Total solar irradiance absolute level from DIARAD/SOVIM on the International Space Station

Current measurements from DIARAD/VIRGO, PMO6V/VIRGO and ACRIM3 radiometers are of the same order of magnitude, but differ from TIM/SORCE by about 4.5 W m⁻². This difference is higher than the sum of the claimed individual absolute uncertainties of the instruments. In this context, the SOLAR payload on the International Space Station embarks the SOVIM package. We give the results of the differential absolute radiometer DIARAD/SOVIM and discuss its associated uncertainties. Compared to DIARAD/VIRGO, all possible efforts have been made to improve the absolute accuracy. Substantial progress has been made in the aperture area and electrical power measurements. The measured TSI value from the left channel of DIARAD/SOVIM during three days of June 2008 is 1364.50 ± 1.38 W m⁻² (Total) or ±0.49 W m⁻² (if we combine the individual contributions in quadrature). The right channel gives 1364.75 W m⁻² with the same uncertainties. These values are about 1.2 W m⁻² lower than DIARAD/VIRGO and about 4 W m⁻² higher than TIM/SORCE. The difference between the left and right channels measurements is as low as 0.25 W m⁻² which is within the improved uncertainty limits.     

Soil moisture mapping over the Chinese Loess Plateau using ENVISAT/ASAR data

In this paper, we used the available algorithm for soil moisture estimation over LOPEX05 (the Loess Plateau land surface process Experiment (2005)) area. The available algorithm used ENVISAT/ASAR AP mode VV polarization observational data at a low incidence angle and ground measured soil moistures. The ground measurements were performed in the summer of the 2005 during the LOPEX05 field campaign. The validated results indicate that an average difference between the soil moistures estimated from the microwave remote sensing and ground measurements is less than 0.02 cm³/cm³, with a RMS error of 2.0%, and a maximum less than 0.04 cm³/cm³. The algorithm was applied to the surface soil moisture mapping later. The results show that this algorithm is suitable for monitoring soil moisture information of the agricultural fields over the Chinese Loess Plateau, when ground land cover situation and the resolution of imagery data are taken into account. However, we also find that there are large differences over the steep slope region, the edge of mesa. The results are not acceptable for surface soil moisture estimation in these regions. Thus, the surface soil moisture retrieval in the steep slope region of the Loess Plateau need to be further investigated in the future.     

Dynamics of the convection in the inner magnetosphere by observations of the diffuse aurora,SAR arc and ionospheric drift

The first results of the comparison of subauroral luminosity dynamics in 557,7 and 630,0 nm emission with simultaneous measurements of the ionospheric drift in the F2 region with a digisonde DPS-4 at the Yakutsk meridian (CGMC: 55–60N, 200°E) at Kp = 2–6 are presented. It is shown from the analysis of individual events that during the magnetospheric convection intensification after the turn of the IMF B_z – component to the south the equatorward extension of diffuse aurora takes place. At the same time the westward ionospheric drift velocity increases both in the diffuse aurora region and much equatorward of it due to the occurrence of the northward polarization electric field. We suppose that the generation of polarization field can be associated with the development of the region 2 FAC during the intensification of magnetospheric convection. The comparison of ground-based observations with measurements of the plasma drift aboard the DMSP-F15 satellite has been carried out.     

Development of simultaneous imaging polarimeter for asteroids

We are currently developing a polarimeter to study surface physical properties of asteroids. To enhance polarimetric accuracy and observational efficiency, we newly devised the polarimeter whose measurements can provide the two Stokes parameters Q and U, simultaneously. The test-observations of the prototype polarimeter have been carried out in December 2003 and January 2004, mounted on the 101 cm telescope at Bisei Astronomical Observatory, Okayama, Japan. In the observations, unpolarized and polarized standard stars were observed to measure an instrumental polarization and its uncertainty. As a result, an instrumental polarization of 5.06 ± 0.18% has been measured.     

Cosmic ray H/H ratio measured from BESS in 2000 during solar maximum

The Balloon-borne Experiment with a Superconducting Spectrometer (BESS) was flown from Lynn Lake, Manitoba, Canada in August, 2000, during the maximum solar modulation period, with an average residual atmospheric overburden of 4.3 g/cm². Precise spectral measurements of cosmic ray hydrogen isotopes from 0.178 GeV/n to 1.334 GeV/n were made during the 28.7 h of flight. This paper presents the measured energy spectra and their ratio, ²H/¹H. The results are also compared with previous measurements and theoretical predictions.     

