Wavelet Analysis Of Time Series Research Articles

Insights into Spatiotemporal Variations in the NPP of Terrestrial Vegetation in Africa from 1981 to 2018

The net primary productivity (NPP) of vegetation is an important indicator used to evaluate the quality of terrestrial ecosystems and characterize the carbon balance of ecosystems. In this study, the spatiotemporal distribution and dynamic change in NPP in Africa from 1981 to 2018 were analyzed using the long time series data of NPP. The results of the trend and fluctuation analysis showed that the NPP in the Sahara arid region in northern Africa and the arid region in South Africa exhibited a significant reduction and a high degree of fluctuation; most of the NPP in the tropical rainforests in central Africa and the deciduous broadleaved forests and deciduous needle-leaved forests on the north and south sides of the tropical rainforests increased and showed a low degree of fluctuation; the Congo basin, Gabon, Cameroon, Ghana, Nigeria, Tanzania, and other regions were affected by human activities, while the NPP in these regions exhibited a significant reduction and a high degree of fluctuation. Anomaly analysis showed that the NPP in Africa generally exhibited a slow upward trend during the period from 1981 and 2018. The trend was basically consistent in different seasons, and can be segmented into three phases: (1) a phase of descent from 1981 to 1992, with the NPP below the average value in most years; (2) a phase of steady growth from 1993 to 2000, reaching a peak in 2000; (3) a phase of fluctuations from 2001 to 2018, where the NPP value was above the average value in all years except 2015 and 2016, when the NPP value was low due to abnormally high temperatures and drought. The Mann–Kendall test further showed that the annual and seasonal NPP in Africa exhibited a significant upward trend, and the mutation time points occurred around 1995. The wavelet time series analysis revealed obvious periodic changes in the time series of NPP in Africa. The annual and seasonal NPP showed clear oscillations on time scales of 7, 20, 29, and 55 years. The 55-year period had the strongest signal, and was the first main period. The study can provide a scientific gist for the sustainable development of environmental ecology, agricultural production, and the social economy in Africa.

Характеристики транспортного затора на основе данных системы фото- и видеофиксации

The relevance of the present paper is justified by the need to search for a scientifically based criterion for the formation, development and elimination of traffic congestion using modern highly efficient mathematical methods of information processing. It seems necessary to study the results of using the rescaled range, statistical, fractal, harmonic, and wavelet analysis of time series formed by the time (duration) of the movement of cars in a stream along a road section in the absence and presence of traffic congestion. The object of study is a section of the road network equipped with a software and hardware complex that allows measuring the characteristics of any car in the flow of transport. The subject of the study is the patterns of changes in the duration of movement of individual cars in the absence and presence of a congestion situation. The purpose of this study is a quantitative indicator of the formation, evolution, and elimination of traffic congestion. The basis of the theoretical and methodological approach is the use of modern highly efficient mathematical methods for processing information about traffic flows received from stationary complexes of photo and video recording of traffic violations. As a result of the study of time series, decompositions of the analyzed time series by harmonics and wavelets are constructed, statistical and fractal characteristics of the time series under consideration are determined. The analysis of the obtained results is carried out, the features of the obtained dependencies are revealed. The theoretical and practical significance of the work lies in the scientific substantiation of the quantitative characteristics of traffic congestion, which is of practical interest from the point of view of predicting anomalies in the movement of vehicles on the road network, making decisions on managing the operation of traffic lights, etc. The direction of further research is an in-depth analysis of the identified indicator and determination on its basis of a criterion for determining the stages of formation, evolution, and elimination of traffic congestion at intersections of the street and road network of a large industrial city.

