bluuebunny/crossref_metadata_2025 huggingface dataset:
Dissociation of metastable O2 as a potential source of atmospheric odd oxygen
Authors: Frederick John E. , Cicerone Ralph J.
Published: February 2008

An analysis of the possible dissociation of metastable oxygen molecules subject to constraints imposed by selection rules for molecular transitions, airglow observations, and atmospheric chemistry leads to the following conclusions. Dissociation of O2(b1∑g+) must produce a negligible number of oxygen atoms at all altitudes in the earth's atmosphere. However, if the dissociation cross section of O2(a1Δg) has a maximum value in the range 10−20 cm2 to 10−19 cm2, then the process O2(a1Δg) + hν → O2(C3Δu) → O(3P) + O(3P) will constitute a significant, and potentially the major, source of odd oxygen in the uppermost stratosphere and mesosphere.
Dimethyl sulfide in the marine atmosphere
Authors: Andreae M. O. , Ferek R. J. , Bermond F. , Byrd K. P. , Engstrom R. T. , Hardin S. , Houmere P. D. , LeMarrec F. , Raemdonck H. , Chatfield R. B.
Published: February 2008

We have performed over 900 measurements of atmospheric dimethyl sulfide (DMS) in five different marine locations: the equatorial Pacific; Cape Grim, Tasmania; the Bahamas; the North Atlantic; and the Sargasso Sea. At all locations, DMS concentrations were usually in the range of 100–400 ng S m−3, with similar average concentrations of approximately 150 ng S m−3 (107 parts per thousand by volume). Highest concentrations occurred during, but were not limited to, periods of sustained high winds and overcast skies, presumably owing to faster exchange from surface seawater and less photochemical activity in the atmosphere. Lowest values occurred during airflow from continental regions, which provides higher levels of oxidants and free radicals to react with DMS. Averaged over time, the concentrations in clean marine air reached a maximum at night and a minimum in the afternoon, when concentrations were about one third lower than during the nighttime maximum. The observed concentrations of DMS in the marine atmosphere and their diurnal variability agree well with model simulations involving OH and NO3 oxidation of DMS and are consistent with a global sea‐to‐air DMS flux of about 40±20 Tg S yr−1. DMS may represent a major sink for NO3 in the marine troposphere.
The climatic effects of large injections of atmospheric smoke and dust: A study of climate feedback mechanisms with one‐ and three‐dimensional climate models
Authors: Cess R. D. , Potter G. L. , Ghan S. J. , Gates W. L.
Published: February 2008

We have employed two climate models for the purpose of qualitatively understanding climate forcing mechanisms and feedback processes associated with the injection of atmospheric smoke and dust (i.e., atmospheric perturbations due to a nuclear exchange). One of these models is the Oregon State University general circulation model (GCM), modified through the addition of a delta‐Eddington solar radiation routine to accomodate the inclusion of smoke and dust. The second model is a radiative convective model (RCM), which mimics as closely as possible many of the processes portrayed by the GCM. The primary role of the RCM was that of an educational tool used to reveal climate forcing and response processes, which would explain the behavior of the more complex GCM. The RCM served this purpose extremely well. Specific features revealed by the RCM are summarized as follows. (1) Even for very modest smoke loading, convective coupling of the model's surface and troposphere was insufficient to produce conventional surface‐troposphere climate forcing. However, this was not the case when the model's climate was changed by increasing the atmospheric carbon dioxide, by increasing the solar constant, or by the inclusion of natural tropospheric aerosols. (2) Because of the above, for smoke injection the model's climate responded to two distinctly different and opposing radiative forcing mechanisms: direct surface‐troposphere heating and direct surface cooling. (3) For a progressive increase in smoke loading a transition occurred from dominant (but not governing) surface‐troposphere forcing to dominant surface forcing, with this transition being the result of changes both in vertical convection and in infrared radiation incident upon the surface. (4) The above two processes further impacted the nature of the model's climate response to the dual forcing mechanisms, and interactively they produced quite unusual time‐dependent behavior. For example, there were situations in which the short‐term climate response to a smoke injection was that of surface cooling, whereas the long‐term response was one of warming. This understanding of the RCM behavior greatly aided the interpretation of the GCM results under conditions where the smoke loading, the smoke vertical distribution, and the smoke single scattering albedo were both independently and simultaneously varied. The GCM's surface cooling further exhibited a marked dependence upon which day of the control run (a perpetual July) the smoke is injected.
Transport processes and ozone perturbations
Authors: Solomon S. , Garcia R. R. , Stordal F.
Published: February 2008

