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Showing papers by "Goddard Space Flight Center published in 1985"


Journal ArticleDOI
TL;DR: In this paper, a two-stream approximation model of radiative transfer was used to calculate values of hemispheric canopy reflectance in the visible and near-infrared wavelength intervals.
Abstract: A two-stream approximation model of radiative transfer is used to calculate values of hemispheric canopy reflectance in the visible and near-infrared wavelength intervals. Simple leaf models of photosynthesis and stomatal resistance are integrated over leaf orientation and canopy depth to obtain estimates of canopy photosynthesis and bulk stomatal or canopy resistance. The ratio of near-infrared and visible reflectances is predicted to be a near linear indicator of minimum canopy resistance and photosynthetic capacity but a poor predictor of leaf area index or biomass.

2,198 citations


Journal ArticleDOI
TL;DR: In this paper, the authors presented coarse spatial resolution, high temporal frequency satellite data from the NOAA/AVHRR system to demonstrate their utility for monitoring vegetation seasonal dynamics, including forest clearance in Brazil, the productivity of African grasslands, Indian tropical forest and Chinese agriculture.
Abstract: Coarse spatial resolution, high temporal frequency satellite data from the NOAA/AVHRR system are presented to demonstrate their utility for monitoring vegetation seasonal dynamics. The techniques for processing and analysing the data are outlined and examples are given for selected applications at a range of scales. Normalized difference vegetation index images are presented for the entire globe and for the continents of Africa, South America and south-east Asia, with descriptions of the seasonal dynamics of major vegetation formations as portrayed by the transformed AVHRR data. Monitoring of forest clearance in Brazil, the productivity of African grasslands, Indian tropical forest and Chinese agriculture are selected for discussion. The paper concludes that coarse-resolution satellite data provide a valuable tool for vegetation mapping and monitoring at regional and global scales.

1,125 citations


Journal ArticleDOI
25 Jan 1985-Science
TL;DR: Data from the advanced very-high-resolution radiometer sensor on the National Oceanic and Atmospheric Administration's operational series of meteorological satellites were used to classify land cover and monitor vegetation dynamics for Africa over a 19-month period.
Abstract: Data from the advanced very-high-resolution radiometer sensor on the National Oceanic and Atmospheric Administration's operational series of meteorological satellites were used to classify land cover and monitor vegetation dynamics for Africa over a 19-month period There was a correspondence between seasonal variations in the density and extent of green-leaf vegetation and the patterns of rainfall associated with the movement of the Intertropical Convergence Zone Regional variations, such as the 1983 drought in the Sahel of westem Africa, were observed Integration of the weekly satellite data with respect to time for a 12-month period produced a remotely sensed estimate of primary production based upon the density and duration of green-leaf biomass Eight of the 21-day composited data sets covering an 11-month period were used to produce a general land-cover classification that corresponded well with those of existing maps

1,060 citations


Journal ArticleDOI
02 May 1985-Nature
TL;DR: In this article, the climate record obtained from two long Greenland ice cores reveals several brief climate oscillations during glacial time and suggests that these oscillations are caused by fluctuations in the formation rate of deep water in the northern Atlantic.
Abstract: 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

1,049 citations


Journal ArticleDOI
TL;DR: In this article, a strong correlation between the integrated NOAA-7 satellite data and end-of-season above-ground dry biomass was found for ground samples collected over a 3-year period.

