Geoscience Reference
In-Depth Information
basis of TOMS AI, Engelstaedter and Washington (2007a)
show that the onset of dustiness at key hotspots corre-
sponds with the northward passage of near-surface conver-
gence and may be explained by wind gustiness rather than
the mean wind (Engelstaedter and Washington, 2007b).
Based on aircraft observations from a flight made during
the Geostationary Earth Radiation Budget Intercompari-
son of Longwave and Shortwave Radiation (GERBILS)
field campaign (June 2007), Marsham
et al.
(2008) show
significant dust uplift into southward-propagating cold
pool outflows of the monsoon flow immediately south
of the intertropical discontinuity in the western Sahara.
They argue that the asymmetry in the seasonal dust cy-
cle is closely related to the downdraft convective avail-
able potential energy (DCAPE) from convective storms
since there is both more dust and more DCAPE during
monsoon onset than during retreat. Using 3 hourly data
from the Meteosat second generation (MSG) spinning
enhanced visible and infrared imager (SEVIRI), giving
infrared dust index images from March 2006 to Febru-
ary 2008, Schepanski
et al.
(2009) have identified source
regions over the SEQ that differ substantially from the
TOMS AI-based source regions (Figure 20.11). On the
basis of peak dust production between 0600 and 0900
hours, Schepanski
et al.
(2009) argue that the mixing
of the low-level jet is a major factor in causing dust
entrainment.
A notable absence in the understanding of dust produc-
tion from the SEQ is any ground-based geomorphic or
meteorological observations that would help to constrain
the explanation of dust production in this key region. The
impression from satellite data is that numerous diffuse
(a)
(b)
- 0
-10
0 0 0 0 0 0
- 0
-10
0 0 0 0 0 0
40
40
40
40
35
30
25
35
30
25
35
30
25
35
30
25
20
20
20
20
15
15
15
10
15
10
10
5
0
10
5
0
5
0
5
0
-10
0
10
20
30
40
-10
0
10
20
30
40
BMDI dust obs. (days)
Deep Blue aerosol obs. (days)
0.0
100.0
200.0
300.0
0.0
100.0
200.0
300.0
(c)
(d)
- 0
-10
0 0 0 0 0 0
- 0
-10
0 0 0 0 0 0
40
40
40
40
35
35
35
35
30
25
30
25
30
25
30
25
20
20
20
20
15
10
5
0
15
10
15
10
5
0
15
10
5
0
5
0
-10
0
10
20
30
40
-10
0
10
20
30
40
AI aerosol obs. (days)
BMDI obs. - Deep Blue obs. (days)
0.0
100.0
200.0
300.0
0.0
100.0
200.0
300.0
