The 16-day waves in the mesosphere and lower thermosphere over Wuhan (30.6°N, 114.5°E) and Adelaide (35°S, 138°E)

Winds from a meteor radar at Wuhan (30.6°N, 114.5°E) and a MF radar at Adelaide (35°S, 138°E) are used to study the 16-day waves in the mesosphere and lower thermosphere (MLT). The height range is 78–98 km at Wuhan and 70–98 km at Adelaide. By comparison, it is found that the zonal components at both sites are generally larger than the meridional ones, and eastward motion of the zonal background winds is favorable for the 16-day waves penetration to the MLT region. The zonal maximum amplitude appears in the autumn (September–October) around 86–98 km at Wuhan and in the winter months and early spring (July–October) around 72–82 km at Adelaide. Differences are found in wave amplitudes and time of appearance between the two years of 2002 and 2003. In 2003, the intensity of the wave amplitudes is relatively smaller than that for 2002 at both sites. The summer 16-day waves are comparatively weaker at Adelaide in both years, but stronger in 2002 at Wuhan near the mesopause and the lower thermosphere (86–98 km). The strong summer waves at Wuhan may come from the winter southern hemisphere.     

Atmosphere-ionosphere coupling from convectively generated gravity waves

Ionospheric variability impacts operational performances of a variety of technological systems, such as HF communication, Global Positioning System (GPS) navigation, and radar surveillance. The ionosphere is not only perturbed by geomagnetic inputs but is also influenced by atmospheric tides and other wave disturbances propagating from the troposphere to high altitudes. Atmospheric Gravity Waves (AGWs) excited by meteorological sources are one of the largest sources of mesoscale variability in the ionosphere. In this paper, Total Electron Content (TEC) data from networks of GPS receivers in the United States are analyzed to investigate AGWs in the ionosphere generated by convective thunderstorms. Two case studies of convectively generated gravity waves are presented. On April 4, 2014 two distinct large convective systems in Texas and Arkansas generated two sets of concentric AGWs that were observed in the ionosphere as Traveling Ionospheric Disturbances (TIDs). The period of the observed TIDs was 20.8 min, the horizontal wavelength was 182.4 km, and the horizontal phase speed was 146.4 m/s. The second case study shows TIDs generated from an extended squall line on December 23, 2015 stretching from the Gulf of Mexico to the Great Lakes in North America. Unlike the concentric wave features seen in the first case study, the extended squall line generated TIDs, which exhibited almost plane-parallel phase fronts. The TID period was 20.1 min, its horizontal wavelength was 209.6 km, and the horizontal phase speed was 180.1 m/s. The AGWs generated by both of these meteorological events have large vertical wavelength (>100 km), which are larger than the F2 layer thickness, thus allowing them to be discernible in the TEC dataset.     

Simulating planetary wave propagation to the upper atmosphere during stratospheric warming events at different mountain wave scenarios

Parameterization schemes of atmospheric normal modes (NMs) and orographic gravity waves (OGWs) have been implemented into the mechanistic Middle and Upper Atmosphere Model (MUAM) simulating atmospheric general circulation. Based on the 12-members ensemble of runs with the MUAM, a composite of the stratospheric warming (SW) has been constructed using the UK Met Office data as the lower boundary conditions. The simulation results show that OGW amplitudes increase at altitudes above 30 km in the Northern Hemisphere after the SW event. At altitudes of about 50 km, OGWs have largest amplitudes over North American and European mountain systems before and during the composite SW, and over Himalayas after the SW. Simulations demonstrate substantial (up to 50–70%) variations of amplitudes of stationary planetary waves (PWs) during and after the SW in the mesosphere-lower thermosphere of the Northern Hemisphere. Westward travelling NMs have amplitude maxima not only in the Northern, but also in the Southern Hemisphere, where these modes have waveguides in the middle and upper atmosphere. Simulated variations of PW and NM amplitudes correspond to changes in the mean zonal wind, EP-fluxes and wave refractive index at different phases of the composite SW events. Inclusion of the parameterization of OGW effects leads to decreases in amplitudes (up to 15%) of almost all SPWs before and after the SW event and their increase (up to 40–60%) after the SW in the stratosphere and mesosphere at middle and high northern latitudes. It is suggested that observed changes in NM amplitudes in the Southern Hemisphere during SW could be caused by divergence of increased southward EP-flux. This EP-flux increases due to OGW drag before SW and extends into the Southern Hemisphere.     

