Climatology and Diurnal Variation of Ozone Column Abundances for 2.5 Mars Years as Measured by the NOMAD-UVIS Spectrometer

The distribution of Mars ozone (O<SUB>3</SUB>) is well established; however, our knowledge on the dayside diurnal variation of O<SUB>3</SUB> is limited. We present measurements of Mars O<SUB>3</SUB> column abundances, spanning Mars Year (MY) 34 to the end of MY 36, by the Ultraviolet and VIsible Spectrometer (UVIS), part of the Nadir and Occultation for MArs Discovery (NOMAD) instrument, aboard the ExoMars Trace Gas Orbiter. UVIS provides the capability to measure dayside diurnal variations of O<SUB>3</SUB> and for the first time, a characterization of the dayside diurnal variations of O<SUB>3</SUB> is attempted. The observed O<SUB>3</SUB> climatology for Mars Years (MY) 34-36 follows the established seasonal trends observed through previous O<SUB>3</SUB> measurements. At aphelion, the equatorial O<SUB>3</SUB> distribution is observed to be strongly correlated with the water ice distribution. We show that the early dust storm in MY 35 resulted in a near-global reduction in O<SUB>3</SUB> during northern spring and the O<SUB>3</SUB> abundances remained 14% lower in northern summer compared to MY36. Strong latitudinal and longitudinal variation was observed in the diurnal behavior of O<SUB>3</SUB> around the northern summer solstice. In areas with a weak O<SUB>3</SUB> upper layer, O<SUB>3</SUB> column abundance peaks in the mid-morning, driven by changes in the near-surface O<SUB>3</SUB> layer. In regions with greater O<SUB>3</SUB> column abundances, O<SUB>3</SUB> is observed to gradually increase throughout the day. This is consistent with the expected diurnal trend of O<SUB>3</SUB> above the hygropause and suggests that in these areas an upper O<SUB>3</SUB> layer persists throughout the Martian day.