tokens: and E05, PSP arrived at the perihelion of 27.8 R ⊙ (~0.13 AU) on January 29, 2020 and June 7, 2020, respectively. In Sect. 3.1 , we give an overview of the PSP measurements of solar wind density, speed, and energy flux for all available encounters including E01, E02, E04, and E05. We note that E03 observationsare not considered due to the lack of SPC observations near the perihelion. For each encounter, 12-day observations around the perihelion were used for calculations. The heliocentric distance for both E01 and E02 ranges from 35.66 to about 55 R ⊙ , and it ranges from 27.8 to about 57 R ⊙ for both E04 and E05. In Sect. 3.2 , we combine the observations from E01, E02, E04, and E05 to show the histogram distributions and the evolution of the energy flux as a function of heliocentric distance. 3.1 Overview of E01, E02, E04, and E05 Figure 1 shows an overview of the PSP measurements of solar wind density, speed, and energy flux during E01 (from October 31, 2018 00:00:00 to November 12, 2018 00:00:00 UTC). The top panel presents the electron number density ( n e ) obtained by the QTN method. In the second panel, the proton bulk speed is shown. The third and fourth panels present the solar wind energy flux ( W , from Eq. ( 2 )) and its value scaled to one solar radius (, from Eq. ( 6 )), respectively. In Fig. 1 , n α and n p were computed from n e based on n α ∕ n e = 2.5% for calculating W and . Most of the time, V p varies around 300 km s −1 , and varies around 70 W m −2 . The average values of W and are 0.045 and 77.3 W m −2 , respectively. The average value of of E01 is consistent with the long-term observations from Le Chat et al. (2012) (around 79 W m −2 ). We note that does not vary much with V p when V p increases abruptly (i.e., from November 8 to 10, 2018). Figure 2 , which follows the same format as Fig. 1 , summarizes the PSP measurements of solar wind density, speed, and energy flux during E02 (from March 30, 2019 00:00:00 to April 11, 2019 00:00:00 UTC). We deduced n p and n α with the same method used for E01to calculate both W and . We note that n e shows two successive low plateaus near the perihelion of E02 (from April 3 to 8, 2019 UT), as shown in the first panel of Fig. 2 , whereas V p shows two high peaks. This is in agreement with the well-known anticorrelation between the solar wind speed and density (e.g., Richardson et al. 1996 ; Le Chat et al. 2012 ). Both and W also show two low plateaus near the perihelion of E02 (from April 3 to 8, 2019 UT), similar to the solar wind density. Elsewhere, V p remains around 300 km s −1 and varies around 70 W m −2 . The mean values of W and during E02 are 0.032 and 59.4 W m −2 , respectively. Similarly, Fig. 3 illustrates the PSP observations during E04 (from January 23, 2020 00:00:00 to February 4, 2020 00:00:00 UTC). We used n p and n α , which were deduced with the same method used for both E01 and E02, when calculating both W and . The second panel of Fig. 3 shows that V p varies
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