Space weather and commercial airlines

Space weather and commercial airlines

Advances in Space Research 36 (2005) 2258–2267 www.elsevier.com/locate/asr Space weather and commercial airlines J.B.L. Jones a,b,* , R.D. Bentley ...

242KB Sizes 42 Downloads 137 Views

Advances in Space Research 36 (2005) 2258–2267 www.elsevier.com/locate/asr

Space weather and commercial airlines J.B.L. Jones

a,b,*

, R.D. Bentley b, R. Hunter b,c, R.H.A. Iles b, G.C. Taylor d, D.J. Thomas d

a

c

Virgin Atlantic Airways Ltd., The Office, Manor Royal, Crawley, West Sussex RH10 9NU, UK b Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK Civil Aviation Authority, Aviation House,Gatwick Airport South, Gatwick, West Sussex RH6 0YR, UK d National Physical Laboratory, Queens Road, Teddington, Middlesex TW11 0LW, UK Received 1 December 2002; received in revised form 8 April 2004; accepted 8 April 2004

Abstract Space weather phenomena can effect many areas of commercial airline operations including avionics, communications and GPS navigation systems. Of particular importance at present is the recently introduced EU legislation requiring the monitoring of aircrew radiation exposure, including any variations at aircraft altitudes due to solar activity. With the introduction of new ultra-long-haul ‘‘over-the-pole’’ routes, ‘‘more-electric’’ aircraft in the future, and the increasing use of satellites in the operation, the need for a better understanding of the space weather impacts on future airline operations becomes all the more compelling. This paper will present the various space weather effects, some provisional results of an ongoing 3-year study to monitor cosmic radiation in aircraft, and conclude by summarising some of the identified key operational issues, which must be addressed, with the help of the science community, if the airlines want to benefit from the availability of space weather services.  2004 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Space weather effects; Commercial airlines; Cosmic radiation dose; Solar activity

1. Space weather effects 1.1. Space weather phenomena The fact that the Earth is immersed in an extremely tenuous bath of high-energy charged particles called cosmic rays (both galactic and solar in origin) is but just one of many physical processes going on in near-Earth space that can have a direct impact on airline operations. Most of the time space weather is of little concern in our everyday lives. However, when the space environment is disturbed by the variable outputs of the Sun, technologies that we depend on both in orbit and on the ground can be affected. *

Corresponding author. Tel.: +44 1483 684 803; fax: +44 1483 683 481. E-mail address: [email protected] (J.B.L. Jones).

The internationally accepted definition of space weather (SW) is: ‘‘Conditions on the sun and in the solar wind, magnetosphere, ionosphere, and thermosphere that can influence the performance and reliability of space-borne and ground-based technological systems and can endanger human life and health’’ (From US National Space Weather Strategic Plan, August 1995). Included within this definition are the effects of galactic cosmic rays (GCRs) that originate from exploding stars outside our solar system, but which also affect technological systems, and endanger human life and health because their flux is modulated by solar processes. It is these GCRs that are the primary source of the cosmic radiation at aircraft altitudes. From this definition it can be seen that the main influence of SW comes from the Sun and its own ‘‘climate-like’’ variations, which occur on both the short term (hours, days) and the long term (roughly 11-year solar cycle).

0273-1177/$30  2004 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2004.04.017

