Observation of ionospheric disturbances following a 5‐kt chemical explosion 2. Prolonged anomalies and stratifications in the lower thermosphere after shock passage

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Abstract
We have observed unusual stratifications and prolonged spectral deformations of radio echoes after the passage through the E region of the shock wave produced by a 5‐kt chemical explosion. Our observations were obtained by vertical HF pulsed ionospheric sounding. At the total reflection level of the sounding waves, at a horizontal distance of 30 km from the explosion, the passage of the shock wave generated a complex structure suggesting a significant deformation of the reflecting surface. This effect was followed at the E region total reflection level (130 km) by a broadening of the Doppler spectra, persisting several tens of minutes. Two spectral peaks appear at 0.5 Hz, suggesting an amplitude modulation with a period of the order of 2 s. At lower virtual heights (94, 103, and 115 km), stratifications appear after the shock passage and move downward at velocities of the order of 23 m/s. These layers persist for several minutes. Irregularities have also been observed in the E region for over 30 min after the shock passage by a network of continuous wave HF ionospheric sounders located 250 km west of the source. The origin of these structures is discussed.