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Expansion effects dominate the thermal energy budget below 0.3 au.

The divergence of the heat flux is positive at heliocentric distances below 0.33 au, while beyond 0.33 au, there is a measurable degradation of the heat flux. We find that a thermal-energy source must be present in the inner heliosphere over the heliocentric distance range from 0.15 to 0.47 au. We separate contributions to the overall budget from reversible and irreversible processes. We use the macroscopic moments, obtained from our fits to the measured electron distribution function, to evaluate the thermal energy budget based on the second moment of the Boltzmann equation. We present an observational analysis of the electron thermal energy budget using data from Parker Solar Probe. In view of a global perspective of solar wind, it may be a favorable study with the contribution of non-thermal solar wind electrons. We note an increment in the growth rate with the increase of anisotropic ratios associated either with core electrons or halo electrons and or the combination thereof.

growth rate and the range of wave number of unstable mode. We take different sets of temperature anisotropy and beta combinations associated with core-halo electron components that highlight the instability characteristics e.g. We employ Vlasov–Maxwell’s model equations and derive the dispersion relation of the O-wave whose analytical solution characterizes the growth rate of O-mode instability. Looking at the recent developments made by different satellite missions, a dual core-halo electron distribution is employed that represents a true picture of solar wind electrons. The present study considers the excitation of O-mode instability under the excessive electrons parallel temperature condition i.e., T ‖ e > T ⊥ e. Micro-instabilities driven by the temperature anisotropy are investigated as key mechanism which limit an unchecked rise in the temperature anisotropy in dilute space plasmas. In situ measurements reported with different spacecraft reveal the temperature anisotropy constraints of solar wind species.