J.B.L. Jones et al. / Advances in Space Research 36 (2005) 2258–2267

Solar flares with lifetimes ranging from hours for large gradual events, down to tens of seconds for the most impulsive events, release ultraviolet, X-ray and radio emissions, producing ionospheric disturbances in the sunlit hemisphere of minutes to hours duration. Large flares, known as solar particle events (SPEs), can release very energetic particles (primarily protons), which then arrive in our atmosphere within 30 min. The Earths magnetic field does offer some protection, but these particles can spiral down the field lines, entering the upper atmosphere in the polar regions where they produce additional ionisation in the ionosphere and increase the radiation at aircraft altitudes. The explosive release of coronal mass ejections (CMEs) from the Suns outer atmosphere over the course of several hours, can also rapidly shower the Earth with energetic particles and cause severe disturbances in the physical characteristics of the solar wind (e.g., density, composition, and magnetic field strength). Because the solar wind varies over time scales as short as seconds, the boundary between interplanetary space and the Earths magnetosphere is extremely dynamic. One to four days after a solar disturbance a plasma cloud reaches the Earth, buffeting the magnetosphere and resulting in a geomagnetic storm. During these storms very large electrical currents, of up to a million amperes, can flow through the ionosphere and magnetosphere, which can change the direction of the Earths magnetic field at the surface by up to 1 or 2, mainly in the auroral regions. These variations in particle fluences and magnetic fields can impact on the atmospheric radiation levels as well as severely disrupting radio communications. 1.2. Hazards to humans The principal SW hazard to humans is exposure to cosmic radiation, which is caused primarily by GCRs. These energetic particles start interacting with the significant atmosphere at around 130,000 ft causing secondary particles to shower down into the denser atmosphere below. This ‘‘particle shower’’, and the corresponding level of radiation dose, reach a maximum intensity at around 66,000 ft (20 km) and then slowly decreases with decreasing altitude. Dose rates also increase with increasing latitude reaching a constant level at about 50. The dose rate at an altitude of 26,000 ft (8 km) in temperate latitudes is typically up to about 3 microSieverts (lSv) per hour, but near the equator only about 1 to 1.5 lSv/h. At 39,000 ft (12 km), the values are greater by about a factor of two. Typically, a London to Los Angeles flight in current commercial aircraft accumulates 65 lSv (6 lSv/h); however, the solar cycle can give ±20% variations in dose from solar minimum to maximum. The recommended dose limit for EU aircrew is a 5year average dose of 20 mSv per year, with no more than 50 mSv in a single year. In the UK, an administrative

2259

maximum limit of 6 mSv has been adopted for record keeping purposes, which is still workable with current flight profiles and annual block hours. It should be noted that for a pregnant crewmember, starting when she reports her pregnancy to management, her work schedule should be such that the equivalent dose to the child is as low as reasonably achievable and unlikely to exceed 1 mSv during the remainder of the pregnancy. However, if future commercial aircraft are designed for increased range or to utilise the available airspace at higher altitudes, then we can expect to see significant increases in the doses (8 lSv/h at 42,000 ft, 10 lSv/h at 51,000 ft). Quicker flights will reduce doses, but significant increases in cruising speeds will need to be achieved: the still-born Sonic Cruiser flying at Mach 0.98, would have reduced flight times by 15–20%, but with envisaged operating altitudes up to 50,000 ft, the route doses would increase by 30–40%. The impact of SPEs can also increase the dose. Dyer et al. (2003) suggest that during the SPE of 1956 the radiation dose received at 40,000 ft (12 km) on a transatlantic flight would have been approximately 10 mSv. Such events are extremely rare, but smaller more typical events in September and October 1989 indicate 2 mSv for a similar flight. This work also shows that the dose rate increases more significantly with altitude during an SPE than with GCRs. Medical research is inconclusive, but the chances of developing cancer as a result of cosmic radiation is considered to be very unlikely, as the total career dose is received in low doses per flight, and accumulated slowly over the length of a flying career. It is difficult through epidemiological studies to find causation of cancer due to cosmic radiation as other lifestyle risk factors exist, particularly with aircrew. The capture of more accurate data and longer studies will be required to assist medical research of the long-term health effects. 1.3. Aircraft avionics Dyer et al. (2000) and Dyer (2002) shows the increasing hazard to aircraft avionics due to the use of increasingly more sensitive electronic components. These components are becoming more susceptible to damage from the highly ionising interactions of cosmic rays, solar particles and the secondary particles generated in the atmosphere. The heavier and most energetic particles can deposit enough charge in a small volume of silicon to change the state of a memory cell, a one becoming a zero and vice versa. Thus memories can become corrupted and this could lead to erroneous commands. Such soft errors are referred to as ‘‘single event upsets’’ (SEU). Sometimes a single particle can upset more than one bit to give what are called multiple bit upsets (MBU). Certain devices could be triggered into a state

