bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient climate response to external forcing on 100–104 year time scales part 1: Experiments with globally averaged, coupled, atmosphere and ocean energy balance models
Authors: Harvey L. D. Danny , Schneider Stephen H.
Published: February 2008

We present the results of a study of the sensitivity of the transient surface temperature response to a step function solar constant increase using a globally averaged energy balance climate model which is coupled to two different globally averaged thermodynamic ocean models. The first ocean model is a box model, in which the ocean is divided into a small number of isothermal reservoirs. Experiments with this model demonstrate some circumstances in which it is important to treat the mixed layer and deep ocean separately rather than lumping them into a single reservoir, as has been the practice in a number of recent studies using coupled atmosphere‐ocean‐cryosphere models over 104 year time scales. The second ocean model has an isothermal mixed layer which is coupled to an advective‐diffusive deep ocean having a continuous vertical temperature profile. We permit the thermal diffusivity K and the advection velocity w to vary vertically and introduce a variety of plausible feedbacks between K and the vertical temperature gradient, and between w and the perturbation mixed layer wanning. We also permit the bottom water source temperature to change by a prescribed fraction of the mixed layer response. The transient surface response is relatively insensitive to changes in K and w for the nonfeedback cases, but is more sensitive to individual feedback mechanisms. When multiple feedback processes are permitted a complex transient surface temperature response is possible. When applied with a periodic solar constant forcing, these feedback processes can either significantly reduce or increase the amplitude of the surface temperature response compared to the no‐feedback case.
The importance of liquid‐phase oxidation of SO2 in the troposphere
Authors: Hegg Dean A.
Published: February 2008

A recent cloud climatology is employed to estimate the tropospheric liquid water burden as a function of latitude. This burden, coupled with a rate expression for aqueous oxidation of SO2 in atmospheric hydrometeors allows estimation of the aqueous sink for SO2 in the troposphere. This sink appears to be larger than previously assumed. Comparison with estimates of the tropospheric SO2 sink due to homogeneous gas‐phase oxidation suggests that the aqueous sink is at least as large as the gas‐phase sink and that the latter is quite possibly of secondary importance.
The horizontal structure of traveling planetary‐scale waves in the upper stratosphere
Authors: Venne David E.
Published: February 2008

The temperature amplitude and phase structures of zonally propagating planetary waves are determined between 79S and 79N latitudes at the 10 and 1 mbar levels through the use of spectral analysis and complex‐valued empirical orthogonal function analysis. The data are temperatures regressed from Nimbus 4 and 5 satellite infrared radiances during the solsticial seasons of 1970–1974. The structures of three westward moving normal modes and two eastward moving modes linked to instabilities near the winter stratopause are described. Waves of zonal wavenumber 4, 5, and 6 which are eastward moving in the summer Southern Hemisphere are also observed; a wave 1, 16‐day period, westward moving mode commonly observed in geopotential fields is not seen here. The results concur with recent studies of traveling waves and provide estimates of average wave temperature amplitudes in the upper stratosphere.
Recent stratospheric negative ion composition measurements between 22‐ and 45‐km altitude
Authors: Arijs E. , Nevejans D. , Ingels J. , Frederick P.
Published: February 2008

Ion spectra obtained during three balloon flights performed in June 1982, September 1982, and September 1983 are reported. The lower altitude limit of the measurements is imposed by the decrease of the instrument sensitivity and the upper limit by present ballooning techniques. At high altitudes the ion spectra are disturbed by contamination, whereas at low altitudes, ion cluster breakup is a severe problem. Nevertheless knowledge of relative abundances of the different negative ion mass peaks, mainly belonging to the NO3−(HNO3)n and HSO4−(HNO3)m(H2SO4)t cluster families allows the derivation of concentrations of H2SO4 in the altitude region of 22–45 km. At 45 km an increased SO2 mixing ratio, possibly due to volcanic activities, was estimated from the negative ion mass spectra. The data are discussed in terms of previous measurements and models. Special interest is given to the sulfur chemistry and the implications on aerosol formation.
Atmospheric‐electrical implications of 222Rn daughter deposition on vegetated ground
Authors: Willett J.
Published: February 2008

Natural diffusive deposition of radon daughter products from the atmosphere onto an aerodynamically rough, vegetated surface may cause an important enhancement of the ionization rate within the plant canopy. For example, the blades of grass in a lawn may become slightly radioactive, leading to higher ionization in the air between them than above their tops. The impact of this increased ionization rate is estimated from a simple model of the conductivity profile in the turbulent “electrode layer”. It is found that an order‐of‐magnitude augmentation can have substantial effects on the electrical structure. With this motivation a one‐dimensional, steady state model of radon daughter, dry deposition is developed for estimating the magnitude of the deposited activity. The effects of aerosol attachment and of the entire decay chain are included. This model predicts significant enhancements of the “surface radioactivity” under typical continental conditions.
Enhanced ion production in convective storms by transpired radon isotopes and their decay products
Authors: Martell Edward A.
Published: February 2008

