Geoscience Reference
In-Depth Information
Table 1. Total number of days dust was reported each year in the period 1995 to
February 2005.
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
Feb 2005
ocal
——1
—3
1
1
4
2
— —
Long-range
1
1
—
—
—
1
1
26
11
1
1
dust transport was long-range and 12 days on which dust transport was
local (Table 1).
Note that in the spring months of September-November 2002, dust was
reported on a total of 30 days, comprising four local dust transport days
and 26 long-range dust transport days. Without strong synoptic scale low-
level winds, the decadal total of 12 local dust storms contained 8 days dur-
ing which convective gusts were the likely cause. Of the remaining four,
three were from localized wind storms near Whyalla and Adelaide in South
Australia (SA) and one was from a dry, continental southeast wind surge
in tropical Queensland (QLD). Hereafter, we focus only on the long-range
dust storms, all 43 of which are associated in some way with the passage
of a cold front. When these 43 cases were further classified synoptically, 24
were from cold fronts that were linked to zonal westerlies or low-pressure
systems in the Great Australian Bight (GAB). The remaining 19 were post-
frontal, being the result of high pressure systems in the GAB that became
established after the passage of frontal systems. The first group typically is
characterized by pre-frontal northwest winds and west to southwest winds
over central eastern Australia in the immediate post-frontal air, while the
second group is typically characterized by post-frontal south to southeast
winds in the immediate post-frontal air. The low-level temperature inver-
sion in the post-frontal air contributes to the concentration of dust particles
near the surface and hence a reduction in visibility over a one to several
days after the passage of the cold front. Such an inversion was present in
8 days out of the 43. These eight cases fall into the second or post-frontal
southerly wind group just defined.
The main frontal characteristic within the long-range dust transport
category is the length and longevity of the cold front's path. Some frontal
systems moved east more quickly and cleared the east Australian coast, a
distance of several thousand kilometres, while others moved slowly, typically
either stalling or weakening over eastern Australia. The depth of the mixed
layer on dust reporting days was estimated from the nearest radiosonde sta-
tions. Observations of vertical temperature and wind observations typically
