$$\textrm{O}^+$$ density distribution in the nightside ionosphere reconstructed from ISS-IMAP/EUVI data

<jats:title>Abstract</jats:title> <jats:p> The <jats:inline-formula> <jats:alternatives> <jats:tex-math>$$\textrm{O}^+$$</jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mtext>O</mml:mtext> <mml:mo>+</mml:mo> </mml:msup> </mml:math> </jats:alternatives> </jats:inline-formula> density distribution in the nightside ionosphere has been reconstructed from extreme ultraviolet (EUV) images taken by the EUVI-B imager of the International Space Station Ionosphere, Mesosphere, upper Atmosphere, and Plasmasphere mapping (ISS-IMAP) cameras. The EUVI-B imager covers the wavelength range from about 70 nm to 110 nm and mainly observes the 91.1 nm emission from the recombination of <jats:inline-formula> <jats:alternatives> <jats:tex-math>$$\textrm{O}^+$$</jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mtext>O</mml:mtext> <mml:mo>+</mml:mo> </mml:msup> </mml:math> </jats:alternatives> </jats:inline-formula> ions and electrons. Assuming that the electron density is equal to the <jats:inline-formula> <jats:alternatives> <jats:tex-math>$$\textrm{O}^+$$</jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mtext>O</mml:mtext> <mml:mo>+</mml:mo> </mml:msup> </mml:math> </jats:alternatives> </jats:inline-formula> density in the <jats:italic>F</jats:italic> -region where the imager observes, the EUV intensity observed by EUVI-B is approximately proportional to the line-of-sight integral of the square of the <jats:inline-formula> <jats:alternatives> <jats:tex-math>$$\textrm{O}^+$$</jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mtext>O</mml:mtext> <mml:mo>+</mml:mo> </mml:msup> </mml:math> </jats:alternatives> </jats:inline-formula> density. This enables us to estimate the <jats:inline-formula> <jats:alternatives> <jats:tex-math>$$\textrm{O}^+$$</jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mtext>O</mml:mtext> <mml:mo>+</mml:mo> </mml:msup> </mml:math> </jats:alternatives> </jats:inline-formula> density distribution in the <jats:italic>F</jats:italic> -region from a sequence of EUVI-B data in each International Space Station (ISS) orbit with a Bayesian method. We demonstrate the reconstruction of the <jats:inline-formula> <jats:alternatives> <jats:tex-math>$$\textrm{O}^+$$</jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mtext>O</mml:mtext> <mml:mo>+</mml:mo> </mml:msup> </mml:math> </jats:alternatives> </jats:inline-formula> distribution. In particular, the <jats:inline-formula> <jats:alternatives> <jats:tex-math>$$\textrm{O}^+$$</jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mtext>O</mml:mtext> <mml:mo>+</mml:mo> </mml:msup> </mml:math> </jats:alternatives> </jats:inline-formula> ...