bluuebunny/crossref_metadata_2025 huggingface dataset:
Coherent ozone‐dynamical changes during the southern hemisphere spring, 1979–1986
Authors: Newman Paul A. , Randel William J.
Published: February 2008

National Meteorological Center (NMC) data is used in conjunction with Total Ozone Mapping Spectrometer (TOMS) data to study seasonal and interannual variability during the southern hemisphere springs of 1979 through 1986. Virtually perfect spatial correlation is found between October average lower stratospheric temperatures and total ozone for each year. The constant of proportionality between total ozone and lower stratospheric temperature varies significantly (but not systematically) over the years 1979 through 1986 and is in approximate agreement with that calculated for adiabatic air parcel motion. Spatial patterns of change in total ozone over 1979–1986 show remarkable agreement with lower stratospheric temperature changes; in addition to pronounced decreases in the Antarctic region, a slight increase of both is also observed at 50°S to the west of South America. In addition to ozone variability correlated with observed temperature changes, there is a substantial decline not linearly related to the observed temperature change. Spatial and temporal characteristics of interannual changes in NMC temperatures are analyzed in some detail. Extensive comparisons are made between radiosondes and NMC analyses, showing good agreement of monthly means. Trend analyses of zonal mean temperatures over the period 1979–1986 show strongest coolings (−0.7°K/yr) during October in the 10‐ to 100‐mbar region. Cooling patterns are zonally asymmetric, so that seasonal or zonal mean temperature changes underestimate local October changes. Between October 1979 and October 1985 (two extreme years), maximum local temperature changes of 18° and 22°K are observed at 70 and 30 mbar, respectively (coincident with a local 160 Dobson unit total ozone decrease). Interannual variations and trends of stationary wave 1 heat flux in the spring lower stratosphere are found to be coherent with the observed temperature and ozone fluctuations (stationary wave 1 dominates the southern hemisphere spring stratospheric eddy fluxes). In the 1000‐ to 100‐mbar regions, where transient wave fluxes are dominant, large differences between NMC and European Centre for Medium Range Weather Forecasts analyses preclude trend analyses.
Ozone measurements in the troposphere of an Amazonian rain forest environment
Authors: Kirchhoff V. W. J. H. , Browell E. V. , Gregory G. L.
Published: February 2008

Ozone concentration profiles from the ground to above the stratospheric peak have been obtained, for the first time, in an equatorial rain forest environment near Manaus (3°S 60°W). We have described in detail the average ozone profile in the troposphere, the observed variations, and a major biomass‐burning event that occurred near the end of the experiment. The average ozone mixing ratio at 1000 mbar was 13 parts per billion by volume (ppbv), increasing to 45 ppbv at 500 mbar. From 500 mbar upward, in the free troposphere, the mixing ratio stays roughly constant. The peak O3 concentration occurs at 20 mbar (26.6 km) reaching 4.4×1012 molecules cm−3. The values in the troposphere are much lower than results from the low‐latitude Atlantic coast. The average gradient below 1000 m in Manaus is twice as large. The diurnal variation is strongest near the surface, decreasing upward. Close to the surface the ozone gradient is largest in the early morning, decreasing toward noon. A significant pollution (burning) event, near the end of the experiment, was responsible for large changes in ozone concentrations, which increased first in the lower troposphere but eventually reached the free troposphere as well.
Reaction probability of N2O5 on aqueous aerosols
Authors: Mozurkewich Michael , Calvert Jack G.
Published: February 2008

The reaction probability, γ, of N2O5 (to form HNO3) with monodisperse NH3/H2SO4/H2O aerosols has been measured in a flow tube reactor at atmospheric pressure. Experiments were performed at temperatures of 274 and 293 K and at relative humidities of 1–76%. It appears that the presence of a liquid phase is necessary for reaction. With NH4HSO4 aerosol, γ values are nonzero, even below the deliquescence point of the pure salt, and show a gradual increase with increasing relative humidity up to constant values of 0.05 and 0.09 for 293 and 274 K, respectively. Experiments with aerosols of varied NH3/H2SO4 ratios suggest that evaporation of NH3 from the NH4HSO4 aerosols creates excess H2SO4 on the surface. This can take up water vapor to provide the reactant for N2O5 below the deliquescence point of NH4HSO4. The present observations are consistent with the reaction of N2O5 with moist aerosols being a major removal mechanism for odd nitrogen and a major source of HNO3 in the nighttime troposphere. The same reaction on H2SO4 aerosols may be of significance in the stratosphere.
Estimation of Saharan aerosol optical thickness from blurring effects in thematic mapper data
Authors: Tanre D. , Deschamps P. Y. , Devaux C. , Herman M.
Published: February 2008

We present in this paper a method which allows us to derive the aerosol optical thickness over land surfaces from satellite data by using the blurring effect due to the scattering. By assuming the ground reflectance to be constant, variations of the satellite signal may be attributed to variations of the atmospheric optical properties. The time evolution of the structure function then allows us to infer the aerosol content over land surfaces. The method was applied to Saharan aerosols, which represent the most important contribution to the atmospheric aerosol loading. The results derived from Thematic Mapper data proved to be in good agreement with simultaneous ground‐based measurements. Therefore the method seems able to provide the aerosol contents during Saharan dust events.
Precipitation fluctuations over global land areas since the late 1800's
Authors: Diaz Henry F. , Bradley R. S. , Eischeid J. K.
Published: February 2008