801 citations


Journal ArticleDOI
TL;DR: In this article, a new generation of ultra-low-noise millimeter-wave receivers, currently being developed for astronomical observation, utilizes the extremely sharp nonlinearity produced by single-electron quasiparticle tunneling between two superconductors in a superconductor-insulator-superconductor (SIS) tunnel junction.
Abstract: Photon-assisted tunneling of electrons through an insulating barrier may be used to detect long-wavelength radiation with a sensitivity approaching the limit imposed by the Heisenberg uncertainty principle. A new generation of ultra-low-noise millimeter-wave receivers, currently being developed for astronomical observation, utilizes the extremely sharp nonlinearity produced by single-electron quasiparticle tunneling between two superconductors in a superconductor-insulator-superconductor (SIS) tunnel junction. At millimeter wavelengths, the quantum energy $\frac{\ensuremath{\hbar}\ensuremath{\omega}}{e}$ may be larger than the voltage width for onset of quasiparticle tunneling in a SIS junction; and under these conditions the absorption of a single photon can cause one additional electron to tunnel through the barrier. Several newly discovered quantum effects become possible in this regime, including power amplification of an incoming signal during the process of frequency down-conversion in a heterodyne receiver. The experimental development of SIS millimeter-wave receivers is reviewed, along with the quantum theory of mixing which predicts their performance.

763 citations


Journal ArticleDOI
TL;DR: In this paper, the authors studied the intrinsic variability of tropical convection over the Indian Ocean/Pacific region during northern summer using outgoing longwave radiation (OLR) anomaly propagation.
Abstract: Intraseasonal variability Of tropical convection over the Indian Ocean/Pacific region during northern summer is studied using outgoing longwave radiation (OLR). OLR anomalies are found to propagate eastward along the equator from the Indian 0cean to the western Pacific and northward towards the Indian subcontinent and southern China. It is found that the dominant mode of tropical convection consists of a dipole with centers located over the Indian 0cean and the western Pacific/South China Set. This dipole undergoes complex structural changes over a broad period range centered around 40–50 days. During a typical oscillation, an anomaly first develops over the equatorial Indian Ocean. This anomaly then extends eastward to the equatorial western and central Pacific to form an elongated convection zone, while its center is displaced progressively northward from the Indian Ocean into the Indian subcontinent by an anomaly of the opposite sign. The elongated convection zone over the western Pacific then...

719 citations


Journal ArticleDOI
TL;DR: In this article, the authors used a very high-resolution radiometer on the current series of U.S. National Oceanic and Atmospheric Administration meteorological satellites to study the seasonality of North American natural and cultivated vegetation.
Abstract: Spectral vegetation index measurements derived from remotely sensed observations show great promise as a means to improve knowledge of land vegetation patterns. The daily, global observations acquired by the advanced very high resolution radiometer, a sensor on the current series of U.S. National Oceanic and Atmospheric Administration meteorological satellites, may be particularly well suited for global studies of vegetation. Preliminary results from analysis of North American observations, extending from April to November 1982, show that the vegetation index patterns observed correspond to the known seasonality of North American natural and cultivated vegetation. Integration of the observations over the growing season produced measurements that are related to net primary productivity patterns of the major North American natural vegetation formations. Regions of intense cultivation were observed as anomalous areas in the integrated growing season measurements. Significant information on seasonality, annual extent and interannual variability of vegetation photosynthetic activity at continental and global scales can be derived from these satellite observations.

616 citations


Journal ArticleDOI
TL;DR: In this paper, boundary conditions were used as inputs to the GISS general circulation model, and the last glacial maximum (LGM) climate was simulated for six model years.

437 citations


Journal ArticleDOI
TL;DR: In this article, the capacitance and charge of an individual grain in the presence of neighboring grains and the surrounding plasma is investigated. And the effect of neighbors on charging currents is explored.
Abstract: Voyager 1 and 2 observations of the Saturnian ring system have led to the discovery of several interesting phenomena associated with its fine dust component. The dust grains are immersed in a plasma. The present paper is concerned with the electrostatics of a dusty plasma, giving particular attention to the capacitance and charge of an individual grain in the presence of neighboring grains and the surrounding plasma. The Poisson equation and gauge considerations are discussed along with a solution of the Poisson equation for several models, taking into account impermeable grains, permeable grains, and a spherical capacitor model. A comparison of potential shapes for three models is conducted, and the effect of neighbors on charging currents is explored.

