bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of stratospheric winds and temperatures produced by data assimilation
Authors: Coy Lawrence , Swinbank Richard
Published: February 2004

Data assimilation is a vital technique in modern meteorology, allowing information from a wide range of observations to be combined to produce synoptic analyses of the atmospheric circulation. Data assimilation has a number of advantages over conventional analysis methods that stem from the use of a numerical model of the atmosphere as an integral part of the technique. The model provides a framework which allows information from observations to be combined with our understanding of the atmosphere, as embodied in the model, so that a consistent, evolving, three‐dimensional picture of the atmospheric circulation may be constructed. The aim of this paper is to compare results from two different stratospheric data assimilation systems (from Goddard Space Flight Center and the U.K. Meteorological Office) to assess the reliability of analyses derived by using assimilation techniques. In particular, this paper concentrates on assessing the quality of the analyses for long‐term transport studies. First, the zonal mean circulations are compared, with emphasis on the consistency of the residual circulation. Second, horizontal transport processes are compared, with particular emphasis on the representation of features in the neighborhood of the wintertime polar vortex. It is shown that the two analyses give a broadly consistent picture of the atmospheric circulation. Where differences are identified, they can often be attributed to particular shortcomings in one of the assimilation systems. The results presented here stress the usefulness of data assimilation for stratospheric studies.
OH photochemistry and methane sulfonic acid formation in the coastal Antarctic boundary layer
Authors: Jefferson A. , Tanner D. J. , Eisele F. L. , Davis D. D. , Chen G. , Crawford J. , Huey J. W. , Torres A. L. , Berresheim H.
Published: February 2004

Studies of dimethylsulfide (DMS) oxidation chemistry were conducted at Palmer Station on Anvers Island, Antarctica, during the austral summer of 1993/1994. Part of the study involved gas phase measurements of OH, methane sulfonic acid (MSA), and H2SO4 using a chemical ionization mass spectrometer, as well as measurements of the NO, CO, and O3 concentrations. Mean 24 hour concentrations from February 16–23 of OH, MSA, and H2SO4 were 1.1 × 105, 9.5 × 105, and 1.61 × 106 molecules cm−3, respectively. Model calculations of OH compared well with observed levels (e.g., within 30%). The modeling results suggest that the dominant source of OH is from the reaction of O(1D) with H2O, where O(1D) is the product of O3 photolysis. Because of the clean atmospheric environment and predicted low nonmethyl hydrocarbon levels in Antarctica, the dominant OH sink was found to be reaction with CO and CH4. Particulate levels of MSA were higher than could be attributed to condensation of boundary layer (BL) gas phase MSA on to the aerosol surface. Alternate mechanisms for generating MSA in the particle phase were speculated to involve either in‐cloud oxidation of dimethylsulfoxide or OH oxidation of DMS in the atmospheric buffer layer above the boundary layer followed by condensation of gas phase MSA on aerosols and transport back to the BL [Davis et al., this issue].
Total ozone series at Arosa (Switzerland): Homogenization and data comparison
Authors: Staehelin Johannes , Renaud Anne , Bader Jürg , McPeters Richard , Viatte Pierre , Hoegger Bruno , Bugnion Veronique , Giroud Marianne , Schill Herbert
Published: February 2004

Five Dobson and two Brewer spectrophotometers were used for total ozone observations at Arosa, beginning in 1926 and providing the world's longest series. In this paper we present the results of our attempts to provide a homogeneous series and discuss the data quality problems of the record. From the mid‐1950s to 1992, Dobson instrument D15 was calibrated by the statistical Langley plot method. In 1986 the calibration of another Dobson spectrometer at Arosa (D101) was changed by the intercomparison with the primary world Dobson instrument (D83). A statistical model based on simultaneous measurements of D101 and D15 of the period from 1987 to 1990 was used to obtain a total ozone series in line with the primary Dobson spectrophotometer, including a correction for an optical disalignment problem of D15. The series of Dl0l from 1990 to 1995 was corrected on the basis of data from the Dobson intercomparisons of 1990 and 1995 and comparisons with other total ozone measurements of Brewer and Dobson spectrophotometers at Arosa. A transfer function between Dobson and Brewer spectrophotometric measurements of Arosa is presented, and total ozone measurements of Arosa are compared with version 7 daily overpass data of the satellite instrument the total ozone mapping spectrometer (TOMS) which operated on board Nimbus 7 from autumn 1978 to spring 1993. Available information allowing us to track back the total ozone measurements of Arosa to the measurements of the primary Dobson spectrometer reveal that the total ozone series of Arosa fluctuated no more than approximately 1% against D83 in the period from 1978 to 1995. Average shift of Arosa total ozone data against the TOMS instrument was −1.12 (±0.1)% over the lifetime of the TOMS instrument.
A study of new particle formation and growth involving biogenic and trace gas species measured during ACE 1
Authors: Weber Rodney J. , McMurry Peter H. , Mauldin Lee , Tanner David J. , Eisele Fred L. , Brechtel Fred J. , Kreidenweis Sonia M. , Kok Gregory L. , Schillawski Richard D. , Baumgardner Darrel
Published: February 2004

