77 Matching Results

Results open in a new window/tab.

Mass by Energy Loss Quantitation as a Practical Sub-Microgram Balance (open access)

Mass by Energy Loss Quantitation as a Practical Sub-Microgram Balance

A simple device integrating a thin film support and a standard microcentrifuge tube can be used for making solutions of accurately known concentration of any organic compound in a single step, avoiding serial dilution and the use of microgram balances. Nanogram to microgram quantities of organic material deposited on the thin film are quantified by ion energy loss and transferred to the microcentrifuge tube with high recovery.
Date: September 28, 2004
Creator: Palmblad, M; Bench, G & Vogel, J S
System: The UNT Digital Library
Flor-Essence? Herbal Tonic Promotes Mammary Tumor Development in Sprague Dawley Rats (open access)

Flor-Essence? Herbal Tonic Promotes Mammary Tumor Development in Sprague Dawley Rats

Background: Women who are diagnosed with breast cancer often self-administer complementary and alternative medicines to augment their conventional treatments, improve health, or prevent recurrence. Flor-Essence{reg_sign} Tonic is a complex mixture of herbal extracts used by cancer patients because of anecdotal evidence that it can treat or prevent disease. Methods: Female Sprague Dawley rats were given water or exposed to 3% or 6% Flor-Essence{reg_sign} beginning at one day of age. Mammary tumors were induced with a single oral 40 mg/kg/bw dose of dimethylbenz(a)anthracene at 50 days of age and sacrificed at 23 weeks. Rats were maintained on AIN-76A diet. Results: Control rats had palpable mammary tumor incidence of 51.0% at 19 weeks of age compared to 65.0% and 59.4% for the 3% and 6% Flor-Essence{reg_sign} groups respectively. Overall, no significant difference in time until first palpable tumor was detected among any of the groups. At necropsy, mammary tumor incidence was 82.5% for controls compared to 90.0% and 97.3% for rats consuming 3% and 6% Flor-Essence{reg_sign}, respectively. Mean mammary tumor multiplicity ({+-}SES) for the controls was 2.8 ({+-} 0.5) and statistically different from the 3% or 6% Flor- Essence{reg_sign} groups with 5.2 ({+-} 0.7), and 4.8 ({+-} 0.6), respectively (p{<=}0.01). As expected, …
Date: January 28, 2004
Creator: Bennett, L; Montgomery, J; Steinberg, S & Kulp, K
System: The UNT Digital Library
Calculation of Radiative Corrections to E1 matrix elements in the Neutral Alkalis (open access)

Calculation of Radiative Corrections to E1 matrix elements in the Neutral Alkalis

Radiative corrections to E1 matrix elements for ns-np transitions in the alkali metal atoms lithium through francium are evaluated. They are found to be small for the lighter alkalis but significantly larger for the heavier alkalis, and in the case of cesium much larger than the experimental accuracy. The relation of the matrix element calculation to a recent decay rate calculation for hydrogenic ions is discussed, and application of the method to parity nonconservation in cesium is described.
Date: September 28, 2004
Creator: Sapirstein, J & Cheng, K T
System: The UNT Digital Library
Accurate wavelength measurements and modeling of FeXV to FeXIX spectra recorded in high density plasmas between 13.5 to 17 A. (open access)

Accurate wavelength measurements and modeling of FeXV to FeXIX spectra recorded in high density plasmas between 13.5 to 17 A.

