Pertti Makela

The Radio-wave Observations at the Lunar Surface of the photoElectron Sheath (ROLSES) instrument is a radio telescope system designed to characterize the radio and plasma wave environment of the near-side lunar surface at frequencies between 2[Formula: see text]kHz and 30[Formula: see text]MHz. The ROLSES sensor consists of a set of four 2.5[Formula: see text]m radio monopole antennas onboard the Intuitive Machines-1 (IM-1) lander, Odysseus. The antennas were stowed during launch to be deployed after landing on the lunar surface using a frangibolt mechanism. The frequency range is well suited to observing radio waves at frequencies below 15[Formula: see text]MHz that cannot be observed from Earth due to the ionospheric cutoff. The higher frequencies are helpful in cross-calibrating with ground-based observations. Radio waves from the Sun, the Milky Way galaxy, Jupiter, Earth’s auroral region, and ground-based radio transmitters were expected to be present on the lunar surface. In addition, local plasma fluctuations and lunar/interplanetary dust were expected to produce detectable radio signals. Radio data from each of the four antennas, after passing through an isolating pre-amp and signal conditioning analog electronics, are digitized to 14 bits at 120 mega samples per second and then digitally processed by a Field Programmable Gate Array (FPGA) that performs onboard spectral analysis via a Fast Fourier Transform (FFT). Time-averaged spectral values are then stored and returned. ROLSES science data are sent to the lander at ∼16 kb/s and subsequently downlinked for further processing. Also telemetered to Earth are raw waveforms (unprocessed time sequence data) that are useful in studying dust impact on ROLSES antennas. ROLSES data are sent to the lander and subsequently downlinked for further processing. ROLSES is part of NASA’s Commercial Lunar Payload Services (CLPS) program. Odysseus landed close to the south pole at Malapert A (∼80S). This paper describes the complete design and operations of the ROLSES instrument and presents initial observations. Despite the tilted landing of Odysseus, we were able to successfully command, deploy the antennas, and operate the instrument in transit and on the lunar surface. We also describe an enhanced version of this instrument (ROLSES 2) currently under development.

Coronal mass ejections (CMEs) have been suggested to be the source of high-energy protons producing sustained gamma-ray emission (SGRE) events at the Sun, where the >100 MeV gamma-ray emission observed by Fermi Large Area Telescope (LAT) lasts beyond the end of the associated X-ray flare. Large SEP events observed at 1 au are produced by shocks driven by fast and wide (FW) CMEs. However, there are more large SEP events than SGRE events and more FW CMEs than the large SEP events. Magnetic connectivity of the observer to the shock nose affects the detectability of SEP events at 1 au. [Makela et∼al., 2023] found that the SGRE-producing halo CMEs associated with type II radio bursts and/or a large SEP events have higher space speeds and initial accelerations than those without an SGRE event. In this paper, we consider characteristics of CME eruptions associated with co-occurring SEP and SGRE events.

Long-duration gamma-ray flare (LDGRF) events observed by the Fermi/ Large Area Telescope have presented a puzzle for modelers. One of the ideas to account for their long duration is to assume that particles accelerated at shocks driven by fast coronal mass ejections (CMEs) would be the able to be trapped in the space between the shock and the Sun and would be able to precipitate from this volume over an extended amount of time. We present a simple leaky-box type model for the precipitating > 500 MeV proton flux in a system, where a coronal shock feeds accelerated protons into the volume between the shock and the solar surface and a relatively small amount of scattering keeps the distribution isotropic and homogeneous inside the volume. We demonstrate that by choosing fully realistic shock parameters the total number of precipitating protons can be brought to an agreement with observations. We also demonstrate that durations of several hours for these events are fully within reach of the modeling without using unreasonable choices for parameters. Thus, CME-driven shocks in the coronal and inner solar wind plasma are a plausible candidate to account for the LDGRF events.

The sustained gamma-ray emission (SGRE) from the Sun is a prolonged enhancement of >100 MeV gamma-ray emission that extends beyond the flare impulsive phase. The origin of the >300 MeV protons resulting in SGRE is debated, with both flares and shocks driven by coronal mass ejections (CMEs) being the suggested sites of proton acceleration. We compared the near-Sun acceleration and space speed of CMEs with “Prompt” and “Delayed” (SGRE) gamma-ray components. We found that “Delayed”-component-associated CMEs have higher initial accelerations and space speeds than “Prompt Only”-component-associated CMEs. We selected halo CMEs (HCMEs) associated with type II radio bursts (shock-driving HCMEs) and compared the average acceleration and space speed between HCME populations with or without SGRE events, major solar energetic particle (SEP) events, metric, or decameter-hectometric (DH) type II radio bursts. We found that the SGRE-producing HCMEs associated with a DH type II radio burst and/or a major SEP event have higher space speeds and especially initial accelerations than those without an SGRE event. We estimated the radial distances and speeds of the CME-driven shocks at the end time of the 2012 January 23 and March 7 SGRE events using white-light images of STEREO Heliospheric Imagers and radio dynamic spectra of Wind WAVES. The shocks were at the radial distances of 0.6–0.8 au and their speeds were high enough (≈975 km s⁻¹ and ≈750 km s⁻¹, respectively) for high-energy particle acceleration. Therefore, we conclude that our findings support the CME-driven shock as the source of >300 MeV protons.

