1-3. The facts revealed from the observed data
1-3-1. The long term variation of CO
2
The figure shows the observation results of CO2 concentration. This figure shows the data for each latitude band, such as 25゜-30゜N on the top, and then 20゜-25゜N and so on. The solid line shows the observed data and the dotted line shows the long term trends obtained from the observation.
As shown in the figure, the long term trends of CO2 concentration continues to increase at the same rate in all latitude bands.
The primary factor for this increase is the consumption of fossil fuel
such as coal, petroleum, and natural gas.
Furthermore, the annual increasing rate of CO2 concentration obtained from the observation is very close to the rate obtained from land-based and ship-based observatories over the world. This implies that the fluctuation of CO2 concentration near the surface is conveyed to the altitude of at least 10 km.
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1-3-2.
Short term variation of CO2 concentration in the Northern Hemisphere (Seasonal Fluctuation)
In the northern hemisphere, there is a cyclic change of CO2 concentration every year. This is primarily caused by vegetation. From spring to autumn, CO2 concentration is reduced. This is due to the photosynthesis of green plants,
which absorbs CO2. From winter to spring, CO2 concentration increases due to CO2 emitted by fermentation of fallen leaves and by CO2 emitted by the respiration
of plants.
This fact also implies that the change of CO2 concentration near the surface of the earth is conveyed to an altitude
of at least 10 km.
As shown in the figure, there are notable seasonal changes of CO2 at the mid latitude area due to green plant activity. Accordingly, there
should not be any notable seasonal changes at the low latitude area because
of unclear seasons in this area. The observed dada, however, does not support
this presumption, because seasonal change at the middle latitude propagates
to the lower latitude area by the wind circulation in the upper air.
The reason why the seasonal change caused by photosynthesis of plants at the middle latitude area can propagate to the lower latitude area is because of the inherent characteristics of CO2, i.e. the CO2 does not react with other gases easily during their long travel toward
the equator from the middle latitude.
Therefore, “CO2 generated by consumption of fossil fuel” primarily in the middle and high latitudes will have an impact on the whole area of the earth. This long term trend is shown in the figure by dotted lines which have very similar increasing rates of CO2 concentration regardless of latitude.
1-3-3. Variation of CO
2 concentration in the Southern Hemisphere
A close look at the figure shown in the previous section reveals that the
behavior of seasonal changes of the CO2 concentration in the southern hemisphere are very complicated and are quite different from that in the northern hemisphere. The graph shows the average seasonal change at each latitude band. This data has been collected over 10 years for the purpose of understanding why CO2 concentration is different in the southern and northern hemispheres.
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From these figures, it is possible to conclude as follows;
1). A decrease in CO2 concentration around March, is caused by the CO2 absorption by the green plant due to photosynthesis, and the peak of CO2 concentration around November, is caused by plant's respiration and by
the CO2 released from fallen leaf. The southern hemisphere, however, is covered
by a relatively small land area, and the influence of green plants on the
upper atmosphere is insignificant. Thus, the seasonal change of CO2 concentration in the upper atmosphere is very small.
2). Another peak of CO2 concentration around June and July seems to be an extension of the peak
of the northern hemisphere around May. In addition to this finding, another
decrease in CO2 concentration around September and October seems to be an extension of
the decrease in the northern hemisphere around September and October.
3). This implies that seasonal change of CO2 concentration in the upper atmosphere of the southern hemisphere is significantly
affected by the seasonal change in the northern hemisphere. Also, it seems
that the direction of propagation to the south hemisphere around June and
July, (i.e., the peak of CO2 concentration), is north to south, but the direction around September
and October, (i.e., the decrease in CO2 concentration), seems to be south to north.
4). If this direction of the transportation is correct, there must be two
separate flows for the propagation. One is “a route through the upper atmosphere” and
another one is “a route through the extreme upper atmosphere” in which case,
atmosphere is once transported to the high latitude area of the southern
hemisphere through the extreme upper atmosphere and then transported toward
the north.
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Incidentally, the above discussion is quite simplified, because there are
other factors affecting the behavior of CO2 concentration in the southern hemisphere, which lead to complicated consequences.
An example of these factors are the forest fires in south east Asia, Australia,
south America and Africa.
It is important to continue this observation to further understand how
the atmosphere exchanges between both hemispheres. This will improve the
accuracy of the forecasting research for climate change.
A new observation program will start in 2006, and it will enable the measurement of the concentration of SF6 (sulfur hexafluoride) in addition to CO2. Unlike CO2 SF6 is not affected by plants, since SF6 is a purely artificial compound. Therefore, it is anticipated that a clearer understanding will be obtained by combining the observed data of SF6 and that of CO2 together.
As described above, the atmosphere is moving from north to south and from
south to north, i.e., transportation. This is shown in the figure.
