Space weather can severely impact the earth infrastructure. As shown in the past, solar events are capable of damaging space vehicles, causing large power and communication grid failures, and degrading aviation’s communications, navigation and surveillance systems. In addition to this, solar events can cause radiation levels being higher than usual which may lead to an excessive radiation dose for air travellers and crew but also may cause on board system failures. As a consequence, an extreme solar event would potentially impact European Air Traffic. EUROCONTROL, the European Organisation for the Safety of Air Navigation, has launched different projects in order to better assess the risk and define proportionate mitigations.

First, EUROCONTROL launched a project in 2009 to further assess the space weather impact on GNSS-based aviation operations. Indeed, aviation operations, including navigation and surveillance, rely more and more on GNSS services. GNSS performances under nominal ionosphere condition are already well known. However, before increasing reliance on these GNSS-based operations, the aviation community has to better assess GNSS performance under abnormal ionosphere conditions. Using existing GNSS ground station networks (IGS, EGNOS, EDCN, EUREF...), the ionosphere is monitored during the current period of maximum solar activity. These ionosphere measurements, in addition to the characterisation of past events, are being used to develop realistic ionosphere scenarios. These ionosphere scenarios have been evaluated using current and future GNSS receiver parameters and the impact of the ionosphere on the GNSS performance has been assessed. As a result, new mitigations means, either internal or external to the GNSS receiver, are being evaluated.

One such (organizational) mitigation is the European Aviation Crisis Coordination Cell (EACCC), which has identified space weather as a possible hazard for aviation. The EACCC has been established by the European Commission and EUROCONTROL and is composed of EASA, the EU Presidency and nominated representatives of airspace users, air navigation service providers (ANSPs), military and airports. To mitigate the space weather threat, appropriate plans are being developed which are focused on the provision of an early warning to the aviation community and continuous provision of reliable information during the space weather event. For that purpose, coordination between EUROCONTROL and space weather agencies and experts is being set up with organisations such as the US National Oceanic and Atmospheric Administration (NOAA) and the European Space Agency (ESA). Moreover, a number of airlines were approached to learn about operational practices in the event of increased space weather activity - particularly for flight operations over polar routes.

On the global level, International Civil Aviation Organisation has increased its recognition of space weather as a potential threat for the aviation and has mandated the International Airways Volcano Watch Operations Group (IAVWOPSG) to address space weather. This group aims at providing a framework and a standardization process that would allow airlines and other aircraft operators to make best use of the space weather information provided by space weather agencies and experts. EUROCONTROL took part in this process through the US Federal Aviation Agency – EUROCONTROL Memorandum of Cooperation. This MoC includes action plan 29 on meteorological issues, where space weather is included as an area of mutual interest. Consequently, action plan 29 provides a coordination mechanism and allows the development of appropriate joint positions relating to space weather.

This paper will briefly introduce the space weather impact on aviation and then, will further detail the EUROCONTROL activities on space weather. In addition, the space weather activities hosted by the International Civil Aviation Organisation (ICAO), the World Meteorological Organisation (WMO) and the European Aviation Safety Agency (EASA) will be highlighted.

This presentation focusses on an aviation, on a pilots' perspective on space weather. How is it experienced, what practical impact did space weather have in the past ?

A short overview of international efforts to find an appropriate way to deal with space weather is then presented. Practical examples of what space weather and radiation-warning information is available to pilots are given. Many information sources exist, but their products aren't standardized, and have yet to be developed to a point where they are compareable to aviation-standard weather information. Ideas and examples of how airlines can deal with space weather are presented.

