Papers

The downward flux of ionization was investigated using whistler-mode signals recorded at the lowlatitude ground station Jammu (geomagnetic latitude 22°262 , L = 1.17) on 5 June 1997. The whistler observations exhibit a systematic temporal variation in dispersion. This decrease in dispersion is interpreted as a corresponding reduction in the electron content of ionization flux tubes and is compared with the mid-latitude results reported by Park (1972, Technical Report, Stanford University). Using Park’s expressions, the equatorial electron density and total electron tube content (NT) were computed. The whistler measurements indicate an average downward electron flux of 2.8 × 108 electrons cm-2 s-1. The ionization gradient was also estimated using the simple diffusion equation that relates the particle flux to the ambipolar diffusion coefficient. The flux obtained from this diffusion model is found to be within an order of magnitude lower than that derived from the whistler dispersion analysis. This discrepancy suggests that, in addition to diffusion, other processes—such as (E ×B) drifts—play a dominant role in controlling ionospheric plasma transport at low latitudes.