Instruments:tir

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Tirunelveli MF Radar =

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Acknowledgments

The Tirunelveli MF radar is operated by the Indian Institute of Geomagnetism, Mumbai with financial support from the Department of Science and Technology, Government of India.

Instrument/Model Description

The Tirunelveli, India (8.67N, 77.82E; 30 m alt) 1.98 MHz MF radar has been in continuous operation since December 1992. On day 359 of 2001 at 89 km altitude, the apex magnetic coordinates were (6.8, 149.8) degrees. The magnetic inclination and declination angles were 1.4 deg and -2.6 deg. The magnetic local time at 0 Universal Time (UT) is about 0554 MLT. The solar local time (SLT) is UT plus 5 hours and 11 minutes (77.82/15.=5.188).

The original data files are hourly averages of the zonal and meridional velocity in Indian Standard Time (IST), which is 5 hours and 30 minutes later than UT. Samples are taken every 2 min, so a possible 30 samples can be had between IST 0:00:00 and IST 0:59:00, which is labelled as hour 1:00:00 IST. These times have been converted to the mid-point solar local time (or 0:11 SLT or 0.188 SLT for this example).

The MF radar system is identical to the one operating at Christmas island (2E,158W) and designed by Robert Vincent (robert.vincent@adelaide.edu.au) of the University of Adelaide in Australia (Vincent, 1991). The operating frequency is 1.98 MHz, with a peak transmitter power of 25 kW. The radar operates as a spaced-antenna system (Vincent, 1986), relying on coherent echo signals from middle atmosphere ionization. The inter-pulse period is 12.5 millisec during the day and 25 millisec during the night. There are 32 coherent integrations during the day and 16 at night, using 256 samples in the full correlation analysis (FCA) of Briggs [1984] with built-in rejection criteria. [ie, want about 2 min or 102.4 sec integration during day and night, or 12.5x10-3sec * 32 integ * 256 samples = 102.4 sec and 25x10-3sec * 16 integ * 256 samples = 102.4 sec.]

The height coverage is 68-98 km during the day and 70-98 km during the night. The pulse width is 30 microsec, giving a height resolution of 4.5 km assuming a simple rectangular wave pulse [range of heights illuminated by the wave pulse = velocity of light * pulse-width / 2 = 3x10**8 m/s * 30x10-6s / 2 = 4.5 km]. However, neutral velocities are given every 2 km between 80 and 98 km since the ionization is less below 80 km.

Various upgrades to the system are planned, possibly as soon as 2003. The analog to digital (A/D) signals are presently in 8-bits, which should be upgraded to 12-bits to avoid signal saturation problems. The system may also be upgraded to monitor electron densities, and also improve the antenna systems.

Starting in 2002, the data are also contributed to the joint TIMED-CEDAR program of the National Aeronautics and Space Administration (NASA) and the National Science Foundation (NSF). The original hourly velocities are converted to harmonic analyses in UT over sliding 4-day intervals. The Mesosphere-Lower Thermosphere Radars (MLTR) organized for the TIMED-CEDAR program provide horizontal and sometimes 'vertical' neutral winds to the processing center at the University of Colorado. Summary plots from several types of MLTRs in the TIMED-CEDAR program and references for the instruments, analyses using the radars, and comparisons with other satellite or ground-based instruments can be found at: [/instr/mltr.html /instr/mltr.html] The harmonic analyses are also available at that site, or from the University of Colorado at: http://sisko.colorado.edu/TIMED/data/MLTR/

References

Fraser, G., Partial reflection spaced antenna wind measurements, MAP Handbook, Vol. 13, p 233, 1984.
Briggs, B. H., The analysis of spaced sensor records by correlation techniques, MAP Handbook, Vol. 13, 166-186, 1984.
Vincent, R. A., Hardware requirements: A new generation partial reflection radar for studies of the equatorial mesosphere, MAP Handbook, Vol. 20, p 85, 1986.
Vincent, R. A. and D. Lesicar, Dynamics of the equatorial mesosphere: First results with a new generation partial reflection radar, Geophys. Res. Lett., 18, 825-828, 1991.
Rajaram, R. and S. Gurubaran, Seasonal variabilities of low-latitude meosospheric winds, Ann. Geophys., 16, 197, 1998.

Summary Plots for Tirunelveli MF Radar

(No 2002 data for Feb 22-Mar 5, Mar 13-31, Apr 7-10,30, Jun 22-27, Aug 20-22, Aug 27 (after 0029 UT), Aug 30, Sep 13-16, Sep 18-Oct 9, and Nov 16-22.)


-Revised 10 February 2003 by Barbara Emery