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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Characterization of the Optical and X-ray Properties of the Northwestern Wisps in the Crab Nebula

We have studied the variability of the Crab Nebula both in the visible and in X -rays. Optical observations were obtained using the Nordic Optical Telescope in La Palma and X -ray observations were made with the Chandra X -Ray Observatory. We observe wisps forming and peeling off from the region commonly associated with the termination shock of the pulsar wind. We measure a number of properties of the wisps to the Northwest of the pulsar. We find that the exact locations of the wisps in the optical and in X-rays are similar but not coincident, with the X-ray wisp preferentially located closer to the pulsar. Our measurements and their implications are interpreted in terms of a MHD model. We find that the optical wisps are more strongly Doppler boosted than X-ray wisps, a result inconsistent with current MHD simulations. Indeed the inferred optical boosting factors exceed MHD simulation values by about one order of magnitude. These findings suggest that the optical and X-ray wisps are not produced by the same particle distribution, a result which is consistent with the spatial differences. Further, the X -ray wisps and optical wisps are apparently developing independently from each other, but every time a new X ]ray wisp is born so is an optical wisp, thus pointing to a possible common cause or trigger. Finally, we find that the typical wisp formation rate is approximately once per year, interestingly at about the same rate of production of the large gamma-ray flares.

Weisskopf, M. C.↗
NASA NTRS2009

Case Studies of Aerosol Remote Sensing in the Vicinity of Clouds

Studying the spatial variability of aerosol properties in the vicinity of clouds is essential to our ability to determine aerosol direct and indirect effects on climate. In this paper, we describe aerosol observations collected near cloud edges by an airborne Sun photometer over dark ocean waters. Focusing on case studies of aerosol measurements near eight cloud edges within a dissipating stratiform cloud deck, we compare the airborne Sun photometer observations to retrievals of aerosol properties using the standard Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol algorithm applied to 500-m-resolution MODIS spectral reflectances. We find a persistent, spectrally neutral increase in the Sun photometer-derived aerosol optical depth (AOD) of up to 10% (0.015) in the 2-km distances closest to the edges of several distinct clouds. At midvisible wavelengths, the MODIS AOD retrievals show similar increases toward cloud edges, although a larger increase in AOD is found in the MODIS along-scan direction. At shortwave infrared (SWIR) wavelengths (1240-2130 nm), the MODIS-derived AOD increases near cloud edges are of the order of 0.03 and as such three times as large as the Sun photometer-derived values. Hence, in contrast to recently discussed bluing of aerosols near cloud edges, i.e., a preferential apparent increase in the visible reflectances of clear-sky pixels due to 3-D radiative transfer effects in the vicinity of clouds, we find a reddening of aerosols in the MODIS 500-m-resolution aerosol retrievals near clouds. This reddening in our study can be traced to larger absolute increases in SWIR reflectances when compared to visible reflectances near clouds, which in turn seem to stem from larger electronic cross talk in the MODIS SWIR bands (5-7). We note that the lack of bluing in our MODIS observations is likely due to the small geometric and optical thicknesses of the clouds considered.

Redemann, Jens↗
NASA NTRS1994

The dust in the hydrogen-poor ejecta of Abell 30

We present new optical and near-infrared images of the hydrogen-poor planetary nebula Abell 30 and produce detailed models that account for the major observed morphological and IR properties. By imaging the nebula in the K band, we confirm the presence of hot dust in an expanding equatorial ring of H-poor gas. No emission was detected from the H-poor polar knots, suggesting a dust deficiency htere relative to the equatorial ring. The near-IR emission is attributed to small carbonaceous dust grains which are stochastically heated by stellar ultraviolet photons. Using an adaptive version of a matrix method devised by Guhathakurta & Draine (1989) to model stochastic heating, we find that the near-IR spectrum observed by Dinerstein & Lester (1984) requires the presence of dust grains down to approximately 0.0007 microns in radius. This minimum grain radius is in excellent agreement with our calculations of the grain destruction by energetic stellar UV photons: we find that carbon clusters with less than approximately 140 atoms (0.0007 microns in radius) are destroyed by stellar UV photons in approximately 1000 yr, the kinematic age of H-poor ejecta. Modeling of the far-IR dust emission implies that the bulk of the dust mass in A30 must reside at distances several times greater than the distance of the equatorial ring from the central star. This spatial dust distribution is attributed to the interaction of the stellar wind with the inhomogeneous H-poor ejecta. Most of the H-poor gas and dust has been apparently carried outward by the stellar wind, leaving behing dense, H-poor knots with prominent wind-blown tails in the equatorial ring and in the polar knots. This picture is supported by the presence of a stellar wind-blown bubble within the H-rich envelope in our optical images.

