Retrieval of Atmospheric and Cloud Property Anomalies and Their Trend from Temporally and Spatially Averaged Infrared Spectra Observed from Space

Kato, S., et al. (2014), Retrieval of Atmospheric and Cloud Property Anomalies and Their Trend from Temporally and Spatially Averaged Infrared Spectra Observed from Space, J. of Climate, 27, 4403-4420, doi:10.1175/JCLI-D-13-00566.1.
Abstract

A surface, atmospheric, and cloud (fraction, height, optical thickness, and particle size) property anomaly
retrieval from highly averaged longwave spectral radiances is simulated using 28 years of reanalysis. Instantaneous
nadir-view spectral radiances observed from an instrument on a 908 inclination polar orbit are
computed. Spectral radiance changes caused by surface, atmospheric, and cloud property perturbations are
also computed and used for the retrieval. This study’s objectives are 1) to investigate whether or not separating
clear sky from cloudy sky reduces the retrieval error and 2) to estimate the error in a trend of retrieved
properties. This simulation differs from earlier studies in that annual 108 latitude zonal cloud and atmospheric
property anomalies defined as the deviation from 28-yr climatological means are retrieved instead of the
difference of these properties from two time periods. The root-mean-square (RMS) difference of temperature
and humidity anomalies retrieved from all-sky radiance anomalies is similar to the RMS difference derived
from clear-sky radiance anomalies computed by removing clouds. This indicates that the cloud property
anomaly retrieval error does not affect the retrieved temperature and humidity anomalies. When retrieval
errors are nearly random, the error in the trend of retrieved properties is small. Approximately 30% of
108 latitude zones meet conditions that the true temperature and water vapor amount trends are within a 95%
confidence interval of retrieved trends, and that the standard deviation of retrieved anomalies sret is within
20% of the standard deviation of true anomalies sn. If sret/sn 2 1 is within 60.2, 91% of the true trends fall
within the 95% confidence interval of the corresponding retrieved trend.

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Research Program
Radiation Science Program (RSP)
Mission
CLARREO