bluuebunny/crossref_metadata_2025 huggingface dataset:
Hygroscopic growth of aerosol particles in the marine boundary layer over the Pacific and Southern Oceans during the First Aerosol Characterization Experiment (ACE 1)
Authors: Berg Olle H. , Swietlicki Erik , Krejci Radovan
Published: February 2004

The hygroscopic properties of submicrometer aerosol particles were studied with a Hygroscopic Tandem Differential Mobility Analyzer (H‐TDMA) in the remote marine tropospheric boundary layer (MBL) over the Pacific and Southern Oceans in connection with the southern hemisphere marine First Aerosol Characterization Experiment (ACE 1) in October–December 1995. The H‐TDMA was placed on board the ship R/V NOAA Discoverer and measured the hygroscopic diameter growth of individual aerosol particles when taken from a dry state to a relative humidity (RH) of 89–90%. Measurements were performed for the particles with dry diameters of 35, 50, 75, and 150 (or 165) nm. The natural aerosol present in the remote MBL largely consists of two types, a sea‐salt component and a non‐sea‐salt (nss) sulfate component. Since their hygroscopic behavior is significantly different, the H‐TDMA could clearly distinguish between these two types and thus make in situ measurements of the mixing state of the MBL aerosol. During the ACE 1 intensive campaign in the Southern Ocean south of Australia, the hygroscopic diameter growth factors at RH = 90% for the nss‐sulfate aerosol particles were 1.62, 1.66, and 1.78 at dry particle diameters of 35, 50, and 150 nm, respectively, and for time periods with remote marine air masses. These values exceed those normally found in continental polluted environments. The growth factors for the externally mixed sea‐salt particles were even higher (2.12 and 2.14 for 50 and 150 nm). The corresponding values for the Pacific Ocean (at RH = 89%) for the nss‐sulfate particles were 1.56, 1.59, 1.61, and 1.63 for 35, 50, 75, and 165 nm. Particle deliquescence and RH hysteresis between RH = 68–90% was only observed in air masses north of the South Pacific Gyre, and then only for the Aitken mode particles (particle diameters ∼20–80 nm). The occurrence of externally mixed sea‐salt particles could be linked to conditions with high wind speeds in connection with frontal passages or low pressure systems. Nevertheless, the number of externally mixed 150 nm sea‐salt particles was found to be poorly correlated with local wind speed, probably due to a rather long life‐time of these submicrometer particles. Particles with hygroscopic growth factors significantly less than those of the nsssulfate particles (denoted less hygroscopic particles) were only present during periods with anthropogenic influence.
Ozone and meteorology during the 1994 Polar Sunrise Experiment
Authors: Hopper J. F. , Barrie L. A. , Silis A. , Hart W. , Gallant A. J. , Dryfhout H.
Published: February 2004

Observations of ozone mixing ratios in the lower troposphere of Arctic Canada in April 1994 are summarized. Except during a brief period of anomalous transport from high altitude, air depleted in ozone was always observed above sea ice and snow throughout the northern Ellesmere Island/Lincoln Sea region, or whenever air was sampled which had been in recent contact with sea ice and snow. Ozone mixing ratios observed at a camp on the sea ice north of Alert were consistent with a 1992 study. Observations at the ice camp confirmed that ozone was depleted more frequently (74% of all observations <5 ppbv) than at coastal and inland sites near Alert (10% of observations <5 ppbv). Mixing ratios briefly attained a maximum of 36 ppbv at the ice camp but were normally completely depleted or below typical free tropospheric levels of 35–45 ppbv observed elsewhere in the region. Aircraft measurements and vertical profiles of ozone and meteorological parameters from balloon sondes confirmed that ozone depletion existed in a layer above the sea ice, from the surface up to heights of 200–400 m. Some observations showed a very abrupt transition between depleted and nondepleted conditions at the upper boundary of the layer. The occurrence of a layer of fully depleted ozone was well correlated with surface high‐pressure systems. At Alert the appearance of air that was fully depleted in ozone was driven by advection from ocean areas to the north. A fortuitous set of meteorological conditions allowed the use of a simple model for testing general aspects of some proposed hypotheses for ozone destruction, during a period when it is believed the depleted layer was forming. It was found that the observed rate of ozone destruction would require levels of HO and Cl atoms much higher than would be expected for the prevailing conditions but reasonable concentrations of Br atoms. It was also found that an effective ozone deposition velocity of 0.1–0.2 cm s−1 could account for the observed depletion rate during this period. That is, the observed rate of ozone depiction during formation of a depleted layer was consistent with either a volume sink or a surface sink for ozone.
Patterns in volatile organic compound emissions along a savanna‐rainforest gradient in central Africa
Authors: Klinger L. F. , Greenburg J. , Guenther A. , Tyndall G. , Zimmerman P. , M'Bangui M. , Moutsamboté J.‐M. , Kenfack D.
Published: February 2004

