Sheng-Yang Gu

Evidence of nonlinear interaction between quasi 2 day wave and quasi‐stationary wave

The nonlinear interaction between the westward quasi 2 day wave (QTDW) with zonal wave number s = 3 (W3) and stationary planetary wave with s = 1 (SPW1) is first investigated using both Thermosphere, Ionosphere, and Mesosphere Electric Dynamics (TIMED) satellite observations and the thermosphere-ionosphere-mesosphere electrodynamics general circulation model (TIME-GCM) simulations. A QTDW with westward s = 2 (W2) is identified in the mesosphere and lower thermosphere (MLT) region in TIMED/Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature and TIMED/TIMED Doppler Imager (TIDI) wind observations during 2011/2012 austral summer period, which coincides with a strong SPW1 episode at high latitude of the northern winter hemisphere. The temperature perturbation of W2 QTDW reaches a maximum amplitude of ~8 K at ~30°S and ~88 km in the Southern Hemisphere, with a smaller amplitude in the Northern Hemisphere at similar latitude and minimum amplitude at the equator. The maximum meridional wind amplitude of the W2 QTDW is observed to be ~40 m/s at 95 km in the equatorial region. The TIME-GCM is utilized to simulate the nonlinear interactions between W3 QTDW and SPW1 by specifying both W3 QTDW and SPW1 perturbations at the lower model boundary. The model results show a clear W2 QTDW signature in the MLT region, which agrees well with the TIMED/SABER temperature and TIMED/TIDI horizontal wind observations. We conclude that the W2 QTDW during the 2011/2012 austral summer period results from the nonlinear interaction between W3 QTDW and SPW1.

The quasi 2 day wave activities during 2007 austral summer period as revealed by Whole Atmosphere Community Climate Model

The quasi 2 day wave (QTDW) observed during 2007 austral summer period is well reproduced in an reanalysis produced by the data assimilation version of the Whole Atmosphere Community Climate Model (WACCM + Data Assimilation Research Testbed) developed at National Center for Atmospheric Research (NCAR). It is found that the QTDW peaked 3 times from January to February but with different zonal wave numbers. Diagnostic analysis shows that the mean flow instabilities, refractive index, and critical layers of QTDWs are fundamental for their propagation and amplification, and thus, the temporal variations of the background wind are responsible for the different wave number structures at different times. The westward propagating wave number 2 mode (W2) grew and maximized in the first half of January, when the mean flow instabilities related to the summer easterly jet were enclosed by the critical layers of the westward propagating wave number 3 (W3) and wave number 4 (W4) modes. This prevented W3 and W4 from approaching and extracting energy from the unstable region. The W2 decayed rapidly thereafter due to the recession of critical layer and thus the lack of additional amplification by the mean flow instability. The W3 peaked in late January, when the instabilities were still encircled by the critical layer of W4. The attenuation of W3 afterward was also due to the disappearance of critical layer and thus the lack of overreflection. Finally, the W4 peaked in late February when both the instability and critical layer were appropriate.

Ionospheric response to the ultrafast Kelvin wave in the MLT region

The modulation of the ultrafast Kelvin wave (UFKW) on the equatorial ionosphere is investigated, using satellite neutral wind and temperature observations in the mesosphere/lower thermosphere (MLT) and ground-based global maps of total electron content (TEC) observations. The UFKW signatures are identified in the least squares fitting spectra for MLT zonal wind, temperature, TEC, and Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) electron density profiles, providing strong evidence for the neutral-ion coupling through the UFKW. The periods of the UFKW are mostly confined within 2–5.5 days. The UFKW in zonal wind and temperature maximize in the equatorial regions, whereas the UFKW band-pass perturbations in electron density peak at the equatorial ionization anomaly (EIA) crests with minima at the equator. The UFKW band-pass perturbations in TEC show consistent seasonal variability with the UFKW in the MLT region, including the intraseasonal oscillations with periods of 20–70 days. The long-term variability of the absolute UFKW band-pass amplitudes in TEC is in-phase with solar cycle with maximum amplitude of ~7–8 (~1–2) total electron content unit (TECU; 1 TECU = 1016 el m-2) during solar maximum (minimum) years, while the relative amplitudes show little solar activity dependence. The COSMIC electron density profiles show that the UFKW band-pass perturbations maximize at ~300–400 km with fountain-like spatial distributions, indicating the modulation of the UFKW on the EIA through electrodynamics.

Observation of the neutral-ion coupling through 6-day planetary wave

A westward 6 day oscillation with zonal wave number 1 is identified in the global maps of the ionospheric total electron content (TEC) during May 2003. This signature coincides with the wave activities in the mesosphere and lower thermosphere (MLT) region with a similar zonal structure and period, deduced from the temperature and wind observations from the Thermosphere Ionosphere and Mesosphere Electric Dynamics (TIMED) satellite. The vertical wavelength of this 6 day wave is estimated to be ~65 km, which enables it to propagate up into the lower thermosphere and therefore modulate the ionosphere through E region wind dynamo. The zonal wind perturbations of the 6 day wave maximize in the equatorial region with an amplitude of ~30 m/s and the meridional wind perturbations peak at middle latitudes with an amplitude of 15–20 m/s. The 6 day oscillation in TEC peaks at the geomagnetic equatorial ionization anomaly (EIA) crests in both hemispheres with a deep minimum at the equator. The absolute TEC perturbations maximize at ~1400–1800 LT with an amplitude of ~9 (~7) total electron content unit (TECU; 1 TECU = 1016 m−2) in the southern (northern) hemisphere, which account for ~16% (~10%) of the background TEC. Larger relative TEC perturbations of ~20% are found at 0200–0400 LT. The similar wave number-period spectra and the consistent temporal variations of the 6 day periodical signatures in both neutral atmosphere and ionosphere suggest a strong neutral-ion coupling through planetary wave.

