bluuebunny/crossref_metadata_2025 huggingface dataset:
Predicting particle coagulation and sedimentation rates for a pulsed input
Authors: Burd A. , Jackson G. A.
Published: February 2004

Particles provide an important transport mechanism for distributing chemically and biologically reactive elements in the ocean. To aid in predicting the fate of colloidal particles, we update an existing model, developed by Farley and Morel [1986] for predicting particle sedimentation rates in the presence of aggregation. We add some effects of the fractal structure of the particles as well as the hydrodynamic interactions between particles. Changes due to the hydrodynamics have a lesser effect than the fractal dimension. Simulated sedimentation rates can vary by as much as 6 orders of magnitude as the fractal dimension is varied between D=3 and D=2. Following Farley and Morel we develop simple expressions for the sedimentation rate. We make use of special initial conditions and particle input rates as well as a value of 1 for the particle stickiness. Introducing the particle fractal dimension revealed limitations with this class of models, restricting the range of D which we could successfully use.
Determination of surface turbulent fluxes over leads in Arctic sea ice
Authors: Alam Afshan , Curry Judith A.
Published: February 2004

We present a new model to compute turbulent surface heat and momentum fluxes over leads in the Arctic sea ice. The momentum roughness length uses a sea state parameterization which is fully consistent with the surface turbulent flux parameterization. The flux parameterization accounts for the fetch limitation of the airflow over a lead. The surface roughness length for heat is determined from an application of surface renewal theory to the air‐sea interface. The modeled fluxes are compared with in situ observations of lead fluxes. We also compare our model results with a bulk flux algorithm which has been commonly used to evaluate surface heat fluxes from leads. We perform sensitivity studies to examine the role of the surface renewal timescale, the importance of the cool skin, and impact of wave age dependence on the momentum roughness length. We have computed integral heat fluxes as a function of lead width/fetch for various atmospheric states to determine the magnitude of heat flux in a mesoscale model grid in which a lead is present.
Generation of edge waves in shallow water
Authors: Lippmann T. C. , Holman R. A. , Bowen A. J.
Published: February 2004

Theoretical growth rates for resonantly driven edge waves in the nearshore are estimated from the forced, shallow water equations of motion for the case of a plane sloping bed. The forcing mechanism arises from spatial and temporal variations in radiation stress gradients induced by a modulating incident wave field. Only the case of exact resonance is considered, where the difference frequencies and wavenumbers satisfy the edge wave dispersion relation (the specific carrier frequencies are not important, only the forced difference values). The forcing is examined in the region seaward of the breakpoint and also within the fluctuating region of surf zone width. In each region, the forcing is dominated by the cross‐shore gradient of onshore directed momentum flux, except for large angles of incidence and the lowest edge wave modes. Outside the surf zone, the spatial and temporal variation of the forcing is determined by considering the interaction of two progressive shallow water waves approaching the beach obliquely. In the surf zone, incident wave amplitudes are assumed to be proportional to the water depth. Thus inside the breakpoint, radiation stress gradients are constant and no forcing occurs. However, at the breakpoint, gradients arising from breaking and nonbreaking waves are turned on and off (like a wave maker) with timescales and length scales determined by the modulation of the breaker position. The forcing in this region is stronger, with inviscid growth rates resulting in edge waves growing to the size of the incident waves of the order of about 10 edge wave periods, a factor of 2–10 times larger than in the offshore region. Using a simple parameterization for frictional damping, edge wave equilibrium amplitudes are found to depend linearly on the ratio tan β/Cd, where β is the beach slope and Cd is a bottom drag coefficient. For tan β/Cd about 3–10, equilibrium amplitudes can be as much as 75% of the incident waves over most of the infragravity portion of the spectrum. When the forcing is turned off, these dissipation rates result in a half‐life decay timescale of the order of 10–30 edge wave periods.
Sea brightness temperature and effects of spray and whitecaps
Authors: Barber R. P. , Wu Jin
Published: February 2004

Following the approach of Tang [1974], the microwave brightness of the sea surface is recalculated with recent parameterizations in terms of wind velocity for the slope distribution and whitecap coverage of the sea surface and the contribution of sea spray. The difference between this revised calculation with no free parameters and the earlier one becomes more significant as the wind velocity increases; it reaches 10 K or more at a wind velocity of 20 m s−1. Present predictions compare favorably with experimental results, suggesting that this model does include the essential physical mechanisms.
Visual‐stratigraphic dating of the GISP2 ice core: Basis, reproducibility, and application
Authors: Alley R. B. , Shuman C. A. , Meese D. A. , Gow A. J. , Taylor K. C. , Cuffey K. M. , Fitzpatrick J. J. , Grootes P. M. , Zielinski G. A. , Ram M. , Spinelli G. , Elder B.
Published: February 2004

Annual layers are visible in the Greenland Ice Sheet Project 2 ice core from central Greenland, allowing rapid dating of the core. Changes in bubble and grain structure caused by near‐surface, primarily summertime formation of hoar complexes provide the main visible annual marker in the Holocene, and changes in “cloudiness” of the ice correlated with dustiness mark Wisconsinan annual cycles; both markers are evident and have been intercalibrated in early Holocene ice. Layer counts are reproducible between different workers and for one worker at different times, with 1% error over century‐length times in the Holocene. Reproducibility is typically 5% in Wisconsinan ice‐age ice and decreases with increasing age and depth. Cumulative ages from visible stratigraphy are not significantly different from independent ages of prominent events for ice older than the historical record and younger than approximately 50,000 years. Visible observations are not greatly degraded by “brittle ice” or many other core‐quality problems, allowing construction of long, consistently sampled time series. High accuracy requires careful study of the core by dedicated observers.
A laboratory study on the shear instability of longshore currents
Authors: Reniers A. J. H. M. , Battjes J. A. , Falqués A. , Huntley D. A.
Published: February 2004

