Jiangang Xiong

The terdiurnal tide in the mesosphere and lower thermosphere over Wuhan (30°N, 114°E)

Winds measured by an all-sky meteor radar have been used to investigate the terdiurnal tide in the mesosphere and lower thermosphere (MLT) region overWuhan (30.6°N, 114.4°E). We present a climatology of the terdiurnal tide at low-mid latitude site during the period of April 2002 to December 2004. The terdiurnal peak is distinct in the long-term power spectrum of the wind. The monthly and seasonal mean maximum amplitudes have values of 7 m/s and 5 m/s, respectively. The short-term amplitudes can occasionally reach up to 30 m/s, and at times the terdiurnal tide is as large as the diurnal and semidiurnal ones. It seems that the meridional component is more regular than the zonal one. An obvious annual variation is observed in the meridional phases with a phase leading in winter than that in summer. The annual variation for the terdiurnal tidal amplitude is not obvious, and is variable from year to year in our observations. This seasonal trend is slightly different from earlier studies at other locations.

Seasonal behavior of meteor radar winds over Wuhan

A newly installed meteor radar has been installed to measure winds in the mesosphere and lower thermosphere (MLT) over Wuhan (114.4°E, 30.6°N). In the present study, a database of the first 25 months (February 2002–February 2004) of observations has been analyzed to investigate the climatology of mean winds and tides. The daily average zonal wind is charactered by a strong shear in solstices and an intense eastward flow in summer. The daily average meridional wind is northward in winter and southward in other seasons. There are some discrepancies between the radar mean winds and the HWM93 model winds. The summer zonal winds and meridional winds from the model are obviously weaker than our observations. The analysis on tides indicates that the diurnal tide is dominant at Wuhan. The seasonal variability is observed in both the diurnal and semidiurnal tidal amplitudes with the maximum values occurring usually near the equinoxes. Compared with the Global Scale Wave Model (GSWM00), the observed results generally show a smaller diurnal tidal amplitude and a larger semidiurnal tidal amplitude.

Simulated longitudinal variations in the lower thermospheric nitric oxide induced by nonmigrating tides

[1] On the basis of the GCITEM‐IGGCAS model and tides from TIMED/SABER observations, the longitudinal variations in the lower thermosphere nitric oxide (NO), which is induced by nonmigrating tides, are investigated. We simulate the intra‐annual variation of the NO density and find that equinoctial lower thermospheric NO density shows an obvious wave number 4 longitudinal structure both in equinox and in June solstice and a wave number 3 longitudinal structure in December solstice. These simulation results are consistent with the longitudinal variation observed by Oberheide and Forbes (2008b). The simulations support that the wave number 4 structure in NO density is mainly driven by the eastward propagating nonmigrating diurnal tide with zonal wave number 3, and the wave number 3 structure is mainly driven by the eastward propagating nonmigrating diurnal tide with zonal wave number 2. Our simulations also show that the NO density residuals and the neutral mass density residuals in the height range between 90 and 120 km agree well with each other, and the neutral mass density mainly affects the longitudinal variations of lower thermospheric NO density through modulation of the chemical production rate, e.g., through affecting the chemical reaction between excited nitrogen and molecular oxygen.

A measurement of the lunar semidiurnal tide at Wuhan (30°40′N, 114°30′E)

Upper atmospheric winds have been measured at heights from 80 to 100 km overWuhan (30°40N, 114°30′E), China with a meteor radar from 2002 to 2005. The variations of lunar semidiurnal tidal amplitudes and phases with both seasons and heights are studied in detail to reveal the properties of the lunar semidiurnal tide. It is shown that the lunar semidiurnal tide is stronger in January than other months, and its second peak appears near August. For most months the eastward maximum is 3 ± 1 lunar hours later than the northward maximum, as classical theory predicts for a northern hemisphere tide. The observed seasonal and height variations are also compared with the Global Scale Wave Model (GSWM). The phases do not agree well with those of the GSWM model. The maximum amplitude occurs in a different month in the model. There are about 5 lunar hours phase difference between the observed and the model at 90 and 96 km in eastward and northward components. A comparison of the lunar and solar semidiurnal tides is also shown in this paper. The behavior of these two tides in season is different, especially for the month of appearance of maximum amplitude.

