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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Data pre-processing: Stratospheric aerosol perturbing effect on the remote sensing of vegetation: Correction method for the composite NDVI after the Pinatubo eruption

An operational stratospheric correction scheme used after the Mount Pinatubo (Phillipines) eruption (Jun. 1991) is presented. The stratospheric aerosol distribution is assumed to be only variable with latitude. Each 9 days the latitudinal distribution of the optical thickness is computed by inverting radiances observed in the NOAA AVHRR channel 1 (0.63 micrometers) and channel 2 (0.83 micrometers) over the Pacific Ocean. This radiance data set is used to check the validity of model used for inversion by checking consistency of the optical thickness deduced from each channel as well as optical thickness deduced from different scattering angles. Using the optical thickness profile previously computed and radiative transfer code assuming Lambertian boundary condition, each pixel of channel 1 and 2 are corrected prior to computation of NDVI (Normalized Difference Vegetation Index). Comparison between corrected, non corrected, and years prior to Pinatubo eruption (1989 to 1990) NDVI composite, shows the necessity and the accuracy of the operational correction scheme.

Vermote, E.↗
NASA NTRS1994

Heterogeneous conversion of N2O5 to HNO3 in the post-Mount Pinatubo eruption stratosphere

Simultaneous stratospheric volume mixing ration (VMR) profiles of dinitrogen pentoxide (N2O5) and nitric acid (HNO3) at sunrise between 25 deg N and 15 deg S latitude and profiles of HNO3 at sunset between 42 deg S and 53 deg S latitude have been derived from 0.01/cm resolution infrared solar occultation spectra recorded 9.5 months after the massive eruption of the Mount Pinatubo volcano in the Philippine Islands. The measurements were obtained by the atmospheric trace molecule spectroscopy (ATMOS) Fourier transform spectrometer during the ATLAS 1 shuttle mission (March 24 to April 2, 1992). The measured HNO3 VMRs are higher at all altitudes and latitudes than corresponding values measured by the limb infrared monitor of the stratosphere (LIMS) instrument during the same season in 1979, when the aerosol loading was near background levels. The largest relative increase in the HNO3 VMR occurred near the equator at 30-km altitude, where the ATMOS/ATLAS 1 values are about a factor of 2 higher than the LIMS measurements. Two-dimensional model calculations show that the increase in HNO3 and the ATMOS/ATLAS 1 measurement of a steep decrease in the N2O5 VMR below 30 km can be explained by the enhanced conversion of N2O5 to HNO3 on the surfaces of the Mount Pinatubo sulfate aerosols. Our profile results demonstrate the global impact of the N2O5 + H2O yields 2HNO3 heterogeneous reaction in altering the partitioning of stratospheric odd nitrogen after a major volcanic eruption.

Rinsland, C. P.↗
NASA NTRS1994

X-ray observations of a major eruptive flare behind the limb

We analyze X-ray images and spectra of a coronal structure which extended to altitudes over 130000 km above an eruptive flare located 20 deg behind the western solar limb. The images were obtained by the Flat Crystal Spectrometer (FCS) and the spectra were obtained by the Bent Crystal Spectrometer (BCS) aboard the SMM spacecraft. Images in O VIII and Mg XI lines cover the period from before the flare onset (which occurred at 22:31 UT on 16 February, 1986) through 17 UT on 17 February and were used for determination of temperature and emission measure within the structure. BCS obtained Ca XIX spectra of the coronal event, benefiting from the occultation of the active region behind the solar limb. The BCS data show, and FCS data confirm, that the temperature, after an initial rise and decline, stayed almost constant for many hours after 04:30 UT on 17 February. This may indicate that initially we observed the rise and decay of post-flare loops, but later the X-ray emission came predominantly from a post-flare giant arch that formed above them. This has been observed in many previous cases. However, a comparison with other events characterized by very high post-flare loops suggests that we may be observing the same system of slowly growing groups all the time. Therefore, we suggest a third possibility, i.e., that such anomalously high loop systems first behave like post-flare loops but gradually take over some characteristics of a post-flare giant arch. The Soft X-ray Telescope aboard Yohkoh, with spatial resolution improved by nearly an order of magnitude, might be able to check up on the development of such large-scale coronal structures if proper observational modes are applied after the occurrence of major eruptive flares.