2260

J.B.L. Jones et al. / Advances in Space Research 36 (2005) 2258–2267

of high current drain, leading to burn-out and hardware failure; such effects are termed single event latch-up or single event burn-out. These deleterious interactions of individual particles are referred to as single event effects (SEE). Satellites incorporating sensitive RAM chips have had upset rates from one per day at quiet times to several hundred per day during SPEs. In-flight aircraft measurements of SEU sensitivity in 4 Mb SRAM produced a rate of 1 upset per 200 flight hours, and agreed well with the expected upset rate variations due to changing latitude (Taber and Normand, 1993). Research suggests that 100 MB SRAM (i.e., laptop) may suffer upsets every 2 h at 40,000 ft, or 1 upset/minute in 1 GB SRAM due to the 1989 SPEs. This problem is expected to increase as more, low-power, small feature size electronics are deployed in ‘‘more electric’’ aircraft. 1.4. Communications Many communication systems utilise the ionosphere to reflect radio signals over long distances. Ionospheric storms can affect radio communication at all latitudes. Some radio frequencies are absorbed, while others are reflected, leading to rapidly fluctuating signals and unexpected propagation paths. Solar flare ultraviolet and Xray bursts, solar energetic particles, or intense aurora can all bring on these conditions. If the effects become especially strong, it can cause a total communications blackout. SPEs produce a particular type of disturbance called polar cap absorption (PCA) that can last for many days. When very energetic particles enter the atmosphere over the polar regions, the enhanced ionisation produced at these low altitudes is particularly effective in absorbing HF radio signals and can render HF communications impossible throughout the polar regions. At a ‘‘Space Radiation Impacts on Airlines Workshop 2002’’ in Boulder, Colorado, several US air carriers indicated that they have cancelled trans-polar flights due to such space weather events. 1.5. Satellite navigation There are now plans to use GPS for navigating aircraft so that the separation between aircraft can be reduced, and to position the aircraft on approach. There are also studies in progress on the longer-term goal of landing aircraft by GPS. However, the accuracy of the GPS signal, which must pass through the ionosphere, is obviously affected by any ionospheric variations due to solar and geomagnetic activity. Dual-frequency GPS receivers actually measure the effect of the ionosphere on the GPS signals and can better adjust to, but not eradicate, these difficult circumstances. This is accomplished by using a network of fixed ground based GPS receivers, separated by a few hundred km, to derive a map of the ionosphere. The map is then transmitted to

the aircraft so that the GPS receiver on board can make an accurate ionospheric correction. On a smaller scale, irregularities in the density of the ionosphere that produce scintillations occur in varying amounts, depending on latitude. For example, the equatorial region, (the latitude zone that spans 15–20 either side of the magnetic equator) is the site of some of the greatest ionospheric irregularities, even when magnetic storms do not occur. Seemingly unpredictable episodes of density enhancements in the upper ionosphere can occur there in the evening hours and can cause radio waves to be misdirected. These scintillations make GPS operations difficult. GPS signals are generally immune to ionospheric changes in response to large infusions of X-rays following a solar flare. However, GPS and all other satellites (including communications) must contend with the detrimental effects the energetic solar particles have on the on-board systems. 1.6. Terrestrial weather Besides the ionospheric disturbances directly caused by flares and magnetic storms, the ionosphere exhibits irregular variations related to the dynamics of the underlying atmosphere. These depend upon the combination of traditional ‘‘weather’’ near the ground, which produces waves in the atmosphere like the waves in the deep ocean, and the winds between the ground and the upper-atmosphere levels that act like a filter to the passage of those waves. While this aspect of space weather may appear to have a non-solar origin, its effects are most pronounced when the upper-atmosphere winds or lower-ionosphere composition is enhanced by the energy inputs from the active Sun. Optical phenomena called ‘‘red sprites’’ and ‘‘blue jets’’ have been observed at altitudes extending from the tops of strong thunderstorms (at around 15-km altitude) to the lower ionosphere (about 95-km altitude). Possibly related to these optical signatures, intense electromagnetic pulses (10,000 times stronger than lightning-related pulses) have been detected over thunderstorm regions by satellites. These observations suggest that there may be a stronger connection between global thunderstorm activity and the ionosphere and upper atmosphere than previously suspected. Interest in their effects will depend on the future use of this region of Earth-space. There may also be a relationship between increased cloud cover over the USA and the solar maximum. Previous studies have shown that during the solar maximum, the jet stream in the Northern Hemisphere moves Northward possibly due to the Suns varying ultraviolet output, which effects the ozone production in the stratosphere. When the ozone absorbs ultraviolet radiation, it warms the stratosphere, which may affect movement of air in the troposphere where clouds form.