Low‐frequency oscillations in the nearshore velocity field due to the instability of the shear of a longshore current are termed shear waves. Laboratory experiments have been performed to test theoretical predictions of the dispersion relation and growth rates for shear instabilities under controlled conditions and to provide empirical data for model calibration. The results, obtained with a high‐resolution spectral analysis technique (Maximum Entropy Method), show that it is possible to generate instabilities of significant amplitude in a wave basin of limited length. The measurements demonstrate that these instabilities can be attributed to the shear instability of the longshore current. Quantitative comparison showing good correspondence with model predictions has been performed.
Reconstructing the origin and trajectory of drifting Arctic sea ice
Authors: Pfirman S. L. , Colony R. , Nürnberg D. , Eicken H. , Rigor I.
Published: February 2004

Recent studies have indicated that drifting Arctic sea ice plays an important role in the redistribution of sediments and contaminants. Here we present a method to reconstruct the backward trajectory of sea ice from its sampling location in the Eurasian Arctic to its possible site of origin on the shelf, based on historical drift data from the International Arctic Buoy Program. This method is verified by showing that origins derived from the backward trajectories are generally consistent with other indicators, such as comparison of the predicted backward trajectories with known buoy drifts and matching the clay mineralogy of sediments sampled from the sea ice with that of the seafloor in the predicted shelf source regions. The trajectories are then used to identify regions where sediment‐laden ice is exported to the Transpolar Drift Stream: from the New Siberian Islands and the Central Kara Plateau. Calculation of forward trajectories shows that the Kara Sea is a major contributor of ice to the Barents Sea and the southern limb of the Transpolar Drift Stream.
Airborne measurements of aerosols from burning biomass in Brazil related to the TRACE A experiment
Authors: Pereira E. B. , Setzer A. W. , Gerab F. , Artaxo P. E. , Pereira M. C. , Monroe G.
Published: February 2004

Results are reported from an airborne campaign to investigate the impacts of burning biomass upon the loading of lower‐tropospheric aerosols and its composition over the Brazilian tropics. The flights, conducted as part of the NASA/Transport and Atmospheric Chemistry Near the Equator‐Atlantic (TRACE A) mission, started on September 1, 1992, when the dry (fire) season still prevailed in the central part of Brazil, and ended on September 29. Of the total number of burnings detected in Brazil by the advanced very high resolution radiometer (AVHRR)/NOAA satellite sensor, 74% were concentrated in the states of Amazonas, Maranhão, Mato Grosso, Pará, Roraima, and Tocantins during this period. Aerosol particles were sampled from a twin‐engine aircraft in transit and vertical profile flights were made up to 4,000 m altitude. Black carbon measurements made in real time and in areas of burning biomass peaked at ∼2,500 m above the ground, increasing to ∼12,000 ng/m3. In other areas these values were lower by 1 order of magnitude. A condensation nuclei counter measuring small particles (>0.014 μm) produced values ranging from 2,000 to 16,000/cm3for areas with low and high burning biomass, respectively. Deposition filters in a two‐stage cascade impactor, and Nuclepore filters collected aerosols for analysis of 13 elements through particle‐induced X ray emissions (PIXE). Primary elements associated with soil dust (Al, Si, Mn, Fe, Ni) prevailed in the aerosol coarse mode (>1 μm) while the fine mode aerosols were enriched in S, K, Br, and Rb, which are tracers normally associated with burning of biomass. The good correlation between fire spot counts, obtained via AVHRR aboard NOAA satellites, and black carbon, counts of small particles and total aerosol mass, suggests the determining of local concentrations of fire‐derived aerosol fire emissions by satellite to be a new and useful approach.
Observations of dimethyl sulfide over the western North Atlantic Ocean using an airborne tandem mass spectrometer
Authors: Spicer Chester W. , Kenny Donald V. , Chapman Elaine , Busness Kenneth M. , Berkowitz Carl M.
Published: February 2004

An atmospheric sampling tandem mass spectrometer has been evaluated for aircraft monitoring of dimethyl sulfide (DMS) and then used for DMS monitoring during portions of six flights over the western North Atlantic Ocean. Laboratory evaluations demonstrated that the mass spectrometer is highly selective for DMS, and responds linearly over a wide range of mixing ratios. The detection limit for DMS is 1–2 ppt in dry air. However, the response is suppressed in the presence of water vapor, so the sample air must be dried or the response must be corrected for this effect. There appeared to be no consistent effect of altitude/pressure on instrument response. The mass spectrometer was installed on the Battelle Gulf stream G‐1 research aircraft and used to monitor DMS and a number of other chemicals during flights over the western North Atlantic Ocean in August and September, 1992. DMS mixing ratios ranged from <2 ppt to 332 ppt, and were highly variable both horizontally and vertically. Vertical profiles indicated that there are times when the marine boundary layer is stratified by one or more temperature inversions, and that DMS emitted by surface seawater can be confined near the surface within a shallow layer a few hundred meters deep. Under such circumstances, the DMS photooxidation products may be removed rapidly by deposition, lessening the potential for cloud nucleation. The mean DMS mixing ratio in the boundary layer below the lowest observed temperature inversion was 61 ppt, with a range of 7–332 ppt. DMS measurements in the free troposphere were lower than the boundary layer values, but high enough to suggest significant transport from the boundary layer to the free troposphere. Significant horizontal variability was observed during constant altitude flights in the boundary layer. In one case the DMS mixing ratio was observed to vary with the ocean depth under the flight path, with higher mixing ratios observed over the shallower coastal shelf and undersea banks. In several cases we also observed an apparent association between atmospheric DMS mixing ratio at low elevation and sea surface temperature.
The solar cycle variation of total ozone: Dynamical forcing in the lower stratosphere
Authors: Hood L. L.
Published: February 2004