Whitepaper #138 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: basic research; infrastructure/workforce/other programmatic. Additional topics: solar physics; state of the profession; space-based missions/projects; inner heliosphere; […]

It is known that the weak state of the heliosphere due to diminished solar activity in cycle 24 backreacted on coronal mass ejections (CMEs) to make them appear wider for a given speed. One of the consequences of the weak state of the heliosphere is that more CMEs appear as halo CMEs (HCMEs), and halos are formed at shorter heliocentric distances. Current predictions for the strength of solar cycle (SC) 25 range from half to twice the strength of SC 24. We compare the HCME occurrence rate and other properties during the rise phase of cycles 23, 24, and 25 to weigh in on the strength of SC 25. We find that HCME and solar wind properties in SC 25 are intermediate between SCs 23 and 24, but closer to SC 24. The HCME occurrence rate, normalized to the sunspot number, is higher in SCs 24 and 25 than in SC 23. The solar wind total pressure in SC 25 is ∼35% smaller than that in SC 23. Furthermore, the occurrence rates of high-energy solar energetic particle events and intense geomagnetic storms are well below the corresponding values in SC 23, but similar to those in SC 24. We conclude that cycle 25 is likely to be similar to or slightly stronger than cycle 24, in agreement with polar-field precursor methods for cycle 25 prediction.

We report on the solar and interplanetary (IP) causes of the third largest geomagnetic storm (26 August 2018) in solar cycle 24. The underlying coronal mass ejection (CME) originating from a quiescent filament region becomes a 440 km/s magnetic cloud (MC) at 1 au after ∼5 days. The prolonged CME acceleration (for ∼24 hr) coincides with the time profiles of the post‐eruption arcade intensity and reconnected flux. Chen et al. (2019, https://doi.org/10.3847/1538-4357/ab3f36) obtain a lower speed since they assumed that the CME does not accelerate after ∼12 hr. The presence of multiple coronal holes near the filament channel and the high‐speed wind from them seem to have the combined effect of producing complex rotation in the corona and IP medium resulting in a high‐inclination MC. The Dst time profile in the main phase steepens significantly (rapid increase in storm intensity) coincident with the density increase (prominence material) in the second half of the MC. Simulations using the Comprehensive Inner Magnetosphere‐Ionosphere model show that a higher ring current energy results from larger dynamic pressure (density) in MCs. Furthermore, the Dst index is highly correlated with the main‐phase time integral of the ring current injection that includes density, consistent with the simulations. A complex temporal structure develops in the storm main phase if the underlying MC has a complex density structure during intervals of southward IP magnetic field. We conclude that the high intensity of the storm results from the prolonged CME acceleration, complex rotation of the CME flux rope, and the high density in the 1‐au MC.

We report on a study that compares energetic particle fluxes in corotating interaction regions (CIRs) associated with type III radio storm with those in nonstorm CIRs. In a case study, we compare the CIR particle events on 2010October 21 and 2005 November 2. The two events have similar solar and solar wind circumstances, except that the former is associated with a type III radio storm and has a higher CIR particle flux and fluence. We also perform a statistical study, which shows that the proton and electron fluences are higher in the storm associated CIRs by factor of about 6 and 8, respectively than those in the storm-free CIRs.

We report on the solar and interplanetary (IP) causes of the third largest geomagnetic storm (2018 August 26) in solar cycle 24. The 2018 August 20 coronal mass ejection (CME) originating from a quiescent filament region becomes a magnetic cloud (MC) at 1 au after ~5 days. The CME accelerates for about a day as evidenced by the time evolution of the CME speed, the intensity of the associated post-eruption arcade, and the reconnected flux. The presence of multiple coronal holes near the filament channel and the high-speed wind from them seem to have the combined effect of producing complex rotation in the corona and IP medium resulting in a high-inclination MC. The Dst time profile in the main phase steepens significantly (rapid increase in storm intensity) coincident with the density increase in the MC second half of the MC. We confirm that the enhanced strength of the 2018 August 26 storm is a direct result of the enhanced MC density by comparing with two other events: the 2010 May 28 MC that has similar properties except for no density enhancement and the 2014 April 11 MC with a complex density structure. The Comprehensive Inner Magnetosphere-Ionosphere (CIMI) model applied to the three events confirm that higher ring current energy results from larger dynamic pressure in the MCs. A complex temporal structure develops in the storm main phase if the underlying MC has a complex density structure during intervals of southward interplanetary magnetic field.