A Catalog of Type II Radio Bursts Observed by Wind/WAVES and their Statistical Properties (1912.07370v1)

Abstract: Solar type II radio bursts are the signature of particle acceleration by shock waves in the solar corona and interplanetary medium. The shocks originate in solar eruptions involving coronal mass ejections (CMEs) moving at super-Alfvenic speeds. Type II bursts occur at frequencies ranging from hundreds of MHz to tens of kHz, which correspond to plasma frequencies prevailing in the inner heliosphere from the base of the solar corona to the vicinity of Earth. Type II radio bursts occurring at frequencies below the ionospheric cutoff are of particular importance, because they are due to very energetic CMEs that can disturb a large volume of the heliosphere. The underlying shocks accelerate not only electrons that produce the type II bursts, but also protons and heavy ions that have serious implications for space weather. The type II radio burst catalog (https://cdaw.gsfc.nasa.gov/CME_list/radio/waves_type2.html) presented here provides detailed information on the bursts observed by the Radio and Plasma Wave Experiment (WAVES) on board the Wind Spacecraft. The catalog is enhanced by compiling the associated flares, CMEs, solar energetic particle (SEP) events including their basic properties. We also present the statistical properties of the radio bursts and the associated phenomena, including solar-cycle variation of the occurrence rate of the type II bursts.

• The paper presents a detailed catalog of over 500 DH type II radio bursts linked with CMEs, solar flares, and SEP events.
• It employs multi-instrument data to analyze CME kinematics, revealing an average CME speed of ~1164 km/s and a high occurrence of halo CMEs.
• The study identifies clear correlations between radio burst frequencies, solar activity indices, and SEP event likelihood, enhancing space weather forecasting.

Analysis of Type II Radio Bursts: Insights from Wind/WAVES Observations

The paper presents a comprehensive catalog of solar type II radio bursts observed by the Wind/WAVES instrument, focusing on their statistical properties and solar-cycle variations. These radio bursts are markers of solar eruptions involving coronal mass ejections (CMEs) traveling at super-Alfvénic speeds, critical in understanding particle acceleration processes in the heliosphere and their implications for space weather. The associated phenomena, including solar flares, CMEs, and solar energetic particle (SEP) events, have been systematically compiled and analyzed to enhance understanding of these bursts and their geoeffectiveness.

Catalog Composition and Methodology

The catalog documents DH type II radio bursts observed by the Wind/WAVES instrument, coupled with detailed entries related to associated CMEs, flares, and SEPs. It incorporates data from complementary instruments such as SOHO’s LASCO and STEREO, providing a rich dataset over two solar cycles. The bursts are noted for spanning a frequency range from 1 to 14 MHz, capturing the shock-driven emissions below the ionospheric cutoff that are connected to significant heliospheric disturbances.

Each catalog entry comprises temporal attributes of the radio burst, locational data of the solar source eruptions, flare characteristics, and kinematic details of the related CMEs. This attention to detail allows comprehensive studies on various attributes, such as CME speed, width, and correlations with SEP events.

Statistical Characteristics and Observations

The sizable dataset of over 500 events enables a robust statistical examination of DH type II bursts. A major finding is the correlation between the occurrence rates of these radio bursts and solar activity indices, like sunspot numbers and the frequency of fast and wide CMEs. The average speed of CMEs associated with DH type II bursts has been recorded at ~1164 km/s, showcasing minimal variance across solar cycles.

More than half of these CMEs are halo CMEs, implying substantial energy levels. Furthermore, about 50% of the bursts have ending frequencies below 0.5 MHz, suggesting strong shocks capable of significant particle acceleration. The solar source analysis indicates a predominant location in the active region belt (±30° latitude).

Implications on SEP Events

Type II radio bursts serve as indicators for SEP event occurrence due to their shared origin in shock fronts from CMEs. A significant portion of western hemisphere bursts align with large SEP events, contingent on CME characteristics such as speed and connectivity to observer vantage points. The analysis reveals that 27.7% of DH type II bursts correlate with large SEP events, underscoring their utility in assessing shock-driven solar event impacts.

Applications and Future Directions

This catalog provides a valuable resource for exploring CMEs and shock-related phenomena, particularly when white-light observations are unavailable or compromised. The calibration possibilities between radio observations and CME kinematics offer pathways for predicting shock evolution in the interplanetary medium.

The research extends the empirical base for understanding space weather impacts, highlighting the Heliosphere's overall state as a modulating factor for burst properties and associated geomagnetic phenomena. Future work could develop real-time predictive models using this data to enhance space weather forecasting and mitigate the potential impacts on Earth-based technologies and astronaut safety.

Overall, this catalog stands as a critical reference for space weather research, offering deep insights into the dynamics of solar eruptions and their heliospheric consequences.