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Chapter_5_GKM OI 630 nm Night Airglow Emissions During Storm.

Department of Physics, S. U. Kolhapur Page | 132

CHAPTER – 5

OI 630 nm Night Airglow Emissions During Storm.

5.1 Introduction: -

The ground-based investigation by the photometry and

spectrometry gives us a wealth of information about the behaviour

of the upper atmosphere (ionosphere-thermosphere) at different

heights [1-5]. The remote sensing of OI 630 nm nightglow

emissions provides a convenient tool to procure important

information on the ionosphere through the different phases of

geomagnetic storm. Several researchers have studied the effect of

geomagnetic storm over thermosphere-ionosphere system at low

latitude by using both radio techniques (incoherent scatter radar,

rockets, satellites and UHF/VHF scintillation, ionosonde, topside

sounder) and optical techniques (conventional tilting and scanning

photometers and wide imaging system) [1-16]. Several earlier

studies revealed that the storm-time ionosphere vary in somewhat

complicated ways. Due to their complexity, the ionospheric storms

and the underlying physical processes are still to be fully

understood, in spite of many case studies [1, 2, 8 & 9]. The

response of F-region to magnetic storm is characterized by two

phases (effects) positive phase, and negative phase. During positive

phase, electron density enhances as compared to the day time

values, whereas the electron density decreases in reference to the

day time values during the negative phase of the storm. Rajaram et



al. [17] reported that, in general, during magnetic disturbances foF2

increases at low latitude (positive effect), conversely, Danilov and

Morozova [18] pointed out that considerable changes in foF2 may

not be observed at low latitudes. However, the positive effect is

conspicuous for day time values only at low latitudes [19]. More

often, the average pattern, negative effect at mid latitude and

positive effect at low latitude, is violated [20] as the signature of

individual storm varies greatly in their behaviour.

At low latitudes during magnetic disturbances, the ionospheric

perturbations (positive or negative effects) depend on several

complex factors, including storm-induced changes in dynamics,

heating and composition [9]. The Dst or disturbance storm time

index is a measure of geomagnetic activity used to assess the

severity of a magnetic storm. Use of Dst as an index of storm

strength is possible because the strength of the surface magnetic

field at low latitudes is inversely proportional to the energy content

of the ring current, which increases during geomagnetic storms

[21].

The electric field at the equator has an immense influence on the

equatorial F-layer peak height as well as on the longitudinal

distribution of Nmax at low latitude [10]. At mid and low latitudes,

the electric field and current pattern show different observations on

and disturbed conditions. At the equator the east-west electric field

controls EIA and generates a vertical E x B drift, upward during day



time and downward at night. The upward drift uplifts ionization to

higher altitudes and it diffuses to low latitudes through magnetic

field lines thereby producing two peaks of ionization at ±15o of the

geomagnetic equator.

At low latitudes the geomagnetic storms during their main phase

cause significant decrease in the geomagnetic-H field due to the

disturbances in the ring current. The high speed plasma cloud from

the sun initiates the magnetic storm. In the initial phase, the

enhanced H-values are due to northward IMF Bz (Positive Bz).

However, the southward turning of IMF Bz (negative Bz) causes the

transfer of solar wind energy to magnetosphere, thereby energizing

ring current and leading to the large and rapid decrease of H-field

on the surface associated with the main phase [6].

Several latest studies have shown that the magnitude and

different phases of geomagnetic storm depend upon solar wind

speed, IMF magnitude and the presence of large southward IMF BZ.

In fact southward IMF BZ provides prospect for making strong

magnetic reconnection between IMF and Earth’s magnetic field. The

occurrence of large southward IMF BZ during higher solar wind

velocities can produce large geomagnetic storms. Furthermore, the

presence of higher IMF for longer durations is not necessarily more

effective for production of large magnitude geomagnetic storm [12].

The southward turning of IMF BZ component, results in a decrease

in F2 layer critical frequency (foF2) [22].



On typical quiet night condition the [OI] 630 nm nightglow

variations at low latitude show good correlations with the variations

of the electron density. However, with increase in magnetic

disturbance, low latitude ionosphere undergoes rapid height

variations. The height variations of the emitting F2 layer produce

the corresponding signature in observed nightglow in 630 nm. The

ionospheric height variations could be due to large-scale travelling

ionospheric disturbances (TIDs) with periods about 3 hours which

occur at the auroral region during intense magnetic storm [3].