J.B.L. Jones et al. / Advances in Space Research 36 (2005) 2258–2267

It is the jet stream, which plays an important role in cloudiness, precipitation and storm formation in the USA. Future studies hope to establish the mechanisms that may link solar variability with terrestrial weather.

2261

2000. The effects of altitude and latitude are clearly visible on the plot of Total Counts. (Note: local time shows the time corresponding to the aircraft longitude). 2.2. Routes and measured doses

2. Cosmic radiation studies The Mullard Space Science Laboratory (MSSL – the Department of Space and Climate Physics of University College London) began in 2000, a project to monitor the cosmic radiation in aircraft cabins. The study by Bentley et al. (2002) will last for 3 years and is funded by the UK Particle Physics and Astronomy Research Council (PPARC) with Virgin Atlantic Airways (VAA) as the industrial partner. The UK National Physical Laboratory (NPL) and Civil Aviation Authority (CAA) are also collaborating in the study. 2.1. Details of the PPARC study One of the drivers for this study was the requirement by the Council of the European Union for Member States to implement Directive 96/29/Euratom by 13 May 2000. Article 42 of the Directive imposes requirements relating to the assessment and limitation of aircrews exposure to cosmic radiation and the provision of information on the effect of cosmic radiation. This investigation is designed to: compare the measured dose to models used to predict crew radiation exposure, and to determine whether there are significant short-term excursions in the dose-rate caused by solar or geomagnetic activity. The cosmic radiation is measured using a tissue equivalent proportional counter (TEPC) manufactured by Far West Technology. The instrument is designed to mimic human tissue providing a measure of the dose equivalent to a few micrometres of tissue. Measurements are recorded every minute during each flight and later integrated with the aircrafts flight data (including time, latitude, longitude and flight level), to provide an accurate measure of the radiation dose throughout each flight. In particular, this can show how the radiation levels vary during the flight in response to changes in the aircrafts position and more importantly to changes in the cosmic ray flux as a consequence of solar activity. The commercially available Hawk TEPC is ideal for this work, as the entire system fits into a small suitcase, 53 cm · 34 cm · 21 cm, which can be stowed in a floor or overhead locker. One enhancement to the unit employed for this work involved replacing the existing power pack with heavy-duty batteries enabling the instrument to collect data continuously for more than 2 weeks and record over 20 flights without interruption. Fig. 1 shows the combined data plotted against time for a flight between London and Johannesburg in April

To date, five TEPCs have been carried on more than 450 flights using Virgin Atlantic A340 and B747 aircraft. Each route operated by Virgin will be monitored a sufficient number of times to determine the range of doses experienced on that route, as a function of flight profile, time of year and solar activity. The actual routes taken by the aircraft are shown in Fig. 2. The TEPCs have also flown on four CAA flights, two test flights for Emirates (via the North Pole), two Concorde supersonic test flights, and a number of southern hemisphere routes. Some typical doses measured on routes flown by VAA are shown in Table 1. Mean values (with their standard deviation) are given for sectors flown a number of times. Flights affected by Forbush decreases (see below) have been excluded. The entries are listed in order of decreasing dose for the out-bound flight, showing the dramatic difference in exposure for similar length flights going to different parts of the world. For example, the flight to Johannesburg has approximately half the dose

Fig. 1. A combined data plot versus time for a flight from London to Johannesburg.

2262

J.B.L. Jones et al. / Advances in Space Research 36 (2005) 2258–2267

Fig. 2. Routes taken by flights for which details were available – destinations in the study are shown with ‘‘*’’. Note how flights to the Far East and South Africa follow almost exactly the same routes each time, whereas those to North America follow routes spread over a wide range of latitudes depending on weather conditions. To date, only a few measurements have been made in the southern hemisphere.