Measurements are presented of ambient nanoparticle distributions (2.7 to 10 nm diameter) in regions of high biogenic emissions encountered during the First Aerosol Characterization Experiment (ACE 1), November 15 to December 14, 1995. Large numbers of newly formed nanoparticles were observed directly downwind of penguin colonies on Macquarie Island (54.5°S, 159.0°W). In these regions, nanoparticle concentrations were also correlated with sulfuric acid (H2SO4(g)) gas concentrations. The measurements show that biogenic species, possibly ammonia (NH3), either by itself or with H2SO4, nucleated to form new particles at rates much higher than bimolecular H2SO4/H2O nucleation. Nanoparticle distributions evolved as air was advected away from the island showing clear evidence of growth of the newly formed particles. Observed growth rates were in the range of 2 to 5 nm h−1 and were about a factor of 4 to 17 times higher than the growth by condensing H2SO4(g) and associated water. The cause for fast growth of the newly formed particles is unknown.
Measurements of reactive nitrogen in the stratosphere
Authors: Sen B. , Toon G. C. , Osterman G. B. , Blavier J.‐F. , Margitan J. J. , Salawitch R. J. , Yue G. K.
Published: February 2004

We present volume mixing ratio profiles of NO, NO2, HNO3, HNO4, N2O5, and ClNO3 and their composite budget (NOy), from 20 to 39 km, measured remotely in solar occultation by the Jet Propulsion Laboratory MkIV Interferometer during a balloon flight from Fort Sumner, New Mexico (35°N), on September 25, 1993. In general, observed profiles agree well with values calculated using a photochemical steady state model constrained by simultaneous MkIV observations of long‐lived precursors and aerosol surface area from the Stratospheric Aerosol and Gas Experiment II. The measured variation of concentrations of NOx (= NO + NO2) and N2O5 between sunrise and sunset reveals the expected ∼2:1 stoichiometry at all altitudes. Despite relatively good agreement between theory and observation for profiles of NO and HNO3 the observed concentration of NO2 becomes progressively higher than model values below 30 km, with the discrepancy reaching ∼30% at 22 km. This suggests an incomplete understanding of factors that regulate the NO/NO2 and NO2/HNO3 ratios below 30 km. Observations obtained during September 1990, prior to the June 1991 eruption of Mount Pinatubo, as well as during April 1993 and September 1993 provide a test of our understanding of the affect of aerosol surface area on the NOx/NOy ratio at midlatitudes. The observations reveal a decrease in the NOx/NOy ratio for increasing aerosol surface area that is consistent with the heterogeneous hydrolysis of N2O5 being the dominant sink of between altitudes of 18 and 24 km for the conditions encountered (e.g., surface areas as high as 14 μm2 cm−3 and temperatures from 209 to 219 K).
Leader properties determined with triggered lightning techniques
Authors: Lalande P. , Bondiou‐Clergerie A. , Laroche P. , Eybert‐Berard A. , Berlandis J.‐P. , Bador B. , Bonamy A. , Uman M. A. , Rakov V. A.
Published: February 2004

This paper presents current and electric field measurements from two triggered lightning flashes, 9519 and 9516, initiated by the “classical” and “altitude” technique, respectively, at Camp Blanding, Florida, in 1995. The current measurement for flash 9519 shows that the upward positive leader, initiated at the top of the grounded wire unreeled by the triggering rocket, propagates in a discontinuous pattern made of successive current pulses of tens to a few hundreds of amperes and separated by intervals of 20–25 μs. The downward negative leader in flash 9516, initiated from the electrically floating conductor, has a velocity greater than 1.3×105 m s−1, a stepping interval of 18 μs, and step length of about 3–5 m; the associated peak currents inferred from the electric field steps are at least 600 A.
Radiative forcing due to tropospheric ozone and sulfate aerosols
Authors: van Dorland Rob , Dentener Frank J. , Lelieveld Jos
Published: February 2004

The radiative forcing due to tropospheric ozone and sulfate aerosol changes is evaluated using a radiative wideband model. The concentration fields of these constituents and their precursors on a 10°×10° grid are computed with a three‐dimensional transport/chemistry model of the troposphere (MOGUNTIA) for the preindustrial (1850) case, the contemporary atmosphere (1990) and for the future (2050). We find global and annual average radiative forcings over the industrial period (1850–1990) of 0.38 W m−2 and −0.36 W m−2 for tropospheric ozone and sulfate aerosol changes, respectively. These values indicate an approximate balance, which is also due to the fact that both constituents are confined to specific regions since their atmospheric residence times are relatively short, albeit that ozone changes are more zonally dispersed. However, both constituents have characteristic seasonal cycles, and their forcing dependencies on several radiative parameters are quite different. The longwave as well as the shortwave sensitivities are examined so as to estimate the uncertainty ranges of the computed radiative forcings. Subsequently, we present analytical fits of the (normalized) shortwave forcing by both ozone and sulfate. The effects of relative humidity on the optical parameters of the sulfate aerosol and hence on the patterns of radiative forcing are also considered. Our results indicate that the impact as compared to a fixed relative humidity (at 80%) is quite small on a global scale, but regionally, differences up to 5 W m−2 are found. By adding the radiative effects of sulfate and ozone over the period 1850–1990, we find that the continents of the northern hemisphere are dominated by the negative forcing of sulfate throughout the year, whereas a positive forcing in July and no effect in January are found over the oceans. Even if we add the effects of the well−mixed greenhouse gases over the same period, some spots of negative forcing remain. New results are presented for the ozone and sulfate forcings toward 2050. The radiative forcing of ozone is expected to increase by another 70% over the period 1990–2050 as compared to the industrial period, while the negative sulfate forcing is predicted to increase even stronger by 150% comparing the same periods. Maximum changes of both constituents are shifting southward in the northern hemisphere as a result of increasing industrial activities in countries with emerging economies.
Trends in streamflow and rainfall in tropical South America: Amazonia, eastern Brazil, and northwestern Peru
Authors: Marengo José A. , Tomasella Javier , Uvo Cintia R.
Published: February 2004

