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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Analysis of Midlatitude Auroral Emissions Observed During the Impact of Comet Shoemaker-Levy 9 with Jupiter

During the impact of Comet Shoemaker-Levy 9 fragment K on Jupiter observers detected aurora-like emissions near the impact region as well as in the other hemisphere at approximately magnetic conjugate positions equatorward of aurorae latitudes. A number of generation mechanisms were suggested, but investigations of their significance have been hampered by a lack of knowledge about the jovian internal magnetic field, the exact timing, and the geometry of the impact and emission sites. We use the VIP 4 model of the internal magnetic field, high-time-resolution calculations of the fragment K trajectory, and images from the Hubble Space Telescope Wide Field Planetary Camera 2 with advanced processing to reanalyze the relationship between these emissions. The impact location is enclosed to the north and south by two regions of enhanced far-ultraviolet emissions reaching a maximum distance of 18,000 km south of the impact site roughly along the line of the incoming fragment's trajectory. The southern region can be further divided into two subregions, which partly overlap with magnetic projections of two brighter emission regions observed in the northern hemisphere close to the line of footprints of Amalthea. The area of the southern region approximates the area of these projections. No enhanced emissions are found conjugate to the impact site and the northward emission region. The magnetic projections suggest that the Gossamer ring scattered particles coming from the region southward of the impact site and prevented precipitation from the northward region into the northern hemisphere. Particle acceleration by upward accelerating shocks seems feasible to explain the geometry of the southern and northern hemispheric emission regions if we assume that a part of the plume bounced twice and provided enough energy at its second bounce to also generate shock waves.

Bauske, Rainer↗
NASA NTRS2000

Sea Ice Variability in the Sea of Okhotsk from Passive Microwave Satellite Observations

The Sea of Okhotsk, located between 50 and 60 N, is bounded by the Kamchatka Peninsula, Siberia, Sakhalin Island, and the Kuril Island chain and is the largest midlatitude seasonal sea ice zone in the Northern Hemisphere. The winter sea ice cover begins to form in November and expands to cover most of the sea by March. Over the following three months, the ice retreats with only small ice-covered areas remaining by the beginning of June. The sea is ice free or nearly ice free on average for six months of the year, from June through November. The recent compilation of a consistent, long-term record of Northern Hemisphere sea ice extents based on passive microwave satellite observations from the Nimbus 7 Scanning Multichannel Microwave Radiometer and from four Defense Meteorological Satellite Program Special Sensor Microwave Imagers provides the basis for assessing long-term sea ice extent variability in the Sea of Okhotsk. Analysis of this 20-year data record (1979-1998) shows that based on yearly averages the overall extent of the Sea of Okhotsk ice cover is decreasing at the rate of -8.1+/-2.1x10(exp 3) sq km/yr (-17.2%/decade), in contrast to the rate of decrease of -33.3+/-0.7x10(exp 3) sq km/yr (-2.7%/decade) for the Northern Hemisphere as a whole. There is large regional sea ice extent variability of the Arctic ice cover. Two of the nine Arctic regions analyzed, the Bering Sea and the Gulf of St. Lawrence, show increases of 0.8+/-1.4xl0(exp 3) sq km/yr (2.7%/decade) and 1.2+/-0.5xl0(exp 3) sq km/yr (17.1%/decade), respectively. Interestingly, the Sea of Okhotsk and the Gulf of St. Lawrence show about equal percentage changes, but of opposite sign. The Sea of Okhotsk exhibits its greatest percent decrease (-24.3%/decade) during spring (April-June). The year of maximum winter sea ice extent for the Sea of Okhotsk was 1979, whereas the minimum winter sea ice extent occurred in 1984.

Cavalieri, Donald J.↗
NASA NTRS1977

Periodic variations of total ozone and of its vertical distribution

The phase and amplitude of the annual, semiannual, and quasi-biennial oscillations to total ozone data for the Northern Hemisphere in the period 1957-1972 and for Northern Hemisphere ozonesonde data for variable periods from 1962-1974 have been plotted as functions of latitude, longitude, and altitude. The largest annual wave amplitude in total ozone occurs over eastern Siberia. In total ozone, the region of maximum quasi-biennial oscillation (QBO) coincides with that of the annual wave. The major feature of the QBO in the vertical distribution is the maximum amplitude in the arctic just above the tropopause. As for the semiannual wave, the maximum in total ozone lies in the arctic, displaced slightly to the Siberian side. In the vertical, its maximum amplitude is near 18 km. The phase appears to progress poleward, with maxima at high latitudes occurring in March-April.

