bluuebunny/crossref_metadata_2025 huggingface dataset:
The Southern Ocean western boundary currents: Comparison of fine resolution Antarctic model results with Geosat altimeter data
Authors: Feron Raymond C. V.
Published: February 2004

Variability in the major western boundary current systems of the Southern Ocean is studied by comparing results from the United Kingdom fine resolution Antarctic model (FRAM) to 3 years of Geosat altimeter data. Several analysis techniques (harmonic analysis, principal component, and principal oscillating pattern analysis) are applied to both model results and the “real ocean” altimeter data. The analysis results from the very complex altimeter observations were verified, and the interpretation of Geosat data in the three Southern Ocean western boundary systems was improved. This could be achieved by testing a basic hypothesis underlying the analysis of the partially known sea surface topographies from Geosat with the completely known FRAM model results. The hypothesis that ring formations can be catalogued and studied from variations in the decorrelation time of successive sea level anomaly fields (Feron et al.5 1992) is confirmed by FRAM. Applying the technique to altimeter data of the Agulhas, Brazil/Malvinas, and East Australian Currents showed that quasi‐periodic ring formations take place, roughly every 100, 150, and 130 days, respectively. The FRAM model.only generated periodic ring formations in the Agulhas and East Australian Currents, both with a very regular 125 to 130 day period. This period is clearly a model‐favored harmonic (1/3 year) which is, however, close to the observations.
Quantitative analysis of sea ice draft: 1. Methods for stochastic modeling
Authors: Goff John A.
Published: February 2004

This paper seeks to develop a robust set of tools for estimating the stochastic properties of sea ice drafts. Five parameters are estimated, along with their formal uncertainties: mean draft, rms topographic variation, characteristic length, fractal dimension, and normalized skewness. These provide an objective basis for terrain classification. A recent 10‐km by 10‐km upward looking submarine sonar survey serves as a test case. Data profiles are compared with synthetic profiles generated from the statistical parameters estimated from the data. These provide a means of qualitatively assessing the success of the stochastic model at characterizing the principal morphological properties. In general, the comparisons are good, providing confidence in the applicability and versatility of the stochastic model. A few exceptions are notable, but these also provide valuable insight into our understanding of the morphology of sea ice draft.
Bioluminescence and optical variability in the ocean: An overview of the Marine Light‐Mixed Layers Program
Authors: Marra John
Published: February 2004

Bioluminescence is the production of light from a chemiluminescent reaction in living organisms. Although compared to sunlight and moonlight, it is very dim [e.g., Smith et al., 1989], it features prominently in the ecology of the seas, occurring in all oceans, and is produced by a wide variety of marine plankton and nekton [Herring, 1987]. Its commonality across phyla and ecological niches means also that it has general adaptive significance. Even though it is broadly distributed, bioluminescence in the ocean remains largely unexplained because the intensity and the duration of the light produced are complicated functions of the interaction between the organism and its environment.
Evolution of the instability of a mixed‐layer front
Authors: Samelson R. M. , Chapman D. C.
Published: February 2004

Observations from the Frontal Air‐Sea Interaction Experiment (FASINEX), indicating the presence of small‐scale cold‐core features in the North Atlantic Subtropical Convergence Zone, motivated a recent linear analysis of the instability of a geostrophically balanced mixed‐layer front. The results of that analysis suggested that the instability would preferentially form small‐scale cold‐core eddies at finite amplitude. In the present study, the finite‐amplitude evolution of the fastest growing mode of this nongeostrophic baroclinic instability is investigated numerically. The linear prediction of cold‐core eddy formation is confirmed by the nonlinear calculation. There are large horizontal and vertical heat and potential vorticity fluxes associated with the developing disturbance. The heat flux is confined above the thermocline, in the region of sloping frontal isotherms that provide the energy source for the instability, but the potential vorticity fluxes are maximum 50–75 m deeper and reach into the thermocline. A tongue of low‐potential‐vorticity fluid is advected 50–75 m downward along isopycnal surfaces from the cold side of the front into the thermocline at the mixed‐layer base. The small‐scale potential vorticity structure has similarities to estimates of the upper ocean potential vorticity field obtained previously from FASINEX observations. The calculations illustrate the role that frontal instabilities may play in the flux of heat and potential vorticity from the mixed layer into the thermocline. The evolution of the disturbance resembles baroclinic wave life cycles obtained in atmospheric models.
Injected bubble populations in seawater and fresh water measured by a photographic method
Authors: Haines Meredith A. , Johnson Bruce D.
Published: February 2004

Bubbles were injected in a laboratory simulation of a breaking wave by an intermittent waterfall. A photographic method was used to investigate the size spectrum of bubbles in the plume generated by the falling water. Bubbles of diameter larger than 0.01 cm were measured. Snapshot observations were assembled into residence‐time weighted spectra. While the general features (log concentration versus log diameter slopes around −2) are consistent with other literature reports, a more detailed comparison shows considerable differences between seawater arid freshwater populations. Bubbles were more numerous, smaller, and resident longer in the seawater plume than in fresh water. These results suggest that caution should be applied when gas fluxes measured in fresh water are used to infer gas fluxes in seawater when bubble‐mediated gas transfer is likely to be significant.
A laboratory study of frost flower growth on the surface of young sea ice
Authors: Martin Seelye , Drucker Robert , Fort Meredith
Published: February 2004

