Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Pr”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

94 {beta}-Decay Half-Lives of Neutron-Rich 55Cs to 67Ho: Experimental Feedback and Evaluation of the r-Process Rare-Earth Peak Formation

The β-decay half-lives of 94 neutron-rich nuclei 144$-$151 Cs, 146$-$154 Ba, 148$-$156 La, 150$-$158 Ce, 153$-$160 Pr, 156$-$162 Nd, 159$-$163 Pm, 160$-$166 Sm, 161$-$168 Eu, 165$-$170 Gd, 166$-$172 Tb, 169$-$173 Dy, 172$-$175 Ho, and two isomeric states 174m Er, 172m Dy were measured at the Radioactive Isotope Beam Factory, providing a new experimental basis to test theoretical models. Strikingly large drops of β-decay half-lives are observed at neutron-number N = 97 for 58 Ce, 59 Pr, 60 Nd, and 62 Sm, and N = 105 for 63 Eu, 64 Gd, 65 Tb, and 66 Dy. Lastly, features in the data mirror the interplay between pairing effects and microscopic structure. r-process network calculations performed for a range of mass models and astrophysical conditions show that the 57 half-lives measured for the first time play an important role in shaping the abundance pattern of rare-earth elements in the solar system

Wu, J.↗
DOE OSTI2024

Scanning SQUID study of ferromagnetism and superconductivity in infinite-layer nickelates

Infinite-layer nickelates R 1-x Sr x NiO 2 (R = La, Pr, Nd) are a class of superconductors with structural similarities to cuprates. Although long-range antiferromagnetic order has not been observed for these materials, magnetic effects such as antiferromagnetic spin fluctuations and spin-glass behavior have been reported. Different experiments have drawn different conclusions about whether the pairing symmetry is s or d wave. In this paper, we applied a scanning superconducting quantum interference device (SQUID) to probe the magnetic behavior of film samples of three infinite-layer nickelates (La 0.85 Sr 0.15 NiO 2 , Pr 0.8 Sr 0.2 NiO 2 , and Nd 0.775 Sr 0.225 NiO 2 ) grown on SrTiO 3 (STO), each with a nominal thickness of 20 unit cells. In all three films, we observed a ferromagnetic background. We also measured the magnetic susceptibility above the superconducting critical temperature in Pr 0.8 Sr 0.2 NiO 2 and La 0.85 Sr 0.15 NiO 2 and identified a non-Curie-Weiss dynamic susceptibility. Both magnetic features are likely due to NiO x nanoparticles. We investigated superconductivity in Pr 0.8 Sr 0.2 NiO 2 and Nd 0.775 Sr 0.225 NiO 2 , which exhibited inhomogeneous diamagnetic screening. The superfluid density inferred from the diamagnetic susceptibility in relatively homogeneous regions shows T-linear behavior in both samples. Finally, we observed superconducting vortices in Nd 0.775 Sr 0.225 NiO 2 . We determined a Pearl length of 330 µm for Nd 0.775 Sr 0.225 NiO 2 at 300 mK, both from the strength of the diamagnetism and from the size and shape of the vortices. These results highlight the importance of considering NiO x particles when interpreting experimental results for these films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Decentralized Voltage and Power Control of Multi-Machine Power Systems With Global Asymptotic Stability

Maintaining power system stability is becoming urgent due to the large-scale interconnection of power grids and the high penetration of uncertain renewable energy sources. The excitation control and governor control of synchronous generators have been considered as two crucial measures for enhancing the power system stability. However, a major challenge is to simultaneously achieve global asymptotic stability (GAS), voltage regulation (VR), and power regulation (PR) in the excitation and governor control. In this paper, a Lyapunov-based decentralized control (LBC) is proposed to address this challenge. The time-derivative of the Lyapunov function is designed by the feedback control of synchronous generators in order to guarantee GAS. VR and PR are ensured by considering voltage and power deviations as the feedback variables. The simulation results on the New-England ten-machine power system validate the effectiveness of the proposed LBC in improving power system transient stability and simultaneously achieving VR and PR. Although the proportional-integral- and power system stabilizer-based control can also perform VR and PR, the proposed control has much better dynamic performance and can more significantly improve the system transient stability.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2014

