Proton Flux Measurements Research Articles

The east‐west effect in solar proton flux measurements in geostationary orbit: A new GOES capability

Since 1998, the GOES system has made eastward and westward observations of multi‐MeV solar proton fluxes. The gyrocenters of the fluxes observed looking westward (eastward) lie outside (inside) geostationary orbit. Due to this “east‐west effect,” eastward observations of 4.2–82 MeV protons vary with respect to their westward equivalents. At times of high solar wind dynamic pressure (Pdyn > 10 nPa), the “inside” and “outside” fluxes are approximately equal. As Pdyn decreases to ∼1 nPa and the ring current decreases, the “inside” fluxes decrease as much as an order of magnitude with respect to the “outside” fluxes. Under low Pdyn, the “inside” fluxes exhibit short‐lived (1–3 hr) increases, sometimes to the levels of the “outside” fluxes, during periods of enhanced AE index activity. This association suggests that magnetotail topologies associated with substorms enhance the access of solar protons to lower L shells under low Pdyn.

Long-Term Adaptation of Bacillus subtilis 168 to Extreme pH Affects Chemical and Physical Properties of the Cellular Membrane

We characterized physical and chemical properties of cell-membrane fragments from Bacillus subtilis 168 (trpC2) grown at pH 5.0, 7.0 and 8.5. Effects of long-term bacterial adaptation reflected in growth rates and in changes of the membrane lipid composition were correlated with lipid order and dynamics using time-resolved fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene. We demonstrate that the pH adaptation results in a modification of a fatty acid content of cellular membranes that significantly influences both the lipid-chain order and dynamics. For cultivation at acidic conditions, the lipid order increases and membrane dynamics decreases compared to pH 7.0. This results in rigid and ordered membranes. Cultivation at pH 8.5 causes slight membrane disordering. Instant pH changes induce qualitatively similar but smaller effects. Proton flux measurements performed on intact cells adapted to both pH 5.0 and 8.5 revealed lower cell-membrane permeability compared to bacteria cultivated at pH optimum. Our results indicate that both acidic and alkalic pH stress represent a permanent challenge for B. subtilis to keep a functional membrane state. The documented adaptation-induced adjustments of membrane properties could be an important part of mechanisms maintaining an optimal intracellular pH at a wide range of extracellular proton concentrations.

Optimization of the interplanetary energetic proton flux database and its application in modeling radiation conditions

The dissimilarity of the results of solar and galactic proton flux measurements made on different spacecraft is pointed out. It is caused, in addition to instrument errors, by differences in the temporal and spatial conditions of the measurements. We suggest using statistical analysis of proton fluences calculated for different long time intervals, from half a year to 10 years, for the optimization of the interplanetary proton database. An example of such analysis is presented and a probabilistic model of total proton fluences at the Earth’s orbit outside the magnetosphere, constructed using the analysis, is described. A formalized method for separating proton fluxes in solar proton events from protons of galactic cosmic rays is suggested. A conclusion is made that sources of cosmic ray protons with energies of less than 4 MeV should be examined in more detail.

Conversion of the 2 Cl−/1 H+ antiporter ClC-5 in a NO3−/H+ antiporter by a single point mutation

Several members of the CLC family are secondary active anion/proton exchangers, and not passive chloride channels. Among the exchangers, the endosomal ClC-5 protein that is mutated in Dent's disease shows an extreme outward rectification that precludes a precise determination of its transport stoichiometry from measurements of the reversal potential. We developed a novel imaging method to determine the absolute proton flux in Xenopus oocytes from the extracellular proton gradient. We determined a transport stoichiometry of 2 Cl(-)/1 H+. Nitrate uncoupled proton transport but mutating the highly conserved serine 168 to proline, as found in the plant NO3(-)/H+ antiporter atClCa, led to coupled NO3(-)/H+ exchange. Among several amino acids tested at position 168, S168P was unique in mediating highly coupled NO3(-)/H+ exchange. We further found that ClC-5 is strongly stimulated by intracellular protons in an allosteric manner with an apparent pK of approximately 7.2. A 2:1 stoichiometry appears to be a general property of CLC anion/proton exchangers. Serine 168 has an important function in determining anionic specificity of the exchange mechanism.

