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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Forcing of Climate Variations by Mev-gev Particles

Changes in ionization production in the lower stratosphere by a few percent during Forbush decreases have been shown to correlate well with changes in winter tropospheric dynamics by a similar relatively small amount. Changes in ionization production by tens of percent on the decadal time scale have been shown to be correlated with changes in winter storm frequencies by tens of percent in the western North Atlantic. Changes in total solar irradiance or solar UV do not have time variations to match the tropospheric variations on the day to day time scales discussed here. Forcing related to magnetic activity is not supported. Thus solar wind/MeV-GeV particle changes appear to be the only viable forcing function for these day to day variations. If solar wind/particle forcing of a few percent amplitude can produce short term weather responses, then observed changes by tens of percent on the decadal and centennial time scale could produce climate changes on these longer time scales. The changes in circulation involved would produce regional climate changes, as observed. At present the relations between stratospheric ionization, electric fields and chemistry and aerosol and cloud microphysics are as poorly known as the relations between the latter and storm feedback processes. However, the capability for investigating these relationships now exists and has recently been most successfully used for elucidating the stratospheric chemistry and cloud microphysics associated with the Antarctic ozone hole. The economic benefits of being able to predict winter severity on an interannual basis, and the extent to which climate change related to solar variability will add to or substract from the greenhouse effect, should be more than adequate to justify support for research in this area.

Tinsley, Brian A.↗
NASA NTRS1991

Potential vorticity index

Based on the European Center For Medium Range Weather Forecasting (ECMWF) First Global Atmospheric Research Program Global Experiment (FGGE) IIIb data set in the 1978 to 1979 winter, a potential vorticity (PV) index was defined as a measure of the zonally averaged, mid-latitude PV gradient on the 300 K isentropic surface in the Northern Hemisphere. The evolution of that index and its relation to teleconnection patterns of 500 mb geopotential height anomaly are studied. The results of the temporal and spatial variation of blocking and cyclogenesis in the 1978 to 1979 winter and its relation to global and local PV gradients were obtained. Complex empirical orthogonal function (EOF) analyses were performed, using the same FGGE data set for the 1978 to 1979 winter, for a representative high latitude band and mid latitude band geopotential height anomalies at 500 mb, phi sub h, phi sub m, and PV gradient at 300 K, delta(Q), at each longitude for the three month period. The focus of current research is the following: (1) to perform Fourier analyses for the first three EOF's of phi sub h, phi sub m, and delta(Q) at given latitude bands, and to find the dominant wavenumbers and frequencies which are responsible for these EOF's; (2) to compare the results from EOF and Fourier analyses which will be used to explore the relations of blocking and cyclogensis with local and global PV gradients; and (3) to study the time dependence of the local PV gradients and relate it to the PV index vacillation cycles observed in the PV index cycle.

Barcilon, Albert↗
NASA NTRS1989

Studies of ice sheet hydrology using SAR

Analysis of SAR data of the Greenland ice sheet in summer and winter suggest the use of SAR to monitor the temporal hydrology of ice sheets. Comparisons of each SAR data set with summer Landsat TM imagery show an areal-positive correlation with summer SAR data and a negative correlation with winter SAR data. It is proposed that the summer SAR data are most sensitive to the variable concentrations of free water in the surface snow and that the winter SAR data indicate variations in snow grain size.

Bindschadler, R. A.↗
NASA NTRS1991

LIMS (Limb Infrared Monitor of the Stratosphere) observation of traveling planetary waves and potential vorticity advection in the stratosphere and mesosphere

Eastward and westward traveling waves were observed by the Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) during the northern winter 1978-1979. Eastward waves were prevalent in early winter and were involved in a minor Canadian warming in December 1978. A large westward traveling wave, as described by previous authors, was observed in January 1979 during a series of minor warmings. By comparing these two events, it is shown that in both cases the superposition of traveling and quasi-stationary waves led to constructive interference that was responsible for the warmings. However, there was significant asymmetry between eastward and westward traveling components. A local Eulerian analysis of potential vorticity (PV) transport indicates that adiabatic, geostrophic advection by the resolvable scales of motion explains qualitatively (but not quantitatively) the observed potential vorticity tendencies in the LIMS Northern Hemisphere winter. In particular, calculated advection explains the eastward rotation of the main vortex, intrusion of low PV air into the polar cap, and formation of high PV filaments at the vortex periphery.

