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NASA NTRS2010

Aerosol gels

An improved process for the production of ultralow density, high specific surface area gel products is provided which comprises providing, in an enclosed chamber, a mixture made up of small particles of material suspended in gas; the particles are then caused to aggregate in the chamber to form ramified fractal aggregate gels. The particles should have a radius (a) of up to about 50 nm and the aerosol should have a volume fraction (f.sub.v) of at least 10.sup.-4. In preferred practice, the mixture is created by a spark-induced explosion of a precursor material (e.g., a hydrocarbon) and oxygen within the chamber. New compositions of matter are disclosed having densities below 3.0 mg/cc.

Sorensen, Christopher M.↗
NASA NTRS2010

Improving a Spectral Bin Microphysical Scheme Using TRMM Satellite Observations

Comparisons between cloud model simulations and observations are crucial in validating model performance and improving physical processes represented in the mod Tel.hese modeled physical processes are idealized representations and almost always have large rooms for improvements. In this study, we use data from two different sensors onboard TRMM (Tropical Rainfall Measurement Mission) satellite to improve the microphysical scheme in the Goddard Cumulus Ensemble (GCE) model. TRMM observed mature-stage squall lines during late spring, early summer in central US over a 9-year period are compiled and compared with a case simulation by GCE model. A unique aspect of the GCE model is that it has a state-of-the-art spectral bin microphysical scheme, which uses 33 different bins to represent particle size distribution of each of the seven hydrometeor species. A forward radiative transfer model calculates TRMM Precipitation Radar (PR) reflectivity and TRMM Microwave Imager (TMI) 85 GHz brightness temperatures from simulated particle size distributions. Comparisons between model outputs and observations reveal that the model overestimates sizes of snow/aggregates in the stratiform region of the squall line. After adjusting temperature-dependent collection coefficients among ice-phase particles, PR comparisons become good while TMI comparisons worsen. Further investigations show that the partitioning between graupel (a high-density form of aggregate), and snow (a low-density form of aggregate) needs to be adjusted in order to have good comparisons in both PR reflectivity and TMI brightness temperature. This study shows that long-term satellite observations, especially those with multiple sensors, can be very useful in constraining model microphysics. It is also the first study in validating and improving a sophisticated spectral bin microphysical scheme according to long-term satellite observations.

Li, Xiaowen↗
NASA NTRS2009

A Critical Look at Deriving Monthly Aerosol Optical Depth from Satellite Data

Satellite-derived aerosol data sets, such as those provided by NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) instruments, are greatly improving our understanding of global aerosol optical depth (AOD). Yet, there are sampling issues. MODIS specific orbital geometry, convolved with the need to avoid bright surfaces (glint, desert, clouds, etc.), means that AOD can be under- or over-sampled in places. When deriving downstream products, such as daily or monthly gridded AOD, one must consider the spatial and temporal density of the measurements relative to the gradients of the true AOD. Additionally, retrieval confidence criteria should be considered. Averaged products are highly dependent on choices made for data aggregation and weighting, and sampling errors can be further propagated when deriving regional or global mean AOD. Different choices for aggregation and weighting result in estimates of regional and global means varying by 30% or more. The impacts of a particular averaging algorithm vary by region and surface type and can be shown to represent different tolerance for clouds and retrieval confidence.

