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.     

Daytime VHF amplitude scintillations recorded at an Indian low-latitude station,Waltair (17.7°N, 83.3°E) during 1997–2003

In this research, it is presented the daytime amplitude scintillations recorded at VHF frequency (244 MHz) at an Indian low-latitude station, Waltair (17.7°N, 83.3°E) during seven continuous years (1997–2003). Contrary to the nighttime scintillation seasonal trends, the occurrence of daytime scintillations maximizes during summer followed by winter and the equinox seasons. The fade depths, scintillation indices and the patch durations of daytime scintillations are meager when compared with their nighttime counterparts. A co-located digital high frequency (HF) ionosonde radar confirms the presence of sporadic (Es) layers when daytime scintillations are observed. The presence of daytime scintillations is evident when the critical frequency of the Es-layer (foEs) is ≥4 MHz and Es-layers are characterized by a highly diffuse range spread Es echoes as can be seen on ionograms. It is surmised that the gradient drift instability (GDI) seems to be the possible mechanism for the generation of these daytime scintillations. It is quite likely that the spread Es-F-layer coupling is done through polarization electric fields (Ep) that develop inside the destabilized patches of sporadic E layers, which are mapped up to the F region along the field lines as to initiate the daytime scintillations through the GDI mechanism. Further, the presence of additional stratification of ionosphere F-layer, popularly known as the F3-layer, is observed on ionograms once the Es-layers and daytime scintillations are ceased.     

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.     

Satellite monitoring of anomalous effects in the ionosphere probably related to strong earthquakes

The paper presents simultaneously a satellite monitoring of plasma density disturbances and quasi-static electric fields on the one hand, and a ground earthquake monitoring, on the other. The INTERCOSMOS-BULGARIA-1300 satellite was launched on 7th August 1981. It had a perigee of 825 km, an apogee of 906 km and orbit inclination of 81.2°. For satellite’s orbits over sources of earthquakes M ⩾ 5.5 (seismic data of the World Data Center – Denver, Colorado), in the time period 12.08.1981–30.12.1981, some ionospheric effects are investigated. These effects can be considered eventually as possible earthquake precursors. The paper discusses specific anomalous effects observed in the ionosphere, which cannot be explained by factors of solar-magnetospheric origin. They could be associated with the earthquake growing processes in the lithosphere and troposphere zones above the source. In conclusion the results of ionosphere anomalous effects monitoring are proposed.     

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.     

Comparison of vertical E × B drift velocities and ground-based magnetometer observations of DELTA H in the low latitude under geomagnetically disturbed conditions

In the present work, we analyzed the daytime vertical E × B drift velocities obtained from Jicamarca Unattended Long-term Ionosphere Atmosphere (JULIA) radar and ΔH component of geomagnetic field measured as the difference between the magnitudes of the horizontal (H) components between two magnetometers deployed at two different locations Jicamarca, and Piura in Peru for 22 geomagnetically disturbed events in which either SC has occurred or Dst_max < ?50 nT during the period 2006–2011. The ΔH component of geomagnetic field is measured as the differences in the magnitudes of horizontal H component between magnetometer placed directly on the magnetic equator and one displaced 6–9° away. It will provide a direct measure of the daytime electrojet current, due to the eastward electric field. This will in turn gives the magnitude of vertical E × B drift velocity in the F region. A positive correlation exists between peak values of daytime vertical E × B drift velocity and peak value of ΔH for the three consecutive days of the events. It was observed that 45% of the events have daytime vertical E × B drift velocity peak in the magnitude range 10–20 m/s and 20–30 m/s and 20% have peak ΔH in the magnitude range 50–60 nT and 80–90 nT. It was observed that the time of occurrence of the peak value of both the vertical E × B drift velocity and the ΔH have a maximum (40%) probability in the same time range 11:00–13:00 LT. We also investigated the correlation between E × B drift velocity and D_st index and the correlation between delta H and D_st index. A strong positive correlation is found between E × B drift and D_st index as well as between delta H and D_st Index. Three different techniques of data analysis – linear, polynomial (order 2), and polynomial (order 3) regression analysis were considered. The regression parameters in all the three cases were calculated using the Least Square Method (LSM), using the daytime vertical E × B drift velocity and ΔH. A formula was developed which indicates the relationship between daytime vertical E × B drift velocity and ΔH, for the disturbed periods. The E × B drift velocity was then evaluated using the formulae thus found for the three regression analysis and validated for the ‘disturbed periods’ of 3 selected events. The E × B drift velocities estimated by the three regression analysis have a fairly good agreement with JULIA radar observed values under different seasons and solar activity conditions. Root Mean Square (RMS) errors calculated for each case suggest that polynomial (order 3) regression analysis provides a better agreement with the observations from among the three.     