Dunkerton, Timothy J.↗
NASA NTRS1991

Antarctic Sea ice variations and seasonal air temperature relationships

Data through 1987 are used to determine the regional and seasonal dependencies of recent trends of Antarctic temperature and sea ice. Lead-lag relationships involving regional sea ice and air temperature are systematically evaluated, with an eye toward the ice-temperature feedbacks that may influence climatic change. Over the 1958-1087 period the temperature trends are positive in all seasons. For the 15 years (l973-l987) for which ice data are available, the trends are predominantly positive only in winter and summer, and are most strongly positive over the Antarctic Peninsula. The spatially aggregated trend of temperature for this latter period is small but positive, while the corresponding trend of ice coverage is small but negative. Lag correlations between seasonal anomalies of the two variables are generally stronger with ice lagging the summer temperatures and with ice leading the winter temperatures. The implication is that summer temperatures predispose the near-surface waters to above-or below-normal ice coverage in the following fall and winter.

Weatherly, John W.↗
NASA NTRS1990

Energetics diagnosis of numerical simulation of atmospheric blocking

A series of systematic comprehensive diagnoses of Goddard Laboratory for Atmospheres (GLA) General Circulation Model (GCM) simulation experiments was performed in reference to predictability and energetics of the Northern Hemisphere blocking circulation. The simulation experiments were performed. The following subject areas are also covered: an analysis of simulated summer blocking episodes; energetics examination of winter blocking simulations in the Northern Hemisphere; normal mode energetic and error analysis of GLA GCM simulations with the different horizontal resolutions during a winter month; and simulations of winter blocking episodes using observed sea surface temperatures.

Kung, Ernest C.↗
NASA NTRS1992

Observations of Ozone-aerosol Correlated Behaviour in the Lower Stratosphere During the EASOE Campaign

The question of possible interactions between ozone and stratospheric aerosol has been open for a long time. Measurements carried out after the Mt. Agung and El Chicon eruptions showed evidence of negative correlations between the presence of volcanic stratospheric aerosols and ozone concentration. Evidence for negative correlations in the polar winter has been also found. It is only after the discovery of the Antarctic ozone hole that catalytic effects related to low temperature heterogeneous chemistry have become the object of much investigation, now extended to the role of volcanic aerosol in the ozone reduction. These phenomena can be the object of various interpretations, not mutually exclusive, including the effect of transport, diffuse radiation as well as heterogeneous chemistry. The present paper provides preliminary results of simultaneous measurements of ozone and aerosol, carried out at Thule, Greenland, during the winter 1991-92. The European Stratospheric Ozone Experiment (EASOE) was aimed at monitoring the winter Arctic stratosphere in order to obtain a deeper insight of the ozone destruction processes taking place in the polar regions. A large amount of aerosol was injected into the lower stratosphere by the recent eruption of Volcano Pinatubo. A lidar system, already operational in Thule since November 1990, has provided detailed measurements of the stratospheric aerosol concentration during EASOE. In the same period, a large number of ozonesondes were launched. Although no PSC formation was detected over Thule, the simultaneous measurement of the stratospheric aerosol and ozone profiles give the possibility to study interactions occurring in the stratosphere between these two constituents.

