Applications - Surface Based Remote Sensing of the Atmospheric Boundary Layer - page 131

on oil drilling platforms have been made. First texts with a wind LIDAR have been
made on the FINO1 platform in the German bight (Kindler et al. 2007 ).
The land-sea contrast in thermal surface properties leads to the evolution of a
diurnal boundary layer wind system. Due to its importance for coastal meteorol-
ogy and air quality, the land-sea breeze system is a frequently studied phenomenon
(Banta et al. 1993 ). Different remote-sensing techniques allow for the analysis of
the wind speed and the aerosol distribution in the air layers involved in this circula-
tion system. Skakalova et al. ( 2003 ) used an aerosol LIDAR to detect the different
aerosol contents in the onshore and offshore flows at the Black Sea coast. While Fig.
2.9 shows the well-developed land breeze and sea breeze circulations, the results
from Skakalova et al. ( 2003 ) give insight in the transition from a land breeze to
a sea breeze system. They find a new layer evolving near the ground propagating
inland, an old layer from the preceding land breeze regime, and an intermediate
layer, which has the lowest aerosol extinction, in between the other two layers. The
intermediate layer vanishes when the sea breeze is fully developed.
Banta et al. ( 1993 ) employed a Doppler LIDAR to detect the horizontal and
vertical structure of the wind field of a growing sea breeze layer. Like the aerosol
data from Skakalova et al. ( 2003 ), these wind data show the beginnings of the sea
breeze underneath the pre-existing offshore synoptic flow at the coast and the sub-
sequent growth of the sea breeze layer horizontally and vertically. Sometimes a dual
structure to the sea breeze flow in its early formative stages was found. Initially, a
shallow (less than 500 m) sea breeze formed that later became embedded in a weaker
onshore flow that was about 1 km deep. Eventually, these two flows blended together
to form a mature sea breeze about 1 km deep. Darby et al. ( 2002b ) compared
these Doppler LIDAR wind measurements with numerical simulations. Regional
Atmospheric Modeling System (RAMS) two-dimensional simulations successfully
simulated the dual structure of the sea-breeze flow when both the coastal mountain
range just east of Monterey Bay and the Sierra Nevada range, peaking 300 km east
of the shore, were included in the domain.
4.5.4 Flow in Mountainous Terrain, Valley, and Mountain Breeze
The most complex features of atmospheric boundary layers may be found in moun-
tainous terrain. The ABL structure over mountainous terrain is important for local
circulations, cloud formation, boundary layer-free troposphere exchange, and air
quality. ABL features in mountainous terrain may be due to mechanical forcing
of the flow or due to thermal forcing. Sometimes both triggering phenomena act
together. We start in this subsection with mainly mechanically induced ABL fea-
tures, while thermally induced features are addressed in the following subchapter.
Amongst the mechanically induced phenomena are such features as valley boundary
layers, channelling of the flow along the valley axis, speed up of flow over hills and
crestlines, flow through gaps, or foehn flows crossing entire mountain ranges.
Figure 4.37 shows SODAR measurements of vertical profiles of the horizontal
wind speed in a narrow north-south-oriented Alpine valley at the northern fringe of