Iron spectra have been recorded from plasmas created at three different laser plasma facilities, the Tor Vergata University laser in Rome (Italy), the Hercules laser at ENEA in Frascati (Italy), and the Compact Multipulse Terawatt (COMET) laser at LLNL in California (USA). The measurements provide a means of identifying dielectronic satellite lines from FeXVI and FeXV in the vicinity of the strong 2p {yields} 3d transitions of FeXVII. About 80 {Delta}n {ge} 1 lines of FeXV (Mg-like) to FeXIX (O-like) were recorded between 13.8 to 17.1 {angstrom} with a high spectral resolution ({lambda}/{Delta}{lambda} {approx} 4000), about thirty of these lines are from FeXVI and FeXV. The laser produced plasmas had electron temperatures between 100 to 500 eV and electron densities between 10{sup 20} to 10{sup 22} cm{sup -3}. The Hebrew University Lawrence Livermore Atomic Code (HULLAC) was used to calculate the atomic structure and atomic rates for FeXV to FeXIX. HULLAC was used to calculate synthetic line intensities at T{sub e} = 200 eV and n{sub e} = 10{sup 21}cm{sup -3} for three different conditions to illustrate the role of opacity: optically thin plasmas with no excitation-autoionization/dielectronic recombination (EA/DR) contributions to the line intensities, optically thin plasmas that included EA/DR …
Date: September 28, 2004
Creator: May, M.; Beiersdorfer, P.; Dunn, J.; Jordan, N.; Osterheld, A.; Faenov, A. et al.
System: The UNT Digital Library
Neutron Skyshine Considerations For The NIF Shielding Design (open access)

Neutron Skyshine Considerations For The NIF Shielding Design

A series of coupled neutron-photon transport Monte-Carlo calculations was performed to estimate the roof shielding required to limit the skyshine dose to less than 1 mrem/y at the site boundary when conducting DT experiments with annual fusion yields up to 1200 MJ (4.2E20 neutrons/y). The NIF shielding design consists of many different components. The basic components include 10-cm-thick Al chamber with 40-cm-thick target chamber gunite shield having multiple penetrations, 1.83-m-thick concrete Target Bay walls, 1.37-m-thick concrete roof, and multiple concrete floors with numerous penetrations. Under this shielding configuration, the skyshine dose at the nearest site-boundary was calculated to be less than 0.2 mrem/y for all possible target illumination configurations. The potential dose at the site boundary would be about one-tenth of the cosmic neutron dose that we measured with bubble neutron detectors on board a commercial roundtrip flight from SF to Rochester. This incremental dose increase is well within the normal fluctuations (noise) of the natural background radiation in the Livermore area. The skyshine dose has no impact on the public. The skyshine dose trends at ground and elevated levels are plotted as a function of distance from 20 m to 1000 m from the center of the target bay. …
Date: January 28, 2004
Creator: Singh, M S; Mecozzi, J M & Tobin, M T
System: The UNT Digital Library
Probability Density Function for Waves Propagating in a Straight Rough Wall Tunnel (open access)

Probability Density Function for Waves Propagating in a Straight Rough Wall Tunnel

The radio channel places fundamental limitations on the performance of wireless communication systems in tunnels and caves. The transmission path between the transmitter and receiver can vary from a simple direct line of sight to one that is severely obstructed by rough walls and corners. Unlike wired channels that are stationary and predictable, radio channels can be extremely random and difficult to analyze. In fact, modeling the radio channel has historically been one of the more challenging parts of any radio system design; this is often done using statistical methods. The mechanisms behind electromagnetic wave propagation are diverse, but can generally be attributed to reflection, diffraction, and scattering. Because of the multiple reflections from rough walls, the electromagnetic waves travel along different paths of varying lengths. The interactions between these waves cause multipath fading at any location, and the strengths of the waves decrease as the distance between the transmitter and receiver increases. As a consequence of the central limit theorem, the received signals are approximately Gaussian random process. This means that the field propagating in a cave or tunnel is typically a complex-valued Gaussian random process.
Date: January 28, 2004
Creator: Pao, Hsueh-Yuan
System: The UNT Digital Library
National Atmospheric Release Advisory Center (NARAC) Model Development and Evaluation (open access)

National Atmospheric Release Advisory Center (NARAC) Model Development and Evaluation

