Change in the rigidity dependence of the galactic cosmic ray modulation in 2008–2009

Observations of charged particle fluxes in the stratosphere of the polar regions represent the cosmic rays variations with energy above 100 MeV. At the end of 2009 these fluxes reached the highest level for the time of observations from mid 1957 and were by 17% higher than the previous extremum value of May 1965. In the mean time the ground-based neutron monitors showed the remarkably less count rate enhancement. These results argue for the significant change in the energy spectrum of incoming particles in 2008–2009 in the energy range of ∼100–1500 MeV/n.     

Quasi-periodicities in cosmic rays recorded by the KACST muon detector during 2002–2012

In this study, daily cosmic ray data obtained with the KACST muon detector for the period 2002–2012 were analyzed for quasi-periodicities. Power-spectrum analysis was carried out and several periodicities were identified. The results reveal several periodicities at different frequency scales: 817 days (~2.19 years), 617 days (~1.7 years), 475 days (~1.3 years), 421 days (1.15 years), 290 days (~0.8 years), 227 days (~0.62 years), 185 days (~0.52 years), 153 days, 135 days, 120 days, 93 days, 84 days, 73 days, 65 days, 53–45 days, 38 days, 31 days, 25–27 days, 21 days and 13 days. The obtained periodicities are in an agreement with those previously reported by several investigators.The identified periodicities have strong relevance to solar activity parameters such as variations in the interplanetary magnetic field.In comparison, the data from two neutron monitors (NMs), Lomnický ?tít and Oulu NMs, for the same period were used and their power spectra were correspondingly obtained. Similarities and differences in the position of the cosmic-ray peaks measured by the KACST muon detector and by the two NMs have been presented and discussed. While most of the periodicities reported by the muon detector are also found in the NM data, the ~1.7-yr variation is not found. Instead, a shift of 1.6–1.8 years in the NM data is observed which may be due to the limited epoch considered in this study.     

Cosmic ray measurements in High Tatra mountains: 1957–2007

Lomnický Štít (LS, situated at High Tatra mountain, 2634 m above sea level, in the direction of 49.40°N, 20.22°E; geomagnetic vertical cut-off rigidity for cosmic rays ∼4 GV) is a relevant place for cosmic ray studies. After a brief review of the LS research history we present a selection of the results based on the measurements performed by the neutron monitor located at that site. In particular, the characteristics of quasi-periodicities and the diurnal variability amplitude and phase obtained from those data are discussed.     

Empirical model of cosmic ray spectrum in energy interval 1 MeV–100 GeV during 11-year solar cycle

The galactic cosmic rays (GCR) are the main ionization source at altitude of ∼3–35 km in the atmosphere. For high latitude anomalous cosmic ray (ACR) component has also a significant influence on the atmospheric ionization. We propose an empirical model for differential spectra D(E) of galactic and anomalous cosmic rays in energy interval 1 MeV–100 GeV during solar cycle. In the model data are used which cover three solar cycles: 20, 22 and 23. The LEAP87, IMAX92, CAPRICE94, AMS98 and BESS experimental spectra for protons and alpha particles are fitted to the proposed empirical model. The modulated GCR differential spectra are compared with force-field approximation to the one-dimensional transport equation and with solutions of two-dimensional cosmic ray transport equation. For experimental spectra, the calculation of the model parameters is performed by Levenberg–Marquardt algorithm, applied to the special case of least squares. Algorithm that combines the rapid local convergence of Newton–Raphson method with globally convergent method for non-linear systems of equations is applied for theoretically obtained differential spectra. The described programmes are realized in algorithmic language C++. The proposed model gives practical possibility for investigation of experimental data from measurements of galactic cosmic rays and their anomalous component.     

