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NASA NTRSDate not supplied

Diurnal Cycles of Intense Thunderstorms As Seen By Satellites

Spaceborne sensors cannot directly measure aspects of severe weather occurring at ground-level. Tools from Geostationary Earth Orbit (GEO) and Low Earth Orbit (LEO) can be related to storm intensity and likelihood of severe weather. Visible and Infrared (GEO and LEO) measure cloud-top properties and horizontal structure. Some properties have empirical correlations with severe weather occurrence. Precipitation Radar (LEO) measures vertical profile of reflectivity related to particle size and concentration, but attenuates (2.2-cm and shorter wavelengths) well above the surface in intense thunderstorms. Lightning mappers (GEO and LEO) measure lightning flash rates and flash properties, which relate to updraft properties including size and vigor. SAR and optical sensors can detect damage paths on the surface after a storm has passed. (Depends on the vegetation type and maturity.)

Daniel J Cecil↗
NASA NTRS1988

Environments and populations of supernova remnants in the Large Magellanic Cloud

The stellar and interstellar environments of the 32 known SNRs in the LMC have been examined to determine the relative numbers of population I and II progenitors. At least 2/3 of the LMC SNRs are associated with pop I environments. The data suggest that the existing SNR surveys are biased against the detection of SNRs located in evolved star-forming regions, such as supershells produced by OB asociations, and in the cores of luminous H II regions. Therefore, the fraction of SNRs in pop I environments may be even higher. The results are compared to previous studies of SN statistics in late-type galaxies.

Chu, You-Hua↗
NASA NTRS1980

Molecular line observations of AFGL sources

HCN and (with three exceptions) CH emission lines have been detected from 14 molecular clouds associated with AFGL sources and/or Sharpless regions. Eleven are molecular cloud-H II region complexes. The remaining three appear to be similar (perhaps younger) objects; they are strong in the far infrared, but have no visible H II regions. Enhancement of the lower satellite transition of CH is seen in most cases. CH was also detected in association with the Herbig B8-A2e star V380 Ori. This emission was the most intense of all the CH detections. An effort was made to find a maser transition for a carbon-bearing molecule in late-type stars. A search was made for rotational transitions in the HCN bending mode (first overtone at 89.1 GHz) and stretching mode (fundamental at 88.0 GHz) as well as the CH ground state lambda-doublet in carbon stars.

Dinger, A. S. C.↗
NASA NTRS1985

Detection of Ni 2 lambda 7378 in six Seyfert galaxies

A line due to Ni 2 7378 in the Seyfert galaxies NGC 1068, 2110, 3227, 4151, 5506, and Arp 102 B was detected. The average Ni abundance is about 2 times solar, which is 5 times less than in the filaments of the Crab Nebula. This argues for nucleosynthetic processing in the latter. The Ni 2 line is spatially revolved in NGC 1068, and shows at least a factor of 4 enhancement in the Ni abundance away from the nucleus. The off-nuclear abundance of Ni in NGC 1068 approaches that of the Crab, which strongly suggests that type supernovae enriched the off-nuclear gas clouds.

Halpern, J. P.↗
NASA NTRS1986

Detection of forbidden Ni II lambda 7378 in six Seyfert galaxies

A line due to Ni 2 7378 in the Seyfert galaxies NGC 1068, 2110, 3227, 4151, 5506, and Arp 102 B was detected. The average Ni abundance is about 2 times solar, which is 5 times less than in the filaments of the Crab Nebula. This argues for nucleosynthetic processing in the latter. The Ni 2 line is spatially resolved in NGC 1068, and shows at least a factor of 4 enhancement in the Ni abundance away from the nucleus. The off-nuclear abundance of Ni in NGC 1068 approaches that of the Crab, which strongly suggests that type supernovae enriched the off-nuclear gas clouds.