Table 1 Mean doses on routes operated by Virgin Atlantic Airways Route

No. of flights

Mean route dose (lSv)

SD (lSv)

London ! Tokyo Tokyo ! London

4 3

52.5 59.3

3.7 2.7

London ! Los Angeles Los Angeles ! London

3 2

51.5 47.9

2.7 1.5

London ! San Francisco San Francisco ! London

2 2

46.8 38.0

1.4 4.5

London ! Shanghai Shanghai ! London

2 1

43.4 56.8

3.3 –

London ! Hong Kong Hong Kong ! London

1 1

42.9 55.0

– –

London ! Orlando Orlando ! London

2 2

36.6 28.9

1.0 1.3

London ! New York New York ! London

3 2

33.8 29.8

2.3 1.2

London ! Miami Miami ! London

2 1

30.8 27.7

4.7 –

London ! Boston Boston ! London

6 4

30.7 25.9

3.1 3.2

London ! Johannesburg Johannesburg ! London

6 5

25.6 25.0

1.5 3.1

London ! Athens Athens ! London

4 4

11.4 13.0

0.9 0.6

of a similar length flight to Tokyo because of the lower flux of cosmic radiation at lower latitudes where the cosmic ray cutoff rigidity is higher.

Part of the PPARC study is to validate the computer code used by VAA to predict route doses, and also to compare the performance of the different codes available against the measured TEPC data. The codes to be investigated are CARI (developed at the US Federal Aviation Administrations Civil Aerospace Medical Institute), EPCARD (developed under European Commission contracts jointly by several laboratories) and SIEVERT (adapted from CARI by a collaboration of several French laboratories). Other codes, which have become available, will also be included in the study. Details how these comparisons can be made between actual measurements and models that calculate different radiation dose quantities are dealt with by Taylor et al. (2002). For this paper, CARI route dose calculations were performed for 38 VAA flights from London to destinations in China, Greece, Japan, South Africa and the United States for which VAA flight profiles were available, and the results compared with TEPC measurements for those flights. Fig. 3 compares the overall results for the three versions of CARI to the TEPC results. It shows that there is little difference between the versions, with CARI-6M, which should reproduce the flight profile more accurately as it uses actual flight waypoints rather than a great circle route, generally predicting slightly lower doses. Further comparison of the results for CARI-6 (January 2002) to the TEPC estimate of effective dose, but this time coded for destination, shows that CARI under predicts the effective dose by roughly 12%, although the results for the London– Johannesburg and Johannesburg–London flights are remarkably good suggesting that the CARI model per-

J.B.L. Jones et al. / Advances in Space Research 36 (2005) 2258–2267

2263

Fig. 3. Comparison of route doses predicted by three versions of CARI-6 with TEPC measurements: CARI-6 (Feb 2000) (s), CARI-6 (January 2002) (X) and CARI-6M (h). The results from CARI-6M (waypoints) are generally lower than the other versions (Great Circle), as demonstrated by the zero-intercept linear fits: (- - -) CARI-6 (February 2000 and January 2002), (- Æ Æ -) CARI-6M, (straight line) CARI = TEPC.

forms better in the southern hemisphere than the northern. 2.3. Solar geo-effective events On 14 July 2000 (Bastille Day), a TEPC was flown to Hong Kong a few hours after the start of a large solar proton event, although it missed the initial pulse of particles. Following any large event, the flux of cosmic rays reaching the Earth is reduced. These sudden intensity decreases, known as Forbush decreases, are associated with sudden increases in plasma density and magnetic flux emitted from the sun and are associated with ‘‘large’’ solar flares and interplanetary shock structures. The flights in the days following the Bastille Day flare were all affected by the Forbush decrease, and in each case a substantial reduction in the mean dose is observed (compare the doses in Table 2 with the mean values from Table 1). The data taken by the TEPC has been compared with data taken by the particle monitors on the ACE and GOES spacecraft in Fig. 4. Fig. 5 shows the measurements made at four ground neutron monitor

Fig. 4. Data taken by the TEPC following the Bastille Day flare compared to ACE (Protons > 10 and >30 MeV) and GOES 8 X-ray data.

stations and shows the 14th and 21st July London– Hong Kong flights from Table 2. Fig. 5 also clearly shows the Forbush decreases that took place before the flare (due to the passage of a CME), and that continued for several days after the flare event. For this particular event the energetic (>850 MeV) solar flare particles arrived almost immediately and persisted for up to 4–6 h at ground level. Any increased radiation risk is therefore relatively brief, but almost immediate following the SPE. When attempt-

Table 2 Doses on routes for the flights following the Bastille Day flare Date

Route

Post-flare dose (lSv)

Mean route dose (lSv)

14/07/2000 15/07/2000 16/07/2000 17/07/2000 17/07/2000 18/07/2000 19/07/2000 19/07/2000 20/07/2000 21/07/2000 21/07/2000

