Morlet Wavelet Analysis Research Articles

Analysis of Agile Canine Gait Characteristics Using Accelerometry.

The high rate of severe injuries associated with racing greyhounds poses a significant problem for both animal welfare and the racing industry. Using accelerometry to develop a better understanding of the complex gait of these agile canines may help to eliminate injury contributing factors. This study used a single Inertial Measurement Unit (IMU) equipped with a tri-axial accelerometer to characterise the galloping of thirty-one greyhounds on five different race tracks. The dorsal-ventral and anterior-posterior accelerations were analysed in both the time and frequency domains. The fast Fourier transform (FFT) and Morlet wavelet transform were applied to signals. The time-domain signals were synced with the corresponding high frame rate videos of the race. It was observed that the acceleration peaks in the dorsal-ventral accelerations correspond to the hind-leg strikes which were noted to be fifteen times the greyhound’s weight. The FFT analysis showed that the stride frequencies in all tracks were around 3.5 Hz. The Morlet wavelet analysis also showed a reduction in both the frequency and magnitude of signals, which suggests a speed reduction throughout the race. Also, by detecting abrupt changes along the track, the wavelet analysis highlighted potentially hazardous locations on the track. In conclusion, the methods applied in this research contribute to animal safety and welfare by eliminating the factors leading to injuries through optimising the track design and surface type.

Analysis of the Hemispheric Sunspot Number Time Series for the Solar Cycles 18 to 24

In this article, we investigate temporal and periodic variations of the hemispheric sunspot number using sunspot data from Kanzelhohe Solar Observatory (KSO) for the time period of 1944 – 2017, which covers Solar Cycles 18 to 23 and almost the entire Solar Cycle 24 (2009 – 2017). The KSO data set was verified against the International Sunspot Number (ISSN) data. Temporal and periodic variations in the KSO data were analyzed using cross-correlation analysis, Morlet wavelet and multitaper (MTM) period analysis methods. We find that: i) sunspot numbers, as derived from both KSO and ISSN time series, are highly correlated with one another; ii) the temporal evolution of the sunspot number differs from one hemisphere to another with the solar cycle peaking at different times in each hemisphere; iii) the northern hemisphere showed two- and seven-month lead in Solar Cycles 18 and 19, respectively, while the southern hemisphere was leading in the rest of the cycles with the varying lead time ranging from 2 to 14 months; iv) apart from the fundamental mode of ≈ 11 years, Solar Cycle, the KSO data also show several midterm variations in the opposite hemispheres, specifically, Rieger-type and quasi-biennial periodicities – the detected midterm periodicities also differ in the northern and southern hemispheres; v) our results confirm the Waldmeier effect, which correlates the rise time with the cycle amplitude using the new sunspot data set from KSO.

Rolling element bearing fault detection based on the complex Morlet wavelet transform and performance evaluation using artificial neural network and support vector machine

Condition monitoring and fault diagnosis of rolling element bearings are very important to ensure proper working of different types of machinery. Condition monitoring of rotating machines is mainly based on the analysis of machine vibration. The vibration signals from the mechanical fault generally comprise periodic impulses with specified characteristic frequency corresponds to a particular defect. But due to heavy noise in the industry, the vibration signals have a very low signal-to-noise ratio. Hence, it requires an appropriate technique to extract the impulses from the noisy signal. This article emphasized on the fault diagnosis of rolling element bearings having some specific size of defects on various bearing elements using the complex Morlet wavelet analysis. The phase and amplitude map of the complex Morlet wavelet are utilized for identification and diagnosis of the fault in the rolling element bearing. The amplitude and phase map corresponding to the complex Morlet wavelet are found to show unique informative signatures in the presence of bearing faults. The classification technique based on artificial neural network and support vector machine for rolling element bearing fault detection is presented in this article. The classification results of bearing faults clearly indicate that support vector machine has a more precise bearing fault classification ability than artificial neural network.

