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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Monitoring tropical cyclone intensity using wind fields derived from short-interval satellite images

Rapid scan visible images from the Visible Infrared Spin Scan Radiometer sensor on board SMS-2 and GOES-1 were used to derive high resolution upper and lower tropospheric environmental wind fields around three western Atlantic tropical cyclones (1975-78). These wind fields were used to derive upper and lower tropospheric areal mean relative vorticity and their differences, the net relative angular momentum balance and upper tropospheric mass outflow. These kinematic parameters were shown by studies using composite rawinsonde data to be strongly related to tropical cyclone formation and intensity changes. Also, the role of forced synoptic scale subsidence in tropical cyclone formation was examined. The studies showed that satellite-derived lower and upper tropospheric wind fields can be used to monitor and possibly predict tropical cyclone formation and intensity changes. These kinematic analyses showed that future changes in tropical cyclone intensity are mainly related to the "spin-up" of the storms by the net horizontal transport of relative angular momentum caused by convergence of cyclonic vorticity in the lower troposphere and to a lesser extent the divergence of anticyclone vorticity in the upper troposphere.

Rodgers, E. B.↗
NASA NTRS1981

Estimating ocean-air heat fluxes during cold air outbreaks by satellite

Nomograms of mean column heating due to surface sensible and latent heat fluxes were developed. Mean sensible heating of the cloud free region is related to the cloud free path (CFP, the distance from the shore to the first cloud formation) and the difference between land air and sea surface temperatures, theta sub 1 and theta sub 0, respectively. Mean latent heating is related to the CFP and the difference between land air and sea surface humidities q sub 1 and q sub 0 respectively. Results are also applicable to any path within the cloud free region. Corresponding heat fluxes may be obtained by multiplying the mean heating by the mean wind speed in the boundary layer. The sensible heating estimated by the present method is found to be in good agreement with that computed from the bulk transfer formula. The sensitivity of the solutions to the variations in the initial coastal soundings and large scale subsidence is also investigated. The results are not sensitive to divergence but are affected by the initial lapse rate of potential temperature; the greater the stability, the smaller the heating, other things being equal. Unless one knows the lapse rate at the shore, this requires another independent measurement. For this purpose the downwind slope of the square of the boundary layer height is used, the mean value of which is also directly proportional to the mean sensible heating. The height of the boundary layer should be measurable by future spaceborn lidar systems.

Chou, S. H.↗
NASA NTRS1981

Thermal structure and dynamics of the Jovian atmosphere. I - The Great Red Spot

Temperatures and thermal winds over the Great Red Spot (GRS) are derived from Voyager IRIS data for atmospheric pressures between 3 and 500 mbar. A cold tropopause implies a decrease in anticyclonic vorticity with height above 500 mbar through the lower stratosphere. Observations at 5 microns indicate that there is little emission from the GRS itself, although there is enhanced emission from a ring around it. The behavior of the tropopause and 5 micron temperatures are considered to be results of circulation which rises within the GRS and subsides in the area around it. Results are discussed in the context of several theoretical models of the GRS, and latent heat release as an energy source is considered. Dynamical scalings based on an axisymmetric frictionally controlled vortex indicate that the large-scale dynamics of the GRS are linear, as opposed to those of a tropical cyclone which are nonlinear.

Flasar, F. M.↗
NASA NTRS1981

Thermal structure and dynamics of the Jovian atmosphere. II - Visible cloud features

Thermal structures including major white ovals, hot spot regions, barges and a belt zone pair in the Jovian atmosphere are investigated using Voyager IRIS data. Atmosphere above anticyclonic features is cold relative to the immediate surroundings in the upper troposphere and tropopause region, which is consistent with upwelling and divergence in that part of the atmosphere. Localized cyclonic features are warm relative to their surroundings which implies subsidence with accompanying convergence. Thermal wind shear indicates a decay of the vorticity with height in the upper troposphere and lower stratosphere, and vertical velocities imply an upper limit of vertical mixing times near the tropopause of about 20 years. Various possible models are also examined, including radiative heating, vertical wave propagation, and thermally indirect merdional cells.

