bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrous oxide from coal‐fired power plants: Experiments in the plumes
Authors: Khalil M. A. K. , Rasmussen R. A.
Published: February 2012

We report studies of N2O concentrations in the ambient plumes of power plants. The results show that there is very little excess N2O within 100 m of the stack. There is some evidence that N2O is formed in the plumes farther downwind. The magnitude of the effect cannot be quantitatively evaluated with the present data. Based on our results and published studies, we estimate that the global direct emissions of N2O from power plants are about 0.05 Tg/yr out of a total anthropogenic source of about 7 Tg/yr.
Airborne soil moisture measurements for First International Satellite Land Surface Climatology Program Field Experiment
Authors: Peck Eugene L. , Carroll Thomas R. , Lipinski Daniel M.
Published: February 2012

The airborne gamma radiation system of the National Weather Service (NWS) was used to measure soil moisture over a research area near Manhattan, Kansas, in 1987 and in 1989. The research was in support of the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) by the National Aeronautics Space Administration. Twenty‐four flight lines were established in the FIFE research area. A large number of ground soil moisture measurements were collected for calibration of the flight lines. The NWS standard operational method to obtain soil moisture estimates for flight lines that average 16 km in length, using three airborne measurements of gamma radiation fluxes, was adapted for use with the shorter FIFE flight lines. Examples of temporal and spatial variations of soil moisture for the FIFE research area are presented.
Quantifying reflectance anisotropy of photosynthetically active radiation in grasslands
Authors: Middleton Elizabeth M.
Published: February 2012

The fraction of photosynthetically active radiation (PAR) (λ = 0.4–0.7 μm) absorbed (FAPAR) is a critical parameter in canopy processes arid in land surface‐atmosphere interactions. FAPAR is typically inferred indirectly through empirical relationships established between hemispheric measurements of PAR and either (1) canopy bidirectional, usually nadir, reflectances in the visible wavelengths or (2) spectral vegetation indices. However, the bidirectional reflectance distribution function (BRDF) of vegetated surfaces has been shown to exhibit angular and spectral anisotropy, complicating the estimation of average surface reflectances, including that of PAR, from remote observations. Quantifying the surface's reflectance anisotropy was an important element of the First ISLSCP Field Experiment (FIFE), since its major objectives focused on retrieval of surface parameters from satellite‐derived reflectances. Prior to the experiment reported here, the explicit remote measurements for approximating the BRDF of PAR had not been undertaken. The proper expression of reflectance for BRDFs for retrieval of canopy parameters is assessed. A rationale is given for the expression of reflectances as bidirectional reflectance fractions (RFRs), instead of the conventional bidirectional reflectance factors (RFs), when relating spectral data to canopy states or processes. The characterization of the grassland anisotropy in the solar principal plane is markedly different when expressed as RFRs versus RFs. Whereas RFs are extremely useful in addressing important “remote sensing” issues, the “surface only” BRDF is obscured by pixel‐size effects since the projected viewing area increases by a factor of cos(θV)−1 with view angle (θV) for off‐nadir views. The BRDF for RFRs exhibited increased absorption by the canopy in the forward scatter directions; the anisotropy is most pronounced at midday, and more isotropic at intermediate sun angles, at which time the nadir observation was adequate for estimating the mean surface PAR reflectance.
An overview of the measurements of soil moisture and modeling of moisture flux in FIFE
Authors: Wang J. R.
Published: February 2012

Measurements of soil moisture and calculations of moisture transfer in the soil medium and at the air‐soil interface were conducted by a group of investigators over a 15‐km by 15‐km test site south of Manhattan, Kansas, during the First ISLSCP Field Experiment (FIFE) in 1987 and 1989. The measurements included intensive soil moisture sampling at the ground level and surveys at aircraft altitudes by several active and passive microwave sensors as well as a gamma radiation device. The calculations were based on a catchment‐scale water balance model that is driven by spatially interpolated rainfalls and estimated potential evaporation. The results of this group effort are presented in the five papers in this section. They include discussions on the statistics of soil moisture variability within a pixel of a remote sensor, soil moisture measurements by impedance probes, the comparison of active and passive microwave sensing of surface soil moisture, the statistics of soil moisture estimation by a gamma‐radiation technique, and the comparison of the calculated and measured latent heat fluxes at the catchment scale (4 km by 4 km).
Assessing spatial and seasonal variations in grasslands with spectral reflectances from a helicopter platform
Authors: Walthall Charles L. , Middleton Elizabeth M.
Published: February 2012

