bluuebunny/crossref_metadata_2025 huggingface dataset:
Limits on heterogeneous processing in the Antarctic spring vortex from a comparison of measured and modeled chlorine
Authors: Shindell D. T. , de Zafra R. L.
Published: February 2004

Forty‐day photochemical model runs are compared with ground‐based stratospheric ClO observations taken during the austral spring of 1993. Our purpose is to explore the range of required heterogeneous processing within which we can reproduce the duration and degree of chlorine activation within the Antarctic spring vortex. Heterogeneous processing on nitric acid trihydrate (NAT) polar stratospheric clouds (PSCs) or supercooled ternary solution (STS) ‐type particles is shown to be necessary to maintain chlorine in active forms during ozone hole formation in September, even for small HNO3 amounts, or chlorine deactivates sooner than observed. The lower limits for the surface areas required are quite small, however. Thus the record ozone losses observed during September of 1993 may be attributed to catalytic loss due to chlorine maintained in active forms by heterogeneous processing despite the sparse particle loading of the Antarctic lower stratosphere at that time. The ozone loss rates predicted by the model during the formation of the springtime Antarctic ozone hole indeed agree quite well with observations. The one‐dimensional model is also able to reproduce both the observed timing and rate for subsequent deactivation of chlorine. Renitrification from PSC evaporation is not required for this deactivation, as HCl reformation is very rapid at low ozone values.
Spectral characteristics of Schumann resonances observed in central Europe
Authors: Sátori G. , Zieger B.
Published: February 2004

The vertical electric field component in the frequency range of Schumann resonances has regularly been measured at the Nagycenk Observatory in Hungary, in Central Europe since May 1993. The actual peak frequencies and the amplitudes belonging to them are determined for the first three modes. Each mode has its own character and they show distinct daily and seasonal variations. The recurrence tendency of these variations from year to year is also presented. The significant annual and semiannual variations of the amplitudes support the suggestion that the Schumann resonance as a global phenomenon is sensitive to small temperature variations in the tropical atmosphere.
Formaldehyde methods comparison in the remote lower troposphere during the Mauna Loa Photochemistry Experiment 2
Authors: Heikes B. , McCully B. , Zhou X. , Lee Y.‐N. , Mopper K. , Chen X. , Mackay G. , Karecki D. , Schiff H. , Campos T. , Atlas E.
Published: February 2004

Five methods for the measurement of CH2O vapor were compared under remote tropospheric conditions. The techniques included an aqueous‐scrubber enzyme fluorescence method (URIcoil), TDLAS (UNI), 2,4‐dinitrophenylhydrazine (DNPH) impregnated‐cartridges (BNL/WSUcart), an aqueous‐scrubber DNPH method (BNL/WSUcoil), and an unpublished aqueous‐scrubber immobilized‐enzyme fluorescence method (NCARbound). This was part of the Mauna Loa Observatory Photochemistry Experiment 2 (MLOPEX 2) which was performed in four ∼30‐day intensives. In MLOPEX 2a (fall 1991), the URIcoil technique indicated higher concentrations relative to the BNL/WSUcoil which were higher than UNI. The limited number of NCARbound measurements for MLOPEX 2a were greater than the other measurements and least reliable. During MLOPEX 2b (winter 1992), URIcoil, UNI, BNL/WSUcoil, and NCAR‐bound gave comparable measurements of CH2O with the latter again being consistently higher than the first three methods and its performance and reliability was improved over MLOPEX 2a. URIcoil and BNL/WSUcoil were comparable in MLOPEX 2c (spring 1992) and 2d (summer 1992), whereas BNL/WSUcart was consistently higher than both for these intensives. The major source of difference between techniques was ascribed to variations in the analytical‐procedural field blanks. Calibration differences were the most likely cause of URIcoil being higher than BNL/WSUcoil and BNL/WSUcoil being higher than UNI during MLOPEX 2a. Lower free troposphere median concentrations were between 100 and 150 ppt for all seasons and without a seasonal trend. These values were a factor of 2 to 3 lower than model estimates for this study site and were in keeping with earlier work.
ATMOS observations of nitric oxide in the mesosphere and lower thermosphere
Authors: Barth Charles A. , Farmer Crofton B. , Siskind David E. , Perich Jeffrey P.
Published: February 2004

The nitric oxide density in the Earth's atmosphere between 50 and 130 km was measured by the ATMOS (Atmospheric Trace Molecule Spectroscopy) experiment onboard the Spacelab 3 mission on April 30, 1985 and May 1, 1985. Three observations were made at geographic latitudes of 35°N, 34°N, and 29°N which correspond to geomagnetic latitudes of 26°N, 44°N, and 39°N. The ATMOS measurements of nitric oxide in the thermosphere were compared to SME measurements made during the same time period. The two techniques agree within the geophysical variability of thermospheric nitric oxide. The observations show that during a geomagnetic storm there is a strong latitudinal gradient in the nitric oxide density in the lower thermosphere. Comparison of the observations with a one‐dimensional time‐dependent model shows that at midlatitudes, nitric oxide is transported downward from the thermosphere into the mesosphere as low as 70 km but not downward into the stratosphere.
Seasonal variation of mass transport across the tropopause
Authors: Appenzeller Christof , Holton James R. , Rosenlof Karen H.
Published: February 2004

