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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Volcanoes, Polar Clouds and Arctic Ozone

Satellite observations and model calculations show 5 to 10% local column ozone loss in some tropical and mid latitude locations, following El Chichon and Mount Pinatubo eruptions. The rapid deepening of the Antarctic ozone hole in the early 1980s has also been partially attributed to chemistry on volcanic aerosols from a number of large eruptions. Here the effects of volcanoes on Arctic polar processes are explored. Large polar stratospheric cloud particles that cause denitrification cannot form in a volcanically perturbed environment. Denitrification can increase Arctic ozone loss by up to 30% in a future colder climate. However, we show that enhanced chemical processing on volcanic aerosols can increase Arctic ozone loss in a cold year by about 60% independent of denitrification. A coupled chemistry-microphysics model is used to show that widespread distribution of volcanic aerosols in 2000 could have caused severe springtime ozone depletion in the Arctic stratosphere. While, volcanic aerosols can strongly affect the current Arctic column ozone abundance in a cold year, denitrification effects on ozone can only become important in a much colder lower stratosphere.

Tabazadeh, Azadeh↗
DOE OSTI2020

The distribution of neutral hydrogen in the colour–magnitude plane of galaxies

ABSTRACT We present the conditional H i (neutral hydrogen) mass function (HIMF) conditioned on observed optical properties, Mr (r-band absolute magnitude), and Cur (u − r colour), for a sample of 7709 galaxies from Arecibo Legacy Fast ALFA (40 per cent data release – α.40) which overlaps with a common volume in SDSS DR7. Based on the conditional HIMF, we find that the luminous red, luminous blue, and faint blue populations dominate the total HIMF at the high-mass end, knee, and the low-mass end, respectively. We use the conditional HIMF to derive the underlying distribution function of ΩH i (H i density parameter), p(ΩH i), in the colour–magnitude plane of galaxies. The distribution, p(ΩH i), peaks in the blue cloud at $\mathit{ M_{{r}}}^{\text{max}}=-19.25, \mathit{ C_{{ur}}}^{\text{max}}=1.44$ but is skewed. It has a long tail towards faint blue galaxies, and luminous red galaxies. We argue that p(ΩH i) can be used to reveal the underlying relation between cold gas, stellar mass, and the star formation rate in an unbiased way, that is, the derived relation does not suffer from survey or sample selection.

Dutta, Saili (ORCID:0000000288585845)↗
NASA NTRS1984

Stratocumulus simulations with a general circulation model

Stratus and stratocumulus cloud sheets which are among the most common cloud types over the world are discussed. They are characteristic of the undisturbed subtropical marine boundary layer over the eastern oceans, where cool water and large scale sinking motion suppress penetrative cumulus convection. They also occur over the Arctic Ocean, particularly in summer, and behind cold outbreaks over the western oceans in winter. Observational studies were conducted and further observations are planned.

Randall, D. A.↗
NASA NTRS1983

Stratocumulus simulation with a general circulation model

Stratus and stratocumulus cloud sheets which are among the most common cloud types over the world are discussed. They are characteristic of the undisturbed subtropical marine boundary layer over the eastern oceans, where cool water and large scale sinking motion suppress penetrative cumulus convection. They also occur over the Arctic Ocean, particularly in summer, and behind cold outbreaks over the western oceans in winter. Observational studies were conducted and further observations are planned.

Randall, D. A.↗
NASA NTRS1996

Polar Vortex Conditions during the 1995-96 Artic Winter: Meteorology and MLS Ozone

The 1995-96 northern hemisphere (NH) 205 winter stratosphere was colder than in any of the previous 17 winters, with lower stratospheric temperatures continuously below the type 1 (primarily HN03) polar stratospheric cloud (PSC) threshold for over 2 1/2 months. Upper tropospheric ridges in late Feb and early Mar 1996 led to the lowest observed NH lower stratospheric temperatures, and the latest observed NH temperatures below the type 2 (water ice) PSC threshold. Consistent with the unusual cold and chemical processing on PSCS, Upper Atmosphere Research Satellite (UARS) MLS observed a greater decrease in lower stratospheric ozone (03) in 1995-96 than in any of the previous 4 NH winters. 03 decreased throughout the vortex over an altitude range nearly as large as that typical of the southern hemisphere (SH). The decrease between late Dec 1995 and early Mar 1996 was about 2/3 of that over the equivalent SH period. As in other NH winters, temperatures in 1996 rose above the PSC threshold before the spring equinox, ending chemical processing in the NH vortex much earlier than is usual in the SH. A downward trend in column 03 above 100 hPa during Jan and Feb 1996 appears to be related to the lower stratospheric 03 depletion.

