|
|
 |
|
|
Ann. Geophys., 24, 543-553, 2006
www.ann-geophys.net/24/543/2006/
© European Geosciences Union 2006
Saturation and hysteresis effects in ionospheric modification experiments observed by the CUTLASS and EISCAT radars
D. M. Wright1, J. A. Davies2, T. K. Yeoman1, T. R. Robinson1, and H. Shergill1
1Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
2Space Science and Technology Department, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, UK
Abstract. The results of high latitude ionospheric modification experiments utilising
the EISCAT heating facility at Tromsø are presented. As a result of the
interaction between the high power pump waves and upper hybrid waves in the
ionosphere, field-aligned electron density irregularities are artificially
excited. Observations of these structures with the CUTLASS coherent HF
radars and the EISCAT incoherent UHF radar exhibit hysteresis effects as the
heater output power is varied. These are explained in terms of the two-stage
mechanism which leads to the growth of the irregularities. Experiments which
involve preconditioning of the ionosphere also indicate that hysteresis
could be exploited to maximise the intensity of the field-aligned
irregularities, especially where the available heater power is limited.
In addition, the saturation of the irregularity amplitude is considered.
Although, the rate of irregularity growth becomes less rapid at high heater
powers it does not seem to fully saturate, indicating that the amplification
would continue beyond the capabilities of the Tromsø heater - currently
the most powerful of its kind. It is shown that the CUTLASS radars are
sensitive to irregularities produced by very low heater powers (effective
radiated powers <4 MW). This fact is discussed from the perspective of a
new heating facility, SPEAR, located on Spitzbergen and capable of
transmitting high frequency radio waves with an effective radiated power
~10% of that of the Tromsø heater (28MW).
Full Article in PDF (907 KB) |
|
|
