F. Gasperini

Improved short-term variability in the thermosphere-ionosphere-mesosphere-electrodynamics general circulation model

We report on a new source of tidal variability in the National Center for Atmospheric Research thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM). Lower boundary forcing of the TIME-GCM for a simulation of November–December 2009 based on 3-hourly Modern-Era Retrospective Analysis for Research and Application (MERRA) reanalysis data includes day-to-day variations in both diurnal and semidiurnal tides of tropospheric origin. Comparison with TIME-GCM results from a heretofore standard simulation that includes climatological tropospheric tides from the global-scale wave model reveal evidence of the impacts of MERRA forcing throughout the model domain, including measurable tidal variability in the TIME-GCM upper thermosphere. Additional comparisons with measurements made by the Gravity field and steady-state Ocean Circulation Explorer satellite show improved TIME-GCM capability to capture day-to-day variations in thermospheric density for the November–December 2009 period with the new MERRA lower boundary forcing.

Lunar-solar interactions in the equatorial electrojet

To first order the ground magnetic signature of the equatorial electrojet (EEJ) reflects the height integral of J = σE, where σis a conductivity and E represents some combination of the global dynamo-generated electric field and the electric field due to local winds. Day-to-day variations in the conductivity are strongly controlled by the solar flux, while E depends on solar and lunar tides, planetary waves, and the disturbance dynamo. In this study we demonstrate how complexity is introduced into the EEJ due to the interaction between lunar tide variability in the equatorial electric field and solar-driven variability in the E region conductivity. Toward this end, we analyze magnetometer data from the Huancayo observatory both in the time and frequency domain. We present results for the year 1990, and we show that 86% of the variance in the EEJ is due to the lunar-solar interaction.

Evidence of tropospheric 90-day oscillations in the thermosphere†

In the last decade evidence demonstrated that terrestrial weather greatly impacts the dynamics and mean state of the thermosphere via small-scale gravity waves and global-scale solar tidal propagation and dissipation effects. While observations have shown significant intra-seasonal variability in the upper mesospheric mean winds, relatively little is known about this variability at satellite altitudes (c.a., 250-400 km). Using cross-track wind measurements from the CHAMP and GOCE satellites, winds from a MERRA/TIME-CGM simulation, and outgoing long-wave radiation (OLR) data, we demonstrate the existence of a prominent and global-scale 90-day oscillation in the thermospheric zonal mean winds and in the diurnal eastward-propagating tide with zonal wavenumber 3 (DE3) during 2009-2010 and present evidence of its connection to variability in tropospheric convective activity. This study suggests that strong coupling between the troposphere and the thermosphere occurs on intra-seasonal time scales.

Exploring Wave-Wave Interactions in a General Circulation Model: Wave-Wave Interactions

Nonlinear interactions involving Kelvin waves with (periods, zonal wave numbers) = (3.7d, s = −1) (UFKW1) and = (2.4d, s = −1) (UFKW2) and s = 0 and s = 1 quasi 9 day waves (Q9DW) with diurnal tides DW1, DW2, DW3, DE2, and DE3 are explored within a National Center for Atmospheric Research (NCAR) thermosphere-ionosphere-mesosphere electrodynamics general circulation model (TIME-GCM) simulation driven at its ∼30 km lower boundary by interpolated 3-hourly output from Modern-Era Retrospective Analysis for Research and Applications (MERRA). The existence of nonlinear wave-wave interactions between the above primary waves is determined by the presence of secondary waves (SWs) with frequencies and zonal wave numbers that are the sums and differences of those of the primary (interacting) waves. Focus is on 10–21 April 2009, when the nontidal dynamics in the mesosphere-lower thermosphere (MLT) region is dominated by UFKW and when identification of SW is robust. Fifteen SWs are identified in all. An interesting triad is identified involving UFKW1, DE3, and a secondary UFKW4 = (1.5d, s = −2): The UFKW1-DE3 interaction produces UFKW4, the UFKW4-DE3 interaction produces UFKW1, and the UFKW1 interaction with UFKW4 produces DE3. At 120 km the dynamic range of the reconstructed latitude-longitude zonal wind field due to all of the SW is roughly half that of the primary waves, which produced them. This suggests that nonlinear wave-wave interactions could significantly modify the way that the lower atmosphere couples with the ionosphere.

Seminal Evidence of a 2.5-Sol Ultra-Fast Kelvin Wave in Mars' Middle and Upper Atmosphere: UFKW in Mars' middle and upper atmosphere

The structure and dynamics of Mars’ middle and upper atmosphere is significantly impacted by waves propagating from the lower atmosphere. Using concurrent temperature and neutral density measurements taken by the Mars Reconnaissance Orbiter and Mars Atmosphere and Volatile EvolutioN satellites, we demonstrate for the first time that a 2.5-sol ultra-fast Kelvin wave is a prominent global-scale feature of the low-latitude middle (i.e., 30–80 km) and upper (approximately 150 km) atmosphere of Mars. Further, we present evidence of secondary waves arising from nonlinear interactions between this ultra-fast Kelvin wave and solar tides, and based on their amplitudes we surmise that they could represent an important source of tidal and longitudinal variability in the aerobraking region. Plain Language Summary The upper atmosphere of Mars is driven by a combination of effects linked to solar radiation and to waves that originate in the lower and middle atmosphere. Upward propagating waves are responsible for short-term temperature and wind variations in Mars’ middle and upper atmosphere and couple different layers of Mars’ atmosphere. While in the last couple of decades our understanding of the processes responsible for this coupling has considerably improved, there are many unresolved questions regarding the impacts of the entire spectrum of these waves on the upper atmosphere of Mars. In this work we demonstrate that a strong ultra-fast Kelvin wave with a period of 3 sols and the secondary waves generated by its nonlinear interaction with solar tides can be a large source of variability in Mars’ middle and upper atmosphere.