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NASA NTRS1986

Abundances of interstellar atoms from ultaviolet absorption lines

The equivalent widths of interstellar absorption lines of Mg II, P II, Cl I and II, Mn II, Fe II, Cu II, and Ni II, obtained in a Copernicus survey of Bohlin et al (1983) have been analyzed to yield column densities along the lines of sight. The measured depletions are clearly correlated with n sub H, the mean hydrogen column density along the line of sight. Depletions also seem to be weakly correlated with various ratios of hydrogen to extinction by dust grains and also variations of extinction with wavelength, although part of these effects are a secondary result of the correlation with n sub H. The apparent coupling of depletion to the mean density are interpreted in terms of an idealized model due to Spitzer (1985), where each element has one value of depletion in the low-density, warm, neutral gas and an enhanced, different value in cold clouds. The difference of apparent depletions for Mg, P, Cl, Mn, and Fe between warm and cold clouds averages 0.44 + or - 0.12 (rms) dex, and, after an allowance for observational errors is made, the scatter of individual depletions from the overall trend predicted by method is only about 0.10 dex. The identification of the observed apparent depletions with actual ones, while very likely, is not entirely secure, because of the possible presence of highly saturated compoents with very narrow profiles and the possible contamination of the results by H II regions.

Jenkins, E. B.↗

NASA NTRS1991

Ultraviolet interstellar lines in the spectrum of Pi Scorpii recorded at 2 kilometers per second resolution

A spectrum of Pi Scorpii has been recorded from 1003 to 1172 A with a maximum SNR of about 20 and a velocity resolution of 2.4 km/s. Three types of H I as well as two discrete H II regions are distinguished in velocity space, allowing independent analyses of physical conditions and abundances for the individual gas components. A direct evaluation of optical depths and column densities across the absorption features is applied for the first time to the dominant ionization stage of Fe, Si, and P. Based on an analysis of the spectrum, it is concluded that all of the Ti II absorption seen toward Pi Sco arises in the warm, neutral intercloud medium while the other elements have their maximum absorption associated with cold clouds. A conservative value of log delta less than -3.4 is inferred for the Ti depletion in the cold clouds, a value more extreme than any integrated, line-of-sight measurement made to date.

Joseph, Charles L.↗

NASA NTRS1993

Boundary conditions for the paleoenvironment: Chemical and physical processes in the pre-solar nebula

In observations with the NRAO 12m telescope at Kitt Peak, Arizona, Irvine, a new interstellar radical, CH2N, has been detected. This identification is important for the study of hydrogenation processes in the interstellar medium. In particular, although the abundance of hydrogen is some four orders of magnitude higher than that of other reactive elements in this environment, many organic molecules in quiescent clouds are very unsaturated. This is a consequence of activation barriers which cannot be overcome at the temperatures of cold clouds, even when such reactions are energetically allowed. The hydrogenation series based on the cyanide radical (HnCN) has had four members previously detected in the interstellar medium: CN (n equals O), HCN (n equals l), CH2CN (n equals 3), and CH3NH2 (n equals 5). The recent determination of the rotational spectrum of the CH2N radical through microwave spectroscopy in Japan has made possible a search for this species. In addition to its potential importance for interstellar chemistry, the CH2N radical has been proposed as a reaction intermediate for HCN production in the atmosphere of Jupiter, and as a possible species in the expanding envelopes of oxygen--rich evolved stars. We detected CH2N in the cold cloud TMC--1 where the abundance seems to be some three orders of magnitude lower than that of HCN. A tentative detection was made in the Galactic Center molecular cloud Sgr B2. To our knowledge, there are no predicted abundances of CH2N from models of interstellar chemistry.

Irvine, William M.↗

NASA NTRS2014

Hurricane Karl's Structure and Some Thoughts for 2014 Strategy

Karl has interesting data, but far below the standards we should be able to achieve in HS3. We need to fly AV-1 over hurricanes in 2014. Most of the cold cloud shield in the inner core of hurricanes should be safe for AV-1 to fly. Significant convection occupies a small region, but we sometimes unnecessarily apply the 5000-ft separation rule to the entire cold cloud shield.