The annual cycle of the net mass transport across the extratropical tropopause is examined. Contributions from both the global‐scale meridional circulation and the mass variation of the lowermost stratosphere are included. For the northern hemisphere the mass of the lowermost stratosphere has a distinct annual cycle, whereas for the southern hemisphere, the corresponding variation is weak. The net mass transport across the tropopause in the northern hemisphere has a maximum in late spring and a distinct minimum in autumn. This variation and its magnitude compare well with older estimates based on representative 90Sr mixing ratios. For the southern hemisphere the seasonal cycle of the net mass transport is weaker and follows roughly the annual variation of the net mass flux across a nearby isentropic surface.
Landfill methane emissions measured by enclosure and atmospheric tracer methods
Authors: Czepiel P. M. , Mosher B. , Harriss R. C. , Shorter J. H. , McManus J. B. , Kolb C. E. , Allwine E. , Lamb B. K.
Published: February 2004

Methane (CH4) emissions were measured from the Nashua, New Hampshire municipal landfill using static enclosure and atmospheric tracer methods. The spatial variability of emissions was also examined using geostatistical methods. One hundred and thirty nine enclosure measurements were performed on a regular grid pattern over the emitting surface of the landfill resulting in an estimate of whole landfill emissions of 15,800 L CH4 min−1. Omnidirectional variograms displayed spatial correlation among CH4 fluxes below a separation distance of 7 m. Eleven tracer tests, using sulfur hexafluoride (SF6) as a tracer gas, resulted in a mean emissions estimate of 17,750 L CH4 min−1. The favorable agreement between the emission estimates was further refined using the observed relationship between atmospheric pressure and CH4 flux. This resulted in a pressure‐corrected tracer flux estimate of whole landfill emissions of 16,740 L CH4 min−1.
Measurements of UV refractive indices and densities of H2SO4/H2O and H2SO4/HNO3/H2O solutions
Authors: Beyer Keith D. , Ravishankara A. R. , Lovejoy Edward R.
Published: February 2004

Refractive indices of aqueous solutions of sulfuric acid and sulfuric acid/nitric acid were measured at 365, 313, 308, 254, and 214 nm at 298 K. The solution concentrations were H2SO4/H2O: 88.6, 78.7, 63.0, 52.3, 39.8 wt % SA (sulfuric acid); H2SO4/HNO3/H2O: 50.3 SA 2.5 NA (nitric acid), 45.4 SA 5.1 NA, 41.9 SA 7.4 NA, 37.9 SA 10.4 NA wt %. Densities of the solutions were also measured at low temperatures in order to calculate the refractive indices of these solutions at stratospheric temperatures.
Increase in the vertical column abundance of HCFC‐22 (CHClF2) above Lauder, New Zealand, between 1985 and 1994
Authors: Sherlock Vanessa J. , Jones Nicholas B. , Matthews W. Andrew , Murcray Frank J. , Blatherwick Ronald D. , Murcray David G. , Goldman Aaron , Rinsland Curtis P. , Bernardo Cirilo , Griffith David W. T.
Published: February 2004

Total column abundances of CHClF2 (HCFC‐22) have been retrieved from high‐resolution infrared solar absorption spectra recorded at the Network for the Detection of Stratospheric Change (NDSC) station in Lauder, New Zealand (370 m altitude, 45.04°S latitude, 169.68°E longitude). The analysis, based on nonlinear least squares fittings to the unresolved 2v6 band Q branch of CH35ClF2 at 829.05 cm−1, has been applied to a time series of 670 spectra recorded on 394 days between May 1985 and November 1994. The measurements indicate exponential and linear (referenced to the beginning of 1994) increase rates of (7.5±0.3)% yr−1 and (5.9±0.2)% yr−1, 1 σ, corresponding to a doubling of the total column abundance over the 9.5‐year measurement period. Of the two models the exponential increase model yields a slightly better fit to the data than the linear model. A HCFC‐22 south/north hemispheric ratio of 0.83 ±0.04, 1σ, is derived by comparing the Lauder column measurements with column measurements from the International Scientific Station of the Jungfraujoch (46.5°N, 8.0°E), after correction for the altitude difference between the two sites. Using a second, independent method in which the N2O column serves as a surrogate air mass, we have used the Lauder measurements and similar measurements from Table Mountain (34.4°N) to calculate a south/north ratio of 0.91±0.10.
Observations and parameterization of the stratospheric electrical conductivity
Authors: Hu Hua , Holzworth Robert H.
Published: February 2004