Helicopter‐based radiometric measurements of grassland sites were acquired during the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) to quantify the spatial and spectral variations in surface reflectance contributing to variations in albedo and for comparison with surface fluxes. The helicopter instrumentation consisted of an eight‐channel modular multiband radiometer (MMR), video, and photographic cameras. Seasonal and spatial variability of the entire FIFE study area were characterized using 20 MMR data sets from five FIFE sites during the four best (“Golden”) data collection days of 1987. The means and coefficients of variation for each spectral band were calculated and analyzed as a function of spatial and seasonal domains. Linear models describing simple ratio (SR) and normalized difference vegetation index (NDVI) as functions of several surface variables were tested. All eight MMR bands contributed information beneficial for characterizing spatial and temporal variations, and the most useful bands were the red (MMR3, 0.63–0.68 μm) and the third middle infrared (MMR7, 2.08–2.37 μm). The blue band (MMRl, 0.45–0.52 μm) proved to be valuable, whereas the often utilized near infrared band (MMR4, 0.75–0.88 μm) was among the least important bands for discriminating landscape variations. The SR was more sensitive than the NDVI to variations in the Konza grassland at all scales: intrasite and intersite, between management practices of burning and grazing, and over time. Furthermore, the relationship of the NDVI with leaf area index was curvilinear, whereas the relationship of the SR was linear at low‐leaf area index and was improved by the addition of a second variable, the percent of green dry weight biomass. Improvements in data collection methodologies are recommended for future large scale experiments such as the Boreal Ecosystem and Atmosphere Study (BOREAS).
Estimates of solar variability using the solar backscatter ultraviolet (SBUV) 2 Mg II index from the NOAA 9 satellite
Authors: Cebula Richard P. , DeLand Matthew T. , Schlesinger Barry M.
Published: February 2012

The Mg II core to wing index was first developed for the Nimbus 7 solar backscatter ultraviolet (SBUV) instrument as an indicator of solar variability on both solar 27‐day rotational and solar cycle time scales. This work extends the Mg II index to the NOAA 9 SBUV 2 instrument and shows that the variations in absolute value between Mg II index data sets caused by interinstrument differences do not affect the ability to track temporal variations. The NOAA 9 Mg II index accurately represents solar rotational modulation but contains more day to day noise than the Nimbus 7 Mg II index. Solar variability at other UV wavelengths is estimated by deriving scale factors between the Mg II index rotational variations and at those selected wavelengths. Because radiation near the Mg II line core originates at levels in the solar atmosphere comparable to those giving rise to the continuum near 200 nm, the Mg II index accurately tracks the flux in this photochemically important region. Based on the 27‐day average of the NOAA 9 Mg II index and the NOAA 9 scale factors, the solar irradiance change from solar minimum in September 1986 to the beginning of the maximum of solar cycle 22 in 1989 is estimated to be 8.6% at 205 nm, 3.5% at 250 nm, and less than 1% beyond 300 nm.
Sources of nitrate and ozone in the marine boundary layer of the tropical north Atlantic
Authors: Savoie Dennis L. , Prospero Joseph M. , Oltmans Samuel J. , Graustein William C. , Turekian Karl K. , Merrill John T. , Levy Hiram
Published: February 2012

During the period April 1989 through December 1990, O3concentrations in the marine boundary layer at Barbados, West Indies, show a pronounced seasonal cycle. Daily averaged values in the winter and spring often fall in the range of 25–35 ppbv for periods of several days, and they seldom fall below 20 ppbv. In contrast, during the summer, values typically fall in the range of 10–20 ppbv. During the winter‐spring period, there is a very strong negative correlation between O3and a number of aerosol species, including NO3−. These anticorrelations appear to be driven by changing transport patterns over the North Atlantic as opposed to chemical reactions involving O3and nitrogen species in the atmosphere. Analyses of isentropic trajectories clearly show that high O3and low NO3−are associated with transport from higher latitudes and high altitudes. Conversely, high NO3−and relatively low O3are associated with transport from Africa. Our study suggests that North America and the middle troposphere (and stratosphere) are not strong sources for NO3−over the tropical North Atlantic. The strong correlation of NO3−with210Pb and the weaker correlation with Saharan dust indicates that NO3−is derived principally from continental surface sources, probably in Europe and North Africa, but not from the Saharan soil material itself. During several extended periods, NO3−and210Pb were strongly correlated and their concentrations were high relative to nss SO4=; these factors, coupled with trajectories originating in Africa, suggest that African biomass burning was a significant source at these times. In contrast, biomass burning appears to be a minor source for O3as measured at Barbados, perhaps accounting for an enhancement of about 5 ppbv at most during these periods.
Dynamics above a dense equatorial rain forest from the surface boundary layer to the free atmosphere
Authors: Lyra R. , Druilhet A. , Benech B. , Biona C. Bouka
Published: February 2012

During the Dynamique et Chimie de l'Atmosphère en Forêt Equatoriale (DECAFE) campaign, dynamical and thermodynamical measurements were made at Impfondo (1°37′N, 18°04′W), over the dense rain forest of northern Congo during the dry season (February 1988). During the measurement period the experimental site was located south of the intertropical convergence zone ground track which manages the dynamics of the large scale. Above the experimental site, the atmospheric low layers are supplied by monsoon air coming from the Guinean gulf; the upper layers (>1500 m) are supplied by warm and dry air (trade winds) coming from the northern desert region and the savanna. Our experimental approach consists of analyzing the heat and moisture content in the low troposphere from vertical soundings made by a tethered balloon (0–400 m) and an aircraft (0–4000 m). The analysis of the evolution of the observed planetary boundary layer (PBL) is made with a mixed layer one‐dimensional model which is forced to represent correctly the observed PBL height growth. The simulated and observed budgets of the heat and moisture in the PBL are balanced by adding dry air to the simulated PBL in the afternoon. This drying out can be maintained only by high levels of entrainment flux at the PBL top. An entrainment velocity of 3 cm s−1 enables the balancing of the moisture budget. This entrainment velocity seems compatible with physicochemical transfers as those of methane and ozone.
A study of broadband parameterizations of the solar radiative interactions with water vapor and water drops
Authors: Ramaswamy V. , Freidenreich S. M.
Published: February 2012