Frost flowers are fragile ice crystals containing salt which grow to a height of 10–30 mm on the surface of young sea ice. Such flowers are observed all over the Arctic. The importance of the flowers and their accompanying slush layer is that they provide a rapid way to change the surface albedo and increase the surface roughness of young sea ice. This paper describes a laboratory technique for growing frost flowers and the physical processes which accompany the growth. The study was carried out in a saltwater tank located in a cold room. To grow frost flowers, we alternately cool the surface of the growing sea ice with a fan, then supply it with water vapor from a vaporizer. For these conditions and a room temperature of −22°C, the frost flowers begin to grow when the ice thickness reaches 5–8 mm. The flowers form at random locations on the ice and grow vertically to a height of 10–15 mm while spreading laterally from their original sites. Beneath the flowers, the surface is initially dry; then as the flowers spread laterally, a high‐salinity slush layer forms beneath them. This layer, which forms only under the flowers, grows to a thickness of 5 mm in 48 hours and has a characteristic lateral scale of 100–200 mm. The salinity of the slush layer is about 80 psu, compared with a frost flower salinity of 100 psu. Within 24 hours of their appearance, the flowers grow to cover 75–90% of the surface. A surface water budget for the flowers and slush layer shows that most of the water in the flowers and slush layer comes from the ice interior, not from the vaporizer. This implies that an external vapor source may be important in determining the initial growth of the flowers but not in their subsequent development.
Measurement of the diffusion coefficient of sulfur hexafluoride in water
Authors: King D. B. , Saltzman E. S.
Published: February 2004

Sulfur hexafluoride has been widely used in field studies and laboratory experiments to develop a relationship between gas transfer and wind speed. The interpretation of the data from such studies requires the diffusion coefficient of SF6 (DSF6), which has not previously been measured. In this study, DSF6 has been determined in pure water and in 35‰ NaCl over a temperature range of 5–25°C. The measurements were made using a continuous‐flow diffusion cell where SF6 flows beneath an agar gel membrane while helium flows above the gel. The experimental data for pure water yielded the following equation: DSF6=0.029 exp (−19.3/RT, where R is the gas constant and T is temperature in kelvins). Measurements of DSF6 in 35‰ NaCl were not significantly different from the pure water values. On the basis of our data, we estimate the Schmidt numbers for seawater over the temperature range 5–25° C to be Sc=3016.1–172.00t+4.4996t2−0.047965t3, where t is temperature in degrees Celsius.
Generation of mesoscale flows over the shelf and slope by shelf wave scattering in the presence of a stable, sheared mean current
Authors: Yankovsky Alexander E. , Chapman David C.
Published: February 2004

A linearized barotropic model is used to investigate the scattering of barotropic shelf waves by variations of the shelf width in the presence of a sheared but stable mean along‐shelf current located over the continental slope. The mean current is chosen to eliminate all backward propagating waves, so no energy is reflected from the scattering region. In addition, the mean current shear severely limits the number of forward propagating waves which carry energy downstream from the scattering region. For a narrowing shelf this tends to increase the strength of the scattering and, more importantly, generates large‐amplitude evanescent modes which dominate the velocity fields within and slightly upstream and downstream of the scattering region. When viewed in combination with the mean current, the wave scattering forms intense mesoscale flows between the mean current and the coast. This mechanism may be partially responsible for the highly variable and energetic flows often associated with along‐shelf currents found over many continental slopes.
Polar stratospheric cloud climatology based on Stratospheric Aerosol Measurement II observations from 1978 to 1989
Authors: Poole Lamont R. , Pitts Michael C.
Published: February 2004

The probability of polar stratospheric cloud (PSC) occurrence in the Antarctic and Arctic has been estimated using Stratospheric Aerosol Measurement (SAM) II aerosol extinction data from 1978 to 1989. Antarctic PSCs are typically observed by SAM II from mid‐May to early November, with a maximum zonal average probability of about 0.6 at 18–20 km in August. The typical Arctic PSC season extends only from late November to early March, with a peak zonal average probability of about 0.1 in early February at 20–22 km. There is considerable year‐to‐year variability in Arctic PSC sightings because of changes in the dynamics of the northern polar vortex. Year‐to‐year variability in Antarctic sightings is most prominent in the number of late season clouds. Maximum PSC sighting probabilities in both polar regions occur in the region from 90°W through the Greenwich meridian to 90°E, where temperatures are coldest on average. Arctic sighting probabilities approach zero outside this region, but clouds have been sighted in the Antarctic at all longitudes during most months. Inferred PSC formation temperatures remain constant throughout the Arctic winter and are similar to those in early Antarctic winter. PSC formation temperatures in the Antarctic drop markedly in the 15 to 20‐km region by September, a pattern consistent with the irreversible loss of HNO3 and H2O vapor in sedimenting PSC particles.
Antarctic climate modeling with general circulation models of the atmosphere
Authors: Genthon Christophe
Published: February 2004