Simultaneous in situ measurements of the stratospheric electrical conductivity, made from multiple balloon platforms during the 1992–1993 Extended Life Balloon‐Borne Observatories (ELBBO) experiment, have yielded the most comprehensive data set on the stratospheric electrical conductivity. The ELBBO project involved launches of five superpressure balloons into the stratosphere from Dunedin, New Zealand, beginning November 10, 1992, and lasting through March 18, 1993. Most of the balloons floated at a constant altitude of 26 km for over 3 months, covered a wide range of latitudes from the South Pole to 28°S, and circled around the southern hemisphere several times. On average, the positive polar conductivity (conductivity of positive ions alone) was about 15% higher than that of the negative conductivity, suggesting that differences may exist between the mobilities of positive and negative ions. Data from each polarity of polar conductivity also indicate persistent, apparently organized, short‐term and localized variations, with amplitude within 30% of the mean value. In corrected geomagnetic (CGM) coordinates the conductivity variations were found to be a function of latitude but not of longitude. The total conductivity can increase 150% from low latitude to high latitude, and does remain nearly constant at latitudes above 55° (namely, the cosmic ray knee latitude). Calculations based on ionization theory demonstrate that the latitudinal variations in the conductivity measurements were mainly due to the latitudinal variations in incident galactic cosmic ray intensity, with only little effect from the air temperature variations. The calculations shown here also suggest that small ions (as opposed to large ions) provide the main contribution to the stratospheric conductivity. The comparisons between conductivity measurements and models show that commonly used models can underestimate the latitudinal variation by a factor of 2. In this paper the stratospheric conductivity is parameterized based on the measurements, and a simple empirical model is presented in geographic coordinates.
Effect of dry‐season biomass burning on Amazon basin aerosol concentrations and optical properties, 1992–1994
Authors: Holben B. N. , Setzer A. , Eck T. F. , Pereira A. , Slutsker I.
Published: February 2004

Aerosol concentrations and properties have been derived from a network of ground‐based Sun‐sky radiometer measurements in Brazil's Amazon basin region since 1992. The measurements characterize the background aerosol environment and aerosol emissions from biomass burning at eight selected sites. The duration and frequency of the measurements provide the foundation of an aerosol climatology based on direct sun measurements of aerosol optical thickness and retrievals of size distribution from solar aureole measurements. The aerosol optical thickness measurements clearly illustrate that for sites located within regions of biomass burning the duration of smoke above background levels often exceeds 2 months and frequently at levels an order of magnitude above background. The aerosol optical thickness range during preburning conditions was 0.11 to 0.27 at 440 nm. Under these conditions, stratospheric aerosols from Pinatubo constituted a significant part of the signal in 1993 but were about 50% less in 1994. During the burning season, smoke elevated the aerosol optical thickness above 1.0 for seasonally averaged values measured at 440 nm at sites located in active source regions in Mato Grosso, Rondonia, and Tocantins states. The measurement sites are located in the cerrado and forest conversion areas. Analysis of the size distribution of the particles indicated that the increase in aerosol optical thickness was associated with an increase of an accumulation and coarse particle modes. The asymmetry factor “g”, computed from the phase function, showed considerable spectral dependence between the preburning and burning seasonal phases. The 1020‐nm channel was reduced from 0.66 to ∼0.53, while at 440 nm little seasonal phase variation was noted. Conditions of burning were sufficiently strong that the atmospheric conditions associated with the climatological definition of a dry season was subdivided into (1) preburning, (2) transition to burning, (3) burning, and (4) transition to wet season phases for most sites. Averages and frequency distributions were used to characterize each seasonal phase by site. Changes in total column water vapor amount, also retrieved from direct sun measurements, did not have an apparent effect on the optical properties of the aerosols.
Effects of clouds and haze on UV‐B radiation
Authors: Estupiñán Jeral G. , Raman Sethu , Crescenti Gennaro H. , Streicher John J. , Barnard William F.
Published: February 2004

An experiment was conducted over a 6‐month period in Research Triangle Park, North Carolina, to investigate the effects of clouds and haze on ultraviolet (UV) radiation. Data were collected using a Yankee Environmental Systems UVB‐1 pyranometer, an Eppley Laboratory Precision Spectral Pyranometer, and a SCI‐TEC Brewer spectrophotometer. Hourly reports of total cloud cover and surface observations of air temperature, dew point temperature, barometric pressure, and visibility from the National Weather Service located at the nearby Raleigh‐Durham International Airport were also used in this study. An empirical relationship has been formulated for UV‐B attenuation as a function of total solar transmissivity and cloud cover. Cumulus‐type clouds were found to attenuate up to 99% of the incoming UV‐B radiation during overcast conditions. However, these same clouds were found to produce localized increases of UV‐B radiation of up to 27% over timescales less than 1 hour under partly cloudy skies when the direct solar beam was unobstructed. Summer haze was found to attenuate UV‐B radiation in the range of 5% to 23% when compared to a clear day in the autumn. In general, total radiation was attenuated more than UV‐B radiation under cloudy conditions.
Climatology of planetary waves in the northern stratosphere
Authors: Pawson Steven , Kubitz Tassilo
Published: February 2004

