bluuebunny/crossref_metadata_2025 huggingface dataset:
Horizontal electric fields from lightning return strokes
Authors: Thomson E. M. , Medelius P. J. , Rubinstein M. , Uman M. A. , Johnson J. , Stone J. W.
Published: February 2008

Measurements are presented of simultaneous horizontal and vertical electric fields from 42 lightning return strokes in 27 flashes at distances from 7 to 43 km. The data were obtained at the NASA Kennedy Space Center, Florida, using an elevated spherical antenna having a system bandwidth of 3 Hz to 4 MHz. The strokes studied occurred in a 6‐min interval from 1850 to 1856 UT on August 11, 1984. The 42 measured horizontal fields exhibited initial peaks having a mean half width of 0.52 μs. The ratio of the amplitude of the peak horizontal field to the associated vertical field peak had a mean value of 0.030, with a standard deviation of 0.007. The measured horizontal field wave shapes are compared with those obtained from calculations using the measured vertical fields and theory (the “wavetilt” formula) that models the fields as plane wave radiation over a homogeneous ground of uniform conductivity and permittivity. The local ground conductivity, measured as a function of depth using the Wenner four‐probe method, was found to increase with depth within the region relevant to this study, from the surface to a depth of a few meters: the conductivity was 8.2×10−3 mho/m between the surface and a depth of 2.2 m, and 3.1×10−2 mho/m below this layer to a depth of 11 m. If a ground conductivity equal to that of the top layer is used in the wavetilt formula, the calculated horizontal field peaks are found to be, on average, about 33% wider and larger than the measured field peaks. Errors and compensation procedures for tilt of the spherical antenna, for electronic system distortion, and for electric field distortion at the antenna due to proximity of the ground and of the antenna support structure are described.
Climate simulations for 9000 years before present: Seasonal variations and effect of the Laurentide ice sheet
Authors: Mitchell J. F. B. , Grahame N. S. , Needham K. J.
Published: February 2008

A detailed climate model is used to investigate the factors contributing to differences between the climate 9000 years ago and that at present. The climate model comprises an atmospheric general circulation model coupled to a mixed layer ocean in which heat convergence due to oceanic advection is prescribed. In the first experiment, only the Earth's orbital parameters are changed. As in earlier work, it is found that monsoon circulations are enhanced during northern summer and weakened during the northern winter and that mid‐latitudes become drier throughout the year. The simulated changes are in general agreement with paleoclimatic evidence. Various feedback mechanisms modify the local response to the changes in insolation at the top of the atmosphere. In the northern hemisphere the warming in high latitudes is greatest in autumn and winter as a result of changes in sea ice, the mid‐latitude oceans are warmer throughout the year because of changes in cloud, and the surface temperature change over land in summer is reduced in low latitudes and enhanced in mid‐latitudes because of changes in cloud and soil moisture. Thus the climatic response to a simple change in boundary conditions may be complex, a fact which should be borne in mind when interpreting paleoclimatic data. In a second experiment a representation of the Laurentide ice sheet is also included. The warming in high latitudes is substantially reduced, especially just downstream of the ice sheets. This suggests that there may have been a substantial warming in high latitudes just after the Laurentide ice sheet collapsed.
Global climate changes as forecast by Goddard Institute for Space Studies three‐dimensional model
Authors: Hansen J. , Fung I. , Lacis A. , Rind D. , Lebedeff S. , Ruedy R. , Russell G. , Stone P.
Published: February 2008

We use a three‐dimensional climate model, the Goddard Institute for Space Studies (GISS) model II with 8° by 10° horizontal resolution, to simulate the global climate effects of time‐dependent variations of atmospheric trace gases and aerosols. Horizontal heat transport by the ocean is fixed at values estimated for today's climate, and the uptake of heat perturbations by the ocean beneath the mixed layer is approximated as vertical diffusion. We make a 100‐year control run and perform experiments for three scenarios of atmospheric composition. These experiments begin in 1958 and include measured or estimated changes in atmospheric CO2, CH4, N2O, chlorofluorocarbons (CFCs) and stratospheric aerosols for the period from 1958 to the present. Scenario A assumes continued exponential trace gas growth, scenario B assumes a reduced linear growth of trace gases, and scenarioCassumes a rapid curtailment of trace gas emissions such that the net climate forcing ceases to increase after the year 2000. Principal results from the experiments are as follows: (1) Global warming to the level attained at the peak of the current interglacial and the previous interglacial occurs in all three scenarios; however, there are dramatic differences in the levels of future warming, depending on trace gas growth. (2) The greenhouse warming should be clearly identifiable in the 1990s; the global warming within the next several years is predicted to reach and maintain a level at least three standard deviations above the climatology of the 1950s. (3) Regions where an unambiguous warming appears earliest are low‐latitude oceans, China and interior areas in Asia, and ocean areas near Antarctica and the north pole; aspects of the spatial and temporal distribution of predicted warming are clearly model‐dependent, implying the possibility of model discrimination by the 1990s and thus improved predictions, if appropriate observations are acquired. (4) The temperature changes are sufficiently large to have major impacts on people and other parts of the biosphere, as shown by computed changes in the frequency of extreme events and by comparison with previous climate trends. (5) The model results suggest some near‐term regional climate variations, despite the fixed ocean heat transport which suppresses many possible regional climate fluctuations; for example, during Hie late 1980s and in the 1990s there is a tendency for greater than average warming in the southeastern and central United States and relatively cooler conditions or less than average warming in the western United States and much of Europe. Principal uncertainties in the predictions involve the equilibrium sensitivity of the model to climate forcing, the assumptions regarding heat uptake and transport by the ocean, and the omission of other less‐certain climate forcings.
Comparison of cloud amounts derived using GOES and Landsat data
Authors: Minnis Patrick , Wielicki Bruce A.
Published: February 2008