VCI-Based Analysis on Spatiotemporal Variations of Spring Drought in China

The analysis of spatiotemporal variations in drought is important for environmental monitoring and agricultural production. In this study, the spring vegetative drought conditions in China were analyzed by using the vegetation condition index (VCI) as an indicator to reveal the drought characteristics in China from 1981–2015. The results suggest that spring vegetative drought (especially moderate drought) occurs frequently in China, and drought conditions have obvious geographical differences and are highly affected by monsoons. The frequency of spring vegetative drought is relatively high in the southern and northern regions, which are greatly affected by monsoons, and is relatively low in the northwestern and Qinghai-Tibet regions, which are less affected by monsoons. During 1981–2015, the spring VCI in China showed an overall upward trend. In addition, the trend was not a single change but a wave-like increasing trend that can be divided into four stages: (1) a stage of slow growth from 1981–1990, (2) a stage of intense fluctuations from 1991–2000, (3) a stage of steady growth from 2001–2010, and (4) a stage of slow descent after 2010. The Mann–Kendall test confirmed that the spring VCI in China was increasing, and the changes in the southern, northwestern, and Qinghai-Tibet regions reached significant levels. The time point of mutation in the southern region was 2000, and that in the northwestern and Qinghai-Tibet regions was 1992. Wavelet time series analysis showed that spring vegetation drought in China has a short-period oscillation of 5–7 years and a long-period oscillation of approximately 23–28 years. The northwestern and Qinghai-Tibet regions, which are less affected by the monsoons, are dominated by long-period oscillations, while the southern and northern regions, which are more affected by the monsoons, are dominated by short-period oscillations.

The correlation between three teleconnections and leptospirosis incidence in the Kandy District, Sri Lanka, 2004\u20132019

BackgroundLeptospirosis is a bacterial zoonosis. Leptospirosis incidence (LI) in Sri Lanka is high. Infected animals excrete leptospires into the environment via their urine. Survival of leptospires in the environment until they enter into a person and several other factors that influence leptospirosis transmission are dependent upon local weather. Past studies show that rainfall and other weather parameters are correlated with the LI in the Kandy district, Sri Lanka. El Niño Southern Oscillation (ENSO), ENSO Modoki, and the Indian Ocean Dipole (IOD) are teleconnections known to be modulating rainfall in Sri Lanka. There is a severe dearth of published studies on the correlations between indices of these teleconnections and LI.MethodsWe acquired the counts of leptospirosis cases notified and midyear estimated population data of the Kandy district from 2004 to 2019, respectively, from weekly epidemiology reports of the Ministry of Health and Department of Census and Statistics of Sri Lanka. We estimated weekly and monthly LI of Kandy. We obtained weekly and monthly teleconnection indices data for the same period from the National Oceanic and Atmospheric Administration (NOAA) of the USA and Japan Agency for Marine-Earth Science and Technology (JAMSTEC). We performed wavelet time series analysis to determine correlations with lag periods between teleconnection indices and LI time series. Then, we did time-lagged detrended cross-correlation analysis (DCCA) to verify wavelet analysis results and to find the magnitudes of the correlations detected.ResultsWavelet analysis displayed indices of ENSO, IOD, and ENSO Modoki were correlated with the LI of Kandy with 1.9–11.5-month lags. Indices of ENSO showed two correlation patterns with Kandy LI. Time-lagged DCCA results show all indices of the three teleconnections studied were significantly correlated with the LI of Kandy with 2–5-month lag periods.ConclusionsResults of the two analysis methods generally agree indicating that ENSO and IOD modulate LI in Kandy by modulating local rainfall and probably other weather parameters. We recommend further studies about the ENSO Modoki and LI correlation in Sri Lanka. Monitoring for extreme teleconnection events and enhancing preventive measures during lag periods can blunt LI peaks that may follow.

Method of Wavelet Analysis of Time Series to Assess the Effectiveness of the Country’s Energy Security

This article addresses the problems of energy security at the level of Russian regions, which is a particularly urgent in modern economic conditions characterized by global digitalization processes. In this case, the problem arises the need to develop mathematical tools for planning and assessing energy security in conditions of high uncertainty and fluctuations of the studied parameters of the external environment.The paper presents the mathematical justification for the use of wavelet analysis and the construction of spaces of scaling functions in order to obtain the theorem of multifunctional analysis of economic parameters and indicators of regional energy security, based on many intervals and determining the corresponding wavelet spaces.