Equatorial planetary waves in the mesosphere observed by airglow periodic oscillations

Planetary scale waves in the equatorial upper mesosphere were studied by measuring the airglow OI557.7 nm, O₂b(0,1) and OH(6,2) emission intensities and OH rotational temperature at São João do Cariri (7.4°S; 36.5°W). From four years of data, 1998–2001, periodic oscillations of the airglow emissions were analyzed using the Lomb–Scargle spectral analysis. An oscillation of 3–4 days was frequently observed, which might be ultra-fast Kelvin waves. No seasonal dependency of the wave activity was found. On some occasions we found a quasi-5-day oscillation with a phase difference between the emissions, suggesting an upward energy flow. This is interpreted as a normal mode Rossby wave.     

Measurement of turbulent kinetic energy dissipation rates in the mesosphere by a 3 MHz Doppler radar

A new narrow beam Doppler radar operating at 3.17 MHz has been installed close to the Andøya Rocket Range in Andenes, Norway in summer 2002 in order to improve the ground based capabilities for measurements of turbulence in the mesosphere. The main feature of the radar is a Mills Cross transmitting/receiving antenna consisting of 29 crossed half-wave dipoles. In combination with the modular transceiver system this provides high flexibility in beam forming and pointing. In general, vertical and oblique beams with a minimum one way half-power full-beam width (HPFW) of 6.6° are used. The observations are usually performed with a height resolution of 1 km and with off-zenith beams at 7.3° directed towards NW, NE, SE, and SW. Turbulence intensities have been estimated from the width of the observed signal spectra using an computationally intensive correction method which requires precise knowledge of the antenna radiation pattern. The program uses real-time measurements of the wind field in all determinations. Turbulent kinetic energy dissipation rates based on radar observations are presented and compared with corresponding climatological summer and winter profiles from rocket measurements, as well as with single profiles from model runs for selected periods from September 2003 to Summer 2004. The mean turbulent kinetic energy dissipation rates based on these radar measurements are about 5 mW/kg at 60 km altitude and about 20 mW/kg at 80 km, in reasonable agreement with mean turbulence intensities obtained from previous rocket soundings at Andenes.     

The lower ionosphere response to its disturbances by powerful radio waves

The paper presents data from some campaigns at Sura heating facility in 2011–1016. The experiments on probing of the artificial disturbed region of the lower ionosphere were carried out at two observation sites. One of them was located near Vasil’sursk 1 km from Sura facility (56.1°N; 46.1°E) and the other site was located at the Observatory (55.85°N; 48.8°E) of Kazan State University, 170 km to the East. Investigation of the features of the disturbed region of the lower ionosphere based on its diagnostics by the methods of the vertical sounding and oblique backscattering is the main goal of this paper. Ionosphere disturbance was fulfilled by the effect of the powerful radio wave of the ordinary or extraordinary polarization emitted by transmitters of the Sura facility with effective radiated power ERP = 50–120 MW at the frequency of 4.3, 4.7 and 5.6 MHz. Pumping waves were emitted with period from 30 s to 15 min. The disturbed region of the ionosphere in Vasil’sursk was probed by the vertical sounding technique using the partial reflexion radar at the frequency of 2.95 and 4.7 MHz. For the oblique sounding of the disturbed region the modified ionosonde Cyclon-M, operating at ten frequencies from 2.01 to 6.51 MHz was used at the Observatory site. On many heating sessions simultaneous variations of the probing partial reflection signals in Vasil’sursk and backscattered signals in Observatory were observed at the height at 40–100 km below the reflection height of the pumping wave. These observations were correlated with the pumping periods of the Sura facility. Possible mechanisms of the appearance of the disturbance in the lower ionosphere and its effect on the probing radio waves are discussed.     

