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NASA NTRS1974

Satellite views of hurricane Camille

Three periods within the life cycle of Hurricane Camille (1969) are studied with radiometric and camera measurements from Nimbus-3 and camera information from ATS-3 in conjunction with conventional information. These periods are the deepening phase, the interaction of Camille with midlatitude westerlies, and the excessive rain producing period when the cyclone was over the central Appalachian Mountain. Just prior to significant deepening, the Nimbus-3 Medium Resolution Infrared Radiometer (MRIR) showed that a pronounced feeder band had formed southeast of the center which was associated with the rapid transport of moisture into the storm circulation. During the rapid deepening phase the MRIR measurements indicated the development of large scale subsidence throughout the troposphere northwest of the center. When Camille was over the lower Mississippi Valley it acted as an obstruction to the envrionmental wind. A region of widespread subsidence was created west and north of the cyclone center. Increased cloud-top elevations, back to the levels reached when Camille was an intense cyclone over the Gulf of Mexico, were estimated from the Nimbus-3 High Resolution Infrared Radiometer (HRIR) measurements on August 20, 1969, when Camille produced rains of major flood proportions near the east slopes of the Appalachians in central Virginia.

Shenk, W. E.↗

NASA NTRS1972

Ground magnetometer survey in the Valley of Ten Thousand Smokes, Alaska

A reconnaissance magnetometer survey was conducted with both total- and vertical-field magnetometers. The large, sharp, narrow total magnetic anomalies observed over a zone of relict fumaroles in Broken Mountain Valley showed spectacular agreement with the surficial geology. Such a correlation is a strong indication that accumulations of magnetic minerals have been preserved along these fissure vents at shallow depths. Since large magnetic anomalies were measured near fumarolic markings along all of the traverses, it is proposed that the retention of sublimates along fumarolic vents is common throughout the Valley. The generally concentric contours of the vertical magnetic anomaly at the head of the Valley suggest that the dome of Novarupta is merely the surficial expression of a very massive conical-shaped intrusive centered just northeast of the dome. The magnetometer survey indicates that the pyroclastics in the Valley may be over 150 meters thick. Such an estimate is compatible with the volume of eruptive material needed to compensate for the subsidence surrounding Novarupta as well as a sizable amount of other regional subsidence.

Trible, M. C.↗

NASA NTRS1974

Interaction of a cumulus cloud ensemble with the large-scale environment. I

A theory of the interaction of a cumulus cloud ensemble with the large-scale environment is developed. In this theory, the large-scale environment is divided into the subcloud mixed layer and the region above. The time changes of the environment are governed by the heat and moisture budget equations for the subcloud mixed layer and for the region above, and by a prognostic equation for the depth of the mixed layer. In the environment above the mixed layer, the cumulus convection affects the temperature and moisture fields through cumulus-induced subsidence and detrainment of saturated air containing liquid water which evaporates in the environment. In the subcloud mixed layer, the cumulus convection does not act directly on the temperature and moisture fields, but it affects the depth of the mixed layer through cumulus-induced subsidence.

Arakawa, A.↗

NASA NTRS1976

Close-up view of 20 March 1976 tornadoes - Sinking cloud tops to suction vortices

The article describes an airborne mission using a Learjet to secure direct data on a family of tornadoes spawned by a rotating thunderstorm in the Missouri-Illinois-Indiana area in March 1976 following an unusually warm February. Weakening of the tornado following increased cloud-scale vertical motion, predicted by a model constructed by Fujita (1972), was confirmed. The aircraft inspected overshooting cloud tops, examined subsidence (holes and depressions) in anvil tops it overflew, and surveyed footprints left by the tornadoes and tornado-blown litter on the ground traversed by the disturbances. Subsidence of cloud tops in advance of violent tornadoes below was confirmed. Isolated and multiple suction vortices left their characteristic ground marks; three scales of motion: tornado cyclone, tornado, and suction vortex, are evidenced by the ground truth.

