When Will MISR Detect Rising High Clouds?

Abstract

It is predicted by both theory and models that high clouds will occur higher in the atmosphere as a result of climate warming, which is expected to produce a positive longwave feedback and has a substantial impact on the Earth’s response to warming. Although this effect is well described by theory, it is poorly constrained by observation, and there is a large spread in how models simulate the radiative importance of the feedback. Hence, it is necessary to try to apply new observational constraints to rising high clouds. This study uses the Multi-angle Imaging SpectroRadiometer (MISR) to examine changes in Cloud-Top-Height (CTH). Currently the MISR observational record does not show detectable trend in CTH, and in this research project model simulations are used to project when it is expected that MISR will be capable of observing trend in CTH. Trend detection is a matter of determining when the trend overcomes the variability, thus correctly modeling the variability of CTH is a key aspect of this study, and the model output is modified to better match the observations. Two models used for the primary analysis suggest that MISR should be capable of detecting a trend very soon (less than 5 to 10 years). This result indicates the importance of a follow-up mission to MISR, and that if the new instrument is placed on a sufficiently similar orbit to MISR, it may be capable of quickly detecting the trend of CTH, and provide a useful constraint on the associated feedback.