Reconstruction of sunspot activity, cold and warm events, and drought and flood events in the central plain of China during the northern Song Dynasty using historical documents

The Northern Song Dynasty was an important and prosperous dynasty in the history of China, and it existed during a period of climate abnormality. Climate change research for the Northern Song Dynasty era has significance for understanding the interaction between agricultural civilizations in the central plains and nomadic populations in northern China, transfer of the economic and cultural centers of China, and the vicissitudes of the Northern Song Dynasty. There is currently considerable disagreement regarding climate change in the Central Plain during the Northern Song Dynasty era. Many precious and valuable historical documents and records about the Northern Song Dynasty have been collected, and abundant records of sunspot activity, cold and warm weather, drought and flood events have been compiled. Using the Mann-Kendall test, wavelet analysis, R/S analysis, and frequency analysis etc. mathematical statistics methods, sunspot activity, cold and warm events, and drought and flood events were quantitatively reconstructed. There are 15 sunspot maximum years and 16 sunspot minimum years, the cycle length of sunspot activity is 8–14 years, and the average cycle length is 11 years. Hot years account for 11.3% of the total years; warm years account for 12.7%; cold years account for 20.7%; and freezing cold years account for 3.3%. Mann-Kendall test results show that cold and warm variations are natural fluctuations, and there is no indication of abrupt climate change during the Northern Song Dynasty. Morlet wavelet analysis indicates that there are weak high-frequency oscillations and short oscillation periods with three years before 1052 AD, and there are oscillation periods of six years and clear alternations between warmth and cold during 1060-1120 AD. R/S analysis indicates that the Hurst index (H) of cold and warm index series is 0.6155, and the fractal dimension (D) is 1.3845. Since 0.5 < H < 1 and 1 < D < 1.5, fractal structures are evident in the time series of cold and warm indexes, past increments are positively correlated with future increments, and the average cycle length in the time series for cold and warm indexes is 6 years. Temperatures first decreased rapidly followed by a slow increase with long-term fluctuations, and the mean temperature during the Northern Song Dynasty era is 0.4 °C higher than that in the period 1880–1979 AD. Severe drought, moderate drought, moderate flood, severe flood and normal years account for 15.3%, 25.3%, 11.3%, 6.7%, 41.4% of all years, respectively. Frequency analysis indicates that cooling, warming, drought and flood events show a close relationship to sunspot activity.

Determination of GLE of Solar Energetic Particles by Means of Spectral Analysis

Abstract Using three nonstationary solar series, the solar flare index (FS), the sunspots index (SS), and the solar flux (F10.7) index, we apply the Morlet wavelet analysis to determine the most dominant harmonics of solar activity, 1.73, 3.27, 4.9, 10.4, and 11 yr. The periodicities obtained are processed by the fuzzy logic method, which allows us to reproduce the occurrence dates of ground level enhancements (GLE), since 1942–2006, which we use as a training baseline of these spectral techniques to determine the occurrence of solar particle enhancements in solar cycles. Then, the result of fuzzy logic is extended to periods later than the training period so as to cover the end of cycle 24 and the beginning of cycle 25. In addition to the forecastable aspect of this work, the obtained results are of high interest in view of the recent controversy that has arisen in relation to the occurrence of small GLE (namely sub-GLE), during cycle 24.

Characteristics of climate change in Changbai Mountain ecological functional area, Northeast China.

We integrated the meteorological records from 36 national weather stations and CN05.1 gridded daily observation dataset to analyze the climate change characteristics of Changbai Mountain eco-functional area. Linear tendency estimation, Mann-Kendall mutation test, cumulative anomaly method and Morlet wavelet analysis were used to investigate the temporal and spatial variation of temperature (annual temperature, seasonal temperature, extreme temperature), moisture (annual precipitation, seasonal precipitation, relative humidity), radiation (sunshine duration, sunshine percentage) and wind speed from 1961 to 2016. The results showed that, during 1961-2016, the temperature of this area increased, the radiation and wind speed decreased, and the precipitation varied periodically. Specifically, winter temperature [0.45 ℃·(10 a)-1] and the lowest temperature [0.74 ℃·(10 a)-1] significantly increased. The mean annual wind speed significantly decreased [-0.21 m·s-1·(10 a)-1]. No abrupt climate change was observed. The annual precipitation days decreased considerably [-7.01 d·(10 a)-1], which was different from the climate change pattern of Northeast China. The annual precipitation trend coefficient of this area was 16.06 mm·(10 a)-1 , which could not be simply depicted by increase or decrease in trend. The precipitation change in this area was dominated by periodically patterns, and the period was 26 years and 3 years. Our results would be instructive to the regional ecological assessment, and the research on ecosystem responses to climate change and phenological changes.

