bluuebunny/crossref_metadata_2025 huggingface dataset:
“Synoptic” estimates of chemically active species and other diurnally varying parameters in the stratosphere, derived from measurements from the Upper Atmosphere Research Satellite (UARS)
Authors: Huang Frank T. , Reber Carl A.
Published: February 2004

Over the past two decades there have been numerous articles in the literature discussing methods of obtaining global‐scale “synoptic” mathematical representations from asynoptic satellite observations. These studies cover a wide range of viewpoints, ranging from claims of presenting synoptic maps to opinions stating that synoptic representations cannot be obtained from asynoptic data alone, and that physical models are needed to augment the measurements. We review and comment on many of these previous studies. We do not believe that previous published representations generated from Upper Atmosphere Research Satellite data alone for variables that exhibit significant diurnal variations, are indeed synoptic. However, we show that UARS data can be used to estimate useful synoptic approximations without the need for physical models. Using a two‐dimensional Fourier least squares algorithm, we calculate mathematical approximations to “synoptic maps.” We provide examples for ClO, ClONO2, NO2, O3, CH4, temperature, and winds and discuss how they can provide new information on both the chemistry and dynamics of the atmosphere.
Biogenic volatile organic compounds at Azusa and elevated sites during the 1997 Southern California Ozone Study
Authors: Reissell Anni , Arey Janet
Published: February 2004

Biogenic volatile organic compounds (BVOC) were measured at Azusa and at either Pine Mountain or Mount Baldy, elevated sites 11 km north and 25 km northeast of Azusa, respectively, during four intensive sampling periods of the 1997 Southern California Ozone Study. During the sampling periods there was a consistent pattern of isolation of the mountain sites from valley air masses at night, followed by transport of valley air with elevated levels of O3 and NOx to the mountain sites as the mixing height increased throughout the day. Isoprene was the dominant BVOC at the mountain sites with afternoon concentrations reaching 2 ppbv, and its decrease to a low mixing ratio after sunset was attributed to reaction with NO3 radicals. At Azusa the BVOC mixing ratios were highest in the morning with the concentrations of monoterpenes and of methacrolein (MACR) and methyl vinyl ketone (MVK), isoprene photooxidation products, generally exceeding the maximum isoprene measured at Azusa. The high daytime ratio of (MVK + MACR)/isoprene suggested that nighttime drainage flows into Azusa, from elevated sites where the isoprene was depleted by chemical reaction, may have been responsible for much of the isoprene and its photoxidation products. The data also indicated local isoprene sources at Azusa and a possible contribution of MVK and MACR from vehicle emissions. Instances of high mixing ratios of limonene at Azusa suggested an intermittent anthropogenic source. During this study, particularly in early morning, BVOC are calculated to make a significant contribution to peroxy radical formation at Azusa.
A comparison of seasonal and interannual variability of soil dust aerosols over the Atlantic Ocean as inferred by the TOMS AI and AVHRR AOT retrievals
Authors: Cakmur Reha V. , Miller Ron L. , Tegen Ina
Published: February 2004

The seasonal cycle and interannual variability of two estimates of soil (or “mineral”) dust aerosols are compared: advanced very high resolution radiometer (AVHRR) aerosol optical thickness (AOT) and Total Ozone Mapping Spectrometer (TOMS) aerosol index (AI). Both data sets, comprising more than a decade of global, daily images, are commonly used to evaluate aerosol transport models. The present comparison is based on monthly averages, constructed from daily images of each data set for the period between 1984 and 1990, a period that excludes contamination from volcanic eruptions. The comparison focuses on the Northern Hemisphere subtropical Atlantic Ocean, where soil dust aerosols make the largest contribution to the aerosol load, and are assumed to dominate the variability of each data set. While each retrieval is sensitive to a different aerosol radiative property (absorption for the TOMS AI versus reflectance for the AVHRR AOT), the seasonal cycles of dust loading implied by each retrieval are consistent, if seasonal variations in the height of the aerosol layer are taken into account when interpreting the TOMS AI. On interannual timescales, the correlation is low at most locations. It is suggested that the poor interannual correlation is at least partly a consequence of data availability. When the monthly averages are constructed using only days common to both data sets, the correlation is substantially increased: this consistency suggests that both TOMS and AVHRR accurately measure the aerosol load in any given scene. However, the two retrievals have only a few days in common per month, so these restricted monthly averages have a large uncertainty. Calculations suggest that at least 7 to 10 daily images are needed to estimate reliably the average dust load during any particular month, a threshold that is rarely satisfied by the AVHRR AOT due to the presence of clouds in the domain. By rebinning each data set onto a coarser grid, the availability of the AVHRR AOT is increased during any particular month, along with its interannual correlation with the TOMS AI. The latter easily exceeds the sampling threshold due to its greater ability to infer the aerosol load in the presence of clouds. Whether the TOMS AI should be regarded as a more reliable indicator of interannual variability depends on the extent of contamination by subpixel clouds.
Climate change and the middle atmosphere: 5. Paleostratosphere in cold and warm climates
Authors: Rind D. , Chandler M. , Lonergan P. , Lerner J.
Published: February 2004