London–Hong Kong Hong Kong–London London–Los Angeles Los Angeles– London London– New York New York–London London–Chicago Chicago–London London–Tokyo Tokyo–London London–Hong Kong

37.7 40.2 40.2 37.3 26.2 26.4 34.1 30.4 43.5 46.4 37.3

42.9 55.0 51.5 47.9 33.8 29.8 – – 52.5 59.3 42.9

2264

J.B.L. Jones et al. / Advances in Space Research 36 (2005) 2258–2267

Fig. 5. Measurements made at the cosmic ray ground stations at Kiel, Moscow, Beijing and Calgary. The two vertical lines on the top three panels indicate when the 14th and 21st July flights respectively crossed the same longitude as the ground stations.

ing to estimate any alterations in the radiation exposure to aircrew it is necessary to consider a number of factors: the interplanetary conditions, the location of the aircraft for the next few hours (day-side or night-side, magnetic latitude, etc.), and the hardness of the flare particles. The above study of the Bastille Day flare by Iles et al. (2001) show results that may be influenced by a number of external factors and it is therefore unwise to take the results as any more than an indication of what may be happening. Our observations show that the trailing edge of the SPE had little effect on the doses measured at aircraft altitudes on 14th July. The leading edge of the SPE did however cause a significant increase in the measured cosmic ray dose at the high latitude ground stations. It therefore seems reasonable to assume that a hard SPE spectrum, as found at the leading edge of this event, may cause a noticeable and possibly a significant increase in the cosmic ray dose at aircraft altitudes. At present, the best solution for estimating solar flare doses would be to encourage the permanent installation of active monitors like the TEPC, which are installed at the factory, integrated with aircraft power, GPS and communication systems, providing almost world-wide, fulltime coverage.

3. Practical issues Even though the SW hazards are known, there are other practical issues, as discussed by Jones et al. (2001), that must be considered if the airline industry is to ever utilise SW information and eventually forecasting, to reduce the impacts. Aviation is one of the most heavily regulated industries, both nationally and internationally, in terms of safety, security and operational procedures. Therefore, the use of SW information in a similar manner to terrestrial weather should be co-ordinated and agreed by the many world-wide aviation governing bodies, i.e., from International Civil Aviation Organisation (ICAO) and International Air Transport Association (IATA) to national Air Traffic Control (ATC) and aviation regulatory authorities. 3.1. Disseminating space weather information Assuming that the SW science community can produce the necessary models for nowcasting, warning and forecasting for the airline industry, then the next step would be to ensure timely and complete dissemination of the information. A sensible solution would be to

J.B.L. Jones et al. / Advances in Space Research 36 (2005) 2258–2267

‘‘piggy-back’’ space weather onto the present worldwide distribution of terrestrial weather. Besides the possible cost-savings that this could bring, it could also simplify the inclusion of SW information and utilisation procedures into current regulations. If regulatory approval (i.e., ICAO, IATA, CAA, etc.) were obtained to ‘‘piggy-back’’ SW onto the terrestrial weather system, this would ensure that the Worlds Meteorological expertise could be used to develop the data communications to include SW. Distribution of terrestrial weather information around the world is carried out in several ways and summarised in Table 3. SaDis is a single satellite over the Indian Ocean covering UK/Europe, Africa, Asia and Australia, and backed up with ftp and landlines. The American ISCS has two satellites deployed over the Pacific Ocean to complete the coverage. The Internet is another obvious distribution medium, which although it is already utilised by many vendors of terrestrial and SW products, it is not yet approved by ICAO for mission critical information. Improvements in security, transmission rates and reliability may see a change in ICAOs stance in the near future. 3.2. Operational impacts The worlds ATC agencies (e.g., EUROCONTROL in Brussels, National Air Traffic Services (NATS) in the UK and the Federal Aviation Administration (FAA) in the USA) play an integral role in the dissemination of terrestrial weather data so that they, and the flight crews, have the latest information to ensure safe operations. It would therefore be logical for all such agencies to be included in the distribution of SW information. They could then assist with information flow, but more importantly it would ensure that they could safely control the separation between aircraft in their airspace, which may decide to alter their flight profile based on received SW warnings. It is likely that any significant SW events would affect only specific geographic areas. Airspace around the world can also be clearly separated into specific areas. One such area is the North Atlantic, which is controlled by the Scottish and Oceanic Area Control Centre (ScOACC) based at Prestwick in Scotland. It provides an ATC service to aircraft in the eastern part of the North