High frequency spectral features of galactic cosmic rays at different rigidities during the ascending and maximum phases of the solar cycle 24

Galactic cosmic rays (GCR) intensity during the current solar cycle (SC) 24 exhibit unusual modulation characteristics. In this study, the temporal evolution of the daily GCRs recorded over a wide range of particle rigidities by seven neutron monitor stations located at Thule, Nain, Sanae, Newark, Alma-Ata, Mexico and Athens is investigated. The datasets span the time interval from Jan 2009 to Dec 2015 which cover the ascending and the maximum phases of the present SC 24. The Morlet wavelet analysis is employed to examine the periodicities in the range 8–512 day. At high frequency range, the prominent period of band 20–40 day related to the synodic rotation of the Sun along with its harmonics in the band 8–16 day were detected. In the mid-term range, the well-known ‘Rieger-type periodicity’ of 120–170 day was identified specially during the maximum epoch, i.e. 2012. Another period in the range 250–460 day is significantly appears during nearly the entire epoch, and at almost all stations. It may be considered as annual and near-annual period where it is supposed to be related—during these phases—to the solar magnetic field characteristics, and not to the earth’s heliolatitude variations. Possible explanation of the observed periods are discussed in the light of existing models and earlier findings.

Magneto-Rossby Waves in the Solar Tachocline and the Annual Variations in Solar Activity

Abstract Annual oscillations have been detected in many indices of solar activity during many cycles. Recent multi-spacecraft observations of coronal bright points revealed slow retrograde toroidal phase drift (with the speed of ∼3 m s−1) of 1 yr oscillations, which naturally suggested their connection with Rossby-type waves in the interior. We have studied, from a theoretical point of view, the dynamics of global magneto-Kelvin and magneto-Rossby waves in the solar tachocline with toroidal magnetic field. Using spherical coordinates, the dispersion relations of the waves and latitudinal structure of solutions were obtained analytically. We have also obtained the spectrum of unstable magneto-Rossby wave harmonics in the presence of the latitudinal differential rotation. Estimated periods and phase speeds show that the magneto-Rossby waves rather than the Kelvin waves match with the observations of 1 yr oscillations. On the other hand, Morlet wavelet analysis of Greenwich Royal Observatory sunspot areas for the solar cycle 23 has revealed multiple periodicities with periods of 450–460, 370–380, 310–320, 240–270, and 150–175 days in hemispheric and full disk data. Comparison of theoretical results with the observations allow us to conclude that the global magneto-Kelvin waves in the upper overshoot tachocline may be responsible for the periodicity of 450–460 days (∼1.3 yr), while the remaining periods can be connected with different harmonics of global fast magneto-Rossby waves.

Potential impacts of Arctic warming on Northern Hemisphere mid-latitude aerosol optical depth

The weather and climate conditions can provide favorable or unfavorable atmospheric background for the maintenance and development of haze events. This study investigates the potential impacts of Arctic warming on the variation of Northern Hemisphere mid-latitude aerosol optical depth (AOD) in winter when haze often occurs. We first analyze the spatio-temporal variability of wintertime AOD in mid-latitudes of Northern Hemisphere from NASA MERRA-2 for the period of 1980–2016 using the empirical orthogonal function analysis and morlet wavelet analysis. It showes increasing trend for AOD in East China and North India and decreasing trend for AOD in Europe and North America during last 37 years while inter-decadal fluctuations exist. In addition to the temporal trends of AOD, two long-term periodic variations with periods of about 7 and 11 years exist, which implies the potential impacts from natural variabilities. Further analysis shows high correlations between the mid-latitude winter AOD (WA) and Arctic summer (May and June) surface temperature (T56). Moreover, the Arctic summer surface temperature demonstrates similar periodic variations with periods of about 7–9 and 11–13 years. Both of these indicate the potential impacts of Arctic summer warming on mid-latitude winter pollution. We then analyze the temporal correlations between Arctic summer temperature and mid-latitude winter AOD in different regions. Arctic T56 correlates negatively with WA in Europe and North America, and positively with that in East Asia, North India and Middle East. Particularly, T56 in western sea of Novaya Zemlya has the most prominent correlation with the WA in mid-latitudes of East Asia, especially in East China. This implies that Arctic T56 in the Arctic circle of Europe could be used for rough estimates of winter AOD in East Asia.

