Remote sensing of auroral E region plasma structures by radio, radar, and UV techniques at solar minimum


  • Sunanda Basu,

  • S. Basu,

  • R. Eastes,

  • R. E. Huffman,

  • R. E. Daniell,

  • P. K. Chaturvedi,

  • C. E. Valladares,

  • R. C. Livingston


The unique capability of the Polar BEAR satellite to simultaneously image auroral luminosities at multiple ultraviolet (UV) wavelengths and to remote sense large-scale (hundreds to tens of kilometers) and small-scale (kilometers to hundreds of meters) plasma density structures with its multifrequency beacon package is utilized to probe the auroral E region in the vicinity of the incoherent scatter radar (ISR) facility near Sondrestrom. In particular, we present coordinated observations on two nights obtained during the sunspot minimum (sunspot number <10) January–February 1987 period when good spatial and temporal conjunction was obtained between Polar BEAR overflights and Sondrestrom ISR measurements. With careful coordinated observations we were able to confirm that the energetic particle precipitation responsible for the UV emissions causes the electron density increases in the E region. These E region electron density enhancements were measured by the ISR at Sondrestrom. The integrations up to the topside of these ISR electron density profiles were consistent with the total electron content (TEC) measured by the Polar BEAR satellite. An electron transport model was utilized to determine quantitatively the electron density profiles which could be produced by the particle precipitation, which also produced multiple UV emissions measured by the imager; these profiles were found to be in good agreement with the observed ISR profiles in the E region. Surprisingly large magnitudes of phase and amplitude scintillations were measured at 137 and 413 MHz in the regions of TEC enhancements associated with the particle precipitation. Steep phase spectral slopes with spectral index of 4 were found in these regions. Strength-of-turbulence computations utilizing the ISR electron density profiles and observed characteristics of phase and amplitude scintillations are interpreted in terms of an irregularity amplitude varying between 10 and 20% at a several-kilometer outer scale size in the E region extending approximately 50 km in altitude. This outer scale size is also consistent with the measured phase to amplitude scintillation ratio. An estimate of the linear growth rate of the gradient-drift instability in the E region shows that these plasma density irregularities could have been generated by this process. The mutual consistency of these different sets of measurements provides confidence in the ability of the different techniques to remote sense large- and small-scale plasma density structures in the E region at least during sunspot minimum when the convection-dominated high-latitude F region is fairly weak.