bluuebunny/crossref_metadata_2025_split huggingface dataset:
The 1990 Valentine's Day Arctic Outbreak. Part I: Mesoscale and Microscale Structure and Evolution of a Colorado Front Range Shallow Upslope Cloud
Authors: Rasmussen Roy M. , Bernstein Ben C. , Murakami Masataka , Stossmeister Greg , Reisner Jon , Stankov Boba 
Published: August 2010

Abstract
The mesoscale and microscale structure and evolution of a shallow, upslope cloud is described using observations obtained during the Winter Icing and Storms Project (WISP) and model stimulations. The upslope cloud formed within a shallow arctic air mass that moved into the region east of the Rocky Mountains between 12 and 16 February and contained significant amounts of supercooled liquid water for nearly 30 h. Two distinct layers were evident in the cloud. The lower layer was near neutral stability (boundary layer air) and contained easterly upslope flow. The upper layer (frontal transition zone) was thermodynamically stable and contained southerly flow. Overlying the upslope cloud was a dry, southwesterly flow of 20&#x96;25 m s −1, resulting in strong wind shear near cloud top. Within 10 km of the Rocky Mountain barrier, easterly low-level flow was lifted up and over the mountains. The above-described kinematic and thermodynamic structure produced three distinct mechanisms leading to the production of supercooled liquid water: 1) upslope flow over the gently rising terrain leading into the Colorado Front Range, up the slopes of the Rocky Mountains and over local ridges, 2)upglide flow within a frontal transition zone, and 3) turbulent mixing in the boundary layer. Supercooled liquid water was also produced by 1) upward motion at the leading edge of three cold surges and 2) vertical motion produced by low-level convergence in the surface wind field. Large cloud droplets were present near the top of this cloud (approximately 50-µm diameter), which grew by a direct coalescence process into freezing drizzle in regions of the storm where the liquid water content was greater than 0.25 g m −3 and vertical velocity was at 10 cm s −1
Ice crystal concentrations greater than 1 L−1 were observed in the lower cloud layer containing boundary layer air when the top of the boundary layer air when the top of the boundary layer was colder than −12°C. The upper half of the cloud was ice-free despite temperatures as low as −15°C, resulting in long-lived supercooled liquid water in this region of the cloud.
Clustering of Satellite Sounding Radiances to Investigate Intense Low-Level Humidity Gradients
Authors: Fuelberg Henry E. , Rao P. Anil , Hillger Donald W. 
Published: August 2010

Abstract
Satellite-derived profiles of temperature and dewpoint (retrievals) are obtained using radiance data from the Visible-infrared Spin Scan Radiometer Atmospheric Sounder. Individual fields of view that are input to the retrieval algorithm must be horizontally averaged to provide suitable signal-to-noise ratios. This paper investigates three methods for performing this averaging: 1)a blocking approach that is employed operationally, 2) a manual procedure that seeks to maximize atmospheric gradients, and 3) an objective procedure called clustering that takes advantage of similarities in satellite measurements to avoid smearing the gradient information. The three techniques are examined on 10&#x96;11 July 1989 when intense gradients of humidity were present over the Florida peninsula.
Results show that the clustering scheme produced retrievals that were very similar to those obtained manually. Both schemes indicated strong humidity gradients in the lower troposphere. The blocking procedure produced less intense gradients. The retrieval information is used to examine conditions leading to fair weather on 10 July but intense thunderstorm development on 11 July.
Quantitative Assessment of the Sampling Properties of a Spaceborne Lidar (ATLID)
Authors: Ackermann Jörg 
Published: August 2010