Characteristics of Temperature and Precipitation Changes in Wumeng Mountain Natural Reserve in 57 Years

Wumeng Mountain Nature Reserve is a typical region with important characteristics such as national nature reserve, old revolutionary area and the important combination of natural geographical area, and it is a vulnerable and special area under the background of global warming. Based on the annual and monthly mean temperature and precipitation data of two meteorological stations in the protected area from 1959 to 2015. using linear tendency estimation, Mann-Kendall mutation test and Morlet wavelet analysis, the characteristics of temperature and precipitation change in Wumeng Mountain Nature Reserve were studied. The results show that since 1959, the temperature in Wumeng Mountain Nature Reserve has been decreasing, while the precipitation responsibility has been increasing, with the rates of -0.124 C/10a and 15.02mm/10a, respectively. The temperature and precipitation in the nature reserve have changed abruptly, and the temperature change is more obvious than precipitation. The periodicity of the temperature and precipitation change in the nature reserve is the most significant in the medium-long time scale and the inter annual change cycle, both 14a. The possible impact of temperature and precipitation changes on the nature reserve is briefly described, which provides a reference for rational planning and construction of the nature reserve, agricultural production and soil and water conservation in the area.

基于标准化降水蒸散指数的呼伦贝尔草原干旱变化特征及趋势分析

PDF HTML阅读 XML下载 导出引用 引用提醒 基于标准化降水蒸散指数的呼伦贝尔草原干旱变化特征及趋势分析 DOI: 10.5846/stxb201807061481 作者: 作者单位: 北京师范大学地理科学学部,北京师范大学,北京师范大学地理科学学部,北京师范大学地理科学学部 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划（2016YFC0500608-3） SPEI-based analysis of drought characteristics and trends in Hulun Buir grassland Author: Affiliation: Faculty of Geographical Science,Beijing Normal University,Beijing Normal University,Faculty of Geographical Science,Beijing Normal University,Faculty of Geographical Science,Beijing Normal University Fund Project: National Key R&D Program of China 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:呼伦贝尔草原是我国北方地区重要的防风固沙和水源涵养生态功能区，在气候变化的背景下，该区的草原畜牧业和旱作农业深受干旱的影响。研究该区干旱发生的特征及趋势，对当地采取适应气候变化对策具有重要意义。基于1960-2017年呼伦贝尔草原4个气象站逐月降水和气温资料，计算标准化降水蒸散指数（SPEI），并采用Mann-Kendall突变检验、Morlet小波分析和R/S分析法分析了近58年呼伦贝尔草原年、季尺度的气候变化及干旱特征与趋势，并结合该区实际发生的灾害事件对SPEI指数进行了验证。结果表明：1）近58年来呼伦贝尔草原在气温显著上升，降水量减少的背景下干旱化趋势显著。2）该区域年尺度和季节尺度下干旱化特征具有差异性，其中，年尺度下，该区域SPEI指数以-0.218×10 a-1倾向率呈显著下降趋势，1998年是干旱加剧的突变年，未来在11年尺度上有持续偏旱的趋势；季节尺度下，冬季SPEI指数显著增加，且未来在17年尺度上有持续偏湿的趋势，春、夏和秋季的SPEI指数均呈下降趋势，并分别在22年、9年和15年尺度上有持续偏旱的趋势。3）2000年以来，干旱发生的总频率尤其重旱和极旱的发生频率均显著高于其他年代；4）夏季和秋季分别是发生重旱和极旱次数最多的季节。5） SPEI指数在呼伦贝尔草原区的干旱监测与分析中具有较好的适用性。 Abstract:With increases in global warming intensity, the frequency and duration of droughts are showing a clear upward trend, and the global terrestrial extreme drought area is expanding, particularly on the Eurasian and African continents. Hulun Buir grassland is an important wind-fixing and water-reserving ecological functioning area in northern China. However, due to the superimposition of climate change effects, such as the frequency of drought, and human activities, the grasslands have gradually degraded to a simpler community structure with reduced species diversity, intensified desertification, and increased pests and diseases. Based on monthly precipitation and temperature data from four meteorological stations in the Hulun Buir grassland from 1960 to 2017, the standardized precipitation evapotranspiration index (SPEI) was calculated. The Mann-Kendall mutation test, Morlet wavelet analysis, and R/S analysis were used to analyze the drought change characteristics and trends on both annual and seasonal scales in the Hulun Buir grassland over the past 58 years, and the SPEI index was verified by the actual disaster events in the area. The results show that:1) between 1960 and 2017, the temperature of the Hulun Buir grassland increased gradually at a significance level of 0.05, while precipitation showed a slight decrease. In addition, the seasonal variations in temperature and precipitation are different. Among them, summer precipitation is gradually decreasing, while the other seasons are increasing at different rates. In addition to winter temperatures, the interannual temperature changes in other seasons showed an upward trend at a significance level of 0.05. Among them, the spring temperature rose at the fastest rate, reaching 0.46℃×10 a-1, followed by summer (0.39℃×10 a-1). 2) On the annual scale, the SPEI index of this region showed a downward trend with a tendency of -0.218×10a-1 (P < 0.01). 1998 is the year of drought intensified in the region, and there is a trend of persistent drought on the 11 a scale for the future; On the seasonal scale, the winter SPEI index increased significantly, and there is a trend of continuous wetness on the 17 a scale for the future. However, the SPEI index in spring, summer, and autumn showed a downward trend, and there was a trend of persistent drought on the 22 a, 9 a and 15 a scales, respectively; 3) The frequency of moderate drought occurrences is the highest among different years and seasons, and that of extreme drought is the lowest. At the beginning of the 21st century, the frequency of drought, especially severe drought and extreme drought, was significantly higher than for the past four decades. 4) Summer and autumn were the seasons with the most frequent occurrences of severe and extreme droughts, respectively. 5) The SPEI index can well characterize the drought characteristics of the Hulun Buir grassland. 参考文献 相似文献 引证文献

