The Earth’s geomagnetic field is a crucial component of our planet’s protective shield against harmful solar radiation. However, during geomagnetically disturbed times, sudden changes in the surface geomagnetic field can occur, leading to a phenomenon known as geomagnetically induced currents (GICs). These GICs can have a significant impact on various ground-based systems, posing potential risks to our technological infrastructure. In a recent study titled “Intense dB/dt Variations Driven by Near-Earth Bursty Bulk Flows (BBFs): A Case Study,” researchers Dong Wei, Malcolm W. Dunlop, Junying Yang, Xiangcheng Dong, Yiqun Yu, and Tieyan Wang explore the effects of bursty bulk flows on the geomagnetic field and the magnetosphere-ionosphere-ground system.
What are bursty bulk flows (BBFs)?
Bursty bulk flows (BBFs) are transient ion flow bursts observed in the Earth’s magnetosphere, which is the region of space surrounding our planet that is controlled by its magnetic field. These bursts are characterized by abrupt and rapid changes in ion velocities, often exceeding 150 km/s. BBFs are thought to arise from the merging of plasma flows in the magnetotail, the elongated region of the magnetosphere opposite the direction of the Sun.
BBFs exhibit distinct structures within the inner magnetosphere, where they can generate intense magnetic perturbations. These structures have been observed using a combination of space-borne measurements and ground magnetic observations. Multiple BBFs were detected during the January 7, 2015 storm, providing researchers an opportunity to study their characteristics and impact on the geomagnetic field.
How do bursty bulk flows affect the geomagnetic field?
One of the primary consequences of BBFs is the generation of intense variations in the geomagnetic field. These variations are quantified using the rate of change of the geomagnetic field (dB/dt). Due to the close relationship between dB/dt and GICs, understanding the factors that drive intense dB/dt variations is crucial for assessing the potential risks to ground-based systems.
The study revealed that the observed intense dB/dt variations are associated with a large-scale substorm current system driven by multiple BBF events. Field-aligned currents (FACs) connect directly to the intense dB/dt on the ground and the BBFs in the near-Earth region. This finding provides direct evidence that BBFs play a significant role in the generation of geomagnetic perturbations.
What is the significance of intense dB/dt variations?
The intense variations in the rate of change of the geomagnetic field (dB/dt) have important implications for man-made technological systems on the ground. These variations can give rise to geomagnetically induced currents (GICs) which, in turn, can cause significant disruptions or damage to power grids, pipelines, communication networks, and other critical infrastructure.
Understanding the drivers of intense dB/dt variations, such as BBFs, allows scientists and engineers to develop more accurate models and predictive tools to assess the potential impact of GIC events. This knowledge can help stakeholders and policymakers take proactive measures to mitigate the risks associated with geomagnetic disturbances.
How are magnetosphere-ionosphere-ground systems studied during geomagnetically disturbed times?
Studying the complex interactions between the magnetosphere, ionosphere, and ground-based systems during geomagnetically disturbed times requires a multi-point approach. The research conducted by Wei, Dunlop, Yang, Dong, Yu, and Wang employed a combination of space-borne measurements and ground magnetic observations.
During the January 7, 2015 storm, the researchers detected multiple BBFs in the inner magnetosphere. Simultaneously, magnetospheric and ionospheric satellites mapped their magnetic footprints to the same conjugate region surrounded by a group of magnetometer ground stations. This close coordination of measurements allowed the team to analyze the characteristics and responses of the magnetosphere-ionosphere-ground system during the event.
The results of this study provide direct evidence of the link between BBFs and intense dB/dt variations, emphasizing the importance of considering these transient ion flow bursts when studying the behavior of the magnetosphere-ionosphere-ground system during geomagnetically disturbed times.
“Our results provide direct evidence that the wide-range of intense dB/dt variations are associated with a large-scale, substorm current system driven by multiple BBFs.”
By analyzing multiple points of observation, including satellite measurements and ground-based magnetometer data, the researchers were able to gain valuable insights into the effects of BBFs on the geomagnetic field and the interconnected magnetosphere-ionosphere-ground system.
This study contributes to our understanding of the potential risks posed by intense geomagnetic perturbations and highlights the need for continued research into the drivers of GIC events. By improving our knowledge of bursty bulk flows and their impact on the geomagnetic field, scientists can work towards developing more effective strategies for mitigating the risks associated with geomagnetically induced currents.
Source: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL091781
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