Reference radiative transfer solutions in the near‐infrared spectrum, which account for the spectral absorption characteristics of the water vapor molecule and the absorbing‐scattering features of water drops, are employed to investigate and develop broadband treatments of solar water vapor absorption and cloud radiative effects. The conceptually simple and widely used Lacis‐Hansen parameterization for solar water vapor absorption is modified so as to yield excellent agreement in the clear sky heating rates. The problem of single cloud decks over a nonreflecting surface is used to highlight the factors involved in the development of broadband overcast sky parameterizations. Three factors warrant considerable attention: (1) the manner in which the spectrally dependent drop single‐scattering values are used to obtain the broadband cloud radiative properties, (2) the effect of the spectral attenuation by the vapor above the cloud on the determination of the broadband drop reflection and transmission, and (3) the broadband treatment of the spectrally dependent absorption due to drops and vapor inside the cloud. The solar flux convergence in clouds is very sensitive to all these considerations. Ignoring effect 2 tends to overestimate the cloud heating, particularly for low clouds, while a poor treatment of effect 3 leads to an underestimate. A new parameterization that accounts for the aforementioned considerations is accurate to within ∼30% over a wide range of overcast sky conditions, including solar zenith angles and cloud characteristics (altitudes, drop models, optical depths, and geometrical thicknesses), with the largest inaccuracies occurring for geometrically thick, extended cloud systems containing large amounts of vapor. Broadband methods that treat improperly one or more of the above considerations can yield substantially higher errors (>35%) for some overcast sky conditions while having better agreements over limited portions of the parameter range. For example, a technique that considers effect 3 but ignores effect 2 yields a partial compensation of errors of opposite sign, such that the resulting inaccuracy for geometrically thick clouds can be less than 20%. In contrast to the marked sensitivity of the cloud heating rates, the maximum relative errors in the reflected flux at the top of the overcast atmosphere and the transmitted flux at the surface do not vary appreciably under the various broadband treatments; with the new parameterization, the relative errors are less than 15%. In applying the broadband concept to overcast atmospheres with multiple cloud decks, there are cases when the errors can be larger than stated above. Hence a general use of broadband methods in weather prediction and climate models (e.g., general circulation models) should be accompanied by a realization of the potential inaccuracies that can occur for specific overcast sky cases.
A new numerical model of the middle atmosphere: 1. Dynamics and transport of tropospheric source gases
Authors: Garcia Rolando R. , Stordal Frode , Solomon Susan , Kiehl Jeffrey T.
Published: February 2012

A new numerical model of the middle atmosphere is described. In addition to the equations governing the zonal mean state, the model includes a potential vorticity equation for a single planetary‐scale Rossby wave. Nonlinearity associated with large‐amplitude waves is represented by means of the planetary wave breaking parameterization of Garcia [1991]. The formulation of the zonal mean problem differs from our earlier work in that the momentum equation is solved directly to facilitate the study of tropical dynamics. The model also includes an infrared radiative transfer code for the stratosphere and lower mesosphere, which replaces the Newtonian cooling parameterization used previously. It is shown that explicit computation of the planetary‐scale wave field yields a more realistic representation of the zonal mean dynamics and the distribution of trace chemical species. In particular, wave breaking produces a well‐mixed “surf zone” equatorward of the polar night vortex and drives a meridional circulation with downwelling on the poleward side of the vortex. This combination of mixing and downwelling produces shallow meridional gradients of trace gases in the subtropics and middle latitudes, and very steep gradients at the edge of the polar vortex. Mixing ratios of trace gases of tropospheric origin are very low within the vortex in winter. Computed distributions of methane and nitrous oxide are shown to agree well with observations.
Estimation of ice cloud parameters from ground‐based infrared radiometer and radar measurements
Authors: Matrosov S. Y. , Uttal T. , Snider J. B. , Kropfli R. A.
Published: February 2012

A technique is presented to estimate ice cloud particle characteristic sizes and concentrations as well as the integrated ice water path from simultaneous ground‐based radar and infrared radiometer measurements. The approach is based on the theoretical consideration of infrared thermal radiative transfer within a cloud and can be applied to clouds that are semitransparent in the infrared “window” and horizontally extensive. The suggested technique is applied to radar and infrared radiometer data collected during the Cloud Lidar and Radar Exploratory Test (CLARET‐I) experiment. Retrieved values of ice cloud microphysical parameters are in general agreement with results obtained by other methods.
A comparison of Nimbus 7 limb infrared monitor of the stratosphere and radiosonde temperatures in the lower stratosphere poleward of 60N
Authors: Remsberg Ellis E. , Bhatt Praful P. , Miles Thomas
Published: February 2012

