bluuebunny/crossref_metadata_2025 huggingface dataset:
Solar activity‐total column ozone relationships: Observations and model studies with heterogeneous chemistry
Authors: Zerefos C. S. , Tourpali K. , Bojkov B. R. , Balis D. S. , Rognerund B. , Isaksen I. S. A.
Published: February 2004

In the present paper we examine the effect of long‐term solar variability on total column ozone using the longest available ground‐based (1964–1994) and satellite (1979–1992) zonally averaged total column ozone records. Numerical simulations with a two‐dimensional (2‐D) model, which incorporates heterogeneous chemistry, transport, and the representation of the long‐term solar variability, are compared to the observations. Our analysis of the total column ozone records shows that the solar activity signal in total column ozone is better seen in the tropics and during periods with no volcanoes and no synergistic effects from El Nino‐Southern Oscillation (ENSO) and quasibiennial oscillation (QBO). On decadal timescales the solar activity component in total column ozone is confirmed to have a relatively small amplitude (1–2% of the 1964–1994 mean). The slowly varying decadal solar activity component in total column ozone has an amplitude 3 to 5 times larger than that of the 27‐day solar rotation oscillation as seen in total ozone. The observations confirm model calculations of a larger amplitude in total column ozone at solar maximum as compared to solar activity minimum conditions for the 27‐day period. The heterogeneous 2‐D chemical transport model results are in good agreement with the long‐term ground‐based observations. It is noted that in the tropics both the interannual variability of total column ozone and the long‐term impact from chlorofluorocarbons (CFCs) through the action of polar stratospheric clouds (PSCs) are small and therefore the 1–2% solar activity signal in the data can be more clearly seen above the noise level at these lower latitudes.
Modulation of tropospheric ozone by a propagating gravity wave
Authors: Langford A. O. , Proffitt M. H. , VanZandt T. E. , Lamarque J.‐F.
Published: February 2004

The modulation of tropospheric ozone by a propagating gravity wave is inferred from the analysis of more than 200 lidar profiles obtained over a 14‐hour period during September 3–4, 1993, near Rollinsville, Colorado (39.9°N, 105.3°W, 2.68 km ms1). Periodic fluctuations of up to 30% in the ozone mixing ratios are attributed to a nearly monochromatic gravity wave with a downward phase velocity of −0.08±0.01 m s−1, a mean vertical wavelength of 3.0±0.5 km, and an apparent frequency of (1.7±0.4)×10−4 s−1. Wind profiles from nearby radar soundings suggest that these fluctuations are induced by a gravity wave that propagates from the NW to SE with a horizontal wavelength of ∼180 km. These results imply that gravity waves may contribute significantly to the short‐term (≤1 day) variability of ozone and other trace gases in the troposphere.
Satellite retrieval of aerosol properties over the ocean using polarization as well as intensity of reflected sunlight
Authors: Mishchenko Michael I. , Travis Larry D.
Published: February 2004

Most current and proposed satellite remote sensing of tropospheric aerosols relies upon radiance measurements that are interpreted using algorithms that determine best fits to precalculated scattered sunlight for one or more “standard” aerosol models. However, the number of different types of aerosol and the substantial space and time variations typically encountered can pose a severe uniqueness problem even for the multiple constraints provided by multispectral radiances of a scene at a number of observation zenith angles. Experience with polarimetry remote sensing on planetary missions has demonstrated that the measurement of polarization as well as the radiance can resolve such uniqueness problems. We use numerically accurate solutions of the vector radiative transfer equation for a realistic atmosphere‐ocean model to theoretically simulate several types of satellite aerosol retrievals over the ocean utilizing radiance measurements alone, polarization measurements alone, and radiance and polarization measurements combined. We have restricted all simulations to a single near‐infrared wavelength of 0.865 μm and assumed that aerosols are spherical, monomodal, and nonabsorbing. These simplifications permit a study of practical scope that tests the retrieval algorithms under exactly the same conditions, thus clearly demonstrating their relative capabilities. In agreement with previous analyses, we have found that radiance‐only algorithms using multiple‐viewing‐angle observations perform far better than those based on single‐viewing‐angle measurements. However, even multiple‐viewing‐angle radiance measurements taken at a single wavelength are not always sufficient to determine the aerosol optical thickness, effective radius, and refractive index with high enough accuracy. In contrast, high‐accuracy, single‐wavelength, multiple‐viewing‐angle polarimetry alone is capable of uniquely retrieving all three aerosol characteristics with extremely high accuracy (±0.015 in aerosol optical thickness, ±0.03 μm in effective radius, and ±0.01 in refractive index). Furthermore, the accuracy of the optical thickness retrieval can be slightly improved by simultaneously using radiance measurements. Our analysis demonstrates that algorithms utilizing high‐accuracy polarization as well as radiance measurements are much less dependent on the availability and use of a priori information and can be expected to provide a physically based retrieval of aerosol characteristics (optical thickness, refractive index, and size) with accuracy needed for long‐term monitoring of global climate forcings and feedbacks.
NOx from lightning: 2. Constraints from the global atmospheric electric circuit
Authors: Price Colin , Penner Joyce , Prather Michael
Published: February 2004