Airglow OH emission height inferred from the OH temperature and meteor trail diffusion coefficient

Simultaneous observations of the airglow OH(6,2) band rotational temperature, TOH, and meteor trail ambipolar diffusion coefficient, D, were carried out at Shigaraki (35°N, 136°E), during PSMOS 2003 Campaign, January 28 to February 8, 2003. The OH emission height was estimated by cross correlation analysis of the TOH and D nocturnal variations. A good correlation between TOH and D was obtained at 85 km of altitude. From the nocturnal variations of TOH and D, it is found that the OH emission peak height varied from 88 km before the midnight to 84 km in the early morning. The height variation could be caused by an atmospheric tidal effect in the emission height.     

Registration of wave disturbances over Yakutia

The results of investigations of wave processes with periods 2 hours on their influence and on the night sky airglow intensity are given. The observations were carried out by multichannel spectrometer for three seasons of 1985–1988 at the optical testing ground Maimaga (γ = 63°N; λ = 129, 5°E). The synchronous detection of two and sometimes of three emissions of night sky airglow yielded the oppotunity to track a vertical travel of waves and to estimate their parameters. In most cases the waves propagate upward, i.e. the sources of waves were below mesosphere. The estimated vertical velocity change within 0,9-3,3 m/s and vertical wave length - within 18–85 km. A horizontal velocity varies from 83 to 330 m/s. The wave activity (the occurence frequency) and their amplitude in winter is higher than in spring. The estimated energies transfered by waves to the upper atmosphere are in winter 3.8·10⁻³ W/m² and in spring 2.7·10⁻³ W/m².     

The radio signature of a kink unstable loop

Based upon multi-wavelength observations outlined by Huang et al. [Solar Phys. 213 (2003) 341], especially the dynamic spectrum at 4.5–7.5 GHz, we study the physical nature of the radio fine structures (FS) during the flare on August 25, 1999 in AR 8674 (S28E21). The main results are: (1) the helical loop of the event related to the FS is unstable for m = 1 kink mode; (2) the time interval between the beginning of reconnection and relaxation of the unstable loop, inferred from the observation, is quantitatively consistent with the results of the numerical simulations on kink unstable loop; (3) the magnetic field strength estimated from the fast kink standing wave is basically of the same order as that estimated from the photospheric magnetic field, which provides strong support to our analysis.     

The temperature map of the loop and coronal sources of an occulted solar flare

An occulted solar flare occurred at about 06:07 UT on 2002, November 2. The RHESSI X-ray images show two separate parts. The lower part consists of a complete loop and the upper part a coronal source which well extends above the solar limb. The loop source shrank for about 3 min with a speed of ∼24 km s⁻¹ during the early impulsive phase and then expanded at ∼7 km s⁻¹, while the coronal source presented an upward motion at about 6 km s⁻¹. We obtained the temperature map of the loop source from RHESSI image spectrum. The temperature of the loop increases with altitude, indicating that the reconnection X-point of this flare is located above the loop source. However, the apparent coronal source is the top of another independent large-scale loop.     