During magnetic disturbances, high latitude electric field can

penetrate into low latitude ionosphere [23]. The direction of electric

field is important. It is known that the direction of the electric field

in the equatorial region is eastward during day time and westward

at night [24]. If the superposed electric field moves westward, it will

push the F-layer downwards and, as there is more recombination in

the low latitude region, sharp airglow enhancement takes place.

Generally, the correlation coefficient between the OI 630.0 nm

intensity variation and F-layer height variation on the disturbed

night are large as compared to their values on quiet nights [2, 3 &

9].

Generally, the time interval with Kp≥3+ or Ap≥18 are

considered as magnetically disturbed periods [26, 27].



5.2 Experimental Setup and Parameters

In this section we examine several different simultaneous data

sets including optical (photometer data), ionospheric and

geomagnetic data.

5.2.1 Optical Experiment (Airglow)

Airglow observations were made at Physics Department,

Shivaji University, Kolhapur, a low latitude station (16.8 N; 74.2

E; 10.6 N dip lat) (Fig. 5.1), using three tilting photometers

installed at the terrace of the Physics Department, Shivaji

University, by Indian Institute of Geomagnetism (IIG), Mumbai.

The three photometers were given on loan to IIG by La Trobe

University, Melbourne, Australia under scientific collaboration

between India and Australia.

The photometers are portable and can be easily mounted to

point along any desired combination of zenith and azimuth angles.

Hence, the photometers were pointed in three different directions,

thus horizontal motion in the thermosphere can be measured easily.

For the present study they are pointed to the zenith, 30 o east, and

30 o north directions (Fig. 5.2). The tilting photometer has a field of

view of 1o and gives cross section of about 5 km in the F-region

height (250 km) while looking at zenith. Each photometer consists

of an optical interference filter (kept at 30˚C)with tilting

mechanism, normal position gives the signal and background

reading, and the second tilting filter position gives only the



background reading. The difference between two readings gives the

signal of distant OI 630.0 nm airglow variations. This process was

repeated throughout the night to get the airglow intensities during

the night at two-minute interval. The ultimate form of overall

photometer was such that, not only could it be used to monitor

three different small (about 5 km in diameter at 250 km height)

volumes of the F-region ionosphere simultaneously, but also the

separation of three ionospheric volumes being monitored could be

made variable in accordance with the corresponding research

objectives.



5.2.2 Ionosonde Data

The ionospheric parameters (critical frequency) of the F2-

layer (foF2) and the virtual F-layer height (h’F) of the ionosphere

were measured from a nearby station, Ahmedabad (geog. lat.,

23.02o N, long. 72.6o E), station to know ionospheric conditions

during the time of airglow observation. However, whenever

Ahmadabad’s data is not available, ionosonde data from Kodaikanal

(geog. lat., 10.2o N, long. 77.5o E) have been used. The square of

parameter (foF2) is proportional to electron density at the peak of

F2-layer [25] and is given by, Ne(max) cm-3 = 1.24 × 10-24 [foF2

(MHz)2].

5.2.3 Geomagnetic Indices

The magnetic data (H-component) discussed in the present

study were obtained from IIG, Mumbai’s observatory situated at

Alibag. The IIG, collects magnetic data through its network of

magnetic observatories all over India. The Kp, Ap, F10.7 cm flux are

taken from the NOAA-Space Environment Center

[http://www.ngdc.noaa.gov/stp/geomag/kp_ap.html and www.

swpc.noaa.gov] and Dst indices are obtained from the world data

center for geomagnetism, Kyoto [http://wdc.kugi.kyoto-

u.ac.jp/dstdir/]. The IMF Bz data obtained from Space Physics

Interactive Data Resource center’s data bank [SPIDR:

http://spidr.ngdc.noaa.gov/spidr/].



5.3 Results and Discussion

We use in this study ground based nocturnal observations of OI

630.0 nm emissions from Kolhapur, a low latitude station. Here, we

discuss & compare OI 630.0 nm emissions from Kolhapur with

ionospheric parameters, virtual height of the F – layer (h’F) and

critical frequency of F2 - layer ‘(foF2)’ from nearby station

Ahmedabad (23.020 N; 72.60 E). The station Ahmedabad is situated

closer to the EIA crest region. However, whenever, Ahmadabad’s

data is not available, the hourly values of the ionospheric parameter

h’F and foF2 are examined from a near equatorial station,

Kodaikanal (10.20 N; 77.50 E), situated at the same longitude

sector, to determine the condition of equatorial ionosphere during

the time of observations. The OI 630 nm night airglow data

presented in this study is of two minutes interval taken with high

resolution tilting photometers at Kolhapur. To show the magnetic

activity during the period of observations, we depict the magnetic

activity index (Ap), along with solar flux (F10.7 cm) values. The

complementary activity indices Dst and Kp for corresponding nights

are used. In addition to this, the southward turning of IMF Bz during

the period of observation was detected by the WIND satellite to see

electric field penetration from high latitude to low latitude. The

Table-5.1 shows correlation coefficient (r) between 1/I630 and h’F.