The global atmospheric electric circuit can be used to constrain the total amount of NOx produced by lightning (LNOx). Since the global atmospheric electric circuit is regulated by global thunderstorm activity and, more specifically, global lightning currents, we use the global electric circuit to quantify and place limits on the total amount of energy available from lightning. Using a production rate of 10×1016 molecules NO/J, we have calculated the global LNOx production on monthly, annual, and interannual timescales from 1983 to 1991. The 8‐year mean production rate is found to be 13.2 Tg N/yr and agrees with the independent estimate derived in part 1 of this study (12.2 Tg N/yr), which is based on lightning physics and global lightning distributions. After considering the various uncertainties in these calculations, we conclude that the annual production rate of NOx from lightning cannot be less than 5 nor more than 25 Tg N/yr.
Biogenic hydrocarbon emissions from southern African savannas
Authors: Guenther Alex , Otter Luanne , Zimmerman Patrick , Greenberg Jim , Scholes Robert , Scholes Mary
Published: February 2004

Biogenic nonmethane hydrocarbon (NMHC) emissions were investigated at two field sites in the Republic of South Africa that include five important southern African savanna landscapes. Tropical savannas are a globally important biome with a high potential for biogenic emissions but no NMHC emission measurements in these regions or in any part of Africa have been reported. Landscape average hydrocarbon emissions were estimated by characterizing plant species composition and foliar density at each site, identifying and characterizing NMHC emissions of the most abundant plant species, and identifying and characterizing NMHC emissions of plant species with the highest NMHC emission rates. A hand‐held portable analyzer proved to be a useful tool for identifying plants with high emission rates. A branch enclosure system, with gas chromatography and flame ionization detector, was used to quantify isoprene and monoterpene emission rates. Emission rates were species‐specific and several genera had both high and low emitters. At least some species with high emission rates were identified in most savanna types. High and low emitters were found on both nutrient‐rich and nutrient‐poor soils. Landscape average emission capacities for the five savanna types range from 0.6 to 9 mg C m−2 h−1 for isoprene and about 0.05 to 3 mg C m−2 h−1 for monoterpenes. The savanna emission rates predicted by existing global models are within the range estimated for these five savanna types.
Interannual fluctuations in atmospheric angular momentum simulated by the National Centers for Environmental Prediction medium range forecast model
Authors: Mo Kingtse C. , Dickey Jean O. , Marcus Steven L.
Published: February 2004

An earlier study by Dickey et al. [1992] established the existence of globally coherent interannual fluctuations in atmospheric angular momentum (AAM), associated with the El Niño‐Southern Oscillation (ENSO) cycle. In this paper, we pursue the origin and the structure of these fluctuations using an ensemble of experiments generated by the National Centers for Environmental Prediction, medium range forecast model version 9. In the control experiments, where the observed sea surface temperatures (SSTs) were used as the lower boundary conditions, the model captures the characteristic V‐like structure in time‐latitude plots of zonally averaged AAM found by Dickey et al., while experiments with climatological SSTs and those with either perpetual warm or cold ENSO conditions superimposed on the climatological SSTs failed to reproduce this structure. The numerical results indicate that these AAM structures are related to SST variations associated with transitions between different phases of the ENSO cycle and have both propagating and standing components. The largest zonal wind contribution from the levels studied (850, 500, and 200 hPa) is at 200 hPa, where the tropical convective outflow is the strongest. Composites of zonal wind and geopotential height show a clear relationship between the stages of the global AAM oscillation and the ENSO cycle. The strong similarity between the simulated and observed AAM series attests to the model's ability to realistically simulate the interannual response of the atmosphere to ENSO SST anomalies.
Episodic removal of NOy species from the marine boundary layer over the North Atlantic
Authors: Roberts James M. , Parrish David D. , Norton Richard B. , Bertman Steven B. , Holloway John S. , Trainer Michael , Fehsenfeld Fredrick C. , Carroll Mary Anne , Albercook George M. , Wang Tao , Forbes Gerald
Published: February 2004

Measurements of ozone, carbon monoxide, NOy, NOx, HNO3, particulate NO3−, PAN, PPN, and alkyl nitrates were made at Chebogue Point, Nova Scotia, during July, August, and September 1993, and measurements of ozone, carbon monoxide, NOx and N0y were made at Sable Island, Nova Scotia, during August and September 1993 as part of the North Atlantic Regional Experiment (NARE). Periods of photochemical pollution were observed during which concentrations of the above species were elevated relative to average conditions. The best indicator of the extent of impact was found to be the sum of the C1‐C4 alkyl nitrates. The removal of PAN and PPN by fog droplets through thermal decomposition and subsequent uptake of the peroxyacetyl and peroxypropionyl radicals (PA and PP) was suggested by loss of PAN and PPN during fog. The effect of this chemistry on NOy species in the marine environment will need to be considered. The loss of inorganic nitrate (HNO3 and particulate NO3−), PAN (and to a minor extent PPN) resulted in deviation of the O3 versus NOy‐NOx correlations from that observed in eastern North America.
Lightning flashes with high origins
Authors: Proctor David E.
Published: February 2004

