tvf-EMD based time series analysis of 7Be sampled at the CTBTO-IMS network

Abstract A methodology of adaptive time series analysis based on Empirical Mode Decomposition (EMD) has been applied to investigate Be7 activity concentration variability, along with temperature. Analysed data were sampled daily at ground level by 28 different stations of the CTBTO-IMS network. The adopted methodology allows to characterise trend component, yearly cycles and outlier occurrence of Be7. Trend component is first estimated via simple EMD and removed. The recent time-varying filter EMD (tvf-EMD) technique is instead employed to extract local narrowband oscillatory modes from the detrended data. Denoising is carried out using a threshold on the Hurst exponent of extracted oscillatory modes (IMFs). It is found that the phase of the yearly cycles is shifted at high latitudes, possibly due to the Hadley cell dynamics. Furthermore, high values of Be7 yearly cycle are found for some stations in 2009–2010. Due to their location, this is possibly due to the El Nino event occurring that year. Though, further studies are needed in this regard.

[1]  H. Simmons,et al.  Near-Inertial Internal Gravity Waves in the Ocean. , 2016, Annual review of marine science.

[2]  N. Huang,et al.  The empirical mode decomposition and the Hilbert spectrum for nonlinear and non-stationary time series analysis , 1998, Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences.

[3]  Yi Liang,et al.  Wind Speed Forecasting Based on EMD and GRNN Optimized by FOA , 2017 .

[4]  N. Huang,et al.  A study of the characteristics of white noise using the empirical mode decomposition method , 2004, Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences.

[5]  Xenon and radon time series analysis: A new methodological approach for characterising the local scale effects at CTBT radionuclide network. , 2018, Applied radiation and isotopes : including data, instrumentation and methods for use in agriculture, industry and medicine.

[6]  A. Longo,et al.  Evaluation of 7Be and 133Xe atmospheric radioactivity time series measured at four CTBTO radionuclide stations. , 2018, Applied radiation and isotopes : including data, instrumentation and methods for use in agriculture, industry and medicine.

[7]  P. Spudich,et al.  Coherence of Mach Fronts During Heterogeneous Supershear Earthquake Rupture Propagation: Simulations and Comparison With Observations , 2010 .

[8]  C. Huh,et al.  Time series study of a 17-year record of (7)Be and (210)Pb fluxes in northern Taiwan using ensemble empirical mode decomposition. , 2015, Journal of environmental radioactivity.

[9]  Irene Fiori,et al.  Impact of infrasound atmospheric noise on gravity detectors used for astrophysical and geophysical applications , 2018, 1801.04564.

[10]  Min-Sung Koh,et al.  Speech enhancement of color noise using empirical mode decomposition , 2012, 2012 Conference Record of the Forty Sixth Asilomar Conference on Signals, Systems and Computers (ASILOMAR).

[11]  M. Manjula,et al.  Comparison of Empirical Mode Decomposition and Wavelet Based Classification of Power Quality Events , 2012 .

[12]  R. Blender,et al.  Observations and modelling of 1/ f -noise in weather and climate , 2011 .

[13]  Heng Li,et al.  A time varying filter approach for empirical mode decomposition , 2017, Signal Process..

[14]  Aydin Akan,et al.  Detrended fluctuation thresholding for empirical mode decomposition based denoising , 2014, Digit. Signal Process..

[15]  W. Plastino,et al.  Radioxenon Time Series and Meteorological Pattern Analysis for CTBT Event Categorisation , 2010 .

[16]  A. Longo,et al.  A new methodological approach for worldwide beryllium-7 time series analysis , 2018, Physica A: Statistical Mechanics and its Applications.

[17]  R. Akber,et al.  Describing the annual cyclic behaviour of 7Be concentrations in surface air in Oceania. , 2008, Journal of environmental radioactivity.

[18]  Philippe Lognonné,et al.  From Sumatra 2004 to Tohoku‐Oki 2011: The systematic GPS detection of the ionospheric signature induced by tsunamigenic earthquakes , 2013 .

[19]  R. Adhikari,et al.  Subtraction of Newtonian noise using optimized sensor arrays , 2012, 1207.0275.

[20]  Neethu Robinson,et al.  A Comprehensive Assessment of the Performance of Modern Algorithms for Enhancement of Digital Volume Pulse Signals , 2016 .

[21]  P. Saey,et al.  Hadley cell influence on (7)Be activity concentrations at Australian mainland IMS radionuclide particulate stations. , 2014, Journal of environmental radioactivity.

[22]  I. Daglis,et al.  ULF wave activity during the 2003 Halloween superstorm: multipoint observations from CHAMP, Cluster and Geotail missions , 2012 .

[23]  V. Miljković,et al.  Dynamics of beryllium-7 specific activity in relation to meteorological variables, tropopause height, teleconnection indices and sunspot number , 2017, 1807.00776.

[24]  W. Plastino,et al.  Uranium time series analysis: A new methodological approach for event screening categorisation. , 2018, Journal of environmental radioactivity.

[25]  Marek Czosnyka,et al.  Variability and Fractal Analysis of Middle Cerebral Artery Blood Flow Velocity and Arterial Blood Pressure in Subarachnoid Hemorrhage , 2008, Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism.

[26]  Gabriel Rilling,et al.  Empirical mode decomposition, fractional Gaussian noise and Hurst exponent estimation , 2005, Proceedings. (ICASSP '05). IEEE International Conference on Acoustics, Speech, and Signal Processing, 2005..

[27]  C. Wunsch.  The Past and Future Ocean Circulation from a Contemporary Perspective , 2013 .