In future years, the chlorine abundances in the earth's stratosphere are expected to increase as a result of man's activities. Currently accepted photochemistry suggests that this perturbation to the natural stratosphere will modify stratospheric ozone due to photochemical interactions. Quantitative estimates of the effect of this anthropogenic perturbation on the stratospheric ozone column abundance have largely been performed with one‐dimensional models. Current (1985) one‐dimensional models predict a rather small steady state ozone column reduction of about 4–6%. These small values result from a balance between large depletions in the upper stratosphere that are compensated to a substantial degree by increases in the lower stratosphere (the chemical “self‐healing” effect), so that the total column change is a small difference between the two. It is, however, well established that lower stratospheric ozone is dynamically (not chemically) dominated, particularly at middle and high latitudes in the winter season, so that one‐dimensional models may not be the most appropriate tool for evaluation of these effects at those latitudes and seasons. In particular, the lower stratospheric chemical self‐healing effect is likely to be significantly less important at high latitudes than one‐dimensional model projections indicate, resulting in greater total ozone column changes there. In this paper, we present a numerical model study of the ozone response to projected chlorofluorocarbon increases using a two‐dimensional residual Eulerian circulation model. In agreement with some previous studies using classical Eulerian models (in particular, Pyle (1980) and Haigh and Pyle (1982)), we find that the predicted ozone reductions during winter and spring at high latitudes are larger than the values predicted by one‐dimensional models. This occurs because ozone is largely dynamically controlled at these latitudes and seasons, and because the net transport is directed downward from the region where substantial depletions occur. Some uncertainties in the projected depletions are explored.
Thunderstorm electrification: The effect of cloud droplets
Authors: Jayaratne E. R. , Saunders C. P. R.
Published: February 2008

Further laboratory studies have been made of the charge transferred when ice crystals collide and then separate from an ice target. Previous results indicated increased charge transfer when cloud droplets were present. The new data show that the size distribution of the droplets is important. When the cloud droplets are too small to collide with the growing target, it charges negatively; for the same liquid water content but with larger droplets that hit the target, it charges positively. The results suggest that the relative growth rate and the surface states of both the interacting bodies may be important in controlling the sign of the charge transfer. It is suggested that these results may explain the observation of negative charge centers in thunderstorms at temperatures warmer than −20°C.
Dynamics and composition of particles from an aeolian input event to the Sargasso Sea
Authors: Carder Kendall L. , Steward Robert G. , Betzer Peter R. , Johnson David L. , Prospero Joseph M.
Published: February 2008

A major outbreak of Saharan dust ( >40 μg aerosols/m3 air) passed over the western Sargasso Sea in late June 1980. The flux of aeolian particles across the air‐sea interface was calculated based upon free‐floating sediment trap data (30‐m depth). During the early‐to‐middle portions of this event, we observed in the trap samples large numbers of “giant” (>20‐μm diameter) aeolian particles that were not observed in aerosol samples collected at Miami, Florida, 426 km to the west. To better intercompare data collected at the two sites, a simple aeolian particle settling model was developed. Scanning electron microscopy with automated image analysis and X ray energy spectroscopy of individual particles from the two sites provided size and compositional data as primary inputs to the model. The compositional differences between aerosols from the two sites, although not great, may have been due in part to the localized nature of particle sources and storm centers. The time history of the aerosol concentration over the western Sargasso during the month of June as simulated by the model was compared with the time history of aerosols arriving at Miami. These results suggest that a significant portion of the deposition flux is comprised of giant particles. Particles in this size range are not efficiently collected by conventional sampling techniques, and hence reported estimates of depositional fluxes could be significantly biased too low.
Dependence of stratospheric NO3 upon latitude and season
Authors: Norton R. B. , Noxon J. F.
Published: February 2008

The total column abundance of NO3 in the stratosphere at night has been measured for 5 years at 40°N, with additional observations at 19°, 31°, 51°, and 64°N. In this set of measurements the NO3 abundance varied from slightly greater than 1014 cm−2 to below the detection limit of 1013 cm−2. At low latitude the mean abundance appears to be in general agreement with a model based upon simple NOx chemistry, except that the summer values tend to be smaller than spring values. At mid‐latitude, the variation in abundance exceeds a factor of 5, which is greater than predicted. Large day‐to‐day variations in abundance are observed, especially in summer. The winter values mostly fall below the detection limit, which can be as low as 1013 cm−2. The abundance appears to exhibit a close relation to the highest latitude experienced by stratospheric air prior to its arrival at mid‐latitude; the higher the latitude the lower is the NO3 abundance. At 64°N the NO3 abundance was below the detection limit of 1.5 × 1013 cm−2, both in April and November. This is far below what is predicted, especially in April. These observations suggest that a scavenger of NO3 is continually produced in the stratosphere, particularly at high latitude, and when there is a strong equatorward flow, the scavenger can at least reach mid‐latitude. The identity of the scavenger remains unknown, as does the importance of its role as a sink for NOx in the stratosphere.
Possible role of NO3 in the nighttime chemistry of a cloud
Authors: Chameides William L.
Published: February 2008

The NO3 radical in the aqueous phase is a strong oxidizing agent which reacts rapidly with a wide variety of inorganic and organic species. Within nighttime clouds the production of gaseous NO3 from the reaction of NO2 with O3 followed by heterogeneous scavenging of NO3 by cloud droplets can represent a significant source of these reactive radicals to cloud water. Model calculations indicate that in addition to leading to the production of NO3− in cloud water, this aqueous‐phase source of NO3 can, under the appropriate conditions and depending upon the values for a number of uncertain rate constants, have a significant impact upon the rate of conversion of SO2 to H2SO4.
Potential problems with the use of least squares spline fits to filter CO2 data
Authors: Enting I. G.
Published: February 2008

