Rainer Roth

On wind shear at fronts and inversions

SummaryIn the past, experimental investigations as well as theoretical considerations have shown that within fronts and inversions wind shear and vertical temperature gradient adjust in such a way that the Richardson number is at its critical value. Results from aircraft measurements now suggest that the shear within moving cold fronts, warm fronts and inversions shows different behaviour because of the different mechanisms controlling the Richardson numbers. This leads to higher Richardson numbers, and therefore to lower amounts of wind shear within moving cold fronts when compared to warm fronts and inversions.

Errors in aircraft measurements of turbulent fluxes in a boundary layer with strong convection

Abstract During the field experiment EFEDA-91 in central Spain the turbulent fluxes of sensible and latent heat were measured by an aircraft and by surface stations. A comparison of surface measurements and turbulent flux values derived indirectly by simple linear extrapolation of the aircraft-measured fluxes to the surface, shows a general disagreement. Part of the difference can be explained by the aircraft ground speed variation in a convective boundary layer. A second topic is the development of a simple model for calculating aircraft speed under the given meteorological conditions. With this tool it is possible to give an estimation, whether an aircraft is suitable to flight with rigid altitude control in a boundary layer with strong convection.

On the influence of sensor inertia on the estimation of turbulent fluxes from aircraft measurements

If no correction is performed, the inertia of the sensors for temperature and humidity in research aircraft leads to an error in the calculation of turbulent fluxes. Simple considerations give an estimation of the order of magnitude of these errors. A simple method for the in-situ estimation of temperature sensor inertia is given.