Geoscience Reference
In-Depth Information
Flight 21.123 (Upleg) - Andøya, Norway
5 July 1999 - 23:36:30 U.T.
Aft-tip
Langmuir
probe
E
(50-4000 Hz)
53
MHz
Radar power
Aerosols 1-10 nm
Photometer
90
85
80
10
7
10
8
10
9
10
10
Density (m
23
)
10
11
0.0 0.1 0.2
Vol. Scattering
(Arb. Units)
(d)
20
40
dB
60
80
2
20
2
10 10 20
mV/m
0
0 50 100
Current (nA)
(a)
(b)
(c)
(e)
Figure 7.8
Composite measurements gathered on the upleg in the PMSE region. The
in situ data show raw electric fields (a), aft Langmuir probe density data (b), aerosol
measurements (c), and photometer data (d), which indicate the presence of a weak
NLC near 84 km. Panel (e) displays vertical backscatter power from the ALWIN radar.
[After Pfaff et al. (2001). Reproduced with permission of the American Geophysical
Union.]
the upper edge of the bite-out, small aerosols (1-10 nm) were detected while at
the lower edge the rocket-borne photometer revealed larger particles, presumably
an NLC layer. These data argue for a model in which initially small particles,
possibly nucleated by meteoric dust, grow by attaching water molecules, become
charged (leading to the bite-outs), and eventually become snow-like aerosols that
began to fall. They continue to fall and grow to be detected by the photometer
until just below the mesopause where they sublime and disappear. (The electric
field fluctuations in panel a are not yet understood but may indicate that either
ambipolar fields or a dusty plasma instability is operating.)
NLC are usually visible only at high latitudes, between 50
◦
and 60
◦
, but in June
22, 1999, they were observed in Boulder, Colorado
40
◦
N
. This is an indication
that NLC are moving south, which could be due either to upper atmospheric
cooling or increased water vapor caused by rising levels of CH
4
. Either case is
related to human activity, a topic we take up later in this chapter.
(
)
Search WWH ::
Custom Search