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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Surface-based observations of cold-air outbreak clouds during the COMBLE field campaign

Abstract. Cold-air outbreaks (CAOs) are characterized by extreme air–sea energy exchanges and low-level convective clouds over large areas in the high-latitude oceans. As such, CAOs are an important component of the Earth's climate system. The CAOs in the Marine Boundary Layer Experiment (COMBLE) deployment of the US Department of Energy Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) provided the first comprehensive view of CAOs using a suite of ground-based observations at the northern coast of Norway. Here, cloud and precipitation observations from 13 CAO cases during COMBLE are analyzed. A vertical air motion retrieval technique is applied to the Ka-band ARM Zenith-pointing Radar (KAZR) observations. The CAO cumulus clouds are characterized by strong updrafts with magnitudes between 2–8 m s−1, vertical extents of 1–3 km, and horizontal scales of 0.25–3 km. A strong relationship between our vertical air velocity retrievals and liquid water path (LWP) measurements is found. The LWP measurements exceed 1 kg m−2 in strong updraft areas, and the vertical extent of the updraft correlates well with the LWP values. The CAO cumulus clouds exhibit eddy dissipation rate values between 10−3 and 10−2 m2 s−3 in the lowest 10 km of the atmosphere, and using a radar Doppler spectra technique, evidence of secondary ice production is found during one of the cases.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1981

Some observations of surface pressures and the near wake of a blunt trailing edge airfoil

Experiments with a truncated and untruncated airfoils of profiles NACA 640A10, were carried out in subsonic wind tunnels in a velocity range of 19m/s to 54m/s corresponding to Reynolds numbers of 200,000 to 468,000 based on the chord. Airfoil spanned the test section to achieve two dimensionality of the model. Velocity measurements, pressure measurements, and vortex shedding in the wake were measured using a hotwire and pressure transducers. The measured chordwise static pressure distribution on the smooth trailing edge airfoil along the midspan plane, agreed with the theoretical results calculated on the basis of the potential flow for that airfoil. Boundary layer profiles measured in the midspan plane, behind the maximum thickness of the airfoil show no separation of the flow. Spanwise distribution of the measured static pressure on the upper surface of the airfoil shows uniformity for both configurations with and without the boundary layer trip. This uniformity of pressure distribution and separation indicates that the flow on the airfoil was uniform and two dimensional in character.

Digumarthi, R. V.↗
NASA NTRS1985

Lagrangian observations of surface circulation at the Emperor Seamount chain

In a Kuroshio tracking experiment initiated in February 1977, two satellite-reporting buoys, drogued to 100-m depth, were released southeast of Kuyshu Island, Japan. These drifters crossed the Shatskiy Rise in the Kuroshio extension during May and October and then traversed the Emperor Seamount Chain. Although they reached the chain 117 days apart, their movements near the seamounts display remarkably similar patterns, demonstrating upstream meanders in the surface flow; cyclonic eddy activity immediately west of the chain; passage through the same gap associated with the Jingu and Nintoku seamounts; and a wavelike pattern present over the Hess Rise east of the chain. One drifter exhibited cyclonic eddy motion east of the chain in the lee of the Kinmei Seamount.

Vastano, A. C.↗
NASA NTRS1985

ISEE particle observations of surface waves at the magnetopause boundary layer

The dual-spacecraft ISEE mission provides a unique opportunity to study the motions of the magnetopause and adjacent boundary layer. By comparing high-time-resolution energetic particle data from ISEE 1 to those of ISEE 2, the velocity and orientation of the inner boundary of the boundary layer can be determined. Two cases are presented. In one, tailward propagating sinusoidally shaped surface waves with a wavelength in excess of 42,000 km and an amplitude of approximately 5000 km are found. In the other, surface waves are indicated with a wavelength of approximately 40,000 km and an amplitude of approximately 11,000 km having steepened nonsinusoidal shapes. The existence of such large-amplitude waves suggests that the particle dynamics near the magnetopause support nonlinear processes.