Multiple regression methods are applied to estimate the solar cycle variation of (1) zonal mean ozone as a function of altitude and latitude using a combination of Nimbus 7 solar backscattered ultraviolet (SBUV) and National Oceanic and Atmospheric Administration (NOAA) 11 SBUV/2 ozone profile data for a 15‐year period; (2) total ozone as a function of latitude, longitude, and season using Nimbus 7 total ozone mapping spectrometer (TOMS) data for a 13.3‐year period; (3) lower stratospheric temperature as a function of latitude, longitude, and season using microwave sounding unit (MSU) Channel 4 data for a 16‐year period; and (4) lower stratospheric geopotential height as a function of latitude, longitude, and season in the northern hemisphere using Berlin height data for a 30‐year period. According to the SBUV‐SBUV/2 data, most (about 85%) of the 1.5–2% solar cycle variation of global mean total column ozone occurs in the lower stratosphere (altitudes < 28 km). Evidence is obtained for a related solar cycle variation of lower stratospheric temperature (50–150 mbar) and geopotential height (30, 50, and 100 mbar) with geographic dependences similar to that of the solar cycle variation of total ozone. Specifically, total ozone, lower stratospheric temperature, and lower stratospheric geopotential height have annual mean solar regression coefficients in the northern hemisphere that reach a maximum near 30°N latitude within a longitude sector extending from approximately 160°E to 250°E. Maximum variations from solar minimum to maximum in this sector are approximately 11 Dobson units, 0.8 K near 100 mbar, and 60 m at 50 mbar, respectively. Seasonal solar regression coefficients tend to be statistically significant over larger areas in summer but have larger amplitudes within limited regions in winter. These geographic similarities between total ozone, lower stratospheric temperature, and geopotential height solar coefficients suggest that changes in lower stratospheric dynamics between solar minimum and maximum may play an important role in driving the observed total ozone solar cycle variation. To test this hypothesis, a simplified perturbation ozone transport model is applied to calculate the expected total ozone variation owing to dynamical forcing for the calculated geopotential height solar coefficients, climatological ozone mixing ratios, and zonal winds. For the summer season during which the solar regression coefficients are significant over the largest area, both the amplitude and latitude dependence of the observed solar cycle ozone variation are approximately consistent with the model estimates.
VHF echoes from the midlatitude mesosphere and the thermal structure observed by lidar
Authors: Thomas L. , Marsh A. K. P. , Wareing D. P. , Astin I. , Chandra H.
Published: February 2004

Observations with a 46.5‐MHz radar system at Aberystwyth, Wales (52°N, 4°W) over the period February 1990 to May 1994 have shown a pronounced seasonal variation in the height range of mesospheric echoes. These were observed over the range 64–84 km in all seasons, but those at still greater heights were confined to summer months. Coordinated radar and lidar observations at the same site during 1993 have shown that these intense echoes in summer, analogous to polar mesosphere summer echoes (PMSE), are associated with low mesopause temperatures; the weaker echoes observed in winter seem to be associated with regions of superadiabatic lapse rates; and echoes are observed both above and below the maxima in temperature inversions commonly observed below the mesopause. The types of instability implied in these associations of echo height and temperature structure are considered.
Information on aerosol size distribution contained in solar reflected spectral radiances
Authors: Tanré D. , Herman M. , Kaufman Y. J.
Published: February 2004

Information on the aerosol size distribution contained in the reflected solar spectral radiances detected over the oceans can be reduced into two quantities. These quantities have been determined in an unbiased way with the use of the principal components. Consequently, only one to two parameters of the size distribution can be retrieved. For a single‐mode distribution these parameters are the effective radius of the particles and the width of the size distribution. The accuracy of the retrieval depends on the view and illumination directions. Accurate knowledge of the refractive index, real and imaginary parts, is not critically important for the retrieval as long as the retrieved particles are smaller than 1.0 μm. An error budget shows that very clean conditions are not suitable for getting any information on the aerosol size distribution. A surprising result of this investigation is that the spectral reflectance of a bimodal‐lognormal distribution can be simulated very well with spectral reflectance of a single lognormal with an appropriate radius and width of distribution, σ, that do not necessarily correspond to an average of the bimodal values. The present results change drastically our philosophy regarding the retrieval scheme. Additional studies are needed to confirm the present results for nonspherical particles.
Bulk properties of isentropic mixing into the tropics in the lower stratosphere
Authors: Minschwaner K. , Dessler A. E. , Elkins J. W. , Volk C. M. , Fahey D. W. , Loewenstein M. , Podolske J. R. , Roche A. E. , Chan K. R.
Published: February 2004

