STUDY OF TROPOSPHERIC GRAVITY WAVES AT

EQUATORIAL LATITUDE, INDIAM. LAL

EQUATORIAL GEOPHYSICAL RESEARCH LABORATORYINDIAN INSTITUTE OF GEOMAGNETIC

TIRUNELVELI – 627011, INDIAE-MAIL: MLAL@IIG.IIGM.RES.IN

INTRODUCTION

• WE HAVE STUDIED THE INFLUENCE OF GEOMAGNETIC STORM ON THE TROPOSPHERIC ACOUSTIC GRAVITY WAVES (AGW) AT EQUATORIAL LATITUDE STATION, TIRUNELVELI (8.7ON, 77.8OE), INDIA.

• WE HAVE STUDIED THE DAILY VARIATION OF AGW FOR 2000, 2003, AND 2004.

• WE HAVE COMPARED OUR OBSERVATIONS WITH Dst INDEX VARIATION.

• OUR OBSERVATION SAYS THAT THERE IS A SHORT PERIOD DELAY AS WELL AS LONG PERIOD DELAY PRESENT BEWEEN Dst INDEX AND AGW.

JULY 2000

• This figure shows the daily average of the tropospheric gravity wave amplitude obtained during July 2000. The upper panel is the –Dst index for comparison. 0 5 10 15 20 25 30

0.00.20.40.60.81.01.21.4

-Dst

inde

x

avgGW

ampl

itude

day number (July 2000)

0 5 10 15 20 25 30-50

050

100150200250300350

dst

SPT 2000

• This figure shows the power spectral density (psd) of tropospheric gravity waves obtained at equatorial latitude, India during severe geomagnetic storm of Spt 2000. The upper panel is the daily average of gravity waves psd and lower panel is the –Dst index.

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

0

50

100

150

200

-Dst index

-Dst

inde

x

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

0.000.020.040.060.080.100.120.140.16

day number (Spt 2000)

psd

psd(

mb^

2)

Oct – Nov 2003

• This figure shows the tropospheric gravity waves amplitude obtained during Oct to Dec 2003. The upper panel is the –Dst index and the lower panel is the amplitude of gravity waves measured at equatorial latitude station, India.

30 60 900.0080.0100.0120.0140.0160.0180.0200.0220.0240.0260.028

decnovoct

gravity wave

ampl

itude

day number( 20 Oct - 31 Dec 2003)

30 60 90-100

0

100

200

300

400

500

-Dst Index

-Dst

Inde

x

July – Aug 2004

• This figure shows the gravity wave amplitude variation for July to Spt 2004. the upper panel shows the –Dst index variation. There is lag of about 20 days is seen between Dst enhancement and tropospheric gravity wave amplitude.

0 30 60 900.005

0.010

0.015

0.020

0.025

0.030

gravity wave

amp

litud

e

day number (July - Spt 2004)

0 30 60 90

0

50

100

150

200

-Dst index

-Dst

inde

x

Nov 2004

• This figure shows the amplitude of gravity wave variation and the –Dst index variation for the month of Nov 2004. There is a time lag of 5 days is seen between gravity wave maxima and –Dst index maxima.

330 360

050

100150200250300350400

- Dst index

-Dst

inde

x

day number (Nov - Dec 2004)

330 3600.005

0.010

0.015

0.020

0.025

0.030

Gravity Waves

ampl

itude

July – Aug 2004

• This figure shows the contour plot of tropospheric gravity waves obtained during Aug 2004. The presence of Acoustic gravity waves of period about 50 min has been obtained after the July 2004 geomagnetic storm.

0.00 10.00 20.00 30.00

Aug 2004

0.00

40.00

80.00

120.00

160.00

200.00

period in min

0.00

0.00

0.01

0.01

0.02

0.03

0.03

0.04

0.04

0.05

0.05

0.05

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0.06

0.07

Oct – Dec 2003

• This figure shows the contour plot of the tropospheric acoustic gravity waves obtained during Oct – Dec 2003. There is significant increase in the gravity waves amplitude obtained after the geomagnetic storm.

