Applications - Surface Based Remote Sensing of the Atmospheric Boundary Layer - page 128

Fig. 4.34 SODAR wind profile measurements featuring a nocturnal low-level jet near Paris airport
Charles de Gaulle on June 26, 2005. Six subsequent half-hourly averaged profiles are shown. Lower
parts of the profiles are compared to theoretical curves (logarithmic wind profiles for different
stabilities)

sounding. Here, Fig. 4.34 shows an example measured with a SODAR. The phe-
nomenon, which must be described as an inertial oscillation due to the suddenly
waning frictional force at the onset of the night due to radiative cooling of the sur-
face, shows a wind speed maximum at about 300-350 m above ground. Such wind
maxima may be relevant for pollutant dispersion as well as for air traffic security or
wind energy conversion with tall wind turbines. Helmis ( 2007 ) observed low-level
jets at the top of a marine boundary layer and enhanced variance of the vertical wind
component with it from SODAR soundings. Further SODAR measurements of low-
level jets are reported in Kallistratova et al. ( 2009 ). Empirical distributions of the
maximum wind speed of these jets, the height of the jet core, and the wind turning
across these jets were obtained.
Reitebuch et al. (2000) have shown that nocturnal low-level jets may be respon-
sible for secondary nocturnal ozone concentration maxima near the ground. Their
SODAR measurements (see Fig. 4.35 ) for the first time proved from the obtained
time-height cross section of the variance of the vertical wind component, σ w , that

enhanced turbulence underneath the jet maximum takes place. This turbulence,
which is produced mechanically from the wind shear, is the reason for downward
turbulent transport of ozone from the residual layer towards the surface layer and
causes the secondary maximum in near-surface ozone concentration.
Influences of low-level jets on the data availability from RASS instruments have
already been discussed with Fig. 4.5 . Missing night-time RASS temperature data
above a stable nocturnal surface layer is a quite reliable indicator for the presence