Timescales for mixing of midlatitude air into the tropical lower stratosphere are deduced from observations of long‐lived tracers N2O and CCl3F. Bulk mixing between tropical and midlatitude regions is assumed to be isentropic and relatively slow compared with local mixing within each region. The mean value of the mixing timescale ranges from 12 to 18 months near 20 km. There is a tendency for shorter mixing times at higher and lower altitudes, although vertical profiles of mixing cannot be definitively established by the data. A more robust quantity is given by the fraction of midlatitude air entrained into the tropical upwelling region. Implied mixing fractions exceed 50% above 22 km.
Origin of ozone and NOx in the tropical troposphere: A photochemical analysis of aircraft observations over the South Atlantic basin
Authors: Jacob D. J. , Heikes E. G. , Fan S.‐M. , Logan J. A. , Mauzerall D. L. , Bradshaw J. D. , Singh H. B. , Gregory G. L. , Talbot R. W. , Blake D. R. , Sachse G. W.
Published: February 2004

The photochemistry of the troposphere over the South Atlantic basin is examined by modeling of aircraft observations up to 12‐km altitude taken during the TRACE A expedition in September–October 1992. A close balance is found in the 0 to 12‐km column between photochemical production and loss of O3, with net production at high altitudes compensating for weak net loss at low altitudes. This balance implies that O3 concentrations in the 0–12 km column can be explained solely by in situ photochemistry; influx from the stratosphere is negligible. Simulation of H2O2, CH3OOH, and CH2O concentrations measured aboard the aircraft lends confidence in the computations of O3 production and loss rates, although there appears to be a major gap in current understanding of CH2O chemistry in the marine boundary layer. The primary sources of NOx over the South Atlantic Basin appear to be continental (biomass burning, lightning, soils). There is evidence that NOx throughout the 0 to 12‐km column is recycled from its oxidation products rather than directly transported from its primary sources. There is also evidence for rapid conversion of HNO3 to NOx in the upper troposphere by a mechanism not included in current models. A general representation of the O3 budget in the tropical troposphere is proposed that couples the large‐scale Walker circulation and in situ photochemistry. Deep convection in the rising branches of the Walker circulation injects NOx from combustion, soils, and lightning to the upper troposphere, leading to O3 production; eventually, the air subsides and net O3 loss takes place in the lower troposphere, closing the O3 cycle. This scheme implies a great sensitivity of the oxidizing power of the atmosphere to NOx emissions in the tropics.
Simulated global tropospheric PAN: Its transport and impact on NOx
Authors: Moxim W. J. , Levy H. , Kasibhatla P. S.
Published: February 2004

Using the 11‐level Geophysical Fluid Dynamics Laboratory (GFDL) global chemical transport model (GCTM) with all known sources of tropospheric NOx, we simulate the global tropospheric distribution of peroxyacetyl nitrate (PAN) and quantify its impact on tropospheric NOx. The model's global distribution of PAN is in reasonable agreement with most available observations. In the atmospheric boundary layer, PAN is concentrated over the continental sites of NOxemissions, primarily the midlatitudes in the northern hemisphere and the subtropics in the southern hemisphere. PAN is distributed relatively zonally throughout the free troposphere of the northern hemisphere, with the maximum levels found in the coldest regions, while in the southern hemisphere the maximum PAN levels are found in an equator to 30°S belt stretching from South America to Australia. Overall, the simulated three‐dimensional fields of seasonal PAN are a result of the interaction of the type of transport meteorology (convective or synoptic scale storms) occurring in the PAN formation regions and PAN's temperature‐dependent lifetime. We find the impact of PAN chemistry on NOxto be rather subtle. The magnitude and the seasonal cycle of the global tropospheric integral of NOx, which has its maximum in January and the formation of HNO3as its dominant loss path, are barely affected by the inclusion of PAN chemistry, however PAN, as a result of its temperature sensitivity and transport, regionally provides an efficient mechanism for redistributing NOxfar from its source areas. With the inclusion of PAN chemistry, monthly mean NOxconcentrations increase by up to a factor of 5 in the remote lower troposphere and show a spring maximum over areas of the North Atlantic and North Pacific Oceans. In contrast, PAN has only a minor impact in the upper half of the troposphere (±10%). Examining local time series of NOxand PAN, the monthly mean mixing ratios in remote regions are shown to be composed of numerous short‐term (1–2 days) large magnitude events. These episodes are large enough to potentially result in ozone production even when the monthly mean NOxvalues are in the ozone destruction range. While both the direct transport of NOxand its indirect transport as PAN contribute to the elevated NOxepisodes over the remote extratropical oceans, events over the remote subtropical oceans are dominated by midtropospheric PAN that sinks anticyclonically equatorward and decomposes to NOxin the warmer air.
Measurements of PAN, alkyl nitrates, ozone, and hydrocarbons during spring in interior Alaska
Authors: Beine Harald J. , Jaffe Daniel A. , Blake Donald R. , Atlas Elliot , Harris Joyce
Published: February 2004

