Definition

Space weather refers to natural perturbations coming from the sun or from space that can influence the performance and reliability of space-borne, ground-based or airborne systems and can endanger human life or health.

Description

Solar activity is not constant and, from time to time, eruptions appear on the sun’s surface which result in an abnormal level of radiation and of particle ejection. The radiation and particles are thrown into space and, if directed towards the earth, will arrive after a certain interval. Three different space weather events which effect the earth are CME’s (Coronal Mass Ejections), SEP’s (Solar Energetic Particles) and Solar Flares. These vary in times to reach the earth from as little as 8 minutes with solar flares travelling at the speed of light to as long as a day with CME’s.

The occurrence and severity of these eruptions follows an 11-year cycle composed of a period during which the severity and probability of occurrence of eruptions are quite low (but unfortunately not equal to zero), followed by a higher solar activity period called the solar maximum. This cycle can be characterized using the sun spot number (SSN), which is the arithmetic sum of the visible dark spots on the solar surface. As this parameter is quite easy to determine, it has been recorded since 1749.

The disruption caused on Earth is a result of these highly charged particles from the sun interacting with the upper atmosphere and disrupting the magnetic field of the earth.

Figure 1: Monthly Sun Spot Number evolution

Figure (1) shows solar activity as indicated by the monthly SSN and highlights that some of the solar cycles have a higher peak than others. However, the intensity of the solar cycle is not directly linked to the severity of eruptions. As an example, one of the most severe solar storms was recorded in 1859 during a fairly moderate solar cycle. Once the period of minimum solar activity of the previous solar cycle has been reached, prediction of the next solar cycle becomes reliable.

Figure 2: Solar cycle sunspot number progression from ISES

Figure (2) shows the previous solar cycle, known as solar cycle 24. The intensity of this solar cycle was moderate and the peak of maximum solar activity was observed in early 2014. As the solar eruptions are most likely to appear during the period of maximum solar activity but also during the decreasing phase, the occurrence and severity of solar eruptions was highest in the period from 2011 to 2017. The current solar cycle (25) is expected to peak in 2025-2026.

Effect

When a space weather event occurs, a wide range of effects can result. The main impacts on aviation are listed below.

• Degradation of radio/satellite communication: During solar events, some disturbance may happen on HF and satellite communications, which would have side effects on CPDLC, ADS-C, AOC…. However, line of sight VHF communication may not be impacted.
• Onboard system failure due to radiation: During a radiation storm, when striking a sensitive node, radiation may induce shortcuts, change of state, or burnout in onboard electronic devices. This phenomenon is called the “single event effect”. Its impact may vary a lot from unnoticeable to a complete failure of the system. This kind of failure may become more frequent in the future because modern electronic equipment is more vulnerable to radiation due to the smaller size of their devices.
• Radiation doses: During radiation storms, unusually high levels of ionizing radiation may lead to an excessive radiation dose for air travellers and crew. The dose received by passengers and crew is higher at higher altitudes and latitudes. Cosmic ray doses on flight crew is an ongoing project, with civil aircrew flying above 50000' requiring cosmic ray detection equipment to be worn.
• GNSS based aviation operation: High-energy particles ejected by the sun may cause strong disturbances in the upper layers of the atmosphere, mainly in the layer called the Ionosphere. This layer is composed of charged particles and is particularly sensitive to the particles ejected by the sun. The GNSS radio signals emitted by satellites have to travel through this particular layer and, under severe disturbance, are strongly affected. As a result, unexpected position and timing errors[1] can occur at the level of the user receiver. In extreme cases, the GNSS[2] receiver can lose reception of the satellite altogether and the position can no longer be computed. As a side effect, GNSS-based surveillance applications may be unavailable. SBAS or GBAS augmented services, used for approach and landing, are more demanding in terms of accuracy and integrity than the En Route/TMA GNSS-based navigation. As a consequence, the safety monitors of those systems are also more sensitive to space weather events and the unavailability of these services would be more frequent. More operators of commercial air transport are introducing RNAV GNSS type approaches. With the retirement of several ground based navigation aids there is a greater chance of conducting a GNSS approach with no ground based navigation aids as backup and therefore an accurate assessment of the risk from a space weather event should be completed before flight and very accurate monitoring of the system on an approach is required with a contingency procedure decided in the event of a loss of GPS data to continue the approach.
• Magnetic based equipments and compasses: Due to a change in the earth’s magnetic field caused by the magnetic fields of the charged particles from the sun, any magnetic based equipments are not accurate for the duration of the solar event.
• Aircraft electrical systems: Although not well understood at time of writing, solar electrical coupling mechanisms, in particular the consequences of vertical conduction-current through clouds, have been observed to charge cloud droplets at the upper and lower boundaries of layer (Stratiform) clouds. This charging may only have influences on the microphysical processes in clouds, indirectly causing variability on the macroscopic level, and it is unsure whether or not the charging is significant enough to affect aircraft (helicopter and/or fixed wing) electrical and/or communication systems.

Other effects are not under the control of the aviation community. However, side-effects may impact aviation:

• Power grid and ground public communication failure: Magnetic storms create induced electrical currents in the power or communication grids, which may lead to electrical and ground public communication failure (telephone, internet, etc.).
• Satellite failure: High energy particles ejected by the sun may hit satellites and cause failure.