Manney, G. L.↗
NASA NTRS2024

Meteorology Modulates the Impact of GCM Horizontal Resolution on Underestimation of Midlatitude Ocean Wind Speeds

We utilize ocean 10-m wind speed (U 10m ) from the microwave Multi-sensor Advanced Climatology data set to examine the coupling between convective cloud and precipitation processes, synoptic state, and U 10m and to evaluate the representation of U 10m in global climate models (GCMs). We find that midlatitude U 10m is underestimated by GCMs relative to observations. We examine two potential mechanisms to explain this model behavior: cold pool formation in cold air outbreaks (CAOs) associated with downdrafts that enhance U 10m and sea surface temperature (SST) gradients affecting U 10m through thermally forced surface winds at regional scales. When the effects of the CAO index (M) and SST gradients on U 10m are accounted for, a relationship between GCM horizontal resolution and U 10m appears. The strongest correlation between resolution and U 10m is over the western boundary currents characterized by frequent CAOs atop strong SST gradients which drives the strongest surface fluxes on Earth.

surface wind speed↗
NASA NTRS1984

Dynamic evolution of recurrent mass ejections observed in H-alpha and C IV lines

The mass ejections of 1 September, 1980 are studied from observations obtained with the MSDP spectrograph and with the Ultraviolet Spectrometer and Polarimeter aboard the Solar Maximum Mission satellite. The analysis is focused on observations in the chromospheric H-alpha line and the transition region C IV 1548 A line. It is noted that cold and hot material had the same projection, although the upward C IV velocity structure was more extended than the H-alpha one. It is shown that the observed contrast of the H-alpha absorbing structure can be interpreted in terms of a dynamic cloud model overlying the chromosphere. Radial velocities of 25-30 km/s and -40 km/s are estimated for the first and second phases of ejection, respectively.

Schmieder, B.↗
NASA NTRS1999

A Southern California Perspective of the April, 1998 Trans-Pacific Asian Dust Event

The Jet Propulsion Laboratory (JPL) coherent CO2 backscatter lidar has been in almost continuous operation since 1984 and has now accumulated a significant time-series database tracking the long-term and seasonal variability of backscatter from the atmospheric column above the Pasadena, Calif. locale. A particularly noteworthy episode observed by the lidar in 1998 was a particularly extreme instance of incursion by Asian-sourced dust during the closing days of April. Such events are not uncommon during the northern spring, when strong cold fronts and convection over the Asian interior deserts loft crustal material into the mid-troposphere whence it can be transported across the Pacific Ocean, occasionally reaching the continental US. However, the abnormal strength of the initiating storm in this case generated an atypically dense cloud of material which resulted in dramatically reduced visibility along the length of the Western Seaboard. These dust events are now recognized as a potentially significant, non-negligible radiative forcing influence. The progress of the April 1998 dust cloud eastward across the Pacific Ocean was initially observed in satellite imagery and transmitted to the broader atmospheric research community via electronic communications. The use of Internet technology in this way was effective in facilitating a rapid response correlative measurement exercise by numerous atmospheric observation stations throughout the western US and its success has resulted in the subsequent establishment of an ad hoc communications environment, data exchange medium, and mechanism for providing early-warning alert of other significant atmospheric phenomena in the future.