The GISS Global Climate Middle Atmosphere Model is used to investigate how the stratosphere would have changed during two paleotime periods: the cold Last Glacial Maximum (∼21,000 years ago) and the warm Paleocene (58 million years ago). Uncertainties in sea surface temperatures and mountain wave drag over the ice sheets are investigated in sensitivity experiments. In many respects the climate and dynamical forcing of the stratosphere was opposite in these time periods, with reduced CO2, increased topography, and increased latitudinal temperature gradients during the ice age, and increased CO2, reduced topography and latitudinal temperature gradients during the Paleocene, representative of much of the Tertiary. The results show that the stratospheric response was often of an opposite nature as well, with the ice ages featuring a warmer stratosphere, increased residual circulation in the lower stratosphere (and decreased above), and weakened polar vortices, while the Paleocene simulation had a colder stratosphere, decreased residual circulation in the lower stratosphere (and increased above), with strengthened polar vortices. Analysis shows that the stratospheric response is very individualistic to the particular climate regime, and the opposite effects are not necessarily produced by inversely related mechanisms. Of particular importance in both climates is the reduced latitudinal gradient at high latitudes, which weakens high‐latitude zonal winds and limits wave energy vertical propagation. Increased planetary wave forcing in the lower stratosphere accelerates the circulation during the ice ages. A strong increase in zonal winds during the Paleocene is the result of both decreased planetary wave forcing, associated with the reduced topography, and decreased mountain wave drag. The sensitivity experiments show that if tropical sea surface temperatures were warmer, the stratospheric residual circulation was enhanced, while stratospheric warmings are sensitive to the precise sea surface temperature specifications and mountain wave drag.
Adjusting for sampling density in grid box land and ocean surface temperature time series
Authors: Jones P. D. , Osborn T. J. , Briffa K. R. , Folland C. K. , Horton E. B. , Alexander L. V. , Parker D. E. , Rayner N. A.
Published: February 2004

We develop methods for adjusting grid box average temperature time series for the effects on variance of changing numbers of contributing data. Owing to the different sampling characteristics of the data, we use different techniques over land and ocean. The result is to damp average temperature anomalies over a grid box by an amount inversely related to the number of contributing stations or observations. Variance corrections influence all grid box time series but have their greatest effects over data sparse oceanic regions. After adjustment, the grid box land and ocean surface temperature data sets are unaffected by artificial variance changes which might affect, in particular, the results of analyses of the incidence of extreme values. We combine the adjusted land surface air temperature and sea surface temperature data sets and apply a limited spatial interpolation. The effects of our procedures on hemispheric and global temperature anomaly series are small.
LIMBTRAN: A pseudo three‐dimensional radiative transfer model for the limb‐viewing imager OSIRIS on the ODIN satellite
Authors: Griffioen Erik , Oikarinen Liisa
Published: February 2004

A new pseudo three‐dimensional radiative transfer model has been written to calculate scattered light radiances required by inversion algorithms to retrieve minor species profile and column amount information from limb measurements. Stratospheric and mesospheric UV‐visible limb radiances will be measured by the ODIN/OSIRIS (Optical Spectrograph and Infrared Imager System) satellite instrument to be launched in November 2000. This information will be used to study ozone depletion processes and transport dynamics in the Earth's atmosphere through the study of trace species. Model limb radiance simulations have been carried out for a suite of solar zenith and azimuthal angles and lambertian surface albedos over a broad spectral range. The effects of Rayleigh and aerosol scattering as well as ozone absorption have been modeled. Comparisons with a spherical 3‐D Monte‐Carlo model show that there is generally less than 3–4% difference for single‐scattering and less than 10–15% and often significantly better for multiple scattering radiances at a fraction of the computational cost.
Validation of the hydrological cycle of ECMWF and NCEP reanalyses using the MPI hydrological discharge model
Authors: Hagemann Stefan , Gates Lydia Dümenil
Published: February 2004

To validate the hydrological cycle of the European Centre for Medium‐Range Weather Forecasts (ECMWF) and the National Centers for Environmental Prediction (NCEP) reanalyses in comparison with observed river discharge, a hydrological discharge model is used to compute the corresponding river discharge. The HD model requires daily time series of surface runoff and drainage from the soil as input fields. As it turned out that a direct application to the reanalyses was not possible, a simplified land surface scheme was developed to compute runoff and drainage fields from daily reanalysis values of total precipitation and 2 m temperature. These fields were then used as input to the global simulation of river discharge with the discharge model. Results show several shortcomings of the two reanalyses in representing the hydrological cycle at the land surface. The water balance is not closed, and the snowmelt is not incorporated in the runoff and drainage fields of either of the two reanalyses. In addition, the NCEP reanalysis overestimates summer precipitation and evapotranspiration for most parts of the Northern Hemisphere, while the ECMWF reanalysis underestimates 2 m temperatures in high latitudes during the winter and spring. In the monsoon region the hydrological cycle is well represented by both reanalyses, especially over India.
Trace gas signatures of the airstreams within North Atlantic cyclones: Case studies from the North Atlantic Regional Experiment (NARE ’97) aircraft intensive
Authors: Cooper O. R. , Moody J. L. , Parrish D. D. , Trainer M. , Ryerson T. B. , Holloway J. S. , Hübler G. , Fehsenfeld F. C. , Oltmans S. J. , Evans M. J.
Published: February 2004

