Time and Altitude spread F echoes distribution over the Christmas Island VHF radar

The goal of this work is to study the time and altitude echoes characteristics under different solar and seasonality conditions using the VHF radar RTI images. The occurrence of equatorial spread F depends on the existence of conditions that can seed the Raileight-Taylor instability, and these conditions can change with solar flux, seasonality, longitude distributions, and day-to-day variability. So, the equatorial spread F is observed as its time and altitude occurrence. The VHF radar of Christmas Island (2.0° N, 157.4° W, 2.9° N dip latitude) has been operational in the equatorial region for some time now, allowing long-term observations. The occurrence of echoes during solar minimum conditions are observed all throughout the night since the post reversal westward electric field is weaker than the solar maximum and the possibilities for the vertical plasma drift to become positive are larger. On other hand, echoes during solar maximum will be controlled by dynamics near the time of the Pre-reversal Peak (PRE). Our results indicate peak time occurrence of echoes along this period shows a well-defined pattern, with echoes being distributed as closer to local sunset during solar maximum and around/closer midnight during solar minimum conditions, meanwhile, the peak altitude occurrence of echoes shows a slightly regular pattern with higher altitude occurrences during solar maxima and lower altitudes during solar minimum conditions.

Simulating Solar Maximum Conditions Using the Alfvén Wave Solar Atmosphere Model (AWSoM)

To simulate solar coronal mass ejections (CMEs) and predict their time of arrival and geomagnetic impact, it is important to accurately model the background solar wind conditions in which CMEs propagate. We use the Alfvén Wave Solar atmosphere Model (AWSoM) within the the Space Weather Modeling Framework to simulate solar maximum conditions during two Carrington rotations and produce solar wind background conditions comparable to the observations. We describe the inner boundary conditions for AWSoM using the ADAPT global magnetic maps and validate the simulated results with EUV observations in the low corona and measured plasma parameters at L1 as well as at the position of the Solar Terrestrial Relations Observatory spacecraft. This work complements our prior AWSoM validation study for solar minimum conditions and shows that during periods of higher magnetic activity, AWSoM can reproduce the solar plasma conditions (using properly adjusted photospheric Poynting flux) suitable for providing proper initial conditions for launching CMEs.

Carrington Longitudinal and Solar Cycle Distribution of the Super Active Regions From 1976 to 2018

We studied the Carrington longitudinal and solar cycle distribution of the super active regions (SARs) from 1976to 2018. There were 51 SARs during this period. We divided the SARs into SARs1 and SARs2. SARs1 refers tothe SARs that produced extreme space weather events including ≥X5.0 flares, ground level events (GLEs) andsuper geomagnetic storms (SGSs: Dst≤ −250 nT), while SARs2 did not produce extreme space weather events.The total number of SARs1 and SARs2 are 32 and 19, respectively. The statistical results show that 34.4%, 65.6%and 78.1% of the SARs1 appeared in the ascending phase, descending phase and in the period from two yearsbefore to the three years after the solar maximum, respectively, while 52.6%, 47.4% and 100% of the SARs2appeared in the ascending phase, descending phase and in the period from two years before to the three years aftersolar maximum, respectively. The Carrington longitude distribution of the SARs1 shows that SARs1 in thelongitudinal scope of [0,150°] produced ≥X5.0 flares and GLEs, while only the SARs1 in the longitude range of[150°,360°] not only produced ≥X5.0 flares and GLEs, but also produced SGSs. The total number of SARsduring a SC has a good correlation with the SC size. However, the largest flare index of a SAR within a SC has apoor correlation with the SC size, implying that the number of SARs in a weak SC will be small. However, aweak SC may have a SAR that can produce very strong solar flare activities.

