5,795 research outputs found
Interhemispheric comparison of atmospheric circulation features as evaluated from Nimbus satellite data
General circulation parameters in the Northern Hemisphere are calculated using atmospheric thermal structure obtained from Nimbus 3 SIRS multi-channel radiance information. The thermal structure up to 10 mb is obtained by using a regression technique with thickness between pressure levels as the dependent variable. General circulation parameters calculated on a daily basis include zonal and eddy available potential energy, and zonal and eddy kinetic energy. A second set of calculations is performed using National Meteorological Center grid data. A comparison of the two sets of calculations indicates that, although the energies calculated from the SIRS-derived structure underestimate the actual energies, maxima, minima, and trends are well identified. An example of mid-stratospheric energy changes during a breakdown of the polar-night vortex is also given
Some observed seasonal changes in extratropical general circulation: A study in terms of vorticity
Extratropical eddy distributions in four months typical of the four seasons are treated in terms of temporal mean and temporal r.m.s. values of the geostrophic relative vorticity. The geographical distributions of these parameters at the 300 mb level show that the arithmetic mean fields are highly biased representatives of the extratropical eddy distributions. The zonal arithmetic means of these parameters are also presented. These show that the zonal-and-time mean relative vorticity is but a small fraction of the zonal mean of the temporal r.m.s. relative vorticity, K. The reasons for considering the r.m.s. values as the temporal normal values of vorticity in the extratropics are given in considerable detail. The parameter K is shown to be of considerable importance in locating the extratropical frontal jet streams (EFJ) in time-and-zonal average distributions. The study leads to an understanding of the seasonal migrations of the EFJ which have not been explored until now
Atmospheric planetary wave response to external forcing
The tools of observational analysis, complex general circulation modeling, and simpler modeling approaches were combined in order to attack problems on the largest spatial scales of the earth's atmosphere. Two different models were developed and applied. The first is a two level, global spectral model which was designed primarily to test the effects of north-south sea surface temperature anomaly (SSTA) gradients between the equatorial and midlatitude north Pacific. The model is nonlinear, contains both radiation and a moisture budget with associated precipitation and surface evaporation, and utilizes a linear balance dynamical framework. Supporting observational analysis of atmospheric planetary waves is briefly summarized. More extensive general circulation models have also been used to consider the problem of the atmosphere's response, especially in the horizontal propagation of planetary scale waves, to SSTA
Acquiring Correct Knowledge for Natural Language Generation
Natural language generation (NLG) systems are computer software systems that
produce texts in English and other human languages, often from non-linguistic
input data. NLG systems, like most AI systems, need substantial amounts of
knowledge. However, our experience in two NLG projects suggests that it is
difficult to acquire correct knowledge for NLG systems; indeed, every knowledge
acquisition (KA) technique we tried had significant problems. In general terms,
these problems were due to the complexity, novelty, and poorly understood
nature of the tasks our systems attempted, and were worsened by the fact that
people write so differently. This meant in particular that corpus-based KA
approaches suffered because it was impossible to assemble a sizable corpus of
high-quality consistent manually written texts in our domains; and structured
expert-oriented KA techniques suffered because experts disagreed and because we
could not get enough information about special and unusual cases to build
robust systems. We believe that such problems are likely to affect many other
NLG systems as well. In the long term, we hope that new KA techniques may
emerge to help NLG system builders. In the shorter term, we believe that
understanding how individual KA techniques can fail, and using a mixture of
different KA techniques with different strengths and weaknesses, can help
developers acquire NLG knowledge that is mostly correct
Interhemispheric comparison of atmospheric circulation features as evaluated from Nimbus satellite data. A comparison of the structure and flow characteristics of the upper troposphere and stratosphere of the Northern and Southern Hemispheres
The general circulations of the Northern and Southern Hemispheres are compared with regard to the upper troposphere and stratosphere, using atmospheric structure obtained from multi-channel radiance data from the satellite infrared spectrometer instrument aboard the Nimbus 3 spacecraft. The inter-hemispheric comparisons are based on two months of data (one summer month and one winter month) in each hemisphere. Topics studied include: (1) mean meridional circulation in the Southern Hemisphere stratosphere; (2) magnitude and distribution of tropospheric eddy heat flux; (3) relative importance of standing and transient eddies in the two hemispheres; (4) magnitudes of energy cycle components; and (5) the relation of vortex structure to the breakdown climatology of the Antarctic stratospheric polar vortex
Estimating Refractive Index Spectra in Regions of Clear Air Turbulence
Estimation of refractive index spectra in regions of clear air turbulenc
Atmospheric variability and air-sea interaction
The topics studied include: (1) processing of Northern Hemispheric precipitation data, in order to fill in the transition seasons to provide a continuous 40 year data base on the variability of continental precipitation; (2) comparison of seasonally averaged fields of sea surface temperature obtained from ship observations in the North Atlantic and North Pacific in 1970 with the corresponding fields inferred from satellite observations; (3) estimation of seasonal average of total precipitable water at those admittedly few oceanic stations where repeated vertical soundings were made in 1970 and comparison with corresponding values inferred from satellite measurements; (4) comparison of seasonally averaged evaporation fields determined from ground based observations in 1970 with the field of divergence of the seasonal total horizontal water vapor flux inferred from satellite total water measurements and NMC wind data for the lower troposphere; (5) examination of meaning of convection-inversion index
On possible interactions between upper and lower atmosphere
Geomagnetic data was compared with data on tropospheric and stratospheric circulation characteristics; a statistically significant shrinking was found in areal extent of the stratospheric vortex from the third to the eighth day following a 'geomagnetic storm' The meridionality of the 30 640-m contour line at 10 millibars increases markedly from 5 to 8 days after the storm. During the contraction of the polar vortex edge, the mean height of the vortex central contour decreases only slightly. This indicates that a stratospheric warming event is associated with a steepening of the contour gradient rather than a warming over the entire area of the stratospheric polar vortex. The troposphere reacts to these weak, but significant, stratospheric warming events by a shrinkage of the area of the 500-millibar cold air pool. This shrinkage commences about 3 days after the stratospheric warming. The investigation indicates that the energy input into the stratosphere that is received in conjunction with the geomagnetic disturbance has to come at a propitious time, when the stratospheric-tropospheric circulation system is not already undergoing a major readjustment because of an inherent dynamic instability
Mesoscale structure of 11-20 km winds
Wind speed and direction profiles by tracking spherical superpressure balloon
Space-contained conflict revision, for geographic information
Using qualitative reasoning with geographic information, contrarily, for
instance, with robotics, looks not only fastidious (i.e.: encoding knowledge
Propositional Logics PL), but appears to be computational complex, and not
tractable at all, most of the time. However, knowledge fusion or revision, is a
common operation performed when users merge several different data sets in a
unique decision making process, without much support. Introducing logics would
be a great improvement, and we propose in this paper, means for deciding -a
priori- if one application can benefit from a complete revision, under only the
assumption of a conjecture that we name the "containment conjecture", which
limits the size of the minimal conflicts to revise. We demonstrate that this
conjecture brings us the interesting computational property of performing a
not-provable but global, revision, made of many local revisions, at a tractable
size. We illustrate this approach on an application.Comment: 14 page
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