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Are small-scale irregularities in a predominantly non-linear state? Evidence from Dynasonde measurements. N A Zabotin and J W Wright Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, Colorado, 80309-0216. - PowerPoint PPT Presentation
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Are small-scale irregularities ina predominantly non-linear state?
Evidence from Dynasonde measurements
Are small-scale irregularities ina predominantly non-linear state?
Evidence from Dynasonde measurements
N A Zabotin and J W WrightN A Zabotin and J W WrightCooperative Institute for Research in Environmental
Sciences (CIRES),University of Colorado, Boulder, Colorado, 80309-
0216
N A Zabotin and J W WrightN A Zabotin and J W WrightCooperative Institute for Research in Environmental
Sciences (CIRES),University of Colorado, Boulder, Colorado, 80309-
0216Results presented here have been obtained through support from the National Science Foundation, grant ATM0125297
Basic idea of the phase structure function methodBasic idea of the phase structure function method
Because the ionospheric plasma drifts, the radio sounding signal
encounters different realizations of the irregularity field even at only slightly
different times. The consequent phase fluctuations can be measured
by the dynasonde.
The temporal Structure Function
is a very appropriate statistical characteristic of the phase
fluctuations (see Zabotin & Wright, Radio Sci., 36, 757, 2001).
Because the ionospheric plasma drifts, the radio sounding signal
encounters different realizations of the irregularity field even at only slightly
different times. The consequent phase fluctuations can be measured
by the dynasonde.
The temporal Structure Function
is a very appropriate statistical characteristic of the phase
fluctuations (see Zabotin & Wright, Radio Sci., 36, 757, 2001).
2( )D t t
0 1 10 100ô, sec
1E-4
1E-3
1E-2
0.1
1
1E+1
1E+2
Str
uc
ture
fu
nct
ion
, ra
d2
f=5 M Hz; í =3; äR
=0.001;
Lm
=10 km ; z0
=50 km ; ã=0.2 rad;
ö =0.5 rad; è0
=0.2 rad
V=200 m /sec; ö0
=90 deg
V=200 m /sec; ö0
=80 deg
V=200 m /sec; ö 0=0 deg
V=200 m /sec; ö0
= -90 deg
V=50 m /sec; ö0
=90 deg
V=50 m /sec; ö 0=80 deg
V=50 m /sec; ö0
=0 deg
V=50 m /sec; ö0
= -90 deg
Theory (built for a power irregularity spectrum) and experiment both suggest that the small-lag part of the full-scale SF is well approximated by a log-log linear law:
log(D(φ)/rad2) = SIA+SIB·log(τ/sec).
Theory (built for a power irregularity spectrum) and experiment both suggest that the small-lag part of the full-scale SF is well approximated by a log-log linear law:
log(D(φ)/rad2) = SIA+SIB·log(τ/sec).
1
2
3
4
5
0 24 48 72 96 120
13.0 13.5 14.0 14.5 15.0 15.5 16.0 16.5 17.0 17.5
0.0001
0.001
0.01
0.1
= 8/3
October Local Date
Hours Since 2145 UT 12 October 1997
Irr
egu
lari
ty S
pec
tru
m In
dex
Irre
gu
lari
ty A
mp
litu
de
for
the
Sca
le L
eng
th1
km
IONOSPHERIC IRREGULARITY PARAMETERSBEAR LAKE UTAH DYNASONDE; Sequence Begins 97-10-12 2145 UT
Irregularity amplitude ΔN/N, gradients and GDIIrregularity amplitude ΔN/N, gradients and GDIF
reg
ion
F re
gio
nE
reg
ion
E r
eg
ion
SummarySummary
1. Small-scale irregularity spectrum is practically always approximated by power law.
2. There is not asymmetry between irregularity growth and decay.3. Irregularity amplitude never drops down to the thermal
fluctuations level.4. Average irregularity spectrum index is close to Sudan and
Keskinen’s 8/3.5. Horizontal gradients are not the main controlling factor for the
irregularity amplitude.
1. Small-scale irregularity spectrum is practically always approximated by power law.
2. There is not asymmetry between irregularity growth and decay.3. Irregularity amplitude never drops down to the thermal
fluctuations level.4. Average irregularity spectrum index is close to Sudan and
Keskinen’s 8/3.5. Horizontal gradients are not the main controlling factor for the
irregularity amplitude.
Practical ConsequencesPractical Consequences
When modeling evolution of the small-scale irregularities one should not assume “clean” initial state with thermal fluctuations only. It is useful to permit a possibility that initial state was already non-linear.
When modeling evolution of the small-scale irregularities one should not assume “clean” initial state with thermal fluctuations only. It is useful to permit a possibility that initial state was already non-linear.