bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes of tracer distributions in the doubled CO2 climate
Authors: Rind D. , Lerner J. , McLinden C.
Published: February 2004

Changes in tracer distributions in the troposphere and stratosphere are calculated from a control and doubled CO2 climate simulation run with the Goddard Institute for Space Studies Global Climate Middle Atmosphere Model. Transport changes are assessed using seven on‐line tracers. Results show that interhemispheric transport is reduced by 5% along with a reduction in the Hadley circulation. Tropical transport from the troposphere into the stratosphere increases by some 30% associated with an increase in the stratospheric subtropical residual circulation. The tropical pipe becomes significantly more leaky, and greater transport into the lowermost stratosphere in the subtropics appears to be occurring, possibly in conjunction with a poleward shift in wave energy convergences. An increase in the high‐latitude lower stratosphere residual circulation reduces the stratospheric residence time of extratropical injections such as bomb 14C by 11%. Vertical mixing within the troposphere by convection increases, reducing low level concentrations of tracers. The Hadley cell change is affected by the latitudinal gradient of tropical warming. The high‐latitude lower stratosphere residual circulation change depends on the latitudinal gradient of the extratropical warming. Increased penetrating convection to the upper troposphere and the intensified residual circulation in the tropical upper troposphere/lower stratosphere appear to be the most robust of these results, with a magnitude that depends upon the degree of tropical warming. The consequence of this circulation change is to increase trace gas concentrations in the stratosphere and to decrease them in the troposphere for those species that have tropospheric sources.
Controls on ERS altimeter measurements over ice sheets: Footprint‐scale topography, backscatter fluctuations, and the dependence of microwave penetration depth on satellite orientation
Authors: Arthern R. J. , Wingham D. J. , Ridout A. L.
Published: February 2004

We consider the reliability of radar altimeter measurements of ice sheet elevation and snowpack properties in the presence of surface undulations. We demonstrate that over ice sheets the common practice of averaging echoes by aligning the first return from the surface at the origin can result in a redistribution of power to later times in the average echo, mimicking the effects of microwave penetration into the snowpack. Algorithms that assume the topography affects the radar echo shape in the same way that waves affect altimeter echoes over the ocean will therefore lead to biased estimates of elevation. This assumption will also cause errors in the retrieval of echoshape parameters intended to quantify the penetration of the microwave pulse into the snowpack. Using numerical simulations, we estimate the errors in retrievals of extinction coefficient, surface backscatter, and volume backscatter for various undulating topographies. In the flatter portions of the Antarctic plateau, useful estimates of these parameters may be recovered by averaging altimeter echoes recorded by the European Remote Sensing satellite (ERS‐1). By numerical deconvolution of the average echoes we resolve the depths in the snowpack at which temporal changes and satellite travel‐direction effects occur, both of which have the potential to corrupt measurements of ice sheet elevation change. The temporal changes are isolated in the surface‐backscatter cross section, while directional effects are confined to the extinction coefficient and are stable from year to year. This allows the removal of the directional effect from measurement of ice‐sheet elevation change.
Moss and lichen cover mapping at local and regional scales in the boreal forest ecosystem of central Canada
Authors: Rapalee Gloria , Steyaert Louis T. , Hall Forrest G.
Published: February 2004

Mosses and lichens are important components of boreal landscapes [Vitt et al., 1994; Bubier et al., 1997]. They affect plant productivity and belowground carbon sequestration and alter the surface runoff and energy balance. We report the use of multiresolution satellite data to map moss and lichens over the BOREAS region at a 10 m, 30 m, and 1 km scales. Our moss and lichen classification at the 10 m scale is based on ground observations of associations among soil drainage classes, overstory composition, and cover type among four broad classes of ground cover (feather, sphagnum, and brown mosses and lichens). For our 30 m map, we used field observations of ground cover‐overstory associations to map mosses and lichens in the BOREAS southern study area (SSA). To scale up to a 1 km (AVHRR) moss map of the BOREAS region, we used the TM SSA mosaics plus regional field data to identify AVHRR overstory‐ground cover associations. We found that: 1) ground cover, overstory composition and density are highly correlated, permitting inference of moss and lichen cover from satellite‐based land cover classifications; 2) our 1 km moss map reveals that mosses dominate the boreal landscape of central Canada, thereby a significant factor for water, energy, and carbon modeling; 3) TM and AVHRR moss cover maps are comparable; 4) satellite data resolution is important, particularly in detecting the smaller wetland features, lakes, and upland jack pine sites; and 5) distinct regional patterns of moss and lichen cover correspond to latitudinal and elevational gradients.
Toward retrieving properties of the tenuous atmosphere using space‐based lidar measurements
Authors: Stephens Graeme L. , Engelen Richard J. , Vaughan Mark , Anderson Theodore L.
Published: February 2004

