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IJRSP Vol.41 [2012] >
IJRSP Vol.41(2) [April 2012] >
| Title: | Equinoctial asymmetry in the occurrence of equatorial spread-F over Indian longitudes during moderate to low solar activity period 2004-2007 |
| Authors: | Manju, G
Haridas, M K Madhav
Ravindran, Sudha
Pant, Tarun Kumar
Ram, S Tulasi |
| Keywords: | Equinoctial asymmetry
Equatorial spread-F (ESF)
Equatorial ionisation anomaly
Meridional wind |
| Issue Date: | Apr-2012 |
| Publisher: | NISCAIR-CSIR, India |
| PACS No.: | 94.20.dt; 94.20.Vv; 96.60.qd |
| Abstract: | The seasonal pattern of
equatorial spread-F (ESF) was observed at the magnetic equatorial station
Trivandrum and low latitude station SHAR in the Indian sector using ionosonde
data. A clearly higher ESF occurrence percentage is observed during vernal
equinox compared to autumnal equinox at both locations. Post-sunset vertical
drift velocities were observed to be nearly comparable at Trivandrum indicating
the comparable electrodynamical forcing on the post-sunset F-layer during the
two equinoxes. At the off equatorial station SHAR, post-sunset vertical drift
exhibits clear asymmetric pattern, with higher values in the vernal equinox,
indicating the possible role of meridional neutral winds in modulating the
layer height. The meridional winds estimated during the period just prior to
ESF at the two equinoxes reveal much larger poleward winds to be prevalent
during autumnal equinox compared to that in vernal equinox. Large neutral winds
are shown to be related directly to asymmetry factor of the equatorial
ionisation anomaly (EIA) derived from single station Coherent Radio Beacon Experiment (CRABEX) data. The larger
neutral winds in autumnal equinox, results in an increase in off equatorial
E-region conductivity, thereby, inhibiting or weakening the F-region dynamo.
This study, thus, focuses on the role of neutral dynamics, as one possible
candidate producing the asymmetric occurrence pattern of ESF, during the two
equinoxes over Indian longitudes. |
| Page(s): | 240-246 |
| CC License: |  CC Attribution-Noncommercial-No Derivative Works 2.5 India |
| ISSN: | 0975-105X (Online); 0367-8393 (Print) |
| Source: | IJRSP Vol.41(2) [April 2012]
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