quiet-time f2-layer disturbances: morphology and some formation mechanisms quiet-time f2-layer...
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Quiet-time F2-layer Disturbances: Quiet-time F2-layer Disturbances: Morphology and some Formation Morphology and some Formation
Mechanisms Mechanisms
Andrei MikhailovAndrei Mikhailov
Institute of Terrestrial Magnetism Ionosphere and Radio Wave Propagation
(IZMIRAN)Russian Academy of Sciences
Quiet-time Disturbances Quiet-time Disturbances (Q-disturbances)(Q-disturbances)
is a special class of the F2-layer is a special class of the F2-layer perturbations not related to perturbations not related to
geomagnetic activitygeomagnetic activity
1.Their amplitude is comparable to moderate F2-layer storm
effects resulted from increased geomagnetic activity
2. Their morphology is different from the morphology of
usual storm-induced F2-layer disturbances
3. The formation mechanisms are also different
(for Negative disturbances)
Specification of Q-disturbances used in the Specification of Q-disturbances used in the analysisanalysis
1. (NmF2/NmF2med – 1)x100% ≥ 40% If all 3-h ap indices were ≤ 7 for the preceding 24 hours
2. A 27-day NmF2 running median centered to the day in question
3. Only long-lasting, ≥ 3-h disturbances were considered
4. =NmF2/NmF2med were used
An example of negative Q-disturbanceAn example of negative Q-disturbance
5 .5
5 .7
5 .9
6 .1
6 .3
log
Nm
F2,
cm
M o sc o w , A p r 2 1 -2 4 , 1 9 8 0
-3
A p r 2 1 A p r 2 2 A p r 2 3 A p r 2 4
.
.
0 24 4 8 7 2 96U T , h o u rs
30 0
34 0
38 0
42 0
46 0
hmF
2, k
m
A p = 5 A p = 9 A p = 6 A p = 7
.
An example of positive Q-disturbanceAn example of positive Q-disturbance
M o sc o w , A p r 0 6 -0 9 , 1 9 7 3-3
0 24 4 8 7 2 96
4 .6
4 .8
5 .0
5 .2
5 .4
5 .6
5 .8
6 .0
log
Nm
F2,
cm
A p r 0 6 A p r 0 7 A p r 0 8 A p r 0 9
.
0 24 4 8 7 2 96U T , h o u rs
22 0
26 0
30 0
34 0
38 0
hmF
2, k
m
A p = 4 A p = 4 A p = 8 A p = 7
.
Seasonal occurrence frequency variation forSeasonal occurrence frequency variation for negative usual and Q-disturbances negative usual and Q-disturbances
1 2 3 4 5 6 7 8 9 10 11 12M o n th s
0
4
8
12
16
20
24
28
Occ
uren
ce, %
M ax (N = 2 0 6 )
M ed (N = 2 5 3 )
M in (N = 1 8 2 )
(0 9 -1 5 ) L T
.
.
1 2 3 4 5 6 7 8 9 10 11 12M o n th s
0
5
10
15
20
25
30
35
40
Occ
urre
nce,
%
A ll so la r ac tiv itylev e l (N = 7 5 )(0 9 -1 5 ) L T
Q -d is tu rb a n cesU su a l d is tu rb a n ce s
.
Latitudinal occurrence frequency variation forLatitudinal occurrence frequency variation for Negative and Positive usual and Q-disturbances Negative and Positive usual and Q-disturbances
(0 9 -1 5 ) L T S e c to r
A ll n e g a tiv e d is t.N eg a tiv e Q -d is t.
2 0 3 0 4 0 5 0 6 0 7 0In v a ria n t la ti tu d e , d e g
0 .0
0 .2
0 .4
0 .6
0 .8
1 .0
1 .2
Per
cent
of
tim
e
(0 9 -1 5 ) L T S e c to r
A ll p o s itiv e d is t.P o s itiv e Q -d is t.
