taking the log of ozone) because the model ozone differs from the observed. A model run in which the atmospheric chlorine is removed indicates that the magnitude of the ozone change for a given temperature change can be substantial for modifications in the model photochemistry. Another run tested a more realistic change in which a key reaction rate is modified; the results indicate differences of greater than 10% in the ratio of ozone to temperature changes. With improved measurement capabilities differences of this order may now or soon be detectable. The variations of other chemical species in the model with temperature are also presented.
Atmospheric surface layer similarity theory applied to chemically reactive species
Authors: de Arellano Jordi Vilà‐Guerau , Duynkerke Peter G. , Zeller Karl F.
Published: February 2004

The similarity theory proposed by Monin‐Obukhov for the atmospheric surface layer is extended so that it can be used to study the flux‐gradient relationships of chemically reactive species. A second‐order model is developed in order to calculate the flux‐gradient relationships and the (co‐)variances of momentum, temperature, and concentration. The equations of the statistical quantities of the chemical species take chemical reactions into account. The closure constants are adjusted for a near‐neutral surface layer using micrometeorological measurements. All model equations are made nondimensional and without chemistry can be solved as a function of a nondimensional parameter which accounts for the atmospheric stability z/L only. In the case of an irreversible second‐order chemical reaction, three new dimensionless scaling parameters are introduced by the chemical processes: two Damköhler numbers (the ratio of the turbulent timescale to the chemical reaction timescale) and the ratio of the fluxes of the chemical species. Model calculations of the momentum and temperature (co‐)variances are in good agreement with the observations over the whole range of the atmospheric stability. If the concentration of one chemical species (abundant) is much higher than the concentration of the other species (scarce), then one finds the largest deviations from the flux‐gradient relationships and the other statistical quantities for the scarce chemical species with respect to the flux‐gradient relationships and the statistical quantities of temperature. The magnitude of these deviations depends on the Damköhler numbers and on the direction of the transport of the two chemical species, i.e., both deposited/emitted or one deposited and the other emitted. The abundant chemical species behaves as a passive scalar, i.e., temperature or moisture. Therefore in the case of scarce chemical species and Damköhler numbers close to unity (moderate chemistry), one cannot use the same flux‐gradient relationship for temperature and for chemically reactive species. A similar behavior is found if one takes into account a backward chemical reaction (photodissociation) to the second‐order chemical reaction. However, the deviations of the flux‐gradient relationships of the scarce chemical species from the flux‐gradient relationship of temperature are less severe if the photodissociation rate is increased. In summary, the model contains all the most important equations for solving the behavior of chemical species over the entire stability range of the atmospheric surface layer. Therefore it can be used to calculate the fluxes and (co‐)variances equations of chemical species in atmospheric chemistry models.
Calibration of the NOAA 11 solar backscatter ultraviolet (SBUV/2) ozone data set from 1989 to 1993 using in‐flight calibration data and SSBUV
Authors: Hilsenrath E. , Cebula R. P. , DeLand M. T. , Laamann K. , Taylor S. , Wellemeyer C. , Bhartia P. K.
Published: February 2004

Total ozone and ozone profiles are currently being measured by solar backscatter ultraviolet (SBUV/2) instruments onboard NOAA polar orbiting spacecraft using the backscattered ultraviolet technique. The NOAA 11 SBUV/2 operational data set was reprocessed from January 1989 to May 1993 and is now called version 6. The version 6 data include an updated algorithm and revised prelaunch and postlaunch calibrations of the geometrical albedo observations used to derive ozone values. Only the calibration revisions are described in this paper. The postlaunch revisions remove time dependent errors in the ozone amounts due to instrument drift, while the revised prelaunch calibration corrects the absolute value of retrieved ozone. The prelaunch corrections are a result of calibration checks from in‐orbit comparisons of ultraviolet geometric albedos measured by shuttle SBUV (SSBUV) and the NOAA 11 SBUV/2. Geometric albedo comparison data are further corrected using a radiative transfer code to account for the small difference in observing conditions between the two spacecraft. The postlaunch corrections rely on in‐flight calibration and solar irradiance data to account for time dependent changes in instrument gain, thermal response, and instrument diffuser degradation over time. Comparison of data from three SSBUV flights, which occurred about one year apart, with concurrent SBUV/2 data provided an independent check of the time dependent change derived from the in‐flight calibration data. Time independent corrections result in an increase of about 1% for total ozone, 5% for ozone at 1 mbar, and near 0% at 15 mbar. The time dependent corrections amount to an increase of 2% for total ozone, 10% for ozone near 1 mbar, and 3% at 15 mbar at the end of the current record in May 1993. Recent laboratory studies indicate that the absolute radiance calibrations may still be in error by a few percent which results in ozone profile values that are too low. The SBUV/2 total and ozone profile data are compared to the Nimbus SBUV data during the period when the data overlapped. Total ozone values agree to about 1%, while ozone profile differences range from −4% to +6%, depending on latitude and altitude, relative to SBUV. These differences are not statistically significant given the uncertainties of the two data sets.
Ozone absorption spectroscopy in search of low‐lying electronic states
Authors: Anderson S. M. , Mauersberger K.
Published: February 2004