Cosmic Ray Energetics And Mass for the International Space Station (ISS-CREAM)

The Cosmic Ray Energetics And Mass (CREAM) instrument is configured with a suite of particle detectors to measure TeV cosmic-ray elemental spectra from protons to iron nuclei over a wide energy range. The goal is to extend direct measurements of cosmic-ray composition to the highest energies practical, and thereby have enough overlap with ground based indirect measurements to answer questions on cosmic-ray origin, acceleration and propagation. The balloon-borne CREAM was flown successfully for about 161 days in six flights over Antarctica to measure elemental spectra of Z = 1–26 nuclei over the energy range 10¹⁰ to >10¹⁴ eV. Transforming the balloon instrument into ISS-CREAM involves identification and replacement of components that would be at risk in the International Space Station (ISS) environment, in addition to assessing safety and mission assurance concerns. The transformation process includes rigorous testing of components to reduce risks and increase survivability on the launch vehicle and operations on the ISS without negatively impacting the heritage of the successful CREAM design. The project status, including results from the ongoing analysis of existing data and, particularly, plans to increase the exposure factor by another order of magnitude utilizing the International Space Station are presented.     

Results of measurements of the response of a delta-doped CCD to neutral and charged particle beams

We report the measurements of the response of a delta-doped Charge Coupled Device (CCD) in imaging mode to beams of charged and neutral particles. That is, the detector imaged the incident beam over its 1024 × 1024 pixels, integrating the number of particles counted in each pixel during the exposure period. In order to count individual particles the exposure time would have had to be reduced considerably compared to the typical ?5 s used in these studies. Our CCD thus operated in a different manner than do conventional particle detectors such as the CEM and MCP that normally are used in a particle counting mode. The measurements were carried out over an energy range from 0.8 to 30 keV. The species investigated include H, H⁺, He⁺, N⁺, N₂⁺, and Ar⁺. The energy and ion mass covered wider ranges than previous measurements for the CCD. The results of these measurements show, as in the case of the previous measurement, for a given ion the CCD response increases with energy and for a given particle energy the response decreases with increasing mass of the particle. These results are in agreement with predictions of the theory of the range of ions in solids. The results also show the possibility for the application of the delta doped CCD as a detector for low energy particle measurements for space plasma physics applications.     

Observations of “zebra” pattern in cm-range with spatial resolution

We present the results of the first observations of the solar microwave burst with fine spectral structure of zebra type at the frequency about 5.7 GHz. The burst has been detected simultaneously by the Siberian Solar Radio Telescope and by the spectropolarimeter of the National Astronomical Observatory of China. Zebra pattern consisted of three parallel stripes with complex frequency drift. The degree of circular polarization of emission reached 100%, the polarization sense corresponded to the extraordinary wave (X-mode). We have determined the plasma parameters in the emission source: plasma density about 10¹¹ cm⁻³, magnetic field strength 60–80 G. We argue that in the given event the most probable mechanism of the zebra pattern generation is non-linear coupling of harmonics of Bernstein modes.     

General Relativity Accuracy Test (GReAT): New configuration for the differential accelerometer

We presents the results of an activity concerning the test of the Einstein Weak Equivalence Principle with an accuracy of about 5 × 10⁻¹⁵. The experiment will be performed in an “Einstein elevator” using a differential accelerometer with a final sensitivity of about 10⁻¹⁴ g_⊕/Hz^1/2. The differential accelerometer is spun about an horizontal axis at a frequency in the range 0.5–1 Hz in order to modulate, during the free fall, the signal from a possible violation of the Equivalence Principle. In the paper the perturbing effects with the same signature of the possible violation are analyzed and constrained. The experimental results obtained in the laboratory with a first prototype of the differential accelerometer are discussed, comparing this results with those obtained using a new prototype.     

Mid-latitude thermospheric zonal winds during the equinoxes

The diurnal variation of the mid-latitude upper thermosphere zonal winds during equinoxes has been studied using data recently generated from CHAMP measurements from 2002 to 2004 using an iterative algorithm. The wind data was separated into two geomagnetic activity levels, representing high geomagnetic activity level (Ap > 8) and low geomagnetic activity level (Ap ? 8). The data were further separated into two solar flux levels; with F10.7 > 140 for high and F10.7 ? 140 for low. Geomagnetic activity is a correlator just as significant as solar activity. The response of mid-latitude thermospheric zonal winds to increases in geomagnetic disturbances and solar flux is evident. With increase in geomagnetic activity, midday to midnight winds are generally less eastward and generally more westward after the about midnight transitions. The results show that east west transitions generally occurred about midnight hours for all the situations analyzed. The west to east transition occurs from 1400–1500 MLT. Enhanced westward averaged zonal wind speeds going above 150 ms⁻¹ are observed in the north hemisphere mid-latitude about sunrise hours (∼0700–1100 MLT). Nighttime winds in the north hemisphere are in good agreement with previous single station ground observations over Millstone Hill. Improved ground observations and multi satellite observations from space will greatly improve temporal coverage of the Earth’s thermosphere.     