This paper introduces a method that can incorporate different information into the lidar retrieval problem as an attempt to address the backscatter‐to‐extinction ambiguity that plagues the usefulness of lidar backscattering measurements. The approach, suited for application to spaceborne lidar data, inverts the lidar equation via an optimal estimation method. This method is illustrated using three examples drawn from LITE data. Retrievals using only lidar backscatter as input were compared to retrievals performed using an iterative solution to the lidar inversion with the same input. The two methods produced essentially identical results. The new method, however, offers a number of advantages compared to other methods, including (1) the ability to incorporate different kinds of information under a common retrieval philosophy. This feature is illustrated with the formal introduction of optical depth into the lidar inversion. In this paper, optical depth information, derived from the ldar transmission estimates, is combined with backscatter measurements making it possible to retrieve the backscatter‐to‐extinction ratio in addition to extinction profiles given certain caveats noted in the paper. (2) The method provides a number of ways for evaluating the quality of the retrieval. Notably, the retrieval approach predicts full error diagnostics identifying sources of error due to measurement uncertainty (instrument noise and calibration uncertainty), model error (containing all the assumptions built into the lidar equation and its parameters), as well as a priori error due to the influence of compiled databases on lidar backscatter of aerosol and cloud. When no optical depth information is available, the retrieval errors are largely dominated by the (large) uncertainty attached to the backscatter‐to‐extinction coefficient k. Under these circumstances the retrievals are only meaningful to the extent that k and its related uncertainty is known. When optical depth is introduced as a form of measurement, the error contributions shift to the extent that retrieval errors become dominated by the measurement error attached to the optical depth itself.
Sulfate trends in a Col du Dôme (French Alps) ice core: A record of anthropogenic sulfate levels in the European midtroposphere over the twentieth century
Authors: Preunkert Susanne , Legrand Michel , Wagenbach Dietmar
Published: February 2004

A high‐resolution sulfate record from a Col du Dôme (CDD, 4250 m above sea level, French Alps) ice core was used to investigate the impact of growing SO2 emissions on the midtroposphere sulfate levels over Europe since 1925. The large annual snow accumulation rate at the CDD site permits examination of the summer and winter sulfate trends separately. Being close to 80±10 ng g−1 in preindustrial summer ice, sulfate CDD summer levels then increase at a mean rate of 6 ng g−1 per year from 1925 to 1960. From 1960 to 1980 the increase continued at a rate of 24 ng g−1 per year. Concentrations reach a maximum of 860 ng g−1 in 1980 and subsequently decrease to 600 ng g−1 in the 1990s. These summer sulfate changes closely follow the course of growing SO2 emissions from source regions located within 700–1000 km around the Alps (France, Italy, Spain, and to a lesser extent, former West Germany). In winter the CDD sulfate levels are 3 to 8 times lower than in summer because of more limited upward transport of air masses from the boundary layer at that season. Being close to 20 ng g−1 in the preindustrial ice, winter levels were regularly enhanced at a mean annual rate of 1.2 ng g−1 from 1925 to 1980. The weak winter change from the preindustrial era to 1980 (a factor of 4 instead of 10 in summer) reflects a limited contamination of the free troposphere which, in contrast to summer, occurs at a larger scale (total Europe/former USSR). Intimately connected to Europe, these long‐term changes in the Alps clearly differ in time and amplitude with the ones revealed by Greenland ice cores which indicate an increase by a factor of 3 between 1880 and 1970 in relation with long‐range transport of pollutants from Eurasia as well as from North America. Furthermore, because of a lower natural contribution to the total sulfate level the anthropogenic changes can be more accurately derived in the Alps than in Greenland. Using the observed relationship between present‐day concentrations in air and snowpack, the CDD ice core record permits reconstruction of present and past atmospheric sulfate concentrations at 4300 m above sea level over Europe in summer and winter. These data are compared with the sulfate levels simulated by current global sulfur models at 600 hPa for which uncertainties still range within a factor of 2. Together with observations made at lower elevation in the early 1990s the atmospheric levels derived for the CDD site (∼20 and 400 ng m−3 STP in winter and summer, respectively) document the vertical sulfate distribution between the ground and 4300 m elevation over western Europe at that time. In this way, data gained at high‐elevation Alpine sites are powerful in evaluating the recent role of sulfate aerosol in forcing the climate over Europe.
Effects of glacial meltwater in the GISS coupled atmosphere‐ocean model: 2. A bipolar seesaw in Atlantic Deep Water production
Authors: Rind D. , Russell G. , Schmidt G. , Sheth S. , Collins D. , deMenocal P. , Teller J.
Published: February 2004

