bluuebunny/crossref_metadata_2025 huggingface dataset:
Stable isotope composition of waters in southeastern California 1. Modern precipitation
Authors: Friedman Irving , Smith George I. , Gleason Jim D. , Warden Augusta , Harris Joyce M.
Published: February 2012

Over a 7‐year period from April 1982 to April 1989, integrated samples of rain and snow were collected at 32 sites by oil‐sealed storage gage stations in (and adjoining) the southeast California desert; station elevations ranged from −65 m to 2280 m, and the collection network covered an area measuring about 400 km in each dimension. Deuterium (δD) analysis of 406 samples shows that the average δD of summer precipitation was −56 per mil (‰) whereas winter values averaged −78‰, averaged annual values were close to −69‰ because most of the area is in a winter‐dominated precipitation regime. We found no correlation between wetness or dryness of a season and the δD of its precipitation. The δ18O versus δD plots show that rain samples define a line of slope 6.5, less than the 8 of the Meteoric Water Line, whereas snow samples define a line of slope 9.2. These differences in slope are the result of isotopic fractionation which occurred during evaporation of raindrops but not during sublimation of snow. Trajectory plots of 68 of the major storm events show that all of the winter storms originated in the Pacific, and passed over high mountains before reaching our collection stations. However, 21 of the 30 summer storms had trajectories that originated either over the Gulf of Mexico or the subtropical Pacific and traveled either west or north to reach our stations, without traversing high mountains. The difference in δD between winter and summer precipitation is due to different air flow patterns during those seasons.
Global aspects of the Los Alamos general circulation model hydrologic cycle
Authors: Roads J. O. , Chen S.‐C. , Kao J. , Langley D. , Glatzmater G.
Published: February 2012

The global hydrologic cycle in the Los Alamos general circulation model (GCM) is compared to available global observations. Global observations of the water vapor, water‐vapor flux and water‐vapor flux divergence are derived from the National Meteorological Center's final analysis for the period 1986–1989. The new precipitation data set of Legates and Willmott (1990) is used for the global precipitation observations. Global evaporation is derived as a residual of the precipitation and water‐vapor flux divergence. There are a number of similarities as well as discrepancies between the GCM and observations. The large‐scale nondivergent and divergent GCM circulations are remarkably similar to the observed circulations; the large‐scale GCM precipitation and evaporation patterns are also qualitatively similar to observations. Discrepancies are mainly quantitative and small‐scale in nature: the GCM atmosphere is relatively dry which results in a slightly greater evaporation and precipitation rate than is observed; the GCM South Pacific convergence zone is displaced too far to the northwest.
Diurnal HO2 cycles at clean air and urban sites in the troposphere
Authors: Hard T. M. , Chan C. Y. , Mehrabzadeh A. A. , O'Brien R. J.
Published: February 2012

We have determined HO2 concentrations at two Oregon sites for continuous periods of 36 to 48 hours, using fluorescence assay with gas expansion. At the sea level coastal site (45°N 124°W), NNW winds prevailed during daytime, and a point measurement of very low total nonmethane hydrocarbon concentration indicated the presence of remote tropospheric air of oceanic origin. At the urban site, HO2 was determined during moderately low ozone pollution levels. At both sites, maximum daily [HO2] was in the range of 1–2 × 108 cm−3 under clear‐sky conditions, with an estimated overall uncertainty of 40%. HO2 was detected by continuous low‐pressure sampling with flowing chemical conversion to HO, which was detected by laser‐excited fluorescence. The instrumental response to HO2 was calibrated by the self‐decay of HO2 at atmospheric pressure. Interference in the measured daytime HO2 concentrations by RO2 was estimated at less than 20%.
Hydrogen peroxide retention in rime ice
Authors: Snider Jefferson R. , Montague Derek C. , Vali Gabor
Published: February 2012

The extent to which H2O2 dissolved in cloud droplets is trapped in rime ice affects the composition of precipitation and the rate of H2O2 removal from the atmosphere. Measurements were conducted in winter stratiform clouds at a remote mountain‐top site in southeastern Wyoming, thus avoiding the difficulties of preparing laboratory clouds whose chemical and physical properties are similar to natural clouds. Quantities directly observed were H2O2 concentrations in cloud water collected as rime, air temperature, gaseous H2O2, O3, and SO2, and cloud liquid water concentration. Values of the retention coefficient, Γ, defined as the ratio of the H2O2 concentration in the melted rime sample divided by the equilibrium concentration in the supercooled droplets, were always less than unity
. Corrections to account for the rapid reaction between dissolved H2O2 and sulfur(IV) increase the average value of the retention coefficient to only 0.30. An observed correlation between Γ and riming rate suggests that H2O2 is released to the gas phase during riming. These field measurements do not agree with laboratory determinations of Γ.
Application of self‐preservation in the diurnal evolution of the surface energy budget to determine daily evaporation
Authors: Brutsaert Wilfried , Sugita Michiaki
Published: February 2012