Microsensor technology for measuring H + flux in buffered media

Nearly all experiments designed to quantify phenomena in biological systems are conducted in the presence of buffers. Most analytical techniques measure free proton activity, and do not account for the activity of protons associated with buffer molecules, potentially leading to an underestimation of biophysical proton transport. In applications where total proton flux activity at the level of biological membranes is of interest, a dynamic biophysical approach is required. This paper presents a simplified method and data filtering algorithm for measuring electrophysiological, transmembrane H + flux activities in buffered media based on the self-referencing microsensor technique. A simplified mathematical model was developed that accounts for chemical H + buffering in a background matrix of buffer molecules. The model and buffer correction algorithm were validated for various biochemically relevant buffers over the 6.1–10.7 pH range. The buffer correction algorithm was used to filter the output of a self-referencing ion-selective H + sensor for the measurement of proton flux. Special emphasis has been placed on the use of pH sensitive microelectrodes when operating as self-referencing flux sensors, but the analytical method is also applicable to the use of static electrodes and pH sensitive dyes.

Function and Subunit Interactions of the N-terminal Domain of Subunit a (Vph1p) of the Yeast V-ATPase

The vacuolar (H+)-ATPases (V-ATPases) are ATP-dependent proton pumps that operate by a rotary mechanism in which ATP hydrolysis drives rotation of a ring of proteolipid subunits relative to subunit a within the integral V(0) domain. In vivo dissociation of the V-ATPase (an important regulatory mechanism) generates a V(0) domain that does not passively conduct protons. EM analysis indicates that the N-terminal domain of subunit a approaches the rotary subunits in free V(0), suggesting a possible mechanism of silencing passive proton transport. To test the hypothesis that the N-terminal domain inhibits passive proton flux by preventing rotation of the proteolipid ring in free V(0), factor Xa cleavage sites were introduced between the N- and C-terminal domains of subunit a (the Vph1p isoform in yeast) to allow its removal in vitro after isolation of vacuolar membranes. The mutant Vph1p gave rise to a partially uncoupled V-ATPase complex. Cleavage with factor Xa led to further loss of coupling of proton transport and ATP hydrolysis. Removal of the N-terminal domain by cleavage with factor Xa and treatment with KNO3 and MgATP did not, however, lead to an increase in passive proton conductance by free V(0), suggesting that removal of the N-terminal domain is not sufficient to facilitate passive proton conductance through V(0). Photoactivated cross-linking using the cysteine reagent maleimido benzophenone and single cysteine mutants of subunit a demonstrated the proximity of specific sites within the N-terminal domain and subunits E and G of the peripheral stalk. These results suggest that a localized region of the N-terminal domain (residues 347-369) is important in anchoring the peripheral stator in V1V0.

Measurement of Proton Beam Energy and Flux by Using a LYSO Crystal

Measurement of Proton Beam Energy and Flux by Using a LYSO Crystal

A new modeling method of solar energetic proton events for ISO specification

Solar energetic protons degrade performance and reliability of spacecraft systems due to single-event effects, total dose effects and displacement damage in electronics components including solar cells. On designing a solar cell panel, a total fluence of solar energetic protons (SEPs) which cause solar cell damage is needed to estimate power loss of the solar cells over mission life. Nowadays a solar panel area of spacecraft is increasing as spacecraft mission life becomes longer (15–18 years). Thus an accurate SEP model is strongly required for the cost-minimum design from the aerospace industry. The SEP model, JPL-91 proposed by Feynman et al., is currently used widely for solar cell designing. However, it is known that the JPL-91 model predicts higher fluences of protons than values actually experienced in space, especially after 7 years on orbit. In addition, the model is based on several assumptions, and also needs Monte-Carlo simulations for calculating fluences. In this study, we propose a new method for modeling SEPs especially focused on solar cell degradation. The newly-proposed method is empirical, which constructs a model based directly upon proton flux measurement data taken by instruments onboard spacecraft. This method has neither assumptions nor dependence on SEP event selection, both of which are needed in JPL-91. The model fluences derived from this method show lower fluences in longer missions compared to JPL-91. This method has been proposed to ISO (International Organization for Standardization) and has been discussed for a new standard SEP model.

