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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Cosmic ray secular variations in terrestrial records and aurorae

The rediscovery that the Sun and the solar wind can undergo important changes on historical time scales has brought into question the stability of the cyclic behavior of past time series of solar and solar-terrestrial origin. It was found by Vector Fourier analysis that the solar 11 year cycle is present in the series of 10Be, delta 180, in ice cores and of thermoluminescence (TL) in sea sediments during the last Millennia with a frequency modulation, related to the Sun behavior, as tested by comparison with the Sunspot number R sub z series. It was shown that the cyclogram of the series of yearly Aurorae from 1721 to 1979 linear-regression-corrected-for-R sub z is straight for the periodicity zeta=11,1y, which indicates that such periodicity is constant in time corresponding to the only line present in the 11y band. The maxima of this component appear at the same time together with the high speed solar wind streams taking place in coronal holes situated in high heliolatitudes. It is evidenced that the 11 year cycle has undergone frequency oscillations on a time scale of two centuries, although it is very difficult to determine the periodicities with high accuracy.

Attolini, M. R.↗
NASA NTRS1984

Atmospheric methane in the recent and ancient atmospheres Concentrations, trends, and interhemispheric gradient

Rasmussen and Khalil (1981) have shown that the concentration of methane is increasing in the earth's atmosphere. A continuing increase of methane may perturb the global environment in the future by warming the earth and leading to more ozone and carbon monoxide in the atmosphere. It appears that the present concentration of methane may be more than twice as high as the natural levels of 150 years ago. An analysis of air bubbles buried long ago in polar ice makes it possible to deduce the concentrations of methane in the old and ancient atmospheres. The present investigation is concerned with the results of an analysis of more than 80 ice core samples, taking into account both polar regions of the earth. The samples range in age from about 100 to nearly 3000 years old. It is found that the concentration of methane started changing significantly about 150 years ago. These findings suggest that the increase of methane is probably indirectly caused by the rapid increase of human population.

Rasmussen, R. A.↗
NASA NTRS1985

Does the ocean-atmosphere system have more than one stable mode of operation?

The climate record obtained from two long Greenland ice cores reveals several brief climate oscillations during glacial time. The most recent of these oscillations, also found in continental pollen records, has greatest impact in the area under the meteorological influence of the northern Atlantic, but none in the United States. This suggests that these oscillations are caused by fluctuations in the formation rate of deep water in the northern Atlantic. As the present production of deep water in this area is driven by an excess of evaporation over precipitation and continental runoff, atmospheric water transport may be an important element in climate change. Changes in the production rate of deep water in this sector of the ocean may push the climate system from one quasi-stable mode of operation to another.

Broecker, W. S.↗
NASA NTRS1986

A possible deuterium anomaly: Implications of the CH3D/CH4 mixing ratios in the atmospheres of Jupiter, Saturn, and Uranus

Observations of CH3D in the atmospheres of the outer planets provide a test of the theory of deuterium fractionation equilibrium in the formation and evolution of these planets. Recent measurements of the CH3D/CH4 mixing ratios made for Saturn and Uranus are presented and intercompared with current values of Jupiter, illustrating large differences between the planets. Their implied D/H ratios are compared to D/H ratios derived from measurements of HD/H2; and, in the cases of Jupiter and Saturn, they may be incompatible. Implications of these comparisons are discussed in terms of the deuterium fractionation chemistry and possible enrichments of deuterium in the core ices of the planets.

Lutz, Barry L.↗
NASA NTRS1988

Volcanic winters

The impact of volcanic eruptions on weather and climate is considered. The data from nineteenth-century eruptions is examined, showing the importance of sulfur volatiles for climate change. Information obtained from ice cores is discussed, and the contrasts between the eruptions of Mt. St. Helens and El Chichon are pointed out. The atmospheric effects of the greatest historic eruptions are recalled. The potential for the occurrence of 'volcanic winters' and the possible role of volcanism in mass extinctions are considered.