Evaporation from natural land surfaces often exhibits a strong variation during the course of a day, mostly in response to the daily variation of radiative energy input at the surface. This makes it difficult to derive the total daily evaporation, when only one or a few instantaneous estimates of evaporation are available. It is often possible to resolve this difficulty by assuming self‐preservation in the diurnal evolution of the surface energy budget. Thus if the relative partition of total incoming energy flux among the different components remains the same, the ratio of latent heat flux (LE) and any other flux component can be taken as constant through the day. This concept of constant flux ratios is tested by means of data obtained during the First ISLSCP Field Experiment (FIFE); the instantaneous evaporation values were calculated by means of the atmospheric boundary layer (ABL) bulk similarity approach with radiosonde profiles and radiative surface temperatures. Good results were obtained for evaporative flux ratios with available energy flux (LE/(Rn ‐ G)), with net radiation (LE/Rn), and with incoming shortwave radiation (LE/S ↓).
Comparison of surface fluxes and conductances at two contrasting sites within the FIFE area
Authors: Stewart J. B. , Verma S. B.
Published: February 2012

Surface flux measurements from two contrasting sites within the FIFE study area are analyzed. The seasonal variation of midday latent heat fluxes and surface conductances at the two sites was found to be very similar even though the ratio of their average total leaf area indices was greater than two to one. Concurrent measurements made at another six flat sites within the FIFE area confirmed the independence of latent heat flux with respect to leaf area index. The surface conductance stress function related to specific humidity deficit was the same for the two sites, whereas the solar radiation stress function showed a difference of 30% at a solar radiation input of 300 W m−2 and the soil moisture stress function showed a difference of 16% when half the extractable soil moisture had been taken up. However, when the stress functions were combined to determine the surface conductance, these differences virtually canceled out.
Formaldehyde and hydroperoxides at Mauna Loa Observatory
Authors: Heikes Brian G.
Published: February 2012

Hydrogen peroxide, formaldehyde, and a measure of organic hydroperoxides are presented from the Mauna Loa Observatory Photochemistry Experiment (MLOPEX). MLOPEX was conducted from May 1 to June 4, 1988, at the Mauna Loa Observatory on the island of Hawaii. A modified dual‐enzyme serial‐coil H2O2/ROOH method was used to quantify these species. A second enzyme method was used to measure CH2O. The location and meteorology at the Mauna Loa Observatory site permitted 35 days of measurements to be made in free tropospheric air and in modified marine boundary layer air. Average concentrations of H2O2, ROOH, and CH2O were 1050, 140, and 100 pptv in free tropospheric, or down‐slope air. In upslope air, or modified marine boundary layer air, average concentrations were 900, 150, and 190 pptv. Maximum concentrations for all three species were experienced during a two day “photochemical haze” episode and were 3230, 440, and 450 pptv for H2O2, ROOH, and CH2O. H2O2 was depleted in air which had recently been processed by cloud or precipitation. The measured concentrations of these three species were comparable to prior measurements in “well‐aged” air, but were lower than previous models have predicted. Part of this discrepancy may be due to the treatment of heterogeneous removal processes, dry and wet deposition, in these models. The measured ratio of ROOH to H2O2 is significantly different than present theory predicts, with ROOH as measured being approximately a factor of 5 too low.
Intercomparison results for FIFE flux aircraft
Authors: MacPherson J. I. , Grossman R. L. , Kelly R. D.
Published: February 2012

Three atmospheric research aircraft were used to explore the atmospheric boundary layer during FIFE: the National Research Council of Canada Twin Otter, the National Center for Atmospheric Research (NCAR) King Air, and the University of Wyoming King Air. The aircraft were used to measure the mean and turbulent structure of the boundary layer and its variation with height, time, and space. These measurements are important to FIFE because they are being used to scale up point surface observations to landscape scales and because they can be used to relate satellite radiance measurements to boundary layer processes. Because the aircraft were used in coordinated flight patterns to investigate changes within and between intensive field campaigns, wing‐to‐wing intercomparisons were made so that measurements from one aircraft could be related to another. Intercomparisons were flown on 4 days in 1987 and 3 days in 1989. The eddy correlation measurements of the mixed layer fluxes of moisture and sensible heat were of particular interest to FIFE. Sensible heat fluxes agreed within 15 W m−2 and moisture fluxes agreed within 21 W m−2. Mean wind component differences were within 1.0 m s−1, air temperature within 0.3°C, and mixing ratio within 2 g kg−1. Standard deviations showed similar good agreement, with mean differences generally less than 0.1 m s−1 for the wind components and 0.03°C for potential temperature. Intercomparisons between the NCAR King Air and the Twin Otter showed better agreement in 1989 than in 1987. Overall, the results suggest that data from the FIFE boundary layer aircraft will need little correction to account for instrument biases and spurious fluctuations. Researchers should consider these intercomparison results before using combined sets of boundary layer aircraft data.
Isotope characteristics of meteoric water and groundwater in the Sahelo‐Sudanese zone
Authors: Joseph Alain , Frangi J. Pierre , Aranyossy J. François
Published: February 2012

