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.