Rampino, Michael R.↗
NASA NTRS1988

Stratospheric feedback from continued increases in tropospheric methane

Tropospheric concentrations of methane have increased steadily over the past ten years at an average rate of 16.5 ppbv per year, to a value in January 1988 of 1.69 ppmv. Measurements of CH sub 4 concentrations in air bubbles trapped in ice cores have shown concentrations of about 0.7 ppmv 200 years ago, with little further change for thousands of years before that. Interpolation earlier into this century suggests a concentration of about 1.1 to 1.2 ppmv in the 1940's. The only important pathway believed to be important for transfer of air from the troposphere to the stratosphere in through the tropical tropopause which is cold enough to reduce the mixing ratio of H sub 2 O in that air to about 3 ppmv. The only other major pathway for the delivery of H to the stratosphere is through the simultaneous injection of gaseous CH sub 4 in the same rising air. The formation of clouds in the stratosphere is dependent upon very low temperatures, and generally upon the amount of water vapor available. The possibility of a positive feedback exists, especially in well-oxidized methane air, that clouds are easier to form than earlier. This could mean enhancement of PSCs in both Antarctic and Arctic locations. Additional H sub 2 O in the stratosphere can also add to some of the greenhouse calculations.

Rowland, F. Sherwood↗
NASA NTRS1989

Volcanic eruptions and solar activity

The historical record of large volcanic eruptions from 1500 to 1980 is subjected to detailed time series analysis. In two weak but probably statistically significant periodicities of about 11 and 80 yr, the frequency of volcanic eruptions increases (decreases) slightly around the times of solar minimum (maximum). Time series analysis of the volcanogenic acidities in a deep ice core from Greenland reveals several very long periods ranging from about 80 to about 350 yr which are similar to the very slow solar cycles previously detected in auroral and C-14 records. Solar flares may cause changes in atmospheric circulation patterns that abruptly alter the earth's spin. The resulting jolt probably triggers small earthquakes which affect volcanism.

Stothers, Richard B.↗
NASA NTRS1989

Implications of the giant planets for the formation and evolution of planetary systems

The giant planet region in the solar system appears to be bounded inside by the limit of water condensation, suggesting that the most abundant astrophysical condensate plays an important role in giant planet formation. Indeed, Jupiter and Saturn exhibit evidence for rock and/or ice cores or central concentrations that probably accumulated first, acting as nuclei for subsequent gas accumulation. This is a 'planetary' accumulation process, distinct from the stellar formation process, even though most of Jupiter has a similar composition to the primordial sun. Uranus and Neptune appear to exhibit evidence of an important role for giant impacts in their structure and evolution. No simple picture emerges for the temperature structure of the solar nebula from observations alone. However, it seems likely that Jupiter is the key to the planetary system, and a similar planet could be expected for other systems. The data and inferences from these data are summarized for the entire known solar system beyond the asteroid belt.

Stevenson, David J.↗
NASA NTRS1990

Testing the Sun-climate Connection with Paleoclimate Data

If there is a significant sun-climate connection, it should be detectable in high-resolution paleoclimate records. Of particular interest is the last few thousand years, where we have both indices of solar variability (C-14 and Be-10) and climate variations (alpine glaciers, tree rings, ice cores, corals, etc.). Although there are a few exceptions, statistical analyses of solar and climate records generally indicates a flickering relationship between the two -- sometimes it seems to be present, sometimes not. The most repeatable solar climate periods occur at approx. 120 and approx. 56 yrs, although there is also evidence for approx. 420 and approx. 200 yrs. power in some records. However, coherence between solar and climate spectra is usually low, and occurrence of solar spectra in climate records is sometimes dependent on choice of analysis program. These results suggest in general a relatively weak sun-climate link on time scales of decades to centuries. This conclusion is consistent with previous studies and with the observation that inferred climate fluctuations of 1.0 to 1.5 C on this time scale would require solar constant variations of approximately 0.5 to 1.0 percent. This change in forcing is almost an order of magnitude greater than observed changes over the last solar cycle and appears to be on the far-outer limit of acceptable changes for a Maunder Minimum-type event.

