Long-Term Datasets for the Understanding of Solar and Stellar Magnetic Cycles Proceedings IAU Symposium No. 340, 2018 D. Banerjee, J. Jiang, K. Kusano & S. Solanki, eds. c  International Astronomical Union 2018 doi:10.1017/S1743921318001266 Phase analysis of solar activity indices using wavelet techniques C. S. Seema and P. R. Prince Department of Physics, University College, Thiruvananthapuram-695 034, Kerala, India email: seemaniran@gmail.com, princerprasad@gmail.com Abstract. A precise knowledge of solar extreme ultraviolet (EUV) irradiance is of great im- portance for better understanding of Earth ′ s ionosphere and thermosphere. The search for an ideal solar EUV proxy is vital since the ionospheric and thermospheric models are based on the solar proxies of EUV radiation. In this study, the phase asynchrony analysis of solar EUV data with other solar activity indices during solar cycle 23 is done. The cross-wavelet transform (XWT) technique is used to reveal the phase difference between the two time series of solar indices. Analysis reveals that the phase relationship between the indices is both time and fre- quency dependent. The solar indices F10.7 and Mg II core-to-wing index are found to be more synchronous with solar EUV data for low frequency components. Keywords. Solar Index, cross-wavelet, solar cycle 23, etc. 1. Introduction Ionospheric parameters are strongly controlled by solar activity, especially solar EUV flux since the production of ions in the F2 layer is mainly controlled by the Solar Extreme Ultraviolet (EUV) and X-ray radiations. All ionospheric models are based on solar EUV index-ionospheric relations. For improving the predictability of ionospheric models, the study of this relationship contributes much. Solar EUV data, Solar 10.7 cm radio noise (F10.7), Coronal Index, Mg II core-to-wing index and Sunspot number (R Z ) are some of the commonly used proxies for studying solar EUV activity(Kane 2002). F10.7 can be considered as a proxy of the Suns corona while the Mg II core-to-wing ratio measures solar chromospheric variability. Coronal index alarms physical processes taking place inside the Sun which are focused on solar magnetic fields whereas the Sunspot number concerns about the photosphere. As the solar EUV data is available since 1996 only, researchers are in search of a solar EUV proxy for long term analysis. 2. Data and Analysis This study reveals the phase relationship of solar EUV index with other solar indices such as sunspot number (R Z ), 10.7 cm solar radio flux (F10.7), Mg II core-to-wing in- dex and Green coronal index over 23rd solar cycle using cross wavelet techniques. The continuous wavelet does the convolution of time series x n with the scaled and trans- lated version of a normalized mother wavelet (Torrence & Compo 1998). A high wavelet power indicates the presence of significant time patterns (periodicities) at a particular time period. The common frequency features or phase difference of the two time series highlighting the temporal variations of their correlation is portrayed by Cross-wavelet power spectrum (Jevrejeva 2003). 165 at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921318001266 Downloaded from https://www.cambridge.org/core. IP address: 117.221.184.239, on 07 Dec 2018 at 16:00:58, subject to the Cambridge Core terms of use, available