436 citations


Journal ArticleDOI
TL;DR: In this article, the simultaneous first-order Fermi shock acceleration of electrons, protons, and alpha particles are compared to observations of solar energetic particle events, and a unique shock compression ratio in the range of approximately 1.6-3 produces spectra in good agreement with observation.
Abstract: The simultaneous first-order Fermi shock acceleration of electrons, protons, and alpha particles are compared to observations of solar energetic particle events. For each event, a unique shock compression ratio in the range of approximately 1.6-3 produces spectra in good agreement with observation. The range in compression ratios predicts that the more than five orders of magnitude spread in electron-to-proton intensity ratios observed at MeV energies is compressed to about three orders of magnitude at an assumed injection energy of 100 keV. The remaining spread can be accounted for with a modest range of injection conditions. The model predicts that the acceleration time to a given energy will be approximately equal for electrons and protons, and for reasonable solar parameters, can be on the order of 1 s to approximately 100 MeV. 37 references.

Journal ArticleDOI
TL;DR: In this paper, the spectral coverage characteristics of two thematic mapper instruments were determined by analyses of spectral measurements of the optics, filters, and detectors, and the following results were presented: (1) band 2 and 3 flatness was slightly below specification, and band 7 flatness is below specification; (2) band 5 upperband edge was higher than specifications; (3) band two band edges were shifted upward about 9 nm relative to nominal; and (4) band 4, 5, and 7 lower band edges are 16 to 18 nm higher then nominal.
Abstract: The spectral coverage characteristics of the two thematic mapper instruments were determined by analyses of spectral measurements of the optics, filters, and detectors. The following results are presented: (1) band 2 and 3 flatness was slightly below specification, and band 7 flatness was below specification; (2) band 5 upper-band edge was higher than specifications; (3) band 2 band edges were shifted upward about 9 nm relative to nominal; and (4) band 4, 5, and 7 lower band edges were 16 to 18 nm higher then nominal.

Journal ArticleDOI
30 Aug 1985-Science
TL;DR: If equilibrium climate sensitivity is 3�C or greater for a doubling of the carbon dioxide concentration, then most of the expected warming attributable to trace gases added to the atmosphere by man probably has not yet occurred and calls into question a policy of "wait and see" regarding the issue of how to deal with increasing atmospheric carbon dioxide and other trace gases.
Abstract: The factors that determine climate response times were investigated with simple models and scaling statements. The response times are particularly sensitive to (i) the amount that the climate response is amplified by feedbacks and (ii) the representation of ocean mixing. If equilibrium climate sensitivity is 3 degrees C or greater for a doubling of the carbon dioxide concentration, then most of the expected warming attributable to trace gases added to the atmosphere by man probably has not yet occurred. This yet to be realized warming calls into question a policy of "wait and see" regarding the issue of how to deal with increasing atmospheric carbon dioxide and other trace gases.

Journal ArticleDOI
08 Mar 1985-Science
TL;DR: In the experiment described here, sulfur hexafluoride was dissolved in lake water, and the rate of escape of the gas with wind speed (at wind speeds up to 6 meters per second) was determined over a 1-month period, in agreement with the results of wind-tunnel studies.
Abstract: Gas-exchange processes control the uptake and release of various gases in natural systems such as oceans, rivers, and lakes. Not much is known about the effect of wind speed on gas exchange in such systems. In the experiment described here, sulfur hexafluoride was dissolved in lake water, and the rate of escape of the gas with wind speed (at wind speeds up to 6 meters per second) was determined over a 1-month period. A sharp change in the wind speed dependence of the gas-exchange coefficient was found at wind speeds of about 2.4 meters per second, in agreement with the results of wind-tunnel studies. However, the gas-exchange coefficients at wind speeds above 3 meters per second were smaller than those observed in wind tunnels and are in agreement with earlier lake and ocean results.