In a number of studies, various workers have used the procedure of fitting cubic splines with nodes spaced 12 months apart in order to remove seasonal effects from atmospheric CO2 observations. A number of trial examples of least squares spline fits are presented, indicating that this procedure can be subject to relatively large end effects. For variations with periods near 2 years the response is extremely sensitive to the position of the nodes and shows beating effects caused by the change in the relative positions of the signal peaks and the spline nodes. A signal whose period is exactly twice the node spacing can either be passed almost unchanged or be completely filtered out, depending on its phase relative to the nodes of the spline. These properties make such spline fitting unsuitable for analyzing the interannual variations in CO2 data.
Sensitivity of the seasonal climate of a general circulation model to ocean surface conditions and solar forcing
Authors: Otto‐Bliesner Bette L. , Houghton David D.
Published: February 2008

The sensitivity of the atmospheric seasonal cycle to ocean conditions and solar forcing is investigated using a low‐resolution spectral atmospheric general circulation model (GCM). The external forcing of the model is grouped into two basic categories: (1) ocean conditions (sea surface temperature and sea ice extent) and (2) radiation specifications (incoming solar radiation, albedo parameters involving cloud cover and land snow cover, and long‐wave emissivity coefficients). These forcing parameters are all prescribed with smoothly time‐varying seasonal cycle variations in the control simulation. In two sensitivity experiments, parameters in only one of the two forcing categories are allowed to vary seasonally; the others are fixed at their annual mean values. Analysis shows that model sensitivity to radiation specifications is effectively a solar‐forcing sensitivity. These experiments show that on a zonally averaged basis at mid‐latitudes in the northern hemisphere, the seasonal variations in the direct heating of the atmosphere and land surfaces by incoming solar radiation are generally more important than seasonal variations in the ocean forcing for determining the fundamental annual harmonic variations of temperature, pressure, zonal wind, and precipitation in the model. In fact, for many of these variables, even in the southern hemisphere, the simulation of the annual harmonics with the radiation forcing alone is not statistically different from simulation of the annual harmonics in the control case. Sea surface temperature and sea ice extent do play an important role in the fundamental harmonic variations in the southern hemisphere for sea level pressure and lower tropospheric temperature on a zonally averaged basis. At tropical latitudes, seasonal variation of sea surface temperature is critical for capturing the fundamental annual harmonic variations of low‐troposphere temperatures, sea level pressure, and precipitation, presumably due to the contributions of convective and boundary layer processes. The results presented in zonally averaged, horizontal map and vertical cross‐section formats, help to describe the variables and specific areas for which the nature of the formulation of the ocean component in an interactive ocean‐atmosphere model, especially in terms of its seasonal variation, will be an important consideration for simulation of the atmospheric annual harmonic cycle climatology.
Assimilation of scatterometer winds into surface pressure fields using a variational method
Authors: Harlan Jack , O'Brien James J.
Published: February 2008

A variational formulation was used to assimilate Seasat‐A scatterometer (SASS) surface wind measurements near and during a severe storm in the North Atlantic into conventional National Meteorological Center sea level pressure fields. An estimate of the relative vorticity at every point on a grid was calculated using each of these two data sets. A solution to a modified geostrophic stream function is found subject to the constraints that (1) the relative vorticities calculated from the data agree as closely as possible with the relative vorticities from the variational solution, and that (2) the average kinetic energy is a minimum. Results are obtained which support the idea that averaged satellite data can be treated as synoptic data. Direct substitution rather than a time‐weighted insertion made from SASS winds generally resulted in more accurate pressure analyses. In addition, this relatively simple model provides surface pressure fields which agree extremely well with surface truth and the results of other investigators who required additional sources of input data into more complex models. It will be possible to obtain improved wind field maps from future scatterometer pressure fields in mid‐latitudes.
Sensitivity of an atmospheric photochemistry model to chlorine perturbations including consideration of uncertainty propagation
Authors: Stolarski R. S. , Douglass A. R.
Published: February 2008

Models of stratospheric photochemistry are generally tested by comparing their predictions for the composition of the present atmosphere with measurements of species concentrations. These models are then used to make predictions of the atmospheric sensitivity to perturbations. Here the problem of the sensitivity of such a model to chlorine perturbations ranging from the present influx of chlorine‐containing compounds to several times that influx is addressed. The effects of uncertainties in input parameters, including reaction rate coefficients, cross sections, solar fluxes, and boundary conditions, are evaluated using a Monte Carlo method in which the values of the input parameters are randomly selected. Results are probability distributions for present atmospheric concentrations and for calculated perturbations due to chlorine from fluorocarbons. For more than 300 Monte Carlo runs the calculated ozone perturbation for continued emission of fluorocarbons at today's rates had a mean value of −6.2%, with a 1‐sigma width of 5.5%. Using the same runs but only allowing the cases in which the calculated present atmosphere values of NO, NO2, and ClO at 25 km altitude fell within the range of measurements yielded a mean ozone depletion of −3%, with a 1‐sigma deviation of 2.2%. The model showed a nonlinear behavior as a function of added fluorocarbons. The mean of the Monte Carlo runs was less nonlinear than the model run using mean values of the input parameters.
Henry's law determinations for aqueous solutions of hydrogen peroxide, methylhydroperoxide, and peroxyacetic acid
Authors: Lind John A. , Kok Gregory L.
Published: February 2008