This study reveals how airstreams within midlatitude cyclones draw and export trace gases from the polluted continental boundary layer, the midtroposphere, and the stratosphere of North America to the troposphere of the North Atlantic Ocean. The North Atlantic Regional Experiment (NARE) produced aircraft‐based trace gas measurements from eight midlatitude cyclones during the autumn of 1997. Meteorological and back trajectory analysis identified the various component airstreams of several cyclones, including a cold conveyor belt, two warm conveyor belts, a dry airstream, a previously undefined post cold front air‐stream, and a streamer fragment that originated in a dry airstream off the coast of California. O3, CO, and NOy mixing ratio distributions and relationships were determined for each airstream. Airstream chemical composition was related to the origin and transport history of the associated air mass. The lowest O3 values were associated with airstreams originating in Canada or the Atlantic Ocean marine boundary layer; the highest O3 values were associated with airstreams with a recent stratospheric component. The highest CO values were associated with lower tropospheric outflow from New England and a warm conveyor belt that advected boundary layer CO from the southeast United States to the mid and upper troposphere. The highest NOy values were also the result of lower troposphere polluted outflow from New England. Most NOy was removed from the airstreams that transported polluted boundary layer air to the free troposphere. A steep and positive O3/NOy slope was found for all airstreams in the free troposphere regardless of air mass origin.
Transects of atmospheric CO, CH4, and their isotopic composition across the Pacific: Shipboard measurements and validation of inverse models
Authors: Bergamaschi Peter , Lowe David C. , Manning Martin R. , Moss Rowena , Bromley Tony , Clarkson Tom S.
Published: February 2004

Measurements of carbon monoxide, methane, and their isotopic composition are presented for samples collected on six ship voyages across the Pacific between New Zealand and the United States between 1996 and 1998. The data cover a latitude range from approximately 40°S to 40°N and clearly define significant latitudinal gradients in mixing ratios and isotopic composition and their seasonal variations. Observational data are compared with recent three‐dimensional inverse modeling studies of the global CO and CH4 distributions (Bergamaschi et al., 2000a, b, c) constrained by CO and CH4 mixing ratio data from the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory network and additional isotope measurements from a set of five globally distributed stations. Thus the shipboard measurements represent a unique opportunity for independent validation of the inverse models. In general, we see a very good agreement between measurements and model results, both for CO and CH4 mixing ratios and their stable isotopic composition (δ13CO, δC18O, δ13CH4). This is in particular true for the simulation of mean latitudinal gradients of these quantities. For some voyages, however, significant deviations in the “fine structure” of the latitudinal profiles are apparent and are attributed to synoptic scale variations that are not captured by the model (for which a standard meteorology is applied). In most cases, deviations between observations and model results exhibit similar patterns for CH4 and CO, and the deviations in mixing ratios are linked with corresponding deviations in the isotopic signature. Furthermore, a clear correlation between CO and ethane mixing ratios is visible. Observations of 14CO show a general minimum around the equator and cycles of opposite phase in each hemisphere. Virtually identical 14CO minima were observed in both hemispheres in 1997, indicating similar OH levels. We also show model results for δCH3D and the mass‐independent isotope fraction in C17O (despite the absence of observational data for the ship voyages) in our discussion to illustrate the potential of these isotopic signatures for the understanding of the global cycles of CH4 and CO, respectively.
Bromine oxide—ozone interaction over the Dead Sea
Authors: Matveev Valeri , Peleg Mordechai , Rosen David , Tov‐Alper Dafna Siman , Hebestreit Kai , Stutz Jochen , Platt Ulrich , Blake Donald , Luria Menachem
Published: February 2004

Atmospheric measurements were performed during a 1 month period in early summer of 1997 at the Dead Sea in Israel in an attempt to identify bromine monoxide BrO, and evaluate its effect on ozone chemistry. The differential optical absorption spectroscopy (DOAS) technique was utilized to identify and measure BrO present in the air masses. Concurrent to the DOAS measurements, continuous monitoring of SO2, NO/NOx, O3, and CO was performed. Filter samples for aerosol analysis and whole air canister samples for bromocarbon analysis were also collected. The present paper reports the complete comprehensive data set of the measurements at the Dead Sea site and is a continuation to our preliminary communication [Heberstreit et al., 1999]. The more complete data now available enable a more detailed examination of the sources and mechanisms of the reactive halogen species and the presentation of new conclusions. The results showed a diurnal repeating cycle of O3 and BrO variations, correlated with solar radiation and wind direction. During the elevated BrO events, where bromine oxide rose to daily maximum values often exceeding 100 ppt, a clear negative correlation with O3 was observed. During these episodes, the O3 regularly decreased from noontime levels of 50–80 ppb or higher down to 10–30 ppb and occasionally to levels below the detection limit of 2 ppb. The enhanced BrO levels were associated with southerly winds that are typical for the location during midday hours. This suggests that a possible source for the reactive bromine species is the interaction of atmospheric oxidants with bromide at the surface of the large salt pans located at the southern end of the Dead Sea. Research flights flown over the area showed that ozone destruction to levels well below the background values were observed over large areas of the Dead Sea Valley.
Solar‐atmospheric coupling by electrons (SOLACE): 3. Comparisons of simulations and observations, 1979–1997, issues and implications
Authors: Callis Linwood B. , Natarajan Murali , Lambeth James D.
Published: February 2004