Space weather affects aviation in several dimensions:

Global Navigation Satellite Systems (GNSS) in combination with Ground Based Augmentation Systems (GBAS) allow precision landing approaches under normal ionospheric conditions. However, the ionosphere is subject to perturbations, due to the strong temporal and spatial variability of the ionospheric plasma. In particular ionospheric gradients and scintillations can prevent an aircraft precision approach since signal integrity cannot be ensured. Both perturbations are hard to predict and will lead to conditions, which are strongly deviate from the regular ionospheric behaviour.
While, to a certain extent, a disturbed ionosphere can be corrected by GBAS, these systems have difficulties in respect the disturbances mentioned above, i.e. ionospheric gradients and scintillations. To take into account ionospheric gradients, a threat model has been developed, which can estimate the worst case ionospheric threat from ionospheric gradients. This worst case is then added to the uncertainty of the positioning solution. We will discuss the threat model and its application to Germany.
While ionospheric gradients can be taken into account via the threat model, spontaneous signal scintillations are another big source of positioning uncertainty due to their random and uncorrelated nature. They can even lead to a complete loss of the signal in extreme cases. We will show that the new frequencies from Galileo and Glonass are also affected by signal scintillations.

In some cases the shortest (and hence fastest and most economical) airline routes between cities (e.g. those on the eastern seaboard of the USA and those in China) cross the polar cap. In the polar regions, air traffic control relies on HF radio communications since ground-based VHF radio facilities are lacking (and are non-existent on the Russian side of the pole) and satellite communication systems are either not available or expensive to retrofit to current aircraft. Unfortunately, space weather can significantly affect the propagation of HF radio signals at these latitudes and the forecasting techniques currently employed by the airline industry are somewhat crude and overly conservative. In this paper, we will present some preliminary results from a new project that aims to provide forecasting of HF propagation characteristics for use by civilian airlines operating over polar routes. Previous work in this area [e.g. Stocker et al., 2007] has focussed on taking HF signal measurements (e.g. SNR, delay and Doppler spread, and direction of arrival) on a limited number of propagation paths and developing an ionospheric model that incorporates high latitude features (e.g. polar patches and arcs) which, when combined with raytracing, allows the broad characteristics of the observations to be reproduced [Warrington et al., 2012]. The new project will greatly extend this work and consists of a number of stages. Firstly, HF measurements from an extensive network of purpose built transmitters and receivers spanning the Arctic regions will be collected and analysed for a period covering the current (so far weak) solar maximum and part of the declining phase. 
In order to test a wide variety of scenarios, the propagation paths will have different characteristics, e.g. they will be of different lengths and cover different parts of the northern ionosphere (i.e. polar cap paths where both terminals are in the polar cap, trans-auroral paths, and sub-auroral paths) and observations will be taken at a range of HF frequencies. Simultaneously, high latitude absorption measurements utilising the Global Riometer Array (GLORIA) will be collected and analysed. Next, the observations of the signal characteristics (i.e. both reflection and absorption properties) will be related to prevailing space weather parameters. Furthermore, an auroral absorption prediction model based on solar wind and interplanetary data will be developed by Lancaster University taking into account the riometer observations. 
Algorithms for nowcasting and forecasting of radio propagation conditions for trans-polar aircraft
 will then be developed from the ionospheric model. In addition to the approach described above, the benefits of ground station diversity using both the experimental data and the models developed during the project will also be investigated. In this presentation, we will concentrate on the space weather effects on HF propagation.

Stocker A.J., E.M. Warrington, and D.R. Siddle, Comparison between the measured and predicted parameters of HF radio signals propagating along the mid-latitude trough and within the polar cap, Radio Science, 42, RS3019, doi:10.1029/2006RS003557, 2007.

Warrington EM, Zaalov NY, Stocker AJ, Naylor JS, HF propagation modelling within the polar ionosphere, Radio Science, 47, Article number RS0L13, doi:10.1029/2011RS004909, 2012.

During very energetic and intense solar energetic particle events, observed on Earth e.g. by ground-based cosmic ray detectors as Ground Level Enhancements (GLE), the radiation dose rates at flight altitudes can increase by orders of magnitude for a short time. Especially on polar routes the combined effects of Solar Cosmic Rays (SCR) and Galactic Cosmic Rays (GCR) may have the potential of becoming hazardous. In contrast to the radiation effects due to GCR, where a number of validated codes are available for flight dose assessments, procedures for the sporadic GLEs satisfying the needs of airline companies are still under development and evaluation (e.g. within EURADOS). At present, respective radiation dose rates are typically determined in post event analysis by computer models using as input SCR flux and anisotropy parameters that are derived from worldwide neutron monitor and/or satellite measurements. However, for a specific GLE, published SCR characteristics may vary considerably. This may lead to significant differences in the radiation exposure assessment.
We will review the field and illustrate results of dose assessments for specific flights during selected GLEs. In particular, we will compare published SCR characteristics for the GLEs on 15 April 2001 and 20 January 2005, and we will demonstrate the effect of discrepancies in these characteristics on flight dose calculations. In conclusion, we will discuss perspectives of improvements in SCR dose estimates.