The contribution of radioisotopes of continental surface origin to the production of ions in convective storms has not been adequately assessed. The average 222Rn flux from bare soils and average distributions of 222Rn versus altitude in the troposphere for the normal range of vertical eddy mixing rates provide an inadequate basis for such an assessment. The influence of the biosphere, particularly the substantially higher fluxes for transpired 222Rn and 220Rn, and enhanced ion production by high concentrations of 222Rn and 220Rn decay products on aerosols and vegetation surfaces, have not been considered. Effective transpiration of 222Rn and 220Rn by vegetation is due to their high concentrations in soil gas and their solubility in soil moisture. Substantially enhanced fluxes of 222Rn over a mature corn field (6 times higher than the average flux over bare soils), and of 220Rn over a wheat field, illustrate the effectiveness of plant transpiration. Conditions favoring effective transpiration include mature vegetation, excess soil moisture throughout the root zone, strong radiative heating of the leaf canopy, and moderate surface winds. Rising air parcels with transpired water vapor, 222Rn, 220Rn, and their decay products may contribute importantly to the development of cumulus clouds and air mass storms. The dynamic lift of surface air, which feeds updrafts of convective storms, transports radioisotopes and ions from several sources within the vegetation canopy: transpired 222Rn, 220Rn, and their decay products; ions produced by the decay products of 220Rn and 222Rn on aerosol and vegetation surfaces; and biological aerosols and plant debris with high surface concentrations of radioisotopes. Observed frequencies of lightning flashes are highly correlated with areas of effective transpiration and their variations with season, latitude, and time of day.
Atmospheric electric field and current configurations in the vicinity of mountains
Authors: Tzur I. , Roble R. G. , Adams J. C.
Published: February 2008

A quasi‐static, two‐dimensional numerical model of atmospheric electricity that solves the continuity equation of the conduction current has been constructed. This model is used to calculate the local electric structure of the atmosphere in the vicinity of various orographic features and to determine how these features affect the mapping of electric phenomena out of the boundary layer to higher altitudes. The model uses a realistic conductivity profile that includes the equalization layer above 65 km produced by the presence of electrons in the daytime D region of the ionosphere. Anisotropic conductivity resulting from the earth's geomagnetic field is considered in this layer. The results illustrate the dependence of the electric field and current distributions above mountains upon the curvature of the mountain slope, the horizontal scale of the mountain, and the columnar resistance above the mountain (or mountain height). Wide mountains can map current and field distortions upward very efficiently, e.g., a mountain with a height of 3 km and a horizontal scale of 50 km is able to maintain 70% of the increase in the vertical surface current at ionospheric altitudes, while a mountain with the same height and a horizontal scale of 35 km maps only 40%. It is demonstrated that this width effect also exists for a system of mountains. The current above a mountain is always magnified, but the electric field increases above a curved mountain and decreases above a mountain plateau. Horizontal currents also develop around a mountain and can reach values comparable to the fair‐weather current. The magnified currents produced by a mountain can extend to ionospheric heights, where the direction of the geomagnetic field lines becomes important and influences the current configuration in the anisotropic region (above about 70 km).
Thunderstorm electrification: A case study
Authors: Lhermitte Roger , Williams Earle
Published: February 2008

The paper presents interpretation of triple Doppler radar observations of a thunderstorm that occurred at the Kennedy Space Center, Florida. Precipitation particle motions inside the storm, as evaluated from the three radial velocity radar data sets, are presented in a selected vertical plane throughout the storm development. These data are interpreted and compared with observations of VHF radio emission sources and lightning charge centers derived from an earlier analysis (Krehbiel, 1981). The main feature of the particle motion field is the persistence, at nearly the same altitude throughout the entire period of analysis, of a “balance level” characterized by a zero value of the precipitation particle mean vertical velocity. Further analysis based on considerations of radar reflectivity and air velocity suggests the presence, at this altitude, of relatively large precipitation particles suspended in an updraft. The lightning negative charge centers appear to be less than 1 km above the particle balance level.
Nighttime observations of thunderstorm electrical activity from a high altitude airplane
Authors: Brook M. , Rhodes C. , Vaughan O. H. , Orville R. E. , Vonnegut B.
Published: February 2008

Two sets of observations from a NASA U‐2 airplane looking down on the tops of nocturnal thunderstorms are reported. Photographs show both diffuse illumination in the cloud and unobscured segments of lightning channels a kilometer or longer in clear air around and above the cloud. Multiple images of lightning channels indicate multiple discharges in the same channel. Lightning spectra were obtained similar to those observed beneath cloud base. Field changes correlate with pulses measured with a photocell optical system. Optical signals corresponding to dart leader, return stroke, and continuing current events are readily distinguished in the scattered light emerging from the cloud surface. The variation of light intensity with time in lightning events such as dart leaders, which radiate light first from a location within the cloud and later from outside (beneath) the cloud, are consistent with the predicted modification of optical lightning signals by clouds as given by Thomason and Krider (1982). As a result it appears that satellite based optical sensor measurements cannot provide reliable information on current rise times in return strokes. On the other hand, discrimination between cloud‐to‐ground and intracloud flashes and the counting of ground strokes is possible, using the optical pulse pairs identified with leader, return stroke events in the cloud‐to‐ground flashes studied. If confirmed by further studies as a regularly identifiable occurrence, the pulse pairs, together with other criteria, could form the basis for the reliable identification of ground strokes from a satellite. A multitude of weak lightning channels commonly exists in the clear air above or around cloud tops, indicating that lightning is capable of introducing chemical species, ions, and space charge directly into the upper troposphere and lower stratosphere.
Optical aspects of winter lightning discharges triggered by the rocket‐wire technique in Hokuriku district of Japan
Authors: Kito Yukio , Horii Kenji , Higashiyama Yoshio , Nakamura Koichi
Published: February 2008