Several middle atmospheric simulations have been carried out from January 1979 to December 1997 including most effects important to stratospheric O3. Results of these simulations for several species and species ratios have been compared in detail with observations made by the Halogen Occultation Experiment, the Polar Ozone and Aerosol Measurement II, the Total Ozone Mapping Spectrometer, the Jet Propulsion Laboratory Mark IV Interferometer, and during the Photochemistry of Ozone Loss in the Arctic Summer mission. For the simulation including all effects, comparisons of all species and ratios show excellent agreement. Comparisons of simulated sunset NO2 with and without the effects of energetic electron precipitation show excellent agreement with observations with the effects of the electrons included but poor agreement when they are excluded. The validated simulations indicate that the effects of a polar source of NOy must be included for an adequate simulation of stratospheric O3 and NOy. A comparison of simulations, during the 11‐year solar cycle, of the relative effects on O3 of solar UV flux variations and the energetic electron precipitation has been made. For global total O3 the effects are comparable. For the global column above 25 km, the effects of energetic electron precipitation are significantly larger. The implications of, and some issues raised by, these findings are briefly discussed.
Chemical composition of marine aerosol in a Mediterranean coastal zone during the FETCH experiment
Authors: Sellegri Karine , Gourdeau Justine , Putaud Jean‐Philippe , Despiau Serge
Published: February 2004

The chemical composition of marine aerosols was studied during the Flux, Etats de la mer, Télédétection en Conditions de fetch variable (FETCH) experiment that took place in the northwestern Mediterranean Sea in March/April 1998. Coastal marine aerosols were collected using a 13‐stage low‐pressure impactor and analyzed by ion chromatography. Samples were characterized according to their continental or marine origin in order to better understand the processes affecting the chemical composition of particles during advection over a coastal zone. Strong anthropogenic influence was observed up to 100 km from the coast illustrated by (1) NH4/nss‐SO4 association with ratios ranging from 0.9 to 2.1, and for some cases NH4/nss‐SO4‐NO3 bicorrelation; (2) chloride depletion associated with supermicron NO3, indicating previous reaction between nitric acid and NaCl; and (3) elevated NO3 fraction in the submicron range when the air mass was rain‐washed. New particle formation was not detected during the campaign from either bubble bursting or from dimethylsulfide oxidation products. Nss sulfate and methanesulfonic acid appear to condense on the numerous preexisting particles rather than undergoing gas‐to‐particle conversion. Formation of sea‐salt supermicron aerosol takes place rapidly to represent 80% of the total ionic species as little as 25 km from the coast.
Role of stratospheric air in a severe weather event: Analysis of potential vorticity and total ozone
Authors: Goering Melissa A. , Gallus William A. , Olsen Mark A. , Stanford John L.
Published: February 2004

The role of dry stratospheric air descending to low and middle tropospheric levels in a severe weather outbreak in the midwestern United States is examined using NCEP Eta model output, Rapid Update Cycle (RUC) analyses, and Earth probe Total Ozone Mapping Spectrometer (EP/TOMS) total ozone data. While stratospheric air was not found to play a direct role in the convection, backward trajectories show stratospheric air descended to 800 hPa just west of the convection. Damaging surface winds not associated with thunderstorms also occurred in the region of greatest stratospheric descent. Small‐scale features in the high‐resolution total ozone data compare favorably with geopotential heights and potential vorticity fields, supporting the notion that stratospheric air descended to near the surface. A detailed vertical structure in the potential vorticity appears to be captured by small‐scale total ozone variations. The capability of the total ozone to identify mesoscale features assists model verification. The total ozone data suggest biases in the RUC analysis and Eta forecast of this event. The total ozone is also useful in determining whether potential vorticity is of stratospheric origin or is diabatically generated in the troposphere.
A fast method for retrieval of cloud parameters using oxygen A band measurements from the Global Ozone Monitoring Experiment
Authors: Koelemeijer R. B. A. , Stammes P. , Hovenier J. W. , de Haan J. F.
Published: February 2004