The relationship between the Northern Hemisphere and Southern Hemisphere deep water circulation systems is explored in experiments with gradual and impulsive freshwater input through the St. Lawrence. With sufficient freshwater volume input (50 Sv years), North Atlantic Deep Water (NADW) cessation occurs, as does substantial cooling in the Northern Hemisphere. The colder temperatures are accompanied by increased mass and sea level pressure in the Northern Hemisphere, with corresponding lower pressure in the Southern Hemisphere. The low‐pressure response occurs at high southern latitudes, consistent with the Antarctic Annular Mode, the leading mode of variability in the current climate. Stronger winds, associated with this increased cyclonicity, intensify the Antarctic Circumpolar Current (ACC) with heat flux divergences in the South Atlantic and convergences and warming in the Indian Ocean. Weddell Sea Bottom Water production increases in response to the South Atlantic high‐latitude cooling and sea ice growth, hence acting as a “seesaw” with the decreasing NADW, and even global Antarctic Bottom Water increases, although not as strongly. The initial “seesaw” response occurs within a few years, although it takes some 100 years to maximize due to the response time of the ACC. The South Atlantic cooling occurs approximately in phase with the North Atlantic, so the “seesaw” is not in temperature within that ocean basin; however, warming in portions of the southern Indian Ocean occurs out of phase with the Northern Hemisphere cooling. NADW does not resume of its own accord once complete cessation occurs even when freshwater input is stopped, but when increased evaporation is used to force NADW formation temporarily, Weddell Sea Bottom Water decreases accordingly.
Ozone and tracer transport variations in the summer northern hemisphere stratosphere
Authors: Cordero E. C. , Kawa S. R.
Published: February 2004

Constituent observations from the Upper Atmosphere Research Satellite (UARS) in combination with estimates of the residual circulation are used to examine the transport and chemical budgets of HF, CH4 and O3 in the summer Northern Hemisphere. Budget calculations of HF, CH4 and O3 show that the transport tendency due to the residual circulation increases in magnitude and is largely opposed by eddy motions through the summer months. Ozone budget analyses show that between 100 and 31 hPa, the magnitudes of the mean circulation and eddy transport terms increase through the summer months, producing tendencies that are factors of 2 to 3 times larger than the observed ozone change in the stratosphere. Chemical loss dominates the observed ozone decrease only at the highest latitudes, poleward of about 70°N. A comparison of observations from the Total Ozone Mapping Spectrometer with UARS‐calculated total ozone suggests that poleward of 50°N, between 35% and 55% of the seasonal ozone decline during the summer occurs at altitudes below 100 hPa. The overall uncertainties, associated primarily with calculations of the residual circulation and eddy transport, are relatively large, and thus prevent accurate and useful constraints on the ozone chemical rate in the lower stratosphere.
New methodology for Ozone Depletion Potentials of short‐lived compounds: n‐Propyl bromide as an example
Authors: Wuebbles Donald J. , Patten Kenneth O. , Johnson Matthew T. , Kotamarthi Rao
Published: February 2004

A number of the compounds proposed as replacements for substances controlled under the Montreal Protocol have extremely short atmospheric lifetimes, on the order of days to a few months. An important example is n‐propyl bromide (also referred to as 1‐bromopropane, CH2BrCH2CH3 or simplified as 1‐C3H7Br or nPB). This compound, useful as a solvent, has an atmospheric lifetime of less than 20 days due to its reaction with hydroxyl. Because nPB contains bromine, any amount reaching the stratosphere has the potential to affect concentrations of stratospheric ozone. The definition of Ozone Depletion Potentials (ODP) needs to be modified for such short‐lived compounds to account for the location and timing of emissions. It is not adequate to treat these chemicals as if they were uniformly emitted at all latitudes and longitudes as normally done for longer‐lived gases. Thus, for short‐lived compounds, policymakers will need a table of ODP values instead of the single value generally provided in past studies. This study uses the MOZART2 three‐dimensional chemical‐transport model in combination with studies with our less computationally expensive two‐dimensional model to examine potential effects of nPB on stratospheric ozone. Multiple facets of this study examine key questions regarding the amount of bromine reaching the stratosphere following emission of nPB. Our most significant findings from this study for the purposes of short‐lived replacement compound ozone effects are summarized as follows. The degradation of nPB produces a significant quantity of bromoacetone which increases the amount of bromine transported to the stratosphere due to nPB. However, much of that effect is not due to bromoacetone itself, but instead to inorganic bromine which is produced from tropospheric oxidation of nPB, bromoacetone, and other degradation products and is transported above the dry and wet deposition processes of the model. The MOZART2 nPB results indicate a minimal correction of the two‐dimensional results in order to derive our final results: an nPB chemical lifetime of 19 days and an Ozone Depletion Potential range of 0.033 to 0.040 for assumed global emissions over landmasses, 19 days and 0.021 to 0.028, respectively, for assumed emissions in the industrialized regions of the Northern Hemisphere, and 9 days and 0.087 to 0.105, respectively, for assumed emission in tropical Southeast Asia.
A microwave land emissivity model
Authors: Weng Fuzhong , Yan Banghua , Grody Norman C.
Published: February 2004