The abilities of the National Aeronautic and Space Administration Goddard Institute for Space Studies (GISS) and METEO‐FRANCE Arpège General Circulation Models (GCMs) of the atmosphere to simulate surface climate variables that have direct and indirect impacts on the mass balance of the Antarctic ice sheet are evaluated. Deficiencies in reproducing the surface temperature are identified. Some of the flaws are associated with an incorrect specification of the Antarctic continent real topography, a problem which can be partially corrected by an adequate processing of model output. Shortcomings can also be consequent to the use of inappropriate climate variable formulations and prescribed boundary conditions. A coarse‐resolution version of the GISS GCM is used to demonstrate how model results can be improved if snow albedo and sea ice coverage are more adequately set. A barrier to thoroughly analyzing and validating model results is the lack of numerous and reliable enough observational data. This point is particularly critical for accumulation, a first‐order term in the ice sheet mass balance. Although accumulation is very different in the GISS and Arpège models, uncertainties about the available observational references preclude firmly asserting that one model is better than the other. Finally, typical GCM resolution remains an essential limitation to improving model performances and promoting the effective use of model results for the Antarctic region.
Moisture profiles over the tropics from NOAA/TOVS satellite data
Authors: Simon B. , Joshi P. C. , Desai P. S.
Published: February 2004

The scale height of water vapor over tropical Indian Ocean was computed from NOAA/TOVS satellite data. This scale height of water vapor obtained from satellite data was compared with ship radiosonde data and was found to be within 10% rms error. Variable scale height of water vapor computed at each grid point was used to correct the moisture profile over tropical Indian Ocean. The results indicate that rms of specific humidity computed at different levels reduces significantly using a variable scale height model in comparison to constant scale height model.
Transport distance of ammonia and ammonium in Northern Europe: 2. Its relation to emissions of SO2 and NOx
Authors: Hov Øystein , Hjøllo Bjørn Aage
Published: February 2004

The transport distances of NH3 and the species derived from NH3 emissions are investigated as a function of the emissions of SO2 and NOx. This is done by Lagrangian model calculation of long‐range transport to six Scandinavian European Monitoring and Evaluation Programme measurement sites in August–October 1985. In the presence of SO2 and NOx emissions, NH3 forms ammonium aerosols (NH4HSO4, (NH4)2SO4, and NH4NO3) which are transported over longer distances than NH3. When the SO2 emissions are set to zero in the model, the fraction of airborne ammonia and ammonium (defined as the ratio between the concentration at the receptor site averaged over 3 months divided by the source, i.e., the initial concentration plus the sources along the trajectories averaged over the same 3 months) at the six receptor sites drops from 9% at Keldsnor to 18% at Utø. When both NOx, and SO2 emissions are set to zero in the calculations, only the initial concentrations of NOy and S contribute to ammonium aerosol formation and most of the NH3 emissions then remain as airborne NH3 before dry deposition or rain out. In this case the fraction of NH3 or ammonium aerosols which remains airborne at the receptor sites dropped from 19% of the sources along the trajectories arriving at Keldsnor to 30% at Birkenes. This is a substantial change in the airborne fraction, and in the deposition calculation for the grid boxes where the receptor sites are located, a similar drop in NH3 + NH4+ deposition is found.
Air truth validation of cloud albedo estimated from NOAA advanced very high resolution radiometer data
Authors: Hayasaka Tadahiro , Kuji Makoto , Tanaka Masayuki
Published: February 2004

A comparison was carried out between cloud albedos observed in situ by aircraft and cloud albedos calculated with visible optical thickness retrieved from the NOAA advanced very high resolution radiometer channel 1 radiance data. The results show that the observed and calculated cloud albedos in the visible region are coincident with each other in a few percent for both homogeneous stratus and rather inhomogeneous stratocumulus clouds as long as the cloud amount is large. In the near‐infrared region, on the other hand, the observed albedo is lower than that evaluated from the satellite data for stratocumulus clouds, while the observed and calculated albedos are consistent for stratus clouds. From the aircraft observation of solar radiative flux this discrepancy is not ascribed to the uncertainty in the near‐infrared absorption processes as discussed in previous studies.
On the interannual oscillations in the northern temperate total ozone
Authors: Krzyścin Janusz W.
Published: February 2004

The interannual variations in total ozone are studied using revised Dobson total ozone records (1961–1990) from 17 stations located within the latitude band 30°N‐60°N. To obtain the quasi‐biennial oscillation (QBO), El Niño‐Southern Oscillation (ENSO), and 11‐year solar cycle manifestation in the “northern temperate” total ozone data, various multiple regression models are constructed by the least squares fitting to the observed ozone. The statistical relationships between the selected indices of the atmospheric variabilities and total ozone are described in the linear and nonlinear regression models. Nonlinear relationships to the predictor variables are found. That is, the total ozone variations are statistically modeled by nonlinear terms accounting for the coupling between QBO and ENSO, QBO and solar activity, and ENSO and solar activity. It is suggested that large reduction of total ozone values over the “northern temperate” region occurs in cold season when a strong ENSO warm event meets the west phase of the QBO during the period of high solar activity.
Fine mode aerosol composition at three long‐term atmospheric monitoring sites in the Amazon Basin
Authors: Artaxo Paulo , Gerab Fábio , Yamasoe Marcia A. , Martins José V.
Published: February 2004