Table 5.1. Correlation coefficient (r) between 1/I630 and h’F.

Date Period of

Observations

(IST)

Correlation (r)

between

1/I630 and h’F

Remark

03-04 Feb 1997 20:00 to 05:00 0.35 Quiet

09-10 Feb 1997 20:00 to 05:00 0.25 Disturbed

27-28 Dec 1997 20:00 to 05:00 0.72 Quiet

30-31 Dec 1997 20:00 to 05:00 0.65 Disturbed

31 Dec 1997- 1

Jan 1998

20:00 to 05:00 -0.30 Quiet

23-24 April 1998 20:00 to 05:00 0.80 ---

26-27 April 1998 20:00 to 05:00 0.70 Disturbed

15-16 Jan 1999 20:00 to 05:00 No Ionosonde

Data

Disturbed

20-21 Jan 1999 20:00 to 05:00 0.04 ---

21-22 Jan 1999 20:00 to 05:00 0.45 ---

22-23 Jan 1999 20:00 to 05:00 0.19 ---

4-5 Dec 1999 20:00 to 05:00 -0.07 Disturbed

6-7 Dec 1999 20:00 to 05:00 -0.52 ---

31 Dec 1999 - 1

Jan 2000

20:00 to 05:00 0.75 Disturbed

6-7 Jan 2000 20:00 to 05:00 0.20 ---


Data

Quiet

28-29 Jan 2000 20:00 to 05:00 0.76 Disturbed


Data

Disturbed

6-7 March 2000 20:00 to 05:00 -0.51 ---

31 March 2000 -

1 April 2000

20:00 to 05:00 0.40 Disturbed



Zenith

9 - 10 Feb 97 OI 630 nm

F 10.7 = 73Ap = 20

230

300

h'F

(km

)

3+

4

5+

4

Kolhapur

(foF2)2

h' FKodaikanal

20 22 00 02 04 IST (Hrs)

-60

-10

Dst

(nT)

1

5

Kp

Inde

x

0

2.5O

I 630

nm

Inte

nsity

(a

rb. u

nits

)

3 - 4 Feb 97 OI 630 nm

F 10.7 = 80Ap = 07

30

60

(foF

2)2 (M

Hz)

2

0+1 1+

3 -

Zenith

Kolhapur

Kodaikanal (foF2)2

h' F

20 22 00 02 04 IST (Hrs)

-9

0

9

Bz (n

T)(a)

(b)

(c)

(d)

(e)

Fig. 5.3 Temporal variation of (b) h’F & (foF2)2 values at Kodaikanal,

(c) IMF Bz, (d) H variation at nearby low latitude station, Alibag,

(e) Kp and (f) Dst values on the night of 3/4 and 9/10 February

1997. The topmost panel (a) depicts the temporal variation of OI

630 nm intensity at Kolhapur on the above nights.



In Fig. 5.3 the top panel (a) depicts the OI 630.0 nm nocturnal

intensity variations on a set of magnetically quiet and disturbed

night, 3-4 February 1999 and 9-10 February 1999. The following

panel (b) shows the variation of h’F & (foF2)2 parameters, panel (c)

IMF BZ, panel (d) Kp index and (e) Dst index respectively. The

purpose of plotting h’F, (foF2)2, IMF BZ, Kp and Dst index in the

same figure is to find out any correlation between these parameters

with airglow intensity variations.

On the quiet night of 3-4 February-1999, the F-region height

data (h’F) shows local time variation with the lower in heights seen

at 23:00 and 02:30 IST associated with the OI 630.0 nm emission

enhancement during pre-midnight hours. The square of (foF2)2 is

proportional to the electron density at the peak of F2-layer [25].

This feature is common and perceived in the (foF2)2 variations at

Kodaikanal. No southward turning of IMF Bz and significant change

in Kp and Dst was registered. The correlation coefficient (r) between

1/I630.0 and h’F is r=0.35. A magnetic storm with a sudden

commencement occurred at 12:30 IST on 8 February 1997 and

continued for next three days.