Cloud amounts derived from Landsat digital data over 22 regions with various cloud types are compared to cloudiness derived from collocated, nearly simultaneous 4 × 8 km GOES visible and infrared data using a hybrid bispectral threshold method (HBTM). The mean and rms differences between the Landsat and GOES cloud amounts are −0.008 and 0.075, respectively. A sensitivity analysis showed that underestimation of approximately 0.01 in clear‐sky reflectance by the HBTM increased the mean GOES cloud amount by 0.06, more than twice the decrease in cloud amount obtained by an equivalent increase in clear‐sky reflectance. Accuracy limits were estimated for the Landsat analyses by considering the fraction of cloud‐edge pixels in a scene. For scenes having relatively homogeneous backgrounds, the Landsat cloudiness has an estimated accuracy of −0.02 to +0.04, while cloud amount in scenes with variable background reflectance is more susceptible to underestimation, having accuracy limits of −0.02 to +0.12. The lower bound for the Landsat cloud cover is reliable when considered in terms of most working definitions of cloud cover. The upper bound will remain uncertain until an absolute definition of cloud cover is established which sets the bounds on the optical properties which dictate when a cloud does or does not exist. Many of the scenes contained a substantial proportion of partially cloud‐filled GOES pixels. Landsat imagery and cloud properties derived from the Landsat data are used to explain how the partially cloud‐filled GOES pixels were treated by the HBTM. Most of the rms difference occurred over two regions: one where many of the GOES pixels were partially cloud‐filled with very bright cloud cells and one where the GOES pixels were mostly overcast with both bright (thick) and very dim (thin) clouds. It is concluded that the HBTM accounts for the effects of partially cloud‐filled fields of view in most of the cases in this study. The reflectance limits used to constrain the HBTM appear to be reasonable but cannot account for the effects of anomalously bright or dark cloud fields. Techniques are discussed for improving the HBTM's retrieval of cloud fraction in the more difficult cases. This study, though only the beginning of a validation of the HBTM, demonstrates the potential for using Landsat data to improve routine cloud parameter retrievals from the low‐resolution sensors on meteorological spacecraft. Since the scenes used in this study represent only a limited number of cloudiness conditions and viewing and illumination situations, there remains much more work ahead in order to completely validate the HBTM or any other satellite cloud retrieval algorithm. Future cloud studies using Landsat should include both visible and infrared channels.
Tropospheric reactions of H+(NH3)m(H2O)n with pyridine and picoline
Authors: Viggiano A. A. , Morris Robert A. , Dale F. , Paulson John F.
Published: February 2008

Rate constants for the reactions of H+(NH3)m(H2O)n with pyridine and all three picolines have been measured for m + n ≤ 5. The rate constants were found to be large for all m and n studied. The reactions proceed by proton transfer, with an undetermined number of ligands transferred. Estimates of the rate constants at 300 K have been made for the reactions needed to derive pyridine and picoline concentrations in the atmosphere.
Variability of pigment biomass in the California Current System as determined by satellite imagery: 1. Spatial variability
Authors: Smith Raymond C. , Zhang Xueyun , Michaelsen Joel
Published: February 2008

Spatial variability of chlorophyll in the California Current system was analyzed using Coastal Zone Color Scanner (CZCS) imagery. A total of 48 images were analyzed to produce seasonal averages and variances, gradients, and power spectra. Roughly one third to one half of the variance in pigment biomass can be explained by consistent, large‐scale gradients. In general, biomass is higher in the north and in nearshore areas. Nearshore areas also have proportionally more small‐scale variability than the areas offshore. Slopes of the power spectra for nearshore areas are about −2.2 (for spatial scales of 10–100 km), while slopes for offshore areas are about −3. In addition, the power spectra show evidence of a change in slope at about 10 km, with slopes of about −1 for shorter‐length scales. This may indicate that biological processes dominate the smaller scales, while mesoscale eddies and geostrophic currents dominate the larger scales.
Cluster analysis of multiple planetary flow regimes
Authors: Mo Kingtse , Ghil Michael
Published: February 2008