TU-C-12A-02: Development of a Multiparametric Statistical Response Map for Quantitative Imaging

Purpose: Quantitative imaging biomarkers (QIB) are becoming increasingly utilized in early phase clinical trials as a means of non-invasively assessing treatment response and associated response heterogeneity. The aim of this study was to develop a flexible multiparametric statistical framework to predict voxel-by-voxel response of several potential MRI QIBs. Methods: Patients with histologically proven glioblastomas (n=11) were treated with chemoradiation (with/without bevacizumab) and underwent one baseline and two mid-treatment (3–4wks) MRIs. Dynamic contrast-enhanced (3D FSPGR, 6.3sec/phase, 0.1 mmol/kg Gd-DTPA), dynamic susceptibility contrast (2D GRE-EPI, 1.5sec/phase, 0.2mmol/kg Gd-DTPA), and diffusion tensor (2D DW-EPI, b=0, 1200 s/mm{sup 2}, 27 directions) imaging acquisitions were obtained during each study. Mid-treatment and pre-treatment images were rigidly aligned, and regions of partial response (PR), stable disease (SD), and progressive disease (PD) were contoured in consensus by two experienced radiation oncologists. Voxels in these categories were used to train ordinal (PR<SD<PD) and logistic (PR/SD<PD) models incorporating the apparent diffusion coefficient, fractional anisotropy, Ktrans, ve, vp, and relative cerebral blood volume imaging biomarkers, as well as treatment type. Leave-one-out cross-validation was performed at the patient level to assess model prediction accuracy. Results: Ordinal regression resulted in model prediction accuracies of 60% (PR), 0% (SD), 81% (PD), and 69% (overall), with coefficients of variation (COV) of 9.4%, 9.6%, and 23.6%, respectively. Logistic regression resulted in accuracies of 82.0% (PR/SD), 46.2% (PD), and 76.2% (overall) with COVs of 22.4%, 45.7%, and 23.8%, respectively. Conclusion: Despite limited patient numbers, this feasibility pilot study demonstrates that ordinal and logistic regression models potentially provide a flexible statistical framework for incorporating longitudinal multiparametric quantitative imaging data and, for these particular data, can potentially distinguish PR from PD. Additional training data exhibiting a full range of treatment responses is expected to allow prediction of all three treatment outcomes. Moreover, these models are extensible to multi-modality, multiparametric analyses.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

TU-AB-201-10: Novel Conformal Skin Brachytherapy Device

Purpose: A novel conformal skin brachytherapy (CSBT) device was developed to provide patient specific treatment for small inoperable lesions and irregular surfaces that are not good candidates for electron external beam, e.g. eyelids, nose, lips, ears, etc. Methods: A prototype was built and tested using radioactive seeds spaced by 1.5 mm attached to a 3D printed template. Seeds were allowed to move independently at treatment surface to conform to target geometry. Beta-emitter Praseodymium-142 (half-life: 19.12 h, average beta energy: 809 keV) and Iodine-125 Model 6711 (half-life: 59.4 days, average gamma energy: 28 keV) seeds were used to test the feasibility of the device in solid water phantom for different prescription depths and surface areas. Percent depth doses and dose profiles were analyzed. MCNPX2.6 Monte Carlo Simulation and Gafchromic EBT3 film measurements were performed for a single Pr-142 seed. Treatment with nineteen I-125 seeds was planned in BrachyVision and measured experimentally for a total dose of 500 cGy at 5.0 mm depth. Results: For a single Pr-142 seed, dose was 500.0 cGy at surface and 17.4 cGy at 5.00 mm. BrachyVision planned and film doses for I-125 seed matrix were 500 cGy and 473.5 cGy at 5 mm depth and 171.0 cGy and 201.0 cGy at 10 mm depth. Total covered surface area for Pr-142 and I-125 were 2.35 mm{sup 2} and 88.24 mm{sup 2} respectively. Profile dose fall-off showed to be very conformal to contact area with 50% of the total surface dose from a single Pr-142 and array of I-125 seeds being deposited at 0.72 mm and 0.65 mm respectively from the central axis. Conclusion: CSBT device provides a high conformal dose to small surfaces. BrachyVision can be used to predict clinical dose distributions for multiple seeds matrix. Different radioactive seeds can be used to suit prescription depth and treatment area.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-F-J-184: Proton Computed Tomography Using 1D Silicon Diode Array