Multi-year behaviour of the midnight OH1 temperature according to observations at Zvenigorod over 2000–2016

Using spectral measurements of the hydroxyl airglow at the Zvenigorod station (56° N, 37° E), Moscow region, over 2000–2016, we obtained the long-term set of data comprising 1822 midnight values of the OH¹ temperature in the mesopause region. These data revealed a 17-year series of its mean annual values, as well as amplitudes and phases of the first two harmonics of its annual variation. The obtained parameters were analyzed to determine statistically relevant characteristics of their long-term variations. As a result, we found that the long-term behaviour of the mean annual OH¹ temperature features a small negative linear trend (?0.07 ± 0.03 K/year) over the addressed period. Besides, its dependence on solar activity is shown to be 4.1 ± 0.5 K/100 SFU. Regarding the long-term behaviour of the mean annual OH¹ temperature, we revealed the existence of two oscillations with 3-year (the amplitude being 1.3 ± 0.2 K) and 4.1-year (the amplitude being 0.6 ± 0.2 K) periods. We obtained empirical relations describing year-to-year variations in the amplitudes and phases of the annual and semi-annual harmonics.     

Storm time spatial variations in TEC during moderate geomagnetic storms in extremely low solar activity conditions (2007–2009) over Indian region

The total electron content (TEC) measurements from a network of GPS receivers were analyzed to investigate the storm time spatial response of ionosphere over the Indian longitude sector. The GPS receivers from the GPS Aided Geo Augmented Navigation (GAGAN) network which are uniquely located around the ∼77°E longitude are used in the present study so as to get the complete latitudinal coverage from the magnetic equator to low mid-latitude region. We have selected the most intense storms but of moderate intensity (−100 nT < Dst < −50 nT) which occurred during the unusually extremely low solar activity conditions in 2007–2009. Though the storms are of moderate intensity, their effects on equatorial to low mid-latitude ionosphere are found to be very severe as TEC deviations are more than 100% during all the storms studied. Interesting results in terms of spatial distribution of positive/negative effects during the main/early recovery phase of storms are noticed. The maximum effect was observed at crest region during two storms whereas another two storms had maximum effect near the low mid-latitude region. The associated mechanisms like equatorial electrodynamics and neutral dynamics are segregated and explained using the TIMED/GUVI and EEJ data during these storms. The TEC maps are generated to investigate the storm time development/inhibition of equatorial ionization anomaly (EIA).     

Rare observation of daytime whistlers at very low latitude (L = 1.08)

The source region and propagation mechanism of low latitude whistlers (Geomag. lat. <30°) have puzzled scientific community for last many decades. In view of recent reports, there is consensus on the source region of low latitude whistlers in the vicinity of the conjugate point. But the plausible conditions of ionospheric medium through which they travel are still uncertain. In addition to that, the whistlers in daytime are never observed at geomagnetic latitudes less than 20°. Here, for the first time, we present a rare observations of whistlers during sunlit hours from a very low-latitude station Allahabad (Geomag. Lat: 16.79°N, L = 1.08) in India on 04 February 2011. More than 90 whistlers are recorded during 1200–1300 UT during which the whole propagation path from lightning source region to whistler observation site is under sunlit. The favorable factors that facilitated the whistlers prior to the sunset are investigated in terms of source lightning characteristics, geomagnetic and background ionospheric medium conditions. The whistler activity period was found to be geomagnetically quiet. However, a significant suppression in ionospheric total electron content (TEC) compared to its quiet day average is found. This shows that background ionospheric conditions may play a key role in low latitude whistler propagation. This study reveals that whistlers can occur under sunlit hours at latitudes as low as L = 1.08 when the source lightning and ionospheric medium characteristics are optimally favorable.     