Digirolamo, P.↗
NASA NTRS1992

Deuterium in North Atlantic storm tops

During the ERICA project in 1989, ice crystals were collected from the tops of two winter storms and one broad cirrus cloud. Deuterium concentration in the storm ice samples, together with a model of isotope fractionation, are used to determine the temperature where the ice was formed. Knowledge of the ice formation temperature allows us to determine whether the ice has fallen or been lofted to the altitude of collection. In both storms, the estimated fall distance decreases upward. In the 21 January storm, the fall distance decreases to zero at the cloud top. In the 23 January storm, the fall distance decreases to zero at a point 2 km below the cloud top and appears to become negative above, indicating lofted ice. Cloud particle data from the cloud tops show an ice-to-vapor ratio greater than one and indicate the presence of particles with small terminal velocities; both observations support the idea of ice lofting. The satellite-derived cloud tops lie well below the actual cloud top (e.g., 2.5 km below on 23 January), indicating that the lofted ice in winter storms may not be detectable from space using IR radiance techniques. A comparison of deuterium in cloud-top ice and clear-air vapor suggests that even in winter, when vertical air motions are relatively weak, lofted ice crystals are the dominant source of water vapor in the upper troposphere.

Smith, Ronald B.↗
NASA NTRS1993

Mountain-wave drag in the stratosphere and mesosphere inferred from observed winds and a simple mountain-wave parameterization scheme

A daily analysis of mountain-wave propagation through observed, global wind, and temperature fields in January and August is presented. Winds and temperatures are obtained from the daily 18-level NMC Climate Analysis Center. Mountain-wave properties are deduced from a simple, gravity wave parameterization scheme in which the effects of topographic anisotropy (ridge orientation) are explicitly included. Planetary waves in the northern winter stratosphere are found to play an important role in modulating the magnitude and distribution of inferred mountain-wave drag in the middle atmosphere. The Aleutian anticyclone is found to effectively block mountain waves generated over western North America from reaching the mesosphere by inducing local mountain-wave-critical levels in the stratosphere. Stratospheric sudden warmings have a similar effect at all longitudes so that during months with sudden warmings the average inferred drag in the mesosphere is reduced by a factor of 4 to 5 from its normal value. Partly as a consequence of larger planetary-wave filtering in the Northern Hemisphere, inferred mountain-wave drag in the southern winter mesosphere is found to be comparable to that in the northern winter mesosphere. Almost all of the mountain wave drag exerted on the southern middle atmosphere is found to originate over the southern Andes and Antarctic Peninsula.

Bacmeister, Julio T.↗
NASA NTRS1993

Parameterized study of the ionospheric modification associated with sun-aligned polar cap arcs

The local ionospheric modification that is due to a generalized steady state solar aligned (SA) arc structure is addressed. For a representative set of SA arc parameters which includes both convection and precipitation, emphasis is placed on the modification by SA polar cap arcs upon the F region electron density and the height integrated conductivity. At low fluxes and low characteristic energies, SA polar cap arcs have the most pronounced relative effect at F region altitudes in darkness for winter solar minimum conditions. The absolute enhancement in summer solar minimum and winter solar maximum is equivalent to that of winter solar minimum, but the higher ambient densities make the relative enhancement less. The TEC enhancement associated with an SA arc may be used to indicate the degree of plasma cross flow across the arc.

Crain, D. J.↗
NASA NTRS1993

Sensitivity of Asian and African climate to variations in seasonal insolation, glacial ice cover, sea surface temperature, and Asian orography

A general circulation model was used to investigate the sensitivity of Asian and African climate to prescribed changes in boundary conditions with the objective of identifying the relative importance of individual high-latitude glacial boundary conditions on seasonal climate and providing a physical basis for interpreting the paleoclimate record. The circulation model is described and results are presented. Insolation forcing increased summer Asian monsoon winds, while increased high-latitude ice cover strengthened winter Asian trade winds causing decreased precipitation. These factors had little effect on African climate. Cooler North Atlantic sea surface temperatures enhanced winter trade winds over North Africa, southern Asian climate was relatively unaffected. Reducing Asian orography enhanced Asian winter circulation while decreasing the summer monsoon. These model results suggest that African and southern Asian climate respond differently to separate elements of high-latitude climate variability.