A 30‐year record of subjectively‐analyzed daily temperature and geopotential height data from the lower and middle stratosphere (50, 30, and 10 hPa) is used to derive a climatology of planetary waves, with zonal wavenumbers s = 1, 2, and 3, of temperature T and geopotential height Z. This should be useful as (1) a reference data set for intercomparison with shorter records and validation of general circulation models and (2) for fundamental understanding of the nature of stratospheric wave disturbances. First, seasonal (December, January and February) statistics are presented. The steady, standing waves are strongest at 60°–70°N and generally lead to northward eddy heat and momentum fluxes consistent with vertically propagating, dissipated disturbances, in broad agreement with previous studies based on shorter data sets. At 30 hPa the stationary eddies provide about 50–60% of the net northward heat flux, but the transients contribute a similar proportion to the net northward momentum flux. Statistical analysis of the transient wave amplitudes reveals unimodal distributions, which are skew for higher wavenumbers. Transient variations in the eddy fluxes are shown to be mainly due to amplitude variations rather than changes in the barotropic or baroclinic structure of the eddies. It is shown that changes in the geographical location of the waves contribute a considerable amount to the transience, so that a composite mean based on the wave amplitude maximum contributes a much larger fraction of the net eddy fluxes than the stationary waves. The importance of the long data record for these statistical distributions is emphasized by examining a 10‐year subsample. Finally, the occurrence of “preferred flow regimes” through the 30‐year data record is examined; neither trends nor definite links with possible external forcing mechanisms are found, despite considerable low‐frequency (biennial to decadal) variability.
Scavenging of aerosol particles by large water drops: 1. Neutral case
Authors: Pranesha T. S. , Kamra A. K.
Published: February 2004

A laboratory experiment to measure the collection efficiency of millimeter‐sized neutral water drops collecting micron‐sized aerosol particles has been conducted. In agreement with the previous studies, the results show that the collection efficiency increases with the decrease in drop size and/or increase in particle size. Further, the collection efficiency is observed to increase with impaction parameter and decrease with the drop Reynold's number. The limited and sparse data obtained in our experiment suggets that the collection efficiency of large drops may attain an upper limit which may be less than unity as the particle diameter approaches 10 μm. Moreover, the maximum collection efficiency attained by such large drops seems to decrease with the increasing drop size. Shape oscillations and the eddy shedding capability of large water drops have been proposed to explain the observed results.
Relationship between surface conditions and subsequent rainfall in convective storms
Authors: Eltahir Elfatih A. B. , Pal Jeremy S.
Published: February 2004

This paper describes the relationship between surface conditions (temperature and humidity) and subsequent rainfall. The focus is on convective storms that are forced and maintained locally due to conditional instability in the vertical distribution of atmospheric temperature. These storms are described using two probabilistic measures: (1) the probability of occurrence of storms given surface conditions and (2) the average storm rainfall. The surface conditions are described by a single variable: surface wet‐bulb temperature. The proposed theoretical relationships are tested using an hourly data set on rainfall and wet‐bulb temperature from the Amazon region. These observations confirm that both measures increase linearly with wet‐bulb temperature. However, for the occurrence of any storm the wet‐bulb temperature has to exceed a threshold of about 22°C. The sensitivity of the frequency of storms to changes in the climatology of surface wet‐bulb temperature is larger than the corresponding sensitivity of the average storm rainfall. These general concepts are applied in discussing the potential impact of changes in land cover on rainfall patterns using two specific examples: deforestation in the Amazon region and development of irrigation projects in the Columbia River basin.
Doppler imager wind measurements with simulations from the NCAR thermosphere‐ionosphere‐mesosphere electrodynamics circulation model
Authors: Wu Dong L. , Hays Paul B. , Roble Raymond G.
Published: February 2004

In this paper a comparison is presented between simulations of the diurnal and semidiurnal tides in the middle and upper atmosphere from the thermosphere‐ionosphere‐mesosphere‐electrodynamics general circulation model (TIMEGCM) and satellite observations from the Upper Atmosphere Research Satellite (UARS) high‐resolution Doppler imager (HRDI). Reasonable agreement is found between the model and observations for a March condition when a strong diurnal tide was observed. The model is able to reproduce many tidal features at altitudes between 65 and 110 km as observed in the HRDI wind measurements. Of interest in these features is the shortening vertical wavelength of the (1,1) tide in the upper mesosphere and lower thermosphere, which appears in both model simulations and the wind observations. The HRDI data also show large longitudinal variations in the diurnal tide, of which the amplitude can be as high as ∼50% of the migrating tide. The wavelike structures in latitude and altitude dimensions suggest that the longitudinal variations are likely due to the presence of propagating nonmigrating tides in the upper mesosphere and lower thermosphere. For further investigations of the observed tidal variability the model demonstrates great potential with the use of more realistic heating/cooling and wave forcing schemes.
One‐dimensional statistical dynamic representation of subgrid spatial variability of precipitation in the two‐layer variable infiltration capacity model
Authors: Liang Xu , Lettenmaier Dennis P. , Wood Eric F.
Published: February 2004