The stable isotopic concentration (18O and 2H) of water in phreatic aquifers in the Sahelo‐Sudanese zone of Africa is representative of the original mean rainfall contributing to ground water recharge. The isotopic decrease of 18O in the rainwater and groundwater (−0.084 ‰ 100 km−1) showed an east‐west gradient. This suggests a supply of water vapor transported by the zonal flows East African Jet, Tropical Easterly Jet, and Easterly Waves, thus increasing the contribution from the evaporating surfaces of the Indian Ocean in relation to that of the Guinean monsoon. The gradient also indicates the importance of atmospheric recycling of continental water through evapotranspiration. A model of conservation of the isotopic masses is presented which takes into account the return of continental vapor toward the rain‐giving clouds. The remaining fraction of water vapor during the east‐west transit between Djibouti and Dakar is thus determined by evapotranspiration.
Retrieval of precipitation from satellite microwave measurement using both emission and scattering
Authors: Liu Guosheng , Curry Judith A.
Published: February 2012

In this paper an algorithm for retrieving precipitation from Special Sensor Microwave/Imager (SSM/I) satellite microwave data is presented for rainfall occurring over both ocean and land. This algorithm is basically derived from the results of a microwave radiative transfer model of plane‐parallel rain clouds and combines the emission and scattering regimes. The features of the algorithm are as follows: (1) a linear function of horizontally polarized brightness temperature at both 19.35 and 85.5 GHz is used as a parameter to relate rainfall rate, which shows no saturation for rainfall rates up to 50 mm/h; (2) the relationship between the linear function and the rainfall rate is closer to linearity than the relationship between brightness temperature of a single channel and rainfall rate, and therefore the beam‐filling problem is less serious than for single‐channel algorithms; (3) the algorithm includes a correction to a beam‐filing problem that was made on the basis of observational evidence; (4) the threshold for precipitation is derived from the SSM/I data themselves, which includes climatological information; and (5) the algorithm is less sensitive to freezing level height and surface temperature than emission‐based algorithms. Validation of the algorithm is made using surface radar and rain gauge data. The validation shows that rainfall retrievals over ocean are in a satisfactory agreement with the surface observations. Over land, heavy rainfall rate can be detected although the disagreement is significant.
Transport and mixing processes in the lower troposphere over the ocean
Authors: Paluch I. R. , Lenschow D. H. , Hudson J. G. , Pearson R.
Published: February 2012

Aircraft observations during the summer over the eastern Pacific Ocean, ≥400 km offshore, show that the free troposphere has a distinctly nonuniform, layered structure. Analysis of plots of ozone versus total water mixing ratio indicates that the layers typically consist of a mixture of air from several sources: (1) moist, ozone‐depleted boundary layer air, (2) very dry air with high ozone content, which probably originated in the middle or upper troposphere, and (3) air with relatively low ozone and moderate, varying moisture contents, which may represent residues of convective clouds that had formed over the ocean upstream of the research area. On two research days we also observed what we infer to be continental air. On one day in the usual research area we encountered air with elevated concentrations of aerosols whose trajectories, traced backward in time, indicated that it had passed over the Alaskan continent. On another day, when soundings were made about 100 km off the California coast, we observed a layer just above the marine inversion containing unusually high amounts of ozone, aerosols, and moisture. This layer probably represents a direct intrusion of polluted air from the coast, which could have been the result of baroclinic flow associated with boundary layer warming over land. Over the eastern Pacific Ocean in summer the subtropical high results in stably stratified, subsiding air, where discrete horizontal layers with differing flow velocities transport air over long distances with little vertical mixing. Here, localized large‐scale flows (such as tropospheric folding, deep convection, or baroclinic flow from coastal areas) “inject” air of different properties at various levels in the lower troposphere. This air is then subject to buoyancy sorting and differential advection. Because the lower troposphere is very stably stratified, the mixing eddies are small compared to the air mass size, and small‐scale turbulent diffusion is slow. Here, wind shear plays an important role through stretching and thinning the different air masses until small‐scale diffusion completes the mixing process.
Delta‐Eddington approximation for solar radiation in the NCAR community climate model
Authors: Briegleb Bruce P.
Published: February 2012

Motivated by the desire for a more flexible and general solar radiation calculation in the NCAR community climate model (CCM), the δ‐Eddington approximation has been employed in the CCM version 2 (CCM2). Eighteen spectral intervals span the solar spectrum from 0.2 to 5.0 μm. Absorption parameterizations for H2O, O3, CO2, and O2 were developed by making use of the latest theoretical calculations. Water droplet scattering and absorption are parameterized as shown by Slingo (1989). An accurate and efficient convolution of the H2O vapor spectrum with water droplet clouds is presented that yields good agreement with available line‐by‐line (LBL) calculations for single‐layer clouds. A simple and efficient method to simulate partial cloud cover and cloud overlap is included. The simulated albedo‐solar zenith angle dependence agrees very well with adding/doubling scattering calculations. The CCM2 δ‐Eddington method will make possible many interesting applications of CCM2 in the years to come.
Variations in the methanesulfonate to sulfate molar ratio in submicrometer marine aerosol particles over the south Pacific Ocean
Authors: Bates Timothy S. , Calhoun Julie A. , Quinn Patricia K.
Published: February 2012

