SDA3: Specification of slab thickness anomalies

The weather-minus-climate (“anomaly”) maps of ionospheric properties (such as peak density NmF2 or peak height hmF2) are useful for rapid evaluation how current ionospheric weather is different from the quiet-time expectations. One example of an ionospheric property whose computation is highly relevant to trans-ionospheric high-frequency (HF) communications is a Maximum Usable Frequency over a 3000 km radiolink, MUF(3000). When MUF(3000) becomes lower than the empirical model prediction (a condition called “MUF depression”), HF communications may fail because suggested frequencies are beyond the range that is supported by current ionosphere.

The SDA3 was formulated with the monitoring of MUF(3000) depression in mind: the effective slab thickness of the ionosphere, τ, defined as ratio of the vertical TEC (VTEC) and peak density NmF2, showed high relevance to MUF(3000)F2 dynamics in preliminary testing.

Several steps were taken to evaluate SDA3 techniques for their inclusion in the DISPEC Demonstrator:

• Sensitivity analysis of how key properties of the Ne(h), vertical profile of plasma density in the bottomside ionosphere, affect resulting MUF.
  • Sensitivity metrics would define the baseline of MUF dependence on the underlying ionosphere.
• Proxy relevance study of how ionosphere proxies, available as real-time measurements, are relevant to MUF.
  • The relevance metrics would provide practical arguments for monitoring MUF depression.
  • Tested proxies included VTEC and τ.
• Data quality review of available measurements in real-time.