The two‐layer variable infiltration capacity (VIC‐2L) model is extended to incorporate a representation of subgrid variability in precipitation, using an analytical one‐dimensional statistical dynamic representation for partial area coverage of precipitation. The analytical approach allows the effects of subgrid‐scale spatial variability of precipitation on surface fluxes, runoff production, and soil moisture to be represented explicitly. With this method, spatially integrated representations of surface fluxes, runoff, and soil moisture due to subgrid‐scale spatial variability in precipitation, infiltration, and vegetation cover are obtained. The results are compared with those obtained using an exhaustive pixel‐based approach, and the results obtained by applying uniform precipitation over the precipitation‐covered area. The precipitation coverage over a grid cell is shown to play a primary role in estimating the surface fluxes, runoff, and soil moisture. In general, the spatial distribution of precipitation within the precipitation‐covered area plays a secondary role, in part because VIC‐2L represents the subgrid spatial variability of soil properties. While the analytical approach gives good approximations to the pixel‐based approach, and is superior to the uniform precipitation approach in general, the differences are not large.
Hodographic analysis of gravity waves: Relationships among Stokes parameters, rotary spectra and cross‐spectral methods
Authors: Eckermann Stephen D.
Published: February 2004

The elliptical rotation with height of horizontal velocities produced by gravity waves provides considerable information about the wave field. Methods of statistically characterizing velocity ellipses from data currently fall into three main categories: (1) hodographic analyses, (2) cross‐spectral analyses, and (3) rotary spectral analyses. The three methods have some intuitive similarities, yet precise interrelationships among them are presently unclear. The three techniques are interrelated here using the so‐called “Stokes parameters” of the wave field, which initially provide a concise description of the hodographic analysis method (1). On Fourier transforming the Stokes parameters, standard formulae employed in rotary‐spectral and cross‐spectral analysis methods can then be expressed in terms of the resulting “Stokes‐parameter spectra.” The results highlight some drawbacks in the use of cross‐coherence spectra between velocity components to verify the existence of a coherent wave motion. A more robust measure is suggested, based on the “degree of polarization” of classical hodograph‐based Stokes‐parameter analysis, which can be generalized to provide an analogous spectral measure for evaluation in rotary‐spectral and cross‐spectral analyses.
Tunable diode laser absorption spectrometer for ground‐based measurements of formaldehyde
Authors: Fried Alan , Sewell Scott , Henry Bruce , Wert Bryan P. , Gilpin Tim , Drummond James R.
Published: February 2004

We describe here a sensitive tunable diode laser absorption spectrometer (TDLAS) which was employed for ambient measurements of formaldehyde (HCHO) during the 1993 Idaho Hill/Fritz Peak Photochemistry Experiment. This system incorporated many new features and approaches including a novel astigmatic Herriott sampling cell which achieves a 100‐m pathlength in a 3‐L volume. We also describe procedures and tests carried out to ensure high accuracy, including the verification of HCHO standards by means of four techniques. During the field campaign, ambient HCHO measurements were acquired with an average 1σ measurement precision of 0.17 ppbv employing 1–5 min integration times. When combined with a maximum systematic uncertainty of 10%, ambient HCHO concentrations around 1.5 ppbv were measured with an average total (random plus systematic) 1σ uncertainty of 15% during the field campaign. In the intervening 2 years since the field experiment, additional features have been implemented for continuous unattended operation and improved performance. Rapid background subtraction now routinely allows HCHO measurements to be acquired with replicate precisions of 0.040 to 0.056 ppbv employing a 5‐min integration period. This corresponds to routine minimum detectable absorbances of 1.2 to 1.6×10−6 in an actual mobile laboratory field environment.
The tropical tropopause over the western Pacific: Wave driving, convection, and the annual cycle
Authors: Reid G. C. , Gage K. S.
Published: February 2004

The annual cycles in height and temperature of the tropopause over the tropical western Pacific island of Truk (7.5°N, 151.8°E) are derived for the period 1980–1988 from daily radiosonde profiles. Earlier work has shown that tropopause properties are fairly uniform over large areas of the tropics, so that conclusions drawn from the Truk observations can be taken as representative of the western Pacific warm pool region, and can be applied with caution to wider regions of the tropics. The relative roles of tropical convection and extratropical wave driving in determining the tropopause properties are discussed, and it is suggested that the chief role of wave driving is to lower the temperature in the uppermost part of the troposphere during the northern winter months, causing a decrease in local stability, and allowing penetrative overshooting of convective turrets to take place more readily than during the rest of the year. As the winter progresses, the overshooting convective turrets create widespread cirrus anvils, incorporating stratospheric air with a high potential temperature, and establishing a new higher tropopause. Anomalously high tropopause potential temperatures during the northern spring months are tentatively attributed to the combined wave‐driving action of the two hemispheres, as wave activity increases with the approach of winter in the southern hemisphere, but still remains at a high level during northern spring. The day‐to‐day variability in tropopause height and temperature is discussed, and is shown to have implications for troposphere‐stratosphere exchange. The use of monthly mean tropopause temperatures to calculate the saturation vapor pressure of water entering the stratosphere may give misleading results, since injection is likely to take place primarily in association with the transient rises in tropopause height and decreases in temperature that occur more or less randomly from day to day, while the monthly means also include the drops in height and increases in temperature that do not represent injections into the stratosphere.
Variability in the mesosphere observed by the Nimbus 6 pressure modulator radiometer
Authors: Lawrence Bryan N. , Randel William J.
Published: February 2004