Relativistic electron fluxes and dose rate variations during April–May 2010 geomagnetic disturbances in the R3DR data on ISS

Space radiation has been monitored successfully using the Radiation Risks Radiometer-Dosimeter (R3D) installed at the ESA EXPOSE-R (R3DR) facility outside of the Russian Zvezda module of the International Space Station (ISS) between March 2009 and January 2011. R3DR is a Liulin type spectrometer–dosimeter with a single Si PIN detector 2 cm² of area and 0.3 mm thick. The R3DR instrument accumulated about 2 million measurements of the absorbed dose rate and flux of 10 s resolution. The total external and internal shielding before the detector of R3DR device is 0.41 g cm⁻². The calculated stopping energy of normally incident particles to the detector is 0.78 MeV for electrons and 15.8 MeV for protons. After the Coronal Mass Ejection (CME) at 09:54 UTC on 3 April 2010, a shock was observed at the ACE spacecraft at 0756 UTC on 5 April, which led to a sudden impulse on Earth at 08:26 UTC. Nevertheless, while the magnetic substorms on 5 and 6 of April were moderate; the second largest in history of GOES fluence of electrons with energy >2 MeV was measured. The R3DR data show a relatively small amount of relativistic electrons on 5 April. The maximum dose rate of 2323 μGy day⁻¹ was reached on 7 April; by 9 April, a dose of 6600 μGy was accumulated. By the end of the period on 7 May 2010 a total dose of 11,587 μGy was absorbed. Our data were compared with AE-8 MIN, CRESS and ESA-SEE1 models using SPENVIS and with similar observations on American, Japanese and Russian satellites.     

Mid 19th century minimum of galactic cosmic ray flux inferred from Ti in Allegan meteorite

Measurements of ⁴⁴Ti activity in meteorites show that the galactic cosmic ray (GCR) intensity has been declining in the interplanetary space during the past three centuries and has a component of cyclic variation, with periodicity of about 87 years [Taricco, C., Bhandari, N., Cane, D., et al. Galactic cosmic ray flux decline and periodicities in the interplanetary space during the last 3 centuries revealed by ⁴⁴Ti in meteorites. J. Geophys. Res. 111, A08102, 2006.]. In order to verify these results, we have measured ⁴⁴Ti activity in Allegan meteorite which fell in 1899 and in some other meteorites with better precision. The measurements confirm low cosmic ray flux and consequently high solar activity near the middle of 19th century.     

Laser measurements to space debris from Graz SLR station

In order to test laser ranging possibilities to space debris objects, the Satellite Laser Ranging (SLR) Station Graz installed a frequency doubled Nd:YAG pulse laser with a 1 kHz repetition rate, a pulse width of 10 ns, and a pulse energy of 25 mJ at 532 nm (on loan from German Aerospace Center Stuttgart – DLR). We developed and built low-noise single-photon detection units to enable laser ranging to targets with inaccurate orbit predictions, and adapted our standard SLR software to include a few hundred space debris targets. With this configuration, we successfully tracked – within 13 early-evening sessions of each about 1.5 h – 85 passes of 43 different space debris targets, in distances between 600 km and up to more than 2500 km, with radar cross sections from >15 m² down to <0.3 m², and measured their distances with an average precision of about 0.7 m RMS.     

Properties of traveling atmospheric disturbances (TADs) inferred from CHAMP accelerometer observations

Densities derived from accelerometer measurements on the CHAMP satellite near 400 km are used to statistically establish characteristics of large-scale (>1000 km) traveling atmospheric disturbances (TADs). Only TADs that at least propagate from the auroral zone to the equator are analyzed here, and a total of 21 identifiable events are found over the years 2001–2007. The average speed of all TADs, regardless of local time, is 646 ± 122 ms⁻¹. The average speeds on the dayside and nightside are 595 ± 127 ms⁻¹ and 685 ± 106 ms⁻¹, respectively, i.e., the speed appears to be 10% higher on average on the nightside. On six occasions TADs were only detected on the night side; however, TADs on the dayside often appear more distinctly in the data. Moreover, contrary to some theoretical expectations, dayside TADs do not dissipate more readily than night side TADs, although much less are detected between 8–20 solar local time. No clear dependence of TAD amplitude or phase speed with respect to Kp, or rate of increase of Kp, is found.     

