bluuebunny/crossref_metadata_2025 huggingface dataset:
On the use of smoothing splines to filter CO2data
Authors: Enting I. G.
Published: February 2008

The use of smoothing splines in the analysis of CO2data is reviewed in the light of recent mathematical studies of spline fitting considered as a filtering operation. The digital filtering interpretation is particularly appropriate because many recent analyses of CO2data can be regarded as signal extraction studies. It is suggested that the most appropriate formulation of smoothing splines for analyzing CO2and similar data is the form in which the trade‐off between smoothness and data fitting is expressed by fixing the relative scaling factor, λ. This form has a direct interpretation as a digital filter with a specific transfer function and so spline fits for different stations can be standardized for comparisons. The scaling factor should be chosen according to the spectral characteristics of the signal that is to be estimated. Smoothing splines are particularly suitable for interpolating irregularly spaced data, since the filtering properties are only weakly dependent on the data density. However, for signal estimation problems involving uniformly spaced data, special‐purpose digital filters will frequently give performance superior to smoothing splines. The discussion is illustrated by an analysis of CO2data from Cape Grim, Tasmania.
Impact of natural hydrocarbons on hydroxyl and peroxy radicals at a remote site
Authors: Trainer M. , Hsie E. Y. , McKeen S. A. , Tallamraju R. , Parrish D. D. , Fehsenfeld F. C. , Liu S. C.
Published: February 2008

The impact of non‐methane hydrocarbons of natural and anthropogenic origin on the photochemistry of the nonurban lower atmosphere has been studied using a photochemical model with detailed planetary boundary layer transport. The research was undertaken to evaluate the increase in peroxy radical concentrations due to hydrocarbon oxidation and their contribution to observed imbalances in the NOx, O3 photostationary state (Parrish et al., 1986a). The results show that these hydrocarbons, at concentrations observed in the atmosphere, reduce the hydroxyl radical concentration in clean air and increase the peroxy radical concentration to levels that are needed to explain the observed imbalance in the photostationary state. For the conditions simulated here, natural hydrocarbons are the principal contributors to the increase in the peroxy radical concentration at low NOx mixing ratios. At higher NOx levels the anthropogenic hydrocarbons that scale with NOx gain in importance. Model simulations that include the hydrocarbons reproduce the observed dependence of the concentration of ozone on various NOx concentrations.
Seasonal differences in the vertical distributions of NO, NO2, and O3 in the stratosphere near 50°N
Authors: Ridley B. A. , McFarland M. , Schmeltekopf A. L. , Proffitt M. H. , Albritton D. L. , Winkler R. H. , Thompson T. L.
Published: February 2008

Simultaneous in situ measurements of NO, NO2, and O3 were obtained from balloon flights near 50°N in August and December 1982. NOx (NO + NO2) was reduced by a factor of 10 in the 21‐ to 28‐km region in winter. Both NO and NO2 exhibited very sharp vertical gradients in the vicinity of 29 km. NO, for example, increased by nearly 20 times over only a 1‐km increase in altitude. By considering air mass trajectories for the time of the winter flight, the reduction in NOx in the lower and middle stratosphere was determined to be consistent with photochemical conversion, principally to N2O5.
A statistical model for horizontal mass flux of erodible soil
Authors: Babiker A. G. A. G. , Eltayeb I. A. , Hassan M. H. A.
Published: February 2008

It is shown that the mass flux of erodible soil transported horizontally by a statistically distributed wind flow has a statistical distribution. Explicit expression for the probability density function of the flux is derived for the case in which the wind speed has a Weibull distribution. The statistical distribution for a mass flux characterized by a generalized Bagnold formula is found to be Weibull for the case of zero threshold speed. Analytic and numerical values for the average horizontal mass flux of soil are obtained for various values of wind parameters by evaluating the first moment of the flux density function.
Aerosol measurements in the winter/spring Antarctic stratosphere: 1. Correlative measurements with ozone
Authors: Hofmann D. J. , Rosen J. M. , Harder J. W.
Published: February 2008

During the period from August 25 to November 3, 1986, the r ≧ 0.15 μm and r ≧ 0.25 μm aerosol profiles were measured on six occasions at McMurdo Station (78°S) by balloon‐borne optical particle counters. In addition, condensation nuclei (r ≧ 0.01 μm) profiles were measured on three occasions between October 16 and November 3. Several of these measurements corresponded to times when McMurdo was located near the point of minimum springtime ozone, as indicated by ozone and temperature measurements conducted on 33 occasions during the period. The height of the stratospheric sulfate layer was observed to decrease over the period of measurement, indicating continued subsidence in the vortex during the period that ozone was decreasing. This observation suggests that upwelling in the vortex is not important in the ozone depletion process. Low concentrations of condensation nuclei in the region of the ozone minimum supports this conclusion. Enhanced condensation nuclei above 20 km in the vortex and the discovery of an apparent permanent layer in the springtime vortex at the top of the ozone depletion region suggests that they may be related to the ozone depletion process, although the nature of this relationship is not clear.
Aerosol measurements in the winter/spring Antarctic stratosphere: 2. Impact on polar stratospheric cloud theories
Authors: Rosen J. M. , Hofmann D. J. , Harder J. W.
Published: February 2008