Deformation of the ionosphere structure during the space weather events on October–November 2003

We present the spatial maps of the ionosphere–plasmasphere slab thickness τ (ratio of the vertical total electron content, TEC, to the F-region peak electron density, NmF2) during the intense ionospheric storms of October–November 2003. The model-assisted technology for estimate of the upper boundary of the ionosphere, hup, from the slab thickness components in the bottomside and topside ionosphere – eliminating the plasmasphere contribution of τ – is applied at latitudes 35° to 70°N and longitudes −10° to 40°E, from the data of 20 observatories of GPS-TEC and ionosonde networks, for selected days and hours of October and November 2003. The daily–hourly values of NmF2, hmF2 and TECgps are used as the constrained parameters for the International Reference Ionosphere extended to the plasmasphere, IRI-Plas, during the ionospheric quiet days, positive and negative storm phases for estimate of τ and hup. Good correlation has been found between the slab thickness and the upper boundary of the ionosphere for the intense ionospheric storms at October–November 2003. During the negative phase of the ionospheric storm, when the ionospheric plasma density is exhausted, the nighttime upper boundary of the ionosphere is greatly uplifted towards the magnetosphere tail, while the daytime upper boundary of the ionosphere is reduced below 500 km over the Earth.     

Multiple Coulomb scattering method to reconstruct low-energy gamma–ray direction in the GAMMA-400 space-based gamma–ray telescope

The GAMMA-400 currently developing space-based gamma-ray telescope is designed to measure the gamma-ray fluxes in the energy range from ～20?MeV to several TeV in the highly elliptic orbit (without shadowing the telescope by the Earth) continuously for a long time. The physical characteristics of the GAMMA-400 gamma-ray telescope, especially the angular and energy resolutions (at 100-GeV gamma rays they are ～0.01° and ～1%, respectively), allow us to consider this space-based experiment as the next step in the development of extraterrestrial high-energy gamma-ray astronomy. In this paper, a method to improve the reconstruction accuracy of incident angle for low-energy gamma rays in the GAMMA-400 space-based gamma-ray telescope is presented. The special analysis of topology of pair-conversion events in thin layers of converter was performed. Applying the energy dependence of multiple Coulomb scattering for pair components, it is possible to estimate the energies for each particle, and to use these energies as weight in the angle reconstruction procedure. To identify the unique track in each projection the imaginary curvature method is applied. It allows us to obtain significantly better angular resolution in comparison with other methods applied in current space-based experiments. When using this method for 50-MeV gamma rays the GAMMA-400 gamma-ray telescope angular resolution is about 4°.     

Signatures of the Sudden Stratospheric Warming events of January–February 2008 in Seoul,S. Korea

The period January–February 2008 was characterized by four Sudden Stratospheric Warmings (SSWs) in the Northern Hemisphere, of which the last warming, at the end of February 2008, was a major warming. A significant decrease in mesospheric water vapour (H₂O) of more than 2 ppmv (∼40%) was observed by the ground-based microwave (GBMW) radiometer in Seoul, S. Korea [37.3°N, 126.3°E] during the major SSW. A comparison with ground-based mesospheric H₂O observations from the mid-latitude station in Bern [46.9°N, 7°E] revealed an anticorrelation in the mesospheric H₂O data during the major SSW. In addition, prior to the major warming, strong periodic fluctuations were recorded in the Aura MLS vertical temperature distribution between 15 and 0.05 hPa at Seoul. The mesospheric temperature oscillation was found to have a period of ∼10–14 days with a persistency of 3–4 cycles.     

Spectrophotometric observations of the auroras in the far UV range on board the Intercosmos-Bulgaria-1300 satellite during the magnetic storm of 2–3 March 1982

The storm-time HI(1216Å), OI(1304Å), OI(1356Å) emission lines and NO molecule γ (1,1) band computed from the onboard Intercosmos-Bulgaria-1300 measurements are examined. The auroral particles and ring current development are discussed as possible sources of the observed storm-time intensity increase over the theoretical intensity-solar zenith angle dependencies in the evening-midnight sector.     

