Atmospheric boundary layer exacerbated mega heat waves

Apr 21, 2014 by Dr.ir. Aj (Ryan) Teuling
Vegetation on dry soils, such as in this picture from Australia, have limited water available for evaporation. Because of reduced evaporation, heat can accumulate in the lowest part of the atmosphere, the so-called boundary layer. Through this process, extreme heatwaves can occur during drought conditions in regions that are normally humid.

The extreme nature of the heat waves of 2003 in Western Europe and of 2010 in Russia and Eastern Europe even surprised scientists at the time. NWO Veni researcher Ryan Teuling from Wageningen University says that the extreme temperatures can be explained by the interaction between dry soils with the atmospheric boundary layer - the lowest part of the atmosphere. The role of this boundary layer has received too little attention in studies using existing weather models, he claims in Nature Geoscience.

The mega of August 2003 in Western Europe broke various temperature records at the time, with temperatures of 40°C in France. The economic damage was estimated at between five and ten billion euros, due to forest fires, air pollution and loss of agricultural productivity . In Paris alone, thousands died as a consequence of the high temperatures. Researchers were unfamiliar with such heat waves in Europe and thought that it was a one-off, exceptional event. At least that was the case until 2010 when new records were set, this time in Eastern Europe and Russia.

Atmospheric boundary layer

In case of an atmospheric blocking situation, soil desiccation and a build-up of heat in the atmospheric all occur at the same time, then exceptional heat waves are possible. That is the conclusion of Dr Ryan Teuling, assistant professor in hydrology and quantitative water management in Wageningen. The unusual atmospheric situation had previously been demonstrated to be the most important cause of the two heat waves. A high-pressure area blocked the penetration of low-pressure areas with colder air and wind. The researchers demonstrated that for both heat waves the same developments in the boundary layer conditions occurred in combination with an enhanced interaction between soil desiccation and heat accumulation in the atmospheric boundary layer. This lowest part of the troposphere is several tens to hundreds of metres thick at night, and up to several kilometres thick during the day.

Atmospheric boundary layer exacerbated mega heat waves

Over a period of several days to several weeks heat was built up in an increasingly thicker atmospheric boundary layer, helped by heat convection from more southerly situated warm areas. During this period the soil dried out even further , leading to a reduced cooling effect of water evaporation from the surface. This process was enhanced by the . Due to cooling at night, the warm air layer became decoupled from the earth's surface, as a result of which the heat of the following day could lead to increasingly higher temperatures. The blanket of warm air above the earth's surface became increasingly thicker during the heat wave.

45 degrees Celsius

Teuling: 'With this new knowledge we can make predictions about possible temperatures during heat waves. Temperatures that gradually build up to 40°C are indeed possible in this part of the world. However, sudden rises to 45°C as occurred during heat waves in, for example, Melbourne are unlikely here. Therefore the distance to the Equator and to large desert areas is too great.'

The researchers made use of satellite data and measurements from weather balloons of the situation in France in 2003 and Russia in 2010. They combined these data with a coupled soil-water-atmosphere model.

Explore further: Future heat waves pose risk for population of Greater London

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User comments : 2

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antigoracle
1 / 5 (5) Apr 23, 2014
So much for the CO2 lie.
runrig
5 / 5 (4) Apr 27, 2014
Ignoring Anti, as all that he deserves.

Just read this ... and what do I discover...........
The standard description of how heat-waves develop over land at distance from seas/lakes, in stagnant HP conditions as soils dry out.
The "boundary layer" thing again is just a description of how heat is managed by the atmosphere with regard to an ELR/DALR and surface inversion overnight and a rapid reheating of that cooler layer beneath the sun the next day. The extra heat that day rises with convection (dry - so no/little cloud) and the process starts again the next day with the inversion "nose" at a slightly higher temp and consequently a higher temp is needed for convection to pass that nose.
I suggest they ask Meteorologists what the process is and not re-invent the science again and say it's exceptional.
It is of course modulated by AGW - in that with a more "sluggish" jet, then these set-ups will last longer and the heat build up last longer.
Not Earth shattering.
just Meteorology.