A series of aerosol soundings sensitive to particle sizes less than about 1 μm was made from McMurdo, Antarctica, beginning in August 1986, while the stratosphere was still cold, and continuing through the spring warming and polar vortex circulation breakdown. The statistical analysis of polar stratospheric cloud (PSC) occurrences at low temperature indicates that there was a combined high probability of sampling such a cloud on at least one of three occasions, but no unusual or definitve features in the profiles were noted that could unquestionably be associated with PSCs. Photographically documented ground observations indicate that there was very likely a PSC or unusual stratospheric aerosol condition present during the first sounding at about 20 km. These aerosol observations impact the present explanations of PSCs and indicate that the possibility of these clouds being made up of low concentrations of relatively large (greater than ∼5 μm) particles must be taken seriously. The low concentrations would effectively render the PSCs undetectable by the aerosol‐sounding equipment employed in this study. It is argued that the fall speed associated with the cloud particles would not measurably change the natural aerosol profile, but that there could be a tendency for some water vapor to be transported to lower altitudes. Because of atmospheric mixing and transport processes, the redistribution of water vapor may not be easily detected.
Particle size distribution, turbidity, and angular scattering in the Harmattan regime
Authors: Oluwafemi C. O.
Published: February 2008

Aerosol size distribution in harmattan weather is studied, using a combination of the Yue‐Deepak size inversion procedure and the data from photographed aerosol filter samples, for a typical moderate episode in Lagos. Accuracy of retrievals by this method depends sensitively on knowledge of the complex index of refraction of the aerosol. At Lagos, some 1,500 km south of the harmattan dust source, about 57% of the extinction of solar radiation appears due to the particulate mode r > 1 μm, a modal extinction less than those obtainable at stations nearer the Sahara.
Long‐term climate change and the geochemical cycle of carbon
Authors: Marshall Hal G. , Walker James C. G. , Kuhn William R.
Published: February 2008

We study the interactions between the geochemical cycles of carbon and long‐term changes in climate. Climate change is studied with a simple, zonally averaged energy balance climate model that includes the greenhouse effect of carbon dioxide explicitly. The geochemical model balances the rate of consumption of carbon dioxide in silicate weathering against its release by volcanic and metamorphic processes. The silicate weathering rate is expressed locally as a function of temperature, carbon dioxide partial pressure, and runoff. The global weathering rate is calculated by integrating these quantities over the land area as a function of latitude. Carbon dioxide feedback stabilizes the climate system against a reduction in solar luminosity and may contribute to the preservation of equable climate on the early Earth, when solar luminosity was low. The system responds to reduced land area by increasing carbon dioxide partial pressure and warming the globe. Our model makes it possible to study the response of the system to changing latitudinal distribution of the continents. A concentration of land area at high latitudes leads to high carbon dioxide partial pressures and high global average temperature because weathering of high‐latitude continents is slow. Conversely, concentration of the continents at low latitudes yields a cold globe and ice at low latitudes, a situation that appears to be representative of the late Precambrian glacial episode. This model is stable against ice albedo catastrophe even when the ice line occurs at low latitudes. In this it differs from energy balance models that lack the coupling to the geochemical cycle of carbon.
Sensitivity of a coupled atmosphere/mixed layer ocean model to changes in orbital forcing at 9000 years B.P.
Authors: Kutzbach J. E. , Gallimore R. G.
Published: February 2008

Experiments were made with an atmospheric general circulation model coupled to a 50‐m mixed layer ocean in order to study the sensitivity of the climate to the changed seasonal and latitudinal distribution of solar radiation for 9000 years ago. At 9000 years B.P. (before present), when perihelion was in July (compared to January at present) and the axial tilt was greater than at present, the July (January) solar radiation in the northern hemisphere was increased (decreased) by about 7% compared to that at present. The coupled atmosphere/ocean model simulated warmer continents in summer and intensified northern summer monsoons at 9000 years B.P., compared to the present, that were similar to previous results with an atmospheric model. Owing to small positive feedbacks, the coupled atmosphere/ocean model produced a slightly greater intensification of the 9000‐year B.P. monsoon than the atmospheric model. The ocean temperature changes were less than 1 K and lagged the solar radiation changes; the 9000‐year B.P. ocean was warmer in September and colder in March than the control simulation. The annual‐average ocean temperature was slightly lower in the tropics because the annual‐average incoming solar radiation was lower at 9000 years B.P. In middle latitudes the annual‐average ocean temperature was decreased because of feedbacks associated with seasonality. In high northern latitudes, sea ice thickness was reduced at 9000 years B.P. in response to increased summer and annual‐average solar radiation. The reduced high‐latitude sea ice caused somewhat warmer wintertime conditions over the northwestern portions of northern continents.
Carbon dioxide in the atmosphere over the Amazon Basin
Authors: Wofsy Steven C. , Harriss Robert C. , Kaplan Warren A.
Published: February 2008