Some Investigations on the Ionosphere during 2012–2014 in China

In this national biannual report, we will outline some recent progresses in ionospheric studies conducted by Chinese scientists since 2012. The mentioned aspects include: the solar activity control of the ionosphere; couplings between the ionosphere, lower atmosphere and plasmasphere;ionospheric climatology and disturbances; ionospheric irregularities and scintillation; models, data assimilation and simulations; unusual phenomena of the ionosphere; possible seismic signatures presented in ionospheric observations, and some methodology progresses. These progresses will enhance our ability to observe the ionosphere, provide more reasonable understanding about the states of the ionosphere and underlying fundamental processes, and stimulate ionospheric modeling, forecasting and related applications.     

Satellite-observed biological variability in the equatorial Pacific during the 2009–2011 ENSO cycle

The event of 2009–2011 El Niño Southern Oscillation (ENSO) provides an opportunity to gain insight into the biological variability of the equatorial Pacific Ocean for an entire ENSO cycle with satellite and in situ observations. Even though El Niño and La Niña in general led to respectively weakened and enhanced chlorophyll-a concentration and net primary production (NPP) along the equatorial Pacific Ocean during the 2009–2011 ENSO cycle, biological responses were highly disparate along the equator and attributed to different driving mechanisms. In the eastern equatorial Pacific east of 150°E, the El Niño-La Niña biological change was in general small except for the transition period even though sea surface temperature (SST) showed over ∼5 °C drop from El Niño to La Niña. In the central-eastern (170°W–140°W) equatorial Pacific, moderate change of biological activity is attributed to the changes of thermocline driven by the eastward propagating equatorial Kelvin waves and changes of zonal currents and undercurrents. Highest biological response in this ENSO cycle was located in the central (170°E–170°W) and central-western (150°E–170°E) equatorial Pacific with quadruple chlorophyll-a concentration and over ∼400 mg C m⁻² d⁻¹ increase of NPP from El Niño in 2009 to La Niña in 2010. However, spatial pattern of ENSO biological variability as represented with NPP is not exactly the same as chlorophyll-a variability. Wind-driving mixing of nutrients and eastward advection of the oligotrophic warm pool waters are attributed to this significant biological variability in this region.     

Planetary wave coupling of the atmosphere–ionosphere system during the Northern winter of 2008/2009

This paper presents the global spatial (latitude and altitude) structure and temporal variability of the ∼23-day ionospheric zonally symmetric (s = 0) planetary wave (PW) seen in the Northern winter of 2008/2009 (October 2008–March 2009). It is shown that these ∼23-day ionospheric oscillations are forced from PWs propagating from below. The COSMIC ionospheric parameters f_oF2 and h_mF2 and electron density at fixed altitudes and the SABER temperatures were utilized in order to define the waves which are present simultaneously in the atmosphere and ionosphere. The long-period PWs from the two data sets have been extracted through the same data analysis method. The similarity between the lower thermospheric ∼23-day (s = 0) temperature PW and its ionospheric electron density response provides valuable and strong experimental evidence for confirming the paradigm of atmosphere–ionosphere coupling.     

Variation of ionospheric total electron content in Indian low latitude region of the equatorial anomaly during May 2007–April 2008

The ionospheric total electron content (TEC), derived by analyzing dual frequency signals from the Global Positioning System (GPS) recorded near the Indian equatorial anomaly region, Varanasi (geomagnetic latitude 14°, 55′N, geomagnetic longitude 154°E) is studied. Specifically, we studied monthly, seasonal and annual variations as well as solar and geomagnetic effects on the equatorial ionospheric anomaly (EIA) during the solar minimum period from May 2007 to April 2008. It is found that the daily maximum TEC near equatorial anomaly crest yield their maximum values during the equinox months and their minimum values during the summer. Using monthly averaged peak magnitude of TEC, a clear semiannual variation is seen with two maxima occurring in both spring and autumn. Statistical studies indicate that the variation of EIA crest in TEC is poorly correlated with Dst-index (r = −0.03) but correlated well with Kp-index (r = 0.82). The EIA crest in TEC is found to be more developed around 12:30 LT.     