Long hydrological records, from the Amazon Basin, northeastern Brazil, and northwestern Peru spanning most of this century, are examined for trends in rainfall (three wettest months) and runoff (three months of highest flow) or stage, where no rating curves exist. Trends are tested for significance using the Mann‐Kendall statistic. In basins where large soil, aquifer, or man‐made reservoirs give rise to appreciable over‐year storage, flows and water levels may be serially correlated. Where serial correlation exists, the usual statistical tests (linear regression, t‐test, and Mann‐Kendall) will overestimate the significance of trends, showing significance where none exists. Analysis for trend therefore requires particular care when data are serially correlated, and to avoid misleading results, additional supportive evidence must be sought. For example, rainfall records within the same river basin can be checked for trends; serial correlation in rainfall records, in particular, is less likely to be present, so the validity of any trends in rainfall is less open to question. Strong negative trends were found in flow data from the coast of northern Peru and the São Francisco River, while positive significant trends were detected in the Parnaíba River basin. No significant trends were found in the discharge or stage records from Amazonia, while rainfall in northeastern Brazil shows a slow increase over long periods. In the Parnaíba and in some rivers of northern Peru unusually large discharges at the beginning or end of the records seem to account for the direction and significance of trends.
Seasonal variability in foliar characteristics and physiology for boreal forest species at the five Saskatchewan tower sites during the 1994 Boreal Ecosystem‐Atmosphere Study
Authors: Middleton E. M. , Sullivan J. H. , Bovard B. D. , Deluca A. J. , Chan S. S. , Cannon T. A.
Published: February 2004

Leaf‐level measurements of gas exchange, chemistry, morphology, and spectral optical properties were acquired at the five instrumented tower sites during the three 1994 growing season intensive field campaigns (IFCs) conducted near Prince Albert, Saskatchewan, as part of the Boreal Ecosystem‐Atmosphere Study (BOREAS). Stands included old and young aspen (OA, YA) associated with the hazelnut shrub, old and young jack pine (OJP, YJP) stands, and an old black spruce (OBS) stand; white spruce (at YA) and an understory herb (dogbane, at OJP) were also examined. Midsummer peak photosynthesis for aspen leaves in the field (A, light saturated) and laboratory (Amaxlight and CO2saturated) was ∼12.6 and 33–41 μmol CO2m−2s−1. Black spruce exhibited the lowest A, 3 μmol CO2m−2s−1. Jack pine and black spruce attained their highestAmax(17–20 μmol CO2m−2s−1) in late summer/early fall. Gas exchange by white spruce was significantly higher and stomatal limitation lower than for other conifers, at levels comparable to broadleaf responses. White spruce foliage had the highest chlorophyll content in fall (∼41 μg cm−2), followed by aspen (OA) and hazelnut (YA) in midsummer (∼31 μg cm−2). Specific leaf mass of aspen, hazelnut, and conifer foliage was 86, ∼47, and ∼174 g m−2, respectively. Leaf nitrogen content of broadleaves (18–40 g N g−1dry wt) was 2–3 times greater than conifer needles (8–12 g N g−1). Significantly larger needles were produced at OJP versus YJP, but needle number per age class was greater at YJP. The absorbed photosynthetically active radiation fraction (fAPAR) in June/July averaged ∼80% for broadleaves and ∼83% in conifer needles. The simple ratio (SR, near‐infrared/red ratio) calculated from foliar transmittances was more strongly related tofAPAR than SR calculated from reflectances, with stronger correlation for broadleaves (r=0.92) than for conifers (r=0.78).
Propagation effect on field waveforms in relation to time‐of‐arrival technique in lightning location
Authors: Honma N. , Suzuki F. , Miyake Y. , Ishii M. , Hidayat S.
Published: February 2004

The propagation effect on electromagnetic pulses associated with negative return strokes is evaluated from data observed by direction finders for lightning location equipped with GPS clocks. Nine direction finders constitute a network in the northern part of the Honshu Island of Japan, which locates lightning by a method combining the direction finding and the time‐of‐arrival (TOA) technique. The delay of the peak of an electromagnetic pulse was evaluated to be negligible in propagation over seawater for distances less than 300 km, and its average was about 1.8 μs in the east‐west propagation over land for the distance of about 130 km. The timing error of 1.8 μs may cause maximum location error of about 0.5 km within a TOA lightning‐location network, and larger error is anticipated outside of the network. The evaluated propagation delay in this area corresponds to the average ground conductivity of about 0.003 S/m, except for the southwest part with slightly lower conductivity of about 0.002 S/m. These findings were confirmed by an analysis based on ground‐truth data obtained by still cameras equipped with precise clocks. The measured delay in the north‐south propagation corresponded to the average ground conductivity of about 0.003 S/m.

