Excitation of frequency-upshifted Langmuir waves by HF heater waves in the ionosphere

Summary form only given, as follows. We have analyzed a parametric process that can excite the frequency-upshifted Langmuir waves in the ionosphere. The pump waves are the langmuir waves produced by the injected O-mode HF heater wave. These HF-produced Langmuir waves propagate parallelly along the geomagnetic field. Each of them is intense enough to excite two obliquely propagating Langmuir sidebands together with a lower-hybrid mode. One Langmuir sideband is frequency-upshifted, while the other is frequency-downshifted. However, the frequency-upshifted Langmuir sidebands are more intense than the frequency-downshifted Langmuir sidebands by several orders of magnitude, because the frequency-upshifted sidebands are normal modes but the frequency-downshifted modes are not. Our analysis shows that the frequency-upshifted Langmuir waves propagate obliquely with a narrow cone around the geomagnetic field. The frequencies of these Langmuir waves are different from the HF heater frequency by small values that are slightly greater than the lower hybrid resonance frequency. This process can only be detected at high latitudes such as Tromso, Norway where the geomagnetic field has a large dip angle, but one at mid-latitudes such as Arecibo, Puerto Rico.