Impact of heliogeophysical disturbances on ionospheric HF channels

The article presents the results of the observation of a strong magnetic storm and two X-ray flares during the summer solstice in 2015, and their impact on the HF signals characteristics in ionospheric oblique sounding. It was found that the negative phase of the magnetic storm led to a strong degradation of the ionospheric channel, ultimately causing a long blackout on paths adjacent to subauroral latitudes. On mid-latitude paths, the decrease in 1FMOF reached ～50% relative to the average values for the quiet ionosphere. It is shown that the propagation conditions via the sporadic Es layer during the magnetic storm on a subauroral path are substantially better than those for F-mode propagation via the upper ionosphere. The delay of the sharp decrease in 1FMOF during the main phase of the magnetic storm allowed us to determine the propagation velocity of the negative phase disturbances (～100 m/s) from subauroral to mid-latitude ionosphere along two paths: Lovozero – Yoshkar-Ola and Cyprus – Nizhny Novgorod. It is shown that both the LOF and the signal/noise ratio averaged over the frequency band corresponding to the propagation mode via the sporadic Es layer correlate well with the auroral AE index. Using an over-the-horizon chirp radar with a bistatic configuration on the Cyprus – Rostov-on-Don path, we located small-scale scattering irregularities responsible for abnormal signals in the region of the equatorial boundary of the auroral oval.     

L-band nighttime scintillations at the northern edge of the EIA along 95°E during the ascending half of the solar cycle 24

The characteristics of nighttime ionospheric scintillations measured at the L-band frequency of 1.575 GHz over Dibrugarh (27.5°N, 95°E, MLAT ～ 17°N, 43° dip) during the ascending half of the solar cycle 24 from 2010 to 2014 have been investigated and the results are presented in this paper. The measurement location is within or outside the zone of influence of the equatorial ionization anomaly depending on solar and geomagnetic activity. Maximum scintillation is observed in the equinoxes irrespective of solar activity with clear asymmetry between March and September. The occurrence frequency in the solstices shifts from minimum in the June solstice in low solar activity to a minimum in the December solstice in high solar activity years. A significant positive correlation of occurrence of scintillations in the June solstice with solar activity has been observed. However, earlier reports from the Indian zone (～75°E) indicate negative or no correlation of scintillation in June solstice with solar activity. Scintillations activity/occurrence in solstices indicates a clear positive correlation with Es recorded simultaneously by a collocated Ionosonde. In equinoxes, maximum scintillations occur in the pre-midnight hours while in solstices the occurrence frequency peaks just after sunset. The incidence of strong scintillations (S₄ ≥ 0.4) increases with increase in solar activity. Strong (S₄ ≥ 0.4) ionospheric scintillations accompanied by TEC depletions in the pre-midnight period is attributed to equatorial irregularities whereas the dusk period scintillations are related to the sporadic-E activity. Present results thus indicate that the current location at the northern edge of the EIA behaves as low as well as mid-latitude location.     

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.     

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.     

The high altitude student platform (HASP) for student-built payloads

An outstanding issue with aerospace workforce development is what should be done at the university level to attract and prepare undergraduates for an aerospace career. One approach adopted by many institutions is to lead students through the design and development of small payloads (less than about 500 grams) that can be carried up to high altitude (around 30 km) by a latex sounding balloon. This approach has been very successful in helping students to integrate their content knowledge with practical skills and to understand the end-to-end process of aerospace project development. Sounding balloons, however, are usually constrained in flight duration (∼30 min above 24 km) and payload weight, limiting the kinds investigations that are possible. Student built picosatellites, such as CubeSats, can be placed in low Earth orbit removing the flight duration constraint, but the delays between satellite development and launch can be years. Here, we present the inexpensive high altitude student platform (HASP) that is designed to carry at least eight student payloads at a time to an altitude of about 36 km with flight durations of 15–20 h using a small zero-pressure polyethylene film balloon. This platform provides a flight capability greater than sounding balloons and can be used to flight-test compact satellites, prototypes and other small payloads designed and built by students. The HASP includes a standard mechanical, power and communication interface for the student payload to simplify integration and allows the payloads to be fully exercised. HASP is lightweight, has simple mission requirements providing flexibility in the launch schedule, will provide a flight test opportunity at the end of each academic year.     

