SSAI Obtains and Integrates Loon Stratospheric Balloon Observations for Global Data Assimilation
While satellites routinely measure Earth’s global temperatures from space, in-situ wind measurements are relatively scarce and mostly consist of a network of ground-based weather balloons. Since a limited number of the weather balloons reach stratospheric altitudes, and these launches are mostly over land masses in the Northern Hemisphere, there is a need for additional stratospheric observations — especially over the Southern Hemisphere and its oceans. To meet this need, an SSAI-led team successfully employed “loon” balloons.
Along with improved wind analyses, adding the loon balloon data to the data assimilation system (DAS) improved the system’s forecast of the loon balloon’s position. These results provided direction to improve future models and analyses.
Overview
Wind information can be obtained by using experimental super-pressure balloons (SPB), which can remain in the stratosphere for months. As the SPBs travel with the winds, they provide in-situ wind observations and report their changing positions, even when above oceans and other remote regions.
An example of loon balloon coverage
These SPB experiments are often limited in their experimental duration and the number of balloons. However, over the past few years, Project Loon launched hundreds of SPBs — also called “loon balloons” — which gave more consistent wind observations in the stratosphere. The original loon balloons were designed to provide communication links over remote regions so they were often empoyed to cover the Southern Hemisphere and its oceans — where traditional wind observations weren't available.
Results
SSAI team members leveraged this opportunity and began assimilating the loon balloon winds into the Goddard Earth Observing System (GEOS) global DAS, as part of our work in support of the Global Modeling Assimilation Office (GMAO). The DAS combines all observations with an atmospheric model to produce global analysis of winds and temperatures. Along with improved wind analyses, adding the Loon balloon data to the DAS improved the system’s forecast of the Loon balloon’s position. As such, these results provide direction for future model and analysis improvements.
Forecast Improvement
Loon balloon launches ended in January 2021 but retained a legacy of SPB observation that contribute to new 21st century reanalysis (R21C), a current project of SSAI scientists and team members with GMAO. The data collected from the loon balloons will enable R21C to provide more realistic wind fields in the lower stratosphere, particularly in the tropics, which will lead to more accurate modeling.