Fujita, T. T.↗

NASA NTRS1977

Comparison of drag and mass spectrometer measurements during small geomagnetic disturbances

During small geomagnetic disturbances, ESRO 4 and OGO 6 gas analyzer measurements at high altitudes suggest that helium and atomic oxygen concentrations in the lower thermosphere decrease, whereas satellite drag measurements indicate that density increases. This discrepancy is explained by the corresponding temperature increases maximizing at high latitudes. ESRO 4 data suggest that at altitudes where atomic oxygen or helium predominates, the temperature increase compensates for the decrease in lower thermospheric concentrations. This yields a net density increase with geomagnetic disturbances. The Explorer 39 drag satellite measurements verify this conclusion. It is felt that the composition variations associated with minor disturbances indicate the upwelling of the polar atmosphere, circulation towards the equator, and subsidence in the equatorial region. ESRO measurements show that at low latitudes the increases in helium concentrations with geomagnetic disturbances are chiefly caused by the circulation from high latitudes and the subsidence at lower latitudes.

Keating, G. M.↗

NASA NTRS1978

Origin of multi-ring basin ridge systems - An upper limit to elastic deformation based on a finite-element model

A finite-element model of a 500-km diameter lunar basin flooded with 10 km of basalt was used to represent the central portion of a multi-ring basin undergoing elastic deformation as a result of basin subsidence. Gravitational forces due to the weight of the basalt were set as the initial forces in the model; elastic constants computed from seismic velocities of lunar samples provided strength specifications. In addition, the crust was constrained by permitting no displacements at a depth of 60 km. Because of the strength of the lithosphere, surface subsidence amounted to only 20 m. This magnitude of elastic deformation does not equal that found on the lunar surface, but the orientation of principal stress and the position of circumferential compressional stress are compatible with the evolution of inner-ring and radial ridge systems by gravitational-induced downdropping.

Maxwell, T. A.↗

NASA NTRS1980

Properties of African squall lines inferred from time-lapse satellite imagery

Analysis of 48 h of time-lapse satellite imagery of a family of squall lines in Africa links the phenomena with a characteristic cloud cluster and with a wind field perturbation which is enhanced in passing through an African easterly wave trough. A thin 'arc line' of low-level developing cumulus, a salient feature of the squall lines on the imagery, is shown to occur at the front boundary of the mesoscale/convective scale subsidence. Analysis of the wind field indicates that a squall line is associated with a vorticity center in the mid-level easterly flow which accompanies the mesoscale subsidence which, in turn, contributes to further forced ascent of subcloud air along the front of the squall line into convective towers which merge into an extensive anvil. The squall lines evolved through a life cycle of 6 to 12 h while the larger cloud cluster and wind perturbation lasted over 48 h. The magnitude of the vertical mass exchange suggests that squall-line families contribute significantly to the tropical energy balance.

Fortune, M.↗

NASA NTRS1980

The enviornmental assessment of a contemporary coal mining system

A contemporary underground coal mine in eastern Kentucky was assessed in order to determine potential off-site and on-site environmental impacts associated with the mining system in the given environmental setting. A 4 section, continuous room and pillor mine plan was developed for an appropriate site in eastern Kentucky. Potential environmental impacts were identified, and mitigation costs determined. The major potential environmental impacts were determined to be: acid water drainage from the mine and refuse site, uneven subsidence of the surface as a result of mining activity, and alteration of ground water aquifers in the subsidence zone. In the specific case examined, the costs of environmental impact mitigation to levels prescribed by regulations would not exceed $1/ton of coal mined, and post mining land values would not be affected.

Dutzi, E. J.↗

NASA NTRS1981

Possible terrestrial analogs of Valhalla and other ripple-ring basins

The most remarkable feature on Callisto is Valhalla, a 3000 km wide structure comprised of dozens of concentric ridges and scarps surrounding a central smooth zone. Conventionally, Valhalla is interpreted as a multi-ring impact basin (similar to those on the terrestrial planets) whose morphology has been strongly effected by a thin and weak icy lithosphere in which it formed. Alternatively, Valhalla may have been formed by some non-impact related processes. In particular, ice cauldrons formed in Iceland by subsidence of glacier ice into voids created by geothermal melting are grossly similar to Valhalla in that both formed in ice and have multiple rings. Theoretical support for a similar subsidence mode of origin for Valhalla is provided by models of the thermal evolution of ice-silicate planets that result in diapiric sinking of lithospheric material into a water mantle (e.g., Paramentier and Head, 1979).

