Solar Cycle Response of CO₂ Over the Austral Winter Mesosphere and Lower Thermosphere Region

Abstract

This work uses Sounding of the Atmosphere using Broadband Emission Radiometry CO2 data from 2002 to 2015 and Specified Dynamics‐Whole Atmosphere Community Climate Model (SD‐WACCM) outputs from 1979 to 2014 to show, for the first time, the solar cycle response of CO2 in the Austral winter mesosphere and lower thermosphere region. Both Sounding of the Atmosphere using Broadband Emission Radiometry and SD‐WACCM show that CO2 experiences a decrease during solar maximum throughout the Austral winter mesosphere and lower thermosphere region. This work highlights the regions where CO2 experiences its strongest and weakest solar cycle responses as modeled by SD‐WACCM. The region with the strongest solar cycle response experiences around 5% reduction in CO2 between solar maximum and solar minimum. The region with weakest solar cycle response experiences less than 1% reduction in CO2 between solar maximum and solar minimum. It is shown that the region of the strongest CO2 response is driven by photodissociation, downwelling, and reduced eddy diffusion. On the other hand, the region of the weakest CO2 response is driven by the opposing effects of photodissociation and enhanced eddy diffusion. This is the first work to show that the solar cycle could affect the Austral winter lower thermosphere circulation and eddy diffusion processes. These anomalies in the lower thermospheric circulation and eddy diffusion are found to be related to the solar cycle response in the Austral winter mesosphere wave‐mean flow dynamics. This work therefore concludes that the solar cycle affects lower thermospheric CO2 via modulations of the lower thermospheric circulation and eddy diffusion processes.

Solar Cycle Modulation of Nighttime Ozone Near the Mesopause as Observed by MLS

“…It becomes complicated to determine what processes (i.e., dynamical vs. chemical) contribute mostly to the observed ozone 11‐year variation, despite the clear in‐phase correlation with the solar cycle. Salinas et al () showed that k zz may have an 11‐year variation, which can in turn modulate the [O] and [CO] concentrations and subsequently nighttime [O 3 ] in the UMLT. If the solar cycle variation of nighttime [O 3 ] were dominated by chemical processes, one would expect its 11‐year amplitude to be proportional to its background mean.…”

Impact of Solar Activity on Global Atmospheric Circulation Based on SD-WACCM-X Simulations from 2002 to 2019

“…Therefore, the ~11 year cycle of the atmospheric circulation may be due to changes in CO 2 . Salinas et al showed that CO 2 decreases during solar maxima throughout the Austral winter mesosphere and lower thermosphere region [45]. This does not lead to enhanced atmospheric circulation in these regions during years with high solar activity.…”

“…They also indicated that the results were in excellent agreement with other analyses of observations. Based on SD-WACCM simulations, Salinas et al [45] identified the solar cycle response of CO 2 in the lower thermosphere via modulations of the circulation in the lower thermosphere. This discovery was also demonstrated using the satellite observations.…”

“…Based on the Canadian Middle Atmosphere Model (CMAM), Karlsson and Kuilman [44] investigated the influences of solar activity on middle atmospheric residual circulation close to the solstics. Salinas et al [45] indicated that solar activity can affect the circulation in the lower thermosphere which can modulate the content of CO 2 in the lower thermosphere. Rao et al [46] studied the responses of the Brewer-Dobson circulation to the solar cycle and found that the Brewer-Dobson circulation in the lower stratosphere intensifies during solar minima.…”