On the magnetically disturbed (moderately disturbed) night 9-10

February,1999, OI 630.0 nm emissions showed periodic variations

(period of about 2.5 h), and ionospheric data (h’F-component) from

Kodaikanal shows similar pattern with some time difference. It is

noted that during the negative excursion of Dst (>-56 nT) two giant



peaks were observed. It is interesting to see that, the fluctuations

in h’F are in phase with 1/I630.0 especially during the negative

excursion of Dst. Mukherjee et al. [3], reported that during the

disturbed conditions, the ionospheric height variation could be due

to travelling ionospheric disturbances (TIDs). The southward turning

of IMF Bz (>-9 nT) started at 23:30 IST and lasted till 02:30 IST

during the period of observation. The disturbed ionosphere is also

influenced by the solar wind and interplanetary magnetic field,

which modulate the energy sources of the storm circulation [28].

The magnitudes and different phases of the geomagnetic storm

depend upon solar wind speed, IMF magnitude and the presence of

large southward IMF Bz [12].

In Fig. 5.4 we present night airglow data obtained on 27-28, 30-

31 1997 and 31 Dec 1997 – 1 Jan 1998 along with h’F, foF2, BZ, KP,

and Dst parameter. The ionospheric parameters were taken from

Kodaikanal. The night of 27-28 December 1997 is typical quiet

(Ap=2) night. On this night there is remarkable rapid fall in OI 630

nm intensity from 22:30 hours IST to post midnight. This is

common feature [25] and also observed at Kodaikanal. The inverse

of 630 nm intensity variation shows good correlation (c.c. = 0.72)

with the variation of the F-region height. A sudden commencement

of magnetic storm occurred on 29-30 December 1998 at 23:30 IST



followed by main phase on the night 30-31 December 1997. During

this storm the maximum negative excursion of Dst was about -77

nT at 00:30 IST, Kp reached 5-, and Bz = -12 nT. The Kp index

reached a value of 5- during the period of main phase of the storm.

The main phase of storm started on 30 December 1997 with a

prominent southward turning of Bz for more than 8 hours (i.e. Bz

becoming negative). On 30-31 December 1998, the OI 630 nm

variation shows periodic (~3 hours) intensity variations during the

strong magnetic variations (Ap=25). Similar pattern was observed

in variations in F-region height (h’F) at Kodaikanal. The inverse of

OI 630 nm intensity variation shows good correlation (c.c. = 0.65)

with the variation of the F-region height. It is also reported that the

correlation coefficient between inverse of OI 630 nm intensity

variation and F-region height (h’F) variation were large for disturbed

nights as compared to quiet nights [3, 9]. The OI 630 nm emissions

are due to dissociative recombination and mainly depend on the

vertical movement of the F-layer, and more specifically on the

heights of the F-layer bottomside, with an inverse relation between

I630 and F-layer height [3, 29]. The third night in this figure is 31

December 1997-01 January 1998, a quiet (Ap=04) night, and

somewhat similar nature is observed.



Zen

ith

OI 6

30 n

mF

10.7

= 1

01A

p =

25

3

5 -

1+

30 -

31 D

ec 9

7

(foF

2)2

h' F

Kod

aika

nal

Kolh

apur

-8

0

0

Dst (nT)

0.5

4.5 Kp Index

OI 6

30 n

mF

10.7

= 1

05A

p =

04

31 D

ec 9

7- 1

Jan

98

1 0+

230

330 h' F (km)

Zeni

th

Koda

ikan

al

Kol

hapu

r

-8

00

Dst (nT)0.5

4.5

Kp Index

0

2.5

OI 630 nm Intensity (arb. units)

OI 6

30 n

mF

10.7

= 9

6A

p =

02

0

0+

3070 (foF2)2 (Mhz)2

27 -

28 D

ec 9

7 Zeni

th

Kod

aika

nal

(foF2

)2

h' F

0

-12012 Bz (nT)

-12

012

Bz (nT)

(a)K

olha

pur

(foF2

)2

h' F

(b)

(c)

(d)

(e)

20

22

00

02

04

IS

T (H

rs)

20

22

00

02

04

IS

T (H

rs)

20

22

00

02

04

IS

T (H

rs) Fi

g. 5

.4 S

ame

as fi

g. 5

.3 b

ut fo

r the

nig

ht o

f 27/

28, 3

0/31

and

31

Dec

97-

01 Ja

n 97

.