Response of the lower ionosphere to solar proton event on July 14, 2000. Model simulations over both poles

Response of the middle atmosphere and especially of electron and ion concentrations in the lower ionosphere to one of the strongest Solar Proton Events (SPE) of the 23rd solar cycle on July 14, 2000 is studied with the emphasis on the differences in ionosphere over the North and the South Pole. General circulation model (GCM) and 3D chemical global transport-photochemical middle atmosphere model are used for simulations of neutral composition, wind and temperature response. Using these results, concentrations of the short-living ions are calculated by 1D photochemical model of the lower ionosphere. SPE-induced ionization rates in the polar atmosphere are calculated using high time-resolution satellite measurements of solar proton fluxes provided by GOES-10. SPEs are known to produce significant amounts of odd nitrogen, odd hydrogen and ion species that affect neutral and ion constituents in stratosphere and mesosphere. Our simulations show that electron concentrations over both poles increase by several orders of magnitude. In the north polar cap (NPC) in polar summer, this enhancement lasts longer than in the south polar cap (SPC) at polar night. Contribution of the significant temperature changes after the SPE found by Krivolutsky et al. [2006. Advances in Space Research 37 (8), 1602] in north polar mesosphere to the SPE-induced electron concentration enhancement is of the order of 10% at 88–98 km on day 5–8 after the SPE onset. The present simulations show that the overall negative ion concentration increased by about 2 orders of magnitude during SPE in the sun-lit NPC and slightly less in the dark SPC ionosphere. Response of the positive clusters is found similar in both hemispheres. Calculated decrease of ion composition parameter f + = [ Σ Clust + ] / ( [ NO + ] + [ O 2 + ] ) by 2 orders of magnitude over both poles is in agreement with measurements.

Energetic proton precipitation related to ion–cyclotron waves

This brief review summarizes recent findings related to particle precipitation associated with electromagnetic ion–cyclotron (EMIC) waves seen on the ground as geomagnetic Pc1 and IPDP pulsations. Particle precipitation signatures of ion–cyclotron interaction are described as revealed from low-altitude satellite measurements of the energetic proton fluxes as well as from observations of the proton aurora. As a result, localized proton precipitation patterns situated equatorward of the isotropy boundary are disclosed. One of the patterns is a proton precipitation spot in the morning sector, presumably mapped onto plasmapause; another one is an elongated region of the precipitation, presumably mapped onto the plasmaspheric plume. Clear evidence of the pitch-angle scattering associated with the ion–cyclotron wave activity is found near the equatorial plane in the region conjugated with the localized proton precipitation at low altitude. Thus, the revealed precipitation patterns determine the location of the region of intense pitch-angle scattering of energetic protons, and, therefore, their observations can be used to monitor the region of the ion–cyclotron interaction and to study its origin and properties. Some examples of such application of the low-altitude observations of energetic particles are described.

Measurement of proton and oxide ion fluxes in a working Y-doped BaCeO 3 SOFC

Y-doped BaCeO 3 (BCY), a solid state ion conductor which exhibits mixed proton and oxide ion conductivity under some conditions, was used as an electrolyte in a solid oxide fuel cell (SOFC). The conductivities of 10% and 25% Y-doped BaCeO 3 (BCY10 and BCY25) were measured under a single gas atmosphere of 5% hydrogen in argon (5% H 2/Ar), air and pure argon (Ar). Furthermore, a dual-chamber SOFC reactor was used to investigate the conductivities of the BCY10 and BCY25 electrolytes under fuel cell conditions, i.e., 5% hydrogen in argon at the anode with air at the cathode. The performance of BCY-based SOFC with Pt electrodes was measured over a temperature range of 500–800 °C using a galvanostat/potentiostat. Both anode and cathode product stream compositions were analysed using a gas chromatograph and a hygrometer. A material balance for the system was performed in order to estimate proton and oxygen ion fluxes across the electrolyte. Water transport across the electrolyte in the absence of an external circuit was also studied.

