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Climate observations from aircraft are being used to improve the quality of weather forecasts for the first time since 2022.
Forecasts are made by collecting data about the current state of the atmosphere from a variety of sources including satellites, weather stations and previously planes.
‘Mode-S’ aircraft observations were formerly incorporated into the data used by the European Centre for Medium-Range Weather Forecasts (ECMWF) to improve the accuracy of forecasts. The body is one of the most important sources of information for meteorologists in weather services.
Aircraft observations of wind and temperature can provide key insights into the Earth’s weather patterns, and were second only to satellite data in their usage by ECMWF. For example, they include the speed of the aircraft relative to the air. From that, with positions of the aircraft a few minutes apart, the wind can be determined.
But the data is derived from air traffic control databases that is not intended for meteorological use. To make it beneficial, ECMWF needed to process it so that weather services could use it in their predictions.
The Mode-S data sets were first incorporated in July 2020 when flight volumes were at historical lows due to the Covid-19 pandemic. But by November 2022, the major rebound in flying activity was causing a rapid increase in data volumes, which overwhelmed the systems used and required the development of mechanisms to control data density.
According to the International Civil Aviation Organization, in 2022 passenger numbers for flights increased 47% over 2021, taking overall recovery to 74% of pre-pandemic levels.
Routine monitoring in the wake of the pandemic showed that, in parts of Europe, using a large number of Mode-S observations led to particularly large deviations of the wind speed analysis from observations. This led to doubts within ECMWF about the continued utility of the data sets.
A new system was introduced last November – after not using any Mode-S data for 12 months – that includes a new method of thinning the data.
“In the previous system, individual aircraft tracks were considered and time-thinning was applied to them,” ECMWF scientist Bruce Ingleby said. “This led to too much data overall. The new system uses ‘box thinning’: the atmosphere is divided into boxes, and just one aircraft report is used for each box.”
The team have found that the impact of using a smaller number of Mode-S observations with the new thinning method is beneficial when compared against using no Mode-S data.
“This example shows the importance of constant vigilance when monitoring the global observing system. Not just the quality of observations but also data numbers are having an impact upon the analysis and forecasts,” Ingleby added. “In this case, there was nothing wrong with the observations – we were simply using too many of them.”