Seawater concentrations of dimethylsulfide (DMS) and atmospheric concentrations of DMS, sulfur dioxide, methanesulfonate (MSA), and non‐sea‐salt (nss) sulfate were measured over the eastern Pacific Ocean between 105° and 110°W from 20°N to 60°S during February and March 1989. Although the samples collected in the southern hemisphere appear to be of marine origin, no significant correlation was found between the latitudinal distributions of DMS, SO2, MSA, and nss SO4=. However, an inverse correlation (r2 = 0.87) was found between atmospheric temperature and the MSA to nss SO4= molar ratio in submicrometer aerosol particles with a decrease in temperature corresponding to an increase in the molar ratio. Although this trend is consistent with laboratory results indicating the favored production of MSA at lower temperatures, it is contrary to southern hemisphere baseline station data. This suggests either a decrease in the supply of DMS relative to nonmarine sources of nss SO4= at the baseline stations in winter or additional mechanisms that affect the relative production of MSA and nss SO4=.
An inventory of nitric oxide emissions from soils in the United States
Authors: Williams E. J. , Guenther A. , Fehsenfeldi F. C.
Published: February 2012

A national inventory of soil nitric oxide (NO) emissions with county spatial resolution and monthly time resolution has been developed from empirical relationships that were derived from soil NO emissions data. The empirical relationships used to develop the inventory relate the emission of NO to soil temperature and a factor which is representative of an ecosystem or type of land use. Most of the ecosystem/land use factors were derived from analyses of NO emission data from seven different sites in the United States that are representative of three ecosystems and two agricultural land use types. Other agricultural (crop) land use factors were estimated from the two calculated factors based on differences in fertilization associated with the crops. This soil emission inventory exhibits three general features. First, croplands, especially where corn is grown, appear to be significant sources of NO. This has important implications because agricultural activities tend to be localized to certain regions in the United States (i.e., the Midwest) and are highest during the summer, when photochemistry is also most active. Second, undisturbed areas, such as grasslands, forests, and wetlands, do not appear to contribute substantially to atmospheric NO. Third, extensive areas in the western United States have not been included because soil NO emission data are lacking.
Interrelationships between mixing ratios of long‐lived stratospheric constituents
Authors: Plumb R. Alan , Ko Malcolm K. W.
Published: February 2012

Recent analyses have revealed simple relationships between the simultaneously measured mixing ratios of certain stratospheric constituents. In some cases, the relationship appears to be nearly linear, so that measured concentrations of one can be used to predict the other. We argue here that such relationships are to be expected for species of sufficiently long lifetime. Species whose local lifetimes are longer than quasi‐horizontal transport time scales are in climatological slope equilibrium, i.e., they share surfaces of constant mixing ratio, and a scatter plot of the mixing ratio of one versus that of the other collapses to a compact curve whose slope at any point is the ratio of the net global fluxes of the two species through the corresponding surface of constant mixing ratio. Species whose local lifetimes are greater than vertical transport time scales are in gradient equilibrium and their mixing ratios display a linear relationship. For species whose atmospheric lifetimes are determined by removal in the stratosphere, the slope of this relationship in the lower stratosphere can be related to the ratio of their atmospheric lifetimes. These statements are illustrated using results from a two‐dimensional chemistry‐transport model.
A three‐dimensional modeling study of the influence of planetary wave dynamics on polar ozone photochemistry
Authors: Austin John , Butchart Neal
Published: February 2012

The influence of planetary wave dynamics on polar ozone photochemistry is examined using a three‐dimensional model of the stratosphere and lower mesosphere. The model contains a comprehensive range of photochemical reactions and includes heterogeneous reactions and polar ozone chemistry. The model is forced at its lower boundary (316 mbar) with a specified wavenumber one geopotential height field. Idealized experiments are performed using the same zonally symmetric initial conditions but with different wave amplitudes at the lower boundary. The wave amplitudes are chosen to cover the range from a zonally symmetric integration, through typical southern hemisphere wave amplitudes to typical northern hemisphere springtime amplitudes. In each experiment the model is integrated for 100 days covering the winter and springtime period during which the Antarctic ozone hole is observed to develop and partially recover. The modeled ozone amounts over the polar region in these experiments show a considerable sensitivity to the planetary wave forcing. With small‐amplitude forcing, substantial ozone depletion occurs and continues until the end of the integration (equivalent to early November in the southern hemisphere). For medium‐amplitude forcing, substantial ozone destruction is followed by a recovery in the column amount after a time corresponding approximately to the middle of October. For the largest amplitude forcing, little ozone depletion occurs. These results are broadly consistent with the known phenomenology of polar ozone chemistry in both northern and southern hemispheres. An analysis of the mechanisms through which planetary wave amplitudes influence polar ozone chemistry in these experiments is presented. In particular, wave‐induced mean descent over the whole polar region is identified as an important ingredient for determining the different behavior of polar ozone in the experiments.
Characterization of atmospheric aerosols and of suspended particles in seawater in the western Pacific Ocean
Authors: Zhou Mingyu , Lu Naiping , Miller John , Parungo Farn P. , Nagamoto Clarence , Yang Shao‐Jing
Published: February 2012