2 0 3 0 4 0 5 0 6 0 7 0In v a ria n t la ti tu d e , d e g
0 .0
0 .2
0 .4
0 .6
0 .8
1 .0
Per
cent
of
tim
e
(1 6 -2 2 ) L T S e c to r
A ll n e g a tiv e d is t.N eg a tiv e Q -d is t.
2 0 3 0 4 0 5 0 6 0 7 0In v a ria n t la ti tu d e , d e g
0 .0
0 .4
0 .8
1 .2
1 .6
2 .0
2 .4
Per
cent
of
tim
e
(1 6 -2 2 ) L T S e c to r
A ll p o s itiv e d is t.P o s itiv e Q -d is t.
2 0 3 0 4 0 5 0 6 0 7 0In v a ria n t la ti tu d e , d e g
0 .0
0 .4
0 .8
1 .2
1 .6
2 .0
2 .4
Per
cent
of
tim
e
2-D distribution of NmF2/NmF22-D distribution of NmF2/NmF2medmed in the case of in the case of
Positive Q-disturbance Positive Q-disturbance
0 60 120 180 240 300 360
G eodetic lon g itu de , deg
2 0
3 0
4 0
5 0
6 0
7 0
Inva
rian
t lat
itu
de, d
egP o sitiv e Q -d istu rb a n ce A p r 0 6 , 1 9 7 3
Notice latitudinal dependence for NmF2/NmF2med variations
2-D distribution of NmF2/NmF22-D distribution of NmF2/NmF2medmed in the case of in the case of
Negative Q-disturbance Negative Q-disturbance
0 60 120 180 240 300 360
G eodetic lon g itu de , deg
2 0
3 0
4 0
5 0
6 0
7 0
Inva
rian
t lat
itu
de, d
eg
N eg a tiv e Q -d istu rb a n ce J a n 0 6 , 1 9 7 0
Notice latitudinaly independent NmF2/NmF2med variations
Longitudinal variations of the NmF2/NmF2med ratio under Q-disturbance events
P o sitiv e Q -d istu rb a n ce A p r 0 6 -0 9 , 1 9 7 3
In v a r. L a t = 6 0 (1 1 -1 4 L T )
0 60 1 20 1 80 240 300 36 0G e o d e tic lo n g itu d e , d e g
0 .8
1 .0
1 .2
1 .4
1 .6
1 .8
2 .0
2 .2
Nm
F2/
Nm
F2 m
ed
A p r 6A p r 7A p r 8A p r 9
0 60 1 20 1 80 240 300 36 0G e o d e tic lo n g itu d e , d e g
0 .5
0 .6
0 .7
0 .8
0 .9
1 .0
Nm
F2/
Nm
F2 m
ed
Jan 6Jan 7Jan 8
N eg a tiv e Q -d istu rb a n ce J a n 0 6 -0 8 , 1 9 7 0
In v a r. L a t = 6 0 (1 1 -1 4 L T )
Steep front
Steep front
Physical Physical InterpretationInterpretation
Positive and Negative Q-disturbances observedPositive and Negative Q-disturbances observed
by Millstone Hill ISR by Millstone Hill ISR
5 .8
6 .0
6 .2
6 .4
6 .6
log
Nm
F2
A p r 1 1 , 2 0 0 0A p r 1 2 , 2 0 0 0M e d ia n
1 3 1 5 1 7 1 9 2 1 2 3U T , h o u rs
2 8 0
3 0 0
3 2 0
3 4 0
3 6 0
hmF2
, km
P o sitiv e Q -d is tu rb an ce
A p r 1 6 , 2 0 0 2A p r 1 5 , 2 0 0 2M e d ia n
5 .8
6 .0
6 .2
6 .4
log
Nm
F2
1 3 1 5 1 7 1 9 2 1 2 3U T , h o u rs
2 6 0
2 8 0
3 0 0
3 2 0
3 4 0
hmF2
, km
N e g a tiv e Q -d is tu rb an c e
Date Tex (K)
log [O]300 (cm-3)
log [O2]300 (cm-3)
log [N2]300 (cm-3)
log300 (s-1)
W (m/s)
Apr 11 1457 1312
9.019 9.095
7.150 6.884
8.602 8.588
-3.309 0
Apr 12 1427 1303
8.751 9.094
7.102 6.848
8.519 8.568
-3.381 7.6
Apr 15 1447 1344
8.889 9.078
6.866 6.921
8.404 8.588
-3.511 1.0
Apr 16 1439 1326