1-3-4. CO
2 concentration on the surface of the earth and in the upper atmosphere
The figures shows a comparison of the changes in the carbon dioxide concentration
in the upper troposphere and at ground level, which were obtained approximately
at the same latitudes from our observation.
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The solid line on the figure shows the seasonal changes extracted from our
data; the broken line shows the seasonal changes extracted from the data
collected at ground level (sea level) in areas applicable to each latitude
zone.
Note: The data used as the basis for the broken line was gathered by the
National Oceanic and Atmospheric Administration (NOAA) of the USA.
As shown in the figure, during the season indicating the peak CO2 concentration in the northern hemisphere, there is a small time lag between
data measured at the ground surface and data from the upper troposphere
during the seasonal change caused by photosynthesis. In addition, the amplitude
of the fluctuation in CO2 concentration seems to diminish gradually toward the upper troposphere.
From this data, it becomes quite obvious that the seasonal changes attributable
to photosynthesis occurring at the ground surface influence a lot of the
changes in the upper atmosphere, due to the circulation of air(convection).
On the other hand, in the southern hemisphere, it seems that the amplitude
of the change in carbon dioxide concentration diminish gradually toward
the ground. This is thought to be the results of the seasonal changes (attributable
to photosynthesis) of the northern hemisphere reaching the southern hemisphere.
This fact supports the idea that, “a route through the extreme upper atmosphere
exists. In which case, the atmosphere is transported to the high latitude
area of the southern hemisphere, through the extreme upper atmosphere and
then transported toward the north”. This is described in chapters 1-3-3
(Change of CO2 concentration in the Southern Hemisphere).
1-3-5. Variation of CH
4 concentration
The figure shows the observation results of CH4 concentration.
As shown in the figure, CH4 concentration fluctuates notably in the short term. This is caused by
the fact that CH4 is turning into other chemical species by oxidation during
the transport process in the atmosphere, due to the relatively short life
of CH4 compared to that of CO2.
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1-3-6. Variation of CO concentration
The figure shows the observation results of CO concentration. As shown
in the figure, CO concentration is also fluctuating significantly in the
short term. This is also due to the relatively short life of CO comparing
to that of CO2. This causes other chemical species to oxidate and change
while they are transported in the atmosphere. In other words, the CO concentration
is affected by local situation.
For example, the data shows a steep peak of the CO in the southern hemisphere
in October 1997. It seems to be caused by biomass burning in the Indonesia
region due to the tremendous dry condition lead by the strong El-Nino phenomena.
Such a sharp increase of carbon monoxide in the southern hemisphere is also
found in October 1994, and it is confirmed that there was also a strong
El-Nino phenomena.
Consequently, it is important to continue such long term observations to
understand relatively unusual events such as the El-Nino phenomena.
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Incidentally, how can we conclude the sharp increase of the carbon monoxide
in the southern hemisphere is caused by the biomass burning?
It is known that the ratio of methane and carbon monoxide in the smoke of biomass burning and the smoke of fossil fuel burning is quite different. Fortunately, both the CH4 and CO are measured in this observation, so the ratio of CH4 and CO can be used to distinguish the source of the smoke.
1-3-7. Dispersion of the CO into the upper troposphere
A large amount of CO was released from the Southeast Asia in 1997, by the
tremendous forest fire caused by a strong El-Nino phenomena. An investigation
was conducted by Dr. Hidekazu Matsueda of the Meteorological Research Institute
to find out how CO released from ground level reached the upper troposphere.
Dr. Matsueda is responsible for analyzing data obtained from the this observation
program.
Carbon monoxide produces other compounds in the air, especially in the
tropospheric ozone through an extremely complex processes . This function
is referred to as “ozone precursors”, and investigation of the behavior
of these compounds is important because the tropospheric ozone is one of
the strong greenhouse gases. Dr. Matsueda was presented with the 1999 Horiuchi
Award, due to his investigations into the dispersion of carbon monoxide.
These investigations assists in understanding how these gases react with
each other, by combining the actual observed data and the model calculation.
The relationship between the concentration of “ozone precursors” and the
concentration of ozone has been already clarified in the laboratory. However
it is quite complex to determine precisely where the origin of the carbon
monoxide observed in the upper atmosphere is, how the wind conveys the carbon
monoxide, and eventually, what is the concentration and distribution of
carbon monoxide in the upper atmosphere at an arbitrary location. One of
the methods for such research is a simulation using a powerful computer.
For this simulation, a “General Circulation Model” is used.
In the model, carbon monoxide is emitted from an arbitrary place on the
ground, and the dispersion of the carbon monoxide due to the winds and convection
are calculated. The strength and distribution of the emission area is tuned
until the model result and the actual observed data appropriately coincide.
This simulation was done with the cooperation of Dr. Shoichi Taguchi of
the National Institute of Advanced Industrial Science and Technology (AIST).