We studied detailed, time‐resolved maps of 21 cloud flashes that began at heights above 7.4 km above mean sea level by mapping sources of radio noise emitted by the flashes at 355 MHz. The electric field changes caused by these flashes were also recorded. All 21 flashes began as negative flashes, but one changed polarity while its stepped leader was in progress. Stepped leaders all emitted pulses at rates near one pulse per millisecond. Stepped leaders extended at speeds whose median value was 7.5×104 m/s. Their line charge densities ranged from 0.7 to 8.7 C/km, and the median value was 3.3 C/km. Stepped leader currents range from 37 A to 630 A; the median of 13 was 130 A. Most flashes (17 of 21) produced more than one stepped leader; 10 of 21 path‐lengths were longer than 17 km. Of 93 stepped leader channels, 53 were mainly horizontal, 26 were directed mostly upward, and 14 were mainly downward. The overall behavior of these cloud flashes was similar to that reported previously by Proctor et al. [1988] for ground flashes. Stepped leader paths extended in “forward” directions while emitting pulses and registering large, slow changes in electric field at ground level. The combined action of many rapid and intermittent Q streamers caused the flashes to extend slowly in “reverse” directions. A model for high cloud flashes is proposed. Most of these flashes began where the radar reflectivities were 20 dBZ. Some of the stepped leader paths were influenced by 20‐dBZ contours. We concluded that the origins were regions of high electric field that bordered charged regions that were probably screening layers, and that positive screening layers were threaded by the flashes. Evidently, positively and negatively charged screening layers existed simultaneously at separate regions in the thunderclouds. All 21 flashes extended beyond the 20 dBZ surfaces; 19 protruded extensively. We concluded that these regions contained diffuse, positive charge.
Ozone production and loss rate measurements in the middle stratosphere
Authors: Jucks K. W. , Johnson D. G. , Chance K. V. , Traub W. A. , Salawitch R. J. , Stachnik R. A.
Published: February 2004

We present the first simultaneous measurements of HOx, NOx and Clx radicals in the middle stratosphere obtained during a balloon flight at 34°N in September 1989, along with calculations from a photochemical model, to show that NOx catalytic cycles dominate loss of ozone (O3) for altitudes between 24 and 38 km; the observed abundance of ClO is lower than that expected for altitudes above 30 km on the basis of models using recommended rates and cross sections, reducing the relative importance of the Clx catalytic cycles for loss of O3; and removal rates of O3 derived from observed concentrations of rate limiting HOx, NOx, and Clx radicals balance computed production rates for altitudes between 32 and 38 km, a region where ozone is expected to be regulated primarily by photochemical processes.
Zonal variance of nitric acid vapor as an indicator of meridional mixing in the subtropical lower stratosphere
Authors: Remsberg Ellis E. , Bhatt Praful P.
Published: February 2004

Several transport scenarios have been advanced in the literature to account for the exchange of tracers between the extratropics and tropics in the lower stratosphere. Each scenario involves a slow, net upward transport at low latitudes and varying degrees of mixing at middle latitudes plus detrainment across a subtropical region of enhanced tracer gradients. In situ observations for differentiating among these scenarios are generally lacking above about 21 km altitude. Existing satellite data sets can provide useful information throughout the lower stratosphere. In particular, we have looked for such exchange by examining time series of the daily zonal variance of the Nimbus 7 limb infrared monitor of the stratosphere distributions of nitric acid vapor (HNO3) mixing ratio. This species is characterized by strong subtropical meridional gradients between about 10 and 100 hPa, which develop in response to extratropical wave activity and any associated mixing processes. The subtropical variance is a measure of that activity, its region of maximum values moving equatorward during late autumn and then relaxing and retreating in late spring. At and below the 45‐hPa level there is not a clear maximum of variance at a given latitude, perhaps a result of the secondary circulation that was present during the 1978/1979 winter in response to the easterly phase of the quasi‐biennial oscillation cycle. At the 30‐hPa and 50‐hPa levels, while we find occasions in winter when tongues of subtropical air were transported to higher latitudes, we find no clear evidence for a large‐scale transport of extratropical air to lower latitudes through a subtropical region of enhanced gradients.
Atmospheric peroxy radical measurements by ion molecule reaction‐mass spectrometry: A novel analytical method using amplifying chemical conversion to sulfuric acid
Authors: Reiner Thomas , Hanke Markus , Arnold Frank
Published: February 2004

A novel method for measuring atmospheric peroxy radical concentrations has been developed and tested in various field and laboratory studies. The method relies on amplifying chemical conversion of peroxy radicals to gaseous sulfuric acid via the chain reaction with NO and SO2 (NO/SO2 chemical amplifier) and detection of the reaction product sulfuric acid by ion molecule reaction‐mass spectrometry (IMR‐MS). The high sensitivity of IMR‐MS and the low atmospheric background of gaseous H2SO4 allows for work with small chain lengths and short reaction times, which reduces the impact of potential interference and loss processes. The basic kinetic foundations of the amplification process including its sensitivity to interference and radical loss processes are discussed. Field and laboratory measurements indicate nominal operation of the NO/SO2 chemical amplifier system and its suitability for highly sensitive peroxy radical measurements even under atmospheric conditions characterized by low peroxy radical concentrations such as nighttime, winter, and high‐latitude conditions.
Effect of volcanic particles on the O2 and O3 photolysis rates and their impact on ozone in the tropical stratosphere
Authors: Huang Theresa Y. W. , Massie Steven T.
Published: February 2004

