21-15 Table 21-1. Wind Speed and Characteristic House Damage for the Saffir-Simpson Hurricane Wind Scale Saffir-Simpson Hurricane Wind Scale Wind speed Characteristic House Damage 5 ≥157 mph ≥137 knots ≥252 km/h Almost complete destruction of all mobile homes will occur, regardless of age or construction A high percentage of frame homes will be destroyed, with total roof failure and wall collapse.
Extensive damage to roof covers, windows, and doors will occur.
Large amounts of windborne debris will be lofted into the air.
Windborne debris damage will occur to nearly all unprotected windows and many protected windows.
4 130-156 mph 113-136 knots 209-251 km/h Nearly all older (pre-1994) mobile homes will be destroyed. A high percentage of newer mobile homes also will be destroyed. Poorly constructed frame homes can sustain complete collapse of all walls as well as the loss of the roof structure. Well-built homes also can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Extensive damage to roof coverings, windows, and doors will occur. Large amounts of windborne debris will be lofted into the air. Windborne debris damage will break most unprotected windows and penetrate some protected windows.
3 111-129 mph 96-112 knots 178-208 km/h Nearly all older (pre-1994) mobile homes will be destroyed. Most newer mobile homes will sustain severe damage with potential for complete roof failure and wall collapse. Poorly constructed frame homes can be destroyed by the removal of the roof and exterior walls. Unprotected windows will be broken by flying debris.
Well-built frame homes can experience major damage involving the removal of roof decking and gable ends.
2 96-110 mph 83-95 knots 154-177 km/h Older (mainly pre-1994 construction) mobile homes have a very high chance of being destroyed, and the flying debris generated can shred nearby mobile homes. Newer mobile homes can also be destroyed. Poorly constructed frame homes have a high chance of having their roof structures removed, especially if they are not anchored properly. Unprotected windows will have a high probability of being broken by flying debris. Well-constructed frame homes could sustain major roof and siding damage. Failure of aluminum, screened-in, swimming pool enclosures will be common.
1 74-95 mph 64-82 knots 119-153 km/h Older (mainly pre-1994 construction) mobile homes could be destroyed, especially if they are not anchored properly as they tend to shift or roll off their foundations. Newer mobile homes that are anchored properly can sustain damage involving the removal of shingle or metal roof coverings, and loss of vinyl siding, as well as damage to carports, sunrooms, or lanais. Some poorly constructed frame homes can experience major damage, involving loss of the roof covering and damage to gable ends, as well as the removal of porch coverings and awnings. Unprotected windows may break if struck by flying debris. Masonry chimneys can be toppled. Well- -constructed frame homes could have damage to roof shingles, vinyl siding, soffit panels, and gutters. Failure of aluminum, screened-in, swimming pool enclosures can occur.
22-1 CHAPTER 22. ARCTIC WEATHER
22.1 Introduction. Strictly speaking, the Arctic is the region shown below in Figure 22-1, which lies within the Arctic Circle (66.5° N latitude). However, it is loosely defined as the northern regions, in general. This chapter includes Alaskan weather, even though much of Alaska lies south of the Arctic Circle.
As an introduction to Arctic weather, this chapter surveys climate, air masses, and fronts of the Arctic, introduces you to some Arctic weather peculiarities, and discusses weather hazards in the Arctic.
Figure 22-1. The Arctic Circle
22.2 Climate, Air Masses, and Fronts. There are a number of factors that influence Arctic climate. Climate of any region, especially in the Arctic, is largely determined by the amount of energy received from the sun; however, local characteristics of the area, such as mountains and ice cover, also influence climate.
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22.2.1 Long Days and Nights. A profound seasonal change in length of day and night occurs in the Arctic because of the Earth’s tilt and its revolution around the sun. Any point north of the Arctic Circle has fall and winter days when the sun stays below the horizon all day and has spring and summer days with 24 hours of sunshine when the sun stays above the horizon. The number of these days increases toward the North Pole; there the sun stays below the horizon for 6 months and shines continuously during the other 6 months.
Twilight in the Arctic is prolonged because of the shallow angle of the sun below the horizon. In more northern latitudes, it persists for days when the sun remains just below the horizon. This abundance of twilight often makes visual reference possible at night.
22.2.2 Land and Water. Figure 22-1 shows the water and the land distribution in the Arctic.
Arctic mountain ranges are effective barriers to air movement. Large masses of air stagnate over inland continental areas; thus, Arctic continental areas are air mass source regions.
