Tracking and prediction of large-scale organized tropical convection by spectrally focused two-step space-time EOF analysis

2011 ◽  
Vol 138 (665) ◽  
pp. 919-931 ◽  
Author(s):  
Paul E. Roundy
Keyword(s):  
Large Scale ◽  
Space Time ◽  
Tropical Convection ◽  
Eof Analysis

scholarly journals Space–time reduced order model for large-scale linear dynamical systems with application to Boltzmann transport problems

2021 ◽  
Vol 424 ◽  
pp. 109845
Author(s):  
Youngsoo Choi ◽  
Peter Brown ◽  
William Arrighi ◽  
Robert Anderson ◽  
Kevin Huynh
Keyword(s):  
Dynamical Systems ◽  
Large Scale ◽  
Space Time ◽  
Reduced Order Model ◽  
Boltzmann Transport ◽  
Order Model ◽  
Linear Dynamical Systems ◽  
Reduced Order ◽  
Transport Problems

Новый критерий оптимальности пространственно-временных матриц

2020 ◽  
Author(s):  
A.A. Reznev ◽  
V.B. Kreyndelin
Keyword(s):  
Computational Complexity ◽  
Large Scale ◽  
Noise Immunity ◽  
Optimality Criterion ◽  
Mimo Systems ◽  
Optimality Criteria ◽  
Space Time ◽  
Space Time Codes ◽  
Golden Code ◽  
New Criterion

The application of optimality criteria for the study of space-time codes is considered. Known rank and determinant criteria are described. The computational complexity of determinant criteria is presented taking into account some estimation of the real CPUs specifications. An algorithm for calculating a new optimality criterion is described. The computational complexity of the new optimality criterion is evaluated. The new criterion is applied to the study of the space-time Golden matrix. The obtained criterion value is used to modify the Golden code. The modeling for Golden code demonstrates that criterion works and gives us better levels for noise immunity. The proposed optimality criterion is acceptable in terms of computational complexity even for a large number of antennas, which is typical for large-scale MIMO systems. Рассматривается применение критериев оптимальности для исследования пространственно-временных кодов.Описаны известные ранговый и детерминантный критерии. Для детерминантного критерия оценена вычислительная сложность с учетом определения специальных высокопроизводительных процессоров. Описан алгоритм расчета нового критерия оптимальности. Проведена оценка вычислительной сложности нового критерия оптимальности. Новый критерий применен для исследования пространственно-временной матрицы Голден. Полученное значение критерия использовано для модификациикода Голден. Продемонстрированы кривые помехоустойчивости для кода Голден и кода Голден с модифицированным параметром, получен энергетический выигрыш. Предложенный критерий оптимальности приемлем с точки зрения вычислительнойсложности даже при большом числе антенн, характерном для систем широкомасштабного MIMO.

scholarly journals Methods to describe barotropic vortices by global fields and vortex characteristics

2002 ◽  
Vol 9 (3/4) ◽  
pp. 189-200 ◽  
Author(s):  
W.-G. Früh
Keyword(s):  
Large Scale ◽  
Solid Boundary ◽  
Eof Analysis ◽  
Vortex Identification ◽  
Global Mode ◽  
Local Structures ◽  
Local Mechanism ◽  
Mode 2 ◽  
Identification Technique ◽  
Analyse Time

Abstract. Results from an experimental study of vortices in a rotating shear layer are presented. The data are in the form of maps of the instantaneous horizontal velocity field obtained by a particle tracking technique. Two fundamentally different methods to analyse time series of these velocity fields are presented and compared. One technique is the empirical orthogonal function (EOF) analysis, and the other method describes the flow field in terms of a few individual localised vortices. The flows discussed here are time-dependent two-vortex flows, which could either be described as a global mode 2 or as a collection of four unequal vortices. The results show that, while EOF analysis is a very powerful tool to detect fairly regular travelling modes or stationary features, it cannot detect local dynamics. The vortex identification technique is very good at detecting local structures and events but cannot put them into the context of a global flow structure. The comparison of the techniques shows indications that the time-dependence found in the system for low mode numbers could arise from an interaction of the large scale, global-mode flow with a local mechanism of vortex generation and shedding at a solid boundary.

scholarly journals The role of the observed tropical convection in the generation of frost events in the southern cone of South America

2008 ◽  
Vol 26 (6) ◽  
pp. 1379-1390 ◽  
Author(s):  
G. V. Müller ◽  
T. Ambrizzi ◽  
S. E. Ferraz
Keyword(s):  
South America ◽  
Large Scale ◽  
Rossby Waves ◽  
Tropical Convection ◽  
The Other ◽  
Linear Wave ◽  
Frequency Of Occurrence ◽  
The South ◽  
Cold Events ◽  
Extreme Cold