An analysis of southern hemisphere land precipitation records for the last 100 years indicates an increase in mean annual precipitation since the 1940's, with positive anomalies, compared to the 1921–1960 reference period, occurring during approximately the last 15 years in all seasons except southern summer (December–February). There is little or no temporal correlation with corresponding precipitation indices for the northern hemisphere (Bradley et al., 1987a). Furthermore, while trends in the northern hemisphere temperate regions were opposite those in the northern tropical areas, in the southern hemisphere both zones exhibit similar trends. The change toward higher precipitation in middle latitudes begins about 10 years earlier in the northern than in the southern hemisphere (in the 1940's versus the 1950's, respectively). For the northern hemisphere, the overall linear trend from 1890 to 1986 is not significantly different from zero. However, a decline is evident since the 1950's, primarily due to lower rainfall amounts south of about 30°N. Globally, the trend is toward higher values in annual and seasonal precipitation, except for the boreal summer season (June–August). Most of the observed increases, however, took place from about 1940 to the mid‐1950's, after which time the record has displayed little overall trend, instead exhibiting decade‐long fluctuations. The observations are only broadly consistent with zonally averaged profiles of precipitation changes derived from general circulation model (GCM) simulations of climate using doubled atmospheric CO2 concentrations, although we note that there is considerable variability in precipitation response from one model to another. One possible discrepancy occurs in the northern hemisphere tropics, where most GCMs indicate relatively little change in precipitation in response to CO2 doubling (Gutowski et al., 1988), whereas in the past couple of decades there has been a major decline in rainfall in this region. The overall increase in southern hemisphere precipitation is consistent with marine observations for the tropics and extratropical southern latitudes, which show an increase in sea surface temperature of about 0.3°C since the mid‐1970's and an increase in surface wind speed of between 0.4 and 0.8 m/s since 1950. The potential increase in evaporation could have contributed to the observed rainfall trends. We note, however, that precipitation in tropical land areas is strongly influenced by the phases of the El Niño/Southern Oscillation (ENSO), being generally lower during warm events and higher during the opposite cold phase. The effects of the strong ENSO warm events of 1982–1983 and around 1940 are clearly evident in the global record, as are precipitation peaks during cold years, such as 1974–1975 and 1954–1956.
Trace gas emissions from chaparral and boreal forest fires
Authors: Cofer Wesley R. , Levine Joel S. , Sebacher Daniel I. , Winstead Edward L. , Riggan Philip J. , Stocks Brian J. , Brass James A. , Ambrosia Vincent G. , Boston Penelope J.
Published: February 2008

Low‐level helicopter flights were used to collect samples of smoke from burning chaparral in southern California and over a boreal forest fire in northern Ontario, Canada. The smoke plume samples were analyzed for carbon dioxide (CO2), carbon monoxide (CO), hydrogen (H2), methane (CH4), total nonmethane hydrocarbons (TNMHC), and nitrous oxide (N2O). Samples of gas were also analyzed from upwind of the burns to determine the ambient background levels. CO2‐normalized emission ratios (ΔX/ΔCO2; where X is equal to each gas; vol/vol) were determined for each trace gas for conditions of flaming, mixed, and smoldering combustion. The emission ratios for these trace gases were found highest during smoldering combustion, generally thought to be the least efficient combustion stage. However, indications that high emission ratios for these trace gases can be produced during very vigorous flaming combustion are also indicated by our results. Whether this results from quenching processes due to rapid entrainment of air or from localized pockets of oxygen‐depleted air, or both, deserves further study. Emission ratios determined for ethane (C2H6), ethylene (C2H4), propane (C3H8), and propylene (C3H6), obtained over an earlier chaparral fire at the same approximate site, are presented for the first time. While emission ratios for these hydrocarbons ranged from a factor of 15 to 100 less than their corresponding methane emission ratios, they strongly supported the production of highly reduced trace gases during vigorously flaming combustion; that is, ethylene was generated in higher proportion than ethane, and propylene in higher proportion than propane.
A physical model of lightning initiation on aircraft in thunderstorms
Authors: Mazur Vladislav
Published: February 2008

A physical model of initiation of lightning flashes by aircraft in thunderstorms, based on the “bi‐directional, uncharged leader” concept of Kasemir, is verified with airborne data from lightning strikes to instrumented airplanes (NASA F‐106B and FAA CV‐580). Characteristics of electromagnetic processes during lightning attachment to aircraft are identified with those in negative stepped leaders and positive leaders in natural lightning, in flashes triggered by wire‐trailing rockets, and in laboratory discharges. It is shown that (1) a triggered flash starts on aircraft with either a negative corona or a positive leader that depends on the ambient electric field vector and the vehicle form factors; (2) the positive leader with continuous current that increases with time to the level of several hundred amperes is followed in a few milliseconds by the negative stepped leader with current pulses of a few kiloamperes; and (3) the two leaders develop in space simultaneously and bi‐directionally from the oppositely charged extremities of the airplane.
Elemental and isotopic composition of occluded O2 and N2 in polar ice
Authors: Sowers Todd , Bender Michael , Raynaud Dominique
Published: February 2008

