STUDY OF TROPOSPHERIC GRAVITY WAVES AT EQUATORIAL LATITUDE, INDIA M. LAL EQUATORIAL GEOPHYSICAL RESEARCH LABORATORY INDIAN INSTITUTE OF GEOMAGNETIC TIRUNELVELI – , INDIA

INTRODUCTION WE HAVE STUDIED THE INFLUENCE OF GEOMAGNETIC STORM ON THE TROPOSPHERIC ACOUSTIC GRAVITY WAVES (AGW) AT EQUATORIAL LATITUDE STATION, TIRUNELVELI (8.7 O N, 77.8 O E), INDIA. WE HAVE STUDIED THE DAILY VARIATION OF AGW FOR 2000, 2003, AND 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 The upper panel is the –Dst index for comparison.

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 The upper panel is the daily average of gravity waves psd and lower panel is the –Dst index.

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

July – Aug 2004 This figure shows the gravity wave amplitude variation for July to Spt 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.

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

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

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

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

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

Jan – Feb 2004

This figure shows the diurnal variation of pressure changes for Jan and Feb 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.

CONCLUSION WE HAVE MADE AN ATTEMPT TO STUDY THE INFLUENCE OF GEOMAGNETIC STORM ON THE TROPOSPHERIC GRAVITY WAVES AT EQUATORIAL LATITUDE STATION, TIRUNELVELI (8.7 O N, 77.8 O E), INDIA SOME OF THE SEVERE GEOMAGNETIC STORM STUDIES IN THE PRESENT CASE ARE NOV 2004, OCT-NOV 2003, AND SPT SOME THE STRONG STORM STUDIED IN THE PRESENT CASE ARE JULY 2004, AUG 2003, JULY 2000, AND JAN-FEB 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.

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Mar _April 04

Mar _Apr 04