None
Date: March 28, 2004
Creator: Sugiyama, G
System: The UNT Digital Library
rVISTA 2.0: Evolutionary Analysis of Transcription Factor Binding Sites (open access)

rVISTA 2.0: Evolutionary Analysis of Transcription Factor Binding Sites

Identifying and characterizing the patterns of DNA cis-regulatory modules represents a challenge that has the potential to reveal the regulatory language the genome uses to dictate transcriptional dynamics. Several studies have demonstrated that regulatory modules are under positive selection and therefore are often conserved between related species. Using this evolutionary principle we have created a comparative tool, rVISTA, for analyzing the regulatory potential of noncoding sequences. The rVISTA tool combines transcription factor binding site (TFBS) predictions, sequence comparisons and cluster analysis to identify noncoding DNA regions that are highly conserved and present in a specific configuration within an alignment. Here we present the newly developed version 2.0 of the rVISTA tool that can process alignments generated by both zPicture and PipMaker alignment programs or use pre-computed pairwise alignments of seven vertebrate genomes available from the ECR Browser. The rVISTA web server is closely interconnected with the TRANSFAC database, allowing users to either search for matrices present in the TRANSFAC library collection or search for user-defined consensus sequences. rVISTA tool is publicly available at http://rvista.dcode.org/.
Date: January 28, 2004
Creator: Loots, G G & Ovcharenko, I
System: The UNT Digital Library
PROSPECTS FOR PENTAQUARK SEARCHES IN E+D- ANNIHILATIONS AND VV COLLISIONS. (open access)

PROSPECTS FOR PENTAQUARK SEARCHES IN E+D- ANNIHILATIONS AND VV COLLISIONS.

Recent strong experimental evidence of a narrow exotic S = +1 baryon resonance, {Theta}{sup +}, suggests the existence of other exotic baryons. We discuss the prospects of confirming earlier experimental evidence of {Theta}{sup +} and the observation of additional hypothetical exotic baryons in e{sup +}e{sup -} annihilations and {gamma}{gamma} collisions at LEP and B Factories.
Date: June 28, 2004
Creator: ARMSTRONG,S.; MELLADO,B. & WU,S. L.
System: The UNT Digital Library
Seal Monitoring System for an Explosive Containment Vessel (open access)

Seal Monitoring System for an Explosive Containment Vessel

Researchers at Lawrence Livermore National Laboratory are developing high-performance explosive firing vessels to contain (one time) explosive detonations that contain toxic metals and hazardous gases. The filament-wound polymer composite vessels are designed to contain up to 80 lb (TNT equivalent) explosive in a 2-meter sphere without leakage. So far, two half-scale (1-meter diameter) vessels have been tested; one up to 150% of the design explosive limit. Peak dynamic pressures in excess of 280 MPa (40 Ksi) in the vessel were calculated and measured. Results indicated that there was a small amount of gas and particle leakage past the first two of the seven o-ring seals. However, the remaining five seals prevented any transient leakage of the toxic gases and particulates out of the vessel. These results were later confirmed by visual inspection and particulate analysis of swipes taken from the sealing surfaces.
Date: June 28, 2004
Creator: Pastrnak, J. W.; Henning, C. D.; Switzer, V. A.; Grundler, W.; Holloway, J. R.; Morrison, J. J. et al.
System: The UNT Digital Library
Assesing the Impacts of Local Deposition of Mercury Associated With Coal-Fired Power Plants. (open access)

Assesing the Impacts of Local Deposition of Mercury Associated With Coal-Fired Power Plants.