The cycle of atmospheric CO2 in the Amazon Basin was studied using measured vertical profiles of CO2 concentrations in the canopy and aloft and direct measurements of CO2 emissions from soils. The results provide detailed information on daily exchanges of air between the tropical forest (0–30 m) and the atmospheric boundary layer (30–2000 m). The forest was a net source of CO2 at night and a sink during the day. High concentrations of CO2 (380–400 ppm) accumulated in the forest at night and were transported into the nascent mixed layer in the morning. Between 1000 and 1200 LT, CO2 in the mixed layer declined to concentrations 4–6 ppm lower than free tropospheric values and remained low for the rest of the afternoon. The afternoon mixed layer became isolated at night, and the low values of CO2 were preserved until a new mixed layer developed the next morning. Entrainment of air into the mixed layer appeared to be a one‐way process during the early stages of mixed layer growth. The rate for uptake of atmospheric CO2 by forests (soil and canopy) near midday was estimated to be 9(±4) kg C ha−1 hr−1, and mean uptake over the sunlit period was about 2.8(±1.2) kg C ha−1 hr−1. Forest soils emitted CO2 at a mean rate of 1.8(±0.2) kg C ha−1 hr−1. The atmospheric CO2 cycle over wetlands was weaker than over forests, with daytime uptake rates of approximately 1.6 kg C ha−1 hr−1. Rivers remained net sources of CO2 throughout the day.
Carbon monoxide over the Amazon Basin during the 1985 dry season
Authors: Sachse G. W. , Harriss R. C. , Fishman J. , Hill G. F. , Cahoon D. R.
Published: February 2008

During the Amazon Boundary Layer Experiment (ABLE 2A), approximately 100 hours of in situ, carbon monoxide (CO) measurements were obtained using a tunable diode laser sensor that provided continuous, fast‐response (≈1 s) measurements. This extensive data set, taken on board the NASA Electra between July 12 and August 12, 1985, characterizes the temporal and spatial changes in the CO distribution over the Amazon basin as meteorological conditions progressed from the early to middle phases of the 1985 day season. Early dry‐season CO values of 75–95 parts per billion by volume (ppbv) were generally observed in the planetary boundary layer (PBL). As the dry season became well established, biomass burning and a persistent capping inversion at ≈3 km profoundly altered the CO distribution, with PBL values typically reaching 150–275 ppbv. Concentrations as high as 800 ppbv were measured within identifiable haze layers. An analysis of satellite imagery shows that biomass burning was occurring along the Amazon River system and in savannah areas located more than 1000 km south of the region sampled.
Tropospheric ozone and aerosol distributions across the Amazon Basin
Authors: Browell E. V. , Gregory G. L. , Harriss R. C. , Kirchhoff V. W. J. H.
Published: February 2008

Ozone and aerosol distributions were measured during July–August 1985 over the tropical rain forest of Brazil as part of the NASA Global Tropospheric Experiment to study the Amazon boundary layer. Remote and in situ measurements of O3 and aerosols were made from a NASA Electra aircraft on several long‐range flights spanning different areas between Tabatinga and Belem, Brazil. Continuous O3 distributions were obtained between the aircraft altitude and the ground with an airborne differential absorption lidar (DIAL) system. Aerosol distributions were also continuously measured above and below the aircraft with the DIAL system. In situ O3 measurements were made on the aircraft and from ground‐launched ozonesondes at Manaus and Natal. Large‐scale variations in the vertical and horizontal distributions of O3 and aerosols were observed on nearly all flights over the Amazon Basin, with O3 exceeding 50 parts per billion by volume (ppbv) in some regions. Both positive and negative correlations were observed between O3 mixing ratios and aerosol concentrations. In nearly all cases, when O3 and aerosols were negatively correlated, this represented clean midtropospheric air, and when they were positively correlated, the air mass had undergone photochemical O3 production as a result of biomass burning. A 59% increase in the planetary boundary layer (PBL) O3 level was observed between the initial Manaus‐Belem flights on July 23–24, 1985 and the later flights on August 8–9, 1985. This was attributed to the increase in biomass burning near the Rio Amazonas and its tributaries and in savannah regions south of the Amazon Basin. Flights to the west of Manaus measured enhanced O3 and aerosol levels near the Rio Solimões, while the area sampled upwind of the river exhibited lower O3 levels. This was explained by the increased incidence of biomass burning near the river. This paper also examines the variability of the trade wind inversion (TWI) height across the Amazon Basin and the influence of O3 levels above the TWI on the budget of O3 in the PBL. Measurements reported for the early dry season characterize the background distribution of O3 and aerosols in the PBL prior to the onset of extensive biomass burning. These data provide the basis for a basin‐scale estimate of photochemical O3 production from biomass‐burning emissions.
Photochemistry of biogenic emissions over the Amazon forest
Authors: Jacob Daniel J. , Wofsy Steven C.
Published: February 2008

The boundary layer chemistry over the Amazon forest during the dry season is simulated with a photochemical model. Results are in good agreement with measurements of isoprene, NO, ozone, and organic acids. Photochemical reactions of biogenic isoprene and NOx can supply most of the ozone observed in the boundary layer. Production of ozone is very sensitive to the availability of NOx, but is insensitive to the isoprene source strength. High concentrations of total odd nitrogen (NOy,) are predicted for the planetary boundary layer, about 1 ppb in the mixed layer and 0.75 ppb in the convective cloud layer. Most of the odd nitrogen (≈70%) is present as PAN‐type species, which are removed by dry deposition to the forest. The observed daytime variations of isoprene are explained by a strong dependence of the isoprene emission flux on sun angle. Nighttime losses of isoprene exceed rates of reaction with NO3 and O3 and appear to reflect dry‐deposition processes. The 24‐hour averaged isoprene emission flux is calculated to be 38 mg m−2 d−1. Photooxidation of isoprene could account for a large fraction of the CO enrichment observed in the boundary layer under unpolluted conditions and could constitute an important atmospheric source of formic acid, methacrylic acid, and pyruvic acid.
Emissions of N2O from tropical forest soils: Response to fertilization with NH4+, NO3−, and PO43−
Authors: Keller M. , Kaplan W. A. , Wofsy S. C. , Da Costa Jose Maria
Published: February 2008

