Has the Solar Cycle 24 Maximum Already Occurred?

Infrared radiative cooling of the thermosphere by carbon dioxide and nitric oxide has been observed continuously since January 2002 by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the NASA Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite. SABER has documented dramatic variability in the radiative cooling on timescales ranging from days to longer than the nominal 11-year solar cycle. SABER radiance measurements from emission by CO2 (at 15 um) and NO (at 5.3 um) are used to calculate global daily emitted thermosphere power. This unique dataset shows the direct effects of solar variability on the temperature (via CO2 emission) and composition (from NO emission) for nearly twelve years. The deep solar minimum between solar cycles 23 and 24 is evident in the low values of global mean radiative cooling that occur in the 2008-2009 period. Since then radiative cooling has been observed to increase in response to the transition into solar cycle 24. To more clearly identify extrema in the time series of radiative cooling, NO and CO2 cooling rates are deseasonalized to remove effects of the spacecraft yaw cycle. The deseasonalized data show a clear peak of radiative cooling in NO and CO2 occurring in December 2011. This peak in cooling corresponds to similar peaks in the ultraviolet flux emitted from the Sun measured by the SORCE and SEE instruments. These results show that a maximum in solar activity has clearly occurred. This may be a local maximum in time, depending on the future activity of the Sun in solar cycle 24. Reprocessing of version 2.0 of the SABER dataset is nearly complete and results from this new release will be presented. The SABER thermosphere power dataset will be continuously updated as new data are acquired to monitor the occurrence of solar maximum from the perspective of atmospheric cooling.