CLUSTER observation of collisionless transport at the magnetopause

On May 10, 2002 the CLUSTER spacecraft (SC) encountered a ∼450 km (five magnetosheath thermal proton gyro‐radii) wide high‐latitude magnetopause (MP). Magnetic field observations indicate the crossing of a ∼130 km thick MP current sheet (CS) located inside a magnetic hole. Proton flux measurements diagnose a dense boundary layer (BL) directly attached to the MP and an additional rare BL located earthwards from the MP. Enhanced magnetic fluctuations are found near the local proton‐cyclotron frequency Ωcp (0.4–2 Hz). Applying the phase‐differencing technique we obtained a wavelength of 150–250 km and the propagating direction earthward perpendicular to the MP. Inside the MP the pitch‐angle proton distribution demonstrates the presence of a transverse population. The formation of the two BLs can be understood by enhanced collisionless diffusion of magnetosheath protons due to wave‐particle interaction, while higher‐energy protons (Wp > 300 eV) penetrate into the BLs also via finite gyro‐radius effect.

Modeling a large solar proton event in the southern polar atmosphere

We have modeled the effects of the Sodankylä Ion Chemistry model (SIC) electron density profiles on VLF propagation across the southern polar region during the first few days of the 4–10 November 2001 solar proton event (SPE). The results show that the SIC model is accurately reproducing the changes in ionization during the SPE. These results were obtained by approximating the SIC electron density profiles to the Wait β and h′ profiles where the densities were below 1000 el cm−3, a limitation that means during SPEs the technique is typically sensitive in the altitude range 50–60 km. The calculated values of β and h′ were applied to the part of the propagation path poleward of the L = 4 boundary for the Hawaii (NPM)–Halley great circle path. Comparing the change in amplitude of NPM at Halley during the SPE with the GOES satellite proton flux measurements, we observe a good correlation and thus conclude that the variability observed in the VLF data is primarily caused by >50 MeV proton fluxes. This suggests that the SPE produced ionization dominates all other precipitation sources at these altitudes during 4 and 5 November 2001. Consequently, these results suggest that the assumption made during the SIC modeling runs of 4–5 November 2001 of only having proton precipitation and no significant energetic electron precipitation was reasonable. Our work strongly suggests that VLF subionospheric propagation is a reliable tool for the study of SPEs and that it is particularly effective when used in conjunction with an atmospheric model such as SIC.

Dynamical response of the middle atmosphere to solar proton event of July 2000: Three-dimensional model simulations

3D general circulation and chemical global transport-photochemical middle atmosphere models have been used for simulation of ozone, wind and temperature response to one of the strongest solar proton events (SPEs) of the 23rd solar cycle – 14 July 2000. It was assumed in the photochemical scheme that approximately one molecule of NO and two molecules of OH are produced for each pair of ions that are created due to the ionization of the air by solar protons. These NO and OH molecules disturb the photochemical system in the stratosphere and mesosphere. SPE-induced ionization rates have been calculated using high time-resolution satellite measurements of solar proton fluxes provided by GOES. According to the calculations a maxima of ionization rates occurred on 15 July 2000, and it was localized in the mesosphere at high latitudes. 3D photochemical calculations showed that ozone was strongly reduced in the mesosphere and stratosphere over the Northern polar region during and after SPE. A similar effect in ozone was found in HALOE/UARS data by different groups of authors including present study. At the same time a weak negative response of ozone over the South Pole (night conditions) was found in the simulations. The calculated ozone response has been introduced into the radiative module of the GCM. The results of model runs showed that ozone depletion caused by SPE leads to the disturbances in temperature and dynamics mostly over high latitudes of the Northern hemisphere. The simulations revealed a cooling (several Kelvin) and reduced zonal wind in the region of ozone depletion in the middle atmosphere. No response was found over the south polar region (nigh in July). The response in temperature, wind, and amplitude of the tides was found above the levels of ozone depletion. A preliminary analysis showed that this unusual effect is mostly connected by non-linear interaction between gravity waves and the zonal mean state, but a clear and detailed explanation needs further investigation.

