bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes of the lower stratospheric ozone over Europe and Canada
Authors: Bojkov Rumen D. , Fioletov Vitali E.
Published: February 2004

Ozonesonde measurements from Europe arid Canada for the period 1973–1994, stratified to the height of the tropopause, were analyzed to estimate regional changes in stratospheric ozone. The calculations were performed for 1‐km layers from the actual tropopause up to 30 km and within ±4 km around the tropopause. The long‐term changes in ozone partial pressure are very similar for both regions, and ozone anomalies show many common features. Negative deviations of 15–25 nbar (or 10–20%) are clearly seen in 1976 (at 12–20 km), 1983 (at 17–22 km), 1985 and 1988 (at 18–25 km), 1989 and 1990 (at 12–20 km), and 1992 and 1993 (at 12–23 km). In January‐April 1995, negative deviations of 15–25 nbar (at 12–23 km) were observed again over the two regions, Trend estimations demonstrate that the strongest decline, in units of ozone partial pressure, takes place at 17–20 km over Europe in January‐April and for Canadian stations from March through June. For the period 1973–1994 the decline over both regions is 10–13 nbar per decade (or 5–10% per decade) and is ∼1.5 times larger for the shorter time interval 1979–1994. The estimation of trends as a function of altitude from the actual tropopause level reduces the relative error in the 7 to 13‐km layer by more than one third, which permits better understanding of the ozone changes in these critical altitudes. Using stratified ozone data around the height of the tropopause, the negative stratospheric winter‐spring trends became significant (10–15 nbar per decade or 12–17% per decade) at only 1–2 km above the tropopause.
Global evolution of the Mt. Pinatubo volcanic aerosols observed by the infrared limb‐sounding instruments CLAES and ISAMS on the Upper Atmosphere Research Satellite
Authors: Lambert A. , Grainger R. G. , Rodgers C. D. , Taylor F. W. , Mergenthaler J. L. , Kumer J. B. , Massie S. T.
Published: February 2004

The cryogenic limb array etalon spectrometer (GLAES) and the improved stratospheric and mesospheric sounder (ISAMS) instruments on board the Upper Atmosphere Research Satellite (UARS) have been used to produce global information on the Mt. Pinatubo volcanic aerosol for the period from October 1991 to April 1993. The satellite infrared extinction measurements near 12 μm are converted into the aerosol‐related parameters necessary for modelling the effects of the volcanic aerosol on the aeronomy of the stratosphere and are presented as zonal mean distributions for 80°S to 80°N averaged over ∼35‐day periods. The aerosol composition is derived from the GLAES and ISAMS temperature measurements and the water vapour abundances are obtained from the microwave limb sounder (MLS). The aerosol volume density is obtained from the extinction measurements from which the surface area density and the effective particle radius are estimated. The maximum aerosol surface area density has a value of about 50 μm2 cm−3 at a height of 24 km at the equator in October 1991, before decaying exponentially with a time constant of 443±10 days. The surface area density remained well above preemption values in April 1993. The effective particle radius in the tropics decays monotonically from 0.65 μm in October 1991 to 0.4 μm in April 1993. The global aerosol sulphate mass loading is 19.5 Mt in October 1991 and decays exponentially with a time constant of 342±8 days to a value of 4.3 Mt by April 1993. Four months after the eruption the calculated optical thickness at 1.02 μm was ∼0.25 in the tropics. Rate constants are derived for the heterogeneous reactions of N2O5 and ClONO2 on the sulphate aerosols. The application of the aerosol parameters to the investigation of tracer transport, heterogeneous chemistry, and radiative transfer is discussed.
NASA GTE TRACE A experiment (September–October 1992): Overview
Authors: Fishman Jack , Hoell James M. , Bendura Richard D. , McNeal Robert J. , Kirchhoff Volker W. J. H.
Published: February 2004

An overview of the Transport and Atmospheric Chemistry near the Equator‐Atlantic (TRACE A) field mission is presented. TRACE A was conducted to provide a comprehensive investigation of the chemical composition, transport, and chemistry of the atmosphere over the tropical South Atlantic Ocean and the adjacent South American and African continents. Measurements for TRACE A consisted of a remote sensing component to derive tropospheric ozone and biomass burning patterns, an airborne atmospheric chemistry component to determine the composition of the air in the most pristine areas of our research domain as well as to characterize the photochemistry and transport of trace gas emissions from both fire and biogenic sources, a series of ozonesonde observations, and an enhanced radiosonde network and airborne meteorological measurements that provided information about the transport of trace gases and the physical processes that were responsible for their observed distributions. The data were interpreted through the use of both photochemical and meteorological numerical models. The picture that emerges from TRACE A is that widespread biomass burning in both South America and southern Africa is the dominant source of the precursor gases necessary for the formation of the huge amounts of ozone over the South Atlantic Ocean. In addition, however, the meteorology in this region of the world is favorable for the accumulation of these pollutants over the tropical Atlantic basin so that photochemical processes produce large quantities of ozone in situ. The generation of ozone occurs over scales of thousands of kilometers and is unusually enhanced in the upper troposphere where relatively high concentrations of nitrogen oxides (NOx) prevail. This latter finding suggests that convective processes (or other lifting mechanisms) may play an important role in the generation of tropospheric ozone or that there may be an additional significant upper tropospheric source of NOx, such as from lightning.
The December 1981 eruption of Nyamuragira Volcano (Zaire), and the origin of the “mystery cloud” of early 1982
Authors: Krueger A. J. , Schnetzler C. C. , Walter L. S.
Published: February 2004