Book ChapterDOI
TL;DR: In this paper, the statistical properties of over 7000 hard X-ray flares detected with the Hard X-Ray Burst Spectrometer are presented including the spectrum of peak rates and the distribution of the photon number spectrum.
Abstract: The major results from SMM are presented as they relate to our understanding of the energy release and particle transportation processes that lead to the high-energy X-ray aspects of solar flares. Evidence is reviewed for a 152–158 day periodicity in various aspects of solar activity including the rate of occurrence of hard X-ray and gamma-ray flares. The statistical properties of over 7000 hard X-ray flares detected with the Hard X-Ray Burst Spectrometer are presented including the spectrum of peak rates and the distribution of the photon number spectrum. A flare classification scheme introduced by Tanaka is used to divide flares into three different types. Type A flares have purely thermal, compact sources with very steep hard X-ray spectra. Type B flares are impulsive bursts which show double footpoints in hard X-rays, and soft-hard-soft spectral evolution. Type C flares have gradually varying hard X-ray and microwave fluxes from high altitudes and show hardening of the X-ray spectrum through the peak and on the decay. SMM data are presented for examples of type B and type C events. New results are presented showing coincident hard X-rays, O v, and UV continuum observations in type B events with a time resolution of ≤ 128 ms. The subsecond variations in the hard X-ray flux during ≲10% of the stronger events are discussed and the fastest observed variation in a time of 20 ms is presented. The properties of type C flares are presented as determined primarily from the non-imaged hard X-ray and microwave spectral data. A model based on the association of type C flares and coronal mass ejections is presented to explain many of the characteristics of these gradual flares.

Journal ArticleDOI
TL;DR: In this article, a technique for extracting cloud cover parameters from multispectral satellite radiometric measurements is described, where three channels from the Advanced Very High Resolution Radiometer (AVHRR) on NOAA polar orbiting satellites are used to retrieve four parameters for each pixel: cloud fraction within the FOV, optical thickness, cloud-top temperature and a microphysical model parameter.
Abstract: A technique is described for extracting cloud cover parameters from multispectral satellite radiometric measurements. Utilizing three channels from the AVHRR (Advanced Very High Resolution Radiometer) on NOAA polar orbiting satellites, it is shown that one can retrieve four parameters for each pixel: cloud fraction within the FOV, optical thickness, cloud-top temperature and a microphysical model parameter. The last parameter is an index representing the properties of the cloud particle and is determined primarily by the radiance at 3.7 microns. The other three parameters are extracted from the visible and 11 micron infrared radiances, utilizing the information contained in the two-dimensional scatter plot of the measured radiances. The solution is essentially one in which the distributions of optical thickness and cloud-top temperature are maximally clustered for each region, with cloud fraction for each pixel adjusted to achieve maximal clustering.

Journal ArticleDOI
TL;DR: In this paper, the effect of aerosols on satellite measurements of surface properties for the visible and near-infrared spectrum has been investigated, and the effects on classification of surface features, measuring vegetation index, and measuring surface reflectance are presented.
Abstract: Previous attempts to explain the effect of aerosols on satellite measurements of surface properties for the visible and near-infrared spectrum have emphasized the amount of aerosols without consideration of their absorption properties. In order to estimate the importance of absorption, the radiances of the sunlight scattered from models of the Earth-atmosphere system are computed as functions of the aerosol optical thickness and absorption. The absorption effect is small where the surface reflectance is weak, but is important for strong reflectance. These effects on classification of surface features, measuring vegetation index, and measuring surface reflectance are presented.

Journal ArticleDOI
TL;DR: In this paper, a downward-looking lidar system over the Atlantic Ocean during a cold air outbreak was used to observe a convective planetary boundary layer (PBL) with high vertical and horizontal resolution.
Abstract: Observations of a convective planetary boundary layer (PBL) were made with an airborne, downward-looking lidar system over the Atlantic Ocean during a cold air outbreak. The lidar data revealed well-organized, regularly spaced cellular convection with dominant spacial scales between two and four times the height of the boundary layer. It is demonstrated that the lidar can accurately measure the structure of the PBL with high vertical and horizontal resolution. Parameters important for PBL modeling such as entrainment zone thickness, entrainment rate, PBL height and relative heat flux can be inferred from the lidar data. It is suggested that wind shear at the PBL top may influence both entrainment and convective cell size.

