Dept. of Geosciences Colloquium: Earth’s Infrared Background

Zoom: https://tau-ac-il.zoom.us/j/83294569872?pwd=WmdPUWRPdGVQejIvcXhsQmFJY094UT09

​Abstract:

The study of physical processes based on Outgoing Longwave Radiation (OLR) necessitates a quantitative estimation of its background, in order to distinguish the processes in question from natural variability. We first obtain an objective definition of the background by considering its physical origins and mathematical properties. Physically, the background may be attributed to the fluctuation-dissipation theorem. Mathematically, the key property of the background, setting it apart from all other processes on Earth, is (spatial) statistical isotropy. Next, we employ a stochastic model, which embodies the physical and mathematical essence and is capable of explaining the natural variability in OLR observations on subseasonal timescales. The model provides a lower bound on the amount of variability which is due to random noise. Specifically, according to the model, at least 18% of the observed global mean variance and 40% of the total variance ought to be attributed to noise. By repeating the analysis for simulated OLR data from a CMIP6 climate model, we find that the background is subject to model biases and depends on the climate state. For example, the surface temperature, moisture, and stratification affect the infrared background by changing the emission and absorption properties of the atmosphere, and the scales of atmospheric motions from convection to the deformation radius. Therefore, our results provide observational constraints, which can be used for improving climate model parameterizations.

Event Organizer: Dr. Roy Barkan