The Global Ozone Monitoring Experiment (GOME) on board the ERS‐2 is designed to measure trace gas column densities in the Earth's atmosphere. Such retrievals are hindered by the presence of clouds. The most important cloud parameters that are needed to correct trace gas column density retrievals for the disturbing effects of clouds are the (effective) cloud fraction and cloud top pressure. At present, in the operational GOME data processor an effective cloud fraction is derived for each pixel, but cloud top pressure is assumed a priori and is deduced from a climatological database. Here we report an improved cloud retrieval scheme, which simultaneously retrieves the effective cloud fraction and cloud top pressure from GOME data. This algorithm, called Fast Retrieval Scheme for Clouds from the Oxygen A band (FRESCO), makes use of reflectivities as measured by GOME inside and outside the oxygen A band (758–778 nm). For validation, the results of FRESCO are compared to effective cloud fractions and cloud top pressures derived with standard methods from colocated measurements made by the Along Track Scanning Radiometer‐2 (ATSR‐2). The brightness temperatures of the cloudy pixels as measured by ATSR‐2 are related to cloud top pressures using temperature profiles from the European Center for Medium‐range Weather Forecasts model. Generally, the results from FRESCO and ATSR‐2 agree reasonably well. For the effective cloud fractions the average difference (based on a comparison of 322 points) is 0.04; the standard deviation is 0.09. For the cloud top pressures, only points with an effective cloud fraction larger than 0.1 have been compared. For these 236 points the average difference in cloud top pressure is 65 hPa, and the standard deviation is 92 hPa.
Deviation from reciprocity in bidirectional reflectance
Authors: Leroy Marc
Published: February 2004

The subject of the paper is to discuss and quantify deviations from reciprocity of the bidirectional reflectance distribution function (BRDF), i.e., the difference of BRDF obtained when inverting illumination and viewing directions. Directional reciprocity is not valid in general, because when the illumination beam has a spatial extension larger than the viewed area (as is most often the case for BRDF measurements), some of the scatterers building up the observed radiance are located at different places in reciprocal measurements. The physical systems under consideration in the two experiments are different, hence the breakdown of reciprocity. The paper develops a theory aiming at a quantitative estimation of deviations from directional reciprocity due to this factor. The theory is based on integral forms of the radiative transfer equation in a horizontal slab of heterogeneous absorbing and scattering media. The observed scene radiance is expanded in a series of scattering orders. Integral expressions of the single‐ and multiple‐scattering radiance are derived and put in a form suitable for the analysis of the reciprocity problem. The first‐order expression leads to an estimate of the order of magnitude ε of the relative deviations from reciprocity,
, where D is the size of the viewed area (pixel size for imaging sensors), h is the vertical photon mean free path, δQ/Q is a measure of the scene heterogeneity, and θi, θv, and ϕ are the illumination and view zenith angles and the relative azimuth between illumination and view directions. It is argued that this order of magnitude should remain approximately valid if all orders of scattering are taken into account. A discussion of practical applications in various fields, laboratory optical reflectometry, Earth radiation budget monitoring, and terrestrial surfaces remote sensing is given.
Particle production and aeolian transport from a “supply‐limited” source area in the Chihuahuan desert, New Mexico, United States
Authors: Gillette Dale A. , Chen Weinan
Published: February 2004

Wind erosion mechanisms were investigated for the “scrape site” at the Jornada Experimental Range near Las Cruces, New Mexico, in the Chihuahuan desert. The scrape site was denuded of vegetation and scraped flat in 1991. We adopted the site in 1994 because it offered an opportunity to study wind erosion mechanisms for a large area of unprotected sandy and crusted soil in an otherwise natural setting and over a period of several years. We installed and operated the following instrumentation for a period of 35 months: three meteorological towers, each 2 m in height, with wind speed sensors at 0.2, 0.5, 1.0, and 2.0 m above ground; air temperature at 0.2 and 2 m height; rain gauge; seven sets of particle collectors at 0.1, 0.5, and 1.0 m heights; and three fast‐response particle mass flux sensors at 0.02, 0.1, 0.2, and 0.5 m heights; all along a transect crossing the site and parallel to the predominant southwesterly wind direction. The minimum threshold friction velocity for the scrape site with a thin layer of loose material was 25 cm s−1. This minimum threshold velocity increased to as high as 100 cm s−1 depending on the degree of particle depletion and the site's status which varied between supply unlimited just after a high wind episode and supply limited which was more typical for the rest of the time. The dominant mechanism producing fresh sediment for transport was sandblasting of the surface crust. The measurements showed that supply and availability of loose, fine particles on the surface is a strong control of rates of erosion rather than wind energy alone.
Local and remote atmospheric response to tropical instability waves: A global view from space
Authors: Hashizume Hiroshi , Xie Shang‐Ping , Liu W. Timothy , Takeuchi Kensuke
Published: February 2004