Discrepancies have been noted in the literature between distributions of HNO3 and NO2 from Nimbus 7 limb infrared monitor of the stratosphere (LIMS) and from gas‐phase model calculations, particularly in polar winter. The inclusion of heterogeneous chemistry processes into models gives improved agreement for HNO3 but not for NO2. For this reason we considered whether there were temperature bias errors for LIMS that would have an impact on its species retrievals in polar regions. The 7 months of Nimbus 7 LIMS mapped temperatures are compared with daily, lower stratospheric radiosonde (RAOB) observations at 1200 UTC from a set of 22 stations poleward of 60N. The 7‐month average LIMS minus RAOB differences for the set are within ± 0.3 K at 30, 50, and 70 hPa; LIMS minus RAOB equals −1.2 K ± 2.2 K at 100 hPa. Springtime comparisons at 30 hPa were improved after recommended solar corrections were applied to the subset of daylight RAOB temperatures. Time series comparisons were conducted at 10 hPa for four stations in the Aleutian sector. After a correction for radiative cooling was applied to the RAOB data, the LIMS minus RAOB differences at 10 hPa were within ± 2 K, except in winter when LIMS was still significantly warmer by several degrees. Much of that bias is attributed to spatial temperature variations for LIMS/RAOB comparisons in regions of temperature extremes and to the finite vertical resolution of LIMS. All of this means that there is almost no significant error in the LIMS temperatures that could impact the accuracy of LIMS constituent retrievals throughout much of the polar lower stratosphere. The LIMS cold bias at 100 hPa is most pronounced for the 22 station set in November and December (about −1.9 K) and is statistically significant for many of the stations. LIMS tends to smooth through the vertical structure associated with elevated warm layers near 100 hPa. This negative temperature bias leads to retrieved overestimates of LIMS species concentrations below about the 70‐hPa level.
On the age of stratospheric air and ozone depletion potentials in polar regions
Authors: Pollock W. H. , Heidt L. E. , Lueb R. A. , Vedder J. F. , Mills M. J. , Solomon S.
Published: February 2012

Observations of the nearly inert, man‐made chlorofluorocarbon CFC‐115 obtained during January 1989 are used to infer the age of air in the lower stratosphere. These observations together with estimated release rates suggest an average age of high‐latitude air at pressure altitudes near 17–21 km of about 3 to 5 years. This information is used together with direct measurements of HCFC‐22, HCFC‐142b, CH3Br, H‐1301, H‐1211, and H‐2402 to examine the fractional dissociation of these species within the Arctic polar lower stratosphere compared to that of CFC‐11 and hence to estimate their local ozone depletion potentials in this region. It is shown that these HCFCs are much less efficiently dissociated within the stratosphere than CFC‐11, lowering their ozone depletion potentials to only about 30–40% of their chlorine loading potentials. In contrast, the observations of CH3Br and the Halons considered here confirm that they are rapidly dissociated within the stratosphere, with important implications for their ozone depletion potentials.
Directional and spectral reflectance of the Kuwait oil‐fire smoke
Authors: King Michael D.
Published: February 2012

The angular reflectance pattern of the Kuwait oil‐fire smoke was measured from an aircraft at 13 discrete wavelengths between 0.5 and 2.3 μm. Measurements at 0.75 and 1.64 μm showed that the reflectance of the smoke layer was about 12% in the nadir direction with considerable limb brightening toward the horizon. Furthermore, these observations revealed a backscattering maximum in the antisolar direction and an enhanced scattering near the rainbow direction. These characteristics suggest that the smoke layer 90 km downwind of the Kuwait oil fires was composed of a significant number of oil drizzle droplets that scatter solar radiation as a layer composed of spherical particles.
A comparison of surface sensible and latent heat fluxes from aircraft and surface measurements in FIFE 1987
Authors: Kelly Robert D. , Smith Eric A. , MacPherson J. Ian
Published: February 2012

Surface fluxes of sensible and latent heat over a tall grass prairie in central Kansas, as measured by 22 surface stations during FIFE 1987, are compared with values gained indirectly by simple linear extrapolation of aircraft‐measured flux profiles to the surface. The results of 32 such comparisons covering the period June 26 to October 13, 1987, indicate that (1) the flux profiles were generally linear, as expected in a convective boundary layer; 2) in general, aircraft‐derived surface fluxes were 30% less than the surface averages for sensible heat and 10% less for latent heat; (3) high‐pass filters, with cutoffs at 5 km, acted to reduce the uncertainty of the aircraft flux estimates, without changing the magnitude or sign of the disagreement between the aircraft and the surface fluxes; (4) undersampling of high frequencies by the aircraft could have caused as much as a 15% underestimate of the surface sensible heat fluxes; and (5) the aircraft and surface Bowen ratios also disagreed, with the greatest disagreement occurring during the dry periods with decreased plant activity (IFC 4).
Water vapor column abundance retrievals during FIFE
Authors: Bruegge Carol J. , Conel James E. , Green Robert O. , Margolis Jack S. , Holm Ronald G. , Toon Geoff
Published: February 2012