Methodology of wavelet analysis in research of dynamics of phishing attacks

Safety of transfer and reception of various data over the internet can be accompanied by a presence of harmful components in a passed content. The phishing attack is one of versions of such harmful components. Thus it is important to know the relationship between the phishes verified as valid and suspected phishes Submitted. This is necessary for the forecast. To solve this problem, we use the wavelet analysis of time series which represent phishes verified as valid and suspected phishes submitted. We are considering the change of Hurst indicator; we analyse of a spectrum of wavelet energy. This allows you to identify the features of the main characteristics of time series which are considered. Conducted researches have shown the presence of essential duration of long-term dependence of investigated data. We also identified presence of trend component in structure of investigated series of data. It allows you to investigate recurrence of occurrence of phishing attacks that allows concentrating forces and means during the periods of activisation of such harmful influences. The analysis is spent on real data that reflects the importance of the conclusions obtained.

Wavelet analysis of time series in the model of nomads and tillers

The article is devoted to the study of time series obtained in earlier works by econometric and wavelet analysis. At the first stage of this study, econometric analysis was conducted, regression was constructed. In the regression influence of the number of nomads and the amount of resource on the number of plowmen was studied. The coefficient of determination (R2) of the constructed regression turned out to be 0.81, the Durbin-Watson statistics equals to 0.94, which indicates the presence of positive first-order autocorrelation of errors. The next stage is an analysis based on wavelet transforms, which helps to get rid of high-frequency "noise" and interference in considered time series. Within the framework of this paper, the Haar wavelet and the Daubechies 2 tap wavelet were considered (the remaining wavelets give similar results). After the time series had been cleared by the wavelet analysis, regression analysis was applied again. The coefficient of determination of new regressions depending on which wavelet was applied and the interference of what frequency were removed took values in the range from 0.86 to 0.93. The coefficient of determination of new regressions depends on which wavelet was applied and the interference of what frequency were removed. It takes values in the range from 0.86 to 0.93. However, the Durbin-Watson statistics decreased its values and began to take values in the range from 0.01 to 0.46, which still indicates the presence of positive first-order autocorrelation of errors. In the end, we learn that in this situation, the application of wavelet analysis significantly increases the explanatory power of regression, on the other hand, the problem of autocorrelation of errors can not be resolved in this way, in some sense it is only getting worse.

Distribution of eddy scales for wave current combined flow

This paper illustrates the modulation of the eddy scale distribution due to superimposition of surface wave on only current flow. Time series data of three-dimensional velocity components were measured in a laboratory flume by a three-dimensional (3D) 16-MHz micro-acoustic Doppler velocimeter (Micro-ADV). The velocity time series of only current case and waves following the current were analysed to obtain the phase-averaged mean velocities, turbulent intensities, and Reynolds stress. The probability density function of phase-averaged stream-wise and vertical velocity fluctuations showed bimodal oscillations towards the free surface for higher frequency surface waves. It was revealed that surface waves along the current effectively decrease the intermittency of turbulence of the only current flow. Surface wave changed the intermittent structure of only current flow by modulation of the energy cascade mechanism of the only current flow by introduction of wave induced length scales. Also the scale of the finer dissipative eddies were prominently enhanced by the increase in surface wave frequency. Wavelet analysis of time series of velocity signals provided information on the eddy scale and their frequency of occurrence. It was found that the large eddies are carried by the crest regions of the progressive wave while the small scale eddies are carried by the trough regions.

