Effect of 2009 Major SSW Event on the Mesospheric CO2 ${\text{CO}}_{2}$ Cooling

Abstract Carbon dioxide (), an important trace species that is gradually increasing in the atmosphere due to anthropogenic activities, causes enhanced warming in the lower atmosphere. The increased concentration of in the upper atmosphere results in enhanced radiative cooling rates leading to the contraction of the upper atmosphere. Due to its long lifetime and large vertical gradient, concentration is also influenced by large dynamic events. We report a startling case of variability in density and its infrared radiative cooling rates in the mesosphere and lower thermosphere during a major sudden stratospheric warming (SSW) event. A counter‐intuitive connection between density and resulting radiative cooling has been observed during the 2009 major SSW event. The behavior of cooling rates during such a dramatic events draws attention to our current understanding of infrared cooling variation and its connection to changes in concentration. The significance of temperature and atomic oxygen variability in the observed cooling patterns despite changes in concentration, is also highlighted.