Madden-Julian Oscillation (MJO) Effects in the GOLD O/N2 and Swarm-C
neutral density during 2018-2019?
Abstract
The extent to which terrestrial weather below 30 km in altitude can
influence the dynamics and mean state of the thermosphere (ca., 100-500
km) is a fascinating discovery of the last two decades or so. Waves that
are excited by deep convection in the tropical troposphere and propagate
vertically into the thermosphere are responsible for much of this
influence. Tropospheric convection associated with the Madden
JulianOscillation(MJO), the dominant mode of intra-seasonal variability
in tropical convection and circulation, has been known to modulate the
intensity of upward propagating gravity waves and Kelvin waves. An MJO
impact on tides was already proposed over two decades ago, but only
recent gains in satellite observational capabilities allows one to
quantify their effect from observations. Previous work by Gasperini et
al. [2017a] demonstrate that a 90-day oscillation in tropospheric
convection during 2009-2010 is imprinted on both thermospheric mean
winds and the eastward propagating wavenumber 3 diurnal (DE3) tidal
amplitudes observed by the GOCE and CHAMP satellites and modeled with
the TIME-GCM. In a follow-on modeling-based study, Gasperini at al.
[2020] present statistical evidence for a strong connection
(+/-12%) between the phase of the tropospheric MJO and the amplitudes
of the thermospheric DE3 and 3-day ultra-fast Kelvin wave (UFKW), two of
the most prominent and well-established waves from the tropical wave
spectrum that preferentially propagate into the thermosphere. These
recent studies demonstrate that strong coupling between the troposphere
and the thermosphere occurs on intra-seasonal timescales, raising
important questions that have implications for the whole atmosphere
system. In this work, we present evidence for a strong quasi-60 day
oscillation in GOLD column-integrated O/N2 and Swarm-C total mass
density during 2018-2019. A similar and concurrent oscillation is
observed in the DE3 and SE2 tidal amplitudes derived from SD/WACCM-X.
Spectral analysis of OLR reveals a similar oscillation in tropical
tropospheric convection that is shown to be eastward propagating with
s=-1 and is thus consistent with an MJO event.