-60

-30

0

30

Dst

(nT)

0.5

5.5

Kp

Inde

x

1 -

5 4+

210

380

h'F

(km

)

AhmedabadWaltair

0

3O

I 630

nm

Inte

nsity

(a

rb. u

nits

)

ZenithNorth

23 - 24 April 98 OI 630 nm

F 10.7 = 90Ap = 15

5 5 -

3 4

AhmedabadWaltair

North

Zenith

Kolhapur OI 630 nmF 10.7 = 91

Ap = 31

26 - 27 April 98

20 22 00 02 04

IST (Hrs)

-14

0

14

Bz

(nT)

Kolhapur

20 22 00 02 04 IST (Hrs)

(a)

(b)

(c)

(d)

(e)

30

120

(foF

2)2 Ahmedabad Ahmedabad

(f)

Fig. 5.5 Variation of optical emission (630.0 nm) during the nights

of 23/24 April and 26/27 April 1998, compared with ionospheric

parameters [h’F and (foF2)2] at Ahmedabad, h’F at Waltair, IMF Bz

component, Kp and Dst Index.



A data set for the nights 23-24 and 26-27 April 1998 obtained at

Kolhapur is presented in Fig. 5.5 along with h’F, foF2, BZ, KP, and

Dst parameter. The values of ionospheric parameters were obtained

from Ahmedabad and Waltair (17.70 N; 83.30 E). Two photometers

(300 N and Zenith) were operative on these nights. On the night 23-

24 April, the F-layer height data (h’F) shows a lower in heights,

seen at both the stations (Ahmedabad & Waltair) at 20:45 IST and

02:30 IST, associated with the OI 630 nm emission pre-and post-

midnight enhancements. At 23:55 IST, sudden commencement of

magnetic storm occurred on 23-April 1998. After about an hour, the

Dst started decreasing and attained lowest value on the following

day i.e., 24 April 1998. In addition, the Bz turned southward almost

at the same time and attained its value of -14 nT, and remained for

prolonged time. When the Bz component turn southward, it strongly

couple with magnetosphere and most dramatic magnetospheric

effects take place. The Kp too reached to 5. Significant lower in

height (=210 km) of F-layer is observed at both stations, Waltair &

Ahmedabad after ~3-hours of commencement of storm. It shows

good correlation (0.80) between inverse of OI 630 nm intensity and

F-layer height. It is very interesting to see that, both photometers

(Zenith & North looking) observed similar structure however their

occurrence was not simultaneous, but with time delay of 18

minutes. The north looking photometer observed peak earlier than

that of zenith. This means there is velocity propagation from North



to Zenith (equatoward) direction. The airglow structure moves with

velocity 134 ms-1 before midnight. The strength of equatorial

ionization anomaly (EIA) was good. On a disturbed (Ap=31) night

26-27 April 1998, the OI 630 nm emission shows a large intensity

enhancement at about 20:30 IST, which coincides with a minimum

in h’F and maximum in foF2. On the disturbed nights OI 630 nm

emission signifies the important role of F-layer dynamics. The

inverse of OI 630 nm intensity variation shows good correlation

(c.c. =0.70) with the variation of the F-layer height and almost anti-

correlation with (foF2)2. The h’F values are low (210 km) during

occurrence time of airglow peak. The sharp descend in OI 630 nm

intensity is observed following rapid rise in h’F height variations

around midnight. It is very exciting to witness that, both

photometers (Zenith & North looking) observed similar structure

and their occurrence was almost simultaneous.

In Fig. 5.6 we show the data obtained on the nights of 15-16

January 1999 (disturbed) and 20-21 January 1999. On night of 15-

16 January 1999, the OI 630 nm emissions show periodic intensity

variations (period of about 2.5 h). Sahai et al. [8] reported that

during magnetic disturbances the OI 630 nm emission shows

periodic intensity variations associated with vertical oscillations in

the ionospheric F-layer. Our results are in good agreement with

Sahai [8]. For this night, ionosonde data was not available for

correlation.



-45

-15

Dst

(nT)

0.5

3.5

Kp

Inde

x 3+ 4 - 3

2

0

2O

I 630

nm

Inte

nsity

(a

rb. u

nits)

15-16 Jan 99

OI 630 nmF 10.7 = 143

Ap = 20

40

150

(foF2

)2 (M

Hz)

2

Zenith

-10

0

10

Bz

(nT)

200

260

h'F

(km

)

OI 630 nmF 10.7 = 172

Ap = 08

21-22 Jan 99 Kolhapur

Zenith

(foF2)2h' FAhmedabad

NO Data

(a)

(b)

(c)

(d)

(e)

Kolhapur

20 22 00 02 04 IST (Hrs)

20 22 00 02 04 IST (Hrs)

2-

1-0+

Fig. 5.6 Same as Fig. 5.3 but for the date 15/16 and 21/22 January

1999.