A large portion of the Arctic Ocean is covered throughout the year by a deep layer of ice, known as the permanent ice pack. This ice pack goes through a seasonal cycle where ice melts in the spring and summer and increases in the fall and winter. Even though a large portion of the Arctic Ocean is ice-covered through much of the year, the ice and the water below contain more heat than the surrounding cold land, thus moderating the climate.
Oceanic and coastal areas have a milder climate during winter and a cool climate in summer. As opposed to large water bodies, large land areas show a more significant seasonal temperature variation.
22.2.3 Temperature. As one would expect, the Arctic is very cold in winter, but due to local terrain and the movement of pressure systems, occasionally some areas are surprisingly warm. During winter, coastal areas are warmer than the interior. During summer, interior areas are pleasantly warm due to many hours of sunshine, while coastal areas have relatively short, cool summers due to their proximity to water.
22.2.4 Clouds and Precipitation. Cloudiness over the Arctic is at a minimum during winter due to the ice pack being more widespread. Spring brings many cloudy days, with cloudiness reaching a maximum in summer and fall when a portion of the sea ice melts and exposes additional water in the Arctic Ocean.
During summer afternoons, scattered cumulus clouds forming over the interior occasionally grow into thundershowers. These thundershowers move generally from northeast to southwest in the polar easterlies, which is opposite the general movement in the mid-latitudes.
During the winter, polar lows can form over the open ocean. Polar lows are small, intense low-pressure systems that can develop rapidly when cold air flows over warm water.
They produce severe weather, strong surface winds, and heavy precipitation. Polar lows dissipate quickly once they move over land.
Precipitation in the Arctic can vary drastically per region, but is generally light. Some areas are known as polar deserts. In winter, the only precipitation received in the Arctic
22-3 is snow, while in summer precipitation falls mostly in the form of snow over ice caps and oceanic areas and rain over interior areas. Annual amounts of precipitation over the ice pack and along the coastal areas tend to be less than the interior areas.
22.2.5 Wind. Typically, Arctic winds are light. Strong winds occur more often along the coastal areas in fall and winter. Wind speeds are generally light in the continental interior throughout the entire year, but are normally at their strongest during summer and fall.
22.2.6 Air Masses—Winter. In winter, air masses form over the expanded ice pack and adjoining snow-covered land areas. These air masses are characterized by very cold surface air, very low humidity, and strong low-level temperature inversions.
Occasionally, air from unfrozen ocean areas flows northward over the Arctic. These intrusions of moist, cold air account for most of the infrequent wintertime cloudiness and precipitation in the Arctic.
22.2.7 Air Masses—Summer. During the summer, the top layer of the Arctic permafrost layer melts, leaving very moist ground, and the open water areas of the Polar Basin increase markedly. Thus, the entire area becomes more humid, relatively mild, and semi-maritime in character. The largest amounts of cloudiness and precipitation occur inland during the summer months.
22.2.8 Fronts. Occluded fronts are the rule. Weather conditions with occluded fronts are much the same in the Arctic as elsewhere: low clouds, precipitation, poor visibility, and sudden fog formation. Fronts are much more frequent over coastal areas than over the interior.
22.3 Arctic Peculiarities. Several Arctic phenomena are peculiar to the region.
22.3.1 Effects of Temperature Inversion. The Arctic experiences frequent low-level temperature inversions, which occur when temperature increases with height (i.e., cold air settled near the ground with warm air directly above). Inversions can slow down surface winds and trap pollutants, creating smoggy and hazy conditions that persist until the inversion ends.
In addition, light rays are bent as they pass at low angles through the inversion, creating an effect known as looming, which is a form of mirage that causes objects beyond the horizon to appear above the horizon. These low-level inversion mirages distort the shape of the sun, moon, and other objects.
22.3.2 Light Reflection by Snow-Covered Surfaces. Much more light is reflected by snow-covered surfaces than by darker surfaces. Snow often reflects Arctic sunlight sufficiently to blot out shadows, thus decreasing the contrast between objects. Dark, distant mountains may be easily recognized, but a crevasse normally directly in view may be undetected due to lack of contrasts.
22.3.3 Light from Celestial Bodies. Illumination from the moon and stars is much more intense in the Arctic than in lower latitudes. Even illumination from the stars creates visibility far beyond that found elsewhere. Only under heavy overcast skies does the night darkness in the Arctic begin to approach the degree of darkness in lower latitudes.