8.667 9.073
6.824 6.891
8.311 8.570
-3.624 -7.1
lgNmF2 = 4/3lg[O] - 2/3lg + 1/2lgTn
Both Positive and Negative Q-disturbances are mainly due to [O] variations presumably resulted from the vertical gas
motion in the whole thermosphere
Retrieved Aeronomic Parameters at 300 km for Positive (Apr 11, Retrieved Aeronomic Parameters at 300 km for Positive (Apr 11, 2000) and Negative (Apr 16, 2002) Q-disturb. 2000) and Negative (Apr 16, 2002) Q-disturb.
Second line (Italic) – NRLMSISE-00 model values Second line (Italic) – NRLMSISE-00 model values
Negative daytime Q-disturbances Negative daytime Q-disturbances correspond to low [O] and an enhanced correspond to low [O] and an enhanced
poleward thermospheric wind.poleward thermospheric wind.
Opposite situation takes place for Opposite situation takes place for Positive Q-disturbances Positive Q-disturbances
The 27-day running median level from which Positive and Negative
Q-disturbances are counted from is the essential point in the mechanism of their
formation.These median levels are different
Average Ap over the 27-day period:9.87±3.88 for Negative (35 cases) 16.96±6.78 for Positive (105 cases)
The role of the foF2 median level in Negative and Positive Q-disturbances formation
Quiet 27-day periodresults in relativelyhigh median level
Disturbed 27-day period
results in relatively lowmedian level
M E D I A NArea
of PositiveQ-disturbances
M E D I A N
Areaof Negative
Q-disturbances
Negative Q-disturbances occur under very low geomagnetic activity
Month 1962 1963 1964 1965 1966 Nov 12.8 (1) 12.3 (1) 7.3 (1) 6.0 (3) 9.5 (1) Dec 12.8 (0) 10.9 (2) 5.3 (5) 7.1 (1) 11.6 (1) Jan 7.0 (4) 11.3 (1) 11.8 (0) 6.2 (1) 7.5 (4)
Monthly Ap indices and number (in brackets) of negative disturbances observed at Slough for three months and
years around solar minimum.
A sketch to illustrate the place of Q-disturbances A sketch to illustrate the place of Q-disturbances on the Ap index scaleon the Ap index scale
0 5 1 0 1 5 2 0 2 5 3 0A p
0 .0
0 .5
1 .0
1 .5
2 .0
Nm M ed ia n
Neg
ativ
eQ
-dis
turb
ance
sar
eaPo
sitiv
eQ
-dis
turb
ance
sar
ea
L o n g -d u ra tio np o sitiv e d is tu rb an ce sa rea
U su a ln e g a tiv ed is tu rb an ce sa rea
The Ground State of the ThermosphereThe Ground State of the Thermosphere
The Ground State corresponds to a very low The Ground State corresponds to a very low geomagnetic activity with an unconstrained geomagnetic activity with an unconstrained
solar-driven (poleward) thermospheric solar-driven (poleward) thermospheric circulation and low [O] at middle and circulation and low [O] at middle and
subauroral latitudes. subauroral latitudes.