Satellite observations using microwave radiometers operating near the window regions are strongly affected by surface emissivity. Presently, the measurements obtained over land are not directly utilized in numerical weather prediction models because of uncertainties in estimating the emissivity. This study develops a new model to quantify the land emissivity over various surface conditions. For surfaces such as snow, deserts, and vegetation, volumetric scattering was calculated using a two‐stream radiative transfer approximation. The reflection and transmission at the surface‐air interface and lower boundary were derived by modifying the Fresnel equations to account for cross‐polarization and surface roughness effects. Several techniques were utilized to compute the optical parameters for the medium, which is used in the radiative transfer solution. In the case of vegetation, geometrical optics is used because the leaf size is typically larger than the wavelength. For snow and deserts, a dense medium theory was adopted to take into account the coherent scattering of closely spaced particles. The emissivity spectra at frequencies between 4.9 and 94 GHz simulated and compared with the ground‐based radiometer measurements for bare soil, grass land, and snow conditions. It is shown that the features including the spectra, variability, and polarization agree well with the measurements. The simulated global distribution of land surface emissivity is also compared with the satellite retrievals from the Advanced Microwave Sounding Unit (AMSU). It is found that the largest discrepancies primarily occur over high latitudes where the snow properties are complex and least understood.
Airglow imaging of gravity waves: 1. Results from a small network of OH nightglow scanning imagers
Authors: Stockwell R. G. , Lowe R. P.
Published: February 2004

Images of the variations of OH nightglow intensities have been recorded by a three‐station network of scanning radiometers in southwestern Ontario during the period from May until September 1998. Each radiometer performs a 16 by 16 point raster scan of the night sky every minute, turning itself on and off when the solar depression angle is <6°. The horizontal phase velocity, horizontal wavelength, and frequency of the internal gravity waves are derived from the OH intensity measurements using joint time‐frequency analysis techniques, including the S transform, localized cross‐spectral analysis, and generalized instantaneous frequency. The ensemble of gravity waves seen in all three instruments are analyzed and observed to have a strong dependence in their propagation direction with the majority of waves seen at each of the three sites having a horizontal wave vector in the northeast direction. The most common parameters observed for horizontal phase speed is 45 m/s, horizontal wavelength is 25 km, and period is 10 min.
Parameterization of drop effective radius for drizzling marine stratocumulus
Authors: Kogan Z. N. , Kogan Y. L.
Published: February 2004

We describe a parameterization of cloud drop effective radius Re developed for drizzling marine stratocumulus clouds. The parameterization was derived using data from the CIMMS LES model with explicit formulation of drop size resolving microphysics. We showed that in the case of moderate drizzle an accurate parameterization of Re in the 8 ÷ 20 μm radius range can be obtained on the basis of two microphysical variables: liquid water content and drop concentration. For heavy drizzle, only a three‐variable parameterization proves to be sufficiently accurate. We developed two versions of the parameterization. The first one is based on traditional cloud microphysical prognostic variables representing partial moments of the drop distribution function: cloud water content, drizzle water content, and cloud drop concentration. The second one is based on the full moments of the drop size distribution function: drop concentration, total liquid water content, and radar reflectivity. The first version of the parameterization is rather sensitive to the value of the threshold radius that divides cloud and drizzle water. As a result, the errors are larger than in the second full moment version. It is concluded that a three‐variable full moment parameterization provides the most accurate representation of effective radius in precipitating stratocumulus cloud layers.
Near‐surface climate in the boreal forest
Authors: Betts Alan K. , Ball John H. , McCaughey J. Harry
Published: February 2004

This paper addresses processes that affect near‐surface climate over the boreal forest, using data from the Boreal Ecosystem‐Atmosphere Study (BOREAS) northern study area just west of Thompson, Manitoba. The boreal forest is marked by a very large seasonal cycle with below‐freezing temperatures for half the year. The freezing and thawing of the soil plays an important role in the climate at high latitudes. It moderates winter temperatures (together with the insulating snow cover), because during the freeze process, the effective heat capacity of the soil is greatly increased, and it introduces a significant lag into the climate system. Perhaps the most important consequence is that water is unavailable for evaporation and photosynthesis until snow melts and the ground thaws, which occurs late in spring. As a result, in April and in early May, relative humidity (RH) is a minimum, the surface sensible heat flux is large, and the daytime boundary layer (BL) is very deep, because of this unavailability of water. The situation reverses in the fall, when the ground is warmer than the cooling atmosphere, and mean RH is high and BL depths low. This asymmetry between spring and fall can be seen in both seasonal and diurnal cycles. The forest is heterogeneous, and there is a marked difference in summer in daytime evaporative fraction between the conifers and the deciduous forest and fens. However, above the forest the daytime BL has a strong homogenizing effect, and it is the dominant coniferous forest that controls the mean BL depth. The impact of recent rainfall, stored on the canopy, in the surface moss layer, and in the top soil layer can be readily seen in summer. BL depths rise on succeeding days without rain. A comparison of the fen and young jack pine sites shows the important role of the stomatal control by conifers on transpiration. Since evaporation goes down at high net radiation and low RH for conifer sites, it is clear that the low RH and high BL depth over the forest are a direct consequence of stomatal control. At night, however, temperature, relative humidity, and CO2 are quite heterogeneous under the stable BL. We show that uncoupling of the stable BL at night inside the forest canopy occurs at low wind speeds and high outgoing net radiation and can lead to a 5K cooling within the canopy.
A new ice thickness and bed data set for the Greenland ice sheet: 1. Measurement, data reduction, and errors
Authors: Bamber J. L. , Layberry R. L. , Gogineni S. P.
Published: February 2004