Undisturbed oxisols in a central Amazon tropical forest were fertilized with ammonium, nitrate, or phosphate. Enhanced emissions of N2O were observed for all treatments within 1 day of fertilization, with the response NO3−≫NH4+≫PO43−. Approximately, 0.5% of applied NO3− was converted to N2O within 2 weeks after application, with less than 0.1% of the NH4+ converted to N2O. These experiments reveal a potentially large source of N2O from microbial reduction of NO3− in the clay soils of Amazonia.
Diurnal variations of atmospheric isoprene and monoterpene hydrocarbons in an agricultural area in summertime
Authors: Yokouchi Yoko , Ambe Yoshinari
Published: February 2008

Diurnal variations of isoprene and monoterpenes in the atmosphere were precisely measured at an interval of 1–2 hours in the rainy season and in fine midsummer in an agricultural area in Japan. It was observed that the mixing ratio of isoprene was much larger in fine daytime than in nighttime or in cloudy daytime; in contrast, a higher mixing ratio of monoterpenes was usually observed in nighttime. In fine midsummer the concentration of atmospheric isoprene increased gradually after midnight, reaching its maximum late in the afternoon, and decreased rapidly after sunset. The significant difference between atmospheric isoprene and monoterpenes was explained by suggesting that isoprene emission is more strongly affected by temperature and/or solar radiation.
Enhanced biogenic emissions of nitric oxide and nitrous oxide following surface biomass burning
Authors: Anderson Iris C. , Levine Joel S. , Poth Mark A. , Riggan Philip J.
Published: February 2008

Recent measurements indicate significantly enhanced biogenic soil emissions of both nitric oxide (NO) and nitrous oxide (N2O) following surface burning. These enhanced fluxes persisted for at least 6 months following the burn. Simultaneous measurements indicate enhanced levels of exchangeable ammonium in the soil following the burn. Biomass burning is known to be an instantaneous source of NO and N2O resulting from high‐temperature combustion. Now we find that biomass burning also results in significantly enhanced biogenic emissions of these gases, which persist for months following the burn.
Equatorial semiannual oscillation in zonally averaged temperature observed by the Nimbus 7 SAMS and LIMS
Authors: Delisi Donald P. , Dunkerton Timothy J.
Published: February 2008

Observations of zonally averaged equatorial temperature obtained from the stratospheric and mesospheric sounder (SAMS) aboard Nimbus 7 are presented and compared to similar data from the limb infrared monitor of the stratosphere (LIMS). The SAMS observations demonstrate that a significant seasonal asymmetry exists in the equatorial semiannual oscillation in the sense that the temperature cycle beginning in the northern winter (the “first” cycle) is much stronger than the “second” cycle beginning six months later. This asymmetry is also seen in the temperature curvature about the equator, implying via thermal wind balance a corresponding asymmetry in the vertical shear of the mean zonal wind. The SAMS data, which provide a true zonal average and extend over several semiannual cycles (1979–1983), therefore confirm the seasonal asymmetry in semiannual wind regimes previously seen in rocketsonde observations near the equator. Two explanations of the asymmetry are offered. First, an improved Kelvin and gravity wave transmissivity in stronger equatorial easterlies implies stronger westerly mean flow acceleration in the first cycle than in the second. Stronger equatorial easterlies, in turn, may result from planetary Rossby wave momentum transport. Second, evidence of strong polar‐tropical coupling in the northern winter indicates that mean meridional circulations are present on a global scale. Nonlinear advection by these circulations is quantitatively significant in the semiannual oscillation.
Stratospheric responses to solar ultraviolet variations: Comparisons with photochemical models
Authors: Hood L. L. , Douglass A. R.
Published: February 2008

At latitudes and altitudes where transport effects on ozone mixing ratio can be neglected, ozone and temperature responses to short‐term changes in solar ultraviolet flux can be used to calculate implied bounds on two basic photochemical parameters: the odd oxygen photochemical relaxation time and the chemical sensitivity of odd oxygen to local temperature changes. Seasonally averaged values of these parameters are derived from response measurements and are compared with model calculations between 0.7 and 4 mbar at tropical latitudes. Results are in agreement within measurement and model uncertainties at all pressure levels. Model values of mean ozone and of the response of ozone to perturbations are functions of the same photochemical data. Therefore this agreement provides a constraint which should be considered when changes are proposed in model input data for the purpose of improving agreement between measured and calculated high‐altitude ozone.
Atlas of stratospheric submillimeter lines: 2. The 20‐ to 40‐cm−1 interval
Authors: Baldecchi Maria Grazia , Carli Bruno , Mencaraglia Francesco , Barbis Alessandra , Bonetti Alberto , Carlotti Massimo
Published: February 2008