Purpose: Proton radiography and proton computed tomography (PCT) can be used to measure proton stopping power directly. However, practical and cost effective proton imaging detectors are not widely available. In this study, the authors investigated the feasibility of proton imaging using a silicon diode array. Methods: A one-dimensional silicon-diode detector array (1DSDA) was aligned with the central axis (CAX) of the proton beam. Polymethyl methacrylate (PMMA) slabs were used to find the correspondence between the water equivalent thickness (WET) and 1DSDA channel number. 2D proton radiographs (PR) were obtained by translation and rotation of a phantom relative to CAX while the proton nozzle and 1DSDA were kept stationary. A PCT image of one slice of the phantom was reconstructed using filtered backprojection. Results: PR and PCT images of the PMMA cube were successfully acquired using the 1DSDA. The WET of the phantom was measured using PR data with an accuracy of 4.2% or better. Structures down to 1 mm in size could be resolved. Reconstruction of a PCT image showed very good agreement with simulation. Limitations in spatial resolution are attributed to limited spatial sampling, beam collimation, and proton scatter. Conclusion: The results demonstrate the feasibility of using silicon diode arrays for proton imaging. Such a device can potentially offer fast image acquisition, high spatial and energy resolution for PR and PCT.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

TH-CD-209-03: Feasibility of CBCT-Based Proton Dose Calculation Using a Histogram-Matching Algorithm in Proton Beam Therapy

Purpose: The aim of this study was to confirm On-Board Imager cone-beam computed tomography (CBCT) using a histogram-matching algorithm as a useful method for proton dose calculation in head and neck radiotherapy. Methods: We studied one head and neck phantom and ten patients with head and neck cancer treated using intensity-modulated radiation therapy (IMRT) and proton beam therapy. We modified Hounsfield unit (HU) values of CBCT (mCBCT) using a histogram-matching algorithm. In order to evaluate the accuracy of the proton dose calculation, we compared dose differences in dosimetric parameters (Dmean) for clinical target volume (CTV), planning target volume (PTV) and left parotid and proton ranges (PR) between the planning CT (reference) and CBCT or mCBCT, and gamma passing rates of CBCT and mCBCT. To minimize the effect of organ deformation, we also performed image registration. Results: For patients, the average differences in Dmean for CTV, PTV, and left parotid between planning CT and CBCT were 1.63 ± 2.34%, 3.30 ± 1.02%, and 5.42 ± 3.06%, respectively. Similarly, the average differences between planning CT and mCBCT were 0.20 ± 0.19%, 0.58 ±0.43%, and 3.53 ±2.40%, respectively. The average differences in PR between planning CT and CBCT or mCBCT of a 50° beam for ten patients were 2.1 ± 2.1 mm and 0.3 ± 0.5 mm, respectively. Similarly, the average differences in PR of a 120° beam were 2.9 ± 2.6 mm and 1.1 ± 0.9 mm, respectively. The average dose and PR differences of mCBCT were smaller than those of CBCT. Additionally, the average gamma passing rates of mCBCT were larger than those of CBCT. Conclusion: We evaluated the accuracy of the proton dose calculation in CBCT and mCBCT with the image registration for ten patients. Our results showed that HU modification using a histogram-matching algorithm could improve the accuracy of the proton dose calculation.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Light-induced protein structural dynamics in bacteriophytochrome revealed by time-resolved x-ray solution scattering