A procedure has been developed to measure the relative concentrations of N2, O2, Ar, the δ18O of O2, and the δ15N of N2 trapped in Antarctic and Greenland ice cores. To date, we have analyzed 13 samples of trapped air in recent (<2200 years B.P.) ice from eight sites. The composition of the trapped gases was determined by mass spectrometry and the results expressed in delta notation relative to the present‐day atmosphere. The average δ15N of N2 and δ18O of O2 in samples from the various ice cores ranged from +0.05 to +0.41‰ and from +0.18 to +1.1‰, respectively. The heavy isotope enrichments are apparently due to gravitational settling accompanying diffusive equilibrium between the base of the firn and the overlying atmosphere. The δO2/Ar and δN2/Ar values ranged from −9.2 to +1.0‰ and from −4.8 to +4.6‰, respectively. The differences between the elemental composition of ice core trapped gases and air result from gravitational fractionation, as well as separation of O2 and Ar relative to N2 during either bubble close‐off or retrieval and storage of the ice cores.
Isotopic abundances of stratopheric ozone from balloon‐borne high‐resolution infrared solar spectra
Authors: Goldman A. , Murcray F. J. , Murcray D. G. , Kosters J. J. , Rinsland C. P. , Flaud J.‐M. , Camy‐Peyret C. , Barbe A.
Published: February 2008

Infrared solar absorption spectra recorded at 0.002–0.003 cm−1 resolution in the 10 μm region during two recent balloon flights from near 32°N latitude have been analyzed to determine the isotopic ratios of 16O16O18O and 16O18O16O, the two most abundant forms of isotopically substituted ozone, relative to normal ozone, in the stratosphere. The analysis has used recent improvements in the line parameters for 16O3, 16O16O18O, and 16O18O16O. Normalized to the standard isotopic ratios in ozone, the results show column‐averaged isotopic enhancement ratios of 1.20±0.14 and 1.40±0.18 for 16O18O16O/16O16O16O and 16O16O18O/16O16O16O, respectively, above 37 km altitude for flight measurements on November 18, 1987, and corresponding values of 1.16±0.08 and 1.25±0.12 for flight measurements on June 6, 1988. These measurements are the first such results obtained at high altitude using infrared techniques. The values are compared with heavy‐to‐normal O3 ratios reported previously from other techniques.
Modeling climate change: An assessment of sea ice and surface albedo feedbacks
Authors: Ingram W. J. , Wilson C. A. , Mitchell J. F. B.
Published: February 2008

The net strength of the sea ice and surface albedo feedbacks in simulations of climate change has been estimated for several general circulation models (GCMs) using a variety of methods. Here several methods are applied to quantify this feedback in a single CO2‐doubling experiment with the United Kingdom Meteorological Office GCM. Different methods give values differing by up to a factor of 2 and are shown to be estimating different quantities. An unbiased comparison of models is made using consistent methods, and an attempt is made to explain the differences in model sensitivity in terms of control climate and parameterization. Comparing the standard experiment to a parallel experiment using prescribed sea ice extents allows examination of the feedback as it actually operates in the model. The importance of cloud is emphasized, both in shielding surface albedo changes and so reducing their effect, and in providing its own contribution to planetary albedo changes. Statistical methods are used to examine the relationship between surface albedo changes, which are given directly by the surface heat balance and albedo parameterization, and planetary albedo changes, which incorporate the effects of clouds and determine the net feedback. Estimates of the magnitude of the feedback in various GCMs vary from 0.16 to 0.7 W m−2 K−1, with the highest value exaggerated by the method of analysis. We conclude that care is needed in quantifying these feedbacks and that previously published numbers are not all comparable. The feedbacks in two of the GCMs are exaggerated by unrealistically extensive sea ice, but the smaller values given by other GCMs may still be unrealistic, because of uncertainties in the treatment of clouds.
Dehydration in the lower Antarctic stratosphere during late winter and early spring, 1987
Authors: Kelly K. K. , Tuck A. F. , Murphy D. M. , Proffitt M. H. , Fahey D. W. , Jones R. L. , McKenna D. S. , Loewenstein M. , Podolske J. R. , Strahan S. E. , Ferry G. V. , Chan K. R. , Vedder J. F. , Gregory G. L. , Hypes W. D. , McCormick M. P. , Browell E. V. , Heidt L. E.
Published: February 2008

Measurements of total water were made with Lyman α resonance fluorescence hygrometers mounted on the ER‐2 and DC‐8 aircraft. Direct evidence was obtained for dehydration of the lower stratosphere over Antarctica; minimum values were about 1.5 parts per million by volume (ppmv), compared with values of 3.0 4.5 ppmv immediately outside the region high potential vorticity gradient in the potential temperature range 420<θ<460 K. On one flight, ice crystals large enough to have appreciable sedimentation velocities were observed. The DC‐8 data at 300<θ<320 K frequently showed extensive belts of dry, ozone‐rich air between 60° and 75°S latitude, with the equatorward “edge” in water well correlated with that observed by the ER‐2 some 8–9 km higher. Data from near Punta Arenas and from the ferry flights are used to argue that the effects of dehydration over Antarctica were visible at mid‐latitudes.
A chemical definition of the boundary of the Antarctic ozone hole
Authors: Proffitt M. H. , Powell J. A. , Tuck A. F. , Fahey D. W. , Kelly K. K. , Krueger A. J. , Schoeberl M. R. , Gary B. L. , Margitan J. J. , Chan K. R. , Loewenstein M. , Podolske J. R.
Published: February 2008