Global MGS TES data and Mars-GRAM validation

Mars Global Reference Atmospheric Model (Mars-GRAM 2001) is an engineering-level Mars atmosphere model widely used for many Mars mission applications. From 0 to 80 km, it is based on NASA Ames Mars General Circulation Model (MGCM), while above 80 km it is based on University of Michigan Mars Thermospheric General Circulation Model. Mars-GRAM 2001 and MGCM use surface topography from Mars Global Surveyor Mars Orbiter Laser Altimeter (MOLA). Validation studies are described comparing Mars-GRAM with a global summary data set of Mars Global Surveyor Thermal Emission Spectrometer (TES) data. TES averages and standard deviations were assembled from binned TES data which covered surface to ∼40 km, over more than a full Mars year (February 1999–June 2001, just before start of a Mars global dust storm). TES data were binned in 10° × 10° latitude–longitude bins (36 longitude bins, centered at 5°–355°, by 18 latitude bins, centered at −85° to +85°), and 12 seasonal bins (based on 30° increments of L_s angle). Bin averages and standard deviations were assembled at 23 data levels (temperature at 21 pressure levels, plus surface temperature and surface pressure). Two time-of-day bins were used: local time near 2 or 14 h. Two dust optical depth bins were used: infrared optical depth, either less than or greater than 0.25 (which corresponds to visible optical depth less than or greater than about 0.5). For interests in aerocapture and precision entry and landing, comparisons focused on atmospheric density. TES densities versus height were computed from TES temperature versus pressure, using assumptions of perfect gas law and hydrostatics. Mars-GRAM validation studies used density ratio (TES/Mars-GRAM) evaluated at data bin center points in space and time. Observed average TES/Mars-GRAM density ratios were generally 1 ± 0.05, except at high altitudes (15–30 km, depending on season) and high latitudes (>45°N), or at most altitudes in the southern hemisphere at L_s ∼ 90° and 180°. Compared to TES averages for a given latitude and season, TES data had average density standard deviation about the mean of ∼2.5% for all data, or ∼1–4%, depending on time of day and dust optical depth. Average standard deviation of TES/Mars-GRAM density ratio was 8.9% for local time 2 h and 7.1% for local time 14 h. Thus standard deviation of observed TES/Mars-GRAM density ratio, evaluated at matching positions and times, is about three times the standard deviation of TES data about the TES mean value at a given position and season.     

Application of heterogeneous mesospheric ion-chemistry model to MST radar echoes over low latitude

MST radar studies at low latitude stations have documented regions in the mesosphere from where enhanced echoes (Low Latitude Mesospheric Echoes (LMEs)) are observed. Such echoes cannot, in general, be explained by considering the dynamical aspects (such as turbulence, winds, waves, etc.) of the region alone. Mesospheric dust/aerosols can enhance the radar echoes considerably and dust is known to exist at all heights and latitudes of the mesosphere. This study investigates the presence of dusty plasma in the mesosphere through the heterogeneous ion-chemistry of the region.Dust of meteoric origin is incorporated in the conventional ion chemistry scheme and the equilibrium height profiles of charged and neutral dust densities corresponding to effective dust sizes (radii) of 1, 10 and 30 nm are computed for the equatorial quiet daytime conditions.The model derived dust density profiles show structures with respect to dust size, height and season that are indicative of the possible role of mesospheric dust in the production/enhancement mechanisms of the LMEs observed over the equatorial station at Gadanki (13.5°N, 79.2°E), India.     

Near-infrared,optical, and X-ray observations of the anomalous X-ray pulsar 4U 0142 + 61

We present results from the simultaneous observations of an anomalous X-ray pulsar (AXP) 4U 0142 + 61 on Sep. 2003. We used RXTE, Subaru, and UH88 telescopes to cover X-ray, near-infrared (NIR) (JHK′), and optical (BVRI) bands, respectively. We obtained a simultaneous broadband spectrum for the first time among AXPs. We found NIR excess in the spectrum, which may be another component different from the optical one. We also found a R band dip. We discuss the broadband spectrum covering the optical and X-ray bands in the framework of a self absorbed synchrotron emission from the magnetosphere of magnetar. We also discuss about the R band dip feature, which could put a restriction on the emission models of magnetars.     

