Diurnal cycle of cloud cover in São Paulo derived from measurements of a low-cost skyimager

• Grant number: 16/18515-5
• Support type: Scholarships in Brazil - Scientific Initiation
• Effective date (Start): November 01, 2016
• Effective date (End): October 31, 2017
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Meteorology
• Principal Investigator: Henrique de Melo Jorge Barbosa
• Grantee: Giovanni Souza
• Home Institution: Instituto de Física (IF). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 13/05014-0 - GoAmazon: interactions of the urban plume of Manaus with biogenic forest emissions in Amazonia, AP.PFPMCG.TEM

Abstract

Clouds reflect part of the incident solar radiation, cooling the planet, but absorb the longwave radiation that would be lost to space, warming it. These effect on the energy budget are so important that a mere 1 increase in the albedo of low clouds would produce a negative forcing that cancel that of CO2. Although its importance, physical processes that control clouds are still not fully understood and there is a lack of continuous observations of high temporal and spatial resolution to resolve them. Numerical models, for instance, still fail in reproducing the diurnal cycle of cloudiness and precipitation. On instrument that can observe cloud cover with high temporal resolution is a skyimager. In our laboratory, we have developed a low-cost instrument that takes pictures of the sky every 5-min. In this project, the main objective will be to use this data to study the diurnal cycle of cloud cover in Sao Paulo. The student will program the instrument to take 4 consecutive photos with different exposures and will combine them into a single photo of higher dynamical range. The identification of clouds in each image will be done using the ratio of the red and blue channels, maximizing the difference between the clear- and cloud-sky regions. All the analysis will be perform using Matlab, which the student is already getting familiar with. The validation will be done by comparison with a commercial instrument of astronomy grade, which we operate in partnership with IPEN and UNIFESP. Finally, the student will run our skyimager for three months in Sao Paulo to collect the data for the diurnal cycle study.