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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 199 records · Page 11
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NASA NTRS1998

Time-Resolved O3 Chemical Chain Reaction Kinetics Via High-Resolution IR Laser Absorption Methods

Excimer laser photolysis in combination with time-resolved IR laser absorption detection of OH radicals has been used to study O3/OH(v = 0)/HO2 chain reaction kinetics at 298 K, (i.e.,(k(sub 1) is OH + 03 yields H02 + 02 and (k(sub 2) is H02 + 03 yields OH + 202). From time-resolved detection of OH radicals with high-resolution near IR laser absorption methods, the chain induction kinetics have been measured at up to an order of magnitude higher ozone concentrations ([03] less than or equal to 10(exp 17) molecules/cu cm) than accessible in previous studies. This greater dynamic range permits the full evolution of the chain induction, propagation, and termination process to be temporally isolated and measured in real time. An exact solution for time-dependent OH evolution under pseudo- first-order chain reaction conditions is presented, which correctly predicts new kinetic signatures not included in previous OH + 03 kinetic analyses. Specifically, the solutions predict an initial exponential loss (chain "induction") of the OH radical to a steady-state level ([OH](sub ss)), with this fast initial decay determined by the sum of both chain rate constants, k(sub ind) = k(sub 1) + k(sub 2). By monitoring the chain induction feature, this sum of the rate constants is determined to be k(sub ind) = 8.4(8) x 10(exp -14) cu cm/molecule/s for room temperature reagents. This is significantly higher than the values currently recommended for use in atmospheric models, but in excellent agreement with previous results from Ravishankara et al.

Kulcke, Axel↗
NASA NTRS1998

Tropical Oceanic Precipitation Processes over Warm Pool: 2D and 3D Cloud Resolving Model Simulations

Rainfall is a key link in the hydrologic cycle as well as the primary heat source for the atmosphere, The vertical distribution of convective latent-heat release modulates the large-scale circulations of the tropics, Furthermore, changes in the moisture distribution at middle and upper levels of the troposphere can affect cloud distributions and cloud liquid water and ice contents. How the incoming solar and outgoing longwave radiation respond to these changes in clouds is a major factor in assessing climate change. Present large-scale weather and climate models simulate cloud processes only crudely, reducing confidence in their predictions on both global and regional scales. One of the most promising methods to test physical parameterizations used in General Circulation Models (GCMS) and climate models is to use field observations together with Cloud Resolving Models (CRMs). The CRMs use more sophisticated and physically realistic parameterizations of cloud microphysical processes, and allow for their complex interactions with solar and infrared radiative transfer processes. The CRMs can reasonably well resolve the evolution, structure, and life cycles of individual clouds and cloud systems, The major objective of this paper is to investigate the latent heating, moisture and momenti,im budgets associated with several convective systems developed during the TOGA COARE IFA - westerly wind burst event (late December, 1992). The tool for this study is the Goddard Cumulus Ensemble (CCE) model which includes a 3-class ice-phase microphysical scheme, The model domain contains 256 x 256 grid points (using 2 km resolution) in the horizontal and 38 grid points (to a depth of 22 km depth) in the vertical, The 2D domain has 1024 grid points. The simulations are performed over a 7 day time period. We will examine (1) the precipitation processes (i.e., condensation/evaporation) and their interaction with warm pool; (2) the heating and moisture budgets in the convective and stratiform regions; (3) the cloud (upward-downward) mass fluxes in convective and stratiform regions; (4) characteristics of clouds (such as cloud size, updraft intensity and cloud lifetime) and the comparison of clouds with Radar observations. Differences and similarities in organization of convection between simulated 2D and 3D cloud systems. Preliminary results indicated that there is major differences between 2D and 3D simulated stratiform rainfall amount and convective updraft and downdraft mass fluxes.