Characterization of the semi-annual-oscillation in mesospheric temperatures at low-latitudes

Novel measurements of the seasonal variability in mesospheric temperature at low-latitudes have been obtained from Maui, Hawaii (20.8°N, 156.2°W) during a 25-month period from October 2001 to January 2004. Independent observations of the OH (6, 2) Meinel band (peak height ∼87 km) and the O₂ (0–1) atmospheric band emission (∼94 km) were made using the CEDAR Mesospheric Temperature Mapper. The data revealed a coherent oscillation in emission intensity and rotational temperature with a well-defined periodicity of 181 ± 7 days. The amplitude of this oscillation was determined to be ∼5–6 K in temperature and ∼8–9% in intensity for both the OH and O₂ data sets. In addition, a strong asymmetry in the shape of the oscillation was also observed with the spring maximum significantly larger than the fall peak. These data provide new evidence in support of a semi-annual-oscillation in mesospheric temperature (and airglow emission intensities) and help quantify its seasonal characteristics.     

Ionospheric response to the storm-time disturbance of 29 May, 2010

The Ionospheric F2-layer peak parameters response to a magnetic storm had been investigated over Ilorin, Nigeria (Lat. 8:53°N, Long. 4.5°E, dip angle, −2.96°), Jicamarca, Peru (11.95°S, 76.87°W, dip angle, 0.8°) and Hermanus, South Africa (34.42°S, 19.22°E, dip angle, −60.77°), using percentage enhancement/depletion values. Our results showed an enhancement in NmF2 at all of these stations. Averagely, pre-noon and post-noon peaks are highest at Ilorin during quiet time. The similar pattern observed for quiet condition between Ilorin and Jicamarca was due to their latitudinal positions. For disturbed NmF2 condition, Jicamarca and Ilorin recorded higher peaks at nighttime than during the daytime for the storms main phase, and the reverse over Hermanus. The nighttime and daytime increases were observed respectively at Ilorin and Hermanus during the recovery period. The hmF2 variation recorded higher enhancement at Jicamarca during the daytime and at Hermanus at nighttime during the main phase. During the recovery phase, the highest enhancement was recorded during the daytime at Jicamarca, and over Hermanus at nighttime. These observations find their explanation in the magnetospheric current, solar wind and E × B drift.     

Ground-based measurement of strato–mesospheric CO by a FTIR spectrometer over Poker Flat,Alaska

Upper atmospheric CO above 24 km has been observed over Poker Flat (147°W, 65°N, altitude 0.61 km), Alaska using ground-based solar absorption infrared spectroscopy. This is the first reported detection of stratospheric–mesospheric CO using this method from the ground. The results clearly indicate that there is a seasonal variation of the CO profile with enhanced abundances in spring while remaining low from May onwards.The Poker Flat Research Range is one of the many measurement sites that constitute the Network for the Detection of Stratospheric Change (NDSC). The method used in this work, estimating the CO partial column abundances above the middle stratosphere, can be applied to spectra observed using FTIR spectrometry at many other NDSC sites. This suggests the availability of this established technique as a new method for CO measurements in the upper atmosphere.     

GNSS global real-time augmentation positioning: Real-time precise satellite clock estimation,prototype system construction and performance analysis