Levy, R. C.↗
NASA NTRS2011

Microgravity-Enhanced Stem Cell Selection

Stem cells, both embryonic and adult, promise to revolutionize the practice of medicine in the future. In order to realize this potential, a number of hurdles must be overcome. Most importantly, the signaling mechanisms necessary to control the differentiation of stem cells into tissues of interest remain to be elucidated, and much of the present research on stem cells is focused on this goal. Nevertheless, it will also be essential to achieve large-scale expansion and, in many cases, assemble cells in 3D as transplantable tissues. To this end, microgravity analog bioreactors can play a significant role. Microgravity bioreactors were originally conceived as a tool to study the cellular responses to microgravity. However, the technology can address some of the shortcomings of conventional cell culture systems; namely, the deficiency of mass transport in static culture and high mechanical shear forces in stirred systems. Unexpectedly, the conditions created in the vessel were ideal for 3D cell culture. Recently, investigators have demonstrated the capability of the microgravity bioreactors to expand hematopoietic stem cells compared to static culture, and facilitate the differentiation of umbilical cord stem cells into 3D liver aggregates. Stem cells are capable of differentiating into functional cells. However, there are no reliable methods to induce the stem cells to form specific cells or to gain enough cells for transplantation, which limits their application in clinical therapy. The aim of this study is to select the best experimental setup to reach high proliferation levels by culturing these cells in a microgravity-based bioreactor. In typical cell culture, the cells sediment to the bottom surface of their container and propagate as a one-cell-layer sheet. Prevention of such sedimentation affords the freedom for self-assembly and the propagation of 3D tissue arrays. Suspension of cells is easily achievable using stirred technologies. Unfortunately, in conventional bioreactors, stirring invokes deleterious forces that disrupt cell aggregation and results in cell death. First-generation rotating bioreactors provided rotation on the horizontal axis, which resulted in the suspension of cells without stirring, thus providing a suitable environment to propagate cells without sedimentation to a surface. The rotating wall bioreactors did not provide a way to remove air bubbles that were causing shear and disrupting 3D cultures. Johnson Space Center successfully engineered the hydrofocusing bioreactor (HFB) that resolved the problem of removing the air bubbles from the fluid medium of NASA's rotating-wall space bioreactors. The HFB uses the principle of hydrodynamic focusing that simultaneously produces a low-shear fluid culture environment and a variable hydrofocusing force that can control the movement, location, and removal of suspended cells, tissues, and air bubbles from the bioreactor. The HFB is a rotating, domeshaped cell culture vessel with a centrally located sampling port and an internal viscous spinner. The vessel and spinner can rotate at different speeds either in the same or opposite directions. Rotation of the vessel and viscous interaction at the spinner generate a hydrofocusing force. Adjusting the differential rotation rate between vessel and spinner controls the magnitude of the force.

Claudio, Pier Paolo↗
NASA NTRS2010

Modeling Nucleation and Grain Growth in the Solar Nebula: Initial Progress Report

The primitive solar nebula was a violent and chaotic environment where high energy collisions, lightning, shocks and magnetic re-connection events rapidly vaporized some fraction of nebular dust, melted larger particles while leaving the largest grains virtually undisturbed. At the same time, some tiny grains containing very easily disturbed noble gas signatures (e.g., small, pre-solar graphite or SiC particles) never experienced this violence, yet can be found directly adjacent to much larger meteoritic components (chondrules or CAIs) that did. Additional components in the matrix of the most primitive carbonaceous chondrites and in some chondritic porous interplanetary dust particles include tiny nebular condensates, aggregates of condensates and partially annealed aggregates. Grains formed in violent transient events in the solar nebula did not come to equilibrium with their surroundings. To understand the formation and textures of these materials as well as their nebular abundances we must rely on Nucleation Theory and kinetic models of grain growth, coagulation and annealing. Such models have been very uncertain in the past: we will discuss the steps we are taking to increase their reliability.

Nuth, Joseph A.↗
NASA NTRS2009

Multiscale Computer Simulation of Tensile and Compressive Strain in Polymer- Coated Silica Aerogels

While the low thermal conductivities of silica aerogels have made them of interest to the aerospace community as lightweight thermal insulation, the application of conformal polymer coatings to these gels increases their strength significantly, making them potentially useful as structural materials as well. In this work we perform multiscale computer simulations to investigate the tensile and compressive strain behavior of silica and polymer-coated silica aerogels. Aerogels are made up of clusters of interconnected particles of amorphous silica of less than bulk density. We simulate gel nanostructure using a Diffusion Limited Cluster Aggregation (DLCA) procedure, which produces aggregates that exhibit fractal dimensions similar to those observed in real aerogels. We have previously found that model gels obtained via DLCA exhibited stress-strain curves characteristic of the experimentally observed brittle failure. However, the strain energetics near the expected point of failure were not consistent with such failure. This shortcoming may be due to the fact that the DLCA process produces model gels that are lacking in closed-loop substructures, compared with real gels. Our model gels therefore contain an excess of dangling strands, which tend to unravel under tensile strain, producing non-brittle failure. To address this problem, we have incorporated a modification to the DLCA algorithm that specifically produces closed loops in the model gels. We obtain the strain energetics of interparticle connections via atomistic molecular statics, and abstract the collective energy of the atomic bonds into a Morse potential scaled to describe gel particle interactions. Polymer coatings are similarly described. We apply repeated small uniaxial strains to DLCA clusters, and allow relaxation of the center eighty percent of the cluster between strains. The simulations produce energetics and stress-strain curves for looped and nonlooped clusters, for a variety of densities and interaction parameters.