Tao, W.- K.↗
NASA NTRS1997

Development of a prototype algorithm for the operational retrieval of height-resolved products from GOME

Global ozone monitoring experiment (GOME) level 2 products of total ozone column amounts have been generated on a routine operational basis since July 1996. These products and the level 1 radiance products are the major outputs from the ERS-2 ground segment GOME data processor (GDP) at DLR in Germany. Off-line scientific work has already shown the feasibility of ozone profile retrieval from GOME. It is demonstrated how the retrievals can be performed in an operational context. Height-resolved retrieval is based on the optimal estimation technique, #and cloud-contaminated scenes are treated in an equivalent reflecting surface approximation. The prototype must be able to handle GOME measurements routinely on a global basis. Requirements for the major components of the algorithm are described: this incorporates an overall strategy for operational height-resolved retrieval from GOME.

Spurr, Robert J. D.↗
NASA NTRS1999

Effects of Precipitation on Ocean Mixed-Layer Temperature and Salinity as Simulated in a 2-D Coupled Ocean-Cloud Resolving Atmosphere Model

A two-dimensional coupled ocean-cloud resolving atmosphere model is used to investigate possible roles of convective scale ocean disturbances induced by atmospheric precipitation on ocean mixed-layer heat and salt budgets. The model couples a cloud resolving model with an embedded mixed layer-ocean circulation model. Five experiment are performed under imposed large-scale atmospheric forcing in terms of vertical velocity derived from the TOGA COARE observations during a selected seven-day period. The dominant variability of mixed-layer temperature and salinity are simulated by the coupled model with imposed large-scale forcing. The mixed-layer temperatures in the coupled experiments with 1-D and 2-D ocean models show similar variations when salinity effects are not included. When salinity effects are included, however, differences in the domain-mean mixed-layer salinity and temperature between coupled experiments with 1-D and 2-D ocean models could be as large as 0.3 PSU and 0.4 C respectively. Without fresh water effects, the nocturnal heat loss over ocean surface causes deep mixed layers and weak cooling rates so that the nocturnal mixed-layer temperatures tend to be horizontally-uniform. The fresh water flux, however, causes shallow mixed layers over convective areas while the nocturnal heat loss causes deep mixed layer over convection-free areas so that the mixed-layer temperatures have large horizontal fluctuations. Furthermore, fresh water flux exhibits larger spatial fluctuations than surface heat flux because heavy rainfall occurs over convective areas embedded in broad non-convective or clear areas, whereas diurnal signals over whole model areas yield high spatial correlation of surface heat flux. As a result, mixed-layer salinities contribute more to the density differences than do mixed-layer temperatures.

Li, Xiaofan↗
NASA NTRS2000

Comments on "The Sensitivity Study of Radiative-Convective Equilibrium in the Tropics with a Convective Resolving Model"

In general, there are two broad scientific objectives when using cloud resolving models (CRMs or cloud ensemble models-CEMs) to study tropical convection. The first one is to use them as a physics resolving models to understand the dynamic and microphysical processes associated with the tropical water and energy cycles and their role in the climate system. The second approach is to use the CRMs to improve the representation of moist processes and their interaction with radiation in large-scale models. In order to improve the credibility of the CRMs and achieve the above goals, CRMs using identical initial conditions and large-scale influences need to produce very similar results. Two CRMs produced different statistical equilibrium (SE) states even though both used the same initial thermodynamic and wind conditions. Sensitivity tests to identify the major physical processes that determine the SE states for the different CRM simulations were performed. Their results indicated that atmospheric horizontal wind is treated quite differently in these two CRMs. The model that had stronger surface winds and consequently larger latent and sensible heat fluxes from the ocean produced a warmer and more humid modeled thermodynamic SE state. In addition, the domain mean thermodynamic state is more unstable for those experiments that produced a warmer and more humid SE state. Their simulated wet (warm and humid) SE states are thermally more stable in the lower troposphere (from the surface to 4-5 km in altitude). The large-scale horizontal advective effects on temperature and water vapor mixing ratio are needed when using CRMs to perform long-term integrations to study convective feedback under specified large-scale environments. In addition, it is suggested that the dry and cold SE state simulated was caused by enhanced precipitation but not enough surface evaporation. We find some problems with the interpretation of these three phenomena.