Excitation of flare-induced waves in coronal loops and the effects of radiative cooling

EUV imaging observations from several space missions (SOHO/EIT, TRACE, and SDO/AIA) have revealed a presence of propagating intensity disturbances in solar coronal loops. These disturbances are typically interpreted as slow magnetoacoustic waves. However, recent spectroscopic observations with Hinode/EIS of active region loops revealed that the propagating intensity disturbances are associated with intermittent plasma upflows (or jets) at the footpoints which are presumably generated by magnetic reconnection. For this reason, whether these disturbances are waves or periodic flows is still being studied. This study is aimed at understanding the physical properties of observed disturbances by investigating the excitation of waves by hot plasma injections from below and the evolution of flows and wave propagation along the loop. We expand our previous studies based on isothermal 3D MHD models of an active region to a more realistic model that includes full energy equation accounting for the effects of radiative losses. Computations are initialized with an equilibrium state of a model active region using potential (dipole) magnetic field, gravitationally stratified density and temperature obtained from the polytropic equation of state. We model an impulsive injection of hot plasma into the steady plasma outflow along the loops of different temperatures, warm (～1 MK) and hot (～6 MK). The simulations show that hot jets launched at the coronal base excite slow magnetoacoustic waves that propagate to high altitudes along the loops, while the injected hot flows decelerate rapidly with heights. Our results support that propagating disturbances observed in EUV are mainly the wave features. We also find that the effect of radiative cooling on the damping of slow-mode waves in 1–6 MK coronal loops is small, in agreement with the previous conclusion based on 1D MHD models.     

On long-term changes of electron density in the upper mesosphere

Recent review study done jointly by 19 experts of 17 institutes shows zero trend of temperature in the upper mesosphere. In the light of this latest development, we have examined the long-term changes in electron density, [e], in this region. The study has been concentrated at 80 km. At this altitude, electrons are mainly produced by the interaction of nitric oxide, NO, by solar Ly-α. Any long-term change in this flux will affect trend of [e]. Considering this flux proportional to 10.7 cm solar flux, analysis of available 10.7 cm solar flux data from 1948 to 2003 has been made. A decreasing trend up to about 1970 and then an increasing trend are found. The over-all increasing trend of Ly-α flux during the past five decades is ∼0.17% per year. This increase also gives a ∼0.17% increasing trend per year in [e]. This non-anthropogenic increase is much less compared to the observed increase in [e] which is reported to be >0.7% per year. The observed increase in [e] of this magnitude will then, predominantly, be due to the anthropogenic effect. In zero trend in temperature, significant change in electron loss coefficient, α_eff, and [NO] are unlikely to take place to cause a significant change in [e]. The increase in [e] > 0.7% per year then can be explained by considering a decreasing trend in [O₂].     

The temporal variation of mean gravity of atmosphere

One of the precise widely used global Zenith Hydrostatic Delay (ZHD) model is based on the gravity value at the centroid of the atmospheric column at the station of observation and gravity value at the centroid is constant in this model for a specific location throughout the year. However, as the content and extent of atmosphere varies temporally, its centroid and consequently gravity value at the centroid also varies. Apart from this, the actual atmospheric condition of different region is not alike. Therefore, there is a need to develop a regional mean gravity model and development of such model has been discussed in this paper. To obtain the mean gravity model, first a regional model of centroid height of atmospheric column was developed as a function of the surface pressure and temperature. It was developed by multiple regressions between estimated centroid of the atmosphere and surface pressure, surface temperature using radiosonde data of five radiosonde stations spread over the Indian subcontinent. Three years radiosonde data from 2006 to 2008 was used for each station. The root mean square error in estimating centroid of the atmospheric column is about ±326 m, which is negligible considering the variability of the atmosphere and its content. The centroid height model has been used to formulate the mean gravity model, considering uniform lapse rate in gravity with height. It is found that proposed mean gravity model provides temporal variation of mean gravity values at the centroid and thus matches with the reality. The interesting advantage of the developed model is that the model shows diurnal variation of mean gravity. The accuracy of ZHD has shown of the order of about 0.3 mm using the developed regional mean gravity model. However, already developed ZHD model has shown a slight inferior result compared to the developed model. These models have shown accuracy of about 0.8 mm and 0.6 mm.     