The radiative effect of Pinatubo sulfate aerosol and ash particles on the O2 and O3 photolysis rates in the tropics and the effect of these photolysis rate changes on stratospheric ozone are examined. The impact of volcanic ash particles on the JO2 and JO3 ranges from negligible to significant, dependent on the relative ash content specified. However, regardless of the magnitude of the ash effect on the photolysis rates, the total ozone column loss is only slightly affected. The O2 and O3 photolysis rate perturbation by sulfate aerosols is shown to be rather sensitive to solar zenith angle. However, since JO2 (which predominantly determines ozone production at the equator) varies several orders of magnitude during the course of the diurnal cycle, using a diurnally averaged solar zenith angle simulates fairly well the volcanic aerosol effect on ozone through photodissociation.
Two‐dimensional model calculations of nitric oxide transport in the middle atmosphere and comparison with Halogen Occultation Experiment data
Authors: Siskind David E. , Bacmeister J. T. , Summers M. E. , Russell J. M.
Published: February 2004

A two‐dimensional chemical transport model has been used to examine the physical processes governing the transport of high levels of thermospheric nitric oxide (NO) downward into the middle atmosphere. Three different facets of this transport are studied. The first facet involves diffusion from the thermosphere to the summertime mesopause region. The second facet involves downward advection by the mean meridional circulation in the wintertime mesosphere and the effects of planetary wave mixing on the latitudinal gradient of NO. The third facet is the residual amount of NO deposited in the springtime upper stratosphere and its senstivity to the magnitude and duration of the unmixed descent which occurred the previous winter. Comparison of the model with observations by the Halogen Occultation Experiment (HALOE) suggest the following: (1) A clear auroral enhancement in summertime NO exists at 89 km. Model calculations suggest this results from both in situ ionization and dissociation of N2 as well as downward diffusion from the thermosphere above 100 km. (2) Using HALOE CH4 observations as a tracer, enhanced NO in the wintertime mesosphere is seen to be transported to latitudes as far equatorward as 30°–40°. The model is in good agreement with these observations when planetary wave mixing is included. Without this mixing, the enhanced NO remains confined to high latitudes that are not observed by HALOE in winter. (3) The model overestimates the net NO deposited into the upper stratosphere. This appears to be related to the model springtime warming being delayed relative to the real atmosphere. Inclusion of an additional source of drag in the polar stratosphere in late winter yields better agreement with observations.
Heterogeneous reactions on stratospheric background aerosols, volcanic sulfuric acid droplets, and type I polar stratospheric clouds: Effects of temperature fluctuations and differences in particle phase
Authors: Borrmann Stephan , Solomon Susan , Dye James E. , Baumgardner Darrel , Kelly Ken K. , Chan K. Roland
Published: February 2004

Northern hemispheric ER‐2 (NASA) data from stratospheric aerosol measurements during background conditions, periods disturbed by the influence of Mount Pinatubo, and polar stratospheric cloud (PSC) type I events are used to study the heterogeneous reactions of ClONO2 with H2O and of HOCl and ClONO2 with HCl in comparison to the gas phase reaction rate of OH with HCl. To calculate the reaction rates, the measured data of pressure, temperature, water vapor, and aerosol surface are utilized together with recent laboratory results for the heterogeneous reactive uptake coefficients. Because observations are limited, the mixing ratios of the gas phase species entering these rate calculations (i.e., ClONO2, HOCl, HCl, and N2O5) are taken from a two‐dimensional model. It is found that in dense volcanic clouds at temperatures below 200 K the resulting heterogeneous reaction rates of chlorine activation can be of similar magnitude as the gas phase reaction rate. The heterogeneous rates in PSCs can exceed the gas phase rates by more than 2 orders of magnitude. For the ClONO2 and HOCl reactions the measured aerosol surfaces during the PSC events are treated both as liquid (e.g., ternary solution) droplets and as solid NAT to compare the effects of the different phases. The reaction rates on NAT are significantly lower than on liquid droplets. Indeed, this study shows that a transition from liquid ternary solutions to NAT is expected to reduce the rate of chlorine activation based on present chemical understanding and on observed aerosol surface areas. Additionally, the effect of temperature and surface area fluctuations on the heterogeneous reaction rates is discussed.
Effect of an improved cloud climatology on the total ozone mapping spectrometer total ozone retrieval
Authors: Hsu N. Christina , McPeters Richard D. , Seftor Colin J. , Thompson Anne M.
Published: February 2004

The 14.5 years of Nimbus 7 total ozone mapping spectrometer (TOMS) gridded data have been reprocessed using the Version 7 (V7) algorithm. Among a number of improvements made in the TOMS V7 algorithm, a new cloud top height climatology, based upon the International Satellite Cloud Climatology Project (ISCCP) data set, has been included to correct for the cloud height effect on total ozone. The new algorithm also contained an improved cloud model that used a modified Lambertian surface assumption in the partially clouded scenes. As a result, reductions in TOMS V7 total ozone, as compared to Version 6 data, could be more than 20 Dobson units over marine stratocumulus, while in high cloud regions the V7 measured total ozone amounts are generally higher than V6 values. The high correlation between TOMS V6 total ozone and reflectivity has been greatly reduced using the V7 data, particularly in the low cloud region of the tropical eastern Atlantic. Also, the land‐ocean contrast in total ozone associated with the inadequate cloud height climatology and partial cloud model has diminished in the V7 data. The land‐ocean contrast in total ozone due to the sensitivity of the lower tropospheric ozone to ground reflectivity, however, still remains.
Observations of the diurnal tide in the mesosphere and lower thermosphere over Christmas Island
Authors: Chang J. L. , Avery S. K.
Published: February 2004