The “mystery” volcanic aerosols observed in early 1982 were produced by the eruption of Nyamuragira in eastern Zaire. Large sulfur dioxide clouds associated with this volcano were found in the total ozone mapping spectrometer data beginning on December 26, 1981, continuing into early January 1982. This fissure eruption produced 3 million tons of sulfur dioxide in clouds that rose only to the tropopause level on the basis of winds and inferred chemical loss rates (about 20%/day), which are faster than stratospheric loss rates. Two thirds of the SO2was produced in the first 3 days of the eruption. In the 1980s this eruption was exceeded in sulfur dioxide output only by the April 1982 eruption of El Chichon.
Factors influencing the upper free tropospheric distribution of reactive nitrogen over the South Atlantic during the TRACE A experiment
Authors: Smyth S. B. , Sandholm S. T. , Bradshaw J. D. , Talbot R. W. , Blake D. R. , Blake N. J. , Rowland F. S. , Singh H. B. , Gregory G. L. , Anderson B. E. , Sachse G. W. , Collins J. E. , Bachmeier A. S.
Published: February 2004

This paper evaluates the potential sources of the enhanced levels of NO that were observed throughout the upper troposphere over the equatorial and tropical South Atlantic. During September/October 1992 NOx (NO + NO2) mixing ratios in the 8‐ to 13‐km region averaged 150 parts per trillion by volume (pptv) and were greatly affected by what appeared as spatially large “plumes” (100 to 1000 km) with NO enhancements of over 800 parts per trillion by volume. Other trace gases were also enhanced within these plumes (e.g., CO, CO2, CH4, CH3Cl, C2H2, C2H6, C3H8, and PAN). However, for these tracers of surface emissions, inconsistent patterns of enhancement were found with respect to one another and to NO. We analyzed these plumes for indications of coherent relationships between the enhanced levels of NO and the enhanced levels of biogenic and combustion‐related tracers. This analysis indicated that the tracer relationships were primarily produced by their common injection via deep convection into the upper troposphere. A corollary analysis using a combustion tracer reference frame in combination with meteorological analysis indicates a longer than expected lifetime of NOx in the upper troposphere. This analysis also suggests that an efficient mechanism may exist in the upper troposphere for recycling HNO3 back into NOx with a rate comparable to that predicted for the HNO3 formation. During the Transport and Atmospheric Chemistry Near the Equator Atlantic study period this in‐situ formation of NOx is estimated to provide the equivalent of approximately 0.7 TgN/yr of NOx within the South Atlantic basin's upper troposphere. This magnitude of local in situ source is estimated to be comparable to the combined inputs from lightning and biomass burning, which are both injected via deep convection. Our analysis also suggests that lightning can contribute as much as half of the external input of NOx into this region of the upper troposphere with biomass burning possibly representing the remainder.
Comparison of modeled and empirical approaches for retrieving columnar water vapor from solar transmittance measurements in the 0.94‐μm region
Authors: Schmid B. , Thorne K. J. , Demoulin P. , Peter R. , Mätzler C. , Sekler J.
Published: February 2004

Four atmospheric transmittance models, LOWTRAN 7, MODTRAN 3, FASCOD3P, and the Thomason model, are investigated to quantify the relationship between water vapor transmittance as function of water vapor amount,Tw(U), for an instrument specific band pass in the 0.94‐μm region. In a second step an empiricalTw(U) function is established using long term measurements with our high‐precision Sun photometer (SPM) in Bern, Switzerland along with 1300 simultaneous and collocated water vapor retrievals performed with a dual‐channel microwave radiometer (MWR). In order to avoid a possible bias in the empiricalTw(U) function, the MWR data set is prescreened by comparing retrievals coincident with radiosonde ascents. Over a 2½‐year period of common observations, radiosondes and SPM agreed to within 0.19 cm (13%) of columnar water vapor (CWV) using the empiricalTw(U) relationship. Completely independent comparisons with an additional MWR and two Fourier transform spectrometers yielded agreement within 13% and 9%, respectively. Comparing empirical and modeled results, we found that with respect to the experimental data, LOWTRAN 7, MODTRAN 3, and FASCOD3P reported higher water vapor transmittances over almost the entire range of realistic absorber amounts. By relating these differences to differences in retrieved CWV for the case of two standard atmospheres, we found that usingTw(U) predicted by LOWTRAN 7, MODTRAN 3, and FASCOD3P leads to an overestimate of CWV by about 18–30%, 7–20%, and 2–18%, respectively. The Thomason model yields good agreement with respect to the experimental data up to medium absorber amounts, whereas at slant path amounts larger than 10 cm, errors up to 60% in retrieved CWV occurred. We also show in this work that a misinterpretation of the LOWTRAN 7 water vapor output counterbalances incorrectly predictedTw, leading to results that agree well with experimental ones.
Tropospheric cycle of nitrous acid
Authors: Harrison Roy M. , Peak John D. , Collins Gareth M.
Published: February 2004

