Over the last 24 hours, many European cities have recorded very high atmospheric (or barometric) pressures.
In Belgium, atmospheric pressure reached 1048,3 hPa (hectoPascal), a new record. The previous record was set 88 years ago, in January 1932 (1048,0 hPa).
Atmospheric pressure is usually corrected to Mean Sea Level (MSL). As such, it is known in the world of aviation as ‘QNH’. Otherwise, atmospheric pressure at an aerodrome itself is known as ‘QFE’.
QNH is used by pilots and air traffic control (ATC). Why is this so important, you may ask? Well, pilots need to have the correct QNH of any given aerodrome to set an aircraft’s altimeter so the altimeter will give a correct readout of the altitude of an aircraft above mean sea level within a certain region.
Because it is so important for pilots to know the QNH of the airport he is flying from or flying to, the QNH is – for instance – reported in an aerodromes’ weather report known as METAR. This report is updated every thirty minutes. Here is one of today’s METAR reports for Brussels Airport (EBBR):
EBBR 200650Z 17001KT 0200 R25L/0700N R25R/0900N R01/0600N FG BKN001 01/01 Q1048 TEMPO 0100 FG
This METAR was reported at 20 January (2020) at 0650Z or 07:50 CET (hence the ‘200650Z‘). Note the ‘Q1048‘, meaning that the airport reports a QNH of 1048 hPa.
When an aircraft takes off from a certain aerodrome or airport and climbs out to a higher altitude, it may reach a ‘transition altitude’. Above this transition altitude, aircraft pilots will be asked to set their altimeter to 1013 hPa. As such, the altimeter may not give a 100% correct readout of an aircraft’s real altitude above mean sea level, but every aircraft flying above the transition altitude will be using the same barometric setting and, as such, each aircraft flying at an indicated altitude of e.g. FL150 will indeed be flying at the exact same altitude.
In Belgium, the transition altitude is 4,500 feet. In the United States and Canada, the transition altitude is 18,000 feet.
A (very) high atmospheric pressure of 1048 hPa (or even 1050 hPa as recorded in some weather stations in the United Kingdom) has no real consequences to humans. It means that the pressure of the column of air in the atmosphere above our head is much higher than normal (1013 hPa) but we don’t feel any real change. In general, such high pressures only occur during winter months and bring quiet, steady weather and (often) a windless, foggy day. This was the case in Brussels Airport, where most of the day the sky was (very) foggy and the cloud ceiling was low.
— ClearOfCloud (@clearofcloud) January 19, 2020
Two flights in two days for the first time in weeks. It was pretty clear despite a very high QNH of 1046 on the south coast. pic.twitter.com/Ng4Ezpn4ss
— *#3ńry? (@LRD90) January 19, 2020
Quite possibly the highest QNH I’ve seen! pic.twitter.com/NydZjDu5NK
— Jai Dillon (@jaidillon) January 19, 2020
One for the #avgeeks – do you remember a higher pressure than this? EGLL 192020Z AUTO 31003KT 9999 NCD 03/01 Q1049 NOSIG
— EUROCONTROL (@eurocontrol) January 20, 2020
20 January 2020