A La Niña took place in the equatorial Pacific in 1999, and strong tropical instability waves (TIWs) developed, causing large meanders of a sea surface temperature (SST) front between the equator and 3°N. High‐resolution satellite measurements are used to describe the variability of SST, surface wind velocity, column‐integrated water vapor, cloud liquid water, and precipitation associated with these strong TIWs in 1999. Coherent ocean‐atmosphere patterns emerge in both the Pacific and Atlantic, revealing rich regional characteristics. In the far eastern Pacific, southeasterly trades strengthen (weaken) over positive (negative) SST anomalies, apparently due to enhanced (reduced) mixing with high‐speed winds aloft. In the central Pacific we find evidence that SST‐induced sea level pressure changes also contribute substantially to wind fluctuations. Similar SST‐wind covariability also exists in the Southern Hemisphere along 2°S, but the wind variability induced by unit SST anomaly is much larger than that north of the equator. In the central Pacific where the equatorial front is broad, the northern SST pattern has a large meridional scale and reaches as far north as 6°N. Further to the north in the Intertropical Convergence Zone (ITCZ) where local SST anomalies are small, significant variability is found in clouds and precipitation, which is further correlated with surface wind convergence. In the Atlantic, TIW signals in SST are strongly trapped near the equator, but they induce significant remote response in the ITCZ, which takes a more southern position than its Pacific counterpart and thus more susceptible to TIW influence.
A diagnostic analysis of the Kennedy Space Center LDAR network: 1. Data characteristics
Authors: Boccippio D. J. , Heckman S. , Goodman S. J.
Published: February 2004

An analytic framework is developed in which to analyze climatological VHF (66 MHz) radiation measurements taken by the Kennedy Space Center Lightning Detection and Ranging (LDAR) network. A 19 month noise‐filtered sample of LDAR observations is examined using this framework. It is found that the climatological impulsive VHF source density as observed by LDAR falls off ∼10 dB every 71 km of ground range away from the network centroid (a 31 km e‐folding scale). The underlying vertical distribution of impulsive VHF sources is approximately normally distributed with a mean altitude of 9 km and a standard deviation of 2.7 km; this implies that the loss of below‐horizon sources has a negligible effect on column‐integrated source densities within a 200 km ground range. At medium to far ranges, location errors are primarily radial and have a slightly asymmetric distribution whose standard deviation increases as r2. Error moments estimated from observed lightning are significantly higher than those from aircraft‐based signal generator or analytic estimates. LDAR bulk flash detection efficiency is predicted to be above 90% to 94–113 km range from the network centroid and to fall below 10% at ranges greater than 200–240 km.
Carbon and hydrogen kinetic isotope effects for the reaction of Cl with CH4: Consolidating chemical kinetics and molecular dynamics measurements
Authors: Michelsen H. A.
Published: February 2004

In order to estimate carbon and hydrogen kinetic isotope effects for the reaction Cl+ CH4 at atmospheric temperatures, measured values of the rates of Cl reacting with 13CH4, 12CH3D, 12CH2D2, 12CHD3, and 12CD4 relative to those of Cl+12CH4 were fit using a model that accounts for quantum mechanical tunneling. The model also includes vibrational enhancement of the reaction rate by excitation of the bending and stretching modes of CH4. These fits allow extrapolation of measured values to temperatures outside the range in which they were measured. In addition, the kinetic isotope effect for Cl+14CH4 was predicted using this model based on the results for Cl+ 13CH4. The model results for Cl+14CH4, Cl+13CH4, and Cl+12CH3D were parameterized for use in atmospheric models.
Spatial patterns of pollen deposition in arctic snow
Authors: Bourgeois J. C. , Gajewski K. , Koerner R. M.
Published: February 2004

The pollen content of 77 snow samples, collected at 41 sites in the Canadian Arctic, the adjacent Arctic Ocean and Greenland can be used to identify source regions that produced the assemblages. The major vegetation zones of northern Canada produce distinctive pollen assemblages, and principal components analysis (PCA) indicate that these assemblages are retained even in snow on the sea ice surface. It is shown that pollen percentages and concentrations are related to the density of the regional vegetation and to the distance to the source of more productive regions. Because the pollen grains may be transported for great distances (even to the central regions of the Arctic Ocean), they may be used to indicate the source of that pollen and the trajectory of the air masses that carried and deposited them. Pine is particularly valuable in this sense because it has longer trajectories than other tree pollen. For example, there are indications of “over‐the‐pole” transport of pollen from higher pine pollen concentrations at the North Pole than on northern Ellesmere Island. Pollen concentrations of certain taxa change significantly at ∼75°N, north of which the concentrations become lower, thereby suggesting that there is a climatic boundary at that latitude. Therefore it would appear that studies of the concentration of pollen in snow have the potential for determining past and present characteristics of atmospheric circulation and also for helping in the development and interpretation of paleoenvironmental records in regions without vegetation, such as ice caps.
Relationship between OH measurements on two different NASA aircraft during PEM Tropics B
Authors: Eisele F. L. , Mauldin R. L. , Tanner D. J. , Cantrell C. , Kosciuch E. , Nowak J. B. , Brune B. , Faloona I. , Tan D. , Davis D. D. , Wang L. , Chen G.
Published: February 2004

