4:30 PM - 4:45 PM
[AAS02-11] Estimating the amount of water vapor over Syowa Station by observing the spectrum of stars
Keywords:H2O, ground-based observation
Water vapor contained in the earth's atmosphere is important for understanding various phenomena in the atmosphere. Especially at Syowa Station in the Antarctic Circle, it is important to predict the snow and blizzards caused by the condensation of water vapor in order to protect the safety of the station. For that purpose, it is necessary to measure the change in the amount of water vapor contained in the atmosphere. However, the water vapor observations around Syowa Station that are currently being conducted are radiosonde observations once every half a day and humidity observations on the ground surface, and there are temporal and spatial limits. Therefore, in this study, we propose a method to estimate the amount of water vapor column in the Earth's atmosphere by spectroscopic observation of standard stars.
There are some methods for measuring atmospheric water vapor, such as radiosonde observations by Hicke et al. (2008), and Microwave Limb Sounder (EOS MLS) observations from the Aura satellite (Waters et al., 2006).
This method uses the standard star list VizieR Online Data Catalog: Moscow Spectrophotometric Catalog (MSC) (Glushneva et al., 1998), whose spectra are widely known, and observes these stars from Syowa Station. Comparing catalog data and observed data, We can estimate the effect of water vapor in the atmosphere in the direction of the line of sight. We had spectral observations more than 10 celestial bodies centered on the western sky at intervals of 10 to several tens of minutes in one cycle. It takes about an hour and a half. This observation was performed on a clear night from February 2021 to October 2021. In order to investigate the change in the depth of absorption, we took the ratio of the absorption of H20 at 735 nm to the absorption of O2 at 770 nm, as shown by Turnbull et al. (2006). As a result, we succeeded in capturing the absorption of water vapor even at the Syowa Station, where the maximum water vapor pressure on the ground surface is 300 Pa. Comparing this absorption ratio and another data, for example, vertical distribution of water vapor taken by radiosonde, we may estimate horizontal distribution of water vapor. As a result of initial analysis, there are no clear relationship between the absorption ratio and water vapor pressure on the ground. This may show water vapor in troposphere above the surface has more effect than water vapor in the surface. We will continue further analysis.
There are some methods for measuring atmospheric water vapor, such as radiosonde observations by Hicke et al. (2008), and Microwave Limb Sounder (EOS MLS) observations from the Aura satellite (Waters et al., 2006).
This method uses the standard star list VizieR Online Data Catalog: Moscow Spectrophotometric Catalog (MSC) (Glushneva et al., 1998), whose spectra are widely known, and observes these stars from Syowa Station. Comparing catalog data and observed data, We can estimate the effect of water vapor in the atmosphere in the direction of the line of sight. We had spectral observations more than 10 celestial bodies centered on the western sky at intervals of 10 to several tens of minutes in one cycle. It takes about an hour and a half. This observation was performed on a clear night from February 2021 to October 2021. In order to investigate the change in the depth of absorption, we took the ratio of the absorption of H20 at 735 nm to the absorption of O2 at 770 nm, as shown by Turnbull et al. (2006). As a result, we succeeded in capturing the absorption of water vapor even at the Syowa Station, where the maximum water vapor pressure on the ground surface is 300 Pa. Comparing this absorption ratio and another data, for example, vertical distribution of water vapor taken by radiosonde, we may estimate horizontal distribution of water vapor. As a result of initial analysis, there are no clear relationship between the absorption ratio and water vapor pressure on the ground. This may show water vapor in troposphere above the surface has more effect than water vapor in the surface. We will continue further analysis.