Solar cycle dependence of middle atmosphere temperatures

Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature data during 2002 through 2013 and covering 20–110 km altitude between ±83° latitude are analyzed to determine the dependence of middle atmosphere temperatures on solar flux, as parameterized by a linear relation with 81 day mean values of the 10.7 cm solar radio flux, F₁₀.₇a. The basic data analyzed are 60 day mean values, which represent zonal and local-time means. Analysis is conducted on both fixed altitude and fixed pressure levels. Below 70 km, the sensitivity of SABER annual mean temperatures is of order 1–2 K per 100 solar flux units (100 sfu) when data are analyzed on fixed altitude levels. At 85 km this increases to 3–6 K/100 sfu between ±60°latitude. At 95 km, values of order 4–6 K/100 sfu are found over the latitude range ±50° with values of order 10–14 K/100 sfu at higher latitudes in both hemispheres; these values increase to 5–11 K/100 sfu and 13–29 K/100 sfu, respectively, at 105 km. Comparisons are made with similarly analyzed temperatures from the National Center for Atmospheric Research Whole Atmosphere Community Climate Model (WACCM). At 85 km, the WACCM response is similar to observed but above that level WACCM predicts a lower response by a factor of about 2 at 95 km. On the other hand, below 70 km, the sensitivity of WACCM annual mean temperatures is stronger than SABER (∼3 K/100 sfu). When analysis is instead performed on pressure levels, the response in the lower thermosphere increases, especially at 105 km where changes of 29 to 51 K/100 sfu are seen in SABER annual mean temperatures.