Weather and climate 90 km above Svalbard

Weather and climate 90 km above Svalbard

Top image: Green oxygen airglow is seen as a thin line beneath the red and green aurora. Photo: International Space Station/NASA

Observations of airglow and meteors above Svalbard reveal important information about the weather and climate changes in the upper part of the atmosphere, according to Margit Dyrland’s PhD research. Dyrland will defend her thesis at UNIS on Thursday February 25.

23 February 2010
Press release from UNIS and the University of Tromsø

Most of us consider weather phenomena to be something we can observe visually in the lower part of the atmosphere. However, in order to study climate changes and to understand the Earth’s energy balance, knowledge of weather conditions in the higher levels of the atmosphere is of vital importance.

The polar mesopause region (80-100 km above ground) is one of the most dynamic regions of the Earth’s atmosphere, and may offer important clues to understand the Earth’s energy and climate balance. It is the coldest part of the atmosphere and the air is very thin. Making temperature measurements in this region is therefore not an easy task.

One possibility is to derive temperatures from the intensity of airglow emissions emanating from this region. Airglow is the faint light sent out by molecules and atoms “warmed” by solar UV light in the upper atmosphere. Dyrland has used a multi-instrument approach combining data from a ground based spectrometer with data from satellites and radars, and have gained important new insight into the relationship between temperature and hydroxyl airglow variations and dynamical processes occurring in the mesopause region above Svalbard.

With global warming of the lower parts of the atmosphere, it is expected that the upper part (including the mesopause region) will cool. The majority of studies published so far do not document the expected decrease in temperature. The main question then becomes: why do we not observe a decrease in the mesopause temperature and which processes govern the temperature variations in this part of the atmosphere?

Altitude of airglow and temperatures dictated by winds
By studying the variations in strength of hydroxyl airglow observed over Svalbard, Dyrland has estimated the temperatures at about ~87 kilometers altitude, and updated the scientific time-series which was started at the beginning of the 1980’s. No significant temperature trend was revealed in the 25 year long time series.

Comparison of these measurements with simultaneous measurements done by satellites show that the altitude of the airglow origin varies with up to 10 km and that this altitude variation can explain up to 30 percent of the temperature variations observed in the same time interval.

Dyrland’s study shows that the stronger the intensity in the airglow is, the lower the altitude from where it originates. The large variations in altitude are probably unique for the dynamic polar atmosphere and are probably part of the explanation to why there has not been the expected decrease in temperatures in the mesopause region over the last couple of decades.

Studies of winds estimated from radar measurements of meteors that burn up in the atmosphere in 70-100 km altitude, show a clear connection between the direction of the meridional (north-south) wind and the altitude, temperature and intensity of the hydroxyl airglow.

Northward winds will lead to air descending over the northern hemisphere pole and it will thereby be warmed up. The production of hydroxyl will also increase. For southward winds, the opposite process will occur, air will rise and be cooled. The observed direct link between meridional wind and temperature has been observed before, but that it also affects the altitude of the OH layer has never been observed before.

Dissertation
Margit Dyrland will defend her PhD thesis “Multi-instrument studies of polar mesopause region temperature and airglow variability” at UNIS on Thursday February 25, 2010. The candidate will give a trial lecture called “Earth’s climate – a global and whole-atmosphere perspective” the same day.

Margit Dyrland

Margit Dyrland

About the candidate
Margit Elisabet Dyrland (born 1979) is from Seljord in Telemark.

Dyrland completed her Cand. Scient. degree at the research group for plasma- and space physics at the University in Oslo in 2005.

In autumn 2005 she started her PhD studies at the University Centre in Svalbard (UNIS) and the University of Tromsø (UIT).

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