Bacteriophytochromes (BphPs) are photoreceptors that regulate a wide range of biological mechanisms via red light–absorbing (Pr)–to–far-red light–absorbing (Pfr) reversible photoconversion. The structural dynamics underlying Pfr-to-Pr photoconversion in a liquid solution phase are not well understood. We used time-resolved x-ray solution scattering (TRXSS) to capture light-induced structural transitions in the bathy BphP photosensory module of Pseudomonas aeruginosa. Kinetic analysis of the TRXSS data identifies three distinct structural species, which are attributed to lumi-F, meta-F, and Pr, connected by time constants of 95 μs and 21 ms. Structural analysis based on molecular dynamics simulations shows that the light activation of PaBphP accompanies quaternary structural rearrangements from an “II”-framed close form of the Pfr state to an “O”-framed open form of the Pr state in terms of the helical backbones. This study provides mechanistic insights into how modular signaling proteins such as BphPs transmit structural signals over long distances and regulate their downstream biological responses.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Intermediate Temperature Proton‐Conducting Solid Oxide Electrolysis Cells with Improved Performance and Durability

Technical understanding: A high-performance and stable intermediate temperature proton-conducting solid oxide electrolysis cell (PCEC) will add significantly to the hydrogen roadmap of EERE. However, the low electrocatalytic activity of the air electrode and the instability of the electrolyte are technical barriers. In this research, we utilized computational fluid dynamic modeling and materials/microstructure engineering to investigate the complex reaction chain and to improve the performance and reliability of the protonic ceramic electrochemical cells. An active and stable Pr 1.8 Ba 0.2 NiO 4+δ -BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3-δ (BZCYYb) scaffold conformal coating electrode was rationally designed where the robust Pr 1.8 Ba 0.2 NiO 4+δ functions both as a catalytic active and a protective layer. The PCECs with porosity-optimized scaffold conformal coating electrodes demonstrate 1.46 Acm -2 under 1.3 V at 600°C, which is among the highest in recent years. The final optimization by computational fluid dynamic modeling and conformal coating technique was applied to evolve the PCEC air electrode from Pr 2 NiO 4+δ to Pr 1.8 Ba 0.2 NiO 4+δ -BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3-δ scaffold conformal coating. The electrolysis current was boosted from 0.445A/cm 2 to 1.46A/cm 2 at 600°C and 1.3V. A superior low degradation rate of 1mV/kh was achieved in a 5000-hour of operation. Technical effectiveness and economic feasibility: The effectiveness of this TCO conformal coating on electrolyte backbone as air electrode has been proven by long-term demonstration. Based on the highly conductive BZCYYb electrolyte and the TCO steam electrode PNO, this project rationally took advantage of the existent materials to structure a PCEC device with high TRL and low risk. The solution infiltration method used to structure the conformal coating is a standard method used by the solid oxide cell community. Very minimal adoption is needed in the current SOC fabrication process. It is a cost-effective, scalable method for manufacturing, and brings up remarkable impact on the current technical status of PCEC. Benefit to the public: The findings in the research showed the industry that the severe challenge in PCEC can be overcome in a practical way. A various energy-hydrogen ecosystem is not beyond reach. The success of this technology provides sustainable and affordable H 2 to society. It will stimulate investment from the governmental and private sectors in response to the device manufacture and deployment, and the related infrastructure construction. It will generate high-pay domestic jobs and environmental benefits to the general public in the United States.

08 HYDROGEN↗
DOE OSTI2017

Measure the Propagation of a Halo CME and Its Driven Shock with the Observations from a Single Perspective at Earth