Tratt, David M.↗
DOE OSTI2025

Tropospheric aerosols over the western North Atlantic Ocean during the winter and summer deployments of ACTIVATE 2020: life cycle, transport, and distribution

The Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) is a NASA mission to characterize aerosol–cloud interactions over the western North Atlantic Ocean (WNAO). Such characterization requires understanding of life cycle, composition, transport pathways, and distribution of aerosols over the WNAO. This study uses the GEOS-Chem model to simulate aerosol distributions and properties that are evaluated against aircraft, ground-based, and satellite observations during the winter and summer field deployments in 2020 of ACTIVATE. Transport in the boundary layer (BL) behind cold fronts was a major mechanism for the North American continental outflow of pollution to the WNAO in winter. Turbulent mixing was the main driver for the upward transport of sea salt within and ventilation out of BL in winter. The BL aerosol composition was dominated by sea salt, which increased in the summer, followed by organics and sulfate. Aircraft in situ aerosol measurements provided useful constraints on wet scavenging in GEOS-Chem. The model generally captured observed features such as continental outflow, land–ocean gradient, and mixing of anthropogenic aerosols with sea salt. Model sensitivity experiments with elevated smoke injection heights to the mid-troposphere (versus within BL) better reproduced observations of smoke aerosols from the western US wildfires over the WNAO in the summer. Model analysis suggests strong hygroscopic growth of sea salt particles and their seeding of marine BL clouds over the WNAO (< 35° N). Future modeling efforts should focus on improving parameterizations for aerosol wet scavenging, implementing realistic smoke injection heights, and applying high-resolution models that better resolve vertical transport.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Broken into Pieces: ATLAS and Aliqa Uma as One Single Stream

We present the first spectroscopic measurements of the ATLAS and Aliqa Uma streams from the Southern Stellar Stream Spectroscopic Survey (S 5), in combination with the photometric data from the Dark Energy Survey and astrometric data from Gaia. From the coherence of spectroscopic members in radial velocity and proper motion, we find that these two systems are extremely likely to be one stream with discontinuity in morphology and density on the sky (the “kink” feature). We refer to this entire stream as the ATLAS-Aliqa Uma stream, or the AAU stream. We perform a comprehensive exploration of the effect of baryonic substructures and find that only an encounter with the Sagittarius dwarf ∼0.5 Gyr ago can create a feature similar to the observed “kink.” In addition, we also identify two gaps in the ATLAS component associated with the broadening in the stream width (the “broadening” feature). These gaps have likely been created by small mass perturbers, such as dark matter halos, as the AAU stream is the most distant cold stream known with severe variations in both the stream surface density and the stream track on the sky. With the stream track, stream distance, and kinematic information, we determine the orbit of the AAU stream and find that it has been affected by the Large Magellanic Cloud, resulting in a misalignment between the proper motion and stream track. Together with the Orphan-Chenab Stream, AAU is the second stream pair that has been found to be a single stream separated into two segments by external perturbation.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

Observations of lunar atmosphere.

A cold cathode ionization gauge was left on the lunar surface by the Apollo 14 astronauts to measure the neutral gas density on the moon. The gauge has detected the presence of a very low concentration of atmospheric particles at night, about 200,000 per cu cm. Gas clouds of locally greater concentrations have been observed at times, and, while the possibility that these are artifacts associated with the Apollo hardware cannot be conclusively ruled out, the clouds appear to be of natural origin. Contaminant gases due to the Apollo operation dominate during the lunar day, but these may dissipate within a few months.

Johnson, F. S.↗
NASA NTRS1994

Jim Pollack's Contributions to Planetary Science

Jim Pollack was an extraordinary scientist. Since receiving his Ph.D. from Harvard in 1965, he published hundreds of papers in scientific journals, encyclopedias, popular magazines, and books. The sheer volume of this kind of productivity is impressive enough, but when considering the diversity and detail of his work, these accomplishments seem almost superhuman. Jim studied and wrote about every planet in the solar system. For, this he was perhaps the most distinguished planetary scientist of his generation. He successfully identified the composition of Saturn's rings and Venus's clouds. With his collaborators, he created the first detailed models for the formation of the outer planets, and the general circulation of the Martian atmosphere. His interest in Mars dust storms provided a foundation for the "nuclear winter" theory that ultimately helped shape foreign policy in the cold war era. Jim's creative talents brought him many awards including the Kuiper Award of the Division of Planetary Sciences, the Leo Szilard Award of the American Physical Society, H. Julian Allen award of the Ames Research Center, and several NASA medals for exceptional scientific achievement.