Halpern, J. P.↗
NASA NTRS2011

Developing and Evaluating RGB Composite MODIS Imagery for Applications in National Weather Service Forecast Offices

Satellite remote sensing has gained widespread use in the field of operational meteorology. Although raw satellite imagery is useful, several techniques exist which can convey multiple types of data in a more efficient way. One of these techniques is multispectral compositing. The NASA Short-term Prediction Research and Transition (SPoRT) Center has developed two multispectral satellite imagery products which utilize data from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA's Terra and Aqua satellites, based upon products currently generated and used by the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT). The nighttime microphysics product allows users to identify clouds occurring at different altitudes, but emphasizes fog and low cloud detection. This product improves upon current spectral difference and single channel infrared techniques. Each of the current products has its own set of advantages for nocturnal fog detection, but each also has limiting drawbacks which can hamper the analysis process. The multispectral product combines each current product with a third channel difference. Since the final image is enhanced with color, it simplifies the fog identification process. Analysis has shown that the nighttime microphysics imagery product represents a substantial improvement to conventional fog detection techniques, as well as provides a preview of future satellite capabilities to forecasters.

Oswald, Hayden↗
NASA NTRS1990

The analysis of polar clouds from AVHRR satellite data using pattern recognition techniques

The cloud cover in a set of summertime and wintertime AVHRR data from the Arctic and Antarctic regions was analyzed using a pattern recognition algorithm. The data were collected by the NOAA-7 satellite on 6 to 13 Jan. and 1 to 7 Jul. 1984 between 60 deg and 90 deg north and south latitude in 5 spectral channels, at the Global Area Coverage (GAC) resolution of approximately 4 km. This data embodied a Polar Cloud Pilot Data Set which was analyzed by a number of research groups as part of a polar cloud algorithm intercomparison study. This study was intended to determine whether the additional information contained in the AVHRR channels (beyond the standard visible and infrared bands on geostationary satellites) could be effectively utilized in cloud algorithms to resolve some of the cloud detection problems caused by low visible and thermal contrasts in the polar regions. The analysis described makes use of a pattern recognition algorithm which estimates the surface and cloud classification, cloud fraction, and surface and cloudy visible (channel 1) albedo and infrared (channel 4) brightness temperatures on a 2.5 x 2.5 deg latitude-longitude grid. In each grid box several spectral and textural features were computed from the calibrated pixel values in the multispectral imagery, then used to classify the region into one of eighteen surface and/or cloud types using the maximum likelihood decision rule. A slightly different version of the algorithm was used for each season and hemisphere because of differences in categories and because of the lack of visible imagery during winter. The classification of the scene is used to specify the optimal AVHRR channel for separating clear and cloudy pixels using a hybrid histogram-spatial coherence method. This method estimates values for cloud fraction, clear and cloudy albedos and brightness temperatures in each grid box. The choice of a class-dependent AVHRR channel allows for better separation of clear and cloudy pixels than does a global choice of a visible and/or infrared threshold. The classification also prevents erroneous estimates of large fractional cloudiness in areas of cloudfree snow and sea ice. The hybrid histogram-spatial coherence technique and the advantages of first classifying a scene in the polar regions are detailed. The complete Polar Cloud Pilot Data Set was analyzed and the results are presented and discussed.

Smith, William L.↗
NASA NTRS1995

Optical and infrared observations of SGR 1806-20

The soft gamma-ray repeater (SGR) 1806-20 is associated with the center-brightened nonthermal nebula G10.0-0.3, thought to be a plerion. As in other plerions, a steady X-ray source, AX 1805.7-2025, has been detected coincident with the peak of the nebular radio emission. Vasisht et al. have shown that the radio peak has a core-jet appearance and argue that the core marks the true position of the SGR. At optical wavelengths, we detect three objects in the vicinity of the radio core. Only for the star closest to the core, barely visible in the optical but bright in the infrared (K-8.4 mag), the reddening is consistent with the high extinction (A(sub V) is approximately equal to 30 mag) that has been inferred for AX 1805.7 - 2025. From the absence of CO band absorption, we infer that the spectral type of this star is earlier than late-G/early-K. The large extinction probably arises in a molecular cloud located at a distance of 6 kpc, which means that the star, just like AX 1805.7-2025, is in or behind this cloud. This implies that the star is a supergiant. Since supergiants are rare, a chance coincidence with the compact radio core is very unlikely. To our knowledge, there are only three other examples of luminous stars embedded in nonthermal radio nebulae: SS 433, Cir X-1, and G70.7+1.2. Given this and the low coincidence probability, we suggest that the bright star is physically associated with SGR 1806-20, making it the first stellar indentification of a high-energy transient.