In temperate regions the chemistry of the lower troposphere is known to be significantly affected by biogenic volatile organic compounds (VOCs) emitted by plants. The chemistry of the lower troposphere over the tropics, however, is poorly understood, in part because of the considerable uncertainties in VOC emissions from tropical ecosystems. Present global VOC models predict that base emissions of isoprene from tropical rainforests are considerably higher than from savannas. These global models of VOC emissions which rely mainly on species inventories are useful, but significant improvement might be made with more ecologically based models of VOC emissions by plants. Ecosystems along a successional transect from woodland savanna to primary rainforest in central Africa were characterized for species composition and vegetation abundance using ground surveys and remotely sensed data. A total of 336 species (mostly trees) at 13 sites were recorded, and 208 of these were measured for VOC emissions at near‐optimal light and temperature conditions using a leaf cuvette and hand‐held photoionization detector (PID). A subset of 59 species was also sampled using conventional VOC emission techniques in order to validate the PID technique. Results of ecological and VOC emission surveys indicate both phylogenetic and successional patterns along the savanna‐rainforest transect. Genera and families of trees which tend to emit isoprene include Lophira, Irvingia, Albizia, Artocarpus, Ficus, Pterocarpus, Caesalpiniaceae, Arecaceae, and Moraceae. Other taxa tend to contain stored VOCs (Annonaceae and Asteraceae). Successional patterns suggest that isoprene emissions are highest in the relatively early successional Isoberlinia forest communities and progressively decrease in the later successional secondary and primary rainforest communities. Stored VOCs appear to increase along the savanna‐rainforest succession, but these data are more tentative. These findings are consistent with successional patterns of isoprene and terpene fluxes in North American forests and highlight the feasibility of constructing better predictive models of VOC emissions.
Temperature‐dependent nucleation rate constants and freezing behavior of submicron nitric acid dihydrate aerosol particles under stratospheric conditions
Authors: Bertram A. K. , Sloan J. J.
Published: February 2004

The freezing of a submicron‐sized aerosol composed of H2O and HNO3 in a precise 2:1 concentration ratio has been measured using Fourier transform infrared extinction spectroscopy. The measurements were carried out in a flow tube operating at temperatures and pressures appropriate to the polar stratosphere. On the timescale of this measurement, about 15 s, detectable nucleation occurred at 179±1.6 K. Ten percent of the sample was frozen after 15 s at a temperature of 178.8 K; 50% was frozen at 177.5 K, and 90% was frozen at 175.8 K. Using the known (constant) aerosol flow velocity, the nucleation rate constant was obtained from the freezing point measurements. Values of this rate constant are reported over the temperature range between 176 K and 179 K. In this range the freezing temperature is in excellent agreement with that measured by Barton et al. [1993], and the temperature dependence of the nucleation rate constant agrees well with that calculated using the method of MacKenzie et al. [1997]. It does not agree with that reported by Tisdale et al. [1997]. Extrapolation of the rates indicate that nitric acid dihydrate nucleation from liquid aerosol droplets having a 2:1 H2O:HNO3 composition would occur on the stratospherically relevant timescales of 1 hour and 1 day at temperatures of 183 and 185 K, respectively.
Sudden narrow temperature‐inversion‐layer formation in ALOHA‐93 as a critical‐layer‐interaction phenomenon
Authors: Huang T. Y. , Hur H. , Tuan T. F. , Li X. , Dewan E. M. , Picard R. H.
Published: February 2004

A sudden and dramatic mesospheric heating event was observed over Haleakala, Maui, on October 21, 1993 (day 294), during the ALOHA‐93 Campaign. It consisted of a persistent, narrow temperature‐inversion layer about 3–4 km wide near 87 km altitude with a peak temperature rise approaching 40 k, lasting for about 3.5 hours. Owing to the large number of ground‐based instruments recording the event, it is possible to attempt to seek out a physical explanation for this temperature rise. There is powerful evidence to suggest that the temperature‐inversion layer is associated with energy deposition, direct and indirect, resulting from gravity wave/critical layer interaction. Indeed, lidar wind profiles and mesospheric wave structures simultaneously observed with CCD imagers reveal the presence of a critical layer at the appropriate altitude. The data also show a narrow unstable background wind profile over a 2–3 km thickness in the immediate vicinity of the critical layer. We will show quantitatively that there is sufficient energy available from the dissipation of the observed gravity wave and from the observed instability in the background winds to account for the heating. After the critical layer has disappeared, the temperature rise subsides, and the background wind again becomes stable at all height levels of interest.
High‐latitude, summertime NOx activation and seasonal ozone decline in the lower stratosphere: Model calculations based on observations by HALOE on UARS
Authors: Brühl Christoph , Crutzen Paul J. , Grooß Jens‐Uwe
Published: February 2004

Between May and September a continuous decrease of ozone concentrations is observed in the lower stratosphere at high latitudes in the northern hemisphere. Low local ozone concentrations are correlated with high concentrations of NO and NO2, and HCl. A detailed photochemical box model and a two‐dimensional chemical model initialized by the Halogen Occultation Experiment (HALOE) data are used to calculate ozone destruction rates between 20 and 31 km altitude for different situations during the observational periods in mid and late summer. The largest ozone destruction rates are computed for ozone‐rich midlatitude air masses that are transported to high latitudes reaching low Sun, but 24 hours per day sunlight conditions. It is shown that the observed summertime low ozone concentrations and much of the seasonal course of ozone is due to catalytic ozone destruction by NO and NO2, which become the main odd nitrogen compounds under these conditions.
Mesoscale airborne in situ and lidar observations of variance and spatial structure in the troposphere and stratosphere regions
Authors: Gao X. , Meriwether J. W.
Published: February 2004