Borkowski, Kazimierz J.↗
NASA NTRS1990

Long-term study of longitudinal dependence in primary particle precipitation in the north Jovian aurora

The wavelength-dependent absorption apparent in IUE spectra of the north Jovian aurora is analyzed to determine the column density of hydrocarbons above the altitude of the FUV auroral emission. Both the magnetotail and torus auroral zone models are considered in estimating zenith angles, with very similar results obtained for both models. It is found that the hydrocarbon column density above the FUV emission displays a consistent dependence on magnetic longitude, with the peak density occurring approximately coincident with the peak in the observed auroral intensity. Two distinct scenarios for the longitude dependence of the column density are discussed. In one, the Jovian upper atmosphere is longitudinally homogeneous, and the variation in optical depth is due to a variation in penetration, and thus energy, of the primary particles. In the other, the energy of the primaries is longitudinally homogeneous, and it is aeronomic properties which change, probably due to auroral heating.

Livengood, T. A.↗
DOE OSTI2024

Bulk reconstruction and non-isometry in the backwards-forwards holographic black hole map

The backwards-forwards map, introduced as a generalization of the non-isometric holographic maps of the black hole interior of Akers, Engelhardt, Harlow, Penington, and Vardhan to include non-trivial dynamics in the effective description, has two possible formulations differing in when the post-selection is performed. While these two forms are equivalent on the set of dynamically generated states — states formed from unitary time evolution acting on well-defined initial configurations of infalling matter — they differ on the generic set of states necessary to describe the apparent world of the infalling observer. We show that while both versions successfully reproduce the Page curve, the version involving post-selection as the final step, dubbed the backwards-forwards-post-selection (BFP) map, has the desirable properties of being non-isometric but isometric on average and providing state-dependent reconstruction of bulk operators, while the other version does not. Thus the BFP map is a suitable non-isometric code describing the black hole interior including interior interactions.

3-D Image Reconstruction↗
DOE OSTI2021

Structure of Molten Alkali Chlorides at Charged Interfaces and the Prediction and Interpretation of Their X-ray Reflectivity

The fundamental properties of molten salts have been the subject of research that spans a century. Yet, in the past few years, there has been an unprecedented surge in interest for these systems in the bulk and under confinement by walls and interfaces including under applied potentials. This is driven by the prospect of exciting and very practical energy technologies, including those in the solar and nuclear fields. This article sets to answer two simple but fundamental questions. How does the liquid structure of alkali chlorides change at a real interface when it is charged? Also, how would such changes on the liquid side of the interface be detected in X-ray reflectivity experiments? We use an interface mimicking conductive diamond, which because of its lattice spacing, is an excellent choice for reflectivity experiments. The reason for our interest in X-ray reflectivity is that, as opposed to electrochemical measurements alone, this is likely the only technique in which atomic level information at the liquid side of the interface can be gained under the extreme temperature environments of molten salts. As it will become apparent, the interpretation of reflectivity results in terms of atomic positions is complex when multiple species with different X-ray contrasts on the liquid side are considered. A theoretical scheme termed “the peaks and antipeaks analysis of reflectivity” originally introduced in our prior work (J. Phys. Chem. C2019, 123 (8), 4914–4925) is expanded to interpret the structural changes at the interface as a function of applied electrical bias.

36 MATERIALS SCIENCE↗
NASA NTRS1980

Structure and optical properties of evaporated films of the Cr- and V-group metals

Thin films of Cr, Mo, and W rapidly evaporated in high vacuum (5 x 10 to the -7th torr) onto room-temperature substrates show anomalously low reflectance (compared to bulk samples). From electron and X-ray diffraction and electron microscopy, the normal bcc crystal structure is found, but with very fine grains. Columnar grains about 100 A in diameter were separated by a less dense grain-boundary network about 10-A wide. The measured optical conductivity agrees with an inhomogeneous-medium model that assumes the normal crystalline conductivity for the grain interiors, with model parameters that correlate to the observed columnar grain size. In contrast, V and Nb films rapidly evaporated onto room-temperature substrates have the reflectance of bulk crystalline material. On liquid-nitrogen temperature substrates, however, V and Nb have normal bcc crystal structure but with small flat-plate grains, and the same model, with appropriate parameters, accounts for the optical conductivity. The difference between these two groups apparently depends on residual gases segregated at the grain boundaries in the Cr-group films.