We present a detailed study of an Earth-directed coronal mass ejection (full-halo CME) event that happened on 2011 February 15, making use of white-light observations by three coronagraphs and radio observations by Wind /WAVES. We applied three different methods to reconstruct the propagation direction and traveling distance of the CME and its driven shock. We measured the kinematics of the CME leading edge from white-light images observed by Solar Terrestrial Relations Observatory ( STEREO ) A and B , tracked the CME-driven shock using the frequency drift observed by Wind /WAVES together with an interplanetary density model, and obtained the equivalent scattering centers of the CME by the polarization ratio (PR) method. For the first time, we applied the PR method to different features distinguished from LASCO/C2 polarimetric observations and calculated their projections onto white-light images observed by STEREO-A and STEREO-B . By combining the graduated cylindrical shell (GCS) forward modeling with the PR method, we proposed a new GCS-PR method to derive 3D parameters of a CME observed from a single perspective at Earth. Comparisons between different methods show a good degree of consistence in the derived 3D results.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Scaling of Turbulent Viscosity and Resistivity: Extracting a Scale-dependent Turbulent Magnetic Prandtl Number

Turbulent viscosity νt and resistivity ηt are perhaps the simplest models for turbulent transport of angular momentum and magnetic fields, respectively. The associated turbulent magnetic Prandtl number Pr t ≡ ν t /η t has been well recognized to determine the final magnetic configuration of accretion disks. Here, we present an approach to determining these "effective transport" coefficients acting at different length scales using coarse-graining and recent results on decoupled kinetic and magnetic energy cascades. By analyzing the kinetic and magnetic energy cascades from a suite of high-resolution simulations, we show that our definitions of ν t , η t , and Pr t have power-law scalings in the "decoupled range." We observe that Pr t ≈ 1–2 at the smallest inertial-inductive scales, increasing to ≈5 at the largest scales. Furthermore, based on physical considerations, our analysis suggests that Pr t has to become scale independent and of order unity in the decoupled range at sufficiently high Reynolds numbers (or grid resolution) and that the power-law scaling exponents of velocity and magnetic spectra become equal. In addition to implications for astrophysical systems, the scale-dependent turbulent transport coefficients offer a guide for large-eddy simulation modeling.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Long-term observations of cloud condensation nuclei over the Amazon rain forest - Part 2: Variability and characteristics of biomass burning, long-range transport, and pristine rain forest aerosols

For this study, size-resolved measurements of atmospheric aerosol and cloud condensation nuclei (CCN) concentrations and hygroscopicity were conducted over a full seasonal cycle at the remote Amazon Tall Tower Observatory (ATTO, March 2014–February 2015). In a preceding companion paper, we presented annually and seasonally averaged data and parametrizations (Part 1; Pöhlker et al., 2016a). In the present study (Part 2), we analyze key features and implications of aerosol and CCN properties for the following characteristic atmospheric conditions: Empirically pristine rain forest (PR) conditions, where no influence of pollution was detectable, as observed during parts of the wet season from March to May. The PR episodes are characterized by a bimodal aerosol size distribution (strong Aitken mode with D Ait ≈ 70nm and N Ait ≈ 160cm -3 , weak accumulation mode with D acc ≈ 160nm and N acc ≈ 90cm -3 ), a chemical composition dominated by organic compounds, and relatively low particle hygroscopicity (κ Ait ≈ 0.12, κ acc ≈ 0.18). Long-range-transport (LRT) events, which frequently bring Saharan dust, African biomass smoke, and sea spray aerosols into the Amazon Basin, mostly during February to April. The LRT episodes are characterized by a dominant accumulation mode ( DAit ≈ 80nm, N Ait ≈ 120cm -3 vs. D acc ≈ 180nm, N acc ≈ 310cm -3 ), an increased abundance of dust and salt, and relatively high hygroscopicity (κ Ait ≈ 0.18, κ acc ≈ 0.35). The coarse mode is also significantly enhanced during these events. Biomass burning (BB) conditions characteristic for the Amazonian dry season from August to November. The BB episodes show a very strong accumulation mode (D Ait ≈ 70nm, N Ait ≈ 140cm -3 vs. D acc ≈ 170nm, N acc ≈ 3400cm -3 ), very high organic mass fractions (~90%), and correspondingly low hygroscopicity (κ Ait ≈ 0.14, κ acc ≈ 0.17). Mixed-pollution (MPOL) conditions with a superposition of African and Amazonian aerosol emissions during the dry season. During the MPOL episode presented here as a case study, we observed African aerosols with a broad monomodal distribution (D ≈ 130nm, N CN, 10 ≈ 1300cm -3 ), with high sulfate mass fractions (~20%) from volcanic sources and correspondingly high hygroscopicity (κ < 100 nm ≈ 0.14, κ > 10 nm ≈ 0.22), which were periodically mixed with fresh smoke from nearby fires (D ≈ 110nm, N CN, 10 ≈ 2800cm -3 ) with an organic-dominated composition and sharply decreased hygroscopicity (κ < 150 nm ≈ 0.10, κ > 150 nm ≈ 0.20). Insights into the aerosol mixing state are provided by particle hygroscopicity (κ) distribution plots, which indicate largely internal mixing for the PR aerosols (narrow κ distribution) and more external mixing for the BB, LRT, and MPOL aerosols (broad κ distributions). The CCN spectra (CCN concentration plotted against water vapor supersaturation) obtained for the different case studies indicate distinctly different regimes of cloud formation and microphysics depending on aerosol properties and meteorological conditions. The measurement results suggest that CCN activation and droplet formation in convective clouds are mostly aerosol-limited under PR and LRT conditions and updraft-limited under BB and MPOL conditions. Normalized CCN efficiency spectra (CCN divided by aerosol number concentration plotted against water vapor supersaturation) and corresponding parameterizations (Gaussian error function fits) provide a basis for further analysis and model studies of aerosol–cloud interactions in the Amazon.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1990

