Investigating the impact of IR surface emissivity knowledge & uncertainties on climate & weather-forecasting timescales

Lead Research Organisation: Imperial College London
Department Name: Dept of Physics

Abstract

The magnitude and pace of human-induced climate change is projected to be at its largest in high-latitude (polar) regions. The radiative interaction between the surface & atmosphere is key to understanding climate change, enhanced in Polar Regions by the interplay between the cryosphere & open ocean under an exceptionally transparent atmosphere in the mid- to far-IR. Surface reflection/emissivity has been studied extensively throughout the visible and NIR for many surface types across the globe. However, recent climate model simulations have highlighted that a hitherto unrecognised feedback process may significantly accelerate the rate of warming in arctic areas through IR interactions. Termed the 'ice-emissivity' feedback, the process is postulated to rely on differential surface emission of far infrared (FIR) radiation (wavelengths between ~ 15 and 100 microns) from snow covered and ocean surfaces (Feldman et al., 2014). In the FIR, theoretical estimates of surface emissivity suggest that the ocean is less emissive than overlying ice and snow layers, hence as snow/ice melts additional heat can be trapped within the upper ocean, accelerating ice melt and leading to further near surface and surface warming.
Existing studies evidence a need for improvements in current estimates of the surface emissivity across the full infrared spectrum. These studies also indicate that snow and ice surfaces do indeed have an emissivity spectrum that is significantly different from that of a perfect, blackbody emitter (an assumption made in most current weather and climate prediction models).
Very recent work within Imperial College's Space and Atmospheric Physics group has delivered the first ever in-situ estimates of FIR surface emissivity from airborne observations (Bellisario et al., 2017). We are also currently developing the capability to make measurements of surface emissivity extending across the infrared via a purpose designed portable ground-based system. Current modelling efforts have focused on the long-term response of the polar regions to infrared surface emissivity, but its unstudied impact on shorter 'weather' time-scales and the large source of uncertainty it adds to monthly-scale predictions should not be estimated.
In this project you will thus:
(1) Further exploit arctic flight campaign data to assess the robustness of our initial results and perform additional evaluation of theoretical snow/ice surface emissivity estimates.
(2) Utilise our new ground-based interferometer system to obtain in-situ estimates of infrared emissivity spanning the mid- and far infrared for a range of different surfaces and conditions, focusing initially on snow/ice covered high latitudes.
(3) Work with the co-supervisor institutions to assess the impact of new robust IR surface reflectance/emissivity measurements on EO cal/val, climate studies & numerical weather prediction application areas.

Publications

10 25 50

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/R511961/1 01/10/2017 30/09/2022
2119013 Studentship EP/R511961/1 01/09/2018 01/09/2022 Laura Rachel WARWICK