A modified cluster analysis method has been developed to identify spatial patterns of planetary flow regimes and to study transitions between them. This method has been applied first to a simple deterministic model and second to northern hemisphere (NH) 500‐mbar data. The dynamical model is governed by the fully nonlinear, equivalent‐barotropic vorticity equation on the sphere. Clusters of points in the model's phase space are associated either with a few persistent events or with many transient events. Two stationary clusters have patterns similar to unstable stationary model solutions, zonal or blocked. Transient clusters of wave trains serve as way stations between the stationary ones. For the NH data, cluster analysis was carried out in the subspace of the first seven empirical orthogonal functions (EOFs). Stationary clusters are found in the low‐frequency band of more than 10 days, and transient clusters are found in the band‐pass frequency window between 2.5 and 6 days. In the low‐frequency band, three pairs of clusters determine EOFs 1, 2, and 3, respectively. They exhibit well‐known regional features, such as blocking, the Pacific/North American (PNA) pattern, and wave trains. Both model and low‐pass data show strong bimodality. Clusters in the band‐pass window show wavetrain patterns in the two jet exit regions.
A coupled energy balance climate‐sea ice model: Impact of sea ice and leads on climate
Authors: Ledley Tamara Shapiro
Published: February 2008

A coupled climate‐sea ice model that includes land‐sea resolution in the atmosphere, a mixed layer ocean, and a ground layer is used to investigate the impact of sea ice and leads within the ice pack on climate. Results show that a feedback process between the ocean and atmosphere exists, called the lead‐temperature feedback, such that changes in the winter minimum lead fraction can cause large changes in the simulated annual zonally averaged surface air temperature in the north polar regions. Compared to a control case where the minimum lead fraction is 1.1%, these changes in temperature range from a decrease of about 1.0°K, when leads are eliminated, to an increase of 1.0°K, when the winter minimum lead fraction is increased to 4.3%. Seasonally, this temperature change ranges up to 2.0°K. An examination of the surface energy fluxes shows that the changes in the sensible heat flux, in response to changes in the lead fraction, contribute the most to these temperature changes. The absorbed solar radiation is also affected by the changes in the winter minimum lead fraction; however, the small changes in lead area during the winter and the period of open ocean during the summer reduce its impact. The increase in the sensible heat flux to the atmosphere, along with the changes in the other fluxes, in response to increases in winter minimum lead fraction, forms the positive lead‐temperature feedback between larger lead area and warming. This feedback process has major implications for both polar and global climate.
Two‐dimensional simulations of possible mesoscale effects of nuclear war fires: 1. Model description
Authors: Giorgi Filippo
Published: February 2008

In this paper and the companion paper by Giorgi and Visconti [this issue] a two‐dimensional mesoscale meteorological model is coupled to an aerosol model to investigate possible mesoscale effects of nuclear war fires. The meteorological model used in this study is a two‐dimensional analog of the Penn State/NCAR mesoscale model with enhancements in the areas of radiative transfer, surface physics, and moisture physics. The aerosol model solves equations for the hygroscopic and hydrophobic fractions of particulate material and includes particle transport, sedimentation, dry‐deposition, in‐cloud and below‐cloud scavenging, and a first order term accounting for aerosol aging. In this paper the meteorological model and the aerosol model are first described and then applied, as an illustrative example, to a simulation of the development of sea‐breezelike circulations induced by contrasts in soil moisture available for evaporation.
Historical temperature trends in the United States and the effect of urban population growth
Authors: Balling R. C. , Idso S. B.
Published: February 2008

The linear change in temperature between 1920 and 1984 is calculated for 961 stations in the conterminous United States. Annual, winter, and summer maps of these temperature changes reveal pronounced geographical patterns, with widespread cooling in the major south‐central portion of the United States and general warming in the northeast and west. Stepwise multiple regression analysis identifies a statistically significant impact of population change on these temperature trends, even though the stations utilized in this study had a median population of only 5832 in 1980. Both the observed mean annual cooling of the country and the warming bias provided by these small urban centers suggest that we may not yet have a proper perspective on global climatic change.
Antarctic atmospheric tracer experiments
Authors: Mroz Eugene J. , Alei Mohammed , Cappis John H. , Guthals Paul R. , Mason Allen S. , Rokop Donald J.
Published: February 2008

Although the Antarctic circulation cell is a statistical construct, its ability to transport trace gases and aerosols to the continent has been discerned experimentally by the use of deuterated methane atmospheric tracers. Atmospheric tracer experiments were conducted in 1984 to study transport from the mid‐latitudes of the southern hemisphere to Antarctica. The tracer was transported to the polar plateau within a few days following tracer releases that took place in the summer and spring. However, in winter, poleward transport of the tracer was inhibited by the winter circumpolar vortex. The tracer concentration pattern was consistent with a “lumpy, streaky” distribution produced by a numerical model of global circulation.
Investigations of internal gravity waves using three vertically directed closely spaced wind profilers
Authors: Carter D. A. , Balsley B. B. , Ecklund W. L. , Gage K. S. , Riddle A. C. , Garello R. , Crochet M.
Published: February 2008

A network of three wind profilers spaced about 5 km apart was operated in southern France during the Alpine Experiment (ALPEX) program. The wind profilers measured vertical motions, and the experiment was designed to study traveling internal waves by comparing the vertical velocity fluctuations observed at each station. The measured phase velocities, together with the observed periods, were used to deduce the horizontal wavelength of the waves. Only a relatively few cases of monochromatic waves could be identified using this array. Most of the waves that were detected had phase velocities opposite to the prevailing wind and had the speeds required to cause trapping as the intrinsic frequency was Doppler shifted upward to the Brunt‐Väisälä frequency.
A study of the sulfur cycle in the Antarctic marine boundary layer
Authors: Pszenny Alexander A. P. , Castelle Andrew J. , Galloway James N. , Duce Robert A.
Published: February 2008