Good, Brian↗
NASA NTRS2011

Constraint Embedding Technique for Multibody System Dynamics

Multibody dynamics play a critical role in simulation testbeds for space missions. There has been a considerable interest in the development of efficient computational algorithms for solving the dynamics of multibody systems. Mass matrix factorization and inversion techniques and the O(N) class of forward dynamics algorithms developed using a spatial operator algebra stand out as important breakthrough on this front. Techniques such as these provide the efficient algorithms and methods for the application and implementation of such multibody dynamics models. However, these methods are limited only to tree-topology multibody systems. Closed-chain topology systems require different techniques that are not as efficient or as broad as those for tree-topology systems. The closed-chain forward dynamics approach consists of treating the closed-chain topology as a tree-topology system subject to additional closure constraints. The resulting forward dynamics solution consists of: (a) ignoring the closure constraints and using the O(N) algorithm to solve for the free unconstrained accelerations for the system; (b) using the tree-topology solution to compute a correction force to enforce the closure constraints; and (c) correcting the unconstrained accelerations with correction accelerations resulting from the correction forces. This constraint-embedding technique shows how to use direct embedding to eliminate local closure-loops in the system and effectively convert the system back to a tree-topology system. At this point, standard tree-topology techniques can be brought to bear on the problem. The approach uses a spatial operator algebra approach to formulating the equations of motion. The operators are block-partitioned around the local body subgroups to convert them into aggregate bodies. Mass matrix operator factorization and inversion techniques are applied to the reformulated tree-topology system. Thus in essence, the new technique allows conversion of a system with closure-constraints into an equivalent tree-topology system, and thus allows one to take advantage of the host of techniques available to the latter class of systems. This technology is highly suitable for the class of multibody systems where the closure-constraints are local, i.e., where they are confined to small groupings of bodies within the system. Important examples of such local closure-constraints are constraints associated with four-bar linkages, geared motors, differential suspensions, etc. One can eliminate these closure-constraints and convert the system into a tree-topology system by embedding the constraints directly into the system dynamics and effectively replacing the body groupings with virtual aggregate bodies. Once eliminated, one can apply the well-known results and algorithms for tree-topology systems to solve the dynamics of such closed-chain system.

Woo, Simon S.↗
NASA NTRS2012

An Initial Comparison of Selected Earth Departure Options for Solar Electric Propulsion Missions

Earth departure options such as the location for deployment, aggregation, and crew rendezvous as well as the type of propulsion leveraged for each mission phase effect overall mission performance metrics such as number of critical maneuvers, mass of propellant to achieve departure, and initial mass required in low Earth orbit. This paper identifies and compares a subset of tactical options for deployment, crew rendezvous, and Earth departure that leverage electric propulsion and hybrid chemical electric propulsion with a goal of improving system efficiency. Departure maneuver specific limitations and penalties are then identified for missions to specific targets for human interplanetary missions providing a better understanding of the impact of decisions related to aggregation and rendezvous locations as well as Earth departure maneuvers on overall system performance.

Merrill, Raymond Gabriel↗
NASA NTRS2012

Constructing a Database from Multiple 2D Images for Camera Pose Estimation and Robot Localization

The LMDB (Landmark Database) Builder software identifies persistent image features (landmarks) in a scene viewed multiple times and precisely estimates the landmarks 3D world positions. The software receives as input multiple 2D images of approximately the same scene, along with an initial guess of the camera poses for each image, and a table of features matched pair-wise in each frame. LMDB Builder aggregates landmarks across an arbitrarily large collection of frames with matched features. Range data from stereo vision processing can also be passed to improve the initial guess of the 3D point estimates. The LMDB Builder aggregates feature lists across all frames, manages the process to promote selected features to landmarks, and iteratively calculates the 3D landmark positions using the current camera pose estimations (via an optimal ray projection method), and then improves the camera pose estimates using the 3D landmark positions. Finally, it extracts image patches for each landmark from auto-selected key frames and constructs the landmark database. The landmark database can then be used to estimate future camera poses (and therefore localize a robotic vehicle that may be carrying the cameras) by matching current imagery to landmark database image patches and using the known 3D landmark positions to estimate the current pose.