Dosimetry of aircrew is nowadays done routinely by calculation for a large number of aircrews among the world. This numerical approach has been validated by comparison with numerous on board measurements performed with adequate instrumentations such as Tissue Equivalent Proportionnal Counter (TEPC).This approach to assess the occupational exposure of aircrew is approved and recommended in many countries. In case of Solar proton event (SPE) classified as Ground Level Event (GLE), dose rates at flight altitudes can possibly increased, leading to an additional dose that has also to be taken account for aircrew dose records. Some routine dosimetry softwares give an estimation of these extra doses. Nevertheless, the models used for dosimetry are based or compared to very few sets of in flight measurements during GLE. There is obviously a clear need of additional data to improve the existing models. The dedicated instrumentations for aircrew and space dosimetry are rather expensive and need most of the time connection to on board power supply, regular maintenance... As a consequence, very few systems only are continuously operated on board commercial flights, limiting the probability to measure such events.
Thus, IRSN and Air France has launched a joint program for monitoring the GLE effect on the dose rate at flight altitude. The objective is to have at least 2 measurement devices flying at the same time on different routes.
The approach lies in selecting small electronic dosimeters that offer the advantage to be cheap , with a large battery autonomy (up to 6 months), and to discriminate neutron component and high LET particles from photon and low LET radiation, having a FIFO memory type (no limitation due to data storage). After installation on board, the dosimeters are collected and analyzed only in case of GLE. Such dosimeters are able to assess a 30% increase of dose rate. The easiness of installation and maintenance makes possible to install a significant number of devices on different commercial aircrafts. With a dozen of this type of dosimeter, it is possible to cover the main long haul route flights. As this type of dosimeters is not design for cosmic radiation, a specific calibration has been established by comparing data from electronic dosimeters with a reference instrumentation during a long haul flight.
In addition, this approach, based on measurements, makes also possible to estimate rapidly and accurately the effect of a GLE on dose rate and thus on additional dose by flight received by public and aircrew.

Primary cosmic radiation from the depth of the universe interacts with atmospheric molecules, leading to the generation of neutrons and other charged particles at flight altitudes. Several factors determine the exposure of aircrew and passengers, among them flight altitude and flight trajectory as well as solar cycle. Annual effective doses for flight crew have been estimated to be in the order of 2-5mSv, with maximum lifetime doses usually below 100mSv. The recognition that aircrew is exposed to appreciable doses of cosmic ionizing radiation has motivated a fair number of epidemiological studies in this occupational group over the last 15-20 years, usually with a focus on radiation-associated cancer. The fact that aircrew is a highly selected group with many specific characteristics and exposures, among them disruption of the biological day-night rhythm, poses a major challenge for these investigations.

Both cancer incidence and mortality have been evaluated in large cohorts of cockpit and cabin crew in North America, Europe and several other countries. Cohort data from 9 European countries with follow-up into the late 1990ies were jointly analysed in the ESCAPE project, with an extended follow-up conducted in 2009. Nordic studies were jointly analysed regarding cancer incidence. Some results showed consistency across most relevant studies: overall cancer risk was not elevated, while malignant melanoma (standardised incidence ratios SIR= 1.85, 95% CI 1.41-2.38), other skin cancers (2.47, 95% CI 1.18-4.53) and breast cancer in female aircrew (1.50, 95% CI 1.32-1.69) have shown elevated incidence (Pukkala et al. 2002, 2012), with lesser risk elevations in terms of mortality (Zeeb et al. 2003). In some studies including the large German cohort, brain cancer risk of cockpit crew appears elevated with a two-fold increase compared to the general population (Standardised Mortality Ratio SMR= 2.13, 95% CI 1.03-3.93) (Zeeb et al. 2010). Cardiovascular mortality risks were generally very low probably partly due to the so-called health worker effect.