Ice thickness data collected between 1993 and 1999 using a coherent ice‐penetrating radar system developed at the University of Kansas have been combined with data collected by the Technical University of Denmark in the 1970s to produce a new ice thickness grid for Greenland. Crossover analysis was used to assess the relative accuracy of the two data sets and they were weighted accordingly and interpolated onto a regular 5‐km spacing grid using a kriging interpolation procedure. A high‐resolution land‐ice mask was used to help constrain the interpolation of the ice thickness data near the ice sheet margins where, in the past, the relative errors have been largest. The ice thickness grid was combined with a new digital elevation model of the ice sheet and surrounding rock outcrops to produce a new bed elevation data set for the whole of Greenland. The ice thickness grid was compared with the currently available data set. Differences in the center of the ice sheet, where the ice is thickest, were of the order of a few percent. Near the margins, however, large differences, of as much as a factor of 10, were found. The total volume of ice contained in the ice sheet was reestimated and found to have a value of 2.93×106 km3. The ice thickness grid was used to calculate the spatial pattern of gravitational driving stress over the ice sheet. Anomalous patterns of stress were found in areas that appeared to be associated with areas of rapid flow.
Mapping neural network computation of high‐resolution radiant fluxes of inhomogeneous clouds
Authors: Faure Thierry , Isaka Harumi , Guillemet Bernard
Published: February 2004

In this study, we evaluated the ability of Mapping Neural Networks (MNNs) to calculate the high‐resolution radiant fluxes of one‐dimensional and two‐dimensional inhomogeneous clouds. The tests were done for different types of clouds, radiant fluxes, and wavelengths under different conditions of illumination. The MNNs were trained with training data sets composed of the Monte Carlo (MC) radiant fluxes of bounded cascade clouds and used to compute first the high‐resolution MC radiant fluxes (reflectance, transmittance, and absorptance) of bounded cascade inhomogeneous clouds. The tests showed their rather good performance, which was compared with that of the Nonlocal Independent Pixel Approximation when possible. Their generalization ability was, second, tested with inhomogeneous clouds of other types: white noise clouds and bounded cascade inhomogeneous clouds with fractional cloud cover. In these cases, the MNNs, trained with different fields, have still good performance. However, the results were found to be much better for the reflectance than for the transmittance and absorptance. In the case of fractional cloud cover, debased responses appear as well in transition zones. We show that the generalization ability could be improved significantly by completing the training sets with new additional patterns when they are applied to types of inhomogeneous clouds different than the clouds of the training set. These results reveal that the MNNs represent a flexible method of function approximation to compute the high‐resolution radiant flux of bounded cascade and other inhomogeneous clouds.
Seasonality of multidecadal and centennial variability in European temperatures: The wavelet approach
Authors: Datsenko N. M. , Shabalova M. V. , Sonechkin D. M.
Published: February 2004

Temperature variability on multidecadal and longer timescales is studied by application of the wavelet transform (WT) to seven seasonal early instrumental temperature series at locations in Europe. The WT spectra are computed for all four seasons of each record. A few spatially coherent components of temperature variability are detected on timescales longer than 60 years. All components appear seasonally dependent; the major differences in time‐frequency patterns occur between late winter and early autumn. The WT‐estimated monotonic trends indicate warming in winter at all locations, with the mean rate 0.4°C per century, and little change or cooling in summer. Superimposed on this monotonic trend, a quarter‐millennial oscillation tends to show the opposite phases in winter and summer, enhancing both the winter warming and the summer cooling trends. A regular oscillatory signal with a timescale of 60–80 years detected earlier in annual mean European temperatures impacts central and eastern Europe during summer and autumn; over northwestern Europe and in Scandinavia the warm‐season multidecadal signal is either weak or irregular. The cold‐season temperature variations are dominated by the centennial (∼120 years) rather than multidecadal timescales. The present WT analysis extends the earlier results based on multichannel singular spectrum analysis of the same data set and confirms the presence of long timescales of variability in European temperatures; it further indicates the crucial role of seasonality in the spatiotemporal structure of low‐frequency temperature variability.
Dating the Vostok ice core record by importing the Devils Hole chronology
Authors: Landwehr J. M. , Winograd I. J.
Published: February 2004

The development of an accurate chronology for the Vostok record continues to be an open research question because these invaluable ice cores cannot be dated directly. Depth‐to‐age relationships have been developed using many different approaches, but published age estimates are inconsistent, even for major paleoclimatic events. We have developed a chronology for the Vostok deuterium paleotemperature record using a simple and objective algorithm to transfer ages of major paleoclimatic events from the radiometrically dated 500,000‐year δ18O‐paleotemperature record from Devils Hole, Nevada. The method is based only on a strong inference that major shifts in paleotemperature recorded at both locations occurred synchronously, consistent with an atmospheric teleconnection. The derived depth‐to‐age relationship conforms with the physics of ice compaction, and internally produces ages for climatic events 5.4 and 11.24 which are consistent with the externally assigned ages that the Vostok team needed to assume in order to derive their most recent chronology, GT4. Indeed, the resulting V‐DH chronology is highly correlated with GT4 because of the unexpected correspondence even in the timing of second‐order climatic events that were not constrained by the algorithm. Furthermore, the algorithm developed herein is not specific to this problem; rather, the procedure can be used whenever two paleoclimate records are proxies for the same physical phenomenon, and paleoclimatic conditions forcing the two records can be considered to have occurred contemporaneously. The ability of the algorithm to date the East Antarctic Dome Fuji core is also demonstrated.
From generalized Pareto to extreme values law: Scaling properties and derived features
Authors: Salvadori Gianfausto , De Michele Carlo
Published: February 2004