Mercury emissions from coal fired plants will be limited by regulations enforced by the Environmental Protection Agency. However, there is still debate over whether the limits should be on a plant specific basis or a nationwide basis. The nationwide basis allows a Cap and Trade program similar to that for other air pollutants. Therefore, a major issue is the magnitude and extent of local deposition. Computer modeling suggests that increased local deposition will occur on a local (2 to 10 Km) to regional scale (20 to 50 Km) with the increase being a small percentage of background deposition on the regional scale. The amount of deposition depends upon many factors including emission rate, chemical form of mercury emitted (with reactive gaseous mercury depositing more readily than elemental mercury), other emission characteristics (stack height, exhaust temperature, etc), and meteorological conditions. Modeling suggests that wet deposition will lead to the highest deposition rates and that these will occur locally. Dry deposition is also predicted to deposit approximately the same amount of mass as wet deposition, but over a much greater area. Therefore, dry deposition rates will contribute a fraction of total deposition on the regional scale. The models have a number of …
Date: March 28, 2004
Creator: Sullivan, T.; Bowerman, B.; Adams, J.; Ogeka, C.; Lipfert, F. & Renninger, S.
System: The UNT Digital Library
A New Detailed Term Accounting Opacity Code: TOPAZ (open access)

A New Detailed Term Accounting Opacity Code: TOPAZ

A new opacity code, TOPAZ, which explicitly includes configuration term structure in the bound-bound transitions is being developed. The goal is to extend the current capabilities of detailed term accounting opacity codes such as OPAL that are limited to lighter elements of astrophysical interest. At present, opacity calculations of heavier elements use statistical methods that rely on the presence of myriad spectral lines for accuracy. However, statistical approaches have been shown to be inadequate for astrophysical opacity calculations. An application of the TOPAZ code will be to study the limits of statistical methods. Comparisons of TOPAZ to other opacity codes as well as experiments are presented.
Date: April 28, 2004
Creator: Iglesias, C A; Chen, M H; Isaacs, W; Sonnad, V & Wilson, B G
System: The UNT Digital Library
Recovery and Visualization of 3D Structure of Chromosomes from Tomographic Reconstruction Images (open access)

Recovery and Visualization of 3D Structure of Chromosomes from Tomographic Reconstruction Images

The objectives of this work include automatic recovery and visualization of a 3D chromosome structure from a sequence of 2D tomographic reconstruction images taken through the nucleus of a cell. Structure is very important for biologists as it affects chromosome functions, behavior of the cell and its state. Chromosome analysis is significant in the detection of deceases and in monitoring environmental gene mutations. The algorithm incorporates thresholding based on a histogram analysis with a polyline splitting algorithm, contour extraction via active contours, and detection of the 3D chromosome structure by establishing corresponding regions throughout the slices. Visualization using point cloud meshing generates a 3D surface. The 3D triangular mesh of the chromosomes provides surface detail and allows a user to interactively analyze chromosomes using visualization software.
Date: April 28, 2004
Creator: Babu, S; Liao, P; Shin, M C & Tsap, L V
System: The UNT Digital Library
Dispersion of waves in porous cylinders with patchy saturation Part I. Formulaton and torsional waves (open access)

Dispersion of waves in porous cylinders with patchy saturation Part I. Formulaton and torsional waves

Laboratory experiments on wave propagation through saturated and partially saturated porous media have often been conducted on porous cylinders that were initially fully saturated and then allowed to dry while continuing to acquire data on the wave behavior. Since it is known that drying typically progresses from outside to inside, a sensible physical model of this process is concentric cylinders having different saturation levels--the simplest example being a fully dry outer cylindrical shell together with a fully wet inner cylinder. We use this model to formulate the equations for wave dispersion in porous cylinders for patchy saturation (i.e. drainage) conditions. In addition to multiple modes of propagation obtained numerically from these dispersion relations, we find two distinct analytical expressions for torsional wave modes. We solve the dispersion relation for torsional waves for two examples: Massillon sandstone and Sierra White granite. The drainage analysis appears to give improved agreement with the data for both these materials.
Date: July 28, 2004
Creator: Berryman, J G & Pride, S R
System: The UNT Digital Library
Assessing the Mercury Health Risks Associated With Coal-Fired Power Plants: Issues in Atmospheric Processes. (open access)

Assessing the Mercury Health Risks Associated With Coal-Fired Power Plants: Issues in Atmospheric Processes.