The Henry's law constants for aqueous solutions of hydrogen peroxide, methylhydroperoxide, and peroxyacetic acid were measured over the temperature range 278°–293°K. These determinations were made by measuring the vapor pressure of the peroxide in a gas stream of nitrogen or air that was in equilibrium with a solution of known peroxide concentration. The aqueous phase concentrations ranged from 5 × 10−5 M to 5 × 10−3 M for hydrogen peroxide, and from 1 × 10−6 M to 1 × 10−4 M for methylhydroperoxide and peroxyacetic acid. In all cases, Henry's law was obeyed over the concentration range investigated. The temperature dependence of the Henry's law constant is expressed by KH = e[A/T−B], where KH is in the units of molar concentration per atm, and T is in degrees Kelvin. The coefficients' values are A = 6621, B = 11.00 for hydrogen peroxide; A = 5607, B = 13.41 for methylhydroperoxide; and A = 6171, B = 14.55 for peroxyacetic acid. The experimental errors on KH at the 95% confidence level are ±8.3% for hydrogen peroxide, ±11% for methylhydroperoxide, and ±17% for peroxyacetic acid. In addition, the Henry's law behavior of hydrogen peroxide in aqueous solutions of sulfuric acid and ammonium sulfate was investigated. The Henry's law constant of hydrogen peroxide decreased with increasing sulfuric acid concentration and increased with increasing ammonium sulfate concentration.
Climate record in varved sediments of the Eocene Green River formation
Authors: Crowley Kevin D. , Duchon Claude E. , Rhi Jaeyoung
Published: February 2008

Three time series of varves from the Eocene Green River Formation in Colorado, consisting of 1469, 1869, and 4158 annual thickness measurements, were analyzed by a variety of statistical techniques to characterize climate variations. The analyses reveal that the time series are lognormal after adjustment for a trend. Moreover, the analyses suggest that the time series are generally nonstationary and are noiselike in structure. Fourier spectra and maximum entropy spectra of the time series are “reddish,” indicating the importance of nonoscillatory changes in varve thickness at time scales ranging from tens to hundreds of years. There are no statistically significant peaks in Fourier spectra for the entire time series; however, one segment of one of the three time series displays statistically significant peaks corresponding to periods of 10.8 and 5.4 years. Overall, the time series are suggestive of a nonperiodic and weakly predictive climate during the time periods corresponding to deposition of the varves.
Reactive nitrogen species in the troposphere: Measurements of NO, NO2, HNO3, particulate nitrate, peroxyacetyl nitrate (PAN), O3, and total reactive odd nitrogen (NOy) at Niwot Ridge, Colorado
Authors: Fahey D. W. , Hübler G. , Parrish D. D. , Williams E. J. , Norton R. B. , Ridley B. A. , Singh H. B. , Liu S. C. , Fehsenfeld F. C.
Published: February 2008

Measurements of NO, NO2, HNO3, particulate nitrate, peroxyacetyl nitrate (PAN), O3, and total reactive odd nitrogen (NOy) were made in the nonurban troposphere during the summer and fall of 1984. The field site was located near Niwot Ridge, Colorado, at an elevation of 3 km. NOy was measured by catalytic reduction to NO, followed by the detection of NO with a chemiluminescence instrument. The other species were measured with conventional techniques. The data and interpretation presented focus primarily on the relationships between a measurement of NOy and concurrent measurements of the individual species, as examined through ratio and correlation plots. Through the separate display of daytime and nighttime data, the plots provide insight into the photochemical nature of the individual species. In addition, the composition of NOy is addressed through a comparison of the measured NOy level with that found for the sum of the measured component species. The NOy level systematically exceeded the sum level, with the difference being larger in the summer than in the fall. The presence of organic nitrate species other than PAN is proposed as one way to account for the observed difference.
Chemistry of OH in remote clouds and its role in the production of formic acid and peroxymonosulfate
Authors: Jacob Daniel J.
Published: February 2008

