9:00 AM - 10:30 AM
[AAS01-P07] Antarctic water vapor column estimated from absorption spectra of the Earth's atmosphere
Keywords:Water Vapor, Spectroscopy, Antarctica
Water vapor plays a large role in meteorological phenomena on earth. Condensation of water vapor forms clouds and precipitation. Clouds change the albedo of the earth, are related to changes in the heat balance of the entire earth, and bring about bad weather such as blizzards. Since the Antarctic region is located at the edge of the global atmospheric circulation, clarifying the distribution and transport of water vapor in the Antarctic region will provide a foothold for understanding global atmospheric circulation and water vapor transport. Therefore, observations of water vapor have been carried out by observation teams and artificial satellites in various countries. However, observations up to now have temporal and spatial limitations, and changes in the distribution of water vapor have not been fully elucidated. Therefore, we have developed a simple measurement method to observe amount of water vapor column. we conducted spectral observations of celestial bodies, mainly standard stars whose spectral types are widely known, and analyzed the effects of the Earth's atmosphere on the spectra obtained.
We used a instrument that combines a 203 [mm] Schmidt-Cassegrain telescope with a visible light spectrometer, set up on the roof of the observation building at Syowa Station, the base for Japan's Antarctic observations. This instrument can observe the spectrum of the target object in the 600-900 [nm] wavelength range. And we made two types of observations, All-sky observation that takes 10 or so objects centered on the western sky, during about 1 hour, and One-point observation that takes 1 object at near zenith every 10 minutes. The observation period is from February 11, 2021 to October 4, 2021. Target objects were selected from the SIMBAD database with a magnitude of 5 or higher in the V band.
By dividing the acquired standard star spectrum by the catalog value, the absorption spectrum derived from the Earth's atmosphere was calculated, and the ratio of the equivalent width of H2O and the equivalent width of O2 was derived as the absorption ratio. In observations targeting HR74, the correlation between surface water vapor pressure and absorption ratio was -0.4. However, this result is not surprising, radiosonde observations conducted during the course of this study suggests that the relationship between surface water vapor pressure and precipitable water content is not a simple one. On the other hand, the correlation between the amount of precipitable water and the absorption ratio was 0.9, indicating a strong correlation between the two. Therefore, it can be said that it is possible to estimate the amount of precipitable water by using the absorption ratio obtained by this observation method. Spectral observation can be performed in about one minute per star, so this method can be a stepping stone to capture changes in precipitable water over several tens of minutes to several minutes, which has not been observed so far. Furthermore, if it is possible to observe multiple locations in the sky simultaneously using an all-sky camera, we can expect to clarify the horizontal distribution of the amount of water vapor column.
We used a instrument that combines a 203 [mm] Schmidt-Cassegrain telescope with a visible light spectrometer, set up on the roof of the observation building at Syowa Station, the base for Japan's Antarctic observations. This instrument can observe the spectrum of the target object in the 600-900 [nm] wavelength range. And we made two types of observations, All-sky observation that takes 10 or so objects centered on the western sky, during about 1 hour, and One-point observation that takes 1 object at near zenith every 10 minutes. The observation period is from February 11, 2021 to October 4, 2021. Target objects were selected from the SIMBAD database with a magnitude of 5 or higher in the V band.
By dividing the acquired standard star spectrum by the catalog value, the absorption spectrum derived from the Earth's atmosphere was calculated, and the ratio of the equivalent width of H2O and the equivalent width of O2 was derived as the absorption ratio. In observations targeting HR74, the correlation between surface water vapor pressure and absorption ratio was -0.4. However, this result is not surprising, radiosonde observations conducted during the course of this study suggests that the relationship between surface water vapor pressure and precipitable water content is not a simple one. On the other hand, the correlation between the amount of precipitable water and the absorption ratio was 0.9, indicating a strong correlation between the two. Therefore, it can be said that it is possible to estimate the amount of precipitable water by using the absorption ratio obtained by this observation method. Spectral observation can be performed in about one minute per star, so this method can be a stepping stone to capture changes in precipitable water over several tens of minutes to several minutes, which has not been observed so far. Furthermore, if it is possible to observe multiple locations in the sky simultaneously using an all-sky camera, we can expect to clarify the horizontal distribution of the amount of water vapor column.