 |
| Titel |
Imperfect coupling between northern and southern ionospheres: asymmetry in TEC anomalies before earthquakes |
| VerfasserIn |
Hau-Kun Jhuang, Yi-Ying Ho, Lou-Chuang Lee |
| Konferenz |
EGU General Assembly 2016
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250124280
|
| Publikation (Nr.) |
 EGU/EGU2016-3689.pdf |
|
|
|
|
|
| Zusammenfassung |
| The northern ionosphere is coupled to the conjugate southern ionosphere through the highly
conducting geomagenetic field lines. The coupling is very strong or “perfect” if the
geomagnetic field lines are equipotential (the parallel electric field E||=0) and hence the
perpendicular electric field (E⊥) at the conjugate sites of both ionospheres are equal. The
coupling is “imperfect” if some of the geomagnetic field lines are non-equipotential
(E||≠0). The field-aligned electric field E|| can be associated with electron inertia,
pressure gradient and collisions appearing in the form of double layer, kinetic Alfvén
waves and finite field-aligned conductivity σ||. We use the Global Ionospheric Maps
(GIM) data to examine the conjugate effect of total electron content (TEC) for six
significant earthquakes. The anomalous (ΔTEC)source in the source ionosphere and
(ΔTEC)conjugate in the conjugate ionosphere are obtained for 85 events before the six
earthquakes. The ΔTEC ratio β = (ΔTEC)conjugate / (ΔTEC)source is calculated for each
anomaly. For a “perfect” coupling, β=1. There are 85 anomalous events before the six
significant earthquakes, with 62 events occurring in the daytime (07-18 LT) and
23 events in the nighttime (19-06 LT). The average value of daytime (07-18 LT)
TEC variations in the source ionosphere is |ΔTEC|source =20.13 TECu, while
the average value in the nighttime (19-06 LT) ionosphere is |ΔTEC|source=14.43
TECu. The value of ΔTEC ratio β ranges from 0.05 (very weak coupling) to 0.98
(nearly perfect coupling) with an average of 0.52. There are 14 strong coupling
cases with β ≥0.8, which take place from 11 LT to 19 LT. The daytime (07-18
LT) β average value is 0.57 and the nighttime (19-06 LT) β average is 0.37. The
south-north ionosphere coupling is stronger (weaker) in the daytime (nighttime). |
|
|
|
|
|
|