Measurements of the atmospheric mixing ratios of ozone, peroxyacetylnitrate (PAN), hydrocarbons, and alkyl nitrates were made in a boreal forest ecosystem in the interior of Alaska from March 15 to May 14, 1993. During this period the mixing ratios of PAN, alkyl nitrates, and nonmethane hydrocarbons (NMHCs) generally decreased due to the influence of both meteorology and OH removal. Mean mixing ratios of ozone, PAN, C2 ‐ C6 alkyl nitrates, and total C2 ‐ C5 NMHC during southerly flow periods were 24.4 parts per billion (ppbv), 132.1 parts per trillion (pptv ), 34 pptv, and 8.2 ppbCv, respectively. During a short period of northerly flow, mixing ratios of PAN and total NMHC were approximately 2 times the southerly flow mixing ratios. PAN is correlated with ozone, and alkyl nitrates are correlated with alkanes. PAN and ozone mixing ratios exhibit similar diurnal variations on a number of days with an early morning minimum and afternoon maximum. This is likely due to a diurnal cycle in the boundary layer ‐ free troposphere exchange and loss processes in the boundary layer for both O3 and PAN. Higher molecular weight (mw) hydrocarbons and alkyl nitrates are observed to decrease more quickly than the lower mw hydrocarbons, consistent with removal by OH as the primary loss process.
A tractable physical model of shortwave radiation interception by vegetative canopies
Authors: Roujean Jean‐Louis
Published: February 2004

Characterizing and understanding shortwave radiative transfer inside a vegetation canopy is essential because of the climatologically significant interactions between the Earth's atmosphere and the land surface. Particularly relevant is the radiation intercepted by the canopy elements which reveals the structural and optical vegetation properties. In this study, a tractable physical model of radiation interception is developed which accounts for multiple scattering to be applicable for near infrared. This model performs rather well whenever compared to the exact computation of the radiative transfer equation or a detailed code of radiative transfer. It seems to be, however, less relevant for thin vegetation canopies having large single‐scattering albedo. Its simple expression makes it useful to derive quantitative estimates of radiation intercepted by the canopy which will lead to improved retrievals of main vegetation parameters such as leaf area index.
Noctilucent clouds and the thermal structure near the Arctic mesopause in summer
Authors: Lübken F.‐J. , Fricke K.‐H. , Langer M.
Published: February 2004

In the summers of 1993 and 1994 a series of meteorological rockets and sounding rockets were launched from the Andøya Rocket Range (69°N) during the SCALE and ECHO campaigns in order to investigate the state of the mesosphere and lower thermosphere (SCALE = “SCAttering Layer Experiment”; ECHO indicates that radar and lidar echoes are investigated). At the same location a Rayleigh lidar was operational during these campaigns and searched for enhanced backscatter signals from the upper mesosphere indicative of the presence of noctilucent clouds (NLC). In five cases the lidar detected a NLC and the atmospheric temperature profile was obtained simultaneously by in situ techniques. A literature survey shows that there are only three more cases of unambiguous and simultaneous observations of NLC temperature and altitude. The temperature profiles obtained during SCALE and ECHO are as expected for the high‐latitude summer season: The mean mesopause temperature is 135 K at an altitude of 87.5 km. The variability of the temperatures is smaller above ∼84 km altitude than below. The mean temperature below the mesopause shows a remarkable repeatability ever since the first measurements 30 years ago; at the lower edge of the NLC heights (82 km) it is again and again observed to be in the range 150 ± 2 K and the variability within each data set is only a few Kelvins. Such an “equithermal submesopause” in summer puts a serious constraint on any model prediction of secular changes of temperatures in the upper mesosphere. The mean altitude of the NLCs as determined from our lidar measurements is 83.1 km which is surprisingly close to the very first height determinations more than 100 years ago. It is conceivable that this repeatability in altitude reflects a similar repeatability of the thermal structure. There is no apparent correlation between the conditions at the mesopause and the occurrence of NLCs at lower altitudes. The physical reason behind this is presumably related to the fact that the wind direction changes at ∼87 km height, which implies that the air masses observed above the rocket site near mesopause altitudes have been advected from different locations than those at NLC heights. The NLCs are always located below the mesopause, and the temperature in the NLC layer is observed to be lower than 154 K. Our results are compatible with the idea that NLCs consist of ice particles which start to nucleate around the mesopause, sediment to lower altitudes while growing, become observable by the lidar and/or by the naked eye, and finally evaporate once they approach the higher temperatures around 82 km.
Aerosol observations at Chebogue Point during the 1993 North Atlantic Regional Experiment: Relationships among cloud condensation nuclei, size distribution, and chemistry
Authors: Liu P. S. K. , Leaitch W. R. , Banic C. M. , Li S.‐M. , Ngo D. , Megaw W. J.
Published: February 2004