Optical aspects of winter lightning flashes triggered by the rocket‐wire technique from 1977 to 1982 in Hokuriku district of Japan are described. Thirty‐nine flashes out of 45 successfully triggered ones were photographed by high‐speed cameras with framing speed of around 1000 frames/s. Each flash starts with an upward leader from the tip of the ascending steel wire, regardless of the polarity of the cloud charge. Observations made at a distance of 70 m from the launch site gave clear images of the initial development of upward leaders. Positive leaders started at a speed of around 0.1×105 m/s with a number of branches, while negative one started at a speed of 0.5 to 1×105 m/s with a few branches. The established flashes kept their brightness for 19 ms up to 706 ms and four flashes for more than 600 ms. The long life flashes are apt to occur when the electric field on the ground keeps high value for a long period. After inspecting darkness of the channel images in the film, the time variation of luminous intensity of the flashes are classified into four patterns.
Reactive nitrogen compounds in the Arctic
Authors: Dickerson Russell R.
Published: February 2008

Measurements of NO, NOx (NO + NO2), and NOy (NOx + 2N2O5 + NO3 + HONO + HO2NO2 + PAN + R‐ONOx) were made in March 1983 between 200 and 12,000 m altitude on several flights in the Arctic and from Spitsbergen, Norway, to Cologne, West Germany. NO values were always below the detection limit (10 ppt); NOx values (determined with a FeSO4 converter) were high, ∼600 ppt, in the boundary layer and generally decreased sharply with altitude, although distinct strata of high NOx were observed at altitudes up to 8000 m. NOy (measured with a 425°C Mo converter) showed altitude profiles similar to NOx profiles with boundary layer values as high as 1500 ppt. Ratios of NOx to NOy were 0.81 near the surface and 0.46 at 6400 m, probably owing to higher levels of PAN or other organic compounds in the free troposphere. The possible global impact of high concentrations of reactive nitrogen compounds in the Arctic is discussed.
Stratospheric photochemical studies using Nimbus 7 data: 1. Ozone photochemistry
Authors: Natarajan Murali , Callis Linwood B. , Boughner Robert E. , Russell James M. , Lambeth James D.
Published: February 2008

The consistency of contemporary stratospheric ozone photochemistry is examined in the light of recent data from the Nimbus 7 satellite. Temperature, O3, H2O, HNO3, and NO2 data from the limb infrared monitor of the stratosphere experiment and CH4 from the stratospheric and mesospheric sounder experiment are used in conjunction with a simplified photochemical model to compare calculated and observed O3 for 30°N during March. The photochemical model underestimates the ozone in the upper stratosphere by 15–32%. Calculated and observed mixing ratios of NO2 and OH and the daytime value of the ratio HNO3/NO2 are presented. Results from a Monte Carlo analysis of the uncertainty due to errors in the input data are also given. The sensitivity of the model results to modification of certain key reaction rate constants is studied. These changes result in higher ozone mixing ratios in the upper stratosphere, which are in better agreement with the data. The effect of such modifications on other photochemical parameters is shown. The level of agreement between theory and observations with regard to the temperature sensitivity of O3 and the diurnal variations in O3 is discussed.
Infrared line intensities of chlorine monoxide
Authors: Kostiuk Theodor , Faris James L. , Mumma Michael J. , Deming Drake , Hillman John J.
Published: February 2008

Absolute infrared line intensities of several ClO lines in the rotational‐vibrational (1–0) band were measured using infrared heterodyne spectroscopy near 12 μm. A measurement technique using combined ultraviolet absorption and infrared line measurements near 9.5 μm and 12 μm permitted an accurate determination of the column densities of O3 and ClO in the absorption cell and thus improved ClO line intensities. Results indicate ClO line and band intensities ∼2.4 times lower than previous experimental results. Effects of possible failure of local thermodynamic equilibrium conditions in the absorption cell and the implication of the results for stratospheric ClO measurements in the infrared are discussed.
Photochemistry of methane and the formation of hydrocyanic acid (HCN) in the Earth's early atmosphere
Authors: Zahnle Kevin J.
Published: February 2008

