For the transition range around ion scales, the turbulent energy is believed to further cascade and the kinetic physics begins (Alexandrova et al. 2013; Kiyani et al. 2015). Various forms of coherent structures (i.e., current sheet, vortex filaments) are usually found to reside near this range (i.e., between the end of the MHD range and proton scales in Lion et al. 2016; Perrone et al. 2016, 2017). Hence, in the following analysis we focus on fluctuations of similar scales, where the frequency ranges is chosen as [0.4, 3] Hz, and the timescale is [0.3, 3] s. It has been shown recently that, in case of a collisionless turbulent system as the solar wind, the intermittency, non-Gaussian fluctuations, and phase coherence of magnetic field components are interrelated (Perrone et al. 2017). We expect this relation to be present here and thus take similar procedures as in Perrone et al. (2017) to search for the intermittent events. The first step is to reconstruct the fluctuations using the bandpass filter based on wavelet transforms (Torrence & Compo 1998; He et al. 2012; Wang et al. 2014; Perrone et al. 2016). The magnetic field fluctuations are thus defined as
1





where i represent the magnetic field components, j represent the scale index, 





 is the constant scales step, 





 is the real part of the wavelet coefficient 





, Cδ = 0.776. 





 is the Morlet mother function and 





 at time t = 0 (Torrence & Compo 1998), 





 and 





 are taken to be 0.3 and 3 s, respectively. The second step is to determine the threshold energy as defined by 





, where 





 is the standard deviation of the Gaussian fit for each magnetic field fluctuation component. 





 are fitted to be 0.36, 0.32, and 0.49 nT, leading to a 





 ∼  4.3 nT2. From a statistical point of view, 99.7% of all the values in Gaussian distribution are within 





 from the mean. In other words, the events whose total energy 





 are larger than 





 could contribute to the non-Gaussian part of the distributions. Figure 1(e) presents the PDFs of the normalized magnetic field fluctuations 





 together with their Gaussian fits. The presence of clear non-Gaussian tails suggest the abundance of intermittent events during the whole interval. The last step is to locate these events. As seen in Figure 1(b), there are approximately 14 events (with at least 10 s in duration) with 





 larger than 5 nT2. We have picked one interval during 10:59:41.5–10:59:48.5 UT for further study. This event is characterized by large magnetic energy ∼150  nT2 and strong flow vorticity up to ∼1.4 /s as compared to the mean value of ∼0.4 /s. Furthermore, the local intermittency measure (LIM) exhibits an extension of temporal scale from several tens of seconds to sub-seconds, as seen in the LIMtotal of Figure 1(c). The LIM spectrogram, as a function of time and scales, is computed as the instantaneous energy of fluctuations normalized to its mean value over the studied time interval (Farge 1992):
2





where 





 is the total fluctuation energy. For the coherent structures (space or time localized energetic events), one of its intrinsic properties is the energy coupling over many scales (Farge 1992; Frisch 1995), which is usually manifested in the spanning of LIM at a wide range of spatial scales (or temporal scales if the Taylor frozen-in hypothesis is assumed; Lion et al. 2016; Perrone et al. 2017). While for the wave phenomenon, the energy distribution is typically focused around a certain frequency, i.e., Alfvén ion cyclotron (Alexandrova et al. 2004) or electron cyclotron waves (Lacombe et al. 2014). Therefore, the extension of LIM provides evidence of coupling from MHD to sub-ion scales and hence implies the presence of a coherent structure (Farge 1992; Frisch 1995; Lion et al. 2016; Perrone et al. 2017). Note that because 





, 





, and LIMtotal exhibit nearly the same features in this event, only LIMtotal is presented here.
Citation: Torrence & Compo 1998
Citation function: Uses
Citation: Torrence & Compo 1998
Citation function: Uses