Kulkarni, S. R.↗
NASA NTRS2019

Micrometeoroid Events in LISA Pathfinder

The zodiacal dust complex, a population of dust and small particles that pervades the solar system, provides important insight into the formation and dynamics of planets, comets, asteroids, and other bodies. We present a new set of data obtained from direct measurements of momentum transfer to a spacecraft from individual particle impacts. This technique is made possible by the extreme precision of the instruments flown on the LISA Pathfinder spacecraft, a technology demonstrator for a future space-based gravitational wave observatory. Pathfinder employed a technique known as drag-free control that achieved rejection of external disturbances, including particle impacts, using a micropropulsion system. Using a simple model of the impacts and knowledge of the control system, we show that it is possible to detect impacts and measure properties such as the transferred momentum, direction of travel, and location of impact on the spacecraft. In this paper, we present the results of a systematic search for impacts during 4348 hr of Pathfinder data. We report a total of 54 candidates with transferred momenta ranging from 0.2 to 230 μNs. We furthermore make a comparison of these candidates with models of micrometeoroid populations in the inner solar system, including those resulting from Jupiter-family comets (JFCs), Oort Cloud comets, Halley-type comets, and asteroids. We find that our measured population is consistent with a population dominated by JFCs, with some evidence for a smaller contribution from Halley-type comets, in agreement with consensus models of the zodiacal dust complex in the momentum range sampled by LISA Pathfinder.

Thorpe, J. I.↗
NASA NTRS1993

Molecular clouds in the centers of galaxies: Constraints from HCN and CO-13 line emission

We have searched for HCN J=1-0 line emission in the centers of 12 galaxies and have detected it in 10 of them. We have obtained complementary data on J=1-0 and 2-1 transitions of CO-12 and CO-13 in these systems. The ratio of integrated intensities, I(CO 1-0)/I(HCN 1-0) = 25 +/- 11 for this sample. We find that HCN emission of this strength can be produced under conditions of subthermal excitation. In combination with the line ratios in CO and CO-13, HCN puts constraints on the mean conditions of molecular clouds and on the mix of cloud types within the projected beam.

Aalto, S.↗
NASA NTRS1980

An evaluation of satellite data for estimating the area of small forestland in the southern lower peninsula of Michigan

A winter black and white band 5, a winter color, a fall color, and a diazo color composite of the fall scene were used to assess the use and potential of LANDSAT images for mapping and estimating acreage of small scattered forest tracts in Barry County, Michigan. Forests as small as 2.5 acres were mapped from each LANDSAT data source. The maps for each image were compared with an available forest-type map. Mapping errors detected were categorized as boundary and identification errors. The most frequently misclassified areas were agriculture lands, treed-bogs, brushlands and lowland and mixed hardwood stands. Stocking level affected interpretation more than stand size. The overall level of the interpretation performance was expressed through the estimation of classification, interpretation, and mapping accuracies. These accuracies ranged from 74 between 74% and 98%. Considering errors, accuracy, and cost, winter color imagery is the best LANDSAT alternative for mapping small forest tracts. However, since the availability of cloud-free winter images of the study area is significantly lower than images for other seasons, a diazo enhanced image of a fall scene is recommended as the best next best alternative.

Karteris, M. A.↗
NASA NTRS2001

Evolution of the Large Scale Circulation, Cloud Structure and Regional Water Cycle Associated with the South China Sea Monsoon During May-June, 1998

In this paper, changes in the large-scale circulation, cloud structures and regional water cycle associated with the evolution of the South China Sea (SCS) monsoon in May-June 1998 were investigated using data from the Tropical Rainfall Measuring Mission (TRMM) and field data from the South China Sea Monsoon Experiment (SCSMEX). Results showed that both tropical and extratropical processes strongly influenced the onset and evolution of the SCS monsoon. Prior to the onset of the SCS monsoon, enhanced convective activities associated with the Madden and Julian Oscillation were detected over the Indian Ocean, and the SCS was under the influence of the West Pacific Anticyclone (WPA) with prevailing low level easterlies and suppressed convection. Establishment of low-level westerlies across Indo-China, following the development of a Bay of Bengal depression played an important role in building up convective available potential energy over the SCS. The onset of SCS monsoon appeared to be triggered by the equatorward penetration of extratropical frontal system, which was established over the coastal region of southern China and Taiwan in early May. Convective activities over the SCS were found to vary inversely with those over the Yangtze River Valley (YRV). Analysis of TRMM microwave and precipitation radar data revealed that during the onset phase, convection over the northern SCS consisted of squall-type rain cell embedded in meso-scale complexes similar to extratropical systems. The radar Z-factor intensity indicated that SCS clouds possessed a bimodal distribution, with a pronounced signal (less than 30dBz) at a height of 2-3 km, and another one (less than 25 dBz) at the 8-10 km level, separated by a well-defined melting level indicated by a bright band at around 5-km level. The stratiform-to-convective cloud ratio was approximately 1:1 in the pre-onset phase, but increased to 5:1 in the active phase. Regional water budget calculations indicated that during the active phase, the SCS was a strong sink (E-P much less than 0) of atmospheric moisture, with the primary source of moisture coming from regions further west over Indo-China and the eastern Indian Ocean. Before onset and during the break, the SCS was a moisture source (E-P greater than ) to the overlying atmosphere. In particular, the SCS provided the bulk of moisture to the torrential rain over the YRV in mid-June 1998.