0.00 20.00 40.00 60.00 80.00

O CT NO V DEC 2003

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

160.00

180.00

200.00

GRAVIT

Y WAVE

(PERIO

D IN MI

NUTE)

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.11

0.12

0.13

M AGNET I C ST O RM O N 20 NO V 2003

Nov 2004

• This figure shows the contour plot of acoustic gravity waves obtained during Nov 2004. The prominent presence of gravity waves is seen after the Geomagnetic Storm. 0 10 20 30

day num ber (Nov 2004)

0

20

40

60

80

100

120

140

160

180

200

PERIOD

IN

MIN

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.11

0.12

0.13

0.14

0.15

0.16

0.17

Jan-Feb 2004

• This figure shows the amplitude of gravity waves obtained during Jan-Feb 2004. The lower panel is the –Dst index variation. There is time lag of 5 and 20 days are found.

0 30 60-20

020406080

100120140160

- Dst index

ampl

itude

day number (Jan - Feb 2004)

0 30 60

0.010

0.015

0.020

gravity wave

-dst

inde

x

Jan – Feb 2004

0 10 20 30 40 50 60

DAY NUM BER ( J AN - FEB 2004)

0

20

40

60

80

100

120

140

160

180

200

PERIOD I

N MIN

0.00

0.00

0.01

0.01

0.02

0.03

0.03

0.04

0.04

0.05

0.05

0.05

0.06

0.06

0.07

Jan – Feb 2004

• This figure shows the diurnal variation of pressure changes for Jan and Feb 2004. The sharp change in the pressure obtained at the second half of the Feb 2004, which is after 20 days of the geomagnetic storm event.

0 300 600 900 1200 1500-900

-600

-300

0

300

600

900

jan1flt

0 300 600 900 1200 1500-900

-600

-300

0

300

600

900

jan2flt

0 300 600 900 1200 1500-900

-600

-300

0

300

600

900

feb1flt

pre

ssur

e va

riat

ion

0 300 600 900 1200 1500-900

-600

-300

0

300

600

900

feb2flt

time in minute

CONCLUSION

• WE HAVE MADE AN ATTEMPT TO STUDY THE INFLUENCE OF GEOMAGNETIC STORM ON THE TROPOSPHERIC GRAVITY WAVES AT EQUATORIAL LATITUDE STATION, TIRUNELVELI (8.7ON, 77.8OE), INDIA

• SOME OF THE SEVERE GEOMAGNETIC STORM STUDIES IN THE PRESENT CASE ARE NOV 2004, OCT-NOV 2003, AND SPT 2000. SOME THE STRONG STORM STUDIED IN THE PRESENT CASE ARE JULY 2004, AUG 2003, JULY 2000, AND JAN-FEB 2004.

• DAILY AVERAGE OF AMPLITUDE OF ACOUSTIC GRAVITY WAVE (AGW) HAVE BEEN DERIVED AND COMPARED WITH Dst INDEX.

• SHORT PERIOD AS WELL AS LONG PERIOD TIME LAG HAS BEEN OBTAINED BETWEEN DsT INDEX AND AGW.

cont…• SHORT PERIOD DELAY OCCURRED IN SEVERE

GEOMAGNETIC STORM AND LONG PERIOD DELAY FOUND TO BE PRESENT IN STRONG GEOMAGNETIC STORM.

• PRESENCE OF JET STREAM HAS BEEN OBSERVED DURING THE GEOMAGNETIC STORM AND FOUND TO BE CONTINUE FOR ABOUT FEW WEEKS PERIOD.

• THE FORMATION OF CYCLONE HAS BEEN OBSERVED AFTER THE SEVERE GEOMAGNETIC STORM AT THE TIME DELAY OF ABOUT 60 DAYS.

• OUR STUDY CLEARLY SHOWS THE INFLUENCE OF GEOMAGNETIC STORM ON THE TROPOSPHERIC AGW DESPITE PRESENCE OF SEVERAL OTHER SOURCES OF AGW.

THANK YOU

Any question, please send me an e-mail.

Mar _April 04

60 90 120

0.010

0.015

0.020

0.025

0.030amplitude

am

plit

ud

e

day number (Mar_April 2004)

60 90 120-20

020406080

100120140160 -Dst index

-Dst

ind

ex

Mar _Apr 04

0.00 20.00 40.00 60.00

Day Number(M ar Apr 2004)

0.00

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Period

in Min

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