Studies of iron impurities in YxPr1-xBa2Cu3O7-delta

Pr is the only rare earth which, when substituted for Y in YBa2Cu3O7, significantly alters the superconducting transition temperature T(sub c) without changing the crystal structure. For YxPr1-xBa2Cu3O7-delta with delta approx. equal to 0, T(sub c) is reduced rapidly as x is increased, reaching zero for x about 0.5. For x above 0.5 the compound is antiferromagnetic with a Neel temperature that increases with increasing x, rising to above room temperature for x near 1. A similar behavior is observed when the oxygen deficit delta is increased from zero to 1 with x=0. For the case of Pr substitution, the drop in T(sub c) is believed due to magnetic interactions. For the case of varying delta with x=0, the drop can be attributed to a combination of magnetic interactions, band filling, and changes in crystal structure. To study these effects, the Mossbauer effect of 57 Fe atoms substituted for the Cu atoms has been observed as a function of delta, x, and temperature. The observed spectra are all well described by a two quadrupole-split pairs, a central singlet, and a six-line magnetic hyperfine field pattern. For several Pr compositions both delta and temperature were varied, and the results support the hypothesis that a magnetic interaction exists between the Fe in the Cu lattice and the substitutional Pr atoms.

Swartzendruber, L. J.↗
NASA NTRS1991

Turbulent Prandtl number in the near-wall region of a turbulent channel flow

Calculations are presented of the turbulent Prandtl number Pr(T) in the near-wall region of a turbulent channel flow. It is shown that only the first-order terms in the Taylor series expansions for the eddy diffusivity and the Pr(T) are independent of the molecular Prandtl number Pr, at least to a first approximation. Also presented are calculations of the near-wall behavior of the correlations between temperature fluctuations and velocity fluctuations, as well as for their dependence on Pr.

Antonia, R. A.↗
NASA NTRS1996

Oscillatory Thermocapillary Convection

Stability analysis of thermocapillary convection in rectangular cavities is performed using direct numerical simulation. The influence of the Reynolds number (Re), the fluid Prandtl number (Pr) and cavity aspect ratio (Ar) on the motion is investigated. Neutral stability curves for transition to time-dependent convection are delineated in the Re-Ar plane for fluids with Pr=1.0, 4.4, 6.78, and 10. Several interesting features of these diagrams are discussed. One important conclusion is that Ar(epsilon tau) increases as Pr decreases. Thus large values of both Ar and Re are necessary to induce thermocapillary oscillations for small Pr fluids such as liquid metals and semiconductor melts. Energy analysis is also performed for the oscillatory flow in the neighborhood of critical points in order to gain insight into the mechanisms leading to instability.