Detecting the Onset of Strain Localization Using Two‐Dimensional Wavelet Analysis on Sandstone Deformed at Different Effective Pressures

AbstractLaboratory brittle deformation experiments have shown that a rapid transition exists in the behavior of porous materials under stress: At a certain point, early formed and spatially distributed tensile cracks interact and coalesce forming a shear plane. In this work, we present and apply a novel image processing tool that is able to quantify this transition between distributed (“stable”) damage accumulation and localized (“unstable”) deformation, in terms of the size, density, and orientation of cracks at the point of strain localization. Our technique, based on a two‐dimensional Morlet wavelet analysis, can recognize, extract, and visually separate the multiscale changes occurring in the crack network during the deformation process. We first performed a series of triaxial experiments (σ1&gt;σ2=σ3) on core plugs of Hopeman Sandstone (Scotland, UK) at different effective pressures (from 5 to 30 MPa). We then processed high‐resolution backscattered electron microscope images of thin sections of these core plugs and found differences in the strain localization process as effective pressure was increased. The critical length of tensile cracks required before the onset of strain localization was reduced from 0.24 to 0.15 mm as the effective pressure was increased to 30 MPa, resulting in a narrow fracture zone. Critically, by comparing patterns of fractures in these deformed sandstone samples, we can quantitatively explore the relationship between the observed geometry of the cracks and the inferred mechanical processes. This will eventually help us to better understand the physics underlying the initiation of catastrophic events, such as earthquakes, landslides, and volcanic eruptions.

Characteristics of Annual and Seasonal Precipitation Variation in the Upstream of Minjiang River, Southwestern China

Characteristics of annual and seasonal precipitation variation are explored in the upstream of Minjiang River (UMR), Southwestern China, spanning from 1960 to 2015. The moment of method (MOM), linear regression method, Mann–Kendall test, sequential cluster analysis, and Morlet wavelet analysis were utilized. The results clearly show the following: (1) Distribution of precipitation is uneven in space, with more in the south and less in the southeast. Decade average of annual precipitation reached the lowest in the 2000s and increased during 2010–2015 at all gauging stations and UMR. (2) Areal annual precipitation exhibited an insignificant decreasing trend with a rate of 4.47 mm/10a, which was mainly attributable to decreased summer precipitation. Spring precipitation exhibited an insignificant increasing trend and winter precipitation remained unchanged. (3) The change points mainly appeared in the 1980s and 1990s. And the almost periods of study area were generally 2–5 years, 7–11 years, and 15–20 years. (4) The increasing trend of annual precipitation is relatively obvious at higher altitudes, while the decreasing trend is more significant at low altitude stations.

A first arrival detection method for low SNR microseismic signal

Most of the microseismic signals have low signal-to-noise ratio (SNR) due to the strong background noise, which makes it difficult to locate the first arrival time. Both accuracy and stability of conventional methods are poor in this situation. To overcome this problem, here we proposed a new method based on the adaptive Morlet wavelet and principal component analysis process in wavelet coefficients matrix. The three components of microseismic signal make it possible to extract the features in wavelet coefficients domain. Then the reconstructed signal from weighted features presents an obvious first arrival. Tests on synthetic signals and real data provide a solid evidence for its feasibility in low SNR microseismic signal.