On the 21-22 January 1999 the enhancement observed in the OI

630 nm emission intensity is associated with decrease in the

bottomside of F-layer, as evidenced from the h’F nocturnal

variations. The rapid fall in intensity from 22:15 IST to post

midnight and this feature is common and also seen in the (foF2)2

variations at Ahmadabad. The inverse of OI 630 nm intensity

variation shows very poor correlation (c.c. =0.04).

In the Fig. 5.7 the top panel (a) portrays nocturnal variations

of 630.0 nm airglow on night of 4-5 December and 6-7 December,

1999. Three photometer (30o E, 30o N, and Zenith) were working.

The following panel (b) depicts variation of h’F & (foF2)2 parameters,

panel (c) IMF BZ, panel (d) Kp index, (e) magnetogram data, H-

component from Alibag and (f) Dst index respectively. The solar flux

(F10.7 cm), magnetic activity index Ap. The night of 4-5 December

1999 is a magnetically disturbed night with Ap=30.

It is interesting to notice that there are two prominent peaks

in 630 nm airglow intensity, one at 23:30 IST and second at 3:30

IST. It clearly shows that the peaks in the airglow intensity are

associated with lowering in the height of F-region. It is remarkable

that, all the three photometers are showing intense enhancement in

airglow intensity almost around the same time, during the period of

magnetic disturbances (Kp=5 to 4-). It shows that there is no

meridional and longitudinal change in the phase, indicating the

absence of propagation. Sahai[8] on one occasion reported absence



4 - 3

2+

(foF2)2

h' F

200

250

h' F

(km

)

ZenithNorthEast

OI 630 nmF 10.7 = 143

Ap = 16

Kolhapur

Ahmedabad

6 - 7 Dec 99

-35

-5

Dst

(nT)

2.2

5.2

Kp

Inde

x

4+ 5

4 - 3+

30

130

(foF2

)2 (M

Hz)

2

(foF2)2

h' F

0

2.5

OI 6

30 n

m In

tens

ity

(arb

. uni

ts)

East

NorthZenith

OI 630 nmF 10.7 = 148

Ap = 30

Ahmedabad

4 - 5 Dec 99

550

590

H (n

T)

-7

0

7

Bz

(nT)

Kolhapur

20 22 00 02 04 IST (Hrs)

20 22 00 02 04 IST (Hrs)

(a)

(b)

(d)

(c)

(e)

(f)

Fig. 5.7 The topmost panel (a) depicts the temporal variation of OI

630 nm intensity at Kolhapur. The panel (b) depicts temporal

variation of h’F & (foF2)2 values at Ahmedabad, (c) IMF Bz, (d) Kp

Index (e) H variation at nearby low latitude station, Alibag, and (f)

Dst values on the night of 4/5 and 6/7 December 1999.



of propagation during magnetic disturbances. This is a peculiar

behaviour on a very magnetically disturbed night, when the two

peaks are not separated. These results are in good agreement with

Mukherjee [3, 5] and Sahai [8]. This behavior of OI 630 nm

emission on a disturbed night shows the significant role played by

F-region dynamics. The night of 6-7 December 1999 is a night with

magnetic activity index Ap=16 and solar flux as 143 units. There

are two prominent peaks observed in night airglow data (OI 630

nm). The first peak occurs at 20:30 hrs and the second

enhancement takes place around 23:20 hrs, both are at pre-

midnight hours. The time of the two peaks does not coincides in all

three (Zenith, 30oE and 30o N) directions. The intensity decreases

sharply in these three directions after midnight hours. It is seen

that the peak at North appears first and then it is seen by the

Zenith photometer after 25 minutes, this gives rise to drift velocity

in meridional direction towards the equator assuming the same

structure is moving towards the equator. We determine the

apparent drift speeds simply from the time delay of common

features in the data which gave drifts as 97 m/s.

In the Fig. 5.8 we show the data obtained on 31 December

1999-1 January 2000 (magnetic storm, Ap=36) and 6-7 January

2000. On the night 31 December 1999-1 January 2000, OI 630 nm

emission does not show any periodic variations. However, both

(30oN and Zenith) the photometers shows strong enhancement in



-50

-10

Dst

(nT)

3

6

Kp

Inde

x

4 4 -

5 -5+

210

390

h' F

(km

)

h' F0

2.5O

I 630

nm

Inte

nsity

(a

rb. u

nits

)

Zenith

North

OI 630 nmF 10.7 = 130

Ap = 36

Kolhapur

Kodaikanal

31 Dec 99 - 1 Jan 2000

540

590

H (n

T)