2265

Atlantic from the south of Iceland to north of the Azores. Radar only has a range of some 200 miles, so aircraft over the Atlantic are controlled by using position reports and estimates passed to the controllers by the pilots using HF communications or more recently by an automatic satellite data message. During the aircrafts passage, the ground controllers will assess requests (received primarily via HF; however a satellite computer data link has recently become operational) for any changes to level, speed or route, and will coordinate with adjacent Oceanic Control Centres before authorising any such change. Due to passenger demands, time zone differences and airport noise restrictions, much of the North Atlantic traffic is concentrated at particular times: westbound in the late morning/afternoon, and eastbound during the night/early morning. Because of this concentration and the limited height band for economical jet operation, the airspace is comparatively congested. Therefore, a system of organised tracks is used, which change daily due to the prevailing terrestrial weather conditions. Procedural operations ensure that lateral, longitudinal and vertical separation minima are maintained on these tracks between 29,000 and 41,000 ft. As an example of the operational impact that a SW event (i.e., a solar flare) could have on this particular ATC environment, statistics for August 2001 and a ‘‘snapshot’’ for 19 November 2001 are given in Table 4. In the event of a Solar Radiation Nowcast advising descent below 36,000 ft being issued to some, or all of these aircraft, maintaining safe separation minima between aircraft could prove extremely difficult, especially if non-standardised procedures are used. It is likely that the airspace capacity would be reduced to approximately 40 aircraft/h with large delays affecting all airTable 4 North Atlantic statistics from ScOACC N. Atlantic tracks (maximum figures for August 2001) No. of aircraft/h 110 No. of aircraft/day 1100 No. of aircraft > 41,000 ft (13 km) 5–7% of Traffic No. of aircraft < 28,000 ft (8.5 km) 2% of Traffic Snapshot 19 November 2001 13:47:44 (Now to +3 h) No. of aircraft at or above 36,000 ft (11 km) 67 Aircraft on random or crossing track routing 50%

Table 3 Terrestrial weather distribution systems currently deployed, with examples of utilisation of the facility Distribution systems

Utilisation

Global telecommunications system (GTS)

Between national weather services (i.e., UK Met Office to US NWS) Between national aviation authorities (e.g., CAA to FAA) Direct to airline operations and 3rd party vendors

Aeronautical fixed telecommunications network (AFTN) UK WAFC – satellite dissemination (SaDis), USA – WAFC International satellite communications system (ISCS) SATCOM & HF radio

Direct to aircraft

2266

J.B.L. Jones et al. / Advances in Space Research 36 (2005) 2258–2267

craft on the ground. This scenario becomes all the more complex when terrestrial weather and increased fuel consumption is superimposed on the decision process. Therefore a variety of carefully planned, and ATC controlled procedures should be designed to react to a rising scale of SW severity. For westbound traffic, the entry onto the tracks is a major choke point due to the relatively short distance between most of the major European Airports and the start of the Atlantic routing. The ScOACC believes it would require a minimum of 2 h warning to safely implement the flow management necessary to allow all aircraft to reduce their altitude. With an increasing number of private business jets and future commercial traffic above 43,000 ft, then the requirement for meticulous procedures becomes all the more compelling.

its possible impacts. This in part stems from a poor ‘‘Educational/Outreach Programme’’ (E/OP), but also that the impacts have never been sufficiently proven to warrant the cost of further research or risk assessment. These failings need to be addressed immediately if the industry is to assist with additional research. Even though the present risks may be considered commercially low, the understanding of SW must be improved to make all areas of the industry aware that technological advances in future aircraft, and the use of higher altitudes, will significantly enhance the risks. To achieve these goals it would be useful to see the creation of science/industry Airline SW Working Groups, certainly on both sides of the Atlantic.