Observations of aerosol chemistry and microphysics were made at Chebogue Point, Nova Scotia, from August 16 to September 8, 1993 as part of the North Atlantic Regional Experiment (NARE) intensive. Most of the aerosols were classified into two groups according to the geometric mean volume diameter (Dgv) of the particles which contributed the greatest volume (sub‐0.5 μm). The group‐1 aerosols, representing 33% of the data, are characterized by Dgv of 0.18–0.19 μm; the group‐2 aerosols, representing 50% of the data, are characterized by Dgv of 0.20–0.22 μm; and the remaining aerosols bear similarities to either groups 1 or 2 but lie outside the Dgv ranges. The differences between these aerosol groups are consistent with the addition of sulfate to the group‐2 aerosols via recent processing through cloud. Factors supporting this possibility include the presence of low marine stratus upwind of the site only on days when the group‐2 aerosol was observed, the higher Dgv for the group‐2 aerosols consistent with the observed size threshold for activation in these clouds, and the association of non‐sea‐salt SO4= (nssSO4=) with larger particle sizes for the group‐2 aerosols. In general, the masses of the most abundant inorganic and organic ions, nssSO4= and oxalate, were associated with the main volume of the sub‐0.5‐μm particles. Cloud condensation nucleus (CCN) concentrations active at 0.4% supersaturation (CCN0.4) were highly correlated with the concentrations of particles >0.01 μm and oxalate and moderately correlated with nssSO4=. Concentrations of CCN active at 0.06% supersaturation (CCN0.06) correlate very well with the concentrations of particles >0.19 μm diameter. In the case of the recently cloud‐processed aerosols, for which nssSO4= is more strongly associated with particles >0.19 μm, the CCN0.06 also correlate well with nssSO4=. CCN spectra computed using the measured size distributions and aerosol chemistry agree well with the measured CCN.
Analysis of satellite‐based estimates of tropospheric diurnal temperature range
Authors: Balling Robert C. , Christy John R.
Published: February 2004

A decrease in the diurnal temperature range has been identified throughout this century in many of the world's land‐based climate records. However, documentation of the seasonality, magnitude, and geography of these changes has been hampered by the lack of homogeneous maximum and minimum temperature measurements over most of the planet. In this investigation, we attempt to use satellite‐based measurements of tropospheric temperatures to assess spatial and temporal trends in the diurnal temperature range over the period 1979 to 1994. Although quite exploratory and preliminary in nature, we find that the satellite‐based estimates of the diurnal temperature range are (1) larger over land areas than ocean areas, (2) high in summer, particularly in low latitudes, and low in winter, especially in the higher latitudes, and (3) decreasing substantially in the winter season for the land areas between 30°N and 60°N. The results are potentially compromised by many factors including orbital drift problems and changes in satellites. Despite the potential pitfalls of the satellite‐based measurements in this investigation our findings support other results showing a reduction in diurnal temperature range in the midlatitudes of the northern hemisphere during the low‐sun season.
Seasonal variation of the ozone production efficiency per unit NOx at Harvard Forest, Massachusetts
Authors: Hirsch Adam I. , Munger J. William , Jacob Daniel J. , Horowitz Larry W. , Goldstein Allen H.
Published: February 2004

Weekly values of the net O3 production efficiency (OPE), defined as the net number of O3 molecules produced per molecule of NOx (NO + NO2) consumed, are estimated from a 1990–1994 record of O3, NOx, NOy, CO, and C2H2 concentrations at Harvard Forest, Massachusetts. The OPE is inferred from the slope ΔO3/Δ(NOy − NOx) of the linear regression between O3 and NOy‐NOx concentrations (NOy is the sum of NOx and its oxidation products); and alternatively from the slopes ΔO3/ΔCO and ΔO3/ΔC2H2 multiplied by regional estimates of the CO/NOx and C2H2/NOx emission ratios. The mean OPE values inferred from ΔO3/Δ(NOy − NOx) are 3–5 times higher than those inferred from ΔO3/ΔCO or ΔO3/ΔC2H2; the discrepancy may be due to the effects of HNO3 and O3 deposition and also to uncertainties in the CO/NOx and C2H2/NOx emission ratios. The relative seasonal trends of the OPE derived from ΔO3/Δ(NOy − NOx), ΔO3/ΔCO, and ΔO3/ΔC2H2 are, however, similar. Thus ΔO3/Δ(NOy − NOx) increases from about 4 mol/mol in May to 8 mol/mol in June–July, and gradually decreases back to 4 mol/mol by early October. The sharp rise of the OPE from May to June is attributed to onset of emission of the biogenic hydrocarbon isoprene. The decline from July to October is attributed to decreases in isoprene emission and in solar radiation. The O3 background at Harvard Forest, defined by the y intercept of the O3 versus NOy‐NOx regression line, decreases from 40 ppbv in May to 25 ppbv in September, consistent with observations at remote sites in northern midlatitudes. The seasonal trend in the background explains why mean O3 concentrations at Harvard Forest peak in May–June even though the OPE peaks in June–July.
Chlorine deactivation in the lower stratospheric polar regions during late winter: Results from UARS
Authors: Santee M. L. , Froidevaux L. , Manney G. L. , Read W. G. , Waters J. W. , Chipperfield M. P. , Roche A. E. , Kumer J. B. , Mergenthaler J. L. , Russell J. M.
Published: February 2004