The photochemistries of methane and HCN are discussed in the context of the primitive terrestrial atmosphere, using a detailed numerical model. In the absence of abundant O2, absorption of solar EUV (λ < 1023Å) by N2 provides a large thermospheric source of atomic nitrogen. Methane is oxidized cleanly and efficiently, provided CO2 is more abundant than CH4. Otherwise, a large fraction of the methane present is polymerized, forming alkanes in the troposphere and polyacetylenes and nitriles in the upper atmosphere. The combination of low O2, high N2, and moderately high levels of CO2 would have made the ancient terrestrial atmosphere a favorable environment for the production of HCN from CH4. Once formed, HCN is rather long‐lived; it is removed from the atmosphere either by direct photodissociation at Ly α (∼100 years) or by rainfall (∼10 years). Chemical loss would have been unimportant. Owing to its stability, transport of HCN from the top to the bottom of the atmosphere can be efficient; nevertheless, our results are sensitive to the assumed eddy diffusion profile. For small amounts of methane a small constant fraction of order 0.1% to 1% of the carbon in the methane is returned to the surface as hydrocyanic acid rain. For larger methane sources exceeding a critical value of order 1011 molecules cm−2 s−1 (corresponding to ƒ(CH4) of order 10−4–10−3), rainout of HCN increases abruptly to more than 10% of the carbon supplied as methane, limited by the primary production of N. Under favorable conditions, hydrolysis of HCN could have supported atmospheric NH3 mixing ratios approaching 1 ppm.
A comparison between high‐altitude horizon photography and direct sampling of El Chichón cloud particles
Authors: Coletti A. , Hofmann D. J. , Rosen J. M.
Published: February 2008

Perturbations to the visible radiation by the El Chichón aerosol layers in the stratosphere have been observed using in situ time‐lapse photography of the earth horizon from a balloon gondola. The measurements were performed on May 18, 1982, from Laredo, Texas (27.3°N, 99.5°W), during a sounding performed with optical particle counters that measured aerosol size distributions in six different size ranges. The results of the microdensitometry of the photographic film agree well with the corresponding quantities determined from the optical counter data by applying Mie theory for spherical particles. The optical thickness of the stratosphere from a height of about 18.8 km to the top of the atmosphere, averaged over visible wavelengths, was found to be on the order of 0.18. At a height close to the maximum reached by the balloon (27 km) the residual optical thickness due to aerosol particles was found to be on the order of 0.7 × 10−3. The isodensity contours in the stratosphere described the main pattern of the intensity distributions of multiply scattered sunlight in the vicinity of the earth horizon. This pattern, observed at relatively high solar elevation, indicated that both the upward and downward intensities, besides depending on the particle characteristics and on their vertical distribution, also depend on variations of the general distribution in the underlying cloud coverage.
Surface ozone distributions and variations from 1973–1984: Measurements at the NOAA Geophysical Monitoring for Climatic Change Baseline Observatories
Authors: Oltmans Samuel J. , Komhyr Walter D.
Published: February 2008

Surface ozone data are presented from up to 12 years of continuous measurements at Point Barrow, Alaska; Mauna Loa, Hawaii; American Samoa, South Pacific; and South Pole, Antarctica. Annual cycle characteristics of the data are described relative to atmospheric mixing and transport processes that give rise to the observed annual ozone distributions. Both positive and negative long‐term trends are exhibited by the data. From examination of trends in the seasonal and monthly data, it is concluded that the cause of the trends is most likely a fluctuation over the years in the stratospheric‐tropospheric exchange and tropospheric circulation processes that distribute ozone within the troposphere, coupled with tropospheric circulation disturbances such as those associated with the El Niño/Southern Oscillation events of 1976 and 1982–1983. Because the positive ozone trend at Barrow occurs during summer months, photochemical ozone production in increasingly polluted Arctic air cannot be ruled out. Ozonesonde data are used to show that the surface ozone observations at Mauna Loa observatory in the downslope wind regimes, and at South Pole, are representative of ozone measurements in the free troposphere, and that the ozone trends observed at Point Barrow and Samoa are likely representative of the lower free troposphere even though the measurements are made in air modified within the boundary layer.
Lightning in the Jovian water cloud
Authors: Borucki W. J. , Williams M. A.
Published: February 2008

Voyager images of Jupiter show numerous luminous spots on the nightside. These spots have been attributed to lightning superbolts because of their extreme brightness and because of their transitory nature. In order to determine the vertical location of the lightning, a comparison is made between the measured spot sizes for single flashes, with intensity distributions calculated from various assumptions about the altitude of the flash. A Monte Carlo model is used to describe the light scattering in the clouds, aerosols, and gases of the Jovian atmosphere. Best agreement between the measurements and the model predictions is obtained when the lightning activity is assumed to occur in a lower cloud centered at 5 bars. A sensitivity study shows that the assumed position of the lightning within the cloud, the optical thickness of the clouds, and variations in the scattering and absorption properties of the clouds have only a minor influence on the predictions of the spot sizes. Because the model predictions of the spot sizes for the lower cloud and ammonia cloud lightning are so different, realistic variations in the parameters do not alter the conclusion that the observed lightning activity must be in the lower cloud rather than in the ammonia cloud. The lower cloud is expected to be composed of water or a mixture of water and ammonium hydrosulfide.
On the occurrence of positive ground flashes
Authors: Takagi N. , Takeuti T. , Nakai T.
Published: February 2008