Lau, William K.-M.↗
NASA NTRS2006

An X-ray Observation of the L1251 Dark Cloud

An X-ray image of the L1251 dark cloud in Cepheus was obtained with the XMM-Newton telescope. More than three dozen sources were detected above a 3 delta limit in X-ray luminosity of L(sub X = 10(exp 29) ergs/s. Among the detections are eight optically visible T Tauri stars, which had been identified in earlier work from their emission at H(alpha). The two strongest X-ray sources have steady luminosities of L(sub X) approx. 10(exp 31) ergs/s and are at the saturation limit for X-ray activity in late-type stars, L(sub X)/L(sub bol) approx. 10(exp -3). X-ray emission was also observed from two CO emission cores in L1251, core C (L1251A) and core E (L1251B). Both regions contain high-velocity molecular gas, bright IRAS sources (Class I protostars), thermal radio sources, and Herbig-Haro (HH) jets. In L1251A strong X-ray emission was discovered in close proximity to the near-inbred and radio source IRSA/VLA 7 and to IRAS 22343+7501. IRSA/VLA 7 thus appears to be the most likely source of the molecular and HH outflows in L1251A. In L1251B X-ray emission was observed from a visible T Tauri star, KP2-44, which is thought to be the driving source for HH 189. Also reported is the tentative detection of X-ray emission from VLA 3, a thermal radio continuum source in L1251B that is closely associated with the extreme Class I protostar IRAS 22376+7455.

Simon, Theodore↗
NASA NTRS1994

Hubble Space Telescope images of the Seyfert galaxies NGC 5929 and MCG 8-11-11

We present the initial results of a program to obtain high resolution images of Seyfert galaxies with the Planetary Camera aboard the Hubble Space Telescope (HST). In this paper we discuss the images of the type 2 Seyfert NGC 5929 and the type 1.5 Seyfert MCG 8-11-11 (= UGC 3374). The images were obtained in the emission lines of (O III) lambda lambda 4959 and 5007 A and H alpha + (N II) lambda lambda 6548 and 6583 A and their adjacent continua. The high-excitation gas in the narrow line region (NLR) of NGC 5929 is resolved into individual clouds in the central 1 sec .5. Although the (O III) emission is clearly not spherically symmetric with respect to the nucleus, it does not define a distinct 'bicone' morphology, as observed by the HST in a few other Seyfert galaxies. We find no direct evidence for the reddening and/or obscuration effects characteristic of a dusty torus, which, in the context of 'unified models', is expected to obscure the active galactic nucleus (AGN) in type 2 Seyfert galaxies. The correspondence between the emission line gas and the radio morphology suggests that the structure of the NLR in NGC 5929 is governed by matter ejected from the AGN. A comparison of the recombination rate of hydrogen in the brightest emission line cloud with an upper limit on the ionizing luminosity emitted toward Earth provides no evidence that the central ionizing source radiates anisotropically. The images of MCG 8-11-11 show only an unresolved nuclear source. No emission line gas associated with the extended radio source is detected. We estimate upper limits on the intensity of extended line emission in this galaxy and examine their significance.