The chemistry of OH in a remote nonprecipitating tropical cloud is studied with a coupled gas‐phase and aqueous‐phase chemical model. The model takes into account the radial dependence of the concentrations of short‐lived aqueous‐phase species, in particular O3(aq) and OH(aq). The radical OH(aq) is produced rapidly by the aqueous‐phase reactions O2− + O3 and H2O2 + hν and is removed primarily by oxidation of H2C(OH)2, H2O2, and HCOO−. Gas‐droplet transfer of OH must be modeled as a reversible process, that is, the droplets cannot be assumed to be diffusion‐limited OH(g) sinks. A strong OH(aq) concentration gradient exists between the surface and the interior of the droplets. The concentration of OH(aq) is strongly dependent on pH but is only weakly dependent on the sticking coefficient, the droplet radius, or the liquid water content of the cloud. Formic acid is rapidly produced by the aqueous‐phase reaction H2C(OH)2 + OH, but HCOO− is in turn rapidly oxidized by OH(aq). The HCOOH concentration in cloud is shown to be strongly dependent on cloud water pH; clouds with pH greater than 5 are not efficient HCOOH sources. A novel mechanism is proposed for the oxidation of S(IV) by OH(aq). The main product is predicted to be HSO5− (peroxymonosulfate). Peroxymonosulfate appears to be stable in remote clouds and could contribute a large fraction of total cloud water sulfur.
Observations of the electric field in the stratosphere over an arctic storm system
Authors: Barcus J. R. , Iversen I. , Stauning P.
Published: February 2008

Observations by balloon‐borne instrumentation in the stratosphere (30–35 km) near Sondre Stromfjord, Greenland, have revealed disturbed vertical electric fields of the order of volts per meter of both polarities above an arctic storm system which moved onto the continent from the Davis Strait on August 11, 1982. This disturbance persisted at the balloon position for more than 10 hours, exhibiting order of magnitude variations with time scales ranging from minutes to hours. Simultaneous measurements of the stratospheric electrical conductivity did not show significant storm‐related variations. No lightning signals were detected, either at the balloon or at meteorological stations in the Davis Strait area. The disturbed field was predominantly downward (normal fair‐weather direction), and estimates of the total current indicate that at any instant a current of the order of 0.5 A was communicated to the storm system via the overlying stratosphere. The responsible storm system has been uniquely identified by NOAA 7 satellite IR (10.5–11.5 μm) imagery, and the infrared measurement of cloud‐top temperatures has revealed zones of enhanced convection lying in the storm's interior. Meteorological measurements taken at the surface and from balloon radiosondes by stations in the path of the storm also suggest that the storm possessed convective instabilities of the type likely to produce cloud electrification. In tropospheric features this type of storm occurs rather frequently on the western Greenland coast; therefore electrical charging of the storm cloud systems may not be as rare as indicated in the low probabilities observed for thunder and lightning.
Simulation of solar tides in the Canadian Climate Centre general circulation model
Authors: Zwiers Francis , Hamilton Kevin
Published: February 2008

Two 60‐day simulations of the global atmospheric circulation produced by the Canadian Climate Centre general circulation model were analyzed to determine the solar diurnal and semidiurnal variations in the wind, pressure, and precipitation fields. In these simulations the radiative transfer calculations were performed every hour in order to resolve adequately the diurnal cycle. One simulation was for boreal summer, and the other was for winter conditions. The diurnal and semidiurnal surface pressure variations in the model were found to be quite realistic, although somewhat smaller than actually observed. Even some fairly subtle details of the geographical and seasonal variability of the solar tidal pressure oscillation were well simulated. The daily cycle of the wind in the model also appears to be reasonably consistent with the limited observations available. By contrast, the diurnal and semidiurnal variations of precipitation were not successfully simulated by the model. Linear tidal theory calculations were performed with thermal forcings, vertical resolution, and boundary conditions similar to those in the full general circulation model. These calculations allowed an evaluation of the effects of the different numerical approximations in the general circulation model on the simulated tide. One striking result of these linear computations was the indication of a tendency for the effects of the “rigid‐lid” upper boundary condition to compensate for the omission of the thermal tidal forcing above the top level of the model.
A rapid and accurate method for calculation of stratospheric photolysis rates with molecular scattering
Authors: Boughner Robert E.
Published: February 2008

A method is presented for rapid and accurate calculations of photodissociation rates needed for photochemical modeling of the stratosphere, which include the effects of molecular scattering. Under the assumption of isotropic scattering and diffuse surface reflection, the linearity of the radiative transfer equation is used to decompose the total diffuse radiance field into two subfields that are referred to as the atmospheric and surface components. The atmospheric component accounts for the portion of the diffuse field that arises from scattering of the direct solar beam, while the surface component accounts for the portion of the diffuse field associated with radiation (direct plus diffuse) reflected by the surface that is subsequently scattered. Furthermore, the surface component has been normalized with respect to the total reflected radiation, so that it represents a relative field that is independent of solar angle and surface radiation properties that are contained in a surface scaling parameter. This independence can be effectively utilized when calculating photolysis rates for a series of sun angles, since the surface field need only be computed once. When the atmospheric and surface components are appropriately normalized, the wavelength variation of the resultant fields is sufficiently smooth that by using nine nodal points between 300 and 730 nm and cubic spline interpolation, accurate values of these fields at intermediate wavelengths are rapidly obtained. Further reductions in computational time are achieved by applying Sokolov's iterative procedure of averaging functional corrections to calculate approximate solutions for the atmospheric and surface fields at the nodal points. For wavelengths greater than 340 nm, a single iteration is sufficient to give results that agree with the exact values to better than 10% at altitudes above 15 km. Three iterations are used at shorter wavelengths due to increases in optical depth. The accuracy of the method for calculating photodissociation rates of 27 photolysis processes at 40 altitude levels between 0 and 53 km is typically better than 5% for altitudes above 10 km and all zenith angles.
Atmospheric characteristics of the equatorial Pacific during the 1982–1983 El Niño, deduced from satellite and aircraft observations
Authors: Garcia Oswaldo , Khalsa Siri Jodha Singh , Steiner Ellen J.
Published: February 2008