Positive ground flashes are a relatively rare occurrence in ordinary summer thunderstorms, but a higher frequency of 30% to 100% is found during winter thunderstorms in Japan and Norway, although both summer and winter thunderclouds have the same polarity of electric dipole with a net positive charge located above a net negative charge. We have computed the fraction of positive ground flashes occurring for various locations of lightning charges in a thundercloud, using the stepped leader model in which a streamer progresses in the direction of maximum potential gradient at its tip. The calculation is in good agreement with observations in that both the vertical wind shear and the height of the lightning charge contribute significantly to the occurrence of positive ground flashes.
Middle and upper tropospheric carbon monoxide mixing ratios as measured by a satellite‐borne remote sensor during November 1981
Authors: Reichle Henry G. , Connors Vickie S. , Holland J. Alvin , Hypes Warren D. , Wallio H. Andrew , Casas Joseph C. , Gormsen Barbara B. , Saylor Mary S. , Hesketh Wilfred D.
Published: February 2008

Mixing ratios of tropospheric carbon monoxide measured by a gas filter radiometer carried aboard the space shuttle during November 1981 are reported. The data represent average mixing ratios in the middle and upper troposphere between 38°N and 38°S latitude. Approximately 10,000 individual measurements were obtained in each of the two channels of the instrument. The data are presented in the form of plots that show the individual carbon monoxide mixing ratio measurements as a function of latitude and longitude and in the form of maps that show the data averaged over 5° latitude by 5° longitude squares. The data show relatively little variation in the mixing ratio in the southern hemisphere; however, the data from both the tropics and the northern hemisphere show strong gradients with both latitude and longitude.
A chemical mechanism for use in long‐range transport/acid deposition computer modeling
Authors: Lurmann Frederick W. , Lloyd Alan C. , Atkinson Roger
Published: February 2008

A chemical mechanism for the gas phase atmospheric oxidation of nitrogen oxides (NOx) and sulfur dioxide (SO2) in the presence of reactive hydrocarbons (RHC) has been developed for use in long‐range transport modeling. The mechanism includes numerous reactions important for nighttime and multiday simulations which have been previously ignored in photochemical mechanisms designed for urban scale applications. This mechanism is capable of simulating the decay of NOx/SO2/RHC precursors and the formation of oxidation products such as nitric acid, sulfuric acid, ozone, hydrogen peroxide, hydroperoxides, and organic peroxides which have recognized roles in the acidification of precipitation. Testing of detailed and condensed versions of the chemical mechanism is reported.
Emissions of N2O, CH4 and CO2 from tropical forest soils
Authors: Keller Michael , Kaplan Warren A. , Wofsy Steven C.
Published: February 2008

Emissions of nitrous oxide, methane, and carbon dioxide were measured at diverse locations in tropical forests of Brazil, Ecuador, and Puerto Rico, using a static open chamber technique. Mean fluxes to the atmosphere were 1.7 × 1010, −0.7 × 1010, and 1.5 × 1014 molecules cm−2s−1 for N2O, CH4, and CO2, respectively. The data indicate that tropical forests contribute a significant fraction of the global source for atmospheric N2O, about 40% of the current source and possibly 75% of the preindustrial source. Methane is consumed by soils on average, but the sink is an insignificant part (<5%) of the atmospheric cycle for the gas. Emissions of CO2 from forest soils are higher at equatorial sites than at middle or high latitudes, as expected from ecological considerations. Soils emit CO2 at rates more than twice as large as the rate of carbon infall in litter; hence much of the emitted CO2 must arise from root metabolism.
A numerical model for sulfur and nitrogen scavenging in narrow cold‐frontal rainbands: 2. Discussion of chemical fields
Authors: Hegg Dean A. , Rutledge Steven A. , Hobbs Peter V.
Published: February 2008

The kinematic, diagnostic model of the physics and chemistry of narrow cold‐frontal rainbands (described by Rutledge et al. (this issue)) is used to explore chemical interactions within convective precipitation systems. Cloud microphysical and dynamical processes are found to be comparable with chemical processes in affecting chemical deposition. In‐cloud sulfate production contributes up to ∼50% to wet sulfate deposition. Hydrogen peroxide appears to be the primary oxidant for the production of sulfate in clouds, but the sulfate production is not a linear function of H2O2 concentration, and different sulfate production mechanisms can dominate at different heights in a cloud system. The model predicts that the relationships between sulfur input and sulfate deposition, and nitrogen input and nitrate deposition in narrow cold‐frontal rainbands, are, in general, nonlinear. Under certain conditions, the model shows that chemical species, particularly SO2, can be redistributed over significant heights by convective cloud systems. The model predicts concentrations of chemical species in precipitation that are similar to the limited field observations that are available.
Recent solar radio astronomy at centimeter wavelengths: The temporal variability of the 10.7‐cm flux
Authors: Tapping K. F.
Published: February 2008

Studies made by means of high‐resolution radio telescopes indicate that solar centimetric emission contains contributions from many different sources and involves more than one radiation mechanism. Two emission components have been identified: bright, compact sources and weaker, diffuse emission which is distributed over the plage and surrounding areas of enhanced magnetic field. There is evidence for the occurrence of weaker but widely distributed radiation from elements of the active network. The good correlation between the 10.7‐cm flux and shorter‐wavelength indicators of solar activity, such as Ca II emission, suggests that gyromagnetic processes contribute little to the total centimetric flux. If the 10.7‐cm flux is predominantly thermal (free‐free) emission, its intensity will be a measure of the total amount of magnetic flux emerging through the photosphere and supporting density enhancements in the lower solar atmosphere.
Nitrate, non‐sea‐salt sulfate, and mineral aerosol over the northwestern Indian Ocean
Authors: Savoie D. L. , Prospero J. M. , Nees R. T.
Published: February 2008