OH measurements were performed on both the P3‐B and the DC‐8 aircraft throughout Pacific Exploratory Mission (PEM) Tropics B, using two very different measurement techniques. While no direct comparison was possible because of the difference in flight paths of the two aircraft, two brief measurement periods in close proximity allow at least a glimpse of how the two measurements compare. The first comparison took place in the marine boundary layer and showed exceptionally good agreement between the two aircraft OH measurements. The second set of close proximity flights at 5.5‐km altitude resulted in an average concentration difference approximately equal to the uncertainty limit associated with either individual instrument but much less than the combined uncertainties from all the contributing measurements. In both cases the comparisons were made by normalizing the data with a photostationary state model. In addition, a comparison of the OH concentrations measured by each aircraft from 25°N latitude to 25°S latitude over the entire longitude and altitude range of the mission resulted in agreement within ∼10% but with a trend of higher DC‐8/P‐3B OH ratios at higher altitudes. While a definitive comparison of these two OH instruments must await a far more rigorous future test, the present results show that there were no clear OH measurement discrepancies observed. The dramatic differences in these two measurement techniques also minimizes the chance of common interferences or calibration errors.
A new accurate wavelength calibration for the ozone absorption cross section in the near‐UV spectral region, and its effect on the retrieval of BrO from measurements of zenith‐scattered sunlight
Authors: Mohamed‐Tahrin N. , South A. M. , Newnham D. A. , Jones R. L.
Published: February 2004

Measurements of BrO in the atmosphere are now routinely made using UV absorption spectroscopy, but it has recently been noted that the retrieved BrO amounts are critically dependent on the wavelength dependence of the ozone absorption cross sections used in the retrieval procedure (ozone absorbs in the same wavelength region and must therefore be accounted for in the analysis). Although atmospheric BrO measurements are typically made at a spectral resolution of ∼1 nm, it has been shown that an inaccuracy of just 0.02 nm in the wavelength calibration of the ozone cross section can result in large errors in the retrieved BrO amount. Ozone absorption cross sections calibrated to <10−3 nm are presented here in the wavelength region generally used for the retrieval of BrO from observations of scattered solar radiation (345–360 nm), and for a wide range of temperatures (223–292 K). This level of accuracy in the wavelength calibration was achieved using Fourier transform spectroscopy, to record ozone absorption spectra at a maximum instrument resolution of 1.0 cm−1. Comparisons of these well‐calibrated cross sections with those currently in general use for measurements of BrO, that is, those measured for the Global Ozone Monitoring Experiment (GOME) satellite instrument, reveal that the GOME cross sections must be shifted by an amount in the range +0.02 to +0.03 nm in order to correct their wavelength calibration. This correction to the wavelength calibration is shown to result in a significant reduction (10–20%) in the column amounts of BrO retrieved from ground‐based measurements of zenith‐scattered sunlight. An additional decrease of 5–10% is seen when the high‐resolution cross sections reported here replace the GOME wavelength‐corrected cross sections in the analysis procedure, reducing estimates of total atmospheric BrO correspondingly.
Satellite detection of dust using the IR imagery of Meteosat: 1. Infrared difference dust index
Authors: Legrand M. , Plana‐Fattori A. , N'doumé C.
Published: February 2004

The Infrared Difference Dust Index (IDDI) is a satellite dust product designed for climatological applications, designed specifically for dust remote sensing in arid regions such as the Sahel and Sahara. It is based on the atmospheric response to dust, extracted from midday Meteosat‐IR imagery, and takes advantage of the impact of dust aerosols on the thermal infra‐red radiance outgoing to space. Simulations show a quasi‐linear relationship between satellite response to dust and shortwave optical depth, with a sensitivity depending on particle size distribution and radiative surface properties. Comparison of measured satellite response with photometric optical depth agrees with the simulations. Water vapor significantly affects the satellite signal for cases of large columnar amounts and oceanic air masses advected inland. Hence apart from possible coastal effects, the water vapor effect can be neglected in the Sahelian‐Saharan zone north of the Intertropical Convergence Zone, coinciding with the major regions of African dust emission and transport. The construction of the IDDI involves the processing of reference images, theoretically representing the outgoing radiance obtaining under clear‐sky conditions. Errors may arise from (1) dust remaining in the reference images and (2) seasonal shifts of the reference level; however, the latter error will be offset by averaging used in climatological processing. An error budget is presented for the station of Gao. A statistical comparison of IDDI data with visibility measured at synoptic stations results in (1) a validation of the product, and (2) a climatologically relevant visibility‐IDDI relation, valid for the arid regions of northern Africa. The latter relation is consistent with both simulations and photometric measurements. IDDI maps over Africa compare successfully with optical depth over adjacent ocean regions derived from Meteosat‐VIS imagery. The observed continuity of dust plumes across the African coast demonstrates the consistency between both products.
Retrieval and characterization of cloud liquid water path using airborne passive microwave data during INDOEX
Authors: Liu Guosheng , Curry Judith A. , Haggerty Julie A. , Fu Yunfei
Published: February 2004