The rationale for regulating air emissions of mercury from U.S. coal-fired power plants largely depends on mathematical dispersion modeling, including the atmospheric chemistry processes that affect the partitioning of Hg emissions into elemental (Hg{sub 0}) and the reactive (RGM) forms that may deposit more rapidly near sources. This paper considers and evaluates the empirical support for this paradigm. We consider the extant experimental data at three spatial scales: local (< 30 km), regional (< {approx}300 km), and national (multi-state data). An additional issue involves the finding of excess Hg levels in urban areas.
Date: March 28, 2004
Creator: Lipfert, F.; Sullivan, T. & Renninger, S.
System: The UNT Digital Library
Pre-bomb {Delta}{sup 14}C variability and the Suess Effect in Cariaco Basin Surface Waters as Recorded in Hermatypic Corals (open access)

Pre-bomb {Delta}{sup 14}C variability and the Suess Effect in Cariaco Basin Surface Waters as Recorded in Hermatypic Corals

The {Delta}{sup 14}C content of surface waters in and around the Cariaco Basin were reconstructed from {sup 14}C measurements on sub-annually sampled coral skeletal material. During the late 1930s - early 1940s surface waters within and outside of the Cariaco Basin are similar. Within the Cariaco Basin at Islas Tortugas coral {Delta}{sup 14}C averages -51.9 {+-}3.3 {per_thousand}. Corals collected outside of the basin at Boca de Medio and Los Testigos have {Delta}{sup 14}C values of -53.4 {+-} 3.3 {per_thousand} and -54.3 {+-} 2.6 respectively. Additional {sup 14}C analyses on the Isla Tortugas coral document an {approx} 11 {per_thousand} decrease between {approx}1905 (-40.9 {+-}4.5 {per_thousand}) and {approx}1940. The implied Suess Effect trend (-3 {per_thousand}/decade) is nearly as large as that observed in the atmosphere over the same time period. If we assume that there is little to no fossil fuel {sup 14}CO{sub 2} signature in Cariaco surface waters in {approx}1905, the waters have an equivalent reservoir age of {approx}312 years.
Date: October 28, 2004
Creator: Guilderson, T; Cole, J & Southon, J
System: The UNT Digital Library
Janus Intense Short Pulse (ISP), the Next Ultrahigh Intensity Laser at LLNL (open access)

Janus Intense Short Pulse (ISP), the Next Ultrahigh Intensity Laser at LLNL

The Janus ISP upgrade is being developed at LLNL to provide a high-energy (hundreds of Joules) short duration (0.5 to 200 ps) laser pulse with variable delay from a second high-energy (up to 1kJ) long duration (0.2 to 20 ns) laser pulse on target. A new target chamber will allow the angle between the long and short pulse beams to be varied from about 35 to near 180 degrees. Commissioning of the system will begin in the summer of 2005.
Date: September 28, 2004
Creator: Caird, J A; Bonlie, J D; Britten, J A; Cross, R R; Ebbers, C A; Eckart, M J et al.
System: The UNT Digital Library
HADES, A Code for Simulating a Variety of Radiographic Techniques (open access)

HADES, A Code for Simulating a Variety of Radiographic Techniques

It is often useful to simulate radiographic images in order to optimize imaging trade-offs and to test tomographic techniques. HADES is a code that simulates radiography using ray tracing techniques. Although originally developed to simulate X-Ray transmission radiography, HADES has grown to simulate neutron radiography over a wide range of energy, proton radiography in the 1 MeV to 100 GeV range, and recently phase contrast radiography using X-Rays in the keV energy range. HADES can simulate parallel-ray or cone-beam radiography through a variety of mesh types, as well as through collections of geometric objects. HADES was originally developed for nondestructive evaluation (NDE) applications, but could be a useful tool for simulation of portal imaging, proton therapy imaging, and synchrotron studies of tissue. In this paper we describe HADES' current capabilities and discuss plans for a major revision of the code.
Date: October 28, 2004
Creator: Aufderheide, Maurice B.; Henderson, Gary; Schach von Wittenau, Alexis E.; Slone, Dale M.; Barty, Anton & Martz, Harry E., Jr.
System: The UNT Digital Library
Application of the Extended Pairing Model to Heavy Isotopes (open access)