Given the fact that, assuming a generalized Pareto distribution for a process, it is possible to derive an asymptotic generalized extreme values law for the corresponding maxima, in this paper we consider the theoretical relations linking the parameters of such distributions. In addition, temporal scaling properties are shown to hold for both laws when considering proper power‐law forms for both the position and the scale parameters; also shown is the relation between the scaling exponents of the distributions of interest, how the scaling properties of one distribution yield those of the other, and how the scaling features may be used to estimate the parameters of the distributions at different temporal scales. Finally, an application to rainfall is given.
Multiyear measurements of aerosol optical depth in the Atmospheric Radiation Measurement and Quantitative Links programs
Authors: Michalsky J. J. , Schlemmer J. A. , Berkheiser W. E. , Berndt J. L. , Harrison L. C. , Laulainen N. S. , Larson N. R. , Barnard J. C.
Published: February 2004

The U.S. Department of Energy funded the development of the multifilter rotating shadowband radiometer (MFRSR) as part of the Atmospheric Radiation Measurement (ARM) program. This seven‐channel radiometer began operation at the first ARM site in 1992 and at the Department of Energy Quantitative Links (QL) sites in the fall of 1991; three of the QL sites continue to operate, although this program was discontinued after 1995. This paper describes the use of the MFRSR in acquiring aerosol optical depth data, including the in‐field calibration procedure and a partial validation of this process. Multiyear measurements of aerosol optical depth from three of the sites indicate similar phasing of seasonal and interannual changes, but with notable differences in the magnitude of the aerosol optical depth. Published papers that use these aerosol data are highlighted, and public access to these and future data sets for scientific studies are explained.
Description and evaluation of a six‐moment aerosol microphysical module for use in atmospheric chemical transport models
Authors: Wright D. L. , Kasibhatla P. S. , McGraw R. , Schwartz S. E.
Published: February 2004

We describe and evaluate a six‐moment aerosol microphysical module, 6M, designed for implementation in atmospheric chemical transport models (CTMs). The module 6M is based upon the quadrature method of moments (QMOM) [McGraw, 1997] and the multiple isomomental distribution aerosol surrogate (MIDAS) method [Wright, 2000]. The module 6M evolves the lowest six radial moments of H2SO4‐H2O aerosols for a comprehensive set of dynamical processes including the formation of new particles via binary H2SO4‐H2O nucleation, condensational growth, coagulation, evolution due to cloud processing, size‐resolved dry deposition, and water uptake and release with changing relative humidity. Performance of the moment‐based aerosol evolution is examined and evaluated by comparison with results obtained using a high‐resolution discrete model of the particle dynamics for a range of conditions representative of the boundary layer and lower troposphere. Overall, the performance of 6M is good relative to uncertainties associated with other processes represented in CTMs for the 30 test cases evaluated. Differences between 6M and the discrete model in the mass/volume moment and in the partitioning of sulfur (VI) between the gas and aerosol phases remain under 1% whenever significant aerosol is present, and differences in particle number rarely exceed 15%. Estimates of cloud droplet number from 6M are on average within 16% of those of the discrete model, with a significant part of these differences attributable to limitations of the discrete dynamics. Multimodal lognormal (MIDAS) surrogates to the underlying size distributions derived from the 6M moments are in good agreement with the benchmark size distributions.
Impact of temperature‐driven cycling of hydrogen peroxide (H2O2) between air and snow on the planetary boundary layer
Authors: Hutterli Manuel A. , McConnell Joseph R. , Stewart Richard W. , Jacobi Hans‐Werner , Bales Roger C.
Published: February 2004

Hydrogen peroxide (H2O2) contributes to the atmosphere's oxidizing capacity, which determines the lifetime of atmospheric trace species. Measured bidirectional summertime H2O2 fluxes from the snowpack at Summit, Greenland, in June 1996 reveal a daytime H2O2 release from the surface snow reservoir and a partial redeposition at night. The observations also provide the first direct evidence of a strong net summertime H2O2 release from the snowpack, enhancing average boundary layer H2O2 concentrations approximately sevenfold and the OH and HO2 concentrations by 70% and 50%, respectively, relative to that estimated from photochemical modeling in the absence of the snowpack source. The total H2O2 release over a 12‐day period was of the order of 5×1013 molecules m−2 s−1 and compares well with observed concentration changes in the top snow layer. Photochemical and air‐snow interaction modeling indicate that the net snowpack release is driven by temperature‐induced uptake and release of H2O2 as deposited snow, which is supersaturated with respect to ice‐air partitioning, approaches equilibrium. The results show that the physical cycling of H2O2 and possibly other volatile species is a key to understanding snowpacks as complex physical‐photochemical reactors and has far reaching implications for the interpretation of ice core records as well as for the photochemistry in polar regions and in the vicinity of snowpacks in general.
Influence of cyclonic perturbations on surface winds around Dumont d'Urville, East Antarctica, using wavelet transform
Authors: Naithani Jaya , Mastrantonio G. , Argentini S. , Pettré Paul
Published: February 2004