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22.4 Weather Hazards. Weather hazards include visibility restricting phenomena, blowing snow, icing, frost, and lack of contrast (whiteout).
22.4.1 Fog and Ice Fog. Fog occurs when water droplets or ice particles are suspended in the air at the Earth’s surface. Water-droplet fog occurs in coastal areas during the summer.
Ice fog (also called ice-crystal fog, frozen fog, frost fog, frost flakes, air hoar, rime fog, and pogonip) is a type of fog formed by direct freezing of supercooled water droplets.
Ice fog is composed of suspended particles of ice, partly ice crystals 20-100 micron in diameter, but chiefly (especially when dense) ice particles about 12-20 micron in diameter. It occurs at very low temperatures, and usually in clear, calm weather in high latitudes. The sun may cause the appearance of a halo. Effective visibility is reduced considerably more when looking toward the sun. Ice fog is rare at temperatures warmer than -30 °C, and increases in frequency with decreasing temperature until it is almost always present at air temperatures of -45 °C in the vicinity of a source of water vapor.
Such sources of water vapor are the open water of fast-flowing streams or of the sea, herds of animals, volcanoes, and especially products of combustion for heating, automobiles, and aircraft. At temperatures warmer than -30 °C, these sources can cause steam fog of liquid water droplets, which may turn into ice fog when cooled.
22.4.2 Blowing and Drifting Snow. Over the frozen Arctic Ocean and along the coastal areas, blowing snow, drifting snow, and strong winds are common hazards during fall and winter. Blowing snow is wind-driven falling or accumulated snow that reduces surface visibility. Drifting snow is an uneven distribution of snowfall or snow depth caused by strong surface winds, which may occur during or after a snowfall. Drifting snow is usually associated with blowing snow. In the Arctic, because the snow is dry and fine, it can be picked up easily by light winds that raise the snow several feet off the ground, obliterating objects. A sudden increase in surface wind may cause an unlimited visibility to drop to near zero in a few minutes. This sudden loss of visibility occurs frequently without warning in the Arctic.
22.4.3 Frost. Frost is the formation of thin ice crystals on the ground or other surfaces on solid objects below the freezing point of water. It develops in Arctic coastal areas during spring, fall, and winter.
22.4.4 Whiteout. Whiteout is a visibility-restricting phenomenon that occurs most often in the spring and fall in the Arctic when the sun is near the horizon. It occurs when a layer of overcast clouds overlies a snow- or ice-covered surface. Parallel rays of the sun are broken up and diffused when passing through the cloud layer so that they strike the snow surface from many angles. The diffused light then reflects back and forth countless times between the snow and the cloud, eliminating all shadows. The result is a loss of depth perception. Buildings, people, and dark-colored objects appear to float in the air, and the horizon disappears.
23-1 CHAPTER 23. SPACE WEATHER
23.1 The Sun—Prime Source of Space Weather. The sun is the dominant source of the conditions commonly described as space weather. The term space weather is used to designate processes occurring on the sun and in Earth’s magnetosphere, ionosphere, and thermosphere, which have the potential to affect the near-Earth environment.
Emissions from the sun are both continuous (e.g., solar luminescence and solar wind) and eruptive (e.g., coronal mass ejections (CME) and flares). These solar eruptions may cause radio blackouts, magnetic storms, ionospheric storms, and radiation storms at Earth.
Similar to the charged particles that come from the sun, Galactic Cosmic Rays (GCR) are charged particles that originate in more distant supernovae and contribute to the space weather conditions near Earth. Essentially, these charged particles comprise a steady drizzle of radiation at Earth.
The sum of the solar and nonsolar components equal the full extent of the potential radiation dose received. The size of the GCR flux varies inversely with the sunspot cycle (sunspots are described in later paragraphs); that is, during sunspot minimums when the interplanetary environment near Earth is laminar and steady, the GCR component is large due to its easier access to the near-Earth environment. At sunspot maximum, the turbulence and energetics associated with solar eruptions reduce GCR access to the vicinity of the Earth.
23.2 The Sun’s Energy Output and Variability. The sun is a variable star. That means the balance between the continuous emissions and the eruptive emissions changes with time.
One metric that is commonly used to track this variability is the occurrence of sunspots.