The estimated arrival time of an electromagnetic pulse, based on the arrival time of the peak and the trigger time, gives smaller delay than the simple arrival time of the peak, but the difference is not significant. It would be better to compensate the peak time by evaluating the propagation effect in obtaining an estimate of the arrival time, to improve the accuracy of lightning location by using the TOA technique.
Use of stable isotopes to determine methane oxidation in landfill cover soils
Authors: Liptay K. , Chanton J. , Czepiel P. , Mosher B.
Published: February 2004

The mean isotopic composition of CH4 emitted from six New England (United States) landfills was 13C and D enriched (−48.1 to −50.4‰ and −273 to −281‰) relative to anoxic zone landfill CH4 (mean values of −55.9 to −56.2‰ and −296 to −300‰) owing to the oxidation of methane as it was transported from the landfill to the atmosphere through the soil cap. The fraction of methane oxidized f0 during its passage through the soil cap was calculated from the degree of 13C enrichment in emitted CH4 relative to anoxic zone CH4 in conjunction with values determined for the preference of soil methane oxidizing bacteria for 12CH4 over 13CH4 (α = 1.022 ± 0.008). Mean values for methane oxidation in six landfills were from 24 to 35% of the total flux through the soil during the warm season, depending upon how the data were grouped. Our results bracket recent estimates of methane oxidation of about 30% in the warm summer period produced using a model with the input terms of soil temperature, moisture, depth, and oxygen concentration. Because of variations in the response of methane oxidation to temperature at these New England sites, our study is consistent with the modeling results of Czepiel et al. [1996b] that the best estimate for the annual value for methane oxidation in the landfills considered is about 10%.
Seasonal variability of the diurnal tide: Results from the Canadian middle atmosphere general circulation model
Authors: McLandress Charles
Published: February 2004

The seasonal variability of the migrating diurnal tide is studied using a general circulation model (GCM) that extends from the Earth's surface to 97km. Results from a 2‐year simulation reveal a strong semiannual variation in the amplitude of the tide at low latitudes in the mesosphere, in agreement with recent observations from the upper atmosphere research satellite. The northward wind and temperature attain maximum amplitudes at equinox of approximately 60 m/s and 20°K, respectively, and minima at solstice that are a factor of 2 or more weaker. The reasons for this seasonal variation are explored by diagnosing the migrating diurnal tide solar and deep convective heating in the GCM and by implementing that heating in a linear mechanistic model. The agreement between the two models is quite good in April, but much less so in July when the diurnal tide simulated by the GCM has a much weaker amplitude and longer vertical wavelength in the mesosphere. It is concluded that seasonal variations in the thermal heating in the troposphere and stratosphere cannot account for the seasonal variations in the amplitude of the tidal winds and temperatures in the mesosphere. Although the exact cause of the semiannual amplitude variation has not yet been identified, nonlinear effects are most likely important since a very close correspondence is found between the Eliassen‐Palm flux divergence and the tidal amplitudes, with the times and locations of the strongest divergence coinciding with the weakest tidal wind amplitudes.
Vertical distribution of the spectral aerosol optical depth in the Arctic from 1993 to 1996
Authors: Nagel Dagmar , Herber Andreas , Thomason Larry W. , Leiterer Ullrich
Published: February 2004

During the period from summer 1993 to spring 1996, 51 profiles of spectral aerosol optical depth were measured with airborne Sun photometers throughout the Arctic. This period was influenced by volcanic aerosols after the Pinatubo eruption and the removal of volcanic material from the stratosphere into the troposphere. By 1996, stratospheric aerosol concentration has decreased to pre‐Pinatubo levels. Mean values of aerosol optical depth have changed during the period from 1993 to 1996 from 0.09 to 0.02 at 403 nm and from 0.065 to 0.01 at 1041nm/1057 nm, respectively. Size spectra of stratospheric aerosol also show the influence of volcanic aerosols. A bimodal distribution was found with main radius modes at 0.1 μm to 0.3 μm and 0.75 μm to 0.9 μm. The typical vertical distribution of tropospheric aerosols in the Arctic in this time period and inferred size spectra are presented. The seasonal change in the spectral aerosol optical depth with a minimum in summer and high values in spring is shown, as well as the high extinction and distinct layering of Arctic haze up into the free troposphere. Size spectra of Arctic haze also change with height and show, in addition to particles with radii smaller than 0.1 μm, main radius modes between 0.1 μm and 0.2 μm and between 1 μm and 2 μm. Possible influence of tropospheric aerosols on the radiation balance is also discussed for the spring and summer season. While in summer the influence on the radiation balance of the very small amount of tropo‐spheric aerosols is negligible, in spring, haze layers with high extinction can result in a slight warming.
Temporal and spatial variability of snow accumulation in central Greenland
Authors: Kuhns H. , Davidson C. , Dibb J. , Stearns C. , Bergin M. , Jaffrezo J.‐L.
Published: February 2004

