 |
| Titel |
Simultaneous observations of ESF irregularities over Indian region using radar and GPS |
| VerfasserIn |
S. Sripathi, S. Bose, A. K. Patra, T. K. Pant, B. Kakad, A. Bhattacharyya |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
0992-7689
|
| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 26, no. 11 ; Nr. 26, no. 11 (2008-10-21), S.3197-3213 |
| Datensatznummer |
250016265
|
| Publikation (Nr.) |
 copernicus.org/angeo-26-3197-2008.pdf |
|
|
|
|
|
| Zusammenfassung |
| In this paper, we present simultaneous observations of temporal and spatial
variability of total electron content (TEC) and GPS amplitude scintillations
on L1 frequency (1.575 GHz) during the time of equatorial spread F (ESF)
while the MST radar (53 MHz) located at Gadanki (13.5° N, 79.2° E,
Dip latitude 6.3° N), a low latitude station, made simultaneous
observations. In particular, the latitudinal and longitudinal extent of TEC
and L-band scintillations was studied in the Indian region for different
types of ESF structures observed using the MST radar during the low solar
activity period of 2004 and 2005. Simultaneous radar and GPS observations
during severe ESF events in the pre-midnight hour reveal that significant
GPS L band scintillations, depletions in TEC, and the double derivative of
the TEC index (DROTI), which is a measure of fluctuations in TEC, obtained
at low latitudes coincide with the appearance of radar echoes at Gadanki. As
expected, when the irregularities reach higher altitudes as seen in the
radar map during pre-midnight periods, strong scintillations on an L-band
signal are observed at higher latitudes. Conversely, when radar echoes are
confined to only lower altitudes, weak scintillations are found and their
latitudinal extent is small. During magnetically quiet periods, we have
recorded plume type radar echoes during a post-midnight period that is
devoid of L-band scintillations. Using spectral slopes and cross-correlation
index of the VHF scintillation observations, we suggest that these
irregularities could be "dead" or "fossil" bubbles which are just drifting
in from west. This scenario is consistent with the observations where
suppression of pre-reversal enhancement (PRE) in the eastward electric field
is indicated by ionosonde observations of the height of equatorial F layer
and also occurrence of low spectral width in the radar observations relative
to pre-midnight period. However, absence of L-band scintillations during
post-midnight event, when radar observed plume like structures and
scintillations were recorded on VHF band, raises questions about the process
of evolution of the irregularities. A possible explanation is that whereas
small scale (~3 m) irregularities are generated through secondary
waves that grow on the walls of km scale size irregularities, in this case
evolution of the Rayleigh-Taylor instability itself did not extend to
irregularities of scale sizes of a few hundred meters that produce
scintillation on a L-band signal. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|