Doppler Oscillations in the Solar Spicules based on IRIS data

In this research, we study the oscillating properties of the solar spicules in the line of sight with spectral measurements recorded by Interface Region Imaging Spectrograph (IRIS) on August 17, 2014. The primary purpose of IRIS is the observation of the movement of materials, fluctuations, and energy absorption and heat production in the lesser- known region of the solar atmosphere which affect the behavior of the Earth's atmosphere, the performance of satellites, power transmission networks and radio communications. The transmission of energy through waves and oscillations can play an important role in understanding of the solar dynamics, and responding to the problems about the sudden rise of the solar atmosphere temperature to several million Kelvin from the transition layer to the solar corona. The source of energy required to heat the solar corona plasma to a temperature of one million Kelvin in the Sun's dynamic photosphere is a matter of debate in solar physics. One of the mechanisms of energy transfer is the propagation of magneto-hydrodynamic waves. These waves in photospheric magnetic tubes can be generated by granular shock motions and then propagate along the chromospheric magnetic field and penetrate the corona to transfer energy in the form of heat. Therefore, observations of oscillating motions in the chromosphere are a crucial test for the theory of corona heating. Quasi-periodic fluctuations in spicules appear mainly as displacement of these structures in image observations or periodic shifts in spectral lines. We use Interface Region Imaging Spectrograph (IRIS) to measure the spectrum around a narrow slit. By fitting a Gaussian profile of the Si IV profiles, we can calculate Doppler velocity shifts up to an altitude of 4200 km along the spicules. The Doppler velocity range from the edge of the sun to an altitude of 4200 km was obtained from 12 to 15 kms-1 (blue- shift), and from10 to 15 kms-1 (red- shift). For determining the dominant periods of Doppler shift oscillations, it is needed that the maximum intensity positions of 150 spectral profiles are collected, and a set of temporal signals is generated as a temporal signal. Any physical quantity that changes according to an independent parameter or variable is called a signal. If the parameter is a time variable, it is called a temporal signal, and if it is a position, the signal is called a spatial signal. These signals contain information about their sources, for example, period. So by processing signals, the behavior of resources can be studied and predicted. After processing temporal signals, we apply the wavelet analysis. Wavelet analysis is a useful method for simultaneous diagnosis of the power in time and frequency domains for temporal signals. The results of wavelet analysis revealed Doppler shift fluctuations with dominant periods of 3, 5 and 8 minutes. According to the results of this study, it is suggested that the main contribution of Doppler shift fluctuations in the solar spicules, observed transversely perpendicular to the axis of the solar spicules, is due to kink and alfven waves. These waves can play an essential role in heating the solar corona to millions of Kelvin.