Atmospheric tidal variations in the mesosphere wind field have been studied extensively using radars. Most of the climatological studies of the tide have been done at middle and high latitudes. Previous tropical observations of the diurnal oscillation derived from campaign studies have shown the dominance of the migrating diurnal tide in the mesosphere and lower thermosphere. By using wind measurements obtained with a meteor radar system located at Christmas Island, the diurnal tidal behavior in the upper atmosphere of the equatorial Pacific has been characterized over several years. The data collected from August 1988 to December 1993 are presented in this paper and compared to various model results. Our observations show the meridional wind component of the diurnal tide maximizes in April near 94 km. The observed meridional vertical wavelengths are large and indicate upward propagating energy. Even though the vertical wavelengths for the zonal diurnal component are also large, the phase progression is upward corresponding to downward propagating energy. There is considerable interannual and intraseasonal variation in the diurnal amplitudes throughout the year.
Wonderland climate model
Authors: Hansen J. , Ruedy R. , Lacis A. , Russell G. , Sato M. , Lerner J. , Rind D. , Stone P.
Published: February 2004

We obtain a highly efficient global climate model by defining a sector version (120° of longitude) of the coarse resolution Goddard Institute for Space Studies model II. The geography of Wonderland is chosen such that the amount of land as a function of latitude is the same as on Earth. We show that the zonal mean climate of the Wonderland model is very similar to that of the parent model II.
Empirical model of 90–120 km horizontal winds from wind‐imaging interferometer green line measurements in 1992–1993
Authors: Wang D. Y. , McLandress C. , Fleming E. L. , Ward W. E. , Solheim B. , Shepherd G. G.
Published: February 2004

An empirical model of horizontal winds is developed based on wind‐imaging interferometer (WINDII) green line observations between 90 and 120 km in 1992–1993. The model includes mean winds, solar diurnal and semidiurnal tides, and some planetary wave components, as well as annual and semiannual variations in these fields. Its formulation is similar to that of HWM‐90 and HWM‐93 of Hedin et al. [1991, 1996], but greatly modified and extended to use the higher resolution global wind measurements now available from WINDII. While the technique will only reach fruition when results can be combined from the wind measurements of several years by the different instruments on the UARS satellite, this interim, but updated model provides improved representation of the temporal and geographic variations of the wind fields compared to the current reference models. The model generated climatological mean wind, diurnal tides, and some samples of the entire wind motion fields are presented and compared with the WINDII measurements and analysis results obtained from the data sets by different methods to check the consistencies between the model representations and the observations. This study also reveals a dual cell structure in the meridional component of the diurnal tides with two amplitude maxima centered around 95 and 102 km near 20° latitude and strongly symmetric about the equator at equinox. Large interannual variabilities are found to exist in both diurnal wind components with maximum amplitudes of ∼ 40 and 55 m/s for the zonal and meridional, respectively, at the vernal equinox of 1992.
Radiative forcing and temperature trends from stratospheric ozone changes
Authors: de F. Forster Piers M. , Shine Keith P.
Published: February 2004

Detailed shortwave and longwave radiative transfer models are used to calculate the radiative forcing and temperature trends due to stratospheric ozone depletion. These were calculated using the fixed dynamical heating approximation to adjust the stratospheric temperatures. Recent estimates of stratospheric ozone loss between 1979 and 1991 (from solar backscattered ultraviolet (SBUV) and stratospheric aerosol and gas experiment (SAGE) instruments) and updated radiative transfer schemes are used to obtain improved estimates of the radiative forcings. An annually and globally averaged radiative forcing of −0.13±0.02 W m−2 decade−1 (−0.22±0.03 W m−2 for the 1979–1996 period) was found from SBUV total column ozone trends, applying a constant percentage ozone depletion to a 7 km thick layer directly above the tropopause. SAGE ozone trends gave forcing estimates of −0.10±0.02 W m−2 decade−1 (−0.17±0.03 W m−2 for the 1979–1996 period), although assumptions needed to be made about the choice of the vertical profile of the ozone depletion below 17 km. Using Dobson instrument trends from 1964 to 1996, the total ozone forcing could be as negative as −0.26±0.05 W m−2. The quoted error bars derive from uncertainties in the total ozone trends. Using these values, the stratospheric ozone change may have offset about 30% of the forcing due to increases in well‐mixed greenhouse gases since 1979, and about 15% of the forcing since 1964, at least on a global and annual mean. The ozone forcings are shown to be nearly a linear function of the ozone amount depleted from the atmospheric column, provided the vertical profile of the depletion remains constant. As in previous studies, it was found that stratospheric adjustment altered the sign of the ozone forcing by strongly cooling the lower stratosphere. It is shown that (depending on the vertical structure of ozone depletion) coolings of up to 0.4 K decade−1 can be found at altitudes of 35 km; this provides a mechanism for cooling the stratosphere nearly as large as that from well‐mixed greenhouse gas increases, at altitudes where ozone changes were previously thought not to strongly affect stratospheric temperature trends. Previous studies have examined the effect of ozone trends by looking at the response of the surface temperature to a fixed absolute ozone change at different heights in the atmosphere. We argue that using absolute ozone perturbations places an unrealistically large emphasis on ozone changes near the tropopause. As the vertical profile of ozone change is more often reported as a percentage change, we present the sensitivity of the surface temperature to constant percentage, rather than absolute, changes in ozone.
Numerical advection schemes, cross‐isentropic random walks, and correlations between chemical species
Authors: Thuburn John , McIntyre Michael E.
Published: February 2004

