Cloud Fractions Estimated from Shipboard and Satellite Observations between East Asia and Antarctica.

Abstract:

Shipboard observations on cloud fraction were conducted along the round research cruise between East Asia and Antarctica from November 2017 to April 2018 using a whole-sky camera, a ceilometer, and visual observation onboard Research Vessel (R/V) Shirase.

We retrieved cloud fraction from the whole-sky camera based on the contrasts of brightness and color in the images, while we estimated cloud fraction from the ceilometer as a frequency of cloud occurrence.

As a result, the daily averaged cloud fractions over outward open ocean, sea ice region, and returning open ocean were approximately 53% (63%), 77% (73%), and 68% (68%), respectively, with the whole-sky camera (ceilometer).

Furthermore, we estimated cloud fraction from geostationary satellite Himawari-8 which covered the ship tracks of R/V Shirase. The observation was frequent by ten minutes as much as the whole-sky camera and the ceilometer. Match-up analyses show that the correlation coefficients (mean biases) were 0.82 (5.3%), 0.93 (0.6%), and 0.93 (-3.1%) with the whole-sky camera, ceilometer, and visual observations, respectively.

The shipboard observations are very valuable for the validation of products from satellite observation, because we do not have many validation sites necessarily over Southern Ocean and sea ice region in particular. We will continue to perform the analyses on cloud fractions during extended period from 2018 to 2019.