The Effect of Midnight Temperature Maximum Winds on Post‐Midnight Equatorial Spread F.

The SAMI3/equatorial spread F (Sami3 is also a model of the ionosphere/ESF) code is used to simulate the growth of equatorial plasma bubbles in the presence of a background wind field based on measured winds. The measured winds exhibit the well‐known "midnight temperature maximum" (MTM) pattern, in which an equatorward wind occurs simultaneously with a cessation in the zonal wind. The MTM is often preceded by strong equatorward winds (about 100 m/s). The circumstance where the MTM winds are symmetric across the equator is considered; here the meridional wind component in the southern hemisphere is the reverse of the northern meridional wind. The timing of the wind pattern relative to the imposition of a seed for the ESF instability is explored. We find that the simultaneous occurrence of a seed wave and a strong converging meridional wind pattern can produce post‐midnight ESF. We further find that the seed wave and the sudden cessation of the zonal winds can also produce post‐midnight ESF. The Magnetic mEridional NeuTrAl Thermospheric code verifies the occurrence of converging meridional wind patterns such as those simulated here, based on ionosonde data. Results suggest that regional‐scale wind measurements would aid in the prediction signal‐disrupting ionospheric bubbles. Plain Language Summary: The local ionosphere often becomes unstable after dusk, with low‐density "bubbles" rising from the bottom of the ionosphere F layer upwards to altitudes of 1,000 km or more. The jump in the local ionosphere density at the edges of these bubbles can disrupt signal transmission between Earth and space. The instability usually occurs after dusk but sometimes also occurs after midnight. We consider nighttime winds measured over an area covering most of the continental United States. The applicability of such measurements to prediction of bubbles is explored. The measured winds, which exhibit a phenomenon known as the midnight temperature maximum (MTM), are shown to enable post‐midnight bubbles. Two separate mechanisms are considered: (1) a north/south converging meridional wind of the sort that often precedes the MTM and (2) the sudden cessation of the zonal wind that often occurs during the MTM. In each case, post‐midnight equatorial spread F can occur if the timing between the winds and a "seed" wave is optimum. Key Points: The timing of midnight temperature maximum winds affects the growth of post‐midnight equatorial spread F (ESF)Regional area wind measurements can aid in the prediction of ionospheric bubbles associated with the ESF instabilityPrediction of ESF bubbles requires wind measurements or wind predictions in both hemispheres [ABSTRACT FROM AUTHOR]