Atmospheric sampling was conducted aboard R/V Polar Duke from March 21 to April 27, 1986, in the southern Drake Passage and in the coastal waters west of the Antarctic Peninsula. Average atmospheric concentrations (n = 6) of sulfur dioxide (SO2) vapor, aerosol methanesulfonate (CH3SO3−), and aerosol non‐sea‐salt sulfate (nss−SO4=) were 0.36, 0.22, and 0.34 nmol m−3, respectively. Cascade impactor data indicated that more than 85% of the masses of both CH3SO3− and nss−SO4= were on particles of <0.25‐μm mean aerodynamic radius. Average concentrations (n = 8) of CH3SO3− and nss−SO4= in precipitation were 0.09 and 0.57 μM, respectively. Box model calculations based on this limited data suggest a total sulfur removal rate from the local marine boundary layer of 0.3–7.2 μmol m−2 day−1. This removal approximately balances the oceanic source of dimethylsulfide (DMS) sulfur of 1.2–4.4 μmol m−2 day−1 (±100%) estimated by Berresheim [1987] from data obtained during the same cruise. The box model calculations also suggest that heterogeneous SO2 oxidation may be the major pathway for DMS to sulfate conversion (∼75%) and/or that other sources of sulfate may not be negligible. Observed mineral aerosol and 222Rn concentrations were low but slightly elevated above “pure” remote marine background levels, suggesting a weak but discernible continental character in sampled air. Uncertainties are large owing to the limited sampling time, study area, and numbers of samples obtained, but overall, the sulfur cycle in the coastal Antarctic marine boundary layer appears not to differ remarkably from that in other remote marine regions.
An analysis of northern middle‐latitude Umkehr measurements corrected for stratospheric aerosols for 1979–1986
Authors: DeLuisi John J. , Longenecker David U. , Mateer Carlton L. , Wuebbles Donald J.
Published: February 2008

Umkehr observations of ozone profile for five northern middle‐latitude Dobson spectrophotometer stations are objectively corrected for stratospheric aerosol during the period 1979–1986. The corrections are done by means of theoretical calculations, using observations of stratospheric ozone and aerosols. Stratospheric ozone and aerosol profile data to correct the Umkehr measurements are derived from ozonesonde observations and observations provided by five lidar stations in the northern hemisphere middle latitudes. Optical properties of the stratospheric aerosol existing during and after the major injection by El Chichón are derived from surface and aircraft photometric observations and in situ aircraft observations of aerosol size distribution. The corrected Umkehr data display some noteworthy ozone reductions in the upper stratosphere. The magnitude of these reductions does not seem to be extraordinary when considering features seen in long‐term Umkehr data. However, the rates may be extraordinary, for example, in layers 8 and 9, in which decreases in ozone concentration during 1979–1986 were 9% and 15% respectively, using corrected data.
Altitude and seasonal characteristics of aerosol backscatter at thermal infrared wavelengths using lidar observations from coastal California
Authors: Menzies Robert T. , Ancellet Gerard M. , Tratt David M. , Wurtele Morton G. , Wright Jeffrey C. , Pi Wilfred
Published: February 2008

A calibrated CO2 lidar has been used to measure boundary layer aerosol backscatter and vertical profiles of tropospheric and lower stratospheric aerosol backscatter over a 1984–1987 time period from a site in Pasadena, California. The lidar data have been taken at two wavelengths, 9.25 and 10.6 μm. Data are presented which show altitude, seasonal, and trend characteristics of backscatter for various air mass histories. Results of trajectory studies indicate the influences of convective activity and other factors on the backscatter profiles.
Self‐limiting physical and chemical effects in volcanic eruption clouds
Authors: Pinto Joseph P. , Turco Richard P. , Toon Owen B.
Published: February 2008

We have constructed one‐dimensional aerosol microphysical and photochemical models to examine the chemistry of stratospheric volcanic clouds. Estimates of the stratospheric inputs of several key volcanic gases were made. Our results suggest that the aerosol microphysical processes of condensation and coagulation produce larger particles as the SO2injection rate is increased, rather than a larger number of particles of the same size. Larger particles have a smaller optical depth per unit mass than do smaller ones. They also settle out of the stratosphere at a faster rate, thereby restricting the total number of particles in the stratosphere. These processes moderate the impact of volcanic clouds on the Earth's radiation budget and climate and suggest that volcanic effects may be self‐limiting. However, following large eruptions, the scattering of solar radiation by the aerosol and reaction with SO2can deplete the abundance of OH radicals in the stratosphere. The injection of HCl into the stratosphere, which could lead to large ozone changes, is limited by a cold trap effect in which HCl and water vapor condense on ash particles in the rising volcanic plume and fall out as ice.
The planning and execution of ER‐2 and DC‐8 aircraft flights over Antarctica, August and September 1987
Authors: Tuck A. F. , Watson R. T. , Condon E. P. , Margitan J. J. , Toon O. B.
Published: February 2008

