Geoscience Reference
In-Depth Information
Empirical model
DF5
33 kV
}
RCM
20
0.5
Initial time response
10
0
0.0
t
1
10 min
210
t
1´
t
160 min
10
0
0.0
210
220
20.5
02
06
10
Local time
14
18
22
Figure 3.27
Equatorial ionospheric perturbation electric field patterns calculated for
three times after an increase in the Region 1 field-aligned currents. Ionospheric dynamo
effects were not included. [After Fejer and Scherliess (1995). Reproduced with permission
of the American Geophysical Union.]
corresponding zonal electric field data measured at Jicamarca are given. In each
of the latter plots the mean field pattern is shown as the solid line. The abrupt
change in the Jicamarca field between 2300 and 0300 local time on August
8/9 has been studied by Gonzales et al. (1979) and has a waveform identical
to that of the electric field measured simultaneously at Chatanika, Alaska. (See
also Fig. 3.25a for identical auroral and equatorial waveforms.) This is a clear
case of rapid penetration of high-latitude electric fields to low latitudes. On the
next day the Jicamarca zonal field component displayed a long-lived deviation
from the average, commencing at 2200 local time and lasting for 8 h. Fejer et al.
(1983) argue that such slowly developing, delayed electric field changes are due
to a worldwide change in the thermosphere winds. These changes alter the E
region and equatorial F-region dynamo and thereby change the electric field at
low latitudes from the normal pattern.
Taken together, we see that these and other high-latitude effects contribute to
the “weather” in the low-latitude electric field and neutral wind patterns. Their
study therefore yields information on both high- and low-latitude phenomena.
Much can be learned about global electrodynamics and thermospheric physics
through events of these types. The true test of global electrodynamic model calcu-
lations may be their ability to predict the low-latitude ionospheric effects of such
diverse external influences. Such studies are well under way (Maruyama et al.,
2005). In Chapter 5 we discuss further the penetration of high-latitude electric
fields to midlatitudes. The origins of the high-latitude electric fields themselves
are considered in some detail in Chapter 8.
Search WWH ::
Custom Search