ВЕЙВЛЕТ И КРОСС-ВЕЙВЛЕТ АНАЛИЗ СУММ АТМОСФЕРНЫХ ОСАДКОВ И ПРИПОВЕРХНОСТНОЙ ТЕМПЕРАТУРЫ НА ЕВРОПЕЙСКОЙ ТЕРРИТОРИИ РОССИИ

Wavelet analysis of time series of surface air temperature and sums of precipitation in some cities of European Russia, with an estimate of the statistical significance of the obtained results is carried out with the purpose of identifying periodicities in the data of station meteorological observations. A cross-wavelet analysis was used to establish a link between variations in series of temperature and precipitation with important climate indices such as the North Atlantic oscillation (NAO), Atlantic multidecade oscillation (AMO) and Arctic oscillation (AO). A number of important cycles in different frequency ranges is identified. Cross-wavelet analysis of the NAO, AO with precipitation and temperature series showed a higher density of links compared to AMO. The strong link of high frequency oscillations in precipitation and temperature of the study area with fluctuations of the NAO, AMO and AO is established that can be determined not only by these climate indices, but the relationship of these Atlantic fluctuations with the El Nino phenomenon. Possibly, mid-frequency oscillations of meteorological data of the area with periods of 7–11 years are the evidence of the link with the fluctuation of the NAO. The established coherence of the index of the AMO and observational data is localized at time intervals before and after 1970, which is consistent with quasi-cyclic changes in the Earth’s climate.

The correlation between dengue incidence and diurnal ranges of temperature of Colombo district, Sri Lanka 2005–2014

BackgroundMeteorological factors affect dengue transmission. Mechanisms of the way in which different diurnal temperatures, ranging around different mean temperatures, influence dengue transmission were published after 2011.ObjectiveWe endeavored to determine the correlation between dengue incidence and diurnal temperature ranges (DTRs) in Colombo district, Sri Lanka, and to explore the possibilities of using our findings to improve control of dengue.DesignWe calculated the weekly dengue incidence in Colombo during 2005–2014, after data on all of the reported dengue patients and estimated mid-year populations were collected. We obtained daily maximum and minimum temperatures from two Colombo weather stations, averaged, and converted them into weekly data. Weekly averages of DTR versus dengue incidence graphs were plotted and correlations observed. The count of days per week with a DTR of >7.5°C and <7.5°C were also calculated. Wavelet time series analysis was performed to determine the correlation between dengue incidence and DTR.ResultsWe obtained a negative correlation between dengue incidence and a DTR>7.5°C with an 8-week lag period, and a positive correlation between dengue incidence and a DTR<7.5°C, also with an 8-week lag.ConclusionsLarge DTRs were negatively correlated with dengue transmission in Colombo district. We propose to take advantage of that in local dengue control efforts. Our results agree with previous studies on the topic and with a mathematical model of relative vectorial capacity of Aedes aegypti. Global warming and declining DTR are likely to favor a rise of dengue, and we suggest a simple method to mitigate this.

The interrelationship between dengue incidence and diurnal ranges of temperature and humidity in a Sri Lankan city and its potential applications

BackgroundTemperature, humidity, and other weather variables influence dengue transmission. Published studies show how the diurnal fluctuations of temperature around different mean temperatures influence dengue transmission. There are no published studies about the correlation between diurnal range of humidity and dengue transmission.ObjectiveThe goals of this study were to determine the correlation between dengue incidence and diurnal fluctuations of temperature and humidity in the Sri Lankan city of Kandy and to explore the possibilities of using that information for better control of dengue.DesignWe calculated the weekly dengue incidence in Kandy during the period 2003–2012, after collecting data on all of the reported dengue patients and estimated midyear populations. Data on daily maximum and minimum temperatures and night-time and daytime humidity were obtained from two weather stations, averaged, and converted into weekly data. The number of days per week with a diurnal temperature range (DTR) of >10°C and <10°C and the number of days per week with a diurnal humidity range (DHR) of >20 and <15% were calculated. Wavelet time series analysis was performed to determine the correlation between dengue incidence and diurnal ranges of temperature and humidity.ResultsThere were negative correlations between dengue incidence and a DTR >10°C and a DHR >20% with 3.3-week and 4-week lag periods, respectively. Additionally, positive correlations between dengue incidence and a DTR <10°C and a DHR <15% with 3- and 4-week lag periods, respectively, were discovered.ConclusionsThese findings are consistent with the results of previous entomological studies and theoretical models of DTR and dengue transmission correlation. It is important to conduct similar studies on diurnal fluctuations of humidity in the future. We suggest ways and means to use this information for local dengue control and to mitigate the potential effects of the ongoing global reduction of DTR on dengue incidence.

A study of the correlation between dengue and weather in Kandy City, Sri Lanka (2003 -2012) and lessons learned.