Snow accumulation records from central Greenland are explored to improve the understanding of the accumulation signal in Greenland ice core records. Results from a “forest” of 100 bamboo poles and automated accumulation monitors in the vicinity of Summit as well as shallow cores collected in the Summit and Crete areas are presented. Based on these accumulation data, a regression has been calculated to quantify the signal‐to‐noise variance ratio of ice core accumulation signals on a variety of temporal (1 week to 2 years) and spatial (20 m to 200 km) scales. Results are consistent with data obtained from year‐round automated accumulation measurements deployed at Summit which suggest that it is impossible to obtain regional snow accumulation data with seasonal resolution using four accumulation monitors positioned over a length scale of ∼30 km. Given this understanding of the temporal and spatial dependence of noise in the ice core accumulation signal, the accumulation records from 17 shallow cores are revisited. Each core spans the time period from 1964 to 1983. By combining the accumulation records, the regional snow accumulation record has been obtained for this period. The results show that 9 of the 20 years can be identified as having an accumulation different from the 20 year mean with 99% confidence. The signal‐to‐noise variance ratio for the average accumulation signal sampled at annual intervals is 5.8±0.5. The averaged accumulation time series may be useful to climate modelers attempting to validate their models with accurate regional hydrologic data sets.
Sources, sinks, and mechanisms of hydroxyl radical (•OH) photoproduction and consumption in authentic acidic continental cloud waters from Whiteface Mountain, New York: The role of the Fe(r) (r = II, III) photochemical cycle
Authors: Arakaki Takemitsu , Faust Bruce C.
Published: February 2004

Hydroxyl radical (•OH) photoproduction in 25 authentic acidic (pH = 2.9–4.4) continental cloud waters from Whiteface Mountain, New York was quantified by phenol formed from the •OH‐mediated oxidation of benzene (1.2 mM) that was added as an •OH scavenger. Based on the effect of added bisulfite (HSO3−/HOSO2−), an HOOH sink, the •OH photoproduction in these samples was apportioned into two categories: HOOH‐dependent sources (dominant), and HOOH‐independent sources (minor). On average only a small percentage (median = 9.4%, mean±standard deviation = 16±12%) of the HOOH‐dependent •OH source is due to direct photolysis (313 nm) of HOOH. Nearly all of the HOOH‐dependent •OH source is accounted for by an iron(II)‐HOOH photo‐Fenton reaction mechanism (Fe(II) + HOOH → Fe(III) + •OH + OH−) that is initiated by photoreduction of Fe(III) to Fe(II) in the presence of HOOH. A photostationary state is established, involving rapid photolysis of Fe(III) to form Fe(II), and rapid reoxidation of Fe(II) to Fe(III). Consequently, a new term is introduced, Fe(r) (r = II, III), to represent the family of labile Fe(III) and Fe(II) species whose rapid photoredox cycling drives the Fenton production of •OH. The Fe(r) photochemical cycle, which drives the aqueous phase photoformation of •OH, is analogous to the classical NOx photochemical cycle, which drives the gas phase formation of O3 and thus •OH. Based on the cloud waters studied here, the iron(II)‐HOOH photo‐Fenton reaction is a significant source of •OH to acidic continental cloud waters in comparison to gas‐to‐drop partitioning processes. Filtering (0.5 μm Teflon) cloud water samples had little effect on the •OH photoformation kinetics. Measured lifetimes of aqueous •OH ranged from 2.4 to 10.6 μs in these cloud waters, and decreased with increasing concentration of dissolved organic carbon. In acidic atmospheric water drops, the principal aqueous sinks for •OH will be reactions with dissolved organic compounds, bisulfite, and Cl−. Given such short chemical reaction lifetimes, little of the aqueous phase photoformed •OH is likely to escape to the gas phase.
Treatment of retardation effects in calculating the radiated electromagnetic fields from the lightning discharge
Authors: Thottappillil Rajeev , Uman Martin A. , Rakov Vladimir A.
Published: February 2004

The analytical treatment of retardation effects in calculating lightning electromagnetic fields far from the source has often involved the use of a so‐calledFfactor. The literature concerning theFfactor in the lightning field equations is often confusing and sometimes in error. The aim of this paper is to clarify, to correct when needed, and to extend previous views of theFfactor by considering and consolidating the various situations, both mathematically and physically, in which this factor can occur. TheFfactor arises because of the retardation effects occurring when the distance to the observer from a point on a propagating current is changing with time. In this paper we (1) discuss the various situations in which theFfactor can arise, such as in the determination of the “radiating” channel length “seen” by the observer, in the calculation of fields due to a propagating current wave up or down the discharge channel, and in the calculation of fields due to a propagating current discontinuity extending the channel upward; (2) give a unifying physical interpretation for this factor; and (3) show that the retardation effects in calculating lightning fields can be accounted for without the explicit use of anFfactor. Relative to item 2 above, we will show that for simple return‐stroke models like the transmission line (TL) and traveling current source (TCS) models, in which the current at one point on the channel appears at another point at another time, theFfactor associated with current behind the front can be interpreted physically as the ratio of the apparent propagation speed (upward or downward) of the current wave “seen” by a distant observer to its actual speed. In the TL model, a current wave moves upward at speed ν, the same speed as that of the front, and theFfactor is given by [1‐(ν/c) cos θ]−1, where θ is the angle between the direction of propagation of the source and the line joining the source point and the field point (observer), andcis the speed of light in vacuum. In the TCS model, a current wave moves downward at a speed equalc, and theFfactor is given by [1+cosθ]−1. TheFfactor associated with an upward propagating current discontinuity can always (in any model) be interpreted physically as the ratio of the apparent propagation speed of the discontinuity to its actual speed and is given by the same expression as for theFfactor for the upward propagating current wave in the TL model.
Three months of continuous monitoring of atmospheric water vapor with a network of Global Positioning System receivers
Authors: Emardson T. Ragne , Elgered Gunnar , Johansson Jan M.
Published: February 2004