Influence of solar-geomagnetic disturbances on SABER measurements of 4.3 μm emission and the retrieval of kinetic temperature and carbon dioxide

Thermospheric infrared radiance at 4.3 μm is susceptible to the influence of solar-geomagnetic disturbances. Ionization processes followed by ion-neutral chemical reactions lead to vibrationally excited NO⁺ (i.e., NO⁺(v)) and subsequent 4.3 μm emission in the ionospheric E-region. Large enhancements of nighttime 4.3 μm emission were observed by the TIMED/SABER instrument during the April 2002 and October–November 2003 solar storms. Global measurements of infrared 4.3 μm emission provide an excellent proxy to observe the nighttime E-region response to auroral dosing and to conduct a detailed study of E-region ion-neutral chemistry and energy transfer mechanisms. Furthermore, we find that photoionization processes followed by ion-neutral reactions during quiescent, daytime conditions increase the NO⁺ concentration enough to introduce biases in the TIMED/SABER operational processing of kinetic temperature and CO₂ data, with the largest effect at summer solstice. In this paper, we discuss solar storm enhancements of 4.3 μm emission observed from SABER and assess the impact of NO⁺(v) 4.3 μm emission on quiescent, daytime retrievals of Tk/CO₂ from the SABER instrument.     

Comet West 1976 VI: Photopolarimetry by the Helios 2 Zodiacal Light Experiment

Shortly after it passed through perihelion on February 25, 1976 Comet West was observed by the Helios Zodiacal Light Experiment. Broadband photopolarimetric measurements of the head and of the tail were performed in three wavelength bands (U, B, V). The phase angles encountered range from 67° to 85°. The polarization measurements indicated wavelength independent linear polarization. The maximum degree of polarization in the visual channel was found to be .28 at a phase angle of 83°.     

Coronal mass ejections acceleration problem

A statistical study of acceleration and its error of coronal mass ejections (CMEs) observed by the Large Angle Spectrometric Coronagraph (LASCO) is performed. A total of 5594 CMEs events have been analyzed by using a least-square method and using the error in the height measures. We verify that slower CMEs (velocities in the interval from 200 to 500 km s⁻¹) tend to have a positive acceleration (about 1 m s⁻²) at heights above 5 solar radii, while less than 10% CMEs show an average negative acceleration (about −2.2 m s⁻²) as they propagate from 5 to 30 solar radii. For most individual CMEs one can not say if they are accelerated or decelerated, only for 8% of all observed CMEs events one can extract the sign of the acceleration in the 5–30 solar radii.     

Heliospheric implications of structure in the interstellar medium

Equilibrium models of diffuse interstellar material (ISM) near the Sun show a range of cloud densities, ionization, and temperatures which are consistent with data, although the local ISM must be inhomogeneous over ∼2 pc scales. The ISM close to the Sun has properties that are consistent with the sheetlike warm neutral (and partially ionized) gas detected in the Arecibo Millennium Survey. Local interstellar magnetic fields are poorly understood, but data showing weak polarization for nearby stars indicate dust may be trapped in fields or currents in the heliosheath nose region. Implications of this dust capture are widespread, and may impact the interpretation of the cosmic microwave background data. Observations of interstellar H⁰ inside of the solar system between 1975 and 2000 do not suggest any variation in the properties or structure of local interstellar H⁰ over distance scales of ∼750 AU to within the uncertainties.     

Evidence for the lowering of the centroid of daytime thermospheric O(D) 630.0 nm emission over the magnetic equator: First results

It is shown in this paper for the first time that the intensity of the daytime thermospheric O(¹D) 630.0 nm airglow as measured by the ground-based dayglow photometer over Trivandrum (8.5°N; 77°E; dip lat. 0.5°N), a geomagnetic dip equatorial station, exhibit a direct correlation with the electron density at 180 km. This altitude is about ∼40 km lower than the believed centroid of the O(¹D) 630.0 nm dayglow emission i.e. 220 km. This observation is contrary to the understanding of the behavior of O(¹D) 630.0 nm dayglow over equatorial/low latitudes. Over these latitudes, the variations of the measured intensity of O(¹D) 630.0 nm dayglow are known to be associated with the changes in the electron density at altitudes around 220 km, the centroid of this emission. In this context, the present results indicating the lowering of the peak altitude of O(¹D) 630.0 nm emission from ∼220 to ∼180 km over the dip equator is new. Recent results on solar XUV flux indicate that this could be an important parameter that controls the O(¹D) 630.0 nm dayglow excitation rates through modulations in the neutral and ionic composition in lower thermosphere-ionosphere region. However, the lowering of the centroid of O(¹D) 630.0 nm emission, as shown in this study, has been ascribed primarily to the fountain effect associated with the equatorial ionization anomaly.