103
Thermal Radiation and Energy Closure Assessment
originating far beyond the local surface. This has implications for interpreting the
LE and H fluxes during periods of intense wind speed and substantial instability. The
asymptote for the LE fluxes occurs around 0.0004, which is approximately 42 min
substantially less than for H.
Figure 5.9 shows computed H and LE fluxes for 27 July, 0900–2300 h, computed
as 5- (Figure 5.9a) and 30-min (Figure 5.9b) averages. Normally, 5-min averages
are considered too short of a time period to compute a valid flux. However, what is
interesting is that, for both H and LE, the general diurnal trend, as well as the major
flux peaks, is clearly present as observed in the 30-min average fluxes. This suggests
that, under the conditions in this study, with large available energy, strong winds,
and advection, shorter averaging times for the EC data produce essentially the same
fluxes as those with a longer averaging period (30 min), suggesting that these conditions represent a well-coupled surface–boundary layer capturing the dominant features of turbulent flux exchanges as well as individual bursts of flux exchange readily
observed in the 5-min averages. Note that the bursts are oscillatory—high one
moment, low another—indicating the numerous spatially and temporally variable
0
100
200
300
400
500
600
LE (W m –2
)
LE (W m –2
)
–100
–50
0
50
100
150
9:00
9:40
10:20
11:00
11:40
12:20
13:00
13:40
14:20
15:00
15:40
16:20
17:00
17:40
18:20
19:00
19:40
20:20
21:00
21:40
22:20
23:00
23:40
9:00
9:40
10:20
11:00
11:40
12:20
13:00
13:40
14:20
15:00
15:40
16:20
17:00
17:40
18:20
19:00
19:40
20:20
21:00
21:40
22:20
23:00
23:40
H (W m –2
)
H (W m –2
)
(a) 5-min averages
0
100
200
300
400
500
600
July 27, 2008
–100
–80
–60
–40
–20
0
20
40
60
80
100
120
900 1100 1300 1500 1700 1900 2100 2300
900 1100 1300 1500 1700 1900 2100 2300
CST
CST
CST
CST
July 27, 2008
July 27, 2008
July 27, 2008
(b) 30-min averages
FIGURE 5.9 July 27, 2008, H and LE fluxes as averages of 5 (a) and 30 (b) min from 0900
to 2300 h.
Thermal Radiation and Energy Closure Assessment
originating far beyond the local surface. This has implications for interpreting the
LE and H fluxes during periods of intense wind speed and substantial instability. The
asymptote for the LE fluxes occurs around 0.0004, which is approximately 42 min
substantially less than for H.
Figure 5.9 shows computed H and LE fluxes for 27 July, 0900–2300 h, computed
as 5- (Figure 5.9a) and 30-min (Figure 5.9b) averages. Normally, 5-min averages
are considered too short of a time period to compute a valid flux. However, what is
interesting is that, for both H and LE, the general diurnal trend, as well as the major
flux peaks, is clearly present as observed in the 30-min average fluxes. This suggests
that, under the conditions in this study, with large available energy, strong winds,
and advection, shorter averaging times for the EC data produce essentially the same
fluxes as those with a longer averaging period (30 min), suggesting that these conditions represent a well-coupled surface–boundary layer capturing the dominant features of turbulent flux exchanges as well as individual bursts of flux exchange readily
observed in the 5-min averages. Note that the bursts are oscillatory—high one
moment, low another—indicating the numerous spatially and temporally variable
0
100
200
300
400
500
600
LE (W m –2
)
LE (W m –2
)
–100
–50
0
50
100
150
9:00
9:40
10:20
11:00
11:40
12:20
13:00
13:40
14:20
15:00
15:40
16:20
17:00
17:40
18:20
19:00
19:40
20:20
21:00
21:40
22:20
23:00
23:40
9:00
9:40
10:20
11:00
11:40
12:20
13:00
13:40
14:20
15:00
15:40
16:20
17:00
17:40
18:20
19:00
19:40
20:20
21:00
21:40
22:20
23:00
23:40
H (W m –2
)
H (W m –2
)
(a) 5-min averages
0
100
200
300
400
500
600
July 27, 2008
–100
–80
–60
–40
–20
0
20
40
60
80
100
120
900 1100 1300 1500 1700 1900 2100 2300
900 1100 1300 1500 1700 1900 2100 2300
CST
CST
CST
CST
July 27, 2008
July 27, 2008
July 27, 2008
(b) 30-min averages
FIGURE 5.9 July 27, 2008, H and LE fluxes as averages of 5 (a) and 30 (b) min from 0900
to 2300 h.