Cecil, Dan↗

NASA NTRS1991

Application of lightning data to satellite-based rainfall estimation

Information on lightning may improve rain estimates made from infrared images of a geostationary satellite. We address this proposition through a case from the Cooperative Huntsville Meteorological Experiment (COHMEX). During the afternoon and evening of 13 July 1986 waves of showers and thunderstorms developed over and near the lower Tennessee River Valley. For the shower and thunderstorm region within 200 km of the National Weather Service radar at Nashville, Tennessee, we measure cold-cloud area in a sequence of GOES infrared images covering all but the end of the shower and thunderstorm period. From observations of the NASA/Marshall direction-finding network in this small domain, we also count cloud-to-ground lightning flashes and, from scans of the Nashville radar, we calculate volume rain flux. Using a modified version of the Williams and Houze scheme, over an area within roughly 240 km of the radar (the large domain), we identify and track cold cloud systems. For these systems, over the large domain, we measure area and count flashes; over the small domain, we calculate volume rain flux. For a temperature threshold of 235K, peak cloud area over the small domain lags both peak rain flux and peak flash count by about four hours. At a threshold of 226K, the lag is about two hours. Flashes and flux are matched in phase. Over the large domain, nine storm systems occur. These range in size from 300 to 60,000 km(exp 2); in lifetime, from about 2 1/2 h to 6 h or more. Storm system area lags volume rain flux and flash count; nevertheless, it is linked with these variables. In essential respects the associations were the same when clouds were defined by a threshold of 226K. Tentatively, we conclude that flash counts complement infrared images in providing significant additional information on rain flux.

Martin, David W.↗

NASA NTRS1991

Positron annihilation in the interstellar medium

Positronium formation and annihilation are studied in a model for the interstellar medium consisting of cold cloud cores, warm partially ionized cloud envelopes, and hot intercloud gas. The gamma-ray spectra resulting from positron annihilation in these components of the interstellar medium are calculated. The spectra from the individual components are then combined, using two limiting assumptions for the propagation of the positrons, namely, that the positrons propagate freely throughout the interstellar medium, and that the positrons are excluded from the cold cloud cores. In the first case, the bulk of the positrons annihilate in the cloud cores and the annihilation line exhibits broad wings resulting from the annihilation of positronium formed by charge exchange in flight. In the second case, the positrons annihilate mainly in the warm envelopes, and the line wings are suppressed.

Guessoum, Nidhal↗

NASA NTRS1991

The discovery of large amounts of cold, X-ray absorbing matter in cooling flows

The discovery of significant excess absorption in the X-ray spectra of 12 clusters of galaxies is reported. The spectra also require a cooling-flow component, which confirms the results of imaging studies of the clusters showing the strongly peaked emission characteristic of cooling flows. The total mass of absorbing gas is determined on the assumption that it is distributed through the cooling flow region and has cosmic abundance. It is shown that the gas is most likely in the form of small cold clouds. The excess absorption is interpreted as being due to photoelectric absorption in cold gas clouds distributed through the cooling flows.

White, D. A.↗

NASA NTRS2007

Nitric Acid Particles in Cold Thick Ice Clouds Observed at Global Scale: Link with Lightning, Temperature, and Upper Tropospheric Water Vapor

Signatures of nitric acid particles (NAP) in cold thick ice clouds have been derived from satellite observations. Most NAP are detected in the Tropics (9 to 20% of clouds with T less than 202.5 K). Higher occurrences were found in the rare mid-latitudes very cold clouds. NAP occurrence increases as cloud temperature decreases and NAP are more numerous in January than July. Comparisons of NAP and lightning distributions show that lightning is the main source of the NOx, which forms NAP in cold clouds. Qualitative comparisons of NAP with upper tropospheric humidity distributions suggest that NAP play a role in the dehydration of the upper troposphere when the tropopause is colder than 195K.

Chepfer, H.↗

NASA NTRS2000

Overcast Clouds Determined By Trmm Measurements

Using the Tropical Rainfall Measuring Mission (TRMM) Visible and Infra-Red Scanner (VIRS) and TRMM Microwave Radiometer (TMI) measurements, this study retrieves cloud optical depth (tau), liquid water path (LWP), and the frequency of co-occurrence of ice and water clouds based on radiative transfer models. Results show that LWP values for warm non-precipitating clouds are approximately 0.06mm and cold clouds have large ice water amount (approximately 0.1mm). The cloud systems with significant amounts of water below ice occur about 10 to approximately 20% of the time.

