Response of the thermosphere and ionosphere to an ultra fast Kelvin wave

Abstract

[1] Ultra Fast Kelvin (UFK) waves are eastward propagating planetary waves with periods between 3 and 5 days, which are capable of penetrating into the thermosphere and ionosphere where they may modulate phenomena occurring in this region. A sensitivity study has been conducted to examine the effect of an Ultra Fast Kelvin wave on the thermosphere and ionosphere using the NCAR Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) under June solstice solar minimum conditions. It is found that realistic ultra fast Kelvin waves with amplitudes in the MLT region of approximately 20-40 m s −1 in zonal wind fields and 10-20 K in temperature fields, can result in approximately 8-12% perturbations in hourly neutral density at 350 km, as well as hourly total electron content (TEC) perturbations of 25-50% in regions corresponding to the equatorial ionization anomalies (EIAs), with the largest relative changes resolved during the nighttime due to the lower electron densities. The electrodynamical calculations in the model were then disabled to identify the relative importance of ionospheric electrodynamics and direct wave propagation in generating the aforementioned changes. The subsequent results show that changes in thermospheric neutral density are relatively insensitive to the presence of the dynamo electric field, while UFK wave modulation of the dynamo accounts for most of the TEC perturbations due to changes of ionospheric vertical plasma drift.

Strong Kelvin wave activity observed during the westerly phase of QBO – a case study

“…Importantly, note that when the waves are fast the vertical wavelengths are larger and vice versa. Thus, the fast waves can propagate to higher altitudes compared to the slow waves (Hirota, 1978(Hirota, , 1979Salby et al, 1984;Lieberman and Riggin, 1997;Forbes, 2000;Forbes et al, 2009;Chang et al, 2010). …”

“…However, waves of very small periods ranging from 3 to 5 days are termed as ultra-fast KW and play a very important role in the vertical coupling of the atmosphere (Forbes, 2000). These waves have very large vertical wavelengths and are capable of propagating through the stratosphere and reach mesosphere and lower thermosphere or higher (Hirota, 1978(Hirota, , 1979Lieberman and Riggin, 1997;Forbes et al, 2009) and can significantly perturb the thermospheric neutral densities and total electron content (Chang et al, 2010). Ultra-fast KW were observed in meteor measurements and Thermosphere Ionosphere Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER) temperatures in the mesosphere and lower thermosphere and simultaneously in the critical frequency foF2, suggesting the propagation of the waves to ionospheric heights (Takahashi et al, 2007).…”

Observations of thermosphere and ionosphere changes due to the dissipative 6.5-day wave in the lower thermosphere

“…A number of observation and simulation works in literature have shown that planetary-scale waves, including atmospheric tides and various stationary and traveling planetary waves in the mesosphere and lower thermosphere (MLT), are able to impact the ionosphere/thermosphere (IT) system substantially (Laštovička, 2006;Forbes et al, 2009;Pedatella et al, 2009;Chang et al, 2010;Liu et al, 2010;England, 2012;Yue et al, 2013a;Yamazaki and Richmond, 2013;Yue and Wang, 2014;Chang et al, 2014). The planetary-scale wave signals with the same period and zonal wavenumber as those in the lower atmosphere are often observed in the IT system, which are thought to be the result of either the direct vertical propagation of the planetary-scale waves into the upper thermosphere or via the wave modulation on the neutral wind and dynamo electric fields in the ionosphere E region (Laštovička and Sauli, 1999;Pancheva et al, 2002;England et al, 2006).…”

The ultra-fast Kelvin waves in the equatorial ionosphere: observations and modeling

“…used the NCAR thermosphere-ionosphere-mesosphere electrodynamics general circulation model (TIME-GCM) to demonstrate that the presence of a quasi-stationary planetary wave could generate large ionospheric changes, including changes in the dynamo electric field/ion drift, F2 peak height and electron density, and TEC (total electron content) for solar minimum conditions. Using the same model, Chang et al (2010) investigated the effect of an UFK wave on the thermosphere and ionosphere. They found that UFK waves with amplitudes of approximately 20-40 m s −1 in zonal wind fields and 10-20 K in temperature fields in the MLT region could result in approximately 8-12 % of neutral density perturbations at 350 km of altitude.…”

“…Miyoshi and Fujiwara (2006) demonstrated in their general circulation model that the UFK wave could propagate upward to the lower thermosphere. Chang et al (2010) showed that the effects of a UFK wave can be transmitted to the thermosphere by wind dynamo modulation and direct vertical wave propagation, affecting the thermosphere neutral densities at 350 km and the total electron content.…”