Geoscience Reference
In-Depth Information
dust scenario in Ref. 14, and can be represented by the following analytic
formulae:
τ
∗
(
L
s
)=0
.
05 +
τ
max
−
0
.
05
[1 + tanh
{
(
L
s
−
L
s0
)
α
}
] or
L
s
<L
s1
,
2
(1)
β
τ
∗
(
L
s
)=0
.
05 + (
τ
max
−
0
.
05)
{
cos((
L
s
−
L
s1
)
/
2)
}
for
L
s
≥
L
s1
,
where
τ
∗
(
L
s
) denotes the infrared (9-10
µ
m) dust opacity at 7 hPa calcu-
lated at the equator, south, and north poles as
τ
eq
,
τ
S
,and
τ
N
, respectively.
The factor
τ
max
is the maximum opacity in each region,
L
s0
is the aerocen-
tric longitude at the time of the most intense dust storm,
L
s1
is the aero-
centric longitude for the time when the dust opacity begins to decrease, and
α
and
β
are the rates of the opacity increase and decrease, correspondingly.
These factors are presented in Table 1. The optical depth at all latitudes
φ, τ
(
φ, L
s
), is then prescribed as follows:
τ
(
φ, L
s
)=
τ
N
+
τ
eq
−
τ
N
1 + tanh[5(45
◦
−
{
φ
)]
}
,
φ>
0
,
2
(2)
τ
(
φ, L
s
)=
τ
S
+
τ
eq
−
τ
S
1 + sin[2(45
◦
+
φ
)]
{
}
,
φ<
0
.
2
The vertical distribution of the dust mixing ratio
Q
is given by the follow-
ing formulae, in accordance with those adopted by LMD-AOPP Martian
AGCMs.
9
,
18
Q
=
Q
0
exp
0
.
007
1
70
/z
max
,
p
0
p
−
(3)
160
◦
)
22 sin
2
φ,
z
max
(
φ, L
s
)=60+18sin(
L
s
−
−
where
z
max
is the cut-off altitude of the dust [km],
p
the pressure,
p
0
the
standard pressure (7 hPa), and
Q
and
Q
0
are the dust mixing ratios at the
levels
p
and
p
0
, respectively.
Table 1. Values of the factors used in Eq. (1) for prescribing the
time-latitude profiles (from Ref. 14).
N
,EQ,and
S
correspond
to the factors for calculating
τ
N
,
τ
eq
,and
τ
S
, respectively.
N
EQ
S
τ
max
0.1
0.7
1.0
210
◦
190
◦
192
◦
L
s0
230
◦
205
◦
205
◦
L
s1
α
10
18
22
β
20
20
15