From January 14 to June 1, 1979, 96 bulk aerosol samples were collected aboard three ships in the northwestern Indian Ocean as part of the Global Weather Experiment. These samples were analyzed to determine the atmospheric concentrations of nitrate, non‐sea‐salt (NSS) sulfate, mineral aerosol, and NSS calcium. On the basis of geographical location, mineral aerosol concentration, and wind regime, the samples were divided into three distinct sets. The highest mean concentrations of nitrate, NSS sulfate, and mineral aerosol (1.0, 2.7, and 7.6 μg/m3, respectively) were observed during dust outbreaks transported from desert regions of the Middle East. The eolian dust comprises a significant fraction of the sediments off the coast of the Arabian peninsula and the Horn of Africa. A portion of the NSS sulfate appears to be derived from the soil material itself. Between dust outbreaks, the mean concentrations of nitrate and NSS sulfate are about 0.4 and 0.9 μg/m3, respectively; a substantial portion of these concentrations are probably transported from the Indian subcontinent. The lowest concentrations were measured in southern hemisphere air, which is transported into the region by the southeast monsoons. Nitrate concentrations in this air, 0.16 μg/m3, are consistent with the estimated input of NOx from lightning and from the stratosphere. Mean NSS sulfate concentrations ranged from 0.3 μg/m3 prior to the onset of upwelling to 0.6 μg/m3 after the onset; estimated dimethyl sulfide emission rates from the ocean are sufficient to account for both of these means. Mineral aerosol concentrations in, the southern hemisphere air averaged 0.27 μg/m3.
A dynamic threshold method for obtaining cloud cover from satellite imagery data
Authors: Coakley James A.
Published: February 2008

Errors in cloud cover derived by using a fixed threshold applied to imagery data depend not only on the fractional cover but also on cloud size. As a result, a fixed threshold applied to two scenes having the same cloud cover will produce different estimates of the cover when the clouds in the two scenes have different sizes. To allow for this influence due to cloud size, a dynamic threshold method is presented. In this method an infrared threshold is adjusted to achieve the highest correlation between the threshold‐derived cloud cover and the mean emitted radiance for mesoscale‐sized subregions within the scene. For single‐layered cloud systems this threshold achieves a cancellation of errors in the cloud cover for the subregions so that the resulting cloud cover for the region and the associated estimates of cloud properties are in fair agreement with estimates obtained using the spatial coherence method. The agreement illustrates the validity of the layered cloud model used in different ways by the two methods. The performance of the dynamic threshold method is contrasted with that of a fixed threshold applied to the same data in order to illustrate the merits of applying a scene‐dependent threshold.
The role of earth radiation budget studies in climate and general circulation research
Authors: Ramanathan V.
Published: February 2008

Two decades of near‐continuous measurements of earth radiation budget data from satellites have made significant contributions to our understanding of the global mean climate, the greenhouse effect, the meridional radiative heating that drives the general circulation, the influence of radiative heating on regional climate, and climate feedback processes. The remaining outstanding problems largely concern the role of clouds in governing climate, in influencing the general circulation, and in determining the sensitivity of climate to external perturbations, i.e., the so‐called cloud feedback problem. In this paper a remarkably simple and effective approach is proposed to address these problems, with the aid of the comprehensive radiation budget data collected by the Earth Radiation Budget Experiment (ERBE). ERBE is a multisatellite experiment which began collecting data in November 1984. The simple approach calls for the estimation of clear‐sky fluxes from the high spatial resolution scanner measurements. A cloud‐radiative forcing (or simply cloud forcing) is defined which is the difference between clear‐sky and cloudy‐sky (clear plus overcast skies) fluxes. The global average of the sum of the solar and long‐wave cloud forcing yields directly the net radiative effect (i.e., cooling or warming) of clouds on climate. Furthermore, analyses of variations in clear‐sky fluxes and the cloud forcing in terms of temperature variations would yield the radiation‐temperature feedbacks, including the mysterious cloud feedback, that are needed to verify present theories of climate. Finally, general circulation model results are used to discuss the nature of the cloud radiative forcing. It is shown that the long‐wave effect of clouds is to enhance the meridional heating gradient in the troposphere, while the albedo or solar effect of clouds is largely to reduce the available solar energy at the surface. The long‐wave cloud‐induced drive for the circulation is particularly large in the monsoon regions. Thus it is concluded that analyses of ERBE data in terms of cloud forcing would add much needed insights into the role of clouds in the general circulation. With respect to the future, the scientific need is discussed for continuing broadband measurements of earth radiation budget data into the next century in order to understand the processes that govern interannual and decadal climate trends. Finally, the spectral variations in clear‐sky fluxes and cloud forcing and the need for broadband data to obtain the desired accuracies are described.
Nimbus 7 earth radiation budget wide field of view climate data set improvement: 2. Deconvolution of earth radiation budget products and consideration of 1982–1983 El Niño event
Authors: Ardanuy Phillip E. , Kyle H. Lee , Hucek Richard R. , Groveman Brian S.
Published: February 2008