Smith, Kermit L.↗
NASA NTRS1994

Radiatively forced dispersion of the Mt. Pinatubo volcanic cloud and induced temperature perturbations in the stratosphere during the first few months following the eruption

A combined 3-dimensional circulation model and aerosol microphysical/transport model is used to simulate the dispersion of the Mt. Pinatubo volcanic cloud in the stratosphere for the first few months following the eruption. Radiative heating of the cloud due to upwelling infrared radiation from the troposphere is shown to be an important factor affecting the transport. Without cloud heating, cloud material stays mostly north of the equator, whereas with cloud heating, the cloud is transported southward across the equator within the first two weeks following the eruption. Generally the simulations agree with Total Ozone Mapping Spectrometer (TOMS), Advanced Very High Resolution Radiometer (AVHRR), and Stratospheric Aerosol and Gas Experiment (SAGE) satellite observations showing the latitude distribution of cloud material to be between about 20 deg S and 30 deg N within the first few months. Temperature perturbations in the stratosphere induced by the aerosol heating are generally 1-4 K, in the range of those observed.

Young, Richard E.↗
NASA NTRS1994

Mars: Review and analysis of volcanic eruption theory and relationships to observed landforms

We present a theoretical treatment of the ascent, emplacement, and eruption of magma on Mars. Because of the lower gravity, fluid convective motions and crystal settling processes driven by positive and negative buoyancy forces, as well as overall diapiric ascent rates, will be slower on Mars than on Earth, permitting larger diapirs to ascend to shallower depths. Martian environmental conditions operate to modulate the various eruption styles and the morphology and morphometry of resulting landforms, providing new insight into several volcanological problems.

Wilson, Lionel↗
NASA NTRS1993

State of stress, faulting, and eruption characteristics of large volcanoes on Mars

The formation of a large volcano loads the underlying lithospheric plate and can lead to lithospheric flexure and faulting. In turn, lithospheric deformation affects the stress field beneath and within the volcanic edifice and can influence magma transport. Modeling the interaction of these processes is crucial to an understanding of the history of eruption characteristics and tectonic deformation of large volcanoes. We develop models of time-dependent stress and deformation for the Tharsis volcanoes on Mars. By means of a finite element code, we calculate stresses and displacements due to a volcano-shaped load emplaced on an elastic plate overlying a viscoelastic mantle. Models variously incorporate growth of the volcanic load with time and a detachment between volcano and lithosphere. The models illustrate the manner in which time-dependent stresses induced by lithospheric plate flexure beneath the volcanic load may affect eruption histories, and the derived stress fields can be related to tectonic features on and surrounding Martian volcanoes. As a result of flexure there are three regions where stresses become sufficiently large to cause failure by faulting, according to the Mohr-Coulomb criterion: at the surface of the plate just outward of the volcano, near the base of the elastic lithosphere beneath the center of the volcano, and on the upper flanks of the volcano early in its growth history.

Mcgovern, Patrick J.↗
NASA NTRS1995

GOES weather satellite observations and measurements of the May 18, 1980, Mount St. Helens eruption

We demonstrate the use of Geostationary Operational Environmental Satellite (GOES) images of the May 18, 1980, Mount St. Helens volcanic plume in providing details of the dynamics and changing character of this major explosive eruption. Visible and thermal infrared (IR) data from a sequence of images at 30-min intervals from 0850 to 1720 Local Time (LT) give information on dispersal and plume top temperature. Initial visible and IR images at 0850 show the top of a spreading co-ignimbrite-like umbrella plume and an overshooting column emerging from it, both rising off the ground-hugging pyroclastic gravity flow generated by the opening directed blast. The overshooting column had a minimum temperature significantly colder than local ambient atmosphere, indicating substantial undercooling, and a maximum altitude of 31 +/- 2 km at 0920. This large plume system then formed a high-velocity, radially spreading, gravitationally driven current before becoming advected in the wind field at an average downwind velocity of 29 m/s. Reflectance values from visible GOES data change from lower to higher during periods of transition from darker toned Plinian to lighter toned co-ignimbrite plumes indicating that in this case satellite data resolved changes in eruptive style from plumes with a coarser to a finer dominant particle size.

