[1] A newly discovered 1000-km scale longitudinal variation in ionospheric densities is an unexpected and heretofore unexplained phenomenon. Here we show that ionospheric densities vary with the strength of nonmigrating, diurnal atmospheric tides that are, in turn, driven mainly by weather in the tropics. A strong connection between tropospheric and ionospheric conditions is unexpected, as these upward propagating tides are damped far below the peak in ionospheric density. The observations can be explained by consideration of the dynamo interaction of the tides with the lower ionosphere (E-layer) in daytime. The influence of persistent tropical rainstorms is therefore an important new consideration for space weather.

Coupling between the lower and upper atmosphere, combined with loss of gas from the upper atmosphere to space, likely contributed to the thin, cold, dry atmosphere of modern Mars. To help understand ongoing ion loss to space, the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft made comprehensive measurements of the Mars upper atmosphere, ionosphere, and interactions with the Sun and solar wind during an interplanetary coronal mass ejection impact in March 2015. Responses include changes in the bow shock and magnetosheath, formation of widespread diffuse aurora, and enhancement of pick-up ions. Observations and models both show an enhancement in escape rate of ions to space during the event. Ion loss during solar events early in Mars history may have been a major contributor to the long-term evolution of the Mars atmosphere.

[1] We report on a series of simulations with the National Center for Atmospheric Research (NCAR) thermosphereionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM) which were designed to replicate and facilitate the interpretation of the longitudinal structure discovered in IMAGE satellite airglow observations of the equatorial ionization anomaly (EIA) at the far-ultraviolet (FUV) 135.6-nm wavelength during March -April 2002 equinox. Our TIME-GCM results indicate that the fourpeaked longitudinal variation in the EIA observed by IMAGE-FUV near 20:00 local solar time can be explained by the effects of an eastward propagating zonal wavenumber-3 diurnal tide (DE3) that is excited by latent heat release associated with raindrop formation in the tropical troposphere.

Polarization electric fields created by the E‐ and F‐region dynamos cause the uplift of F‐region plasma. The subsequent redistribution of that plasma along the magnetic field lines creates the equatorial ionospheric anomaly (EIA). Observations of the post‐sunset EIA made by the IMAGE and TIMED satellites are compared here with CHAMP, Ørsted and SAC‐C observations of the noontime equatorial electrojet (EEJ). During magnetically quiet periods around equinox, the EIA and EEJ show a remarkably similar four‐peaked wave‐like longitudinal variation. Its structure is consistent with the longitudinal variation in the strength of diurnal tides that drive the E‐region dynamo. This indicates a strong vertical coupling between the ionosphere and troposphere because the four‐peaked tidal structure is driven by tropospheric weather. Furthermore, the dayside ionospheric conditions are found to perform the global‐scale longitudinal structure of the post‐sunset ionosphere at low latitudes.

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