A deconvolution technique is employed that permits recovery of daily averaged earth radiation budget (ERB) parameters at the top of the atmosphere from a set of the Nimbus 7 ERB wide field of view (WFOV) measurements. Improvements in both the spatial resolution of the resultant fields and in the fidelity of the time averages is obtained. The algorithm is evaluated on a set of months during the period 1980–1983. The albedo, outgoing long‐wave radiation, and net radiation parameters are analyzed. The amplitude and phase of the quasi‐stationary patterns that appear in the spatially deconvolved fields describe the radiation budget components for “normal” as well as the El Niño/Southern Oscillation (ENSO) episode years. They delineate the seasonal development of large‐scale features inherent in the earth's radiation budget as well as the natural variability of interannual differences. These features are underscored by the powerful emergence of the 1982–1983 ENSO event in the fields displayed. The conclusion is that with this type of resolution enhancement, WFOV radiometers provide a useful tool for the observation of the contemporary climate and its variability.
Sources and sinks of acetone in the troposphere: Behavior of reactive hydrocarbons and a stable product
Authors: Chatfield Robert B. , Gardner Edward P. , Calvert Jack G.
Published: February 2008

Acetone, a relatively unreactive carbonyl compound in the atmosphere, has been detected in concentrations of ≃500 parts per trillion in surface air over the central Atlantic and several hundred ppt (volume) near the tropopause. This represents a substantially higher mixing ratio than anticipated from previous descriptions of its sources which are primarily much more reactive hydrocarbon emissions and skinks. We assimilate new information about the tropospheric sources and sinks of this substance into a numerical model of its chemistry, cloud transport, and removal. Simulations relevant to the tropical and the mid‐latitude atmosphere are presented. Photolysis provides a rather slow sink, giving a first‐order decay time scale of 40 days (near the surface) to 10 days (at 200 mbar). Attack by HO radicals is of comparable importance, with a time scale of about 20 days (near the surface) to a hundred days (at 200 mbar). A significant amount of carbon, approximately 70 Tg (C) yr−1, appears to be cycled as acetone. Many of the sources of acetone involve the oxidation of higher molecular weight hydrocarbons, but the relative contribution of primary, nonanthropogenic, sources, e.g., biogenic and oceanic, may be significant. Acetone, like CO, is a useful tracer recording previous photochemical activity in an air parcel, a tracer that might be used to describe the photochemical production of compounds like ozone. The mid‐latitude simulations required some adaptation of the Chatfield (1982) transport model. The activity of vertical transport was constrained to reproduce available 222Rn data. Simulations of these data suggest that mid‐latitude vertical transport is less active than tropical, but rather more active than Kz parameterizations suggest.
Dynamical factors affecting ozone mixing ratios in the Antarctic lower stratosphere
Authors: Shiotani Masato , Gille John C.
Published: February 2008

This paper describes the climatology and interannual variability of dynamical quantities and ozone mixing ratios during the southern hemisphere spring. Analyses are made mainly for 6 years, from 1979 to 1984, September through December, using the temperature and geopotential height data provided by the National Meteorological Center (NMC) and the ozone mixing ratio data derived from the solar back‐scatter ultraviolet (SBUV) instrument on board the Nimbus 7. The seasonal variation of temperature in the southern hemisphere lower stratosphere is rather repeatable, indicating that means over a few years should provide a useful estimate of the climatology. The zonal mean quantities show that the coldest temperatures and zonal winds move poleward and downward from September through November, probably in response to wave forcing. A steep decrease in zonal mean ozone mixing ratios is observed around 60° S toward the south pole in September. With time, this high‐latitude ozone minimum (or “ozone hole”) gets shallower in association with minor warmings and a final warming. Climatological synoptic charts in the lower stratosphere show the circumpolar circulation in the geopotential height field and a prominent planetary wave 1 in the temperature and ozone fields. The phases of the temperature and ozone waves in the lower stratosphere are very similar. The year‐to‐year variations of the ozone mixing ratio at high latitudes is related to that of the wave activity during the winter and spring. When the wave activity is vigorous, there are weaker westerlies, higher temperatures and higher ozone mixing ratios at high latitudes. The seasonal evolution and the year to year variation appear to be clearly related to wave activity. It is possible that the long term changes in the lower stratosphere are also related to a long‐term trend in wave activity, although the evidence is not clear. Because the wave activity in 1979 was very vigorous, a simple comparison of atmospheric states between the 1979 and other recent years could lead to misleading conclusions on the rate of ozone decrease over the Antarctic. A long‐term chemical effect is not precluded.
Infrared spectroscopic measurements of halogenated sink and reservoir gases in the stratosphere with the ATMOS instrument
Authors: Raper O. F. , Farmer C. B. , Zander R. , Park J. H.
Published: February 2008