Radiation environment for future human exploration on the surface of Mars: the current understanding based on MSL/RAD dose measurements

Potential deleterious health effects to astronauts induced by space radiation is one of the most important long-term risks for human space missions, especially future planetary missions to Mars which require a return-trip duration of about 3 years with current propulsion technology. In preparation for future human exploration, the Radiation Assessment Detector (RAD) was designed to detect and analyze the most biologically hazardous energetic particle radiation on the Martian surface as part of the Mars Science Laboratory (MSL) mission. RAD has measured the deep space radiation field within the spacecraft during the cruise to Mars and the cosmic ray induced energetic particle radiation on Mars since Curiosity’s landing in August 2012. These first-ever surface radiation data have been continuously providing a unique and direct assessment of the radiation environment on Mars. We analyze the temporal variation of the Galactic Cosmic Ray (GCR) radiation and the observed Solar Energetic Particle (SEP) events measured by RAD from the launch of MSL until December 2020, i.e., from the pre-maximum of solar cycle 24 throughout its solar minimum until the initial year of Cycle 25. Over the long term, the Mars’s surface GCR radiation increased by about 50% due to the declining solar activity and the weakening heliospheric magnetic field. At different time scales in a shorter term, RAD also detected dynamic variations in the radiation field on Mars. We present and quantify the temporal changes of the radiation field which are mainly caused by: (a) heliospheric influences which include both temporary impacts by solar transients and the long-term solar cycle evolution, (b) atmospheric changes which include the Martian daily thermal tide and seasonal CO$$_2$$ 2 cycle as well as the altitude change of the rover, (c) topographical changes along the rover path-way causing addition structural shielding and finally (d) solar particle events which occur sporadically and may significantly enhance the radiation within a short time period. Quantification of the variation allows the estimation of the accumulated radiation for a return trip to the surface of Mars under various conditions. The accumulated GCR dose equivalent, via a Hohmann transfer, is about $$0.65 \pm 0.24$$ 0.65 ± 0.24 sievert and $$1.59 \pm 0.12$$ 1.59 ± 0.12 sievert during solar maximum and minimum periods, respectively. The shielding of the GCR radiation by heliospheric magnetic fields during solar maximum periods is rather efficient in reducing the total GCR-induced radiation for a Mars mission, by more than 50%. However, further contributions by SEPs must also be taken into account. In the future, with advanced nuclear thrusters via a fast transfer, we estimate that the total GCR dose equivalent can be reduced to about 0.2 sievert and 0.5 sievert during solar maximum and minimum periods respectively. In addition, we also examined factors which may further reduce the radiation dose in space and on Mars and discuss the many uncertainties in the interpreting the biological effect based on the current measurement.

The Effect of the Thermosphere on Ionosphere Outflows

The Naval Research Laboratory (NRL) Sami2 is Another Model of the Ionosphere (SAMI2) and Sami3 is Also a Model of the Ionosphere (SAMI3) ionosphere/plasmasphere codes have shown that thermosphere composition and winds significantly affect H+ outflows from the topside ionosphere. In particular, O density inhibits upward diffusion of O+ from the ionosphere F layer, especially during solar maximum conditions. In addition, winds affect the quiet-time latitudinal extent of the F layer, affecting densities at mid-to-high latitudes that are the source of plasmasphere refilling outflows. Evidence for these effects is reviewed and prospects for forecasting these outflows are explored. Open questions for future research are highlighted.

Signs of anomalous behavior of the ionosphere in 2003–2014 at F1-layer heights over Irkutsk

We have detected an anomalous electron density Ne increase in winter months in Irkutsk in some years of the period 2003–2014. This effect was manifested when we compared the experimental values obtained by the Irkutsk ionosonde with model calculations at F1-layer heights (120–200 km). Two anomalous time zones have been found. The first was observed in the period 2003–2006 near solar minimum. In this zone, 2003 is the year of maximum manifestation of the winter Ne increase over the entire research period. The second anomalous zone — 2012, 2013, 2014 — was detected during solar maximum. We have explored possible causes of the Ne change in winter at the F1-layer heights in all the years under study. We have found that the main factor causing the winter increase in Ne is significant geomagnetic disturbances in the above time periods.