Spectral Signatures of Earth's Climate Variability over Five Years from CrIS, AIRS, and IASI

The CLARREO mission has been established by NASA’s Langley Research Center to establish benchmark measurements using traceable international standards (SI) through various independent paths. Wielicki et al. (2013) showed that the time to detect trends in the atmosphere depends on several factors, including the magnitude of the trend, the natural variability, temporal auto-correlation, and measurement error. The CLARREO mission has proposed sensors which emphasize absolute accuracy in order to minimize the time to detect climate trends. However, the natural variability and auto-correlation of the atmosphere can be characterized with existing observations which have similar spectral coverage and resolution. The objective of the current study is to compute an estimate of the inter-annual variability and auto-correlation of outgoing spectrally resolved infrared emission from operational polar orbiting hyperspectral infrared sensors in sun synchronous orbits. The nominal mission lifetime needed to establish a baseline measurement for the infrared benchmark is five years. The NASA Suomi-NPP satellite recently completed a five year record of observations covering the period April 2012 – March 2017 in the early afternoon orbit. On the Suomi-NPP satellite, the Cross-track InfaRed Sounder (CrIS) measures outgoing radiance in the spectral range 3.5 to 15 microns with a resolving power of 1000. Coincident with the nadir CrIS infrared radiance observations, profiles of ozone are available from the Ozone Mapping Profiler Suite (OMPS) limb profiler sensor also on the Suomi-NPP satellite. The coincident CrIS and OMPS data provides a unique dataset for the characterization of the correlation of observed brightness temperature and ozone on zonal, monthly space and time scales. Comparison will be made between brightness temperature natural variability computed from the CrIS sensor and that from the NASA Atmospheric InfraRed Sounder (AIRS) on the Aqua satellite in a similar afternoon sun-synchronous orbit. If possible, comparison will also be made with the EUMETSAT Infrared Atmospheric Sounding Interferometer (IASI) and the JAXA GOSAT TANSO FTS which are in orbits which sample different times of day. The range of natural variability estimates will be used to estimate a corresponding range of time to detect predicted brightness temperature trends from a climate model. Previous findings (Brindley et al. 2015) imply that at the largest spatial scales, fluctuations in the mid to upper tropospheric temperatures and water vapor, and not cloud or surface temperature, play the dominant role in determining the level of interannual variability in all sky outgoing longwave radiation. Enhanced variability was seen in the 9.6 micron ozone band.