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Absorbing Layer of the Ionosphere at Low Height


THE ionosphere is now generally regarded as divided into two main regions of intense ionisation. The upper (F or Appleton) region commences at a height of about 250 km., while the lower (E or Kennelly-Heaviside) region begins at a height of about 90 km. Besides these two main regions, the existence of a so-called D or absorbing layer has been suggested from time to time1. The presence of such a layer has not, however, until now been experimentally demonstrated, and it has rather been the tendency in recent years to discredit its existence. Recently we have, however, in the course of our ionospheric studies at Calcutta been able to detect echoes of radio waves returned from a virtual height of about 55 km. by the well-known pulse method. The echoes from the E layer were at the same time observed to be returned from a virtual height of 119 km. The present communication gives a preliminary account of the observations we have made in connexion with the existence of a low-lying absorbing layer.

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  1. 1

    Appleton and Ratcliffe, Proc. Roy. Soc., A, 128, 155; 1930. M. A. Bontch-Bruewitch, Proc. I.R.E., 22, 1135; 1934. S. Sillitoe, Canad. J. Res., 11, 163; 1934.

  2. 2

    F. W. G. White, Proc. Phys. Soc., 46, 101; 1934.

  3. 3

    Appleton and Naismith, Proc. Roy. Soc., A, 137, 39; 1932 (Fig. 1). Mary Taylor, Proc. Phys. Soc., 46, 415; 1934. D. F. Martyn, Proc. Phys. Soc., 47, 335, 338; 1935.

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    G. M. B. Dobson and D. N. Harrison, Proc. Roy. Soc., A, 114, 537, 540; 1927. Chapman, Proc. Roy. Soc., A, 132, 356; 1931.

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    Chapman, Quart. J. Roy. Met. Soc., 52, 231; 1926.

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