Abstract
The European Space Agency plans to install the backscatter lidar system ATLID (atmospheric lidar) on a polar-orbiting platform at the beginning of the next century. This kind of active remote sensing will provide highly accurate information about cloud-top height, which, in addition to collocated passive sounder's measurements of brightness temperature, might improve retrieved vertical temperature profiles and serve as a supplementation of present cloud climatologies. Due to technical constraints, ATLID will not provide spatially continuous information about cloud-top height. The representativeness of the lidar measurements for the whole cloud field constitutes the sampling problem and is investigated in two steps: first, a scan mode for ATLID is developed, which on the assumption that the cloud field is a two-dimensional random variable gives an equal pixel spacing along and across the flight track of the orbiter. Second, the simulated lidar measurements given by the elaborated scan mode are contributed to a spatially continuous cloud field represented by Advanced Very High Resolution Radiometer images. From the dispersed lidar measurements with a footprint diameter of about 1 km the cloud field is restored by a spatial interpolation scheme and compared with the original cloud field by a linear regression analysis. It turns out that the sampling error and hence the benefits of ATLID strongly depend on the meteorological situation: if the required vertical accuracy of the lidar measurement is about 250 m corresponding approximately to half of the vertical resolution of present retrieval schemes, the probability for a meaningful ATLID information is between 40% and 70%. Since an imager cannot provide a useful brightness temperature in case of multilayered or broken clouds within one imager pixel, the synergism of ATLID with a passive instrument also depends on the homogeneity of cloud-top height within the range of 1 km. To cheek this small-scale variability of cloud tops data from the European Lidar Airborne Campaign 1990 are evaluated. Results show that for optically thick clouds the variability exceeds in 3% to 38% of all considered cases a threshold of 250 m. Additionally, power-spectrum analyses confirm the result of the sampling analyses.
Summertime Cloud-to-Ground Lightning Activity around Major Midwestern Urban Areas
Authors: Westcott Nancy E. 
Published: August 2010

Abstract
Cloud-to-ground lightning flash data collected by the National Lightning Detection Network were analysed in and around 16 central U.S. cities for the period 1989&#x96;92. Lightning data are well suited to study storm activity in and around large urban areas since their continuity and coverage in space and time is superior to historical, spatially limited records of thunderstorm activity. Frequency of cloud-to-ground lightning flashes (of negative and positive polarity) in the area immediately upwind, within, and immediately downwind of the cities were compared. An enhancement of lightning frequency on the order of 40%&#x96;85% was found over and downwind of many of these cities.
A number of possible urban-related causal factors were examined including effects of increased urban concentrations of cloud condensation nuclei, urban population and size, and the presence of distinct topographic features in and around the cities. Various factors, physical and anthropogenic, appeared to interact in diverse ways to account for changes in lightning flash frequency. The enhancement of lightning activity was largest during the afternoon hours when the urban&#x96;rural temperature differences are usually smallest, but when the atmosphere is generally the most unstable and when there is often a maximum in convective activity. The spatial distribution of the first 50 lightning flashes from each storm suggested that the urban area did not initiate new lightning storms. Thus, the overall results suggested that existing thunderstorms were the most strongly affected.
Evaluation of the Effect of Horizontal Diffusion on the Long-Range Atmospheric Transport Simulation with Chernobyl Data
Authors: Ishikawa Hirohiko 
Published: August 2010

Abstract
The effect of horizontal diffusion on the long-range transport simulation is examined with a Lagrangian particle transport model. The transport of radioactivity released from Chernobyl is simulated by the model with different values of horizontal diffusivity. The computed concentrations are statistically compared with measured concentration. The best simulation is found when the magnitude of the horizontal diffusivity is between 3.3 × 104 and 1.0 × 105 m2 s−1. The performance of empirical formulas of horizontal diffusion, in which mean-square displacement σy is specified as a function of time, is also examined.
A part of measured concentrations, which are relatively low concentrations, cannot be explained by transport and diffusion only. It is shown that these measured concentrations can be explained by resuspension of deposited radioactivity.
A Simple Method for Spatial Interpolation of the Wind in Complex Terrain
Authors: Palomino I. , Martín F. 
Published: August 2010

