scholarly journals Network-based study of Lagrangian transport and mixing

2017 ◽  
Author(s):  
Kathrin Padberg-Gehle ◽  
Christiane Schneide
Keyword(s):  
Clustering Algorithms ◽  
Transfer Operator ◽  
Polar Vortex ◽  
Local Network ◽  
Node Degree ◽  
Trajectory Data ◽  
Mixing Processes ◽  
Stratospheric Polar Vortex ◽  
Spatio Temporal ◽  
Transport And Mixing

Abstract. Transport and mixing processes in fluid flows are crucially influenced by coherent structures and the characterization of these Lagrangian objects is a topic of intense current research. While established mathematical approaches such as variational or transfer operator based schemes require full knowledge of the flow field or at least high resolution trajectory data, this information may not be available in applications. Recently, different computational methods have been proposed to identify coherent behavior in flows directly from Lagrangian trajectory data. In this context, spatio-temporal clustering algorithms have been proven to be very effective for the extraction of coherent sets from sparse and possibly incomplete trajectory data. Inspired by these recent approaches, we consider an unweighted, undirected network, where Lagrangian particle trajectories serve as network nodes. A link is established between two nodes if the respective trajectories come close to each other at least once in the course of time. Classical graph concepts are then employed to analyze the resulting network. In particular, local network measures such as the node degree serve as indicators of highly mixing regions, whereas spectral graph partitioning schemes allow us to extract coherent sets. The proposed methodology is very fast to run and we demonstrate its applicability in two geophysical flows – the Bickley jet as well as the antarctic stratospheric polar vortex.

scholarly journals Network-based study of Lagrangian transport and mixing

2017 ◽  
Vol 24 (4) ◽  
pp. 661-671 ◽  
Author(s):  
Kathrin Padberg-Gehle ◽  
Christiane Schneide
Keyword(s):  
Clustering Algorithms ◽  
Transfer Operator ◽  
Polar Vortex ◽  
Clustering Coefficient ◽  
Local Network ◽  
Node Degree ◽  
Trajectory Data ◽  
Mixing Processes ◽  
Stratospheric Polar Vortex ◽  
Transport And Mixing

Abstract. Transport and mixing processes in fluid flows are crucially influenced by coherent structures and the characterization of these Lagrangian objects is a topic of intense current research. While established mathematical approaches such as variational methods or transfer-operator-based schemes require full knowledge of the flow field or at least high-resolution trajectory data, this information may not be available in applications. Recently, different computational methods have been proposed to identify coherent behavior in flows directly from Lagrangian trajectory data, that is, numerical or measured time series of particle positions in a fluid flow. In this context, spatio-temporal clustering algorithms have been proven to be very effective for the extraction of coherent sets from sparse and possibly incomplete trajectory data. Inspired by these recent approaches, we consider an unweighted, undirected network, where Lagrangian particle trajectories serve as network nodes. A link is established between two nodes if the respective trajectories come close to each other at least once in the course of time. Classical graph concepts are then employed to analyze the resulting network. In particular, local network measures such as the node degree, the average degree of neighboring nodes, and the clustering coefficient serve as indicators of highly mixing regions, whereas spectral graph partitioning schemes allow us to extract coherent sets. The proposed methodology is very fast to run and we demonstrate its applicability in two geophysical flows – the Bickley jet as well as the Antarctic stratospheric polar vortex.

scholarly journals Spectral Early-Warning Signals for Sudden Changes in Time-Dependent Flow Patterns

Fluids ◽  
2021 ◽  
Vol 6 (2) ◽  
pp. 49
Author(s):  
Moussa Ndour ◽  
Kathrin Padberg-Gehle ◽  
Martin Rasmussen
Keyword(s):  
Transfer Operator ◽  
Polar Vortex ◽  
Fluid Flows ◽  
Flow Patterns ◽  
Time Dependent ◽  
Mixing Processes ◽  
Dependent Flow ◽  
Antarctic Polar Vortex ◽  
Transport And Mixing ◽  
The Antarctic

Lagrangian coherent sets are known to crucially determine transport and mixing processes in non-autonomous flows. Prominent examples include vortices and jets in geophysical fluid flows. Coherent sets can be identified computationally by a probabilistic transfer-operator-based approach within a set-oriented numerical framework. Here, we study sudden changes in flow patterns that correspond to bifurcations of coherent sets. Significant changes in the spectral properties of a numerical transfer operator are heuristically related to critical events in the phase space of a time-dependent system. The transfer operator approach is applied to different example systems of increasing complexity. In particular, we study the 2002 splitting event of the Antarctic polar vortex.

scholarly journals Insights on the three-dimensional Lagrangian geometry of the Antarctic Polar Vortex

2017 ◽  
Author(s):  
Jezabel Curbelo ◽  
Victor J. García-Garrido ◽  
Carlos R. Mechoso ◽  
Ana M. Mancho ◽  
Stephen Wiggins ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Polar Vortex ◽  
Reanalysis Data ◽  
Late Winter ◽  
Mixing Processes ◽  
Stratospheric Polar Vortex ◽  
Atmospheric Flows ◽  
Vertical Barriers ◽  
Antarctic Polar Vortex ◽  
Transport And Mixing