Aerosol samples were collected to study the variabilities of marine aerosols at different times and in different ocean areas. The samples were collected during the first three cruises (December 12, 1985, to February 21, 1986; November 11, 1986, to March 1, 1987; September 27 to November 4, 1987) operated by the cooperative program between the United States and the People's Republic of China. The concentrations of crustal and pollution elements in aerosols were high over the ocean area close to the China coast and decreased very rapidly with increasing distance from land. For the third cruise, in the ocean area northeast of the Philippines, the concentrations of crustal and pollution elements in aerosols were high, especially Fe, whose values reached 3.15 × 10−5 g m−3. For all three cruises, the mass size distributions of crustal elements and pollution elements in aerosols showed more large particles. The morphology and elemental composition of aerosol particles showed that sea‐salt particles may conglomerate with small crustal and pollution particles from land to form large particles. The size distributions of suspended particles (d > 0.3 μm) in surface seawater approximately fitted the Junge size distribution. The concentration of suspended particles in surface seawater decreased with increasing distance from land except at the equator, where particle concentrations were high. In addition, results from rain chemistry show that the relative importance between wet deposition and dry deposition varies with trace elements.
On the relative importance of quasi‐biennial oscillation and El Nino/Southern Oscillation in the revised Dobson total ozone records
Authors: Zerefos Christos S. , Bais Alkiviadis F. , Ziomas Ioannis C. , Bojkov Rumen D.
Published: February 2012

The interannual variability of the ozone layer is studied with the largest available revised Dobson (RD) total ozone records through March 1991. The analysis of this new data set, as well as the revised Total Ozone Mapping Spectrometer (TOMS) zonal mean total ozone, shows that the phase of the ozone Quasi‐Biennial Oscillation (QBO) relative to the 50 hPa zonal wind at Singapore varies linearly with latitude, being nearly in‐phase at low latitudes and more symmetric about the equator than published in earlier studies. The phase progression of the QBO is about 2 months per 10 degrees of latitude, ozone following the 50 hPa zonal wind at Singapore. After removing the QBO and solar cycles from the RD total ozone records, a relatively large part of the remaining total ozone variance can be explained by El Nino/Southern Oscillation (ENSO) events in the tropics. It is also shown that only very large ENSO events (1982–1983 and possibly 1972) are followed within a few months time lag by low total ozone values in middle and even higher latitudes. This analysis also shows that at individual stations there are other significant total ozone anomalies which cannot be explained by the QBO or ENSO. Tentative circulational aspects of the ENSO disturbance and its relation to total ozone are also discussed.
Lightning subsequent‐stroke electric field peak greater than the first stroke peak and multiple ground terminations
Authors: Thottappillil R. , Rakov V. A. , Uman M. A. , Beasley W. H. , Master M. J. , Shelukhin D. V.
Published: February 2012

For 46 multiple‐stroke flashes in which each stroke ground termination was located using a TV camera network and thunder ranging, 15 flashes (33%) had one or more subsequent return strokes whose initial electric field peak normalized to 100 km was greater than the first‐stroke field peak of the flash. In 9 of these 15 flashes the subsequent strokes with field peaks greater than the first stroke followed the same channel as the first stroke; in five flashes the subsequent strokes with the greater peaks followed a different channel to ground; and in one flash the subsequent strokes with the greater peaks occurred both in the first‐stroke channel and in a different channel. The interstroke intervals immediately preceding the 13 larger subsequent strokes that followed the first‐stroke channel had a geometric mean (GM) duration of 98 ms, 1.7 times greater than the GM of 57 ms for all 199 interstroke intervals (46 flashes) without any selection. Eight of the 13 larger subsequent strokes for which leader durations were measurable had a GM leader duration of 0.55 ms, 3.3 times smaller than the GM of 1.8 ms for 117 subsequent leaders with measurable duration in a previously formed channel of the 46 multiple‐stroke flashes. For the six larger subsequent strokes that created a new channel to ground, the preceding interstroke interval had a GM of 130 ms, and the leader duration had a GM of 15 ms. No subsequent stroke with peak field exceeding the first in any category had a preceding interstroke interval less than 35 ms. Analysis of direct current measurements from Switzerland shows that subsequent‐stroke currents exhibit many features similar to those of Florida subsequent‐stroke electric fields. In 22 Florida single‐stroke and multiple‐stroke ground flashes the distances between multiple channel terminations in a given flash (33 measurements) ranged from 0.3 km to 7.3 km, with a GM of 1.7 km.
Observed dart leader speed in natural and triggered lightning
Authors: Jordan Douglas M. , Idone Vincent P. , Rakov Vladimir A. , Uman Martin A. , Beasley William H. , Jurenka Henry
Published: February 2012