Wolf, Michael↗
NASA NTRS2012

Cis-Lunar Base Camp

Historically, when mounting expeditions into uncharted territories, explorers have established strategically positioned base camps to pre-position required equipment and consumables. These base camps are secure, safe positions from which expeditions can depart when conditions are favorable, at which technology and operations can be tested and validated, and facilitate timely access to more robust facilities in the event of an emergency. For human exploration missions into deep space, cis-lunar space is well suited to serve as such a base camp. The outer regions of cis-lunar space, such as the Earth-Moon Lagrange points, lie near the edge of Earth s gravity well, allowing equipment and consumables to be aggregated with easy access to deep space and to the lunar surface, as well as more distant destinations, such as near-Earth Asteroids (NEAs) and Mars and its moons. Several approaches to utilizing a cis-lunar base camp for sustainable human exploration, as well as some possible future applications are identified. The primary objective of the analysis presented in this paper is to identify options, show the macro trends, and provide information that can be used as a basis for more detailed mission development. Compared within are the high-level performance and cost of 15 preliminary cis-lunar exploration campaigns that establish the capability to conduct crewed missions of up to one year in duration, and then aggregate mass in cis-lunar space to facilitate an expedition from Cis-Lunar Base Camp. Launch vehicles, chemical propulsion stages, and electric propulsion stages are discussed and parametric sizing values are used to create architectures of in-space transportation elements that extend the existing in-space supply chain to cis-lunar space. The transportation options to cis-lunar space assessed vary in efficiency by almost 50%; from 0.16 to 0.68 kg of cargo in cis-lunar space for every kilogram of mass in Low Earth Orbit (LEO). For the 15 cases, 5-year campaign costs vary by only 15% from 0.36 to 0.51 on a normalized scale across all campaigns. Thus the development and first flight costs of assessed transportation options are similar. However, the cost of those options per flight beyond the initial operational capability varies by 70% from 0.3 to 1.0 on a normalized scale. The 10-year campaigns assessed begin to show the effect of this large range of cost beyond initial operational capability as they vary approximately 25% with values from 0.75 to 1.0 on the normalized campaign scale. Therefore, it is important to understand both the cost of implementation and first use as well as long term utilization. Finally, minimizing long term recurring costs is critical to the affordability of future human space exploration missions. Finally minimizing long term recurring costs is critical to the affordability of future human space exploration missions.

Merrill, Raymond G.↗
NASA NTRS2012

High-Performance, Multi-Node File Copies and Checksums for Clustered File Systems

Modern parallel file systems achieve high performance using a variety of techniques, such as striping files across multiple disks to increase aggregate I/O bandwidth and spreading disks across multiple servers to increase aggregate interconnect bandwidth. To achieve peak performance from such systems, it is typically necessary to utilize multiple concurrent readers/writers from multiple systems to overcome various singlesystem limitations, such as number of processors and network bandwidth. The standard cp and md5sum tools of GNU coreutils found on every modern Unix/Linux system, however, utilize a single execution thread on a single CPU core of a single system, and hence cannot take full advantage of the increased performance of clustered file systems. Mcp and msum are drop-in replacements for the standard cp and md5sum programs that utilize multiple types of parallelism and other optimizations to achieve maximum copy and checksum performance on clustered file systems. Multi-threading is used to ensure that nodes are kept as busy as possible. Read/write parallelism allows individual operations of a single copy to be overlapped using asynchronous I/O. Multinode cooperation allows different nodes to take part in the same copy/checksum. Split-file processing allows multiple threads to operate concurrently on the same file. Finally, hash trees allow inherently serial checksums to be performed in parallel. Mcp and msum provide significant performance improvements over standard cp and md5sum using multiple types of parallelism and other optimizations. The total speed-ups from all improvements are significant. Mcp improves cp performance over 27x, msum improves md5sum performance almost 19x, and the combination of mcp and msum improves verified copies via cp and md5sum by almost 22x. These improvements come in the form of drop-in replacements for cp and md5sum, so are easily used and are available for download as open source software at http://mutil.sourceforge.net.