The advection schemes used in numerical models of chemistry and transport at fixed resolution must unavoidably cause the models to misrepresent the transport in some way. This can include failure to establish or preserve the functional relations between long‐lived chemical tracers that are often observed in the atmosphere. We show that linear functional relations will be preserved exactly by purely linear advection schemes and also, less obviously, by certain “semi‐linear” flux‐limited schemes despite the unavoidable nonlinearity introduced by the flux limiter. In practice, semi‐linear flux‐limited schemes will also preserve nonlinear functional relations better than linear centered difference or spectral schemes that suffer from dispersion errors. The reason is that the dispersion errors lead to spurious oscillations of the mixing ratio field in physical space, artificially expanding the range of mixing ratios in any neighborhood, and hence to a spurious scatter in the relation between any two mixing ratio fields that are nonlinearly related to begin with. Examples of correlations not only preserved, but established, by real and model transport are discussed in this light, including the case of stratospheric transport on timescales of years, for which we discuss and extend earlier results on the ways in which tracer functional relations can arise, for sufficiently long‐lived tracers, purely from transport. The stratospheric results are shown not to depend on the quasi‐horizontal Fickian eddy diffusivity assumption used in the earlier work. The reason is that, whenever the quasi‐horizontal (isentropic) mixing is fast enough—even if it is non‐Fickian as expected in real stratospheric surf zones—the chaotic part of the quasi‐vertical, cross‐isentropic transport has the nature of a random walk with small vertical steps.
Nontrivial scaling in the loss of prediction information with aggregation in hourly precipitation occurrences
Authors: Cârsteanu Alin , Foufoula‐Georgiou Efi
Published: February 2004

Predicting the occurrence of rainfall from past patterns of rain/no rain sequences is an issue that has recently regained attention through the application of information theory and dynamical systems, claiming the existence of an underlying complexity of deterministic origin. The present work reports a rather unexpected facet that appeared in the study of hourly precipitation occurrence pattern prediction: the temporal scale invariance of the probability of prediction failure for scales up to the order of magnitude of a storm duration.
Infrared spectral radiance measurements in the tropical Pacific atmosphere
Authors: Han Yong , Shaw Joseph A. , Churnside James H. , Brown Patrick D. , Clough Shepard A.
Published: February 2004

Downwelling thermal infrared emission from the tropical atmosphere is affected strongly by the typically large amounts of water vapor. In two experiments within the last 2 years we have used a Fourier transform spectroradiometer to measure tropical atmospheric emission, concentrating on the “window” region between about 800 and 1200 cm−1. Shortly after the first of these experiments, substantial differences between measured and calculated radiances led to the development of a new water vapor continuum model. This model subsequently has been incorporated into several widely distributed radiative transfer codes (LBLRTM, MODTRAN, FASCODE). Measurements from the second tropical experiment, which occurred during March and April 1996, validate this new continuum model. This is an important comparison because the new measurements were taken with an improved instrument under better defined clear‐sky conditions than the original tropical data on which the continuum correction was based. Model residuals are of the order of the uncertainty in measurements, especially of the atmospheric water vapor and temperature profiles.
Asian dust aerosol: Optical effect on satellite ocean color signal and a scheme of its correction
Authors: Fukushima H. , Toratani M.
Published: February 2004

The paper first exhibits the influence of the Asian dust aerosol (KOSA) on a coastal zone color scanner (CZCS) image which records erroneously low or negative satellite‐derived water‐leaving radiance especially in a shorter wavelength region. This suggests the presence of spectrally dependent absorption which was disregarded in the past atmospheric correction algorithms. On the basis of the analysis of the scene, a semiempirical optical model of the Asian dust aerosol that relates aerosol single scattering albedo (ωA) to the spectral ratio of aerosol optical thickness between 550 nm and 670 nm is developed. Then, as a modification to a standard CZCS atmospheric correction algorithm (NASA standard algorithm), a scheme which estimates pixel‐wise aerosol optical thickness, and in turn ωA, is proposed. The assumption of constant normalized water‐leaving radiance at 550 nm is adopted together with a model of aerosol scattering phase function. The scheme is combined to the standard algorithm, performing atmospheric correction just the same as the standard version with a fixed Angstrom coefficient except in the case where the presence of Asian dust aerosol is detected by the lowered satellite‐derived Angstrom exponent. Some of the model parameter values are determined so that the scheme does not produce any spatial discontinuity with the standard scheme. The algorithm was tested against the Japanese Asian dust CZCS scene with parameter values of the spectral dependency of ωA, first statistically determined and second optimized for selected pixels. Analysis suggests that the parameter values depend on the assumed Angstrom coefficient for standard algorithm, at the same time defining the spatial extent of the area to apply the Asian dust scheme. The algorithm was also tested for a Saharan dust scene, showing the relevance of the scheme but with different parameter setting. Finally, the algorithm was applied to a data set of 25 CZCS scenes to produce a monthly composite of pigment concentration for April 1981. Through these analyses, the modified algorithm is considered robust in the sense that it operates most compatibly with the standard algorithm yet performs adaptively in response to the magnitude of the dust effect.
Dynamical proxies of column ozone with applications to global trend models
Authors: Ziemke J. R. , Chandra S. , McPeters R. D. , Newman P. A.
Published: February 2004