Bower, Gary A.↗
NASA NTRS2004

Clear-Sky Narrowband Albedo Variations Derived from VIRS and MODIS Data

A critical parameter for detecting clouds and aerosols and for retrieving their microphysical properties is the clear-sky radiance. The Clouds and the Earth's Radiant Energy System (CERES) Project uses the visible (VIS; 0.63 m) and near-infrared (NIR; 1.6 or 2.13 m) channels available on same satellites as the CERES scanners. Another channel often used for cloud and aerosol, and vegetation cover retrievals is the vegetation (VEG; 0.86- m) channel that has been available on the Advanced Very High Resolution Radiometer (AVHRR) for many years. Generally, clear-sky albedo for a given surface type is determined for conditions when the vegetation is either thriving or dormant and free of snow. Snow albedo is typically estimated without considering the underlying surface type. The albedo for a surface blanketed by snow, however, should vary with surface type because the vegetation often emerges from the snow to varying degrees depending on the vertical dimensions of the vegetation. For example, a snowcovered prairie will probably be brighter than a snowcovered forest because the snow typically falls off the trees exposing the darker surfaces while the snow on a grassland at the same temperatures will likely be continuous and, therefore, more reflective. Accounting for the vegetation-induced differences should improve the capabilities for distinguishing snow and clouds over different surface types and facilitate improvements in the accuracy of radiative transfer calculations between the snow-covered surface and the atmosphere, eventually leading to improvements in models of the energy budgets over land. This paper presents a more complete analysis of the CERES spectral clear-sky reflectances to determine the variations in clear-sky top-of-atmosphere (TOA) albedos for both snow-free and snow-covered surfaces for four spectral channels using data from Terra and Aqua.. The results should be valuable for improved cloud retrievals and for modeling radiation fields.

Sun-Mack, Sunny↗
NASA NTRS2024

Regimes of Cloud Vertical Structure From Active Observations

We introduce a new type of cloud class, which we call “active cloud regime” (ACR), owing to its provenance from active (lidar and cloud radar) spaceborne cloud observations. ACRs intend to provide a climatological description based on cloud vertical structure (CVS) of the most prevalent monthly CVS mixtures encountered at large spatial scales of ~400 km. ACRs are thus a way to create a gridded dataset of a vertically-resolved cloud mask that can facilitate joint analysis with other gridded datasets. The detailed 2D cloud mask comes from the 2B-CLDCLASS-LIDAR CloudSat dataset fusing CALIPSO (lidar) and CloudSat (cloud radar) cloud detections. We show that the global classification of cloudiness under the ACR framework provides valuable insights on how the world’s dominant cloud systems regulate the two major components of atmospheric energetics, precipitation and radiative cooling. NASA’s GEOS model allows us to demonstrate the feasibility of applying the ACR concept in Earth System Models that have the capability to produce subgrid cloudiness obeying pre-specified vertical overlap rules. Comparison of observed and simulated ACRs provides thus another means to assess the realism of modeled clouds.

cloud vertical structure↗
NASA NTRS1976

CO observations of NGC 1579 /S222/ and S239

The 2.6-mm lines of (C-12)O and (C-13)O have been observed toward the small galactic diffuse nebulae NGC 1579 (S222) and S239. The H92-alpha recombination line has also been detected from NGC 1579. Toward NGC 1579, evidence was observed for self-absorption in the (C-12)O line. For both regions, high-velocity wings and line broadening are observable in the (C-12)O line; the features observed toward S239 suggest ordered free-fall collapse of a localized region of the cloud onto a newborn stellar cluster. Examination of the available data suggests that NGC 1579 is both a reflection nebula (illuminated by LKH-alpha 101) and an obscured H II region excited by a star of spectral type near B1, while S239 is a reflection nebula or a Herbig-Haro object. The present studies of these regions show that line widening in CO is at least as important an indicator of star-formation activity as enhanced line emission.

Knapp, G. R.↗
NASA NTRS1978

H109-alpha recombination line observations of S187 and of S298

The H109-alpha recombination line has been detected in S187 and S298. These observations and previously reported 6-cm continuum observations have been used to derive the large-scale properties of the core-envelope-type structure of these nebulae. An electron temperature of 9750 K and a core-to-envelope electron density ratio of 4 are derived for S298. In S187 an electron temperature of 6200 K and a core-to-envelope electron density ratio of greater than 10 are found. The relationship of the common centrally condensed structure of H II regions to the morphology of dark cloud complexes is considered.

Rossano, G. S.↗