In this paper we give the second part, covering the interval 20–40 cm−1, of the atlas of submillimeter lines observed in the atmospheric emission spectrum from 38.2‐km altitude with a resolution of 0.0033 cm−1. This resolution appears to be adequate for detailed interpretation of the spectrum in terms of rotational transitions of most trace molecules relevant to the photochemistry of the atmosphere. A table of assignments of the observed features to expected molecular transitions is given, together with a comparison of the measured spectrum with a synthetic spectrum obtained from radiative transfer calculation.
Rossby wave activity in a two‐dimensional model: Closure for wave driving and meridional eddy diffusivity
Authors: Hitchman Matthew H. , Brasseur Guy
Published: February 2008

A parameterization of the effects of Rossby waves in the middle atmosphere is proposed for use in two‐dimensional models. By adding an equation for conservation of Rossby wave activity, closure is obtained for the meridional eddy fluxes and body force due to Rossby waves. Rossby wave activity is produced in a climatological fashion at the tropopause, is advected by a group velocity which is determined solely by model zonal winds, and is absorbed where it converges. Absorption of Rossby wave activity causes both an easterly torque and an irreversible mixing of potential vorticity, represented by the meridional eddy diffusivity, Kyy. The distribution of Rossby wave driving determines the distribution of Kyy, which is applied to all of the chemical constituents. This provides a self‐consistent coupling of the wave activity with the winds, tracer distributions, and the radiative field. Typical winter stratospheric values for Kyy of 2×106 m2 S−1 are obtained. Poleward tracer advection is enhanced and meridional tracer gradients are reduced where Rossby wave activity is absorbed in the model.
Variability of pigment biomass in the California Current System as determined by satellite imagery: 2. Temporal variability
Authors: Michaelsen Joel , Zhang Xueyun , Smith Raymond C.
Published: February 2008

Characteristics of temporal variability in the California Current system are analyzed using a 30‐month time series of Coastal Zone Color Scanner (CZCS) imagery. About 20–25% of the variance is produced by a periodic annual cycle with peak values in winter. Analysis of ship‐based chlorophyll measurements indicates that the winter peak is only characteristic of the upper portion of the euphotic zone and that total water column chlorophyll peaks during the spring upwelling season. Satellite studies of intra‐annual variability are modulated by strong 5‐ to 6‐day oscillation in the availability of usable imagery, resulting from a combination of satellite orbital dynamics, which produces images of the study area roughly 4 out every 6 days, and an oscillation in cloud cover, which controls the availability of clear imagery. The cloud cover oscillation, which is also present in coastal winds, undoubtedly affects the ocean surface and biases the data obtained by satellites. Analysis of data using a 5‐day time step indicates that the predominant mode of nonseasonal variability is characterized by inphase fluctuations throughout the southern and central California coastal region.
An operational multifield analog/antianalog prediction system for United States seasonal temperatures: 1. System design and winter experiments
Authors: Livezey Robert E. , Barnston Anthony G.
Published: February 2008

The theoretical framework developed by Barnett and Preisendorfer (1978) for multifield analog prediction of United States seasonal temperatures has been modified and expanded to accommodate the use of composites of analogs and antianalogs to form predictions. Major changes have also been made both in predictor data and in the way it is processed, although the general strategy of Barnett and Preisendorfer served as a guide in this regard. Cross‐validation tests on a 35‐year record suggest that substantial gains in winter forecast skill have been achieved through both the previously mentioned architectural changes and several predictor data set changes. The latter include the use of a different El Niño/Southern Oscillation index and United States surface temperature data but not precipitation data. It was found that significant model skill depends most on these two data sets, along with well‐filtered 700‐mbar heights, and depends least on sea surface temperatures. Considerable skill was found over the eastern half and the north‐central portion of the United States. Forecasts were found to be effectively independent of and to outperform those of persistence and were comparable in skill to official forecasts. In a quasi‐operational test most of the system's skill was reproduced, even under very disadvantageous circumstances. Because of all these factors, the mixed analog and antianalog prediction system has been adopted as a major input for operational use by official forecasters. Development of models for other seasons will be described in a subsequent paper.
Annual cycle, quasi‐biennial oscillation, and southern oscillation in global precipitation
Authors: Lau K.‐M. , Sheu P. J.
Published: February 2008

The spatial and temporal variations in global precipitation associated with the annual cycle (AC), the tropospheric quasi‐biennial oscillation (QBO), and the Southern Oscillation (SO) are studied using 80 years (1901–1980) of global station rainfall data. The spatial scale and migration of the major climatological precipitation regimes are identified from the zeroth and first harmonic of the rainfall data. From the annual mean anomaly it was found that the dominant global precipitation pattern fluctuates irregularly, with 2‐ to 5‐year periods associated with the SO. This pattern is characterized by a center of action in the form of an east‐west dipole located over the equatorial central Pacific and the maritime continent of Indonesia. The occurrence of an El Niño/Southern Oscillation (ENSO) corresponds to an extreme phase of this dipole anomaly. Viewed in terms of the total rainfall amount (including the AC), the large rainfall anomalies that occurred during ENSOs represent major dislocations of the normal global rainfall pattern, affecting regions of the western Pacific/maritime continent and, to a lesser extent, China, Brazil, Argentina, southeast Africa, and southeast United States. Using the monthly rainfall anomaly, the same pattern again emerges as the dominant mode of variation. However, the temporal variation shows, in addition to the SO time scale, a distinct QBO signal. Using various time series analyses techniques, it was found that the QBO appears to be well correlated with the square of the SO signal. This result is also confirmed by bispectral analyses. The best correlation appears to occur during ENSO, with an apparent phase locking between the QBO and SO. A nonlinear interaction mechanism consistent with these results is illustrated by a conceptual model. The model suggests that the QBO may be an even more fundamental long‐term oscillation of the tropical ocean‐atmosphere system than the SO. ENSO‐like cycles can arise from a basic 2 year oscillation in the tropical ocean‐atmosphere system through its lagged effect from one year to the next. In addition, long‐term trends and amplitude modulation of the QBO can also arise from this effect. The role of the possible influence of the AC and other factors involved in this QBO–SO interaction is also discussed.
Shortwave radiative parameterization of large atmospheric aerosols: Dust and water clouds
Authors: Ackerman Steven A. , Cox Stephen K.
Published: February 2008

