Adiabatic Invariants Calculations for Cluster Mission: A Long‐Term Product for Radiation Belts Studies

The Cluster mission has produced a large data set of electron flux measurements in the Earth's magnetosphere since its launch in late 2000. Electron fluxes are measured using Research with Adaptive Particle Imaging Detector (RAPID)/Imaging Electron Spectrometer (IES) detector as a function of energy, pitch angle, spacecraft position, and time. However, no adiabatic invariants have been calculated for Cluster so far. In this paper we present a step‐by‐step guide to calculations of adiabatic invariants and conversion of the electron flux to phase space density (PSD) in these coordinates. The electron flux is measured in two RAPID/IES energy channels providing pitch angle distribution at energies 39.2–50.5 and 68.1–94.5 keV in nominal mode since 2004. A fitting method allows to expand the conversion of the differential fluxes to the range from 40 to 150 keV. Best data coverage for phase space density in adiabatic invariant coordinates can be obtained for values of second adiabatic invariant, K, ∼10 2, and values of the first adiabatic invariant μ in the range ≈5–20 MeV/G. Furthermore, we describe the production of a new data product “LSTAR,” equivalent to the third adiabatic invariant, available through the Cluster Science Archive for years 2001–2018 with 1‐min resolution. The produced data set adds to the availability of observations in Earth's radiation belts region and can be used for long‐term statistical purposes. Key Points Calculations of the adiabatic invariants for Cluster mission are described as a step‐by‐step guide New data product, LSTAR, was created with 1‐min resolution for 18 years of Cluster mission Examples of phase space density (PSD) calculations in adiabatic invariant coordinates are provided