First measurements of cosmic-ray nuclei at high energy with CREAM

The balloon-borne cosmic-ray experiment CREAM-I (Cosmic-Ray Energetics And Mass) recently completed a successful 42-day flight during the 2004–2005 NASA/NSF/NSBF Antarctic expedition. CREAM-I combines an imaging calorimeter with charge detectors and a precision transition radiation detector (TRD). The TRD component of CREAM-I is targeted at measuring the energy of cosmic-ray particles with charges greater than Z ∼ 3. A central science goal of this effort is the determination of the ratio of secondary to primary nuclei at high energy. This measurement is crucial for the reconstruction of the propagation history of cosmic rays, and consequently for the determination of their source spectra. First scientific results from this instrument are presented.     

Saturn kilometric radiation as a monitor for the solar wind?

Since the Voyager mission it is known that Saturn Kilometric Radiation (SKR) is strongly influenced by external forces, i.e., the solar wind and in particular the solar wind ram pressure. Recent studies using Cassini data essentially confirmed these findings for particular periods during the first Cassini orbit of Saturn. The data coverage of SKR by the Cassini/RPWS experiment for the period of six months prior to Saturn Orbit Insertion (July 1, 2004) is rather continuous, whereas there are gaps in the solar wind plasma data. The strong correlation of SKR with the solar wind may provide an indication on the variations of the solar wind plasma, specifically during the gap periods. These periods lacking solar wind data are substituted by Ulysses solar wind data which have been propagated over ∼4 AU, applying magnetohydrodynamic propagation models. Cross correlation studies showed that Ulysses solar wind data can be taken as a substitute for missing Cassini data. The use of SKR as monitor for solar wind variations is discussed. With the present set of observations the SKR proxy lacks significant reliability.     

The Engineering Radiation Monitor for the Radiation Belt Storm Probes Mission

An Engineering Radiation Monitor (ERM) has been developed as a supplementary spacecraft subsystem for NASA’s Radiation Belt Storm Probes (RBSP) mission. The ERM will monitor total dose and deep dielectric charging at each RBSP spacecraft in real time. Configured to take the place of spacecraft balance mass, the ERM contains an array of eight dosimeters and two buried conductive plates. The dosimeters are mounted under covers of varying shielding thickness to obtain a dose-depth curve and characterize the electron and proton contributions to total dose. A 3-min readout cadence coupled with an initial sensitivity of ～0.01 krad should enable dynamic measurements of dose rate throughout the 9-hr RBSP orbit. The dosimeters are Radiation-sensing Field Effect Transistors (RadFETs) and operate at zero bias to preserve their response even when powered off. The range of the RadFETs extends above 1000 krad to avoid saturation over the expected duration of the mission. Two large-area (～10 cm²) charge monitor plates set behind different thickness covers will measure the dynamic currents of weakly-penetrating electrons that can be potentially hazardous to sensitive electronic components within the spacecraft. The charge monitors can handle large events without saturating (～3000 fA/cm²) and provide sufficient sensitivity (～0.1 fA/cm²) to gauge quiescent conditions. High time-resolution (5 s) monitoring allows detection of rapid changes in flux and enables correlation of spacecraft anomalies with local space weather conditions. Although primarily intended as an engineering subsystem to monitor spacecraft radiation levels, real-time data from the ERM may also prove useful or interesting to a larger community.     

Comparison of diurnal,seasonal and latitudinal effect of MUF VR and NmF2 VR during some solar cycle epochs

The diurnal and seasonal changes of the variability (VR) of Maximum Useable Frequency (MUF) are compared with those of peak electron density (NmF2) at Ibadan (7.4°N, 3.9°E, 6°S dip) in the African sector. Also compared is the latitudinal effect on both characteristics by combining data from Singapore (1.3°N, 103.8°E, 17.6°S dip) in the East Asian sector and Slough (51.5°N, 359.4°E, 66.5°S dip) in the European sector. MUF VR is found to be about half of NmF2 VR at all the hours and seasons and during the solar cycle epochs considered for the three stations. While nighttime MUF VR is greater in June Solstice and September Equinox during both low and moderate solar activities and in September Equinox and December Solstice during high solar activity, nighttime NmF2 VR is greater in June Solstice and September Equinox during high solar activity and greater at the equinoxes during low and moderate solar activities. This signifies a shift in nighttime MUF peak VR from the middle six months during low and moderate solar activities to the last half of the year during high solar activity. Daytime VR of both characteristics are not observed to show any seasonal variation. MUF VR and that of NmF2 are found to increase and decrease alternately with the Zurich sunspot number (Rz) for Ibadan and Singapore. For Slough, the VR of both characteristics increases with Rz during the first half of the day. It then increases and decreases alternately with Rz during the remaining hours of the day. While nighttime MUF VR decreases with latitude, just like nighttime NmF2 VR, no latitudinal effect is found for daytime VR of both characteristics.     