A campaign utilizing an ER‐2 high‐altitude aircraft and a DC‐8 aircraft, both fitted with state‐of‐the‐art instrumentation to study the Antarctic ozone hole, was conducted out of Punta Arenas, Chile, from August 17 through September 22, 1987. Data indicated a chemically perturbed region roughly coincident with the Antarctic polar vortex and with the region of large temporal decrease of ozone that is usually referred to as the Antarctic ozone hole. A rapid rise in ClO was observed as the ER‐2 proceeded into the ozone hole at about 18 km altitude, and it is this feature that is used to define the boundary of the chemically perturbed region as that latitude along the flight track where ClO reaches 130 parts per trillion by volume (pptv). In situ data taken simultaneously aboard the ER‐2, as well as Total Ozone Mapping Spectrometer (TOMS) satellite ozone data along the flight tracks, are analyzed at fixed positions relative to this boundary and are presented as averages over the duration of the mission. These analyses indicate a narrow transition zone at the boundary for the chemically active species ClO, O3, NOy, and NO. A somewhat wider transition zone for the chemical species N2O and H2O and for the meteorological parameters of temperature, wind speed, and potential vorticity is also seen, indicating the dynamical character of the chemically defined boundary. TOMS column values of about 260 Dobson units (DU) generally persisted at the boundary during this period. One‐month temporal trends of the in situ data both inside and outside this boundary are also presented. Interpretations of these analyses are offered that are consistent with ongoing diabatic cooling, accompanying advective poleward transport across the boundary. These data strongly implicate man's release of chlorine into the atmosphere as a necessary ingredient in the formation of the Antarctic ozone hole.
Trace gases in the Antarctic atmosphere
Authors: Heidt L. E. , Vedder J. F. , Pollock W. H. , Lueb R. A. , Henry B. E.
Published: February 2008

Fundamentally, the hypotheses that have been presented to explain the late winter loss of Antarctic ozone fall into two broad categories. One is that it is essentially chemical in origin, the other that it is caused by dynamically induced ingress of ozone‐poor air from the troposphere. Whole‐air samples collected aboard both the NASA ER‐2 and DC‐8 aircraft as part of the Airborne Antarctic Ozone Experiment (AAOE) were analyzed in a field laboratory set up at Punta Arenas, Chile. Mixing ratios obtained from gas chromatographic analyses of these samples are presented for CH4, CO, N2O, CFCl3, CF2Cl2, C2F3Cl3, CH3CCl3, and CCl4. Variations in the mixing ratios of these trace gases provide valuable information for both categories of postulation as indicators of the presence, motions, and history of air masses in the Antarctic atmosphere. Evidence of sustained subsidence is clearly indicated by comparison of CFCl3/N2O mixing ratios from the flights of September 16–29, 1987.
Charge transfer during single crystal interaction with a rimed target
Authors: Kumar P. Pradeep , Saunders C. P. R.
Published: February 2008

Laboratory experiments were carried out to investigate the charge transfer resulting from a limited number of growing ice crystal interactions with a previously rimed target. Crystal sizes up to 200 μm were used for the study. It was observed that the sign of the charge transfer was controlled by the relative growth rates of the interacting particles with the faster growing particle charging positively. The charge transfer magnitude was of the same order as was obtained in multiple ice crystal collision experiments, thus giving confidence to those measurements.
Seasonal variation of cloud‐to‐ground lightning flash characteristics in the coastal area of the Sea of Japan
Authors: Hojo J. , Ishii M. , Kawamura T. , Suzuki F. , Komuro H. , Shiogama M.
Published: February 2008

Cloud‐to‐ground lightning flashes in a coastal area of the Sea of Japan have been observed for a few years by a magnetic direction‐finding system for lightning return strokes. Through the operational evaluation of the system, the data obtained so far have been carefully analyzed and corrected. In winter the activity of lightning does not move inland farther than 20–30 km from the coastline, and most of the flashes are detected on the sea. Seasonal variations are also found in polarities and magnetic signal strengths of lightning return strokes.
Photoelectric return‐stroke velocity and peak current estimates in natural and triggered lightning
Authors: Mach Douglas M. , Rust W. David
Published: February 2008