We present the results of a series of research flights over the eastern equatorial Pacific that took place during various stages of the 1982–1983 El Niño/Southern Oscillation (ENSO) event. A continuous background was provided by satellite observations of significant convection (highly reflective cloud) and of atmospheric moisture and stability obtained from the TIROS Operational Vertical Sounder (TOVS). TOVS data showed a progressive moistening and destabilization of the lower troposphere in the eastern equatorial Pacific. Between April and July 1983, frequent periods of organized convective activity in this area were associated with incursions of surface westerly winds originating in the central and western Pacific. The flights across the equator in the eastern Pacific in early January 1983 recorded large positive sea surface temperature anomalies and corresponding strong moisture flux from the ocean to the lower troposphere, although there were no episodes of significant convection in the area until February 1983. A comparison with non‐ENSO conditions is provided by the data from a flight along a similar track in 1980. Flights in July and September 1983 took place after the reestablishment of trade winds in the area and show a gradual return toward normal conditions in the meteorological variables examined.
Climatic effects of anthropogenic arctic aerosols: An illustration of climate feedback mechanisms with one‐ and two‐dimensional climate models
Authors: MacCracken Michael C. , Cess Robert D. , Potter Gerald L.
Published: February 2008

Two climate models, a one‐dimensional radiative‐convective model and a seasonal statistical‐dynamical model, have been used to obtain a qualitative understanding of climate forcing mechanisms and feedback processes associated with the climatic impact of carbonaceous Arctic aerosols. The models are consistent in suggesting that such aerosols should produce surface warming in Arctic regions, but the manner in which this is accomplished is a bit unusual. Since the aerosols appear in a region and season for which the atmosphere exhibits strong static stability, aerosol‐induced changes in the surface radiation budget would be expected to govern the change in surface climate. Although the direct impact of the aerosol is to reduce absorbed solar radiation at the surface, this effect is minimized by the high surface albedos, which in turn, due to the large surface reflection, enhance aerosol solar absorption. This aerosol‐induced atmospheric heating then results in increased infrared emission from the atmosphere to the surface that more than compensates for the reduced surface solar absorption, thus producing surface warming. The seasonal statistical‐dynamical model further exhibits interesting cryospheric feedback processes, while suggesting springtime Arctic warming that is roughly consistent in timing with observed trends in high latitude temperatures, an effect some have attributed to CO2‐induced changes.
Transport of nitric oxide and the D region winter anomaly
Authors: Garcia Rolando R. , Solomon Susan , Avery Susan K. , Reid George C.
Published: February 2008

Observations of D region electron density and radio wave absorption are anomalous during winter in two important respects. Absorption measured at a constant zenith angle is greater in winter than in summer (the “smooth anomaly”), and large absorption enhancements occur in winter on time scales of the order of days (the “sporadic anomaly”). Proposed explanations for the winter anomaly include temperature changes, water vapor variability, energetic particle precipitation, and transport of nitric oxide. In this study we examine the smooth and sporadic anomalies using a coupled model, which includes neutral and ion photochemistry, as well as transport by the mean meridional circulation and planetary waves. We find that both smooth and sporadic absorption enhancements can be understood in terms of auroral production of nitric oxide in polar night and its subsequent transport and ionization. In particular, our results indicate that horizonal wave transport can account for many of the observed features of the sporadic anomaly.
Evidence for stratospheric hydrogen peroxide
Authors: Chance K. V. , Traub W. A.
Published: February 2008

We have obtained a statistically significant measurement of H2O2 in the stratosphere. The results were obtained from the 112.19 cm−1 RQ5 branch of the torsional‐rotational spectrum with a remote‐sensing far‐infrared Fourier transform spectrometer during the Balloon Intercomparison Campaign (BIC‐2), on June 20, 1983. The concentration above the balloon gondola is unexpectedly large, corresponding to 0.68±0.21 parts per billion by volume (ppbv) at an effective altitude of 38.3 km. Below the gondola altitude the concentration of H2O2 is slightly less than expected from the model predictions at 33.2 km (0.19±0.05 ppbv) and significantly less than expected at 29.3 km (0.08±0.03 ppbv).
Upper limit of the rate constants for the reactions of N2O5 with OH, HO2, Cl, and ClO at 293 K
Authors: Mellouki A. , Poulet G. , Le Bras G.
Published: February 2008