A spectrometer capable of detecting ozone absorption features 9 orders of magnitude weaker than the Hartley band has been employed to investigate the molecule's near‐infrared absorption spectrum. At this sensitivity a wealth of information on the low‐lying electronically excited states often believed to play a role in atmospheric chemistry is available in the form of vibrational and rotational structure. We have analyzed these spectra using a combination of digital filtering and isotope substitution and find evidence for three electronically excited states below 1.5 eV. The lowest of these states is metastable, bound by ∼0.1 eV and probably the 3A2 rather than the 3B2 state. Its adiabatic electronic energy is 1.24±0.01 eV, slightly above the dissociation energy of the ground state. Two higher states, at 1.29±0.03 and 1.48±0.03 eV, are identified as the 3B2 and the 3B1, respectively. Combined with other recent theoretical and experimental data on the low‐lying electronic states of zone, these results imply that these are, in fact, the lowest three excited states; that is, there are no electronically excited states of ozone lying below the energy of O(3P) + O2(3∑−, υ = 0). Some of the implications for atmospheric chemistry are considered.
A numerical study of the influence of the diurnal cycle on the surface energy and water budgets
Authors: Delire Christine , Gérard Jean‐Claude
Published: February 2004

Global models including atmospheric, oceanic, and biogeochemical processes are needed for the study of possible environmental changes, but they require efficient approximations of physical processes in order to reduce the computing time. The need to resolve the diurnal cycle when treating such problems is questionable. The Interaction Soil Biosphere Atmosphere (ISBA) model describing soil‐vegetation‐atmosphere interactions is used to analyze the importance of the diurnal cycle on the surface energy and water budgets. Stand‐alone simulations are first performed using the Hydrologic Atmospheric Pilot EXperiment‐MOdélisation du BILan HYdrique (HAPEX‐MOBILHY) and Amazonian Region Micrometeorological Experiment (ARME) data sets to assess the need of an explicit diurnal variation of the atmospheric forcing for different sites. As a reference, the run is forced by measured values of atmospheric variables and radiative fluxes. As a test, ISBA is run forced by the 24‐hour means of these atmospheric and radiative forcings. The surface and deep water content, the total evaporation, and the net radiation flux are correctly evaluated without the diurnal cycle. In contrast, the interception reservoir is highly overestimated. The model is then coupled with a one‐dimensional atmospheric model in which, as test, the solar flux at the top of the atmosphere is replaced by a daily constant mean insolation. The superficial soil moisture content and the total evapotranspiration flux are correctly estimated. The surface temperature and the sensible heat flux are not satisfactorily predicted. Thus it appears that neglecting the diurnal cycle is adequate when considering the hydrologic balance of the surface but not the surface temperature.
Contribution to the study of thermal erosion on Mars
Authors: Aguirre‐Puente J. , Costard F. , Posado‐Cano R.
Published: February 2004

Similar to the coldest terrestrial periglacial regions like Yakutia (Siberia), the planet Mars exhibits wide outflow channels. This analogy and the presence of permanent ground ice suggest that thermal erosion have existed during Martian fluvial outbursts 3000 m.y. ago. Thermal erosion here is considered to be the result of ground thawing produced by heat transfer between the water flow and the frozen ground, followed by a transport of unfrozen sediments. This paper proposes a qualitative explanation of thermal erosion with the help of some physical models. From the quantitative point of view, two thermal mathematical models are proposed and discussed. The zones undergoing the most efficient erosion are river banks. The first model studied here describes extreme thermomechanical actions: a constant thermal flux on the ground surface produces ground thaw, and the unfrozen sediments are immediately removed by water flow. It is an ablation model. It allows a theoretical evaluation of the river bank recession. Validity of theoretical estimations is acquired by comparing the calculations to the observed backwearing of the banks of some Siberian rivers which can reach 25 m yr−1. Thermal erosion acting upon the bottom of wide rivers (on Mars or in Siberia as well) is a very complex mechanism. Indeed, the mathematical modeling requires the study of interaction between thermal processes and transport of sediments laws. These laws are not yet well defined and are very difficult to establish. Thus another model presented in this paper concerns only one‐dimensional thermal actions of water flow upon the bottom of wide rivers. It considers fluvial flow at positive Celsius temperature producing a thermal flux from the bottom to the initially frozen semi‐infinite ground. This model considers a constant convective heat transfer coefficient and allows an estimation of the thickness of the thawed ground beneath the river (talik). Calculated thickness of the melted ground is given in the paper for different periods of time.
Spectrophotometry of zonal cloud structure variations on Jupiter, 1988–1993
Authors: Tejfel V. G. , Vdovichenko V. D. , Sinyaeva N. V. , Mosina S. A. , Gajsina W. N. , Kharitonova G. A. , Aksenov A. N.
Published: February 2004

