Lightning activity is one of the global natural hazards that poses significant risks on human life and numerous aspects of the society's technological infrastructure. Understanding the linkage ...between aerosols present in the atmosphere and lightning activity is important to further advance our knowledge of the global lightning activity cycle. The southwestern region of the Arabian Peninsula (AP) is home to one of the 500 hottest lightning spots in the world, and is not far from the largest contiguous sand desert in the world, the Empty Quarter (al-Rubea Al-Khali). Using data of individual lightning strokes from the the Global Lightning Detection Network (GLD360), in conjunction with remote sensing measurements of the aerosol optical depth (AOD) obtained at 500 nm from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument onboard the Terra and Aqua satellites during active lightning days, we examine the evolution of lightning activity in two geographically and topologically different regions over the AP. One region extends inland to the desert (R1) and the other is in the southwest mountainous region that is close to the Red Sea (R2). In both regions, results from thunderdays-only indicate that lightning is strongly and positively correlated with the AOD loading, up to AOD ~ 0.8, after which the trend flattens or reverses direction. Results suggest the two opposite effects that aerosols could indirectly have on lightning activity are at play. Mountainous region exhibits much stronger linear relation compared to the inland region. Furthermore, both regions exhibit seasonal and asynchronous lightning activity and AOD loading. Year 2018 in R1 shows very high lightning activity, likely linked to the 2018 intense dust storms in the region.
•Effect of aerosols on lightning activity over Flat (R1) and Mountainous (R2) terrains in the Arabian Peninsula is studied.•R1 and R2 show seasonality of lightning and AOD; the trend is asynchronous indicating activity in both regions is independent.•In R1 and R2, an increase in AOD (below ~0.8) results in increased lightning. Above AOD ~0.8, the trend flattens or reverses.•Behavior of the AOD-Lightning trend suggests that aerosols play a dual role in enhancing or suppressing lightning activity.•Year 2018 in R1 shows very high lightning activity, likely linked to the intense dust storms in that year.
Abstract
Energetic neutral atom (ENA) measurements by IBEX reveal that the heliotail comprises an energy-dependent multilobe structure. We examine the heliotail evolution over 11 yr of IBEX ...observations covering a full solar cycle (SC). We find the following: (1) The heliotail structure persists over the entire SC, comprising three ENA-enhanced and two ENA-suppressed lobes. (2) Lobe sizes and locations are generally stable but exhibit variations in ENA fluxes driven by the SC. (3) Lobe centers follow a cyclic behavior over multiple SC phases, indicating direct signatures of slow and fast solar wind (SW) interactions in the inner heliosheath (IHS). (4) The tilted plane passing through the port–starboard lobes’ centers oscillates in latitude but maintains its tilt from the ecliptic plane, likely a consequence of the interstellar magnetic field draping around the heliosphere. (5) The transition of the central heliotail from a single lobe at ∼1.1 keV to two lobes above ∼2 keV is SC-dependent and directly reflects the IHS plasma properties, i.e., when ENA fluxes from fast SW from the polar coronal holes change over time. (6) The central lobe exhibits a substructure that is enhanced and offset from the downwind direction, possibly indicating an asymmetric ENA emission or an asymmetry in the parent plasma distribution. These results reveal the general stability of the heliotail structure over time and distinct variations in individual lobes’ properties in relation to the SC phases. Furthermore, results show the effects of multiple SC phases in the tail, reflecting different ENA travel times and source histories.