Haberle, Robert M.↗
NASA NTRS2010

Cryogenic Storage Tank Non-Destructive Evaluation

This slide presentation reviews the work in non-destructive evaluation (NDE) of cryogenic storage tanks. Four large cryogenic tanks, constructed in 1965 with perlite insulation in the annular regions, are of concern. The construction of the tanks, two Liquid Oxygen (LOX) and two Liquid Hydrogen (LH2), are described. The loss rate for the LOX tank at Pad A is slightly higher than that for the one at Pad B. The concerns for the LH2 tank at Pad B are that there is a significantly higher boil-off rate than that at Pad A, that there is mold growth, indicative of increased heat flow, that there is a long down-time needed for repairs, and that 3 of 5 full thermal cycles have been used on the Pad B LH2 tank. The advantages and disadvantages of thermal imaging are given. A detailed description of what is visible of the structures in the infra-red is given and views of the thermal images are included. Missing Perlite is given as the probable cause of the cold spot on the Pad B LH2 tank. There is no indications of problematic cold regions on the Pad A LH2 tank, as shown by the thermal images given in the presentation. There is definite indication of a cold region on the Pad A LOX tank. There is however concerns with thermal imaging, as thermal images can be significantly effected by environmental conditions, image differences on similar days but with different wind speeds. Other effects that must be considered include ambient temperature, humidity levels/dew, and cloud reflections

Arens, Ellen↗
NASA NTRSDate not supplied

Multi-angle Imaging SpectroRadiometer

MISR views the sunlit Earth simultaneously at nine widely spaced angles and provides ongoing global coverage with high spatial detail. Its imagery is carefully calibrated to provide accurate measures of the brightness, contrast, and color of reflected sunlight. MISR provides new types of information for scientists studying Earth's climate, such as the regional and global distribution of different types of atmospheric particles and aerosols. The change in reflection at different view angles provides the means to distinguish aerosol types, cloud forms, and land surface cover. Combined with stereoscopic techniques, this enables construction of 3-D cloud models and estimation of the total amount of sunlight reflected by Earth's diverse environments. MISR was built for NASA by the Jet Propulsion Laboratory (JPL) in Pasadena, California. It is part of NASA's first Earth Observing System (EOS) spacecraft, the Terra spacecraft, which was launched into polar orbit from Vandenberg Air Force Base on December 18, 1999. MISR has been continuously providing data since February 24, 2000. [Mission Objectives] The MISR instrument acquires systematic multi-angle measurements for global monitoring of top-of-atmosphere and surface albedos and for measuring the shortwave radiative properties of aerosols, clouds, and surface scenes in order to characterize their impact on the Earth's climate. The Earth's climate is constantly changing -- as a consequence of both natural processes and human activities. Scientists care a great deal about even small changes in Earth's climate, since they can affect our comfort and well-being, and possibly our survival. A few years of below-average rainfall, an unusually cold winter, or a change in emissions from a coal-burning power plant, can influence the quality of life of people, plants, and animals in the region involved. The goal of NASA's Earth Observing System (EOS) is to increase our understanding of the climate changes that are occurring on our planet, and the reasons for these changes, so we are better equipped to anticipate and prepare for the future. The MISR instrument is a part of EOS. Its role is to measure the amount of sunlight scattered in different directions under natural conditions. These measurements will help quantify the amount of solar energy that heats the Earth's surface and atmosphere, and the changes that occur in them over the lifetime of the MISR instrument. From the MISR observations, we are also learning more about those components of the Earth's environment that scatter sunlight: particles in the atmosphere, the planet's surface, and clouds. MISR monitors changes in surface reflection properties, in atmospheric aerosol content and composition, and in cloudiness. Scientists use these data to study land use changes, air pollution, volcanic eruptions, as well as processes such as desertification, deforestation, and soil erosion. As part of the EOS program, computer models that predict future climate will be improved by the results of these studies. [Temporal_Coverage: Start_Date=2000-02-24; Stop_Date=] [Spatial_Coverage: Southernmost_Latitude=-90; Northernmost_Latitude=90; Westernmost_Longitude=-180; Easternmost_Longitude=180].

Diner, David J.↗
NASA NTRS1972

Lunar atmosphere measurements.