Diurnal variation of ozone depletion during the October–November 2003 solar proton events

We have studied the short‐term effect of the October–November 2003 series of solar proton events on the middle atmosphere. Using the proton flux measurements from the GOES–11 satellite as input, we modeled the effect of the precipitating particles between 26 October and 6 November with a one–dimensional ion and neutral chemistry model. Then we compared the results with ground‐based radio propagation measurements, as well as with NO2 and ozone profiles made by the GOMOS satellite instrument. The very low frequency signal experiences up to −7 dB absorption during the largest solar proton event, subsequently varying with time of day during the recovery phase. The model and radio propagation observations show very good agreement, suggesting that the model is capturing the impact of solar protons on the ionosphere. The model results show order‐of‐magnitude changes in odd hydrogen and odd nitrogen concentrations, as well as ozone depletion varying from 20% at 40 km altitude to more than 95% at 78 km. The magnitude and altitude distribution of ozone depletion is found to depend not only on the flux and energy of the protons but also on the diurnal cycle of atomic oxygen and ozone‐depleting constituents so that the largest depletions of ozone are seen during sunrise and sunset. The after‐event recovery of ozone is altitude‐dependent because of the differences in the recovery of odd hydrogen and odd nitrogen and also because of a relatively faster ozone production at higher altitudes. The modeled and measured NO2 profiles agree well at altitudes 35–60 km, particularly during times of large concentrations observed after the solar proton event onset. A comparison of the time series of ozone depletion shows a good agreement between the model and observations.

Atmospheric muon and neutrino flux from 3-dimensional simulation

The atmospheric muon and neutrino flux have been simulated using the same approach which successfully accounted for the recent secondary proton, electron, and positron flux measurements in orbit by the AMS experiment. For the muon flux, good agreement is obtained with the CAPRICE and HEAT data for altitudes ranging from sea level up to about 38 km. The general features of the calculated atmospheric neutrino flux are reported and discussed. The flux obtained at the Super-Kamiokande experiment location are reported and compared with other calculations. For low neutrino energies the flux obtained is significantly smaller than that used in the data analysis of underground experiment. The simulation results for the SOUDAN experiment site are also reported.

The cosmic-ray proton and helium spectra measured with the CAPRICE98 balloon experiment

A new measurement of the primary cosmic-ray proton and helium fluxes from 3 to 350 GeV was carried out by the balloon-borne CAPRICE experiment in 1998. This experimental setup combines different detector techniques and has excellent particle discrimination capabilities allowing clear particle identification. Our experiment has the capability to determine accurately detector selection efficiencies and systematic errors associated with them. Furthermore, it can check for the first time the energy determined by the magnet spectrometer by using the Cherenkov angle measured by the RICH detector well above 20 GeV n −1. The analysis of the primary proton and helium components is described here and the results are compared with other recent measurements using other magnet spectrometers. The observed energy spectra at the top of the atmosphere can be represented by (1.27±0.09)×10 4 E −2.75±0.02 particles (m 2 GeV sr s) −1, where E is the kinetic energy in GeV, for protons between 20 and 350 GeV and (4.8±0.8)×10 2 E −2.67±0.03 particles (m 2 GeV n −1 sr s) −1, where E is the kinetic energy in GeV per nucleon, for helium nuclei between 15 and 150 GeV n −1.

