The mere mention of the word, "aurora" brings to mind mysterious and spectacular images, and thousands of people travel to the Arctic and Antarctic regions each year to see it with their own eyes. Lighting up the sky at altitudes over 100km from the Earth, the aurora fascinates us with its fantastic beauty. Nikon products play a vital role in researching this incredible phenomenon by helping determine changes in the upper atmosphere, of which little is known.
We asked Makoto Taguchi, Associate Professor at the National Institute of Polar Research (NIPR) to talk about his work in upper atmosphere research.
NIPR was established in 1973 as one of the Inter-University Research Institutes for researchers belonging to universities and other research institutions. It oversees observation, scientific studies and education concerned with the polar regions. There are a total of five research groups at the institute, and I belong to the group concerned with upper atmosphere physics research. We mainly study physics in the upper atmosphere, the ionosphere and the magnetosphere of the earth. At present, I am studying the dynamics of the upper atmosphere, especially wind and temperature changes that happen when aurora appears.
The atmosphere of the earth can be divided roughly into four layers: from the ground to about 10km above the lowest layer is called the troposphere, from there to about 50km is the stratosphere, from there to about 80km is the mesosphere and above that is the thermosphere. The upper atmosphere includes both the mesosphere and the thermosphere. Since part of the thermosphere is ionized (i.e. atoms and molecules split into ions and electrons), it is also called the ionosphere. Above this is the very thin atmosphere connected to outer space. Outside the atmosphere, you find the earth's magnetic field. The area under the force of the magnetic field is called the earth's magnetosphere. This reaches distances of over 60,000km, or 10 to 30 times of the earth's radius (6,378km).
The aurora appears mainly in the upper atmosphere, about 100 to 500km above the ground, centering around the auroral zone (from approximately 60 to 70 degrees in latitude) of the earth's two poles. As you know, the aurora constantly changes its shape and color. Upper atmosphere studies hope to clarify exactly how the atmosphere in the upper sky moves, what energy is produced when the aurora appears and where that energy goes.
In the magnetosphere of the earth, on opposite side from the sun, there is a region called the plasma sheet where large quantities of hot plasma (electrons and protons) are gathered. When magnetic force pulls these electrons and protons to the earth, they enter the atmosphere and hit molecules of oxygen and nitrogen. The energy generated by this collision is emitted as light. This phenomenon creates the aurora, which appears at both the north and south polar regions. You may think this happens only in the winter, but auroras -- including dark ones -- occur all the time. Because there are extended periods of daylight (called midnight sun) at the poles, the aurora is not visible during the summer.
That's right. The changes in the aurora's color are caused by the different atoms and molecules that emit light. The color seen most frequently is green, although it appears whitish to the naked eye. The green color emitted is caused by oxygen atoms. Other colors such as red and pink are caused by oxygen atoms and nitrogen molecules, respectively. During observation, we can see the aurora changing dynamically. It brightens rapidly or flickers violently, its beauty spectacular. This phenomenon is called an auroral substorm. It happens when the solar wind (streams of plasma from the sun) shakes the magnetosphere and makes electrons and protons in the plasma sheet fall to the earth in larger quantities than usual.
At present, observation is conducted mainly by remote sensing methods using optical instruments and radar. By using a rocket, it has become possible to directly measure the variety of atoms, quantity of electrons and status of the electromagnetic field existing on a flight course. However, the launch costs are quite high and observation is possible only for the short time period during a flight. With optical instruments and radar, regular and long-term observations of large areas are possible. Most of my observations are conducted with optical instruments. By measuring the light from the upper sky with an optical instrument called an All-Sky Camera (ASC), I can photograph the entire sky in one 180° image and observe what is occurring. I use an instrument called a Fabry-Perot Imager (FPI) to carefully analyze every minute detail in the data. By observing light interference found in the data, I can determine the wind speed and temperature of atmosphere up to about 300km above the earth.
Observation of the aurora at Syowa Station in Antarctica began in the 1950s. In the beginning, film was used and long exposure times were required due to the film's low sensitivity. Since 1997, however, observation has been conducted with the highly sensitive CCD of the ASC. It can take pictures of fast-moving aurora without shaking as it selects light with specific wavelengths. And it captures these images with exposures within 2 seconds.
Mainly at the Antarctic and Arctic regions, just as the name of the institute indicates. In the Antarctic, over 20 countries including Japan have more than 30 observation stations, but only a small portion of them conduct observations of aurora. NIPR has observation instruments at the South Pole station, in Norway and in Ireland, with Syowa Station utilizing more equipment than any other facility. About 40 people stay throughout the winter at Syowa Station every year to conduct various scientific observations. At present, there are two members in charge of observation related to the upper atmosphere. Enormous amounts of data obtained by our observations are sent to Japan and analyzed daily.