Abstract. The present paper introduces an algorithm for the visualization, analysis and verification of transport and mixing processes in three-dimensional atmospheric flows. This algorithm is based on the methodology of Lagrangian descriptors (LDs), a technique from Dynamical Systems Theory. The algorithm is applied to reanalysis data in order to illustrate the evolution of the flow above Antarctica during a period of rapid changes in the southern spring of 1979. The evolution of Lagrangian coherent structures is discussed and connections with the stratosphere is examined. The results suggest that the cyclonic stratospheric polar vortex during late winter appears to extend down to the troposphere. The results are also indicative of features related to invariante manifolds that can act as deep vertical barriers to transport between vortices.

scholarly journals A Simple Kinematic Model for the Lagrangian Description of Relevant Nonlinear Processes in the Stratospheric Polar Vortex

2016 ◽  
Author(s):  
Victor José García-Garrido ◽  
Jezabel Curbelo ◽  
Carlos Roberto Mechoso ◽  
Ana María Mancho ◽  
Stephen Wiggins
Keyword(s):  
Kinematic Model ◽  
Polar Vortex ◽  
Reanalysis Data ◽  
Planetary Waves ◽  
Lagrangian Description ◽  
Lagrangian Analysis ◽  
Mixing Processes ◽  
Geometrical Structures ◽  
Stratospheric Polar Vortex ◽  
Fourier Decomposition

Abstract. In this work we study the Lagrangian footprint of the planetary waves present in the Southern Hemisphere stratosphere during the Sudden Stratospheric Warming event that took place during September 2002. The Lagrangian analysis of the transport and mixing processes is carried out in the framework of dynamical systems theory, by means of a Lagrangian descriptor. We seek to describe the Lagrangian skeleton of geometrical structures that lead to filamentation phenomena and the breakdown of the polar vortex, and establish its relation with how planetary waves interact. Our approach is based on the construction of a simple kinematic model, inspired by the Fourier decomposition of the geopotential field. We show that this model is capable of reproducing the key Lagrangian features present on the reanalysis data such as the formation of filaments eroding the stratospheric polar vortex and the breakdown of the vortex.

scholarly journals Insights into the three-dimensional Lagrangian geometry of the Antarctic polar vortex

2017 ◽  
Vol 24 (3) ◽  
pp. 379-392 ◽  
Author(s):  
Jezabel Curbelo ◽  
Víctor José García-Garrido ◽  
Carlos Roberto Mechoso ◽  
Ana Maria Mancho ◽  
Stephen Wiggins ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Polar Vortex ◽  
Reanalysis Data ◽  
Strong Mixing ◽  
Mixing Processes ◽  
Stratospheric Polar Vortex ◽  
Vertical Extension ◽  
Antarctic Polar Vortex ◽  
The Antarctic ◽  
Lagrangian Geometry

Abstract. In this paper we study the three-dimensional (3-D) Lagrangian structures in the stratospheric polar vortex (SPV) above Antarctica. We analyse and visualize these structures using Lagrangian descriptor function M. The procedure for calculation with reanalysis data is explained. Benchmarks are computed and analysed that allow us to compare 2-D and 3-D aspects of Lagrangian transport. Dynamical systems concepts appropriate to 3-D, such as normally hyperbolic invariant curves, are discussed and applied. In order to illustrate our approach we select an interval of time in which the SPV is relatively undisturbed (August 1979) and an interval of rapid SPV changes (October 1979). Our results provide new insights into the Lagrangian structure of the vertical extension of the stratospheric polar vortex and its evolution. Our results also show complex Lagrangian patterns indicative of strong mixing processes in the upper troposphere and lower stratosphere. Finally, during the transition to summer in the late spring, we illustrate the vertical structure of two counterrotating vortices, one the polar and the other an emerging one, and the invariant separatrix that divides them.

scholarly journals Measuring Accessibility Based on Improved Impedance and Attractive Functions Using Taxi Trajectory Data

2020 ◽  
Vol 13 (1) ◽  
pp. 112
Author(s):  
Helai Huang ◽  
Jialing Wu ◽  
Fang Liu ◽  
Yiwei Wang
Keyword(s):  
Waiting Time ◽  
Urban Areas ◽  
Transportation Systems ◽  
Trajectory Data ◽  
Peak Period ◽  
Important Indicator ◽  
Destination Attractiveness ◽  
Urban Accessibility ◽  
Spatio Temporal ◽  
Taxi Trajectory