Recovery from enhanced chlorine conditions in the lower stratospheric polar regions of both hemispheres is investigated using data from the Upper Atmosphere Research Satellite (UARS). Microwave Limb Sounder (MLS) measurements of ClO within the polar vortices are used to infer ClOx (ClO + 2Cl2O2) abundances that are then correlated with simultaneous Cryogenic Limb Array Etalon Spectrometer (CLAES) measurements of ClONO2 and Halogen Occultation Experiment (HALOE) measurements of HCl obtained starting within 5 days of the end of the MLS and CLAES high‐latitude observing periods in each hemisphere. Time series of vortex‐averaged mixing ratios are calculated on two potential temperature surfaces (585 K and 465 K) in the lower stratosphere for approximately month‐long intervals during late winter: August 17 – September 17, 1992, in the southern hemisphere and February 12 – March 16, 1993, in the northern hemisphere. The observed mixing ratios are adjusted for the effects of vertical transport using diabatic vertical velocities estimated from CLAES tracer data. In the northern hemisphere, the decrease in ClOx is balanced on both surfaces by an increase in ClONO2. In the southern hemisphere, continuing polar stratospheric cloud activity prevents ClO from undergoing sustained decline until about September 3. In contrast to the northern hemisphere, there is no significant chemical change in vortex‐averaged ClONO2 at 465 K, and there is an apparent decrease in ClONO2 at 585 K, even after the enhanced ClO abundances have started to recede. Results from the SLIMCAT chemical transport model [Chipperfield et al., this issue] initialized with UARS data and run with OH + ClO → HCl + O2 as an 8% channel suggest that the primary recovery product in the south during this time period is not ClONO2, but HCl. HALOE HCl mixing ratios are extrapolated back to the time of the MLS and CLAES data. At 585 K, the chlorine budget can be made to balance by extrapolating HCl back to a value of 0.6 parts per billion by volume (ppbv) at the beginning of the study period; at 465 K, the contribution from extrapolated HCl is not sufficient to offset the loss in ClOx, and there is a slight imbalance between the decrease in reactive chlorine and the change in chlorine reservoirs. The difficulty in closing the chlorine budget in the southern hemisphere may arise from complications caused by ongoing activation, incomplete photochemical assumptions, and/or inadequate data quality.
Three‐dimensional chemical forecasting: A methodology
Authors: Lee A. M. , Carver G. D. , Chipperfield M. P. , Pyle J. A.
Published: February 2004

During the recent ASHOE (Airborne Southern Hemisphere Ozone Experiment) and SESAME (Second European Stratospheric Arctic and Middle‐Latitude Experiment) field campaigns we produced a number of 10‐day chemical forecasts of the stratosphere to aid in flight planning and interpretation of the observations. A general circulation model was integrated at high resolution to produce a 10‐day meteorological forecast. These forecast fields were then used to specify the circulation in an off‐line three‐dimensional chemical transport model to produce a medium‐range chemical forecast of the stratosphere. The chemical model has a detailed stratospheric chemistry scheme, including heterogeneous reactions on polar stratospheric clouds and sulfate aerosols. The NASA ER‐2 high‐altitude research aircraft made in situ measurements of chemical tracers in the lower stratosphere during the ASHOE campaign, which took place in four deployments from March to October 1994. This paper presents examples from the chemical forecasts made during the second and fourth deployments. We show that the ability to indicate the likely composition of the atmosphere is an important improvement over the standard meteorological forecasts, especially in air perturbed by chemical processing on polar stratospheric clouds. Of particular interest was the ability to forecast the chemical composition of filaments, which had been eroded from the vortex edge. Furthermore, immediate post‐flight comparison between observed data and synoptic model data gave useful chemical interpretation of the observations.
Ground‐based radiometry of stratomesospheric ozone employing a superconductive receiver
Authors: Kawabata K. , Ogawa H. , Yonekura Y. , Suzuki H. , Suzuki M. , Iwasaka Y. , Shibata T. , Sakai T.
Published: February 2004

The J = 61,5–60,6 (110.836 GHz) line of stratomesospheric O3 has been measured employing a Nb SIS mixer receiver cooled by a closed cycle 4 K refrigerator on the Higashiyama Campus of the Nagoya University (35°N, 137°E, 70 m above sea level) since January 1992 in a sporadic manner. Relative diurnal variations of O3 in January 1995 are in good agreement with a zero‐dimensional model, ignoring transport in the 3.2 to 0.1‐hPa range. Time profiles of the O3 mixing ratio in dawn and dusk are shown with a time resolution of 6 min in the step of 0.25 of log10p, where p denotes the total atmospheric pressure in hectopascals. Amplitudes of seasonal variations are small at around 20, 3.2, and 0.056 hPa, respectively, and the type or phase of seasonal variations changes at these altitudes. Mixing ratio is high in summer between 10 and 5.6 hPa and is high in winter between 1.8 and 0.1 hPa. Seasonal variations of mixing ratio appear to show biennial variations between 1. and 0.1 hPa and semiannual variations above 0.032 hPa, though the period of observations is not long enough to get a definite conclusion. O3 mixing ratio above 0.032 hPa appears to be high from March to April and from October to November.
Three‐dimensional global modeling studies of the transport and photochemistry over the North Atlantic Ocean
Authors: Atherton C. S. , Sillman Sanford , Walton J.
Published: February 2004

A three‐dimensional, global model is used to characterize the troposphere over the North Atlantic Ocean. In August, tropospheric ozone appears to be transported from North America across the Atlantic Ocean in “events,” one of which is presented. The North Atlantic Ocean may be characterized by three regions (western, central, and eastern) with distinct photochemical and transport signatures. In the western Atlantic, emissions are fresh and O3 and CO, O3 and NOy, and O3 and (NOy‐NOx) show a strong positive correlation. As air travels eastward across the Atlantic Ocean, it photochemically ages, selected species are deposited, and the degree of correlation tends to decrease. Ozone is photochemically removed more rapidly than CO, and the slope ΔO3/ΔCO tends to decrease with time and distance. Conversely, the slope ΔO3/Δ(NOy‐NOx) tends to increase with time and distance, because HNO3 and PAN tend to be removed more quickly than O3. A region within the central Atlantic (35°–45°N, 35°–50°W) is much less affected by episodic transport from North America than the three regions above. Concentrations and correlations of species are compared with observations from North Atlantic Regional Experiment and the eastern United States. Differences between simulated concentrations and measurements may be due to a combination of effects that include boundary layer phenomena, fog events, the scale of the model, and uncertainties in emission inventories.
Ozone monitoring with TIROS‐N operational vertical sounders
Authors: Neuendorffer Arthur C.
Published: February 2004