The kinetics of the reactions of N2O5 with free radicals (OH, HO2, Cl, ClO) have been investigated in a discharge‐flow system to assess the importance of these reactions in atmospheric chemistry. The upper limit rate constants obtained at 293 K and at low pressure strongly suggest that these reactions will be of negligible importance under atmospheric conditions.
Satellite sensing of aerosol absorption
Authors: Kaufman Yoram J.
Published: February 2008

A method is developed for remote sensing of aerosol absorption from satellite images of the earth's surface. The method is based on the measurement of the change in the upward radiances between a clear and a hazy day over a varying surface reflectance. For a zero change a balance between brightening due to scattering and darkening due to absorption and scattering is reached. This balance is utilized via a radiative transfer model to derive the aerosol single‐scattering albedo. A sensitivity study is performed and the method is tested against laboratory measurements. It is suggested that for the case of haze introduced on top of an existing background aerosol (e.g., forest fire smoke, dust storms, etc.) and with a fair estimate of the scattering phase function, the error in the remotely sensed single‐scattering albedo (ω0, ratio between scattering and scattering plus absorption) is in the range of 0.03–0.05. The method is applied to Landsat Multi‐Spectral Sensor imagery of forest fire smoke detected over the Washington D.C., area, resulting in ω0 = 0.90. The variability of the remotely sensed ω0 across the image was Δω0 = ±0.01. No substantial dependence on wavelength between 550–750 nm was found. Application of the method to aircraft radiances measured during regional industrial air pollution resulted in ω0 = 0.94 ± 0.04. The main advantage of the method is that it provides a simple measure of ω0 of the undisturbed aerosol. The main errors in the method arise from variations in the surface reflectance between the clear and the hazy days, uncertainty in the scattering phase function, and variation of the aerosol and gaseous absorption between these two days. If the satellite calibration varies with time, the measurements of ω0 can be substantially affected.
Modeling of outgoing long‐wave radiation in the presence of broken clouds
Authors: Zuev V. E. , Zhuravleva T. B. , Titov G. A.
Published: February 2008

The transfer of long‐wave radiation in a model of broken clouds constructed on the basis of Poisson point flux is investigated. Formulas are obtained for the expected value of the radiance, taking into account the influence of finite horizontal dimensions of clouds on the radiation field. The results of calculations show a differnce of 2–8°K between the mean brightness temperatures of stratus and cumulus clouds in the wide range of variations of optical‐geometric parameters and viewing angle.
A statistical analysis of solar flux variations over time scales of solar rotation: 1978–1982
Authors: Lean J. L. , Repoff T. P.
Published: February 2008

Differences in the temporal behavior of the ultraviolet irradiance at 205 nm and the 10.7‐cm radio flux, the ultraviolet irradiance at 121.6 nm, model calculations of the 205‐nm irradiance derived from Ca II K plage emission, and the sunspot‐blocking function are examined during a 5‐year period near the maximum of solar cycle 21. Because of solar rotation the dominant variance in each of these time series occurs at 27 days, but real temporal differences arise because the five solar time series are each formed at different heights within the solar atmosphere and are associated with a variety of solar active region phenomena having different spatial and temporal characteristics on the solar disc. These differences may be important if the ground‐based solar activity time series are used instead of the measured UV irradiances in correlation studies of solar variability with atmospheric parameters such as ozone densities and temperature. Recognizing the presence of autocorrelation in the UV irradiance time series is also important in solar terrestrial correlation studies, since it complicates the use of classical statistical techniques for estimating the significance of the results.
Radiative transfer models of the appearance of city lights obscured by clouds observed in nocturnal satellite images
Authors: Weinman James A. , Masutani Michiko
Published: February 2008

Measurements of transmitted urban light through clouds that are provided by nocturnal satellite images yield information regarding the optical parameters of clouds. While the albedo for optically thick clouds becomes insensitive to changes in optical thickness, the fractional change in the zenith‐directed transmission of city light through thick clouds is relatively sensitive to changes in optical thickness. Models are derived and evaluated to compute the radiances from Lambertian point and extended light sources that are transmitted toward zenith through clouds of varying albedos for single scattering, asymmetry factors, cloud heights, and optical thickness. It is shown that radiances from reflected moonlight and transmitted city light may be used to estimate van de Hulst's similarity parameters of clouds above and near cities.
General interpretation of surface electric field variations between lightning flashes
Authors: Chauzy Serge , Soula Serge
Published: February 2008

The evolution of the electric field underneath a thunderstorm is measured and modeled, taking into account ion production by corona at ground level. Measurements of electric field and calculations of charge densities were made at various levels above the surface during two summer experiments. The collected data show that although the corona effect drastically influences the surface electrical parameters, some information about thunderstorm electrification can be obtained from consideration of the Maxwell current density. Thus the rate of change of electric field as well as the rate of generation of corona ions are obtained from the evolution of the surface electric field. Average charge densities ranging up to 6 nC/m3 are commonly found over intervals of several minutes within the lowest 15 m, especially during periods of intense lightning activity. Modeling reveals the influence of field changes due to lightning flashes and of the corona threshold on the surface electric field variation. The orders of magnitude computed by the model agree reasonably well with the experimental data.
Transient changes in Doppler spectra of precipitation associated with lightning
Authors: Mazur Vladislav , Zrnic' Dusan S. , Rust W. David
Published: February 2008

