Simultaneous observations of several nightglow emissions have been carried out at Fortaleza (40S, 380W) and<br>Cachoeira Paulista (23oS, 45o W), Brazil, since 1987. Using the OH Meinel (9,4) and O2 atmospheric b(0,1) bands<br>observed at these two stations during the period from 1987 to 1994, we present and discuss the night-time<br>reduction in chemical heating rates by these mesospheric airglow emissions. The total emission rates of the OH<br>Meinel bands and O2 atmospheric b(0,0) and O2 infrared atmospheric (1Δg) bands were calculated using the<br>reported data for the relative band intensities I(ν/,ν//)/I(9,4), I(O2b(0,0))/I(O2 b(0,1)) and I(O2 (1Δg))/ I(O2b(0,1)). This<br>study showed that the reduction in chemical heating rates (RCH) by the OH Meinel bands, at both the locations,<br>has seasonal variations with monthly mean values varying from 0.4 K/day* to 0.9 K/day* (where day* means<br>averaged over the night). However, the RCH rates due to the radiation in the Meinel bands at Cachoeira Paulista<br>presented a weak ter-annual variations, whereas at Fortaleza semi-annual variations were observed. Also, the<br>RCH rates by O2* showed semi-annual variations at both locations, presenting values from 0.05 K/day* to 0.25<br>K/day*.


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