Holasek, R. E.↗
NASA NTRS1995

CME stimulated by eruptive prominence

A model of CME arising due to drift motion in the corona in the presence of an eruptive prominence is presented. Magnetic field configuration is in accordance with a model of inverse polarity. In a region where a magnetic pressure of the filament magnetic field is greater than a gas pressure, plasma motion can be assumed as a drift motion. Its characteristic is such that the further one gets from the filament, the higher is drift velocity of a plasma. That sort of motion leads to a rarefaction of plasma and formation of a cavity around the filament. But a current strength in eruptive prominences estimated from observations is such that the region b is less than 1 has a limited size. Near the boundary b = 1 plasma deceleration is occurred and as a result of it coronal density is increasing. Plasma condensation near the surface b = 1 leads to formation of a dense envelope which can be collated with an outer loop of CME. Two dimensional numerical MHD simulation displays a process of cavity and loop formation. If a current is large enough, two compact regions of compressed dense matter arise at both sides of the rising filament and two narrow jets are developed. This scenario, perhaps, corresponds to CMEs in which a top of the loop is faint or it is absent at all.

Filippov, B. P.↗
NASA NTRS1995

Comparing Simultaneous Stratospheric Aerosol and Ozone Lidar Measurements with SAGE 2 Data after the Mount Pinatubo Eruption

Stratospheric aerosol and ozone profiles obtained simultaneously from the lidar station at the University of L'Aquila (42.35 deg N, 13.33 deg E, 683 m above sea level) during the first 6 months following the eruption of Mount Pinatubo are compared with corresponding nearby Stratospheric Aerosol and Gas Experiment (SAGE) 2 profiles. The agreement between the two data sets is found to be reasonably good. The temporal change of aerosol profiles obtained by both techniques showed the intrusion and growth of Pinatubo aerosols. In addition, ozone concentration profiles derived from an empirical time-series model based on SAGE 2 ozone data obtained before the Pinatubo eruption are compared with measured profiles. Good agreement is shown in the 1991 profiles, but ozone concentrations measured in January 1992 were reduced relative to time-series model estimates. Possible reasons for the differences between measured and model-based ozone profiles are discussed.

Yue, G. K.↗
NASA NTRS1997

Geology and Topography of Ra Patera, Io, in the Voyager era: Prelude to Eruption

Voyager era stereo images are used to map the geology and topography of Ra Patera (a major active volcanic center and possible site of sulfur eruptions on Io). The summit of Ra Patera reaches only approx.1 km above the surrounding plains. Pre-Voyager-era lava flows occur on slopes of 0.1-0.3 deg, comparable to the lunar mare. These flows were emplaced at either low viscosities, high eruption rates, or both. A 600- km-long ridged mountain unit (rising to approx. 8 km near Carancho Patera) forms a 60 by 90 km wide plateau approx. 0.5 km high 50 km east of Ra Patera. The new lava flows observed by Galileo flowed around the southern edge of this plateau.

Schenk, Paul M.↗
NASA NTRS1998

X-Ray Observations of Recurrence of Eruptive Flares and Active Regions

In a study of soft X-ray coronal images obtained with the Yohkoh spacecraft, two eruptive flares with remarkably similar X-ray structures were noted -- most remarkably because the flares occurred at the same solar location (approximately 10 degrees north latitude on the east limb) yet separated in time by three solar rotations. Between the times of the eruptions, the active region responsible for the first flare disappeared from Yohkoh images. An extremely similar X-ray active region replaced it by the third solar rotation. The recurring X-ray active region appearance and recurring flare activity after 86 days suggest that persistent subsurface flux emergence patterns might be responsible, and support previous arguments that 'active longitudes' exist.