Demenocal, Peter B.↗
NASA NTRS1993

Arctic sea ice signatures for passive microwave algorithms

Two new sets of global pure type signatures are defined, and the precision of the concentration estimates made using the Team algorithm and the new signatures is estimated. One set varies temporally but not spatially and is defined by the modes of major peaks in histograms of brightness temperature. The other set is defined as the overall means of the temporally varying signatures; these are called 'new constant signatures'. Both sets of new signatures have essentially the same precision: 0.05 (fractional area) for winter ice concentration, 0.10 for summer ice concentration, and 0.15 to 0.3 for winter multilayer ice concentrations. Both sets result in about 0.6 to 0.7 winter multiyear ice for the Arctic Ocean, substantially more than the 0.3 to 0.4 computed using the original team algorithm signatures, and in the same range as several independent estimates of the multiyear ice, 0.54 to 0.75.

Thomas, D. R.↗
NASA NTRS1993

Intraseasonal interactions between the tropics and extratropics in the Southern Hemisphere

Observational evidence is presented of connections between tropical heating and circulation changes in subtropical and extratropical latitudes of the Southern Hemisphere (SH) in summer and winter, and the processes responsible for these interactions are described. The observational evidence suggests that, during SH summer (but not SH winter), both the acceleration of westerly winds south of the heating region through meridional overturnings and excitation of Rossby waves are possible. During winter, the enhanced tropical convective activity results again in local meridional overturning with zonal wind acceleration of Rossby waves farther south.

Berbery, Ernesto H.↗
NASA NTRS1993

Impact of the CO2 and H2O clouds of the Martian polar hood on the polar energy balance

Clouds covering extensive areas above the martian polar caps have regularly been observed during the fall and winter seasons of each hemisphere. These 'polar hoods' are thought to be made of H2O and CO2. In particular, the very cold temperatures observed during the polar night by Viking and Mariner 9 around both poles have been identified as CO2 clouds and several models, including GCM, have indicated that the CO2 can condense in the atmosphere at all polar latitudes. Estimating the impact of the polar hood clouds on the energy balance of the polar regions is necessary to model the CO2 cycle and address puzzling problems like the polar caps assymetry. For example, by altering the thermal radiation emitted to space, CO2 clouds alter the amount of CO2 that condenses during the fall and winter season. The complete set of Viking IRTM data was analyzed to define the spatial and temporal properties of the polar hoods, and how their presence affects the energy radiated by the atmosphere/caps system to space was estimated. The IRTM observations provide good spatial and temporal converage of both polar regions during fall, winter, and spring, when a combination of the first and the second Viking year is used. Only the IRTM brightness temperatures at 11, 15, and 20 microns are reliable at martian polar temperatures. To recover the integrated thermal fluxes from the IRTM data, a simple model of the polar hood, thought to consist of 'warm' H2O clouds lying above colder and opaque CO2 clouds was developed. Such a model is based on the analysis of the IRIS spectra, and is consistent with the IRTM data used.

Forget, Francois↗
NASA NTRS1994

Martian atmospheric radiation budget

A computer model is used to study the radiative transfer of the martian winter-polar atmosphere. Solar heating at winter-polar latitudes is provided predominately by dust. For normal, low-dust conditions, CO2 provides almost as much heating as dust. Most heating by CO2 in the winter polar atmosphere is provided by the 2.7 micron band between 10 km and 30 km altitude, and by the 2.0 micron band below 10 km. The weak 1.3 micron band provides some significant heating near the surface. The minor CO2 bands at 1.4, 1.6, 4.8 and 5.2 micron are all optically thin, and produce negligible heating. O3 provides less than 10 percent of the total heating. Atmospheric cooling is predominantly thermal emission by dust, although CO2 15 micron band emission is important above 20 km altitude.

