Fri. Apr 3rd, 2020

Coronavirus affects weather predictions: why do they lose reliability?

The global pandemic caused by the coronavirus, already widespread throughout the planet except Antarctica, is also causing changes in the weather and indirectly affects predictions as a result of restrictions on air traffic, since planes collect data from the atmosphere, as warned by the European Center for Medium Range Weather Predictions (ECMWF).

This is the reference model that is used in Europe and that, according to the Meteored meteorological portal, HRES-IFS (ECMWF), is indirectly affected by the coronavirus since meteorological data and observations have been reduced by 65 percents that the planes pick up in their transit between the United States and Europe, due to the restrictions established between both continents by the pandemic.

The ECMWF admits that airplane-based observations for weather forecast centers have been reduced and that these observations, along with others, are those used to estimate the state of the Earth’s system. In fact, the agency points out that the reports of the aircraft are only surpassed by the data from the satellites.

Despite the lack of data, he trusts that recently added satellite wind observations will help mitigate the drop in the number of aircraft-based observations.

On March 23, the number of aircraft reports about Europe received and used decreased by 65 percent compared to March 3, when the air restrictions were not yet in force. In addition, globally the reduction was 42 percent between March 23 and March 3.

Likewise, it also sees a general reduction in reporting density between March 2 and March 23, particularly in Italy and parts of eastern Europe, according to Eumetnet data.

Precisely, he points out that the United States airlines provide many reports, especially on its territory, while the programs and reports of the European planes, coordinated by EUMETNET, were “particularly affected last week” although he also points out that “other programs have decreased substantially in the last days ”, according to the European center ECMWF.

Meteorologists point out that COVID-19 can continue in summer

EUETNET Abo Program Manager Steve Stringer further warns that the latest information available from airlines suggests that European AMDAR coverage will be reduced by 65 per “or more over the next month, which is currently expected to continue through the summer. ” Data reduction and geographic coverage could be reduced in the coming weeks in other areas of the world.

From the United States National Oceanic and Atmospheric Administration (NOAA), Christopher Hill warns that they are “anticipating a substantial reduction in the availability of US AMDAR data.” “To continue in the coming weeks, which will probably generate some measure of impact on the production of our numerical climate prediction systems,” he adds.

Along the same lines, the Australian AMDAR program could be affected because a significant change is expected “soon”, since Qantas airline has suspended “all” international flights since the end of this month and is reducing domestic flights in Australia by a 60 percent, according to Douglas Body of the Australian Bureau of Meteorology (BoM).

Thus, the European center is confident that “a small proportion” of the reports of cargo aircraft, whose flights are less affected than those of passengers, will be saved. Regarding the impact of aircraft observations, ECMWF analyzed forecasts without using aircraft reports but with all the other data to study the state of the Earth’s system, compared to those that do include aerial data.

Precisely, the greatest impacts on the forecasts are centered on the predictions at around 250-200 hPa, that is, at approximately 11 or 12 kilometers above sea level.

In addition, geographically, the greatest impacts are in the northern hemisphere, according to the European Center for Long-term Prediction ECMWF, which states that significant differences can be given at the 95 percent confidence level at the statistical level.

In this line, he adds that the greatest impacts are in the range of up to 24 hours ahead, but a significant impact is observed in the forecasts up to 7 days in advance. In fact, 12-hour temperature forecasts in the northern hemisphere are more than 9 percent worse.

ECMWF scientist Bruce Ingleby has stated that the removal of half of the aircraft reports is expected to produce “slightly less than half the impact of the removal of all aircraft.”

For the ECMWF, these sensitivity studies demonstrate that deleting all aircraft data degrades short-range wind and temperature forecasts by up to 15 percent at those levels, with significant degradations in all forecast ranges of up to seven days. .

There is a minor, but still statistically significant, impact on near-surface fields, up to 3 percent on surface pressure. However, he is confident that other observations will be less affected and that some additional radiosondes can be launched to mitigate the lack of aircraft data.

For its part, from the weather portal Meteored, highlight the importance of these data, which represent 13 percent of the total used by the ECMWF for their computers to perform mathematical calculations to make predictions.

Finally, Meteored warns that it is “foreseeable” that in the coming weeks it will be even more noticeable, as more flights in Europe and around the world are canceled. Ep


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