Atmospheric Boundary Layer: Concepts and Measurements
23
(temperature and humidity) are the same and due to the same eddies, the height of
the CBL derived from both profi les should match. For the structure of the SBL, the
tethered balloon (Figure 2.8) is the suitable device as it measures the same climatic
variables (horizontal winds, temperature, humidity, and pressure) but its ascension
rate is very low (around 1 m/s). During the lift, the detailed structure of the SBL can
be measured. It should be emphasized that the rawinsoundings is not a suitable device
to carefully measure the structure of the SBL. Figure 2.9 shows the profi le of potential
temperature made at a tropical forest during the LBA TRMM experiment (see Fisch
et al., 2004) for soundings at 6:00, 7:00, and 8:00 LT (local time). The sunrise is at 6:30
LT. The profi les at 6:00 and 7:00 LT are almost the same; the difference in the thermal
structure can be seen only very close to the surface. For the profi le at 8:00 LT (about
1:30 h after the sunrise), the lower structure (up to 220 m in depth) has been heated by
the sensible heat fl uxes from the surface. The erosion of SBL is an important issue for
air quality problems because the pollutants released during the night are trapped by
the SBL and its dispersion will depend on how fast this SBL will be eroded at early
morning. This is an issue that is being investigated by the scientists.
During the last two decades, different techniques to measure both CBL and SBL
have been developed, especially using the remote-sensing technique. The new sensors, which are both based on transmitting a sound (SODAR) and light (LIDAR) wave
308
0
500
1000
1500
2000
2500
3000
3500
4000
4500
310
(a)
(b)
312
314
θ (K)
Height (m)
316
318
0
0
500
1000
1500
2000
2500
3000
3500
4000
4500
2
4
6
Specific humidity (g/kg)
Height (m)
8
1 0
1 2
1 4
FIGURE 2.7 The development of the CBL using rawinsounding dataset.
© 2010 by Taylor and Francis Group, LLC
23
(temperature and humidity) are the same and due to the same eddies, the height of
the CBL derived from both profi les should match. For the structure of the SBL, the
tethered balloon (Figure 2.8) is the suitable device as it measures the same climatic
variables (horizontal winds, temperature, humidity, and pressure) but its ascension
rate is very low (around 1 m/s). During the lift, the detailed structure of the SBL can
be measured. It should be emphasized that the rawinsoundings is not a suitable device
to carefully measure the structure of the SBL. Figure 2.9 shows the profi le of potential
temperature made at a tropical forest during the LBA TRMM experiment (see Fisch
et al., 2004) for soundings at 6:00, 7:00, and 8:00 LT (local time). The sunrise is at 6:30
LT. The profi les at 6:00 and 7:00 LT are almost the same; the difference in the thermal
structure can be seen only very close to the surface. For the profi le at 8:00 LT (about
1:30 h after the sunrise), the lower structure (up to 220 m in depth) has been heated by
the sensible heat fl uxes from the surface. The erosion of SBL is an important issue for
air quality problems because the pollutants released during the night are trapped by
the SBL and its dispersion will depend on how fast this SBL will be eroded at early
morning. This is an issue that is being investigated by the scientists.
During the last two decades, different techniques to measure both CBL and SBL
have been developed, especially using the remote-sensing technique. The new sensors, which are both based on transmitting a sound (SODAR) and light (LIDAR) wave
308
0
500
1000
1500
2000
2500
3000
3500
4000
4500
310
(a)
(b)
312
314
θ (K)
Height (m)
316
318
0
0
500
1000
1500
2000
2500
3000
3500
4000
4500
2
4
6
Specific humidity (g/kg)
Height (m)
8
1 0
1 2
1 4
FIGURE 2.7 The development of the CBL using rawinsounding dataset.
© 2010 by Taylor and Francis Group, LLC