Observations of Radiative Cooling By Nitric Oxide and Carbon Dioxide in the E and F Regions: Implications for Space Weather and Space Climate

Abstract:

Infrared emission by nitric oxide (NO, 5.3 um), carbon dioxide (CO₂, 15 um), and atomic oxygen (O, 63 um) is the mechanism for radiative cooling of the thermosphere. Heat conduction transports energy from the warmer, higher layers of the thermosphere to lower layers where CO₂ and NO ultimately radiate the energy. These radiative processes play a large role in governing the neutral temperature of the ionosphere E and F regions. The SABER instrument on the NASA TIMED satellite has been observing radiative cooling by NO and CO₂ for 13 years. Substantial variability in the radiative cooling is observed on timescales ranging from one day to the 11-year solar cycle. Harmonics of the annual cycle are evident in the CO₂ cooling rates, implying strong coupling to the lower atmosphere. Harmonics of the solar rotation period are evident in the NO cooling, but only during solar minimum conditions. To date the NO cooling data have been helpful in understanding space weather forecasts and the interaction of co-rotating interaction regions with the ionosphere. The cooling rate data will be reviewed in light of their observed variability over the past 13 years, including the implications for variations in the thermal structure of the E and F regions. The potential for development of proxies and empirical models of the NO and CO₂ emissions will also be presented. Such models could become part of an overall space weather forecasting tool.