Scenarios

The most severe events have the lowest probability of occurrence.

Figure 3: Probability of space weather events versus impact on Earth

Figure 3 presents the probability of occurrence depending on the magnitude of the event. Events have been separated into three different categories:

1. “Usual bad space weather”: these events are quite common (several times a year) during the period of high solar activity, but the impact on earth infrastructures is very low, if noticeable at all.
2. “Severe to Extreme event”: these events occur between one and five times per 11-year solar cycle. The impact may be significant on infrastructure.
3. “Super-Extreme event”: these events are very rare and may happen only once every 100 to 500 years. One such event was recorded in 1859.

Possible impact of a severe to extreme space weather event

• Communication: HF and, potentially, satellite communication may be degraded or temporally lost. As an example, on 7 September 2005, solar activity severely impacted all HF communications over the US. However, line of sight VHF was not significantly impacted.
• Satellite failure: Potential loss of one or more satellites. Depending on which satellites are lost, the impact may vary significantly. As an example, the March 1989 space weather event may have caused the loss of four US Navy satellites.
• GNSS-based navigation: En-route GNSS-based navigation might be lost in a contained area for a limited duration. GNSS-based landing systems (SBAS[3], GBAS[4]) may be unavailable for tens of hours. As an example, in October 2003 the US SBAS system (named WAAS[5]) was unavailable for 9 and 15 hours.
• Surveillance: As a side-effect, GNSS-based surveillance applications[6] may be degraded.
• Power failure: Potential power failure over part of a country for tens of hours. As an example, at 2.45 a.m. on 13 March 1989 the entire Quebec power grid collapsed and 6 million people suffered a power black-out for 9 hours.
• Increase in the radiation level: Passenger and crew flying at high altitude and latitude may be exposed to a higher radiation level than usual. This increased level of radiation might also lead to onboard system failure. Actual impact is difficult to assess.

Possible impact of a super-extreme space weather event

• Communication: HF and, potentially, satellite communication could be temporally lost. However, line of sight VHF may not be impacted.
• Satellite failure: From experts’ assessment, up to 50% of the space vehicles may be lost. Depending on which space vehicles are lost, impact can vary significantly.
• GNSS-based navigation: Space vehicle failure combined with ionosphere storms may lead to a partial or complete loss of GNSS services.
• Surveillance: As a side-effect, GNSS-based surveillance applications may be unavailable.
• Power failure: Simulations on the US power grid estimated that 50% of the US may be under a power black-out. Similar results may happen over Europe. The recovery time may vary between dozens of hours to months, depending on the system failure.
• Increase in the radiation level: Passenger and crew flying at high altitude and latitude may be exposed to a higher than usual radiation level. This increased level of radiation may also lead to onboard system failure. Actual impact is difficult to assess.

Some Solutions

• Satellite failure and GNSS-based applications: A back-up to satellite communication and navigation should remain available. Depending on the flight phase, area and aircraft equipment, this back-up could be HF/VHF/SATCOM voice communication, ground based navigation, radar vectoring, inertial navigation, etc.
• Power failure: Air traffic control centres have alternate power generation in case of power failure to ensure the safety of air navigation.
• Increase in the radiation level: As the radiation dose is higher at higher altitude and latitude, a possible solution is to decrease the aircraft altitude and latitude. However, the geographic and altitude limit are difficult to determine. Currently, airlines are not flying polar routes when a radiation storm is in progress.
• Forecasting for Aviation. The Met Office in the UK have recently created a Space Weather Centre to monitor and inform flight crews of space weather related events and risks. This will be expanded over the coming years.

Further reading

EASA

• Safety Information Bulletin 2012/09: "Effects of Space Weather on Aviation"
• Safety Information Bulletin 2012/10: "Single Event Effects (SEE) on Aircraft Systems caused by Cosmic Rays"

ICAO

• Concept of operations, high-level requirements and manual available here.

EU OPS

• EU-OPS 1.390 - Paragraph 1.390 addresses Cosmic radiation (see note).

Note: EU-OPS 1.390 is not transposed into IR-OPS; This rule is covered by Directive (EC) 96/29.

ESA - Navipedia

1. ^ Ionospheric Delay
2. ^ GNSS Receivers General Introduction
3. ^ SBAS General Introduction
4. ^ GBAS Systems
5. ^ WAAS General Introduction
6. ^ Surveying, Mapping and GIS Applications

Others

• World Meteorological Organization site - This site contains a space weather portal that provide links to several other organisations dealing with space weather
• European Space Agency (ESA): Space Weather Web Server - This site provides information on “today’s space weather” and a link to the prediction centre of NOAA
• NOAA: Space Weather Prediction Center - This is the site of the space weather prediction centre of NOAA; a subscription service is available to receive alerts.
• FAA AC 120-61B In-Flight Radiation Exposure, Nov 2014
• The Royal Academy of Engineering conducted an investigation to the issue of what technology will space weather affect:
  • Full Report and
  • Summary Report
• The Royal Meteorological Society's monthly publication "Weather" has devoted an entire issue on space weather; namely September 2014, Vol. 69, No. 9