An ionospheric index suitable for estimating the degree of ionospheric perturbations

Abstract

-Space weather can strongly affect trans-ionospheric radio signals depending on the used frequency. In order to assess the strength of a space weather event from its origin at the sun towards its impact on the ionosphere a number of physical quantities need to be derived from scientific measurements. These are for example the Wolf number sunspot index, the solar flux density F10.7, measurements of the interplanetary magnetic field, the proton density, the solar wind speed, the dynamical pressure, the geomagnetic indices Auroral Electrojet, Kp, Ap and Dst as well as the Total Electron Content (TEC), the Rate of TEC, the scintillation indices S4 and s(') and the Along-Arc TEC Rate index index. All these quantities provide in combination with an additional classification an orientation in a physical complex environment. Hence, they are used for brief communication of a simplified but appropriate space situation awareness. However, space weather driven ionospheric phenomena can affect many customers in the communication and navigation domain, which are still served inadequately by the existing indices. We present a new robust index, that is able to properly characterize temporal and spatial ionospheric variations of small to medium scales. The proposed ionospheric disturbance index can overcome several drawbacks of other ionospheric measures and might be suitable as potential driver for an ionospheric space weather scale.

Estimation of Spatial Gradients and Temporal Variations of the Total Electron Content Using Ground‐Based GNSS Measurements

“…This is valid if data from only one GNSS satellite and different ground stations are used in a country with a lateral extension of less than 1,000 km, like Germany (cf. Wilken et al, ).…”

“…Here we suggest naming referring to the TEC gradients defined in equations , , and as the Gradient Ionosphere indeX (GIXx, GIXy, GIX) to distinguish it from related DIX approaches which use the calibration independent rate of TEC data (Jakowski, Borries, et al, ; Wilken et al, ).…”

“…Principally, GIX, GIXS, and GIXP 95 can mainly be defined by absolute values (e.g., measured in mTECU/km) or by a dimensionless index that is referred to nominal threshold values (e.g., ∇ TEC T in the order of a few mTECU/km for GIX) that have been found to be representative for the quiet ionosphere. The definition of such thresholds, as suggested by Wilken et al () for the Disturbance IndeX Spatial Gradient approach, would be a matter for discussion by the international user community in order to define internationally acceptable standards as recently has been discussed at the COSPAR 2018 42nd Assembly in Pasadena, United States (http://cospar2018.org/scientific-program/associated-events/).…”

“…If a dimensionless approach is preferred, the current index value must be referred to a threshold value, for example, for GIX this might be where ∇ TEC T defines a threshold value characterizing the average behavior of TEC gradients over the selected area. For scaling dimensionless spatial and temporal indices, the actual index parameters must primarily refer to basic values characterizing “normal” or “quiet” ionospheric conditions (Wilken et al, ). Such basic values should be defined by the international community, standardized, and be valid for all subsequent applications.…”

“…To overcome this problem, Jakowski, Borries, et al () proposed a so‐called Disturbance Ionosphere Index (DIX) that is able to separate horizontal TEC gradient effects and rapid TEC changes in near real‐time. A slightly modified DIX approach has been shown to be able to describe the regional and global perturbations via spatial gradients of TEC (Wilken et al, ). This paper presents a study for demonstrating another modification of the original DIX concept that enables the estimation of absolute values of spatial gradients and temporal changes of TEC.…”