The Amazon Basin tropical rain forest is a key region to study processes that are changing the composition of the global atmosphere, including the large amount of fine mode aerosol particles emitted during biomass burning that might influence the global atmosphere. Three background monitoring stations, Alta Floresta, Cuiabá, and Serra do Navio, are operating continuously measuring aerosol composition. Fine (dp < 2.0 μm) and coarse (2.0 < dp < 10 μm) mode aerosol particles were collected using stacked filter units. Particle‐induced X‐ray emission was used to measure concentrations of up to 20 elements in the fine mode: Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Br, Rb, Sr, Zr, and Pb. Soot carbon and gravimetric mass analysis were also performed. Absolute Principal Factor Analysis (APFA) has derived absolute elemental source profiles. APFA showed four aerosol particle components: soil dust (Al, Ca, Ti, Mn, Fe), biomass burning (soot, fine mode mass concentration, K, Cl), natural primary biogenic particles with gas‐to‐particle component (K, S, Ca, Mn, Zn), and marine aerosol (Cl). Biogenic and biomass burning aerosol particles dominate the fine mode mass concentration, with the presence of K, P, S, Cl, Zn, Br, and fine mode mass concentration (FPM). At the Alta Floresta and Cuiabá sites, during the dry season, a strong component of biomass burning is observed. Inhalable particulate matter (dp < 10 μm) mass concentration up to 700 μg/m3 was measured. Fine particle mass concentration alone can go as high as 400 μg/m3 for large regions. The fine mode biogenic and biomass burning components show remarkable similarities in the elemental composition, even though the sampling sites are more than 3000 km apart. Fine mode sulfur concentration is entirely associated with the primary biogenic aerosol particles, with gas‐to‐particle conversion and the biomass burning component. Large amounts of essential plant nutrients like P are mobilized into the atmosphere and possibly lost from the Amazon Basin ecosystem by long‐range transport.
Application of static and dynamic enclosures for determining dimethyl sulfide and carbonyl sulfide exchange in Sphagnum peatlands: Implications for the magnitude and direction of flux
Authors: de Mello William Z. , Hines Mark E.
Published: February 2004

A static enclosure method was applied to determine the exchange of dimethyl sulfide (DMS) and carbonyl sulfide (OCS) between the surface of Sphagnum peatlands and the atmosphere. Measurements were performed concurrently with dynamic (flow through) enclosure measurements with sulfur‐free air used as sweep gas. This latter technique has been used to acquire the majority of available data on the exchange of S gases between the atmosphere and the continental surfaces and has been criticized because it is thought to overestimate the true flux of gases by disrupting natural S gas gradients. DMS emission rates determined by both methods were not statistically different between 4 and >400 nmol m−2 h−1, indicating that previous data on emissions of at least DMS are probably valid. However, the increase in DMS in static enclosures was not linear, indicating the potential for a negative feedback of enclosure DMS concentrations on efflux. The dynamic enclosure method measured positive OCS flux rates (emission) at all sites, while data using static enclosures indicated that OCS was consumed from the atmosphere at these same sites at rates of 3.7 to 55 nmol m−2 h−1. Measurements using both enclosure techniques at a site devoid of vegetation showed that peat was a source of both DMS and OCS. However, the rate of OCS efflux from decomposing peat was more than counterbalanced by OCS consumption by vegetation, including Sphagnum mosses, and net OCS uptake occurred at all sites. We propose that all wetlands are net sinks for OCS.
Effects of a polar stratospheric cloud parameterization on ozone depletion due to stratospheric aircraft in a two‐dimensional model
Authors: Considine David B. , Douglass Anne R. , Jackman Charles H.
Published: February 2004

A parameterization of Type 1 and 2 polar stratospheric cloud (PSC) formation is presented which is appropriate for use in two‐dimensional (2‐D) photochemical models of the stratosphere. The calculation of PSC frequency of occurrence and surface area density uses climatological temperature probability distributions obtained from National Meteorological Center data to avoid using zonal mean temperatures, which are not good predictors of PSC behavior. The parameterization does not attempt to model the microphysics of PSCs. The parameterization predicts changes in PSC formation and heterogeneous processing due to perturbations of stratospheric trace constituents. It is therefore useful in assessing the potential effects of a fleet of stratospheric aircraft (high speed civil transports, or HSCTs) on stratospheric composition. The model calculated frequency of PSC occurrence agrees well with a climatology based on stratospheric aerosol measurement (SAM) II observations. PSCs are predicted to occur in the tropics. Their vertical range is narrow, however, and their impact on model O3 fields is small. When PSC and sulfate aerosol heterogeneous processes are included in the model calculations, the O3 change for 1980–1990 is in substantially better agreement with the total ozone mapping spectrometer (TOMS) ‐derived O3 trend than otherwise. However, significant discrepancies in the northern midlatitudes remain. The overall changes in model O3 response to standard HSCT perturbation scenarios produced by the parameterization are small and tend to decrease the model sensitivity to the HSCT perturbation. However, in the southern hemisphere spring a significant increase in O3 sensitivity to HSCT perturbations is found. At this location and time, increased PSC formation leads to increased levels of active chlorine, which produce the O3 decreases.
Analysis of cloud top height and cloud coverage from satellites using the O2A and B bands
Authors: Kuze Akihiko , Chance Kelly V.
Published: February 2004