Observations over the Canadian terrain of the Rocky Mountains and the Plains by airborne in situ and lidar measurements during two flights of the ALOHA/ANLC‐93 campaign were used to study orographic effects on the tropospheric and stratospheric dynamics. The variance of the tropospheric vertical wind at 6 km altitude is found to be about 2.6 times larger for the air above rough terrain than for the air over the Plains. The amplitudes of the zonal wavenumber spectra of the tropospheric horizontal and vertical wind components were considerably larger for data collected over the Rocky Mountain area than that collected over the Plains with much higher energy at wavenumbers <10−5 cycles/m. Comparison of the 589 nm Rayleigh lidar data observed for the two flights for altitudes between 30 and 45 km showed higher root‐mean‐square amplitudes of atmospheric density fluctuations between 30 to 35 km over rough terrain. No significant difference between the two flights was seen for heights above 35 km.
Aerosol size distributions obtained from HALOE spectral extinction measurements
Authors: Hervig Mark E. , Deshler Terry , Russell James M.
Published: February 2004

A technique was developed to use multiwavelength aerosol extinction measurements from the Halogen Occultation Experiment (HALOE) to determine the size distribution of stratospheric H2O‐H2SO4 aerosols. Although the HALOE extinction spectrum alone cannot be used to reliably infer the aerosol size distribution (except when the aerosol population contains particles larger than about 0.5 μm), the inverse problem becomes highly defined when the effective radius is known. Using theoretical relationships derived from in situ aerosol measurements, we found that the effective radius can be determined from the HALOE 2.45 μm extinction with uncertainties of about ±15%. Using extinction ratios with the effective radii determined from the HALOE extinctions, we obtained unimodal lognormal size distributions. The HALOE size distributions are generally unbiased with respect to coincident in situ aerosol measurements. Error analysis reveals that uncertainties in the inferred surface areas and volumes are less than 30% and 15%, respectively. Inferring size distributions from the HALOE data set provides global and temporal aerosol information, which can satisfy important needs for investigations of the Earth's radiative and chemical balance.
The Jungfraujoch high‐alpine research station (3454 m) as a background clean continental site for the measurement of aerosol parameters
Authors: Nyeki S. , Baltensperger U. , Colbeck I. , Jost D. T. , Weingartner E. , Gäggeler H. W.
Published: February 2004

The first annual data set of climatically important aerosol parameters, measured at the Jungfraujoch (JFJ) high‐alpine research station (3454 m, Switzerland) from an ongoing field campaign since July 1995, is presented. Analysis of diurnal variations in continuous measurements of the total and backward hemispheric scattering coefficients (σSP, σBSP), the absorption coefficient (σAP, from aethalometer data), condensation nuclei (CN) concentration, and epiphaniometer signal (related to surface area (S) concentration) established the diurnal period 0300 – 0900 as being representative of the free tropospheric background aerosol. The annual data set was then edited to omit (1) the period 0900–0300 (i.e., 18 hours), taken to represent possible planetary boundary layer influenced conditions and (2) in‐cloud conditions using a cloud liquid‐water monitor. The seasonal aerosol cycle exhibited a July maximum and a December minimum in most aerosol parameters. Typical monthly median values for the free troposphere exhibit the following seasonal maxima and minima, respectively: σSP (550 nm) ∼ 16.1 and 0.43 × 10−6 m−1, σBSP (550 nm) ∼ 2.10 and 0.09 × 10−6 m−1, σAP (550 nm) ∼ 10.4 and 0.76 × 10−7 m−1 (≈ 104 and 7.6 ng m−3 black carbon), CN concentration ∼ 670 and 280 cm−3, and epiphaniometer signal ∼ 9.26 and 0.67 counts s−1 (S concentration ≈24.1 and 1.7 μm2 cm−3). Aerosol parameters were found to be comparable in magnitude to other NOAA baseline and regional stations and suggest that a clean continental designation for the JFJ site is applicable, when removing the planetary boundary layer influenced period.
Fallout of chlorine 36 to the Earth's surface in the southern hemisphere
Authors: Keywood M. D. , Fifield L. K. , Chivas A. R. , Cresswell R. G.
Published: February 2004

Chlorine 36 is a radioactive isotope produced in the atmosphere by the cosmic‐ray spallation of 40Ar. It has many applications as an environmental tracer which require an understanding of 36Cl in modern deposition. Data are currently available only for high latitudes in the northern hemisphere and for Antarctica. In the present work, the first data for 36Cl in modern deposition for the southern hemisphere are presented. Excluding the tropical data, the latitude dependence of this fallout is found to follow the form predicted by Lal and Peters, and its magnitude is within 40% of their predictions. In tropical Australia, however, a substantial excess of 36Cl is observed in rainfall from sites that derived most of their precipitation from the summer monsoon. If the high‐latitude northern hemisphere data are representative of the entire hemisphere, then the southern hemisphere fallout appears to be 2–3 times less than in the northern hemisphere. It is suggested that this may be due to enhanced stratosphere‐troposphere exchange north of the equator promoted by the greater area of landmass, while the symmetric thermal structure of the southern atmosphere dampens this exchange.
Seasonal budgets of reactive nitrogen species and ozone over the United States, and export fluxes to the global atmosphere
Authors: Liang Jinyou , Horowitz Larry W. , Jacob Daniel J. , Wang Yuhang , Fiore Arlene M. , Logan Jennifer A. , Gardner Geraldine M. , Munger J. William
Published: February 2004