Using data from a mobile photoelectric device, we present two‐dimensional return‐stroke velocities from 130 strokes that consist of 86 negative natural, 41 negative triggered, one positive triggered, and two positive natural return‐strokes. The velocity measurements are divided into two groups: “short‐channel” values with channel segments starting near the ground and less than 500 m in length and “long‐channel” values that start near the ground and exceed 500 m in length. The average long‐channel velocity is 1.3 ± 0.3 × 108 m s−1 for natural return‐strokes and 1.2 ± 0.3 × 108 m s−1 for triggered return‐strokes. For the short channels, natural return‐strokes have a statistically higher (at the 98% confidence level) average velocity of 1.9 ± 0.7 × 108 m s−1 than triggered strokes with an average velocity of 1.4 ± 0.4 × 108 m s−1. We compare our results with previous measurements of the return‐stroke velocity for comparable channel segment lengths and find that there is no statistical difference between our results and the previous ones. A qualitative analysis indicates that the optical waveform from a return‐stroke generally increases in risetime and decreases in amplitude at greater altitudes. Using the transmission line model (TLM), the shortest segment one‐dimensional return‐stroke velocity, and either the maximum or plateau electric field, we find natural strokes have a peak current distribution that is lognormal with a median value of 16 kA (maximum E) or 12 kA (plateau E) while triggered lightning has a median peak current value of 21 kA (maximum E) or 15 kA (plateau E). We find substantial differences between TLM and the shunt‐measured peak currents and find no significant correlation between shunt peak currents and triggered return‐stroke velocities. We do find correlations between TLM peak currents and velocities for triggered and natural subsequent return‐strokes but not between TLM peak currents and natural first return‐stroke velocities. In both cases where a correlation is found, the trend is for greater peak currents to be associated with lower return‐stroke velocities. Our peak current calculations are approximately half as large as previously reported. This difference is attributed to the greater return‐stroke velocity measured by our photoelectric device and used in the transmission line model. Hence previous estimates of the return‐stroke peak current seem too high. Two natural single‐stroke positive cloud‐to‐ground flashes had velocities of 1.0 and 1.7 × 108 m s−1 and peak currents of 120–150 kA.
Positive lightning strokes to ground
Authors: Brook Marx , Henderson R. W. , Pyle Richard B.
Published: February 2008

Lightning stroke occurrences often appear to have been sorted polarity‐wise in both space and time, especially in winter storms. This phenomenon raises a number of important questions related to charge separation in meteorological environments which may favor one polarity over the other. If the lightning locating hardware is correctly identifying ground stroke polarities, then additional considerations need be given to charging processes that are operative when the main convective phase of the thunderstorm is over. Clearly, a check on the validity of the network polarity determinations is warranted. We have studied the correctness of the polarity assignments as determined by the LLP hardware used in the SUNYA lightning detection network. From a very limited sample of waveforms recorded during the winters of 1986–1987 and 1987–1988, we conclude that present acceptance criteria are adequate, provided that distances from strokes to stations do not exceed 600 km. Polarity determinations with present algorithms can often be incorrect for strokes beyond 700 km as a result of the misidentification of the ionospheric reflection for the strongly attenuated ground wave.
Positive cloud‐to‐ground lightning detection by a direction‐finder network
Authors: MacGorman Donald R. , Taylor William L.
Published: February 2008

We have investigated how reliably an automatic direction‐finder network manufactured by Lightning Location and Protection, Inc. (LLP), identifies cloud‐to‐ground (CG) flashes that effectively lower positive charge to ground (+CG flashes). To provide independent verification of the occurrence of +CG flashes, we examined records from an extremely low frequency (ELF) system to determine whether 340 +CG flashes detected by the LLP system had coincident ELF waveforms characteristic of +CG flashes. The fraction of +CG flashes that had coincident ELF waveforms increased from 0.67 for flashes with range‐normalized amplitudes of 0–25 LLP units to an average of 0.93 for flashes with range‐normalized amplitudes of at least 75 LLP units. We also analyzed ELF coincidence for −CG flashes recorded by video systems and by the LLP system. A comparison of the results for +CG flashes and CG flashes suggests (1) that false detection is negligible in the LLP system for +CG flashes with range‐normalized amplitudes of at least 50 LLP units and (2) that no more than about 15% of the +CG flashes detected by the LLP system at smaller amplitudes are false detections. The true percentage of +CG flash detections that are false is probably even lower, because at least some of the decrease in ELF coincidence at low amplitudes appears to have been caused by an increase in the fraction of coincident ELF signals that occurred below the ELF system's noise level.
Intercomparison of ozone measurements over Antarctica
Authors: Margitan J. J. , Brothers G. A. , Browell E. V. , Cariolle D. , Coffey M. T. , Farman J. C. , Farmer C. B. , Gregory G. L. , Harder J. W. , Hofmann D. J. , Hypes W. , Ismail S. , Jakoubek R. O. , Komhyr W. , Kooi S. , Krueger A. J. , Larsen J. C. , Mankin W. , McCormick M. P. , Mount G. H. , Proffitt M. H. , Ravishankara A. R. , Schmeltekopf A. L. , Starr W. L. , Toon G. C. , Torres A. , Tuck A. F. , Wahner A. , Watterson I.
Published: February 2008

Measurements of the abundances of ozone over Antarctica in August and September 1987 obtained during the Airborne Antarctic Ozone Experiment are intercompared. These measurements of ozone concentrations and total column abundance were obtained by three satellite instruments, two IR and one UV column‐measuring instruments aboard the DC‐8, one in situ DC‐8, and two in situ ER‐2 instruments, an upward looking lidar aboard the DC‐8, and ozonesondes from four sites in Antarctica. Given the natural variability of ozone in the Antarctic and the fact that the data were not truly coincident spatially and temporally, this intercomparison is suitable only for identifying gross disparities among the techniques, rather than confirming the accuracies as rigorously as is normally done in an intercomparison. This paper presents a summary of the ozone data, using the data and accuracies given by the individual investigators in the individual papers in this issue, without any attempt to critically review or evaluate the data. In general, very good agreement (within about 10–20%, limited by natural variability) among the various techniques was found, with no systematic biases detected. These observations confirm the low ozone amounts reported in the Antarctic stratosphere.
Evaluation of the atmospheric transport of marine‐derived particles using long‐chain unsaturated ketones
Authors: Sicre M.‐A. , Gagosian R. B. , Peltzer E. T.
Published: February 2008