Cloud height and cloud coverage detection are important for total ozone retrieval using ultraviolet and visible scattered light. Use of the O2 A and B bands, around 761 and 687 nm, by a satellite‐borne instrument of moderately high spectral resolution viewing in the nadir makes it possible to detect cloud top height and related parameters, including fractional coverage. The measured values of a satellite‐borne spectrometer are convolutions of the instrument slit function and the atmospheric transmittance between cloud top and satellite. Studies here determine the optical depth between a satellite orbit and the Earth or cloud top height to high accuracy using FASCODE 3. Cloud top height and a cloud coverage parameter are determined by least squares fitting to calculated radiance ratios in the oxygen bands. A grid search method is used to search the parameter space of cloud top height and the coverage parameter to minimize an appropriate sum of squares of deviations. For this search, nonlinearity of the atmospheric transmittance (i.e., leverage based on varying amounts of saturation in the absorption spectrum) is important for distinguishing between cloud top height and fractional coverage. Using the above‐mentioned method, an operational cloud detection algorithm which uses minimal computation time can be implemented.
Denitrification mechanism of the polar winter stratosphere by major volcanic eruptions
Authors: Bekki S.
Published: February 2004

The uptake of HNO3 by volcanic sulfuric acid droplets is investigated using a one dimensional sulfate aerosol model and recent laboratory data. HNO3 uptake by volcanic sulfate particles coupled with the sedimentation of the particles may lead to irreversible transfer of HNO3 from higher to lower altitudes in the polar stratosphere during winter. This denitrification mechanism is found to be strongly dependent on the sulfate aerosol loading and temperature. Model calculations suggest that anomalously large volcanic eruptions have caused a severe denitrification of the Arctic winter lower stratosphere. There is conflicting evidence for this mechanism in ice core nitrate records.
Diurnal variation of ionization rate close to ground
Authors: Dhanorkar Savita , Kamra A. K.
Published: February 2004

Ionization rates for different times on two fair‐weather days are computed using Hoppel's (1985) theoretically deduced aerosol‐size‐dependent attachment coefficients and the aerosol‐size spectra derived from our measurements of mobility spectra of atmospheric ions made at a height of 1 m above ground at Pune (18°32′N, 73°51′E, 559 m above mean sea level), India. The ionization rates are minimum in the afternoon and increase to their maximum values of 116.52 and 103.93 ion pairs cm−3 s−1 in the early morning. Increase in ionization rate is found to accompany with the increase in the total aerosol concentration. Our results suggest that this increase in ionization rate may be due to addition of some radioactive aerosol particles, primarily in the size range of 0.002 to 0.004 μm.
Large‐scale circulation associated with westerly wind bursts and deep convection over the western equatorial Pacific
Authors: Kiladis George N. , Meehl Gerald A. , Weickmann Klaus M.
Published: February 2004

The relationship between deep equatorial convection over the western Pacific and atmospheric circulation during November to February, 1986–1992 is studied using cross correlations between outgoing longwave radiation (OLR) and National Meteorological Center global analyses. We focus on intraseasonal convective events on the 6‐ to 30‐day timescale over two regions: just east of Borneo and over the Tropical Ocean and Global Atmosphere (TOGA) Coupled Ocean‐Atmosphere Response Experiment (COARE) domain to the northeast of New Guinea. Although comparatively little work has been done on this timescale, we show that the bulk of the intraseasonal variability in both convection and low‐level circulation over the tropical western Pacific occurs in this period range. As a comparison with these higher‐frequency events, the evolution of COARE convection on the 30‐ to 70‐day timescale is also considered. The results of the historical data analysis are compared to a case study of deep convection associated with strong surface westerly winds during November 1989. This analysis is meant to serve as a benchmark for future case studies from the Tropical Ocean‐Global Atmosphere COARE experiment and other periods. In general, 6‐ to 30‐day equatorial convection in the regions studied occurs in conjunction with low‐level equatorial westerly wind anomalies, paired anomalous cyclonic circulations straddling the equator, and a strengthening of the sea level pressure gradient along the equator. The increase in the pressure gradient appears most often tied to the simultaneous equatorward movement of high‐pressure systems originating over southeastern Asia and Australia. A surge of trades over the central Pacific also accompanies the development of convection over both study regions. Following the convective peak, the low‐level westerlies slowly decay, as the northern cyclone moves northwestward away from the equator in a track characteristic of a tropical depression. It is also observed that low‐level westerly anomalies occur frequently without deep convection. The vertical structure during convective events along the equator on the 30‐ to 70‐day timescale and over Indonesia in the 6‐ to 30‐day band is baroclinic, with easterly anomalies at upper levels overlying low‐level westerlies. At 200 mbar a strengthened meridional outflow from the OLR signal into a wave train on the equatorward side of the Asian jet is observed to develop following the convective peak, suggesting forcing of this circulation by the convection. Over the COARE domain there is evidence that 6‐ to 30‐day convection often occurs in conjunction with deep westerly flow. It is suggested that these types of events are frequently characterized by vertical propagation of westerlies from the surface to the upper troposphere, as is shown for a case study from November 1989. This westerly burst episode is shown to have many features in common with the “typical” case as defined from historical data.
Profiles of stratospheric chlorine nitrate (ClONO2) from atmospheric trace molecule spectroscopy/ATLAS 1 infrared solar occultation spectra
Authors: Rinsland C. P. , Gunson M. R. , Abrams M. C. , Zander R. , Mahieu E. , Goldman A. , Ko M. K. W. , Rodriguez J. M. , Sze N. D.
Published: February 2004