Previous regression trend models for total column ozone have included only the quasi‐biennial oscillation (QBO) winds and the El Nino Southern Oscillation (ENSO) ocean surface pressure as dynamical proxies. Trends derived from these regression models generally differ (are more negative) from two‐dimensional (2‐D) chemical transport trends by about 2–5% decade−1 in midlatitudes during spring. The present study introduces additional dynamical proxies of total ozone in regression models in an effort to reduce errors in local ozone trends and reduce these model differences. Nimbus 7 total ozone mapping spectrometer (TOMS) version 7 total column ozone for 1979–1992 are used in conjunction with analyses from National Centers for Environmental Prediction (NCEP, formerly National Meteorological Center). Dynamical proxies investigated include winds (including diabatic winds), relative vorticity, potential vorticity, temperatures, and geopotential heights. Inclusion of additional dynamical proxies improves statistics by reducing residuals and uncertainty regions in both zonal mean and zonally asymmetric trend models. RMS reductions, relative to a trend model with only QBO, solar, and trend terms, are as large as 50% in 14‐year means in the southern hemisphere. For zonal mean or zonally asymmetric global trend models with one optional surrogate, a favorable choice is prefiltered (at least deseasonalized and detrended) lower stratospheric temperatures. Relative vorticity, potential vorticity, and geopotential heights all exhibit similar relationships with total ozone, with highest correlative behavior near 200 hPa (midlatitudes year‐round) and 10 hPa (high latitudes in winter‐spring months). For models incorporating these latter proxies, combined 10‐and 200‐hPa (or similar) pressure levels are effective in reducing global residuals. ENSO, as a surrogate by itself or included with other dynamical proxies, has a comparatively small effect because of its episodic nature. Decadal variabilities in NCEP and microwave sounding unit channel 4 (MSU4) data as surrogates in trend models indicate maximal 1–3% decade−1 reductions anywhere in TOMS trends. Total ozone trends derived from the Goddard 2‐D heterogeneous chemistry and transport model agree favorably with trends in TOMS ozone, generally to within 2–3% decade−1 in both hemispheres. Inclusion of possible decadal variabilities in dynamics may yield yet smaller differences.
Surface solar irradiance from the International Satellite Cloud Climatology Project 1983–1991
Authors: Bishop James K. B. , Rossow William B. , Dutton Ellsworth G.
Published: February 2004

An 8 year (July 1983 through June 1991) time series of daily and monthly mean surface solar irradiance has been produced for the globe using data from the International Satellite Cloud Climatology Project (ISCCP) and a revised Bishop and Rossow [1991] algorithm. We present a detailed validation analysis of the ISCCP solar irradiance fields with contemporaneous surface observations at buoys, at remote islands, and from the Global Energy Balance Archives (GEBA) [Ohmura et al., 1991]. The validation is hampered to some degree by the scale difference between the 280 km ISCCP product and the single‐point measurements, some of which are affected by orographic clouds and other local meteorological effects. Our analysis suggests criteria for siting of island or coastal monitoring locations to minimize such biases. Particularly, eastward or poleward facing oceanic exposures are to be avoided. In addition, we suggest that deep sea buoys should be investigated for validation of oceanic surface fluxes. At open‐ocean, clean‐air sites, the ISCCP product is shown to be good to within 10 W m−2 in the monthly mean. The high‐frequency (daily) systematics of solar irradiance variability at the open‐ocean sites are also well duplicated by the ISCCP product. An identifiable error in the revised solar irradiance product is the neglect of spatially and temporally varying aerosol extinction. This error, when translated into an equivalent aerosol extinction coefficient, can be as large as 0.6 in known polluted and mineral dust‐affected regions. We cannot determine additional satellite sensor calibration errors beyond those already corrected in the ISCCP processing. This uniquely long data set has been publicly available since 1994 at the National Center for Atmospheric Research. The data documents significant differences in solar fluxes received by the major oceans as well as significant flux variability on seasonal to interannual timescales.
Amplitude, phase, and period variations of the quasi 2‐day wave in the mesosphere and lower thermosphere over London, Canada (43°N, 81°W), during 1993 and 1994
Authors: Thayaparan T. , Hocking W. K. , MacDougall J.
Published: February 2004

