Larsermann Hiils: astroclimate study

The 3rd Symposium of Polar Scientific The 3rd Symposium of Polar Scientific Research, Bucharest 27 June 2008Research, Bucharest 27 June 2008

Larsemann Hills:Larsemann Hills: astroclimate studyastroclimate study

Popescu, P.*, Negoita, T.Popescu, P.*, Negoita, T.****, Nedelcu, A. *, Badescu, O. *, , Nedelcu, A. *, Badescu, O. *, Paraschiv, P.,*Dumitrescu, A. *Paraschiv, P.,*Dumitrescu, A. *

*Astronomical Institute of Romanian Academy*Astronomical Institute of Romanian Academy**Romanian Polar Research Institute**Romanian Polar Research Institute


IntroductionIntroduction

The unprecedented development of astronomy calls for the development of the observational facilities. Moreover, as space astronomy still implies extremely high costs, the polar zones with special environment conditions, pratically not polluted, have priority.

In Antarctica, the extension of the observation stations in areas with very high altitudes is extremely important.

In our study we have to set different objectives, form those of a classical astroclimate study. Thus, we have already fixed the place where the telescope will be set up.

Logistic reasons, transport restrictions and our means of access into the area, have forced us to take into consideration, in a first approximation, only the region of Larsemann Hills, where the stations Law-Racoviţă, Zhongshan and Progress II are situated.


IntroductionIntroduction

- This study contains important information on the location of the Australian-Romanian base Law – Racoviţă, as well as on the astroclimatic conditions specific to that place.

- The material makes up also a conceptual study of the Antarctic area, where different zones and astronomical projects are under way. In 2008 we had also investigated an Arctic zone, namely western Greenland.

- We want to set up in this way a sub-system of astronomical and technological problems by means of the objectives specific to the zone, the definition of the activities which will be carried out there, as well as of the technological requirements related to them.


Astroclimatic conditionsAstroclimatic conditions

The fundamental conditions for the choice of a favourable place for astronomical observations are determined by:

- A good image quality, with an optimal seeing. We have to point out that adaptive optics works well only in excellent observational conditions.

- A high percentage of clear days and nights, as weather produces the greatest number of time losses, in the case of astronomical observations. To obtain the best results it is crucial that durring the time used, there should be a great number of observation nights (eg: photometrical, with a good seeing and/or a low level of water vapours)

- A sky background as weak as possible, which implies a luminous pollution as low as possible.

- An observation place situated above the inversion stratum, above the water vapors accumulation. The inversion stratum will tend to capture the water vapors, making the site dry and consequently adequate for IR measurements. It will also keeps luminous pollution away from the sea level.

- A good atmospheric transmission in the atmospheric windows.- A temperature as low as possible. The sky background flux doubles at an increase of

100C. - Very slow temperature variations, also predicitble in time, for a correct operation of

the telescope. The different parts of the telescope coal of at different rates; sudden temperature changes might disort the structure and cause focus and objects identification errors.


Astroclimatic conditionsAstroclimatic conditions

- The restrictions required by logistics considerations do not allow us to meet all this conditions, the positioning in the Antarctic zone accentuating favorable some of them. We refer here to temperature, humidity conditions, as well as to the advantages of the austral night.

- There are conditions, such as the action of the ice microscopic crystals, the operation of the devices at work, or in stand-by and the lack of means for fixing some flaws, all of this create problems which have to be solved during the research phases.

- We have also encounter difficulties due to the impossibility of carrying out a direct and continuous study in the zone of Larsemann Hills. This would have required important sums of money.