Stratospheric volume mixing ratio profiles of chlorine nitrate (ClONO2) have been retrieved from 0.01‐cm−1 resolution infrared solar occultation spectra recorded at latitudes between 14°N and 54°S by the atmospheric trace molecule spectroscopy Fourier transform spectrometer during the ATLAS 1 shuttle mission (March 24 to April 2, 1992). The results were obtained from nonlinear least squares fittings of the ClONO2 ν4 band Q branch at 780.21 cm−1 with improved spectroscopic parameters generated on the basis of recent laboratory work. The individual profiles, which have an accuracy of about ±20%, are compared with previous observations and model calculations.
Three‐dimensional model interpretation of NOx measurements from the lower stratosphere
Authors: Folkins Ian , Weinheimer A. J. , Brasseur Guy , Lefèvre Franck , Ridley Brian A. , Walega James G. , Collins James E. , Pueschel R. F.
Published: February 2004

A three‐dimensional off‐line chemistry transport model, driven by European Centre for Medium‐Range Weather Forecasts winds and temperatures, is used to interpret measurements of NO and NO2 taken from the DC‐8 during the second Airborne Arctic Stratospheric Expedition. The model was run in three configurations: gas phase chemistry alone, inclusion of the N2O5 aerosol reaction, and inclusion of both N2O5 and ClONO2 aerosol reactions. The run including the N2O5 aerosol reaction alone usually agreed best with measured NOx/NOy ratios in midlatitude air masses. The NOx/NOy ratios of the run with both aerosol reactions were always too low, while the gas phase ratios were usually too high, especially during March. All three simulations generated extremely low NO2/NOy ratios in air parcels that had spent several days or more in the polar night. Measured NO2/NOy ratios in these types of air masses were sometimes equally low but could also be considerably higher. Observed NO/NO2 ratios differed strongly from known theory.
Is chemical heating a major cause of the mesosphere inversion layer?
Authors: Meriwether John W. , Mlynczak Martin G.
Published: February 2004

A region of thermal enhancement of the mesosphere has been detected on numerous occasions by in situ measurements, remote sensing from space, and lidar techniques. The source of these “temperature inversion layers” has been attributed in the literature to the dissipation relating to dynamical forcing by gravity wave or tidal activity. However, the conclusion that the dynamics of the mesopause region is the principal source for such anomalies is open to question. While it is certain that the dynamics of gravity wave breaking plays an important role in providing the source of momentum flux required to drive the diabatic circulation, evidence that gravity wave breaking can produce the inversion layer with amplitude as large as that observed in lidar measurements has been limited to results of numerical modeling. We note that an alternative source exists for the production of the thermal inversion layer in the mesosphere, i.e., the direct deposition of heat by exothermic chemical reactions. Two‐dimensional modeling combining a comprehensive model of the mesosphere photochemistry with the dynamical transport of long‐lived species shows that the region from 80 to 95 km may be heated as much as 3 to 10 K/d during the night and half this rate during the day. Given the uncertainties in our understanding of the dynamics and chemistry for the mesopause region, separating the two sources by passive observations of the mesosphere thermal structure looks to be difficult. Therefore we have considered an active means for producing a mesopause thermal layer, namely the release of ozone into the upper mesosphere from a rocket payload. The induced effects would include artificial enhancements of the OH and Na airglow intensities as well as the mesopause thermal structure. The advantage of the rocket release of ozone is that detection of these effects by ground‐based imaging, radar, and lidar systems and comparison of these effects with model predictions would help quantify the partition of the artificial inversion layer production into sources of dynamical and chemical forcing.
Atlantic atmospheric aerosol studies: 1. Program overview and airborne lidar
Authors: Alejandro S. B. , Koenig G. G. , Bedo D. , Swirbalus T. , Frelin R. , Woffinden J. , Vaughan J. M. , Brown D. W. , Callan R. , Davies P. H. , Foord R. , Nash C. , Wilson D. J.
Published: February 2004

During the period 1988–1990, studies of atmospheric aerosol have been made over the Atlantic. These include measurement programs out of Ascension Island (8°S, 14°W), the Azores (38°N, 25°W), Iceland (63°N, 23°W), and from the United Kingdom over the Northeast Atlantic. For these studies the equipment deployed included an airborne backscatter lidar (operating at 10.6 μm), airborne particle‐sounding probes, ground‐based lidars (operating at 10.6, 0.53, and 0.35 μm), balloon radiosondes, and a Sun‐tracking photometer. In addition, standard meteorological information has been incorporated along with, when appropriate, data from the SAGE II limb‐sounding satellite. The present paper thus introduces an overview of the program together with an outline of the technology, measurement characteristics, and performance of the airborne equipment that determined the strategic planning of much of the work. The measurements themselves, made in the relatively clean period for the atmosphere before the Mount Pinatubo eruption, will be presented in a subsequent series of papers.
Atmospheric 14CO observations and their use for estimating carbon monoxide removal rates
Authors: Mak John E. , Brenninkmeijer Carl A. M. , Tamaresis John
Published: February 2004

