TECH LOG Shining a light on solar radiation The suns solar cycle not only affects the Earths climate, but as regular inhabitants of the stratosphere it influences a pilots work environment, too By Dr Robin Davies, Chairman BALPA ADO-AGE Study Group he weather has been somewhat quiet of late. Im not referring to tropospheric weather, but to solar weather. If you thought the two were mutually exclusive, you would be wrong. As of 1st December 2019, the highest number of consecutive days without any observable sunspots reached 25, making a total of 254 spotless days in the year to date (75%). As a result, and with a month to go, 2019 surpassed the 222 spotless days observed in 2018. It even looks set to eclipse 2008s total of 269 spotless days (73%), when the sun had just gone through its weakest solar cycle and, consequently, its deepest solar minimum of the past 100-plus years. So, what does this mean for us? As inhabitants of Earth, the suns solar cycle can have a huge effect on the climate we experience. Furthermore, as pilots and inhabitants of the stratosphere (at times), the solar cycle influences the environment in which we work not always to our advantage. Sunspots are an indication of the activity in the outer layers of the sun, typically the photosphere. Moreover, their number is proportional to the suns magnetic field strength. Each spot is an area of reduced surface temperature caused by concentrations of magnetic field flux that inhibit convection currents. So sunspots usually appear in pairs of opposite magnetic polarity. Their number varies according to the approximate 11-year solar cycle. Sunspots accompany secondary solar phenomena such as coronal loops, prominences, and reconnection events. Most solar flares and coronal mass ejections originate in magnetically active regions around visible sunspot groupings. Similar phenomena observed on stars other than the sun are aptly named starspots. Strong solar magnetic fields and activity in the sun are beneficial in a number of ways. First, a strong magnetic field creates a stronger solar wind. Second, it attracts interstellar cosmic rays/charged particles telltale remnants of past supernova events. So, a strong solar magnetic field and subsequent solar wind will prevent many of these harmful particles reaching the vicinity of the Earth. It also has a suppressing effect on the Earths volcanic activity. Conversely, at the low point of the solar cycle or solar minimum, with a weaker solar magnetic field, more of these harmful particles approach Earth. Then, its magnetic field takes over and they are attracted away from equatorial regions and concentrated around the poles. Here, the charged particles interact with the magnetosphere, producing the coloured dancing lights of aurora borealis and aurora australis at high northerly and southerly latitudes respectively. The charged particles are also known to promote the condensation of water vapour into clouds at lower altitudes. The last deep solar minimum occurred in 1815 and was called the Dalton minimum. The following year, 1816, was named the year without a summer; there was increased volcanic activity with two major eruptions. Global temperatures took a fall and precipitation increased. This led to floods, mass crop failures and food riots on the streets of western European capitals as a famine set in. Another deep solar minimum, the Maunder minimum, was a period of muchreduced sunspot activity observed between the years 1645 and 1715. It coincided with the coldest part of whats commonly called the little ice age in the northern hemisphere. Currently, we are experiencing a deep solar minimum, with increased rainfall and unusual weather events hitting the news daily. This also means that, if you regularly inhabit the stratosphere at high latitudes, you will be subjected to higher levels of cosmic rays/particles. How does the new generation of composite hull jetliners affect the crews radiation dose? Northern lights (aurora borealis) from an aeroplane Cosmic radiation is similar to X-ray and gamma radiation in terms of energy and speed, and because of this high energy and penetration ability, airlines monitor our general radiation-exposure levels. However, the calculations are based on outdated research data, so some of us could be exposed to higher radiation levels than the current model predicts. Concorde operated at around FL600 and research was carried out to measure the doses of cosmic radiation the crews were likely to receive at those higher altitudes. Although Concorde crossed the Atlantic at the edge of the stratosphere, it was only there for about three hours at a time. However, a great deal has changed since the 1970s. The new Boeing 787 was groundbreaking in many ways, with its large flight-deck windows, the use of carbon fibre throughout, and its longer range and endurance at higher altitudes and latitudes. These are all influential factors in the radiation levels experienced by flight crews inside the hull, and, the fact is, we dont know how they affect the levels. The radiation prediction outside the hull has gained fidelity over the years, but it is the dose rate inside the hull that has become more vague. Research undertaken for Concorde measured the doses received through the aluminium alloy, hiduminium-RR58 fuselage. Most airliners are alclad duralumin, but the B787 and A350 are carbon fibre, reinforced polymer composites. So, we now need to focus on bringing this transmission and exposure data up to date. The BALPA Aircraft Design and Operations/Aircraft Ground Environment (ADOAGE) study group, together with academic researchers and other interested bodies, are advancing new research in this area. The fundamental question is: how does the new generation of composite hull jetliners with their increased range and endurance, operating at higher altitudes and latitudes affect the radiation dose we receive as flight crews? We have many interested groups involved, with the possibility of more coming on board, and data gathering should start within the next month. Whatever the results, BALPAs technical groups and flight-safety department are determined to keep us flying in a safe and healthy environment. If you are an active pilot and interested in joining the ADO-AGE study group, where many similar subjects are addressed, please contact flightsafety@balpa.org