Ionospheric plasma bubble generated by Arecibo heater

Abstract

Abstract.During recent experiments ionospheric plasma bubbles were excited by the upgraded HF heater at Arecibo. These plasma bubbles were observed by radar in the midnight sector with the entire flux tube in darkness. A simple model is outlined to explain the dynamics of density depletions generated during O-mode wave heating of the F layer. We suggest that thermal expansion of plasma away from the heated volume leads to enhanced recombination along the flux tube. In the absence of photoionization sources, density depletions develop along the excited flux tube. The discontinuity of gravity-driven currents at the walls of the depleted region requires development of polarization electric fields. Eastward polarization electric fields of •,2.5 mV/m within the flux tube caused an observed plasma bubble to drift vertically at a speed of 70 m/s.

Time-Dependent Nuclear Measurements of Mix in Inertial Confinement Fusion

“…Artificial space plasma disturbances are often generated during controlledstudies of space plasma using ground-based radio frequency (RF) heater, as an attempt to study various aspects of physics involved in the plasma turbulence. During the 1997 experimental campaign at the Arecibo Observatory, sheet-like plasma density irregularities were formed at ionospheric F region altitudes as a result of injection of powerful high-frequency (HF) heater waves [Lee et al, 1998]. These parallel-plate structures were succesfully detected by the Arecibo incoherent scatter radar (ISR)…”

Generation of Artificial Acoustic-Gravity Waves and Traveling Ionospheric Disturbances in HF Heating Experiments

“…Effective heating of ionospheric plasmas using HF heater in continuous wave O-mode can yield a depleted magnetic flux tube, due to thermal expansion as well as chemical reactions caused by the heated ions (Lee et al 1998). Thus, we may expect that the temperature of neutrals inside the heated region can be increased to form significant thermal gradients.…”

Interhemispheric propagation of VLF transmissions in the presence of ionospheric HF heating

“…The resulting pressure force causes the plasma to expand, driving the effects both up and down the magnetic field line through a range of altitudes and speeding recombination through charge exchange and dissociation. As the hot plasma mixes with the colder preexisting ionization and this process continues, a detectable depletion of density is produced along the field line [Lee et al, 1998b]. This depleted flux tube persists until the heat source is removed.…”

“…All three nights suggest that O-mode CW heater operation may influence the local entry of VLF transmissions into preexisting or enhanced natural ducts. The I-IF heater is incapable of directly producing the large-scale and farreaching density perturbations necessary to duct very low frequencies interhemispherically, but it can significantly affect the local plasma environment where signals couple into the ionosphere, possibly altering the coupling efficiency of the bottomside ionosphere through the generation of largescale field-aligned irregularities and the depletion of magnetic flux tubes [Lee et al, 1998a[Lee et al, , 1998b[Lee et al, , 1999. It is then reasonable to expect that the heater might influence the local trapping of signals in existing ducts at higher altitudes.…”

“…Recent experiments using the heating facility at the Arecibo Observatory in Puerto Rico have shown that the heater is capable of producing large-scale sheet-like irregularities through instability processes [Lee et al, 1998a] and depleted flux tubes corresponding to plasma bubbles [Lee et al, 1998b[Lee et al, , 1999. These results confirm the longstanding suspicion of some that heater effects need not remain confined locally and to small scales and support the idea that heating may affect the ducting of VLF emissions on nearby field lines by enhancing the coupling of wave energy into the plasma [Lee et al, 1992].…”