Antarctic radar data improves forecasts for Southern Hemisphere atmospheric rivers in tests
Weather forecasts in the Southern Hemisphere (SH) are generally less accurate than those in the Northern Hemisphere because Antarctica and the surrounding Southern Ocean have relatively few weather observations. With limited information about atmospheric conditions in one of the world's most remote regions, forecasting models often struggle to predict the movement of weather systems. This is especially true for atmospheric rivers that can trigger heavy rain, snowfall, flooding and strong winds across Australia, New Zealand, South America and Antarctica. Improving forecasts of these weather systems is essential for protecting lives and property, supporting aviation and shipping, and helping communities prepare for hazardous weather.
To address this problem, researchers from Japan investigated whether continuous radar observations from Antarctica could improve weather forecasts across the SH. In a study published in the journal Scientific Reports , Assistant Professor Kazutoshi Sato of the National Institute of Polar Research (NIPR), Japan, and colleagues found that incorporating hourly wind observations from an Antarctic radar into a numerical weather prediction system could improve forecasts of atmospheric circulation and atmospheric rivers over the SH. His co-authors were Professor Jun Inoue and Associate Professor Yoshihiro Tomikawa of NIPR; Dr. Akira Yamazaki of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Japan; and Professor Kaoru Sato of The University of Tokyo, Japan.
"Observations from the Antarctic radar are not currently incorporated into operational numerical weather prediction systems. Our findings show that assimilating these observations can improve forecast accuracy, demonstrating the value of continuous radar measurements for weather forecasting," Kazutoshi Sato says.
Continuous winds from Syowa Station
The researchers used wind observations collected by the Program of the Antarctic Syowa Mesosphere–Stratosphere–Troposphere/Incoherent Scatter (MST/IS) Radar (PANSY) at Japan's Syowa Station in Antarctica. The PANSY radar continuously measures wind conditions in the atmosphere, providing observations much more frequently than weather balloons or radiosondes, which are routinely used for weather forecasting but cannot be launched frequently in Antarctica because of financial and operational constraints.
The team compared weather analyses and forecasts generated with and without assimilated PANSY radar observations during the 2022 austral winter. They used a data assimilation and forecasting system called " ALEDAS ," developed and managed by JAMSTEC on the Earth Simulator, JAMSTEC's supercomputer. Both experiments included enhanced radiosonde observations from the Year of Polar Prediction in the Southern Hemisphere (YOPP-SH) campaign and covered seven atmospheric river events over the midlatitudes of the SH, allowing the researchers to assess the added value of the Antarctic radar.
Sharper atmospheric river forecasts
The results showed that assimilating Antarctic radar observations improved the representation of atmospheric conditions, including wind speed, temperature and geopotential height, over Antarctica and the Southern Ocean in (re)analysis. The presence or absence of PANSY radar observations resulted in a difference of more than 30% in atmospheric river moisture transport.
These improvements persisted during the forecast period and enhanced predictions of atmospheric circulation and integrated water vapor associated with atmospheric rivers over the SH midlatitudes. Across all seven SH midlatitude atmospheric river cases examined, forecasts that included the radar observations showed lower prediction errors than those based only on conventional observations.
"Although radiosonde observations are routinely performed to improve weather forecasts, high-frequency launches are challenging in extremely cold environments. We therefore proposed a new method for improving forecast accuracy using instruments capable of continuous, high-temporal-resolution observations," Inoue explains.
Benefits beyond daily forecasts
The study also highlights the importance of strengthening weather observations in data-sparse regions. Because uncertainties in Antarctic atmospheric conditions can spread far beyond the polar continent, improving observations there can enhance forecasts across much of the SH. As weather prediction models continue to advance, integrating continuous observations from atmospheric radars and other emerging technologies could help make forecasts more reliable, benefiting disaster preparedness, transportation, scientific operations and communities affected by extreme weather.
Reanalysis datasets with large uncertainties are also widely used to estimate the Antarctic Ice Sheet surface mass balance under climate change. Assimilating PANSY radar observations may therefore improve our understanding of climate change.
