Meteorological measurements taken from aircraft have plummeted by an average 75-80% compared to normal, but with very large regional variations; in the southern hemisphere, the loss is closer to 90%. Surface-based weather observations are in decline, especially in Africa and parts of Central and South America where many stations are manual rather than automatic.
 
WMO’s Global Observing System serves as a backbone for all weather and climate services and products provided by the 193 WMO Member states and territories to their citizens. It provides observations on the state of the atmosphere and ocean surface from land-, marine- and space-based instruments. This data is used for the preparation of weather analyses, forecasts, advisories and warnings.
 
“National Meteorological and Hydrological Services continue to perform their essential 24/7 functions but are facing increasingly severe challenges as a result of the Coronavirus pandemic, especially in developing countries” said WMO Secretary-General Petteri Taalas. “We salute their dedication to protecting lives and property but we are concerned about the increasing constraints on capacity and resources,” he said.
 
“The impacts of climate change and growing amount of weather-related disasters continue, as we have seen with Tropical Cyclone Harold in the Pacific, and the floods in East Africa. As we approach the Atlantic hurricane season, the COVID-19 pandemic poses an additional challenge, and may exacerbate multi-hazard risks at a single country level. Therefore it is essential that governments pay attention to  their national early warning and weather observing capacities,” said Mr Taalas.
 
Large parts of the observing system, for instance its satellite components and many ground-based observing networks, are either partly or fully automated. They are therefore expected to continue functioning without significant degradation for several weeks, in some cases even longer. But if the pandemic is prolonged, then missing repair, maintenance and supply work, and missing redeployments will become of increasing concern.
 
Meteorological data from aircraft
 
Commercial airliners contribute to the WMO Aircraft Meteorological Data Relay programme (AMDAR), which uses onboard sensors, computers and communications systems to automatically collect, process, format and transmit meteorological observations to ground stations via satellite or radio links.
 
The AMDAR observing system produces over 800 000 high-quality observations per day of air temperature and wind speed and direction, together with the required positional and temporal information, and with an increasing number of humidity and turbulence measurements being made. Currently 43 airlines and several thousand aircraft contribute to the AMDAR programme, which is expected to be significantly expanded in the coming years as a result of a joint collaboration on the programme with IATA.

Overall, the decrease in the number of commercial flights has resulted in a reduction of around 75-80 percent in observations of meteorological measurements from aircraft platforms. The loss is closer to 90% in some of the most vulnerable areas where other surface-based observations are scarce, i.e. in the tropics and in the Southern Hemisphere.
 
Some countries are launching extra radiosondes to partly mitigate the loss of aircraft data. This is taking place especially in Europe under coordination by the European Meteorological Services Network (EUMETNET). Radiosondes are flown on weather balloons and transmit measurements critical meteorological variables back to the ground during their flight from the surface up to altitudes of 20 to 30 kilometers.
  
Additionally, WMO, EUMETNET and national AMDAR programme partners have collaborated with the avionics company FLYHT to ensure any available additional aircraft observations from their own network of airlines are made available during the COVID-19 emergency period to WMO and its members.

Surface-based observations
 
In most developed countries, surface-based weather observations are now almost fully automated.
However, in many developing countries, the transition to automated observations is still in progress, and the meteorological community still relies on observations taken manually by weather observers and transmitted into the international networks for use in global weather and climate models.
 
“These human links in the observation and data delivery chain are highly vulnerable to current lockdowns and mandatory teleworking policies, and we have seen a substantial reduction in the current availability of surface pressure observations compared to the pre-COVID-19 baseline (January 2020), especially over Africa and parts of Central and South America,” said Lars Peter Riishojgaard, Director, Earth System Branch in WMO’s Infrastructure Department.
 
“The coronavirus pandemic clearly demonstrates the importance of having resilience in the observing system,” said Mr Riishojgaard.
 
“The overall impact of the missing observations probably will not be fully assessed and understood until well after the virus outbreak is over. However, at this point, none of the global Numerical Weather Prediction (NWP) centres have reported catastrophic losses in skill due to the lack of observations,” he said.
 
“Aircraft observations are a good illustration of this. They are universally considered to be among the most important contributors to NWP skill. However, the current crisis reminds us that aircraft observations are data of opportunity that may come and go due to circumstances that are beyond any control of the WMO community. Having complementary systems and maintaining the possibility to mitigate such losses will be important also once the COVID-19 crisis belongs to history, hopefully in the not too distant future,” said Mr Riishojgaard.

Marine Observations

WMO is also monitoring the exchange of observations from the marine observing systems, which provide critical information from the 2/3 of the earth’s surface that are covered by the oceans.
 
The ocean observing systems also rely on a high degree of automation, and most parts are expected to continue to be working well for a period of up to several months. However, drifters and floats will need to be redeployed, moorings will need to be serviced and ship observing systems will need to be maintained, calibrated and resupplied. Over time a gradual decline in observation numbers may therefore be expected, and this will continue until the necessary supply and maintenance activities can resume. At this point, the most significant impact is on the Voluntary Observing Ships (VOS) program, where a reduction in data availability of about 20% compared to normal levels is seen.
 
Space-based observations
 
On a positive note, the present situation demonstrates the importance and stability of the space-based observing system component, on which WMO Member are increasingly relying. Currently, there are 30 meteorological and 200 research satellites, providing continuous, highly automated observations. The satellites are operated by members of the Coordination Group for Meteorological Satellites (CGMS) and of the Committee on Earth Observation Satellites (CEOS). While in the short run the space-based observing system component is expected to remain unaffected and fully operational, WMO is in contact with meteorological satellite operators to assess the possible long-term impact of COVID-19.
 
In addition, there are over 10 000 manned and automatic surface weather stations, 1 000 upper-air stations, 7 000 ships, 100 moored and 1 000 drifting buoys, hundreds of weather radars and 3 000 specially equipped commercial aircraft measure key parameters of the atmosphere, land and ocean surface every day.