Lin, Bing↗

NASA NTRS1990

Turbulent mixing layers in the interstellar and intracluster medium

Cold clouds embedded in hot turbulent gas are often observed in the interstellar medium of galaxies and in the intracluster medium. Mixing layers develop around the clouds by the action of the turbulent gas. It is shown that their column density is limited by cooling and their mean temperature by the momentum flux. Provided that mixing is efficient, the mean temperature is the geometric mean of the hot and cold gas temperatures. EUV radiation from mixing layers around filaments in cluster cooling flows photoionizes the colder gas and may produce the commonly observed optical and UV emission lines. Mixing layers around cold galactic clouds can produce absorption by O VI and similar species with a column density consistent with observations.

Begelman, Mitchell C.↗

NASA NTRS1990

New observations of interstellar organic molecules

Discussed here are new observations of 3-carbon-containing interstellar molecules which play an important role in the chemistry of dense molecular clouds: protonated carbon dioxide, formic acid, and propynal. In 1984 a new oxide of carbon, C3O, was discovered in the interstellar medium (Matthews et al. 1984; Brown et al. 1985). Theoretical models suggest that C3O is produced by dissociative electron recombination with the ion H3C3O+. Although no laboratory data for the branching ratios of such a recombination exist, it seemed to us likely that additional products would include H2C3O. This molecule has more than one isomeric form, but one stable species is propynal (HC2CHO), which had been suggested as a possible interstellar molecule by Winnewisser (1973). In observations at the National Radio Astronomy Observatory 43 m telescope in Green Bank earlier this year, researchers detected a line in the cold cloud TMC-1 which they assign to the 2(0,2)-1(0,1) transition of propynal. The observed line agrees with the laboratory frequency to well within the experimental uncertainty a few parts in 10 to the 7th power. Researchers sought and failed to detect the corresponding 2(1,1)-1(1,0) line, which is understandable given the presence of both a and b components of the electric dipole moment in propynal. The b type transitions will drain population from energy levels with K(sub p) does not equal 0 into the K(sub p) equal 0 stack. If the researchers' assignment is correct, this is the first interstellar detection of propynal. Assuming typical rotational temperatures for TMC-1 and that the line is optically thin, the column density determined is about 5 times 10 to the 12th power cm to the -2nd power, or about three times that for C3O. Formic acid (HCOOH) was the first organic acid to be observed in the interstellar medium, in the Galactic center source Sgr B2. The only other interstellar detection has been recently made in the giant molecular cloud in Orion. As part of the same project that led to the detection of propynal, researchers sought formic acid in the nearby, cold dark clouds TMC-1 and L134N. It is seen only in L134N. This difference between the two clouds appears to be consistent with a model in which the oxygen/carbon ratio is higher in L134N. This would be consistent with the higher abundances for SO and SO2, observed in that cloud, and the higher abundances of many carbon-rich species in TMC-1 (Irvine et al. 1985).

Irvine, W. M.↗

NASA NTRS1990

The October 27-28, 1986, FIRE cirrus case study: Cloud microstructure

Using aircraft in-situ measurements, the microphysics of cirrus clouds observed on 28 Oct. 1986 during FIRE were examined. Results are presented as one component of a coordinated study of the cirrus on the day. The study contributes to the understanding of cold clouds by: (1) providing microphysical data to supplement satellite and aircraft data for investigating cirrus cloud radiative effects; (2) providing more complete information on ice particle evolution and cloud forcing mechanisms than has been available through the use of instrumentation with higher resolution and more accurate calibration; (3) expanding the knowledge of the particle characteristics in cold liquid water clouds, through improved instrumentation and by making use of sensors on other platforms, such as lidar; and (4) by estimating the ice nucleus concentrations active at low temperatures in the upper troposphere from the concentrations of ice particles in colloidally stable liquid water clouds.

