Total electron content

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TEC plot for the continental USA, made on 2013-11-24.

Total electron content (TEC) is an important descriptive quantity for the

columnar number density. It is often reported in multiples of the so-called TEC unit, defined as TECU=1016el/m2≈1.66×10−8 mol⋅m−2.[1]

TEC is significant in determining the

solar activity
.

Formulation

The TEC is path-dependent. By definition, it can be calculated by integrating along the path ds through the ionosphere with the location-dependent electron density ne(s):

TEC =

The vertical TEC (VTEC) is determined by integration of the electron density on a perpendicular to the ground standing route, the slant TEC (STEC) is obtained by integrating over any straight path.

Propagation delay

To first order, the ionospheric

phase delay compared to propagation in vacuum reads:[2]
: eq. (9.41) 

while the ionospheric group delay has the same magnitude but opposite sign:

The ionospheric delay is normally expressed in units of length (meters), assuming a delay duration (in seconds) multiplied by the vacuum speed of light (in m/s). The proportionality constant κ reads:[2]: eq.(9.21), (9.20), (9.19), (9.14) [3]

where q, me, re are the

vacuum speed of light and ϵ0 is the vacuum permittivity. The value of the constant is approximately κ ≈ 40.308193 m3·s−2;[4][5]
the units can be expressed equivalently as m·m2·Hz2 to highlight the cancellation involved in yielding delays τ in meters, given f in Hz and TEC in m−2.

Typical daytime values of TEC are expressed on the scale from 0 to 100 TEC units. However, very small variations of 0.1-0.5 TEC units can be also extracted under the assumption of relatively constant observational

gravity waves propagating upward from lower atmosphere. [8]

References

  1. ISBN 978-3-211-83534-0
    .
  2. ^
    IERS Technical Note No.36
  3. ISBN 978-0-521-88974-2
    .
  4. better source needed
    ]
  5. better source needed
    ]
  6. doi:10.5194/angeo-32-1511-2014
    .
  7. doi:10.1029/2007GL031663
    . Retrieved 2023-01-23.
  8. doi:10.5194/angeo-41-409-2023
    .
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