A three‐dimensional, continental‐scale photochemical model is used to investigate seasonal budgets of O3 and NOy species (including NOx and its oxidation products) in the boundary layer over the United States and to estimate the export of these species from the U.S. boundary layer to the global atmosphere. Model results are evaluated with year‐round observations for O3, CO, and NOy species at nonurban sites. A seasonal transition from NOx to hydrocarbon‐limited conditions for O3 production over the eastern United States is found to take place in the fall, with the reverse transition taking place in the spring. The mean NOx/NOy molar ratio in the U.S. boundary layer in the model ranges from 0.2 in summer to 0.6 in winter, in accord with observations, and reflecting largely the seasonal variation in the chemical lifetime of NOx. Formation of hydroxy organic nitrates during oxidation of isoprene, followed by decomposition of these nitrates to HNO3, is estimated to account for 30% of the chemical sink of NOx in the U.S. boundary layer in summer. Model results indicate that peroxyacylnitrates (PANs) are most abundant in the U.S. boundary layer in spring (25% of total NOy.), reflecting a combination of active photochemistry and low temperatures. About 20% of the NOx emitted from fossil fuel combustion in the United States in the model is exported out of the U.S. boundary layer as NOx or PANs (15% in summer, 25% in winter). This export responds less than proportionally to changes in NOx emissions in summer, but more than proportionally in winter. The annual mean export of NOx and PANs from the U.S. boundary layer is estimated to be 1.4 Tg N yr−1, representing an important source of NOx on the scale of the northern hemisphere troposphere. The eventual O3 production in the global troposphere due to the exported NOx and PANs is estimated to be twice as large, on an annual basis, as the direct export of O3 pollution from the U.S. boundary layer. Fossil fuel combustion in the United States is estimated to account for about 10% of the total source of O3 in the northern hemisphere troposphere on an annual basis.
In situ measurements of stratospheric ozone depletion rates in the Arctic winter 1991/1992: A Lagrangian approach
Authors: Rex M. , von der Gathen P. , Harris N. R. P. , Lucic D. , Knudsen B. M. , Braathen G. O. , Reid S. J. , De Backer H. , Claude H. , Fabian R. , Fast H. , Gil M. , Kyrö E. , Mikkelsen I. S. , Rummukainen M. , Smit H. G. , Stähelin J. , Varotsos C. , Zaitcev I.
Published: February 2004

A Lagrangian approach has been used to assess the degree of chemically induced ozone loss in the Arctic lower stratosphere in winter 1991/1992. Trajectory calculations are used to identify air parcels probed by two ozonesondes at different points along the trajectories. A statistical analysis of the measured differences in ozone mixing ratio and the time the air parcel spent in sunlight between the measurements provides the chemical ozone loss. Initial results were first described by von der Gathen et al. [1995]. Here we present a more detailed description of the technique and a more comprehensive discussion of the results. Ozone loss rates of up to 10 ppbv per sunlit hour (or 54 ppbv per day) were found inside the polar vortex on the 475 K potential temperature surface (about 19.5 km in altitude) at the end of January. The period of rapid ozone loss coincides and slightly lags a period when temperatures were cold enough for type I polar stratospheric clouds to form. It is shown that the ozone loss occurs exclusively during the sunlit portions of the trajectories. The time evolution and vertical distribution of the ozone loss rates are discussed.
Air‐snow exchange of HNO3 and NOy at Summit, Greenland
Authors: Dibb Jack E. , Talbot Robert W. , Munger J. William , Jacob Daniel J. , Fan Song‐Miao
Published: February 2004

Ice core records of NO3− deposition to polar glaciers could provide unrivaled information on past photochemical status and N cycling dynamics of the troposphere, if the ice core records could be inverted to yield concentrations of reactive N oxides in the atmosphere at past times. Limited previous investigations at Summit, Greenland, have suggested that this inversion may be difficult, since the levels of HNO3 and aerosol‐associated NO3− over the snow are very low in comparison with those of NO3− in the snow. In addition, it appears that some fraction of the NO3− in snow may be reemitted to the atmosphere after deposition. Here we report on extensive measurements of HNO3, including vertical gradients between 1.5 and 7 m above the snow, made during the summers of 1994 and 1995 at Summit. These HNO3 data are compared with NO3− concentrations in surface snow and the first measurements of the concentrations and fluxes of total reactive nitrogen oxides (Ny) on a polar glacier. Our results confirm that HNO3 concentrations are quite low (mean 0.5 nmol m−3) during the summer, while NO3− is the dominant ion in snow. Daytime peaks in HNO3− appear to be due at least partly to emissions from the snow, an assertion supported by gradients indicating a surface source for HNO3− on many days. Observed short‐term increases in NO3− inventory in the snow can be too large to be readily attributed to deposition of HNO3− suggesting that deposition of one or more other N oxides must be considered. We found that the apparent fluxes of HNO3 and NOy were in opposite directions during about half the intervals when both were measured, with more cases of HNO3 leaving the snow, against an NOy flux into the snow, than the reverse. The concentrations of NOy are generally about 2 orders of magnitude greater than those of HNO3; hence deposition of only a small, non‐HNO3, fraction of this pool could dominate NO3− in snow, if the depositing species converted to NO3−, either in the snowpack or upon melting for analysis.
Nightglow zenith emission rate variations in O(1S) at low latitudes from wind imaging interferometer (WINDII) observations
Authors: Zhang S. P. , Wiens R. H. , Solheim B. H. , Shepherd G. G.
Published: February 2004