A parameterization of the single scattering properties of an aerosol for a dust layer in the solar spectral region is presented. The parameterization scheme accounts for the microphysical changes of an aerosol layer and is applied to dust and water clouds. A scaling parameter is presented which describes, simply and effectively, the optical properties of an aerosol layer with a large effective size parameter.
Characterization of stratospheric aerosol from polarization measurements
Authors: Santer R. , Herman M. , Tanré D. , Lenoble J.
Published: February 2008

A balloon‐borne polarimetric device was developed in 1983 for the purpose of monitoring stratospheric aerosols from limb scannings of the radiance and the polarization of scattered sunlight. The first flight of the experiment was launched on December 15, 1983. A preliminary interpretation of the results has been given previously. The main purpose of this paper is to develop an improved and extended analysis of the data. First, we study how limb observations depend on variations of the solar elevation, particularly with respect to signal contamination by tropospheric light. A simple modeling of this effect is proposed. Comparison of the radiance and polarization measurements allows us to check this model, which may be useful for analyses of limb experiments. Second, variations of the atmospheric transmission as a function of the solar elevation are shown to permit a calibration‐free and improved determination of the aerosol slant optical thicknesses. Finally, Monte Carlo calculations in spherical geometry fix the contribution of multiply scattered light in the signals. These various points allow us to improve the aerosol characteristic retrieval. A very accurate estimate of the particle mean dimension is obtained, some insight is gained about the actual form of the aerosol size distribution, and the particle refractive index is shown to be in the range 1.45±0.05 around 1000‐nm wavelength, which corroborates, from purely passive measurements, the presence of a hydrated sulfuric acid aerosol.
Oxygen isotope changes in tropical ice, Quelccaya, Peru
Authors: Grootes P. M. , Stuiver M. , Thompson L. G. , Mosley‐Thompson E.
Published: February 2008

Low average δ18O values and large seasonal variations in δ18O in snow accumulating on the tropical Quelccaya ice cap in Peru can be quantitatively explained by a balance calculation of water vapor mass and isotopes. Important factors are (1) variations in air mass stability over the Amazon Basin, (2) the surface elevation of Quelccaya, and (3) seasonal changes over Quelccaya. Seasonal changes in evaporation of snow on the surface of the ice cap amplify the seasonal δ18O cycle. Air circulation and air mass stability, rather than temperature, determine the seasonal δ18O cycle at Quelccaya and, probably, at other low‐latitude sites.
NH3 column abundances over Lauder, New Zealand
Authors: Murcray Frank J. , Matthews Andrew , Goldman Aaron , Johnston Paul , Rinsland Curtis
Published: February 2008

Gaseous NH3 has been observed in the atmosphere over central New Zealand with infrared absorption spectra. The amount of NH3 shows marked variability, which is strongly correlated with time of day and season. The pattern is similar to data obtained in Denver, Colorado, but is much more variable than data from Hampton, Virginia. The rapid variability indicates a residence time of 8 hours in some cases.
Effect of improved physical parameterizations on simulations of cloudiness and the Earth's radiation budget
Authors: Slingo A. , Wilderspin R. C. , Smith R. N. B.
Published: February 2008

The development of a new version of the United Kingdom Meteorological Office 11‐layer atmospheric general circulation model is described, with particular emphasis on the prediction of the fractional cloud cover and of the Earth's Radiation Budget. Results are shown first from an integration of an earlier version with model‐predicted cloudiness. These demonstrate that there were serious shortcomings, particularly in the distribution of low cloud over the subtropical oceans. Analysis of this problem showed that it was due to systematic errors in the thermo dynamic structure of the marine boundary layer. Various changes to the model's physical parameterizations were made to remove these errors, including revisions to the convection scheme to treat more accurately the effects of shallow cumulus convection. The new version of the model produces simulations of the geographical distribution of the components of the Earth's Radiation Budget which are generally in good agreement with satellite measurements.
Triggered lightning strikes to aircraft and natural intracloud discharges
Authors: Mazur Vladislav
Published: February 2008