Journal ArticleDOI
TL;DR: In this article, the frequency and spatial distributions of blocking and persistent anomalies of geopotential height over the Southern Hemisphere are analyzed based on daily height fields at 1000 and 500 mb for both summer and winter.
Abstract: The focus of this Paper is on the frequency and spatial distributions of blocking and persistent anomalies of geopotential height over the Southern Hemisphere. The analysis is based upon daily height fields at 1000 and 500 mb for both summer and winter. Histogram frequency distributions of height anomalies and maps of the skewness and kurtosis have been computed. Blocking events are objectively defined by requiring a large positive anomaly to exist for 5 days or more. Composite flow and anomaly fields for several cases are presented and examined in detail. The geographical distribution of the frequency of lame amplitude ⩾150 gpm anomalies at 500 mb that persist for only 1–3 days is very similar to that of the high-frequency band (2–8 day period) variances that identity the storm tracks in the Southern Hemisphere. The primary location for blocking in the Southern Hemisphere is in the New Zealand sector and blocking occurs through a local enhancement of the climatological split in the mean westerli...

Journal ArticleDOI
TL;DR: In this paper, the MAGSAT spacecraft data from November 1979 through April 1980 and from 91 magnetic observatories for 1978 through 1982 were used to derive a spherical harmonic model of the Earth's main magnetic field and its secular variation.
Abstract: Data from the MAGSAT spacecraft for November 1979 through April 1980 and from 91 magnetic observatories for 1978 through 1982 are used to derive a spherical harmonic model of the Earth's main magnetic field and its secular variation. Constant coefficients are determined through degree and order 13 and secular variation coefficients through degree and order 10. The first degree external terms and corresponding induced internal terms are given as a function of Dst. Preliminary modeling using separate data sets at dawn and dusk local time showed that the dusk data contains a substantial field contribution from the equatorial electrojet current. The final data set is selected first from dawn data and then augmented by dusk data to achieve a good geographic data distribution for each of three time periods: (1) November/December, 1979; (2) January/February; 1980; (3) March/April, 1980. A correction for the effects of the equatorial electrojet is applied to the dusk data utilized. The solution included calculation of fixed biases, or anomalies, for the observation data.

Journal ArticleDOI
TL;DR: When Voyager 2 was near 11 AU, the counting rate of nuclei ≳75 MeV/nucleon decreased during the interval from July 1982 to November 1982, and it increased thereafter until August 1983 as mentioned in this paper.
Abstract: When Voyager 2 was near 11 AU, the counting rate of nuclei ≳75 MeV/nucleon decreased during the interval from July 1982 to November 1982, and it increased thereafter until August 1983. The counting rate fluctuated within this “minicycle” with short-term decreases lasting 1 to 4 days and recoveries lasting several days. A decrease in cosmic ray flux was generally associated with the passage of an “interaction region” in which the magnetic field strength B was higher than that predicted by the spiral field model, Bp. Several large enhancements in B/Bp were associated with “merged interaction regions” which probably resulted from the interaction of two or more distinct flows. During the passage of interaction regions the cosmic ray intensity decreased at a rate proportional to (B/Bp - 1), and during the passage of rarefaction regions (where B/Bp < 1) the cosmic ray intensity increased at a constant rate. The general form of the cosmic ray intensity profile during this ∼13 month minicycle can be described by integrating these relations using the observed B(t), and it can be understood in terms of the sizes and separations of interaction regions. Latitudinal variations of the interaction regions and of the short-term cosmic ray variations were identified by comparing Voyager 2 observations with Voyager 1 observations made at higher latitudes (14° to 20°). The interaction regions were turbulent, with an f−5/3 spectrum from at least 3×10−4 Hz to fc = (1 to 2) × 10−6 Hz. A break in the spectrum at fc corresponds to the characteristic width of the interaction regions, and it represents a “stirring scale” for the solar wind. The interaction regions, including merged interaction regions, may be viewed as “turbulent boundary layers” which grow in size with increasing distance from the sun. They act as barriers which impede the net flow of cosmic rays toward the sun.