-6

0

6

Bz

(nT)

Alibag

(foF2)2

50

130

(foF

2)2 (M

Hz)

2 h' F

Zenith

North

OI 630 nmF 10.7 = 145

Ap = 18

4+

3 3+

Ahmedabad

6 - 7 January 2000 Kolhapur

20 22 00 02 04 IST (Hrs)

20 22 00 02 04 IST (Hrs)

(a)

(b)

(c)

(d)

(e)

(f)

Fig. 5.8 Same as Fig. 5.7 but for nights of 31 December 99/ 1

January 2000 and 6/7 January 2000.



airglow intensity at the same time during the period of magnetic

disturbances (Kp=4- to 5+) indicating the absence of propagation

[5, 8]. Throughout the night the BZ component remained negative

and it is BZ=-6. It shows good correlation between 1/I630 nm and F-

region height (c.c. =0.75).

The h’F values at Kodaikanal are also low during occurrence

time of airglow peak and shows sharp fall and rise in their values

during the night. The H-component from Alibag also shows similar

structure to that of f-region height variations. The sharp descend in

OI 630 nm intensity is observed following rapid rise in h’F height

variations till 1:30 IST. Post midnight enhancement in the OI 630

nm intensity is also observed, but the peak are not on the same

time. The night of 6-7 January 2000 is a night with magnetic activity

index Ap=18 and solar flux as 145 units. The OI 630.0 nm intensity

shows monotonic decrease in intensity variation during the night.

The maxima in intensity takes place around 22:30 IST. Around the

same time h’F values are minimum and thereafter keep on

increasing and OI 630.0 nm shows inverse relationship with height

variation. It is also observed that 630.0 nm intensity and (f0F2)2

variation shows a good correlation during the night [3]. It is

generally seen that 630.0 nm intensity shows good correlation with

electron density parameter (f0F2)2 during quite period. The

photometers 30 N and Zenith are showing peaks in OI 630 nm

intensity but their occurrence is not simultaneous. During the first



peak the North looking photometer observes maxima at first around

22:20 hrs and the Zenith photometer at around 22:40 hrs. This

gives rise to drift velocity in meridional direction towards the

equator assuming the same structure is moving towards the

equator. During magnetically quiet conditions the meridional wind in

the upper thermosphere remains poleward during daytime and

equator ward during nighttime [16]. We determine the apparent

drift speeds simply from the time delay of common features in the

data which gave drifts as 161 m/s.

The Fig. 5.9 depicts the typical variations in 630.0 nm airglow

during night of 28-29 January 2000 and 29-30 January 2000. In the

subsequent panels we plot ionospheric parameters (h’f & fof2) from

Ahmedabad, BZ component, Kp-index, H-component from Alibag,

and Dst-index as a function of local time.

The night of 28-29 January 2000 is magnetically disturbed

night as the geomagnetic activity index Ap is 32. It is clear from the

figure that the airglow intensity shows three peaks, two before

midnight (20:00 & 22:30 IST) and one post midnight (02:30 IST). It

is seen that in the beginning intensity of the airglow sharply

decreases due to increase in height of F-layer (h’F). After comparing

the ionosonde data with the photometer data it is seen that,

whenever the peak occurs, the height of F-layer (h’F) is lowered due

to magnetic disturbance. This shows dependence of vertical motion

of F-layer where volume emission rate is more. The dynamical

effects are more pronounced on the disturbed nights with larger h’F

changes.



-40

-10

Dst

(nT)

4+4 - 3+ 4+

15

65

(foF2

)2 (MH

z)2

(foF2)2

h' F

0

2.5

OI 6

30 n

m In

tens

ity

(arb

. uni

ts)

Zenith

OI 630 nmF 10.7 = 126

Ap = 32

Kolhapur

Ahmedabad

28-29 Jan 2000

-6

0

6

Bz

(nT)

560

620

H (n

T)

Zenith

OI 630 nmF 10.7 = 128

Ap = 30

Kolhapur

29-30 Jan 2000

4+ 5 - 4+ 4 -

210

260

h'F

(km

)

No Data

20 22 00 02 04 IST (Hrs)

20 22 00 02 04 IST (Hrs)

(a)

(b)

(c)

(e)

(f)

0.5

4.5

Kp

Inde

x

(d)

Fig. 5.9 Same as Fig. 5.8 but for nights of 28-29 January 2000, 29-

30 January 2000.



The ionospheric height variations (positive and negative

effect) at low latitudes during magnetic storms are dependent on

factors like changes in dynamics, heating and composition of the

ionosphere which takes place depending on latitude, longitude, local

time and on the phase of the geomagnetic storm [30]. It shows

good correlation between 1/I630 nm and F-region height (c.c. =0.76).