Conrath, B. J.↗
NASA NTRS1982

Global observations of a SAR arc

A description is presented of the first results from observations of a stable auroral red (SAR) arc with the global auroral imaging instrumentation on board Dynamics Explorer (DE) 1. This instrumentation includes three spin-scan imaging photometers and a data control unit. The last visible-wavelength imaging sequence prior to onset of the geomagnetic storm begins at 0517 UT on October 20, 1981. An auroral substorm is observed in progress two orbits later, and as the substorm subsides and the diffuse aurora retreats poleward a narrow band of 630-nm emissions is observed at latitudes previously occupied by the aurora. This band is detected at 630 nm only, and is identified as the first optical observation of the SAR arc with DE 1. The third orbit of observations commences at 0830 UT on October 21 with the arc remaining visible across the nightside of earth. No visual signature of the SAR arc is detected during the sixth orbit.

Craven, J. D.↗
NASA NTRS1982

Convective thinning of the lithosphere: A mechanism for rifting and mid-plate volcanism on Earth, Venus, and Mars

Thinning of the Earth's lithosphere by heat advected to its base is a possible mechanism for continental rifting and continental and oceanic mid-plate volcanism. It might also account for continental rifting-like processes and volcanism on Venus and Mars. Earth's continental lithosphere can be thinned to the crust in a few tens of million years by heat advected at a rate of 5 to 10 times the normal basal heat flux. This much heat is easily carried to the lithosphere by mantle plumes. The continent is not required to rest over the mantle hot spot but may move at tens of millimeters per year. Because of the constant level of crustal radioactive heat production, the ratio of the final to the initial surface heat flow increases much less than the ratio of the final to initial basal heat flow. For large increases in asthenospheric heat flow, the lithosphere is almost thinned to the crust before any significant change in surface heat flow occurs. Uplift due to thermal expansion upon thinning is a few kilometers. The oceanic lithosphere can be thinned to the crust in less than 10 million years if the heat advection is at a rate around 5 or more times the basal heat flow into 100 Ma old lithosphere. Uplift upon thinning can compensate the subsidence of spreading and cooling lithosphere.

Spohn, T.↗
NASA NTRS1982

The airborne laser ranging system, its capabilities and applications

The airborne laser ranging system is a multibeam short pulse laser ranging system on board an aircraft. It simultaneously measures the distances between the aircraft and six laser retroreflectors (targets) deployed on the Earth's surface. The system can interrogate over 100 targets distributed over an area of 25,000 sq, kilometers in a matter of hours. Potentially, a total of 1.3 million individual range measurements can be made in a six hour flight. The precision of these range measurements is approximately + or - 1 cm. These measurements are used in procedure which is basically an extension of trilateration techniques to derive the intersite vector between the laser ground targets. By repeating the estimation of the intersite vector, strain and strain rate errors can be estimated. These quantities are essential for crustal dynamic studies which include determination and monitoring of regional strain in the vicinity of active fault zones, land subsidence, and edifice building preceding volcanic eruptions.

Kahn, W. D.↗
NASA NTRS1983

The inference of tropical cyclone dynamics using GOES VISSR/VAS data

The sequence of events observed during tropical cyclone Emily, was suggested as a possible mechanism for cyclogenesis. Geostationary Operational Environmental Satellite (GOES) East VISSR/VAS sensors were used. The VISSR visible imagery obtained every 15 minutes was used to define the low tropospheric cyclonic vortex and upper tropospheric horizontal convergence. The VAS water vapor (channels 9 and 10) and carbon dioxide (channels 3 and 4) channels were used to infer upper and middle tropospheric subsidence by monitoring the Adiabatic compressional drying and warming, respectively, occurring within this layer. Evidence of an existing lower tropospheric cyclonic vortex was seen. The satellite derived wind vectors (length of vector is proportional to wind velocity, where the strongest winds were approximately 35 knots) are superimposed on the GOES visible image of tropical storm Emily. Vectors and low level clouds depict the center of the cyclonic vortex immediately south of the large convective cell in the center of the image. Upper tropospheric cloud tracers and rawinsonde reports along the Eastern United States suggest that the southwesterly environmental upper atmospheric flow is converging with the outflow from the convective cell north of the vortex.

Rodgers, E. B.↗
NASA NTRS1983

NASA's Space Research and Technology Program. Report of a workshop

The status of the spacecraft and subsystem industry and the civil and military uses of space were examined. Genetic and specific enabling technologies were identified. It was found that U.S. spacecraft manufacturers support civil and commercial uses, the military and NASA and, in turn, are supported by subsystem suppliers. However, no single spacecraft program carries sufficient resources to develop advanced critical subsystem technologies and increasingly, U.S. suppliers are facing strong competition from foreign industry that is government subsidized.