A variation of the modified Langley plot algorithm is reported here and applied to the retrieval of atmospheric water column abundance from a filtered sunphotometer. In this new methodology an absorption data base (LOWTRAN 7) is used to compute a water abundance versus transmittance curve of growth, rather than the square‐root dependence previously assumed. Validation of the technique is provided from an uncertainty analysis, and plans to further validate using Fourier transform spectrometers are detailed. The new sunphotometer technique is used to report total column water vapor during the First ISLSCP Field Experiment (FIFE), and comparisons are made with abundances retrieved via FIFE radiosonde observations. The sunphotometer data can best be utilized, however, to in turn validate data from airborne or in‐orbit measurements of water vapor. With these flight sensors, horizontal and topographic variability within the scene can be viewed. An example of the airborne data set is given using an image from the airborne visible infrared imaging spectrometer (AVIRIS), as acquired on August 31, 1990.
Aircraft lightning initiation and interception from in situ electric measurements and fast video observations
Authors: Moreau Jean‐Patrick , Alliot Jean‐Claude , Mazur Vladislav
Published: February 2012

Multipoint electric field measurements on the French C‐160 research airplane presented additional verification for a physical model of aircraft‐triggered lightning as a bidirectional leader initiated on the aircraft. For the few lightning strikes to aircraft that were not aircraft‐triggered, the multipoint electric field measurements proved that these strikes resulted from interception of the aircraft by natural lightning flashes. Video images of lightning channels at 200 frames per second provided the first and only physical evidence of the presence of a positive leader exiting from the positive pole of the airplane's electrical dipole. The existence of a small (<1 A) positive leader current had been predicted in the physical model but had not yet been measured. Weak pulse processes found in magnetic field variations during positive leader development confirm the presence of small amplitude streamers in addition to a continuous leader process.
Aerosol optical properties over the midcontinental United States
Authors: Halthore Rangasayi N. , Markham Brian L. , Ferrare Richard A. , Aro Theo. O.
Published: February 2012

Solar and sky radiation measurements were analyzed to obtain aerosol properties such as the optical thickness and the size distribution. The measurements were conducted as part of the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) during the second intensive field campaign (IFC) from June 25 to July 14, 1987, and the fifth IFC from July 25 to August 12, 1989, on the Konza Prairie near Manhattan, Kansas. Correlations with climatological and meteorological parameters show that during the period of observations in 1987, two types of air masses dominated the area: an air mass with low optical thickness and low temperature air associated with a northerly breeze, commonly referred to as the continental air, and an air mass with a higher optical thickness and higher temperature air associated with a southerly wind which we call “Gulf air.” The size distributions show a predominance of the larger size particles in Gulf air. Because of the presence of two contrasting air masses, correlations with parameters such as relative humidity, specific humidity, pressure, temperature, and North Star sky radiance reveal some interesting aspects. In 1989, clear distinctions between continental and Gulf air cannot be made; the reason for this will be discussed.
Relations between surface conductance and spectral vegetation indices at intermediate (100 m2 to 15 km2) length scales
Authors: Sellers Piers J. , Heiser Mark D. , Hall Forrest G.
Published: February 2012

The theoretical analysis of Sellers et al. (1992) indicates that the relative response of the unstressed canopy conductance (g*c) to changes in incident (nonsaturating) PAR flux (F0) should be proportional to some spectral vegetation indices (SVI), specifically the simple ratio (SR) vegetation index, for vegetation covers of similar physiology and physiognomy; or ∇F ≡ (∂g*c/∂F0) ∝ SR. This relationship was tested using the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) flux station data set (g*c) and the FIFE Landsat thematic mapper image data (SVI). The flux station data were used to invert a soil‐plant‐atmosphere model (the simple biosphere model (SiB) of Sellers et al., 1986) to derive estimates of g*c separate from the soil evaporation contribution and corrected for the “stress” effects of vapor pressure deficit and soil moisture deficit. The Landsat imagery was sampled to produce SR vegetation index values for small areas (90 × 90 m) centered on each flux station. The derived ∇F and SR values were found to be near‐linearly related on a site‐by‐site basis. Differences between sites are thought to be related to the fractional cover of C3 versus C4 vegetation so that ∇S,F ≡ (∂∇F/∂(SR)) ∝ V3, where V3 is the fractional cover of C3 vegetation. The above equations form the basis for a simple biophysically based model of canopy‐scale conductance. The model was applied on the flux station scale (100 m)2 and was also used to calculate fluxes for the entire FIFE site (15 × 15 km)2; the latter results were compared with airborne flux measurements. It is demonstrated that because the proposed relationship between ∇F and SR is near‐linear, the calculation of evapotranspiration rates for large areas using this model is effectively scale‐invariant.
The effects of high liquid water content on thunderstorm charging
Authors: Saunders C. P. R. , Brooks I. M.
Published: February 2012