Yes. At present, we use mainly three observation instruments: the ASC, the ASI (All-Sky Imager) and the FPI. All of our lenses are made by Nikon. We have asked other makers to produce observation instruments for us before, but the light quantity and resolution in the peripheral view field decreased dramatically. At that time, we found a Nikon lens that was used for the previous ASC kept in a storehouse. It was a very fast 6mm f/1.4 lens with a 180° field of view. Although it had been in storage for a long time, it had a perfect optical performance. To re-utilize this lens for the new ASI, we decided to consult with its manufacturer, Nikon and
Nikon Engineering (in Japanese language only). As a result, the first camera is now being used at the South Pole station. After that, three ASIs of the same type were produced, and are in use in both the Arctic and Antarctic, as well as an equatorial area. At present, newly-innovated ASCs are being produced. They are planned to be sent to Syowa Station and to Iceland to observe the aurora at both poles at the same time.
I went to Syowa Station as a member of the 42nd Antarctic wintering party. This year, the 45th party is wintering. Each wintering party leaves Japan in November, conducts observations for about a year and a half and returns home two years later around the end of March. I have also been to the South Pole station twice. It was a short stay -- about a week during the summer for maintenance and gathering data from the ASI we have there.
Ever since childhood, I have loved nature. I was especially interested in stars and other heavenly bodies. While at university, I did a special geophysics study which included research on earthquakes, the atmosphere and the ocean. Out of those three, I took special interest in the physics of the upper atmosphere. I think that was the start. This was also just after one of my professors at the time had just returned to Japan after leading one of the Antarctic wintering parties. I may have been influenced by that, as well.
As long as you stay inside the Syowa Station, it is quite comfortable and not as severe as you might think. Hokkaido's cold climate may be rather severe. However, at the inland Dome Fuji Station, the average temperature is -35°C in the summer and about -65°C in the winter. This is because it is located on the top of an ice sheet with an altitude of over 3,800m. It is a very severe environment with 60% air density compared with that of the surface of the sea. If I step out of the station, the barren landscape is very beautiful. I often took pictures, and not only of the aurora but also of the glowing skies of the morning and evening. These views were stunning. There are certain clouds that only appear in the stratosphere around the polar regions, called
Polar Stratospheric Clouds (PSCs) (in Japanese language only). These clouds shine with a reddish-violet light after the sun sets over the horizon. The views I had there made a strong impression on me.
No. Until recently, the Antarctic observation vessel Shirase carried with it an enormous amount of data every time it returned to Japan. But Shirase comes home only once a year -- at the beginning of April. Starting this year, however, by using the Intelsat satellite, Syowa Station and the institute are connected all the time. It will soon be possible to take data from hundreds of aurora images captured every night and send it to Japan the very next day.
We are still gathering data, since it has only been a few years since the start of regular observation, but some positive results have already been obtained. For example, by analyzing minute details in the auroral light, the temperature and wind speed at the aurora's altitude can be estimated. Although most changes in temperature are caused by the changes of altitude, unexplained phenomena have been found. I believe that the atmosphere is regionally heated by some sort of energy that accompanies the auroral activity and causes the temperature to rise. In this way, we are speculating on these phenomena from the measurement data. We hope that as we accumulate further data, things will be become clearer.
Direct relationships between the atmosphere near the surface of the earth and that of the upper atmosphere are not clear, since they are so far apart. However, I believe that there is some sort of connection. There are possibilities that the amount of water vapor that flows from the troposphere into the upper layer of the atmosphere has changed due to global warming, or it could be possible that nitrogen oxide produced by the auroral activity influences the composition of the lower layers of atmosphere. There is also a wave phenomenon in which a density change in the lower layer of atmosphere propagates to the upper atmosphere as a wave. It has also been observed that waves in the atmosphere that were thought to originate in the polar regions where the aurora appears travel to Japan's upper sky like tsunami (seismic sea waves). In that sense, various phenomena in the earth's atmosphere have influence in every direction.
There are many possible results. It will soon be possible to estimate the orbit and life span of satellites more accurately. Some satellites inhabit the thin atmosphere under the thermosphere. Temperature and density changes found here influence the satellite's air resistance. If the changes in the thermosphere are known, the orbit and life span of a satellite can be estimated more accurately.
A better example may simply be aurora tourism. A more accurate auroral forecast -- one that tells when and where the aurora can be seen -- may be possible in the near future. This way, there will be less cases of people being disappointed because they hardly see the aurora after paying large traveling expenses to view it.
Presently, there is a new movement to construct a network of observation instruments, including an ASC, for atmospheric observation on a global scale. Since the more data we have, the more useful it is for research, I hope this plan will be realized as soon as possible. Moreover, there is also a plan in progress to observe the upper atmosphere and plasma around the earth -- not only from the ground, but also by utilizing satellites. With so much happening at once, results from our research should be just around the corner. Look forward to it.
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