Dementia associated with the Alzheimer's disease is thought to be correlated with the conversion of the beta - Amyloid (Abeta) peptides from soluble monomers to aggregated oligomers and insoluble ...fibrils. We present a discrete-time mathematical model for the aggregation of Abeta monomers into oligomers using concepts from chemical kinetics and population dynamics. Conditions for the stability and instability of the equilibria of the model are established. A formula for the number of monomers that is required for producing oligomers is also given. This may provide compound designers a mechanism to inhibit the Abeta aggregation.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Observations from the Interstellar Boundary Explorer (IBEX) of energetic neutral atoms (ENAs) reveal two populations, those emitted from a narrow (∼20°-40°) ribbon that is centered on the local ...interstellar magnetic field, and a globally distributed flux (GDF) that is controlled by processes in the heliosheath. This is a third study utilizing a previously developed technique to separate ENA emissions in the ribbon from the GDF. In the first ribbon separation study, we analyzed the first year of IBEX data at the energies of 0.7 keV and above; the second study analyzed data down to 0.2 keV using the first five years of IBEX data. Here, we utilize the separation analysis from 0.7 keV and above to study time evolution in 3 year intervals over the first nine years of IBEX data. This study is the first to reveal the global time evolution of the GDF distinct from that of the IBEX ribbon. We show that the time evolution of the GDF within 40° of the upwind pressure maximum is driven by changes in the solar wind ram pressure through compression and rarefaction in the heliosheath. In contrast, the GDF is relatively stable in the region centered on the heliotail downwind with respect to the interstellar flow. The evolution of the IBEX ribbon is observed to have a time lag with respect to the upwind GDF evolution, likely due to the secondary (neutral) solar wind source. The time lag observed in the ribbon evolution is consistent with the generation of ions retained for several years beyond the heliopause. These observations lend further support to secondary solar wind models of the IBEX ribbon, but also require that there is a significant several year time lag for reneutralization of ions that form the IBEX ribbon. We use this study of the 9 year separation of the IBEX ribbon from the globally distributed flux to prepare for a formal IBEX data release of ribbon and globally distributed flux maps to the heliophysics community.
3He-rich solar energetic particles (SEPs) are believed to be accelerated in solar flares or jets by a mechanism that depends on the ion charge-to-mass (Q/M) ratio. It implies that the flare plasma ...characteristics (e.g., temperature) may be effective in determining the elemental abundances of 3He-rich SEPs. This study examines the relation between the suprathermal (≲0.2 MeV nucleon−1) abundances of the He–Fe ions measured on the Advanced Composition Explorer and temperature in the solar sources for 24 3He-rich SEP events in the period 2010–2015. The differential emission measure technique is applied to derive the temperature of the source regions from the extreme ultraviolet imaging observations on the Solar Dynamics Observatory. The obtained temperature distribution peaks at 2.0–2.5 MK that is surprisingly consistent with earlier findings based on in situ elemental abundance or charge state measurements. We have found a significant anticorrelation between 3He/4He ratio and solar source temperature with a coefficient −0.6. It is most likely caused by non-charge-stripping processes, as both isotopes would be fully ionized in the inferred temperature range. This study shows that the elemental ratios 4He/O, N/O, Ne/O, Si/O, S/O, Ca/O, Fe/O generally behave with temperature as expected from abundance enhancement calculations at ionization equilibrium. The C and Mg, the two species with small changes in the Q/M ratio in the obtained temperature range, show no such behavior with temperature and could be influenced by similar processes as for the 3He/4He ratio.
Abstract
3
He-rich solar energetic particles (SEPs) are believed to be accelerated in solar flares or jets by a mechanism that depends on the ion charge-to-mass (
Q
/
M
) ratio. It implies that the ...flare plasma characteristics (e.g., temperature) may be effective in determining the elemental abundances of
3
He-rich SEPs. This study examines the relation between the suprathermal (≲0.2 MeV nucleon
−1
) abundances of the He–Fe ions measured on the Advanced Composition Explorer and temperature in the solar sources for 24
3
He-rich SEP events in the period 2010–2015. The differential emission measure technique is applied to derive the temperature of the source regions from the extreme ultraviolet imaging observations on the Solar Dynamics Observatory. The obtained temperature distribution peaks at 2.0–2.5 MK that is surprisingly consistent with earlier findings based on in situ elemental abundance or charge state measurements. We have found a significant anticorrelation between
3
He/
4
He ratio and solar source temperature with a coefficient −0.6. It is most likely caused by non-charge-stripping processes, as both isotopes would be fully ionized in the inferred temperature range. This study shows that the elemental ratios
4
He/O, N/O, Ne/O, Si/O, S/O, Ca/O, Fe/O generally behave with temperature as expected from abundance enhancement calculations at ionization equilibrium. The C and Mg, the two species with small changes in the
Q
/
M
ratio in the obtained temperature range, show no such behavior with temperature and could be influenced by similar processes as for the
3
He/
4
He ratio.