Tao, W.-K.↗
NASA NTRS2000

Resolving the Wind Structure of Eta Carinae

Space Telescope Imaging Spectrograph (STIS) spectral observations of Eta Carinae have resolved the wind structure of the star(s) from the central point source. These observations were done with a 52 x 0.1" aperture, resolving power of about 5000 and complete spectral coverage from 1640A to 10400A. Various broad stellar Lines are seen to change within the central 0.511 of the nebular region. The Balmer lines, relative to the continuum, drop in strength while some Fe II lines scale with the continuum. Other Fe II lines increase in intensity while still others decrease. The structure to the southeast of the central source shows considerable variation in the stellar line strengths. To the Northwest, the emission is dominated by the very bright nebular knots, Weigelt blobs B and D. Three sets of observations have been done: March 1998, February 1999 and March 2000 to monitor the spectral variations. The stellar, wind and nebular emission changes considerably during this two year period. This work was done under the STIS GTO and HST GO funding.

Gull, T.↗
NASA NTRS2001

Tropical Oceanic Precipitation Processes Over Warm Pool: 2D and 3D Cloud Resolving Model Simulations

Rainfall is a key link in the hydrologic cycle as well as the primary heat source for the atmosphere. The vertical distribution of convective latent-heat release modulates the large-scale circulations of the topics. Furthermore, changes in the moisture distribution at middle and upper levels of the troposphere can affect cloud distributions and cloud liquid water and ice contents. How the incoming solar and outgoing longwave radiation respond to these changes in clouds is a major factor in assessing climate change. Present large-scale weather and climate model simulate processes only crudely, reducing confidence in their predictions on both global and regional scales. One of the most promising methods to test physical parameterizations used in General Circulation Models (GCMs) and climate models is to use field observations together with Cloud Resolving Models (CRMs). The CRMs use more sophisticated and physically realistic parameterizations of cloud microphysical processes, and allow for their complex interactions with solar and infrared radiative transfer processes. The CRMs can reasonably well resolve the evolution, structure, and life cycles of individual clouds and clouds systems. The major objective of this paper is to investigate the latent heating, moisture and momentum budgets associated with several convective systems developed during the TOGA COARE IFA - westerly wind burst event (late December, 1992). The tool for this study is the Goddard Cumulus Ensemble (GCE) model which includes a 3-class ice-phase microphysics scheme.

Tao, W.-K.↗
NASA NTRS2001

Resolving the Structure of Ionized Helium in the Intergalactic Medium with the Far Ultraviolet Spectroscopic Explorer

The neutral hydrogen and the ionized helium absorption in the spectra of high-redshift quasi-stellar objects (QSOs) are unique probes of structure in the universe at epochs intermediate between the earliest density fluctuations seen in the cosmic background radiation and the distribution of galaxies visible today. We present Far-Ultraviolet Spectroscopic Explorer (FUSE) observations of the line of sight to the QSO HE2347-4342 in the 1000-1187 angstrom band at a resolving power of 15,000. Above redshift z = 2.7, the IGM is largely opaque in He II Ly-alpha (304 angstroms). At lower redshifts, the optical depth gradually decreases to a mean value tau = 1 at z = 2.4. We resolve the He II Ly-alpha absorption as a discrete forest of absorption lines in the z = 2.3 - 2.7 redshift range. Approximately 50% of these spectral features have H I counterparts with column densities N(sub HI) > 10(exp 12.3)/sq cm visible in a Keck spectrum. These account for most of the observed opacity in He II Ly-alpha. The remainder have N(sub HI) < 10(exp 12.3)/sq cm, below the threshold for current observations. A short extrapolation of the power-law distribution of H I column densities to lower values can account for these new absorbers. The He II to H I column density ratio eta averages approximately 80, consistent with photoionization of the IGM by a hard ionizing spectrum resulting from the integrated light of quasars at high redshift, but there is considerable scatter. Values of eta > 100 in many locations indicate that there may be localized contributions from starbursts or heavily filtered QSO radiation.