Abstract
The topographical elevation difference is proposed as a new variable for spatial interpolation of the sparse surface wind measurements to a finer mesh in a complex terrain area. The most used method for the initialization of diagnostic wind field models is based on the inverse-distance-squared weighted averaging interpolation technique regardless of the topographical elevation. Analysis of experimental data obtained from six meteorological towers deployed at several heights on the slopes along a valley in the South of Spain has shown a good correlation between wind speed and elevation above valley bottom. The efficiency of the inverse absolute elevation difference and the inverse distance squared as averaging weights for interpolation of the wind vector at several locations is checked; this is done for two meteorological synoptic weather types: strong synoptic winds, and thermal low over the Iberian Peninsula. For the latter weather type, the formation of nocturnal thermal inversion and the drainage flows are taken into account. Wind fields in the valley resulting from the two interpolation methods are compared. The elevation difference between meteorological station and grid point seems to be an important variable to be included in the wind field initialization process, that is, interpolation of the wind vector to a grid, when complex terrain areas are considered.
Simulated Urban Climate Response to Modifications in Surface Albedo and Vegetative Cover
Authors: Sailor David J. 
Published: August 2010

Abstract
Three-dimensional meteorological simulations have been conducted to investigate the potential impact of urban surface characteristic modifications on local climate. Results for a base case simulation for the Los Angeles basin are compared to results from cases in which urban albedo or vegetative cover are increased. The methodology for determining the distribution and magnitude of these simulated surface modifications is presented. Increasing albedo over downtown Los Angeles by 0.14 and over the entire basin by an average of 0.08 decreased peak summertime temperatures by as much as 1.5°C. This level of albedo augmentation also lowered boundary layer heights by more than 50 m and reduced the magnitude and penetration of the sea breeze. A second simulation, in which vegetative cover was increased, showed qualitatively similar impacts. The results from these simulations indicate a potential to reduce urban energy demand and atmospheric pollution by 5%&#x96;10% through application of reasonable surface modification strategies.
Some Recent Long-Range Diffusion Observations
Authors: Gifford F. A. 
Published: August 2010

Abstract
Recent atmospheric cloud-spreading (relative diffusion) data from a variety of sources are combined to show that the horizontal spreading rate is approximately linear over a time range from 1 to 10 or more hours (20&#x96;200 or more km) of downwind cloud travel. This result agrees with earlier observational studies, in which the horizontal cloud standard deviation σy has consistently been found to vary as tp, where t is the downwind travel time and p is in the range 1&#x96;1.2. For the present dataset, σy is found to vary as t1.1. A recent theoretical prediction, p = 7/6, valid over the entire range of t, is very close to these observed values.
Variability of Microphysical Parameters in High-Altitude Ice Clouds: Results of the Remote Sensing Method
Authors: Matrosov Sergey Y. 
Published: August 2010

AbstractThe remote sensing method for retrieving vertical profiles of microphysical parameters in ice clouds from ground-based measurements taken by the Doppler radar and IR radiometer was applied to several cloud cases observed during different field experiments including FIRE-II, ASTEX, and the Arizona Program. The measurements were performed with the NOAA Environmental Technology Laboratory instrumentation. The observed ice clouds were mostly cirrus clouds located in the upper troposphere above 5.6 km. Their geometrical thicknesses varied from a few hundred meters to 3 km. Characteristic cloud particle sizes expressed in median mass diameters of equal-volume spheres varied from about 25 μm to more than 400 μm. Typically, characteristic particle sizes were increasing toward the cloud base, with the exception of the lowest range gates where particles were quickly sublimating. Highest particle concentrations were usually observed near the cloud tops. The vertical variability of particle sizes inside an individual cloud could reach one order of magnitude. The standard deviation of the mean profile for a typical cloud is usually factor of 2 or 3 smaller than mean values of particle characteristic size. Typical values of retrieved cloud ice water content varied from 1 to 100 mg m−3; however, individual variations were as high as four orders of magnitude. There was no consistent pattern in the vertical distribution of ice water content except for the rapid decrease in the vicinity of the cloud base. The relationships between retrieved cloud parameters and measured radar reflectivities were considered. The uncertainty of estimating cloud parameters from the power-law regressions is discussed. The parameters of these regressions varied from cloud to cloud and were comparable to the parameters in corresponding regressions obtained from direct particle sampling in other experiments. Relationships between cloud microphysical parameters and reflectivity can vary even for the same observational case. The variability diminishes if stronger reflectivities are considered. A procedure of “tuning” cloud microphysics–reflectivity regressions for individual profiles is suggested. Such a procedure can simplify the radar–radiometer method and make it applicable for a broader range of clouds.
Differential Doppler Velocity: A Radar Parameter for Characterizing Hydrometeor Size Distributions
Authors: Wilson Damian R. , Illingworth Anthony J. , Blackman T. Mark 
Published: August 2010