Nestell, J. E., Jr.↗
DOE OSTI2023

The Demographics, Stellar Populations, and Star Formation Histories of Fast Radio Burst Host Galaxies: Implications for the Progenitors

We present a comprehensive catalog of observations and stellar population properties for 23 highly secure host galaxies of fast radio bursts (FRBs). Our sample comprises 6 repeating FRBs and 17 apparent nonrepeaters. We present 82 new photometric and 8 new spectroscopic observations of these hosts. Using stellar population synthesis modeling and employing nonparametric star formation histories (SFHs), we find that FRB hosts have a median stellar mass of ≈10 9.9 M ⊙ , mass-weighted age ≈5.1 Gyr, and ongoing star formation rate ≈1.3 M ⊙ yr -1 but span wide ranges in all properties. Classifying the hosts by degree of star formation, we find that 87% (20 of 23 hosts) are star-forming, two are transitioning, and one is quiescent. The majority trace the star-forming main sequence of galaxies, but at least three FRBs in our sample originate in less-active environments (two nonrepeaters and one repeater). Across all modeled properties, we find no statistically significant distinction between the hosts of repeaters and nonrepeaters. However, the hosts of repeating FRBs generally extend to lower stellar masses, and the hosts of nonrepeaters arise in more optically luminous galaxies. While four of the galaxies with the clearest and most prolonged rises in their SFHs all host repeating FRBs, demonstrating heightened star formation activity in the last ≲100 Myr, one nonrepeating host shows this SFH as well. Our results support progenitor models with short delay channels (i.e., magnetars formed via core-collapse supernova) for most FRBs, but the presence of some FRBs in less-active environments suggests a fraction form through more delayed channels.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

Mars aqueous chemistry experiment

Mars Aqueous Chemistry Experiment (MACE) is designed to conduct a variety of measurements on regolith samples, encompassing mineral phase analyses, chemical interactions with H2O, and physical properties determinations. From these data, much can be learned or inferred regarding the past weathering environment, the contemporaneous soil micro-environments, and the general chemical and physical state of the Martian regolith. By analyzing both soil and duricrust samples, the nature of the latter may become more apparent. Sites may be characterized for comparative purposes and criteria could be set for selection of high priority materials on future sample return missions. The second year of the MACE project has shown significant progress in two major areas. MACE Instrument concept definition is a baseline design that has been generated for the complete MACE instrument, including definition of analysis modes, mass estimates and thermal model. The design includes multiple reagent reservoirs, 10 discrete analysis cells, sample manipulation capability, and thermal control. The MACE Measurement subsystems development progress is reported regarding measurement capabilities for aqueous ion sensing, evolved gas sensing, solution conductivity measurement, reagent addition (titration) capabilities, and optical sensing of suspended particles.

Clark, Benton C.↗
NASA NTRS2020

Increasing Activity in T CrB Suggests Nova Eruption Is Impending

Estimates of the accretion rate in symbiotic recurrent novae (RNe) often fall short of theoretical expectations by orders of magnitude. This apparent discrepancy can be resolved if the accumulation of mass by the white dwarf(WD)is highly sporadic, and most observations are performed during low states. Here we use a re-analysis of archival data from the Digital Access to a Sky Century @Harvard survey to argue that the most recent nova eruption in symbiotic RN T CrB, in 1946, occurred during—and was therefore triggered by—a transient accretion high state. Based on similarities in the optical light curve around 1946 and the time of the prior eruption, in 1866,we suggest that the WD in T CrB accumulates most of the fuel needed to ignite the thermonuclear runaways (TNRs) during accretion high states. A natural origin for such states is dwarf-nova like accretion-disk instabilities, which are expected in the presumably large disks in symbiotic binaries. The timing of the TNRs in symbiotic RNe could thus be set by the stability properties of their accretion disks. T CrB is in the midst of an accretion high state like the ones we posit led to the past two nova eruptions. Combined with the approach of the time at which a TNR would be expected based on the 80 yr interval between the prior two novae (2026 ± 3), the current accretion high state increases the likelihood of a TNR occurring in T CrB in the next few years.