Abstract. Based on previous results obtained from observations and linear wave theory analysis, the hypothesis that large-scale patterns can generate extreme cold events in southeast South America through the propagation of remotely excited Rossby waves was already suggested. This work will confirm these findings and extend their analysis through a series of numerical experiments using a primitive equation model where waves are excited by a thermal forcing situated in positions chosen according to observed convection anomalies over the equatorial region. The basic state used for these experiments is a composite of austral winters with maximum and minimum frequency of occurrence of generalized frosts that can affect a large area known as the Wet Pampas located in the central and eastern part of Argentina. The results suggest that stationary Rossby waves may be one important mechanism linking anomalous tropical convection with the extreme cold events in the Wet Pampas. The combination of tropical convection and a specific basic state can generate the right environment to guide the Rossby waves trigged by the tropical forcing towards South America. Depending on the phase of the waves entering the South American continent, they can favour the advection of anomalous wind at low levels from the south carrying cold and dry air over the whole southern extreme of the continent, producing a generalized frost in the Wet Pampa region. On the other hand, when a basic state based on the composites of minimum frosts is used, an anomalous anticyclone over the southern part of the continent generates a circulation with a south-southeast wind which brings maritime air and therefore humidity over the Wet Pampas region, creating negative temperature anomalies only over the northeastern part of the region. Under these conditions even if frosts occur they would not be generalized, as observed for the other basic state with maximum frequency of occurrence of generalized frosts.

scholarly journals Potential Impacts of Assimilating All-Sky Satellite Infrared Radiances on Convection-Permitting Analysis and Prediction of Tropical Convection

2020 ◽  
Vol 148 (8) ◽  
pp. 3203-3224
Author(s):  
Man-Yau Chan ◽  
Fuqing Zhang ◽  
Xingchao Chen ◽  
L. Ruby Leung
Keyword(s):  
Data Assimilation ◽  
Brightness Temperature ◽  
Large Scale ◽  
Spatial Scales ◽  
Tropical Convection ◽  
Tropical Oceans ◽  
Geostationary Meteorological Satellite ◽  
Infrared Radiances ◽  
Cloud Patterns ◽  
Dry Bias

Abstract Geostationary infrared satellite observations are spatially dense [>1/(20 km)2] and temporally frequent (>1 h−1). These suggest the possibility of using these observations to constrain subsynoptic features over data-sparse regions, such as tropical oceans. In this study, the potential impacts of assimilating water vapor channel brightness temperature (WV-BT) observations from the geostationary Meteorological Satellite 7 (Meteosat-7) on tropical convection analysis and prediction were systematically examined through a series of ensemble data assimilation experiments. WV-BT observations were assimilated hourly into convection-permitting ensembles using Penn State’s ensemble square root filter (EnSRF). Comparisons against the independently observed Meteosat-7 window channel brightness temperature (Window-BT) show that the assimilation of WV-BT generally improved the intensities and locations of large-scale cloud patterns at spatial scales larger than 100 km. However, comparisons against independent soundings indicate that the EnSRF analysis produced a much stronger dry bias than the no data assimilation experiment. This strong dry bias is associated with the use of the simulated WV-BT from the prior mean during the EnSRF analysis step. A stochastic variant of the ensemble Kalman filter (NoMeanSF) is proposed. The NoMeanSF algorithm was able to assimilate the WV-BT without causing such a strong dry bias and the quality of the analyses’ horizontal cloud pattern is similar to EnSRF’s analyses. Finally, deterministic forecasts initiated from the NoMeanSF analyses possess better horizontal cloud patterns above 500 km than those of the EnSRF. These results suggest that it might be better to assimilate all-sky WV-BT through the NoMeanSF algorithm than the EnSRF algorithm.

scholarly journals Some Space–Time Spectral Analyses of Tropical Convection and Planetary-Scale Waves

2008 ◽  
Vol 65 (9) ◽  
pp. 2936-2948 ◽  
Author(s):  
Harry H. Hendon ◽  
Matthew C. Wheeler
Keyword(s):  
Zonal Wind ◽  
Space Time ◽  
Tropical Convection ◽  
Kelvin Waves ◽  
Equatorial Waves ◽  
Background Spectrum ◽  
Noise Process ◽  
Equatorial Wave ◽  
Spectral Peaks ◽  
Wave Modes

Abstract Three aspects of space–time spectral analysis are explored for diagnosis of the organization of tropical convection by the Madden–Julian oscillation (MJO) and other equatorial wave modes: 1) definition of the background spectrum upon which spectral peaks are assessed, 2) alternate variance preserving display of the spectra, and 3) the space–time coherence spectrum. Here the background spectrum at each zonal wavenumber is assumed to result from a red noise process. The associated decorrelation time for the red noise process for tropical convection is found to be half as long as for zonal wind, reflecting the different physical processes controlling each field. The significance of spectral peaks associated with equatorial wave modes for outgoing longwave radiation (OLR), which is a proxy for precipitating deep convection, and zonal winds that stand out above the red background spectrum is similar to that identified using a background spectrum resulting from ad hoc smoothing of the original spectrum. A variance-preserving display of the space–time power spectrum with a logarithmic frequency axis is useful for directly detecting Kelvin waves (periods 5–15 days for eastward zonal wavenumbers 1–5) and for highlighting their distinction from the MJO. The space–time coherence of OLR and zonal wind is predominantly associated with the MJO and other equatorial waves. The space–time coherence is independent of estimating the background spectrum and is quantifiable; thus, it is suggested as a useful metric for the MJO and other equatorial waves in observations and simulations. The space–time coherence is also used to quantify the association of Kelvin waves in the stratosphere with convective variability in the troposphere and for detection of barotropic Rossby–Haurwitz waves.