Charge transfer to a riming graupel target during interactions with ice crystals has been investigated in the laboratory. When liquid water contents sufficiently high to cause wet growth are achieved, the charge transfer falls to values which are insignificant to thunderstorm electrification. The implications of this null result to a recent analysis of thunderstorm‐charging processes by Williams et al. (1991) are discussed.
Effects of liming and nitrogen fertilization on emissions of CO2 and N2O from a temperate forest
Authors: Brumme R. , Beese F.
Published: February 2012

Fluxes of N2O and CO2 were measured simultaneously in control, N‐fertilized, and limed plots in a 145‐year‐old beech stand in the Solling area in Germany using an automated chamber method. The N‐fertilized plot received annually 140 kg of nitrogen as NH4SO4 since 1982; the limed plot was treated with 30 t/ha of dolomitic limestone once in 1982. On all plots, fluxes of N2O and CO2 underwent strong diel, daily, and seasonal variations. For the control plot, N2O and CO2 effluxes averaged about 1 mg N/m2/d and 2.9 g CO2/m2/d from October until May and 3 mg N/m2/d and 4.5 g CO2/m2/d from May until September. Annual fluxes for N2O and CO2 were 5.6 kg N/ha/yr and to 3.2 t C/ha/yr, respectively. Nitrogen saturation of the system due to high rates of N deposition for several decades may be responsible for the high N2O losses. Liming drastically reduced the N2O emission to 1.5 kg N/ha/yr and increased the CO2 emission to 4.1 t C/ha/yr, 5 years after the treatment. Changes in N2O/N2 ratios are assumed to be the reason for the lower N2O emission. Fertilization increased the N2O emission, resulting in 7.8 kg N/ha/yr, whereas the effect on CO2 emission with 3.8 t C/ha/yr was less pronounced.
Smoke and fire characteristics for cerrado and deforestation burns in Brazil: BASE‐B Experiment
Authors: Ward D. E. , Susott R. A. , Kauffman J. B. , Babbitt R. E. , Cummings D. L. , Dias B. , Holben B. N. , Kaufman Y. J. , Rasmussen R. A. , Setzer A. W.
Published: February 2012

Fires of the tropical forests and savannas are a major source of particulate matter and trace gases affecting the atmosphere globally. A paucity of quantitative information exists for these ecosystems with respect to fuel biomass, smoke emissions, and fire behavior conditions affecting the release of emissions. Five test fires were performed during August and September 1990 in the cerrado (savannalike region) in central Brazil (three fires) and tropical moist forest (two fires) in the eastern Amazon. This paper details the gases released, the ratios of the gases to each other and to particulate matter, fuel loads and the fraction consumed (combustion factors), and the fire behavior associated with biomass consumption. Models are presented for evaluating emission factors for CH4, CO2, CO, H2, and particles less than 2.5 μm diameter (PM2.5) as a function of combustion efficiency. The ratio of carbon released as CO2(combustion efficiency) for the cerrado fires averaged 0.94 and for the deforestation fires it decreased from 0.88 for the flaming phase to <0.80 during the smoldering phase of combustion. For tropical ecosystems, emissions of most products of incomplete combustion are projected to be lower than previous estimates for savanna ecosystems and somewhat higher for fires used for deforestation purposes.
Distribution of tropospheric ozone at Brazzaville, Congo, determined from ozonesonde measurements
Authors: Cros Bernard , Nganga Dominique , Minga Alexis , Fishman Jack , Brackett Vincent
Published: February 2012

An analysis of 33 ozonesonde launches in Brazzaville, Congo (4°S, 15°E), between June 1990 and May 1991 is presented. The data indicate highest tropospheric amounts between June and early October, coincident with the dry season and with the presence of enhanced widespread biomass burning. The seasonal cycle of ozone derived from the ozonesonde measurements is in good agreement with the climatological seasonal cycle inferred from the use of satellite data and both seasonal cycles peak in September. Averaged throughout the year, the integrated amount of ozone derived from the ozonesondes is 44 Dobson units (DU) and is 39 DU using the satellite data. Within the troposphere the highest partial pressures are generally found at pressure levels near 700 mbar (∼3 km). Using simultaneous ozonesonde data from Ascension Island (8°S, 15°W), examples are presented illustrating that differences in the troposphere are primarily responsible for the observed spatial gradients of total ozone observed by TOMS. Calculation of correlation coefficients suggests that total ozone measurements may be a better indicator of the amount of ozone in the troposphere than are surface measurements.
Interaction of HCl vapor with water‐ice: Implications for the stratosphere
Authors: Abbatt J. P. D. , Beyer K. D. , Fucaloro A. F. , McMahon J. R. , Wooldridge P. J. , Zhang R. , Molina M. J.
Published: February 2012