The following night 29-30 January 2000 is also disturbed night with

Ap=30 and Kp=5- to 4- during period of observations. Unfortunately

the ionosonde data is not available for this night to see any relation

between h’F and OI 630.0 nm intensity. Two sharp peaks are

noticed around 22:00 and 03:00 hrs IST with previous enhancement

is more in intensity compared to subsequent enhancement. The

peaks are around the time of high Dst or Kp-index [2]. Mukherjee et

al. [3] also observed double maxima in OI 630 nm in connection

with magnetic disturbances and is common at the Kolhapur station,

and our results are in good agreement with it. With increase in

magnetic disturbance, low latitude ionosphere experiences rapid

height variations. This height variation in the emitting F2-layer lead

to corresponding signature in observed OI 630 nm nightglow.

Fig. 5.10 portray OI 630 nm intensity observed at Kolhapur

during magnetically disturbed night 31 March-1 April 2000, Ap=23.

The ionospheric data, BZ-component, Kp-index, H-component and

Dst indices are plotted in the following panels. Two photometers

(30o N & Zenith) are operative.



-55

0

Dst

(nT)

2.3

4.3

Kp

Inde

x

4+

3 -

3+4 -

45

130(f

oF2)

2 (MH

z)2

(foF2)2

210

310

h' F

(km

)

h' F

Zenith

0

2

OI 6

30 n

m In

tens

ity

(arb

. uni

ts)

North

OI 630 nmF 10.7 = 225

Ap = 23

Kolhapur

Ahmedabad

31 March 2000- 1 April 2000

-7

0

7

Bz

(nT)

530

600

H (n

T)

Alibag

20 22 00 02 04 IST (Hrs)

Fig. 5.10 (a) Nocturnal variation of relative airglow intensity (630 nm) 31 March -01 April 2000 observed at Kolhapur. (b) temporal variation of h’F & (foF2)2 values at Ahmedabad, (c) IMF Bz, (d) Kp Index (e) H variation at nearby low latitude station, Alibag, and (f) Dst values.



Two prominent peaks are observed by both the photometers

with similar structure. The first peak is observed before midnight

and latter after midnight. It is clear from the observations that, the

enhancements in the OI 630 nm emission intensities are associated

with decrease in the bottomside of the F-layer, as evidence from the

F-layer nocturnal variations. On the quiet nights such double

maxima in intensity of IO 630 nm have not appeared [31]. It is seen

that the peak at North appears first and the Zenith records after 45

minutes, this gives rise to drift velocity in meridional direction

towards the equator assuming the same structure is moving

towards the equator. We determine the apparent drift speeds simply

from the time delay of common features in the data which gave

drifts as 69 m/s.

5.4 Conclusions:

On the basis of above discussion and observational evidence,

the main features associated with the nightglow observations can

be summarized as follows:

a) During both magnetically quiet and disturbed conditions, the

nocturnal OI 630.0 nm airglow variations observed at low

latitude stations are well correlated with the dynamic variations

seen in the F-region ionospheric parameters. The dynamical

effects observed are more pronounced during disturbed

conditions. The time variation in OI 630.0 nm is governed by

electron density fluctuations whereas during the magnetic



disturbance variation in OI 630.0 nm is more controlled by height

variations. Mukherjee [3] and Sahai [9] reported the correlation

coefficient between 1/I630.0 and h’F is generally large for the

disturbed nights. It is possibly because of larger height changes

in F-regions during the disturbed nights.

b) Sharper intensity peak in OI 630.0 nm intensity fluctuations

with pronounced double peak observed. Such occurrence of

double maxima in 630 nm during magnetic disturbance has also

been noted by Misawa and Takeuchi [31] and Sahai [9].

c) It was also found that, the airglow structure was moving

equatoward before midnight with speed between 60 to 161 m/s.

Balan [16] during his campaign observed that under magnetically

conditions, the meridional wind is poleward during daytime and

equatoward during night.

d) The OI 630.0 nm emission shows periodic intensity variations

associated with vertical oscillations in the ionospheric F-region

plasma during magnetic disturbances. The vertical oscillations in

the ionospheric F-region plasma are possibly associated with

magnetospheric sub-storms electric fields penetrating to low

latitude, and with thermospheric neutral wind variations due to

high latitude thermospheric heating [8].

e) The enhancement of OI 630.0 nm emission correlates well with

the Kp index.



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