613 Seminar Series: Dong L. Wu

NASA/Climate & Radiation Laboratory
The net Earth radiation at the top-of-atmosphere (TOA) is a balance between incoming solar radiation and the sum of reflected shortwave (SW) and outgoing longwave (LW) radiant energy emitted by the planet. The Earth radiation balance (ERB) is a key indicator of the health of Earth’s climate system. A positive (negative) value of the net TOA ERB, or Earth energy imbalance (EEI), indicates that the planet takes in more (less) energy than it releases to space. Earth’s climate system has to consume the excess or deficit EEI internally, through warming or cooling the planet. Making accurate and precise measurements of the EEI has been one of the greatest challenges in climate research. Because EEI is such an important external forcing and fundamental to the climate system, it should be determined from space, independently without relying on any assumptions about Earth’s internal processes such as ocean heat content and circulation.
In this study we evaluated various configurations of satellite constellation that can sufficiently capture large EEI diurnal and seasonal variabilities, using observation system simulation experiments (OSSEs) with the MERRA-2 hourly TOA flux data. The simulations led to an optimal solution for a six-satellite GEO-MEO constellation: four GEO satellites to cover the diurnal variations (e.g., clouds) and two polar-orbiting MEO satellites to cover the seasonal variations in the polar processes (e.g., sea ice and snow cover). One MEO orbit, at 28520-km altitude and 0.75-day period, is particularly useful for inter-sensor calibration. At the locations along the equator where simultaneous nadir overpass (SNO) between GEO and MEO satellites occurs repeatably, their radiometers can be cross-calibrated to 0.15% in total irradiance and 0.4% in the shortwave. The six-satellite constellation provides a manageable and affordable set of sensors for future ERB observations, which can leverage the state-of-the-art broadband radiometer technologies (e.g., CERES) to achieve long-term stability and inter-sensor consistency. It is also scalable to more satellites for denser sampling in space and time.
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