From a data base consisting of (1) correlated optical and electric field measurements for 11 natural lightning strokes in Florida, (2) correlated optical and current measurements for 32 artificially initiated (triggered) lightning strokes in New Mexico, and (3) correlated optical and current measurements for 36 triggered lightning strokes in Florida, dart leader speed is examined as a function of the following return stroke initial electric field peak, of the following return stroke current peak, and of the duration of the previous interstroke interval (excluding the duration of continuing current, if present). Return stroke current peaks in both New Mexico and Florida triggered lightning were converted to electric field peaks via the field‐current regression equation obtained by Willett et al. (1989), while the electric field peaks in Florida natural lightning were converted to current peaks using the current‐field regression equation derived by Rakov et al. (1992), both formulas being based on the same Florida triggered lightning measurements. For each of the three data sets, dart leader speed and the following return stroke field peak or current peak are positively correlated. The relations between leader speed and field or current peak for Florida triggered and Florida natural lightning are similar, possibly indicating a similarity between at least some features of dart leaders and return strokes in natural and in triggered lightning at the same geographic location. On the other hand, leaders in New Mexico triggered lightning are, for the same value of return stroke field or current peak, about twice as fast as those in both triggered and natural lightning in Florida, the difference being likely associated with the relatively short preceding interstroke intervals in New Mexico triggered lightning. For all triggered and natural lightning data taken together, there is a weak but statistically significant tendency for lower leader speed to be associated with a longer previous interstroke interval. However, neither the New Mexico triggered lightning data nor the Florida triggered lightning data, when taken separately, show this tendency.
Odd oxygen formation in the laser irradiation of O2 at 248 nm: Evidence for reactions of O2 in the Herzberg states with ground state O2
Authors: Shi Jichun , Barker John R.
Published: February 2012

Although the 248‐nm KrF laser photon energy is less than the O2 dissociation energy by about 0.12 eV, O3 is still produced in the laser irradiation of O2 at this wavelength. The O3 is produced by two processes: an initiation process and an autocatalytic process. In the present work, these two O3 formation processes have been studied in pure O2 and in O2+N2 and O2+Ar mixtures at pressures between 200 and 1600 torr and at temperatures between 298 and 370°K. Evidence is presented that the initiation process produces O3 through chemical reactions between ground state O2 and excited O2 in the Herzberg states (A3Σu+, A′3Δu and c1Σu−), which are produced by the photoabsorption of O2 at 248‐nm. For the autocatalytic process, the results are consistent with the proposal that the O3 formation is accelerated by photodissociating vibrationally excited O2(ν), produced in the photolysis of O3 following its initial formation. Both the O2 Herzberg states and O2(ν) may play important roles in the odd oxygen (Ox) chemistry in the middle atmosphere. It is estimated in the present work that the O2(A3Σu+)+O2 reaction may yield up to ∼6% of the total odd oxygen production rate near 50 km; this odd oxygen source is not included in current photochemical models.
A 2XCO2 climate change scenario over Europe generated using a limited area model nested in a general circulation model: 1. Present‐day seasonal climate simulation
Authors: Marinucci M. R. , Giorgi F.
Published: February 2012

In this and the companion paper by Giorgi et al. (this issue) we present a regional climate change scenario for Europe and the western Mediterranean basin induced by doubling of carbon dioxide concentration as produced with a limited area model (LAM) nested in a general circulation model (GCM). In this paper we analyze the seasonal climatology of the present‐day climate simulation which is used as a control run in the generation of the scenario. The GCM and the LAM employed for this study are versions of the community climate model (CCM) of the National Center for Atmospheric Research (NCAR) and the NCAR/Pennsylvania State University mesoscale model (MM4). The CCM simulation generally reproduces the basic seasonal migration patterns of the storm tracks which affect the European region but also shows significant biases: (1) a general weakening and southward shift of the cold season North Atlantic jet; (2) cold sea surface temperature bias of up to 4°–6°C in the North Atlantic and the Mediterranean; (3) cold tropospheric temperature bias of several degrees; (4) low tropospheric relative humidity bias; and (5) underprediction of July precipitation, resulting in low soil moisture conditions and exceedingly high surface temperatures. Overall, the nested MM4 produces large‐scale circulations similar to those of the driving CCM and, because of its finer representation of topography and coastlines, substantially improves the spatial distribution of precipitation and surface air temperature not only at high resolution but also at resolutions close to the CCM's. Among the main biases in the nested MM4 simulation are (1) cold bias over land of 1°–5°C in January, April, and October and warm bias in July; (2) underprediction of precipitation over most of continental Europe, maximum in July (simulated precipitation is 60–80% lower than observed) and less pronounced in January, April, and October (simulated precipitation is 10–40% lower than observed). A strong contribution to these biases is given by errors in the driving CCM tropospheric fields. Overall, temperature and precipitation are better simulated in the colder seasons than in summertime and the seasonal cycle is captured better over the Mediterranean regions than over the continental interior.
Modeling a case of particle nucleation in the marine boundary layer
Authors: Hegg Dean A. , Covert David S. , Kapustin Vladimir N.
Published: February 2012

A diagnostic modeling study is performed on a hypothesized case of particle nucleation in the marine boundary layer. A three‐mode integral nucleation model is used and predicts particle concentrations in accord with observations when initialized with the appropriate field measurements. Further analysis of the data suggests the conditions favorable for nucleation at the surface were due to mixing of air at the top of the boundary layer down to the surface.
Polynomial coefficients for calculating O2 Schumann‐Runge cross sections at 0.5 cm−1 resolution
Authors: Minschwaner K. , Anderson G. P. , Hall L. A. , Yoshino K.
Published: February 2012