Lindner, Bernhard Lee↗
NASA NTRS1994

On long-term ozone trends at Hohenpeissenberg

More than 2000 ozone soundings and a large number of Dobson observations have been performed since 1967 in a unique procedure. The achieved very homogeneous data sets were used to evaluate significant long-term trends both in the troposphere and the stratosphere. The trend amounts to about plus 2 percent per year in the troposphere and to about minus 0.5 percent per year in the stratosphere. Extremely low ozone records obtained during winter 1991/92 are discussed in the light of the long term series. The winter mean of the ozone column is the lowest one of the series. The ozone deficit occurred mainly in the lower stratosphere. One cause may be the Pinatubo cloud. Even compared with the extreme winter mean following the El Chichon eruption the ozone content was lower. Additionally ozone was reduced by dynamical effects due to unusual weather situations.

Claude, H.↗
NASA NTRS1994

Long-term changes in the statistical distribution of Dobson total ozone in selected Northern Hemisphere geographical regions

The daily averages of total column amount of ozone taken in the period 1964-1988 at a network of 24 Dobson stations have been analyzed. Year-round data as well as summer data (May - Aug.) and winter data (Dec. - March) have been examined in the following regions: latitude bands (30 deg N - 39 deg N, 40 deg N - 52 deg N, 30 deg N - 60 deg N), North America, Europe, and Japan. To find year-to-year changes in the shape of the annual statistical distribution of total ozone (ASDTO) for these regions, we analyze trends in the following statistic characteristics of ASDTO: mean, standard deviation, median, and 10 and 90 percentiles. Time series of the statistical characteristics for the selected regions have been combined by averaging the individual stations values of these characteristics. The trends have been calculated by the multiple regression model adjusted for: the 11-year solar cycle, the Southern Oscillations effects, and for serial correlations. We have found that: a) in all regions (excluding Japan, North America), the shape of ASDTO has been drifting towards low ozone values. The drift seems to be not accompanied with a transformation in the shape of ASDTO. The drift speed (the rate of decrease in the annual means of total ozone) is of order 1-3 percent per decade (in the period 1970-1988). b) In Japan, the interannual changes in the shape of ASDTO have not been revealed. c) In North America, the drift of the year-round ASDTO (the year-round ASDTO comprises all the daily means of total ozone in a given year) has been accompanied with a transformation in the shape. The shape of the year round ASDTO becomes narrower. d) In all regions, except Japan and the band 30 deg - 39 deg N, the winter ASDTO (the winter ASDTO comprises the data taken in the period December in a given year through March next year) moves faster towards low ozone values than the summer ASDTO (the summer ASDTO comprises the data taken in the period May through August in a given year).

Krzyscin, Janusz W.↗
NASA NTRS1994

The global distribution of ozone destruction rates obtained from 13 years of Nimbus/TOMS data (1979-1991)

Long-term ozone trends (percentage change) have been computed from 13 years of Nimbus/TOMS (Total Ozone Mapping Spectrometer) data as a function of latitude, longitude, and month for the period January 1, 1979 to December 31, 1991. In both hemispheres, the ozone column content has decreased at latitudes above 30 deg by amounts that are larger than predicted by homogeneous chemistry models for the 13-year time period. The largest rates of ozone decrease occur in the Southern Hemisphere during winter and spring, with recovery during the summer and autumn. The large winter ozone loss rates are consistent with observed low stratospheric temperatures, ice-cloud formation, and heterogeneous chemistry at middle and high latitudes. There are similar, but smaller changes observed in the Northern Hemisphere. At midlatitudes, (40 deg N to 50 deg N) there are increased zonal average ozone depletion rates that correspond to 5 geographically localized regions of increased ozone depletion rates. Only the equatorial band between plus or minus 20 deg shows little or no long-term ozone change since January, 1979. The long-term winter ozone depletion rate data for both hemispheres suggests that heterogeneous chemistry processes may operate over a wide range of latitudes during half of the year.

Herman, Jay R.↗