Measurements of the land surface exchange of nitrous acid over grass and sugar beet surfaces reveal both upward and downward fluxes with flux reversal occurring at an ambient concentration of nitrogen dioxide of about 10 ppb. This confirms earlier preliminary findings and strengthens the hypothesis that substantial production of nitrous acid can occur on land surfaces from reaction of nitrogen dioxide and water vapor. Detailed measurements of nitrous acid have been made in central urban, suburban, and rural environments. These measurements, in conjunction with a simple box model, indicate that the atmospheric concentrations of nitrous acid are explicable in terms of a small number of basic processes in which the most important are the surface production of nitrous acid from nitrogen dioxide, atmospheric production from the NO‐OH reaction and loss of nitrous acid by photolysis and dry deposition. In the suburban atmosphere, concentrations of nitrous acid are strongly correlated with nitrogen dioxide. In the rural atmosphere a different behavior is seen, with much higher nitrous acid to nitrogen dioxide ratios occurring in more polluted air with nitrogen dioxide concentrations in excess of 10 ppb. At lower nitrogen dioxide concentrations, net deposition of nitrous acid at the ground leads to very low concentrations in advected air. The model study indicates that during daytime in the suburban atmosphere, production of HONO from the NO‐OH reaction can compete with photolysis giving a HONO concentration of a few tenths of a part per billion. At the highest observed daytime concentrations of HONO, production of OH radical from its photolysis can proceed at a rate more than 10 times faster than from photolysis of ozone.
Convective transport of biomass burning emissions over Brazil during TRACE A
Authors: Pickering Kenneth E. , Thompson Anne M. , Wang Yansen , Tao Wei‐Kuo , McNamara Donna P. , Kirchhoff Volker W. J. H. , Heikes Brian G. , Sachse Glen W. , Bradshaw John D. , Gregory Gerald L. , Blake Donald R.
Published: February 2004

A series of large mesoscale convective systems that occurred during the Brazilian phase of GTE/TRACE A (Transport and Atmospheric Chemistry near the Equator‐Atlantic) provided an opportunity to observe deep convective transport of trace gases from biomass burning. This paper reports a detailed analysis of flight 6, on September 27, 1992, which sampled cloud‐ and biomass‐burning‐perturbed regions north of Brasilia. High‐frequency sampling of cloud outflow at 9–12 km from the NASA DC‐8 showed enhancement of CO mixing ratios typically a factor of 3 above background (200–300 parts per billion by volume (ppbv) versus 90 ppbv) and significant increases in NOx and hydrocarbons. Clear signals of lightning‐generated NO were detected; we estimate that at least 40% of NOx at the 9.5‐km level and 32% at 11.3 km originated from lightning. Four types of model studies have been performed to analyze the dynamical and photochemical characteristics of the series of convective events. (1) Regional simulations for the period have been performed with the NCAR/Penn State mesoscale model (MM5), including tracer transport of carbon monoxide, initialized with observations. Middle‐upper tropospheric enhancements of a factor of 3 above background are reproduced. (2) A cloud‐resolving model (the Goddard cumulus ensemble (GCE) model) has been run for one representative convective cell during the September 26–27 episode. (3) Photochemical calculations (the Goddard tropospheric chemical model), initialized with trace gas observations (e.g., CO, NOx, hydrocarbons, O3) observed in cloud outflow, show appreciable O3 formation postconvection, initially up to 7–8 ppbv O3/d. (4) Forward trajectories from cloud outflow levels (postconvective conditions) put the ozone‐producing air masses in eastern Brazil and the tropical Atlantic within 2–4 days and over the Atlantic, Africa, and the Indian Ocean in 6–8 days. Indeed, 3–4 days after the convective episode (September 30, 1992), upper tropospheric levels in the Natal ozone sounding show an average increase of ∼30 ppbv (3 Dobson units (DU) integrated) compared to the September 28 sounding. Our simulated net O3 production rates in cloud outflow are a factor of 3 or more greater than those in air undisturbed by the storms. Integrated over the 8‐ to 16‐km cloud outflow layer, the postconvection net O3 production (∼5–6 DU over 8 days) accounts for ∼25% of the excess O3 (15–25 DU) over the South Atlantic. Comparison of TRACE A Brazilian ozonesondes and the frequency of deep convection with climatology [Kirchhoff et al., this issue] suggests that the late September 1992 conditions represented an unusually active period for both convection and upper tropospheric ozone formation.
Simulating equilibrium within aerosols and nonequilibrium between gases and aerosols
Authors: Jacobson Mark Z. , Tabazadeh Azadeh , Turco Richard P.
Published: February 2004

A numerical method to solve chemical equilibrium equations and a method of coupling the equilibrium calculations to nonequilibrium growth and evaporation are discussed. The equilibrium program solves any number of equations for gas, aqueous, ionic, and solid equilibrium concentrations over large spatial grids and particle size grids. It also simultaneously computes electrolyte mean mixed activity coefficients and aerosol liquid water content. Mean mixed activity coefficient calculations require mean binary activity coefficient information. Temperature‐dependent mean binary activity coefficient polynomials were constructed using mean binary activity coefficient data at 298 K, apparent molal enthalpy data, and apparent molal heat capacity data. The equilibrium solver is mole and charge conserving, requires iteration, but always converges. Solutions to the equilibrium equations are used for two purposes. The first is to estimate surface vapor pressures over particles containing a solution and/or a solid phase. Such vapor pressures are then applied in gas‐aerosol transfer equations. The second is to estimate intraparticle composition and size immediately after gas‐aerosol transfer.
Biomass burning emissions and vertical distribution of atmospheric methyl halides and other reduced carbon gases in the South Atlantic region
Authors: Blake Nicola J. , Blake Donald R. , Sive Barkley C. , Chen Tai‐Yih , Rowland F. Sherwood , Collins James E. , Sachse Glen W. , Anderson Bruce E.
Published: February 2004

