Scientists from Poland and Taiwan are developing a new way to measure humidity in the lower atmosphere more accurately and investigate whether better atmospheric data can improve forecasts of severe weather.
Researchers from the Wrocław University of Environmental and Life Sciences and two Taiwanese institutions – National Central University and National Taipei University – are collaborating on the SWIM-GNSS project.
“We are particularly interested in humidity in the lower troposphere, because that is where processes crucial to the development of many intense weather phenomena take place,” said SWIM-GNSS project leader Estera Trzcina, PhD, from the Institute of Geodesy and Geoinformatics at the Wrocław University of Environmental and Life Sciences.
Taiwan provides a natural laboratory for the research. The region regularly experiences heavy rainfall, storms and typhoons and has an extensive observation infrastructure. More than 200 ground-based GNSS stations operate on the island, while a wealth of radio occultation data is also available.
GNSS signals are primarily associated with satellite navigation and positioning, but they can also provide highly accurate information about the atmosphere. As a signal passes through different atmospheric layers, its properties change. Analysing these changes makes it possible to determine parameters such as water vapour content.
In the SWIM-GNSS project, co-financed by the Polish National Centre for Research and Development under the 13th Polish-Taiwanese call for proposals, scientists will use two different observation methods.
The first is GNSS radio occultation. A receiver on a low-Earth-orbit satellite observes signals transmitted by navigation satellites as they pass through the atmosphere. This makes it possible to reconstruct the atmosphere’s structure at different altitudes and obtain information on parameters including temperature, pressure and humidity.
“A major advantage of radio occultation is the possibility of conducting observations virtually anywhere in the world, also over oceans, where the number of conventional meteorological stations is limited. However, the method has a weakness: data obtained from the lowest layers of the atmosphere may contain systematic errors; therefore, ground-based GNSS observations will serve as a second data source,” Trzcina said.
The second source of data will be ground-based GNSS observations and the TOMO2 tropospheric tomography model, which is being developed at the Wrocław university’s Institute of Geodesy and Geoinformatics.
Combining the two techniques is a key element of the project. By comparing the two types of data, researchers aim to identify and reduce errors in radio occultation profiles in the lower atmosphere.
Methods including interpolation, regression models and machine learning will be used to develop correction techniques. But the goal goes beyond improving the measurements themselves. The corrected profiles will ultimately be assimilated into the WRF weather model to determine whether more accurate humidity data can lead to more precise forecasts.
“We aim to do more than just develop a new method for atmospheric observation. It is also crucial to test it against real-world cases of severe weather events and answer whether better humidity data translate into better forecasts,” Trzcina said.
The project brings together researchers specialising in different atmospheric observation methods. The team from the Wrocław University of Environmental and Life Sciences includes Trzcina, Professor Witold Rohm and Paweł Hordyniec, PhD, whose work focuses primarily on ground-based GNSS observations, tropospheric tomography and GNSS radio occultation. (PAP)
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