Wilcox, R. W.↗
NASA NTRS1993

A preliminary study of the impact of the ERS 1 C band scatterometer wind data on the European Centre for Medium-Range Weather Forecasts global data assimilation system

A preliminary assessment of the impact of the ERS 1 scatterometer wind data on the current European Centre for Medium-Range Weather Forecasts analysis and forecast system has been carried out. Although the scatterometer data results in changes to the analyses and forecasts, there is no consistent improvement or degradation. Our results are based on comparing analyses and forecasts from assimilation cycles. The two sets of analyses are very similar except for the low level wind fields over the ocean. Impacts on the analyzed wind fields are greater over the southern ocean, where other data are scarce. For the most part the mass field increments are too small to balance the wind increments. The effect of the nonlinear normal mode initialization on the analysis differences is quite small, but we observe that the differences tend to wash out in the subsequent 6-hour forecast. In the Northern Hemisphere, analysis differences are very small, except directly at the scatterometer locations. Forecast comparisons reveal large differences in the Southern Hemisphere after 72 hours. Notable differences in the Northern Hemisphere do not appear until late in the forecast. Overall, however, the Southern Hemisphere impacts are neutral. The experiments described are preliminary in several respects. We expect these data to ultimately prove useful for global data assimilation.

Hoffman, Ross N.↗
NASA NTRS1999

The global topography of Mars and implications for surface evolution

Elevations measured by the Mars Orbiter Laser Altimeter have yielded a high-accuracy global map of the topography of Mars. Dominant features include the low northern hemisphere, the Tharsis province, and the Hellas impact basin. The northern hemisphere depression is primarily a long-wavelength effect that has been shaped by an internal mechanism. The topography of Tharsis consists of two broad rises. Material excavated from Hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary. The present topography has three major drainage centers, with the northern lowlands being the largest. The two polar cap volumes yield an upper limit of the present surface water inventory of 3.2 to 4.7 million cubic kilometers.

Water↗
NASA NTRS2000

Shape and Topography of Mars

Observations by the Mars Orbiter Laser Altimeter (MOLA) on the Mars Global Surveyor (MGS) spacecraft are showing a new planet in its range of topography and in the detail of the geological features. MGS arrived at Mars in Sept 1997 and since Feb. 28, 1999 the laser altimeter has operated continuously. By the end of April 2000 MOLA had acquired over 350 million measurements of the planet's shape and topography. These observations show a strong down-hill topographic gradient from the south pole to the north pole with an extremely low and flat basin encompassing most of the northern hemisphere. Large outflow channels are seen in the Chyrse region that strongly suggest considerable quantities of water once flowed into the lower northern hemisphere from the south. The northern icecap, which rises to a height of three kilometers above the surrounding terrain, is shown to be largely composed of water ice and at the center of a large basin. The southern hemisphere is about five kilometers higher than the low northern plains and dominated by the Hellas impact basin whose ejecta is the major contributor to the topography of the hemisphere and the crustal dichotomy. The south polar icecap, which is part of a much larger region of layered terrain composed of water ice and dust, reaches an elevation of nearly five kilometers and except for the large Tharsis volcanoes is the highest part of the planet.

