Night-time Mesospheric/Lower Thermospheric Tropical Ozone Response to the 27-day Solar Rotational Cycle: ENVISAT-GOMOS Satellite Observations versus HAMMONIA Idealized Chemistry-Climate Model Simulations

International audienceGlobal Ozone Monitoring by Occultation of Stars (GOMOS) satellite data are analyzed to estimate the first observation‐based night‐time (22:00 median local time) ozone response to the 27‐day solar rotational cycle in the tropical mesosphere/lower thermosphere (50‐110 km altitude). The ozone response to solar rotational variability is derived from linear correlation and regressions using Lyman‐⍺ line (121.6 nm) as solar index which varies by about 10‐15% over solar rotational cycles. In the lower mesosphere (50‐70 km), the GOMOS ozone is found to be correlated with the solar fluctuations and exhibits a sensitivity of ~0.1 (expressed in % change of ozone for 1% change in Lyman‐⍺). In the upper mesosphere/lower thermosphere (above 80 km), ozone variations become anti‐correlated with solar rotational variations. In this region, the vertical profile of ozone sensitivity to the 27‐day solar cycle exhibits a maximum of 1.8 at 81 km, a minimum of 0.3 at 100 km and a sharp increase above. Such high ozone sensitivities are observed for the first time. The observed ozone response is compared with chemistry‐climate simulations from the Hamburg model of the neutral and ionized atmosphere (HAMMONIA) which is forced with an idealized 27‐day solar spectral irradiance time series. Although observational and model results share some common features, substantial discrepancies are found. Namely, the altitude of transition from positive to negative solar‐ozone correlation signal in the model simulation is found about 10 km below the altitude of the observations and the amplitude of the ozone sensitivity is generally vastly underestimated by the model