Cold cathode ionization gauges were left on the lunar surface during Apollo missions 14 and 15 to measure the amount of lunar gas. The observed nighttime concentration is very low, about 200,000 per cu cm, which is less than the neon concentration that might be expected from the solar wind. This suggests that the lunar surface is not saturated with solar wind neon, and hence that less neon is being released from the surface than impinges upon it. The low nighttime concentration shows that contaminant gases from the Apollo operations freeze out at night or become adsorbed on the cold lunar surface. Observed daytime concentrations have been two orders of magnitude greater than the nighttime values and appear to be due mainly to contamination in the landing area. The rate at which the contamination is decreasing is characterized by a time constant of a few months. Gas clouds have been seen at times and these appear to have been released from Apollo hardware left on the lunar surface.

Johnson, F. S.↗
NASA NTRS1984

A model for the estimation of the surface fluxes of momentum, heat and moisture of the cloud topped marine atmospheric boundary layer from satellite measurable parameters

A model is developed for the estimation of the surface fluxes of momentum, heat, and moisture of the cloud topped marine atmospheric boundary layer by use of satellite remotely sensed parameters. The parameters chosen for the problem are the integrated liquid water content, q sub li, the integrated water vapor content, q sub vi, the cloud top temperature, and either a measure of the 10 meter neutral wind speed or the friction velocity at the surface. Under the assumption of a horizontally homogeneous, well-mixed boundary layer, the model calculates the equivalent potential temperature and total water profiles of the boundary layer along with the boundary layer height from inputs of q sub li, q sub vi, and cloud top temperature. These values, along with the 10m neutral wind speed or friction velocity and the sea surface temperature are then used to estimate the surface fluxes. The development of a scheme to parameterize the integrated water vapor outside of the boundary layer for the cases of cold air outbreak and California coastal stratus is presented.

Allison, D. E.↗
NASA NTRS1993

Mesoscale characteristics of monsoonal convection and associated stratiform precipitation

Observations undertaken on 12 January 1990 at Darwin (Australia) are used to document the structure of a monsoonal rainband in a low convective available potential energy low-shear tropical environment. Dual-Doppler radar analyses are employed to investigate the structure and kinematics of the convective and stratiform regions. A system with the characteristics of a relatively short-lived squall line in which warm rain processes play a significant role in the production of precipitation is evident. Planetary boundary layer cold-pool production is important in the organization and motion of the system. A trailing stratiform region is evident with a mean updraft-downdraft circulation, but is composed of in situ decaying convective cells. A storm-relative mesoscale cyclonic circulation is also observed within the stratiform cloud. This vortex was maintained by thermodynamically induced midlevel convergence, convectively generated storm-scale circulations, and their interaction with the background monsoon flow.

Keenan, Thomas D.↗
NASA NTRSDate not supplied

Characteristics and Origins of Frontal Convection During IMPACTS on 25 January 2020

This presentation will discuss the characteristics of frontal convection and its estimation from the ER-2 multifrequency nadir reflectivity and Doppler velocity from a warm-occlusion frontal system that traversed across the Northeast U.S. on 25 January 2020. This system that occurred during the IMPACTS field deployment, brought widespread clouds and precipitation to the Northeast. The system brought primarily rain in most areas of more intense rainfall associated with embedded convection near the frontal band and some freezing rain and/or snowfall in the northern regions or higher terrain due to the pre-existing low-level cold air. The NASA ER-2 instrumented with multifrequency radar and the NASA P-3 with in situ microphysics measurements both collected data from this system. The focus of this presentation is on the estimation of vertical velocity in convective and non-convective regions using the ER-2 nadir Doppler measurements. Vertical velocities are inherently difficult to estimate in frontal systems at mesoscale and below other than from direct in situ measurement because of their small magnitudes and errors in the measurements. Estimates from nadir Doppler measurements such as from the ER-2 are challenging because of both Doppler velocity uncertainties and the need to estimate particle fallspeed since the Doppler measurement is the vertical velocity plus the hydrometeor fallspeed. In the presentation, the vertical velocity estimation, its associated errors, and a possible mitigation scheme are described. The characteristics of the convective and stratiform regions on 25 January 2020 are discussed. The vertical velocity estimated from the nadir Doppler measurements are compared with P-3 in situ measurements. Estimation of vertical velocity is one of the goals for upcoming spaceborne missions such as EarthCare and ACCP.

Gerald M. Heymsfield↗