Xu, Jieyong↗
NASA NTRS1999

TMI Rain Rate Estimation Over Land and Ocean Utilizing Convective and Stratiform Discrimination

Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) radiometer brightness temperature data in the 85 GHz channel (T85) reveal distinct local minima in a regional map containing a Mesoscale Convective System (MCS). This is because of relatively small footprint size (approximately 5.5 km) and strong extinction properties in this channel of the TMI. A map of rain rate for that region, deduced from simultaneous measurements made by the Precipitation Radar (PR) on board the TRMM satellite, reveals that these T85 minima, produced by scattering, correspond to local PR rain maxima. Utilizing the PR rain rate map as a guide, we infer from TMI data the presence of three different kinds of thunderstorms or Cbs. They are young, mature, and decaying Cbs that have a scale of about 20 km on the average. Two parameters enable us to infer these three kinds of Cbs objectively: a) the magnitude of scattering depression deduced from local T85 minima and b) the mean horizontal gradient of T85 around such minima. Knowing the category of a given Cb, we can estimate the rain rate associated with it. Such estimation is done with the help of relationships linking T85 minimum to rain rate in each Cb type. Similarly, a weak background rain rate in all the areas where T85 is less than 260 K is deduced with another relationship linking T85 to rain rate. In our rain retrieval model, this background rain constitutes the stratiform rain where the Cbs are absent. Initially, these relationships are optimized or tuned utilizing the PR and TMI data of a few MCS events. After such tuning, the model is applied to independent MCS cases. The areal distribution of light (1-10 mm/hr), moderate (10-20 mm/hr), and intense (> 20 mm/hr) rain rates are retrieved satisfactorally. Accuracy in the estimates of the light, moderate and intense rain areas and the mean rain rates associated with such areas in these independent MCS cases is on the average about 15%. Taking advantage of this ability of our retrieval method, one could derive the latent heat input into the atmosphere over the 760 km wide swath of the TMI radiometer in the tropics.

Prabhakara, C.↗
NASA NTRS1999

A TRMM Microwave Radiometer Rain Rate Estimation Method with Convective and Stratiform Discrimination

Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) radiometer brightness temperature data in the 85 GHz channel (T85) reveal distinct local minima (T85min) in a regional map containing a Mesoscale Convective System (MCS). This is because of relatively small footprint size (approximately 5.5 km) and strong extinction properties in this channel of the TMI. A map of surface rain rate for that region, deduced from simultaneous measurements made by the Precipitation Radar (PR) on board the TRMM satellite, reveals that these T85(sub min), produced by scattering, correspond to local PR rain maxima. Utilizing the PR rain rate map as a guide, we infer empirically from TMI data the presence of three different kinds of thunderstorms or Cbs. These Cbs are classified as young, mature, and decaying types, and are assumed to have a scale of about 20 km on the average. Two parameters are used to classify these three kinds of Cbs based on the T85 data: a) the magnitude of scattering depression deduced from local T85(sub min) and b) the mean horizontal gradient of T85 around such minima. Knowing the category of a given Cb, we can estimate the rain rate associated with it. Such estimation is done with the help of relationships linking T85min to rain rate in each Cb type. Similarly, a weak background rain rate in all the areas where T85 is less than 260 K is deduced with another relationship linking T85 to rain rate. In our rain retrieval model, this background rain constitutes stratiform rain where the Cbs are absent. Initially, these relationships are optimized or tuned utilizing the PR and TMI data of a few MCS events. After such tuning, the model is applied to independent MCS cases. The areal distribution of light (1-10 mm/hr), moderate (10-20 mm/hr), and intense (>= 20 mm/hr) rain rates are retrieved satisfactorily. Accuracy in the estimates of the light, moderate, and intense rain areas and the mean rain rates associated with such areas in these independent MCS cases is on the average about 15 %. Taking advantage of this ability of our retrieval method, one could derive the latent heat input into the atmosphere over the 760 km wide swath of the TMI radiometer in the tropics.

Prabhakara, C.↗