Smith, David E.↗
NASA NTRS2013

Multiple Satellite Observations of Cloud Cover in Extratropical Cyclones

Using cloud observations from NASA Moderate Resolution Imaging Spectroradiometer, Multiangle Imaging Spectroradiometer, and CloudSat-CALIPSO, composites of cloud fraction in southern and northern hemisphere extratropical cyclones are obtained for cold and warm seasons between 2006 and 2010, to assess differences between these three data sets, and between summer and winter cyclones. In both hemispheres and seasons, over the open ocean, the cyclone-centered cloud fraction composites agree within 5% across the three data sets, but behind the cold fronts, or over sea ice and land, the differences are much larger. To supplement the data set comparison and learn more about the cyclones, we also examine the differences in cloud fraction between cold and warm season for each data set. The difference in cloud fraction between cold and warm season southern hemisphere cyclones is small for all three data sets, but of the same order of magnitude as the differences between the data sets. The cold-warm season contrast in northern hemisphere cyclone cloud fractions is similar for all three data sets: in the warm sector, the cold season cloud fractions are lower close to the low, but larger on the equator edge than their warm season counterparts. This seasonal contrast in cloud fraction within the cyclones warm sector seems to be related to the seasonal differences in moisture flux within the cyclones. Our analysis suggests that the three different data sets can all be used confidently when studying the warm sector and warm frontal zone of extratropical cyclones but caution should be exerted when studying clouds in the cold sector.

imaging spectrometers↗
NASA NTRS1982

The quasi-biennial oscillation in atmospheric ozone

It is noted that the region of strongest relationship between tropical stratospheric zonal winds and total ozone (that is, maximum ozone associated with strong west winds) is in the tropics, in the midlatitudes of the Southern Hemisphere, and, it is thought, at high latitudes of the Northern Hemisphere. The observed period of the ozone quasi-biennial oscillation (QBO) decreases from 27 months at the equator to approximately 24 months in midlatitudes, possibly due to local modification of the QBO, as it propagates poleward. In the tropics the ozone variation is seen to be nearly in phase with the tropical wind QBO while at middle and high latitudes of the Northern Hemisphere and midlatitudes of the Southern Hemisphere and ozone oscillation seems to lag the wind oscillation by about 12-14 months. The out-of-phase relationship at middle and high latitudes indicates a possible interaction between the tropical stratosphere QBO in zonal winds and the annual variation in the poleward transport of ozone by quasi-horizontal eddies.

Oltmans, S. J.↗
NASA NTRS2018

Interpreting Precession-Driven δ O-18 Variability in the South Asian Monsoon Region

Speleothem records from the South Asian summer monsoon (SASM) region display variability in the ratio of O-18 and O-16 (δ O-18) in calcium carbonate at orbital frequencies. The dominant mode of variability in many of these records reflects cycles of precession. There are several potential explanations for why SASM speleothem records show a strong precession signal, including changes in temperature, precipitation, and circulation. Here we use an Earth system model with water isotope tracers and water-tagging capability to deconstruct the precession signal found in SASM speleothem records. Our results show that cycles of precession-eccentricity produce changes in SASM intensity that correlate with local temperature, precipitation, and δ O-18. However, neither the amount effect nor temperature differences are responsible for the majority of the SASM δ O-18 variability. Instead, changes in the relative moisture contributions from different source regions drive much of the SASM δ O-18 signal, with more nearby moisture sources during Northern Hemisphere summer at aphelion and more distant moisture sources during Northern Hemisphere summer at perihelion. Further, we find that evaporation amplifies the δ O-18 signal of soil water relative to that of precipitation, providing a better match with the SASM speleothem records. This work helps explain a significant portion of the long-term variability found in SASM speleothem records.

paleoclimate↗
NASA NTRS1992

The structure of the polar vortex

The paper develops a comparative picture of the 1987 Southern Hemisphere and 1989 Northern Hemisphere lower stratospheric, polar vortex circulation and constituent distributions as observed by the Airborne Antarctic Ozone Experiment, August 17-September 22, 1987, and Airborne Arctic Stratospheric Expedition, January 3-February 19, 1989 aircraft campaigns. Overall, both polar vortices define a region of highly isolated air, where the exchange of trace gases occurs principally at the vortex edge through erosional wave activity. Aircraft measurement showed that between 50 and 100 mbar, horizontally stratified long-lived tracers such as N2O are displaced downward 2-3 km on the cyclonic (poleward) side of the jet with the meridional tracer gradient sharpest at the jet core. Eddy mixing rates, computed using parcel ensemble statistics, are an order of magnitude or more lower on the cyclonic side of the jet compared to those on the anticyclonic side. Poleward zonal mean meridional flow on the anticyclonic side of the jet terminates in a descent zone at the jet core.

