Madden-Julian Oscillation Effects on Ultra-Fast Tropical Waves in the Whole Atmosphere-Ionosphere System during 2018-2019

Abstract:

The extent to which terrestrial weather can influence the ionosphere-thermosphere (IT) is a fascinating discovery of the last two decades or so. Due to the geometry of magnetic field lines near the equator, much of this coupling occurs at low latitudes, and is driven by waves that are excited by deep convective processes in the tropical troposphere and that propagate upwards into the IT system (i.e., 100-500 km). Prominent among these wave types are 'Ultra-Fast Tropical Waves' (UFTW) with periods between about 0.5 days to 3.5 days. However, relatively little is known about what aspects of tropical meteorology control the amplitudes and variability of UFTW sources, how background atmospheric conditions filter the tropical wave spectrum and modulate UFTW in particular, and exactly what is the signature and variability of UFTW in the IT system. The large-scale Madden Julian Oscillation (MJO) can modify the global distribution of latent heat release with intra-seasonal (~30-90 day) cycles and therefore modulate the UFTW. Recent evidence suggests that UFTW may play a large role in coupling MJO variability into the thermosphere, however, how exactly the MJO impacts the thermosphere through UFTW propagation, how significant the impacts are, and the resulting effects in the ionosphere are not fully understood. In this work, we take advantage of TIMED-SABER temperatures near 110 km, Swarm-A total mass densities near 400 km, GOLD O/N2 column density ratios, Outgoing Longwave Radiation (OLR) data, along with Specified-Dynamics (SD) Whole Atmosphere Community Climate Model eXtended (WACCM-X) numerical simulations to demonstrate a significant connection between the MJO and the intra-seasonal variability observed during 2018-2019 in the IT amplitudes of the diurnal eastward propagating tide with zonal wavenumber 3 (DE3) and the quasi-3-day ultra-fast Kelvin wave, two prominent UFTW excited by deep tropical tropospheric convection. This study suggests that UFTW may play a large role in coupling MJO variability into the IT system.