Accessibility has attracted wide interest from urban planners and transportation engineers. It is an important indicator to support the development of sustainable policies for transportation systems in major events, such as the COVID-19 pandemic. Taxis are a vital travel mode in urban areas that provide door-to-door services for individuals to perform urban activities. This study, with taxi trajectory data, proposes an improved method to evaluate dynamic accessibility depending on traditional location-based measures. A new impedance function is introduced by taking characteristics of the taxi system into account, such as passenger waiting time and the taxi fare rule. An improved attraction function is formulated by considering dynamic availability intensity. Besides, we generate five accessibility scenarios containing different indicators to compare the variation of accessibility. A case study is conducted with the data from Shenzhen, China. The results show that the proposed method found reduced urban accessibility, but with a higher value in southern center areas during the evening peak period due to short passenger waiting time and high destination attractiveness. Each spatio-temporal indicator has an influence on the variation in accessibility.

scholarly journals Seasonal prediction of the boreal winter stratosphere

2021 ◽  
Author(s):  
Alice Portal ◽  
Paolo Ruggieri ◽  
Froila M. Palmeiro ◽  
Javier García-Serrano ◽  
Daniela I. V. Domeisen ◽  
...  
Keyword(s):  
Southern Oscillation ◽  
Polar Vortex ◽  
Seasonal Prediction ◽  
Wave Activity ◽  
Boreal Winter ◽  
Quasi Biennial Oscillation ◽  
Stratospheric Polar Vortex ◽  
Eddy Heat Flux ◽  
Prediction Systems ◽  
Model Database

AbstractThe predictability of the Northern Hemisphere stratosphere and its underlying dynamics are investigated in five state-of-the-art seasonal prediction systems from the Copernicus Climate Change Service (C3S) multi-model database. Special attention is devoted to the connection between the stratospheric polar vortex (SPV) and lower-stratosphere wave activity (LSWA). We find that in winter (December to February) dynamical forecasts initialised on the first of November are considerably more skilful than empirical forecasts based on October anomalies. Moreover, the coupling of the SPV with mid-latitude LSWA (i.e., meridional eddy heat flux) is generally well reproduced by the forecast systems, allowing for the identification of a robust link between the predictability of wave activity above the tropopause and the SPV skill. Our results highlight the importance of November-to-February LSWA, in particular in the Eurasian sector, for forecasts of the winter stratosphere. Finally, the role of potential sources of seasonal stratospheric predictability is considered: we find that the C3S multi-model overestimates the stratospheric response to El Niño–Southern Oscillation (ENSO) and underestimates the influence of the Quasi–Biennial Oscillation (QBO).

scholarly journals Extracting Stops from Spatio-Temporal Trajectories within Dynamic Contextual Features

2021 ◽  
Vol 13 (2) ◽  
pp. 690
Author(s):  
Tao Wu ◽  
Huiqing Shen ◽  
Jianxin Qin ◽  
Longgang Xiang
Keyword(s):  
Moving Objects ◽  
Major Effect ◽  
Location Based Services ◽  
Trajectory Data ◽  
The Road ◽  
Contextual Features ◽  
Novel Approach ◽  
Gps Trajectories ◽  
Time Distance ◽  
Spatio Temporal

Identifying stops from GPS trajectories is one of the main concerns in the study of moving objects and has a major effect on a wide variety of location-based services and applications. Although the spatial and non-spatial characteristics of trajectories have been widely investigated for the identification of stops, few studies have concentrated on the impacts of the contextual features, which are also connected to the road network and nearby Points of Interest (POIs). In order to obtain more precise stop information from moving objects, this paper proposes and implements a novel approach that represents a spatio-temproal dynamics relationship between stopping behaviors and geospatial elements to detect stops. The relationship between the candidate stops based on the standard time–distance threshold approach and the surrounding environmental elements are integrated in a complex way (the mobility context cube) to extract stop features and precisely derive stops using the classifier classification. The methodology presented is designed to reduce the error rate of detection of stops in the work of trajectory data mining. It turns out that 26 features can contribute to recognizing stop behaviors from trajectory data. Additionally, experiments on a real-world trajectory dataset further demonstrate the effectiveness of the proposed approach in improving the accuracy of identifying stops from trajectories.

Forest path condition monitoring based on crowd-based trajectory data analysis

2020 ◽  
pp. 1-18
Author(s):  
Francisco Arcas-Tunez ◽  
Fernando Terroso-Saenz
Keyword(s):  
Information Acquisition ◽  
Road Network ◽  
Road Networks ◽  
Trajectory Data ◽  
Country Road ◽  
Wide Range ◽  
Sport Activities ◽  
Path Condition ◽  
Spatio Temporal ◽  
The City

The development of Road Information Acquisition Systems (RIASs) based on the Mobile Crowdsensing (MCS) paradigm has been widely studied for the last years. In that sense, most of the existing MCS-based RIASs focus on urban road networks and assume a car-based scenario. However, there exist a scarcity of approaches that pay attention to rural and country road networks. In that sense, forest paths are used for a wide range of recreational and sport activities by many different people and they can be also affected by different problems or obstacles blocking them. As a result, this work introduces SAMARITAN, a framework for rural-road network monitoring based on MCS. SAMARITAN analyzes the spatio-temporal trajectories from cyclists extracted from the fitness application Strava so as to uncover potential obstacles in a target road network. The framework has been evaluated in a real-world network of forest paths in the city of Cieza (Spain) showing quite promising results.

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