The NASA TRACE A experiment (September – October 1992) investigated effects of dry season biomass burning emissions from both South America and southern Africa on the tropical South Atlantic troposphere. Whole air canister samples were collected aboard the NASA DC‐8 aircraft and analyzed for a wide range of nonmethane hydrocarbons (NMHCs) and halocarbons. Fast response in situ quantification of CH4, CO, and CO2 were also performed on the DC‐8. Sampling took place over Brazilian agricultural areas and southern African savanna where there was active biomass burning. The vertical distribution of the measured gases revealed that the concentrations of most hydrocarbons, methyl halides, CH4, CO, and CO2, were enhanced in the boundary layer of these regions principally as a result of biomass fires. Brazilian and African biomass burning emission ratios were calculated for CH3Br, CH3Cl, CH3I, and NMHCs relative to CO and CO2. Although both fire regions were dominated by efficient (flaming) combustion (CO/CO2 ratios <0.1), the Brazilian samples exhibited the lower (more flaming) CO/CO2 ratio of 0.037 compared with the African savanna value of 0.062. This difference in combustion efficiency was reflected in lower ratios versus CO2 for all correlated gases. However, the gases more closely associated with smoldering combustion (e.g., C3H8 and CH3Cl) exhibited significantly higher ratios relative to CO for the Brazilian fires, while the African samples exhibited higher values versus CO for compounds associated more closely with flaming combustion (e.g., C2H2). This variation in the trace gas ratios versus CO is most likely caused by different fuel characteristics. On the basis of the emission ratios obtained, the total biomass burning emission rates for savannas and worldwide were calculated for the hydrocarbons and methyl halides. From these it was estimated that roughly 25% and 20% of global CH3Cl and CH3Br emissions, respectively, derive from biomass burning but that the contribution of biomass burning to total CH3I emissions was not significant.
Aerosols from biomass burning over the tropical South Atlantic region: Distributions and impacts
Authors: Anderson Bruce E. , Grant William B. , Gregory Gerald L. , Browell Edward V. , Collins James E. , Sachse Glen W. , Bagwell Donald R. , Hudgins Charles H. , Blake Donald R. , Blake Nicola J.
Published: February 2004

The NASA Global Tropospheric Experiment (GTE) Transport and Atmospheric Chemistry Near the Equator‐Atlantic (TRACE A) expedition was conducted September 21 through October 26, 1992, to investigate factors responsible for creating the seasonal South Atlantic tropospheric ozone maximum. During these flights, fine aerosol (0.1–3.0 μm) number densities were observed to be enhanced roughly tenfold over remote regions of the tropical South Atlantic and greater over adjacent continental areas, relative to northern hemisphere observations and to measurements recorded in the same area during the wet season. Chemical and meteorological analyses as well as visual observations indicate that the primary source of these enhancements was biomass burning occurring within grassland regions of north central Brazil and southeastern Africa. These fires exhibited fine aerosol (N) emission ratios relative to CO (dN/dCO) of 22.5 ± 9.7 and 23.6 ± 15.1 cm−3parts per billion by volume (ppbv)−1over Brazil and Africa, respectively. Convection coupled with counterclockwise flow around the South Atlantic subtropical anticyclone subsequently distributed these aerosols throughout the remote South Atlantic troposphere. We calculate that dilute smoke from biomass burning produced an average tenfold enhancement in optical depth over the continental regions as well as a 50% increase in this parameter over the middle South Atlantic Ocean; these changes correspond to an estimated net cooling of up to 25 W m−2and 2.4 W m−2during clear‐sky conditions over savannas and ocean respectively. Over the ocean our analyses suggest that modification of CCN concentrations within the persistent eastern Atlantic marine stratocumulus clouds by entrainment of subsiding haze layers could significantly increase cloud albedo resulting in an additional surface radiative cooling potentially greater in magnitude than that caused by direct extinction of solar radiation by the aerosol particles themselves.
Chemical composition of single aerosol particles at Idaho Hill: Negative ion measurements
Authors: Murphy D. M. , Thomson D. S.
Published: February 2004