Ionospheric parameters in the European sector during the magnetic storm of August 25–26, 2018

Variations of ionospheric parameters Total Electron Content (TEC) by GNSS, critical frequency (foF2) by vertical sounding and electron density (Ne) by low-altitude satellite were studied at high, mid and low latitudes of the European sector during the magnetic storm of August 25–26, 2018. During the main phase of the storm the ionospheric F2-layer was under the positive disturbance at mid and low latitudes. Then the transition from the positive to negative ΔfoF2 values occurred at all latitudes. The recovery phase was characterized by negative ionospheric disturbance at all latitudes. This is due to the decrease of thermospheric O/N2 ratio during the recovery phase of the storm. The intense Es layers screened the reflections from the F2-layer on August 26th at high and at low latitudes but at different times. Some blackouts occurred due to the high absorption level at high latitudes. In general, foF2 and TEC data were highly correlated. The major Ne changes were at the low latitudes. In general, Ne data confirmed the ionospheric dynamics revealed with foF2 and TEC.     

Vertical motions in Thailand after the 2004 Sumatra–Andaman Earthquake from GPS observations and its geophysical modelling

Following previous findings from ongoing GPS research in Thailand since 2004 we continue to exploit the GPS technique to monitor and model land motions induced by the Sumatra–Andaman Earthquake. Our latest results show that up to the end of 2010, Thailand has been co-seismically displaced and is subsequently undergoing a post-seismic horizontal deformation with total displacements (co-seismic plus post-seismic) ranging from 10.5 to 74.7 cm. We observed the largest horizontal displacements in the southern part of Thailand and moderate and small displacements in the central and northern parts. In addition to horizontal displacements throughout Thailand, continuous GPS measurements show that large parts of Thailand are subsiding at rates up to 1 cm/yr. It is the first time that such vertical post-seismic deformations at large distances (650–1500 km away from the Earthquake’s epicentre) have been recorded. We have investigated the physical processes leading to the observed subsidence. While after-slip on the subduction interface induces negligible or even slightly positive vertical motions, relaxation in the asthenosphere is associated with a sizable subsidence. Predictions from a 3D finite element model feature an asthenosphere with an effective viscosity of the order of 3 * 10¹⁸ Pas, fit the horizontal post-seismic data and the observed subsidence well. This model is then used to predict the subsidence over the whole seismic cycle. The subsidence should go on with a diminishing rate through the next two decades and its final magnitude should not exceed 10 cm in the Bangkok area.     

Aerosols and clouds in the upper troposphere–lower stratosphere region detected by GOMOS and ACE: Intercomparison and analysis of the years 2004 and 2005

Satellite-based limb occultation measurements are well suited for the detection and mapping of polar stratospheric clouds (PSCs) and cirrus clouds. PSCs are of fundamental importance for the formation of the Antarctic ozone hole that occurs every year since the early 1980s in Southern Hemisphere spring. Despite progress in the observation, modeling and understanding of PSCs in recent years, there are still important questions which remain to be resolved, e.g. PSC microphysics, composition, formation mechanisms and long-term changes in occurrence. In addition, it has recently become clear that cirrus clouds significantly affect the global energy balance and climate, due to their influence on atmospheric thermal structure.     

Interseismic slip rate of the Garze–Yushu fault belt in the Tibetan Plateau from C-band InSAR observations between 2003 and 2010

InSAR time series techniques can provide high-spatial resolution deformation fields across an active fault belt, even for zones with heavy vegetation coverage. An interseismic deformation map across the Garze–Yushu fault belt in the Tibetan Plateau, ∼300 km by ∼100 km, is derived from C-band Envisat/ASAR imagery collected between 2003 and 2010. Unlike previous research, we obtain a lookup figure which relates the slip rate with the fault locking depth, the dip angle and the rake angle. The estimated slip rate changes significantly with the locking depth and the rake angle, but relatively little with the dip angle. When considering the focal mechanism solutions of historical earthquake along the Garze–Yushu fault, the interseismic slip rate of the Garze–Yushu fault is close to a value of 6.4 mm/yr, which is between the highest (18.2 mm/yr) and the lowest (3.1 mm/yr) slip rate from GPS estimations, but slightly less than the minimum value (∼ 7 mm/yr) from the geological estimations. The earthquake recurrence interval on the Yushu part of Garze–Yushu fault equals 272 yr, and the April 14, 2010 Mw 6.9 earthquake has not completely released the accumulated strain energy between 1738 and 2010.     