Volume emission rate data of the O(1S) nightglow layer measured by the wind imaging interferometer (WINDII) aboard the Upper Atmosphere Research Satellite (UARS) are vertically integrated to give equivalent zenith column emission rates. The data are restricted to tropical latitudes and categorized according to season. The migrating tidal signature is extracted by plotting zonally averaged data as a function of local time. The main features are a premidnight maximum at the equator during equinox intervals and a midnight maximum at 20°N and S. The two equinoxes are not equivalent, nor is the behavior identical in the two hemispheres. Winter periods show little or no well‐defined tidal signature. Longitudinal variations at fixed local time were also studied. These variations are larger than the tidal signature and are geographically random, showing no consistent identification with land masses. Some of these variations could be of planetary scale, while others are probably long‐wavelength gravity waves, but in any case they were seen to extend over 10° of latitude at least. Zenithal emission rate measurements exceeding 500 R occurred at the coincidence of these longitudinal wave structures and the tidal maxima. The suggestion is put forward that much of the perceived tidal variability in the tropical lower thermosphere may be explained by such wave‐tide superpositions.
Quantitative evaluation of the post‐Mount Pinatubo NO2 reduction and recovery, based on 10 years of Fourier transform infrared and UV‐visible spectroscopic measurements at Jungfraujoch
Authors: De Mazière Martine , Van Roozendael Michel , Hermans Christian , Simon Paul C. , Demoulin Philippe , Roland Ginette , Zander Rodolphe
Published: February 2004

The colocation of two technically different instruments for ground‐based remote sensing of NO2 total column amounts at the primary Network for the Detection of Stratospheric Change Alpine station of the Jungfraujoch (46.5°N, 8.0°E) has been exploited for mutual validation of the long‐term NO2 time series from both instruments and for a quantitative evaluation of the impact of the Mount Pinatubo eruption on the NO2 abundance above this northern midlatitude observatory. The two techniques are high‐resolution Fourier transform infrared solar absorption spectrometry and zenith‐sky differential optical absorption spectroscopy in the UV visible. The diurnal variation of NO2 has been simulated by a simple photochemical model that allows a comparison between the data from the two techniques. This model is shown to reproduce the observed morning to evening ratios to 2.3%, on average, which is fully adequate for the needs of this study. From the 1985–1996 combined time series of NO2 morning and evening abundances, it has been concluded that the enhanced aerosol load injected into the stratosphere by Mount Pinatubo caused a maximum NO2 reduction above the Jungfraujoch by 45% in early January 1992 that died out quasi‐exponentially to zero by the beginning of 1995.
Observational limits for lidar, radar, and airglow imager measurements of gravity wave parameters
Authors: Gardner Chester S. , Taylor Michael J.
Published: February 2004

By examining the observational limits and biases for lidar, radar, and airglow imager measurements of middle atmosphere gravity waves, we provide plausible explanations for the characteristics of the monochromatic wave parameters that have been reported during the past decade. The systematic dependencies of vertical and horizontal wavelength on wave period, reported in many lidar and some radar studies, are associated with diffusive damping. The prominent waves with the largest amplitudes, most often observed by lidars and radars, are those with vertical phase speeds near the diffusive damping limit. The narrow range of horizontal phase velocities of the waves seen by OH imagers is a consequence of the combined effects of the gravity wave spectrum and the OH layer response to wave perturbations. The strongest airglow fluctuations are associated with waves having vertical wavelengths comparable to the width of the OH layer. These waves have fast horizontal phase speeds near 70 m/s. Simple formulas which describe the regions of the wave spectrum observed by each instrument are derived and compared with published data. Lidars, radars, and imagers are often most sensitive to waves in largely different regions of the spectrum so that their measurements are truly complementary. However, these ground‐based techniques are often incapable of observing the large‐scale waves with periods longer than about 5 hours and both long vertical (>15 km) and horizontal (>1000 km) wavelengths. Spaceborne instruments, such as the high‐resolution Doppler imager (HRDI) and wind imaging interferometer (WINDII) on UARS, are the techniques most likely to provide the key observations of the low wavenumber, low‐frequency region of the gravity wave spectrum.
Dynamical and chemical aspects of the mesospheric Na “wall” event on October 9,1993 during the Airborne Lidar and Observations of Hawaiian Airglow (ALOHA) campaign
Authors: Swenson G. R. , Qian J. , Plane J. M. C. , Espy P. J. , Taylor M. J. , Turnbull D. N. , Lowe R. P.
Published: February 2004