Wood, C. A.↗

NASA NTRS1982

Dynamical implications of the observed thermal contrasts in Venus' upper atmosphere

Observational data on the Venusian upper atmosphere are analyzed to determine the dynamical implications of the large pressure change across the terminator, to study the change in diurnal contrast pattern at the 100 km level, and to investigate the viability of the most straightforward explanation of the cooling, radiative emission by CO2 in the 15 micron bands. Evidence is discussed that a major subsidence or downward vertical contraction of the upper atmosphere occurs across the terminator. The observation that supersonic velocities would be induced in horizontal, inviscid flow by the observed pressure distributions affected by the described flow subsidence is investigated by generalizing the equations for adiabatic inviscid flow along streamtubes to the case of nonhorizontal inviscid flow with heat addition. Nightside cooling is discussed, showing variations in cooling rates. Finally, zonal winds below 100 km are considered.

Seiff, A.↗

NASA NTRS1983

Grabens, basin tectonics, and the maximum total expansion of the moon

Information from lunar grabens is used to address the question of whether the grabens and wrinkle ridges are tectonic or volcanic in origin. The geometry of simple grabens is discussed, and the kinematics and mechanics are addressed in terms of an elastic response model, a brittle response model, the mechanics of the megaregolith, and total extension for all lunar grabens. Constraints on the thermal evolution of the moon are considered, including thermal history calculations and grabens in space and time. Mare basin tectonics is discussed in terms of two kinematic models/ subsidence by increased radius of curvature and subsidence with no increase in radius of curvature. It is concluded that the observable geological history of the moon is inconsistent with any significant expansion of the moon since about 3.9 billion years ago. Both thermal and tectonic models of lunar evolution are critized.

Golombek, M. P.↗

NASA NTRS1985

Extensional tectonics and collapse structures in the Suez Rift (Egypt)

The Suez Rift is a 300 km long and 50 to 80 km wide basin which cuts a granitic and metamorphic shield of Precambrian age, covered by sediments of Paleozoic to Paleogene age. The rift structure is dominated by tilted blocks bounded by NW-SE normal faults. The reconstruction of the paleostresses indicates a N 050 extension during the whole stage of rifting. Rifting began 24 My ago with dikes intrusions; main faulting and subsidence occurred during Early Miocene producing a 80 km wide basin (Clysmic Gulf). During Pliocene and Quaternary times, faulting is still active but subsidence is restricted to a narrower area (Present Gulf). On the Eastern margin of the gulf, two sets of fault trends are predominant: (1) N 140 to 150 E faults parallel to the gulf trend with pure dip-slip displacement; and (2) cross faults, oriented NOO to N 30 E that have a strike-slip component consistent with the N 050 E distensive stress regime. The mean dip cross fault is steeper (70 to 80 deg) than the dip of the faults parallel to the Gulf (30 to 70 deg). These two sets of fault define diamond shaped tilted block. The difference of mechanical behavior between the basement rocks and the overlying sedimentary cover caused structural disharmony and distinct fault geometries.

Chenet, P. Y.↗

NASA NTRS1985

El Nino and atmospheric water vapor - Observations from Nimbus 7 SMMR

Atmospheric water vapor content over the global oceans is measured to study the air-sea interactions associated with El Nino/Southern Oscillation. A scanning multichannel microwave radiometer measured brightness temperatures of the earth-atmosphere system at 6.6, 10.7, 18, 21, and 37 GHz, and from these data water vapor content is derived. The seasonal mean distribution of water vapor for the regular season cycle from 1979-1981 are examined; the minima associated with the subtropical anticyclones in the Pacific and Atlantic Oceans in the Northern and Southern hemispheres, and the Walker circulation in the tropical Pacific Ocean are analyzed. The positive and negative anomalies in water vapor during the 1982-1983 El Nino event, which correspond to convergence and enhanced convective activity, are investigated. It is concluded that during El Nino events a system of convection and subsidence exists; the subsidence slows the supply of water vapor and cloud growth in the convectively active center and the Walker circulation is reversed.

Prabhakara, C.↗

NASA NTRS1986

Convection beneath young oceanic lithosphere - Implications for thermal structure and gravity

Small-scale convection under the oceanic lithosphere which begins in the first 5 m.y. of cooling can produce a gravity signal with the amplitude and wavelength observed for large areas of the central Pacific and southern Indian oceans using Seasat altimeter data. The trend of the observed anomalies is parallel to the direction of plate motion as might be expected if they were produced by small-scale convection. Models predict that the wavelengths of gravity anomalies increase more rapidly with age than is observed. The persistence of short relatively uniform wavelength anomalies (less than 200 km) to crustal ages of 50 Ma may indicate that they were produced when the lithosphere was very young and thin and were 'frozen in' as cooling thickened the elastic lithosphere. Small-scale convection which begins under very young lithosphere does not violate other geophysical data such as the rate of seafloor subsidence and variations of geoid height with age. After convection has begun, the subsidence due to thermal contraction within the lithosphere varies linearly with age, in the absence of mantle heat sources, although the rate of change of these quantities is affected by convection. Much of the variation of the geoid height across fracture zones can be fit by a model which includes small-scale convection.