BackgroundWeather variables affect dengue transmission. This study aimed to identify a dengue weather correlation pattern in Kandy, Sri Lanka, compare the results with results of similar studies, and establish ways for better control and prevention of dengue.MethodWe collected data on reported dengue cases in Kandy and mid-year population data from 2003 to 2012, and calculated weekly incidences. We obtained daily weather data from two weather stations and converted it into weekly data. We studied correlation patterns between dengue incidence and weather variables using the wavelet time series analysis, and then calculated cross-correlation coefficients to find magnitudes of correlations.ResultsWe found a positive correlation between dengue incidence and rainfall in millimeters, the number of rainy and wet days, the minimum temperature, and the night and daytime, as well as average, humidity, mostly with a five- to seven-week lag. Additionally, we found correlations between dengue incidence and maximum and average temperatures, hours of sunshine, and wind, with longer lag periods. Dengue incidences showed a negative correlation with wind run.ConclusionOur results showed that rainfall, temperature, humidity, hours of sunshine, and wind are correlated with local dengue incidence. We have suggested ways to improve dengue management routines and to control it in these times of global warming. We also noticed that the results of dengue weather correlation studies can vary depending on the data analysis.Electronic supplementary materialThe online version of this article (doi:10.1186/s40249-015-0075-8) contains supplementary material, which is available to authorized users.

Influence of ocean–atmospheric oscillations on lake ice phenology in eastern North America

Our results reveal long-term trends in ice out dates (1836–2013) for twelve lakes in Maine, New Brunswick and New Hampshire, in eastern North America. The trends are remarkably coherent between lakes (rs = 0.462–0.933, p < 0.01) and correlate closely with the March–April (MA) instrumental temperature records from the region (rs = 0.488–0.816, p < 0.01). This correlation permits use of ice out dates as a proxy to extend the shorter MA instrumental record (1876–2013). Mean ice out dates trended progressively earlier during the recovery from the Little Ice Age through to the 1940s, and gradually became later again through to the late 1970s, when ice out dates had returned to values more typical of the late nineteenth century. Post-1970’s ice out dates resumed trending toward earlier dates, with the twenty-first century being characterized by the earliest ice out dates on record. Spectral and wavelet time series analysis indicate that ice out is influenced by several teleconnections including the Quasi-biennial Oscillation, El Nino-Southern Oscillation, North Atlantic Oscillation, as well as a significant correlation between inland lake records and the Atlantic Multidecadal Oscillation. The relative influence of these teleconnections is variable with notable shifts occurring after ~1870, ~1925, and ~1980–2000. The intermittent expression of these cycles in the ice out and MA instrumental record is not only influenced by absolute changes in the intensity of the various teleconnections and other climate drivers, but through phase interference between teleconnections, which periodically damps the various signals.

Chapter 2 Cyclic phenomena at the Soufrière Hills Volcano, Montserrat

Abstract Cycles of eruptive activity are generally interpreted as evidence of one or more mechanisms operating in equilibrium. Modulation of cycle characteristics thus reflects changes in the conditions affecting those mechanisms. This kind of semi-deterministic behaviour at the Soufrière Hills Volcano has occurred on multiple timescales and with a range of eruptive intensity. By documenting cyclic phenomena, it is possible to investigate the mechanisms that modulate the state of the eruption and examine conceptual models. Pattern recognition and model development allows some degree of short-term forecasting ability for volcanic activity. We report the cyclic eruptive phenomena that have occurred on Montserrat on scales of hours to centuries. We identify four dominant types of cyclicity: sub-daily variations in lava flux; sub-annual cycles in eruption intensity; multi-annual ‘on–off’ switching of lava extrusion; and multi-decadal recurrence of seismic crises. We exploit a wealth of multi-parameter datasets (including seismic, geodetic, thermal, archive and visual observations), and present the evidence and observations for each type of cyclicity, some of which are documented here for the first time. Wavelet time-series analysis is used to constrain cycle characteristics, where appropriate. We discuss the implications of these observations in understanding the eruptive mechanisms of the Soufrière Hills Volcano. Supplementary material: Details of all sub-daily cycles are listed in a supplementary table that is available at http://www.geolsoc.org.uk/SUP18700 .

