Highly rotationally excited NO(υ,<i>J</i>) in the thermosphere from CIRRIS 1A limb radiance measurements

Abstract

Earthlimb spectra of thermospheric NO fundamental band emissions, obtained in the CIRRIS 1A Space Shuttle experiment, have been analyzed using nonlinear least‐squares spectral fitting. Absolute NO(υ≥1, J ) column densities have been determined in the 100 to 260‐km tangent height region and inverted to yield altitude‐dependent number densities for both a rotationally thermalized and a highly rotationally excited population component. Emissions from high‐ J levels are predicted to dominate the Δυ=2 overtone bands during the daytime. The rotationally excited population is found to decrease more at night than the rotationally thermalized component. In addition, radiance from the CO υ=1→0 fundamental band is observed in the NO R ‐branch band head region, with greater relative importance at night. The derived CO rotational temperatures are significantly greater than modeled local kinetic temperatures. These results provide important inputs to models of NO(υ, J ) formation mechanisms, and of the chemistry, radiative processes, and energy budget of the thermosphere.