Crowley, Thomas J.↗
NASA NTRS1990

A Review and Reflections on the Sun-Climate Connection

The field of sun-climate is beset with an extraordinary number of numerical correlations attempting to relate various periodicities of solar activity with changes in the Earth's weather and climate. Signatures representing climatological variability have been sought for cycles as short as the solar 28-day rotational period up to Milankovich periods of thousands of years, although a majority of correlations have concentrated on the 11-year sunspot and 22-year Hale double sunspot cycles. For the shorter term, parameters including temperature, pressure, winds storm tracks, rainfall, and water levels in rivers and lakes, etc. have been correlated with solar variability. For longer periods, it has been necessary to seek more indirect evidence in ice cores, tree rings, and geologic deep sea cores. Other atmospheric parameters relating to atmospheric electricity and the global electric circuit have also been correlated in similar fashion. Unfortunately, few, if any, of this wide spectrum of numerical correlations have been associated with any viable physical explanation, making most studies in the field an exercise in numerical statistics. More recently, a few suggestions for plausible coupling processes have begun to appear. These, coupled with new and stronger correlations involving selective binning of climatological data sets have injected new life and hope to this field. An overview is given of the historical past and current perspectives, to evaluate possible avenues for defining physical linking processes in the future.

Goldberg, Richard A.↗
NASA NTRS1991

Volcanism-Climate Interactions

The range of disciplines in the study of volcanism-climate interactions includes paleoclimate, volcanology, petrology, tectonics, cloud physics and chemistry, and climate and radiation modeling. Questions encountered in understanding the interactions include: the source and evolution of sulfur and sulfur-gaseous species in magmas; their entrainment in volcanic plumes and injection into the stratosphere; their dissipation rates; and their radiative effects. Other issues include modeling and measuring regional and global effects of such large, dense clouds. A broad-range plan of research designed to answer these questions was defined. The plan includes observations of volcanoes, rocks, trees, and ice cores, as well as satellite and aircraft observations of erupting volcanoes and resulting lumes and clouds.

Walter, Louis S.↗
NASA NTRS1993

The atmospheric CH4 increase since the Last Glacial Maximum. II - Interactions with oxidants

Results of two studies of the effect of changing CH4 fluxes on global tropospheric oxidant levels, O3, OH, and H2O2, performed with a multibox photochemical model, are presented. A sensitivity study is conducted by scaling back CH4, CO, and NO emissions relative to the present-day budget. When the CH4 ice core record is compared to calculated CH4 abundances, corresponding CH4 fluxes for the preindustrial Holocene (PIH) and Last Glacial Maximum (LGM) are fairly well-constrained: 175-225 Tg CH/4/yr for PIH and 100-130 Tg CH4/yr for LGM. Specific scenarios for CH4/CO/NO are selected to represent sources for the PIH and LGM. The CH4 budget is taken from an evaluation of wetlands and other natural sources.

Thompson, Anne M.↗
NASA NTRS1993

Milankovitch insulation forcing and cyclic formation of large-scale glacial, fluvial, and eolian landforms in central Alaska

Continuous marine and ice-core proxy climate records indicate that the Earth's orbital geometry modulates long-term changes. Until recently, little direct evidence has been available to demonstrate correlations between Milankovitch cycles and large-scale terrestrial landforms produced during worldwide glaciations. In central Alaska large areas of loess and sand fill valleys and basins near major outwash streams. The streams themselves are bordered by sets of outwash terraces, and the terraces grade up valley into sets of moraines. The discovery of the Stampede tephra (approximately 175,000 yr ago) reworked within push moraines of the Lignite Creek glaciation suggests that this event correlates with the glaciation of marine isotope stage 6. A new occurrence of the Old Crow tephra (approximately 140,000 yr ago) on the surface of the oldest outwash terrace of the Tanana River, correlated with Delta glaciation, suggests this event also occurred at this time. The penultimate Healy glaciation apparently correlates with marine isotope stage 4, while radiocarbon dates indicate the latest Pleistocene moraines correlate with marine isotope stage 2. Recognition of the importance of orbital forcing to the cyclical formation of glacial landforms and landscapes can help in interpretations of remotely sensed glacial and proglacial land forms.

Beget, J. E.↗
NASA NTRS1993

The thumbprint terrain: What will Mars Observer tell us?

Some of the more puzzling features seen on Mars are those known as curvilinear features or 'thumb print' terrain, types of patterned ground found in the northern plains. The thumbprint terrain, named for its resemblance to the lines of a human thumbprint is found on what appears to be level, relatively low-lying ground near the crustal dichotomy boundary. It is often found near the termini of large channels. There are three types of thumbprint terrain in the classification of Rossbacher and Judson. The first consists of ridges and depressions about a kilometer wide, separated by a few kilometers, and with an apparent relief of 40-100 m. The second consists of steep-sided, flat-floored depressions about a kilometer wide, separated by a few kilometers, and with an apparent relief of 10-290 m. The third consists only of albedo markings, with a typical scale of about a kilometer. Many models were proposed to explain the origin of this terrain. It was suggested that it was caused by lava flows, removal of debris mantles, glaciers, or karst. However, the most popular models at present involve the action of subsurface ice to form such thermokarst features as striped ground, solifluction lobes, and/or linear, ice-cored ridges. There are several instruments on the Mars Observer spacecraft that will be able to provide us with information useful in distinguishing between these models.