Application of the Extended Pairing Model to Heavy Isotopes

The binding energies of three isotopic chains ({sup 100-130}Sn, {sup 152-181}Yb, and {sup 181-202}Pb) are studied using the extended pairing model. By using the exact solvability of the model one determines the pairing strength G(A) that reproduces the experimental binding energies. For these isotopic chains, log (G(A)) has a smooth systematic behavior. In particular, G(A) for the Pb and Sn isotopes can be described by a two parameter expression that is inversely proportional to the dimensionality of the model space.
Date: September 28, 2004
Creator: Gueorguiev, V G; Pan, F & Draayer, J P
System: The UNT Digital Library
Direct Conversion of Carbon Fuels in a Molten Carbonate Fuel Cell (open access)

Direct Conversion of Carbon Fuels in a Molten Carbonate Fuel Cell

Anodes of elemental carbon may be discharged in a galvanic cell using a molten carbonate electrolyte, a nickel-foam anode-current collector, and a porous nickel air cathode to achieve power densities of 40-100 mW/cm{sup 2}. We report cell and anode polarization, surface area, primary particle size and a crystallization index for nine particulate carbon samples derived from fuel oil, methane, coal, charred biological material and petroleum coke. At 800 C, current densities of 50-125 mA/cm{sup 2} were measured at a representative cell voltage of 0.8 V. Power densities for cells with two carbon-anode materials were found to be nearly the same on scales of 2.8- and 60 cm{sup 2} active area. Constant current operation of a small cell was accompanied by constant voltage during multiple tests of 10-30 hour duration. Cell voltage fell off after the carbon inventory was consumed. Three different cathode structures are compared, indicating that an LLNL fabricated porous nickel electrode with <10 {micro}m pores provides improved rates compared with nickel foam with 100-300 {micro}m pores. Petroleum coke containing substantial sulfur and ash discharges at a slightly lower rate than purified petroleum coke. The sulfur leads to degradation of the anode current collector over time. A conceptual model …
Date: January 28, 2004
Creator: Cherepy, N. J.; Fiet, K. J.; Krueger, R.; Jankowski, Alan Frederic & Cooper, J. F.
System: The UNT Digital Library
An Investigation of Solid-State Amidization and Imidization Reactions in Vapor Deposited Poly (amic acid) (open access)

An Investigation of Solid-State Amidization and Imidization Reactions in Vapor Deposited Poly (amic acid)

The condensation polymerization reaction of 4,4'-oxydianiline (ODA) with pyromellitic dianhydride (PMDA) to form poly(amic acid) and the subsequent imidization reaction to form polyimide were investigated for films prepared using vapor deposition polymerization techniques. Fourier-transform infrared spectroscopy (FT-IR), thermal analysis, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) of films at different temperatures indicate that additional solid-state polymerization occurs prior to imidization reactions. Experiments reveal that, upon vapor deposition, poly(amic acid) oligomers form that have a number-average molecular weight of about 1500 Daltons. Between 100 - 130 C these chains undergo additional condensation reaction to form slightly higher molecular weight oligomers. Calorimetry measurements show that this reaction is exothermic ({Delta}H {approx} -30 J/g) with an activation energy of about 120 kJ/mol. Experimental reaction enthalpies are compared to results from ab initio molecular modeling calculations to estimate the number of amide groups formed. At higher temperatures (150 - 300 C) imidization of amide linkages occurs as an endothermic reaction ({Delta}H {approx} +120 J/g) with an activation energy of about 130 kJ/mol. Solid-state kinetics were found to depend on reaction conversion as well as the processing conditions used to deposit films.
Date: June 28, 2004
Creator: Anthamatten, M; Letts, S A; Day, K; Cook, R C; Gies, A P; Hamilton, T P et al.
System: The UNT Digital Library
General, Closed-Form Expressions for the Time-Domain Surface Impedances of a Homogeneous, Lossy Half-Space (open access)