The Committee on Space Research (COSPAR) is updating its Roadmap on Space Weather. As input for this update, the COSPAR International Space Weather Action Teams (ISWAT) were asked to provide an ...overview of the current state-of-the-art and advancements since the last Roadmap (Schrijver et al., 2015), identifying gaps and opportunities for moving forward within the next 5 years — based on ongoing and planned missions, available modeling, and observational capabilities — and presenting an outlook beyond 5 years and recommendations on reaching long-term goals. While space weather is typically associated with short-term solar activity, knowledge of past solar variability observed and recorded through various parameters, including historical space weather events, informs us about the range of possible solar fluctuations. This long-term solar variability, belonging to the domain of space climate, is the prime focus of the ISWAT S1 Cluster. The goal of this paper is to describe the key objectives of the three S1 Action Teams, summarize the current state of knowledge of the topic that each team is focusing on, and identify the key science gaps that need to be addressed in each area.
The Earth-Moon-Mars Radiation Environment Module (EMMREM) is a numerical model for characterizing the time-dependent radiation environment in the Earth-Moon-Mars and interplanetary space ...environments. In this work we demonstrate the capabilities of the module for performing analyses of time-dependent exposures from solar energetic particle (SEP) events near Earth and Mars by calculating time-dependent dose rates, dose equivalent rates, and accumulated dose and accumulated dose equivalents for surrogates of the skin and the blood forming organs (BFOs) of crew members shielded by as much as 10 g/cm
2
of aluminum shielding for the January 15, 2005, SEP event. The motivation for the development of EMMREM is the need to better understand the radiation hazards in deep space and near Earth and other planetary bodies, in near real time in support of possible future space exploration by manned and unmanned spacecraft. Characterizing the radiation environment for different locations on and close to Earth for SEP events is fairly well developed. However, estimating the probable radiation environment near Mars and other locations throughout the solar system is not currently supported for SEP events. Such capability is critical for future human exploration of the Moon and Mars in the upcoming decades. The calculated doses for the skin and BFO surrogates are compared with the National Aeronautics and Space Administration's short-term permissible exposure limits.
The polytropic process characterizes the thermodynamics of space plasma particle populations. The polytropic index, \({\gamma}\), is particularly important as it describes the thermodynamic behavior ...of the system by quantifying the changes in temperature as the system is compressed or expanded. Using Wind spacecraft plasma and magnetic field data during \(01/1995 - 12/2018\), we investigate the thermodynamic evolution in 336 Interplanetary Coronal Mass Ejection (ICME) events. For each event, we derive the index \({\gamma}\) in the sheath and magnetic ejecta structures, along with the pre- and post- event regions. We then examine the distributions of all \({\gamma}\) indices in these four regions and derive the entropic gradient of each, which is indicative of the ambient heating. We find that in the ICME sheath region, where wave turbulence is expected to be highest, the thermodynamics takes longest to recover into the original quasi-adiabatic process, while it recovers faster in the quieter ejecta region. This pattern creates a thermodynamic cycle, featuring a near adiabatic value \({\gamma}\) ~ ${\gamma}$${_a}\( (=5/3) upstream of the ICMEs, \){\gamma}$${_a}\( - \){\gamma}\( ~ 0.26 in the sheaths, \){\gamma}$${_a}\( - \){\gamma}\( ~ 0.13 in the ICME ejecta, and recovers again to \){\gamma}\( ~ \){\gamma}$${_a}$ after the passage of the ICME. These results expose the turbulent heating rates in the ICME plasma: the lower the polytropic index from its adiabatic value and closer to its isothermal value, the larger the entropic gradient, and thus, the rate of turbulent heating that heats the ICME plasma.
PDF