Davis Station (Australia): latitude 68°,6 S, longitude 78°EDavis Station (Australia): latitude 68°,6 S, longitude 78°E

Temperaturi lunare

-25.0

-20.0

-15.0

-10.0

-5.0

0.0

5.0

1 2 3 4 5 6 7 8 9 10 11 12

Luna

Te

mp

era

tura

(C

els

ius

)

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006


Davis Station (Australia): latitude 68°,6 S, longitude 78°EDavis Station (Australia): latitude 68°,6 S, longitude 78°E

Presiuni lunare

965

970

975

980

985

990

995

1000

1 2 3 4 5 6 7 8 9 10 11 12

Luna

Pre

siu

nea

(h

Pa)

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006


Law-Racovita StationLaw-Racovita Station

Temperaturi Low-Racovita

-25

-20

-15

-10

-5

0

5

luna

gra

de

C

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006


The meteorological conditions in Larsemann Hills in the last 3 The meteorological conditions in Larsemann Hills in the last 3 yearsyears

1. Minimum and maximum temperatures: -220C; +20C

2. Spread and direction of the wind Average: 7.5 m/s E; Max.: 50.3 m/s E

3. Level of humidity 60% in average

4. Nebulosity (the frequency of the clear sky days, dynamics): 145 days

5. Precipitations is unlikely to exceed 250 mm water equivalent annually.


Zhong Shan Station (China): latitude 69°,4 S, longitude 76°,4 EZhong Shan Station (China): latitude 69°,4 S, longitude 76°,4 E

Presiunea lunara

940

950

960

970

980

990

1000

1010

1 2 3 4 5 6 7 8 9 10 11 12

Luna

Pre

siu

nea

(h

Pa)

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006


Zhong Shan Station (China): latitude 69°,4 S, longitude 76°,4 EZhong Shan Station (China): latitude 69°,4 S, longitude 76°,4 E

Temperatura lunara

-25

-20

-15

-10

-5

0

5

1 2 3 4 5 6 7 8 9 10 11 12

Luna

Tem

per

atu

ra (

Cel

siu

s)

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006


ConclusionsConclusions

• The reduced quantity of water vapors is a general characteristic of the entire Antarctic Plateau. In our site, the precipitation level of 2500mm of water annually represents an extremely valuable parameter, favorable to our studies. The number of water molecules per volume nit is very low, atmospheric extinction being low, and consequently improves significantly the quality of infrared observations and milimetric wavelengths in particular.

• Average humidity, which is rather high (average value 60%), is due especially to the currents from North-East direction, coming from the ocean. It is worth mentioning that this is a priority direction which has determined us to design and orientate the protection system of the instrument.

• Wind speed is generally constant and does not take particularly high values. Therefore, we consider that astronomical observations can be carried out in good conditions, the period of austral summer – the one studied by us directly - is rich in extreme meteorological phenomena. Austral winter, on the other hand, due to the extension of the ice cap and the moving off of the ocean (in the studied zone with over 200km) there is a humidity drop (under 50%) at the same time with the low temperatures of the night and a stable weather with slow winds, of constant direction and intensity. This favors precisely the most adequate periods for astronomical observations. We have analyzed only the data obtained by the exploratory mission of 31 December 2005 – 15 March 2006 of the Romanian Institute of Polar Researches.

• The temperature study has led us to the conclusion that temperatures seldom drop under -220C, being significantly constant in the winter/night period. Absolutely by way of exception the temperatures reach -400C, our instruments being designed to work up to that temperature. We have set the work period in the interval -400C ; -50C and the entire project is focused on the temperature range.


ConcluziiConcluzii

• Seeing determinations were not carried out directly. We used the studies of M. Ashley of New South Wales University, Australia, in the site Dome C, as well as those of J.Vernin from LUAN, Nice University, France. Thus, during daytime average seeing varies between 0″.54 and 0″.65. At night, at a height of 8 m it is of 1″.6 - 1″.2, and at 30 m it is of 0″.4!

• An astroclimate study was carried out on the basis of the meteorological data from the tree neighboring stations. The good seeing quality, the stability of the meteorological conditions over relatively long periods, the moderate negative temperatures and the absence of polluted air lead us to the conclusion that the zone is favorable to high quality astronomical observations. The configuration of the telescope ordered has been chose so as to cope with the extreme temperature and wind conditions.

• As a result of this stage of documentation and elaboration of the project technical topics we have obtained all basic technical data for the best carrying out of the design activity of telescope mounting ensemble, of the mechanisms and electric systems of automatic positioning respectively. We have also created the conditions for the purchasing of special devices.

• The expedition to Law-Racovita basis, has finalized with: the setting up of the database, a logistic insurance of the observer, the study of instrument location.

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Larsermann Hiils: astroclimate study