Abstract
Observations of Doppler-resolved spectra of differential radar reflectivity provide estimates of particle shapes as a function of their terminal velocity, and they can be derived by having the antenna at a significant elevation angle. Turbulence tends to smear out the details of the actual spectra observed, but the difference in the mean values of velocity using horizontal and vertical polarizations, which the authors call the “differential Doppler velocity” (DDV), is unaffected. Larger raindrops fall faster and are oblate, so values of DDV are positive. If a gamma function is used for the raindrop size spectrum, then the observed DDV and ZDR correspond to particular values of median drop diameter D0 and the dispersion index m. The scaling parameter N0 is derived from Z. Estimates of m have a mean value of 5 but vary substantially. An error in rainfall rate of up to ±15% results if the rainfall rate is computed from Z and ZDR alone, and m is assumed constant at 5. An overestimation of more than 30% occurs if m is assumed to be 0. DDV values in stratiform ice are slightly negative. The values in ice are explicable in terms of a mixture of slowly falling oblate crystals and faster-falling spherical aggregates. In the bright band, DDV is consistent with the coexistence of oblate snowflakes and faster-falling raindrops.
Large-Scale Analysis of Cirrus Clouds from AVHRR Data: Assessment of Both a Microphysical Index and the Cloud-Top Temperature
Authors: Giraud V. , Buriez J. C. , Fouquart Y. , Parol F. , Seze G. 
Published: August 2010

AbstractAn algorithm that allows an automatic analysis of cirrus properties from Advanced Very High Resolution Radiometer (AVHRR) observations is presented. Further investigations of the information content and physical meaning of the brightness temperature differences (BTD) between channels 4 (11 μm) and 5 (12 μm) of the radiometer have led to the development of an automatic procedure to provide global estimates both of the cirrus cloud temperature and of the ratio of the equivalent absorption coefficients in the two channels, accounting for scattering effects. The ratio is useful since its variations are related to differences in microphysical properties. Assuming that cirrus clouds are composed of ice spheres, the effective diameter of the particle size distribution can be deduced from this microphysical index.The automatic procedure includes first, a cloud classification and a selection of the pixels corresponding to the envelope of the BTD diagram observed at a scale of typically 100 × 100 pixels. The classification, which uses dynamic cluster analysis, takes into account spectral and spatial properties of the AVHRR pixels. The selection is made through a series of tests, which also guarantees that the BTD diagram contains the necessary information, such as the presence of both cirrus-free pixels and pixels totally covered by opaque cirrus in the same area. Finally, the cloud temperature and the equivalent absorption coefficient ratio are found by fitting the envelope of the BTD diagram with a theoretical curve. Note that the method leads to the retrieval of the maximum value of the equivalent absorption coefficient ratio in the scene under consideration. This, in turn, corresponds to the minimum value of the effective diameter of the size distribution of equivalent Mie particles.The automatic analysis has been applied to a series of 21 AVHRR images acquired during the International Cirrus Experiment (ICE’89). Although the dataset is obviously much too limited to draw any conclusion at the global scale, it is large enough to permit derivation of cirrus properties that are statistically representative of the cirrus systems contained therein. The authors found that on average, the maximum equivalent absorption coefficient ratio increases with the cloud-top temperature with a jump between 235 and 240 K. More precisely, for cloud temperatures warmer than 235 K, the retrieved equivalent absorption coefficient ratio sometimes corresponds to very small equivalent spheres (diameter smaller than 20 μm). This is never observed for lower cloud temperatures. This change in cirrus microphysical properties points out that ice crystal habits may vary from one temperature regime toanother. It may be attributed to a modification of the size and/or shape of the particles.
The Potential of a Spaceborne Cloud Radar for the Detection of Stratocumulus Clouds
Authors: Fox Neil I. , Illingworth Anthony J. 
Published: August 2010