The potential for using the TIROS‐N operational vertical sounder (TOVS) on NOAA polar‐orbiting weather satellites to monitor stratospheric ozone is examined. TOVS 9.7‐μm high resolution infrared sounder (HIRS) ozone channel is found to be particularly well suited for monitoring the lower stratospheric ozone layer. A 3 Dobson unit drop in lower stratospheric ozone produces a measurable (i.e., ≈0.2°C) increase in HIRS 9.7‐μm brightness temperatures even in the vicinity of Antarctica. A two‐layer physical retrieval algorithm is presented that uses the TOVS HIRS 9.7‐μm signal to determine lower stratospheric ozone and to estimate total ozone. Trend analysis of TOVS ozone confirms the fact that there have been significant losses of lower stratospheric ozone in the spring equinox extratropics of both hemispheres. Much of this loss persists into the summer solstice time period.
Biases in Earth radiation budget observations: 2. Consistent scene identification and anisotropic factors
Authors: Ye Qian , Coakley James A.
Published: February 2004

Simple threshold scene identification methods are developed to reduce the effects of errors in scene identification on the anisotropy of reflected and emitted radiances inferred from Earth Radiation Budget Experiment (ERBE) scanner observations. The ERBE maximum likelihood estimate (MLE) scene identification is assumed to be accurate for nadir fields of view. Various combinations of neighboring ERBE scanner fields of view at nadir are used to determine the population of cloud scene types as a function of field of view size. Longwave and shortwave thresholds are then determined for each of the ERBE solar zenith, satellite view zenith, and relative azimuth angular bins so that the population of cloud scene types at a particular satellite view zenith angle is consistent with the field of view size at the particular satellite view zenith angle. Differences between the anisotropy of reflected sunlight and emitted longwave radiation obtained using the new scene identification method and that obtained using the ERBE MLE method show that the ERBE radiative fluxes have satellite view zenith angle dependent biases. Thresholds are also developed for cloud scene identification with fields of view that are constructed to have a constant size with satellite view zenith angle. The angular dependence of reflected sunlight and emitted longwave radiation for scenes identified with these thresholds show little dependence on field of view size. This lack of dependence is a necessary condition for using scanning radiometer data to obtain radiative fluxes.
Historical biomass burning: Late 19th century pioneer agriculture revolution in northern hemisphere ice core data and its atmospheric interpretation
Authors: Holdsworth G. , Higuchi K. , Zielinski G. A. , Mayewski P. A. , Wahlen M. , Deck B. , Chylek P. , Johnson B. , Damiano P.
Published: February 2004

Ice core data from Yukon and Greenland spanning from ∼1750 to 1950 indicate that between ∼1850 and ≤1910 a clear atmospheric signal exists of an episodic biomass burning event that is referred to as the Pioneer Agriculture Revolution. This is best seen in NH4+ion and particulate concentrations but also in some limited black carbon concentration data, where for all three quantities maximum levels reach about 3 times the prerevolution background concentrations. Tree cellulose δ13C data and some early, controversial, French, air CO2data, occurring within the same time interval, are interpreted as providing other independent evidence for the same, mainly North American, late 19th century biomass burning event. Some hitherto problematic northern hemisphere ice core derived CO2concentration data may now be interpreted as containing a biomass burn signal, and these data are compared, especially as to the time of occurrence, with all the other results. A global carbon cycle model simulation of atmospheric CO2mixing ratios using a maximum input of 3 Gt(C)/yr at northern midlatitudes produces “anomalous” CO2levels close to some of the ice core carbon dioxide values. However, other values in this data set do not reasonably represent fully mixed atmospheric values. This suggests that these values might be transients but still “tracers” for biomass burning. Nevertheless, it appears possible that interhemispheric CO2gradients of similar magnitude to the present one could have existed briefly late last century.
Trace gas and aerosol measurements using aircraft data from the North Atlantic Regional Experiment (NARE 1993)
Authors: Buhr Martin , Sueper Donna , Trainer Michael , Goldan Paul , Kuster Bill , Fehsenfeld Fred , Kok Gregory , Shillawski Richard , Schanot Allan
Published: February 2004

Measurements of the concentrations of O3, CO, NO, NOy, condensation nuclei, and aerosols in 12 size bins ranging from 0.1 to 3.1 μm as well as a variety of meteorological parameters were collected aboard the NCAR King Air in August 1993 during 16 flights over or near the Gulf of Maine. The purpose of this measurement campaign was to describe the sources and variation of ozone and its precursors in the western NARE region during the summer season. Correlations between O3 and CO, O3 and NOy, and other chemical and aerosol measurements are examined. Several features in the altitude profiles are investigated using principal component analysis. The results of the trace gas analyses indicate that anthropogenically influenced ozone production dominated ozone throughout the experimental region at altitudes below 1500 m. Other factors identified include a distinct signature from fresh emissions below 1500 m. Above 1500 m the sources of ozone were determined by transport from a variety of sources.