Astronomers have made sunspot observations continuously for hundreds, maybe even thousands, of years. Though the underlying physics is still not well understood, on average sunspots come and go in an 11-year period. The magnitude and duration of individual cycles varies, but typically more eruptive events occur near the solar maximum, while few are observed near solar minimum. All solar electromagnetic emissions, from radio to x rays, are also stronger during solar maximum and less intense near solar minimum.
23.3 Sunspots and the Solar Cycle. Because space weather activity varies with sunspot activity, they are often used as a proxy index for changing space weather conditions. This is because sunspots, by their very nature, exist due to strong local magnetic fields. When these fields erupt, severe space weather can occur. While sunspots are easily seen, other events such as GCR, CMEs, and increased solar wind are more difficult to observe from the ground and may not be related to long historical records of sunspots.
23.4 Solar Wind. The solar wind is the continuous flow away from the sun of charged particles and magnetic field, called plasma. Solar wind is a consequence of the very high temperature of the solar corona and the resultant expansion of the plasma into space.
23-2 The solar wind carries the energy from most solar eruptions that affect the near-Earth environment. The sole exception, solar flare photons consisting of light and x rays, carry the energy released in solar flares. Even in the absence of an eruption, the constant flow of plasma fuels Earth’s geomagnetic field. The solar wind may be fast and energetic if an eruption occurs, or can gradually increase due to a coronal-hole structure which allows unimpeded high-speed solar wind to escape from the corona. As seen from the Earth, the sun rotates on approximately a 27-day period, so well-established coronal-hole structures that persist for several months will swing by Earth on schedule, roughly every 27 days.
23.5 Solar Eruptive Activity. Most solar eruptions originate in areas that have strong magnetic fields. Usually marked with sunspots, these areas are commonly called active regions. Active regions are numerous and common during solar maximum and scarce during solar minimum.
Flares and CMEs are the two major types of solar eruptions. They may occur independently or at the same time. Solar flares have been recognized for more than 100 years, as they can be seen from the ground. In the past 50 years, Hydrogen-Alpha
(656.3 nanometer wavelength) filter-equipped ground-based telescopes have been used to observe flares.
Flares are characterized by a very bright flash phase which may last for a few minutes to a few hours during the largest flares. Flares can emit at all frequencies across the electromagnetic emission spectrum, from gamma rays to radio.
CMEs, in contrast to solar flares, are difficult to detect, not particularly bright, and may take hours to fully erupt from the sun. CMEs literally are an eruption of a large volume of the solar outer atmosphere, the corona. Prior to the satellite era, they were very difficult to observe. The energy released in a large solar flare is on par with that released in a CME, however CMEs are far more effective in perturbing Earth’s magnetic field and are known to cause the strongest magnetic storms. A typical travel time for a CME from the sun to Earth may range from less than 1 day to more than 4 days. The travel time of the electromagnetic emission produced during flares, by comparison, is at the speed of light. They instantaneously affect the dayside of Earth upon observation.
The frequency of solar flares and CMEs tracks with the solar cycle. As many as 25 solar flares may occur per day during the maximum phase of the solar cycle. At solar minimum, it may take 6 months or more for 25 flares to occur. CME frequency varies from about 5 per day near solar maximum to one per week or longer at solar minimum.
Many CMEs observed lifting off the sun are not Earth-directed.
23.6 Geospace. Geospace is the volume of space that surrounds Earth, influenced by the Earth’s magnetic field in the solar wind. If Earth did not have a magnetic field, the solar wind would blow past unimpeded, affected only by the mass of Earth and its atmosphere.
Earth’s magnetic field extends outward in all directions. This forms a cocoon for the planet, protecting it from the flow of the solar wind. The cocoon is called the
23-3 magnetosphere. The magnetosphere typically extends towards the sun about 10 Earth radii on the dayside and stretches away from the sun many times more on the night side.
The shape is similar to a comet tail with it being extended during strong solar wind conditions and less so during more quiet times. On its flanks, the magnetosphere extends outward roughly 20 Earth radii in the dawn and dusk sectors.
The magnetosphere deflects most of the energy carried by the solar wind, while making a fraction of it available to be absorbed by the near-Earth system. When the sun is active and CMEs interact with Earth, the additional energy disrupts the magnetosphere, resulting in a magnetic storm. Then, over time, the magnetosphere adjusts through various processes and once more returns to normal.