Abstract
The radar reflectivity and liquid water content of stratocumulus clouds have been computed from cloud droplet spectra recorded during more than 4000 km of cloud penetrations by an aircraft, and the probability of detecting various values of liquid water content as a function of the radar sensitivity threshold has been derived. The goal of the study is to specify the sensitivity required for any future spaceborne cloud radar. In extensive marine stratocumulus deeper than about 200 m, occasional but ubiquitous drizzle-sized droplets of up to 200 μm dominate the radar return and increase it by between 10 and 20 dB above the cloud droplet contribution to the return, making radar detection easier, although the concentration of the drizzle drops is so low that they have no effect on the liquid water content or effective radius. These occasional drizzle-sized droplets are present throughout the vertical and horizontal extent of such clouds but should evaporate within 200 m of cloud base. On occasion, the drizzle can fall farther and may yield a false measurement of cloud-base altitude, but such cases can be recognized by examining the vertical profile of reflectivity. A radar sensitivity threshold of −30 dBZ would detect 80%, 85%, and 90% of the marine stratocumulus, with a liquid water content above 0.025, 0.05, and 0.075 g m−3, respectively. Because nonprecipitating drizzle droplets are rare in continental stratocumulus, the equivalent figures are reduced to 38%, 33%, and 25%. Improving the sensitivity to −40 dBZ increases detection probability to nearly 100% for both types of cloud. These figures are based on the assumption that the cloud is deep enough to fill the radar pulse volume.
Model-Simulated Influences of Shelterbelt Shape on Wind-Sheltering Efficiency
Authors: Wang Hao , Takle E. S. 
Published: August 2010

Abstract
The authors report results of a numerical model used to simulate wind and turbulence fields for porous, living shelterbelts with seven different cross-sectional shapes. The simulations are consistent with results of Woodruff and Zingg whose wind-tunnel study demonstrated that all shelterbelts with very different shapes have nearly identical reduction of wind and turbulence. The simulations also showed that the pressure-loss (resistance) coefficient for smooth-shaped or streamlined shelterbelts is significantly smaller than that for rectangle-shaped or triangle-shaped shelterbelts with a windward vertical side. However, the shelter effects are not proportional to the pressure-loss coefficient (drag). Analysis of the momentum budget demonstrated that in the near lee and in the far lee, both vertical advection and pressure gradient have opposite roles in the recovery of wind speed. This behavior, combined with differences in permeability, is the likely cause of reduced sensitivity of shelter effects to shelterbelt shape.
Validation of a Long-Range Trajectory Model Using Gas Balloon Tracks from the Gordon Bennett Cup 95
Authors: Baumann Kathrin , Stohl Andreas 
Published: August 2010

Abstract
In September 1995, 18 gas balloon teams competed at the Gordon Bennett Cup, a long-distance ballooning event. The landing positions, travel times of all teams, and detailed information on the tracks of four teams are available. A special version of the trajectory model FLEXTRA (flexible trajectories) is used that allows the heights of calculated trajectories to be adjusted to the respective balloon heights at every computation time step. The comparison of calculated and observed balloon trajectories allows a validation of the trajectory model. In this case study, the agreement between calculated and balloon trajectories was good, with average relative transport errors of less than 20% of the travel distance after 46 h of travel time. Most of the trajectory errors originate from interpolation errors and from amplifications of small position disturbances in divergent wind fields. Trajectory ensembles, taking into account stochastic errors occurring during the trajectory calculations, are shown to be very reliable in assessing the uncertainties of the computed trajectories. In the present study, the balloon tracks were enveloped by the ensemble trajectories most of the time, suggesting that errors in the analyzed wind fields were relatively small.