Ionization effect in the Earth's atmosphere during the sequence of October-November 2003 Halloween GLE events (2011.00048v1)

Abstract: The effect of precipitating high-energy particles on atmospheric physics and chemistry is extensively studied over the last decade. In majority of the existing models, the precipitating particles induced ionization plays an essential role. For such effects, it is necessary to possess enhanced increase in ion production, specifically during the winter period. In this study, we focus on highly penetrating particles - cosmic rays. The galactic cosmic rays are the main source of ionization in the Earth's stratosphere and troposphere. On the other hand, the atmospheric ionization may be significantly enhanced during strong solar energetic particle events, mainly over the polar caps. A specific interest is paid to the most energetic solar proton events leading to counting rate enhancement of ground-based detectors, namely the so-called ground level enhancements (GLEs). During solar cycle 23, several strong ground level enhancements were observed. A sequence of three GLEs was observed in October-November 2003, the Halloween events. Here, on the basis of 3-D Monte Carlo model, we computed the energetic particles induced atmospheric ionization, explicitly considering the contribution of cosmic rays with galactic and solar origin. The ion production rates were computed as a function of the altitude above sea level using reconstructed solar energetic particles spectra. The 24 hours and event averaged ionization effects relative to the average due to galactic cosmic rays were also computed.

• The paper demonstrates that high-energy solar energetic particles markedly enhance ion production by modeling atmospheric cascades with 3-D Monte Carlo simulations.
• It shows that geomagnetic conditions, particularly during Forbush decreases, critically modulate the interplay between SEPs and galactic cosmic rays.
• The study details how ionization rates vary with altitude and latitude, providing key insights into atmospheric impacts during intense solar events.

Atmospheric Ionization During the Halloween 2003 GLE Events

The paper "Ionization effect in the Earth's atmosphere during the sequence of October-November 2003 Halloween GLE events," authored by A.L. Mishev and P.I.Y. Velinov, investigates the atmospheric ionization effects caused by the high-energy particles during the Ground Level Enhancements (GLEs) observed in late 2003. These events provide a substantial opportunity to paper ionization effects due to cosmic ray interactions in the Earth's atmosphere, especially as they coincided with significant solar activity.

The research involves an intricate analysis using a 3-D Monte Carlo model to calculate the ion production rates in the atmosphere initiated by energetic particles, including both cosmic rays of galactic and solar origin. The authors focused on the October-November 2003 Halloween events, which are noteworthy for their intense solar activity and subsequent extraordinary GLEs. Three major events occurred on 28 October (GLE #65), 29 October (GLE #66), and 2 November (GLE #67), providing a rich dataset to paper ionization effects immediately following significant solar eruptions.

Methodology Overview

The core of the methodology employed in this paper is the Monte Carlo simulation, which enables comprehensive modeling of the atmospheric cascade prompted by cosmic ray interactions. The simulations incorporate data on the differential cosmic ray spectra, atmospheric density, and the energy necessary for ion pair creation. This allows for detailed calculation of ionization rates in the Earth's stratosphere and troposphere. The model is enhanced with the reconstructed spectra of solar energetic particles (SEPs) and takes into account the modulation of galactic cosmic rays (GCRs) as they propagate through the heliosphere. Precision in simulation is further ensured by accounting for local geomagnetic conditions using the MAGNETOCOSMICS code and IGRF geomagnetic and Tsyganenko models.

Significant Findings

1. Ionization Rates and Spectra Dependence: The paper reveals considerable variability in ion production rates, heavily influenced by the energy spectra of SEPs. High-energy particles are capable of penetrating deep into the atmosphere, significantly affecting ion production in the polar regions, particularly during GLEs #65 and #67.
2. Impact of Geomagnetic Conditions: GLE #66, occurring during a profound Forbush decrease, exhibits unique characteristics due to the temporary reduction in GCR emittance. This highlights the complex interplay between SEPs and GCRs under varied geomagnetic scenarios.
3. Latitude and Altitude Variability: The results underscore the variation of ionization effects with altitude and latitude. In the high-latitude regions, corresponding to a rigidity cut-off of R_c ≤ 1 GV, significant ion production is observed primarily due to the contribution from SEPs, whereas in higher rigidity cut-off regions, GCRs predominate.
4. Temporal Ionization Effects: The ionization effect was assessed over various time scales, demonstrating the nuanced differences in ionization profiles when evaluated over an entire 24-hour period versus the event duration. These findings elucidate the potential for significant atmospheric impacts during and following major solar events.

Implications and Future Directions

The implications of these findings are multifaceted, impacting both atmospheric science and space weather research. Ionization induced by SEPs through atmospheric showers can influence the chemical processes in the atmosphere, potentially affecting climate patterns and atmospheric electricity. The results provide a groundwork for further exploration of the consequences of high-energy particle events on atmospheric constituents and dynamics.

Future research could expand on the temporal resolution and geographical extent of ionization models to better predict and understand the broader climatic and environmental effects. Additionally, integrating observational data from contemporary satellite missions could refine model parameters and increase the fidelity of predictions concerning solar-terrestrial interactions.

This paper presents a robust framework for understanding high-energy particle interactions within Earth's atmosphere, a critical component of advancing both theoretical and applied atmospheric science in the context of solar storm phenomena.