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

Abstract

Carbon dioxide (${\text{CO}}_2$), 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 ${\text{CO}}_2$ 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, ${\text{CO}}_2$ concentration is also influenced by large dynamic events. We report a startling case of variability in ${\text{CO}}_2$ 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 ${\text{CO}}_2$ density and resulting ${\text{CO}}_2$ radiative cooling has been observed during the 2009 major SSW event. The behavior of ${\text{CO}}_2$ cooling rates during such a dramatic events draws attention to our current understanding of ${\text{CO}}_2$ infrared cooling variation and its connection to changes in ${\text{CO}}_2$ concentration. The significance of temperature and atomic oxygen variability in the observed cooling patterns despite changes in ${\text{CO}}_2$ concentration, is also highlighted.