Batchelor, David↗
NASA NTRS2000

Environmental Effects on Volcanic Eruptions:From Deep Ocean to Deep Space. Chapter 3. Volcanism and Ice Interactions on Earth and Mars

CONCLUSION Volcano/ice interactions produce meltwater. Meltwater can enter the groundwater cycle and under the influence of hydrothermal systems, it can be later discharged to form channels and valleys or cycled upward to melt permafrost. Water or ice-saturated ground can erupt into phreatic craters when covered by lava. Violent mixing of meltwater and volcanic material and rapid release can generate lahars or jokulhlaups, that have the ability to freight coarse material, great distances downslope from the vent. Eruption into meltwater generate unique appearing edifices, that are definitive indicators of volcano/ice interaction. These features are hyaloclastic ridges or mounds and if capped by lava, tuyas. On Earth, volcano/ice interactions are limited to alpine regions and ice-capped polar and temperate regions. On Mars, where precipitation may be an ancient phenomenon, these interactions may be limited to areas of ground ice accumulation or the northern lowlands where water may have ponded fairly late in martian history. The recognition of features caused by volcano/ice interactions could provide strong constraints for the history of volatiles on Mars.

Chapman, Mary G.↗
NASA NTRS2002

Mars Global Surveyor Data Analysis Program. Origins of Small Volcanic Cones: Eruption Mechanisms and Implications for Water on Mars

The goal of the proposed work was to determine the origins of small volcanic cones observed in Mars Global Surveyor (MGS) data, and their implications for regolith ice stores and magma volatile contents. For this 1-year study, our approach involved a combination of: Quantitative morphologic analysis and interpretation of Mars Orbiter Camera (MOC) and Mars Orbiter Laser Altimeter (MOLA) data; Numerical modeling of eruption processes responsible for producing the observed features; Fieldwork on terrestrial analogs in Iceland. Following this approach, this study succeeded in furthering our understanding of (i) the spatial and temporal distribution of near-surface water ice, as defined by the distribution and sizes of rootless volcanic cones ("pseudocraters"), and (ii) the properties, eruption conditions, and volatile contents of magmas producing primary vent cones.

Fagents, Sarah A.↗
NASA NTRS2006

Initiation of the Slow-Rise and Fast-Rise Phases of an Erupting Solar Filament by Localized Emerging Magnetic Field via Microflaring

EUV data from EIT show that a filament of 2001 February 28 underwent a slow-rise phase lasting about 6 hrs, before rapidly erupting in a fast-rise phase. Concurrent images in soft X-rays (SXRs) from Yohkoh/SXT show that a series of three microflares, prominent in SXT images but weak in EIT approx.195 Ang EUV images, occurred near one end of the filament. The first and last microflares occurred respectively in conjunction with the start of the slow-rise phase and the start of the fast-rise phase, and the second microflare corresponded to a kink in the filament trajectory. Beginning within 10 hours of the start of the slow rise, new magnetic flux emerged at the location of the microflaring. This localized new flux emergence and the resulting microflares, consistent with reconnection between the emerging field and the sheared sigmoid core magnetic field holding the filament, apparently caused the slow rise of this field and the transition to explosive eruption. For the first time in such detail, the observations show this direct action of localized emerging flux in the progressive destabilization of a sheared core field in the onset of a coronal mass ejection (CME). Similar processes may have occurred in other recently-studied events, NASA supported this work through NASA SR&T and SEC GI grants.