During August and September 1987, instrumented ER‐2 and DC‐8 aircraft flew 12 and 13 flights over Antarctica, respectively, to investigate the dramatic loss of ozone that has occurred there in the lower stratosphere during recent austral springs. The flights, which are documented in some detail, provided a wealth of data on homogeneous gas phase composition, upon polar stratospheric clouds, and upon tracers for dynamic motion. An important aspect of the ER‐2 data is that periods of high surface winds at Punta Arenas, Chile, which generally prevented a flight, frequently coincided with equatorward extension of the vortex toward the flight track region (53°–72° S, 60°–80° W). The ER‐2 flights are thus biased toward days when the vortex was being pushed away from the tip of South America and the Antarctic Peninsula. Any attempt to use the ER‐2 data as a time series must take into account the variable position of the vortex edge along the flight track. At DC‐8 flight levels, numerical weather prediction models had a tendency to underestimate the wind speeds by up to 50% in situations of strong meridional flow. Since such events had detectable effects on the lower stratospheric vortex, this too could be an important limitation.
Persistence of polar stratospheric clouds in the southern polar region
Authors: McCormick M. P. , Trepte C. R. , Pitts M. C.
Published: February 2008

Observations of Antarctic polar stratospheric clouds (PSCs) were examined using the 1‐μm aerosol extinction ratio data from the SAM II satellite experiment for the years 1979–1982 and 1984–1987. PSCs were sighted between 10 and 25 km and were usually first observed by mid‐June. Clouds disappeared earlier at higher altitudes (late August near 24 km, in most cases) and later at lower altitudes (late September or October near 16 km). It was found that PSCs persisted longer in 1985 and 1987 at 18 km and were more frequently observed in September and October 1987 than the other years. Inference of likely PSC formation regions from National Meteorological Center temperature data indicated that clouds would begin forming in late May and usually disappear in September. This analysis confirmed the persistence of colder conditions during the spring of 1987.
Filter measurement results from the Airborne Antarctic Ozone Experiment
Authors: Gandrud B. W. , Sperry P. D. , Sanford L. , Kelly K. K. , Ferry G. V. , Chan K. R.
Published: February 2008

During the Airborne Antarctic Ozone Experiment (AAOE), filter samples were obtained for the determination of the total nitrate, sulfate, acidic chloride and acidic fluoride content along the flight path of the NASA ER‐2. On three flights of the 12‐flight series, filters were flown that allowed the separate but simultaneous collection of these species in the aerosol and vapor phase. The ratio of particulate sulfate observed outside the chemically perturbed region (CPR) of the vortex to that inside the CPR was 2.6. The total nitrate levels observed inside the CPR were less than those outside the CPR with one exception. The total nitrate levels observed inside the CPR decreased at a rate of 0.06 parts per billion by volume (ppbv) nitrate d−1 over the 36‐day period of the measurements. Nitrate was observed in the particulate phase on two flights and was correlated with the coldest temperatures observed on the flights. Vapor phase nitrate within the CPR was measured on two flights and it ranged from 1.3 to 2.8 ppbv. Chloride and fluoride were not observed in the particulate phase at concentrations above the detection limits for those determinations. Total acidic fluoride was observed to be larger inside the CPR than outside in contrast to the other measured species. Ratios of total acidic chloride to total acidic fluoride observed at flight altitude exhibit values near 1, rather than the accepted mid‐latitude value of 4–5, suggesting a loss of chloride from the reservoir species HCl and ClONO2. The existence of larger amounts of total acidic fluoride inside the CPR compared to outside the CPR, coupled with the observation of less sulfate inside than outside suggests that the air inside the CPR had descended from a higher altitude.
Indicators of transport and vertical motion from correlations between in situ measurements in the Airborne Antarctic Ozone Experiment
Authors: Murphy D. M. , Tuck A. F. , Kelly K. K. , Chan K. R. , Loewenstein M. , Podolske J. R. , Proffitt M. H. , Strahan S. E.
Published: February 2008

Analysis of small‐scale structure in the in situ measurements made from the ER‐2 during the Airborne Antarctic Ozone Experiment shows the existence of a region at the boundary of the chemically perturbed region where the mixing ratios and small‐scale structure of trace gases are influenced by transport across the boundary. This transition region is characterized by horizontal interchange and vertical layering of air parcels from within and outside of the chemically perturbed region and negative small‐scale correlations between ClO and ozone. The horizontal transport in this region creates large surface areas between dissimilar air masses, providing the potential for substantial mixing. This paper does not attempt to quantify the amount of mixing. Correlations between ClO and O3 show that the transition region extends to 2°–4° of latitude to either side of the boundary of the chemically perturbed region. A ±4°‐wide transition region would contain nearly as much air as the chemically perturbed region proper. Analysis of water vapor and nitrous oxide data suggests that diabatic descent is associated with dehydration. This could be caused by strong radiative cooling of those polar stratospheric clouds in which enough water condenses for the particles to fall and dehydrate the air.
Can Milankovitch orbital variations initiate the growth of ice sheets in a general circulation model?
Authors: Rind D. , Peteet D. , Kukla G.
Published: February 2008

