Other
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sa31a14r&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SA31A-14
Other
2415 Equatorial Ionosphere, 2423 Ionization Mechanisms, 2427 Ionosphere/Atmosphere Interactions (0335), 2437 Ionospheric Dynamics, 3334 Middle Atmosphere Dynamics (0341, 0342)
Scientific paper
The free propagating or normal resonant or Rossby mode (sometimes called slow moving second symmetric Kelvin wave) 16-day (12-20 day periodicity band) planetary wave in the mesosphere and its influence on the equatorial electrojet strength (EEJS) is searched in the present work. Hourly averaged wind data obtained from the medium frequency (MF 1.98 MHz) partial reflection (spaced antenna) radar located at the near dip equatorial station Tirunelveli (8.7° N, 77.8° E, geographic; 0.35° N magnetic dip) India and the ground based magnetic field measurements obtained from Trivandrum (8.5° N, 77.0° E, geographic; 0.65° N magnetic dip) and Alibag (18.6° N, 72.9° E, geographic; 25.5° N magnetic dip) India are subjected to fast Fourier transform (FFT) spectral analysis for the years 1995 and 1996. Hourly solar X-ray flux (1-8 Å) data obtained from GOES-7 satellite is read manually from the analog charts published in the solar geophysical data reports (NGDC) and subjected to the same FFT analysis. Our observation shows that the hourly averaged raw data (both wind and EEJS) itself shows a noticeable ~16-day periodicity modulation. However, the actual period of oscillation lies in the 12-20 day band. More often it is concentrated near 15-day and its amplitudes are accordingly with theory and earlier observations made both in the Northern and Southern midlatitudes. The four data segments (1024 hours each) for the year 1996 is looked more closely and presented here. The first segment, 1 January to 25 March, shows a pronounced peak near 15.2 day in both the zonal wind and EEJS. This shows that the periodiocity of 15.2 day found in the EEJS is associated more with the influence of the upward propagation of the mesospheric planetary wave. However, the peak near the 16-day period found in the EEJS is not seems to be associated with the mesospheric planetary wave for the second segment 26 March to 18 June 1996. In this case, we found that the X-ray flux showed a well pronounced peak (burst like) near this periodicity. Again, in the third segment 19 June to 12 September, we found a well pronounced spectrum near 13.1-day period in both the wind and EEJS. However, near 19.5-day oscillation found in the EEJS is associated neither with the wind nor with X-ray flux data. Here, it may be associated with other important high energy solar emissions such as Lyman Alpha, EUV etc. One more interesting feature we found in the fourth segment 13 September to 6 December is that near 18.1 day periodicity found in the winds is not associated with the corresponding enhancements in the EEJS. Here, it may be suggested that before reaching above about 100 km, the wave might have damped heavily and hence not able to see the influence of it in the EEJS. Some times the time lag of several days, between the intense long period planetary wave activity in the EEJS and the MLT winds suggests an idea that the dynamo region is first influenced by the direct solar high energy emissions and it takes some days for the planetary waves to propagate to higher altitudes from the lower atmosphere to the EEJS region. The two strong sources of high energy emissions (x-rays, EUV etc.,) located almost 180° apart on the solar (longitude) surface may be the causal effect of the influence on the EEJS, since the average solar rotation period is 27 days.
Gurubaran S.
Rajaram Ramaswamy
Ramkumar T. K.
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