Effects of St. Patrick's Day Geomagnetic Storm of March 2015 and of June 2015 on Low‐Equatorial D Region Ionosphere

AbstractD region effects of the 17–19 March 2015, a St Patrick's Day super geomagnetic storm (Dst = −223 nT), using a navigational transmitter very low frequency (VLF) signal (NWC, 19.8 kHz) recorded at a low‐latitude Indian station, Allahabad (geomag. lat., 16.45°N), have been analyzed and compared with similar strength of the 22–25 June 2015 storm (Dst = −204 nT). During the March storm, NWC signal amplitude decreased on 17 March (main phase of the storm) and recovered on 27 March, which is 1 day after the recovery of the storm, whereas for the June storm, VLF amplitude decreased for 2 days only during its recovery phase. The decrease in the amplitude was pronounced during evening terminator for both the storms. The modeling of VLF signal anomaly on 17 March and on 25 June using Long‐Wave Propagation Capability code shows an increase in the D region reference height (h′) by ~2.6 km and ~2.5 km, for March and June storms, respectively. The D region electron density (Ne) determined using storm time h′ and sharpness factor β shows a decrease in the Ne during the main phase followed by a slow recovery during the recovery phase of the March storm, whereas June 2015 storm showed a decrease in the Ne only on 25 and 26 June. Morlet Wavelet analysis of the amplitude for both the storms shows a presence of strong wave‐like signatures, suggesting propagation of atmospheric gravity waves/traveling ionosphere disturbances to the low latitude D region due to the Joule heating at high latitudes.

A review of Morlet wavelet analysis of radial profiles of Saturn's rings.

Spiral waves propagating in Saturn's rings have wavelengths that vary with radial position within the disc. The best-quality observations of these waves have the form of radial profiles centred on a particular azimuth. In that context, the wavelength of a given spiral wave is seen to change substantially with position along the one-dimensional profile. In this paper, we review the use of Morlet wavelet analysis to understand these waves. When signal to noise is high and the cause of the wave is well understood, wavelet analysis has been used to solve for wave parameters that are diagnostic of local disc properties. Waves that are not readily perceptible in the spatial domain signal can be clearly identified. Furthermore, filtering in wavelet space, followed by the reverse wavelet transform, has been used to isolate the part of the signal that is of interest. When the cause of the wave is not known, comparing the phases of the complex-valued wavelet transforms from many profiles has been used to determine wave parameters that cannot be determined from any single profile. When signal to noise is low, co-adding wavelet transforms while manipulating the phase has been used to boost a wave's signal above detection limits.This article is part of the theme issue 'Redundancy rules: the continuous wavelet transform comes of age'.

Spatial and temporal stability of temperature in the first-level basins of China during 1951–2013

In recent years, global warming has attracted great attention around the world. Temperature change is not only involved in global climate change but also closely linked to economic development, the ecological environment, and agricultural production. In this study, based on temperature data recorded by 756 meteorological stations in China during 1951–2013, the spatial and temporal stability characteristics of annual temperature in China and its first-level basins were investigated using the rank correlation coefficient method, the relative difference method, rescaled range (R/S) analysis, and wavelet transforms. The results showed that during 1951–2013, the spatial variation of annual temperature belonged to moderate variability in the national level. Among the first-level basins, the largest variation coefficient was 114% in the Songhuajiang basin and the smallest variation coefficient was 10% in the Huaihe basin. During 1951–2013, the spatial distribution pattern of annual temperature presented extremely strong spatial and temporal stability characteristics in the national level. The variation range of Spearman’s rank correlation coefficient was 0.97–0.99, and the spatial distribution pattern of annual temperature showed an increasing trend. In the national level, the Liaohe basin, the rivers in the southwestern region, the Haihe basin, the Yellow River basin, the Yangtze River basin, the Huaihe basin, the rivers in the southeastern region, and the Pearl River basin all had representative meteorological stations for annual temperature. In the Songhuajiang basin and the rivers in the northwestern region, there was no representative meteorological station. R/S analysis, the Mann-Kendall test, and the Morlet wavelet analysis of annual temperature showed that the best representative meteorological station could reflect the variation trend and the main periodic changes of annual temperature in the region. Therefore, strong temporal stability characteristics exist for annual temperature in China and its first-level basins. It was therefore feasible to estimate the annual average temperature by the annual temperature recorded by the representative meteorological station in the region. Moreover, it was of great significance to assess average temperature changes quickly and forecast future change tendencies in the region.