The Goddard Institute for Space Studies climate model is used to investigate whether the growth of ice sheets could have been initiated by solar insolation variations. Three different orbital configurations are used, corresponding to 116 and 106 kyr B.P., and a modified insolation field with greater reductions in summer insolation at high northern latitudes. The time periods chosen are those in which geophysical evidence suggests ice sheets may have been growing rapidly. The reduced summer insolation field characteristic of all the experiments is thought to be a necessary condition for allowing snow to last through the summer, and ice sheets to build. The results show that the model fails to maintain snow cover through the summer at locations of suspected initiation of the major ice sheets, despite the reduced summer and fall insolation. When 10‐m‐thick ice was inserted in all locations where continental ice sheets existed during the Last Glacial Maximum, the model failed to maintain it as well, producing energy and mass imbalances which would remove the ice within 5 years. Only when the ocean surface temperatures were adjusted to their peak ice age values was the model able to keep any of the additional ice, and then only in a very restricted region of northern Baffin Island. The experiments indicate there is a wide discrepancy between the model's response to Milankovitch perturbations and the geophysical evidence of ice sheet initiation. As the model failed to grow or sustain low‐altitude ice during the time of high‐latitude maximum solar radiation reduction (120–110 kyr B.P.), it is unlikely it could have done so at any other time within the last several hundred thousand years. If the model results are correct, it indicates that the growth of ice occurred in an extremely ablative environment, and thus demanded some complicated strategy, or else some other climate forcing occurred in addition to the orbital variation influence (and CO2 reduction), which would imply we do not really understand the cause of the ice ages and the Milankovitch connection. If the model is not nearly sensitive enough to climate forcing, it could have implications for projections of future climate change.
Bipolar lightning in winter at Maki, Japan
Authors: Narita K. , Goto Y. , Komuro H. , Sawada S.
Published: February 2008

The observation of winter lightning has been continued using magnetic links, digital recording systems for the current oscillograms, field mills, still cameras and video camera systems for the images of lightning channels on the west coast of Japan. Of the 59 magnetic link records, 59% were negative in polarity, 29% were positive, and the remaining 12% were unknown. The maximum peak current was over 270 kA in a positive flash, and the largest peak currents were found in positive flashes. The measured current oscillograms show that winter lightning stroke or ground flash often has a very long duration or continuing current. Moreover, two kinds of bipolar strokes were frequently recorded in the winter season. Nine of the 45 flashes showed bipolar strokes, 24 flashes were negative in polarity, seven were positive, and five were unknown.
Power spectra at radio frequency of lightning return stroke waveforms
Authors: Lanzerotti L. J. , Thomson D. J. , Maclennan C. G. , Rinnert K. , Krider E. P. , Uman M. A.
Published: February 2008

The power spectra of the wideband (10 Hz to 100 kHz) magnetic field signals in a number of lightning return strokes (primarily first return strokes) measured during a lightning storm which occurred in Lindau in August 1984 have been calculated. The RF magnetic field data were obtained with the engineering unit of the Galileo Jupiter Probe lightning experiment. In the analysis, each return stroke data set is first passed through an adaptive filter designed to whiten its spectrum. The largest sample in the filtered output is set to zero, and the power spectrum of the filtered data stream is computed using five orthogonal prolate spheroidal data windows in the time domain and a fast Fourier transform algorithm. The spectra of the magnetic field data definitely show fine structure, with two or three distinct peaks appearing in the spectra of many of the waveforms. An enhancement of power at ƒ ∼60–70 kHz is often seen in the spectra of the waveform time segments preceding and following the rise‐to‐peak amplitude of the return stroke.
A review of the photochemistry of selected nightglow emissions from the mesopause
Authors: Meriwether John W.
Published: February 2008

The substantial research activity of recent years on the photochemistry of the hydrogen‐oxygen family has improved our understanding of the production of nightglow emissions in the mesopause region of the atmosphere between 80 and 100 km; this work is reviewed with specific attention paid to the emissions of OH, the 557.7‐nm emission of O, and the atmospheric bands of O2(b 1Sg). These emissions are closely related to the O atom concentration profile and would provide a wealth of useful photochemical data in studies of noctilucent cloud displays. Ground‐based and rocket measurements of the OH nightglow show that the kinetics are well represented by the combination of the production reaction, H + O3 → OH(v′) + O2, with significant collisional deactivation by N2 and O2 for the higher vibrational levels of OH. In contrast, the perhydroxyl radical, HO2, plays a negligible role in the vibrational excitation of OH and the production of OH optical emission in the mesopause region. Atomic oxygen quenching is important for the lower vibrational states of OH(v′). Improved experimental determination of the electric dipole moment function of OH has resulted in a new set of transition probabilities that agrees well with the theoretical set published by Mies for low v rovibrational transitions of OH. The Mies values for the higher overtone transitions do not agree well with the empirical results derived from airglow intensities. Recent papers on the results of the sounding rocket campaign called Energy Transfer in the Oxygen Nightglow (ETON) have demonstrated the substantial progress made once the consequences of mesospheric dynamics are decoupled from the photochemistry of the mesopause region by in situ measurements of the atomic oxygen concentration. The work of recent years utilizing this approach has produced strong evidence for the deduction that the major source of several important oxygen metastable energy states is an intermediate metastable state formed in the first step of a two step reaction chain (known as the Barth process). Energy transfer and quenching reactions involving these metastable states complicate the analysis of the measurements. Continued progress requires laboratory experiments designed to explore the relationship of energy transfer processes to the vibrational development of the precursor species. The production of global maps of atomic oxygen concentration profiles becomes feasible once the details of the mesopause photochemical processes are fully understood.
Aerosol size distributions in the southwest Pacific
Authors: Lechner I. S. , Fisher G. W. , Larsen H. R. , Harvey M. J. , Knobben R. A.
Published: February 2008