Sterling, A. C.↗
NASA NTRS2006

Thermal Analysis of Post-eruption Loops from 80,000 to 1.6 million K

We analyze the thermal properties of a set of post eruptive loops which appeared after a prominence eruption on April 30, 2004. The event was observed by TRACE and SOHO/SUMER. The SUMER data was taken from a single slit location with a 90 second cadence and included a number of lines spanning the temperature range 80,000 to 1.6 million K. We perform a differential emission measure analysis of the loops in order to study their thermal evolution.

Kucera, T.↗
NASA NTRS2009

A Hybrid Model for Leveed Lava Flows: Implications for Eruption Styles on Mars

Many cehannelized lava flows on the plains of Mars have substantial embanking margins and levees inferred to have been stationary while the central channel was active. Levee formation can be attributed to two end-member processes during emplacement; construction during passage of the flow front and growth along the entire length of the flow while it is active. It is shown here that the amount of lava that can be deposited by the flow front alone is limited. Estimates of the levee volume for many Mars plains flows exceed this limit and must have formed by processes that continued after the passage of the front. Experimental studies of analogous laboratory flows also indicate a combination of both modes of emplacement. A model that combines both modes of levee formation. is presented, including a method for estimating volumetric flow rate, eruption duration, and viscosity. Six lava flows on the plains of the Tharsis volcanic province are used as illustrative examples. Crustal thicknesses for the six flows examined range from 9 to 23 m. Estimated emplacement times required to cool crusts of these thicknesses range from I year to 10 years. Correspondini viscosities are on the order of 10 5-106 Pa s. Effusion rates range from 25 to 840 m 3 s - and are all within the range of terrestrial observations. Therefore, the large leveed plains flows on Mars are not dramatically different in eruption rate or lava viscosity from large terrestrial analogs.

Glaze, Lori S.↗
NASA NTRS2011

Major Influence of Tropical Volcanic Eruptions on the Stratospheric Aerosol Layer During the Last Decade

The variability of stratospheric aerosol loading between 1985 and 2010 is explored with measurements from SAGE II, CALIPSO, GOMOS/ENVISAT, and OSIRIS/Odin space-based instruments. We find that, following the 1991 eruption of Mount Pinatubo, stratospheric aerosol levels increased by as much as two orders of magnitude and only reached background levels between 1998 and 2002. From 2002 onwards, a systematic increase has been reported by a number of investigators. Recently, the trend, based on ground-based lidar measurements, has been tentatively attributed to an increase of SO2 entering the stratosphere associated with coal burning in Southeast Asia. However, we demonstrate with these satellite measurements that the observed trend is mainly driven by a series of moderate but increasingly intense volcanic eruptions primarily at tropical latitudes. These events injected sulfur directly to altitudes between 18 and 20 km. The resulting aerosol particles are slowly lofted into the middle stratosphere by the Brewer-Dobson circulation and are eventually transported to higher latitudes.

Vernier, Jean-Paul↗
NASA NTRS2012

Observations of a Two-Stage Solar Eruptive Event (SEE): Evidence for Secondary Heating

We present RHESSI, SDO/AIA, SOHO/LASCO, STEREO, and GOES observations of a partially occulted solar eruptive event (SEE) that occurred at the South-West limb on 8 March, 2011. The GOES X-ray light curve shows two peaks separated by almost two hours that we interpret as two stages of a single event associated with the delayed eruption of a CME. A hot flux rope formed during the first stage and continued expanding and rising throughout the event. The speed of the flux rope decreased from approx.120 to 14 km/s during the decay phase of the first stage and increased again during the second stage to become the CME with a speed of approx.516 km/s. RHESSI and GOES data analyses show that the plasma temperature reached over 20 MK in the first stage, then decreased to approx.10 MK and increased to 15 MK in the second stage. This event provides clear evidence for a secondary heating phase. The enhanced EUV and X-ray emission came from the high corona ( approx.60 arcsec above the limb) in the second stage, approx.40 arcsec higher than the site of the initial flare emission. STEREO-A on-disk observations indicate that the post-flare loops during this stage were of larger scale sizes and spatially distinct from those in the first stage.

Su, Yang↗