During the 1999 intensive observation period of the Indian Ocean Experiment (INDOEX), the Airborne Imaging Microwave Radiometer (AIMR) was deployed on the National Center for Atmospheric Research (NCAR) C‐130 aircraft to measure up welling microwave radiation that can be used to retrieve cloud liquid water path (LWP). In this study, we present a LWP retrieval algorithm that is optimized for tropical atmospheric conditions, typical of conditions observed in INDOEX. Radiative transfer modeling and error analysis are conducted for the four AIMR channels, to guide selection of AIMR channels used for the LWP retrievals. Results show that the horizontal polarization channels outperform vertical polarization channels at both 37 and 90 GHz. Additionally, for LWP less than ∼300 g m−2, the best results are expected from the 90 GHz horizontal polarization channel, while the 37 GHz horizontal polarization channel performs better for higher LWPs. On the basis of these findings we formulated the LWP retrieval algorithm from the combination of the retrievals of 37 and 90 GHz horizontal polarization channels. Results of several indirect validations show that in nearly clear condition the LWP retrievals have essentially no bias and a random error of about 28 g m−2. The image of the retrieved LWP compares well with observations by a 0.64 μm visible channel, and the magnitude of the retrieved LWP for large convective cells is comparable to the estimation based on in situ measurements. It is also shown that the retrieved LWPs for convective cells are smaller than those estimated by assuming adiabatic process while the two have a similar trend in the LWP versus cloud top temperature diagram. By analyzing all available AIMR observations, it is found that the mean LWP for cloudy pixels measured during the INDOEX experiment is about 50 g m−2. A significant north‐south gradient of the mean LWP is found in INDOEX domain during this period, with the mean LWP in the region south of 5°S being twice as high as that in the region north of 50N. The LWP frequency distribution shows that clouds with larger LWPs occur more often in the southern region than in the northern region.
Biomass fire consumption and carbon release rates of rainforest‐clearing experiments conducted in northern Mato Grosso, Brazil
Authors: Carvalho João A. , Costa Fernando S. , Gurgel Veras Carlos A. , Sandberg David V. , Alvarado Ernesto C. , Gielow Ralf , Serra Aguinaldo M. , Santos José C.
Published: February 2004

Biomass consumption and carbon release rates during the process of forest clearing by fire in five test plots are presented and discussed. The experiments were conducted at the Caiabi Farm, near the town of Alta Floresta, state of Mato Grosso, Brazil, in five square plots of 1 ha each, designated A, B, C, D, and E, with different locations and timing of fire. Plot A was located in the interface with a pasture, with three edges bordering on the forest, and was cut and burned in 1997. Plots B, C, D, and E were located inside the forest. Plot B was cut and burned in 1997. Plot C was inside a deforested 9‐ha area, which was cut and burned in 1998. Plot D was inside a deforested 4‐ha area, which was cut in 1998 and burned in 1999. Plot E was inside a deforested 4‐ha area, which was cut and burned in 1999. Biomass consumption was 22.7%, 19.5%, 47.5%, 61.5%, and 41.8%, for A, B, C, D, and E, respectively. The effects of an extended curing period and of increasing the deforested area surrounding the plots could be clearly observed. The consumption, for areas cut and burned during the same year, tended toward a value of nearly 50% when presented as a function of the total area burned. The aboveground biomass of the test site and the amount of carbon before the fire were 496 Mg ha−1 and 138 Mg ha−1, respectively. Considering that the biomass that remains unburned keeps about the same average carbon content of fresh biomass, which is supported by the fact that the unburned material consists mainly of large logs, and considering the value of 50% for consumption, the amount of carbon released to the atmosphere as gases was 69 Mg ha−1. The amounts of CO2 and CO released to the atmosphere by the burning process were then estimated as 228 Mg ha−1 and 15.9 Mg ha−1, respectively. Observations on fire propagation and general features of the slash burnings in the test areas complete the paper.
In‐cloud oxidation of SO2 by O3 and H2O2: Cloud chamber measurements and modeling of particle growth
Authors: Caffrey Peter , Hoppel William , Frick Glendon , Pasternack Louise , Fitzgerald James , Hegg Dean , Gao Song , Leaitch Richard , Shantz Nicole , Albrechcinski Tom , Ambrusko John
Published: February 2004

Controlled cloud chamber experiments were conducted to measure particle growth resulting from the oxidation of SO2 by O3 and H2O2 in cloud droplets formed on sulfuric acid seed aerosol. Clouds were formed in a 590 m3 environmental chamber with total liquid water contents ranging from 0.3–0.6 g m−3 and reactant gas concentrations <10 ppbv for SO2 and H2O2 and <70 ppbv for O3. Aerosol growth was measured by comparison of differential mobility analyzer size distributions before and after each 3–4 min cloud cycle. Predictions of aerosol growth were then made with a full microphysical cloud model used to simulate each individual experimental cloud cycle. Model results of the H2O2 oxidation experiments best fit the experimental data using the third‐order rate constant of Maass et al. [1999] (k = 9.1 × 107 M−2 s−1), with relative aerosol growth agreeing within 3% of measured values, while the rate of Hoffmann and Colvert [1985] produced agreement within 4–9%, and the rate of Martin and Damschen [1981] only within 13–18%. Simulation results of aerosol growth during the O3 oxidation experiments were 60–80% less than the measured values, confirming previous results [Hoppel et al., 1994b]. Experimental results and analyses presented here show that the SO2 ‐ O3 rate constants would have to be more than 5 times larger than currently accepted values to explain the measured growth. However, unmeasured NH3 contamination present in trace amounts (<0.2 ppb) could explain the disagreement, but this is speculative and the source of this discrepancy is still unknown.