Variability and change of cloudiness diurnal cycle over the past 30 years


The project "Variability and change of cloudiness diurnal cycle over the past 30 years: a global analysis based on polar orbiting satellites" is funded by the National Science Centre, Poland (NCN) via POLONEZ grant no 2015/19/P/ST10/03990. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 665778.

Project duration: 01.01.2017-31.12.2018
Team: Jędrzej S. Bojanowski (PI, Institute of Geodesy and Cartography), Jan P. Musiał (Institute of Geodesy and Cartography ) and Krzysztof Markowicz (University of Warsaw)

Project objectives:

Clouds have a major impact on the Earth’s radiation budget and thus play a crucial role in the Earth’s climate system. Yet the most uncertain component of climate models is cloud feedback. It has been estimated to very likely range from -0.2 to 0.6 Wm-2 for 1°C of air temperature increase, thus its sign is still unclear (IPCC). Diurnal evolution of clouds, including their physical properties, has been studied, but its variability and change over the last decades have not been thoroughly investigated on a global scale. Therefore, as a part of the United Nations Framework Convention on Climate Change, the Global Climate Observing System (GCOS) has included cloud properties in the set of essential climate variables, with a special emphasis on satellite-based retrievals.

Cloud property datasets derived from passive sensors onboard a series of polar orbiting satellites (such as NOAA and MetOp) have a global coverage and now span a climatological time period (30 years). However, changes in a number of simultaneously operating satellites, drift of their orbits and varying equatorial crossing times of consecutive satellite missions lead to a different frequency of image acquisitions per day, and to their different local time. When observing the atmospheric state of a distinct diurnal cycle, such as cloud formation, the changing number and local time of measurements lead to uncertainty in cloud characteristics in the same order of magnitude as the GCOS requirements on decadal stability of cloud fraction data (3%).

The primary goal of this study is to fulfill these requirements, and thus render the satellite-derived dataset suitable for climate analysis. We aim to:

1) develop and validate a method for statistical reconstruction of cloud cover diurnal cycle,
2) create a 30-year global cloud fraction climatology (1°×1°) suitable for trend analysis by correcting the satellite orbital drift issue,
3) quantify global changes in cloud cover distribution and in diurnal cycle of cloud formation over the last 30 years.

Publications supported by the grant:

• Bojanowski J.S., Stöckli, R., High temporal resolution cloud amount estimates at the Baseline Surface Radiation Network, under review in Journal of Geophysical Research

• Bojanowski J.S., Stöckli, R., et al., A Meteosat Bayesian Cloud Fractional Cover Climate Data Record: evaluation, homogeneity assessment and intercomparison with existing climate data records, in preparation.

Conference and workshop appearances supported by the grant:

• Aerosol Research Network (Poland AOD) 3rd Conference on Atmospheric Aerosol Properties and Climate Impacts, Warsaw, Poland, 2-4 July 2017.
• SPIE Remote Sensing Conference, Warsaw, Poland, 11-14 September 2017.
• XXXVIII Ogólnopolski Zjazd Agrometeorologów i Klimatologów, 18-20 September  2017, Puławy, Poland.
• EUMETSAT Meteorological Satellite Conference, Rome, Italy, 2-6 October 2017.