Trends in the Airglow Temperatures in the MLT Region—Part 1: Model Simulations

Abstract

Airglow intensity-weighted temperature variations induced by the CO2 increase, solar cycle variation (F10.7 as a proxy) and geomagnetic activity (Ap index as a proxy) in the Mesosphere and Lower Thermosphere (MLT) region were simulated to quantitatively assess their influences on airglow temperatures. Two airglow models, MACD-00 and OHCD-00, were used to simulate the O(1S) greenline, O2(0,1) atmospheric band, and OH(8,3) airglow temperature variations induced by these influences to deduce the trends. Our results show that all three airglow temperatures display a linear trend of ~−0.5 K/decade, in response to the increase of CO2 gas concentration. The airglow temperatures were found to be highly correlated with Ap index, and moderately correlated with F10.7, with the OH temperature showing an anti-correlation. The F10.7 and Ap index trends were found to be ~−0.7 ± 0.28 K/100SFU and ~−0.1 ± 0.02 K/nT in the OH temperature, 4.1 ± 0.7 K/100SFU and ~0.6 ± 0.03 K/nT in the O2 temperature and ~2.0 ± 0.6 K/100SFU and ~0.4 ± 0.03 K/nT in the O1S temperature. These results indicate that geomagnetic activity can have a rather significant effect on the temperatures that had not been looked at previously.

Trends in the Airglow Temperatures in the MLT Region—Part 2: SABER Observations and Comparisons to Model Simulations

“…This indicates that the annual mean SABER temperature at 89 km had a moderate correlation with the F10.7 and a modest correlation with the Ap index. The simulated OH temperature taken from [13] had a low correlation with the F10.7 (−0.69 ± 0.28 K/100 SFU, R = 0.31) and a modest correlation with the Ap index (−0.12 ± 0.02 K/nT, R = 0.54). In addition, both the F10.7 and Ap index trends were negative.…”

“…The authors of [13] simulated the airglow-intensity weighted OH (8,3), O 2 , and O( 1 S) temperatures for the aforementioned location to deduce the F10.7, Ap index, and CO 2 trends in the simulated temperatures. Intensity-weighted temperature was obtained from the kinetic temperature weighted by airglow intensity [18], so the intensity-weighted temperature at peak height could be considered as kinetic temperature at that altitude.…”

“…Intensity-weighted temperature was obtained from the kinetic temperature weighted by airglow intensity [18], so the intensity-weighted temperature at peak height could be considered as kinetic temperature at that altitude. The SABER temperature data at 3 altitudes (89 km, 95 km, and 97 km) were selected for comparison to the OH (8,3), O 2 , and O( 1 S) intensity-weighted temperatures, respectively, from the Scenario 3 simulations by the authors of [13]. These airglow intensity-weighted temperatures are called airglow temperatures hereafter to be consistent with the terminology used in the Part 1 paper, i.e., OH temperature stands for OH airglow intensity-weighted temperature and so forth.…”

“…The 3 altitudes were chosen because they are near the peak heights of the airglow emissions under consideration. Detailed information about the simulation results and the F10.7 and Ap index data sources used in this study can be found in the Part 1 paper [13]. The F10.7 values and Ap index values from 2002 to 2019 were taken from NASA's website and the World Data Center for Geomagnetism at the Kyoto website, respectively.…”

“…In Part 1 of this series by the authors of [13], the OHCD and the MACD model were used to simulate airglow intensity-weighted temperatures of the aforementioned airglow under the influence of the CO 2 increase and F10.7 and Ap index variations from 1960 to 2019. Their simulation results were in agreement with the findings from other studies, i.e., solar response in temperature still remains one of the major sources of variations.…”