Schoeberl, Mark R.↗
NASA NTRS1993

Mars atmospheric dynamics as simulated by the NASA Ames General Circulation Model. II - Transient baroclinic eddies

A large set of experiments performed with the NASA Ames Mars General Circulation Model is analyzed to determine the properties, structure, and dynamics of the simulated transient baroclinic eddies. There is strong transient baroclinic eddy activity in the extratropics of the Northern Hemisphere during the northern autumn, winter, and spring seasons. The eddy activity remains strong for very large dust loadings, though it shifts northward. The eastward propagating eddies are characterized by zonal wavenumbers of 1-4 and periods of about 2-10 days. The properties of the GCM baroclinic eddies in the northern extratropics are compared in detail with analogous properties inferred from Viking Lander meteorology observations.

Barnes, Jeffrey R.↗
NASA NTRS2003

Pressure Balance at Mars and Solar Wind Interaction with the Martian Atmosphere

The strongest crustal fields are located in certain regions in the Southern hemisphere. In the Northern hemisphere, the crustal fields are rather weak and usually do not prevent direct interaction between the SW and the Martian ionosphere/atmosphere. Exceptions occur in the isolated mini-magnetospheres formed by the crustal anomalies. Electron density profiles of the ionosphere of Mars derived from radio occultation data obtained by the Radio Science Mars Global Surveyor (MGS) experiment have been compared with the crustal magnetic fields measured by the MGS Magnetometer/Electron Reflectometer (MAG/ER) experiment. A study of 523 electron density profiles obtained at latitudes from +67 deg. to +77 deg. has been conducted. The effective scale-height of the electron density for two altitude ranges, 145-165 km and 165-185 km, and the effective scale-height of the neutral atmosphere density in the vicinity of the ionization peak have been derived for each of the profiles studied. For the regions outside of the potential mini-magnetospheres, the thermal pressure of the ionospheric plasma for the altitude range 145-185 km has been estimated. In the high latitude ionosphere at Mars, the total pressure at altitudes 160 and 180 km has been mapped. The solar wind interaction with the ionosphere of Mars and origin of the sharp drop of the electron density at the altitudes 200-210 km will be discussed.

A M Krymskii↗
NASA NTRS2004

Stratospheric Impact of Varying Sea Surface Temperatures

The Finite-Volume General Circulation Model (FVGCM) has been run in 50 year simulations with the: 1) 1949-1999 Hadley Centre sea surface temperatures (SST), and 2) a fixed annual cycle of SSTs. In this presentation we first show that the 1949-1999 FVGCM simulation produces a very credible stratosphere in comparison to an NCEP/NCAR reanalysis climatology. In particular, the northern hemisphere has numerous major and minor stratospheric warming, while the southern hemisphere has only a few over the 50-year simulation. During the northern hemisphere winter, temperatures are both warmer in the lower stratosphere and the polar vortex is weaker than is found in the mid-winter southern hemisphere. Mean temperature differences in the lower stratosphere are shown to be small (less than 2 K), and planetary wave forcing is found to be very consistent with the climatology. We then will show the differences between our varying SST simulation and the fixed SST simulation in both the dynamics and in two parameterized trace gases (ozone and methane). In general, differences are found to be small, with subtle changes in planetary wave forcing that lead to reduced temperatures in the SH and increased temperatures in the NH.

Newman, Paul A.↗
NASA NTRS2018

Total Ozone Trends from 1979 to 2016 Derived from Five Merged Observational Datasets - The Emergence into Ozone Recovery