Dose information in these studies was usually derived from reconstruction approaches based on routine licence information, types of aircraft and routes/hours flown, but not from direct measurements. However, dose estimates have shown high validity when compared with measured values. No clear cut dose-response patterns pointing to a higher risk for those with higher cumulative doses were found in statistical analyses. Overall, aircrew is exposed to low levels of ionizing radiation of cosmic origin, but radiation-associated health effects have not been clearly established.

A third follow-up of the large German cohort is currently in the planning stages to provide more robustness in the statistical analyses due to the extended follow-up period with regard to radiation-associated health effects. Routine dose monitoring data from the German radiation protection registry will be used for this study.

References

Pukkala E, Helminen M, Haldorsen T, Hammar N, Kojo K, Linnersjo A, et al. Cancer incidence among Nordic airline cabin crew. International Journal of Cancer 2012; 131: 2886-2897.

Pukkala E, Aspholm R, Auvinen A, Eliasch H, Gundestrup M, Haldorsen T, et al. Incidence of cancer among Nordic airline pilots over five decades: occupational cohort study. Br Med J 2002; 325: 567.

Zeeb H, Hammer G, Langner I, Schafft T, Bennack S, Blettner M Cancer mortality among German aircrew: second follow-up. Radiat Environ Biophys 2010; 49: 187-194.

Zeeb H, Blettner M, Langner I, Hammer GP, Ballard TJ, Santaquilani M, et al. Mortality from cancer and other causes among airline cabin attendants in Europe - a collaborative cohort study in eight countries. American Journal of Epidemiology 2003; 158: 35-46.

Solar Particle Events (SPEs), which are often referred to as solar flares in aviator's jargon, can temporarily contribute to the radiation field at aviation altitudes and generate a significant increase in the corresponding dose rates. TV reported on these SPEs and gave rise to public awareness all over the world. Due to the public pressure some airlines even operated their flights at lower altitudes between 29th and 31st October 2003. This paper presents a case study of dealing with an SPE (GLE 65) concerning radiation protection in aviation during the Halloween solar storms.’

An increasing number of aircraft operate on polar routes for which radio communications via VHF or geosynchronous satellite relays are unavailable. Airlines and air traffic control (ATC) authorities nonetheless require reliable HF communications with high availability and the ability to predict outages several hours in advance of a flight departure. However, ionisation of the D region polar cap and auroral ionosphere due to solar flares and energetic particle precipitation increases the absorption of HF radio waves in this region.

This paper describes a new research programme at the University of Lancaster in collaboration with the University of Leicester, Solar Metrics Ltd and Natural Resources Canada that addresses these issues. The project will develop a nowcasting and forecasting model of HF radio absorption in high northern latitudes that incorporates measurements from a Global Riometer Array (GLORIA). Real-time satellite measurements of the solar wind, interplanetary magnetic field, solar X-ray flux and energetic particle precipitation will be utilised as input to the model to improve its forecast capability.

Maps of absorption will be combined with the Leicester University three-dimensional HF ray tracing model. As part of this project, the Leicester HF propagation model will utilise data from a network of HF transmitters (collocated with ATC stations) and direction-finding receivers at high northern latitudes. Measurements on these paths will further improve and validate the HF predictions by ensuring that non-great-circle propagation paths are adequately modelled. The main product of the research programme will be an online HF communications planning and forecasting tool designed for the particular needs of civilian airlines.

This presentation will focus on the space weather effects on auroral absorption.