Biomarker source information provided by long‐chain alkenone (LCA) distribution patterns was used to assess the transport pathways of marine aerosols. The C37–C39 LCA were found in significant amounts in aerosols collected in New Zealand. Their occurrence in the atmosphere stems from their introduction by bubble‐bursting processes during wave breaking. The surface water temperatures calculated from the U37k ratios suggested a local origin and short atmospheric residence times of the LCA. They were not detected in aerosol samples collected on American Samoa due to the absence of the source organisms in surface waters. The distribution of LCA was also investigated in size‐fractionated aerosols over a range of <0.5 to >7.2 μm equivalent diameter. Their distribution over the size spectrum demonstrated that they were only associated with large particles (deq > 3.0 μm), suggesting a direct injection of algal cells and/or their fragments into the atmosphere.
Numerical simulation of the August 1986 heavy rainfall event in the Sydney area
Authors: Hess G. D.
Published: February 2008

In the 24‐hour period beginning 2300 UTC on August 4, 1986, an intense east coast cyclone produced 328 mm of rain in Sydney, Australia, causing widespread flooding. The operational quantitative precipitation forecast, based on 150‐km resolution, was poor, predicting only 16 mm of rain. In this study, numerical simulations of this event are carried out after modifying the large‐scale and cumulus convection precipitation mechanisms. These changes make the mechanisms mutually exclusive at a given time and grid point, and more sensitive to orographic forcing and surface energy fluxes. Marked improvement in the amounts of predicted rainfall occurs as the horizontal resolution of the model increases. These results indicate that mesoscale processes play an important role in determining rainfall amounts associated with east coast cyclones and demonstrate the potential to accurately simulate very heavy rainfall events.
Hydrologic modeling Of New England river basins using radar rainfall data
Authors: Wyss Jonathan , Williams Earle R. , Bras Rafael L.
Published: February 2008

Quantitative weather radar measurements of rainfall provide the input to a hydrologic forecast model designed to use the full spatial resolution of the radar data. The gridded model, which incorporates a detailed map of the stream network, is based on a simple kinematic representation of the river basin response. Only two parameters control the shape of the hydrograph: the velocity characteristic of subsurface flow to the nearest stream, and the streamflow velocity itself. Comparisons are made between model hydrograph forecasts and observed streamflow records for the Souhegan (440 km2), and the Squannacook (160 km2) river basins. A single Z‐R relation was used for all storms (Z = 230R1.4), except for one case with strong convection (Z = 400R1.3). A linear scaling of the volume of the radar‐derived storm rainfall produces reasonable agreement between the predicted and observed hydrographs. The volume scale factor, which varies from 20% or less in the summer to 100% in the spring, is consistent with the climatological mean monthly rainfall‐runoff ratio. In the two basins studied, for hydrograph peaks of moderate amplitude, overland flow and other quickflow components of the hydrograph are not generally observed. The hillslope response is modeled by a single characteristic subsurface flow velocity (2 × 10−3 m s−1), with a streamflow velocity of 0.6 m s−1 in the Souhegan, (0.3 m s−1 in the Squannacook). The results suggest that models which utilize the basin geometry and rainfall data to a maximum, but which otherwise contain few parameters, can be very successful.
Estimating the exceedance probability of rain rate by logistic regression
Authors: Chiu Long S. , Kedem Benjamin
Published: February 2008

Recent studies have shown that the fraction of an area with rain intensity above a fixed threshold is highly correlated with the area‐averaged rain rate. To estimate the fractional rainy area, a logistic regression model, which estimates the conditional probability that rain rate over an area exceeds a fixed threshold given the values of related covariates, is developed. The problem of dependency in the data in the estimation procedure is bypassed by the method of partial likelihood. Analyses of simulated scanning multichannel microwave radiometer and observed electrically scanning microwave radiometer data during the Global Atlantic Tropical Experiment period show that the use of logistic regression in pixel classification is superior to multiple regression in predicting whether rain rate at each pixel exceeds a given threshold, even in the presence of noisy data. The potential of the logistic regression technique in satellite rain rate estimation is discussed.
Distribution of tropospheric ozone determined from satellite data
Authors: Fishman Jack , Watson Catherine E. , Larsen Jack C. , Logan Jennifer A.
Published: February 2008