Kolano, Paul Z.↗
NASA NTRS2011

Assessment of Resistance of Bacillus Horneckiae Endospores to UV Radiation and Function of Their Extraneous Layer in Resistance

Spore-forming microbes are highly resistant to various physical and chemical conditions, which include ionizing and UV radiation, desiccation and oxidative stress, and the harsh environment of outer space or planetary surfaces. The spore's resistance might be due to their metabolically dormant state, and/or by the presence of a series of protective structures that encase the interior-most compartment, the core, which houses the spore chromosome. These spores have multiple layers surrounding the cell that are not found in vegetative cells, and some species have an outer layer of proteins and glycoproteins termed the "exosporium" or a fibrous "extraneous layer" (EL). Bacillus horneckiae is an EL-producing novel sporeformer isolated from a Phoenix spacecraft assembly clean room, and it has previously demonstrated resistance to UV radiation up to 1000 J/m(sup 2). The EL appears to bind B. horneckiae spores into large aggregations, or biofilms, and may confer some UV resistance to the spores. Multiple culturing and purification schemes were tried to achieve high purity spores because vegetative cells would skew UV resistance results. An ethanol-based purification scheme produced high purity spores. Selective removal of the EL from spores was attempted with two schemes: a chemical extraction method and physical extraction (sonication). Results from survival rates in the presence and absence of the external layer will provide a new understanding of the role of biofilms and passive resistance that may favor survival of biological systems in aggressive extra-terrestrial environments. The chemical extraction method decreased viable counts of spores and lead to an inconclusive change UV resistance relative to non-extracted spores. The physical extraction method lead to non-aggregated spores and did not alter viability; however, it produced UV resistance profiles similar to non-extracted spores. In addition to the EL-removal study, samples of B. horneckiae spores dried on aluminum coupons and exposed to increasing UV (200-400 nm range) levels (0 to 8.0 x 105 kJ/m(sup 2)) were tested for viability, which indicated that the maximum UV exposure level that still resulted in viable spores was 5.0 x 10? kJ/m(sup 2).

resistance↗
NASA NTRS2012

Scalable SCPPM Decoder

A decoder was developed that decodes a serial concatenated pulse position modulation (SCPPM) encoded information sequence. The decoder takes as input a sequence of four bit log-likelihood ratios (LLR) for each PPM slot in a codeword via a XAUI 10-Gb/s quad optical fiber interface. If the decoder is unavailable, it passes the LLRs on to the next decoder via a XAUI 10-Gb/s quad optical fiber interface. Otherwise, it decodes the sequence and outputs information bits through a 1-GB/s Ethernet UDP/IP (User Datagram Protocol/Internet Protocol) interface. The throughput for a single decoder unit is 150-Mb/s at an average of four decoding iterations; by connecting a number of decoder units in series, a decoding rate equal to that of the aggregate rate is achieved. The unit is controlled through a 1-GB/s Ethernet UDP/IP interface. This ground station decoder was developed to demonstrate a deep space optical communication link capability, and is unique in the scalable design to achieve real-time SCPP decoding at the aggregate data rate.

Quir, Kevin J.↗
NASA NTRS2007

Observed Enhancement of Reflectivity and Electric Field in Long-Lived Florida Anvils

A study of two long-lived Florida anvils showed that reflectivity >20 dBZ increased in area, thickness and sometimes magnitude at mid-level well downstream of the convective cores. In these same regions electric fields maintained strengths >10 kV m1 for many tens of minutes and became quite uniform over tens of kilometers. Millimetric aggregates persisted at 9 to 10 km for extended times and distances. Aggregation of ice particles enhanced by strong electric fields might have contributed to reflectivity growth in the early anvil, but is unlikely to explain observations further out in the anvil. The enhanced reflectivity and existence of small, medium and large ice particles far out into the anvil suggest that an updraft was acting, perhaps in weak convective cells formed by instability generated from the evaporation and melting of falling ice particles. We conclude that charge separation must have occurred in these anvils, perhaps at the melting level but also at higher altitudes, in order to maintain fields >10 kV m 1 at 9 to 10 km for extended periods of time over large distances. We speculate that charge separation occurred as a result of ice-ice particle collisions (without supercooled water being present) via either a non-inductive or perhaps even an inductive mechanism, given the observed broad ice particle spectra, the strong pre-existing electric fields and the many tens of minutes available for particle interactions. The observations, particularly in the early anvil, show that the charge structure in these anvils was quite complex.