From radar observations obtained at vertical incidence, a transient increase (5–10 dB on the average) of noise power in the Doppler spectra associated with lightning is analyzed. To explain this effect, three hypothesized causes are tested: (1) a sudden increase in echo power caused by lightning within the Fourier analysis window, (2) refractive index discontinuity, and (3) drop oscillation; refractive index discontinuity and drop oscillation are both produced by a lightning shock wave propagating through the sampling volume. The data analysis strongly suggests that the refractive index discontinuity is mainly responsible for the transient effect.
Visible spectroscopy at McMurdo Station, Antarctica: 2. Observations of OClO
Authors: Solomon S. , Mount G. H. , Sanders R. W. , Schmeltekopf A. L.
Published: February 2008

The column abundance of OClO at McMurdo Station, Antarctica, was measured by visible absorption spectroscopy during austral spring in 1986. Observations were obtained during the day using scattered sunlight and at night using direct light from the moon. The observed total column amounts in Antarctica were about 20–50 times larger than would be expected for standard homogeneous photochemistry, suggesting that the halogen chemistry of Antarctic spring is profoundly different from such standard theoretical expectations and may play a role in the development of the springtime Antarctic ozone “hole.”
Monsoon variability over the past 150,000 years
Authors: Prell Warren L. , Kutzbach John E.
Published: February 2008

Paleoclimatic records adjacent to India and Africa show major variability that is related to large fluctuations in the wind and precipitation fields associated with monsoonal circulations. Much of the variability occurs at orbital periodicities, and all of the paleoclimatic time series show four monsoon maxima that occur during interglacial conditions and coincide with precession maxima and maxima of northern hemisphere summer radiation. During glacial conditions, paleoclimatic records are less distinct and show more individual variability. To identify the processes causing changes in monsoon circulation, we used 13 general circulation model (National Center for Atmospheric Research (NCAR) community climate model (CCM)) simulations that incorporate a large range of solar radiation and surface (modern to full glacial) boundary conditions. The spatial patterns of climate variables and their zonal and regional averages revealed that under interglacial conditions increased northern hemisphere solar radiation produced a larger land‐ocean pressure gradient, stronger winds, and greater precipitation over southern Asia and North Africa. Under glacial conditions, however, the monsoon is weakened in southern Asia (decreased winds and precipitation), but precipitation is increased in the equatorial west Indian Ocean and equatorial North Africa. Sensitivity coefficients are used to estimate the change in model‐simulated precipitation (ΔP) relative to the changes in northern hemisphere summer radiation (ΔS) and glacial age boundary conditions (ΔGBC); the coefficients are then used with time series of ΔS and ΔGBC to simulate past precipitation (ΔP) for a specific area. Simulated records of ΔP for southern Asia and equatorial North Africa over the past 150,000 years show four monsoon maxima that are related to solar radiation maxima and are observed in the paleoclimatic data. The simulations also indicate that southern Asia is drier than today (weaker monsoon) for the period with extensive glacial boundary conditions, especially between 75,000 and 15,000 years ago. Conversely, equatorial North Africa is simulated to be wetter than today during glacial conditions. Both areas show stronger monsoons with increasing solar radiation during interglacial conditions. The agreement of simulated and observed paleoclimatic time series suggests that both orbitally produced solar radiation changes and glacial age boundary condition changes are necessary to explain the major regional features of monsoon climates at millenial or longer time scales. For southern Asia and equatorial North Africa the influence of these two factors is approximately additive.
Comparisons of gauge and satellite rain estimates for the central United States during August 1979
Authors: Griffith Cecilia Girz
Published: February 2008

Rainfall estimates, inferred from the thermal infrared channel of the Geostationary Operational Environmental Satellite‐East (GOES‐East) for August 1979, are compared with gauge rainfalls over hourly and daily time frames for area‐averaged amounts and point values. The area of interest is a 3.6×106 km2 region in the central third of the United States. Over the month the satellite rainfalls tend to be smaller by 20–40% than the corresponding gauge amounts, but mean sampling errors inherent in a gauge network of this density (1 gauge/4000 km2) are estimated to be minimally 100% of the areal mean rainfall. Root‐mean‐square errors are approximately 1 mm for daily and 0.1 mm for hourly area‐averaged rainfalls and are 14 mm for daily and 5 mm for hourly point rainfalls. Satellite‐gauge differences of daily (hourly) point values can be large, but 50% of the satellite amounts are within ±4 (±2) mm of the gauge amount, and 90% are within ±20 (±8) mm, reinforcing the fact that the satellite‐derived rainfall is an area‐averaged rather than a point estimate of rain amount. Timing of rain events is comparable for daily area‐averaged satellite and gauge data. However, hourly area‐averaged gauge data exhibit considerably more short‐term fluctuations than the hourly satellite data. For the two satellite algorithms tested, the streamlined technique requires the least computation time (10% of that needed by the life history technique) and shows a little difference in its comparisons with the gauges.