Satellite observations of high nighttime ozone at the equatorial mesopause

Abstract

[1] Measurements by the Sounding of the Atmosphere using Broadband Emission Radiometry instrument enable the characterization of the seasonal variation of ozone and temperature in the upper mesosphere. These are the first global measurements that resolve both the structure of the secondary ozone maximum at night and the temperature over all seasons of the year. The average nighttime mixing ratios at the altitude of the maximum vary with latitude and season. Analysis shows that the highest mixing ratios are clustered near the equator during equinoxes. The high ozone mixing ratios are observed in exactly the place and time at which the diurnal tide is largest. The diurnal tidal phase is such that coldest temperatures at 95 km occur near midnight. The high ozone is coincident with regions that have both low temperature and low amounts of atomic hydrogen. We focus particularly on ozone mixing ratios in the range of 18-50 ppmv; these occur intermittently in the equinoctial tropics on days when the night temperature is particularly cold. The occurrence of ozone maxima over 20 ppmv was unexpected but is shown in this paper to be consistent with theory and is a result of large-amplitude diurnal tides. The same seasonal and latitudinal characteristics are seen in ozone density measured by Global Ozone Monitoring by Occultation of Stars.

The roles of vertical advection and eddy diffusion in the equatorial mesospheric semi-annual oscillation (MSAO)

“…Kyrölä et al (2006Kyrölä et al ( , 2010, using Envisat/GOMOS (Global Ozone Monitoring by Occultation of Stars) data, found that ozone (O 3 ) at 90 km peaked in equinox periods and was approximately a factor of three lower in solstice periods. Huang et al (2008) and Smith et al (2008) found a similar variation in O 3 using data from TIMED/SABER (Sounding of the Atmosphere using Broadband Emission Radiometry). Seasonal oscillations in mesospheric atomic oxygen (O) were inferred by Sheese et al (2011) using observations from OSIRIS (Optical Spectrograph and InfraRed Imaging System) (Llewellyn et al, 2004) on Odin, and by Smith et al (2010) using TIMED/SABER data.…”

“…Huang et al (2008) and Smith et al (2008) found a similar variation in O 3 using data from TIMED/SABER (Sounding of the Atmosphere using Broadband Emission Radiometry). Seasonal oscillations in mesospheric atomic oxygen (O) were inferred by Sheese et al (2011) using observations from OSIRIS (Optical Spectrograph and InfraRed Imaging System) (Llewellyn et al, 2004) on Odin, and by Smith et al (2010) using TIMED/SABER data. Both of these O studies also showed diurnal variations.…”

“…Yee et al (1997) demonstrated the effects of diurnal tides in their extensive model simulations of the UARS/HRDI observations. Smith et al (2010) have also successfully simulated the significant diurnal tidal effects in the O observations made with SABER. Studies by Wu et al (2008) and John and Kumar (2011) provide further insight into the details of the tides.…”

“…3b for August conditions provides an opportunity to check the validity of the simulated tides. The local time phases of the model O tides as a function of altitude can be compared with the diurnal variations described by Smith et al (2010) for O derived from the SABER observations. Beginning at 82 km, for equatorial vernal equinox, the O maximum from SABER data occurs between 23:00 LT and 02:00 LT (their Fig.…”

“…As noted by Adler-Golden (1997) this rate is very uncertain. However, Smith et al (2010) concluded that the collision rate with O must be reduced to satisfy the SABER O density measurements.…”