Because there is as yet no conclusive evidence pointing to the source of the quasi 2‐day wave, further observations are required in order to resolve questions about the generating mechanism as well as to better understand the role of the wave in the middle atmosphere. In this paper we investigate the period, amplitude, phase, and vertical wavelength for the quasi 2‐day wave in the mesosphere and lower thermosphere, using the University of Western Ontario 2 MHz radar near London, Canada, and in addition, we look at possible coupling with atmospheric tides. The results of the present study bring out certain new aspects of the quasi 2‐day wave at midlatitude in the northern hemisphere that have not been previously reported. In particular, we show that the period of the quasi 2‐day wave determined from our study is smaller (46–47 hours) than the 51‐ to 52‐h period generally suggested by other northern hemisphere results, and our periods also showed variability as a function of time. We also draw attention to the annual variability and especially highlight the occurrence of the wave in nonsummer months. For example, a brief occurrence in April is not uncommon. Our study also contributes additional midlatitude geographical data that should aid in developing a better picture of the quasi 2‐day wave.
Controls on CH4 and CO2 emissions along two moisture gradients in the Canadian boreal zone
Authors: Moosavi Sadredin C. , Crill Patrick M.
Published: February 2004

Controls on the emission of CH4 and CO2 along moisture gradients in the northern study area of the Boreal Ecosystem‐Atmosphere Study (BOREAS), west of Thompson, Manitoba, were examined in the summer of 1994. A transect stretching from three forested upland sites to an open graminoid fen contained within a black spruce (OBS) palsa was compared with a similar transect from upland lichen and Sphagnum moss sites to wetland mire and pond sites adjacent to an active beaver pond (BP). Mean seasonal CH4 (dark CO2) fluxes were −0.51 (7.99), −0.14 (10.3), 0.15 (8.68), and 2.83 (8.22) mg/m2/d (g/m2/d) from the OBS feather moss, lichen, sphagnum moss, and fen sites. Mean seasonal CH4 (dark CO2) fluxes were −1.58 (9.16), 2.03 (7.62), 1144, and 153 mg/m2/d (g/m2/d) from the BP lichen, sphagnum moss, mire, and pond sites. Rates of CH4 oxidation typical of uplands were observed at all sites except for the BP mire and pond. CH4 efflux was observed in all sites. Rates varied by 4 orders of magnitude along the transition from the driest uplands to moist uplands to inundated wetlands. A high water table appears to be necessary for a strong CH4 source. Low soil temperatures inhibit high CH4 flux rates despite inundation. The potential for the conversion of upland sites from net sinks to sources of CH4 by minor changes in the water table was observed. Prediction of CH4 fluxes by plant community analysis appears to require knowledge of the thermal and hydrologic regime of particular sites over the course of the summer period. Dark CO2 fluxes, by contrast, appear more uniform across similar plant community types.
Albedo over the boreal forest
Authors: Betts Alan K. , Ball John H.
Published: February 2004

Using the Boreal Ecosystem‐Atmosphere Study mesonet data, we show the annual cycle of albedo for 1994 and 1995 at 10 sites; two over grass, one over an aspen forest, and an average of seven over coniferous forests. Representative daily average albedo values in summer are 0.2 over grass, 0.15 for aspen, and 0.083 for the conifer sites. In winter the corresponding mean albedo for snow‐covered grass, aspen, and conifer sites with snow under the canopy are 0.75, 0.21, and 0.13. The jack pine sites have a higher mean winter albedo of 0.15 than the predominantly spruce sites for which mean albedo is only 0.11. Forest albedo increases at all sites in winter (with snow on the ground under the canopy) as the ratio of diffuse to total solar flux increases. The albedo of the conifer sites in winter rarely reaches 0.3.
Solar Lyman α irradiance measurements during two solar cycles
Authors: Woods Thomas N. , Rottman Gary J.
Published: February 2004

The solar Lyman α radiation is the dominant source of energy for the Earth's mesosphere; thus accurate knowledge of its variability is important for many studies of the middle and upper atmosphere. The measurements of the solar Lyman α irradiance taken during solar cycles 21 and 22 by the Atmospheric Explorer‐E (AE‐E), the Solar Mesospheric Explorer (SME), and the Upper Atmosphere Research Satellite (UARS) are compared and then combined to construct a long‐term data set. The UARS measurements, from both the Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) and Solar Stellar Irradiance Comparison Experiment (SOLSTICE), have the best photometric accuracy yet achieved with 2‐σ uncertainties of 10%; thus the SME and AE‐E measurements, which have 2‐σ uncertainties of 40% and 60% respectively, are adjusted to agree with the UARS values. Because none of these satellite measurements overlapped in time, solar indices representative of the upper chromosphere are used in determining these adjustments. The solar indices considered for this analysis are the National Oceanic and Atmospheric Administration (NOAA) Mg II core‐to‐wing ratio, the National Solar Observatory (NSO) He 1083 nm equivalent width, the Penticton (Ottawa) 10.7 cm flux, and the Pioneer Venus Langmuir probe solar signal. For this long‐term data set, the SME Lyman α irradiances are adjusted up by 25%, and the AE‐E Lyman α irradiances are scaled down by a time dependent factor ranging from 10% to 40%. The relationships to the solar indices are also presented so that the estimates for the solar Lyman α irradiance can be extended back as far as 1947 using the solar 10.7 cm flux with an estimated uncertainty of 20%.