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Large-scale irregularundulations of theionosphere asobserved by theFalkland IslandsSuperDARN radarS. E. Milan, A. Grocott, M. Lester,T. K. Yeoman, M. P. Freeman, and G. Chisham
Auroral scatter
Subauroral electrodynamics
South Atlantic Anomaly
Vertical coupling
Gravity waves
Orographic gravity waves
Mesospheric winds and tides
First light, 14th Feb 2010
Expected removal ofelectronics, Sept 2011
Very modest amountsof ionospheric scatter
Ionospheric motions
Wot, no interferometer? Milan et al. (1997)
Dskip ray
radar operating frequency fr
ionospheric critical frequency fc
h
Secant law ccr ff sec
Skip distance
fc
Dskip ray
radar operating frequency fr
fc
ionospheric critical frequency fc
h
Secant law ccr ff sec
Skip distanceskip distance S
proportional to h
dt
dh
dt
dScsec2
S21S2
1
Dskip ray
a particular range gate corresponds to a ray with a fixed path length
h
Range gate
fc
Dskip ray
h
Range gatea particular range gate corresponds to a ray with a fixed path length
as the ionosphere lifts, the ray footprint movestowards the radar; the motion relative to surfacefeatures produce a Doppler shift apparentlyaway from the radar
dt
dhdt
dR
dt
Pd
sin2
cos2
R
fc
dt
dh
dt
Pd
sin2
dt
dh
dt
dScsec2
54sin
sec
c
dt
Pd
dt
dS
skip distance ground range
fc is associated with skip ray, D appropriate for a particular range gate
At further ranges, D decreases and the ratio increases
This decrease in Doppler shift with range is observed
Observations consistent with ascent and descent ofthe ionosphere with an amplitude of ±50 [email protected]
ConclusionsFIR observes irregular undulations of the ionosphere;
ionospheric motions may be ±50 km in altitude(test with ray tracing?)
They appear predominantly at night; more needs tobe done to understand the propagation mode(e.g. ray tracing)
Tend to occur as pairs of positive-then-negative,towards-then-away motions
In contrast, most gravity waves are observed onthe dayside
The appearance of undulations may be related togeomagnetic activity, in two casespossibly associated with solar wind [email protected]