Three months of continuous data from the Global Positioning System (GPS) using 20 sites in Sweden and 5 sites in Finland have been used to estimate the integrated amount of atmospheric water vapor. The quality of the data has been assessed by comparisons with a microwave radiometer (water vapor radiometer (WVR)) at the Onsala Space Observatory and with data from four different radiosonde stations. We found the agreement in integrated water vapor (IWV) between the GPS estimates and the radiometer data to be 1–2 kg/m2in terms of daily root‐mean‐square (rms) differences. A major part of these rms differences were caused by a bias between the data sets. This bias (WVR‐GPS) varied from day to day between −1.0 and +2.5kg/m2with a mean value of +1.3kg/m2. Comparisons with radiosonde data showed rms differences around or slightly above 2kg/m2for each station using the entire 3 month data set. Also here the GPS estimates were, on the average, below the radiosonde results. We show that the radomes used to protect the GPS antennas are likely to cause a large part of the observed bias. Spatial structure functions were calculated by using the GPS and the radiosonde data. An overall consistency between the GPS‐based and the radiosonde‐based structure functions indicates that the spatial correlations between the GPS estimates are not affected by the estimation process used in the GPS data analysis.
Beryllium 10/beryllium 7 as a tracer of stratospheric transport
Authors: Koch Dorothy , Rind David
Published: February 2004

We use the ratio between cosmogenic radionuclides beryllium 10 (t1/2 = 1.5×106 years) and beryllium 7 (t1/2 =53 days) to study stratospheric transport, particularly the exchange between the tropics and the high latitudes and as an indicator of stratosphere‐troposphere exchange. Both tracers are generated steadily, with maximum production occurring at midlatitudes of the stratosphere. During transport away from their source the ratio 10Be/7Be increases and thus acts as a clock for air mass age. According to model (GISS GCM) calculations, the tropics is a reservoir of high‐ratio air with the high magnitude of 10Be/7Be partly a consequence of air mixed in from higher latitudes. The observations of Dibb et al. [1994] show a vertical maximum in 10Be/7Be in the lower arctic stratosphere during the spring of 1989; model results qualitatively reproduce this maximum and suggest that it may result from transport of tropical air to high latitudes during winter. The model ratio values are not so large as in these observations, possibly due to either excessive leakage into the troposphere near the pole or to insufficient transport from the tropical stratosphere to the pole. Beryllium 10 and 7Be observations, combined with model analysis, can be a useful indicator of transport processes in the troposphere/stratosphere system.
Layering in stratospheric profiles of long‐lived trace species: Balloon‐borne observations and modeling
Authors: Orsolini Yvan J. , Manney Gloria L. , Engel Andreas , Ovarlez Joelle , Claud Chantal , Coy Larry
Published: February 2004

A series of balloon flights conducted in March 1993 from Aire‐sur‐Adour, in southern France, aimed at making in situ measurements of a variety of trace gases in the polar vortex during a dynamically active period. Meteorological analyses indicate that the balloons were launched when the vortex edge was passing aloft. These mid latitude balloon flights revealed coincident layering in long‐lived tropospheric source gases such as nitrous oxide, methane and halocarbons as well as in ozone and water vapor. At low altitudes, well‐resolved laminations appeared clearly in all these gases. A layer of mid latitude air, enriched in trace gases, was detected at the highest sampled level, near 15 mbar, inducing a pronounced reversal in the profiles of tropospheric source gases. Using global meteorological analyses, trace constituent data derived from the UARS observations and high‐resolution advection models, fine‐scale distributions of ozone, nitrous oxide, methane, and halocarbons have been constructed. The calculations show qualitatively how such profile reversal arises near 15 mbar, when a filament of air enriched in trace gases is drawn into the outer portion of the vortex. Very high resolution calculations furthermore provide reasonable quantitative agreement between predicted tracer mixing ratios and in situ balloon‐borne measurements.
Observed atmospheric collision‐induced absorption in near‐infrared oxygen bands
Authors: Mlawer Eli J. , Clough Shepard A. , Brown Patrick D. , Stephen Thomas M. , Landry Joseph C. , Goldman Aaron , Murcray Frank J.
Published: February 2004