Schaefer, M. W.↗
NASA NTRS1993

Most recent fall deposits of Ksudach Volcano, Kamchatka, Russia

Three of four Plinian eruptions from Ksudach Volcano are among the four largest explosive eruptions in southern Kamchatka during the past 2000 years. The earliest of the eruptions was voluminous and was accompanied by an ignimbrite and the fifth and most recent C~ddera collapse event at Ksudach. The isopach pattern is consistent with a column height of 23 km. The three more recent and smaller eruptions were from the Shtyubel' Cone, within the fifth caldera. Using isopach and grain size isopleth patterns, column heights ranged from >10 to 22 kin. Although the oldest eruption may have produced a large acidity peak in the Greenland ice, the three Shtyubel' events may not be related to major acid deposition. Thus it is possible that few if any of the uncorrelated acidity peaks of the past 2000 years in Greenland ice cores result from eruptions in southern Kamchatka.

Bursik, M.↗
NASA NTRS1994

Stellar activity: Astrophysics relevant to global change

FRESIP will obtain a great deal of data on stellar activity and flares on F, G and K dwarfs. Rotation periods, flare distributions and possibly stellar cycles will emerge. This apparently curiosity-driven research actually has implications for our understanding of global climate change. Significant climate change during the seventeenth-century Maunder Minimum is thought to be related to a change in the solar condition. Recently acquired data from the Greenland Ice-core Project suggest that far greater climate changes on decade time scales may have occurred during the previous interglacial. It is possible that a yet more drastic change in state of the Sun was responsible. We have no relevant solar data, but can begin to explore this possibility by observing an ensemble of solar-like stars.

Haisch, Bernhard M.↗
NASA NTRS1994

Stable water isotope behavior during the last glacial maximum: A general circulation model analysis

Global water isotope geochemisty during the last glacial maximum (LGM) is simulated with an 8 deg x 10 deg atmospheric general circulation model (GCM). The simulation results suggest that the spatial delta O-18/temperature relationships observed for the present day and LGM climates are very similar. Furthermore, the temporal delta O-18/temperature relationship is similar to the present-day spatial relationship in regions for which the LGM/present-day temperature change is significant. This helps justify the standard practice of applying the latter to the interpretation of paleodata, despite the possible influence of other factors, such as changes in the evaportive sources of precipitation or in the seasonality of precipitation. The model suggests, for example, that temperature shifts inferred from ice core data may differ from the true shifts by only about 30%.

Jouzel, Jean↗
NASA NTRS1998

Water Isotopes in Precipitation: Data/Model Comparison for Present-Day and Past Climates

Variations of HDO and H2O-18 concentrations are observed in precipitation both on a geographical and on a temporal basis. These variations, resulting from successive isotopic fractionation processes at each phase change of water during its atmospheric cycle, are well documented through the IAEA/WMO network and other sources. Isotope concentrations are, in middle and high latitudes, linearly related to the annual mean temperature at the precipitation site. Paleoclimatologists have used this relationship to infer paleotemperatures from isotope paleodata extractable from ice cores, deep groundwater and other such sources. For this application to be valid, however, the spatial relationship must also hold in time at a given location as the location undergoes a series of climatic changes. Progress in water isotope modeling aimed at examining and evaluating this assumption has been recently reviewed with a focus on polar regions and, more specifically, on Greenland. This article was largely based on the results obtained using the isotopic version of the NASA/GISS Atmospheric General Circulation Model (AGCM) fitted with isotope tracer diagnostics. We extend this review in comparing the results of two different isotopic AGCMs (NASA/GISS and ECHAM) and in examining, with a more global perspective, the validity of the above assumption, i.e. the equivalence of the spatial and temporal isotope-temperature relationship. We also examine recent progress made in modeling the relationship between the conditions prevailing in moisture source regions for precipitation and the deuterium-excess of that precipitation.

Jouzel, J.↗