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Due to the El Nino phenomena which occurs only once every several years,
it is quite difficult to encounter and to obtain sample air affected by
the phenomena. In 1997, however, the effects of the El Nino were very strong
and extremely dry weather conditions caused severe bush fires in South East
Asia, particularly Indonesia and Australia. During this time, the current
observation program obtained massive quantities of carbon monoxide emitted
from the bush fires. This occurred for the first time in 1997, though the
observation program started in 1993.
1-4. Mechanism to collect the sample air
ASE (Automatic Air Sampling Equipment), an equipment to collect
sample air is installed on Boeing 747 (Jumbo) operated by JAL between Australia
to Japan.
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ASE Location
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ASE
The ASE was developed taking into consideration the following elements;
the preservation of the air samples, the practicality of installation and
removal, and the safety of the aircraft.
This equipment consists of two boxes, and each box contains 6 cylinders
(the volume of each cylinder is 1.9 liters) which preserve the sampled air.
The ASE has 12 cylinders in total, so that it can collect air samples at
12 different points in the upper atmosphere. An air sample is taken every
40 min approximately.
The most outstanding feature of the ASE is that it can collect air samples
completely and automatically without any manual operation of the flight
crew. The ASE starts to work automatically by detecting the cabin pressure
by the built-in pressure sensor and computer, and takes air samples at preprogrammed
time intervals.
Data such as sampling time is recorded on the built-in computer, so that
sampling points can be defined by altitude, latitude, and longitude, by
comparing them with the data recorded in the aircraft's condition monitoring
system, after the flight.
In particular, the ASE was designed with special attention to safety so
that the ASE never jeopardizes the aircraft or passengers by working with
dual safety devices. Furthermore, as a requirement for the long term operation
of the ASE, several tests were conducted to confirm that the ASE met all
of the safety requirements. For this purpose, environmental tests for temperature
and humidity were conducted, and a test to confirm the strength of the ASE
was conducted by a centrifugal force machine.
As a final test of the function of the ASE under actual flight conditions,
a test flight was conducted on 9th April 1993. The test flight were reviewed
by the Civil Aviation Bureau, and the operation of the ASE on regular flights
was certified.
1-5. Air to be collected
After the joint atmospheric observation program commenced in September
1991, the Meteorological Research Institute (MRI) and the Research and Development
center of Japan Airlines, developed together the system required for air
sampling within a one and half year period.
During this period, several problems had to be overcome, as passenger aircraft
are not specifically designed for this kind of operation. This program was
the first of its kind in the world, thus installing such a system on a passenger
aircraft was challenging.
The most important issue was to find a solution for collecting the ambient
air in flight, to make the observation more accurate.
At first, it was discussed to collect the ambient air directly from an
air intake port specially and newly fitted for this program, but, it was
obvious that there were many difficulties to both from financial and safety
perspective. An examination of another idea took place, which suggested
collecting the air from the air conditioning ducts. This air is supplied
from the aircraft's engines through the aircraft's air conditioning system.
In the case of the Boeing 747, the ambient air taken from its four engines
is supplied to the cabin compartment, after temperature and pressure are
regulated by the air conditioning system. The sampled air will not be contaminated
by any polluted cabin air,as the air is collected at a point just downstream
of the air cycle machine.
However, it was not proved that the concentration of the greenhouse gases
in the sampled air is retained at the same level in the ambient air, because
the temperature increases when extracted from the engines.
Another issue was, whether the sampled air changed its quality or not, as
the air passes through the device called the “ozone converter” which is
installed for removal of the ozone from the air to be supplied to the cabin.
To confirm these issues, a test flight was carried out on 29th January,
1991.
In this test, two sets of air samples were collected, one from the
point just after the air cycle machine, and the other one from an air intake
port temporary installed on the cabin window to take the ambient air
directly.
Analysis proved that there was no difference between the concentration level
of carbon dioxide and methane in the two separate samples. Thus the idea
to collect the air extracted from the aircraft's air conditioning system
was adopted.
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Pitot Tube installed to take ambient air during experimental flight
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1-6. The modification of the observation route and airplane
In July 1994, due to route restructuring, the airplane on which the ASE
to be installed was changed(from airplane registration number JA8127 to
JA8131). Due to this modification, the location to install the ASE was also
changed from the cabin ceiling to the back of the bulkhead, in the forward
cargo compartment.
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Installing the ASE
At the same time, the observation route was extended to Sydney=Narita,
and also from September 1994 the frequency of the observations increased
to twice a month. Furthermore, in February 1999, an additional airplane(JA8130)
was modified to install the ASE. another two airplane then became available
for atmospheric observation (airplane registration number JA8130 and JA8131).
Later on, in April 2002, due to the renewal of fleet utilized between Sydney=Narita,
the observation route was changed to Brisbane=Narita.
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