Couzens, D.↗
NASA NTRS1988

Microstructural effects on fracture toughness of polycrystalline ceramics in combined mode I and mode II loading

Fracture toughness of polycrystalline alumina and ceria partially-stabilized tetragonal zirconia (CeO2-TZP) ceramics were assessed in combined mode I and mode II loading using precracked disk specimens in diametral compression. Stress states ranging from pure mode I, combined mode I and mode II, and pure mode II were obtained by aligning the center crack at specific angles relative to the loading diameter. The resulting mixed-mode fracture toughness envelope showed significant deviation to higher fracture toughness in mode II relative to the predictions of the linear elastic fracture mechanics theory. Critical comparison with corresponding results on soda-lime glass and fracture surface observations showed that crack surface resistance arising from grain interlocking and abrasion was the main source of the increased fracture toughness in mode II loading of the polycrystalline ceramics. The normalized fracture toughness for pure mode II loading, (KII/KIc), increased with increasing grain size for the CeO2-TZP ceramics. Quantitative fractography confirmed an increased percentage of transgranular fracture of the grains in mode II loading.

Singh, D.↗
NASA NTRS1991

Creep behavior of copper at intermediate temperatures. II - Surface microstructural observations. III - A comparison with theory

Three different types of microstructural slip features are noted to occur during the creep of Cu at 0.46-0.72 of absolute melting point. While single slip is associated with higher temperatures and lower stresses, complex wavy slip features are observed at higher temperatures and higher stresses as well as with increasing strains: suggesting the importance of cross-slip mechanisms. At lower temperatures and higher stresses the multiple-slip morphologies observed indicate that cross-slip mechanisms may control the creep of polycrystalline Cu only over a limited stress and temperature range. A phenomenological model is proposed which assumes that (1) cell boundaries within subgrains act as both sources of, and obstacles to, gliding dislocations, and (2) dislocation annihilation occurs at the cell boundaries by climb and cross-slip.

Raj, S. V.↗
NASA NTRS2002

Statistics of link blockage due to cloud cover for free-space optical communications using NCDC surface weather observation data

Cloud opacity is one of the main atmospheric physical phenomena that can jeopardize the successful completion of an optical link between a spacecraft and a ground station. Hence, the site location chosen for a telescope used for optical communications must rely on knowledge of weather and cloud cover statistics for the geographical area where the telescope itself is located.

optical communication cloud cover↗
NASA NTRS1994

Satellite Observation of Surface Forcing Over the Warm Pool

Daily variations of wind and solar forcing derived from satellite data were compared with sea surface temperature and temperature tendency during the Tropical Ocean Global Atmosphere - Coupled Ocean Atmosphere Response Experiment.

sea surface temperature wind speed thermal respons↗
NASA NTRS2009

Assessing the Potential to Derive Air-Sea Freshwater Fluxes from Aquarius-Like Observations of Surface Salinity

A state-of-the-art numerical model is used to investigate the possibility of determining freshwater flux fields from temporal changes io sea-surface salinity (SSS), a goal of the satellite salinity-measuring mission, Aquarius/SAC-D. Because the estimated advective temporal scale is usually longer than the Aquarius/SAC-D revisit time, the possibility of producing freshwater flux estimates from temporal salinity changes is first examined by using a correlation analysis. For the mean seasonal cycle, the patterns of the correlations between the freshwater fluxes and surface salinity temporal tendencies are mainly zonally oriented, and are highest where the local precipitation is also relatively high. Nonseasonal (deviations from the monthly mean) correlations are highest along mid-latitude moon tracks and are relatively small in the tropics. The complex correlation patterns presented here suggest that a global retrieval of the difference between evaporation and precipitation (E-P) from salinity changes requires more complex techniques than a simple consideration of local balance with surface forcing.

Zhen, Li↗