The most visible manifestation of the energy being absorbed from the solar wind into the magnetosphere is the aurora, both in the Northern and Southern Hemispheres. The aurora occurs when accelerated electrons from the sun follow the magnetic field of Earth down to the polar regions, where they collide with oxygen and nitrogen atoms and molecules in Earth’s upper atmosphere. In these collisions, the electrons transfer their energy to the atmosphere, thus exciting the atoms and molecules to higher energy states. When they relax to lower energy states, they release their energy in the form of light. Simply put, the more energy in the solar wind, the brighter and more widespread the aurora glow becomes.
Nearer to Earth is another region called the ionosphere. It is a shell of weak plasma, where electrons and ions exist embedded in the neutral atmosphere. The ionosphere begins at roughly 80 kilometers in altitude and extends out many Earth radii, at the topside.
Extreme Ultraviolet (EUV) solar emissions create the ionosphere by ionizing the neutral atmosphere. The electrons and ions created by this process then engage in chemical reactions that progress faster in the lower ionosphere. The ionosphere changes significantly from day to night. When the sun sets, chemical processes, together with other dynamic processes, allow some of the ionization to remain until the new day brings the solar EUV once again. An important point is that the energy that comes from the sun in the solar wind makes its way to the ionosphere, where it alters the ambient conditions during space weather storms.
23.7 Galactic Cosmic Radiation. Galactic Cosmic Radiation, more commonly known as Galactic Cosmic Rays (GCR), are a consequence of distant supernovae raining charged particles, heavy ions, protons, and electrons onto the inner heliosphere.
The abundance of GCR is inversely rated to the solar cycle. At solar maximum, when the solar wind flow is turbulent and strong, the GCR flux is inhibited and therefore low.
At solar minimum, the GCR flux increases by about 30 percent in the near-Earth environment. When high-energy GCR enter Earth’s atmosphere, it creates a cascade of interactions resulting in a range of secondary particles, including neutrons that make their way to Earth’s surface.
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23.8 Geomagnetic Storms. Geomagnetic storms are strong disturbances to Earth’s magnetic field in the solar wind. These storms pose problems for many activities, technological systems, and critical infrastructure. The topology of Earth’s magnetic field changes in the course of a storm, as the near-Earth system attempts to adjust to the jolt of energy from the sun. CMEs and the shocks they drive are often the causative agent, and can send the geomagnetic field into a disturbed state.
The most obvious, and probably the only pleasing, attribute of an energized geomagnetic field are the auroras. Geomagnetic storms tend to brighten auroras and allow them to move equatorward.
The duration of geomagnetic storms is usually on the order of days. The strongest storms may persist for almost 1 week. A string of CMEs may cause prolonged disturbed periods related to the additional energy being pumped toward the Earth.
Although the frequency of geomagnetic storms reflects the solar cycle, a closer look shows a bimodal distribution. Large numbers of storms cluster at solar maximum resulting from frequent CMEs, and again in the declining phase due to high-speed solar wind streams. Typically, the most intense storms occur near solar maximum, with weaker storms occurring during the declining phase.
23.9 Solar Radiation Storms. Solar radiation storms occur when large quantities of charged particles, primarily protons, are accelerated by processes at or near the sun, then bathe the near-Earth environment with these charged particles. These particles cause an increase in the radiation dose to humans, and increase the possibility of single-event upsets in electronics. Earth’s magnetic field and atmosphere offer some protection from this radiation, but protection decreases with altitude, latitude, magnetic field strength, and direction. The polar regions on Earth are most open to these charged particles.
The magnetic field lines at the poles extend vertically downwards, intersecting Earth’s surface. This allow the particles to spiral down the field lines and penetrate into the atmosphere and increase the ionization.
A significant factor related to the criticality of the radiation increase at Earth is the energy distribution of the solar protons. Protons of varying energies will bathe Earth as a function of the site of the eruption at the sun and the magnetic connection between the sun and Earth. High-energy protons cause radiation dose increases that are of concern to human beings. Lower energy protons have little effect on humans, but have a severe impact on the polar ionosphere.
The duration of solar radiation storms is a function of the magnitude of the solar eruption as well as the energy level of protons. For events that are of a large magnitude but low energy, the duration may last for 1 week. Events that are of high energy may last for only a few hours. There is a great diversity in the duration of solar radiation storms, as there are many factors that contribute to the acceleration and propagation of the charged particles near Earth.
23-5 Solar radiation storms can occur at any point in the solar cycle, but tend to be most common during the years around solar maximum.