This follows from the model calculations by Rishbeth and Müller-Wodarg (1999)
Negative and Positive Q-disturbances Formation
LatitudeAur
oral
zon
e
Unconstrained solar-driven Vnx(Minimal geomagnetic activity)
Neutral gas upwellingLatitudinal independent(Rishbeth and Müller- Wodarg, 1999)
LatitudeAur
oral
zon
e
Solar-driven Vnx(Slightly enhanced geomagnetic activity)
Neutral gas downwellingLatitudinal dependent(Rishbeth, 1998)
[O] decrease
[O] increase
[O] decrease
The differences between The differences between F2-layer Negative Storm-inducedF2-layer Negative Storm-induced
and Q-disturbances are in: and Q-disturbances are in:
11. hmF2 variations. hmF2 variations
2. Ne(h) distribution2. Ne(h) distribution
Different hmF2 VariationsDifferent hmF2 Variations
1. Magnetically storm-induced F2-layer changes
always result in the hmF2 increase
2. Q-disturbance hmF2 always decreases
A statistical check
169 (station/date) Negative Q-disturbance cases
were analyzed:
Average hmF2 deviation = -13.49.7 km
Student parameter t = 17.96 (The deviation is significant at any confidence level)
Negative Q-disturbance on Apr 16 and Storm-induced on Apr 17-18, 2002 variations observed by Millstone Hill digisonde
0 24 48 72 96
U T , h o u rs
200
250
300
350
400
450
hmF
2, k
m
0 24 48 72 96
4
6
8
10
12
foF
2, M
Hz
0
40
80
120
160
3-ho
ur a
p
A p r 1 8A p r 1 6A p r 1 5
0 6 12 1 8 0 6 1 2 1 8 0 6 1 2 1 8 0 6 1 2 18 24
A p r 1 7
G G
G-condition(NmF2 < NmF1)Incorrect hmF2 interpretation in such conditions
Millstone Hill ISR observations for the period in questionMillstone Hill ISR observations for the period in question
A p r 1 6 , 2 0 0 2
A p r 1 5 , 2 0 0 2
M e d ia n
5 .5
5 .6
5 .7
5 .8
5 .9
6 .0
6 .1
6 .2
6 .3
Log
Nm
F2
1 3 1 5 1 7 1 9 2 1 2 3U T , h o u rs
250
270
290
310
330
350
370
hmF
2, k
m
A p r 1 8 , 2 0 0 2
ISR facility provides correct hmF2 underG-conditions
Date UT
Tex (K)
log [O]300 (cm-3)
log [O2]300 (cm-3)
log [N2]300 (cm-3)
log300 (s-1)
W (m/s)
Apr 15 1830-1930
1453 1460
8.796
6.857
8.319
-3.575 0.0
Apr 16 1830-1930
1417 1420
8.600
6.776
8.256
-3.680 -2.8
Apr 18 2000-2100
1466 1480
8.853 7.109 8.411 -3.428 +8.8
Retrieved Aeronomic Parameters at 300 km forRetrieved Aeronomic Parameters at 300 km for Apr 15, 16, 18, 2002 Apr 15, 16, 18, 2002
Italic – Millstone Hill Tex estimates Italic – Millstone Hill Tex estimates
Dates Tex log[O]300 log300 W
Apr 16/15, 2002 -36 -0.196 -0.105 -2.8
Apr 18/15, 2002 +13 +0.06 +0.147 +8.8
Variations of aeronomic parameters for the two pairs of dates
A contribution of the main parameters to hmF2 A contribution of the main parameters to hmF2 variationsvariations
][][;/
54.0loglog]log[
3
3.2
2221
2
ONmgkTH
cWd
HO
Hhm
n
All controlling parameters: log[O], log, Tn, and W
are < 0 for Q-disturbance decreasing hmF2, [O] providing the main contribution
and these parameter contributions
are > 0 for Storm-induced disturbance increasing hmF2, the [O] contribution being small due to the competition between Tn increase and storm-induced thermospheric circulation
Different Ne(h) distributionsDifferent Ne(h) distributions
10 0
20 0
30 0
40 0
50 0
60 0
70 0
Hei
ght,
kmA p r 1 5 , 2 0 0 2A p r 1 6 , 2 0 0 2A p r 1 8 , 2 0 0 2
5 .0 5 .2 5 .4 5 .6 5 .8 6 .0 6 .2 6 .4L o g N e , cm -3
10 0
20 0
30 0
40 0
50 0
60 0
Hei
ght,
km
M a r 1 7 , 1 9 9 0M ar 2 2 , 1 9 9 0
R efe ren c e d ay
R efe ren c e d ay
The difference in Ne(h) distributions results from The difference in Ne(h) distributions results from different plasma temperatures, i.e. plasma scale heights different plasma temperatures, i.e. plasma scale heights
dh
TTd
TTTTk
gmH ie
ieie
ip
)(1
)(1
Observed at Millstone Hill plasma temperatures, their gradient and plasma scale heights at 500 km for quiet and disturbed days.