Kriss, G. A.↗
NASA NTRS2001

Time Resolved 3-D Mapping of Atmospheric Aerosols and Clouds During the Recent ARM Water Vapor IOP

The HARLIE lidar was deployed at the ARM SGP site in north central Oklahoma and recorded over 100 hours of data on 16 days between 17 September and 6 October 2000 during the recent Water Vapor Intensive Operating Period (IOP). Placed in a ground-based trailer for upward looking scanning measurements of clouds and aerosols, HARLIE provided a unique record of time-resolved atmospheric backscatter at 1 micron wavelength. The conical scanning lidar images atmospheric backscatter along the surface of an inverted 90 degree (full angle) cone up to an altitude of 20 km. 360 degree scans having spatial resolutions of 20 meters in the vertical and 1 degree in azimuth were obtained every 36 seconds. Various boundary layer and cloud parameters are derived from the lidar data, as well as atmospheric wind vectors where there is Sufficiently resolved structure that can be traced moving through the surface described by the scanning laser beam. Comparison of HARLIE measured winds with radiosonde measured winds validates the accuracy of this new technique for remotely measuring atmospheric winds without Doppler information.

Schwemmer, Geary↗
NASA NTRS2002

Mesoscale Convective Systems During SCSMEX: Simulations with a Regional Climate Model and a Cloud-Resolving Model

The South China Sea Monsoon Experiment (SCSMEX) was conducted in May-June 1998. One of its major objectives is to better understand the key physical processes for the onset and evolution of the summer monsoon over Southeast Asia and southern China (Lau et al. 2000). Multiple observation platforms (e.g., soundings, Doppler radar, ships, wind seafarers, radiometers, etc.) during SCSMEX provided a first attempt at investigating the detailed characteristics of convection and circulation changes, associated with monsoons over the South China Sea region. SCSMEX also provided precipitation derived from atmospheric budgets (Johnson and Ciesielski 2002) and comparison to those obtained from the Tropical Rainfall Measuring Mission (TRMM). In this paper, a regional climate model and a cloud-resolving model are used to perform multi-day integrations to understand the precipitation processes associated with the summer monsoon over Southeast Asia and southern China. The regional climate model is used to understand the soil - precipitation interaction and feedback associated with a flood event that occurred in and around China's Atlantic River during SCSMEX. Sensitivity tests on various land surface models, cumulus parameterization schemes (CASE), sea surface temperature (SST) variations and midlatitude influences are also performed to understand the processes associated with the onset of the monsoon over the S. China Sea during SCSMEX. Cloud-resolving models (CRMs) use more sophisticated and physically realistic parameterizations of cloud microphysical processes with very fine spatial and temporal resolution. One of the major characteristics of CRMs is an explicit interaction between clouds, radiation and the land/ocean surface. It is for this reason that GEWEX (Global Energy and Water Cycle Experiment) has formed the GCSS (GEWEX Cloud System Study) expressly for the purpose of improving the representation of the moist processes in large-scale models using CRMs. The Goddard Cumulus Ensemble (GCE) model is a CRM and is used to simulate convective systems associated with the onset of the South China Sea monsoon in 1998. The BRUCE model includes the same land surface model, cloud physics, and radiation scheme used in the regional climate model. A comparison between the results from the GCE model and regional climate model is performed.

