Temperature spectra in the solar wind turbulence

We study Alfvenic turbulent fluctuations and their spectral properties from MHD to kinetic scales and compare with recent measurements of the Spektr-R spacecraft. An apparent contradiction is found between the temperature spectra derived from the Spektr-R data and the temperature spectra predicted theoretically. To resolve this contradiction, we show that the temperature fluctuations can be correctly estimated from the Spektr-R data only if the mean temperature is isotropic. Since the mean temperature in the solar wind is usually anisotropic, the derived fluctuations appear to be pseudo-temperature rather than temperature. These pseudo-temperature fluctuations are driven by the high-amplitude magnetic fluctuations in Alfven waves rather than the fluctuations of temperature or thermal velocity. That is why their amplitudes are usually significantly larger than the amplitudes of authentic temperature fluctuations.