Dye, James E.↗
NASA NTRS2013

Understanding the Lunar System Architecture Design Space

Based on the flexible path strategy and the desire of the international community, the lunar surface remains a destination for future human exploration. This paper explores options within the lunar system architecture design space, identifying performance requirements placed on the propulsive system that performs Earth departure within that architecture based on existing and/or near-term capabilities. The lander crew module and ascent stage propellant mass fraction are primary drivers for feasibility in multiple lander configurations. As the aggregation location moves further out of the lunar gravity well, the lunar lander is required to perform larger burns, increasing the sensitivity to these two factors. Adding an orbit transfer stage to a two-stage lunar lander and using a large storable stage for braking with a one-stage lunar lander enable higher aggregation locations than Low Lunar Orbit. Finally, while using larger vehicles enables a larger feasible design space, there are still feasible scenarios that use three launches of smaller vehicles.

Arney, Dale C.↗
NASA NTRS2013

Evaluation of Model Microphysics Within Precipitation Bands of Extratropical Cyclones

Recent studies evaluating the bulk microphysical schemes (BMPs) within cloud resolving models (CRMs) have indicated large uncertainties and errors in the amount and size distributions of snow and cloud ice aloft. The snow prediction is sensitive to the snow densities, habits, and degree of riming within the BMPs. Improving these BMPs is a crucial step toward improving both weather forecasting and climate predictions. Several microphysical schemes in the Weather Research and Forecasting (WRF) model down to 1.33‐km grid spacing are evaluated using aircraft, radar, and ground in situ data from the Global Precipitation Mission Coldseason Precipitation Experiment (GCPEx) experiment, as well as a few years (15 winter storms) of surface measurements of riming, crystal habit, snow density, and radar measurements at Stony Brook, NY (SBNY on north shore of Long Island) during the 2009-2012 winter seasons. Surface microphysical measurements at SBNY were taken every 15 to 30 minutes using a stereo microscope and camera, and snow depth and snow density were also recorded. During these storms, a vertically-pointing Ku-band radar was used to observe the vertical evolution of reflectivity and Doppler vertical velocities. A Particle Size and Velocity (PARSIVEL) disdrometer was also used to measure the surface size distribution and fall speeds of snow at SBNY. For the 15 cases at SBNY, the WSM6, Morrison (MORR), Thompson (THOM2), and Stony Brook (SBU-YLIN) BMPs were validated. A non-spherical snow assumption (THOM2 and SBU-YLIN) simulated a more realistic distribution of reflectivity than spherical snow assumptions in the WSM6 and MORR schemes. The MORR, WSM6, and SBU-YLIN schemes are comparable to the observed velocity distribution in light and moderate riming periods. The THOM2 is ~0.25 meters per second too slow with its velocity distribution in these periods. In heavier riming, the vertical Doppler velocities in the WSM6, THOM2, and MORR schemes were ~0.25 meters per second too slow, while the SBU-YLIN was 0.25 to 0.5 meters per second too fast. Overall, the BMPs simulate a size distribution close to the observed for D < 4 mm in the dendritic, plates, and mixed habit periods. The model BMPs underestimate the size distribution when large aggregates were observed. For D > 6 mm in the dendrites, side planes, and mixed habit periods, the BMPs are likely not simulating enough aggregation to create a larger size distribution, although the MORR (double moment) scheme seemed to perform best. These SBNY results will be compared with some results from GCPEx for a warm frontal snow band observed at 18 February 2012.