Gerardo J M Luna↗
NASA NTRS1999

Mars Global Surveyor TES Results: Observations of Water Ice Clouds

On July 31, 1999, Mars Global Surveyor completed its first martian year in orbit. During this time, the Thermal Emission Spectrometer (TES) experiment gathered extensive data on water ice clouds. We report here on three types of martian clouds. 1) Martian southern summer has long been characterized as the season when the most severe dust storms occur. It is now apparent that northern spring/summer is characterized as a time of substantial low latitude ice clouds [1]. TES observations beginning in the northern summer (Lsubs=107) show a well developed cloud belt between 10S and 30N latitude; 12 micron opacities were typically 0.15. This system decreased dramatically after Lsubs= 130. Thereafter, remnants were most persistent over the Tharsis ridge. 2) Clouds associated with major orographic features follow a different pattern [2]. Clouds of this type were present prior to the regional Noachis dust storm of 1997. They disappeared with the onset of the storm, but reappeared rather quickly following its decay. Typical infrared opacities were near 0.5. 3) Extensive, very thin clouds are also widespread [3]. Found at high altitudes (above 35 km), their opacities are typically a few hundredths. At times, such as in northern spring, these clouds are limited in their northern extent only by the southern edge of the polar vortex. We describe the distribution, infrared optical properties, and seasonal trends of these systems during the first martian year of TES operations.

Pearl, John C.↗
NASA NTRS1993

Satellites of spiral galaxies

We present a survey of satellites around a homogeneous set of late-type spirals with luminosity similar to that of the Milky Way. On average, we find fewer than 1.5 satellites per primary, but we argue that we can treat the survey as an ensemble and so derive the properties of the halo of a 'typical' isolated spiral. The projected density profile of the ensemble falls off approximately as 1/r. Within 50 kpc the azimuthal distribution of satellites shows some evidence for the 'Holmberg effect', an excess near the minor axis of the primary; however, at larger projected distances, the distribution appears isotropic. There is a weak but significant correlation between the size of a satellite and its distance from its primary, as expected if satellites are tidally truncated. Neither Hubble type nor spectral characteristics correlate with apparent separation. The ensemble of satellites appears to be rotating at about 30 km/s in the same direction as the galactic disk. Satellites on prograde orbits tend to be brighter than those on retrograde orbits. The typical velocity difference between a satellite and its primary shows no clear dependence either on apparent separation, or on the rotation speed of the primary. Thus our survey demonstrates that isolated spiral galaxies have massive halos that extend to many optical radii.

Zaritsky, Dennis↗
NASA NTRS1997

X-Ray Activity in the Open Cluster IC 4665

We present the results of a joint ROSAT High Resolution Imager (HRI) and optical investigation of the open cluster IC 4665. The ROSAT data contains detections for 28 stellar sources in the field, including 22 cluster members and candidate members spanning the color range -0.18 less than or equal to (B - V(sub o)) less than or equal to +1.63 (approx. B3 - M3). Upper limits are given for the remaining members (or candidate members) in the HRI field. Keck HIRES spectra have been obtained that yield radial and rotational velocity measures, respectively, for faint, low mass candidate members located within the field of the ROSAT HRI observation. In addition, photometry of possible optical counterparts to previously uncatalogued X-ray sources in the HRI field is presented. The trends in X-ray properties with (B - V) color in IC 4665 are found to be quite similar to that for other, more nearby young clusters such as the Pleiades and alpha Persei. In particular, a maximum in normalized X-ray luminosity of log (L(sub x)/L(sub bol)) approx. equal 3 is observed, beginning in the color range of (B - V)(sub o) = 0.7 - 0.8. This is similar to the corresponding color range among Pleiades members, in agreement with the earlier estimate, that the age of IC 4665 is similar to the age of the Pleiades. The correlation of rotation and X-ray emission levels is consistent with that in other young clusters. Among the high mass stars in IC 4665, five B stars are detected as X-ray sources. Of these, one is a spectroscopic binary while the remaining objects are apparently single staxs. The level of intrinsic X-ray emission observed in the rapidly rotating (v sini greater than 200 km/ s), single B stars is consistent with an origin due to shock heating of the ambient medium by radiatively driven, rotationally enhanced winds. On the basis of these observations and the results for other clusters, we argue that observed levels of X-ray emission in high mass stars of log (L(sub x)/L(sub bol)) greater than -6.0 are likely due to intrinsic emission associated with the B stax itself rather than emission from a late-type secondary. Finally, our results suggest that the initial angular momentum distributions and the subsequent evolution of rotation, L(sub x), and (L(sub x)/L(sub bol)) occur in practically identical fashions in clusters with ages approx. less than 100 Myr.