Source record↗
NASA NTRS1983

Vertical movements following a dip-slip earthquake

The results of finite element (FEM) computations based on elastic dislocation theory are presented. It is shown that the ratio of fault depth to the lithospheric thickness is a significant factor in the sign of the rebound. Subsidence occurs if the fault penetrates less than approximately 0.68 of the way through the lithosphere. An uplift occurs if the fault cuts deeper. The FEM employed consisted of a 546 node, 500 element grid and a quasi-plane strain algorithm. The situation modeled consisted of a 30 deg dip fault in an initially planar elastic lithosphere overlying a Maxwell viscoelastic asthenosphere. It is suggested that postseismic rebound may be measurable over a several year interval, thus providing data on lithosphere thicknesses.

Melosh, H. J.↗
NASA NTRS1983

On the maintenance of the Marine boundary layer-free tropospheric gradient of transient tracers

A simple model of the marine boundary layer is used to arrive at a steady-state budget for trace gases in this layer. Five processes maintain the tracer balance in the layer. The first is a large-scale horizontal convergence of the tracer; the second is the pumping by clouds of the tracer out of the boundary layer into the free troposphere; the third is penetration by the tracer from the free troposphere into the marine boundary from compensating subsidence in the cloud-free air surrounding cumulus clouds; the fourth is sea surface emission or deposition of the tracer; and the fifth is in situ photochemical production or loss of the tracer within the marine boundary layer. The budget equation is used in deriving an expression for the mixing ratio difference between the two regions. A scale analysis suggests that the mixing ratio difference between the marine boundary layer and the free troposphere can be an order of magnitude smaller in disturbed weather conditions than in suppressed conditions, showing that the difference in chemical concentrations between the free troposphere and the marine boundary layer cannot be rationalized solely on the basis of chemical measurements.

Gidel, L. T.↗
NASA NTRS1983

The Airborne Laser Ranging System - Its capabilities and applications

The Airborne Laser Ranging System is a proposed multibeam short pulse laser ranging system on board an aircraft. It simultaneously measures the distances between the aircraft and six laser retroreflectors (targets) deployed on the earth's surface. Depending on the host aircraft and terrain characteristics, the system can interrogate hundreds of targets distributed over an area as large as 60,000 sq. km in a matter of hours. Potentially, a total of 1.3 million individual range measurements can be made in a 6 hr flight. The precision of these range measurements is approximately 1 cm. These measurements are then used in a procedure which is basically an extension of trilateration techniques to derive the intersite vector between the laser ground targets. By repeating the estimation of the intersite vector, strain and strain rate errors can be estimated. These quantities are essential for crustal dynamic studies which include determination and monitoring of regional strain in the vicinity of active fault zones, land subsidence, and edifice building preceding volcanic eruptions.

Kahn, W. D.↗
NASA NTRS1984

Ancient Volcano-Tectonic Structures of the Olympus Mons Region, Mars

Two old volcano-tectonic collapse structures are exposed north and northeast of the huge shield volcano, Olympus Mons. They are semicircular and were probably low shield volcanoes similar to Alba Patera, but whose central portions have subsided or collapsed. They form the basement upon which younger volcanic materials of Alba Patera Olympus Mons have been emplaced. The oldest structure, Acheron Fossae is over 700 km across and is north of Olympus Mons. It has a surface of considerable relief broken by graben and extensive en echelon and parallel fractures and faults with varied displacements. Acheron Fossae is the most densely cratered in the Olympus Mons region. The structure must have formed very early in martian time. The second is Halex Fossae, northeast of Olympus Mons. Where exposed, it is cut by a series of arcuate grabens that become closer spaced toward its center. The radii of the fractures indicate that the structure may be at least 250 km across and centered beneath the Olympus Plains. Lava flows appear to have issued from some of the arcuate fractures and to have flowed radially away from the center of Halex Fossae. North of Halex Fossae, material of the same age as Halex Fossae overlaps Acheron Fossae. The density of craters on the Halex Fossae material (3,200-4,400 >1km/10 6 km 2 indicates an old age for its formation but one younger than that of Acheron Fossae. These two ancient volcanic-tectonic structures are evidence that the Olympus Mons region has been the locus of major volcanism over much of martian history.

