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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Measurements of stratospheric hydrogen cyanide at McMurdo Station, Antarctica - Further evidence of winter stratospheric subsidence?

Measurements of hydrogen cyanide in the springtime Antarctic stratosphere were made using ground-based millimeter wave spectroscopy. A steeper decrease in volume mixing ratio with altitude was found, than that found at tropical latitudes, from an assumed value of about 160 pptv in the troposphere to a value of 65 + or - 30 pptv at 40 km, which may be further evidence of substantial vertical subsidence of the Antarctic winter stratosphere.

Jaramillo, M.↗
NASA NTRS1990

Thermal stresses, differential subsidence, and flexure at oceanic fracture zones

Geosat geoid undulations over four Pacific fracture zones have been analyzed. After correcting for the isostatic thermal edge effect, the amplitudes of the residuals are shown to be proportional to the age offset. The shape of the residuals seems to broaden with increasing age. Both geoid anomalies and available ship bathymetry data suggest that slip must sometimes occur on the main fracture zone or secondary faults. Existing models for flexure at fracture zones cannot explain the observed anomalies. A combination model accounting for slip and including flexure from thermal stresses and differential subsidence is presented. This model accounts for lateral variations in flexural rigidity from brittle and ductile yielding due to both thermal and flexural stresses and explains both the amplitudes and the shape of the anomalies along each fracture zone. The best fitting models have mechanical plate thicknesses that are described by the depth to the 600-700 C isotherms.

Wessel, Pal↗
NASA NTRS1992

Caldera subsidence and magma chamber depth of the Olympus Mons volcano, Mars

An axisymmetric finite element model is constructed to calculate elastic stresses in a volcanic edifice to examine the relationship between surface tectonism, caldera subsidence, and the physical characteristics of Olympus Mons' magmatic reservoir. Model results indicate that the surface stress state is not strongly sensitive to the aspect ratio or pressure distribution of the magma chamber, or to the contrast in stiffness between the magma chamber and surroundings, but is strongly dependent on the depth and width of the chamber. A gross similarity is suggested between the configurations of the magmatic plumbing systems of Olympus Mons and several well-studied terrestrial volcanoes such as the Hawaiian shields.

Zuber, M. T.↗
NASA NTRS1994

Subsidence of aircraft engine exhaust in the stratosphere: Implications for calculated ozone depletions

The deposition altitude of nitrogen oxides and other exhaust species emitted by stratospheric aircraft is a crucial parameter in determining the impact of these emissions on stratospheric ozone. We have utilized a model for the wake of a High-Speed Civil Transport (HSCT) to estimate the enhancements in water and reductions in ozone in these wakes as a function of time. Radiative calculations indicate differential cooling rates as large as -5K/day at the beginning of the far-wake regime, mostly due to the enhanced water abundance. These cooling rates would imply a net sinking of the wakes of about 1.2 km after three days in the limit of no mixing. Calculated mid-latitude column ozone reductions due to emissions from a Mach 2.4 HSCT would then change from about -1% to -06%. However, more realistic calculations adopting moderate mixing for the wake reduce the net sinking to less than 0.2 km, making the impact of radiative subsidence negligible.

Rodriguez, J. M.↗
NASA NTRS2007

Post-glacial Sediment Load and Subsidence in Coastal Louisiana

Sea level rise in the Gulf of Mexico has occurred at a rate of 1.8-2.2 mm/yr during the 20th century, or nearly the same as observed globally due to combined steric and water mass changes. Tide gauges in coastal Louisiana, however, record a substantially larger rate of rise and while a number of causal mechanisms may be responsible, their specific contribution is poorly understood. Using a realistic viscoelastic Earth model, detailed geologic parameters for south Louisiana and new GPS data, we demonstrate that Holocene sedimentary loading in the Gulf and Mississippi River delta is capable of contributing to 1-8 mm/yr of subsidence over areas of 30-0.75 x 10(exp 3) km(exp 2).

rheology mantle↗
NASA NTRS1999

Subsidence, Mixing and Denitrification of Arctic Polar Vortex Air Measured During POLARIS

A new technique is presented to determine the degree of denitrification that occured during the 1996/97 Arctic winter, based on balloon and aircraft borne measurements of NOy, N2O and CH4. In this study high-altitude balloon measurements are used to define the properties of air masses that later descend in the polar vortex to altitudes sampled by the ER-2 aircraft and mix isentropically with mid-latitude air.

stratosphere↗