Space Weather Awareness is a crucial factor in the field of airborne radiation monitoring since solar radiation storms can significantly affect measurement results. For instance, a Solar Particle Event (SPE) can lead to an additional contribution to the radiation exposure of aircrew at aviation altitudes, which is generated by interactions of primary high-energetic particles of cosmic origin with atoms of the Earth's atmosphere.
Here, a case study of a measuring flight is presented, which was performed by the German Aerospace Center on 23rd March 2011, twelve days after the nuclear disaster of Fukushima, where large amounts of radioactive isotopes were released and spread across the entire globe. The flight aimed at gaining information about and samples from the radioactively unpolluted atmosphere at aviation altitudes in Germany. Radiation protection of aircrew and scientists required online-monitoring of the dose rate aboard the research aircraft in order to detect potential elevated airborne radioactivity in addition to the radiation exposure at aviation altitudes due to galactic cosmic rays and prevent the aircraft from contamination.
The fact that two days before the measuring flight NOAA had issued an alert due to a solar radiation storm, which indicated the possibility of an event that could lead to increased dose rates at aviation altitudes as well, required the permanent observation of the space weather situation in order to attribute a possible additional contribution to either a space weather event or the nuclear accident.

Solar Energetic Particles (SEPs) with energy in the GeV range can propagate to Earth from their acceleration region at the Sun and produce Ground Level Enhancements (GLEs). These events cause large increases in the radiation experienced by air passengers and crew. Many questions related to the production and propagation of GeV-energy particles remain unanswered. For example, while it is established that GLEs are associated with very large flares and fast CMEs at the Sun, there are many examples of such solar events that did not produce a GLE. We present results of test-particle simulations of the transport of GeV-energy solar particles from the Sun to Earth, showing how gradient and curvature drifts influence their propagation. We also analyse GLE data and >100 MeV proton data from the GOES satellite, made available through the SEPEM project, to verify whether drift patterns can help to explain and predict the occurrence or non-occurrence of a GLE following a solar event at the Sun. This work has received funding from the European Commission FP7 Project COMESEP (263252).

In 2000, the European Commission directive (EU directive 96/29/EURATOM) set limits to the exposure of aircraft crew to cosmic radiation. The effective dose should not be higher than 100 mSv over 5 years with a maximum of 50 mSv for a given year (specific rules apply to pregnant air crew). The radiation doses onboard aircraft are due to two sources: Galactic Cosmic Rays (GCR) and Solar Proton Events (SPE). The doses are the result of the numerous secondary particles created in the atmosphere by high energy primary particles. The galactic component is permanent but modulated by the solar activity in the course of the 11-year solar cycle. The SPE, when detected at ground level by neutron monitors (GLE), may enhance significantly the doses received onboard aircraft. A specific semi-empirical model named SiGLE was developed (Lantos & Fuller, 2003) to take into account these events. Within the European Radiation Dosimetry Group (EURADOS), doses computed by several models were compared and assessed for the GCR. The same comparison is ongoing for SPEs models and a measurement campaign initiated by IRSN (Institute for Radiation Protection and Nuclear Safety) should give important clues to validate the different approaches in the near future. Using EPCARD and SiGLE, the computerized system for flight assessment of exposure to cosmic radiation in air transport, or "SIEVERT" (Bottollier-Depois, 2003), was proposed to airline companies to assist them in the application of this legal requirement. This professional service is also accessible to any passenger who whish to estimate the dose received during a given flight (www.sievert-system.org). SIEVERT was developed by the French General Directorate of Civil Aviation (DGAC), the IRSN and Paris Observatory.

Ground Based Augmentation Systems (GBAS) can correct the majority of the GNSS pseudo range errors experienced by an aircraft in the vicinity of an airport. The normal behavior of the ionosphere has a very limited impact on the position error. However, the ionospheric medium is subject to perturbations due to the strong temporal and spatial variability of the ionospheric plasma. In particular short term disturbances of the ionosphere lead to fluctuations of phase and amplitude in the GNSS signals. These fluctuations are called signal scintillations and can be caused by ionization fronts, Travelling Ionospheric Disturbances, plasma bubbles and plasma turbulences. Therefore scintillations are one of the biggest sources of positioning uncertainty in modern GNSS receivers and can even lead to a complete loss of the signal in extreme cases. Their random and uncorrelated nature cannot be corrected by two frequency measurements. We will present the ionospheric threat model developed at the DLR to provide information about the worst case ionospheric threat, which can occur in each epoch. A mitigation of such scintillation effects can be done by preventing the aircraft from using unsafe combinations of GNSS satellites.