Narrowband sodium lidar for the measurements of mesopause region temperature and wind

We report here a narrowband high-spectral resolution sodium temperature/wind lidar recently developed at the University of Science and Technology of China (USTC) in Hefei, China (31.5 °N, 117 °E). Patterned after the Colorado State University (CSU) narrowband sodium lidar with a dye laser-based transmitter, the USTC sodium temperature/wind lidar was deployed with a number of technical improvements that facilitate automation and ease of operation; these include a home constructed pulsed dye amplifier (PDA), a beam-steering system, a star-tracking program, and an electronic timing control. With the averaged power of ∼1.2 W output from PDA and the receiving telescope diameter of 0.76 m, our lidar system has a power aperture product of ∼0.55 Wm(2) and is comparable to the CSU and the University of Illinois at Urbana-Champaign (UIUC) sodium lidar systems. The uncertainties of typical measurements induced by photon noise and laser locking fluctuation for the temperature and wind with a 2 km vertical and 15 min temporal resolutions under the nighttime clear sky condition are estimated to be ∼1.0 K and ∼1.5 m/s, respectively, at the sodium peak (e.g., 91 km), and 8 K and 10 m/s, respectively, at both sodium layer edges (e.g., 81 km and 105 km). The USTC narrowband sodium lidar has been operated regularly during the night since November 2011. Using the initial data collected, we demonstrate the reliability and suitability of these high resolution and precision datasets for studying the wave perturbations in the mesopause region.

Ionospheric vertical plasma drift perturbations due to the quasi 2 day wave

The thermosphere-ionosphere-mesosphere-electrodynamics–general circulation model is utilized to study the vertical E × B drift perturbations due to the westward quasi 2 day wave with zonal wave numbers 2 and 3 (W2 and W3). The simulations show that both wind components contribute directly and significantly to the vertical drift, which is not merely confined to low latitudes. The vertical drifts at the equator induced by the total wind perturbations of W2 are comparable with that at middle latitudes, while the vertical drifts from W3 are much stronger at middle latitudes than at the equator. The ion drift perturbations induced by the zonal and meridional wind perturbations of W2 are nearly in-phase with each other, whereas the phase discrepancies of the ion drift induced by the individual wind component of W3 are much larger. This is because the wind perturbations of W2 and W3 have different latitudinal structures and phases, which result in different ionospheric responses through wind dynamo.

Ionospheric Variability Due to Tides and Quasi‐Two Day Wave Interactions

The ionospheric variabilities due to planetary waves (PWs) are complicated due to their nonlinear interaction with tides (migrating diurnal and semidiurnal tides [DW1 and SW2]) in the mesosphere and lower thermosphere region. The quasi-two day wave (QTDW) is the most dominant oscillation during austral summer period except tides. This paper quantitatively studies the contribution of W3 QTDW, secondary PWs generated by the QTDW-tide interaction, and the change of tides to the ionospheric vertical drift variabilities. It is found that the secondary PWs generated by the QTDW-DW1 interaction (16 hr W4 and 48 hr E2) contribute more to the ionospheric variability than those generated by the QTDW-SW2 interaction (9.6 hr W5 and 16 hr E1). The latitudinal distribution of the vertical drift induced by tides and PWs varies due to their different wind structures. The vertical drift induced by DW1 is weakened at all latitudes due to the existence of W3 QTDW, whereas the SW2-induced vertical drift is enhanced at low latitudes and decreased at middle latitudes. The W3 QTDW induces weaker vertical drift in the equatorial region than that induced by 16 hr W4, 48 hr E2, and the change of tides. At middle latitudes, the vertical drift induced by W3 QTDW is slightly stronger than that induced by 48 hr E2 and the change of DW1 but is comparable to that induced by 16 hr W4 and the change of SW2. Our simulations show that the changes of tidal amplitudes and secondary PWs are as important as the QTDW itself to the day-to-day ionospheric variabilities.

The modulation of the quasi-two day wave on Total Electron Content as revealed by BeiDou GEO and meteor radar observations over central China

The ground-based Total Electron Content (TEC) observations from BeiDou Geostationary Orbit (GEO) satellites provide more accurate temporal ionospheric variations nearly at the fixed ionospheric pierce points as compared with the non-GEO TEC. BeiDou GEO TEC measurements during 2016, along with the horizontal wind observations from a collocated meteor radar, are utilized to quantitatively study the ionospheric response to the quasi-two day wave (QTDW) in the neutral atmosphere at MengCheng (116.6°E, 33.3°N) over central China. The QTDW peaks during July with amplitudes of ~25-30 m/s for both zonal and meridional winds. It is suggested that the nonlinear interactions between the QTDW and tides and their influences on TEC are insignificant for this QTDW event. Nevertheless, the diurnal tide decreases by ~40-60% during the QTDW episode, which is most likely related to the change of background wind induced by the QTDW. Correspondingly, the 24-hour oscillations in TEC decrease by ~18%. In addition, the wind perturbations of the QTDW can also possibly modulate the mid-latitude electric dynamo and result in a quasi-two-day oscillation (QTDO) of ~1.2 TECU, about ~10% of the background TEC. Our analysis also shows that the background TEC decreases by ~1 TECU (~8%) when the QTDW reaches maximum amplitude. This is probably related to the thermospheric composition changes (e.g., O and N2) induced by the QTDW dissipation.