The chemical compositions of single aerosol particles larger than 0.3 μm optical diameter were measured at Idaho Hill using a laser ionization mass spectrometer. The mass spectrometer can analyze either positive or negative ions; this paper covers the negative ion results. Sulfate, nitrate, organics, O−, and OH− were the most common peaks observed in the negative ion spectra. Other species identified in the negative ion spectra include silicon, chlorine, iodine, organic acids, and elemental carbon. Neither external nor internal mixing completely describes the particles: most of the particles were in various classes that were distinctly different from each other. All air masses had more than one class of particle present. However, most of the particle classes were in themselves mixtures. Sulfate was the most common negative ion in smaller particles whereas nitrate and complicated mixtures were more common in particles larger than about 0.7 μm. However, nearly all types of particles were observed in all size ranges and wind conditions. Aerosol chemistry was not well correlated with gas phase chemistry. Certain combinations, such as nitrate and silicon, were frequently observed together in single particles. Sulfate and chlorine did not coexist in the same particles, nor did silicon and elemental carbon. Small amounts of organics were present in most particles. Sulfate and nitrate were usually, but not always, in different particles. The nitrate/sulfate ratio estimated with the mass spectrometer data correlated well with filter measurements.
An atmospheric energy‐moisture balance model: Climatology, interpentadal climate change, and coupling to an ocean general circulation model
Authors: Fanning Augustus F. , Weaver Andrew J.
Published: February 2004

An atmospheric model incorporating energy and moisture balance equations is developed for use in process studies of the climate system. Given the sea surface temperature and specified surface wind field, the atmospheric model calculates the surface fields of air temperature, specific humidity, as well as heat and freshwater fluxes. The inclusion of the moisture balance in the atmospheric model allows the effects of latent heat transport to be included explicitly in the model. Under fixed climatological sea surface temperature (SST) and surface wind conditions, surface air temperatures, specific humidities, and surface fluxes are comparable to direct estimates. Precipitation compares less favorably with observations. As an extension to the climatological forcing case, we conduct a simple perturbation experiment in which the 1955–1959 pentad is compared to the 1970–1974 pentad by driving the model under the respective SST fields. The model exhibits a global air temperature decrease in the latter pentad of 0.27°C (comparable to direct estimates) with cooling in the northern hemisphere and warming in the southern hemisphere. Such large‐scale cooling in our atmospheric model is driven by equivalent local changes in the prescribed SST fields, subsequently smoothed by atmospheric diffusion of heat. The interpentadal modeled differences are shown to be quite robust through model experiments using parameters representative of several different unrealistic climatologies. The resulting interpentadal difference fields change remarkably little even when the background state has changed dramatically. This emphasizes the almost linear response of the atmospheric model to the imposed SST changes. The atmospheric model is also coupled to an ocean general circulation model without the need for flux adjustments. This coupled climate model faithfully represents deep water formation in the North Atlantic and Southern Ocean, with upwelling throughout the Pacific and Indian Oceans. Water mass characteristics in the vertical compare very favorably with direct observations.
Chemical characteristics of tropospheric air over the tropical South Atlantic Ocean: Relationship to trajectory history
Authors: Gregory Gerald L. , Fuelberg Henry E. , Longmore Scott P. , Anderson Bruce E. , Collins James E. , Blake Donald R.
Published: February 2004

The TRACE A (Transport and Atmospheric Chemistry Near the Equator‐Atlantic) experiment was designed to explore the atmospheric chemistry and meteorology over the tropical South Atlantic Ocean with a focus on the impact of South American and African biomass burning and continental outflow on the region. TRACE A was conducted in September/October 1992. Companion papers in this special issue show that the chemical composition of tropospheric air throughout the region is strongly impacted by biomass burning and outflow from both continents. This paper shows similar results and examines the chemical composition of air measured during NASA DC‐8 aircraft ascents/descents at locations along the coast of both continents as well as at mid‐Atlantic Ocean locations. Chemical composition of the air and backward trajectory calculations are used to illustrate the influences of continental outflow and how influences change with location throughout the region. Included in the examples are data which show that air along the Atlantic coast of Africa is impacted by outflow from both South America and Africa as air at the higher altitudes (e.g., 8 to 10 km) originates from South America, while lower‐altitude air is from African sources. Of additional interest are data measured over the Indian Ocean near the tip of Africa which show aged air from South America being impacted by biomass burning emissions as the air passes over Africa 1 to 2 days prior to sampling.
Laboratory and field studies of biogenic volatile organic compound emissions from Sitka spruce (Picea sitchensis Bong.) in the United Kingdom
Authors: Street Rachel A. , Duckham S. Craig , Hewitt C. Nicholas
Published: February 2004

Isoprene and monoterpene emission rates were measured from Sitka spruce (Picea sitchensis Bong.) with a dynamic flow‐through branch enclosure, both in the laboratory and in the field in the United Kingdom. In the laboratory, emission rates of isoprene comprised over 94% of the identified VOC species, and were exponentially related to temperature over a period of 1 day. This exponential relationship broke down at ∼33°C. Field measurements were taken on five sampling days in 1992 and 1993, in Grizedale Forest, Cumbria. Total emission rates were in the range 36‐3771 ng g−1 h−1. Relative emissions were more variable than suggested by laboratory measurements, with monoterpenes contributing at least 64% to the total emissions in most cases. There was a significant variation in the basal emission rate both across the growing season and between different ages of vegetation, the causes of which are as yet unknown. Total emission rates, in July 1993, were estimated to be between 0.01 and 0.27% of assimilated carbon.
Removal of the El Niño‐Southern Oscillation signal from the gridded surface air temperature data set
Authors: Kelly P. M. , Jones P. D.
Published: February 2004