Atmospheric 14CO can be used as a tracer of the global tropospheric hydroxyl radical (OH) concentration, which is responsible for the destruction of many trace gas species. 14CO is produced throughout the Earth's atmosphere by a 14N neutron capture reaction followed by hot atom oxidation. It subsequently follows the pathway of any other CO molecule and is thus removed from the atmosphere by OH oxidation. From the isotopic information it is also possible to elucidate the histories of CO from otherwise identical air masses. Results from global sampling campaigns are presented which establish the northern hemisphere (NH) latitudinal dependence and seasonal extremes of this trace constituent. We used the Lawrence Livermore National Laboratory two‐dimensional chemistry/transport model to predict 14CO temporal and spatial distributions, keeping in mind the importance of reasonable simulations for validating the accuracy of atmospheric models in general. The measured 14CO latitudinal gradient in the NH is consistent with results from previous campaigns in the southern hemisphere, which reveal lower values than predicted; vertical gradients within the troposphere are similarly exaggerated in model simulations. Differences between model output and observations, which are of the order of 25% and the likely sources of error are discussed. We also examine the difference in 14CO between the hemispheres and estimate this to be between 15 and 25%, with higher levels in the NH.
Methodological dependencies of cloud radiative forcing for the Canadian Climate Centre second‐generation general circulation model
Authors: Barker Howard W.
Published: February 2004

Clear‐sky fluxes at the top of the atmosphere (TOA) are essential for calculating cloud radiative forcings (CRF). Both sets of quantities have been computed by three different methods using data from the Canadian Climate Centre general circulation model (CCC‐GCM) (simulations of July 1985 and January 1986). The methods differ in the way they compute monthly mean clear‐sky fluxes at the TOA (
). The first method, known as method 2, is ideal for intercomparing GCMs, but does not sample clear skies as satellites do. The other two methods compute
by avoiding days with minimum and average cloud amounts that exceed a threshold. These methods are referred to as method 3 and 4, respectively. Thus, while methods 3 and 4 attempt to mimic satellite samplings, they depend on GCM parameterizations of cloud amount. It is shown that for the CCC‐GCM, methods 3 and 4 result in vastly different samplings and that the disparities are perhaps attributable to problems with the GCM's clouds. Globally averaged differences in shortwave CRF (or
) between methods 2, 3, and 4 are less than 1 W m−2 and are therefore relatively unimportant. For longwave (LW) CRF, however, globally averaged differences between methods 4 and 2 are ∼3 W m−2. These values are achieved by computing
for method 4 using only fluxes for days with diurnally averaged cloud amounts less than 0.5. The zonally averaged fraction of days used in this method approximates closely corresponding values obtained by Earth Radiation Budget Experiment analysis. More important than global averages, local differences in LW CRF between methods 4 and 2 exceed ±25 W m−2. Positive extremes occur over the west central Pacific and are associated with methods 4's elimination of very moist days with low atmospheric transmittances. This leads to larger values of
and hence LW CRFs. Negative extremes occur over Antarctica because the clearest days have the lowest surface temperatures. This results in both smaller values of
and LW CRFs. The geographic distributions and magnitudes of LW CRF differences between method 4 and method 2 resemble strongly corresponding fields for the European Centre for Medium‐Range Weather Forecasts and the National Center for Atmospheric Research community climate model 2 GCMs.
Incorporation of multiple cloud layers for ultraviolet radiation modeling studies
Authors: Charache Darryl H. , Abreu Vincent J. , Kuhn William R. , Skinner Wilbert R.
Published: February 2004

Cloud data sets compiled from surface observations were used to develop an algorithm for incorporating multiple cloud layers into a multiple‐scattering radiative transfer model. Aerosol extinction and ozone data sets were also incorporated to estimate the seasonally averaged ultraviolet (UV) flux reaching the surface of the Earth in the Detroit, Michigan, region for the years 1979–1991, corresponding to Total Ozone Mapping Spectrometer (TOMS) version 6 ozone observations. The calculated UV spectrum was convolved with an erythema action spectrum to estimate the effective biological exposure for erythema. Calculations show that decreasing the total column density of ozone by 1% leads to an increase in erythemal exposure by approximately 1.1–1.3%, in good agreement with previous studies. A comparison of the UV radiation budget at the surface between a single cloud layer method and a multiple cloud layer method presented here is discussed, along with limitations of each technique. With improved parameterization of cloud properties, and as knowledge of biological effects of UV exposure increase, inclusion of multiple cloud layers may be important in accurately determining the biologically effective UV budget at the surface of the Earth.
Impact of temperature on oxidant photochemistry in urban, polluted rural and remote environments
Authors: Sillman Sanford , Samson Perry J.
Published: February 2004