Global changes of zonal cloud structure on Jupiter have been observed and analyzed from data obtained with a 1‐m telescope and a low‐dispersion spectrograph in the spectral range λλ 400–680 nm, and with a 70‐cm telescope and planetary three‐channel spectrometer in the spectral range λλ 320–1100 nm during each Jovian apparition from 1988 to 1992. Variations of the observed meridional intensity profiles and relative spectrophotometric gradients are described as well as the changes of absolute spectral reflectivity of five main belts on Jupiter (North and South Equatorial belts, North and South Tropical zones, and Equatorial region). Some peculiarities in the behavior of spectrophotometric gradients may be interpreted as a result of increased Rayleigh scattering in the gas layer over the deeper effective cloud boundary within main dark belts. The polar limb darkening varies only slightly with wavelength and it may be considered as evidence for dark aerosols in the stratosphere at high latitudes. The intensity of the methane absorption band centered at 8860 Å shows an increase from the equator to temperate latitudes throughout the 1988–1992 period, despite the large variations in belt and zone reflectivities observed during this period in the southern hemisphere.
Io's heat flow from infrared radiometry: 1983–1993
Authors: Veeder Glenn J. , Matson Dennis L. , Johnson Torrence V. , Blaney Diana L. , Goguen Jay D.
Published: February 2004

We report the following results from a decade of infrared radiometry of Io: (1) The average global heat flow is more than ∼2.5 W m−2, (2) large warm (≤200 K) volcanic regions dominate the global heat flow, (3) small high‐temperature (≥300 K) “hotspots” contribute little to the average heat flow, (4) thermal anomalies on the leading hemisphere contribute about half of the heat flow, (5) a substantial amount of heat is radiated during Io's night, (6) high‐temperature (≥600 K) “outbursts” occurred during ∼4% of the nights we observed, (7) “Loki” is the brightest, persistent, infrared emission feature, and (8) some excess emission is always present at the longitude of Loki, but its intensity and other characteristics change between apparitions. Observations of Io at M (4.8 μm), 8.7 μm, N (10 μm), and Q (20 μm) with the Infrared Telescope Facility presented here were collected during nine apparitions between 1983 and 1993. These measurements provide full longitudinal coverage as well as an eclipse observation and the detection of two outbursts. Reflected sunlight, passive thermal emission, and radiation from thermal anomalies all contribute to the observed flux densities. We find that a new thermophysical model is required to match all the data. Two key elements of this model are (1) a “thermal reservoir” unit which lowers daytime temperatures, and (2) the “thermal pedestal effect” which shifts to shorter wave‐lengths the spectral emission due to the reradiation of solar energy absorbed by the thermal anomalies. The thermal anomalies are modeled with a total of 10 source components at five locations. Io's heat flow is the sum of the power from these components.
Mid‐infrared spectropolarimetry as a remote sensing tool
Authors: Johnson Paul E. , Watne Bruce , Shipman Russell , Cleavlin Chris
Published: February 2004

We describe our preliminary investigation of mid‐infrared spectropolarimetry as a new technique to accurately measure features in the thermal spectra of planetary regoliths. The 5‐ to 12‐μm polarization of igneous rocks and powders commonly found on planetary surfaces is measured to explore the viability of this technique for future ground‐based and space‐based experiments. We find mid‐infrared polarization to be diagnostic of composition for both whole rock and sand samples.
Aluminum 26, 10Be, and 36Cl depth profiles in the Canyon Diablo iron meteorite
Authors: Michlovich E. S. , Vogt S. , Masarik J. , Reedy R. C. , Elmore D. , Lipschutz M. E.
Published: February 2004

We have measured activities of the long‐lived cosmogenic radionuclides 26Al, 10Be, and 36Cl in 12 fragments of the iron meteorite Canyon Diablo and have constructed production rate‐versus‐depth profiles of those radionuclides. Profiles determined using differential particle fluxes calculated with the LAHET code system are in good agreement with 26Al, 10Be, and 36Cl experimental data, but the agreement for 36Cl was obtained only after neutron‐induced cross sections were modified. Profiles calculated with lunar particle fluxes are much lower than experimental Canyon Diablo profiles. The cosmic ray exposure ages of most samples are near 540 m.y.
Polar margin dunes and winds on Mars
Authors: Thomas Peter C. , Gierasch Peter J.
Published: February 2004

The approximately concentric arrangement of layered deposits and dune fields at the two Martian poles may reflect a nearly steady state dispersal of material from the polar deposits. Data on effective surface winds from high resolution Viking Images combined with theory of local winds suggest that the northern dunes are in part confined to a latitude band by winds generated by their own low albedo. Dispersal of the dark sand from the southern polar region is not subject to this kind of feedback because the irregular topography prevents areal accumulations sufficiently extensive to produce winds.