3.3. Commercial impacts

4. Conclusions

Utilising SW information either means flying lower and/or delaying flights on the ground to avoid the effects from SEP events. The commercial considerations for such actions are the increased fuel burn at lower, less economical altitudes with the possibility of a diversion to refuel. A refuel stop incurs landing, handling and fuel charges. Any significant delay on the ground during the diversion may then lead to a minimum 12-h stopover due to crew duty hour limitations, which would then incur further charges (i.e., hotel accommodation for passengers and crew) as well as severe disruption to the flying programme. Another consideration of flight at lower altitudes is possible increased costs due to operating the engines outside of their optimum parameters. Conversely, there are important considerations if available SW information is ignored. Albeit extremely unlikely, annual dose limits (6 mSv/year) may be reached or even exceeded on a single flight. This would mean either the crew member continues to fly at a reduced rate, or does not fly for a period of time but risks going out of currency and requiring further training. Consideration may need to be given for additional crew numbers to be factored into establishment figures. For a primarily female workforce, these considerations are very important when the more restrictive pregnancy dose limits are applied. Other factors are the cost of avionics maintenance due to SEEs and the potential increases to insurance premiums if information is available but not used. Many airline industry brokers are the same large companies that deal with the satellite and space industries and are therefore, already well educated to the potential risks from SW.

Space weather already affects the commercial airline industry, most notably by the exposure of aircrew and passengers to cosmic radiation and any variations caused by SEP events. The SW hazards to current avionics, communication and navigation systems are also considered to be scientifically significant, although as yet there appears to be insufficient industry interest to support further research. However, technological developments in airspace management systems, aircraft design and the increases in operating altitudes will make future airline operations increasingly at risk to SW impacts. Therefore, to ensure that the safety and security of operations is maintained in the future, the airline industry as a whole must begin to utilise SW information, and make plans for it to be integrated safely into its daily operation. This could include permanent installation of active monitors to give almost worldwide, full-time coverage of SW events. The dissemination of SW information around the globe, and to all aircraft, could be achieved using present terrestrial weather systems and technology. An E/OP should be implemented to improve the awareness and understanding of the SW environment and its many impacts. This programme must reach all levels of this heavily regulated and safety conscious industry: from airlines to ATC agencies to ICAO and IATA. In parallel with the E/OP, the science community should assist the airline industry with more accurate risk assessments of the SW hazards, for both present and future systems, through collaborative working groups.

3.4. Education Within the airline industry there is a poor level of awareness and understanding of SW science and of

References Bentley, R.D., Iles, R.H.A., Jones, J.B.L., et al. Monitoring Cosmic Radiation on Aircraft, in: Sawaya-Lacoste, H. (Ed.), Proceedings of the Second Solar Cycle and Space Weather Conference

J.B.L. Jones et al. / Advances in Space Research 36 (2005) 2258–2267 SOLSPA 2001, ESA-SP-477, ESA-ESTEC, Noordwiijk, The Netherlands, pp. 535–538, 2002. Dyer, C.S. Radiation Effects on Spacecraft and Aircraft, in: SawayaLacoste, H. (Ed.), Proceedings of the Second Solar Cycle and Space Weather Conference SOLSPA 2001, ESA-SP-477, ESA-ESTEC, Noordwiijk, The Netherlands, pp. 505–512, 2002. Dyer, C.S., Lei, F., Clucas, S.N., et al. Calculations and observations of solar particle enhancements to the radiation environment at aircraft altitudes. Adv. Space Res. 32, 81–93, 2003. Dyer, C.S., Truscott, P., Sanderson, C., et al. Cosmic radiation effects on avionics, an increasing hazard in the new millennium, in: Presented at 22nd International Congress on Aeronautical Sciences, Harrogate, UK, September 2000. Iles, R.H.A., Bentley, R.D., Jones, J.B.L., et al. The effect of solar particle events at aircraft altitudes, in: Presented at Looking

2267

Towards a Future European Space Weather Programme. ESAESTEC Space Weather Workshop, December 2001. Jones, J.B.L., Bentley, R.D., Iles, R.H.A., et al. The practical issues of utilising a European space weather programme for airline operations, in: Presented at Looking Towards a Future European Space Weather Programme, ESA-ESTEC Space Weather Workshop, December 2001. Taber, A., Normand, E. Single event upset in avionics. IEEE Trans. Nucl. Sci. 40 (2), 120–125, 1993. Taylor, G.C., Bentley, R.D., Jones, J.B.L., et al. The evaluation and comparison of available cosmic radiation predictive computer programs for assessing aircrew exposure by in-flight active measurement, in: Presented at 7th International Symposium, Natural Radiation Environment, Rhodes, Greece, 20–24th May 2002.