Journal ArticleDOI
TL;DR: In this article, a two-step Lax-Wendroff-type advection scheme was proposed for uniform flow. But the scheme is only third-order accurate in time and space.
Abstract: A two-step advection scheme of the Lax-Wendroff type is derived which has accuracy and phase characteristics similar to that of a third-order scheme. The scheme is exactly third-order accurate in time and space for uniform flow. The new scheme is compared with other currently used methods, and is shown to simulate well the advection of localized disturbances with steep gradients. The scheme is derived for constant flow and generalized to two-dimensional nonuniform flow.

Journal ArticleDOI
TL;DR: In this paper, the authors calculated from monthly mean anomalies of sea level pressure and 500 mb geopotential height for the Southern Hemisphere (10−90°S) for five-month winter and summer seasons.
Abstract: Teleconnections are calculated from monthly mean anomalies of sea level pressure and 500 mb geopotential height for the Southern Hemisphere (10–90°S) for five-month winter and summer seasons. The monthly means were calculated from Australian analyses for the period from June 1972 to November 1980. Zonally averaged anomalies at both sea level and 500 mb display an out-of-phase relation between low and high latitudes and in midlatitudes are negatively correlated with anomalies in the subtropics and polar regions. In winter a striking zonal wavenumber 3 pattern is found over the Southern Ocean. Anomalies in 500 mb geopotential heights at (50°S, 95°E), (58°S, 150°W) and (38°S, 15°W) exhibit strong positive correlations while showing weaker negative correlations with heights over Antarctica and in low latitudes. A similar pattern appears in sea level pressure. In summer anomalies in 500 mb geopotential height over the three subtropical continents appear to occur out of phase with anomalies over the su...

Journal ArticleDOI
TL;DR: The International Satellite Cloud Climatology Project (ISCCP) project as discussed by the authors conducted a pilot study initiated in late 1981 to evaluate currently available cloud analysis algorithms, which focused on the most fundamental step of any cloud algorithm, namely cloud detection.
Abstract: Research related to the International Satellite Cloud Climatology Project (ISCCP) began with a pilot study initiated in late 1981 to evaluate currently available cloud analysis algorithms. Other objectives of this study are related to a test of the effects of data volume compression schemes and the design of the operational algorithms for ISCCP. The present paper summarizes the pilot study by focusing on the most fundamental step of any cloud algorithm, that of cloud detection. An outline is provided of the objectives and limitations of the pilot study, and a description is given of the criteria used to design the operational analysis algorithm. Attention is given to the pilot study data set, a cloud detection intercomparison, a cloud analysis, and ISCCP cloud algorithm design.

01 Feb 1985
TL;DR: In this article, the authors investigated the relationship between the magnetic field strength and the cosmic ray intensity during the passage of an interaction region in which the magnetic fields were higher than that predicted by the spiral field model, B sub p.
Abstract: When Voyager 2 was near 11 AU, the counting rate of nuclei approx 75 MeV/nucleon decreased during the interval from July, 1982 to November, 1982, and it increased thereafter until August, 1983. A decrease in cosmic ray flux was generally associated with the passage of an interaction region in which the magnetic field strength B was higher than that predicted by the spiral field model, B sub p. Several large enhancements in B/B sup p were associated with merged interaction regions which probably resulted from the interaction of two or more distinct flows. During the passage of interaction regions the cosmic ray intensity decreased at a rate proportional to (B/B sup p -1), and during the passage of rarefaction regions (where B/B sup p 1) the cosmic ray intensity increased at a constant rate. The general form of the cosmic ray intensity profile during this approx 13 month minicycle can be described by integrating these relations using the observed B(t). Latitudinal variations of the interaction regions and of the short-term cosmic ray variations were identified.