An analysis of more than 22,000 ozone profiles from Stratospheric Aerosol and Gas Experiment I (SAGE I) (1979–1981) and SAGE II (1984–1987) between 50°N and 50°S is used in conjunction with 9 years (1979–1987) of daily global depictions of total ozone from the Total Ozone Mapping Spectrometer (TOMS) instrument aboard Nimbus 7 to investigate the spatial distribution and seasonal cycle of the integrated amount of ozone in the troposphere. In the tropics, highest concentrations are found in the eastern Atlantic Ocean downwind (west) of Africa and maximize during the time when biomass burning is most prevalent, between July and October. A different seasonal cycle in the tropics is also observed over Indonesia where a relative maximum is present in the March–April time frame, likewise consistent with when biomass burning is most prevalent. At mid‐latitudes, highest concentrations are found downwind of Asia and maximize in the summer. Relatively higher amounts of tropospheric ozone are similarly observed downwind of North America and Europe. At mid‐latitudes, the ratio between the amount of tropospheric ozone in the northern hemisphere and the amount in the southern hemisphere is 1.4, in good agreement with in situ measurements. A detailed comparison of this satellite technique with available ozonesonde measurements suggests that the accuracy of this method for deriving the climatology of tropospheric ozone is probably better than 10% in the tropics and 15% at mid‐latitudes. We also show that TOMS total ozone measurements in the tropics can often be used independently to provide important qualitative insight into the behavior of tropospheric ozone at these low latitudes.
Processing and interpretation of microbarograph signals generated by the explosion of Mount St. Helens
Authors: Delclos C. , Blanc E. , Broche P. , Glangeaud F. , Lacoume J. L.
Published: February 2008

Following the eruption of the Mount St. Helens volcano on May 18, 1980, atmospheric waves were recorded by a network of microbarographs located over 7000 km from the source. Analysis of these data requires the use of complex processing techniques based on a high‐resolution method to extract the signals produced by the St. Helens source from spurious waves or noise in each record. This facilitates interpretation of the wave trains in terms of propagation modes. It is thus shown that Lamb mode L0 is present in the low‐frequency part of all the signals, whereas acoustic modes (more probably A′2) are needed to explain all the properties of the high‐frequency part, which is clearly observed for a westward and a southward propagation.
An assessment of the impact of volcanic eruptions on the northern hemisphere's aerosol burden during the last decade
Authors: Michalsky J. J. , Pearson E. W. , LeBaron B. A.
Published: February 2008

We present an analysis of volcanic aerosol loading above a northern mid‐latitude observing station during the last decade, with particular attention to the decay in the aerosol resulting from the 1982 eruption of El Chichon. The optical depth data at five wavelengths are derived from sunradiometry data. These are tabulated, and inferences regarding size distribution of the volcanic aerosol are drawn. Comparison with a number of other data sets is used to establish the validity of our ground‐based technique, and to draw inferences regarding stratospheric transport. We also report simulation calculations designed to establish the capabilities and limitations of our measurement and analysis techniques. The main conclusions of the study are as follows. Under suitable conditions, ground‐based sunradiometry can reliably monitor variations in the stratospheric aerosol of less than 0.01 optical depths on time scales of a few weeks or longer. Large (on the order of 0.5 micrometer) particles remained present throughout the decay of the El Chichon aerosol, and there is substantial agreement among mid‐latitude data sets collected by several techniques; thus inferences regarding stratospheric transport can be drawn from joint analysis of the available data. The available evidence supports the proposition that mid‐latitude decay is modulated by annual transport of fresh material from low latitudes, primarily, with some transport from polar latitudes.
Satellite measurements of large‐scale air pollution: Measurements of forest fire smoke
Authors: Ferrare Richard A. , Fraser Robert S. , Kaufman Yoram J.
Published: February 2008

The transport, optical properties, total mass, and removal of smoke produced by forest fires in western Canada during late July and early August 1982 are studied using NOAA 7 Advanced Very High Resolution Radiometer (AVHRR) data. Color composite imagery is produced to track the movement of the smoke over Canada and the United States as the smoke traveled thousands of kilometers from the source region. Smoke optical thickness, particle size, and single scattering albedo (ratio of particle scattering to extinction) are computed using radiances measured by AVHRR bands 1 (0.58–0.68 μm) and 2 (0.72–1.10 μm). Results show that smoke optical thickness ranged from less than 0.1 greater than 3.7 and the geometric mean mass radii ranged from 0.3 to 0.9 μm. The smoke single scattering albedo ranged from 0.9 to nearly 1.0. The total smoke mass over the eastern United States, computed using the derived particle size and optical thickness, ranged from 0.1 to 0.5 Tg which is close to the 0.5 Tg estimated to have been produced by the fires based on the forest fuel content. The smoke lifetime is estimated to be between 15 and 20 days.
Potential evapotranspiration and the likelihood of future drought
Authors: Rind D. , Goldberg R. , Hansen J. , Rosenzweig C. , Ruedy R.
Published: February 2008