23.10 Ionospheric Storms. Ionospheric storms arise from large influxes of solar particle and electromagnetic radiation. There is a strong coupling between the ionosphere and the magnetosphere, which means both regimes can be disturbed concurrently.
The symptoms of an ionospheric storm include enhanced currents, turbulence and wave activity, and a nonhomogeneous distribution of free electrons. This clustering of electrons, which leads to scintillation of signals passing through the cluster, is particularly problematic for the Global Navigation Satellite System (GNSS).
The duration of the ionospheric storm impact may range from a few minutes to days-long prolonged events. As a general rule, these ionospheric storms mimic the duration of geomagnetic storms.
The intensity of ionospheric storms varies significantly as a function of local time, season, and time within the solar cycle.
The frequency of occurrence of ionospheric storms is also similar to geomagnetic storms with one important caveat. The near-equatorial ionosphere, a band extending approximately ± 10° in latitude on either side of the magnetic equator, can be very disturbed in the post-sunset to near-midnight hours, even in the absence of a geomagnetic storm. This behavior is related to the internal electrodynamics of the ionosphere rather than external stimulation from the sun. The disturbance is very difficult to predict and is best described by the climatological statistics for that region.
23.11 Solar Flare Radio Blackouts. Radio blackouts primarily affect high frequency (HF) (3-30 megahertz (MHz)), although detrimental effects may spill over to very high frequency (VHF) (30-300 MHz) and beyond, resulting in fading and diminished ability for reception. The blackouts are a consequence of enhanced electron densities caused by the emissions from solar flares that ionize the sunlit side of Earth.
The process consists of x ray and EUV bursts from a solar flare, increasing the number of free electrons in the atmosphere below 90 kilometers, which in turn increases their interaction with the neutral atmosphere that increases the amount of radio energy lost as radio waves pass through this region. During a large flare event, the amount of radio energy lost is sufficient to make the return signal from the ionosphere too small to be useful with normal radio receivers. The net effect of this process is a blackout for HF transmissions.
The duration of dayside solar flare radio blackouts closely follows the duration of the solar flares that cause them beginning with the arrival of the x ray and EUV photons, and abate with their diminution. Usually, the radio blackouts last for several minutes, but they can last for hours.
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23.12 Effects of Space Weather on Aircraft Operations.
23.12.1 Communications. HF communications at low- to mid-latitudes are used by aircraft during transoceanic flights and routes where line-of-sight VHF communication is not an option. HF enables a skip mode to send a signal around the curvature of Earth.
HF communications on the dayside can be adversely affected when a solar flare occurs and its photons rapidly alter the electron density of the lower altitudes of the ionosphere, causing fading, noise, or a total blackout. Usually these disruptions are short-lived (tens of minutes to a few hours), so the outage ends fairly quickly.
HF communications at high latitudes and polar regions are adversely affected for longer periods, sometimes days, due to some space weather events. The high latitude and polar ionosphere is a sink for charged particles, which alter the local ionization and provide steep local ionization gradients to deflect HF radio waves, as well as increase local absorption.
Satellite communication signals pass through the bulk of the ionosphere and are a popular means of communicating over a wide area. The frequencies normally used for satellite communications are high enough for the ionosphere to appear transparent.
However, when the ionosphere is turbulent and nonhomogeneous, an effect called scintillation, a twinkling in both amplitude and phase, is imposed upon the transmitted signal. Scintillations can result in loss-of-lock and inability for the receiver to track a Doppler-shifted radio wave.
23.12.2 Navigation and Global Positioning System (GPS). Space weather adversely affects GPS in three ways: it increases the error of the computed position, it causes a loss-of-lock for receivers, and it overwhelms the transmitted signal with solar radio noise.
23.12.3 Radiation Exposure to Flightcrews and Passengers. Solar radiation storms occurring under particular circumstances cause an increase in radiation dose to flightcrews and passengers. As high polar latitudes and high altitudes have the least shielding from the particles, the threat is the greatest for higher altitude polar flights. The increased dose is much less of an issue for low- and mid-latitude flights.
23.12.4 Radiation Effects on Avionics. The electronic components of aircraft avionic systems are susceptible to damage from the highly ionizing interactions of cosmic rays, solar particles, and the secondary particles generated in the atmosphere. As these components become increasingly smaller, and therefore more susceptible, the risk of damage also increases.
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