Quasi‐biennial oscillation of the ionospheric wind dynamo

Abstract

The interannual variation of the ionospheric solar quiet (Sq) current system is examined. A dense magnetometer network over Japan enables the accurate determination of the central position of the northern Sq current loop or the Sq current focus, during 1999–2015. It is found that the Sq focus latitude undergoes an interannual variation of ±2° with a period of approximately 28 months, similar to the quasi‐biennial oscillation (QBO) in the tropical lower stratosphere. The QBO‐like variation of Sq is particularly evident during 2005–2013. No corresponding interannual variability is found in solar extreme ultraviolet radiation. Comparisons with tidal winds, derived from a whole‐atmosphere model, reveal that the QBO‐like variation of the Sq current focus is highly correlated with the amplitude variations of migrating and nonmigrating diurnal tides in the lower thermosphere. The results suggest that the stratospheric QBO can influence the ionospheric wind dynamo through the QBO modulation of tides.

Interannual Variability of the Daytime Equatorial Ionospheric Electric Field

“…The anomaly Δ V Z , shown in Figure a, was calculated as the deviation of V Z (black line in Figure a) from the seasonal solar cycle climatology (green dashed line in Figure a). Following Yamazaki et al (), a moving average with a 13‐month window was applied to Δ V Z in order to extract the variation on time scales longer than a year. The results, shown in Figure a (red line), reveal an interannual variation of ∼2 m/s.…”

“…The interannual variability of upward propagating tides is due in part to the interannual variability of the background atmosphere, through which the tidal waves propagate (Mayr & Mengel, ; McLandress, ). Some identified sources of the interannual variability of tides include the QBO in the stratosphere (Liu, ; Yamazaki et al, ) and the El Niño–Southern Oscillation (ENSO) in the troposphere (Liu et al, ; Pedatella & Liu, ; ). The QBO has a regular oscillation cycle of ∼28 months, while ENSO consists of longer‐period oscillations (∼43 and ∼62 months) (Liu, ).…”

“…Miyoshi et al () performed a long‐term GAIA simulation for the years 1997–2013. Later, the simulation was extended until 2016 (Liu et al, ; Yamazaki et al, ). The present study uses the model outputs from this long‐term run.…”

“…In this study, we consider the time scales longer than a year up to a solar cycle (∼11 years). Recently, we reported on the interannual variability of the ionospheric solar quiet ( S q ) current system (Yamazaki et al, ). We found an interannual variation with a period of approximately 28 months in the central position of the S q current loop over Japan during 2005–2013, when solar and magnetospheric activities were relatively low.…”

Whole Atmosphere Coupling on Intraseasonal and Interseasonal Time Scales: A Potential Source of Increased Predictive Capability

“…A study of electron density measurements from the Challenging Microsatellite Payload (CHAMP) and the Gravity Recovery and Climate Experiment (GRACE) satellites during the 2000–2014 period by Zhou et al () found evidence for a QBO modulation of the low‐latitude DE3 feature but did not find evidence for any QBO modulation of nonmigrating features at midlatitudes. Yamazaki et al () found a QBO‐like variation in the northern ionospheric current loop observations during solar minimum (when apparent solar QBO variations are not present), which they attributed to QBO modulation of DW1, DE3, and SW2 modes based on a series of whole atmosphere model experiments with constrained meteorology below 30‐km altitude. However, the results of this study could not identify which tidal modes were most important for producing the observed QBO variations.…”