D region electron number density limits for the existence of polar mesosphere summer echoes

We investigate the dependence of polar mesosphere summer echoes (PMSE) and mesosphere summer echoes (MSE) on the background electron number density. Both a lower and upper limit are quantified below and above which PMSE cannot exist. The result is that PMSE occur for a very wide range of electron number densities between ∼300–500/cm3 and ∼105/cm3. A comparison of the diurnal variation of MSE observed at Kühlungsborn (54°N) with current model estimates of the electron number density at midlatitudes shows that at least ∼300–500 electrons /cm3 are necessary for PMSE to exist. This lower limit is consistent with all available electron number density measurements obtained from sounding rockets in the vicinity of PMSE. It is shown that the existence of a lower electron number density limit can be understood in terms of the standard theory of the scattering of VHF waves in the D region. We have then analyzed PMSE observations during the major solar proton event on 14 July 2000. We have estimated the electron number density at PMSE altitudes based on proton and electron flux measurements obtained with detectors on board the GOES‐8 and ACE spacecrafts in combination with an ion‐chemical model. Comparing the electron number densities at 87 km altitude with the average PMSE signal to noise observations (SNR) we find a significant negative correlation between SNR and the electron number densities for densities on the order of ∼105/cm3. We propose that this negative correlation is due to a limited amount of aerosol particles: current PMSE theories assume that electron irregularities in the VHF band can only exist if more than ∼50% of the free electrons are bound to aerosol particles which thus reduce the electron diffusivity due to ambipolar forces. If, however, the electron number density increases significantly above the aerosol number density, this condition can no longer be fulfilled. On the other hand, the fact that PMSE is present up to electron number densities of ∼105/cm3 raises several important questions on our current understanding of aerosol particles around the polar summer mesopause and their role in the creation of PMSE: either many more aerosol particles exist than has been anticipated so far (with corresponding implications for the nucleation of these particles) or our current understanding of the role of aerosol particles in the creation of PMSE is not complete.

SIMULATION OF ATMOSPHERIC SECONDARY HADRON AND LEPTON FLUX FROM SATELLITE TO UNDERGROUND EXPERIMENTS

The successful simulation results obtained in the interpretation of the recent AMS measurements of proton, leptons and light nuclei particle flux, are reviewed. A similar success in being met in the analysis of secondary particle flux measured in teh atmosphere (antiprotons, muons) and in underground experiments (neutrinos).

Oscillations in proton transport revealed from simultaneous measurements of net current and net proton fluxes from isolated root protoplasts: MIFE meets patch-clamp

Proton fluxes were measured non-invasively on patch-clamped protoplasts isolated from wheat roots using an external H + electrode to measure the electrochemical gradient in the external solution. Under voltage clamp in the whole-cell configuration, the H + fluxes across the plasma membrane could be measured as a function of voltage and time and correlated with the simultaneous measurements of membrane current. Protoplasts could exist in three states based on the current–voltage (I–V) curves and the flux–V curves. In the pump-state where the membrane voltage (Vm) was more negative than the electrochemical equilibrium potential for potassium (E K ), a net efflux of H + occurred that was voltage-dependent such that the efflux increased as Vm was clamped more positive. In the K-state, where Vm was close to E K , similar flux–V curves were observed. In the depolarised state where Vm was greater than E K the proton flux was characterised by a net influx of H + (H + -influx state) that reversed direction at more positive values of Vm. The inhibitory effect of DCCD and stimulatory effect of fusicoccin were used to correlate current and H + flux through the H + -ATPase for which there was reasonably good agreement within the limits of the flux measurements. Some protoplasts were kept in the whole-cell configuration for up to 3 h revealing slow sustained oscillations (period about 40 min) in H + flux that were in phase with oscillations in free-running Vm. These oscillations were also observed under voltage clamp, with membrane current in phase with H + flux, but which became damped out after a few cycles. The oscillations encompassed the pump-state, K + -state and H + -influx-state. The H +- flux–V curves and I–V curves were used to model the electrical characteristics of the plasma membrane with H + -ATPase, inward and outward K + rectifiers, a linear conductance, and a passive H + influx possibly through gated proton channels.