The likelihood of future drought is studied on the basis of two drought indices calculated from the Goddard Institute for Space Studies general circulation model (GISS GCM) transient and doubled CO2 climate changes. We use the Palmer drought severity index (PDSI) and a new supply‐demand index (SDDI), the latter being the difference between the precipitation and potential evapotranspiration Ep, i.e., the difference between atmospheric supply of and demand for moisture. Both indices show increasing drought for the United States during the next century, with effects becoming apparent in the 1990s. If greenhouse gas emissions continue to increase rapidly, the model results suggest that severe drought (5% frequency today) will occur about 50% of the time by the 2050s. The results are driven by the large increase in EP, associated with the simulated climate warming. EP increases most where the temperature is highest, at low to mid‐latitudes, while precipitation increases most where the air is coolest and easiest to saturate by the additional moisture, at higher latitudes. Thus atmospheric demand becomes greater than supply for most of the globe by the latter half of next century. We show that large EP changes can lead to soil moisture deficits, as in the PDSI hydrologic budget, and vegetation desiccation, as is implied by vegetation and climate models. We suggest that drought intensification has been understated in most GCM simulations, including the GISS GCM, because of their lack of realistic land surface models. Paleoclimate analogues in the Mesozoic and Cenozoic are reviewed which imply that arid conditions can result from either increased temperatures or decreased precipitation, consistent with our use of the SDDI. The results depend primarily on the temperature increase, in particular the model sensitivity of 4°C warming for doubled CO2. Global precipitation cannot keep pace with increased demand over land because the land surface warms more than the ocean surface; this effect, along with greater atmospheric opacity, reduces low level gradients and evaporation from the ocean. If the forecast temperature changes come to pass, these conclusions suggest that drought conditions will increase dramatically.
A physical model of the bidirectional reflectance of vegetation canopies: 2. Inversion and validation
Authors: Pinty Bernard , Verstraete Michel M. , Dickinson Robert E.
Published: February 2008

A physically based, analytical model of the bidirectional reflectance of porous media was derived in a companion paper (Verstraete et al., this issue). This model is validated against laboratory and ground‐based measurements taken over two vegetation covers, both in the visible and near‐infrared spectral regions. An inversion procedure, based on a nonlinear optimization technique, is used to infer the intrinsic optical properties of the leaves, as well as information on the morphology of the canopies, that is, on the geometrical arrangements of these scatterers in space. The model is then used to generate theoretical bidirectional reflectances, using the values of the relevant parameters retrieved from the inversion procedure, and these values compare favorably with the actual observations over the entire range of illumination and observation angles. The values of the parameters retrieved from the inversion procedure are discussed, validated against actual independent measurements, and interpreted in terms of the physical and morphological properties of the vegetation covers.
Comparison of SAGE II ozone measurements and ozone soundings at Uccle (Belgium) during the period February 1985 to January 1986
Authors: De Muer D. , De Backer H. , Veiga R. E. , Zawodny J. M.
Published: February 2008

The ozone profiles obtained from 24 balloon soundings at Uccle (50°48′N, 4°21′E) made with electrochemical ozonesondes were used as correlative data for SAGE II ozone profiles retrieved within a distance of at most 600 km from Uccle. The agreement between the two data sets is in general quite good, especially for profiles nearly coincident in time and space, and during periods of little dynamic activity over the area considered. The percent difference between the ozone column density of the mean balloon and SAGE profile is 4.4% (−3.3%) in the altitude region between 10 and 26 km (26 and 31 km). From a statistical analysis it appears that there is a small but meaningful difference between the mean profiles at the level of the ozone maximum and around the 30‐km level. An error analysis of both data sets gives similar results, leading to the conclusion that these differences are instrumentally induced. However, differences between the mean profiles in the lower stratosphere are probably real and due to the high ozone variability in time and space in that altitude region.
A descriptive atmospheric transport climatology for the Mauna Loa Observatory, using clustered trajectories
Authors: Harris Joyce M. , Kahl Jonathan D.
Published: February 2008

The climatology of long‐range atmospheric transport to the Mauna Loa Observatory (MLO) is examined through an analysis of 10‐day isobaric back trajectories for the period 1981–1988, computed using the National Meteorological Center's analyzed gridded winds. The trajectories are classified into distinct transport patterns through the use of cluster analysis, a procedure that avoids the somewhat arbitrary classification by compass sector and instead searches for meaningful groupings within the data themselves. The clustering procedure is performed separately for yearly and monthly sets of 500‐ and 700‐hPa trajectories to examine both year‐to‐year and month‐to‐month variability in flow characteristics. The dominant transport features are quite similar from year to year, and include frequent summertime easterly flow associated with the trade winds and strong, wintertime westerly flow close to the mean axis of the subtropical jet stream. Veering westerly patterns that approach MLO from the north and northeast dominate during winter/summer transition periods. Other noteworthy features include recurring air mass transport from Saharan and Asian desert regions, infrequent interhemispheric flow from as far as 10°S, and occasional flow from high northern latitudes. Ten‐day back trajectories that pass over anthropogenic pollution source regions in western North America are rare.
Annual nitrous oxide fluxes from temperate forest soils in the northeastern United States
Authors: Bowden Richard D. , Steudler Paul A. , Melillo Jerry M. , Aber John D.
Published: February 2008

Nitrous oxide (N2O) fluxes were measured from soils in a red pine plantation and a mixed hardwood stand in the northeastern United States. On an annual basis, the pine stand had an efflux of 0.010±0.015 kg N/ha/yr and the hardwood stand had an efflux of 0.017±0.017 kg N/ha/yr. Low net nitrification rates in both stands are suggested as the reason for the low rates of N2O emissions. Slight seasonal trends were noted in both stands, with highest efflux rates in early summer and late fall. Both stands showed small but extended periods of uptake during summer and early fall. Diel patterns were not observed in either stand. This study suggests that on a global basis, a lower limit for N2O emissions from temperate forests is 0.012 Tg N/yr, contributing less than 1% of the estimated total emissions from terrestrial sources.