A recent high‐resolution measurement of surface solar radiance taken under cloud‐free conditions by the Absolute Solar Transmittance Interferometer shows clear indication of continuum absorption associated with the three strongest O2 a1 Δg ← X3Σg− transitions. The differences between these measurements and a calculation by the line‐by‐line radiative transfer model (LBLRTM) were used to determine the properties of these collision‐induced bands and, for two of the bands, led to parameterizations of the spectral behavior of the absorption coefficients. The results indicate that these continuum bands absorb 0.84 W/m2 at the 71.5° solar zenith angle associated with the observation. For the observed 3000–9965 cm−1 spectrum, with the exception of the spectral range in which this collision‐induced absorption occurs, there is good agreement between the measured and calculated radiance values, with no evidence for discrete absorption by unknown gases.
Increases in middle atmospheric water vapor as observed by the Halogen Occultation Experiment and the ground‐based Water Vapor Millimeter‐Wave Spectrometer from 1991 to 1997
Authors: Nedoluha Gerald E. , Bevilacqua Richard M. , Gomez R. Michael , Siskind David E. , Hicks Brian C. , Russell James M. , Connor Brian J.
Published: February 2004

Water vapor measurements made by the Halogen Occultation Experiment (HALOE) from 1991 to 1997 are compared with ground‐based observations by the Water Vapor Millimeter‐wave Spectrometers (WVMS) taken from 1992 to 1997 at Table Mountain, California (34.4°N, 242.3°E), and at Lauder, New Zealand (45.0°S, 169.7°E). The HALOE measurements show that an upward trend in middle atmospheric water vapor is present at all latitudes. The average trend in the HALOE water vapor retrievals at all latitudes in the 40–60 km range is 0.129 ppmv/yr, while the average trend observed by the WVMS instruments in this altitude range is 0.148 ppmv/yr. This trend is occurring below the altitude where changes in Lyman α associated with solar cycle variations should produce a significant increase in water vapor during this period, and is much larger than the ∼0.02 ppmv/yr trend in water vapor associated with increases in methane entering the stratosphere. In addition to the water vapor increase, HALOE measurements show that there is a temporal decrease in methane at altitudes between 40 and 70 km. This indicates an increase in the conversion of the available methane to water vapor, thus contributing to the observed increase in water vapor. The increase in water vapor observed by both instruments is larger than that which would be expected from the sum of all of the above effects. We therefore conclude that there has been a significant increase in the amount of water vapor entering the middle atmosphere. A temperature increase of ∼0.1 K/yr in regions of stratosphere‐troposphere exchange could increase the saturation mixing ratio of water vapor by an amount consistent with the observed increase.
Full‐wave modeling of small‐scale gravity waves using Airborne Lidar and Observations of the Hawaiian Airglow (ALOHA‐93) O(1S) images and coincident Na wind/temperature lidar measurements
Authors: Hickey Michael P. , Taylor Michael. J. , Gardner Chester S. , Gibbons Christian R.
Published: February 2004

Measurements were made of mesospheric gravity waves in the OI (5577 Å) nightglow observed from Maui, Hawaii, during the Airborne Lidar and Observations of Hawaiian Airglow (ALOHA‐93) campaign. Clear, monochromatic gravity waves were observed on several nights. By using a full‐wave model that realistically includes the major physical processes in this region, we have simulated the propagation of four waves through the mesopause region and calculated the O(1S) nightglow response to the waves. Mean winds derived from Na wind/temperature lidar observations were employed in the computations. Wave amplitudes were calculated based on the requirement that the observed and simulated relative airglow fluctuation amplitudes be equal. Although the extrinsic (i.e., observed) characteristics of all four waves studied were quite similar (horizontal wavelengths ∼20 to 30 km; periods ∼9 min; horizontal phase speeds ∼35 to 50 m s−1), the propagation characteristics of the waves are all quite different due to the different background mean winds through which the waves propagate. Three of the waves encounter critical levels in the mesopause region. For two of these waves the upward propagation beyond the 97 km level is severely impeded by their critical levels because the local value of the Richardson number exceeds unity there. The third wave is not severely attenuated at its critical level because the Richardson number there is about 0.25. The fourth wave does not encounter a critical level although it is strongly Doppler shifted to low frequencies over a limited height range by the mean winds. It appears to be able to propagate at least to the 110 km level essentially unimpeded. This study demonstrates that an accurate description of the mean winds is an essential requirement for a complete interpretation of observed wave‐driven airglow fluctuations. The study also emphasizes that although the measured extrinsic properties of waves may be similar, their propagation to higher altitudes depends very sensitively on the mean winds through which the waves propagate.
Bidirectional mixing in an ACE 1 marine boundary layer overlain by a second turbulent layer
Authors: Russell Lynn M. , Lenschow Donald H. , Laursen Krista K. , Krummel Paul B. , Siems Steven T. , Bandy Alan R. , Thornton Donald C. , Bates Timothy S.
Published: February 2004