A physical model of triggered lightning strikes to aircraft is applied to interpret the initiation of intracloud flashes depicted with the French UHF‐VHF interferometric system. It is shown that both intracloud discharges and triggered strikes are initiated in a qualitatively similar way: the simultaneous bi‐directional development of the negative stepped leader and the positive leader‐continuous current process. The airborne visual observations and electromagnetic waveform records during the junction stage of intracloud flashes reveal (1) the presence of continuous current during the entire period, and (2) a “multistroke” feature, observed as variations of the low‐frequency (continuous) current with current pulses superimposed, which occurred only during periods of rising continuous current. It is shown that airborne measurements of lightning strikes to aircraft provide an opportunity to recognize recoil streamers in time domain data and to determine their characteristics (duration and amplitude), which are not obtainable with other techniques. Tortuosity of two scales, tens of centimeters and several meters long, has been observed in visual images of lightning channels at close range with video cameras aboard the NASA F‐106B airplane. The hypothesis is advanced that high‐rate pulse bursts in VHF and UHF bands associated with recoil streamers are radiation pulses attributable to reflection processes at kinks of the highly tortuous channel traversed by a current pulse.
Absorption cross sections of CH3OOH, H2O2, and D2O2 vapors between 210 and 365 nm at 297 K
Authors: Vaghjiani Ghanshyam L. , Ravishankara A. R.
Published: February 2008

The gas phase absolute UV absorption cross sections at 213.9 nm for CH3OOH, H2O2, and D2O2 have been determined to be (22.51±0.78) × 10−20, (33.04±2.17) × 10−20, and (35.37±4.25) × 10−20 cm2 molecule−1, respectively, at 297±1 K. The corresponding values at 253.7 nm for H2O2 and D2O2 were (7.37±0.31) × 10−20 and (7.86±1.04) × 10−20 cm2 molecule−1. The UV absorbance of a slowly flowing mixture of peroxide and helium carrier gas in a Pyrex absorption cell was measured, followed by collection and titration of the eluting peroxide with Fe2+ or I− solutions. The relative cross sections for CH3OOH and H2O2 at 298.1, 326.1, 340.4, and 361.1 nm were also determined, using the absolute values at 213.9 nm. The absorption spectra of these peroxides were recorded in the wavelength region between 210 and 365 nm, using a diode array spectrometer, and normalized to the above cross sections to obtain absolute values for the UV absorption cross sections over this entire wavelength region. The obtained results are compared to those from previous investigations. The atmospheric relevance of our measured cross sections is discussed.
A comparison of three photochemical oxidant mechanisms
Authors: Dodge Marcia C.
Published: February 2008

Three chemical mechanisms recently developed for use in urban‐ and regional‐scale oxidant models have been compared. Approximately 400 simulations were conducted using an atmospheric model to determine the degree to which the mechanisms yield comparable predictions of ozone and other oxidants. The simulations were carried out over a range of initial conditions for a number of scenarios representative of urban and rural environments. Sensitivity studies were conducted to assess the effect of varying parameters, such as the initial ratio of volatile organic compounds (VOC) to oxides of nitrogen (NOx), the composition of the VOC mixture, and the temperature. The mechanisms were found to yield nearly identical predictions for ozone, peroxyacetylnitrate, and nitric acid under most conditions. Differences, however, were noted in simulations with (1) high NOx levels, (2) high levels of aromatic hydrocarbons, and (3) low afternoon temperatures. Predictions of hydrogen peroxide were in good agreement except at high VOC/NOx ratios where differences of as much as a factor of 3 were found.
SAGE II inversion algorithm
Authors: Chu W. P. , McCormick M. P. , Lenoble J. , Brogniez C. , Pruvost P.
Published: February 2008

This paper provides a detailed description of the current operational SAGE II multichannel data inversion algorithm implemented at NASA Langley Research Center, Hampton, Virginia. This algorithm is compared to an independently developed inversion algorithm from the Laboratory of Atmospheric Optics, University of Lille, Lille, France. Inverted aerosol and ozone profiles from these two algorithms are shown to be similar within their respective uncertainties.
Absolute determination of the cross sections of ozone in the wavelength region 339–355 nm at temperatures 220–293 K
Authors: Cacciani Marco , di Sarra Alcide , Fiocco Giorgio , Amoruso Antonella
Published: February 2008

Absolute measurements of the ozone absorption coefficient in the Huggins bands at different temperatures have been carried out. Ozone is produced by an electrical discharge and stored cryogenically; differential absorption measurements are subsequently obtained in a slowly evolving mixture of ozone and molecular oxygen. High resolution (to 0.012 nm) measurements cover a spectral range (339–355 nm) where the ozone absorption shows a strong dependance on temperature. Results at 293 and 220 K are reported; they are particularly interesting in view of the utilization of this spectral region as a low‐absorption reference channel for the observation of atmospheric ozone profiles by active probing techniques. Coherent radiation at two wavelengths, around 355 and 353 nm, respectively, can be obtained as third harmonic of the fundamental output of a Nd:YAG laser and by H2 Raman shifting of a XeCl excimer laser output.
Secular increase of the total vertical column abundance of carbon monoxide above central Europe since 1950
Authors: Zander R. , Demoulin Ph. , Ehhalt D. H. , Schmidt U. , Rinsland C. P.
Published: February 2008

