6:15 PM - 7:30 PM
[PCG32-P03] Mesospheric wind/temperature measurements in the terrestrial planetary atmosphere using the IR heterodyne spectroscopy
Keywords:mesosphere, infrared, heterodyne, error, Mars, Venus
Ultra-high resolution heterodyne spectroscopy of CO2 at mid-IR wavelengths is one of the powerful tools to study wind and temperatures in the terrestrial atmospheres. Kinetic temperature can be calculated from the width of the observed lines and the doppler shift due to the wind is estimated from the difference between the measured line frequency and the CO2 rest frequency. In contrast to existing sub-mm observations, IR heterodyne spectroscopy offers a much higher spatial resolution allowing detailed study of temperature variations with latitude and local time. The IR heterodyne spectroscopy can achieve the spectral resolution 〜 107 and high spatial resolution of 3.5 arcsec with 60cm telescope at 10μm.
The purpose of this study is to investigate the methods to derive wind and temperature and its error estimation on Venus. Observations were carried out using Tuneable Heterodyne Infrared Spectrometer (THIS). The data was obtained in the east limb 33S on Venus in 4th June 2009 at the McMath- Pierce Solar Telescope of the National Solar Observatory on Kitt Peak in Arizona. Integration time is about 20 minutes. Because the exact altitude of the emitting region is predicted by the model to be 〜 110km with a half width of 10km, we can directly derived the wind and temperature in its altitudinal region. Our results indicated that the accuracies of derived wind and temperature were ±11m/s and ±12K respectively. These errors were defined from χ2≤1 of Gaussian fitting of the emission line. The estimated errors are sufficient to discuss disturbance of temperature on Mars and Venus (Mars:5-35K, Venus:5-40K [Deming and Mumma ,1983]) . The estimated error of the wind basically agreed with the expected values from the spectral resolution (±10m/s). The obtained mesospheric temperature 184±12K shows a good agreement with the in-situ measurement by Pioneer Venus([Clancy et al.,2008]).
We developed the new IR heterodyne instrument for the dedicated telescope at the top of Mt. Haleakala, Hawaii. Using the methodology shown here, we plan to perform the continuous monitoring of wind and temperature in the Venus/Mars mesosphere.