In the Lagrangian B flights of the First Aerosol Characterization Experiment (ACE 1), the chemistry and dynamics of the postfrontal air mass were characterized by tracking a constant‐level balloon launched into the air mass for three consecutive 8‐hour flights of the instrumented National Center for Atmospheric Research C‐130 aircraft during a 33‐hour period. The boundary layer extended to a height of 400 to 700 m during this period, with its top defined by changes in the amount of turbulent mixing measured rather than by an inversion. Above the planetary boundary layer to a height of 1400 to 1900 m, a second layer was capped with a more pronounced temperature inversion and contained only intermittent turbulence. Since this layer served as a reservoir and mixing zone for boundary layer and free tropospheric air, we have called it a buffer layer to emphasize its differences from previous concepts of a residual or intermediate layer. Estimates of the entrainment rate of dimethyl sulfide (DMS) and aerosol particles between the boundary layer and the buffer layer demonstrated that exchange occurred across the interface between these two layers in both upward and downward directions. In situ measurements of aerosol particles revealed highly concentrated, nucleation‐mode aerosol particles between 10 and 30 nm diameter at the beginning of the first Lagrangian B flight in the buffer layer, while few were present in the boundary layer. Observations during the second and third flights indicate that aerosol particles of this size were mixing downward into the boundary layer from the buffer layer while DMS was transported upward. This fortuitous enhancement of aerosol particles in the buffer layer allowed simultaneous use of DMS and aerosol particle budgets to track the bidirectional entrainment rates. These estimates were compared to those from measurements of mean vertical motion and boundary layer growth rate, and from estimates of the fluxes and changes in concentration across the layer interface. In addition, three different techniques were used to estimate DMS emission rates from the ocean surface and showed good agreement: (1) evalulation of the DMS and aerosol mean concentration budgets, (2) seawater DMS concentrations and an air‐sea exchange velocity, and (3) the mixed‐layer gradient technique.
Vertical distributions of cloud condensation nuclei spectra over the summertime Southern Ocean
Authors: Hudson James G. , Xie Yonghong , Yum Seong Soo
Published: February 2004

More than 60 hours of airborne cloud condensation nuclei (CCN) measurements made during the First Aerosol Characterization Experiment (ACE 1) south of Australia are presented and analyzed. These ambient measurements covered more than half of the aircraft time on station between 7 km and 30 m altitude during the late spring/early summer season over the Southern Ocean. The complete CCN spectra from 1.2 to 0.02% and condensation nuclei (CN), particles greater than 0.01 μm, concentrations are presented. The CN and CCN concentrations at 1.2 and 0.2% supersaturation compared well with long‐term surface measurements at Cape Grim, Tasmania. Lower concentrations, especially for CN, were associated with cloudier regions. Higher concentrations, especially for CN, were found in air masses that were or had recently been closer to land. Nonetheless, these data should be representative of clean maritime conditions.
Coastal Antarctic aerosol and snowfall chemistry
Authors: Wolff Eric W. , Legrand Michel R. , Wagenbach Dietmar
Published: February 2004

Aerosol samples have been collected at three stations on the coast of Antarctica. At Dumont d'Urville Station, samples have been collected for 4 years, at Halley Station for 2 years, and at Neumayer Station for 12 years. Fresh snow samples have also been collected at the three sites. At Halley, daily surface snow samples were taken, as well as firn cores covering the sampling period. Meteorological (including upper air) data are available at the three sites. In the subsequent papers of this special section, the data from the three stations have been combined in order to make general statements about the chemistry of aerosol in coastal Antarctica, about the differences between sectors of Antarctica, and about the relationship between air concentrations and the chemistry that is eventually seen in ice cores. This paper summarizes the samples collected and the sampling methods used at the three sites. It also highlights the main role of each paper in this special section.
A mesoscale model‐based study of the dynamics of a wintertime polar low in the Weddell Sea region of the Antarctic during the Winter Weddell Sea Program field phase 1986
Authors: Heinemann Günther
Published: February 2004

A wintertime mesocyclone (MC) event occurring during the Winter Weddell Sea Program field phase 1986 is studied by digital advanced very high‐resolution radiometer data and numerical simulations using the mesoscale Norwegian Limited Area Model. The MC considered developed during July 30, 1986, near the sea ice front of the northern Weddell Sea. During its initial and developmental phases it moved eastward parallel to the sea ice front. During the first 24 hours, baroclinic instability and diabatic heating were found to be of great importance for the intensification. During its mature stage (the following 24 hours), a pronounced frontal system formed, and baroclinic instability can be regarded as the main process for its further development. The MC moved over the sea ice during its mature stage, so the forcing by surface energy fluxes was less important. A cyclonic upper level potential vorticity anomaly was found to be present during the mature stage. The MC had a diameter of about 700 km and a lifetime of more than 48 hours and reached the intensity of a polar low (measured near‐surface wind speeds of up to 26 m/s). The model results revealed good agreement with observations (radiosondes and synoptic observations) in the case of the “full physics” run, but in the case of the “no cloud physics” run this was very poor.
New method for identification of sources for chemical time series and its application to the Greenland Ice Sheet Project ice core record
Authors: Ditlevsen Peter D. , Marsh Nigel D.
Published: February 2004

Point measurements of chemical tracers transported via the atmosphere contain information regarding origins, atmospheric mixing, scavenging, and in situ chemical processes. A new technique for accessing this information is presented. The method is based on the physical constraints that are naturally imposed on the data. In order to evaluate the performance of this new technique, we have applied it to artificially generated data sets. Furthermore, the method is used to analyze eight chemical time series obtained from ice core data. Three distinct source vectors dominate the composition throughout the last 41 kyr period. By comparing ratios among the eight chemical species within each source vector, it is possible to show that they describe three source types: oceanic, continental, and biochemical land sources.