The secular increase of the total vertical column abundance of carbon monoxide has been derived from sets of infrared solar spectra recorded from an altitude of 3.58 km at the Jungfraujoch Station, Switzerland, in 1950–1951 and in 1985–1987. The results are based on equivalent width measurements of the R3 line of the 1‐0 vibration‐rotation band of 12C16O at 2159.30 cm−1. The set of 1985–1987 observations indicates a strong seasonal cycle in the total column abundance of CO, with a ±25% modulation between minimum values in late summer and the maximum values in late winter. Variability on shorter time scales is also present in both the old and recent data sets. The mean cumulative rate of increase of the total column abundance of CO above the Jungfraujoch is found to be (0.85 ± 0.20)%/yr between 1950–1951 and 1985–1987. The present findings are compared with trends reported in earlier studies.
Observational results using the microwave temperature profiler during the Airborne Antarctic Ozone Experiment
Authors: Gary Bruce L.
Published: February 2008

The Microwave Temperature Profiler (MTP) measures profiles of air temperature versus altitude. The altitude coverage is about 5 km at a flight altitude of 20 km (66,000 feet), and the profiles are obtained every 14 s. The MTP instrument is installed on NASA's ER‐2 aircraft, which flew 13 missions over Antarctica during the Airborne Antarctic Ozone Experiment. Altitude temperature profiles were used to derive potential temperature cross sections. These cross sections have been useful in detecting atmospheric waves. Many wave encounters have been identified as “mountain waves.” The mountain waves are found to extend from the lowest altitudes measured to the highest (about 24 km). The southern part of the Palmer Peninsula was found to be associated with mountain waves more than half the time. Altitude temperature profiles were also used to measure the lapse rate along the flight track. Lapse rate versus latitude plots do not show significant changes at the ozone hole boundary.
Measurements of ozone in the Antarctic atmosphere during August and September 1987
Authors: Starr Walter L. , Vedder James F.
Published: February 2008

Mixing ratios changed dramatically for ozone in the austral polar stratosphere during August and September 1987. Data were obtained with an ultraviolet photometer mounted in the equipment bay of an ER‐2 aircraft. Measurements were made between the latitudes of 53° and 72°S at pressure altitudes (U.S. Standard Atmosphere (1976)) up to 21 km in a series of flights from Punta Arenas, Chile, over the Palmer Peninsula. Additional data were obtained between 37°N and 53°S on the ferry flights leaving from and returning to Moffett Field, California. The sample‐collecting system and the analytical techniques are described. In September the mixing ratios for ozone at pressure altitudes above 15 km in the southernmost part of the flights over the Palmer Peninsula were significantly lower than values for mid‐latitudes. The various latitudes of the ER‐2 aircraft's encounters with the boundary of the region of depleted ozone lie between 59° and 71°S. Near the 425 K potential temperature surface and well within the vortex, the measured mixing ratio of ozone declined from about 2 parts per million by volume (ppmv) to about 0.6 ppmv during the period of the ER‐2 flights. The distributions of ozone as a function of altitude indicate the presence of layering of ozone.
Decay of the El Chichón aerosol cloud at 23°S
Authors: Simonich Dale M. , Clemesha Barclay R.
Published: February 2008

We present the stratospheric back‐scatter profiles obtained by the São José dos Campos lidar (23°S, 46°W) during the period of the persistence of the El Chichón aerosol cloud (July 1982 to November 1985). The backscatter coefficient integrated from 17 to 27 km shows an overall l/e decay rate of about 13 months, but the decay was considerably more irregular than that observed at other sites. In June and July of 1984 there occurred a significant secondary maximum in the integrated backscatter. It is not clear whether this peak was caused by circulation effects or whether it was the result of the injection of new material by a series of moderate equatorial eruptions during the first half of 1984.
A photochemical kinetics mechanism for urban and regional scale computer modeling
Authors: Gery Michael W. , Whitten Gary Z. , Killus James P. , Dodge Marcia C.
Published: February 2008

A new chemical kinetics mechanism for simulating urban and regional photochemistry has been developed and evaluated. The mechanism, called the Carbon Bond Mechanism IV (CBM‐IV), was derived by condensing a detailed mechanism that included the most recent kinetic, mechanistic, and photolytic information. The CBM‐IV contains extensive improvements to earlier carbon bond mechanisms in the chemical representations of aromatics, biogenic hydrocarbons, peroxyacetyl nitrates, and formaldehyde. The performance of the CBM‐IV was evaluated against data from 170 experiments conducted in three different smog chambers. These experiments included NOx‐air irradiations of individual organic compounds as well as a number of simple and complex organic mixtures. The results of the evaluation indicate substantial improvement in the ability of the CBM‐IV to simulate aromatic and isoprene systems with average overcalculation of ozone concentrations of 1% for the aromatic simulations and 6% for the isoprene simulations. The mechanism also performed well in simulating organic mixture experiments. Maximum ozone concentrations calculated for 68 of these experiments were approximately 2% greater than the observed values while formaldehyde values were low by 9%.
Measurements of collision‐broadened line widths in the 7.66‐μm band of 12CH4 at temperatures relevant to the atmosphere
Authors: Varanasi Prasad , Chudamani Sury
Published: February 2008

N2−, O2−, and air‐broadened half widths of several spectral lines in the fundamental band of 12CH4 at 7.66 μm have been measured at low temperatures between 130 and 295 K, using a tunable diode laser spectrometer. The temperature dependence of the measured line widths is described in terms of an exponent n.