Enhanced seasonal variations for chemical rates with inverse temperature dependencies: Application to seasonal abundance of mesospheric sodium

For a fixed altitude, the known seasonal variations of pressure in the mesosphere are less than a factor of two. However, the components of the pressure, the total concentration and temperature, vary in opposition to each other. Thus, a rate for a process with an inverse temperature dependence can undergo a much larger seasonal variation than does the pressure. In particular, the loss rate associated with the three‐body process , which has a negative temperature dependence, annually varies by a factor of four at 80 and 85 km for 60°N and by less than a factor of two at 30°N. Using a recent sodium model, sodium concentrations for 60°N at 80 and 85 km are shown to change by factors of three and two, respectively. Other possible contributors to the seasonal variation of mesospheric sodium are argued as less important.