We report on updated trends using different merged datasets from satellite and ground-based observations for the period from 1979 to 2016. Trends were determined by applying a multiple linear regression (MLR) to annual mean zonal mean data. Merged datasets used here include NASA MOD v8.6 and National Oceanic and Atmospheric Administration (NOAA) merge v8.6, both based on data from the series of Solar Backscatter UltraViolet (SBUV) and SBUV-2 satellite instruments (1978–present) as well as the Global Ozone Monitoring Experiment (GOME)-type Total Ozone (GTO) and GOME-SCIAMACHY-GOME-2 (GSG) merged datasets (1995-present), mainly comprising satellite data from GOME, the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY), and GOME-2A. The fifth dataset consists of the monthly mean zonal mean data from ground-based measurements collected at World Ozone and UV Data Center (WOUDC). The addition of four more years of data since the last World Meteorological Organization (WMO) ozone assessment (2013-2016) shows that for most datasets and regions the trends since the stratospheric halogen reached its maximum (approximately 1996 globally and approximately 2000 in polar regions) are mostly not significantly different from zero. However, for some latitudes, in particular the Southern Hemisphere extratropics and Northern Hemisphere subtropics, several datasets show small positive trends of slightly below +1 percent decade(exp. -1) that are barely statistically significant at the 2 Sigma uncertainty level. In the tropics, only two datasets show significant trends of +0.5 to +0.8 percent(exp.-1), while the others show near-zero trends. Positive trends since 2000 have been observed over Antarctica in September, but near-zero trends are found in October as well as in March over the Arctic. Uncertainties due to possible drifts between the datasets, from the merging procedure used to combine satellite datasets and related to the low sampling of ground-based data, are not accounted for in the trend analysis. Consequently, the retrieved trends can be only considered to be at the brink of becoming significant, but there are indications that we are about to emerge into the expected recovery phase. However, the recent trends are still considerably masked by the observed large year-to-year dynamical variability in total ozone.

column ozone trends↗
NASA NTRS2018

Arctic Sea Ice and Its Role in Global Change

Sea ice is an important component of the global climate system. Sea ice forms, grows, and melts in the ocean. Sea ice grows during the fall and winter and melts during the spring and summer. Sea ice can melt completely in summer or survive multiple years. Sea ice can be classified by stages of development (thickness and age), that is, first-year sea ice (ice thickness typically <1.8 m) and multiyear sea ice (ice thickness typically >1.8 m). Sea ice occurs in both hemispheres. In the Northern Hemisphere, sea ice develops in the Arctic Ocean and surrounding bodies including Hudson and Baffin Bay, Gulf of St. Lawrence, the Greenland Sea, the Bering Sea, and the Sea of Okhotsk (sea ice can be observed as far south as Bohai Bay, China, ~38°N). In the Southern Hemisphere, sea ice only develops around Antarctica, reaching a maximum equatorward extension at around ~55°S).

Liu, Jiping↗
NASA NTRS2008

Interannual Variability and Trends of Extratropical Ozone, Part II: Southern Hemisphere: Southern Hemisphere - Part 2

A principal component analysis (PCA) is applied to the Southern Hemisphere (SH) total column ozone following the method established for analyzing the data in the Northern Hemisphere (NH) in a companion paper. The interannual variability (IAV) of extratropical O-3 in the SH is characterized by four main modes, which account for 75% of the total variance. The first two leading modes are approximately zonally symmetric and relate to the Southern Hemisphere annular mode and the quasi-biennial oscillation. The third and fourth modes exhibit wavenumber-1 structures. Contrary to the Northern Hemisphere, the third and fourth are nor related to stationary waves. Similar results obtained for the 30 100-hPa geopotential thickness.The decreasing O3 trend in the SH is captured in the first mode. The largest trend is at the South Pole, with value similar to-2 Dobson Units (DU)/yr. Both the spatial pattern and trends in the column ozone are captured by the Goddard Earth Observation System chemistry-climate model (GEOS-CCM) in the SH.

Yung, Y. L.↗
NASA NTRS1981

The Quasi-Biennial Oscillation in atmospheric ozone

Examination of the relationship between tropical stratosphere zonal wind and ozone indicate a variable response in latitude with Northern Hemisphere tropics and polar regions and Southern Hemisphere mid-latitudes showing the strongest response with relatively weaker response at Northern Hemisphere mid-latitudes and the Southern Hemisphere tropics. In tropical regions, the west winds and ozone maxima are in phase while at higher latitudes, a more nearly out-of-phase relationship prevails. At subtropical and middle latitudes, the QBO in ozone does not appear to change phases with altitude. These features are suggestive of an interaction between the tropical zonal winds and poleward transport of horizontal eddies in conjunction with the annual poleward transport of ozone.

Oltmans, S. J.↗