Gravity waves in the mesosphere observed with Wuhan Meteor Radar: A preliminary result

The characteristics of the dominant gravity waves in the vertical profiles of the wind velocities observed in the mesosphere with the Wuhan Meteor Radar, which was setup in February, 2002, are studied. The gravity waves in the mesosphere detected in 2-hourly vertical profiles centered at 6:00LT, when the observation meteor rates reached a maximum, are analyzed by using hodographs. The data used in this study are from February 19 to September 18, 2002. Fifty-one profiles show sinusoidal vertical structure after being smoothed by a band-pass filter with cutoffs at 6km and 15km in order to remove the tides and planetary wave components. There are 55 gravity waves in those profiles. Forty-three waves propagate upward and I I propagate downward. All but 19 gravity waves have a southward component of meridional propagation. The horizontal phase and group velocities are in the range of 15-65 m/s with means of 50.4 m/s and 38.5 m/s,respectively, without significantly monthly variations. The vertical and horizontal wavelengths are mainly from 8 to 12 km, 500 km to 2500 km, with a mean of 10.5 km and 1964 kin. The dominant gravity waves over Wuhan have intrinsic periods from 5 It to 15 h, with a mean of 10.3 h. The averaged wave amplitudes, which decay with height compared with a fixed energy wave, suggest the occurrence of dissipative processes in the middle atmosphere

Influence of DE3 tide on the equinoctial asymmetry of the zonal mean ionospheric electron density

Through respectively adding September DE3 tide and March DE3 tide at the low boundary of Global Coupled Ionosphere-Thermosphere-Electrodynamics Model, Institute of Geology and Geophysics, Chinese Academy of Sciences (GCITEM-IGGCAS), we simulate the influence of DE3 tide on the equinoctial asymmetry of the zonal mean ionospheric electron density. The influence of DE3 tide on the equinoctial asymmetry of the zonal mean electron density varies with latitude, altitude, and solar activity level. Compared with the density driven by the September DE3 tide, the March DE3 tide mainly decreases the lower ionospheric zonal mean electron density and mainly increases the electron density at higher ionosphere. In the low-latitude ionosphere, DE3 tide drives an equatorial ionization anomaly (EIA) structure at higher ionosphere in the relative difference of zonal mean electron density, which suggests that DE3 tide affects the longitudinal mean equatorial vertical E × B plasma drifts. Although the lower ionospheric equinoctial asymmetry driven by DE3 tide mainly decreases with the increase of solar activity, the asymmetry at higher ionosphere mainly increases with solar activity. However, EIA in equinoctial asymmetry mainly decreases with the increase of solar activity.

Structural evolution of long-duration meteor trail irregularities driven by neutral wind

An experiment on spatial domain interferometry observations of meteor trail irregularities at a low-latitude location in China was conducted during August 2013 using the Sanya VHF coherent radar (18.4 degrees N, 109.6 degrees E). More than 3 thousand range-spread meteor trail echoes (RSTEs) were observed. Among the trail echoes, the spatial structure of meteor trail irregularities responsible for a single long-duration RSTE event persisting for similar to 4min was reconstructed. This RSTE was found to be initially generated at 90-115 km altitudes and aligned along the radar beam boresight. After about the first minute of the trail lifetime, the trail echo appeared only in a narrow altitude range of 94-98 km. An analysis on the spatial pattern of the long-duration RSTE showed that the trail irregularities at lower range gates moved away from the region perpendicular to the geomagnetic field. The eastward drifts of the RSTE irregularities were found to decrease with increasing altitude, e.g., from 80 ms(-1) at similar to 94 km to 20 ms(-1) at similar to 100 km. Simultaneous horizontal neutral wind measurements made with the Fuke all-skymeteor radar (located north of Sanya) recorded a similar velocity profile. We suggest that the neutral wind could drive the spatial structural evolution of the RSTE irregularities, and help to determine the altitudes where the longest portion of the RSTE was located.

Sodium lidar‐observed gravity wave breaking followed by an upward propagation of sporadic sodium layer over Hefei, China

The University of Science and Technology of China (USTC) sodium temperature/wind lidar observed a strong zonal wind shear (~60 m/s/km) near 98 km between 1315 and 1330 UT on 29 July 2013 and a cooling near 96–100 km (above a warming near 90–95 km) between 1330 and 1430 UT. This suggests a possible gravity wave (GW) breaking event. Comparison of the lidar results with observations from a nearby meteor radar and with satellite results indicated that the GW likely broke down over a large horizontal area. In addition, the sodium number density suddenly increased by 10–12 times (~13, 000 atmos/cm3) near 95 km at 1400 UT, immediately following the GW breaking. This sporadic sodium layer (SSL), which is different from most previously observed SSL events (which propagate downward), tended to propagate upward and also appeared ~2 minutes earlier in the west channel than in the east channel. The horizontal propagation direction of the SSL was aligned with the horizontal wind direction, which was likely due to the propagation of a high-density sodium layer from the northwest of the lidar site, and was possibly related to the earlier GW breaking event.