Journal ArticleDOI
07 Feb 1985-Nature
TL;DR: This article showed that smoke from fires started by nuclear explosions could continue to cause significant disruption even after it has fallen from the atmosphere, by lowering the reflectivity of snow and sea ice surfaces, with possible effects on climate in northern latitudes caused by enhanced absorption of sunlight.
Abstract: It is shown that smoke from fires started by nuclear explosions could continue to cause significant disruption even after it has fallen from the atmosphere, by lowering the reflectivity of snow and sea ice surfaces, with possible effects on climate in northern latitudes caused by enhanced absorption of sunlight. The reduced reflectivity could persist for several years on Arctic sea ice and on the ablation area of the Greenland ice sheet.

Journal ArticleDOI
TL;DR: In this paper, the authors provided models of the Venus neutral upper atmosphere, based on both in-situ and remote sensing measurements, for the height interval from 100 to 3,500 km.

Journal ArticleDOI
TL;DR: The Presidents' Day cyclone of 18-19 February 1979 is analyzed based on conventional radiosonde data, infrared and visible satellite imagery, water vapor images and ozone measurement as mentioned in this paper.
Abstract: The Presidents' Day cyclone of 18-19 February, 1979 is analyzed based on conventional radiosonde data, infrared and visible satellite imagery, water vapor images and ozone measurement The well-known synoptic-scale characteristics of the PJ-trough system are described, and evidence for the development of the tropopause fold are presented Processes contributing to the formation of the fold are discussed in terms of an evaluation of the Sawyer-Eliassen circulation equation and a diagnostic evaluation of the ageostrophic winds and vertical motion near the polar jet streak The documentation of stratospheric extrusions and their possible role in cyclogenesis is reviewed, and Eulerian and Lagrangian diagnostics are used to establish a connection between the tropopause fold associated with the polar jet streak and rapid cyclogenesis along the East Coast Conservation of potential vorticity expressed in isentropic coordinates is used as a constraint from which to view cyclogenesis

Journal ArticleDOI
TL;DR: The results of long-slit spectroscopy obtained for the core regions of 14 clusters of galaxies are reported in this paper, showing that the presence of optical emission is tied to properties of the hot gas in the cluster and not to the morphology of the central galaxy or cluster, demonstrating that the optical systems are indeed formed by the cooling of hot gas.
Abstract: The results of long-slit spectroscopy obtained for the core regions of 14 clusters of galaxies are reported. The data are presented in detail. It is shown that the presence of optical emission is tied to the properties of the hot gas in the cluster and not to the morphology of the central galaxy or cluster, demonstrating that the optical systems are indeed formed by the cooling of hot gas. Cooling flows occur when the gas density exceeds a critical central value which corresponds to a cooling time scale which, it is argued, weakly favors low values of H(0). The kinematics of the gas flows are discussed. The excitation mechanisms, correlation of optical emission with radio properties, and upper limits on coronal line strengths from the hot gas are discussed.

Journal ArticleDOI
30 May 1985-Nature
TL;DR: The sound speed of the solar interior is directly determinable on the basis of the frequencies of solar 5-min oscillations, irrespective of solar model, and relying only on a simple asymptotic description of the oscillations in terms of trapped acoustic waves as discussed by the authors.
Abstract: The sound speed of the solar interior is directly determinable on the basis of the frequencies of solar 5-min oscillations, irrespective of solar model, and relying only on a simple asymptotic description of the oscillations in terms of trapped acoustic waves. It is plausible that, by using this asymptotic determination as an initial trial in a more accurate inversion, and imposing constraints of smoothness on the solution resulting from the iteration, a good model representing the large scale structure of the sun which satisfies the observed frequencies may be determined.