We attempt the removal of the large‐scale signal associated with one important component of climate variability, the El Niño‐Southern Oscillation (ENSO) phenomenon, from the global surface air temperature data set in order to facilitate analysis of other potential causes of climate change. Previous attempts to remove the ENSO signal from climate records at the global scale have been based on relatively simple regression analysis. We use empirical orthogonal function analysis to identify characteristic spatial patterns of change in the global surface air temperature field and thus define the ENSO signal. The approach successfully identifies two ENSO‐related components of the variability in the global data set, and the removal process results in a significant reduction in variance. Evaluation of the process indicates that attention should be paid to seasonality in the ENSO signal. Moreover, it is clear that other aspects of the statistical generalization inherent in the approach have resulted in a residual ENSO signal in the data set. The remaining signal does, however, appear to be regional in nature and/or only marked in the case of particular ENSO events. We conclude that an approach based on empirical orthogonal function analysis presents an effective means of isolating and removing specific climate signals.
First simultaneous and common volume observations of noctilucent clouds and polar mesosphere summer echoes by lidar and radar
Authors: Nussbaumer V. , Fricke K. H. , Langer M. , Singer W. , von Zahn U.
Published: February 2004

We present the results of first simultaneous and common volume observations of noctilucent clouds (NLC) and polar mesosphere summer echoes (PMSE) by two ground‐based lidars and one VHF radar. The measurements were performed at the ALOMAR facility (69°N, 16°E) during the time period July 23 through August 18, 1994. Throughout this period, NLC layers were observed by the lidars on four occasions. During each of these four lidar‐observed NLC events, PMSE layers were also observed overhead by the radar. These joint NLC/PMSE events divide into two distinct types: (1) tightly coupled and (2) loosely coupled NLC and PMSE layers. In one of the events, the PMSE layer developed into a well‐defined double layer with only 0.8‐km vertical separation, while the lidar‐observed NLC layer matched closely in time and space the lower PMSE sublayer. Within all four NLC/PMSE layers, the wind speed increased sharply with increasing altitude with wind shears amounting to 0.03 s−1 and larger. Current theories can explain some of the observed layer features.
On the potential of assimilating meteorological analyses in a global climate model for the purpose of model validation
Authors: Jeuken A. B. M. , Siegmund P. C. , Heijboer L. C. , Feichter J. , Bengtsson L.
Published: February 2004

A simple four‐dimensional assimilation technique, called Newtonian relaxation, has been applied to the Hamburg climate model (ECHAM), to enable comparison of model output with observations for short periods of time. The prognostic model variables vorticity, divergence, temperature, and surface pressure have been relaxed toward European Center for Medium‐Range Weather Forecasts (ECMWF) global meteorological analyses. Several experiments have been carried out, in which the values of the relaxation coefficients have been varied to find out which values are most usable for our purpose. To be able to use the method for validation of model physics or chemistry, good agreement of the model simulated mass and wind field is required. In addition, the model physics should not be disturbed too strongly by the relaxation forcing itself. Both aspects have been investigated. Good agreement with basic observed quantities, like wind, temperature, and pressure is obtained for most simulations in the extratropics. Derived variables, like precipitation and evaporation, have been compared with ECMWF forecasts and observations. Agreement for these variables is smaller than for the basic observed quantities. Nevertheless, considerable improvement is obtained relative to a control run without assimilation. Differences between tropics and extratropics are smaller than for the basic observed quantities. Results also show that precipitation and evaporation are affected by a sort of continuous spin‐up which is introduced by the relaxation: the bias (ECMWF‐ECHAM) is increasing with increasing relaxation forcing. In agreement with this result we found that with increasing relaxation forcing the vertical exchange of tracers by turbulent boundary layer mixing and, in a lesser extent, by convection, is reduced.
Sensitivity of a general circulation model to changes in northern hemisphere ice sheets
Authors: Felzer Benjamin , Oglesby Robert J. , Webb Thompson , Hyman Dena E.
Published: February 2004

Sensitivity experiments with a general circulation model demonstrate the role of ice sheet size on the local, regional, and global climate. Model experiments isolate the effects of albedo, height, and area of the ice sheets and show how the National Center for Atmospheric Research Community Climate Model 1 responds to changes in the size of northern hemisphere ice sheets. A flat ice sheet with full glacial areal extent but no elevation is used to study albedo effects. A full ice sheet with full glacial areal extent and elevation is used to represent height effects. An ice sheet with half the glacial area of the others but the full glacial elevation is used to represent area effects. All of the sensitivity experiments have (1) interactive sea surface temperatures calculated by a slab ocean and (2) modern boundary conditions except for the ice sheets. The experiments show that both the full and flat ice sheets lower the global mean surface temperatures (GMT) by 2.5°C and that the GMT is dependent upon the area, rather than the height, of the ice sheets. High ice sheets maintain colder temperatures than lower ice sheets over the ice sheets themselves, but compensating warmer temperatures occur downstream from the high ice sheets. The downstream warmer temperatures are the result of (1) glacial anticyclones that cause subsidence and reduced cloud cover during summer as well as reduced soil moisture and (2) increased southwesterly flow across the Atlantic Ocean that results in increased southerly advection of warm air during winter. A dynamical effect of the high ice sheets during summer is to change the wave number of the planetary waves in the midlatitudes, whereas a thermodynamic effect of the flat ice sheets during summer is to lower the geopotential heights throughout the northern hemisphere. In general, northern hemisphere ice sheets induce both a local response over the ice sheets and a regional response downstream from the ice sheets but have little impact on the southern hemisphere except where sea ice expands.
Surface temperature and wind fields over the Skeleton Coast (Namibia) and adjacent interior during SAFARI‐92
Authors: Brimelow Julian C. , van Heerden Johan
Published: February 2004