General, Closed-Form Expressions for the Time-Domain Surface Impedances of a Homogeneous, Lossy Half-Space

The radio channel places fundamental limitations on the performance of wireless communication systems in tunnels and caves. The transmission path between the transmitter and receiver can vary from a simple direct line of sight to one that is severely obstructed by rough walls and corners. Unlike wired channels that are stationary and predictable, radio channels can be extremely random and difficult to analyze. In fact, modeling the radio channel has historically been one of the more challenging parts of any radio system design; this is often done using statistical methods. The mechanisms behind electromagnetic wave propagation are diverse, but can generally be attributed to reflection, diffraction, and scattering. Because of the multiple reflections from rough walls, the electromagnetic waves travel along different paths of varying lengths. The interactions between these waves cause multipath fading at any location, and the strengths of the waves decrease as the distance between the transmitter and receiver increases. As a consequence of the central limit theorem, the received signals are approximately Gaussian random process. This means that the field propagating in a cave or tunnel is typically a complex-valued Gaussian random process.
Date: January 28, 2004
Creator: Pao, H; Zhu, Z & Dvorak, S L
System: The UNT Digital Library
THE COLOR GLASS CONDENSATE: A SUMMARY OF KEY IDEAS AND RECENT DEVELOPMENTS. (open access)

THE COLOR GLASS CONDENSATE: A SUMMARY OF KEY IDEAS AND RECENT DEVELOPMENTS.

We summarize the theory and phenomenology of the Color Glass Condensate reviewed previously by E. Iancu and the author in hep-ph/0303204. In addition, we discuss some of the subsequent developments in the past year both in theory and in phenomenological applications.
Date: March 28, 2004
Creator: Venugopalan, R.
System: The UNT Digital Library
Effects of Model Resolution and Subgrid-Scale Physics on the Simulation of Daily Precipitation in the Continental United States (open access)

Effects of Model Resolution and Subgrid-Scale Physics on the Simulation of Daily Precipitation in the Continental United States

We analyze simulations of the global climate performed at a range of spatial resolutions to assess the effects of horizontal spatial resolution on the ability to simulate precipitation in the continental United States. The model investigated is the CCM3 general circulation model. We also preliminarily assess the effect of replacing cloud and convective parameterizations in a coarse-resolution (T42) model with an embedded cloud-system resolving model (CSRM). We examine both spatial patterns of seasonal-mean precipitation and daily-timescale temporal variability of precipitation in the continental United States. For DJF and SON, high-resolution simulations produce spatial patterns of seasonal-mean precipitation that agree more closely with observed precipitation patterns than do results from the same model (CCM3) at coarse resolution. However, in JJA and MAM, there is little improvement in spatial patterns of seasonal-mean precipitation with increasing resolution, particularly in the Southeast. This is owed to the dominance of convective (i.e., parameterized) precipitation in these two seasons. We further find that higher-resolution simulations have more realistic daily precipitation statistics. In particular, the well-known tendency at coarse resolution to have too many days with weak precipitation and not enough intense precipitation is partially eliminated in higher-resolution simulations. However, even at the highest resolution examined here …
Date: July 28, 2004
Creator: Duffy, P. B.; Iorio, J. P.; Govindasamy, B.; Thompson, S. L.; Khairoutdinov, M. & Randall, D.
System: The UNT Digital Library