On October 9, 1993, observations were made from the National Center for Atmospheric Research Electra aircraft during a flight from Maui, Hawaii, toward a low‐pressure system NW of the island, a flight of 7 hours in total. The leading edge (wall) of a bright airglow layer was observed 900 km NW of Maui at 0815 UT, which was traveling at 75 m s−1 toward the SE, reaching Haleakala, Maui, about 3.25 hours later [see Swenson and Espy, 1995]. An intriguing feature associated with the event was the large increase in the mesospheric Na column density at the wall (∼180%). The enhancement was distributed over a broad region of altitude and was accompanied by significant perturbations in the Meinel (OH) and Na D line airglow emission intensities, as well as the temperature. This paper describes an investigation of the combined measurements from the aircraft and at Haleakala, including an analysis of the event using a gravity wave dynamic model. The modeled atmospheric variations associated with the leading edge of the “wall” wave are then applied to models of the neutral and ionic chemistry of sodium in order to establish whether the enhancement was caused by the release of atomic Na from a local reservoir species, as opposed to redistribution by horizontal convection. The most likely explanation for the Na release was the neutralization of Na+ ions in a sporadic E layer that was first transported downward by a large amplitude (≈10%) atmospheric gravity wave and then vertically mixed as the wave pushed the atmosphere into a super adiabatic state with associated convective instabilities and overturning.
Modeling ozone laminae in ground‐based Arctic wintertime observations using trajectory calculations and satellite data
Authors: Manney G. L. , Bird J. C. , Donovan D. P. , Duck T. J. , Whiteway J. A. , Pal S. R. , Carswell A. I.
Published: February 2004

Reverse‐trajectory calculations initialized with ozone observed by the Upper Atmosphere Research Satellite Microwave Limb Sounder (MLS) provide high‐resolution ozone profiles for comparison with lidar and ozonesonde observations from the Arctic Stratospheric Observatory facility near Eureka in the Canadian Arctic (∼80°N, 86°W). By statistical measures, calculated profiles show a small average improvement over MLS profiles in the agreement of small‐scale structure with that in ground‐based observations throughout the stratosphere, and a larger (although still modest) and more consistent improvement in the lower stratosphere. Nearly all of the calculated profiles initialized with daily gridded MLS data show some improvement in the lower stratosphere. Even in cases where overall agreement between profiles is mediocre, there are frequently one or more individual features in the calculated profiles that strongly resemble laminae in the ground‐based observations. Differential advection of ozone by the large‐scale winds leads to lamination in three distinct ways. Filamentation results in lamination throughout the stratosphere, with comparable features arising from initializations with gridded MLS data and with potential vorticity/θ‐space reconstructions of MLS data (reconstructed (RC) fields). Laminae also form in the middle and lower stratosphere in conjunction with intrusions into the vortex; while calculations initialized with RC fields produce laminae, the agreement of structure calculated using gridded MLS initialization data with ground‐based observations is distinctly better. Inside the lower stratospheric vortex, laminae form by advection of local features in the MLS initialization fields; RC‐initialized calculations fail to produce any significant features since these local ozone variations are not strongly correlated with potential vorticity. That local features observed by MLS are needed to produce laminae resembling those in independent ground‐based observations at Eureka indicates that both datasets are capturing real atmospheric features.
Observations and model calculations of jet aircraft exhaust products at cruise altitude and inferred initial OH emissions
Authors: Tremmel H. G. , Schlager H. , Konopka P. , Schulte P. , Arnold F. , Klemm M. , Droste‐Franke B.
Published: February 2004

Exhaust emissions of NO, HNO2, and HNO3 in the near‐field plume of two B747 jet airliners cruising in the upper troposphere were measured in situ using the research aircraft Falcon of the Deutsches Zentrum für Luft‐ und Raumfahrt. In addition, CO2 was measured providing exhaust plume dilution rates for the species. The observations were used to estimate the initial OH mixing ratio OH0 and the initial NO2/NOx ratio (NO2/NOx)0 at the engine exit and the combustor exit by comparison with calculations using a plume chemistry box model. From the two different plume events, and using two different model simulation modes in each case, we inferred OH emission indices EI(OH) = 0.32–0.39 g (kg fuel)−1 (OH0 = 9.0–14.4 ppmv) and (NO2/NOx)0 = 0.12–0.17. Furthermore, our results indicate that the chemistry of the exhaust species during the short period between the combustion chamber exit and the engine exit must be considered with respect to the amount of OH at the engine exit plane because OH is already consumed to a great extent in this engine section because of conversion to HNO2 and HNO3. For the engines discussed here the modeled OH concentration decreases by a factor of ∼350 between combustor exit and engine exit, leading to OH concentrations of 1–2 × 1012 molecules cm−3 (= 0.3–0.7 ppmv) at the engine exit.
A new inversion for Stratospheric Aerosol and Gas Experiment II data
Authors: Rusch D. W. , Randall C. E. , Callan M. T. , Horanyi M. , Clancy R. T. , Solomon S. C. , Oltmans S. J. , Johnson B. J. , Koehler U. , Claude H. , De Muer D.
Published: February 2004