Colle, Brian A.↗
NASA NTRS2013

Evaluation of Model Microphysics within Precipitation Bands of Extratropical Cyclones

Recent studies evaluating the bulk microphysical schemes (BMPs) within cloud resolving models (CRMs) have indicated large uncertainties and errors in the amount and size distributions of snow and cloud ice aloft. The snow prediction is sensitive to the snow densities, habits, and degree of riming within the BMPs. Improving these BMPs is a crucial step toward improving both weather forecasting and climate predictions. Several microphysical schemes in the Weather Research and Forecasting (WRF) model down to 1.33‐km grid spacing are evaluated using aircraft, radar, and ground in situ data from the Global Precipitation Mission Coldseason Precipitation Experiment (GCPEx) experiment, as well as a few years (15 winter storms) of surface measurements of riming, crystal habit, snow density, and radar measurements at Stony Brook, NY (SBNY on north shore of Long Island) during the 2009-2012 winter seasons. Surface microphysical measurements at SBNY were taken every 15 to 30 minutes using a stereo microscope and camera, and snow depth and snow density were also recorded. During these storms, a vertically-pointing Ku-band radar was used to observe the vertical evolution of reflectivity and Doppler vertical velocities. A Particle Size and Velocity (PARSIVEL) disdrometer was also used to measure the surface size distribution and fall speeds of snow at SBNY. For the 15 cases at SBNY, the WSM6, Morrison (MORR), Thompson (THOM2), and Stony Brook (SBU-YLIN) BMPs were validated. A non-spherical snow assumption (THOM2 and SBU-YLIN) simulated a more realistic distribution of reflectivity than spherical snow assumptions in the WSM6 and MORR schemes. The MORR, WSM6, and SBU-YLIN schemes are comparable to the observed velocity distribution in light and moderate riming periods. The THOM2 is approx 0.25 m/s too slow with its velocity distribution in these periods. In heavier riming, the vertical Doppler velocities in the WSM6, THOM2, and MORR schemes were approx 0.25 m/s too slow, while the SBU-YLIN was 0.25 to 0.5 m/s too fast. Overall, the BMPs simulate a size distribution close to the observed for D < 4 mm in the dendritic, plates, and mixed habit periods. The model BMPs underestimate the size distribution when large aggregates were observed. For D > 6 mm in the dendrites, side planes, and mixed habit periods, the BMPs are likely not simulating enough aggregation to create a larger size distribution, although the MORR (double moment) scheme seemed to perform best. These SBNY results will be compared with some results from GCPEx for a warm frontal snow band observed at 18 February 2012.

Colle, Brian A.↗
NASA NTRS2014

A Preliminary Analysis of Precipitation Properties and Processes during NASA GPM IFloodS

The Iowa Flood Studies (IFloodS) is a NASA Global Precipitation Measurement (GPM) ground measurement campaign, which took place in eastern Iowa from May 1 to June 15, 2013. The goals of the field campaign were to collect detailed measurements of surface precipitation using ground instruments and advanced weather radars while simultaneously collecting data from satellites passing overhead. Data collected by the radars and other ground instruments, such as disdrometers and rain gauges, will be used to characterize precipitation properties throughout the vertical column, including the precipitation type (e.g., rain, graupel, hail, aggregates, ice crystals), precipitation amounts (e.g., rain rate), and the size and shape of raindrops. The impact of physical processes, such as aggregation, melting, breakup and coalescence on the measured liquid and ice precipitation properties will be investigated. These ground observations will ultimately be used to improve rainfall estimates from satellites and in particular the algorithms that interpret raw data for the upcoming GPM mission's Core Observatory satellite, which launches in 2014. The various precipitation data collected will eventually be used as input to flood forecasting models in an effort to improve capabilities and test the utility and limitations of satellite precipitation data for flood forecasting. In this preliminary study, the focus will be on analysis of NASA NPOL (S‐band, polarimetric) radar (e.g., radar reflectivity, differential reflectivity, differential phase, correlation coefficient) and NASA 2D Video Disdrometers (2DVDs) measurements. Quality control and processing of the radar and disdrometer data sets will be outlined. In analyzing preliminary cases, particular emphasis will be placed on 1) documenting the evolution of the rain drop size distribution (DSD) as a function of column melting processes and 2) assessing the impact of range on ground‐based polarimetric radar estimates of DSD properties.

Carey, Lawrence↗