During the Spacelab 3 mission in May 1985, the ATMOS (Atmospheric Trace Molecule Spectroscopy) instrument recorded 19 sets of interferograms during solar occultations occurring in both the northern (∼30°N) and southern (∼47°S) hemispheres. The resulting high‐resolution (0.01 cm−1 unapodized) spectra, covering the 2.0‐ to 16‐μm region of the infrared, have provided concentration profiles for over 25 atmospheric species, with an average vertical resolution of ∼4.1 km. This paper reports on volume mixing ratio profiles for HCl and HF over the 15‐ to 60‐km altitude region, retrieved from the northern sunsets and the southern sunrises. While the southern profiles, because of a more limited data set, are accurate to ∼13% for HCl and ∼18% for HF, northern‐zonal distribution uncertainties are estimated to be ∼7% for HCl and ∼12% for HF; they agree well with recent balloon investigations at 30°N over the altitude range 15–40 km and show no tendency for a volume mixing ratio decrease at the level of the stratopause. The HF/HCl ratios deduced from the present measurements are also in good agreement with model predictions. Vertical profiles of ClONO2 and COF2, and upper limits for HOCl and ClO, obtained from ATMOS data by other investigators, are also summarized in order to evaluate the total chlorine budget in the stratosphere. This value approaches 2.6 parts per billion by volume, in good agreement with the total chlorine determined to be available from source species. The total atmospheric chlorine at 50 km is essentially all in the form of HCl.
Measurement of the mass accommodation coefficient of SO2 (g) on water droplets
Authors: Gardner James A. , Watson Lyn R. , Adewuyi Yusuf G. , Davidovits Paul , Zahniser Mark S. , Worsnop Douglas R. , Kolb Charles E.
Published: February 2008

Heterogeneous reaction pathways involving water droplets in clouds and fogs are important mechanisms for chemical transformation of atmospheric trace gases. One of the fundamental parameters which determines the transfer rate of gases into aqueous droplets is the mass accommodation or “sticking” coefficient for gas molecules on the droplet surfaces. We have developed a laboratory method for directly determining mass accommodation coefficients (γ) and have applied it to SO2. The method combines a monodisperse droplet stream, generated at a vibrating orifice, with a low‐pressure flow reactor. The uptake of the trace gas by the droplets is determined by measuring changes in gas phase concentrations, using tunable diode laser absorption, as the droplet stream is turned on and off. Results for SO2 give a value of γ = (5.4 ± 0.6) × 10−2 at room temperature (295 K). However, this observed value for γ is likely a lower limit to the true mass accommodation coefficient because of limitations imposed by the rate of gas phase diffusion of SO2 to the droplets and by the rate of hydrolysis of SO2 at the droplet surface. This measurement indicates that SO2 transport into clean aqueous cloud and fog droplets will not be limited by interfacial mass transport under normal atmospheric conditions.
Global trends of measured surface air temperature
Authors: Hansen James , Lebedeff Sergej
Published: February 2008

We analyze surface air temperature data from available meteorological stations with principal focus on the period 1880–1985. The temperature changes at mid‐ and high latitude stations separated by less than 1000 km are shown to be highly correlated; at low latitudes the correlation falls off more rapidly with distance for nearby stations. We combine the station data in a way which is designed to provide accurate long‐term variations. Error estimates are based in part on studies of how accurately the actual station distributions are able to reproduce temperature change in a global data set produced by a three‐dimensional general circulation model with realistic variability. We find that meaningful global temperature change can be obtained for the past century, despite the fact that the meteorological stations are confined mainly to continental and island locations. The results indicate a global warming of about 0.5°–0.7°C in the past century, with warming of similar magnitude in both hemispheres; the northern hemisphere result is similar to that found by several other investigators. A strong warming trend between 1965 and 1980 raised the global mean temperature in 1980 and 1981 to the highest level in the period of instrumental records. The warm period in recent years differs qualitatively from the earlier warm period centered about 1940; the earlier warming was focused at high northern latitudes, while the recent warming is more global. We present selected graphs and maps of the temperature change in each of the eight latitude zones. A computer tape of the derived regional and global temperature changes is available from the authors.
Emission of NO and deposition of O3 in a tropical forest system
Authors: Kaplan W. A. , Wofsy S. C. , Keller M. , Da Costa Jose Maria
Published: February 2008

Rates for emission of NO and deposition of O3 were measured at a tropical forest site in Reserve Adolfo Ducke, near Manaus, Brazil. Two independent techniques were used to determine the NO flux: (1) a soil enclosure method and (2) a method based on simultaneous observations of NO and O3 vertical profiles at night, when NO is irreversibly removed by reaction with O3. Results obtained using the two techniques agreed well, giving an average NO flux of 5.2±1.7×1010 molecules cm−2 s−1 and an average vertical exchange coefficient of 2.2×103 cm3 s−1. Sources of NO from tropical forest soils may be important for global atmospheric chemistry. Rapid removal of O3 was observed in the lowest levels of the forest. The nocturnal deposition rate was estimated to be 5.6±2.5 ×1011 molecules cm−2 s−1 through the 6 m level. The large deposition rate for O3 is consistent with the strong sink inferred from observations of ozone in the Amazon region.