We describe a new inversion algorithm for retrieving ozone densities and aerosol extinctions from Stratospheric Aerosol and Gas Experiment (SAGE) II measurements. The primary differences between the new algorithm and the current operational SAGE II inversion are the order of the species and altitude inversions, and the methods used to calculate aerosol extinction and remove saturated signals. Ozone densities retrieved at altitudes from 15 to 30 km using the new algorithm are compared to those from the operational SAGE II inversion, as well as to ozone densities from coincident balloon ozonesonde measurements at four different locations in the northern hemisphere between 1984 and 1991 for low to medium stratospheric aerosol loading conditions. The results of the comparison show that the ozone densities resulting from the operational and new algorithms agree to within 1% above 22 km. Below 22 km, the new results are lower than the operational results by up to 30%, depending on altitude and location. At all four stations the new results agree better with the sondes, decreasing the SAGE II/sonde differences by a factor of 2 or more.
Ground‐based spectroscopic observations of atmospheric ozone from 142 to 359 GHz in southern Europe
Authors: Pardo Juan R. , Cernicharo José , Pagani Laurent
Published: February 2004

During different periods of time between 1991 and 1996 we have achieved ground‐based observations of rotational lines of atmospheric ozone using two different ground‐based radio telescopes located in southern Europe: the 30 meters IRAM radio telescope at Pico Veleta (latitude 37:04:05.60°N, longitude 3:23:58.10°W, altitude 2850 m) and POM‐2 at Plateau de Bure, (Hautes Alpes, France, latitude 44:38:02.00°N, longitude 5:54:28.50°E, altitude 2550 m). A total of eight different ozone lines have been observed with frequencies in the range 142–359 GHz. Several back‐end spectrometers were able to analyze the incoming signal with very different frequency resolutions and total spectral coverage. This has allowed us to retrieve information about the vertical profile of ozone over a relatively wide range of altitudes. The retrieval itself has been achieved by means of a nonlinear least squares fit of the observed line profile, taking into account the spectroscopic, observational, and instrumental parameters of the different observations. A comparison between the ozone amounts retrieved from observations of different ozone lines in winter and summertime is given separately. Ozone amounts obtained from the different instruments and ozone lines are consistent.
Adjoint sensitivity of the Earth's radiation budget in the NCEP medium‐range forecasting model
Authors: Li Zhijin , Navon I. M.
Published: February 2004

We introduced an adjoint technique to study sensitivity of the Earth's radiation budget (ERB) to cloud cover, water vapor, atmospheric temperature, and the Earth's surface temperature. This technique allowed us to calculate the partial derivatives of a defined ERB function with respect to all of the above variables on the model grid points by a single calculation of the adjoint model. We employed the radiation model of the National Centers for Environmental Prediction medium‐range forecasting system to perform such an adjoint sensitivity analysis. For clear sky the absorbed shortwave radiation (ASR) was much more sensitive to the water vapor in the middle troposphere at high latitudes in the summertime hemisphere than at the tropical and subtropical areas. The outgoing longwave radiation (OLR) was 1 order of magnitude more sensitive to water vapor mixing ratios in the upper troposphere than to those in the middle and lower troposphere. In the tropics, more than 80% of a perturbation increase in the Earth's surface emission was trapped by the clear‐sky column atmosphere, while only about 60–70% is trapped at middle and high latitudes. Rapidly decreasing latitude bands of trapping were found within the subtropics, and the semipermanent troughs over the central oceans displayed a significant effect. For the case of cloudy sky the ASR was more sensitive to low clouds than to middle and high clouds. The most sensitive low clouds tended to be located at midlatitudes rather than in the tropical regions. The OLR, as expected, was most sensitive to high clouds and displayed similar sensitivity to middle clouds. The net ERB was most sensitive to low clouds at midlatitudes in the summer hemisphere. The relationship between the results obtained and the greenhouse effect over tropical oceans as well as the influence of clouds on the climate change were explored, and some model deficiencies were discussed.
On light scattering in random media with large densely packed particles
Authors: Kokhanovsky A. A.
Published: February 2004

Simple analytical formulae are presented to calculate the local optical parameters and the spherical albedo r of close‐packed media with large particles. The formulae obtained can be used to describe recent experiments on snow and foam optics. It was found that the value of r of weak absorbing semi‐infinite layers with large particles depends mostly on two parameters (the effective size of particles and the imaginary part of their refractive index). Another important characteristic is the absorption coefficient of low‐level contaminants (soot, dust particles, detergents in foam). This value determines the spherical albedo of snow and foam in the visible. The accuracy of obtained equations is better than 10% at r > 0.2.
Measurements of the relationship between submicron aerosol number and volume concentration
Authors: Hegg D. A. , Kaufman Y. J.
Published: February 2004