Buck, W. R.↗

NASA NTRS1987

Interseismic deformation for normal fault earthquakes

Comparison between the coseismic vertical deformation associated with normal fault earthquakes and permanent deformation indicated by geologic structure indicates that large deformation must occur during the period between earthquakes. When sufficient geodetic and geologic information is available it is possible to estimate the spatial character of this interseismic deformation. A case in point is the 1983 Borah Peak, Idaho earthquake. This normal fault earthquake produced roughly 5 times as much basin subsidence as it did uplift of the adjacent mountain ranges. In contrast, geophysical and geological observations show that the basin is roughly as deep as the bounding range is high. A similar normal fault event in the Basin and Range, the 1959 Hebgen Lake earthquake, was also accompanied by substantially larger subsidence than uplift. In this case, postseismic geodetic measurements show broad regional uplift with a spatial pattern which is roughly consistent with that proposed for the Borah Peak event. Modeling suggests that postseismic viscoelastic relaxation and strain accumulation in an elastic lithosphere overlying a viscoelastic asthenosphere are possible physical mechanisms to generate interseismic uplift. These mechanisms may be the contemporary expression of those processes responsible for the high elevation of the Basin and Range Province.

Reilinger, Robert↗

NASA NTRS1988

Coupling of the radiative, convective, and surface fluxes over the equatorial Pacific

An idealized energy-balance model for a closed tropical circulation is first presented to illustrate the coupling between the net tropospheric cooling, the surface fluxes, and the mean subsidence away from the precipitation zones. Then a one-dimensional diagnostic model and a radiation model with boundary layer clouds are combined to explore this coupling for a specific region, using mean sounding data over the tropical Pacific. The radiatively driven subsidence rate at the top of the convective boundary layer is approximately 35 mb/day and is largely independent of boundary layer cloud fraction. The sensitivity of the corresponding convective heat flux profiles to the mass divergence profile and cloud fraction within the boundary layer is explored. Reasonable assumptions give realistic surface sensible and latent heat fluxes for this region of approximately 10 and 130 W/sq m. The paper illustrates the important background climatic control of the radiation field on the tropical surface fluxes.

Ridgway, W.↗

NASA NTRS1988

Satellite-observed characteristics of midwest severe thunderstorm anvils

The cloud top and anvil structure of severe thunderstorms observed by the GOES satellite are analyzed for five SESAME cases in 1979 and four non-SESAME cases in 1980-1982. The data is compared with previous models and hypotheses, paying particular attention to the V feature and thermal couplets in the IR observations. The characteristics of the cases are examined and related to the upper-level temperature and wind conditions. It is found that the warm points downwind of the cloud top are due to subsidence. The anaylsis suggests the presence of subsidence due to mountainlike waves. A model in which the close-in warm point is produced by both internal cloud air motions and stratospheric flow around and over the cloud top. It is suggested that the distant warm point is due to either a wave perturbation from air flowing over the cloud top, or air flowing horizonatlly around the elevated portion of the cloud top and anvil.

Heymsfield, Gerald M.↗

NASA NTRS1989

Chronology of volcanism and rift basin propagation - Rungwe volcanic province, East Africa

The spatial and temporal development of along-axis segmentation in youthful continental rifts was investigated using the results of field, remote sensing, and K-Ar geochronology studies conducted in four (Rukwa, Songwe, Usangu, and Karonga) rift basins within the Rungwe volcanic province in East Africa. Results indicated that the Rukwa and Karonga border fault segments formed between 7.25 and 5 m.y. ago, the Usangu border fault segment developed between 3 and 2 m.y. ago, and subsidence along the Songwe border fault segment had occurred by 0.5 Ma. It is shown that individual basins developed diachronously, each following a similar sequence: (1) initial border fault development; (2) asymmetric basin subsidence/flank uplift and the development of monoclines opposite the border faults; and (3) continued subsidence and tilting along intrabasinal faults with flexural upwarping of the rift flanks, enhancing basinal asymmetries.

Ebinger, C. J.↗