Increasing disturbance of the geomagnetic field✓Правильный ответ
Decreasing disturbance of the geomagnetic field
Higher levels of solar UV radiation
An increase in the critical frequency
Объяснение
Both indices are derived from magnetometer readings of how far the geomagnetic field has departed from its quiet-day value, so higher numbers mean a more disturbed field. Neither measures ultraviolet output, and a disturbed field generally degrades ionospheric conditions rather than raising the critical frequency.