Tao, W. K.↗
NASA NTRS2002

Convective Systems Over the Japan Sea: Cloud-Resolving Model Simulations

Wintertime observations of MCSs (Mesoscale Convective Systems) over the Sea of Japan - 2001 (WMO-01) were collected from January 12 to February 1, 2001. One of the major objectives is to better understand and forecast snow systems and accompanying disturbances and the associated key physical processes involved in the formation and development of these disturbances. Multiple observation platforms (e.g., upper-air soundings, Doppler radar, wind profilers, radiometers, etc.) during WMO-01 provided a first attempt at investigating the detailed characteristics of convective storms and air pattern changes associated with winter storms over the Sea of Japan region. WMO-01 also provided estimates of the apparent heat source (Q1) and apparent moisture sink (Q2). The vertical integrals of Q1 and Q2 are equal to the surface precipitation rates. The horizontal and vertical adjective components of Q1 and Q2 can be used as large-scale forcing for the Cloud Resolving Models (CRMs). The Goddard Cumulus Ensemble (GCE) model is a CRM (typically run with a 1-km grid size). The GCE model has sophisticated microphysics and allows explicit interactions between clouds, radiation, and surface processes. It will be used to understand and quantify precipitation processes associated with wintertime convective systems over the Sea of Japan (using data collected during the WMO-01). This is the first cloud-resolving model used to simulate precipitation processes in this particular region. The GCE model-simulated WMO-01 results will also be compared to other GCE model-simulated weather systems that developed during other field campaigns (i.e., South China Sea, west Pacific warm pool region, eastern Atlantic region and central USA).

Tao, Wei-Kuo↗
NASA NTRS2003

In-SITU, Time-resolved Raman Spectro-micro-topography of an Operating Lithium Ion Battery

A Raman microscope has been coupled to a computer-controlled, two-dimensional linear translator attached to a custom-designed, sealed optical chamber to allow in situ acquisition of space-, and time-resolved spectra of an operating thin graphite/LiCoO2 Li-ion battery. This unique arrangement made it possible to collect continuously series of Raman spectra from a sharply defined edge of the battery exposing the anode (A), separator (S), and cathode (C), during charge and discharge, while the device was moved back and forth under the fixed focused laser beam along an axis normal to the layered A/S/C plane. Clear spectral evidence was obtained for changes in the amount of Li(+) within particles of graphite in the anode, and, to a lesser extent, of LiCoO2 in the cathode, during battery discharge both as a function of position and time. Analysis of time-resolved Raman spectro-micro-topography (SMT) measurements of the type described in this work are expected to open new prospects for assessing the validity of theoretical models aimed at simulating the flow of Li(+) within Li-ion batteries under operating conditions.

Luo, Yu↗
NASA NTRS2004

Velocity and Temperature Measurement in Supersonic Free Jets Using Spectrally Resolved Rayleigh Scattering

The flow fields of unheated, supersonic free jets from convergent and convergent-divergent nozzles operating at M = 0.99, 1.4, and 1.6 were measured using spectrally resolved Rayleigh scattering technique. The axial component of velocity and temperature data as well as density data obtained from a previous experiment are presented in a systematic way with the goal of producing a database useful for validating computational fluid dynamics codes. The Rayleigh scattering process from air molecules provides a fundamental means of measuring flow properties in a non-intrusive, particle free manner. In the spectrally resolved application, laser light scattered by the air molecules is collected and analyzed using a Fabry-Perot interferometer (FPI). The difference between the incident laser frequency and the peak of the Rayleigh spectrum provides a measure of gas velocity. The temperature is measured from the spectral broadening caused by the random thermal motion and density is measured from the total light intensity. The present point measurement technique uses a CW laser, a scanning FPI and photon counting electronics. The 1 mm long probe volume is moved from point to point to survey the flow fields. Additional arrangements were made to remove particles from the main as well as the entrained flow and to isolate FPI from the high sound and vibration levels produced by the supersonic jets. In general, velocity is measured within +/- 10 m/s accuracy and temperature within +/- 10 K accuracy.

Panda, J.↗
NASA NTRS2004

Sensitivity of Simulated Warm Rain Formation to Collision and Coalescence Efficiencies, Breakup, and Turbulence: Comparison of Two Bin-Resolved Numerical Models

Numerical models that resolve cloud particles into discrete mass size distributions on an Eulerian grid provide a uniquely powerful means of studying the closely coupled interaction of aerosols, cloud microphysics, and transport that determine cloud properties and evolution. However, such models require many experimentally derived paramaterizations in order to properly represent the complex interactions of droplets within turbulent flow. Many of these parameterizations remain poorly quantified, and the numerical methods of solving the equations for temporal evolution of the mass size distribution can also vary considerably in terms of efficiency and accuracy. In this work, we compare results from two size-resolved microphysics models that employ various widely-used parameterizations and numerical solution methods for several aspects of stochastic collection.