Miller, Karen M.↗

NASA NTRS1990

The 27-28 October 1986 FIRE IFO cirrus case study - Cloud microstructure

Heymsfield, Andrew J.↗

NASA NTRS1980

GOES infrared study of tornadic storms

Enhanced convection-initiated gravity waves associated with an isolated tornado in the absence of a squall line are investigated. Ray tracing computations based on data observed on May 29, 1977 indicated that the wave sources were located in north central Oklahoma. Comparison with a radar echo map during the time period when the waves were excited showed that the waves were generated by an isolated cloud with enhanced convection. GOES infrared digital data during the time period from wave excitation to tornado touchdown were analyzed. Results showed that the cloud where the gravity waves were excited was characterized by both a very low temperature at the cloud top and a very high expansion rate of the cold cloud tops area. The lead time between the excitation of the gravity waves and the tornado touchdown is discussed in conjunction with the growth rate of the clouds associated with the tornado.

Hung, R. J.↗

NASA NTRS2014

Quantifying the Amount of Ice in Cold Tropical Cirrus Clouds

How much ice is there in the Tropical Tropopause layer, globally? How does one begin to answer that question? Clouds are currently the largest source of uncertainty in climate models, and the ice water content (IWC) of cold cirrus clouds is needed to understand the total water and radiation budgets of the upper troposphere and lower stratosphere (UT/LS). The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite, originally a "pathfinder" mission only expected to last for three years, has now been operational for more than eight years. Lidar data from CALIPSO can provide information about how IWC is vertically distributed in the UT/LS, and about inter-annual variability and seasonal changes in cloud ice. However, cloud IWC is difficult to measure accurately with either remote or in situ instruments because IWC from cold cirrus clouds is derived from the particle cross-sectional area or visible extinction coefficient. Assumptions must be made about the relationship between the area, volume and density of ice particles with various crystal habits. Recently there have been numerous aircraft field campaigns providing detailed information about cirrus ice water content from cloud probes. This presentation evaluates the assumptions made when creating the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) global IWC data set, using recently reanalyzed aircraft particle probe measurements of very cold, thin TTL cirrus from the 2006 CR-AVE.

Avery, Melody A.↗

NASA NTRS1990

Silicon chemistry in interstellar clouds

A new model of interstellar silicon chemistry is presented that explains the lack of SiO detections in cold clouds and contains an exponential temperature dependence for the SiO abundance. A key aspect of the model is the sensitivity of SiO production by neutral silicon reactions to density and temperature, which arises from the dependence of the rate coefficients on the population of the excited fine-structure levels of the silicon atom. As part of the explanation of the lack of SiO detections at low temperatures and densities, the model also emphasizes the small efficiencies of the production routes and the correspondingly long times needed to reach equilibrium. Measurements of the abundance of SiO, in conjunction with theory, can provide information on the physical properties of interstellar clouds such as the abundance of oxygen bearing molecules and the depletion of interstellar silicon.

Langer, William D.↗

NASA NTRS1993

What determines the cloud-to-ground lightning fraction in thunderstorms?

The ratio of intracloud lightning (IC) to cloud-to-ground lightning (CG) in thunderstorms is observed to vary with latitude. The reason frequently given for this behavior is that the height of the freezing level, and hence the negative charge center in thunderstorms, varies with latitude, resulting in higher ratios in the tropics compared with those in midlatitudes. This study shows that this hypothesis could well be incorrect. Analysis of cloud and lightning data indicates that the IC/CG ratio is linked to the thickness of the cold cloud region in thunderstorms (0 C to cloud top), rather than to the freezing level height.

Price, Colin↗

NASA NTRS1985

Recent observations of organic molecules in nearby cold, dark interstellar clouds

Recent investigations of the organic chemistry of relatively nearby cold, dark interstellar clouds are reported. Specifically, the presence of interstellar tricarbon monoxide (C3O) in Taurus Molecular Cloud 1 (TMC-1) is confirmed. The first detection in such regions of acetaldehyde (CH3CHO), the most complex oxygen-containing organic molecule yet found in dark clouds is reported, as well as the first astronomical detection of several molecular rotational transitions, including the J = 18-17 and 14-13 transitions of cyanodiacetylene (HC5N), the 1(01)-0(00) transition of acetaldehyde, and the J = 5-4 transition of C3O. A significant upper limit is set on the abundance of cyanocarbene (HCCN) as a result of the first reported interstellar search for this molecule.

Suzuki, H.↗