We have fitted O2 cross sections from 49,000 to 57,000 cm−1 with temperature dependent polynomial expressions, providing an accurate and efficient means of determining Schumann‐Runge band cross sections for temperatures 130<T<500 K. The least squares fits were carried out on a 0.5 cm−1 spectral grid, using cross sections obtained from a Schumann‐Runge line‐by‐line model that incorporates the most recent spectroscopic data. The O2 cross sections do not include the underlying Herzberg continuum, but they do contain contributions from the temperature dependent Schumann‐Runge continuum. The cross sections are suitable for use in ultraviolet transmission calculations at high spectral resolution. They should also prove useful for updating existing parameterizations of ultraviolet transmission and O2 photolysis.
A global inventory of volatile organic compound emissions from anthropogenic sources
Authors: Piccot Stephen D. , Watson Joel J. , Jones Julian W.
Published: February 2012

As part of an effort to assess the potential impacts associated with global climate change, the U.S. Environmental Protection Agency's Office of Research and Development is supporting global atmospheric chemistry research by developing global scale estimates of volatile organic compound (VOC) emissions (excluding methane). Atmospheric chemistry models require, as one input, an emissions inventory of VOCs. Consequently, a global inventory of anthropogenic VOC emissions has been developed. The inventory includes VOC estimates for seven classes of VOCs: paraffins, olefins, aromatics (benzene, toluene, xylene), formaldehyde, other aldehydes, other aromatics, and marginally reactive compounds. These classes represent general classes of VOC compounds which possess different chemical reactivities in the atmosphere. The technical approach used to develop this inventory involved four major steps. The first step was to identify the major anthropogenic sources of VOC emissions in the United States and to group these sources into 28 general source groups. Source groups were developed to represent general categories such as “sources associated with oil and natural gas production” and more specific categories such as savanna buming. Emission factors for these source groups were then developed using different techniques and data bases. For example, emission factors for oil and natural gas production were estimated by dividing the United States' emissions from oil and gas production operations by the amount of oil and natural gas produced in the United States. Multiplication of these emission factors by production/consumption statistics for other countries yielded global VOC emission estimates for specific source groups within those countries. The final step in development of the VOC inventory was to distribute emissions into 10° by 10° grid cells using detailed maps of population and industrial activity. The results of this study show total global anthropogenic VOC emissions of about 110,000 Gg/yr. This estimate is about 10% lower than global VOC inventories developed by other researchers. The study identifies the United States as the largest emitter (21% of the total global VOC), followed by the (former) USSR, China, India, and Japan. Globally, fuel wood combustion and savanna burning were among the largest VOC emission sources, accounting for over 35% of the total global VOC emissions. The production and use of gasoline, refuse disposal activities, and organic chemical and rubber manufacturing were also found to be significant sources of VOC emissions.
On the empirical formula of Willett et al. relating lightning return‐stroke peak current and peak electric field
Authors: Rakov Vladimir A. , Thottappillil Rajeev , Uman Martin A.
Published: February 2012

The empirical formula proposed by Willett et al. (1989) for the estimation of lightning return‐stroke peak current, I, from measured peak electric field, E, at a range D, is analyzed and discussed. The formula of Willett et al. (1989), obtained from the regression of E on I, is not the least squares fit and hence is not the best expression for predicting the peak current from the measured peak electric field. Based on the same data, the least squares fit and, hence, the best expression is obtained from the regression of I on E, given by I = 1.5 − 0.037DE, where I is in kA and taken as negative, E is positive and in V/m, and D is in km. The Willett et al. (1989) formula results in an error with respect to the best peak current estimating expression that varies from −15% to +2.6% over the range of peak field values of 1.9 to 11 V/m (normalized to 100 km) used to derive the two relations. When the data of Willett et al. (1989) are separated into a high returnstroke speed group (1.5 × 108 to 1.9 × 108 m/s) and a low return‐stroke speed group (1.2 × 108 to 1.4 × 108 m/s), the I‐E regression lines differ for the two groups, with the difference in the regression line slopes being statistically significant at the 0.01 significance level. If the difference between intercepts of these two regression lines, found to be statistically insignificant, is neglected, the observed difference in slopes suggests that the group with the higher measured return‐stroke speed is associated with a lower peak electric field for the same peak current. Finally, the practical applications of the Willett et al. (1989) formula presently found in the literature are reviewed, and the several cases of improper use, mostly related to misinterpretation of Willett et al. 's (1989) sign convention, are corrected.
Some results from an intercomparison of the climates simulated by 14 atmospheric general circulation models
Authors: Boer G. J. , Arpe K. , Blackburn M. , Déqué M. , Gates W. L. , Hart T. L. , le Treut H. , Roeckner E. , Sheinin D. A. , Simmonds I. , Smith R. N. B. , Tokioka T. , Wetherald R. T. , Williamson D.
Published: February 2012

