Space Weather

Most people know that weather affects how they feel. Fewer people know that space weather does too, and that the evidence for it is more substantial than most would expect.

This page covers what is actually known about how solar and geomagnetic conditions interact with biological systems, grounded in peer-reviewed research. The effects are ranked by how well-established they are.

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What Is Space Weather?

Space weather refers to conditions driven by the Sun: solar wind, magnetic field fluctuations, radiation bursts, and geomagnetic storms. These aren't distant abstract phenomena. Earth's magnetic field is continuously shaped by them, and that field surrounds and penetrates everything on the surface.

The key metrics researchers track: the Kp index (a global measure of geomagnetic disturbance), the southward component of the interplanetary magnetic field (Bz), solar wind speed and pressure, and energetic particle flux from solar events.

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Tier 1: Well Established

Replicated across multiple independent studies with clear biological or physical mechanisms.

Tier 1 · Confirmed

Geomagnetic Disturbance and Cardiovascular Health

The most robust human evidence links geomagnetic disturbance to cardiovascular outcomes. A large study across 263 U.S. cities found that days with higher geomagnetic disturbance were associated with increased total mortality and cardiovascular mortality (Zilli Vieira et al., 2019). A separate study in the Normative Aging Study cohort found that geomagnetic disturbance was associated with reduced heart rate variability, a marker of autonomic nervous system function and cardiovascular resilience (Zilli Vieira et al., 2022). A 2025 study in Brazil found sex-stratified associations between geomagnetic disturbance and myocardial infarction (Rezende et al., 2025).

The proposed mechanism runs through the autonomic nervous system. Geomagnetic disturbance appears to shift the balance between sympathetic and parasympathetic activity, the same system that governs heart rate, stress response, blood pressure, and immune function.

Power Grids, Pipelines, and GPS

On the technological side, the mechanisms are fully established. Geomagnetic storms drive electrical currents through the ground (geomagnetically induced currents, or GICs) that can overwhelm power grid infrastructure. The March 1989 storm knocked out power across Quebec for nine hours. Modern risk models for pipeline corrosion, satellite drag, and GPS positioning error all account for geomagnetic storm conditions as standard inputs.

Solar Flares and Communication

Solar flares release intense X-ray bursts that ionize the upper atmosphere, disrupting HF radio communication and GPS signals within minutes. Airlines that route over polar regions monitor solar flare activity in real time and reroute when flares hit. This is operational, not theoretical.

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Tier 2: Well Supported

Strong evidence or clear mechanisms, with some caveats.

Tier 2 · Well Supported

Galactic Cosmic Rays and Cellular Damage

Galactic cosmic rays, high-energy particles from outside the solar system, reach Earth's surface continuously, modulated by the Sun's magnetic activity. During solar minimum, more get through. Laboratory research shows that high-energy particle exposure can cause DNA damage and misrepair signatures in human cells. This is most relevant for aircrew, frequent flyers, and astronauts, populations with measurably elevated cosmic ray exposure.

Solar Activity and Systemic Conditions

The F10.7 solar radio flux, a proxy for overall solar activity, is used in thermospheric and ionospheric models, satellite drag prediction, and long-term space weather forecasting. Higher solar activity correlates with elevated environmental electromagnetic conditions. The downstream biological implications at the population level are an active area of research.

The IMF and Magnetospheric Coupling

The orientation of the interplanetary magnetic field, particularly its southward component (Bz), controls how much solar wind energy enters Earth's magnetosphere. Sustained southward Bz is the primary trigger for geomagnetic storms. The coupling mechanisms are fully understood at the physics level; the question for biology is how much of that energy transfer propagates to surface-level effects that matter for human physiology.

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Tier 3: Plausible

Mechanistically reasonable. Human outcome evidence is limited or indirect.

Tier 3 · Plausible

Heliospheric Current Sheet Crossings

Earth periodically crosses the heliospheric current sheet, the boundary separating opposite magnetic polarities in the solar wind. Animals including birds and some mammals use the geomagnetic field for navigation, and there is laboratory evidence of light-sensitive radical pair reactions in cryptochrome proteins that are magnetically sensitive. Whether polarity transitions at the current sheet produce measurable effects in humans is not established. It is retained as a signal candidate in Chaerus because the mechanism is biologically plausible, not because the human evidence is there yet.

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What This Means

Multiple independent groups across multiple countries have found associations between geomagnetic conditions and human health outcomes. The effects are not dramatic for most healthy people on most days. The environment is not neutral.

Chaerus and Caemira are built on this foundation, tracking the conditions that the evidence says matter, without overclaiming what those conditions predict.

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Selected references: Boteler (2019); Li et al. (2018); Maeda et al. (2012); Rezende et al. (2025); Toprani et al. (2024); Wiltschko & Wiltschko (2014); Zilli Vieira et al. (2019, 2022).