Global Trends of Sea Ice: Small-Scale Roughness and Refractive Index

Sea ice is one of the most important parameters in the global climate system, specifically the exchange of energy and momentum between the ocean and the atmosphere. In previous studies, a steady decline in Arctic sea ice has been observed over recent decades. The aim of this study is to estimate and analyze the spatial and temporal characteristics of the averaged sea ice extent, surface roughness, and refractive index from March 2003 to September 2009. A unique inversion algorithm is used for deriving the surface roughness and refractive index from Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) daily observations. Surface roughness significantly affects the microwave emission of the sea ice/snow surface. The sea ice, snow, and water show the dielectric contrast in the microwave frequencies. Consequently, the averaged roughness as well as the sea ice extent shows a downward trend, while the averaged refractive index shows the opposite signature. The increased trend of the refractive index in summer on both poles supports more sea ice melting in summer because of the increased temperature. This research can be applied to the climate change studies and supports the previous approaches based on the sea ice concentration in passive microwave remote sensing by the physical explanations.