Measurements of the size distribution and concentration of the atmospheric aerosol were made from an instrumented aircraft at altitudes of up to 6 km around New Zealand (37°S to 46°S) and during flights to other southwest Pacific islands (to 9°S). Measurements were also made at the surface in Antarctica (78°S). Single‐particle optical counters were used to cover the size range 0.06 μm to 8.0 μm radius. The results show that the free troposphere aerosol concentration ranged from 1.8 to 46 cm−3 and the size distribution was characterized by a “Junge” slope around −3.5. In the planetary boundary layer, including Antarctica, the concentrations were generally greater and more variable, and the size distributions often bimodal.
New spectral features of stratospheric trace gases identified from high‐resolution infrared balloon‐borne and laboratory spectra
Authors: Goldman A. , Murcray F. J. , Blatherwick R. D. , Kosters J. J. , Murcray F. H. , Murcray D. G. , Rinsland C. P.
Published: February 2008

A new Michelson‐type interferometer system operating in the infrared at very high resolution (0.002–0.003 cm−1 full width at half maximum) has been used to record numerous balloon‐borne solar absorption spectra of the stratosphere, ground‐based solar absorption spectra, and laboratory spectra of molecules of atmospheric interest. In the present work we report results obtained for several important stratospheric trace gases, HNO3, ClONO2, HO2NO2, NO2, and COF2, in the 8‐ to 12‐μm spectral region. Many new features of these gases have been identified in the stratospheric spectra. Comparison of the new spectra with line‐by‐line simulations shows that previous spectral line parameters are often inadequate and that new analysis of high‐resolution laboratory and atmospheric spectra and improved theoretical calculations will be required for many bands. Preliminary versions of several sets of improved line parameters under development are discussed.
Rapid calculation of radiative heating rates and photodissociation rates in inhomogeneous multiple scattering atmospheres
Authors: Toon Owen B. , McKay C. P. , Ackerman T. P. , Santhanam K.
Published: February 2008

The solution of the generalized two‐stream approximation for radiative transfer in homogeneous multiple scattering atmospheres is extended to vertically inhomogeneous atmospheres in a manner which is numerically stable and computationally efficient. It is shown that solar energy deposition rates, photolysis rates, and infrared cooling rates all may be calculated with simple modifications of a single algorithm. The accuracy of the algorithm is generally better than 10% so that other uncertainties, such as in absorption coefficients, may often dominate the error in calculation of the quantities of interest to atmospheric studies.
Stratospheric infrared continuum absorptions observed by the ATMOS instrument
Authors: Rinsland C. P. , Zander R. , Namkung J. S. , Farmer C. B. , Norton R. H.
Published: February 2008

A quantitative analysis of continuum absorptions in the lower stratosphere is reported based on infrared solar absorption spectra recorded in the occultation mode at 0.01 cm−1resolution. The spectra were obtained during seven sunrises near 48°S latitude and 12 sunsets near 28°N latitude with the atmospheric trace molecule spectroscopy (ATMOS) Fourier transform spectrometer operating April 29 to May 1, 1985, on board the shuttle/Spacelab 3 platform. Continuous absorption produced primarily by the collision‐induced fundamental vibration‐rotation band of O2and to a lesser extent by the superposition of H2O far line wings has been observed in the 1400‐ to 1800‐cm−1interval below tangent heights of about 25 km. Continuum optical depths measured in microwindows nearly free of atmospheric line absorption are 0.78±0.06 times those calculated with the O2absorption coefficients of Timofeyev and Tonkov (1978). This difference is consistent with previous measurements, but more than a factor of 2 improvement in accuracy has been achieved. Transmittance measurements in microwindows between 2395 and 2535 cm−1have been used to study continuous absorption from the collision‐induced fundamental vibration‐rotation band of N2and the far wings of strong CO2lines (primarily those of the ν3fundamental). Below about 2430 cm−1there is fair agreement between the measurements and calculations based on published absorption coefficients for both N2and CO2; at higher wave numbers, where absorption by N2is dominant, the calculated absorption exceeds the measured absorption. The measured transmittances have been analyzed to derive best fit absorption coefficients for the N2pressure‐induced band at lower stratospheric temperatures (∼210 K). An absorption peak has been detected near 1200 cm−1and is believed to result from extinction by the H2SO4stratospheric aerosol layer.
Trend analysis of aerosol‐corrected Umkehr ozone profile data through 1987
Authors: Reinsel Gregory C. , Tiao George C. , DeLuisi John J. , Basu Sabyasachi , Carriere Keumhee
Published: February 2008