The nature of the interaction of HCl vapor with ice has been investigated, using thermal analysis and FTIR spectroscopy to characterize the ice substrate, and mass spectrometry to measure the concentration of HCl and H2O vapors in the gas phase. The results indicate that a liquid layer is formed rapidly at the ice surface for ice exposed to HCl vapor at partial pressures above those characteristic of the ice‐liquid (aqueous HCl solution) equilibrium system. This liquid layer also forms below the eutectic temperature (186 K); that is, it forms even at temperatures at which the liquid is metastable with respect to the formation of HCl trihydrate. For smaller HCl partial pressures such as those prevailing in the stratosphere, the HCl is taken up by the ice surface in amounts corresponding to a large fraction of a monolayer. The chemical reactivity of this surface HCl is very large: Chlorine activation by type II polar stratospheric clouds (consisting of ice particles) should occur efficiently by reaction of the HCl with ClONO2.
The global sources of nitrous oxide
Authors: Khalil M. A. K. , Rasmussen R. A.
Published: February 2012

We use atmospheric and ice core data on the concentrations of nitrous oxide to estimate that the present global anthropogenic emissions are 7±1 tg/yr. If the atmospheric lifetime of N2O is a hundred years or more, this estimate is virtually independent of the actual lifetime. The natural sources are estimated to be about 15 tg/yr. We also find that nitrous oxide started increasing rapidly only during the last century. The trends over the last decade are extremely variable; over 3‐year periods the trends have ranged from 0.5 ± 0.2 parts per billion by volume (ppbv/yr) to 1.2 ± 0.1 ppbv/yr. The average rate of increase is about 0.80 ± 0.02 ppbv/yr or 0.27 ± 0.01 %/yr (1977–1988). There is an indication that N2O may be increasing faster in recent years than during the middle 1970s by about 0.2 ± 0.1 ppbv/yr. It is likely that several small anthropogenic sources may be causing the present trends, all emitting between 0.1 and 1.5 Tg/yr.
Indications of photochemical histories of Pacific air masses from measurements of atmospheric trace species at Point Arena, California
Authors: Parrish D. D. , Hahn C. J. , Williams E. J. , Norton R. B. , Fehsenfeld F. C. , Singh H. B. , Shetter J. D. , Gandrud B. W. , Ridley B. A.
Published: February 2012

Measurements of light hydrocarbons, ozone, peroxyacetyl nitrate (PAN), HNO3, NO3−, NOx, NOy, and meteorological parameters were made during a 10‐day period in April and May 1985 at Point Arena, a coastal inflow site on the Pacific Ocean in northern California. The meteorological measurements indicate that during this study the sampled air was usually from the marine boundary layer with little land influence on the meteorological parameters. In this marine air the mixing ratios of the alkanes, ozone, PAN, and HNO3 showed strong correlations coincident with variations in the origins of calculated air parcel trajectories and with variations in the ratios of the light alkanes. This variation in the ratios is attributed to different degrees of photochemical aging of the alkanes that are generally consistent with the calculated trajectories. This behavior indicates that the alkane levels are determined by transport to the marine area from continental sources, most likely Asian, followed by photochemical removal over the Pacific Ocean. Since the concentrations of PAN and ozone correlate well with the alkane ratios, it is concluded that the observed PAN and ozone were dominated by continental sources and removal processes in the marine areas. This and other marine studies have observed a strong correlation of PAN and ozone, and it is suggested that production over the continents, transport to the marine areas, and parallel removal processes account for much of the observed correlation. From the correlation of these two species with the measured alkane ratios, approximate net lifetimes of PAN and ozone in the marine troposphere of ≤2.5 and ≥19 days, respectively, are derived. The primary conclusion is that the alkanes, ozone, and PAN in these air parcels from the Pacific marine troposphere are dominated by transport from continental sources and removal by photochemical processes. Direct emissions of the alkanes and in situ photochemical production of PAN and ozone from precursors emitted into the marine region from the surface or the stratosphere must play less important roles. Similar indications of continental influence in marine areas have been seen in other studies of ozone, the sulfur cycle, oxidized nitrogen, and hydrocarbons. It is suggested that the ratios of the light alkanes provide photochemical “clocks” that are useful for gauging the importance of continental influence in a particular marine measurement.
Simulation of the last glacial cycle by a coupled, sectorially averaged climate‐ice sheet model: 2. Response to insolation and CO2 variations
Authors: Gallée H. , Van Yperselb J. P. , Fichefet T. , Marsiat I. , Tricot C. , Berger A.
Published: February 2012