Forbush decreases and solar events seen in the 10–20 GeV energy range by the Karlsruhe Muon Telescope

Since 1993, a muon telescope located at Forschungszentrum Karlsruhe (Karlsruhe Muon Telescope) has been recording the flux of single muons mostly originating from primary cosmic-ray protons with dominant energies in the 10–20 GeV range. The data are used to investigate the influence of solar effects on the flux of cosmic rays measured at Earth. Non-periodic events like Forbush decreases and ground level enhancements are detected in the registered muon flux. A selection of recent events will be presented and compared to data from the Jungfraujoch neutron monitor. The data of the Karlsruhe Muon Telescope help to extend the knowledge about Forbush decreases and ground level enhancements to energies beyond the neutron monitor regime.     

Total electron content of the ionosphere at two stations in East Africa during the 24–25 October 2011 geomagnetic storm

The equatorial ionosphere has been known to become highly disturbed and thus rendering space-based navigation unreliable during space weather events, such as geomagnetic storms. Modern navigation systems, such as the Global Positioning System (GPS) use radio-wave signals that reflect from or propagate through the ionosphere as a means of determining range or distance. Such systems are vulnerable to effects caused by geomagnetic storms, and their performance can be severely degraded. This paper analyses total electron content (TEC) and the corresponding GPS scintillations using two GPS SCINDA receivers located at Makerere University, Uganda (Lat: 0.3^o N; Lon: 32.5^o E) and at the University of Nairobi, Kenya (Lat: 1.3^o S; Lon: 36.8^o E), both in East Africa. The analysis shows that the scintillations actually correspond to plasma bubbles. The occurrence of plasma bubbles at one station was correlated with those at the other station by using observations from the same satellite. It was noted that some bubbles develop at one station and presumably “die off” before reaching the other station. The paper also discusses the effects of the geomagnetic storm of the 24–25 October 2011 on the ionospheric TEC at the two East African stations. Reductions in the diurnal TEC at the two stations during the period of the storm were observed and the TEC depletions observed during that period showed much deeper depletions than on the non-storm days. The effects during the storm have been attributed to the uplift of the ionospheric plasma, which was then transported away from this region by diffusion along magnetic field lines.     

Measurements of the radiation quality factor Q at aviation altitudes during solar minimum (2006–2008)

In radiation protection, the Q-factor has been defined to describe the biological effectiveness of the energy deposition or absorbed dose to humans in the mixed radiation fields at aviation altitudes. This particular radiation field is generated by the interactions of primary cosmic particles with the atoms of the constituents of the Earth’s atmosphere. Thus the intensity, characterized by the ambient dose equivalent rate H∗(10), depends on the flight altitude and the energy spectra of the particles, mainly protons and alpha particles, impinging on the atmosphere. These charged cosmic projectiles are deflected both by the interplanetary and the Earth’s magnetic field such that the corresponding energy spectra are modulated by these fields. The solar minimum is a time period of particular interest since the interplanetary magnetic field is weakest within the 11-year solar cycle and the dose rates at aviation altitudes reach their maximum due to the reduced shielding of galactic cosmic radiation. For this reason, the German Aerospace Center (DLR) performed repeated dosimetric on-board measurements in cooperation with several German airlines during the past solar minimum from March 2006 to August 2008. The Q-factors measured with a TEPC range from 1.98 at the equator to 2.60 in the polar region.