Kinetic requirements for the measurement of mesospheric water vapor at 6.8 µm under non‐LTE conditions

Abstract

We present accuracy requirements for specific kinetic parameters used to calculate the populations and vibrational temperatures of the H2O(010) and H2O(020) states in the terrestrial mesosphere. The requirements are based on rigorous simulations of the retrieval of mesospheric water vapor profiles from measurements of water vapor infrared emission made by limb scanning instruments on orbiting satellites. Major improvements in the rate constants that describe vibration‐to‐vibration exchange between the H2O(010) and O2(1) states are required in addition to improved specification of the rate of quenching of O2(1) by atomic oxygen (O). It is also necessary to more accurately determine the yield of vibrationally excited O2(1) resulting from ozone photolysis. A contemporary measurement of the rate of quenching of H2O(010) by N2 and O2 is also desirable. These rates are either highly uncertain or have never before been measured at atmospheric temperatures. The suggested improvements are necessary for the interpretation of water vapor emission measurements at 6.8 µm to be made from a new spaceflight experiment in less than 2 years. The approach to retrieving water vapor under non‐LTE conditions is also presented.