Wavelet analyses of the surface winds at Dumont d'Urville, an East Antarctic station, have been performed for the months April, June, September, and December 1993, representing autumn, winter, spring, and summer, respectively. The 3 hourly 10 min averaged meteorological station data have been used. The site is characterized by intense katabatic winds that arrive from the southeast. During the year 1993 the maximum occurrence of wind was from 160° direction sector. The wavelet transform spectra of horizontal wind show prominent periodicities in the interval between 2 and 20 days. The spectral energies in the diurnal scale are comparatively very low even in summer. A comparison with wavelet spectra of pressure for synoptic scale (2–10 days) confirms the influence of synoptic disturbances that are frequent in coastal regions of the Antarctic continent. The same analysis carried out on the wind components, parallel and transverse to the main katabatic flow direction, reveals that these periodicities are mainly due to the katabatic flow behavior. Although the katabatic wind flow is the dominant force characterizing the day‐to‐day weather conditions, the influence of transient cyclones offshore cannot be ignored; in situations of considerable synoptic activity the intensity and duration of katabatic wind flow are prolonged.
Managing and supporting large integrated and interdisciplinary field studies: The BOREAS example
Authors: Newcomer J. A. , Huemmrich K. F. , Landis D. , Nickeson J. , Conrad S. , Knapp D. , Curd S. , Morrell A. , Hodkinson D. , Nelson E. , Cihlar Josef , Margolis Hank , Goodison Barry , Hall F. , Sellers P. J.
Published: February 2004

Large integrated and interdisciplinary field studies, such as the Boreal Ecosystem‐Atmosphere Study (BOREAS), are conducted to refine our understanding of the interactions between the land surface and the atmosphere. Viewed as a case study, the BOREAS research objectives and final data set exemplify the complex nature and requirements of earth systems science research. The management and data system activities required to execute the study also echo this complexity. Rather than several research teams providing the needed management and data support, BOREAS management used a dedicated project staff to handle these functions. As the study progressed, the project staff transitioned from support of logistics and study management to information system operation and data publication, drawing upon the background knowledge gained from the earlier stages of the project. Data publication involves the creation and distribution of quality‐checked and documented data with all ancillary information required to make it useful to someone unfamiliar with the study. We assert that the success of large integrated and interdisciplinary field studies depends upon having a dedicated staff. This staff focuses on the overall goals of the study throughout all phases of the effort: contributing to project planning, logistics, management, and data collection efforts; distributing, quality checking, and integrating the diverse data sets; working with the science teams to develop standardized data set documentation; integrating the diverse data and documentation for archiving; and publishing the data for long‐term use by the larger scientific community. In this paper, the different phases of BOREAS are discussed, and the contributions that the dedicated staff made are examined. The value of spending resources on a centralized staff for project support and data publication activities is also examined.
Annual net snow accumulation over southern Greenland from 1975 to 1998
Authors: McConnell Joseph R. , Lamorey Gregg , Hanna Edward , Mosley‐Thompson Ellen , Bales Roger C. , Belle‐Oudry Deirdre , Kyne Jay D.
Published: February 2004

As part of NASA's Program for Arctic Regional Climate Assessment (PARCA), extensive ice core measurements of annual net water‐equivalent accumulation have been made recently around the southern Greenland ice sheet. Analysis of these measurements demonstrates that annual and seasonal accumulation patterns are sometimes regional, with temporal variability in accumulation correlated over large areas. Using this unique, widely distributed set of contemporaneous accumulation measurements, as well as available previously published observations, we developed maps of annual net snow accumulation south of ∼73°N for each year from 1975 to 1998. Here net snow accumulation is defined as snow accumulation minus ablation. In order to achieve a more consistent spatial distribution of core measurements for each of the 24 years in the study period, some of the observed records were extrapolated up to 5 years using empirical relationships between monthly precipitation measured at coastal stations and the observed ice core net accumulation records. Initial comparisons between the maps of annual net snow accumulation and similar maps of net accumulation derived from meteorological model simulations show excellent agreement in the temporal variability of accumulation, although significant differences in the magnitude of accumulation remain. Both measurements and model simulations indicate that annual net accumulation, averaged over all higher‐elevation regions (above 2000 m) of the southern ice sheet, varies significantly from one year to the next. The maximum year‐to‐year change during the 24‐year study period occurred between calendar years 1995 and 1996, when the average annual net snow accumulation increased by 101 and 172 kg m−2 yr−1, or 37% and 57%, for observations and model simulations, respectively. Taken alone, this 1‐year change in average net snow accumulation corresponds to a drop in sea level of ∼0.16 and ∼0.28 mm yr−1.
A new method for measuring the dependence of particle size distributions on relative humidity, with application to the Southeastern Aerosol and Visibility Study
Authors: Kreisberg Nathan M. , Stolzenburg Mark R. , Hering Susanne V. , Dick William D. , McMurry Peter H.
Published: February 2004