On the structure of conformal singularities in classical general relativity. II Evolution equations and a conjecture of K. P. Tod

1993 ◽  
Vol 443 (1919) ◽  
pp. 493-515 ◽  
Keyword(s):  
Large Scale ◽  
Evolution Equations ◽  
Physical Space ◽  
Space Time ◽  
Symmetric Hyperbolic System ◽  
First Order ◽  
Initial Hypersurface ◽  
The Cauchy Problem ◽  
Data Subject ◽  
The Universe

Consideration is given to the Cauchy problem for perfect fluid space-times which evolve from an initial singularity of conformal type. The evolution equations for the conformally transformed, unphysical geometry are shown to be expressible as a first order symmetric hyperbolic system, albeit with a singular forcing term. It is concluded that the 3-metric on the initial hypersurface of the unphysical space-time constitutes the freely specifiable initial data. Subject to Penroses’s Weyl Curvature Hypothesis, according to which the Weyl tensor was initially zero, it follows that the physical space-time is Robertson–Walker. This may provide a basis for a new explanation for the large-scale isotropy of the universe.

Complexity of low-frequency earthquakes activity in western Shikoku

2020 ◽  
Author(s):  
Natalia Poiata ◽  
Jean-Pierre Vilotte ◽  
Nikolai Shapiro ◽  
Mariano Supino ◽  
Kazushige Obara
Keyword(s):  
Subduction Zones ◽  
Large Scale ◽  
Active Faults ◽  
Low Frequency ◽  
Space Time ◽  
Interaction Patterns ◽  
Slow Slip Events ◽  
Time Activity ◽  
Tectonic Tremor ◽  
Slow Earthquakes

<p>Short-duration transient seismic events known as low-frequency earthquakes (LFEs) are a component of the slow earthquakes family observed in the transition zone, at the root of seismogenic regions of the subduction zones or active faults. LFEs are the signature of impulse seismic energy radiation associated to and often mixed within complex tectonic tremor signal. Detailed analysis and characterization of LFE space-time activity in relation to other slow earthquake phenomena can provide important information about the state and the processes of fault interface.</p><p>We derive a catalog of LFEs in western Shikoku (Japan) by applying a full waveform coherency-based detection and location method to the 4-year continuous data covering the period of 2013-2016 and recorded at Hi-net seismic stations of NIED. The obtained catalog of over 150,000 detected events allows looking into the details of LFE space-time activity during the tectonic tremor sequences and inter-sequence periods.</p><p>We use this catalogue of LFEs to perform a systematic statistical analysis of the event occurrence patterns by applying correlation and clustering analysis to infer the large-scale (long temporal ~ 1-2 day duration) space-time characteristics and interaction patterns of activity and its potential relation to the structural complexity of the subducting plate. We also analyze the correlation between the migration of clustered LFE activity during energetic tremor sequences and short-term slow slip events occurring in the area during the analyzed period.</p>

scholarly journals A Lane-Level LBS System for Vehicle Network with High-Precision BDS/GPS Positioning

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
Chi Guo ◽  
Wenfei Guo ◽  
Guangyi Cao ◽  
Hongbo Dong
Keyword(s):  
High Precision ◽  
Traffic Safety ◽  
Large Scale ◽  
Space Time ◽  
Mobile Internet ◽  
Network Systems ◽  
Precise Positioning ◽  
Network Location ◽  
Location Service ◽  
Vehicle Network

In recent years, research on vehicle network location service has begun to focus on its intelligence and precision. The accuracy of space-time information has become a core factor for vehicle network systems in a mobile environment. However, difficulties persist in vehicle satellite positioning since deficiencies in the provision of high-quality space-time references greatly limit the development and application of vehicle networks. In this paper, we propose a high-precision-based vehicle network location service to solve this problem. The major components of this study include the following: (1) application of wide-area precise positioning technology to the vehicle network system. An adaptive correction message broadcast protocol is designed to satisfy the requirements for large-scale target precise positioning in the mobile Internet environment; (2) development of a concurrence service system with a flexible virtual expansion architecture to guarantee reliable data interaction between vehicles and the background; (3) verification of the positioning precision and service quality in the urban environment. Based on this high-precision positioning service platform, a lane-level location service is designed to solve a typical traffic safety problem.

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