Lots of ambiguities in un-differenced (UD) model lead to lower calculation efficiency, which isn’t appropriate for the high-frequency real-time GNSS clock estimation, like 1 Hz. Mixed differenced model fusing UD pseudo-range and epoch-differenced (ED) phase observations has been introduced into real-time clock estimation. In this contribution, we extend the mixed differenced model for realizing multi-GNSS real-time clock high-frequency updating and a rigorous comparison and analysis on same conditions are performed to achieve the best real-time clock estimation performance taking the efficiency, accuracy, consistency and reliability into consideration. Based on the multi-GNSS real-time data streams provided by multi-GNSS Experiment (MGEX) and Wuhan University, GPS + BeiDou + Galileo global real-time augmentation positioning prototype system is designed and constructed, including real-time precise orbit determination, real-time precise clock estimation, real-time Precise Point Positioning (RT-PPP) and real-time Standard Point Positioning (RT-SPP). The statistical analysis of the 6 h-predicted real-time orbits shows that the root mean square (RMS) in radial direction is about 1–5 cm for GPS, Beidou MEO and Galileo satellites and about 10 cm for Beidou GEO and IGSO satellites. Using the mixed differenced estimation model, the prototype system can realize high-efficient real-time satellite absolute clock estimation with no constant clock-bias and can be used for high-frequency augmentation message updating (such as 1 Hz). The real-time augmentation message signal-in-space ranging error (SISRE), a comprehensive accuracy of orbit and clock and effecting the users’ actual positioning performance, is introduced to evaluate and analyze the performance of GPS + BeiDou + Galileo global real-time augmentation positioning system. The statistical analysis of real-time augmentation message SISRE is about 4–7 cm for GPS, whlile 10 cm for Beidou IGSO/MEO, Galileo and about 30 cm for BeiDou GEO satellites. The real-time positioning results prove that the GPS + BeiDou + Galileo RT-PPP comparing to GPS-only can effectively accelerate convergence time by about 60%, improve the positioning accuracy by about 30% and obtain averaged RMS 4 cm in horizontal and 6 cm in vertical; additionally RT-SPP accuracy in the prototype system can realize positioning accuracy with about averaged RMS 1 m in horizontal and 1.5–2 m in vertical, which are improved by 60% and 70% to SPP based on broadcast ephemeris, respectively.     

Characterization of the low latitude plasma density irregularities observed using C/NOFS and SCINDA data

Complex electrodynamic processes over the low latitude region often result in post sunset plasma density irregularities which degrade satellite communication and navigation. In order to forecast the density irregularities, their occurrence time, duration and location need to be quantified. Data from the Communication/Navigation Outage Forecasting System (C/NOFS) satellite was used to characterize the low latitude ion density irregularities from 2011 to 2013. This was supported by ground based data from the SCIntillation Network Decision Aid (SCINDA) receivers at Makerere (Geographic coordinate 32.6°E, 0.3°N, and dip latitude ?9.3°N) and Nairobi (Geographic coordinate 36.8°E, ?1.3°N, and dip latitude ?10.8°N). The results show that irregularities in ion density have a daily pattern with peaks from 20:00 to 24:00 Local Time (LT). Scintillation activity at L band and VHF over East Africa peaked in 2011 and 2012 from 20:00 to 24:00 LT, though in many cases scintillation at VHF persisted longer than that at L band. A longitudinal pattern in ion density irregularity occurrence was observed with peaks over 135–180°E and 270–300°E. The likelihood of ion density irregularity occurrence decreased with increasing altitude. Analysis of C/NOFS zonal ion drift velocities showed that the largest nighttime and daytime drifts were in 270–300°E and 300–330°E longitude regions respectively. Zonal irregularity drift velocities over East Africa were for the first time estimated from L-band scintillation indices. The results show that the velocity of plasma density irregularities in 2011 and 2012 varied daily, and hourly in the range of 50–150 m s^?1. The zonal drift velocity estimates from the L-band scintillation indices had good positive correlation with the zonal drift velocities derived from VHF receivers by the spaced receiver technique.     

Experimental and numerical simulation of super-pressure balloon apex section: Mechanical behavior in realistic flight conditions

In order to predict the flight parameters and to improve the life time of long duration super-pressure balloon, a research program on modelization and experimental simulation of the balloon envelope mechanical behavior is carried out.The balloon is a 10 m diameter type made with multilayer polymeric films and tapes. A facility was developed to measure, via a stereo-correlation system, the 3D displacement and the in plane solicitation strain of a 1.5 m diameter balloon envelope part in realistic flight conditions, i.e. pressure, temperature and loading at the sample boundaries. A time dependant non-linear Maxwell model of the polymeric material behavior was identified from uniaxial creep and relaxation tests and implemented in a Finite Elements code, simulating the sample tested in the facility. The Poisson ratio of the transparent and supple balloon film has been measured with an image correlation system.Experimental results are obtained both at room and in cold conditions (−60 °C) for various values of differential pressure.Vertical displacement and in plane 2D strain of apex part deduced from the numerical modeling are compared to experimental results.