Fridlind, Ann↗
NASA NTRS2005

Time and Space Resolved Wall Temperature Measurements during Nucleate Boiling with Constant Heat Flux Boundary Conditions

The lack of temporally and spatially resolved measurements under nucleate bubbles has complicated efforts to fully explain pool-boiling phenomena. The objective of this current work is to acquire time and space resolved temperature distributions under nucleate bubbles on a constant heat flux surface. This was performed using a microheater array with 100 micron resolution that allowed effectively simultaneous measurements of surface temperature while supplying a constant dissipative heat flux. This data is then correlated with high speed (> 1000Hz) visual recordings of the bubble growth and departure from the heater surface acquired from below and from the side of the heater. The data indicate that a significant source of energy during bubble nucleation and initial growth is the superheated layer around the bubble. Bubble coalescence was not observed to decrease surface temperature as significantly as bubble departure from the surface. Since bubble departure is typically followed by a sharp increase in the heater surface temperature, it is surmised that the departing bubble effectively removes the superheated layer, allowing a high local heat transfer rate with the bulk fluid through transient conduction/micro-convection during rewetting.

Myers, Jerry G.↗
NASA NTRS2005

Time and Space Resolved Heat Flux Measurements During Nucleate Boiling with Constant Heat Flux Boundary Conditions

The lack of temporally and spatially resolved measurements under nucleate bubbles has complicated efforts to fully explain pool-boiling phenomena. The objective of this current work was to acquire time and space resolved temperature distributions under nucleating bubbles on a constant heat flux surface using a microheater array with 100x 100 square microns resolution, then numerically determine the wall to liquid heat flux. This data was then correlated with high speed (greater than l000Hz) visual recordings of The bubble growth and departure from the heater surface acquired from below and from the side of the heater. The data indicate that microlayer evaporation and contact line heat transfer are not major heat transfer mechanisms for bubble growth. The dominant heat transfer mechanism appears to be transient conduction into the liquid as the liquid rewets the wall during the bubble departure process.

Yerramilli, Vamsee K.↗
NASA NTRS2004

Towards Measurement of the Time-resolved Heat Release of Protein Conformation Dynamics

We present a way to observe time-resolved heat release using a laminar flow diffusional mixer coupled with a highly sensitive infrared camera which measures the temperature change of the solvent. There are significant benefits to the use of laminar flow mixers for time-resolved calorimetry: (1) The thermal signal can be made position and time- stationary to allow for signal integration; (2) Extremely small volumes (nl/s) of sample are required for a measurement; (3) The same mixing environment can be observed spectroscopically to obtain state occupation information; (4) The mixer allows one to do out of equilibrium dynamic studies. The hope is that these measurements will allow us probe the non-equilibrium thermodynamics as a protein moves along a free energy trajectory from one state to another.

Puchalla, Jason↗
NASA NTRS2005

The Use of Mascons to Resolve Time-Variable Gravity from GRACE

We have analyzed GRACE Level 1B data to resolve time-variable gravity using a local mascon approach. The spherical harmonic solutions released to date resolve the signal from surface hydrology over land areas at spatial scales of 750 to 1000 km over one month intervals [Wahr et al., 2004; Tapley et al., 2004]. In our local approach, we solve explicitly for the mass of water in surface blocks using only the KBRR data collected as GRACE overflies the region of interest. The local representation of gravity minimizes leakage of errors from other areas due to aliasing or mismodelling. In this paper, we report on the analysis of GRACE data from January 2003 through August 2004 over three regions: the Amazon, the Indian subcontinent, and the continental United States. We solve for mass change at 10-day intervals using 4 deg x 4 deg blocks. We give an overview of our latest results, and we present the results of error analyses, and comparisons to both hydrology models and in-situ data.

Lemoine, Frank G.↗