The relationship between aerosol number concentration and volume, or mass, concentration is a key linkage for the impact of aerosols on cloud albedo and thus climate forcing. Furthermore, this relationship is important in interpreting aerosol remote retrievals by satellites. We report here aircraft data, primarily from the TARFOX (Tropospheric Aerosol Radiative Forcing Experiment) study, which suggest a general linear relationship between aerosol number and mass concentration in the effective cloud condensation nucleus (CCN) size range (diameter >0.1 μm) for the locations examined. Limited data on the relationship between aerosol number concentration and chemical composition are also presented, which show a preferential dependence of effective CCN number concentration on sulfate mass. However, an implicit dependence on organic mass is also suggested.
Impact of parameterizations on simulated winter mid‐Holocene and Last Glacial Maximum climatic changes in the northern hemisphere
Authors: Masson Valérie , Joussaume Sylvie , Pinot Sophie , Ramstein Gilles
Published: February 2004

Within the Paleoclimate Modeling Intercomparison Project, we have performed simulations of the present‐day, mid‐Holocene (MH), and Last Glacial Maximum (LGM) climates with two versions of the LMD (Laboratoire de Météorologie Dynamique, CNRS, Paris) atmospheric general circulation model which differ in their horizontal resolution and some parameterizations of the surface processes. This work focuses on the winter simulated climatic changes in northern midlatitudes, and we use energy budget analyses to diagnose the impact of the parameterizations on the climatic sensitivity. The dependency of the surface transfer coefficients on the air stability is shown to play a key role for the climatic sensitivity over regions of stable conditions: the northern Atlantic which is sea‐ice covered at LGM, and the midlatitude continents during MH. For the MH we use a simple mathematical projection method to extract the climatic change signal from its interannual variability.
Cloud properties leading to highly reflective tropical cirrus: Interpretations from CEPEX, TOGA COARE, and Kwajalein, Marshall Islands
Authors: Heymsfield Andrew J. , McFarquhar Greg M. , Collins Williams D. , Goldstein Janine A. , Valero F. P. J. , Spinhirne James , Hart William , Pilewskie Peter
Published: February 2004

This study addresses whether high concentrations of small ice crystals in the upper 1 km or so of high, thick tropical cirrus clouds are principally responsible for the highly reflective clouds observed over the equatorial Pacific “warm pool.” This region of the tropics has recently been shown to contain extensive shields of cirrus clouds which significantly influence the global climate through their effect on the radiation budget of the tropics. In‐situ and remote sensing measurements of cloud microphysical and radiative properties from field programs in the central and western tropical Pacific and radiative transfer calculations are used to derive distributions of cloud microphysical properties with height and their relationship to cloud radiative properties. Clouds associated directly with convection are shown to have sufficiently high optical depths near cloud top to produce localized areas of bright or optically “thick” cirrus, reflecting more than 40% of the incoming solar radiation. However, in general the upper parts of cirrus cannot alone account for the high albedos (fraction of incoming solar energy reflected) but do contribute substantially when high albedos are observed. The lower parts of the cirrus, in some cases extending down to the melting layer or below when they are called stratiform cloud regions, are usually necessary to produce high albedos.
Observations of organic material in individual marine particles at Cape Grim during the First Aerosol Characterization Experiment (ACE 1)
Authors: Middlebrook Ann M. , Murphy Daniel M. , Thomson David S.
Published: February 2004

During the First Aerosol Characterization Experiment (ACE 1) field campaign in November and December 1995, the particle analysis by laser mass spectrometry instrument was used to measure the composition of ambient particles in situ at Cape Grim, Tasmania, under various conditions ranging from clean marine air to moderately polluted air. Internal mixtures of sea‐salt compounds and organic species were detected in over half of the negative spectra during clean marine conditions and in about 62% of the negative spectra during polluted conditions. In clean marine air masses, aerosol organics appeared to have two distinct source mechanisms depending on the extent of aerosol aging. Organic peaks had a positive trend with sodium sulfate peaks, indicating that organics and excess sulfate may accumulate in aged marine aerosol particles by similar mechanisms. When the sodium sulfate content was low, iodine had a positive trend with organics, which is consistent with organics and iodine originating from the surface‐active layer of the ocean and becoming incorporated into fresh marine particles by bursting bubbles. Based on limited laboratory calibrations, the average organic mass is estimated to be of the order of 10% of the sea‐salt content and is consistent with some of the missing mass fraction for Cape Grim particles (S. Howell et al., manuscript in preparation, 1997), which is the measured difference between gravimetric and ionic mass.
A numerical study of thundercloud electrification by graupel‐crystal collisions
Authors: Scavuzzo C. M. , Masuelli S. , Caranti G. M. , Williams E. R.
Published: February 2004

A three‐dimensional numerical study to evaluate the electrification caused by only the ice crystal‐graupel collisions mechanism is presented. The electrification model includes the dependencies of the magnitude of the separated charge with the crystal size and the relative velocity. In addition, the dependence of the reversal temperature (Tr) with the liquid water content is taken into account following two different experimental data sets: Takahashi [1978] and Saunders et al. [1991]. The particle spectrum is discrete with eight categories. The results show that using the first data set, the tripolar structure is obtained producing magnitudes of the charge densities in accordance with in situ measurements, whereas using the second data set, an inverted dipole (negative on positive) is obtained. Possible causes for these discrepancies are discussed. Also, the charge on individual particles is discussed in the frame of experimental data reported by airborne in situ measurements.