A two‐dimensional climate model which links the northern hemisphere atmosphere, ocean mixed layer, sea ice, and continents has been asynchronously coupled to a model of the three main northern ice sheets and their underlying bedrock. The coupled model has been used to test the influence of several factors, including snow surface albedo over the ice sheets, in producing plausible ice age simulations using astronomically derived insolation and CO2 data from the Vostok ice core. The impact of potentially important processes, such as the water vapor transport, clouds, and deep sea circulation, was not investigated in this study. After several sensitivity experiments designed to identify the main mechanisms governing surface temperature and ice accumulation, the model is first run with ice sheet feedback by forcing it only with the astronomical insolation over the past 122 kyr. Large variations of ice volume are simulated between 122 and 55 kyr B.P., with a rapid latitudinal extension of the North American and Eurasian ice sheets starting at 120 kyr B.P. The simulated last glacial maximum is at 19 kyr B.P. The model is able to simulate deglaciation as well. The simulated evolution of the three northern ice sheets is generally in phase with geological reconstructions. The major discrepancy between the simulation and paleoclimate reconstructions lies in the underestimation of temperature variations (linked with an underestimation of the ice sheet extent and an excess in the prescribed CO2 concentration). Sensitivity experiments show that ablation is more important to the ice sheet response than snow precipitation variations. In the model a key mechanism in the deglaciation after the last glacial maximum appears to be the “aging” of snow, which decreases its albedo. The other factors which play an important role are, in decreasing level of importance, the ice sheet altitude, insolation, taiga cover, and ice sheet extent. A final set of experiments addresses the effects of CO2 on the simulated climate of the last glacial maximum and on a new long term experiment covering the last 122 kyr. This last experiment is made by forcing the model with both insolation and CO2 variations. This additional forcing improves the temperature and ice volume results. Despite the limitations inherent to the present modeling approach, the sensitivity experiments performed can provide insight into the relative importance of possible mechanisms responsible for the building and melting of huge ice sheets during the last glacial‐interglacial cycle.
δ15N of N2 in air trapped in polar ice: A tracer of gas transport in the firn and a possible constraint on ice age‐gas age differences
Authors: Sowers Todd , Bender Michael , Raynaud Dominique , Korotkevich Y. S.
Published: February 2012

With respect to gas transport the fim near the surface of an ice sheet can be divided into three zones. The uppermost is a “convective zone” located just below the surface of the ice sheet in which the air is rapidly flushed by convective exchange with the overlying atmosphere. Below the convective zone there is a “diffusive air column” in which diffusion is rapid but there is no convection. Between the bottom of the diffusive air column and the bubble close‐off region there may be a “nondiffusive zone” in which diffusion is so slow that negligible gas transport occurs. The diffusive air column is characterized by progressive enrichment with depth of 15N in N2 (and heavy isotopes of gases in general) as predicted using the barometric equation. In this paper we present data on the δ15N of N2 in recently trapped air samples from 12 ice cores, along with numerous downcore samples from Byrd, Vostok, and Dome C. Bubble close‐off depths for these cores (calculated from a densification model) ranged from 51 to 114 meters below the surface (mbs). We used these data and the barometric equation to calculate the thickness of the diffusive air column, and found that it comprised 46 to 93% of the total firn thickness at our study sites. Paleo‐close‐off depths calculated from the densification model for glacial sections of Byrd, Vostok, and Dome C are 15–25 m deeper than close‐off depths today. Diffusive column heights, calculated from δ15N, varied in a more complex manner. The diffusive column height at Byrd appears to have decreased from 74 m during the last glacial period to 50 m during the Holocene. At Vostok and Dome C the diffusive column height calculated from 15N increase from about 65 m during the last glacial period to about 80 m in the Holocene. We use records of surface temperature and CO2 at Byrd and Vostok, along with their respective chronologies, to constrain the ice age ‐ gas age difference (Δage) throughout the section of the Vostok ice core corresponding to the last glacial termination. In principle, Δage values calculated from these data can be used to discriminate whether gas in the fim mixes to the bubble close‐off depth or to a depth equivalent to the diffusive column height. In practice, however, uncertainties in the chronology of Byrd and Vostok are too great to allow us to distinguish between these two possibilities. One can only say that at the time of the last termination, Δage for Vostok was between 3 and 10.5 kyr. Previous estimates fall within this range.
Calculation of CO2 15‐μm band atmospheric cooling rates by Curtis matrix interpolation of correlated‐k coefficients
Authors: Zhu Xun , Summers Michael E. , Strobel Darrell F.
Published: February 2012

A fast, yet accurate algorithm for calculating CO2 15‐μm band cooling rates by Curtis matrix interpolation is presented based on a computationally efficient method to compute correlated‐k coefficients in an inhomogeneous atmosphere for any spacing in pressure levels and variation of CO2 mixing ratio. The algorithm produces an error in cooling rate of less than 4% in the region where the radiative processes play a major role. This algorithm is easy to use and can be readily adopted for use in general circulation models of the Earth's atmosphere.
Application of a linear spectral model to the study of Amazonian squall lines during GTE/ABLE 2B
Authors: Silva Dias Maria A. F. , Ferreira Rosana Nieto
Published: February 2012

A linear nonhydrostatic spectral model is run with the basic state, or large scale, vertical profiles of temperature and wind observed prior to convective development along the northern coast of South America during the GTE/ABLE 2B. The model produces unstable modes with mesoscale wavelength and propagation speed comparable to observed Amazonian squall lines. Several tests with different vertical profiles of low‐level winds lead to the conclusion that a shallow and/or weak low‐level jet either does not produce a scale selection or, if it does, the selected mode is stationary, indicating the absence of a propagating disturbance. A 700‐mbar jet of 13 m/s, with a 600‐mbar wind speed greater or equal to 10 m/s, is enough to produce unstable modes with propagating features resembling those of observed Amazonian squall lines. However, a deep layer of moderate winds (about 10 m/s) may produce similar results even in the absence of a low‐level wind maximum. The implications in terms of short‐term weather forecasting are discussed.