Exploration of the atmospheric lower layer thermal turbulences by means ofmicrothermocouples

The experiments on the propagation of acoustic air waves in the low atmosph eric layer show a large influence of aerological parameters. In particular, there were only few measurements carried out outdoors to approach thermal turbulent values [I]. There are many thermal sensors ranging from a simple platinum resistance to quartz crystal. Each technology has some advantages depending on the type of measurement one intends to perform. To explore the earth boundary layer, we chose a micro-thermocouple of type S. Its small s ize (1.27 mu m) allows us to obtain a low calorific capacity and a high the rmal conductance. On the other hand, its sensitivity is low and it was nece ssary to associate an amplifier with a gain of 100 000. The whole device wa s set outside on a bar 2 m above the ground. The different experiments carr ied out with one or several microthermocouples showed very small turbulence s of different types depending on the role of the different layers in the l ow atmosphere. They also enabled to visualize convection due to the ground or due to the wind as a function of time.