Giamapapa, Mark S.↗
NASA NTRS2003

Lightning and Other Influences On Tropical Tropospheric Ozone: Empirical Studies of Covariation

Tropical and subtropical tropospheric ozone are important radiatively active species, with particularly large effects in the upper third of the troposphere. Temporal variability of O3 has proved difficult to simulate day by day in process models. Thus, individual roles of lightning, biomass burning, and other pollution in providing precursor NO(x), radicals, and chain carriers (CO, hydrocarbons) remain unquantified by simulation, and it is theoretically reasonable that individual roles are magnified by a joint synergy. We use wavelet analysis and Burg-algorithm maximum entropy spectral analyses to describe time-scales and correlation of ozone with proxies for processes controlling its concentration. Our empirical studies link time variations apparent in several datasets: the SHADOZ (Southern Hemisphere Additional Ozonesondes) network stations (Nairobi, Fiji), and auxiliary series with power to explain ozone-determining processes, with some interpretation based on the TTO (Tropical Tropospheric Ozone) product derived from TOMS (the Total Ozone Mapping Spectrometer). The auxiliary series are The OTD/LIS(Optical Transient Detector/Lightning Imaging Sensor) measurements of the lightning NO(x) source, the OLR (Outgoing Longwave Radiation)measurement of high-topped clouds, and standard meteorological variables from the United States NCEP (National Centers for Environmental Prediction) and Data Assimilation Office analyses. Concentrating on equatorial ozone, we compare the statistical evidence on the variability of tropospheric ozone. Important variations occur on approximately two-week, two-month (Madden-Julian Oscillation) and annual scales, and relations with OLR suggest controls associated with continental clouds. Hence we are now using the Lightning Imaging Sensor data set to indicate NO(x) sources. We report initial results defining relative roles of the process mentioned affecting O3 using their covariance properties.

Chatfield, Robert B.↗
DOE OSTI2024

No ν s is Good News

The baryon acoustic oscillation (BAO) analysis from the first year of data from the Dark Energy Spectroscopic Instrument (DESI), when combined with data from the cosmic microwave background (CMB), has placed an upper-limit on the sum of neutrino masses, ∑m ν < 70 meV (95%). In addition to excluding the minimum sum associated with the inverted hierarchy, the posterior is peaked at ∑m ν = 0 and is close to excluding even the minumum sum, 58 meV at 2σ. In this paper, we explore the implications of this data for cosmology and particle physics. The sum of neutrino mass is determined in cosmology from the suppression of clustering in the late universe. Allowing the clustering to be enhanced, we extended the DESI analysis to ∑m ν < 0 and find ∑m ν =160 ± 90 meV (68%), and that the suppression of power from the minimum sum of neutrino masses is excluded at 99% confidence. We show this preference for negative masses makes it challenging to explain the result by a shift of cosmic parameters, such as the optical depth or matter density. We then show how a result of ∑m ν = 0 could arise from new physics in the neutrino sector, including decay, cooling, and/or time-dependent masses. These models are consistent with current observations but imply new physics that is accessible in a wide range of experiments. In addition, we discuss how an apparent signal with ∑m ν < 0 can arise from new long range forces in the dark sector or from a primordial trispectrum that resembles the signal of CMB lensing.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Excitons in two-dimensional metal-halide perovskites