Spatiotemporal characteristics of droughts and floods in northeastern China and their impacts on agriculture

Heilongjiang Province is a major grain production base in China, and its agricultural development plays an important role in China’s social economy. Drought and flood events are the primary disasters in Heilongjiang Province and have considerable impacts on agriculture. In this study, relatively complete monthly precipitation data from 26 meteorological stations in Heilongjiang Province during the period of 1958–2013 were analyzed using the standardized precipitation index (SPI) combined with principal component analysis, Mann–Kendall trend analysis and Morlet wavelet analysis to determine the spatial and temporal distributions of drought and flood events in this province. The results were as follows: (1) the whole of Heilongjiang exhibited an aridity trend. In northern Heilongjiang, spring and summer experienced a wetting trend, and autumn and winter experienced an aridity trend. (2) The SPI3 exhibited 8- and 16-year periodic variation characteristics in spring, 10- and 22-year periodic variation characteristics in summer, and 10- and 32-year periodic variation characteristics in autumn. In addition to the 10-year periodic variation characteristics in winter, other periodic variation characteristics were observed. (3) The increasing trend in the percentage of stations affected by flood was more obvious than that affected by drought. Therefore, Heilongjiang Province is more vulnerable to flooding. (4) The influence of drought and flood disasters in Heilongjiang Province showed a growth trend, but the flood effect was more remarkable. (5) The agricultural area affected by drought and flood disasters in Heilongjiang Province showed an increasing trend. Although there was a greater increase in flood disaster area, the main types of disasters were drought-dominated.

The Turbulence Magnetic Helicity Signature in the Interplanetary Medium: A Blackman–Tukey and Morlet Wavelet Analysis

Abstract Interplanetary turbulence shows a spectral magnetic helicity signature whose properties could depend on the nature and dissipation of proton-scale fluctuations. A database of Wind spacecraft intervals of turbulence and helicity signatures is evaluated. Spectra are computed by both the Blackman–Tukey method and the Morlet wavelet method. A global mean magnetic field is used in each case, and the wavelet spectrum is averaged over time to facilitate comparison with the Blackman–Tukey spectrum. The maximum magnitude of the signature normalized by the trace of the magnetic spectral power has a frequency that correlates well between the two methods. The sign of the signature is also the same with both approaches, but the magnitudes differ. Statistically, the mean magnitudes of each method do agree, and the difference of individual magnitudes is assigned to uncertainties within each method. The Morlet wavelet method obtains fewer noisy signatures with a tighter overall correlation between magnetic helicity and cross-helicity; however, no trend is confirmed between helicity and the ratio of plasma to magnetic pressure. Subdivision of the analyzed intervals establishes that the helicity signature is persistent but variable. A portion of the variability comes from cross-helicity and possibly from the cascade rate. The observed magnetic helicity is compared to model and simulation results. Two-dimensional hybrid simulations yield results for the magnetic helicity magnitude that are larger than the mean values observed under similar conditions.

Cluster analysis of drought variation and its mutation characteristics in Xinjiang province, during 1961–2015

Abstract The Xinjiang province of China is vulnerable to drought, but the occurrence of drought varies substantially among different sub-areas. This study investigated drought characteristics in Xinjiang province and its sub-area using the Mann–Kendall trend test, cluster analysis and Morlet wavelet analysis. The results show that drought in Xinjiang is generally becoming less severe, and there is a non-uniform spatial variation of drought, which is especially pronounced for stations in northern Xinjiang. There is a unique spatiotemporal distribution trend of drought in Xinjiang, and the inter-decadal variation of drought shows a gradual shift from the east to the west and then back to the east again over the past 55 years. Northern Xinjiang is becoming wetter at a faster rate compared with that of southern Xinjiang, and it also has a higher occurrence of change point sites (70%). The historical drought situation in Xinjiang is better characterized by three clusters. Cluster 1 is the driest, cluster 2 has a clear alleviating tendency of drought, while cluster 3 shows late occurrence of change point. A broader view of the accumulated variation of drought is formulated in this study, which may help to identify potential droughts to support drought disaster management and mitigation.