Improved significance testing of wavelet power spectrum near data boundaries as applied to polar research

AbstractWhen one applies the wavelet transform to analyze ¯nite-length time series, discontinuities at the databoundaries will distort its wavelet power spectrum in some regions which are de¯ned as ...

Method of determination of heat, moisture, and momentum fluxes in the stratified surface layer

The method is proposed to determine the main fluxes characterizing the surface stratified layer of plants’ habitat using the Monin-Obukhov length scale. The gradient measurements of the profiles of wind flow speed, relative humidity, and air temperature are carried out. The experimental data are obtained using the mobile automated system. The wavelet analysis of time series is carried out. The nonlinear equation system is numerically solved to determine the heat, moisture, and momentum fluxes which can be used for the optimum control of the plant moisture supply in the agricultural field.

Wavelet application to the time series analysis of DORIS station coordinates

The topic developed in this article relates to the residual time series analysis of DORIS station coordinates using the wavelet transform. Several analysis techniques, already developed in other disciplines, were employed in the statistical study of the geodetic time series of stations. The wavelet transform allows one, on the one hand, to provide temporal and frequential parameter residual signals, and on the other hand, to determine and quantify systematic signals such as periodicity and tendency. Tendency is the change in short or long term signals; it is an average curve which represents the general pace of the signal evolution. On the other hand, periodicity is a process which is repeated, identical to itself, after a time interval called the period. In this context, the topic of this article consists, on the one hand, in determining the systematic signals by wavelet analysis of time series of DORIS station coordinates, and on the other hand, in applying the denoising signal to the wavelet packet, which makes it possible to obtain a well-filtered signal, smoother than the original signal. The DORIS data used in the treatment are a set of weekly residual time series from 1993 to 2004 from eight stations: DIOA, COLA, FAIB, KRAB, SAKA, SODB, THUB and SYPB. It is the ign03wd01 solution expressed in stcd format, which is derived by the IGN/JPL analysis center. Although these data are not very recent, the goal of this study is to detect the contribution of the wavelet analysis method on the DORIS data, compared to the other analysis methods already studied.

Application of a CCD camera to investigations of oscillations in a thermal plasma jet

The paper shows that image series taken by a high-speed CCD camera can be used for evaluations of spatial distributions of hydrodynamic fluctuations and their temporal evolution in a thermal plasma jet. The evaluation procedure was based on the fast Fourier transform and wavelet analysis of time series reflecting the evolution of the plasma jet optical radiation in each pixel of the camera record. The results demonstrate that the application of the CCD camera may bring new findings concerning the existence of various types of oscillations regarding both the locations of their maximal amplitudes and their temporal stability.

On the relationship between chromospheric oscillations of radio brightness at 1.76 cm with periods from minutes to hours and magnetic field changes

We present the results of Fourier and wavelet time series analysis for the high-cadence observations of an active region NOAA 8011, obtained with the Nobeyama Radioheliograph (NoRH) at the wavelength of 1.76 cm on 17.01.1997. Oscillations in brightness are found to be present with periods in the range from minutes to hours. The relationship between the active region oscillations in the microwave total intensity (I) and circular polarization (V) emission and changes of the magnetic field, deduced from the high-resolution magnetograms from MDI/SoHO, is investigated. We concentrate on the identification of different oscillation modes, the temporal behavior of the oscillations and the spatial distribution of different oscillating frequencies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The solar chromosphere as seen in high-resolution millimeter observations

We report on chromospheric oscillations studied with 15 sec cadence observations obtained at a wavelength of 3.5 mm with the Berkeley-Illinois-Maryland Array (BIMA). Dif- ferent solar structures, including active and quiet-Sun regions, are analyzed. We compare the high-resolution millimeter 2-D images with Ca II K line images from Big Bear Solar Observa- tory. Using Fourier and wavelet time series analysis techniques we find signatures of intensity oscillations with periods in the range of 2-7 minutes. We discuss the results in the context of the dynamical model of the solar atmosphere by Carlsson & Stein (1995, 1997).