The pressure modulator radiometer flew aboard Nimbus 6, collecting radiance data from June 1975 until June 1978. These data have been processed to yield daily temperatures, geopotential heights, and balance wind estimates from the stratosphere and mesosphere (30–85 km) for the entire period. We use these data to examine the variability of both the zonal‐mean and the nonzonal disturbances present in the data. In terms of the zonal‐mean, we show that the COSPAR International Reference Atmosphere (1986), developed from these data, can be misleading in the mesosphere due to the underlying interannual variability and the merging with other data sets. Daily variability of the zonal‐mean flow is examined, and these data show strong evidence of coupling between the stratosphere and mesosphere for such variations. We also find evidence for significant coupling of wave‐like events in the stratosphere and the mesosphere but that not all such disturbances seen in the mesosphere are due to simple propagation from below. Space‐time spectral analysis is used to search for traveling planetary waves: Results show a weak 5‐day normal mode present in the Equinox seasons, which appears to correspond to the first symmetric mode predicted by theory. These data also show clear evidence of the 4‐day wave in all three southern winters examined and are consistent with the hypothesis that this mode grows due to instability of the background zonal flow.
Development of the Antarctic ozone hole
Authors: Schoeberl Mark R. , Douglass Anne R. , Kawa S. Randolph , Dessler Andrew E. , Newman Paul A. , Stolarski Richard S. , Roche Aidan E. , Waters Joe W. , Russell James M.
Published: February 2004

A Lagrangian chemical model is used to simulate the formation of the Antarctic “ozone hole”: the decrease in high‐latitude southern hemisphere ozone between mid‐August and mid‐September of each year. The model benchmark simulation of HNO3, ClONO2, ClO, and ozone for September 17, 1992, is in good agreement with UARS observations. Simulations of the ozone column over the years 1979–1994 show quantitative agreement with the secular decline in Antarctic ozone and change in the area of the ozone hole as observed by the total ozone mapping spectrometer (TOMS). The model calculates that the Antarctic ozone loss and ozone hole area both increased linearly with time after the early 1970s until the early 1990s. After the early 1990s the growth of the area of the ozone hole slows as a result of the slowing of the growth rate of total inorganic chlorine. A hypothetical doubling of the 1992 atmospheric chlorine amount would expand the ozone hole to the very edge of the polar vortex.
The effect of planetary waves on the total ozone zonal deviations in the presence of a persistent blocking anticyclone system
Authors: Engelen Richard J.
Published: February 2004

Strong planetary wave activity enhanced by the external forcing of a persisting anticyclone system can cause large total ozone zonal deviations. In January 1992 such a situation was observed with a high‐pressure system and associated low total ozone concentrations situated over Northern Europe. In this article, measurements from the total ozone mapping spectrometer (TOMS) are analyzed with a simple model based on the linearized stationary ozone continuity equation. It is shown that in such a meteorological situation, vertical advection of ozone caused by the wavenumber‐one quasi‐stationary planetary wave is the most important monthly mean transport mechanism. This is different from the climatological situation, where horizontal and vertical advection are almost equally important and where wavenumbers two and three contribute more to the total ozone zonal deviations. The dominance of vertical motions, which are in phase throughout the lower and middle stratosphere, also explains the high correlations found between temperatures at 50 hPa from National Meteorological Center analyses and total ozone. Under these special meteorological conditions, the high planetary wave activity is responsible for total ozone columns with about 60 Dobson units less ozone over the anticyclonic region than under normal conditions.
Satellite retrieval of tropical precipitation using combined International Satellite Cloud Climatology Project DX and SSM/I Data
Authors: Sheu Rong‐Shyang , Curry Judith A. , Liu Guosheng
Published: February 2004

A new precipitation retrieval scheme for use in the tropics is developed using a combination of visible (VIS)/IR and microwave satellite observations. The new scheme combines the advantages of both the ample coverage of VIS/IR sampling and the physical directness between precipitation and microwave radiances. A VIS/IR algorithm is “trained” using Special Sensor Microwave/Imager (SSM/I) derived values of precipitation. Cloud top temperatures and visible optical depths provided by the International Satellite Cloud Climatology Project (ISCCP) level DX analyses are “binned” by every 10 K and every 10 unit optical depth, respectively. Lookup tables for the probability of rain and mean rainfall rate are constructed for each cloud top temperature/optical depth cell whenever the optical depth is available (daytime). For the nighttime, the tables are based only on cloud top temperature. The instantaneous rainfall rates are obtained by multiplying the mean rainfall rate by the probability of rain, both characterized by the cloud top temperature and/or visible optical depth associated with the satellite pixel. The satellite retrieval always retains results from optimal parameters, which means SSM/I results are used whenever SSM/I samplings are available; otherwise, VIS/IR results are used during daytime, while IR‐only results are used during nighttime. The final precipitation product can have resolution as high as 3 hours in time and about 0.3° in space. However, averaging in space and/or time improves the statistics of the derived rainfall rates, since the statistics of the algorithm are more fully utilized. The satellite‐derived rainfall product compares well with ship rain gauge data in terms of rain/no rain determination, and agrees well with daily rainfall accumulation derived from a large‐scale moisture budget. The satellite retrieved rainfall rates are biased high relative to radar observations. In the absence of satisfactory data with which to validate the satellite‐derived rainfall rates, it can be concluded that there is useful information in the ISCCP data set that relates to precipitation and that the inclusion of visible optical depth information improves the daytime retrieval of precipitation relative to IR‐only methods.
The spatial and temporal development of intracloud lightning
Authors: Shao X. M. , Krehbiel P. R.
Published: February 2004