Date 15.04.02 16.04.02 18.04.02 17.03.90 22.03.90
Te, K 2325 2899 2681 2065 3337
Ti, K 1550 1514 1586 1472 1644
d(Te + Ti)/dh, K/cm 4.85e-5 4.49e-5 3.05e-5 6.00e-5 2.80e-5
Hp, km 184 213 222 159 262
ConclusionsConclusions
Negative Q-disturbancesNegative Q-disturbances
1. Negative Q-disturbances occur under the ground state
of the thermosphere with low [O] and relatively strong
poleward Vnx producing downward plasma drift W.
2. Both low [O] and downward W decrease NmF2
resulting in Negative Q-disturbances.
3. Clustering of the Negative Q-disturbances around
winter solstice is related to the poleward Vnx, which is
the strongest under such conditions.
Negative Q-disturbancesNegative Q-disturbances
4. In fact, the occurrence of Negative Q-disturbances is
not related to any physical process, but depends on
the NmF2 median level they are counted from.
5. For a magnetically disturbed month (low median
level) the probability for Negative Q-disturbances to
occur is lower.
6. For a magnetically quiet month (high median level) the
probability for Negative Q-disturbances to occur
is higher.
Positive Q-disturbancesPositive Q-disturbances
1. Positive Q-disturbances appear under slightly enhanced 1. Positive Q-disturbances appear under slightly enhanced
auroral activity when the high-latitude heating increasesauroral activity when the high-latitude heating increases
and damps the solar-driven poleward thermosphericand damps the solar-driven poleward thermospheric
circulation. circulation.
2. This damping produces a downwelling of the neutral 2. This damping produces a downwelling of the neutral
gas followed by the enrichment of the thermosphere gas followed by the enrichment of the thermosphere
with atomic oxygen [O].with atomic oxygen [O].
3. The downwelling is expected to increase towards the3. The downwelling is expected to increase towards the
auroral oval and this explains the increase with latitudeauroral oval and this explains the increase with latitude
of the amplitude and the occurrence frequency of of the amplitude and the occurrence frequency of
Positive Q-disturbances. Positive Q-disturbances.
Positive Q-disturbancesPositive Q-disturbances
4. The damped poleward wind also reduces the downward4. The damped poleward wind also reduces the downward
plasma drift in the F2-region, thereby increasing NmF2.plasma drift in the F2-region, thereby increasing NmF2.
5. The Positive Q-disturbances just present the left-hand 5. The Positive Q-disturbances just present the left-hand
wing of the positive, long-duration F2-layer wing of the positive, long-duration F2-layer
disturbances area on the Ap-index scale.disturbances area on the Ap-index scale.
6. The mechanism of both types of Positive disturbances is 6. The mechanism of both types of Positive disturbances is
the same: the damped poleward circulation and neutral the same: the damped poleward circulation and neutral
gas downwelling resulting in the [O] abundance gas downwelling resulting in the [O] abundance
increase.increase.