Elliot C Morris↗
NASA NTRS1984

NSSFC: VAS assessment activities

Vertical atmospheric sounder data were evaluated. Basic work thus far has been directed toward evaluating, over the in near real time to determine the instrument's ability to detect regions with potential for severe storm development. A real time hourly water vapor loop 16 hours daily provides data to monitor position and trends of mid and upper level meteorological features. Because water vapor is more uniform than clouds, the water vapor images improve the ability to monitor certain atmospheric features such as jets, shortwaves, vorticity centers, and subsidence zones. Additional products to be evaluated include a version of the split window developed by NASA and cloud drift winds generated from three hourly sequenced CO2 VAS channels. A technique also under evaluation at NSSFC provides hail size potential based on VAS sounding data. Part of a planned upgrade to CSIS linking the 9600 baud phone line to one of the CSIS CPUs to allow access to VAS data via CSIS.

Anthony, R. W.↗
NASA NTRS1983

Analysis of a California Catalina eddy event

During the period 26-29 May 1968 a shallow cyclonic circulation, known locally as a Catalina eddy, developed in the offshore waters of southern California. A synoptic and mesoscale analysis of the event establishes the following: (1) the incipient circulation forms on the coast near Santa Barbara downwind of the coastal mountains, (2) cyclonic shear vorticity appears offshore in response to lee troughing downstream of the coastal mountains between Vandenberg and Pt. Mugu, California, (3) mountain wave activity may be aiding incipient eddy formation in association with synoptic-scale subsidence and the generation of a stable layer near the crest of the coastal mountains, (4) a southeastward displacement and offshore expansion of the circulation occurs following the passage of the synoptic-scale ridge line, and (5) dissipation of the eddy occurs with the onset of a broad onshore flow.

Bosart, L. F.↗
NASA NTRS1984

Cloud distributions in a Bay of Bengal monsoon depression

Much of the volume of a monsoon depression studied over the Bay of Bengal on July 7, 1979 featured thin, fragmentary layers of stratus, implying an absence of strong vertical motion. Coverage by cumulus updrafts was about 20 times less than coverage by inert cumulus remnants, and a great number density of humilis was found moistening the central area, following subsidence and drying. Detailed observations were made of a cloud line growing out of the southwesterly flow south of the center of the depression, which propagated faster than the low level winds. Aircraft altimetry showed an abrupt height drop from 6097 to 6090 m at 483 hPa, over a distance of 50 km from southeast to northwest through the line. Southwesterly momentum was lifted from 900 to 600 hPa and from southeast to northwest through the line. Other colocated singularities in convection and wind fields were found.

Warner, C.↗
NASA NTRS1984

Beta-interferon inhibits cell infection by Trypanosoma cruzi

Beta interferon has been shown to inhibit the capacity of bloodstream forms of the flagellate Trypanosoma cruzi, the causative agent of Chagas' disease, to associate with and infect mouse peritoneal macrophages and rat heart myoblasts. The inhibitory effect was abrogated in the presence of specific antibodies to the interferon. Pretreatment of the parasites with interferon reduced their infectivity for untreated host cells, whereas pretreament of either type of host cell did not affect the interaction. The effect of interferon on the trypanosomes was reversible; the extent of the inhibitory effect was significantly reduced afer 20 min, and was undetectable after 60 min when macrophages were used as host cells. For the myoblasts, 60 min elapsed before the inhibitory effect began to subside and 120 min elapsed before it became insignificant or undetectable.

Kierszenbaum, F.↗
NASA NTRS1984

Mid-tertiary ash flow tuff cauldrons, southwestern New Mexico

Characteristics of 28 known or suspected mid-Tertiary ash-flow tuff cauldrons in New Mexico are described. The largest region is 40 km in diameter, and erosional and block faulting processes have exposed levels as far down as the plutonic roots. The study supports a five-stage process: precursor, caldera collapse, early post-collapse, volcanism, major ring-fracture volcanism, and hydrothermal activity. The stages can repeat or the process can stop at any stage. Post-collapse lavas fell into two categories: cauldron lavas, derived from shallow defluidized residues of caldera-forming ash flow tuff eruption, and framework lavas, evolved from a siliceous pluton below the cauldron complex. The youngest caldera was shallow and formed from asymmetric subsidence and collapse of the caldera walls.

Elston, W. E.↗