A detailed study of the complete sequence of VHF radiation events during intracloud (IC) flashes in Florida has shown that IC flashes often have a bilevel structure connected by a single upward channel. The lower and upper level channels appear to correspond to the main negative and upper positive charge regions of the storm, respectively. The IC flashes are characterized by active and final stages, each comprising about half of the overall flash duration. During the active stage, negative charge is transported upward in the cloud, first as a result of initial breakdown, which establishes the upward channel, and subsequently as a result of repeated breakdown events from the lower to the upper level. For the flashes of this study, the initial breakdown lasted 10 to 20 ms and propagated upward at a speed of 1.5 to 3×105 m s−1. It also established the beginning of one or more horizontal branches in the upper positive charge region, which were extended by the subsequent breakdown. Little or no radiation was detected along the upward channel during the subsequent breakdown, indicating that the channel remained more or less continuously conducting following the initial breakdown. After a time delay, the subsequent breakdown extended the lower‐level channels in a retrograde manner horizontally away from the flash origin. At the end of the active stage the upward channel ceases to be conducting and the remaining, final stage of a flash is characterized by fast (106 to 107 m s−1), well‐defined “K”‐type streamers that begin at successively greater distances along the lower‐level channel and transport negative charge toward or into the base of the upward channel. The streamers are identical to those observed during the interstroke intervals and final stages of cloud‐to‐ground (CG) flashes. Typically, a few late‐flash K streamers continue through the flash origin into and along an upper‐level channel. The overall results are consistent with other observations of IC flashes and explain several features of the observations. Similar results are obtained for IC flashes in New Mexico storms. Comparison of the initial breakdown of IC and CG flashes shows that the IC breakdown is more intermittent than that of CG flashes, even though both have the same polarity and propagate at about the same average speed.
Variability in the chemistry of precipitation in the Pyrenees (northeastern Spain): Dominance of storm origin and lack of altitude influence
Authors: Camarero Lluís , Catalan Jordi
Published: February 2004

The assessment of the effects of atmospheric inputs on the chemistry of mountain lakes requires realistic data on the chemical composition of these inputs. However, precipitation sampling stations are usually at lower altitudes than lakes. The location of the stations may lead to a mistaken appraisal of precipitation chemistry, since orography strongly influences the formation of storms caused by air masses coming from different directions, and altitude affects the mechanisms of transport and deposition of solutes in several ways. The effect of altitude on the chemistry of precipitation in the Pyrenees was studied at three sampling points located at different heights (1600, 1900, and 2200 m above sea level) within the same valley, orientated in a NE‐SW direction. Sampling was carried out over a period (summerautumn 1990) long enough to ensure a statistically representative collection of events with a different origin. Three main results were derived from this study. (1) The main source of variability was the cation‐anion balance, which was determined by the origin of the wet air masses: rains from the Atlantic were more acidic than those coming from the Mediterranean. (2) There was no significant difference in the chemistry of bulk precipitation with altitude within the range 1600–2200 m asl, in which most of the lakes in the Pyrenees are found. (3) Below‐cloud mechanisms of deposition had a significant influence on NO−3 concentration. The concentration of most of the solutes was independent of precipitation volume, except for NO−3.
Modeling ozone and carbon monoxide redistribution by shallow convection over the Amazonian rain forest
Authors: Edy J. , Cautenet S. , Brémaud P.
Published: February 2004

During a “locally occurring system” (LOS) in Amazonian forest characterized by an active mixing layer from surface to 1000 m capped by a fossil mixed layer between 1000 and 1500 m, the vertical mixing effects of a shallow cumulus are examined. The explicit redistribution of CO and O3 has been studied with a two‐dimensional convective cloud model coupled with a chemical model including gas and aqueous phases, for a shallow convective situation taken from the GTE/ABLE 2B campaign. The chemistry describes the main oxidation chains of CH4 and CO in presence of low NOx concentration in a remote troposphere. Model results compare favorably with observations obtained after development of the shallow convection. The analysis of results explains how a growing and decaying cloud field allows exchanges between a mixing layer, a fossil mixed layer and the free troposphere. An inert tracer study has shown that the layer lying between surface to 500 m is transported up to 2000 m. Even small clouds are responsible for the transport and the transformation of chemical species. Sensitivity tests are performed to evaluate the relative importance of dynamical, microphysical and chemical processes. The cumulus venting is the main process which modifies the trace species redistribution. The O3 and CO amounts which are transported by a fair‐weather cumulus through the boundary layer and free troposphere in the wet season, over a tropical rain forest, are respectively 1.2 × 1023 molecules km−2 h−1 and 7.7 × 1023 molecules km−2 h−1. In tropical regions, over rain forest, even with low NOx concentration, several cumulus exist every day and the vertical fluxes of some chemical species (like O3) cannot be neglected.
Interannual and long‐term climate variability over the Zaire River Basin during the last 30 years
Authors: Kazadi Sanga‐Ngoie , Kaoru Fukuyama
Published: February 2004