Some climatological information from 14 atmospheric general circulation models is presented and compared in order to assess the ability of a broad group of models to simulate current climate. The quantities considered are cross sections of temperature, zonal wind, and meridional stream function together with latitudinal distributions of mean sea level pressure and precipitation rate. The nature of the deficiencies in the simulated climates that are common to all models and those which differ among models is investigated; the general improvement in the ability of models to simulate certain aspects of the climate is shown; consideration is given to the effect of increasing resolution on simulated climate; and approaches to understanding and reducing model deficiencies are discussed. The information presented here is a subset of a more voluminous compilation which is available in report form (Boer et al., 1991). This report contains essentially the same text, but results from all 14 models are presented together with additional results in the form of geographical distributions of surface variables and certain difference statistics.
Sources of atmospheric CH4 in early postglacial time
Authors: Nisbet E. G.
Published: February 2012

At the terminations that marked the ends of the Oldest and Younger Dryas, at the close of the last major glaciation, atmospheric methane levels rose sharply. Biological sources may have played a part in this increase, but it is unlikely that they could have accounted for the suddenness of the rise in methane production. Some fossil methane stores, such as marine and continental hydrates, may have become unstable at the time of the terminations, and there is much geological evidence that many catastrophic releases of methane occurred. It is possible that part of the increase in global atmospheric methane may have been the result of these releases, which may also have played a partial role in recharging the inventory of carbon in the atmosphere‐biosphere system. The Younger Dryas cooling may represent a transient response to a later reduction in greenhouse forcing when the CH4 mixing ratio in the atmosphere dropped. This transient response would have been more marked in the northern hemisphere than in the southern. The termination of the Younger Dryas may have occurred after a further catastrophic release of fossil methane.
The ring effect in the sodium D2 Fraunhofer line of day skylight over Mawson, Antarctica
Authors: Conde M. , Greet P. , Jacka F.
Published: February 2012

A dual, scanning Fabry‐Perot spectrometer at Mawson, Antarctica (67.6°S, 62.9°E), was used to obtain simultaneous direct solar and daytime sky spectra of the sodium D2 Fraunhofer absorption line at λ589 nm. The intensity of the Ring component of skylight was determined from these spectra. Our observations indicated that the absolute intensity of this component varied diurnally, maximizing at local noon. Observations over ice and snow gave greater absolute Ring intensities than those over open water. Fractional Ring intensities were typically 6% of the adjacent day sky continuum. During full daylight, no significant variation in fractional Ring intensity was observed with changing solar zenith angle; sharp increases were observed during twilight. These observations are consistent with inelastic molecular scattering in the atmosphere being the cause of the Ring effect.
The Kuwait oil fires as seen by Landsat
Authors: Cahalan Robert F.
Published: February 2012

A mosaic of two Landsat thematic mapper images acquired May 30, 1991, reveals a dark smoke plume 30–60 km wide extending hundreds of kilometers south of Kuwait City along the Persian Gulf. Smoke coming from the Raudhatain and Sabriyah oil fields blew across the Gulf of Kuwait and over Kuwait City, joined with smoke from the Greater Burgan and Minagish fields, and continued southward over smaller villages and regions of desert agriculture consisting of hundreds of axially irrigated fields in both Kuwait and Saudi Arabia. One agricultural region in Kuwait was completely obscured by the smoke. The light colored limestone gravel and sand surface was darkened by oil lakes near the wells, and by oil drizzling out of the plume downwind of the wells. Most fires produced either a light or dark plume, and the separate plumes mixed to form a combined plume much darker than the land surface, but slightly more reflective than the Gulf waters. A few of the hottest fires had no visible plume, and are presumably associated with methane combustion. The last of the Kuwait fires was reportedly extinguished in November of 1991. Continued monitoring is needed to assess the impact of emissions from both burning and nonburning oil wells on the region's climate, as well as on the agriculture, fishing, and other activities essential to life in the region.
Longwave band model for thermal radiation in climate studies
Authors: Briegleb B. P.
Published: February 2012

To accurately simulate the present Earth climate requires an atmospheric longwave radiation model whose computed fluxes agree to within ±1% of the only presently available standard, line by line (LBL) calculations. This standard derives from the agreement to within ±1% of various LBL calculations (Luther et al., 1988). To model potential future climate change requires an atmospheric longwave radiation model that can easily incorporate many trace gases. To meet these requirements, a longwave band model of 100 cm−1 resolution is presented. Random band model transmissions are modified to account for overabsorption compared to LBL calculations, with empirical coefficients chosen to give good agreement with LBL spectral fluxes. The longwave band model (LWBM) integrated fluxes agree to within ±1% of LBL fluxes, while heating rates agree to within ±5%. The LWBM is used in the National Center for Atmospheric Research Community Climate Model Version 1 to compute longwave radiation. It is demonstrated that by not including minor bands of CO2 and O3, other trace gases (CH4, N2O, CFCl3, CF2Cl2), or nonblack surface emissivity effects results in a significant bias in tropical clear‐sky outgoing longwave radiation of 8–10 W m−2 over oceans and up to 15 W m−2 over sandy deserts.