Development of a 2.8 μm film for scientific balloons

Development of a balloon to fly at higher altitudes is one of the most attractive challenges in scientific balloon technologies. After reaching the highest record setting balloon altitude of 53.0 km using the 3.4 μm film in 2002, we tried to make a thinner balloon film. In 2003, we developed a forming die and an air-ring and succeeded in forming a film with a thickness of 3.0 μm and a width of 220 cm. Using this film, we manufactured a balloon with a volume of 5000 m³ and succeeded in flying the balloon up to an altitude of 46.0 km. We then searched for a good combination of resins to make a thinner and wider film and obtained films with widths of 280 cm, and a thickness of 3.0 μm at first, and then 2.8 μm. In 2004, we performed balloon experiments making a 30,000 m³ balloon with the 3.0 μm film and a 5000 m³ balloon with the 2.8 μm film. Both balloons were well manufactured and reached the highest altitudes of 50.7 and 42.6 km, respectively.     

Sporadic sodium layers and the average vertical distribution of atmospheric sodium

We have used atmospheric sodium profiles obtained at São José dos Campos over the period 1993–2004 to study the influence of sporadic layers on the average sodium distribution. All the profiles for the time period 19–22 h local standard time were individually classified as either normal or sporadic. Profiles were considered sporadic if they contained sharp increases above the background profile by more than a factor of 2, occurring on the topside of the layer, with a width of less than 5 km. For each night’s data, the averages of the normal and sporadic profiles were stored separately. A comparison between the long-term means of these two average profiles, for those days on which both normal and sporadic profiles were observed, showed no significant difference between them. This indicates that, on average, there is no additional sodium in the sporadic profiles. This analysis suggests that at least part of the topside of the normal sodium layer originates in a source that also gives rise to sporadic layers, which would occur when the source itself becomes layered. The most likely source is sodium-containing ions, which would be layered by the tide and/or gravity wave driven wind-shear mechanism generally accepted as being responsible for some types of ionospheric sporadic-E.     

On the usefulness of atmospheric and oceanic angular momentum in recovering polar motion and gravity field variations in a unified process

Earth rotation parameters (ERPs) are excited by variations in the mass distribution on the Earth’s surface and the exchange of angular momentum between the atmosphere and oceans and the solid Earth. The same mass redistribution causes temporal changes in the gravity field coefficients with the second degree harmonics related to the rotational deformation and hence to changes in the Earth’s inertial tensor. If precise models of the atmospheric and oceanic angular momentum (AM) are available solution for polar motion and degree 2 Stokes harmonics can be unified. In this study we utilize SLR tracking of LAGEOS to compare (i) degree 2 harmonics from ERPs and gravitation, and (ii) LAGEOS excitation functions and geophysical data (mass + motion). Finally, we investigate to what extent a unified approach is possible with current models for AM data and gravity mass change estimated from ERP within orbit determinations.     

Observed flux density enhancement at submillimeter wavelengths during an X-class flare

We analyse the 30 October, 2004, X1.2/SF solar event that occurred in AR 10691 (N13 W18) at around 11:44 UT. Observations at 212 and 405 GHz of the Solar Submillimeter Telescope (SST), with high time resolution (5 ms), show an intense impulsive burst followed by a long-lasting thermal phase. EUV images from the Extreme Ultraviolet Imaging Telescope (SOHO/EIT) are used to identify the possible emitting sources. Data from the Radio Solar Telescope Network (RSTN) complement our spectral observations below 15 GHz. During the impulsive phase the turnover frequency is above 15.4 GHz. The long-lasting phase is analysed in terms of thermal emission and compared with GOES observations. From the ratio between the two GOES soft X-ray bands, we derive the temperature and emission measure, which is used to estimate the free-free submillimeter flux density. Good temporal agreement is found between the estimated and observed profiles, however the former is larger than the latter.