Climatological data records of temperature, rainfall, and number of rainy days provided by the Zaire Meteorological Agency (METTELSAT) at seven Zairian stations for the 1960–1992 period are analyzed for the first time since the 1970s. Our investigations focus on climate variability as related with environmental changes over the Zaire River Basin, which is climatologically and biogenetically one of the most important regions in the world. On the basis of the 30‐year monthly mean climatologies, it is shown that the solar annual cycle dominates the seasonal changes of both the temperature and rainfall over this region. On the interannual time‐scales, the variability of these climatic variables is characterized by (1) a 2‐to 5‐year oscillation strongly correlated to the southern oscillation index, thus to the ENSO phenomenon, and (2) a nearly 10‐year oscillation (called here the quasi‐decadal oscillation, QDO) with a very remarkable correlationship with the solar activity (sunspots number). On the long‐term timescale, a remarkable decreasing trend in rainfall and number of rainy days, as well as increasing temperatures over the 30‐year period, has been detected as the most dominant climatological features all over the basin. The magnitudes of temperature increase are by far larger than those reported in previous works for both the global mean and hemispherical mean warmings. We postulate that this trend of regional warming and desiccation from within the heart of the African rainforests is due to the increase in surface albedo, itself triggered by uncontrolled land‐use policies and forests development over this area (logging, slash and burn, bushfire, fuelwood, farming, ranching, urbanization, etc.).
Aerosol dynamics in near‐field aircraft plumes
Authors: Brown R. C. , Miake‐Lye R. C. , Anderson M. R. , Kolb C. E. , Resch T. J.
Published: February 2004

A numerical model including gas phase HOx, NOx, and SOx chemistry; H2SO4‐soot adsorption; binary H2SO4‐H2O nucleation; aerosol coagulation; and vapor condensation is used to investigate aerosol formation and growth in near‐field aircraft plumes. The plume flow field is treated using the JANNAF standard plume flow field code, SPF‐II. Model results are presented for a Mach 2.4 high‐speed civil transport at 18 km altitude and 85°N latitude and a subsonic Boeing 707 at 12.2 km, 47°N. The results, based on hydroxyl radical driven oxidation kinetics, indicate that 1–2% of the emitted SO2 is converted to H2SO4 in the near‐field exhaust (1–2 s) and that for typical exhaust SO2 emission indices (≈1 g kg‐fuel) the plume is supersaturated with respect to both the pure liquid acid and H2SO4/H2O solutions. Classical nucleation theory predicts high levels of small (0.3–0.6 nm radius) H2SO4/H2O embryos. Coagulation and gas‐to‐particle conversion are followed to provide estimates for the number density of activated soot particles capable of serving as condensation nuclei for contrail formation. Results are presented illustrating the dependence of water condensation on the number density and size distribution of activated exhaust soot nuclei.
Measurement of carbon dioxide and hydrocarbon fluxes from a Sitka Spruce forest using micrometeorological techniques
Authors: Beverland I. J. , Milne R. , Boissard C. , ÓNéill D. H. , Moncrieff J. B. , Hewitt C. N.
Published: February 2004

CO2 and hydrocarbon fluxes from a sitka spruce forest were measured using a conditional sampling method. The method was used in two ways: (1) an automated system was used to monitor continuously the mixing ratio difference of total hydrocarbons and CO2 in sampling lines for updraught and downdraught air and (2) conditionally sampled updraught and downdraught air was passed through adsorption tubes, which subsequently were analyzed in the laboratory, to determine the fluxes of nonmethane hydrocarbons (NMHCs). Aerodynamic gradient measurements of NMHC fluxes were made over the same period. Method (1) produced a high temporal resolution data set of approximately 4 days of near‐continuous fluxes. Marked diurnal trends in CO2 flux were evident. Peak daylight photosynthetic fluxes ranged from −30 to −90 mmol m−2 h−1. Smaller fluxes were noted during heavy rainfall and diminished photosynthetically active radiation. Nighttime respiration ranged from 0 to 10 mmol m−2 h−l. Total hydrocarbon fluxes were 3 orders of magnitude smaller. During hot, sunny conditions a total hydrocarbon flux of approximately 400 μmol m−2 h−1 (CH4 equivalents) was observed. Fluxes of specific NMHC compounds, from method (2), ranged between 90 and 563 μg m−2 hour−1. The annual carbon flux to Great Britain's conifer forests was estimated to be 1.3 Mt using a simple upscaling model based on the observations of CO2 flux during the field experiment.