Trend analysis of stratospheric Umkehr ozone profile data from 10 stations over the period 1977–1987 is considered. Two different correction methods to adjust the Umkehr data measurements for errors caused by volcanic aerosols, the theoretical model‐based corrections method of DeLuisi et al. (1989) and an empirical method based on use of a composite optical thickness series, are examined and compared. Linear trend models which also include the F10.7 solar flux term to account for solar cycle variations in the Umkehr data were estimated for the Umkehr data at each station using both aerosol error correction methods. The trend and solar flux effect estimates are generally similar for both methods. The results indicate a significant overall negative trend, exclusive of trend variations associated with solar flux variations, of the order of −0.5% per year in Umkehr layers 7–9 over the period 1977–1987, and a significant positive solar cycle association in all layers 4–9, with the maximum solar effect estimated to occur in layer 9. A comparison between the solar backscattered ultraviolet (SBUV) monthly average ozone profile data near the 10 Umkehr stations and the corresponding Umkehr data corrected for aerosol errors is performed to investigate possible drifts, and linear drifts are estimated for the differences between SBUV and corrected Umkehr data at each station. The results show a substantial overall negative linear drift in SBUV data relative to corrected Umkehr data in layers 7–9, with estimated values of the drift of the order of −1.0% per year for layers 8 and 9.
Antarctic stratospheric ice crystals
Authors: Goodman J. , Toon O. B. , Pueschel R. F. , Snetsinger K. G. , Verma S.
Published: February 2008

Ice crystals were replicated over the Palmer Peninsula at approximately 72°S on six occasions during the 1987 Airborne Antarctic Ozone Experiment. The sampling altitude was between 12.5 and 18.5 km (45–65 thousand ft pressure altitude) with the temperature between 190 and 201 K. The atmosphere was subsaturated with respect to ice in all cases. The collected crystals were predominantly solid and hollow columns. The largest crystals were sampled at lower altitudes where the potential temperature was below 400 K. While the crystals were larger than anticipated, their low concentration results in a total surface area that is less than one tenth of the total aerosol surface area. The large ice crystals may play an important role in the observed stratospheric dehydration processes through sedimentation. Evidence of scavenging of submicron particles further suggests that the ice crystals may be effective in the removal of stratospheric chemicals.
In situ ozone measurements within the 1987 Antarctic ozone hole from a high‐altitude ER‐2 aircraft
Authors: Proffitt M. H. , Steinkamp M. J. , Powell J. A. , McLaughlin R. J. , Mills O. A. , Schmeltekopf A. L. , Thompson T. L. , Tuck A. F. , Tyler T. , Winkler R. H. , Chan K. R.
Published: February 2008

In situ ozone measurements were made from the ER‐2 aircraft during the 1987 Airborne Antarctic Ozone Experiment both inside and outside the ozone hole. Midday measurements from late August until late September during aircraft ascent near 53°S latitude indicate no clear temporal trend in ozone mixing ratio but instead reflect the distance of the measurement from the chemically perturbed region. The measurements made within the ozone hole at 72°S show altitude dependent decreases in ozone of 61% at a potential temperature of 425 K down to 39% at 365 K. Temporal trends are also calculated at various positions relative to the boundary of the chemically perturbed region to locate the region of large ozone decreases and thereby accurately locate the boundary of the ozone hole.
Airborne measurements of stratospheric constituents over Antarctica in the Austral Spring, 1987: 2. Halogen and nitrogen trace gases
Authors: Coffey M. T. , Mankin William G. , Goldman Aaron
Published: February 2008

We have used a Fourier transform spectrometer aboard the NASA DC‐8 aircraft during the Airborne Antarctic Ozone Experiment to record infrared absorption spectra of the polar stratosphere. From these high‐resolution spectra we derived vertical column amounts above flight altitude of HCl, HF, NO, NO2, ClONO2, and HNO3 for 10 flights poleward of 60°S. Within the polar vortex, where low values of total ozone are observed during the latter part of the observation period, we observed markedly reduced columns of HCl, NO2, and HNO3. HCl values in the vortex were in the range of 3–9 × 1014 molecules cm−2, compared with values around 15–20 × 1014 molecules cm−2 in mid‐latitudes and ∼30×1014 molecules cm−2 in high northern latitudes. The ratio of HCl to HF was also abnormally low, implying that the HCl had been chemically or physically removed, rather than simply being redistributed by atmospheric motion. NO2 values within the inner vortex were near 5.0×1014 molecules cm−2, about a factor of 4 less than columns outside the vortex boundary. HNO3 values were lower by a factor of 3 within the vortex, compared with a column of approximately 15×1015 molecules cm−2 outside the vortex. HNO3 columns outside the vortex are similar to northern hemisphere values. The ClONO2 column was relatively large within the vortex, peaking at ∼30×1014 molecules cm−2 near the boundary of the vortex. An upper limit of ∼8×1014 molecules cm−2 is placed on the column amount of HOCl inside the vortex.
HNO3 and HCl amounts over McMurdo during the spring of 1987
Authors: Murcray Frank J. , Goldman Aaron , Blatherwick Ronald , Matthews Andrew , Jones Nicholas
Published: February 2008

Infrared solar spectra were obtained from the ground at McMurdo, Antarctica, during September and October 1987. Absorption features due to HNO3 and HCl have been analyzed to determine the vertical column content of these compounds for the days when observations were made. The variation of these column amounts with time is presented and discussed.