A relative humidity‐moderated differential mobility optical particle size spectrometer (RH‐DMOPSS) was developed to measure particle size distributions at different humidity conditions in the 0.1‐ to 1.1‐μm size range. The system has a high‐flow differential mobility analyzer followed by an optical counter and condensation particle counter in parallel. An aerosol dryer or humidity conditioner can be placed in line ahead of the mobility analyzer. A second dryer ahead of the optical counter permits measurements of the decrease in particle size when particles classified at high relative humidity were dried. The RH‐DMOPSS data set includes (1) optical counter response to monodisperse ambient aerosols, (2) accumulation mode particle size distributions for dry and humid conditions, (3) selected hygroscopic growth factors for humid diameters of 0.2 to 1.1 μm, (4) inferred volatile particle water volume, and (5) inferred refractive index for dried particles. The RH‐DMOPSS was operated in Smoky Mountains National Park as part of the Southeastern Aerosol and Visibility Study and compared with other collocated size and aerosol growth measurements. For dried ambient particles, size distribution parameters were correlated with those from impactor measurements, but volume median diameters were 12% smaller, on average. Growth factors for particles below 0.5‐μm diameter were in the same range as those measured by a tandem differential mobility analyzer and, for all sizes, were consistent with the measured differences between dried and humidified particle size distributions. The mean ambient particle real refractive index inferred from the RH‐DMOPSS dry‐particle calibration data was 1.48, equal to that measured by a multiangle light‐scattering instrument.
Quasi‐biennial oscillation signatures in ozone and temperature observed by lidar at Mauna Loa, Hawaii (19.5°N, 155.6°W)
Authors: Leblanc Thierry , McDermid I. Stuart
Published: February 2004

Using nearly 6 years of nighttime differential absorption lidar ozone and Rayleigh/Raman lidar temperature measurements obtained by the Jet Propulsion Laboratory at Mauna Loa Observatory, Hawaii, the stratospheric quasi‐biennial oscillation (QBO) signatures (15–55 km) in ozone and temperature are revealed. Several clear QBO signatures have been observed in both temperature and ozone. The QBO signature in temperature maximizes at 35 km (5 K amplitude) and is seasonally synchronized (winter) and out of phase with the expected signature at the equator. Also, for the periods 1994–1996 and 1998–2000 the QBO is observable above 45 km, and near 24 km, with opposite phase to that observed at 35 km. The clearest QBO signature in stratospheric ozone maximizes near 31 km and is also seasonally synchronized in late winter‐early spring and is out of phase with the expected equatorial ozone QBO anomaly. Other signatures are observed in winter‐spring near 47 km, in summer near 26 km, and in winter‐spring near 22 km, in phase, and out of phase, respectively, with the expected equatorial ozone QBO. These QBO anomalies identified in ozone and temperature are highly consistent with the previously observed and modeled QBO anomalies assuming that Hawaii is located in the subtropical branch of the asymmetrical QBO‐induced meridional circulation. The observed temperature and ozone QBO were both strongly disturbed by the El Niño‐Southern Oscillation below 25–27 km in 1997–1998.
Elevation change of the southern Greenland ice sheet from 1978 to 1988: Interpretation
Authors: Davis C. H. , McConnell J. R. , Bolzan J. , Bamber J. L. , Thomas R. H. , Mosley‐Thompson E.
Published: February 2004

The spatial pattern of elevation change estimates derived from satellite radar altimeter data for the period from 1978 to 1988 for the southern Greenland ice sheet is examined. As reported previously, the results from 12 ice cores widely distributed in the study area indicate that much of the spatial variability in the elevation change estimates can be explained by temporal variations in accumulation. Most notably, the areas of largest thickening and thinning, east and west of the ice divide around 66°N, recently experienced substantial decadal fluctuations in accumulation sufficient to explain the observed elevation change rates that span the range of ±24 cm yr−1. Elevation change estimates in the NW of the study area around the 2000‐m elevation contour were found to be inconsistent with both short‐ and long‐term changes in accumulation fluctuations. Examination of stratigraphy in several shallow ice cores in the NW indicates that significant melting took place in 1977 and 1978, and this was followed by many years of very little melt activity. This likely resulted in a significant downward bias in the 1978–1988 elevation change estimates in the NW. Comparison of measured surface velocities with those calculated assuming steady state balance show very good agreement overall, but there are many instances in the southeast where the steady state velocities are significantly smaller than measured surface velocities. We cannot rule out the possibility that increased ice flow in lower‐elevation outlet glaciers has migrated farther upstream thereby causing negative long‐term mass imbalance in southeast Greenland.