As part of the meteorological component of the Southern African Fire‐Atmosphere Research Initiative (SAFARI), the University of Pretoria erected three automatic weather stations along the Skeleton Coast (Namibia) and adjacent interior. This paper presents the first study of the surface wind regimes and temperature fields north of Walvis Bay. The local circulation patterns in this region are primarily thermotopographically induced, with both the local wind regimes and temperature fields displaying clear diurnal signals. The presence of the Benguela current resulted in marked differences between the temperatures and temperature ranges observed at the coast and further inland. A nocturnal inversion developed regularly at Orupembi, while by day the temperature profile in the lower 10 m was superadiabatic at all three stations. Along the coast the wind speed and direction displayed limited diurnal variation, while further inland a marked diurnal variation was evident. The local circulation along the coast was dominated by the sea breeze. As the sea breeze developed, the wind veered to be southwesterly to westerly at sea breeze maximum. At Orupembi the local circulation was dominated by the draining of cool air from the mountain slopes and valleys by night and by a southerly flow by day, interrupted for a short time in the afternoon by the inland penetration of the sea breeze.
Anthropogenic and natural contributions to tropospheric sulfate: A global model analysis
Authors: Chin Mian , Jacob Daniel J.
Published: February 2004

A global three‐dimensional model is used to examine the export of anthropogenic sulfur from northern midlatitude continents and to assess the relative importance of anthropogenic and natural sources to sulfate levels in different regions of the troposphere. Model results indicate that about 40% of the anthropogenic sulfur emitted in the United States, Europe, or eastern Asia is exported out of the continental boundary layer of these regions; the rest is removed within the regions, primarily by dry deposition of SO2 and wet deposition of SO42−. Export is relatively more efficient in summer than in winter. There is little nonlinearity between the magnitude of sulfur emissions in the northern midlatitude continents and the export of this sulfur to the global atmosphere. Anthropogenic influence on SO42− decreases rapidly with altitude because of efficient scavenging of SO2 and SO42− in deep convective updrafts. Thus it is found that anthropogenic influence accounts on average for less than 20% of SO42− anywhere in the upper troposphere. The main source of SO42− in the tropical upper troposphere in the model is from biogenic dimethylsulfide (DMS) pumped in deep convective events. Volcanic emissions account for 20–40% of SO42− in much of the middle troposphere and for up to 80% over the North Pacific; they also represent a major contributor to SO42− in the upper troposphere at high latitudes. On a global scale, it is estimated that anthropogenic, biogenic, and volcanic emissions account for 70%, 23%, and 7%, respectively, of the global sulfur source, but that they account for 37%, 42%, and 18%, respectively, of the global column of atmospheric SO42−. The disproportionality between source and column contribution reflects the rapid deposition of anthropogenic SO2 and SO42− at low altitudes. It thus appears that the anthropogenic contribution to the SO42− aerosol optical depth is much less than would be expected simply on the basis of emissions.
A new method of deriving time‐averaged tropospheric column ozone over the tropics using total ozone mapping spectrometer (TOMS) radiances: Intercomparison and analysis using TRACE A data
Authors: Kim J. H. , Hudson R. D. , Thompson A. M.
Published: February 2004

Error analysis of archived total O3from total ozone mapping spectrometer (TOMS) (version 6) presented in earlier studies [Hudson and Kim, 1994;Hudson et al., 1995] is extended to include scan angle effects. Daily total O3maps for the tropics, from the period October 6–21, 1992, are derived from TOMS radiances following correction for these errors. These daily maps, averaged together, show a wavelike feature, which is observed in all latitude bands (10°N to 14°S), underlying sharp peaks which occur at different longitudes depending on the latitude. The wave pattern is used to derive both time‐averaged stratospheric and tropospheric O3fields. The nature of the wave pattern (stratospheric or tropospheric) cannot be determined with certainty due to missing data (no Pacific sondes, no lower stratospheric Stratospheric Aerosol and Gas Experiment (SAGE) ozone for 18 months after the Mt. Pinatubo eruption) and significant uncertainties in the corroborative satellite record in the lower stratosphere (solar backscattered ultraviolet (SBUV), microwave limb sounder (MLS)). However, the time‐averaged tropospheric ozone field, based on the assumption that the wave feature is stratospheric, agrees within 10% with ultraviolet differential absorption laser Transport and Atmospheric Chemistry near the Equator‐Atlantic) (TRACE A) O3measurements from the DC‐8 [Browell et al., this issue] and with ozonesonde measurements over Brazzaville, Congo (4°S, 15°W;), Ascension Island (8°S, 15°W), and Natal, Brazil (5.5°S, 35°W), for the period October 6–21, 1992. The derived background (nonpolluted) Indian Ocean tropospheric ozone amount, 26 Dobson units (DU), agrees with the cleanest African ozonesonde profiles for September–October 1992. The assumption of a totally tropospheric wave (flat stratosphere) gives 38 DU above the western Indian Ocean and 15–40% disagreements with the sondes. Tropospheric column O3is high from South America to Africa, owing to interaction of dynamics with biomass burning emissions [Thompson et al., this issue (a, b)]. Comparison with fire distributions from advanced very high resolution radiometer (AVHHR) during October 1992 suggests that tropospheric O3produced from biomass burning in South America and Africa dominates the O3budget in the tropical southern hemisphere during the study period.
Spatiotemporal storm structure and scaling property analysis for modeling
Authors: Onof Christian , Northrop Paul , Wheater Howard S. , Isham Valerie
Published: February 2004