Georgia Tech School of Chemistry and Biochemistry Special Summer Seminar Series, Prof Carlos Silva; While polarons --- charges bound to a lattice deformation induced by electron-phonon coupling --- are primary photoexcitations at room temperature in bulk metal-halide hybrid organic-inorganic perovskites (HOIP), excitons --- Coulomb-bound electron-hole pairs --- are the stable quasi-particles in their two-dimensional (2D) analogues. Here we address the fundamental question: are polaronic effects consequential for excitons in 2D-HIOPs? Based on our recent work, we argue that polaronic effects are manifested intrinsically in the exciton spectral structure, which is comprised of multiple non-degenerate resonances with constant inter-peak energy spacing. We highlight measurements of population and dephasing dynamics that point to the apparently deterministic role of polaronic effects in excitonic properties. We contend that an interplay of long-range and short-range exciton-lattice couplings give rise to exciton polarons, a character that fundamentally establishes their effective mass and radius, and consequently, their quantum dynamics. Given this complexity, a fundamentally far-reaching issue is how Coulomb-mediated many-body interactions---elastic scattering such as excitation-induced dephasing, inelastic exciton bimolecular scattering, and multi-exciton binding---depend upon the specific exciton-lattice coupling within the structured excitation lineshape. We measure the intrinsic and density-dependent exciton dephasing rates of the multiple excitons and their dependence on temperature by means of two-dimensional coherent excitation spectroscopy. We find that diverse excitons display distinct intrinsic dephasing rates mediated by phonon scattering involving different effective phonons, and contrasting rates of exciton-exciton elastic scattering. These findings establish specifically the consequence of distinct lattice dressing on exciton many-body quantum dynamics, which critically define fundamental optical properties that underpin photonics and quantum optoelectronics.

solar cells, metal-halide perovskites, excitons, p↗
DOE OSTI2024

Photolytic Degradation of Water‐Soluble Organic Carbon in Snowmelts: Changes in Molecular Characteristics, Brown Carbon Chromophores, and Radiative Effects

Abstract Water‐soluble organic carbon (WSOC) deposited in ambient snowpack play key roles in regional carbon cycle and surface energy budget, but the impacts of photo‐induced processes on its optical and chemical properties are poorly understood yet. In this study, melted samples of the seasonal snow collected from northern Xinjiang, northwestern China, were exposed to ultraviolet (UV) radiation to investigate the photolytic transformations of WSOC. Molecular characteristics and chemical composition of WSOC and its brown carbon (BrC) constituents were investigated using high‐performance liquid chromatography interfaced with a photodiode array detector and a high‐resolution mass spectrometer. Upon illumination, formation of nitrogen‐ and sulfur‐containing species with high molecular weight was observed in snow samples influenced by soil‐ and plant‐derived organics. In contrast, the representative sample collected from remote region showed the lowest molecular diversity and photolytic reactivity among all samples, in which no identified BrC chromophores decomposed upon illumination. Approximately 65% of chromophores in urban samples endured UV irradiation. However, most of BrC composed of phenolic/lignin‐derived compounds and flavonoids disappeared in the illuminated samples containing WSOC from soil‐ and plant‐related sources. Effects of the photochemical degradation of WSOC on the potential modulation of snow albedo were estimated. Apparent half‐lives of WSOC estimated as albedo reduction in 300–400 nm indicated 0.1–0.4 atmospheric equivalent days, which are shorter than typical photolysis half‐lives of ambient biomass smoke aerosol. This study provides new insights into the roles of WSOC in snow photochemistry and snow surface energy balance.

Meteorology & Atmospheric Sciences↗
NASA NTRS1990

Lidar cloud studies for FIRE and ECLIPS

Optical remote sensing measurements of cirrus cloud properties were collected by one airborne and four ground-based lidar systems over a 32 h period during this case study from the First ISCCP (International Satellite Cloud Climatology Program) Regional Experiment (FIRE) Intensive Field Observation (IFO) program. The lidar systems were variously equipped to collect linear depolarization, intrinsically calibrated backscatter, and Doppler velocity information. Data presented describe the temporal evolution and spatial distribution of cirrus clouds over an area encompassing southern and central Wisconsin. The cirrus cloud types include: dissipating subvisual and thin fibrous cirrus cloud bands, an isolated mesoscale uncinus complex (MUC), a large-scale deep cloud that developed into an organized cirrus structure within the lidar array, and a series of intensifying mesoscale cirrus cloud masses. Although the cirrus frequently developed in the vertical from particle fall-streaks emanating from generating regions at or near cloud tops, glaciating supercooled (-30 to -35 C) altocumulus clouds contributed to the production of ice mass at the base of the deep cirrus cloud, apparently even through riming, and other mechanisms involving evaporation, wave motions, and radiative effects are indicated. The generating regions ranged in scale from approximately 1.0 km cirrus uncinus cells, to organized MUC structures up to approximately 120 km across.

Sassen, Kenneth↗