Coronal Mass Ejections over Solar Cycles 23 and 24

This paper presents the results of in-orbit commissioning of the first Czech technological CubeSat satellite of VZLUSAT-1. The 2U nanosatellite was designed and built during the 2013 to 2016 period. It was successfully launched into Low Earth Orbit of 505 km altitude on June 23, 2017 as part of international mission QB50 onboard a PSLV C38 launch vehicle. The satellite was developed in the Czech Republic by the Czech Aerospace Research Centre, in cooperation with Czech industrial partners and universities. The nanosatellite has three main payloads. The housing is made of a composite material which serves as a structural and radiation shielding material. A novel miniaturized X-Ray telescope with lobster-eye optics and an embedded Timepix detector represents the CubeSat’s scientific payload. The telescope has a wide field of view. VZLUSAT-1 also carries the FIPEX scientific instrument as part of the QB50 mission for measuring the molecular and atomic oxygen concentration in the upper atmosphere.

     

Variability of the ionospheric electron density at fixed heights and validation of IRI-2007 profile’s prediction at Ilorin

A study on the variability of the equatorial ionospheric electron density was carried out at fixed heights below the F2 peak using one month data for each of high and low solar activity periods. The data used for this study were obtained from ionograms recorded at Ilorin, Nigeria, and the study covers height range from 100 km to the peak of the F2 layer for the daytime hours and height range from 200 km to the peak of the F2 layer for the nighttime hours. The results showed that the deviation of the electron density variation from simple Chapman variation begins from an altitude of about 200 km for the two months investigated. Daytime minimum variability of between 2.7% and 9.0% was observed at the height range of about 160 and 200 km during low solar activity (January 2006) and between 3.7% and 7.8% at the height range of 210 and 260 km during high solar activity (January 2002). The nighttime maximum variability was observed at the height range of 210 and 240 km at low solar activity and at the height range of 200 and 240 km at high solar activity. A validation of IRI-2007 model electron density profile’s prediction was also carried out. The results showed that B0 option gives a better prediction around the noontime.     

The response of African equatorial foF2 to geomagnetic storms: Comparison between observations and IRI-2007 predictions

This study examines the response of the African equatorial ionospheric foF2 to different levels of geomagnetic storms, using the foF2 hourly data for the year 1989 from Ouagadougou (12.4°N, 1.5°W, dip: 2.8°N). The study also compares the observed data for the selected storm periods with the latest IRI model (IRI-2007). The foF2 values (both observed and predicted) show typical features of daytime peak and post-midnight minimum peak. The response of the ionospheric foF2 over Ouagadougou to storms events, during the night-time and post-midnight hours indicates negative responses of the ionospheric foF2, while that of the daytime hours indicates positive responses. For the investigation on the variability of the observed foF2 with respect to IRI-2007 model, with the exception of the analysis of the 20–22, October, 1989 data, where a midday peak was also observed on the first day, this study reveals two characteristic daily foF2 variability peaks: post-midnight and evening peaks. In addition, for all the geomagnetic storms considered, the URSI and CCIR coefficients of the IRI-2007 model show reasonable correspondence with each other, except for some few discrepancies. For instance, the event of 28–30 August, 1989 shows comparatively higher variability for the URSI coefficient, and at the foF2 peak values, the event of 20–22 October, 1989 shows that the CCIR coefficient is more susceptible to foF2 variability than the URSI coefficient. This study is aimed at providing African inputs for the future improvement of the IRI model.     

Fast measurements of parameters of the Solar Wind using the BMSW instrument

Design of the plasma spectrometer BMSW (Fast Monitor of the Solar Wind, possessing high temporal resolution) is described in the paper, as well as its characteristics and modes of operation. Some examples of measurements of various properties of the solar wind, made with this instrument installed onboard the high-apogee satellite Spektr-R, are presented.     

GOCE orbit analysis: Long-wavelength gravity field determination using the acceleration approach

The restricted sensitivity of the Gravity field and steady-state Ocean Circulation Explorer (GOCE) gradiometer instrument requires satellite gravity gradiometry to be supplemented by orbit analysis in order to resolve long-wavelength features of the geopotential. For the hitherto published releases of the GOCE time-wise (TIM) and GOCE space-wise gravity field series—two of the official ESA products—the energy conservation method has been adopted to exploit GPS-based satellite-to-satellite tracking information. On the other hand, gravity field recovery from data collected by the CHAllenging Mini-satellite Payload (CHAMP) satellite showed the energy conservation principle to be a sub-optimal choice. For this reason, we propose to estimate the low-frequency part of the gravity field by the point-wise solution of Newton’s equation of motion, also known as the acceleration approach. This approach balances the gravitational vector with satellite accelerations, and hence is characterized by (second-order) numerical differentiation of the kinematic orbit. In order to apply the method to GOCE, we present tailored processing strategies with regard to low-pass filtering, variance–covariance information handling, and robust parameter estimation. By comparison of our GIWF solutions (initials GI for “Geodätisches Institut” and IWF for “Institut für WeltraumForschung”) and the GOCE-TIM estimates with a state-of-the-art gravity field solution derived from GRACE (Gravity Recovery And Climate Experiment), we conclude that the acceleration approach is better suited for GOCE-only gravity field determination as opposed to the energy conservation method.