Taylor's hypothesis and the multiscaling properties of British rainfall data are analyzed and Poisson‐based cluster models are examined for their ability to reproduce these features. Taylor's hypothesis is found to hold for timescales of up to 30–40 min, while at this scale a break is also observed in the temporal scaling properties of moments of several orders. The first property is observed for the spatiotemporal model, while some of the scaling features of the time series are reproduced by the point rainfall model, thus demonstrating the ability of hierarchical models to reproduce self‐similar properties of the data.
Precipitation efficiency of trade wind clouds over the north central tropical Pacific Ocean
Authors: Rauber Robert M. , Laird Neil F. , Ochs Harry T.
Published: February 2004

The magnitude and distribution of precipitation within trade wind clouds east of the Hawaiian Islands and the efficiency of these clouds in returning water evaporated from the ocean surface back to the ocean through precipitation are examined using highresolution visible and infrared DMSP satellite data and 5‐cm wavelength radar data collected during the 1990 Hawaiian Rainband Project. The analyses indicate that on average, precipitation rates greater than 0.1 mm h−1 occur over about 11% of the area occupied by trade wind clouds at any given time, while about 1.5% of the cloudy areas had rainfall rates which exceeded 1.0 mm h−1. None of the clouds in the sample had precipitation rates exceeding 10.0 mm h−1. The average precipitation rate was 1.1 mm d−1. An estimate of the precipitation efficiency of the trade wind clouds, made by comparing the latent heat input into the atmosphere due to precipitation with the ocean surface latent heat flux, suggests that clouds in the trade wind regime are no more than 20–30% efficient in returning evaporated water vapor to the ocean through precipitation processes.
Statistical analysis of gravity waves observed with the middle and upper atmosphere radar in the middle atmosphere: 1. Method and general characteristics
Authors: Gavrilov N. M. , Fukao S. , Nakamura T. , Tsuda T. , Yamanaka M. D. , Yamamoto M.
Published: February 2004

A statistical procedure is developed to obtain the parameters of spectral harmonics of internal gravity waves (IGW) with horizontal wavelengths larger than ∼ 60 km using measurements of wind velocity in the middle atmosphere from the middle and upper atmosphere (MU) radar. The method is applied to find sets of IGW parameters for the winter and summer seasons of 1987–1988 for 6‐km‐thick layers centered at 70, 75, and 80 km at Shigaraki, Japan (34.9°N, 139.4°E). The numbers of selected IGW harmonics having periods from 5 min up to 6 hours vary between 360 and 2000 depending on the season and altitude. Mean vertical wave numbers are 0.6–0.9 km−1 in winter and 0.5–1 km−1 in summer, and horizontal wave numbers are (3–4)×10−2 km−1 and (2–4)×10−2 km−1, respectively. Predominant azimuths of wave vectors and momentum fluxes concentrate near 64° in winter and 90° in summer at all altitudes. In general, the difference between the azimuths of the wave vector and momentum flux is close to zero or 180°. Turbulent and instrumental noise can contribute 20–30% of the observed intensity of the wind variations at altitudes of 70–85 km. The IGW momentum fluxes are 0.2–2.7 m2s−2 in winter and 0.2–1.9 m2s−2 in summer. The wave drag of the mean flow is 0.5–45 m2s−1 in winter and 2–25 m2s−1 in summer. In most cases the momentum flux and wave drag are directed oppositely to the mean wind.
International geosphere‐biosphere programme/international global atmospheric chemistry SAFARI‐92 field experiment: Background and overview
Authors: Lindesay J. A. , Andreae M. O. , Goldammer J. G. , Harris G. , Annegarn H. J. , Garstang M. , Scholes R. J. , van Wilgen B. W.
Published: February 2004

The International Geosphere‐Biosphere Programme/International Global Atmospheric Chemistry (IGBP/IGAC) Southern Africa Fire‐Atmosphere Research Initiative (SAFARI‐92) field experiment was conducted in the 1992 dry season in southern Africa. The objective of the experiment was a comprehensive investigation of the role of vegetation fires, particularly savanna fires, in atmospheric chemistry, climate, and ecology. During SAFARI‐92 experimental fires were conducted in Kruger National Park, South Africa, and at some sites in Zambia, in order to study fire behavior and trace gas and aerosol emissions. Regional studies on atmospheric chemistry and meteorology showed that vegetation fires account for a substantial amount of photochemical oxidants and haze over the subcontinent, and that the export of smoke‐laden air masses contributed strongly to the ozone burden of the remote atmosphere in the southern tropical Atlantic region. The relationships between fire, soil moisture status, and soil trace gas emissions were investigated for several climatically and chemically important gases. Remote sensing studies showed that advanced very high resolution radiometer/local area coverage (AVHRR/LAC) imagery was valuable for fire monitoring in the region and in combination with biomass models could be used for the estimation of pyrogenic emissions.