The impact of temperature on formation of O3and odd nitrogen photochemistry is investigated using urban‐, regional‐ and global‐scale simulations. Urban and polluted rural environments are explored with a regional simulation derived from a specific episode in the midwestern United States. The simulations predict that O3increases with temperature in both urban and polluted rural environments. The O3‐temperature relation is driven largely by chemistry of peroxyacetylnitrate (PAN) which represents an increased sink for both NOxand odd hydrogen at low temperatures. Isoprene emissions, H2O, and solar radiation also contribute to the O3‐temperature relation. Possible correlations between temperature and anthropogenic emissions or stagnant meteorology were not included. Observations at urban and rural sites in the United States suggests that O3increases with temperature at a faster rate than the models predict. Calculations with a one‐dimensional global model suggest that increased temperature in the polluted boundary layer does not lead to increased O3in the free troposphere, because increased export of O3is balanced by decreased export of odd nitrogen species.
Comparison of STOIC 1989 ground‐based lidar, microwave spectrometer, and Dobson spectrophotometer Umkehr ozone profiles with ozone profiles from balloon‐borne electrochemical concentration cell ozonesondes
Authors: Komhyr W. D. , Connor B. J. , McDermid I. S. , McGee T. J. , Parrish A. D. , Margitan J. J.
Published: February 2004

Ground‐based measurements of stratospheric ozone using a Jet Propulsion Laboratory (JPL) lidar, a NASA Goddard Space Flight Center (GSFC) lidar, a Millitech Corporation/NASA Langley Research Center (Millitech/LaRC) microwave spectrometer, and a NOAA Dobson ozone spectrophotometer were compared with in situ measurements made quasi‐simultaneously with balloon‐borne electrochemical concentration cell (ECC) ozonesondes during 10 days of the Stratospheric Ozone Intercomparison Campaign (STOIC). The campaign was conducted at Table Mountain Observatory, California, during the summer of 1989. ECC ozonesondes were flown by NOAA Climate Monitoring and Diagnostics Laboratory (CMDL) personnel as well as by personnel from the NASA Wallops Island Flight Facility (WFF). Within the altitude range of 20–32 km, ozone measurement precisions were estimated to be ±0.6 to ±1.2% for the JPL lidar, ±0.7% for the GSFC lidar, ±4% for the microwave spectrometer, and ±3% for the NOAA ECC ozonesonde instruments. These precisions decreased in the 32 to 38.6‐km altitude range to ±1.3, ±1.5, and ±3% to ±10% for the JPL lidar, GSFC lidar, and the ECC sondes, respectively, but remained at ±4% for the microwave instrument. Ozone measurement accuracies in the 20 to 32 km altitude range were estimated to be ±1.2 to ±2.4% for the JPL lidar, ±1.4% for the GSFC lidar, ±6% for the microwave radiometer, and ±5% for the ECC ozonesondes. The accuracies decreased in the 32 to 38.6‐km altitude range to ±2.6, ±3.0, ±7, and 1 ± 4% to −4 ± 10% for the JPL lidar, the GSFC lidar, the microwave spectrometer, and the ECC ozonesondes, respectively. While accuracy estimates for the ECC sondes were obtained by combining random and estimated bias errors, the accuracies for the lidar instruments were obtained by doubling the measurement precision figures, with the assumption that such doubling accounts for systematic errors. Within the altitude range of 20–36 km the mean ozone profiles produced by the JPL, GSFC, and the Millitech/LaRC groups did not differ from the mean ECC sonde ozone profile by more than about 2, 4, and 5%, respectively. Six morning Dobson instrument Umkehr observations yielded mean ozone amounts in layers 3 and 5–7 that agreed with comparison ECC ozonesonde data to within ±4%. In layer 4 the difference was 7.8%. (Less favorable comparison data were obtained for six afternoon Umkehr observations made in highly polluted near‐surface air.) This good agreement in overall results obtained lends credence to the reliability of the ozone measurements made at Table Mountain Observatory during STOIC 1989.
In situ observations in aircraft exhaust plumes in the lower stratosphere at midlatitudes
Authors: Fahey D. W. , Keim E. R. , Woodbridge E. L. , Gao R. S. , Boering K. A. , Daube B. C. , Wofsy S. C. , Lohmann R. P. , Hintsa E. J. , Dessler A. E. , Webster C. R. , May R. D. , Brock C. A. , Wilson J. C. , Miake‐Lye R. C. , Brown R. C. , Rodriguez J. M. , Loewenstein M. , Proffitt M. H. , Stimpfle R. M. , Bowen S. W. , Chan K. R.
Published: February 2004

Instrumentation on the NASA ER‐2 high‐altitude aircraft has been used to observe engine exhaust from the same aircraft while operating in the lower stratosphere. Encounters with the exhaust plume occurred approximately 10 min after emission with spatial scales near 2 km and durations of up to 10 s. Measurements include total reactive nitrogen, NOy, the component species NO and NO2, CO2, H2O, CO, N2O, condensation nuclei, and meteorological parameters. The integrated amounts of CO2 and H2O during the encounters are consistent with the stoichiometry of fuel combustion (1:1 molar). Emission indices (EI) for NOx (=NO + NO2), CO, and N2O are calculated using simultaneous measurements of CO2. EI values for NOx near 4 g (kg fuel)−1 are in good agreement with values scaled from limited ground‐based tests of the ER‐2 engine. Non‐NOx species comprise less than about 20% of emitted reactive nitrogen, consistent with model evaluations. In addition to demonstrating the feasibility of aircraft plume detection, these results increase confidence in the projection of emissions from current and proposed supersonic aircraft fleets and hence in the assessment of potential long‐term changes in the atmosphere.